AUTOMOTIVE ELECTRICS

AND

AUTOTRONICS

(JNTU HYDERABAD)

BY

MD ABDUL QADEER SIDDIQUI

B-tech (automobile engineering)

INDEX

1) STORAGE BATTERY

2) IGNITION SYSTEM

3 a) STARTER MOTOR

b) ELECTRIC CONTROL OF CARBURATION

4) CHARGING SYSTEM

5) WIRING OF AUTO ELECTRICAL SYSTEM

6) DASH BOARD UNITS AND ELECTRICAL ACCESSORIES

7) NUMBER SYSTEM CODES AND DATA REPRESENTATION

8) LOGIC GATES, ARITHMATIC CIRCUITS AND INTRODUCTION TO MICROPROCESSORS

1) STORAGE BATTERY

Battery Operation.

Lead-acid storage batteries consist of a number of identical cells. These cells containTwo different lead plates. These plates are immersed in electrolyte (a solution ofsulfuric acid and water). As the battery cell receives electrical energy (charges) ordelivers electrical energy (discharges), there is a change in the chemical compositionof the battery plates and the strength of the electrolyte. The voltage developeddepends on the types of electrode materials and the electrolyte used. It isapproximately 2.1 volts per cell in a typical lead-acid battery. Electrical energy isproduced by the chemical action between the electrode materials and the electrolyte.The chemical actions start and electrical energy current flows from the battery as soon

as there is a circuit between the positive and negative terminals (whenever a load suchas the headlamps is connected to the battery). The electrical current flows as electronsthrough the outside circuit, as it does inside the battery.

TYPES OF BATTERIES

1) PRIMARY BATTERY

2) SECONDARY BATTERY

PRIMARY BATTERIES

Primary batteries, or primary cells, can produce current immediately on assembly. Disposable batteries are intended to be used once and discarded. These are most commonly used in portable devices that have low current drain, are used only intermittently, or are used well away from an alternative power source, such as in alarm and communication circuits where other electric power is only intermittently available. Disposable primary cells cannot be reliably recharged, since the chemical reactions are not easily reversible and active materials may not return to their original forms. Battery manufacturers recommend against attempting to recharge primary cells.

Common types of disposable batteries include zinc–carbon batteries and alkaline batteries. In general, these have higher energy densities than rechargeable batteries, but disposable batteries do not fare well under high-drain applications with loads under 75 ohms.

SECONDARY BATTERIES

Secondary batteries, also known as secondary batteries or rechargeable batteries, must be charged before use; they are usually assembled with active materials in the discharged state. Rechargeable batteries are (re)charged by applying electric current, which reverses the chemical reactions that occur during discharge/use. Devices to supply the appropriate current are called chargers.

The oldest form of rechargeable battery is the lead–acid battery ,This technology contains liquid electrolyte in an unsealed container, requiring that the battery be kept upright and the area be well ventilated to ensure safe dispersal of the hydrogen gas it produces during overcharging. The lead–acid battery is also relatively heavy for the amount of electrical energy it can supply. Its low manufacturing cost and its high surge current levels make it common where its capacity (over approximately 10 Ah) is more important than weight and handling issues. A common application is the modern car battery, which can, in general, deliver a peak current of 450 amperes

The sealed valve regulated lead–acid battery (VRLA battery), popular in the automotive industry as a replacement for the lead–acid wet cell. The VRLA battery uses an

immobilized sulfuric acid electrolyte, reducing the chance of leakage and extending shelf life. VRLA batteries immobilize the electrolyte, usually by one of two means:

Gel batteries (or "gel cell") use a semi-solid electrolyte. Absorbed Glass Mat (AGM) batteries absorb the electrolyte in a special fiberglass

matting.

The storage battery is the heart of the charging circuit (fig. 2-2). It is anelectrochemical device for producing and storing electricity. A vehicle battery hasseveral important functions, which are as follows:It must operate the starting motor, ignition system, electronic fuel injection system,and other electrical devices for the engine during engine cranking and starting.It must supply ALL of the electrical power for the vehicle when the engine is notRunning.

It must help the charging system provide electricity when current demands are abovethe output limit of the charging system.

Figure 2-2.- Gross section of a typical storage battery.

It must act as a capacitor (voltage stabilizer) that smoothes current flow through theelectrical system.It must store energy (electricity) for extended periods.The type of battery used in automotive, construction, and weight-handling equipmentis a lead-acid cell-type battery. This type of battery produces direct current (dc)electricity that flows in only one direction. When the battery is discharging (currentflowing out of the battery), it changes chemical energy into electrical energy, thereby,releasing stored energy. During charging (current flowing into the battery from thecharging system), electrical energy is converted into chemical energy. The battery can

then store energy until the vehicle requires it.

BATTERY CONSTRUCTION

The lead-acid cell-type storage battery is built to withstand severe vibration, coldweather, engine heat, corrosive chemicals, high current discharge, and prolongedperiods without use. To test and service batteries properly, you must understandbattery construction. The construction of a basic lead-acid cell-type battery is asfollows:

Battery elementBattery case, cover, and capsBattery terminalsElectrolyte

BATTERY ELEMENT.- The battery element is made up of negative plates, positiveplates, separators, and straps (fig. 2-3). The element fits into a cell compartment in thebattery case. Most automotive batteries have six elements.

Figure 2-3.- Battery element.

Each cell compartment contains two kinds of chemically active lead plates, known aspositive and negative plates. The battery plates are made of GRID (stiff meshframework) coated with porous lead. These plates are insulated from each other bysuitable separators and are submerged in a sulfuric acid solution (electrolyte).Charged negative plates contain spongy (porous) lead (Pb) which is gray in color.Charged positive plates contain lead peroxide (PbO2 ) which has a chocolate browncolor. These substances are known as the active materials of the plates. Calcium orantimony is normally added to the lead to increase battery performance and to

decrease gassing (acid fumes formed during chemical reaction). Since the lead on theplates is porous like a sponge, the battery acid easily penetrates into the material. Thisaids the chemical reaction and the production of electricity.Lead battery straps or connectors run along the upper portion of the case to connect theplates. The battery terminals (post or side terminals) are constructed as part of one endof each strap.To prevent the plates from touching each other and causing a short circuit, sheets ofinsulating material (microporous rubber, fibrous glass, or plastic-impregnatedmaterial), called separators, are inserted between the plates. These separators are thinand porous so the electrolyte will flow easily between the plates. The side of theseparator that is placed against the positive plate is grooved so the gas that formsduring charging will rise to the surface more readily. These grooves also provide roomfor any material that flakes from the plates to drop to the sediment space below.

BATTERY CASE, COYER, AND CAPS.The battery case is made of hard rubber or a high- quality plastic. The case mustwithstand extreme vibration, temperature change, and the corrosive action of theelectrolyte. The dividers in the case form individual containers for each element. Acontainer with its element is one cell.Stiff ridges or ribs are molded in the bottom of the case to form a support for the platesand a sediment recess for the flakes of active material that drop off the plates duringthe life of the battery. The sediment is thus kept clear of the plates so it will not cause ashort circuit across them.The battery cover is made of the same material as the container and is bonded to andseals the container. The cover provides openings for the two battery posts and a cap foreach cell.Battery caps either screw or snap into the openings in the battery cover. The batterycaps (vent plugs) allow gas to escape and prevent the electrolyte from splashingoutside the battery. They also serve as spark arresters (keep sparks or flames fromigniting the gases inside the battery). The battery is filled through the vent plugopenings. Maintenance-free batteries have a large cover that is not removed duringnormal service.

CAUTION

Hydrogen gas can collect at the top of a battery. If this gas is exposed to a flame orspark, it can explode.

BATTERY TERMINALS.- Battery terminals provide a means of connecting thebattery plates to the electrical system of the vehicle. Either two round post or two sideterminals can be used.Battery terminals are round metal posts extending through the top of the battery cover.They serve as connections for battery cable ends. Positive post will be larger than thenegative post. It may be marked with red paint and a positive (+) symbol. Negativepost is smaller, may be marked with black or green paint, and has a negative (-)symbol on or near it.Side terminals are electrical connections located on the side of the battery. They haveinternal threads that accept a special bolt on the battery cable end. Side terminalpolarity is identified by positive and negative symbols marked on the case.

ELECTROLYTE. -The electrolyte solution in a fully charged battery is a solution ofconcentrated sulfuric acid in water. This solution is about 60 percent water and about40 percent sulfuric acid.The electrolyte in the lead-acid storage battery has a specific gravity of 1.28, which

means that it is 1.28 times as heavy as water. The amount of sulfuric acid in the

electrolyte changes with the amount of electrical charge; also the specific gravity ofthe electrolyte changes with the amount of electrical charge. A fully charged batterywill have a specific gravity of 1.28 at 80° F. The figure will go higher with atemperature decrease and lower with a temperature increase.As a storage battery discharges, the sulfuric acid is depleted and the electrolyte isgradually converted into water. This action provides a guide in determining the state ofdischarge of the lead-acid cell. The electrolyte that is placed in a lead-acid battery hasa specific gravity of 1.280.The specific gravity of an electrolyte is actually the measure of its density. Theelectrolyte becomes less dense as its temperature rises, and a low temperature means ahigh specific gravity. The hydrometer that you use is marked to read specific gravity at80° F only. Under normal conditions, the temperature of your electrolyte will not varymuch from this mark. However, large changes in temperature require a correction inyour reading.For EVERY 10-degree change in temperature ABOVE 80° F, you must ADD 0.004 toyour specific gravity reading. For EVERY 10-degree change in temperature BELOW80° F, you must SUBTRACT 0.004 from your specific gravity reading. Suppose youhave just taken the gravity reading of a cell. The hydrometer reads 1.280. Athermometer in the cell indicates an electrolyte temperature of 60° F. That is a normaldifference of 20 degrees from the normal of 80° F. To get the true gravity reading, youmust subtract 0.008 from 1.280. Thus the specific gravity of the cell is actually 1.272.A hydrometer conversion chart similar to the one shown in figure 2-4 is usually foundon the hydrometer. From it, you can obtain the specific gravity correction fortemperature changes above or below 80° F.

Figure 2-4.- Hydrometer conversion chart.

BATTERY CAPACITYThe capacity of a battery is measured in ampere-hours. The ampere-hour capacity isequal to the product of the current in amperes and the time in hours during which thebattery is supplying current. The ampere-hour capacity varies inversely with thedischarge current. The size of a cell is determined generally by its ampere-hourcapacity. The capacity of a cell depends upon many factors, the most important ofwhich are as follows:1. The area of the plates in contact with the electrolyte2. The quantity and specific gravity of the electrolyte3. The type of separators4. The general condition of the battery (degree of sulfating, plates buckled, separatorswarped, sediment in bottom of cells, etc.)5. The final limiting voltage

Battery RatingsBattery ratings were developed by the Society of Automotive Engineers (SAE) and theBattery Council International (BCI). They are set according to national test standardsfor battery performance. They let the mechanic compare the cranking power of one

battery to another. The two methods of rating lead-acid storage batteries are the coldcrankingrating and the reserve capacity rating.

COLD-CRANKING RATING.- The cold-cranking rating determines how muchcurrent in amperes the battery can deliver for thirty seconds at 0° F while maintainingterminal voltage of 7.2 volts or 1.2 volts per cell. This rating indicates the ability of thebattery to crank a specific engine (based on starter current draw) at a specifiedtemperature.For example, one manufacturer recommends a battery with 305 cold-cranking ampsfor a small four-cylinder engine but a 450 cold-cranking amp battery for a larger V-8engine. A more powerful battery is needed to handle the heavier starter current draw ofthe larger engine.

RESERVE CAPACITY RATING.- The reserve capacity rating is the time needed tolower battery terminal voltage below 10.2 V (1.7 V per cell) at a discharge rate of 25amps. This is with the battery fully charged and at 80° F. Reserve capacity will appearon the battery as a time interval in minutes.For example, if a battery is rated at 90 minutes and the charging system fails, theoperator has approximately 90 minutes (1 1/ 2 hours) of driving time under minimumelectrical load before the battery goes completely dead.

BATTERY CHARGINGUnder normal conditions, a hydrometer reading below 1.240 specific gravity at 80° Fis a warning signal that the battery should be removed and charged. Except inextremely warm climates, never allow the specific gravity to drop below 1.225 intropical climates. This reading indicates a fully charged battery.When a rundown battery is brought into the shop, you should recharge it immediately.There are several methods for charging batteries; only direct current is used with eachmethod. If only alternating current is available, a rectifier or motor generator must beused to convert to direct current. The two principal methods of charging are (1)constant current and (2) constant voltage (constant potential).Constant current charging is be used on a single battery or a number of batteries inseries. Constant voltage charging is used with batteries connected in parallel. (Aparallel circuit has more than one path between the two source terminals; a seriescircuit is a one-path circuit). You should know both methods, although the latter ismost often used.CONSTANT CURRENT CHARGING.- With the constant current method, thebattery is connected to a charging device that supplies a steady flow of current. Thecharging device has a rectifier (a gas-filled bulb or a series of chemical disks); thus,the alternating current is changed into direct current. A rheostat (resistor for regulatingcurrent) of some kind is usually built into the charger so that you can adjust theamount of current flow to the battery. Once the rheostat is set, the amount of currentremains constant. The usual charging rate is 1 amp per positive cell. Thus a 21-platebattery (which has 10 positive plates per cell) should have a charging rate no greaterthan 10 amps. When using this method of charging a battery, you should check thebattery frequently, particularly near the end of the charging period. When the battery isgassing freely and the specific gravity remains constant for 2 hours, you can assumethat the battery will take no more charge.The primary disadvantage of constant current charging is that THE CHARGINGCURRENT REMAINS AT A STEADY VALUE UNLESS YOU CHANGE IT. Abattery charged with too high current rate would overheat and damage the plates,making the battery useless. Do NOT allow the battery temperature to exceed 110°while charging.

CONSTANT VOLTAGE CHARGING.- Constant voltage charging, also known asconstant potential charging, is usually done with a motor generator set. The motordrives a generator (similar to a generator on a vehicle); this generator produces currentto charge the battery. The voltage in this type of system is usually held constant. Witha constant voltage, the charging rate to a low battery will be high. But as the batteryapproaches full charge, the opposing voltage of the battery goes up so it more stronglyopposes the charging current. This opposition to the charging current indicates that asmaller charge is needed. As the battery approaches full charge, the charging voltagedecreases. This condition decreases the ability to maintain a charging current to thebattery. As a result, the charging current tapers off to a very low value by the time thebattery is fully charged. This principle of operation is the same as that of the voltageregulator on a vehicle.

CHARGING PRACTICES.- It is easy to connect the battery to the charger, turn thecharging current on, and, after a normal charging period, turn the charging current offand remove the battery. Certain precautions however are necessary both BEFORE andDURING the charging period. These practices are as follows:1. Clean and inspect the battery thoroughly before placing it on charge. Use a solutionof baking soda and water for cleaning; and inspect for cracks or breaks in thecontainer.CAUTIONDo not permit the soda and water solution to enter the cells. To do so would neutralizethe acid within the electrolyte.2. Connect the battery to the charger. Be sure the battery terminals are connectedproperly; connect positive post to positive (+) terminal and the negative post tonegative (-) terminal. The positive terminals of both battery and charger are marked;those unmarked are negative. The positive post of the battery is, in most cases, slightlylarger than the negative post. Ensure all connections are tight.3. See that the vent holes are clear and open. DO NOT REMOVE BATTERY CARSDURING CHARGING. This prevents acid from spraying onto the top of the batteryand keeps dirt out of the cells.4. Check the electrolyte level before charging begins and during charging. Adddistilled water if the level of electrolyte is below the top of the plate.5. Keep the charging room well ventilated. DO NOT SMOKE NEAR BATTERIESBEING CHARGED. Batteries on charge release hydrogen gas. A small spark maycause an explosion.6. Take frequent hydrometer readings of each cell and record them. You can expect thespecific gravity to rise during the charge. If it does not rise, remove the battery anddispose of it as per local hazardous material disposal instruction.7. Keep close watch for excessive gassing, especially at the very beginning of thecharge when using the constant voltage method. Reduce the charging current ifexcessive gassing occurs. Some gassing is normal and aids in remixing the electrolyte.8. Do not remove a battery until it has been completely charged.

PLACING NEW BATTERIES IN SERVICENew batteries may come to you full of electrolyte and fully charged. In this case, allthat is necessary is to install the batteries properly in the piece of equipment. Mostbatteries shipped to NCF units are received charged and dry.Charged and dry batteries will retain their state of full charge indefinitely so long asmoisture is not allowed to enter the cells. Therefore, batteries should be stored in a dryplace. Moisture and air entering the cells will allow the negative plates to oxidize. Theoxidation causes the battery to lose its charge.To activate a dry battery, remove the restrictors from the vents and remove the ventcaps. Then fill all the cells to the proper level with electrolyte. The best results are

obtained when the temperature of the battery and electrolyte is within the range of 60°F to 80° F.Some gassing will occur while you are filling the battery due to the release of carbondioxide that is a product of the drying process of the hydrogen sulfide produced by thepresence of free sulfur. Therefore, the filling operations should be in a well-ventilatedarea. These gases and odors are normal and are no cause for alarm.Approximately 5 minutes after adding electrolyte, the battery should be checked forvoltage and electrolyte strength. More than 6 volts or more than 12 volts, dependingupon the rated voltage of the battery, indicates the battery is ready for service. From 5to 6 volts or from 10 to 12 volts indicate oxidized negative plates, and the batteryshould be charged before use. Less than 5 or less than 10 volts, depending upon therated voltage, indicates a bad battery, which should not be placed in service.If, before placing the battery in service, the specific gravity, when corrected to 80° F,is more than .030 points lower than it was at the time of initial filling or if one or morecells gas violently after adding the electrolyte, the battery should be fully chargedbefore use. If the electrolyte reading fails to rise during charging, discard the battery.Most shops receive ready-mixed electrolyte. Some units may still get concentratedsulfuric acid that must be mixed with distilled water to get the proper specific gravityfor electrolyte.MIXING ELECTROLYTE is a dangerous job. You have probably seen holes appearin a uniform for no apparent reason. Later you remembered replacing a storage batteryand having carelessly brushed against the battery.

