EngineConstruction351页教学课件全书电子教案.ppt

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,*,Unit 1 Automotive Basics,Lesson 1,Fundamentals of Automobile,The modern automobile contains more than 15000 separate individual parts that must work together.These parts can be grouped into four major categories:engine,、,chassis,、,body and electrical equipment,.,There are two types of engine:,gasoline(a spark-ignition engine),diesel(a compression-ignition engine).,1,Engine,Fuel system,1.1,The fuel system is designed to mix air and fuel in the engine for combustion.This air and fuel mixing should produce an efficient combustion process.,Ignition system,1.2,The ignition system is designed to ignite the air and fuel that have been mixed in the fuel system.In order to do this,，,a very high voltage is deeded to produce a spark within the combustion chamber.,Starting and charging systems,1.3,The starting and charging systems are designed to start the engine and keep the battery fully charged during operation.,Lubrication system,1.4,This system is designed to keep all of the engine parts lubricated so that friction is reduced.Without lubrication inside the engine,，,the moving parts that are continuously rubbing against each other would heat upIf overheat,，,they may be damaged by heat.,Cooling system,1.5,The cooling system is used to keep the engine at the most efficient operating temperature.It is very important that the engine run as hot as possible.So the engine has a cooling system to remove just the right amount of heat.,Air intake and exhaust systems,1.6,The air intake and exhaust systems get clean air into the engine and remove the dirty exhaust gases from the combustion chamber with minimum pollution.The engines use the sophisticated duct and exhaust pipe to do this.,Pollution control system,1.7,This system is adopted to reduce varies emissions from the engine.Some of the more common pollutants include carbon monoxide,，,nitrogen oxide,，,and hydrocarbons.,(1)Power train system,conveys the drive to the wheels.,(2)Suspension system,absorbs the road shocks.,(3)Steering system,controls the direction of the movement.,(4)Brake system,slows down the vehicle.,2,Chassis,Power train system conveys the drive to the wheels.The main components are clutch,，,gearbox,，,driveshaft,，,final drive,，,and differential.,Power train system,2.1,The purpose of the complete suspension system is to isolate the vehicle body from road shocks and vibrations,，,which will otherwise be transferred to the passengers and load.It must also keep the tire in contact with the road regardless of road surface.,Suspension system,2.2,The steering system,，,under the control of the driver at the steering wheel,，,provides the means by which the front wheels are directionally turned.The steering system may be the power assisted to reduce the effort required to turn the steering wheel and make the vehicle easier to maneuver.,Steering system,2.3,The braking system has three main functions,，,First,，,to reduce the speed of the vehicle,，,when,Necessary,Second,，,to stop the car in as short a distance as possible,Third,，,to hold the vehicle stationary.,Steering system,2.4,An automobile body is a sheet metal shell with windows,，,doors,，,a hood,，,and a trunk deck built,into it.It provides a protective covering for the engine,，,passengers,，,and cargo.The body is designed to keep passengers safe and comfortable.The body styling provides an attractive,，,colorful,，,modern appearance for the vehicle.,3,Body,The electrical system supplies electricity for the ignition,，,horn,，,lights,，,heater,，,and starter.The electricity level is maintained by a charging circuit.This circuit consists of battery and alternator(or generator).The battery stores electricity.The alternator changes the engine,s mechanical energy into electrical energy and recharges the battery.,4,Electrical equipment,Unit 2 Engine Construction,Internal Combustion Engine Basics,Engine Body,Fuel Injection System,The Fuel Delivery System,Valve System,Lesson 2,Lesson 3,Lesson 6,Lesson 5,Lesson 4,Cooling System,Lubrication System,VR6/W12 Engine,Emission Control Systems,Turbochargers and Superchargers,Lesson 7,Lesson 8,Lesson 11,Lesson 10,Lesson 9,Lesson 12,Hybrid-electric Vehicle,Lesson 2,Internal Combustion Engine Basics,internal combustion engine.,external combustion engine.,1,Engine terms,Engine terms are as shown in Fig.2-1.,TDC,:the position of the crank and piston when the piston is farther away from the crankshaft.,BDC,:the position of the crank and piston when the piston is nearest to the crankshaft.,Stroke,:the distance between BDC and TDC.,Bore,:the internal diameter of the cylinder.,Swept volume,:the volume between TDC and BDC.,Engine capacity,:this is