Chapter 1 - Goodheart
Contents
1. Auto Engine Repair Cylinder Head The cylinder head is bolted to the top of the block deck to enclose the top of the cylinders and form the top of the combustion chamber Figure 1 12 Like the block the cylinder head contains water jackets for cooling and oil passages for lubricating moving parts on or in the cylinder head Valve guides are machined through the top of the head for the valves The valves slide up and down in these guides Cylinder head ports are passages for the air fuel mixture to enter the combustion chamber and for exhaust gasses to flow out of the engine These are located in the cylinder head Valve seats are machined in the opening where the ports enter the combustion chamber The valves close against the seats to make a leakproof seal at high temperatures Engine Valves Engine valves control the flow into and out of the engine cylinder or combustion chamber They fit into the cylinder head operate inside the valve guides and close on the valve seats Valve springs fit over the top end of the valves to keep the valves in a normally closed position Figure 1 13 Figure 1 14 shows how a valve opens and closes the ports in the cylinder head When the valve slides down the valve head moves away from the valve seat and the port is opened When the valve slides up the valve head moves toward the valve seat until the valve face makes contact with the valve seat This seals the combustion chamber from the port2. Cylinder head a Exhaust Exhaust valve seat Intake valve seat Figure 1 12 The cylinder head is bolted to the top of the block It forms a cover over the cylinder The head also holds the valves that control flow into and out of the cylinder Chapter 1 Review of Engine Operation Intake port Exhaust Intake valve valve Figure 1 13 Valves fit into guides in the cylinder head Valve springs hold the valves closed The valves seal against valve seats in the head to close off ports from the combustion chamber There are two types of valves intake and exhaust The intake valve is the larger valve and it allows a fuel charge to flow into the cylinder The exhaust valve is the smaller valve and it opens to let burned gasses exhaust out of the cylinder Figure 1 15 shows how the air fuel mixture flows through the intake port past the valve and into the combustion chamber when the valve is open Four Stroke Cycle The four stroke cycle needs four up or down piston movements or strokes to produce one complete cycle Every two up and two down strokes of the piston results Cylinder head Valve guide Figure 1 14 Study the valve action When the valve slides open the valve face is lifted off of the valve seat This opens the port to the combustion chamber and gasses are free to enter or exit the cylinder Air fuel mixture Port in cylinder head Intake valve open Figure 1 15 Note the action as the
3. B engine block deck B C oil gallery D None of the above Chapter 1 Review of Engine Operation Technician A says the big end of a connecting rod fits around the piston pin Technician B says the big end of a connecting rod fits around the crankshaft Who is correct A A only B B only C Both A and B D Neither A nor B Technician A says the engine s oil rings always fit into the top groove on the pistons Technician B says the engine s oil rings are normally located in the lowest groove on the pistons Who is correct A A only B B only C Both A and B D Neither A nor B All of the following are basic parts of an automotive engine s piston assembly except A connecting rod B piston rings C crankshaft journal D piston pin The intake valve is____ the exhaust valve A smaller than B C larger than D All of the above the same size as 27 While discussing the operation of a four stroke cycle engine Technician A says every two up and down strokes of the engine s piston results in one power producing stroke Technician B says every four up and down strokes of the engine s piston results in one power producing stroke Who is correct A A only B B only C Both A and B D Neither A nor B A n ____is used to increase battery voltage to over 60 000 volts A starter B C ignition coil D magnet alternat
4. ____ out of the combustion chamber 6 Why is a piston pin or wrist pin needed 7 The crankshaft converts the motion of the piston into rotary motion 8 Describe the basic parts of a cylinder head 9 Which type of engine valve is larger and which type is smaller Summarize the four stroke cycle The_ opens the valves and allows them to close Why are the cooling and lubrication systems important An electric ignition system can be found on a n engine but not on a n _ engine What are the two types of fuel systems in use today Describe the three basic subsystems in a computer control system Auto Engine Repair ASE Type Questions Chapter 1 at one half of engine speed Technician B says the camshaft opens the exhaust valve at the beginning of the power stroke Who is correct A A only B B only C Both A and B D Neither A nor B Technician A says that the illustration is of a gasoline injection system Technician B says that a diesel injec tion system injects fuel directly into the cylinder Who is correct A A only B B only C Both A and B D Neither A nor B All of the following are major parts of a modern multi cylinder automotive engine except A valve springs B C piston rings D spool valves connecting rods Aln is the flat surface machined on the top of the cylinder block for the cylinder head A cam housing