WARNINGWhen mixing electrolyte, you are handling pure sulfuric acid, which can burn clothingquickly and severely bum your hands and face. Always wear rubber gloves, an apron,goggles, and a face shield for protection against splashes or accidental spilling.When you are mixing electrolyte, NEVER POUR WATER INTO THE ACID.ALWAYS POUR ACID INTO WATER. If water is added to concentrated sulfuricacid, the mixture may explode or splatter and cause severe burns. Pour the acid intothe water slowly, stirring gently but thoroughly all the time. Large quantities of acidmay require hours of safe dilution.Figure 2-5 shows you how much water and acid to mix for obtaining a certain specificgravity. For example, mixing 5 parts of water to 2 parts of acid produces an electrolyteof 1.300, when starting with 1.835 specific gravity acid. If you use 1.400 specificgravity acid, 2 parts water and 5 parts acid will give the same results.Let the mixed electrolyte cool down to room temperature before adding it to thebattery cells. Hot electrolyte will eat up the cell plates rapidly. To be on the safe side,do not add the electrolyte if its temperature is above 90° F. After filling the batterycells, let the electrolyte cool again because more heat is generated by its contact withthe battery plates. Next, take hydrometer readings. The specific gravity of theelectrolyte will correspond quite closely to the values on the mixing chart if the partsof water and acid are mixed correctly.

BATTERY MAINTENANCEIf a battery is not properly maintained, its service life will be drastically reduced.Battery maintenance should be done during every PM cycle. Complete batterymaintenance includes the following:Visually checking the battery.Checking the electrolyte level in cells on batteries with caps. Adding water if theelectrolyte level is low.Cleaning off corrosion around the battery and battery terminals.

Figure 2-5.- Electrolyte mixing chart.

Checking the condition of the battery by testing the state of charge.

VISUAL INSPECTION OF THE BATTERY.- Battery maintenance should alwaysbegin with a thorough visual inspection. Look for signs of corrosion on or around thebattery, signs of leakage, a cracked case or top, missing caps, and loose or missinghold-down clamps.

CHECKING ELECTROLYTE LEVEL AND ADDING WATER.- On vent capbatteries, the electrolyte level can be checked by removing the caps. Some batterieshave a fill ring which indicates the electrolyte level. The electrolyte should be evenwith the fill ring. If there is no fill ring, the electrolyte should be high enough to coverthe tops of the plates. Some batteries have an electrolyte-level indicator (Delco Eye).This gives a color code vi sual indication of the electrolyte level, with black indicatingthat the level is okay and white meaning a low level.If the electrolyte level in the battery is low, fill the cells to the correct level withDISTILLED WATER (purified water). Distilled water should be used because it doesnot contain the impurities found in tap water. Tap water contains many chemicals thatreduce battery life. The chemicals contaminate the electrolyte and collect in the bottomof the battery case. If enough contaminates collect in the bottom of the case, the cellplates SHORT OUT, ruining the battery.If water must be added at frequent intervals, the charging system may be overchargingthe battery. A faulty charging system can force excessive current into the battery.Battery gassing can then remove water from the battery.Maintenance-free batteries do NOT need periodic electrolyte service under normalconditions. It is designed to operate for long periods without loss of electrolyte.

CLEANING THE BATTERY AND TERMINALS.If the top of the battery is dirty, using a stiff bristle brush, wash it down with amixture of baking soda and water. This action will neutralize and remove the acid-dirtmixture. Be careful not to allow cleaning solution to enter the battery.To clean the terminals, remove the cables and inspect the terminal posts to see if theyare deformed or broken. Clean the terminal posts and the inside surfaces of the cableclamps with a cleaning tool before replacing them on the terminal posts.

CAUTIONDo NOT use a scraper or knife to clean battery terminals. This action removes toomuch metal and can ruin the terminal connection.When reinstalling the cables, coat the terminals with petroleum or white grease. Thiswill keep acid fumes off the connections and keep them from corroding again. Tightenthe terminals just enough to secure the connection. Overtightening will strip the cablebolt threads.

CHECKING BATTERY CONDITION.- When measuring battery charge, youcheck the condition of the electrolyte and the battery plates. As a battery becomesdischarged, its electrolyte has a larger percentage of water. Thus the electrolyte of adischarged battery will have a lower specific gravity number than a fully chargedbattery. This rise and drop in specific gravity can be used to check the charge in abattery. There are several ways to check the state of charge of a battery.Nonmaintenance-free batteries can have the state of charge checked with ahydrometer. The hydrometer tests specific gravity of the electrolyte. It is fast andsimple to use. There are three types of hydrometers- the float type, the ball type, andneedle type.

To use a FLOAT TYPE HYDROMETER, squeeze and hold the bulb. Then immersethe other end of the hydrometer in the electrolyte. Then release the bul b. This actionwill fill the hydrometer with electrolyte. Hold the hydrometer even with your line ofsight and compare the numbers on the hydrometer with the top of the electrolyte.Most float type hydrometers are NOT temperature correcting. However, the newmodels will have a built-in thermometer and a conversion chart that allow you tocalculate the correct temperature.

The BALL TYPE HYDROMETER is becoming more popular because you do nothave to use a temperature conversion chart. The balls allow for a change intemperature when submersed in electrolyte. This allows for any temperature offset.To use a ball type hydrometer, draw electrolyte into the hydrometer with the rubberbulb at the top. Then note the number of balls floating in the electrolyte. Instructionson or with the hydrometer will tell you whether the battery is fully charged ordischarged.

A NEEDLE TYPE HYDROMETER uses the same principles as the ball type. Whenelectrolyte is drawn into the hydrometer, it causes the plastic needle to register specificgravity.A fully charged battery should have a hydrometer reading of at least 1.265 or higher. Ifbelow 1.265, the battery needs to be recharged. or it may be defective. A dischargedbattery could be caused by the following:Defective batteryCharging system problemsStarting system problemsPoor cable connections

Engine performance problems requiring excessive cranking time

Electrical problems drawing current out of the battery with the ignition OFF defectivebattery can be found by using a hydrometer to check each cell. If the specific gravity inany cell varies excessively from other cells (25 to 50 points), the battery is bad. Cellswith low readings may be shorted. When all of the cells have equal specific gravity,even if they are low, the battery can usually be recharged.On maintenance-free batteries a charge indicator eye shows the battery charge. Thecharge indicator changes color with levels of battery charge. For example, theindicator may be green with the battery fully charged. It may turn black whendischarged or yellow when the battery needs to be replaced. If there is no chargeindicator eye or when in doubt of its reliability, a voltmeter and ammeter or a loadtester can also be used to determine battery condition quickly.

BATTERY TESTAs a mechanic you will be expected to test batteries for proper operation andcondition. These tests are as follows:Battery leakage testBattery terminal testBattery voltage testCell voltage testBattery drain testBattery load test (battery capacity test)Quick charge testBATTERY LEAKAGE TEST.- A battery leakage test will determine if current isdischarging across the top of the battery. A dirty battery can discharge when not inuse. This condition shortens battery life and causes starting problems.To perform a battery leakage test, set a voltmeter on a low setting. Touch the probeson the battery, as shown in figure 2-6. If any current is registered on the voltmeter, thetop of the battery needs to be cleaned.BATTERY TERMINAL TEST.- The battery terminal test quickly checks for poorelectrical connection between the terminals and the battery cables. A voltmeter is usedto measure voltage drop across terminals and cables.To perform a battery terminal test (fig. 2-7), connect the negative voltmeter lead to thebattery cable end. Touch the positive lead to the battery terminal. With the ignition orinjection system disabled so that the engine will not start, crank the engine whilewatching the voltmeter reading.

If the voltmeter reading is .5 volts or above, there is high resistance at the battery cableconnection. This indicates that the battery connections need to be cleaned. A good,clean battery will have less than a .5 volt drop.

BATTERY VOLTAGE TEST.- The battery voltage test is done by measuring totalbattery voltage with an accurate voltmeter or a special battery tester (fig. 2-8). This testdetermines the general state of charge and battery condition quickly.The battery voltage test is used on maintenance-free batteries because these batteriesdo not have caps that can be removed for testing with a hydrometer. To perform thistest, connect the voltmeter or battery tester across the battery terminals. Turn on thevehicle headlights or heater blower to provide a light load. Now read the meter ortester. A well-charged battery should have over 12 volts. If the meter readsapproximately 11.5 volts, the battery is not charged adequately, or it may be defective.

CELL VOLTAGE TEST.The cell voltage test will let you know if the battery is discharged or defective. Like ahydrometer cell test, if the voltage reading on one or more cells is .2 volts or morelower than the other cells, the battery must be replaced.To perform a cell voltage test (fig. 2-9), use a low voltage reading voltmeter withspecial cadmium (acid resistant metal) tips. Insert the tips into each cell, starting at oneend of the battery and work your way to the other. Test each cell carefully. If the cellsare low, but equal, recharging usually will restore the battery. If cell voltage readingsvary more than .2 volts, the battery is BAD.

BATTERY DRAIN TEST.- A battery drain test checks for abnormal current drawwith the ignition off. If a battery goes dead without being used, you need to check for acurrent drain.

To perform a battery drain test, set up an ammeter, as shown in figure 2-10. Pull thefuse if the vehicle has a dash clock. Close all doors and trunk (if applicable). Then readthe ammeter. If everything is off, there should be a zero reading. Any reading indicatesa problem. To help pinpoint the problem, pull fuses one at a time until there is a zeroreading on the ammeter. This action isolates the circuit that has the problem.

BATTERY CAPACITY TEST.- A battery load test, also termed a battery capacitytest, is the best method to check battery condition. The battery load test measures thecurrent output and performance of the battery under full current load. It is one of themost common and informative battery tests used today.Before load testing a battery, you must calculate how much current draw should beapplied to the battery. If the ampere-hour rating of the battery is given, load the batteryto three times its amp-hour rating. For example, if the battery is rated at 60 amp-hours,

test the battery at 180 amps (60 x 3 = 180). The majority of the batteries are now ratedin SAE cold-cranking amps, instead of amp-hours. To determine the load test for thesebatteries, divide the cold-crank rating by two. For example, a battery with 400 coldcrankingamps rating should be loaded to 200 amps (400 ÷ 2 = 200). Connect thebattery load tester, as shown in figure 2-11. Turn the control knob until the ammeterreads the correct load for your battery.

After checking the battery charge and finding the amp load value, you are ready to testbattery output. Make sure that the tester is connected properly. Turn the load controlknob until the ammeter reads the correct load for your battery. Hold the load for 15seconds. Next, read the voltmeter while the load is applied.

Figure 2-11.- Instrument hookup for battery capacity test.

Then turn the load control completely off so the battery will not be discharged. If thevoltmeter reads 9.5 volts or more at room temperature, the battery is good. If thebattery reads below 9.5 volts at room temperature, battery performance is poor. Thiscondition indicates that the battery is not producing enough current to run the startingmotor properly.Familiarize yourself with proper operating procedures for the type of tester you haveavailable. Improper operation of electrical test equipment may result in serious damageto the test equipment or the unit being tested.

QUICK CHARGE TEST.- The quick charge test, also known as 3-minute chargetest, determines if the battery is sulfated. If the results of the battery load test are poor,fast charge the battery. Charge the battery for 3 minutes at 30 to 40 amps. Test thevoltage while charging. If the voltage goes ABOVE 15.5 volts, the battery plates aresulfated and the battery needs to be replaced.

NEW DEVELOPMENTS IN ELECTRICAL STRORAGE

2)IGNITION SYSTEM

Structure 1 IntroductionObjectives 2 Ignition System Types 3 Comparison between Battery and Magneto Ignition System

4 Drawbacks (Disadvantages) of Conventional Ignition Systems 5 Advantages of Electronic Ignition System 6 Types of Electronic Ignition System 7 Firing Order 8 Importance of Ignition Timing and Ignition Advance 9 Summary 10 Key Words 1 INTRODUCTIONWe know that in case of Internal Combustion (IC) engines, combustion of air and fueltakes place inside the engine cylinder and the products of combustion expand to producereciprocating motion of the piston. This reciprocating motion of the piston is in turnconverted into rotary motion of the crank shaft through connecting rod and crank.This rotary motion of the crank shaft is in turn used to drive the generators for generatingpower.We also know that there are 4-cycles of operations viz.: suction; compression; powergeneration and exhaust.These operations are performed either during the 2-strokes of piston or during 4-strokesof the piston and accordingly they are called as 2-stroke cycle engines and 4-stroke cycleengines.In case of petrol engines during suction operation, charge of air and petrol fuel will betaken in. During compression this charge is compressed by the upward moving piston.And just before the end of compression, the charge of air and petrol fuel will be ignitedby means of the spark produced by means of for spark plug. And the ignition systemdoes the function of producing the spark in case of spark ignition engines.

Figure shows atypical spark plug used with petrol engines. It mainly consists of acentral electrode and metal tongue. Central electrode is covered by means of porcelaininsulating material. Through the metal screw the spark plug is fitted in the cylinder headplug. When the high tension voltage of the order of 30000 volts is applied across thespark electrodes, current jumps from one electrode to another producing a spark.Whereas in case of diesel (Compression Ignition-CI) engines only air is taken in duringsuction operation and in compressed during compression operation and just before theend of compression, when diesel fuel is injected, it gets ignited due to heat ofcompression of air.Once the charge is ignited, combustion starts and products of combustion expand, i.e.they force the piston to move downwards i.e. they produce power and after producing thepower the gases are exhausted during exhaust operation.Objectives

After studying this unit, you should be able toexplain the different types of ignition systems,differentiate between battery and magneto ignition systemknow the drawbacks of conventional ignition system, andappreciate the importance of ignition timing and ignition advance.

2 IGNITION SYSTEM TYPESBasically Convectional Ignition systems are of 2 types :(a) Battery or Coil Ignition System, and(b) Magneto Ignition System.Both these conventional, ignition systems work on mutual electromagnetic inductionprinciple.Battery ignition system was generally used in 4-wheelers, but now-a-days it is morecommonly used in 2-wheelers also (i.e. Button start, 2-wheelers like Pulsar, KineticHonda; Honda-Activa, Scooty, Fiero, etc.). In this case 6 V or 12 V batteries will supplynecessary current in the primary winding.Magneto ignition system is mainly used in 2-wheelers, kick start engines.(Example, Bajaj Scooters, Boxer, Victor, Splendor, Passion, etc.).In this case magneto will produce and supply current to the primary winding. So inmagneto ignition system magneto replaces the battery.

Battery or Coil Ignition System

Fig shows line diagram of battery ignition system for a 4-cylinder petrolengine. It mainly consists of a 6 or 12 volt battery, ammeter, ignition switch,auto-transformer (step up transformer), contact breaker, capacitor, distributorrotor, distributor contact points, spark plugs, etc.Note that the Figure 4.1 shows the ignition system for 4-cylinder petrol engine,here there are 4-spark plugs and contact breaker cam has 4-corners. (If it is for6-cylinder engine it will have 6-spark plugs and contact breaker cam will be aperfect hexagon).

The ignition system is divided into 2-circuits :(i) Primary Circuit : It consists of 6 or 12 V battery, ammeter, ignitionswitch, primary winding it has 200-300 turns of 20 SWG (SharpsWire Gauge) gauge wire, contact breaker, capacitor.

(ii) Secondary Circuit : It consists of secondary winding. Secondary Ignition Systemswinding consists of about 21000 turns of 40 (S WG) gauge wire.Bottom end of which is connected to bottom end of primary and topend of secondary winding is connected to centre of distributor rotor.Distributor rotors rotate and make contacts with contact points andare connected to spark plugs which are fitted in cylinder heads(engine earth).

(iii) Working : When the ignition switch is closed and engine in cranked,as soon as the contact breaker closes, a low voltage current will flowthrough the primary winding. It is also to be noted that the contactbeaker cam opens and closes the circuit 4-times (for 4 cylinders) inone revolution. When the contact breaker opens the contact, themagnetic field begins to collapse. Because of this collapsing magneticfield, current will be induced in the secondary winding. And becauseof more turns (@ 21000 turns) of secondary, voltage goes unto28000-30000 volts.

Figure 4.2 : Schematic Diagram of Coil/Battery Ignition System

This high voltage current is brought to centre of the distributor rotor. Distributorrotor rotates and supplies this high voltage current to proper stark plug dependingupon the engine firing order. When the high voltage current jumps the spark pluggap, it produces the spark and the charge is ignited-combustion starts-products ofcombustion expand and produce power.

Note :(a) The Function of the capacitor is to reduce arcing at the contactbreaker (CB) points. Also when the CB opens the magnetic field inthe primary winding begins to collapse. When the magnetic field is

collapsing capacitor gets fully charged and then it starts dischargingand helps in building up of voltage in secondary winding.(b) Contact breaker cam and distributor rotor are mounted on the sameshaft.In 2-stroke cycle engines these are motored at the same engine speed. And in4-stroke cycle engines they are motored at half the engine speed.

Magneto Ignition SystemIn this case magneto will produce and supply the required current to the primarywinding. In this case as shown, we can have rotating magneto with fixed coil orrotating coil with fixed magneto for producing and supplying current to primary,remaining arrangement is same as that of a battery ignition system.

Figure 4.3 given on next page shows the line diagram of magneto ignition system.

Figure 4.3 : Schematic Diagram of Magneto Ignition System

3 COMPARISON BETWEEN BATTERY ANDMAGNETO IGNITION SYSTEMBattery Ignition Magneto IgnitionBattery is a must. No battery needed.

Battery supplies current in primary circuit. Magneto produces the required current for primary circuit.

