Halderman ch018 lecture

© 2011 Pearson Education, Inc.All Rights Reserved

Automotive Technology, Fourth EditionJames Halderman

GASOLINE ENGINE OPERATION, PARTS,

AND SPECIFICATIONS

18

18 GASOLINE ENGINE OPERATIONS, PARTS, AND SPECIFICATIONS



ObjectivesObjectives

• The student should be able to:– Prepare for Engine Repair (A1) ASE

certification test content area “A” (General Engine Diagnosis).

– Explain how a four-stroke cycle gasoline engine operates.

– List the various characteristics by which vehicle engines are classified.




ObjectivesObjectives

• The student should be able to:– Discuss how a compression ratio is

calculated.– Explain how engine size is determined.– Describe how displacement is affected by

the bore and stroke of the engine.




PURPOSE AND PURPOSE AND FUNCTIONFUNCTION




Purpose and FunctionPurpose and Function

• Convert heat energy of burning fuel into mechanical energy

• Mechanical energy is used to perform the following:– Propel the vehicle




Purpose and FunctionPurpose and Function

• Mechanical energy is used to perform the following:– Power the air-conditioning system and

power steering– Produce electrical power for use throughout

the vehicle




ENERGY AND POWERENERGY AND POWER




Energy and PowerEnergy and Power

• Engines use energy to produce power• Combustion: fuel is burned at a

controlled rate to convert chemical energy to heat energy





• Combustion occurs within the power chamber in an internal combustion engine

• Engines in automobiles are internal combustion heat engines





• NOTE: An external combustion engine burns fuel outside of the engine itself, such as a steam engine.




ENGINE ENGINE CONSTRUCTIONCONSTRUCTION

OVERVIEWOVERVIEW




Engine Construction OverviewEngine Construction Overview

• Block– Solid frame from which all automotive and

truck engines are constructed– Constructed of cast iron or aluminum





• Rotating Assembly– Constructed of pistons, connecting rods

and a crankshaft




Figure 18-1 The rotating assembly for a V-8 engine that has eight pistons and connecting rods and one crankshaft.





• Cylinder Heads– Seal top of cylinders in the engine block– Contain both intake valves and exhaust

valves– Constructed of cast iron or aluminum

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Figure 18-2 A cylinder head with four valves per cylinder, two intake valves (larger) and two exhaust valves (smaller).




ENGINE PARTS AND ENGINE PARTS AND SYSTEMSSYSTEMS




Engine Parts and SystemsEngine Parts and Systems

• Intake and Exhaust Manifolds– Air and fuel enter and exit the engine

through manifolds– Intake manifolds are constructed of nylon-

reinforced plastic or aluminum





• Intake and Exhaust Manifolds– Exhaust manifolds must withstand hot

gases and are constructed of cast iron or steel tubing





• Cooling System– Controls engine temperature– Vehicles are cooled by circulating

antifreeze coolant





• Cooling System– Coolant picks up heat and releases it

through radiator




Figure 18-3 The coolant temperature is controlled by the thermostat, which opens and allows coolant to flow to the radiator when the temperature reaches the rating temperature of the thermostat.





• Lubrication System– Oil is pumped from oil pan through oil filter,

then into oil galleries to lubricate engine parts




Figure 18-4 A typical lubrication system, showing the oil pan, oil pump, oil filter, and oil passages.





• Fuel System and Ignition System– Fuel system includes the following

components:• Fuel tank – stores fuel and contains most

fuel pumps






components:• Fuel filter and lines - transfer fuel for the fuel

tank to the engine






components:• Fuel injectors - spray fuel into intake

manifold or directly into the cylinder





• Fuel System and Ignition System– Ignition system includes the following

components:• Spark plugs - provide an air gap inside the

cylinder where a spark occurs to start combustion






components:• Sensor(s) - includes crankshaft position

(CKP) and camshaft position (CMP)






components:• Ignition coils - increase battery voltage to

5,000 to 40,000 volts






components:• Ignition control module (ICM) - controls when

the spark plug fires






components:• Associated wiring - electrically connects the

battery, ICM, coil, and spark plugs




FOUR-STROKE CYCLEFOUR-STROKE CYCLEOPERATIONOPERATION




Four-Stroke Cycle OperationFour-Stroke Cycle Operation

• Principles– First four-stroke cycle engine developed by

Nickolaus Otto in 1876– The process begins with the starter motor

rotating the engine until combustion takes place





• Principles– The cycle is repeated for each cylinder of

the engine– Piston is attached to crankshaft with a

connecting rod allowing the piston to move up and down




Figure 18-5 The downward movement of the piston draws the air-fuel mixture into the cylinder through the intake valve on the intake stroke. On the compression stroke, the mixture is compressed by the upward movement of the piston with both valves closed. Ignition occurs at the beginning of the power stroke, and combustion drives the piston downward to produce power. On the exhaust stroke, the upward-moving piston forces the burned gases out the open exhaust valve.