the swept volume of all the cylinder,Clearance volume,:the volume of the space above the piston when it is at TDC.,Two-stroke,:a power stroke every revolution of the crank.,Four-stroke,:a power stroke every other revolution of the crank.,2,The four-stroke engine principle,The most common engine is the four-stroke piston engine.Each stroke is named after the action it performs:intake,，,compression,，,power,，,and exhaust.,Intake stroke,2.1,As the piston moves down,，,the vaporized mixture of fuel and air enters the cylinder through the open intake valve.To obtain the maximum filling of the cylinder,，,the intake valve opens about 10before TDC,，,giving 20overlap.The inlet valve remains open until some 50after BDC to take advantage of incoming mixture.,Compression stroke,2.2,The piston turns up,，,the intake valve closes,，,the mixture is compressed within the combustion Chamber,，,while the pressure rise to about 1MPa,，,depending on various factors including the compression ratio,，,throttle opening and engine speed.Near the top of the stroke the mixture is ignited by a spark which bridges the gap of the spark plug.,Power stroke,2.3,The expanding gases of combustion produces a rise in pressure of the gas to some 3.5MPa,，,and the piston forced down in the cylinder.The exhaust valve opens near the bottom of the stroke.,Exhaust stroke,2.4,The piston moves back up with the exhaust valve open some 50before BDC,allowing the pressure within the cylinder to fall and to reduce“back”pressure on the piston during the exhaust Stroke,，,and the burned gases are pushed out to prepare for next intake stroke.The intake valve usually opens just before the exhaust stroke.,The major parts of the engine are engine block,，,engine head,，,pistons,，,connecting Rods,，,crankshaft,，,and valves.The other parts are joined to make systems.These systems are the fuel System,，,intake system,，,ignition system,，,cooling system,，,lubrication system,，,and exhaust system.,3,Engine systems,Lesson 3,Engine Body,Basic body includes the engine block,，,cylinder head,，,crankshaft,，,pistons,，,connecting rods,，,and flywheel,.,The engine block is the main supporting structure to which all other engine parts are attached.,1,Engine block,The cylinder head fastens to the top of the block.The underside forms the combustion chamber with the top of the piston.,Most cylinder heads are made from cast aluminum or cast iron.The cylinder head contains at least one intake valve and one exhaust valve for each cylinder.,The joint between the engine block and the cylinder head must be tight and able to withstand pressure and the heat developed in the combustion chamber.,2,Cylinder head,The crankshaft,，,in conjunction with the connecting rod,，,converts the reciprocating motion of the piston to the rotary motion needed to drive the vehicle.,3,Crankshaft,The piston converts the potential energy of the fuel into the kinetic energy that turns the crankshaft.,The piston is a cylindrical shaped hollow part that moves up and down inside the cylinder.,The piston is used to ensure a snug,“,air tight,”,fit.,4,Piston,The connecting rod is made of forged high-strength steel.It transmits force and motion from the piston pin,，,or“wrist pin”,，,which connects the rod to the piston,，,the pin is usually pressed into the small end of the connecting rod.Some rods have a lock bolt in the small end.The big end of connecting rod is attached to a crank-pin by a rod bearing cap.,5,Connecting rod,A heavy flywheel is attached to the rear of the crankshaft with bolts.,The function of the flywheel is to smooth out engine speed and keep the crankshaft spinning between power strokes.,6,Flywheel,In some engines,，,the flywheel also serves as a mounting surface for the clutch.,The outer rim of the flywheel has a large ring attached with gear teeth cut into it.,The teeth of the starter motor engage these teeth and spin the flywheel to crank the engine.,When an automatic transmission is used,，,the torque converter assembly works with the flywheel.,Lesson 4,Valve System,The valve system is made up of those parts needed to open and close the valves at just the right time.,These valve moments must take place at exactly the right moments.,The opening of each valve is controlled by a camshaft.,The valve train typically includes the camshaft,，,valves,，,valve springs,，,rocker arms,，,valve lifter,，,and pushed.,1,Valve train types,Overhead camshaft(OHC)valve train,Pushrod valve train,Overhead camshaft(OHC)valve train,1.1,The cam is an egg-shaped piece of metal on a shaft that rotates in coordination with the crankshaft.The metal shaft,，,called the camshaft,，,typically has individual cams for each valve in the engine.,Pushrod valve train,1.2,The camshaft also can be