A good spark is available at low speed During starting the quality of spark is poor due to slow speed.Occupies more space. Very much compact.Recharging is a must in case battery getsdischarged. No such arrangement required.Mostly employed in car and bus for whichit is required to crank the engine. Used on motorcycles, scooters, etc.Battery maintenance is required. No battery maintenance problems. 4 DRAWBACKS (DISADVANTAGES) OFCONVENTIONAL IGNITION SYSTEMS Following are the drawbacks of conventional ignition systems :(a) Because of arcing, pitting of contact breaker point and which will lead toregular maintenance problems.

(b) Poor starting : After few thousands of kilometers of running, the timingbecomes inaccurate, which results into poor starting (Starting trouble).

(c) At very high engine speed, performance is poor because of inertia effects ofthe moving parts in the system.

(d) Some times it is not possible to produce spark properly in fouled spark Ignition Systemsplugs.In order to overcome these drawbacks Electronic Ignition system is used.

5 ADVANTAGES OF ELECTRONIC IGNITIONSYSTEM

Following are the advantages of electronic ignition system :(a) Moving parts are absent-so no maintenance.(b) Contact breaker points are absent-so no arcing.(c) Spark plug life increases by 50% and they can be used for about 60000 kmwithout any problem.(d) Better combustion in combustion chamber, about 90-95% of air fuelmixture is burnt compared with 70-75% with conventional ignition system.(e) More power output.(f) More fuel efficiency.6 TYPES OF ELECTRONIC IGNITION SYSTEM

Electronic Ignition System is as follow :(a) Capacitance Discharge Ignition system(b) Transistorized system(c) Piezo-electric Ignition system

(d) The Texaco Ignition system

Capacitance Discharge Ignition SystemIt mainly consists of 6-12 V battery, ignition switch, DC to DC convertor,charging resistance, tank capacitor, Silicon Controlled Rectifier (SCR),SCR-triggering device, step up transformer, spark plugs.A 6-12 volt battery is connected to DC to DC converter i.e. power circuit throughthe ignition switch, which is designed to give or increase the voltage to250-350 volts. This high voltage is used to charge the tank capacitor (orcondenser) to this voltage through the charging resistance. The charging resistanceis also so designed that it controls the required current in the SCR.

Figure 4.4 : Capacitance Discharge Ignition System

Depending upon the engine firing order, whenever the SCR triggering device,sends a pulse, then the current flowing through the primary winding is stopped.And the magnetic field begins to collapse. This collapsing magnetic field willinduce or step up high voltage current in the secondary, which while jumping thespark plug gap produces the spark, and the charge of air fuel mixture is ignited.Transistorized Assisted Contact (TAC) Ignition System

Advantages(a) The low breaker-current ensures longer life.(b) The smaller gap and lighter point assembly increase dwell timeminimize contact bouncing and improve repeatability of secondaryvoltage.(c) The low primary inductance reduces primary inductance reducesprimary current drop-off at high speeds.Disadvantages(a) As in the conventional system, mechanical breaker points arenecessary for timing the spark.(b) The cost of the ignition system is increased.(c) The voltage rise-time at the spark plug is about the same as before.

Figure 4.5 : Transistorized Assisted Contact (TAC) Ignition System

Piezo-electric Ignition SystemThe development of synthetic piezo-electric materials producing about 22 kV bymechanical loading of a small crystal resulted in some ignition systems for singlecylinder engines. But due to difficulties of high mechanical loading need of theorder of 500 kg timely control and ability to produce sufficient voltage, thesesystems have not been able to come up.

The Texaco Ignition SystemDue to the increased emphasis on exhaust emission control, there has been asudden interest in exhaust gas recirculation systems and lean fuel-air mixtures.To avoid the problems of burning of lean mixtures, the Texaco Ignition system hasbeen developed. It provides a spark of controlled duration which means that thespark duration in crank angle degrees can be made constant at all engine speeds.It is a AC system. This system consists of three basic units, a power unit, a controlunit and a distributor sensor.This system can give stable ignition up to A/F ratios as high as 24 : 1.

4.7 FIRING ORDERThe order or sequence in which the firing takes place, in different cylinders of amulticylinder engine is called Firing Order.In case of SI engines the distributor connects the spark plugs of different cylindersaccording to Engine Firing Order.

Advantages(a) A proper firing order reduces engine vibrations.(b) Maintains engine balancing.(c) Secures an even flow of power.

Firing order differs from engine-to-engine.Probable firing orders for different engines are :− 3 cylinder = 1-3-2− 4 cylinder engine (inline) = 1-3-4-21-2-4-3

− 4 cylinder horizontal opposed engine = 1-4-3-2(Volkswagen engine)− 6-cylinder in line engine = 1-5-3-6-2-4(Cranks in 3 pairs) 1-4-2-6-3-51-3-2-6-4-51-2-4-6-5-3− 8 cylinder in line engine 1-6-2-5-8-3-7-41-4-7-3-8-5-2-68 cylinder V type 1-5-4-8-6-3-7-21-5-4-2-6-3-7-81-6-2-5-8-3-7-41-8-4-3-6-5-7-2Cylinder 1 is taken from front of inline and front right side inV engines.

8 IMPORTANCE OF IGNITION TIMING ANDIGNITION ADVANCEIgnition timing is very important, since the charge is to be ignited just before (fewdegrees before TDC) the end of compression, since when the charge is ignited, it willtake some time to come to the required rate of burning.

Ignition AdvanceThe purpose of spark advance mechanism is to assure that under every conditionof engine operation, ignition takes place at the most favorable instant in time i.e.most favorable from a standpoint of engine power, fuel economy and minimumexhaust dilution. By means of these mechanisms the advance angle is accuratelyset so that ignition occurs before TDC point of the piston. The engine speed andthe engine load are the control quantities required for the automatic adjustment ofthe ignition timing. Most of the engines are fitted with mechanisms which areintegral with the distributor and automatically regulate the optimum spark advanceto account for change of speed and load. The two mechanisms used are :(a) Centrifugal advance mechanism, and

(b) Vacuum advance mechanism.

Centrifugal Advance MechanismThe centrifugal advance mechanism controls the ignition timing for full- loadoperation. The adjustment mechanism is designed so that its operation results inthe desired advance of the spark. The cam is mounted, movably, on the distributorshaft so that as the speed increases, the flyweights which are swung farther andfarther outward, shaft the cam in the direction of shaft rotation. As a result, thecam lobes make contact with the breaker lever rubbing block somewhat earlier,thus shifting the ignition point in the early or advance direction. Depending on thespeed of the engine, and therefore of the shaft, the weights are swung outward agreater or a lesser distance from the center. They are then held in the extendedposition, in a state of equilibrium corresponding to the shifted timing angle, by aretaining spring which exactly balances the centrifugal force. The weights shift thecam either or a rolling contact or sliding contact basis; for this reasons wedistinguish between the rolling contact type and the sliding contact type ofcentrifugal advance mechanism.The beginning of the timing adjustment in the range of low engine speeds and thecontinues adjustment based on the full load curve are determined by the size of theweights by the shape of the contact mechanisms (rolling or sliding contact type),and by the retaining springs, all of which can be widely differing designs. Thecentrifugal force controlled cam is fitted with a lower limit stop for purposes of

setting the beginning of the adjustment, and also with an upper limit stop torestrict the greatest possible full load adjustment. A typical sliding contact typecentrifugal advance mechanism is shown in Figures 4.6(a) and (b).

Figure 4.6 : Sliding Contact Type Centrifugal Advance Mechanism

Vacuum Advance MechanismVacuum advance mechanism shifts the ignition point under partial load operation.The adjustment system is designed so that its operation results in the prescribedpartial load advance curve. In this mechanism the adjustment control quantity isthe static vacuum prevailing in the carburetor, a pressure which depends on theposition of the throttle valve at any given time and which is at a maximum whenthis valve is about half open. This explains the vacuum maximum.The diaphragm of a vacuum unit is moved by changes in gas pressure. Theposition of this diaphragm is determined by the pressure differential at any givenmoment between the prevailing vacuum and atmospheric pressure. The beginningof adjustment is set by the pre-established tension on a compression spring. Thediaphragm area, the spring force, and the spring rigidity are all selected inaccordance with the partial –load advance curve which is to be followed and areall balanced with respect to each other. The diaphragm movement is transmittedthrough a vacuum advance arm connected to the movable breaker plate, and thismovement shifts the breaker plate an additional amount under partial load Ignition Systemscondition in a direction opposite to the direction of rotation of the distributorshaft. Limit stops on the vacuum advance arm in the base of the vacuum unitrestrict the range of adjustment.The vacuum advance mechanism operates independent of the centrifugal advancemechanism. The mechanical interplay between the two advance mechanisms,however, permits the total adjustment angle at any given time to be the result ofthe addition of the shifts provided by the two individual mechanisms operates inconjunction with the engine is operating under partial load. A typical vacuumadvance mechanism is shown in Figure 4.7.

Figure 4.7 : Vacuum Advance Mechanism

4.9 SUMMARYIn SI engines, the combustion process is initiated by a spark between the two electrodesof spark plug. This occurs just before the end of compression stroke. Ignition is only apre-requisite of combustion. In this unit, we have learnt in detail the different types ofignition systems. The difference between battery and magneto ignition systems lies onlyin the source of electrical energy. Battery ignition system uses a battery, magnetoignition system uses a magneto to supply low voltages all other system componentsbeing similar.The order or sequence in which the firing takes place, in different cylinders of amulti-cylinder engine is called firing order.10 KEY WORDSBattery Ignition System : It is commonly used because of its combinedcheapness, convenience of maintenance, attentionand general suitability.Magneto Ignition System : It is an efficient, reliable, self contained unit,which is often preferred for air craft enginesbecause storage batteries are heavy andtroublesome.Firing Order : It is the order in which various cylinders of amulti-cylinder engine fire.Ignition Timing : It is the correct instant for the introduction ofspark near the end of compression stroke in thecycle.

ELECTRONIC IGNITION SYSTEM

The basic difference between the contact point and the electronic ignition system is inthe primary circuit. The primary circuit in a contact point ignition system is open andclosed by contact points. In the electronic system, the primary circuit is open andclosed by the electronic control unit (ECU).The secondary circuits are practically the same for the two systems. The difference isthat the distributor, ignition coil, and wiring are altered to handle the high voltageproduced by the electronic ignition system.One advantage of this higher voltage (up to 60,000 vo lts) is that spark plugs withwider gaps can be used. This results in a longer spark, which can ignite leaner air-fuelmixtures. As a result engines can run on leaner mixtures for better fuel economy and

lower emissions.

Electronic Ignition System Components

The components of an electronic ignition system regardless of the manufacturer allperform the same functions. Each manufacturer has it own preferred terminology andlocation of the components. The basic components of an electronic ignition system areas follows:

TRIGGER WHEEL- The trigger wheel, also known as a reluctor, pole piece, orarmature, is connected to the upper end of the distributor shaft. The trigger wheelreplaces the distributor cam. Like the distributor cam lobes, the teeth on the triggerwheel equal the number of engine cylinders.

PICKUP COIL- The pickup coil, also known as a sensor assembly, sensor coil, ormagnetic pickup assembly, produces tiny voltage surges for the ignition systemselectronic control unit. The pickup coil is a small set of windings forming a coil.

ELECRTONIC CONTROL UNIT AM-PLIFIER- The ignition system electroniccontrol unit amplifier or control module is an "electronic switch" that turns the ignitioncoil primary current ON and OFF. The ECU performs the same function as the contactpoints. The ignition ECU is a network of transistors, capacitors, resistors, and otherelectronic components sealed in a metal or plastic housing. The ECU can be located(1) in the engine compartment, (2) on the side of the distributor, (3) inside thedistributor, or (4) under the vehicle dash. ECU dwell time (number of degrees thecircuit conducts current to the ignition coil) is designed into the electronic circuit ofthe ECU and is NOT adjustable.

Electronic Ignition System OperationWith the engine running, the trigger wheel rotates inside the distributor. As a tooth ofthe trigger wheel passes the pickup coil, the magnetic field strengthens around thepickup coil. This action changes the output voltage or current flow through the coil. Asa result, an electrical surge is sent to the electronic control unit, as the trigger wheelteeth pass the pickup coil.The electronic control unit increases the electrical surges into ON/ OFF cycles for theignition coil. When the ECU is ON, current passes through the primary windings ofthe ignition coil, thereby developing a magnetic field. Then, when the trigger wheeland pickup coil turn OFF the ECU, the magnetic field inside the ignition coil collapsesand fires a sparkplug.

Hall-Effect SensorSome electronic distributors have a magnetic sensor using the Hall effect. When a steelshutter moves between the two poles of a magnet, it cuts off the magnetism betweenthe two poles. The Hall-effect distributor has a rotor with curved plates, calledshutters. These shutters are curved so they can pass through the air gap between thetwo poles of the magnetic sensor, as the rotor turns. Like the trigger wheel, there arethe same number of shutters as there are engine cylinders.

Each time a shutter moves through the air gap between the two poles of the magneticsensor, it cuts off the magnetic field between the poles. This action provides a signal tothe ECU. When a shutter is not in the way, the magnetic sensor is producing voltage.This voltage is signaling the ECU to allow current to flow through the ignition coilsprimary winding. However, when the shutter moves to cut off the magnetic field, thesignal voltage drops to zero. The ECU then cuts off the current to the ignition coilsprimary winding. The magnetic field collapses, causing the coil secondary winding to

produce a high voltage surge. This high voltage surge is sent by the rotor to the properspark plug

PROGRAMMED IGNITION SYSTEM

The term programmed ignition is used by Rover and some other manufacturers. Ford, Bosch and some others name it electronic spark advance (ESA). Constant energy electronic ignition is commonly used in countless applications. Its limitations, however, lies on the dependence upon mechanical components for speed and load advance characteristics. In many cases these did not match ideally the requirements of the engine.Programmed ignition systems operate digitally, which is the major difference compared to earlier systems. In this system sensed information regarding the operating requirements of a particular engine can be programmed into memory of the electronic control unit. The data for storage in read only memory (ROM) is obtained from rigorous testing on an engine under various operating conditions. Programmed ignition has several advantages as follows :(i) The ignition timing can be accurately matched to the individual application under arange of various operating conditions.(ii) Control inputs like coolant temperature and ambient air temperature can be used.Other inputs such as engine knock can be taken into account.(Hi) Starting is improved, fuel consumption as well as emissions are reduced, and idle control is better.(iv) The number of wearing components is considerably reduced in this system.Programmed ignition or ESA can be installed as a separate system or included as part of the fuel control system. This provides numerous possibilities in the management of the engine control.

DISTRIBUTORLESS IGNITION

 An ignition system that does not use a distributor to route high voltage to the spark plugs. The high voltage plug wire runs directly from the ignition coil to the spark plug. Some DIS systems have one coil for every two spark plugs (a shared system), while others have a separate coil for each spark plug (See Coil-On-Plug Ignition). Eliminating the distributor makes the system more reliable and eliminates maintenance.

3a) STARTER MOTOR

STARTING CIRCUIT

Learning Objective: Identify starting-circuit components, their function, operation,and maintenance procedures.The internal combustion engine is not capable of self-starting. Automotive engines(both spark-ignition and diesel) are cranked by a small but powerful electric motor.This motor is called a cranking motor, starting motor, or starter.The battery sends current to the starter when the operator turns the ignition switch tostart. This causes a pinion gear in the starter to mesh with the teeth of the ring gear,thereby rotating the engine crankshaft for starting.The typical starting circuit consists of the battery, the starter motor and drivemechanism, the ignition switch, the starter relay or solenoid, a neutral safety switch(automatic transmissions), and the wiring to connect these components.

STARTER MOTORThe starting motor (fig. 2-37) converts electrical energy from the battery intomechanical or rotating energy to crank the engine. The main difference between anelectric starting motor and an electric generator is that in a generator, rotation of thearmature in a magnetic field produces voltage. In a motor, current is sent through thearmature and the field; the attraction and repulsion between the magnetic poles of thefield and armature coil alternately push and pull the armature around. This rotation(mechanical energy), when properly connected to the flywheel of an engine, causes theengine crankshaft to turn.

Starting Motor ConstructionThe construction of the all starting motors is very similar. There are, however, slightdesign variations. The main parts of a starting motor are as follows:

ARMATURE ASSEMBLY- The windings, core, starter shaft, and commutatorassembly that spin inside a stationary field.

COMMUTATOR END FRAME- The end housing for the brushes, brush springs, andshaft bushings.

Figure 2-37.- Typical starting motor.

PINION DRIVE ASSEMBLY- The pinion gear, pinion drive mechanism, andsolenoid.

FIELD FRAME- The center housing that holds the field coils and pole shoes.

DRIVE END FRAME- The end housing around the pinion gear, which has a bushingfor the armature shaft.

ARMATURE ASSEMBLY.- The armature assembly consists of an armature shaft,armature core, commutator, and armature windings.

The armature shaft supports the armature assembly as it spins inside the starterhousing. The armature core is made of iron and holds the armature windings in place.The iron increases the magnetic field strength of the windings.The commutator serves as a sliding electrical connection between the motor windingsand the brushes and is mounted on one end of the armature shaft. The commutator hasmany segments that are insulated from each other. As the windings rotate away fromthe pole shoe (piece), the commutator segments change the electrical connectionbetween the brushes and the windings. This action reverses the magnetic field aroundthe windings. The constant changing electrical connection at the windings keeps themotor spinning.

COMMUTATOR END FRAME.- The commutator end frame houses the brushes,the brush springs, and the armature shaft bushing.The brushes ride on top of the commutator. They slide on the commutator to carrybattery current to the spinning windings. The springs force the brushes to maintaincontact with the commutator as it spins, thereby no power interruptions occurs. Thearmature shaft bushing supports the commutator end of the armature shaft.