5. compression stroke squeezes the air fuel mixture to make it more combustible See Figure 1 16B Both the intake and exhaust valves are closed The piston slides up and compresses the mixture into the small area in the com bustion chamber Air fuel mixture pulled into Intake valve open Piston and rod moving down A lIntake Stroke The piston slides down with the intake valve open and the exhaust valve closed The air fuel charge is pulled into the cylinder Spark plug fires il jt EE Air fuel mixture burns expands and forms pressure Piston and rod pushed down to turn crankshaft C Power Stroke The spark plug fires and the fuel begins to burn The heat of combustion causes expansion of the gasses and creates pressure This pushes the piston down with tremendous force to spin the crankshaft Intake valve closed Auto Engine Repair Exhaust valve closed Pressure formed on fuel charge Piston and rod moving up B Compression Stroke Both valves are closed and the piston slides up This compresses the air fuel charge and prepares it for combustion Intake valved Burned gasses Exhaust valve open and rod moving up D Exhaust Stroke The piston slides up with the intake valve closed and the exhaust valve open This pushes the exhaust gasses out of the cylinder so a fresh charge can enter Figure 1 16 Review the four stroke cycle You must be able to visualize these eve
6. intake valve opens Downward movement of the piston forms a vacuum in the cylinder Atmospheric pressure pushes the air fuel charge into the cylinder Ford in one power producing cycle Two complete revolutions of the crankshaft are needed to complete one four stroke cycle Automotive engines both gas and diesel are four stroke cycle engines The four strokes are intake compression power and exhaust With the engine operating these strokes happen over and over very rapidly At idle an engine might be running at 800 revolutions per minute rpm which means the crankshaft rotates 800 times in one minute Since it takes two complete revolutions of the crankshaft to complete a four stroke cycle an engine completes 400 four stroke cycles per minute at idle In other words the piston must slide up 800 times and down 800 times per minute You can imagine how fast these events are happening at highway speeds Intake Stroke A gasoline engine s intake stroke draws air and fuel into the combustion chamber Figure 1 16A shows the basic action during the intake stroke Study the position of the valves and movement of the piston The piston slides down to form a vacuum low pressure area The intake valve is open and the exhaust valve is closed Atmospheric pressure outside air pressure pushes the air fuel charge into the vacuum in the cylinder This fills the cylinder with a burnable mixture of fuel and air Compression Stroke The
7. low speeds it must meter a small amount of fuel into the airstream As engine speed and load increase the fuel system must meter more fuel into the airstream The fuel system must also alter the fuel metering with changes in engine temper ature and other variables There are two basic types of automotive fuel systems in Current use gasoline injection and diesel injection A third type of fuel system carburetion has not been commonly used since the mid 1980s Charging system wiring harness Main fuse Voltage regulator Charge indicator Alternator Alt t Battery Oa ernator belt Figure 1 25 The charging system recharges the battery and provides the vehicle s electrical needs while the engine is running Honda Gasoline Injection System A gasoline injection system uses fuel pump pressure to spray fuel into the engine intake manifold usually near the cylinder head s intake port A basic system is pictured in Figure 1 26 An electric fuel pump forces fuel from the fuel tank to the fuel injector A constant pressure is maintained at the injector The fuel injector is simply an electrically operated fuel valve When energized by the control module it opens and squirts fuel into the intake manifold or the com bustion chamber When not energized it closes and pre vents fuel entry into the engine Modern gasoline injection systems open the injector when the engine intake valve opens Then fuel is partial
8. speed transmission gear position road speed turbocharger boost pressure and other condi tions The sensing system sends different electrical current values back to the control module The control subsystem looks at the inputs from the sensors and determines what actions need to take place A control module or computer contains miniaturized electrical circuits that collect store and analyze information The con trol module then provides signals to the actuator subsystem The actuator subsystem serves as the hands of the computer system Based on signals from the control mod ule this system moves parts opens injectors closes the throttle turns on the fuel pump and performs other tasks needed to increase the overall efficiency of the vehicle Electric motors solenoids or relays and switches are the actuators The actuators turn on or off open or close or change position based on the signals from the control module This is discussed in detail later in this textbook Emission Control Systems Emission control systems are designed to reduce the amount of harmful chemicals and compounds emissions that enter the atmosphere from a vehicle There are several types of emission control systems Q PCV The positive crankcase ventilation system pulls fumes from the engine crankcase into the intake manifold so they can be burned before entering the atmosphere Evaporative emissions control This system uses a charcoal fille
9. 3 Combustion is the burning of Piston slides up and down in cylinder Figure 1 3 The piston fits into a cylinder bored through the block The piston slides up and down during engine operation acting as a pumping and power producing element 12 fuel which results in expanding gas inside the cylinder The piston transfers the pressure of combustion to the piston pin connecting rod and crankshaft It also holds the piston rings and piston pin During engine operation the piston slides up and down in the cylinder at tremendous speeds At a vehicle speed of about 55 mph 88 km h the piston can accel erate from zero to 60 miles an hour and then back to zero in one movement from top to bottom in the cylinder This places tremendous stress on the piston and its related parts Piston Rings The piston rings fit into grooves machined into the sides of the piston These rings keep combustion pressure from entering the crankcase and engine oil from entering the combustion chamber Look at Figure 1 4 The compression rings seal the clearance between the block and piston They are normally the two upper piston rings Their job is to contain the pressure formed in the combustion chamber Figure 1 5 Without compres sion rings pressure would blow past the outside diameter of the piston and into the lower area of the engine block The oil ring fits into the lowest groove in the piston It is designed to scrape excess oil from the cylin
