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Akhilnandh Ramesh
AN INSIGHT INTO BASIC AUTO
COMPONENTS AND THEIR FUNCTIONING
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Booklet: version 1: 20th
march 2013
AUTHOR’S NOTE:
I have written this booklet so that a layman can understand the working ofwhat he sees commonly around him: an automobile. Any suggestions to
improve this booklet are always welcomed.
Please contact me through my email: [email protected] with
your feedback and suggestions.
I thank Sundaram Motors, Poonamalee for allowing me to visit them for in-
plant training and for their valuable insights into automotive components.
I thank Dr.Suresh Kumar, Professor, Department of Mechanical Engineering,
SSN College of Engineering, for guiding me to bring out such a booklet.
I thank Dr. V.E.Annamalai , Head of the Department, Department of
Mechanical Engineering, SSN College of Engineering for his encouragement
and support.
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CONTENTS:
TOPIC PAGE NO
INTERNAL COMBUSTION ENGINE 4
AUTOMOBILE TRANSMISSION AND GEARBOX 12
DIFFERENTIAL 20
STEERING SYSTEM 23
SUSPENSION SYSTEM 27
BRAKING SYSTEM 29
AUTO ELECTRICAL SYSTEMS OF A VEHICLE 35
REFERENCES USED 35
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INTERNAL COMBUSTION ENGINE:
An internal combustion engine is an engine in which the combustion of fluid
occurs inside the combustion chamber which is an integral part of an engine.
This is unlike an external combustion engine in which the combustion occurs in
a combustion chamber which is located outside the engine.
The first internal combustion engine was built by OTTO LENOIR in 1860.
A basic internal combustion engine may operate by 4 or 2 strokes:
WORKING OF A 4 STROKE INTERNAL COMBUSTION PETROL
ENGINE:
The 4 strokes which occur in an internal combustion engine are:
1. Intake stroke/suction stroke2. Compression stroke
3. Power stroke
4. Exhaust stroke
These strokes are repeated for every 2 revolutions of the engine.
1. Intake stroke/Suction stroke:
This is is the first stroke of the internal combustion engine. In this stroke, thepiston moves towards is lowermost position (Lower dead centre).The inlet
valve opens to allow enough air to enter the combustion chamber for
combustion. Fuel injectors spray fuel air mixture for combustion
2. Compression stroke:
In this stroke both the inlet valve and the outlet valve are closed. The piston
moves from the lower dead centre to the upper dead centre. Due to the
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upwards motion of the piston, the volume occupied by the fuel air mixture and
air decreases and hence compression occurs
3. Power stroke.
When the compression stroke is nearly complete, a spark plug produces a tiny
spark that ignites the fuel air mixture, causing combustion and thereby
producing power. The power produced due to the expansion of gases is
transmitted to the crankshaft. The piston is pushed to the lower dead centre
4. Exhaust stroke:
At the end of the power stroke, the exhaust stroke occurs. The piston starts
moving from the lower dead centre to the upper dead centre.The exhaust
valve opens and the exhaust gases are sent away from the combustion
chamber through it.
These 4 strokes occur continuously and might also overlap with each other.
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For the purpose of supplying the fuel, the fuel from the fuel tank is sent to the
fuel feed pump which in turn supplies it at great pressure to the fuel filter
which filters any dust particles. It then supplies it to the fuel injection pump.This pump supplies the fuel mixture to the carburettor at high pressure, for
mixing with air. The fuel is then sent to the fuel injectors which spray the fuel
on to the combustion chamber.
The spark produced by the spark plug and the rotation of the piston when an
engine is starting is brought about by auto electrical assembly
Working of the 4 stroke diesel engine is similar to that of the petrol engine.
However in the diesel engine, no spark plug is used and the fuel air mixture is
supplied along with the power stroke through fuel injectors. The combustion of
fuel occurs due to the high pressure occurring inside the combustion chamber
at the end of the compression stroke. The suction stroke is just used to suck in
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the air required to cause combustion .
THE PICTURE SHOWS THE 4 STROKES CYCLE OF AN INTERNAL
COMBUSTION ENGINE
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COMPONENTS AND CONSTRUCTION OF INTERNAL
COMBUSTION ENGINE ALONG WITH THEIR WORKING:
SECTION OF ICE WITH THE CYLINDER BLOCKS AND HEADS REMOVED.WHEEL AT
THE OTHER END OF THE CRANKSHAFT IS THE FLYWHEEL.