PINION DRIVE ASSEMBLYThe pinion drive assembly includes the pinion gear, the pinion drive mechanism, andsolenoid. There are two ways that a starting motor can engage the pinion assembly-( 1)with a moveable pole shoe that engages the pinion gear and (2) with a solenoid and

shift fork that engages the pinion gear.The pinion gear is a small gear on the armature shaft that engages the ring gear on theflywheel. Most starter pinion gears are made as part of a pinion drive mechanism. Thepinion drive mechanism slides over one end of the starter armature shaft. The piniondrive mechanism found on starting motors that you will encounter are of three designs-Bendix drive, overrunning clutch, and Dyer drive.The BENDIX DRIVE (fig. 2-38) relies on the principle of inertia to cause the piniongear to mesh with the ring gear. When the starting motor is not operating, the piniongear is out of mesh and entirely away from the ring gear. When the ignition switch isengaged, the total battery voltage is applied to the starting motor, and the armatureimmediately starts to rotate at high speed.The pinion, being weighted on one side and having internal screw threads, does notrotate immediately with the shaft but because of inertia, runs forward on the revolvingthreaded sleeve until it engages with the ring gear. If the teeth of the pinion and ringgear do not engage, the drive spring allows the pinion to revolve and forces the pinionto mesh with the ring gear. When the pinion gear is engaged fully with the ring gear,the pinion is then driven by the starter through the compressed drive spring and cranksthe engine. The drive spring acts as a cushion while the engine is being crankedagainst compression. It also breaks the severity of the shock on the teeth when thegears engage and when the engine kicks back due to ignition. When the engine startsand runs on its own power, the ring gear drives the pinion at a hi gher speed than doesthe starter. This action causes the pinion to turn in the opposite direction on thethreaded sleeve and automatically disengages from the ring gear. This prevents theengine from driving the starter.

The OVERRUNNING CLUTCH (fig. 2-39) provides positive meshing and demeshingof the starter motor pinion gear and the ring gear. The starting motor armature shaftdrives the shell and sleeve assembly of the clutch. The rotor assembly is connected tothe pinion gear which meshes with the engi ne ring gear. Spring-loaded steel rollers arelocated in tapered notches between the shell and the rotor. The springs and plungershold the rollers in position in the tapered notches. When the armature shaft turns, therollers are jammed between the notched surfaces, forcing the inner and outer membersof the assembly to rotate as a unit and crank the engine.

Figure 2-39.- Typical overrunning clutch.

After the engine is started, the ring gear rotates faster than the pinion gear, thustending to work the rollers back against the plungers, and thereby causing anoverrunning action. This action prevents excessive speed of the starting motor. Whenthe starting motor is released, the collar and spring assembly pulls the pinion out ofmesh with the ring gear.

The DYER DRIVE (fig. 2-40) provides complete and positive meshing of the drivepinion and ring gear before the starting motor is energized. It combines principles ofboth the Bendix and overrunning clutch drives and is commonly used on heavy-dutyengines.

A starter solenoid is used to make the electrical connection between the battery and thestarting motor. The starter solenoid is an electromagnetic switch; it is similar to otherrelays but is capable of handling higher current levels. A starter solenoid, dependingon the design of the starting motor, has the following functions:Closes battery-to-starter circuit.Rushes the starter pinion gear into mesh with the ring gear.Bypass resistance wire in the ignition circuit.

Figure 2-40.- Dyer drive.The starter solenoid may be located away from or on the starting motor. Whenmounted away from the starter, the solenoid only makes and breaks electricalconnection. When mounted on the starter, it also slides the pinion gear into theflywheel.

In operation, the solenoid is actuated when the ignition switch is turned or when thestarter button is depressed. The action causes current to flow through the solenoid(causing a magnetic attraction of the plunger) to ground. The movement of the plungercauses the shift lever to engage the pinion with the ring gear. After the pinion isengaged, further travel of the plunger causes the contacts inside the solenoid to closeand directly connects the battery to the starter.If cranking continues after the control circuit is broken, it is most likely to be causedby either shorted solenoid windings or by binding of the plunger in the solenoid. Lowvoltage from the battery is often the cause of the starter making a clicking sound.When this occurs, check all starting circuit connections for cleanliness and tightness.

FIELD FRAMEThe field frame is the center housing that holds the field coils and pole shoes.The field coil (winding) is a stationary set of windings that creates a strong magneticfield around the motor armature. When current flows through the winding, themagnetic field between the pole shoes becomes very large. Acting against themagnetic field created by the armature, this action spins the motor with extra power.Field windings vary according to the application of the starter motor. The most popularconfigurations are as follows (fig. 2-41):

TWO WINDINGS, PARALLEL- The wiring of the two field coils in parallel willincrease their strength because they receive full voltage. Note that two additional poleshoes are used. Though they have no windings, their presence will further strengthenthe magnetic field.

FOUR WINDINGS, SERIES-PARALLEL- The wiring of four field coils in a seriesparallelcombination creates a stronger magnetic field than the two field coilconfiguration.FOUR WINDINGS, SERIES- The wiring of four field coils in series provides a largeamount of low-speed torque, which is desirable for automotive starting motors.However, series-wound motors can build up excessive speed if allowed to run free tothe point where they will destroy themselves.

Figure 2-41.- Field winding configurations.

SIX WINDINGS, SERIES-PARALLELThree pairs of series-wound field coils provide the magnetic field for a heavy-dutystarter motor. This configuration uses six brushes.

THREE WINDINGS, TWO SERIES, ONE SHUNTThe use of one filled coil that is shunted to ground with a series-wound motor controlsmotor speed. Because the shunt coil is not affected by speed, it will draw a steadyheavy current, effectively limiting speed.

DRIVE END FRAMEThe drive end frame is designed to protect the drive pinion from damage and tosupport the armature shaft. The drive end frame of the starter contains a bushing toprevent wear between the armature shaft and drive end frame.

Types of Starting MotorsThere are two types of starting motors that you will encounter on equipment. These arethe direct drive starter and the double reduction starter. All starters require the use ofgear reduction to provide the mechanical advantage required to turn the engineflywheel and crankshaft.

DIRECT DRIVE STARTERSDirect drive starters make use of a pinion gear on the armature shaft of the startingmotor. This gear meshes with teeth on the ring gear. There are between 10 to 16 teethon the ring gear for every one on the pinion gear. Therefore, the starting motorrevolves 10 to 16 times for every revolution of the ring gear. In operation, the startingmotor armature revolves at a rate of 2,000 to 3,000 revolutions per minute, thus

turning the engine crankshaft at speeds up to 200 revolutions per minute.

DOUBLE REDUCTION STARTERThe double reduction starter makes use of gear reduction within the starter and thereduction between the drive pinion and the ring gear. The gear reduction drive head isused on heavy-duty equipment.Figure 2-42 shows a typical gear reduction starter. The gear on the armature shaft doesnot mesh directly with the teeth on the ring gear, but with an intermediate gear whichdrives the driving pinion. This action provides additional breakaway, or startingtorque, and greater cranking power. The armature of a starting motor with a gearreduction drive head may rotate as many as 40 revolutions for every revolution of theengine flywheel.

Figure 2-42.- Gear reduction starter.

NEUTRAL SAFETY SWITCHVehicles equipped with automatic transmissions require the use of a neutral safetyswitch. The neutral safety switch prevents the engine from being started unless theshift selector of the transmission is in NEUTRAL or PARK. It disables the startingcircuit when the transmission is in gear. This safety feature prevents the accidentalstarting of a vehicle in gear, which can result in personal injury and vehicle damage.The neutral safety switch is wired into the circuit going to the starter solenoid. Whenthe transmission is in forward or reverse gear, the switch is in the OPEN position(disconnected). This action preve nts current from activating the solenoid and starterwhen the ignition switch is turned to the START position. When the transmission is inneutral or park, the switch is closed (connected), allowing current to flow to the starterwhen the ignition is turned.

A misadjusted or bad neutral safety switch can keep the engine from cranking. If thevehicle does not start, you should check the action of the neutral safety switch bymoving the shift lever into various positions while trying to start the vehicle. If the

starter begins to work, the switch needs to be readjusted.To readjust a neutral safety switch, loosen the fasteners that hold the switch. With theswitch loosened, place the shift lever into park (P). Then, while holding the ignitionswitch in the START position, slide the neutral switch on its mount until the enginecranks. Without moving the switch, tighten the fasteners. The engine should now startwith the shift lever in park or neutral. Check for proper operation after the adjustment.If by adjusting the switch to normal operation is not resumed, it may be required to testthe switch. All that is required to test the switch is a 12-volt test light.

To test the switch, touch the test light to the switch output wire connection whilemoving the shift lever. The light should glow as the shift lever is slid into park orneutral. The light should not work in any other position. If the light is not workingproperly, check the mechanism that operates the switch. If the problem is in theswitch, replace it.

Starter Current Draw Test

STARTING CIRCUIT MAINTENANCE

The condition of the starting motor should be carefully checked at each PM service.This permits you to take appropriate action, where needed, so equipment failurescaused by a faulty starter can be reduced, if not eliminated.The starter current draw test measures the amount of amperage used by the startingcircuit. It quickly tells you about the condition of the starting motor and other circuitcomponents. If the current draw is lower or higher than the manufacturer'sspecifications, there is a problem in the circuit.A visual inspection for clean, tight electrical connections and secure mounting at theflywheel housing is the extent of the maintenance check. Then operate the starter andobserve the speed of rotation and the steadiness of operation. To prevent the starterfrom overheating, do NOT operate the starter for more than 30 seconds.To perform a starter current draw test, you may use either a voltmeter or inductiveammeter or a battery load tester. These meters are connected to the battery to measurebattery voltage and current flow out of the battery. For setup procedures, use themanufacturer's manual for the type of meter you intend to use.If the starter is not operating properly, remove the starter, disassemble it, and check thecommutator and brushes. If the commutator is dirty, it may be cleaned with a piece ofNo. 00 sandpaper. However, if the commutator is rough, pitted, or out-of-round or ifthe insulation between the commutator bars is high, it must be reconditioned using anarmature lathe.To keep a gasoline engine from starting during testing, disconnect the coil supply wireor ground the coil wire. With a diesel engine, disable the fuel injection system orunhook the fuel shutoff solenoid. Check the manufacturer's service manual for details.With the engine ready for testing, crank the engine and note the voltage and currentreadings. Check the manufacturer's service manual. If they are not withinspecifications, there is something wrong with the starting circuit.Brushes should be at least half of their original size. If not, replace them. The brushesshould have free movement in the brush holders and make good, clean contact with thecommutator.

Once the starter is checked and repaired as needed, it should be reassembled, makingsure that the starter brushes are seated. Align the housings and install the boltssecurely. Install the starter in the opening in the flywheel housing and tighten theattaching bolts to the specified torque. Connect the cable and wire lead firmly to cleanterminals.

STARTING MOTOR CIRCUIT TESTSThere are many ways of testing a starting motor circuit to determine its operatingcondition. The most common tests are as follows:The starter current draw test is used to measure the amount of amperage used by thestarting circuit.The starter circuit voltage drop tests (insulated circuit resistance test and starter groundtest) are used to locate parts with higher than normal resistance quickly.

WARNINGDo NOT crank the engine for more than 30 seconds or starter damage can result. If thestarter is cranked too long, it will overheat. Allow the starter to cool for a few minutesif more cranking time is needed.Starting Circuit Voltage Drop TestsA voltage drop test will quickly locate a component with higher than normalresistance. This test provides an easy way of checking circuit condition. You do NOThave to disconnect any wires and components to check for voltage drops. The twotypes of voltage drop tests are the insulated circuit resistance test and the starterground circuit test.

INSULATED CIRCUIT RESISTANCE TESTThe insulated circuit resistance test checks ail components between the positiveterminal of the battery and the starting motor for excess resistance.Using a voltmeter, connect the leads to the positive terminal of the battery and thestarting motor output terminal.With the ignition or injection system disabled, crank the engine. Note the voltmeterreading. It should not be over 0.5 volts. If voltage drop is greater, something within thecircuit has excessive resistance. There may be a burned or pitted solenoid contact,loose electrical connections, or other malfunctions. Each component is then to betested individually.

STARTER GROUND CIRCUIT TESTThe starter ground circuit test checks the circuit between the starting motor and thenegative terminal of the battery.Using a voltmeter, connect the leads to the negative terminal of the battery and to theend frame of the starting motor. Crank the engine and note the voltmeter reading. If itis higher than 0.5 volts, check the voltage drop across the negative battery cable. Theengine may not be properly grounded. Clean, tighten, or replace the battery cable ifneeded. A battery cable problem can produce symptoms similar to a dead battery, badsolenoid, or weak starting motor. If the cables do NOT allow enough current to flow,the starter will turn slowly or not at all.

3b) ELECTRONIC CONTROL OF CARBURATION

Electronically controlled carburetor

An electronically controlled carburetor for an internal combustion engine for a vehicle has a variable venturi for varying the venturi cross-section and concurrently varying the amount of air metered into the venturi in response to the engine demands an air flow sensor for sensing the displacement of the variable venturi and producing related electrical signals in response to changes in air flow through the venturi, a main fuel nozzle for discharging metered fuel into the venturi, a fuel flow sensor for sensing pressure differential of fuel across a main fuel jet communicating with the main fuel nozzle and for producing related electrical signals in response to changes in fuel flow through the main fuel jet, an air bleed controlling actuator for controlling the amount of air to be bled into the main fuel nozzle, and a control circuit responsive to the output signals from the air flow sensor and the fuel flow sensor for driving the air bleed controlling actuator. With this arrangement, the amount of air bleed may be controlled so as to set the ratio of air-to-fuel at an arbitrary fixed value at all times.

Electronic Fuel Injection

Both the multi-point and the single-point systems operate in a very similar fashion, having an electromechanically operated injector or injectors opening for a predetermined length of time called the injector pulse width. The pulse width is determined by the engine’s Electronic Control Module (ECM and depends on the engine temperature, the engine load

and the information from the oxygen (lambda) sensor. The fuel is delivered from the tank through a filter, and a regulator determines its operating pressure. The fuel is delivered to the engine in precise quantities and in most cases is injected into the inlet manifold to await the valve’s opening, then drawn into the combustion chamber by the incoming air.

The Fuel Tank

This is the obvious place to start in any full system explanation. Unlike the tanks on early carburettor-equipped vehicles, it is a sealed unit that allows the natural gassing of the fuel to aid delivery to the pump by slightly pressurising the system. When the filler cap is removed, pressure is heard to escape because the fuel filler caps are no longer vented.

The Fuel Pump

This type of high-pressure fuel pump (Fig 1.0) is called a roller cell pump, with the fuel entering the pump and being compressed by rotating cells which force it through the pump at a high pressure. The pump can produce a pressure of 8 bar (120 psi) with a delivery rate of approximately 4 to 5 litres per minute. Within the pump is a pressure relief valve that lifts off its seat at 8 bar to arrest the pressure if a blockage in the filter or fuel lines or elsewhere causes it to become obstructed. The other end of the pump (output) is home to a non-return valve which, when the voltage to the pump is removed, closes the return to the tank and maintains pressure within the system. The normal operating pressure within this system is approximately 2 bar (30 psi), at which the current draw on the pump is 3 to 5 amps. Fuel passing across the fuel pump's armature is subjected to sparks and arcing; this sounds quite dangerous, but the absence of oxygen means that there will not be an explosion!

Figure 1.0The majority of fuel pumps fitted to today’s motor vehicles are fitted within the vehicle’s petrol tank and are referred to as ‘submerged’ fuel pumps. The pump is invariably be located with the fuel sender unit and both units can sometimes be accessed through an inspection hole either in the boot floor or under the rear seat. Mounted vertically, the pump comprises an inner and outer gear assembly that is called the ‘gerotor’. The combined assembly is secured in the tank using screws and sealed with a rubber gasket, or a bayonet-type locking ring. On some models, there are two fuel pumps, the submerged pump acting as a ‘lift’ pump to the external roller cell pump.

Fuel Supply

A conventional ‘flow and return’ system has a supply of fuel delivered to the fuel rail, and the unwanted fuel is passed through the pressure regulator back to the tank. It is the restriction in the fuel line created by the pressure regulator that provides the system operational pressure.

Returnless Fuel Systems

Have been adopted by several motor manufacturers and differ from the conventional by having a delivery pipe only to the fuel rail with no return flow back to the tank.The returnless systems, both the mechanical and the electronic versions, were necessitated by emissions laws. The absence of heated petrol returning to the fuel tank reduces the amount of evaporative emissions, while the fuel lines are kept short, thus reducing build costs.

Mechanical Returnless Fuel Systems

The ‘returnless’ system differs from the norm by having the pressure regulator inside the fuel tank. When the fuel pump is activated, fuel flows into the system until the required pressure is obtained; at this point ‘excess’ fuel is bled past the pressure regulator and back into the tank.The ‘flow and return’ system has a vacuum supply to the pressure regulator: this enables the fuel pressure to be increased whenever the manifold vacuum drops, providing fuel enrichment under acceleration.The ‘returnless’ system has no mechanical compensation affecting the fuel pressure, which remains at a higher than usual 44 to 50 psi. By increasing the delivery pressure, the ECM (Electronic Control Module) can alter the injection pulse width to give the precise delivery, regardless of the engine load and without fuel pressure compensation.

Electronic Returnless Fuel Systems

This version has all the required components fitted within the one unit of the submersible fuel pump. It contains a small particle filter (in addition to the strainer), pump, electronic pressure regulator, fuel level sensor and a sound isolation system. The electronic pressure regulator allows the pressure to be increased under acceleration conditions, and the pump’s output can be adjusted to suit the engine's fuel demand. This prolongs the pump’s life as it is no longer providing a larger than required output delivery.The Electronic Control Module (ECM) supplies the required pressure information, while the fuel pump’s output signal is supplied in the form of a digital squarewave. Altering the squarewave’s duty cycle affects the pump’s delivery output.To compensate for the changing viscosity of the fuel with changing fuel temperature, a fuel rail temperature sensor is installed. A pulsation damper may also be fitted ahead of or inside the fuel rail.