10. This sample chapter is for review purposes only Copyright The Goodheart Willcox Co Inc All rights reserved Chapter 1 Review of Engine Operation After studying this chapter you will be able to Q Summarize the four stroke cycle Q List the major parts of an automotive engine Q Explain the purpose of major engine parts and assemblies Q Describe the relationship between the major parts of an engine Q List and describe the related systems of an engine Know These Terms BDC Camshaft Charging system Combustion Computer system Connecting rod Control module Cooling system Crankcase Crankshaft Cylinder Cylinder block Cylinder head Drive train Emission control systems Engine block Engine valves Exhaust gas recirculation system Exhaust manifold Four stroke cycle Fuel system Gasoline injection Ignition system Intake manifold Internal combustion engine Lubrication system Main bore Oil galleries Piston Piston pin Piston rings Ports Positive crankcase ventilation system Spark plug Starting system TDC Throttle valve Valve guides Valve seats Valve springs Valve train Water jackets Water pump This chapter provides a quick review of the operating principles of a four stroke cycle piston engine The interaction of basic engine components are discussed Related systems cooling lubrication fuel computer control and other systems are explained This review wi
11. air A fan pulls air through the radiator DaimlerChrysler Oil to valve train Oil filter dipstick ade a ons 4 far VA ESN G Oil to crank and camshaft Figure 1 22 The lubrication system prevents excess friction that may damage the engine Note the part names DaimlerChrysler Auto Engine Repair Spark plug wire Battery Ignition coil Ga IPA sy FN IA NNA ss a VX Electronic Paf control unit or switching device Speed sensing device or pickup coil Trigger wheel Figure 1 23 The ignition system is used on a gasoline engine to ignite the fuel in the combustion chamber A coil produces high voltage for the spark plug When the switching device breaks the flow of current to the coil the coil and spark plug fire to ignite the fuel The battery stores chemical energy that can be changed into electrical energy When the driver turns igni tion switch start switch the solenoid high current relay sends battery current to the starter motor The starter motor has a small gear that engages a large gear on the crankshaft flywheel The motor has enough torque turning force to spin the flywheel and thus the crankshaft until the engine starts and runs Then the driver releases the ignition key and deactivates the starting system Wiring harness Starter motor Se Ignition Flywheel Main fuse ye gear Negative or ground Starter solenoid Figure 1 24 The starting system rotat
12. and keep the camshaft in time with the crankshaft Figure 1 19 shows how a timing belt is used to operate the camshaft on our basic engine Intake and Exhaust Manifolds The intake manifold carries the air fuel mixture into the cylinder head intake ports It normally is bolted to the cylinder head Ports in the intake manifold match the intake ports in the cylinder head The exhaust manifold as its name implies carries burned gasses from the cylinder head exhaust port to the other parts of the exhaust system Figure 1 20 shows the basic action of the intake and exhaust manifolds Note With multiport fuel injection the fuel is injected into the airstream at the port However the fuel is injected into the airstream at the beginning of the intake manifold in the throttle body with throttle body injection Cooling System The cooling system is needed to carry the heat of combustion and friction away from the engine Without a cooling system the piston valves cylinder and other parts could be ruined in a matter of minutes The head and block could also crack from the tremendous heat Basically a cooling system consists of a radiator water pump fan thermostat water jackets and connecting hoses Figure 1 21 The water pump circulates an antifreeze and water solution through the water jackets hoses and radiator It is often driven by a fan belt running off of the crankshaft pul ley but may be driven by an electric motor T
13. ankshaft It is fastened to the piston pin at the top and the crankshaft at the bottom It also causes piston move ment on nonpower producing events up and down piston movements See Figure 1 8 The small top end of the connecting rod has a hole machined in it for the piston pin The top of the rod extends inside of the piston The big bottom end of the connecting rod fits around the crankshaft journal It has a removable cap that allows the installation and removal of the rod piston assembly Special rod bolts and nuts hold the cap in place As discussed in later chapters bushings are normally installed in the small end of the rod Rod bearings are installed in the big end of the connecting rod Crankshaft The crankshaft converts the up and down reciprocat ing movement of the connecting rod and piston into rotary motion The rotary motion is used to power gears chains belts and the drive train The crankshaft fits into the main bore of the engine block as shown in Figure 1 9 It mounts on the main bear ings and is free to spin inside the block The connecting rods are attached to the crankshaft journals Figure 1 10 Piston Small end pin Connecting rod l beam Big end Rod bolt for rod bearing Mod cap Rod nut Figure 1 8 The connecting rod links the piston and crankshaft together The large end has a removable cap that allows the rod to be bolted around the crankshaft journal The small end has a hole for the p