CYLINDER BLOCK:
An internal combustion engine consist a cylinder block. This is the basic
component of the an internal combustion engine.
These cylinder blocks consist of numerous cylinders into which the piston is
fitted.
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PISTON ALONG WITH CRANKSHAFTS:
A piston is part of an internal combustion engine which moves up and down
inside the cylinders of the cylinder block.
This motion of the piston is supported by the crankshafts. The crankshaft is a
long metal rod with appropriate grooves in it to which the pistons are fitted.
During the power stroke, when the power released causes the piston to move
downwards, the crankshaft too rotates. One end of the crank shaft is
connected to the flywheel while to the other end connecting rod is connected
FLYWHEEL:
Flywheel is connected to one end of the crank shaft. The flywheel is a rotating
mechanical device which is used to store and transfer rotating mechanical
energy to the components connected to it. The flywheel is connected to the
transmission input shaft which in turn connects the driveshaft.
CYLINDER HEAD AND CAMSHAFT:
Above the cylinder block, the cylinder head is mounted. The cylinder head
fastened on to the cylinder block by means of appropriate bolts.
The cylinder head is provided with valves which serve as inlet for air and outlet
for the exhaust gases. The cylinder head is also provided with appropriate
openings through which the fuel injectors and the spark plug(for petrol engine)
fit.
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The opening and closing of the valves at the end of the suction and exhaust
strokes is controlled by the camshaft. The camshaft draws power for opening
and closing of the valves by a belts or gears connected to the crankshaft. Thus
the rotation of the engine causes the camshaft to work.
INLET AND EXHAUST MANIFOLD:
The system of pipes in red and black are the inlet and exhaust manifolds
The inlet manifold is used to supply the inlet valves with fresh air.The inlet
manifold are connected to the inlet valve of the internal combustion engine.
The inlet manifold draws air from the atmosphere through the air intakes thatopen outside.
The exhaust manifold is used to remove the exhaust gases produced at the end
of the exhaust stroke.
OIL PUMP, SUMP AND LUBRICATION SYSTEM AND COOLING SYSTEM:
When the pistons, the crankshafts, the camshafts rotate, there is friction
between these parts which are in contact. This friction is minimized bylubrication using lubrication oil. The lubrication oil is stored in the oil sump
which is located below the cylinder block. The oil stored in the oil pump is
drawn by the oil pump which is driven by means of a belt or pulley connected
to the connecting rod at one end of the camshaft.
The oil drawn by the pumps is sent to fluid lines which supply the oil to the
rotating parts.
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The rotating motion of the engine components produces heat. The heat
produced by the rotating motion of the pistons and the crankshafts etc are
removed by means of cooling system using a coolant or water.
The coolant or water is stored in a coolant tank from which it is drawn bymeans of a water pump. The water pump is operated by the rotation of the
crankshaft by means of a pulley or a system of gears and is connected to the
connecting rod at one end of the crankshaft.
The water/coolant drawn is sent by water lines throughout the system and
acts as a heat exchanger taking away the engine heat.
ALTERNATOR:
An alternator is a generator which generates ac power. The purpose of
alternator in a vehicle is for charging the batteries which are used for running
the auto electricals and starting the engine after it has stopped.
The alternator gets drive from the connecting rod of the crankshaft which
rotates along with the crankshaft. The drive is provided by means of a
belt/pulley set up or a system of gears.
TURBOCHARGER SYSTEM WITH INTERCOOLER:
The turbocharger system is a method of forced induction by which the
performance of the engine can be improved. The turbocharger is uses exhaust
gases to drive a turbine for drawing more air for better combustion of fuel air
mixture in the combustion chamber thereby ensuring less polluting exhaust
gases.
This air drawn by the turbine is hotter and is less in oxygen content. Therefore
it is passes through an intercooler before being supplied to the inlet valve
which is a heat exchanger for cooling the air and enriching the oxygen content.
The turbocharger ‘s intake system is connected to the exhaust manifold.
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TURBO CHARGER
AIR COMPRESSOR:
Air compressor is an air pump which is used for running the air conditioning
system of a car and also the air brakes and air suspension systems seen in
heavy vehicles. The air compressor again takes drive from the connecting rod
of the crankshaft connected by means of pulley/belt or gears. Depending on
the requirements, many air compressors may be required.