Injectors

The injector is an electromechanical device, which is fed by a 12 volt supply from either the fuel injection relay or the ECM. The voltage is present only when the engine is cranking or running, because it is controlled by a tachometric relay. The injector is supplied with fuel from a common fuel rail. The injector pulse width depends on the input signals seen by the ECM from its various engine sensors, and varies to compensate for cold engine starting and warm-up periods, the initial wide pulse getting narrower as the engine warms to operating temperature. The pulse width also expands under acceleration and contracts under light load conditions.

Bosch electronic injection

Today’s diesel engine is more popular than ever before. Thanks to Bosch technology, every diesel is efficient, clean and powerful. Half of all newly-registered pass-enger cars in Western Europe are powered by a compression-ignition engine nowadays. With its high-pressure injection systems such as the Common Rail System or the Unit Injector System, Bosch has

played a decisive part in this success story. They guarantee the best possible development of performance together with clean fuel combustion.

Electronic Diesel Control (EDC) regulates the functions of the injection system in such a way that the engine provides the demanded engine torque. The injection parameters are constantly matched to the engine and the driving situation. Engines with an electronically controlled diesel system from Bosch combine maximum dynamic performance with minimum fuel consumption and emissions.

Customer benefits

Cleaner and economical engine operation thanks to the rapid adaptation of all injection parameters

4) CHARGING SYSTEMALTERNATORS

The alternator (fig. 2-21) has replaced the dc generator because of its improvedefficiency. It is smaller, lighter, and more dependable than the dc generator. Thealternator also produces more output during idle which makes it ideal for late modelvehicles.The alternator has a spinning magnetic field. The output windings (stator) arestationary. As the magnetic field rotates, it induces current in the output windings.

Alternator ConstructionKnowledge of the construction of an alternator is required before you can understandthe proper operation, testing procedures, and repair procedures applicable to analternator.

Figure 2-22.- Rotor assembly.

The primary components of an alternator are as follows:

ROTOR ASSEMBLY (rotor shaft, slip rings, claw poles, and field windings)

STATOR ASSEMBLY (three stator windings or coils, output wires, and stator core)

RECTIFIER ASSEMBLY (heat sink, diodes, diode plate, and electrical terminals)

ROTOR ASSEMBLY (fig. 2-22).- The rotor consists of field windings (wire woundinto a coil placed over an iron core) mounted on the rotor shaft. Two claw-shaped polepieces surround the field windings to increase the magnetic field. The fingers on one of the claw-shaped pole pieces produce south (S) poles and theother produces north (N) poles. As the rotor rotates inside the alternator, alternating NS-N-S polarity and ac current is produced (fig. 2-23). An external source of electricity

is required to excite the magnetic field of the alternator.Slip rings are mounted on the rotor shaft to provide current to the rotor windings. Eachend of the field coil connects to the slip rings.

STATOR ASSEMBLY (fig. 2-24).- The stator produces the electrical output of thealternator. The stator, which is part of the alternator frame when assembled, consists ofthree groups of windings or coils which produce three separate ac currents. This isknown as three-phase output. One end of the windings is connected to the statorassembly and the other is connected to a rectifier assembly. The windings are wrappedaround a soft laminated iron core that concentrates and strengthen the magnetic fieldaround the stator windings. There are two types of stators- Y -type stator and deltatypestator.

The Y-type stator (fig. 2-25) has the wire ends from the stator windings connected to aneutral junction. The circuit looks like the letter Y. The Y-type stator provides goodcurrent output at low engine speeds.The delta-type stator (fig. 2-26) has the stator wires connected end-to-end. With noneutral junction, two circuit paths are formed between the diodes. A delta-type stator isused in high output alternators.

RECTIFIER ASSEMBLY.The rectifier assembly, also known as a diode assembly, consists of six diodes used toconvert stator ac output into dc current. The current flowing from the winding is

allowed to pass through an insulated diode. As the current reverses direction, it flowsto ground through a grounded diode. The insulated and grounded diodes prevent thereversal of current from the rest of the charging system. By this switching action andthe number of pulses created by motion between the windings of the stator and rotor, afairly even flow of current is supplied to the battery terminal of the alternator.The rectifier diodes are mounted in a heat sink (metal mount for removing excess heatfrom electronic parts) or diode bridge. Three positive diodes are press-fit in aninsulated frame. Three negative diodes are mounted into an uninsulated or groundedframe.

When an alternator is producing current, the insulated diodes pass only outflowingcurrent to the battery. The diodes provide a block, preve nting reverse current flowfrom the alternator. Figure 2-27 shows the flow of current from the stator to thebattery.

A cross-sectional view of a typical diode is shown in figure 2-28. Note that the figurealso shows the diode symbol used in wiring diagrams. The arrow in this symbolindicates the only direction that current will flow. The diode is sealed to keep moistureout.

Alternator Operation

The operation of an alternator is somewhat different than the dc generator. Analternator has a rotating magnet (rotor) which causes the magnetic lines of force torotate with it. These lines of force are cut by the stationary (stator) windings in thealternator frame, as the rotor turns with the magnet rotating the N and S poles to keepchanging positions. When S is up and N is down, current flows in one direction, butwhen N is up and S is down, current flows in the opposite direction. This is calledalternating current as it changes direction twice for each complete revolution. If therotor speed were increased to 60 revolutions per second, it would produce 60-cyclealternating current.

Since the engine speed varies in a vehicle, the frequency also varies with the change ofspeed. Likewise, increasing the number of pairs of magnetic north and south poles willincrease the frequency by the number pair of poles. A four-pole generator can generatetwice the frequency per revolution of a two -pole rotor.

ALTERNATOR OUTPUT CONTROLA voltage regulator controls alternator output by changing the amount of current flowthrough the rotor windings. Any change in rotor winding current changes the strengthof the magnetic field acting on the stator windings. In this way, the voltage regulatorcan maintain a preset charging voltage. The three basic types of voltage regulators areas follows:Contact point voltage regulator, mounted away from the alternator in the enginecompartmentElectronic voltage regulator, mounted away from the alternator in the enginecompartmentElectronic voltage regulator, mounted on the back or inside the alternatorThe contact point voltage regulator uses a coil, set of points, and resistors that limitssystem voltage. The electronic or solid-state regulators have replaced this older type.For operation, refer to the "Regulation of Generator Output" section of this chapter.

The electronic voltage regulators use an electronic circuit to control rotor field strengthand alternator output. It is a sealed unit and is not repairable. The electronic circuitmust be sealed to prevent damage from moisture, excessive heat, and vibration. Arubber like gel surrounds the circuit for protection.

An integral voltage regulator is mounted inside or on the rear of the alternator. This isthe most common type used on modern vehicles. It is small, efficient, dependable, andcomposed of integrated circuits.An electronic voltage regulator performs the same operation as a contact pointregulator, except that it uses transistors, diodes, resistors, and capacitors to regulatevoltage in the system. To increase alternator output, the electronic voltage regulatorallows more current into the rotor windings, thereby strengthen the magnetic fieldaround the rotor. More current is then induced into the stator windings and out of thealternator.To reduce alternator output, the electronic regulator increases the resistance betweenthe battery and the rotor windings. The magnetic field decreases and less current isinduced into the stator windings.Alternator speed and load determines whether the regulator increases or decreasescharging output. If the load is high or rotor speed is low (engine at idle), the regulatorsenses a drop in system voltage. The regulator then increases the rotors magnetic fieldcurrent until a preset output voltage is obtained. If the load drops or rotor speedincreases, the opposite occurs.

Alternator MaintenanceAlternator testing and service call for special precautions since the alternator outputterminal is connected to the battery at all times. Use care to avoid reversing polaritywhen performing battery service of any kind. A surge of current in the oppositedirection could bum the alternator diodes.Do not purposely or accidentally "short" or "ground" the system when disconnectingwires or connecting test leads to terminals of the alternator or regulator. For example,grounding of the field terminal at either alternator or regulator will damage theregulator. Grounding of the alternator output terminal will damage the alternator andpossibly other portions of the charging system.Never operate an alternator on an open circuit. With no battery or electrical load in thecircuit, alternators are capable of building high voltage (50 to over 110 volts) whichmay damage diodes and endanger anyone who touches the alternator output terminal.Alternator maintenance is minimized by the use of prelubricated bearings and longerlasting brushes. If a problem exists in the charging circuit, check for a complete field

circuit by placing a large screwdriver on the alternator rear-bearing surface. If the fieldcircuit is complete, there will be a strong magnetic pull on the blade of thescrewdriver, which indicates that the field is energized. If there is no field current, thealternator will not charge because it is excited by battery voltage.Should you suspect troubles within the charging system after checking the wiringconnections and battery, connect a voltmeter across the battery terminals. If thevoltage reading, with the engine speed increased, is within the manufacturer'srecommended specification, the charging system is functioning properly. Should thealternator tests fail, the alternator should be removed for repairs or replacement. DoNOT forget, you must ALWAYS disconnect the cables from the battery first.

ALTERNATOR TESTINGTo determine what component( s) has caused the problem, you will be required todisassemble and test the alternator.

ROTOR TESTING.- To test the rotor for grounds, shorts, and opens, perform thefollowing:To check for grounds, connect a test lamp or ohmmeter from one of the slip rings tothe rotor shaft (fig. 2-29). A low ohmmeter reading or the lighting of the test lampindicates that the rotor winding is grounded.

Figure 2-29.- Testing rotor for grounds.To check the rotor for shorts and opens, connect the ohmmeter to both slip rings, asshown in figure 2-30. An ohmmeter reading below the manufacturer's specifiedresistance value indicates a short. A reading above the specified resistance valueindicates an open. If a test lamp does not light when connected to both slip rings, thewinding is open.

STATOR TESTING.- The stator winding can be tested for opens and grounds after ithas been disconnected from the alternator end frame.

If the ohmmeter reading is low or the test lamp lights when connected between eachpair of stator leads (fig. 2-31), the stator winding is electrically good.A high ohmmeter reading or failure of the test lamp to light when connected from anyone of the leads to the stator frame (fig. 2-32) indicates the windings are not grounded.It is not practical to test the stator for shorts due to the very low resistance of thewinding.

DIODE TESTING.- With the stator windings disconnected, each diode may be testedwith an ohmmeter or with a test light. To perform the test with an ohmmeter, proceedas follows:Connect one ohmmeter test lead to the diode lead and the other to the diode case (fig.2-33). Note the reading. Then reverse the ohmmeters leads to the diode and again notethe reading. If both readings are very low or very high, the diode is defective. A gooddiode will give one low and one high reading.

An alternate method of testing each diode is to use a test lamp with a 12-volt battery.To perform a test with a test lamp, proceed as follows:Connect one of the test leads to the diode lead and the other test lead as shown infigure 2-34. Then reverse the lead connections. If the lamp lights in both checks, the

diode is defective. Or, if the lamp fails to light in either direction, the diode isdefective. When a good diode is being tested, the lamp will light in only one of the twochecks.

After completing the required test and making any necessary repairs or replacement ofparts, reassemble the alternator and install it on the vehicle. After installation, start theengine and check that the charging system is functioning properly. NEVERATTEMPT TO POLARIZE AN ALTERNATOR. Attempts to do so serves no purposeand may damage the diodes, wiring, and other charging circuit components.

CHARGING SYSTEM TEST

Charging system tests should be performed when problems point to low alternatorvoltage and current. These tests will quickly determine the operating condition of thecharging system. Common charging system tests are as follows:Charging system output test-measures current and voltage output of the chargingsystem.Regulator voltage test- measures charging system voltage under low output, low loadconditions.

Regulator bypass test- connects full battery voltage to the alternator field, leaving theregulator out of the circuit.Circuit resistance tests- measures resistance in insulted and grounded circuits of thecharging system.Charging system tests are performed in two ways- by using a load tester or by using avolt-ohm-millimeter (VOM/ multimeter). The load tester provides the accurate methodfor testing a charging system by measuring both system current and voltage.Charging System Output Test

The charging system output test measures system voltage and current under maximumload. To check output with a load tester, connect tester leads as described by themanufacturer, as you may have either an inductive (clip-on) amp pickup type or a noninductivetype tester. Testing procedures for an inductive type tester are as follows:With the load tester controls set as prescribed by the manufacturer, turn the ignitionswitch to the RUN position. Note the ammeter reading.Start the engine and adjust the idle speed to test specifications (approximately 200rpm).Adjust the load control on the tester until the ammeter reads specified current output.Do not let voltage drop below specifications (about 12 volts). Note the ammeterreading.Rotate the control knob to the OFF position. Evaluate the readings.

To calculate charging system output, add the two ammeter readings. This will give youtotal charging system output in amps. Compare this figure to the specifications withinthe manufacturer's manual.Current output specifications will depend on the size (rating) of the alternator. Avehicle with few electrical accessories may have an alternator rated at 35 amps,whereas a larger vehicle with more electrical requirements could have an alternatorrated from 40 to 80 amps. Always check the manufacturer's service manual for exactvalues.If the charging system output current tested low, perform a regulator voltage test and aregulator bypass test to determine whether the alternator, regulator, or circuit wiring isat fault.

Regulator Voltage TestA regulator voltage test checks the calibration of the voltage regulator and detects alow or high setting. Most voltage regulators are designed to operate between 13.5 to14.5 volt range. This range is stated for normal temperatures with the battery fully'charged. Regulator voltage test procedure is as follows:Set the load tester selector to the correct position using the manufacturer's manual.With the load control OFF, run the engine at 2,000 rpm or specified test speed. Notethe voltmeter reading and compare it to the manufacturer's specifications.If the voltmeter reading is steady and within manufacturer's specifications, then theregulator setting is okay. However, if the volt reading is steady but too high or too low,then the regulator needs adjustment or replacement. If the reading were not steady, thiswould indicate a bad wiring connection, an alternator problem, or a defectiveregulator, and further testing is required.

Regulator Bypass TestA regulator bypass test is an easy and quick way of determining if the alternator,regulator, or circuit is faulty. Procedures for the regulator bypass test is similar to thecharging system output test, except that the regulator be taken out of the circuit. Directbattery voltage (unregulated voltage) is used to excite the rotor field. This should allowthe alternator to produce maximum voltage output.

Depending upon the system there are several ways to bypass the voltage regulator. Themost common ways are as follows:Sorting a test tab to ground on the rear of the alternator (if equipped).Placing a jumper wire across the battery and field terminals of the alternator.With a remote regulator, unplug the wire from the regulator and place a jumper wireacross the battery and field terminals in the wires to the alternator.

CAUTIONFollow the manufacturer's directions to avoid damaging the circuit. You must NOTshort or connect voltage to the wrong wires or the diodes or voltage regulator may beruined.When the regulator bypass test is being performed, charging voltage and currentINCREASE to normal levels. This indicates a bad regulator. If the charging voltageand current REMAINS THE SAME, then you have a bad alternator.

CIRCUIT RESISTANCE TESTA circuit resistance test is used to locate faulty wiring, loose connections, partiallyburnt wire, corroded terminals, or other similar types of problems.There are two common circuit resistance tests- insulated resistance test and groundcircuit resistance test.

INSULATED RESISTANCE TEST

To perform an insulated resistance test, connect the load tester as described by themanufacturer. A typical connection setup is shown in figure 2-35. Note how thevoltmeter is connected across the alternator output terminal and positive batteryterminal.With the vehicle running at a fast idle, rotate the load control knob to obtain a 20-ampcurrent flow at 15 volts or less. All accessories and lights are to be turned OFF. Readthe voltmeter. The voltmeter should NOT read over 0.7-volt drop (0.1 volt perelectrical connection) for the circuit to be considered in good condition. However, ifthe voltage drop is over 0.7 volt, circuit resistance is high and a poor electricalconnection exists.

GROUND CIRCUIT RESISTANCE TESTWith the ground circuit resistance test the voltmeter leads are placed across thenegative battery terminal and alternator housing (fig. 2-36).The voltmeter should NOT read over 0.1 volt per electrical connection. If the readingis higher, this indicates such problems as loose or faulty connections, burnt plug

sockets, or other similar malfunctions.

Bosch compact alternator

Key points-

BOSCH COMPACT ALTERNATOR

5) WIRING OF AUTO ELECTRICAL SYSTEM

When you push the button or insert a key in your car, from the very moment electrical system starts to work. In some cars, electrical system works passively because of security system. Let’s have an idea about Electron, Current and Voltage to go in further depth about electrical circuit.

Electron:

An electron is defined as a subatomic particle, which is charged negatively. It can be either free or bound to the nucleus of an atom.

Current:

The flow of electron is called as current. Just like water flows in pipe, electrons flow in wire.

Voltage:

It is a force which causes electrons to flow in a conductor. The difference in electrical pressure or potential between two terminals in a circuit is called voltage.We can compare current and voltage with velocity and pressure. Also, when there is a flow there is always a resistance or friction. Wires or cables offer very little resistance to flow of electric current through them. The amount of resistance depends on size, which means diameter and length of the cable. The resistance is measured in Ohms.When discussing about electrons, current, voltage and resistance, we must not forget about the very famous Ohm’s law.Ohm’s law:-it states that current flow is directly proportional to the voltage and inversely proportional to the resistance. This law relates the current, voltage and resistance in a circuit.

When you turn on your car, the entire electrical circuit starts working and causes the current to flow form battery to the fuse box, which is then transferred to different elements of the automobile electrical systems. When you start a car, the starting system draws current from battery and turns the engine on. At the same time, charging system and ignition system also starts working. Blower, fan, music system, lights, different signals, dashboard control, wiper motor and all the electronic sensors and actuators will need electric power. This requirement is fulfilled by the charging system and the battery.

All these components are directly or indirectly connected to the battery which itself gets charged with the help of charging system. There are lots of wires and cables which connects all these electrical components to the battery either in series or parallel connection.

The automobile wiring system connected either in series or parallel, can be subdivided into number of simple circuits. These circuits consist of the battery, feed wire, switch wire electrical components, and a return wire.

Earth Return System:

In automobiles, the electrical system needs a return wire in between the components that require electrical supply and also to the battery. Simple solution to this is a single high conductor wire. If any fault occurs in the circuit, this wire can be identified easily. This is called as earth return system. One end of the earth return path is connected to the battery terminal and the other end is bolted to the vehicle chassis to complete the path. Generally, insulated earth return system is used in automobiles and is very useful nowadays for the purpose of safety in the vehicle.