14. body s central nervous system The computer system monitors various conditions by analyzing input signals from sensors Then the control module computer deter mines what action should be taken to maintain maximum efficiency Based on this the control module sends signals to actuators that control the operation of the fuel system ignition system transmission and other devices Emission control systems reduce the amount of harm ful pollutants that enter the atmosphere Some emission control systems prevent fuel vapors from evaporating into 26 the air Others ensure complete combustion of fuel that leaves the combustion chamber and others just increase engine efficiency to reduce air pollution The drive train transfers engine power to the drive wheels Both front wheel and rear wheel drive are found on today s vehicles Front wheel drive vehicles have a transaxle which is the transmission and differential com bined in a single unit Review Questions Chapter 1 Please do not write in this text Write your answers on a separate sheet of paper 1 The ___ is the main supporting structure of an engine These hold the crankshaft in the bottom of the engine block A Cam bearings surround the cylinders in most engines to provide a way for coolant to remove heat from the cylinders What is the basic function of a piston _ keep combustion pressure from blowing into the crankcase and they also keep
15. d canister to collect and store gasoline fumes from the fuel tank when the engine is not running Air is drawn through the canister and into the intake manifold while the engine is running so the collected fumes are burned EGR The exhaust gas recirculation system injects exhaust gasses into the engine to lower combustion temperatures and reduce one form of pollution in the engine exhaust Air injection This system forces air into the exhaust stream leaving the engine to help burn any unburned fuel that exits the combustion chamber Catalytic converter This device chemically converts byproducts of combustion into harmless substances Many of these systems work together all reducing their share of harmful emissions The computer also plays an important part in reducing pollution It improves the efficiency of many systems Drive Train The drive train uses power from the engine to turn the vehicle s drive wheels Drive train configurations vary but Auto Engine Repair can generally be classified as rear wheel drive or front wheel drive Figure 1 30 shows simplified drive trains Clutch The clutch allows the driver to engage or disengage the engine power from the drive train It is mounted onto the engine flywheel between the engine and transmission or transaxle A clutch is needed when the vehicle has a manual transmission A vehicle with an automatic trans mission does not have a clutch Transmission The transmis
16. der wall to keep it from being burned in the combustion chamber Figure 1 6 If oil enters the area above the piston and burns blue smoke blows out of the tailpipe Piston Pin A piston pin also called a wrist pin allows the con necting rod to swing back and forth inside the piston The pin fits through a hole machined in the piston and through a hole in the upper end of the connecting rod Refer to Figure 1 7 Piston Piston clearance clearance Piston gt _ diameter Compression rings Oil ring Piston pin Figure 1 4 The clearance between the piston and cylinder allows the piston to move freely in the cylinder Rings seal the clearance Auto Engine Repair Combustion pressure gt Compression ring Piston Figure 1 5 The compression rings use combustion pressure to help seal against the cylinder wall This keeps pressure in the combustion chamber and out of the crankcase Cylinder wall v Piston Ring groove Oil control ring ms Escaping oil Oil film Oil to crankcase Figure 1 6 Oil rings act as a scraper to keep oil out of the com bustion chamber Deere amp Co Piston pin Piston Piston pin bore Connecting rod Swinging action Figure 1 7 The piston pin fits into a hole bored in the piston The pin attaches the piston to the connecting rod Chapter 1 Review of Engine Operation Connecting Rod The connecting rod transfers the force of the piston to the cr
17. e to the front wheel hubs Summary This chapter reviewed the basic operation of a four stroke cycle piston engine The engine found in most vehicles is called an internal combustion engine because it burns fuel inside of combustion chambers The cylinder block holds the other parts The piston and connecting rod transfer combustion pressure to the crankshaft The crankshaft converts the up and down action of the piston into rotary motion Chapter 1 Review of Engine Operation Engine Clutch Manual transmission lt Drive shaft Differential drive axle Transmission Clutch Differential drive axle Manual transaxle N Dead axle Figure 1 30 The drive train uses engine power and crankshaft rotation to turn the vehicle s drive wheels A A front engine rear wheel drive vehicle B A front engine front wheel drive vehicle Note the differential and transmission in one housing The cylinder head is bolted on top of the cylinder block It contains the valves that control flow into and out of the cylinder The camshaft operates the valves so that they open and close to correspond to piston action pro ducing the four stroke cycle The intake stroke draws air fuel mixture into the engine The compression stroke squeezes the mixture and readies it for burning The power stroke ignites the mixture and the expanding gasses push the piston down with tremendous force The exhaust stroke purges the burned gasses