AUTOMOBILE TRANSMISSION SYSTEM AND GEARBOX
An automobile’s transmission system is used to transmit power from the
engine to the axles which are used to drive the wheels. A transmission system
is used to control and regulate the power supplied by the engine to the speed.The transmission system of an automobile consists of numerous speed and
torque regulating gears, the drive shaft and the clutch and the differential.
NEED FOR TRANSMISSION SYSTEM:
The power output of an internal combustion engine is not suitable for
driving the wheels as it is at a higher rpm. The transmission system
adapts the output and makes it suitable for rotating the wheels by
reducing the speed
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The gears connected to the transmission systems are used to control
speed of rotation of the wheels
The different gears of different sizes regulate the torque applied to the
wheels for rotating.
MANUAL TRANSMISSION
Manual transmission system is the most commonly used transmission system
in India. Most of the cars and commercial vehicles sold here come fitted with
manual transmission.
Universally all the manual transmission systems used today have been
designed as synchronized transmission systems.
However non synchronous transmission systems do exist and find application
in heavy vehicles.
COMPONENTS AND WORKING OF THE MANUAL
TRANSMISSION
A basic transmission system consist of a set of gears, a clutch and drive shafts
which are connected to the differentials located on the driven wheel axles. The
following are the components of the transmission system:
CLUTCH:
A Clutch consists of a clutch plate fitted over the flywheel of the engine.
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A pressure plate is fitted over the clutch plate by means of struts and
bolts.
The pressure plate is connected to diaphragm springs.
These are connected to a clutch housing provided with a fork for
engaging the clutch pedal.
A transmission input shaft connects the clutch and the transmission
system. The fork for engaging the clutch pedal is connected to this drive
shaft. The fork is connected to the clutch pedal by means of a cable.
However in certain cases, for effective pressing of the clutch, one may
also use hydraulic or air mechanisms.
The clutch is said to be in engaged position when the clutch pedal is not
pressed.In this condition, the springs push the pressure plate on the clutch plate
causing the clutch to push against the flywheel. This causes the
transmission input shaft to rotate along with the flywheel in the same
speed.
When the clutch is pressed, the clutch is said to be in disengaged
condition.
In this condition the diaphragm of the clutch is pressed and this in turn
causes a series of pins to pull the springs which are pushing against the
pressure plate away from it. As a result the clutch is not pressed on the
flywheel anymore hence the transmission input shaft/lay shaft does not
rotate with the same speed
When this happens, the transmission output shaft too does not rotate in
the same speed and momentarily slows down. This allows for shifting of
gears. When the clutch
pedal is released theclutch moves to engaged
condition again and the
transmission input shaft
continues to rotate with
the same speed as the
flywheel’s speed.
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An automobile clutch showing the springs (fitted over the pressure
plate) and clutch plate
GEARBOX:
Picture in the previous page shows the gearbox ( with layshaft below
and the driveshaft above).The dog clutches connected to the gear
shifting forks can be clearly seen.
The gear box consist of 2 shafts:
The transmission input shaft which gets the input for rotation
from the flywheel and is connected to the clutch. This shaft has a
series of gears of various sizes.
The drive shaft which is connected to the differentials connected
to the driven wheels. This shaft to has a series of gears of various
sizes. The gears are numbered in increasing order from 1.The size
of the gears decreases as we progressively move from one gear toanother. Hence the speed of rotation of the gears progressively
increases and torque supplied by the gears decreases. Mechanism
for shifting between the gears is provided here.
When a gear is selected, depending on the type of gearboxes, contact
between the both the gears and the drive shaft is established and this
causes the drive shaft to rotate with a particular speed and torque.
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The speed of rotation of the drive shaft and the torque supplied to it
is determined by the size of the gear.
The shaft is connected to the differential which is fitted to the axles
driving the driven wheels.
The working of the differential is explained in the next segment
NON SYNCHRONOUS AND SYNCHRONOUS GEARBOXES:
First type of gearbox that was developed is the sliding mesh gearbox.
In this type of system, the gears are engaged by bringing sliding the
gears on to the shaft. The gears are engaged only when the speed of the
gears rotating in the lay shaft and the speed of the corresponding gearsrotating in the main shaft match.
Thus the gears mesh and gears are engaged. To ensure this , a driver of a
vehicle fitted with such a gearbox needs to control the throttle with
careful timing and reduce the speed of the engine.