All electrical circuits incorporate both a feed and a return conductor between the battery and the component requiring supply of electrical energy. The vehicle with a metal structure can be used as one of the two conducting paths. This is called as the earth return (Fig. 13.51). A live feed wire cable forms the other conductor. To complete the earth-return path, one end of a short thick cable is bolted to the chassis structure while the other end is attached to one of the battery terminal posts. The electrical

Fig. 13.51. Earth-return circuit,component is also required to be earthed in a similar way. Only one battery-to-c hassis conductor is necessary for a complete vehicle’s wiring system and similarly any number of separate earth-return circuits can be wired. An earth-return system, therefore, reduces and simplifies the amount of wiring so that it is easy to trace electrical faults.

Fig. 13.52. Basic wiring circuit of vehicle.

Insulated Return.Some vehicle application requires a separate insulated-cable system for both the feed and the return conductors. It is also safer because with separate feed and return cables, it is practically impossible for the cable conductors to short even if chafed and touching any of the metal bodywork, as the body is not live since it is not a part of the electrical circuits. From the safety reasons, an insulated return (Fig. 13.50) is essential for vehicles transporting highly flammable liquids and gases, where a spark could very easily set off an explosion or a fire. The vehicles, such as coaches and double-decker buses use large quantity of plastic panelling. For these vehicles an insulated return is more reliable and

safer. The insulated return off course uses extra cable that makes the overall wiring harness heavier, less flexible, and bulky, consequently increases the cost to some extent.

Fuses.Fuses are available in different forms as shown in Fig. 13.47. The glass cartridge type is the oldest, which uses a sort length of tinned wire joined at each end to a metal cap and enclosed in a glass cylinder. A strip of paper, colour coded and marked with fuse rating, is placed close to the wire. Different ratings are manufactured to suit the various circuits. If the current exceeds the rating, the fuse ‘blows’, that is the wire melts, and the circuit is broken.Same fuses, e.g. ceramic type, are rated according to the continuous current that can be carried by the fuse. This current is normally half the current required to melt the fuse. Fuses are either mounted centrally on a fuse board or placed in a separate fuse holder ‘in-lined’ to protect an auxiliary. Some vehicles install a fusible link in the main output lead from the battery. This heavy duty fuse melts if an accident causes the main cable short to earth.

Fig. 13.47. Types of fuses.Thermal Circuit Breakers. A bimetallic strip is used in a circuit breaker to control a pair of contacts in the main circuit. An overload current heats and bends the strip, which opens the contacts and temporarily interrupts the circuit. When this is installed in alighting system, a short circuit causes the light to go off and on repeatedly so that the driver can bring the vehicle to rest safely. A single fuse of the normal type placed in the lighting system causes the light to go off totally in the event of its failure giving rise to a dangerous situation ; so separate fuses are used for each headlamp.

Vehicle Electrical Distribution SystemThe increased application of electrical and electronic systems in automobiles has neces-sitated the use for complex electrical distribution systems. A typical mid-priced, medium-size European car of the 1990s uses more than 1.5 km of wiring and more than 2000 terminals, connectors and relays, and the weight of such an electrical distribution system exceeds 30 kg. The wiring harness is the major component of the electrical distribution system. This contains bundles of cables, which connect all of the electrical parts, sensors and actuators with electronic control units in a vehicle. It serves two primary functions.

These include (i) to act as a power distribution network, and (ii) to act as an information distribution network.The majority of vehicle breakdowns are caused by electrical failure, so vehicle reliability is critically dependent upon good wiring harness design and implementation. Generally, the wiring harness is divided into a main harness that runs the length of the vehicle connecting the battery to the charging system, vehicle interior, lighting and accessory circuits, and various sub-harnesses, such as door wiring, tailgate wiring, and roof wiring. For facilitating vehicle assembly and servicing, connector blocks are used for connecting the sub-harnesses to the main harness.

Cables.Electrical cables used in automobiles contain several stands of annealed copper wire bunched together and encased in an insulating covering (generally PVC-polyvinyl chloride) of 0.2-0.4 mm thickness. Each strand of copper wire is typically about 0.32 mm diameter. The number of strands determines the size and hence current-carrying capacity of the cable. Applications requiring greater flexibility, such as in a tax-door sub-harness, flexible cable made from 0.18 mm annealed copper strands, are used. For high temperature applications (usually in the engine compartment) ordinary PVC insulation is not suitable, and hence special plastics such a PTFE, PFA, FED or X-ray treated cross-linked PVC or polyethylene are used.Generally, cables are specified as per the strand diameter and number of strands. A cable with specification as 7/0.3 is made from seven strands each of 0.3 mm diameter. If an insulation thickness of 0.35 mm is provided, a cable normally has a finished diameter of about 1.6 mm and is suitable for carrying current up to about 4 A.To reduce costs, manufacturers use the thinnest possible cable for a particular application in a vehicle, without causing too much voltage drop. As a rule of thumb, a maximum voltage drop of 5% (i.e. 0.6 V in a 12 V system) is allowed for general lighting and control circuits. Normally, a current rating of about 8.5 A per square millimetre of cable cross-section is assumed. A reduced rating of about 6 A per square millimetre is considered for continuously loaded cables. Table 13.1 summarizes typical sizes, current ratings and resistances for commonly used wires in automobiles.

Table 13.1. Sizes and Current

Ratings of Wires used inAutomobile Wiring Harnesses.

Wire Size Current Rating (A) Resistance per metre

Application

7/0.3 4.0 0.032 Side/tail lamps,

9/0.3 5.5 0.027 signals, music

14/0.3 9.0 0.017 system

28/0.3 17.5 0.009 Light, heater, motors

44/0.3 25.0 0.006

65/0.3 35.0 0.004 Alternator, main

84/0.3 42.0 0.003 supply to fuse

97/0.3 50.0 0.002 box

120/0.3 60.0 0.002

37/0.9 170.0 0.001 or less

Starter motor

Harness Routing.Generally the bundle of cables with a diameter in the range 10-30 mm is used for the wiring harness. This bundle is carefully routed around the vehicle, avoiding the locations having trim screws, mounting bolts and extremes of temperature (exhaust system, air-conditioner components). At regular intervals, clamps are used to secure the harness properly to the body-shell so that it is against stressing of the wires. Rubber grommet is fitted at the places where the harness passes through a metal panel thereby protecting the harness against chafing and preventing the ingress of moisture and dirt.The places where many cables run (for example, the rear light clusters), ribbon cable is preferred to use. Ribbon cable is simply a number of conductors laid side-by-side to make a wide, flat, harness and it is easy to conceal this type of cable underneath carpeting and along flat body panels.

Cable Colour Coding.Some form of cable colour coding is provided with the automobile wiring harnesses for fault diagnosis and repair works. The colour codes used invariably vary from one manufacturer to another and sometimes between different models from the same manufacturer. Therefore, it is important to refer to the vehicle repair manual before taking up any electrical work.Most coding systems use a base cable for each cable and then add a contrasting tracer. These colours then are indicated by a letter code on the vehicle wiring diagram, which is usually in black and white. For example, a cable marked ‘BO’ on a wiring diagram indicates black with an orange tracer. To bring down costs, the ‘tracer’ can be a thin painted line added only where the cable enters a connector. Some manufacturers use just a few base colours and then code the wires by adding small coloured sleeves at each end. Table 13.2 provides some of the main colours used for the principal circuits.

Table 13.2. Colours for Circuits.

Circuit BSI Letter Code British

Letter Code German

Earth connections black B SW

Ignition circuits white W WS

Main battery feed brown N BR

Side lamps red R RT

Auxiliaries controlled by ignition switch green G GN

Auxiliaries not controlled by ignition switch purple P VI

Headlamps blue U BL

In view of the different standards used by manufacturers, it is wise to consult the wiring diagram for the vehicle whenever a particular cable or circuit has to be identified.

Circuit Numbering.In addition to colour coding some manufacturers also use numbers to indicate the circuits. Table 13.3 provides the main numbers used as recommended by the German DIN standard.

Table 13.3. Terminal Marking According to DIN Standard.

Circuit Number Application

1 Ignition, earth side of coil

4 Ignition, HT output

15 Ignition, feed (un-fused)

30 Feed from battery

31 Earth

51 Alternator output

54 Ignition, feed (fused)

56 Headlamps

58 Side/tail lamps

75 Accessories

Sub-circuits are identified by adding a number or letter after the main number; e.g. 15-4 is a sub-circuit based on circuit 15, the ignition feed circuit.

Wiring of car

Wiring of a two wheeler

Wiring of Audi A4

6) DASH BOARD UNITS AND ELECTRICAL ACCESSORIES

FOG LAMP

Definition:

Fog lamps produce high intensity beam pointing towards the road surface for clear visibility during rain, fog, dust or snowy conditions.

Requirement:

Fog lamps are required for better visibility of the road surfaces in foggy conditions.

Function:

Fog lamps are meant to provide a wide and bar shaped light beam and are generally mounted below the bumper pointing slightly down. Usually they are white or yellow in color and are intended to be used at low speeds in conditions such as heavy fog, dust, snow or rain.

Fog lamps are different than driving lamps and are meant to provide clear vision of the road ahead of the vehicle, during conditions when normal headlamps would reflect back at he driver. When visibility is affected during rain, snow and foggy weather, the fog lamps improve it by reducing the reflection effect from fog, rain and snow. These lamps usually do not come as standard equipment but, can be added. The use of fog lamps are strictly restricted in some areas. Since fog lamps are essentially a thick, concentrated beam, its light intensity can blind the eyes of other drivers on the road if not aimed properly.   Generally, fog lamps are yellow but are also available in white color. Fog lamps are often confused with the driving lamps, but generally, yellow lights indicate fog lamps while any other auxiliary lamp would be white. In some countries, the use of fog lamp is banned completely. Some studies found that due to such high intensity light, the driver of the vehicle loses vision on the road or become so focused on the beam they see nothing else, actually causing accidents. Figures show that people in the US tend to use fog lamps unnecessarily in dry weather as opposed to when such lights are actually required.

Side Marker Lights

Definition:

Side marker lights are the lights visible from the side of the vehicle.

Requirement:

They are required to indicate the vehicle’s presence to other drivers even at oblique angles.

Function:

Side marker lights help to identify the position and direction of travel of the vehicle in low light conditions. These lights illuminate whenever the parking and tail lamps of the vehicle are ON and when the headlamps are also used. It is a compulsory element in cars for North America.

Side marker lights can be considered as an addition to the lighting system of automobiles which was being made compulsory in US for the vehicles manufacturer, after January 1st 1970. Since then, the vehicles must be equipped with side marker lights or retro reflectors, visible from the sides of the vehicle. Drivers can easily get an idea of a vehicle’s presence and its size during low light conditions. In some cases, these side marker lights also blink with the vehicle taking a turn, along with the turn signal lights so that the other drivers can see the vehicle turning from different angles. According to the regulations framed in US, the side marker lights must possess specific color for front and rear sides of the vehicle. At front side of the vehicle, the side marker lights should have amber color light while, the rear side marker light should be red. These side marker lights are wired and gets power from the battery but illuminate usually when the parking light or braking light is turned on. With such lights fitted around the vehicle, the safety against accidents increases, as other vehicle drivers can have a better idea of the vehicle’s position, size and direction of travel.

Tail Light Assembly 

Definition:

Tail light assembly is an assembly of different lights fitted at the rear end of the vehicle each having its specific function.

Requirement:

Tail light assembly is required to increase the visibility of the vehicle from the rear in a dark environment.

Function:

Tail light assembly consists of rear tail lights, braking lights, turn signal lights and reversing lights. These lights illuminate to warn other drivers of your intentions and to help avoid a collision from behind.

Tail lights of automobiles are considered to be one of the elements that improve vehicle safety. Tails lamps or tail light as they are commonly called are often an assembly of the brake light, parking light and reversing light all together and is placed on the rear right and rear left corner of the vehicle. In many vehicles the tail lights illuminate only when the headlamps are turned on. The tail lights may appear to come on when the brakes are applied but during braking, the intensity of the light is higher. This is because some vehicles use a bulb with a dual filament, one for the tail light and a brighter one for the brake light.   This brighter filament can also be used as the turn signal lamp. This difference in intensities is mainly to warn other drivers of your vehicle stopping or turning. Tail lamps, brake lights and directional lights can be the same light or separate lights, depending on the design of the lamp.  Some vehicles now use LED lights, which greatly improve the flexibility of designs the engineers can use. This type of lighting is not limited to a single bulb, but rather a varying pattern can be used for the tail lamp function, braking function and directional function of the LED.

Turn Signal Lights 

Definition:

Turn signals are lights provided on the front and rear of the vehicle on both sides to indicate a vehicle that is going to turn.

Requirement:

These turn signal lights indicate other vehicle drives about the driver’s intention of changing the lane or taking a turn left or right.

Function:

Turn signal lights are made to blink usually at a rate ranging from 60 to 120 blinks per minute and almost all countries have regulated that the turn signals color should be amber as they are predicted to be more distinguishing as turn signals than other colors.

Turn signal lights have been used on automobiles since 1900. On the early models, they were called trafficators and they would actually extend from the body of the car (usually the door or windshield pillar). The use of  lamps to indicate a driver's intention has been made mandatory for almost all the vehicles manufactured today. Turn signals are also commonly called blinkers, flashers or indicators but all show that the driver is about to make a turn or lane change. Turn signal indicators are placed on both front and rear of the vehicle and on both the left and right side. The driver operates them from a switch normally located on the left side of the steering column. These turn signals are extremely useful when the driver is about to change the lane or is taking a turn, whether left or right. Since these indicators blink with respect to the vehicle direction of travel, the vehicles coming from behind, can have a clear indication of the vehicle’s presence as well as its direction of intended movement. Drivers of other vehicles can adjust their vehicle’s speed and avoid a collision which may have occurred if there was no indication of the lateral change the driver of the first vehicle was about to make. Since all the lighting instruments in the vehicle must meet DOT standards, turn signal lights also have certain rules to follow. The turn signal lights must have pre-specified minimum and maximum intensity levels, along with minimum horizontal and vertical visibility angles. 

LIGHTING CIRCUITLearning Objective: Identify lighting-circuit components, their functions, andmaintenance procedures.

The lighting circuit (fig. 2-54) includes the battery, vehicle frame, all the lights, andvarious switches that control their use. The lighting circuit is known as a single-wiresystem since it uses the vehicle frame for the return.The complete lighting circuit of a vehicle can be broken down into individual circuits,each having one or more lights and switches. In each separate circuit, the lights areconnected in parallel, and the controlling switch is in series between the group oflights and the battery.The marker lights, for example, are connected in parallel and are controlled by a singleswitch. In some installations, one switch controls the connections to the battery, whilea selector switch determines which of two circuits is energized. The headlights, withtheir high and low beams, are an example of this type of circuit.

In some instances, such as the courtesy lights, several switches may be connected inparallel so that any switch may be used to turn on the light.When a wiring diagram is being studied, all light circuits can be traced from thebattery through the ammeter to the switch (or switches) to the individual light.

Figure 2-55.- Lamp construction and configurations.

LAMPSSmall gas-filled incandescent lamps with tungsten filaments are used on automotiveand construction equipment (fig. 2-55). The filaments supply the light when sufficientcurrent is flowing through them. They are designed to operate on a low voltage currentof 12 or 24 volts, depending upon the voltage of the the vehicle will be of the single-ordouble-contact small one-half-candlepower bulbs to large 50- candlepower bulbs. Thegreater the candlepower of the lamp, the more current it requires when lighted. Lampsare identified by a number on the base. When you replace a lamp in a vehicle, be surethe new lamp is of the proper rating. The lamps within Lamps are rated as to size bythe candlepower (luminous intensity) they produce. They range from types with nibsto fit bayonet sockets, as shown in lamp is also whiter than a conventional lamp, whichincreases lighting ability.

HEADLIGHTS HEADLIGHT SWITCHThe headlights are sealed beam lamps (fig. 2-57) that illuminate the road duringnighttime operation. Headlights consist of a lens, one or two elements, and a integralreflector. When current flows through the element, the element gets white hot andglows. The reflector and lens direct the light forward.Many modern passenger vehicles use halogen headlights. A halogen headlightcontains a small, inner halogen lamp surrounded by a conventional sealed housing. Ahalogen headlamp increases light output by 25 percent with no increase in current. Thehalogen

The headlight switch is an ON/ OFF switch and rheostat (variable resistor) in the dashpanel (fig. 2-58) or on the steering column (fig. 2-59). The headlight switch controlscurrent flow to the lamps of the headlight system. The rheostat is for adjusting thebrightness of the instrument panel lights.Military vehicles that are used in tactical situations are equipped with a headlightswitch that is integrated with the blackout lighting switch (fig. 2-60). An importantfeature of this switch is that it reduces the possibility of accidentally turning on the

lights in a blackout.

With no lights on, the main switch can be turned to the left without operating themechanical switch to get blackout marker lights (including blackout taillights andstoplights) and blackout driving lights. But for stoplights for daylight driving orheadlights for ordinary night driving, you must first lift the mechanical switch leverand then turn the main switch to the right. The auxiliary switch gives panel lights whenthe main switch is in any of its ON positions. But it will give parking lights only whenthe main switch is in service drive (to the extreme right). When the main switch is off,the auxiliary switch should not be moved from the OFF position.DIMMER SWITCHThe dimmer switch controls the high and low headlamp beam function and is normallymounted on the floorboard (fig. 2-61) or steering column (fig.2-62). When the operator activates the dimmer switch, it changes the electricalconnection to the headlights.

In one position, the high beams are turned on, and, in the other position, the dimmerchanges them to low beam.

Aiming HeadlightsThe headlights can be aimed using a mechanical aimer or a wall screen. Either methodassures that the headlight beams point in the direction specified by the vehiclemanufacturer. Headlights that are aime d too high can blind oncoming vehicles.Headlights that are aimed too low or to one side will reduce the operator's visibility.