18. es the crankshaft until the engine starts A powerful electric starter motor has a gear that meshes with the gear on the engine flywheel A solenoid makes the electrical connection between the battery and the starter motor when the ignition key is turned to the start position Honda Chapter 1 Review of Engine Operation Charging System The charging system is needed to recharge re energize the battery after starting system or other electrical system operation The battery can become discharged run down after only a few minutes of starter motor operation The charging system also provides all of the vehicle s electrical needs while the engine is running Basically the charging system consists of the alternator and a voltage regulator Look at Figure 1 25 The alternator produces the electricity to recharge the battery It is driven by a belt from the engine crankshaft pulley The alternator sends current through the battery to reactivate the chemicals in the battery This again prepares the battery for starting or other electrical loads The voltage regulator controls the electrical output of the alternator It ensures that about 14 5 volts are produced by the alternator Current then flows back into the battery since battery voltage is only about 12 5 volts Fuel System The fuel system must meter the right amount of fuel usually gasoline or diesel oil into the engine for efficient combustion under different conditions At
19. g gap The ignition coil fires every time the switching device stops current flow from the battery Figure 1 23 This causes the magnetic field in the coil to collapse and induce a higher voltage in the coil s output wire The spark plug is the match that starts the air fuel mixture burning in the combustion chamber When ignition coil fires and sends current through the spark plug wire an electric arc spark forms at the tip of the spark plug This makes the fuel and air start to burn producing the power stroke Note Older ignition systems used a mechanical switching device called points Ignition systems with points have not been used on production vehicles since the mid 1970s If you encounter this type of ignition system refer to the appropriate service manual for service procedures Starting System The starting system turns the engine crankshaft until the engine can begin running on its own power It uses a battery ignition switch high current relay and electric motor to rotate the crankshaft Figure 1 24 Hot coolant Radiator Airflow to remove heat from coolant Cooled coolant Fan belt Crankshaft pulley Figure 1 21 A cooling system is needed to remove heat from the engine and prevent severe engine damage Water jackets allow coolant to flow around the cylinders and through the cylinder head A water pump circulates coolant through the system The radiator dissipates heat into the outside
20. he coolant antifreeze water solution picks up heat from the metal parts of the engine and carries it to the radiator The radiator transfers heat from the coolant to the outside air A fan is used to pull air through the radiator Large radiator hoses connect the radiator to the engine The thermostat is a temperature sensing valve that controls the operating temperature of the engine When the engine is cold the thermostat blocks coolant flow through the radiator and speeds warm up of the engine Auto Engine Repair Camshaft sprocket Adjuster pulley Crankshaft sprocket Figure 1 19 The camshaft is turned at one half of engine speed A timing belt is the most common method of turning the camshaft in time with the crankshaft rotation Note the part names When the engine is warm the thermostat opens to allow coolant to circulate through the radiator thus removing heat from the engine Lubrication System The lubrication system circulates engine oil to high friction points in the engine Without oil friction will result in wear scoring and damage to parts very quickly The lubrication system basically consists of an oil pump oil pickup oil pan and oil galleries See Figure 1 22 The oil pump is the heart of the lubrication system because it circulates oil through the oil galleries The oil galleries are small passages that lead to the crankshaft Chapter 1 Review of Engine Operation Throttle body Inta
21. hown in Figure 1 17 Rocker arm Pivot point 17 The camshaft opens the valves and allows the valve springs to close the valves at the proper times The camshaft has a series of lobes egg shaped bumps that act on the valves or valve train to slide the valve down in its guide See Figure 1 18 Cam lobes Camshaft Figure 1 18 The lobes on the camshaft act on the valves or valve train to open and close the valves As shown here the camshaft fits into the cylinder head on many engines This lets it operate directly on valves without using push rods Rocker arm pushed up by spring Spring Valve closed Valve pushed Cam lobe off seat touches lifter Valve open on seat Lobe away een a from lifter Valve closed Figure 1 17 The camshaft operates the valve train When the cam lobe rotates into a lifter the valve is opened When a lobe moves out of a lifter the valve spring closes the valve Ford In Figure 1 17 note how the cam lobe acts on the valve train When the lobe moves into the lifter the lifter pushrod and one side of the rocker arm are pushed up This opens the valve When the lobe rotates away from the lifter the valve spring pushes the valve and other parts into the closed position Camshaft timing is needed to ensure that the valves properly open and close in relation to the crankshaft Either a belt chain or set of gears is used to turn the camshaft at one half of the crankshaft speed
22. ined through the top of the engine block The piston fits into the cylinder During Cylinder Cylinder Crankcase Main caps Main bolts Figure 1 2 The block is the framework for holding the other engine components Note the parts of the block This is a simplified one cylinder engine 11 engine operation the cylinder also called the cylinder bore guides the piston as it slides up and down The cylin der is slightly larger than the piston to produce a clearance space between the two parts Main caps are bolted to the bottom of the block They hold the crankshaft in place and form the bottom half of the main bore The main bore is a series of holes machined from the front to the rear of the block The crankshaft fits into these holes With the engine running the crankshaft spins or rotates in the main bore The deck is a flat surface machined on the top of the block for the cylinder head The head is bolted to the deck Coolant and oil passages in the deck align with openings in the cylinder head Coolant passages or water jackets surround the cylinders and combustion chamber They are hollow areas inside the block and head for coolant Coolant circulated through the water jackets removes the heat generated by the fuel burning in the cylinders The crankcase is the lower area of the block The crankshaft spins inside the crankcase Piston The piston converts the pressure of combustion into movement See Figure 1