This can be done by engaging the neutral gear for a moment so that the
engine speed is lowered and again engaging the required gear with
proper timing, making such vehicles difficult to control.
To overcome this, constant mesh transmission systems were developed where
the gears mesh at all times and are always rotating. This action is brought
about by means of a dog clutch which is splined on to the drive shaft and slides
into corresponding dog teeths in the drive shaft of the vehicle and rotates
along with the gears.
However if the dog clutch and the dog teeth are not rotating in the same
speed, the gears may not be engaged properly and this may result in
production of grinding noise. Further this also may wear out the dog clutches.
This necessitates the need for careful throttle control and in some cases
bringing the transmission to neutral before engaging the gear
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Sliding mesh transmission system
The gears in the input shaft and the gears in the drive shaft (output shaft)
mesh at all times. Gear action is brought about by the dog clutches which are
engaged by the shift forks connected to gear selector.
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Dog clutches and Dog teeths(on gear)
This problem is overcome by synchromesh gearboxes in which the dog clutch
has a synchronizer mechanism which consist of synchrocones and
synchrorings.
Before the dog clutch engages, the synchrocone engages first, bringing thespeed of both the dog clutches and gears to match by developing friction
between the two.
The synchrorings prevent the dog clutch from making contact with the gear till
the speeds match (synchronization).
When the synchronization occurs, friction on the synchrorings is relieved and
these twist slightly, causing dog clutch to make contact with the gear.
Thus by means of synchrocones and synchrorings,the noise produced when
the transmissions do not engage properly are removed and the need for the
driver of the vehicle to control the throttle with timing is too removed.
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SYNCHRO RINGS
SYNCHRO MESH GEARS
WORKING OF THE REVERSE GEAR
The reverse gear consists of an intermediate gear provided between the
corresponding gear in the lay shaft and the corresponding gear in thedriveshaft.
Generally, when 2 gears rotate, it is seen that the each gear rotates in a
sense opposite to the other.
The general sense of motion of an engine’s flywheel is in clockwise
direction. However since for forward motion the wheels rotate in
anticlockwise direction, the gears ensure that this is achieved.
Now for motion in reverse direction the wheels rotate in clockwise
sense. This is achieved by providing an intermediate gear which rotates
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in the opposite sense with respect to that of the lay shaft between the
gear in the lay shaft and the drive shaft.
This ensures that the gear in the drive shaft rotates in the same sense of
direction as that of the lay shaft, ie clockwise sense.
Hence the wheels rotate in clockwise sense and reverse motion is
achieved.
In certain cases,the first gear and the reverse gear of a synchromesh gearbox
may not be provided with the synchro cones and rings as these gears are
operated only after the vehicle has come to a stop or is moving slowly.
DIFFERENTIAL
A differential is a device which, in automobiles is used to regulate and control
the speed of one of the wheels connected to the propeller shaft with respect
to another. Working of a differential is seen when a vehicle is executing a turn.
When a vehicle makes a turn,say towards the right, then it is seen that the
wheel on the left hand side needs to cover a larger distance and travel faster
when compared to the wheel on the right hand side. In automobiles which do
not posses a differential, it is seen that irrespective of whether the vehicle is
moving straight or executing a turn, both the wheels rotate at the same speed
always. This makes controlling the vehicle very difficult when its turning.
However it is seen that using a combination of gears which regulate the speed
of motion of one wheel with respect to another, can be controlled and hence a
turn can be executed easily
BASIC COMPONENTS AND WORKING OF THE
DIFFERENTIAL
A differential consist of the following:
1. Crown gear which receives the torque by means of an input pinion from
the drive shaft
2 Planet gears connected to the crown gear which can rotate as well as spin as
well as rotate about it’s axis. Input torque is applied to the ring gear (here in
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blue), by means of an input pinion (not shown here) connected to the
driveshaft (Refer Figure 1 )
This turns the entire carrier (also in blue). The carrier is connected to the 2 sun
gears (red and yellow) only through the planet gear (green).
Torque is transmitted to the sun gears through the planet gear. The planet
gear revolves around the axis of the carrier, driving the sun gears.
If the resistance at both wheels is equal, the planet gear revolves without
spinning about its own axis, and both wheels turn at the same rate.