Figure 18-6 Cutaway of an engine showing the cylinder, piston, connecting rod, and crankshaft.





• Operation– Engine cycles are identified by the number

of piston strokes required to complete the cycle





• Operation– Piston stroke: one-way piston movement – Most engines use a four-stroke cycle





• Operation– Most engines use a four-stroke cycle

• Intake stroke• Compression stroke





• Operation– Most engines use a four-stroke cycle

• Power stroke• Exhaust stroke





• The 720-Degree Cycle– In each cycle, the engine crankshaft makes

two complete revolutions (or 720 degrees)





• The 720-Degree Cycle– To find the angle between cylinders of an

engine, divide the number of cylinders into 720 degrees




ENGINE ENGINE CLASSIFICATIONCLASSIFICATION

AND CONSTRUCTIONAND CONSTRUCTION




Engine Classification and Engine Classification and Construction Construction

• Engines are classified by several characteristics including:– Number of strokes– Cylinder arrangement





• Engines are classified by several characteristics including:– Longitudinal and transverse mounting– Valve and camshaft number and location





• Engines are classified by several characteristics including:– Type of fuel– Cooling method– Type of induction pressure





• NOTE: Although it might be possible to mount an engine in different vehicles both longitudinally and transversely, the engine component parts may not be interchangeable. Differences can include different engine blocks and crankshafts, as well as different water pumps.

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Figure 18-7 Automotive engine cylinder arrangements.




Figure 18-8 A horizontally opposed engine design helps to lower the vehicle’s center of gravity.




Figure 18-9 A longitudinally mounted engine drives the rear wheels through a transmission, driveshaft, and differential assembly.




Figure 18-10 Two types of front-engine, front-wheel drive mountings.





• Push rod engine: camshaft is located in the block, the valves are operated by lifters, pushrods, and rocker arms

• Push rod engine also called cam-in-block design and overhead valve (OHV)





• Single overhead camshaft (SOHC) design uses one overhead camshaft

• Double overhead camshaft (DOHC) design uses two overhead camshafts





• NOTE: A V-type engine uses two banks or rows of cylinders. An SOHC design, therefore, uses two camshafts but only one camshaft per bank (row) of cylinders. A DOHC V-6, therefore, has four camshafts, two for each bank.

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Figure 18-11 Cutaway of an overhead valve (OHV) V-8 engine showing the lifters, pushrods, roller rocker arms, and valves.




Figure 18-12 SOHC engines usually require additional components, such as a rocker arm, to operate all of the valves. DOHC engines often operate the valves directly.




Figure 18-13 A DOHC engine uses a camshaft for the intake valves and a separate camshaft for the exhaust valves in each cylinder head.




Figure 18-14 A rotary engine operates on the four-stroke cycle but uses a rotor instead of a piston and crankshaft to achieve intake, compression, power, and exhaust stroke.




Engine Classification and Engine Classification and ConstructionConstruction

• Engine Rotation Direction– SAE standard for automotive engine

rotation is counterclockwise (CCW)





• Engine Rotation Direction– Direction is viewed from the flywheel end

(principal end) of the engine (end to which power is applied to drive vehicle)





• Engine Rotation Direction– Non-principal end is referred to as the front

end and is opposite the flywheel end




Figure 18-15 Inline 4-cylinder engine showing principal and nonprincipal ends. Normal direction of rotation is clockwise (CW) as viewed from the front or accessory belt (nonprincipal) end.




ENGINE ENGINE MEASUREMENTMEASUREMENT




Engine MeasurementEngine Measurement

• Bore– The diameter of a cylinder– Pressure measured in units, such as

pounds per square inch (PSI)




Figure 18-16 The bore and stroke of pistons are used to calculate an engine’s displacement.