23. iston pin Rod journal Flywheel Main journals Counterweight Figure 1 9 The crankshaft takes the reciprocating motion of the piston and produces rotary motion for vehicle s drive train and accessory system Piston at top dead center Piston at J otom dead center Rod and its crankshafl journal up Rod and its crankshaft journal down Figure 1 10 Note how the crankshaft changes the recipro cating motion of the piston into rotary motion 14 shows how the crankshaft changes the reciprocating up and down motion of the piston and connecting rod into a rotary motion The engine flywheel is a very heavy round disk mounted to the back of the crankshaft It helps to keep the crankshaft spinning between power strokes and smooth engine operation It also holds a large gear used by the starter TDC and BDC The abbreviation TDC stands for top dead center This is the point of travel where the piston is at its highest point in the cylinder The abbreviation BDC stands for bottom dead center This is the point of travel where the piston is at its lowest point in the cylinder Refer to Figure 1 11 Top dead center TDC One half revolution Crankshaft 180 One stroke Bottom dead center BDC Connecting rod Figure 1 11 TDC is when the piston is at the top of its stroke BDC is when the piston is at the bottom of its stroke One stroke is the piston movement from TDC to BDC or vice versa Ford
24. ke port Exhaust port Fuel injector Intake manifold Intake runners Exhaust manifold Figure 1 20 This is a cutaway of an engine Note the intake and exhaust manifolds Ports in the intake manifold connect to the intake ports in the cylinder head The exhaust manifold is bolted over the exhaust ports in the cylinder head General Motors bearings camshaft bearings and valve train components These are high friction points in the engine and need oil for protection Ignition System An ignition system is needed on a gasoline engine to ignite and burn the air fuel mixture It must increase battery voltage enough to produce a high voltage electric arc or spark at the tip of each spark plug in the combus tion chamber Refer to Figure 1 23 A fundamental ignition system consists of a spark plug plug wire ignition coil switching device and power source On many late model vehicles the ignition coil is mounted directly on top of the spark plug eliminating the need for a spark plug wire The switching device in the ignition system is an elec tronic control unit that makes and breaks electrical current flow to the ignition coil s Ignition coil operation is timed with crankshaft rotation so that the spark occurs in the combustion chamber at the end of the compression stroke The ignition coil is used to step up battery voltage to over 60 000 volts This is enough voltage to make the elec tricity jump the spark plu
25. ll prepare you for later text chapters that discuss these topics in much more detail This chapter uses words and illustrations to construct a basic one cylinder engine You will see how each part is installed in the basic engine and learn how that part performs an important function Then near the end of the chapter the systems that supplement engine operation and protect the engine from damage are reviewed If you have completed an introductory course that covered engine operation you should still read through this chapter to refresh your memory If you are not familiar with the operation of an engine study this chapter care fully This will let you catch up with the students that have already had some training in engines Intake manifold Timing chains Combustion chamber Crankshaft pulley Crankshaft Oil pan Figure 1 1 Study the general location of parts in an engine This will help you while reviewing the operation of an engine in this chapter Ford Auto Engine Repair Automotive Engine An engine is the source of power for moving the vehi cle and operating the other systems Sometimes termed the power plant it burns a fuel usually gasoline or diesel fuel to produce heat expansion of gasses pressure and result ing part movement Since a vehicle s engine burns fuel inside of itself it is termed an internal combustion engine As you will learn the arrangement of an engine s parts allows it to harnes
26. ly or completely forced into the combustion chamber by pump pressure This helps control how much fuel enters the cylinder and also increases combustion efficiency as you will learn in later chapters A control module computer is used to regulate when and how long the injector opens It uses electrical informa tion from various sensors to analyze the needs and operating conditions of the engine The engine sensors monitor various operating conditions such as engine temperature speed load and so on In this way the computer can deter mine whether more or less fuel is needed and whether the injector should be opened for a longer or shorter period of time based on the current operating conditions A throttle valve controls airflow engine speed and engine power It is connected to the accelerator pedal When the pedal is pressed the throttle valve opens to allow more air into the combustion chambers In turn the control module holds the injectors open for a longer period of time allowing more fuel into the combustion chamber The increase in air and fuel results in an increase in engine power output As the accelerator pedal is released the throttle valve closes reducing the amount of air allowed into the combustion chamber The control module in turn reduces the amount of time the injectors are open thus reducing the amount of fuel released into the injection chamber The decrease in air and fuel results in a decrease in engine p