If the left sun gear (red) encounters resistance, the planet gear (green) spins as
well as revolving, allowing the left sun gear to slow down, with an equalspeeding up of the right sun gear (yellow).(Refer Figure 2)
Now the resistance is recognized by means of change in orientation of the 2
(or 1) planet gears/ planet gear .These are mounted on an axis perpendicular
to the axis on which the sun gears are located. The resistance,ie measure of
change in direction is recognized by means of change in the orientation of the
planet gears which in turn is recognized by means of change in the orientation
of crown gear connected to the propeller shaft
A differential does not reduce or lower the torque supplied to it. Rather it
distributes the torque linearly between the two wheels which it operates thus
regulating the wheel’s angular velocity and hence the vehicle’s speed.
Differential regulates the torque according to the equation
aA=bB+Cc
Where A=angular velocity of the propeller shaft,B and C=angular velocity of the
half axles connected to the wheel. a,b,c being constants.
3.A pair of sun gears, each connected to the axle half shaft connected the
wheels which are used for speeding or slowing down the wheels
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A cut away section of differential showing the crown wheel(big wheel towards
the left),2 planet gears,1 sun gear(the other hidden by the crown wheel, the
axle half shafts which connect to the wheels and the differential carrier.
Working of the differential when both the sun gears do not encounter
resistance and the vehicle is moving in a straight line(FIGURE 1).
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Working of the differential working when left sun gear encounters resistance
when vehicle moves towards left-previous page (FIGURE 2).
STEERING SYSTEM
A steering system consists of a set of devices and components which allow a
vehicle to follow a desired course.
The basic aim of the steering is to ensure that the wheels point towards the
right direction. This is achieved by many links and arms provided inside the
steering system.
The most common type of steering systems in use today are the
Rack and Pinion Steering system
The recirculating ball type steering system
In addition to this, each steering can be power assisted, where the effort done
by the human beings in turning the steering is reduced by means of hydraulics
or electronics.
THE RACK AND PINION STEERING SYSTEM
It is the most common type of steering system. It finds a lot of use in cars and
small trucks.
It has a rack and pinion gear set kept inside a metallic tube. Each end of the
rack protrudes from the metallic tube and a tie rod connects this set up to the
steering arm connected to the wheel.
When the steering column is turned, the gear spins, moving on the rack. this
cause the linear motion of the tie arm in turn connected to the steering arm
which moves the wheels.
The rack and pinion steering system does the following things:
It converts the rotational motion of the steering wheel into linear
motion which is required to turn the wheels
It makes it easier for turning the wheels by producing a gear reduction
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RECIRCULATING BALL TYPE STEERING SYSTEM
This type of steering system is mainly used in trucks and other commercial
vehicles.
This type of steering system consist of a worm gear, ie a metal block with
threaded hole inside it and gears cut on to the outer portion of it.
To this, a corresponding gear is fitted. This gear is used to move the pitman
arm which is connected to the steering rod. The motion of the pitman arm
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causes the linear motion of the track rod which in turn causes the linear
motion of the tie rod which is required to turn the wheels.
Now the steering column coming from the gearbox has a set of grooves which
fit into the threads present inside the metal block. Instead of twistingcompletely and moving all the way down the worm gear, the steering column
with threads is held fixed so that it moves only the gears used to move the
pitman arm.
Now instead of making the steering column directly engage the grooves
present in the worm gear, a system of recirculating ball bearings is provided
these recirculate through the grooves present in the steering arm as they turn.
These balls reduce friction between the grooves thus reducing wear and tear
of contact for a moment,making the steering feel very light and loose.
HYDRAULIC POWER STEERING
(Picture of Rack and pinion power steering)
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The power assisted rack and pinion system reduces the effort done by the
driver of the vehicle in turning the steering wheel and in turn causing the
wheel to turn.
This system makes use of hydraulic fluids to turn the steering column inaddition to the mechanical effort done by the driver thereby reducing driver
effort.
In addition to the basic components of a rack and pinion type and recirculating
ball type steering, a hydraulic power steering has the following:
PUMP
The pump consist of rotary vanes. These are rotated by the engine andare connected to the engine’s connecting rod by means of a pulley and a
belt or by means of gears.
These draw fluid from a fluid reservoir at a lower pressure and supply it
to the fluid lines that are connected to the steering system at a high
pressure.
The amount of flow of the fluid supplied depends on how fast the pump
rotates (determined by the engine’s speed).The pump also contains a
pressure valve that is used for regulating the fluid pressure at high
speeds.