• Stroke– Distance the piston travels from top dead

center (TDC) to bottom dead center (BDC)





• Stroke– Determined by the throw of the crankshaft– The throw is the distance from the

centerline of the crankshaft to the centerline of the crankshaft rod journal





• Stroke– The throw is one-half of the stroke





• NOTE: Changing the connecting rod length does not change the stroke of an engine. Changing the connecting rod only changes the position of the piston in the cylinder. Only the crankshaft determines the stroke of an engine.




Figure 18-17 The distance between the centerline of the main bearing journal and the centerline of the connecting rod journal determines the stroke of the engine. This photo is a little unusual because it shows a V-6 with a splayed crankshaft used to even out the impulses on a 90-degree, V-6 engine design.





• Displacement– Displacement (engine size) is the cubic

inch (cu. in.) or cubic centimeter (cc) volume displaced or how much air is moved by all of the pistons





• Displacement– Most engines today are identified by their

displacement in liters• 1 L = 1,000 cc• 1 L = 61 cu. in.• 1 cu. in. = 16.4 cc





• Conversion– To convert cubic inches to liters, divide

cubic inches by 61.02 – To convert liters into cubic inches, multiply

by 61.02





• Calculating Cubic Inch Displacement– Formula: Cubic inch displacement = π (pi)

× R2 × Stroke × Number of cylinders





• Calculating Cubic Inch Displacement– Applying the formula to a 6-cylinder

engine:• Bore = 4.000 in.• Stroke = 3.000 in.






engine:• π = 3.14• R = 2 inches






engine:• R2 = 4 (22 or 2 × 2)• Cubic inches = 3.14 × 4 (R2) × 3 (stroke) ×

6 (number of cylinders)






engine:• Cubic inches = 226 cubic inches




Chart 18-1 To find the cubic inch displacement, find the bore that is closest to the actual value, then go across to the closest stroke value.




Chart 18-1 (continued) To find the cubic inch displacement, find the bore that is closest to the actual value, then go across to the closest stroke value.





• Engine Size Conversion– Many vehicle manufacturers will round the

displacement so the calculated cubic inch displacement may not agree with the published displacement value




Chart 18-2 Liters to cubic inches is often not exact and can result in representing several different engine sizes based on their advertised size in liters.




COMPRESSION RATIOCOMPRESSION RATIO




Compression RatioCompression Ratio

• Definition– Ratio of the difference in the cylinder

volume when the piston is at the bottom of the stroke to the volume in the cylinder above the piston when the piston is at the top of the stroke




Figure 18-18 Compression ratio is the ratio of the total cylinder volume (when the piston is at the bottom of its stroke) to the clearance volume (when the piston is at the top of its stroke).





• Calculating Compression Ratio– Formula: – CR =

Volume in cylinder with piston at bottom of cylinderVolume in cylinder with piston at top center





• Calculating Compression Ratio– Example: What is the compression ratio of

an engine with 50.3 cu. in. displacement in one cylinder and a combustion chamber volume of 6.7 cu. in.?

• CR = 50.3 + 6.7 cu. in. = 57.0 = 8.5 6.7 cu. in. 6.7




Figure 18-19 Combustion chamber volume is the volume above the piston when the piston is at top dead center.





• Changing Compression Ratio– Factors that can affect compression ratio

include:• Head gasket thickness





• Changing Compression Ratio– Factors that can affect compression ratio

include:• Increasing cylinder size




TORQUE AND TORQUE AND HORSEPOWERHORSEPOWER




Torque and Horsepower Torque and Horsepower

• Definition of Torque– Rotating force that may or may not result

in motion– Measured as the amount of force multiplied

by the length of the lever through which it acts





• Definition of Torque– Twisting force measured at the end of the

crankshaft and measured on a dynamometer





• Definition of Torque– Engine torque is always expressed at a

specific engine speed (RPM) or range of engine speeds

– Metric unit for torque is newton-meters

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• Definition of Power– Rate of doing work– Power equals work divided by time





• Definition of Power– Power is expressed in units of foot-pounds

per minute and power also includes the engine speed (RPM) where the maximum power is achieved




Torque and HorsepowerTorque and Horsepower

• Horsepower and Altitude– Power that a normal engine can develop is

greatly reduced at high altitude




Torque and HorsepowerTorque and Horsepower

• Horsepower and Altitude– According to SAE conversion factors, a

nonsupercharged or nonturbocharged engine loses about 3% of its power for every 1,000 ft (300 m) of altitude

Halderman ch018 lecture

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Transcript of Halderman ch018 lecture