To ensure that the headlights are properly aimed, you should have a half a tank of fuel,the correct tire pressure, and only the spare tire and jack in the vehicle. Somemanufacturers recommend that someone sit in the operator and passenger seats whileaiming the lights.

HEADLIGHT AIMERS are a device for pointing the vehicle headlights in a specifiedposition. They may be permanently installed on a track or may be portable. Somerequire a level floor, and others have internal leveling mechanisms to allow for unevenshop floors. To use the aimer, follow the instructions for the specific type ofequipment.

The HEADLIGHT AIMING SCREEN is a series of measured lines marked on a shop

wall or on a framed easel for aiming the headlights of a vehicle. The screen should beno less than 10 feet wide and 42 inches high. When it is mounted on an easel withcasters, the screen should be no more than 12 inches from the floor. To comply withregulations of most localities, you should place the screen 25 feet ahead of the vehicle.The accepted driving beam pattern for passenger vehicles will show the high intensityportion (hotspot) of the light rays centered on a horizontal line that is 2 inches belowthe center or horizontal reference line on the screen (fig. 2-63). This means that therewill be a 2-inch drop of the light beam for every 25 feet of distance from the headlight.Headlights on large trucks present a special problem because of the effect of a heavyload. At the same 25 feet, truck headlights should be aimed so that none of the highintensity portion of the light will project higher than a level of 5 inches below thecenter on the headlight being tested. This is necessary to compensate for the variationsin loading.

When using a screen for aiming the headlights on a vehicle that uses a four-headlightsystem, adjust the hotspots of the No. 1 (inboard) lights so that they are centered on thevertical lines 2 inches below the horizontal line (fig. 2-64). The low beam of the No. 2(outboard) lights is aimed so that the hotspot does not extend to the left of straightahead or extend more than 6 inches to the right of straight ahead. The top of thehotspot of the No. 2 lights is aimed at the horizontal line. When the No. 2 lights areproperly adjusted, the high beam will be correct.

BLACKOUT LIGHTSBlackout lighting is a requirement for certain combat operations. The purposes ofblackout lighting are as follows:

To provide the vehicle operator with sufficient light to operate the vehicle in totaldarkness

To provide minimum lighting to show vehicle position to a leading or trailing vehiclewhen illumination must be restricted to a level not visible to a distant enemyThe three types of blackout lighting are as follows:

The BLACKOUT DRIVING LIGHT (fig. 2-65) is designed to provide a white light of25 to 50 candlepower at a distance of 10 feet directly in front of the light. The light isshielded so that the top of the low beam is directed not less than 2 degrees below thehorizon. The beam distribution on a level road at 100 feet from the light is 30 feetwide.

The BLACKOUT STOP/ TAILLIGHT and MARKER LIGHT (fig. 2-66) are designedto be visible at a horizontal distance of 800 feet and not visible beyond 1,200 feet. Thelights also must be invisible from the air above 400 feet with the vehicle on upgradesand downgrades of 20 percent. The horizontal beam cutoff for the lights is 60 degreesright and left of the beams center line at 100 feet.

The COMPOSITE LIGHT (fig. 2-67) is currently the standard light unit that is used onthe rear of tactical military vehicles. The composite light combines service stop, tail,and turn signals with blackout stop and taillighting.

Blackout lighting control switches are designed to prevent the service lighting frombeing turned on accidentally. Their operation is described in the "Headlight Switch"section of this TRAMAN.

TURN-SIGNAL SYSTEMSVehicles that operate on any public road must be equipped with turn signals. Thesesignals indicate a left or right turn by providing a flashing light signal at the rear andfront of the vehicle.The turn-signal switch is located on the steering column (fig. 2-68). It is designed toshut off automatically after the turn is completed by the action of the canceling cam.

A wiring diagram for a typical turn-signal system is shown in figure 2-69. A commondesign for a turn-signal system is to use the same rear light for both the stop and turnsignals. This somewhat complicates the design of the switch in that the stoplightcircuit must pass through the turn-signal switch. When the turn-signal switch is turnedoff, it must pass stoplight current to the rear lights. As a left or right turn signal isselected, the stoplight circuit is open and the turn-signal circuit is closed to therespective rear light.

The turn signal flasher unit (fig. 2-70) creates the flashing of the turn signal lights. Itconsists basically of a bimetallic (two dissimilar metals bonded together) stripwrapped in a wire coil. The bimetallic strip serves as one of the contact points.When the turn signals are actuated, current flows into the flasher- first through theheating coil to the bimetallic strip, then through the contact points, then out of theflasher, where the circuit is completed through the turn-signal light. This sequence ofevents will repeat a few times a second, causing a steady flashing of the turn signals.

BACKUP LIGHT SYSTEMThe backup light system provides visibility to the rear of the vehicle at night and awarning to the equipped vehicles is combined with the neutral safety switchpedestrians, whenever the vehicle is shifted into reverse. The backup light system hasa fuse, gearshift-or transmission-mounted switch, two backup lights, and wiring toconnect these components.

The backup light switch closes the light circuit when the transmission is shifted into

reverse. The most common backup light switch configurations are as follows:The backup light switch mounted on the transmission and operated by the shift lever.The backup light switch mounted on the steering column and operated by the gearshiftlinkage.The transmission-or gearshift-mounted backup light switch on many automatictransmission-

STOPLIGHT SYSTEMAll vehicles that are used on public highways must be equipped with a stoplightsystem. The stoplight system consists of a fuse, brake light switch (fig. 2-71), two rearwarning lights, and related wiring.The brake light switch on most automotive equipment is mounted on the brake pedal.When the brake pedal is pressed, it closes the switch and turns on the rear brake lights.On construction and tactical equipment, you may find a pressure light switch. Thistype of switch uses either air or hydraulic pressure, depending on the equipment. It ismounted on the master cylinder of the hydraulic brake system or is attached to thebrake valve on an air brake system. As the brakes are depressed, either air or hydraulicpressure builds on a diaphragm inside the switch. The diaphragm closes allowingelectrical current to turn on the rear brake lights.

EMERGENCY LIGHT SYSTEMThe emergency light system, also termed hazard warning system, is designed to signaloncoming traffic that a vehicle has stopped, stalled, or has pulled up to the side of theroad. The system consists of a switch, flasher unit, four turn signal lights, and relatedwiring. The switch is normally a push-pull switch and is mounted on the steeringcolumn.When the switch is closed, current flows through the emergency flasher. Like a turnsignal flasher, the emergency flasher opens and closes the circuit to the lights. Thiscauses all four turn signals to flash.

CIRCUIT BREAKERS AND FUSESFuses are safety devices placed in electrical circuits to protect wires and electricalunits from a heavy flow of current. Each circuit, or at least each individual electricalsystem, is provided with a fuse that has an ampere rating for the maximum currentrequired to operate the units. The fuse element is made from metal with a low-meltingpoint and forms the weakest point of the electrical circuit. In case of a short circuit orother trouble, the fuse will be burned out first and open the circuit just as a switchwould do. Examination of a burnt-out fuse usually gives an indication of the problem.

A discolored sight gl ass indicates the circuit has a short either in the wiring or in oneof its components. If the glass is clear, the problem is an overloaded circuit. Be surewhen replacing a fuse that it has a rating equal to the one burned out. Ensure that thetrouble of the failure has been found and repaired.A circuit breaker performs the same function as a fuse. It disconnects the power sourcefrom the circuit when current becomes too high. The circuit breaker will remain openuntil the trouble is corrected. Once the trouble is corrected, a circuit breaker willautomatically reset itself when current returns to normal levels. The fuses and circuitbreakers can usually be found behind the instrument panel on a fuse block (fig. 2-72).

INSTRUMENTS, GAUGES, AND ACCESSORIES

Learning Objective: Identify instrument, gauges, and accessories, their functions, andmaintenance procedures.

The instrument panel is placed so that the instruments and gauges can easily be readby the operator. They inform the operator of the vehicle speed, engine temperature, oilpressure, rate of charge or discharge of the battery, amount of fuel in the fuel tank, anddistance traveled. Vehicle accessories, such as windshield wipers and horns, providethe operator with much needed safety devices.

BATTERY CONDITION GAUGEThe battery condition gauge is one of the most important gauges on the vehicle. If thegauge is interpreted properly, it can be used to troubleshoot or prevent breakdowns.The following are the three basic configurations of battery condition gauges- ammeter,voltmeter, and indicator lamp.

The AMMETER is used to indicate the amount of current flowing to and from the

battery. It does NOT give an indication of total charging output because of other unitsin the electrical system. If the ammeter shows a 10-ampere discharge, it indicates thata 100 ampere-hour battery would be discharged in 10 hours, as long as the dischargerate remained the same. Current flowing from the battery to the starting motor is neversent through the ammeter, because the great quantities of amperes used (200 to 600amperes) cannot be measured due to its limited capacity. In a typical ammeter (fig. 2-73), all the current flowing to and from the battery, except for starting, actually is sentthrough a coil to produce a magnetic field that deflects the ammeter needle inproportion to the amount of current. The coil is matched to the maximum currentoutput of the charging unit, and this varies with different applications.The VOLTMETER (fig. 2-74) provides a more accurate indication of the condition ofthe electrical system and is easier to interpret by the operator. During vehicle

operation, the voltage indicated on the voltmeter is considered to be normal in a rangeof 13.2 to 14.5 volts for a 12-volt electrical system. As long as the system voltageremains in this range, the operator can assume that no problem exists. This contrastswith an ammeter, which gives the operator no indication of problems, such as animproperly calibrated voltage regulator, which could allow the battery to be drained byregulating system voltage to a level below normal.

The INDICATOR LAMP has gained popularity as an electrical system condition

gauge over the years. Although it does not provide as detailed analysis of the electricalsystem condition as a gauge, it is considered more useful to the average vehicleoperator. This is because it is highly visible when a malfunction occurs, whereas agauge usually is ignored because the average vehicle operator does not know how tointerpret its readings. The indicator lamp can be used in two different ways to indicatean electrical malfunction, which are as follows:1. LOW VOLTAGE WARNING LAMP (fig. 2-75) is set up to warn the operatorwhenever the electrical system voltage has dropped below the normal operationalrange.2. NO-CHARGE INDICATOR (fig. 2-76) is set up to indicate whenever the alternatoris not producing current.

FUEL GAUGEMost fuel gauges are operated electrically and are composed of two units- the gauge,mounted on the instrument panel; and the sending unit, mounted in the fuel tank. Theignition switch is included in the fuel gauge circuit, so the gauge operates only whenthe ignition switch is in the ON position. Operation of the electrical gauge depends oneither coil action or thermostatic action. The four types of fuel gauges are as follows:

Figure 2-76.- No-charge indiutor schematic. The THERMOSTATIC FUEL GAUGE, SELF-REGULATING (fig. 2-77), containsan electrically heated bimetallic strip that is linked to a pointer. A bimetallic stripconsists of two dissimilar metals that, when heated, expand at different rates, causing itto deflect or bend. In the case of this gauge, the deflection of the bimetallic strip resultsin the movement of the pointer, causing the gauge to give a reading. The sending unitconsists of a hinged arm with a float on the end. The movement of the arm controls agrounded point that makes contact with another point which is attached to anelectrically heated bimetallic strip. The heating coils in the tank and the gauge areconnected to each other in series.

The THERMOSTATIC FUEL GAUGE, EXTERNALLY REGULATED (fig. 2-78),differs from a self-regulating system in the use of a variable resistance fuel tanksending unit and an external voltage-limiting device. The sending unit controls thegauge through the use of a rheostat (wire wound resistance unit whose value varieswith its effective length). Theeffective length of the rheostat is controlled in thesending unit by a sliding brush that is operated by the float arm. The power supply tothe gauge is kept constant through the use of a voltage limiter. The voltage limiterconsists of a set of contact points that are controlled by an electrically heatedbimetallic arm.

The THERMOSTATIC FUEL GAUGE, DIFFERENTIAL TYPE (fig. 2-79), is similarto the other type of thermostatic fuel gauges, except that it uses two electrically heatedbimetallic strips that share equally in operating and supporting the gauge pointer.The pointer position is obtained by dividing the available voltage between the twostrips (differential). The tank unit is a rheostat type similar to that already described;however, it contains a wire-wound resistor that is connected between externalterminals of one of the gauges of the bimetallic strip. The float arm moves a groundedbrush that raises resistance progressively to one terminal, while lowering resistance tothe other. This action causes the voltage division and resulting heat differential to thegauge strips formulating the gauge reading.

The MAGNETIC FUEL GAUGE (fig. 2-80) consists of a pointer mounted on anarmature. Depending upon the design, the armature may contain one or two poles. Thegauge is motivated by a magnetic field that is created by two separate magnetic coilsthat are contained in the gauge. One of these coils is connected directly to the battery,producing a constant magnetic field. The other coil produces a variable field, whosestrength is determined by a rheostat-type tank unit. The coils are placed 90 degreesapart.

A pressure gauge is used widely in automotive and construction applications to keeptrack of such things as oil pressure, fuel line pressure, air brake system pressure, andthe pressure in the hydraulic systems. Depending on the equipment, a mechanicalgauge, an electrical gauge, or an indicator lamp may be used.

The MECHANICAL GAUGE (fig. 2-81) uses a thin tube to carry an actual pressuresample directly to the gauge. The gauge basically consists of a hollow, flexible Cshapedtube, called a bourbon tube. As air or fluid pressure is applied to the bourbontube, it will tend to straighten out. As it straightens, the attached pointer will move,giving a reading.

The ELECTRIC GAUGE may be of the thermostatic or magnetic type as previousdiscussed. The sending unit (fig. 2-82) that is used with each gauge type varies asfollows:1. The sending unit that is used with the thermostatic pressure gauge uses a flexiblediaphragm that moves a grounded contact. The contact that mates with the groundedcontact is attached to a bimetallic strip. The flexing of the diaphragm, which is donewith pressure changes, varies the point tension. The different positions of thediaphragm produce gauge readings.

2. The sending unit that is used with the magnetic-type gauge also translates pressureinto the flexing of a diaphragm. In the case of the magnetic gauge sending unit,however, the diaphragm operates a rheostat.The INDICATOR LAMP (warning light) is used in place of a gauge on manyvehicles. The warning light, although not an accurate indicator, is valuable because ofits high visibility in the event of a low-pressure condition. The warning light receivesbattery power through the ignition switch. The circuit to ground is completed througha sending unit. The sending unit consists of a pressure-sensitive diaphragm thatoperates a set of contact points that are calibrated to turn on the warning lightwhenever pressure drops below a set pressure.TEMPERATURE GAUGEThe temperature gauge is a very important indicator in construction and automotiveequipment. The most common uses are to indicate engine coolant, transmission,differential oil, and hydraulic system temperature. Depending on the type ofequipment, the gauge may be mechanical, electric, or a warning light.The ELECTRIC GAUGE may be the thermostatic or magnetic type, as describedpreviously. The sending unit (fig. 2-83) that is used varies, depending uponapplication.1. The sending unit that is used with the thermostatic gauge consists of two bimetallicstrips, each having a contact point. One bimetallic strip is heated electrically. The otherstrip bends to increase the tension of the contact points. The different positions of thebimetallic strip create the gauge readings.2. The sending unit that is used with the magnetic gauge contains a device called athermistor. A thermistor is an electronic device whose resistance decreasesproportionally with an increase in temperature.The MAGNETIC GAUGE contains a bourbon tube and operates by the sameprinciples as the mechanical pressure gauge.The INDICATOR LAMP (warning light) operates by the same principle as theindicator light previously discussed.

SPEEDOMETER AND TACHOMETERSSpeedometers and tachometers in some form are used in virtually all types of selfpropelledequipment. Speedometers are used to indicate vehicle speed in miles perhour (mph) or kilometers per hour (kph). In most cases, the speedometer also containsthe odometer which keeps a record of the amount of mileage (in miles or kilometersdepending on application) that a vehicle has accumulated. Some speedometers alsocontain a resetable trip odometer so those individual trips can be measured.A tachometer is a device that is used to measure engine speed in revolutions perminute (rpm). The tachometer may also contain an engine-hour gauge which isinstalled on equipment that uses no odometer to keep a record of engine use.Speedometers and tachometers may be driven either mechanically, electrically, orelectronically.

MECHANICAL SPEEDOMETERS AND TACHOMETERSBoth the mechanical speedometer and the tachometer consist of a permanent magnetthat is rotated by a flexible shaft. Surrounding the rotating magnet is a metal cup that isattached to the indicating needle. The revolving magnetic field exerts a pull on the cupthat forces it to rotate. The rotation of the cup is countered by a calibrated hairspring.

The influence of the hairspring and the rotating magnetic field on the cup producesaccurate readings by the attached needle. The flexible shaft consists of a flexible outercasing that is made of either steel or plastic and an inner drive core that is made ofwire-wound spring steel. Both ends of the core are molded square, so they can fit intothe driving member at one end and the driven member at the other end and cantransmit torque.Gears on the transmission output shaft turn the flexible shaft that drives thespeedometer. This shaft is referred to as the speedometer cable. A gear on the ignitiondistributor shaft turns the flexible shaft that drives the tachometer. This shaft isreferred to as the tachometer cable.The odometer of the mechanical speedometer is driven by a series of gears thatoriginate at a spiral gear on the input shaft. The odometer consists of a series of drumswith digits printed on the outer circumference that range from zero to nine. The drumsare geared to each other so that each time the one furthest to the right makes onerevolution, it will cause the one to its immediate left to advance one digit. The secondto the right then will advance the drum to its immediate left one digit for everyrevolution it makes. This sequence continues to the left through the entire series ofdrums. The odometer usually contains six digits to record 99,999.9 miles orkilometers. However, models with trip odometers do not record tenths, thereby containonly five digits. When the odometer reaches its highest value, it will automaticallyreset to zero. Newer vehicles incorporate a small dye pad in the odometer to color thedrum of its highest digit to indicate the total mileage is in excess of the capability ofthe odometer.Electric Speedometers and TachometersThe electric speedometer and tachometer use a mechanically driven permanent magnetgenerator to supply power to a small electric motor (fig. 2-84). The electric motor thenis used to rotate the input shaft of the speedometer or tachometer. The voltage from thegenerator will increase proportionally with speed, and speed will likewise increaseproportionally with voltage enabling the gauges to indicate speed.The signal generator for the speedometer is usually driven by the transmission outputshaft through gears. The signal generator for the tachometer usually is driven by thedistributor through a power takeoff on gasoline engines. When the tachometer is usedwith a diesel engine, a special power takeoff provision is made, usually on thecamshaft drive.