ROTARY VALVE
The rotary valve is a valve which is used to sense the direction of
rotation of the steering wheel .This is used because the power steering
system must assist only when the steering column rotates and not when
the car is moving in a straight line.The rotary valve has a torsion bar, a piece of metal which twists when
torque is applied to it. The top of the bar is connected to the steering
column and the bottom of the bar is connected to the pinion or the
worm gears. The torsion valve is located inside the spool valve assembly
which has ports which open to the fluid lines.
As the torsion bar rotates, it also rotates the spool valve assembly.
Depending upon the direction of rotation, extra ports supplying
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hydraulic fluids open resulting in supplying of more hydraulic fluid in one
direction with respect to the other.
When the steering wheel is not turned, the fluid valves supply a constant
amount of hydraulic fluid. When the wheel is turned towards a
particular direction, more fluid is supplied on that direction when
compared to other side thereby causing the steering column to turn
easier.
SUSPENSION SYSTEMSSuspension is the term given to the system of shock absorbers, linkages
and springs which establishes a contact between the vehicle’s body and
the wheels and allows relative motion between the two.
Suspension systems serve a dual purpose —contributing to the
vehicle's handling and braking for good active safety and driving
pleasure,
Keeping vehicle occupants comfortable and reasonably well
isolated from road noise, bumps, and vibrations etc.
There are several types of suspension systems and their use depends
on the type of application and the type of load which the vehicle carries.
Commercial vehicles and buses of today use air suspension systems
which makes use of compressed air
Semi elliptical leaf spring suspension: most common in commercial vehicles:
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AIR SUSPENSION
An air suspension consists of balloons/bags made of plastics and rubber into
air is fed at right pressure.
An air compressor is used to feed the air into these plastic balloon setups.
These air compressor maybe powered by a vehicle’s on board electrical or by
an air pump connected to the engine.
Valves are provided at appropriate positions for controlling the air pressure
and in modern vehicles ,the system maybe electronically controlled where a
driver can choose several suspension set ups by changing the amount of air in
the plastic balloons.
When a vehicle moves over a rough road,the pressure of air in each plastic
balloon is coordinated so that the occupant of the vehicles get a smooth ride
and the ride height is maintained.
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BRAKING SYSTEM
Braking system of a vehicle is used to inhibit the motion of wheels of the
vehicle. Most common brakes of a vehicle is used to convert the kinetic energy
of motion of the vehicle into heat by means of friction.
TYPES OF BRAKES:
Brakes can be classified into:
FRICTIONAL BRAKES: Frictional brakes use friction to retard the rotating
motion of the wheels by converting it into friction. These type of brakes make
use of brake pads and brake shoes which can grip on to the wheels of vehiclescausind slowing down.
PUMPING BRAKES: These are used wherever a pump is used.For example, if
the piston of an ICE Engine has it’s fuel supply cut, Then the internal pumping
losses can cause braking. The change in energy which occurs when the fuel
supply is cut can be used to retard the motion
ELECTROMAGNETIC BRAKES: These are used in most cases whereelectrical motors are in place. In these, the motion of a rotating component is
hindered by means of introducing eddy currents in the rotating components by
using powerful electromagnets and thus stopping the vehicles. This type of
system is used in electric trains and engines.
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BASIC COMPONENTS AND WORKING OF A HYDRAULIC BRAKE
SYSTEM:
A brake that makes use of the principle of hydraulics and hydraulic fluids to
cause braking action is called a hydraulic brake system.
A hydraulic brake system is better than mechanical braking systems since by
transferring force via incompressible fluids, losses due to friction etc are
minimized and a greater force is available to be exerted on the brake pads.
Further, by means of using piston cylinders of appropriate sizes, the forceapplied when the brake pedal is pressed can be multiplied. On the other hand
when mechanical braking systems are used, there may be loss in the force
exerted as it gets transmitted over mechanical cables.
When the brake pedal is pressed, a force is applied on a rod supported by the
lever. The lever system ensures that the force applied by the leg is multiplied
many times before pushing the brake. This is done by the principle of moments
in mechanics. The end of the lever located near the point of application of
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force is longer than the end of the lever located on the side away from the
support on which the lever is mounted.
This ensures that a greater force is available to push the piston in the master
cylinder.