27. nts to be a competent engine technician Chapter 1 Review of Engine Operation For proper combustion burning it is very important that the valves rings and other components do not allow pressure leakage out of the combustion chamber Leakage during the compression stroke may prevent the mixture from igniting and burning on the power stroke Power Stroke The air fuel mixture is ignited and burned during the power stroke to produce gas expansion pressure and a powerful downward piston movement See Figure 1 16C Both valves are still closed The spark plug fires and the fuel mixture begins to burn As the mixture burns it expands and builds pressure in the combustion chamber Since the piston is the only part that can move it is thrust downward with several tons of force This downward thrust pushes on the connecting rod and crankshaft forcing the crankshaft to turn The power stroke is the only stroke that does not consume use energy Exhaust Stroke The exhaust stroke pushes the burned gasses out of the cylinder and into the vehicle s exhaust system See Figure 1 16D The intake valve remains closed but the exhaust valve is open Since the piston is now moving up the burned gasses are pushed out of the exhaust port to ready the cylinder for another intake stroke Valve Train The valve train operates the engine valves It times valve opening and closing to produce the four stroke cycle Basic valve train parts are s
28. or All of the following are modern automotive emission control systems except A air injection B PCV C intake valve D evaporative emissions control Auto Engine Repair A leveling device is a useful accessory for an engine lift Here a leveling device is attached to the engine lift chain The two mounting brackets must be securely attached to the engine By turning the handle on the leveling device the engine can be shifted up in the front or back OTC Div of SPX Corp
29. ower output Diesel Injection System A diesel injection system forces fuel directly into the engine s combustion chamber as shown in Figure 1 27 The heat resulting from highly compressed air not an elec tric spark plug ignites and burns the fuel When the intake valve opens a full charge of air is allowed to flow into the cylinder Then on the compression stroke the air is squeezed until it is at a high temperature As soon as the fuel is injected into the hot air the fuel burns and expands A diesel injection system basically consists of an injection pump injector and glow plug system The injection pump is a high pressure mechanical pump It is powered by the engine and forces fuel to the diesel injector under very high pressure A conventional fuel pump feeds fuel from the tank to the injection pump Fuel injector fuel valve sprays fuel toward intake valve when open Throttle valve Wires to engine sensors Auto Engine Repair Spark plug ignites mixture Electric fuel pump a Gasoline from tank Figure 1 26 Gasoline injection uses pressure from an electric fuel pump to spray fuel into engine intake manifold through fuel injectors A throttle valve is used to control the airflow into the engine The diesel injector is simply a spring loaded valve It is normally closed and blocks fuel flow However when the injection pump forces fuel into the injector under high pressure the injector opens The fuel i
30. pump draws fuel from the tank and delivers it to the carburetor s fuel bowl The carburetion system is not currently used on late model vehicles but is still found on small gas engines Injection line Fuel ignites as it touches hot air High pressure mechanical pump Diesel fuel from tank Figure 1 27 Diesel injection is primarily mechanical A mechanical injection pump forces fuel into a spring loaded injector nozzle The pressure opens the injector and fuel sprays directly into combustion chamber A diesel does not use a throttle valve or spark plug Chapter 1 Review of Engine Operation Air enters filter Carburetor Fuel pulled into airstream by vacuum Throttle controls airflow and engine speed Air fuel mixture flows to cylinder Mixture ignited by spark plug Low pressure mechanical fuel pump from tank Figure 1 28 Carburetion systems are not used on passenger vehicles but are still used on small gas engines In this type of sys tem airflow into engine pulls fuel out of carburetor s fuel bowl A mechanical fuel pump fills the fuel bowl with fuel but does not force the fuel into the intake manifold Computer System A computer system is used to increase the overall effi ciency of a vehicle The computer or control module can control the ignition system fuel system transmission or transaxle emission control systems and other systems Figure 1 29 shows a diagram of a simplified vehicle com p
31. s the energy of the burning fuel Figure 1 1 illustrates the major parts of a modern multi cylinder engine Study them as they are introduced Q The block is the supporting structure for the engine Q The piston slides up and down in the block Q The piston rings seal the space between the block and sides of the piston Camshaft Valve spring Cylinder head Exhaust manifold Piston Piston rings Connecting rod Chapter 1 Review of Engine Operation The connecting rod connects the piston to the crankshaft The crankshaft converts the up and down action of the piston into rotary motion The cylinder head fits over the top of the block and holds the valves The valves open and close to control fuel entry into and exhaust exit from the combustion chamber The combustion chamber is a cavity formed above the piston and below the cylinder head for containing the burning fuel The camshaft opens the valves at the proper time The valve springs close the valves The timing belt or chain turns the camshaft at one half of the engine speed Engine Block The engine block also called the cylinder block forms the framework or backbone of an engine This is because many of the other components of an engine fasten to the block Cast from iron or aluminum the block is the largest part of an engine Figure 1 2 shows a cutaway view of a basic engine block Note the part names A cylinder is a large hole mach