Electronic Speedometers and TachometersElectronic speedometers and tachometers are self-contained units that use an electricsignal from the engine or transmission. They differ from the electric unit in that theyuse a generated signal as the driving force. The gauge is transistorized and will supplyinformation through either a magnetic analog (dial) or light-emitting diode (LED)digital gauge display. The gauge unit derives its input signal in the following ways:

An electronic tachometer obtains a pulse signal from the ignition distributor, as itswitches the coil on and off. The pulse speed at this point will change proportionallywith engine speed. This is the most popular signal source for a tachometer that is usedon a gasoline engine.A tachometer that is used with a diesel engine uses the alternating current generated bythe stator terminal of the alternator as a signal. The frequency of the ac current willchange proportionally with engine speed.An electronic speedometer derives its signal from a magnetic pickup coil that has itsfield interrupted by a rotating pole piece. The signal units operation is the same as theoperation of the reluctor and pickup coil described earlier in this TRAMAN. Thepickup coil is located strategically in the transmission case to interact with the reluctorteeth on the input shaft.

HORNThe horn currently used on automotive vehicles is the electric vibrating type. Theelectric vibrating horn system typically consists of a fuse, horn button switch, relay,horn assembly, and related wiring. When the operator presses the horn button, it closesthe horn switch and activates the horn relay. This completes the circuit, and current isallowed through the relay circuit and to the horn.Most horns have a diaphragm that vibrates by means of an electromagnetic. When thehorn is energized, the electromagnet pulls on the horn diaphragm. This movement opens a set of contact points inside the horn. This action allows the diaphragm to flexback towards its normal position. This cycle is repeated rapidly. The vibrations of thediaphragm within the air column produce the note of the horn.Tone and volume adjustments are made by loosening the adjusting locknut and turningthe adjusting nut. This very sensitive adjustment controls the current consumed by thehorn. Increasing the current increases the volume. However, too much current willmake the horn sputter and may lock the diaphragm.When a electric horn will not produce sound, check the fuse, the connections, and testfor voltage at the horn terminal. If the horn sounds continuously, a faulty horn switchis the most probable cause. A faulty horn relay is another cause of horn problems. Thecontacts inside the relay may be burned or stuck together.

WINDSHIELD WIPERSThe windshield wiper system is one of the most important safety factors on any piece

of equipment. A typical electric windshield wiper system consists of a switch, motorassembly, wiper linkage and arms, and wiper blades. The description of thecomponents is as follows:The WINDSHIELD WIPER SWITCH is a multiposition switch, which may contain arheostat. Each switch position provides for different wiping speeds. The rheostat, ifprovided, operates the delay mode for a slow wiping action. This permits the operatorto select a delayed wipe from every 3 to 20 seconds. A relay is frequently used tocomplete the circuit between the battery voltage and the wiper motor.The WIPER MOTOR ASSEMBLY operates on one, two, or three speeds. The motor(fig. 2-85) has a worm gear on the armature shaft that drives one or two gears, and, inturn, operates the linkage to the wiper arms. The motor is a small, shunt wound dcmotor. Resistors are placed in the control circuit from the switch to reduce the currentand provide different operating speeds.The WIPER LINKAGE and ARMS transfers motion from the wiper motortransmission to the wiper blades. The rubber wiper blades fit on the wiper arms.The WIPER BLADE is a flexible rubber squeegee-type device. It may be steel orplastic backed and is designed to maintain total contact with the windshield throughoutthe stroke. Wiper blades should be inspected periodically. If they are hardened, cut, orsplit, they are to be replaced.When electrical problems occur in the windshield wiper system, use the servicemanual and its wiring diagram of the circuit. First check the fuses, electrical

connections, and all grounds. Then proceed with checking the components.

7) NUMBER YSTEM CODES AND DATA REPRESENTATION

Arithmetic Operations on Binary Numbers

Because of its widespread use, we will concentrate on addition and subtraction for Two's Complement representation.

The nice feature with Two's Complement is that addition and subtraction of Two's complement numbers works without having to separate the sign bits (the sign of the operands and results is effectively built-into the addition/subtraction calculation).

Remember: −2n−1 ≤ Two's Complement ≤ 2n−1 − 1

−8 ≤ x[4] ≤ +7

−128 ≤ x[8] ≤ +127

−32768 ≤ x[16] ≤ +32767

−2147483648 ≤ x[32] ≤ +2147483647

What if the result overflows the representation?

If the result of an arithmetic operation is to too large (positive or negative) to fit into the resultant bit-group, then arithmetic overflow occurs. It is normally left to the programmer to decide how to deal with this situation.

Two's Complement Addition

Add the values and discard any carry-out bit.

Examples: using 8-bit two’s complement numbers.

1. Add −8 to +32. (+3) 0000 00113. +(−8) 1111 10004. -----------------5. (−5) 1111 10116. Add −5 to −27. (−2) 1111 11108. +(−5) 1111 10119. -----------------10. (−7) 1 1111 1001 : discard carry-out

Overflow Rule for addition

If 2 Two's Complement numbers are added, and they both have the same sign (both positive or both negative), then overflow occurs if and only if the result has the opposite sign. Overflow never occurs when adding operands with different signs.

i.e.

Adding two positive numbers must give a positive result

  Adding two negative numbers must give a negative result

Overflow occurs if

(+A) + (+B) = −C (−A) + (−B) = +C

Example: Using 4-bit Two's Complement numbers (−8 ≤ x ≤ +7)

(−7) 1001+(−6) 1010------------(−13) 1 0011 = 3 : Overflow (largest −ve number is −8)

A couple of definitions:

Subtrahend:

what is being subtracted

Minuhend:what it is being subtracted from

Example: 612 - 485 = 127

485 is the subtrahend, 612 is the minuhend, 127 is the result

Two's Complement Subtraction

Normally accomplished by negating the subtrahend and adding it to the minuhend. Any carry-out is discarded.

Example: Using 8-bit Two's Complement Numbers (−128 ≤ x ≤ +127)

(+8) 0000 1000 0000 1000−(+5) 0000 0101 -> Negate -> +1111 1011----- ----------- (+3) 1 0000 0011 : discard carry-out

Overflow Rule for Subtraction

If 2 Two's Complement numbers are subtracted, and their signs are different, then overflow occurs if and only if the result has the same sign as the subtrahend.

Overflow occurs if

(+A) − (−B) = −C (−A) − (+B) = +C

Example: Using 4-bit Two's Complement numbers (−8 ≤ x ≤ +7)

Subtract −6 from +7

(+7) 0111 0111 −(−6) 1010 -> Negate -> +0110 ---------- ----- 13 1101 = −8 + 5 = −3 : Overflow

Number Circle for 4-bit Two's Complement numbers

Numbers can be added or subtracted by moving round the number circle

Clockwise for addition Anti-Clockwise for subtraction (addtion of a negative number)

Overflow occurs when a transition is made

from +2n−1−1 to −2n−1 when adding from −2n−1 to +2n−1−1 when subtracting

Two's Complement Summary

Addition

Add the values, discarding any carry-out bit

Subtraction

Negate the subtrahend and add, discarding any carry-out bit

Overflow

Occurs when adding two positive numbers produces a negative result, or when adding two negative numbers produces a positive result. Adding operands of unlike signs never produces an overflow

Notice that discarding the carry out of the most significant bit during Two's Complement addition is a normal occurrence, and does not by itself indicate overflow

As an example of overflow, consider adding (80 + 80 = 160)10, which produces a result of −9610 in 8-bit two's complement:

01010000 = 80 + 01010000 = 80 -------------- 10100000 = −96 (not 160 because the sign bit is 1.) (largest +ve number in 8 bits is 127)

Multiplication and Division

No problem with unsigned (always positive) numbers, just use the same standard techiques as in base 10 (remembering that x[n] × y[n] = z[2n])

Multiplication Example 11001012 × 1111012 (10110 × 6110) 1100101   10110

× 111101  × 6110

------- 1100101 +1100101 +1100101 +1100101 +1100101 ------------- ????????????? -------------

Easier to use intermediary results:

1100101   10110

× 111101  × 6110

------- 1100101 +1100101 ---------- 111111001 +1100101 ------------ 10100100001 +1100101------------- 101101110001+1100101-------------1100000010001 = 409610 + 204810 + 1610 + 1 = 616110

-------------

Division Example: 1001012 ÷ 1012 (3710 ÷ 510)

111 result = 710

------- 101)100101 −101 --- 1000 −101 --- 111 −101 --- 10 remainder = 210

---

Multiplication in Two's complement cannot be accomplished with the standard technique since, as far as the machine itself is concerned, for Y[n]:

 −Y    0 − Y    2n − Y

since, when subtracting from zero, need to "borrow" from next column leftwards.

Example:

−1910 in 8-bits

= (28 − 19)10

  = 25610 − 1910

  = 23710

  = 111011012 unsigned

  = −27 + 26 + 25 + 23 + 22 + 20

  = −128 + 64 + 32 + 8 + 4 + 1

  = −128 + 109

  = −1910 in Two's Complement

Consider X × (−Y)

Internal manipulation of −Y is as 2n − Y

Therefore X × (−Y)  =  X × (2n − Y)  =  2n × X − X × Y

However the expected result should be 22n − (X × Y)

since x[n] × y[n] = z[2n]

Can perform multiplication by converting the Two's Complement numbers to their absolute values and then negating the result if the signs of the operands are different.

Similar for Two's Complement division. Can convert the operands to their absolute values, perform the division, and then negating the result if the signs of the operands are different.

Most contemporary architectures implement more sophisiticated algorithms for multiplication and division of Two's Complement numbers.

Decimal To Binary Conversion

To convert a decimal number to binary, first subtract the largest possible power of two, and keep subtracting the next largest possible power form the remainder, marking 1s in each column where this is possible and 0s where it is not.

Example 1 - (Convert Decimal 44 to Binary)

Example 2 - (Convert Decimal 15 to Binary)

Example 3 - (Convert Decimal 62 to Binary)

8) LOGIC GATES,ARITHMATIC CIRCUITS AND INTRODUCTION TO MICROPROCESSORS

Flip-Flop

The SR flip-flop, also known as a SR Latch, can be considered as one of the most basic sequential logic circuit possible. This simple flip-flop is basically a one-bit memory bistable device that has two inputs, one which will "SET" the device (meaning the output = "1"), and is labelled S and another which will "RESET" the device (meaning the output = "0"), labelled R.

Then the SR description stands for "Set-Reset". The reset input resets the flip-flop back to its original state with an output Q that will be either at a logic level "1" or logic "0" depending upon this set/reset condition.

A basic NAND gate SR flip-flop circuit provides feedback from both of its outputs back to its opposing inputs and is commonly used in memory circuits to store a single data bit. Then the SR flip-flop actually has three inputs, Set, Reset and its current output Q relating to it's current state or history. The term "Flip-flop" relates to the actual operation of the device, as it can be "flipped" into one logic Set state or "flopped" back into the opposing logic Reset state.

Half Adder in Digital ElectronicsHalf Adder is a combinational circuit that performs addition of two bits. It has two inputs and two outputs. The two I/Ps are the two 1-bit numbers A and B designated as augend and addend bits. The two O/Ps are the sum ‘S’ of A and B and the carry bit, denoted by ‘C’.Truth Table of a half adder can be derived by performing binary addition of augend and addend bits as follows:

A B S C

0 0 0 0

0 1 1 0

1 0 1 0

1 1 0 1

From the truth table, Boolean Expression can be derived as:S = A’B + AB’ = A ⊕ BC = ABA Half Adder circuit can be implemented using AND & OR logic gates or by using XOR & AND logic gates. Both these implementations are shown in the image below:

Since NAND is considered as Universal Logic Gate which means that all other logic gates can be derived from it, below is the implementation of a Half Addercircuit using NAND logic gate:

Half Subtractor in Digital Electronics

Half Subtractor is a combinational circuit that performs subtraction of two bits and has two inputs and two outputs. The two inputs denoted by A and B represents minuend and subtrahend. The two outputs are the difference “D” and the borrow bit “Bo“.Truth Table of a half subtractor circuit can be derived as follows:

A B D Bo

0 0 0 0

0 1 1 1

1 0 1 0

1 1 0 0

From the truth table, Boolean Expression can be derived as:

D = A’B + AB’ =  A ⊕ BBo = A’BA Half Subtractor circuit can be implemented using AND & OR logic gates or by using XOR, NOT & AND logic gates. Both these implementations are shown in the image below:

SHIFT REGISTER

Shift registers, like counters, are a form of sequential logic. Sequential logic, unlike combinational logic is not only affected by the present inputs, but also, by the prior history. In other words, sequential logic remembers past events.Shift registers produce a discrete delay of a digital signal or waveform. A waveform synchronized to a clock, a repeating square wave, is delayed by "n"discrete clock times, where "n" is the number of shift register stages. Thus, a four stage shift register delays "data in" by four clocks to "data out". The stages in a shift register are delay stages, typically type "D" Flip-Flops or type "JK" Flip-flops.

Formerly, very long (several hundred stages) shift registers served as digital memory. This obsolete application is reminiscent of the acoustic mercury delay lines used as early computer memory.

Serial data transmission, over a distance of meters to kilometers, uses shift registers to convert parallel data to serial form. Serial data communications replaces many slow parallel data wires with a single serial high speed circuit.

Serial data over shorter distances of tens of centimeters, uses shift registers to get data into and out of microprocessors. Numerous peripherals, including analog to digital converters, digital to analog converters, display drivers, and memory, use shift registers to reduce the amount of wiring in circuit boards.

Some specialized counter circuits actually use shift registers to generate repeating waveforms. Longer shift registers, with the help of feedback generate patterns so long that they look like random noise, pseudo-noise.

Basic shift registers are classified by structure according to the following types:

Serial-in/serial-out

Parallel-in/serial-out Serial-in/parallel-out Universal parallel-in/parallel-out Ring counter

Above we show a block diagram of a serial-in/serial-out shift register, which is 4-stages long. Data at the input will be delayed by four clock periods from the input to the output of the shift register.

Data at "data in", above, will be present at the Stage A output after the first clock pulse. After the second pulse stage A data is transfered to stage Boutput, and "data in" is transfered to stage A output. After the third clock, stage C is replaced by stage B; stage B is replaced by stage A; and stage A is replaced by "data in". After the fourth clock, the data originally present at "data in" is at stage D, "output". The "first in" data is "first out" as it is shifted from "data in" to "data out".

Data is loaded into all stages at once of a parallel-in/serial-out shift register. The data is then shifted out via "data out" by clock pulses. Since a 4- stage shift register is shown above, four clock pulses are required to shift out all of the data. In the diagram above, stage D data will be present at the "data out" up until the first clock pulse; stage C data will be present at "data out" between the first clock and the second clock pulse; stage B data will be present between the second clock and the third clock; and stage A data will be present between the third and the fourth clock. After the fourth clock pulse and thereafter, successive bits of "data in" should appear at "data out" of the shift register after a delay of four clock pulses.If four switches were connected to DA through DD, the status could be read into a microprocessor using only one data pin and a clock pin. Since adding more switches would require no additional pins, this approach looks attractive for many inputs.

Above, four data bits will be shifted in from "data in" by four clock pulses and be available at QA through QD for driving external circuitry such as LEDs, lamps, relay drivers, and horns.After the first clock, the data at "data in" appears at QA. After the second clock, The old QA data appears at QB; QA receives next data from "data in". After the third clock, QB data is at QC. After the fourth clock, QC data is at QD. This stage contains the data first present at "data in". The shift register should now contain four data bits.

A parallel-in/parallel-out shift register combines the function of the parallel-in, serial-out shift register with the function of the serial-in, parallel-out shift register to yield the universal shift register. The "do anything" shifter comes at a price– the increased number of I/O (Input/Output) pins may reduce the number of stages which can be packaged.

Data presented at DA through DD is parallel loaded into the registers. This data at QA through QD may be shifted by the number of pulses presented at the clock input. The shifted data is available at QA through QD. The "mode" input, which may be more than one input, controls parallel loading of data from DAthrough DD, shifting of data, and the direction of shifting. There are shift registers which will shift data either left or right.

If the serial output of a shift register is connected to the serial input, data can be perpetually shifted around the ring as long as clock pulses are present. If the output is inverted before

being fed back as shown above, we do not have to worry about loading the initial data into the "ring counter".

Synchronous and Asynchronous Counters in Digital ElectronicsA counter is a sequential circuit that counts in a cyclic sequence. It is essentially a register that goes through a predetermined sequence of states upon the application of input pulses. There are two types of counters – Synchronous Counter & Asynchronous Counter.Synchronous CounterIn a synchronous counter, the input pulses are applied to all clock pulse inputs of all flip flops simultaneously (directly). Synchronous counter is also known as parallel sequential circuit. Examples of Synchronous Counters are as below:

Ring Counter Johnson Counter (Switch Tail or Twisted Ring Counter)

Asynchronous CounterIn an asynchronous counter, the flip flop output transition serves as a source for triggering other flip flops. In other words, the clock pulse inputs of all flip flops, except the first, are triggered not by the incoming pulses, but rather by the transition that occurs in previous  flip flop’s output... Asynchronous counter is also known as serial sequential circuit. Examples of Asynchronous Counters are as below:

Binary Ripple Counter Up Down Counter

Synchronous counters are faster than asynchronous counter because in synchronous counter all flip flops are clocked simultaneously.