The master cylinder consists of a piston or a collection of pistons.
Often many pistons are operated in tandem. Such a master cylinder system is
called tandem master cylinder.
The hydraulic fluid fills the fluid lines from the wheels, upto the master
cylinder.
When the piston is pressed, the hydraulic brake fluids being nearly
incompressible transmit the force on to the wheel cylinders mounted on to the
each wheel. Further by adjusting the cross sectional area of the fluid lines,force
is also multiplied.
The wheel cylinder consists of 2 pistons which in turn are connected to the
brake shoe/pads on the wheels.
The pistons, due to the force transmitted by the hydraulic fluids, move awayfrom each other and hence exert a force on the 2 brake shoes/pads causing
them to grip on to drums/discs present in the wheels the wheels.
These brake shoes/pads convert the kinetic energy of the rotating wheel into
heat energy by friction thus hindering motion.
The brake shoes/pads can be made to grip against a rotating drum or a
rotating disc.
Generally rotating discs are preferred over rotating drums as a disc can cool
more easily compared to a drum. Also a rotating discs are easier to disengage
compared to a rotating drum.
Heat produced during the process of braking might cause the diameter of the
drum to increase, resulting in the shoes/pads having to move further to apply
the force. Further heat produced may also cause changes in frictional property
of the material lowering the friction and may also cause the hydraulic brakefluid to vaporize. Hence rotating discs are preferred over a drum
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this picture shows a disc brake in a motorcycle along with brake
shoes
This picture shows drum brakes in a wheel of a motorcycle along
with brake shoes
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BASIC COMPONENTS AND WORKING OF AN AIR BRAKE:
Most of the commercial vehicles of today use air brakes which make use of
compressed for braking action.
Air compressor: An air compressor is used to pump in the air into the
storage tank for use in the braking system. The air compressor may be
driven by an electric motor or by drive taken from the engine’s rotating
shaft.
Air compressor governor/pressure controller: It is used to keepthe pressure of air supplied below a the safety limit of the air reservoir.It
is provided with a safety valve for release of excess air.
Air reservoir: Holds the compressed air for use in the braking system.
Drain valves: Used to drain the air from the reservoir when vehicle is
stationary
Brake Pedal: It is used to supply air from the reservoir
Pushrod: It is similar to a piston. When it is depressed ,brakes are
released and vice versa.
Slack Adjuster: It is an arm which is used to connect the push rod of
the brake and the s cam of the brake which pushes the shoes against the
brake drums.
S cam: An s cam is an s shaped diaphragm that pushes against the brake
shoe when brake is engaged. Brake shoe: It is used to exert frictional force against the rotating drum
of the wheels
Return springs: These are used to disengage the brake shoes when not
pressed.
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When the brake pedal is not in use, and then the air brake system is filled with
air, the diaphragm is in closed position and does not press the brake shoe.
When the brake pedal is pressed, the pressure decreases and the diaphragm
presses against the brake shoe.
When the pedals are released, the air pressure is comes back to the original
state and the air compressor pumps in more air to make up for the loss.
Emergency brakes in trucks complement the air brake. While starting the
vehicle, the emergency brake has to be released to fill the system with air.
When the emergency brake system is filled with air, there is no braking
however when there s a leak in the system, emergency brakes engage and the
vehicle comes to a stop.
Parking brakes of a vehicle are generally cable operated and cause the brake
shoes to grip against the disc/drum when the vehicle is stationary to prevent
any motion which may occur when a vehicle is stationary.
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AUTOELECTRICAL SYSTEMS OF A VEHICLE:
Auto electrical systems of a vehicle consist of a battery which is recharged by
an alternator attached with the engine.
The battery is used is generally produces 12v while in trucks and buses,2
batteries may be connected in parallel to get an output of 24v.
The batteries are used to provide power to a circuits which are used for
powering the headlamps and cabin lamps etc.
The batteries are also used in ignition circuits.
Ignition circuit gets completed when the ignition is turned on during vehicle
start.The ignition coil is used to step up the voltage of 12v or 24v into 1000s of
volts required for producing a spark.
Further the flywheel and the cranks of the engine are also rotated by means of
solenoid coils due of magnetic fields in them or by means of electrical motors
which cause cranks to rotate.
REFERENCES USED:
Notes taken during practical training at Sundaram Motors,Poonamalee.
www.wikipedia.org
www.google.com- images
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