32. s sprayed directly into the combustion chamber or a precombustion cham ber This is called a direct injection system Note in Figure 1 27 that a diesel does not have a throttle valve or a spark plug Engine power and speed are controlled by the injection pump which is controlled by a control module The more fuel injected into the combus tion chamber the more speed and power are produced by the engine As less fuel is injected into the combustion chamber engine speed and power decrease A glow plug system is used to aid cold starting of a diesel engine The glow plug is an electric heating element that warms the air in the combustion chamber This helps Mechanical injection nozzle sprays fuel into combustion chamber Air enters y No throttle valve Only air flows past intake valve and into combustion chamber Air compressed so tight it becomes red hot the air become hot enough to start combustion until the heat from engine operation can warm the incoming air Carburetion Fuel System Instead of injecting fuel into the airstream or combustion chamber a carburetion system uses engine vacuum suction to pull fuel into the engine Figure 1 28 Airflow through the carbu retor and the vacuum created by the engine s intake stroke draw fuel out of the carburetor s fuel bowl As the throttle valve is opened more air flows through the carburetor and thus more fuel flows into the airstream A low pressure mechanical fuel
33. sion uses a series of gears to allow the amount of torque going to the drive wheels to be varied The driver can shift gears to change the ratio of crankshaft revo lutions to drive wheel rotation When first accelerating more torque is needed to get the vehicle moving Then at higher road speeds less torque is needed to maintain road speed Engine speed also needs to be reduced at highway speeds A manual transmission is shifted by hand Levers cables or rods connect the driver s shift lever to the inter nal parts of the transmission An automatic transmission uses a hydraulic fluid pressure system to shift gears A torque converter fluid clutch and special planetary gear sets provide automatic operation However the driver must manually change the shift lever position to change from forward to reverse A transaxle is a transmission and a differential axle drive mechanism combined into one housing It is commonly used with front wheel drive vehicles but may also be found on rear engine rear wheel drive vehicles A transaxle may be manual or automatic Drive Shaft and Drive Axle A drive shaft is used with a front engine rear wheel drive vehicle It connects the transmission to the differential A drive axle connects the differential to the drive hubs or wheels On most rear wheel drive vehicles the drive axle is a solid steel shaft On vehicles with a transaxle the drive axle is a flexible shaft extending from the transaxl
34. to prepare the cylinder for another intake stroke Every two crankshaft revolutions complete one four stroke cycle Thus one power stroke is produced every two crankshaft revolutions The flywheel helps keep the crankshaft spinning on the nonpower producing strokes and smoothes out engine operation Various systems are needed to keep the engine run ning The cooling system removes excess combustion heat and prevents engine damage The lubrication system also prevents engine damage by reducing friction between moving engine parts The ignition system is needed on a gasoline engine to ignite the fuel and start it burning A diesel engine uses high compression stroke pressure to heat the air in the cylinder enough to start combustion instead of an electric spark Also a diesel does not use a throttle valve to control engine speed The amount of fuel injected into the cylin der controls engine speed and power output The two types of fuel systems in use today are gasoline injection and diesel injection Modern fuel injec tion increases fuel economy over older fuel systems by closer control of the fuel use by each cylinder Carburetion is not used today The starting system uses a powerful electric motor to turn the engine flywheel until the engine can run on its own power The charging system recharges the battery and sup plies electricity to the vehicle while the engine is running A vehicle s computer system is similar to the human
35. uter system A modern vehicle may have several control modules To understand how a vehicle s computer control system works think of the human body s central nervous ACTUATOR Fuel injectors AS AS L Fuel pressure regulator Z Os system For example if your finger touches a hot stove the nerves sensors in your hand send a signal to your brain Your brain control module analyzes these signals and decides that you are in pain Your brain control module quickly activates your muscles actuators to pull your hand away from the hot stove A computer control system works in the same manner It controls actions based on sensory inputs For simplicity a vehicle s computer control system can be divided into three subsystems sensor control and actuator The sensor subsystem checks various operating conditions using sensors A sensor is a device that can CONTROL SENSOR Knock sensor Mass airflow sensor Oxygen sensor Manifold absolute pressure sensor Intake air temperatue sensor l Control module Engine coolant temperature sensor Engine speed sensor Throttle position sensor Catalyst monitor Figure 1 29 This is a simplified diagram of the sensor control and actuator subsystems of a computer control system for fuel injector operation 24 change its electrical signal based on a change in a condi tion Sensors might measure intake manifold vacuum throttle opening engine
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