located in the lower part of the engine,，,within the engine block.To transfer the motion of the cam upward to the valve additional parts are needed.,2,Valve clearance,When the engine runs in compression stroke and power stoke,，,the valves must close tightly on their seats to produce a gas-tight seal and thus prevent the gases escaping from the combustion chamber.,Some clearance is needed in the operating mechanism,，,so that the valves can close fully.,3,Valve timing,The time at which valves open and close(valve timing)and the duration of valve opening is stated in degrees of crankshaft rotation,.,valve overlap,：,the end of the exhaust stroke and the beginning of the intake stoke overlap for a short period of time.,Valve timing and valve overlap vary on different engines.,Lesson 5,The Fuel Delivery System,The fuel system is critical to engine operation.Its function is to store and supply fuel to the cylinder chamber where it can be mixed with air,，,vaporized,，,and burned to produce energy.,1,Gasoline,Gasoline is a complex blend of carbon and hydrogen compounds.Additives are then added to improve performance.The two most important features of gasoline are volatility and resistance to knock(octane).Volatility is a measurement of how easily the fuel vaporizes.,Resistance to knock or octane is simply the temperature the gas will burn at.Higher octane fuel requires a higher temperature to burn.Other factors that affect the octane requirements of the engine are:air/fuel ratio,，,ignition timing,，,engine temperature,，,and carbon build up in the cylinder.,2,Fuel tank,1.The fuel tank is used to store the fuel of engine needed.It is usually located in the rear of the vehicle.The fuel tank is designed to fit around frame and to be protected from impacts.,2.The fuel cap on the fuel tank is used to keep the fuel from splashing out,，,release the vacuum created by the fuel removing,，,and prevent vapors from escaping directly into the atmosphere.,3,Fuel pump,Two types of fuel pumps are used in the automobiles:mechanical and electric.,All fuel injected cars today used electric fuel pumps,，,while most,carburated,cars used mechanical fuel pumps.,Many cars today,，,locate the fuel pump inside the fuel tank.,4,Fuel filters,Fuel filters are used to stop any contamination from getting into the fuel system of both gasoline and diesel engines.,The gasoline engines may have one or two filters in the fuel system.The first filter is usually placed inside the fuel tank to prevent large pieces of contaminant from damaging the fuel pump.The second one is an in-line type or an in-carburetor type used to filter out small dirt particles.,5,Carburetor,A carburetor delivers fuel in proportion to the amount of air flowing through it.To meet complicated demands,，,a carburetor is a highly intricate device,，,with many internal passages and parts.,Venturi,5.1,A venturi is streamlined restriction that partly closes the carburetor bore.The air entering the venturi is forced to speed up.The greater the velocity of air passed through the venturi,，,the greater the vacuum produced,，,and the more the fuel is drawn in.,Throttle valve,5.2,The flow of air and fuel through the carburetor is controlled with a throttle valve.The throttle valve is placed below the venturi and connected to the acceleration pedal.As the drivers foot on the pedal is depressed,，,the throttle valve opens,，,and there is very little restriction of air and fuel.The load and speed are increased.,Float chamber,5.3,The float chamber is a reservoir for storing and supplying fuel to the carburetor.As the engine uses fuel,，,the float chamber replenishes it automatically.,A float rests on top of the fuel in the reservoir.As fuel is used,，,the float level drops.When the float drops,，,a needle valve is opened.The open needle valve permits the flow of fuel from the fuel pump into the carburetor,s float chamber.When the chamber is full again,，,the needle valve is pushed upward and closes the fuel inlet.,Metering the fuel,5.4,The pressure differential between the float chamber and the venturi causes fuel to flow.However,，,to maintain the proper air-fuel ratio,，,the carburetor must provide just the right amount of fuel.To do so,，,the main discharge tube has a small hole.This allows a precise amount of fuel to enter the airstream.In most cases,，,this small hole is in the float chamber at the end of the main discharge tube.There,，,its small size limits fuel flow.,Lesson 6,Fuel Injection System,The Electronic Fuel Injection system can be divided into three basic subsystems.,These are the fuel delivery system,，,air induction system,，,and the electronic control system.,1,Fuel delivery system,The fuel delivery system consists of the fuel tank,，,fuel pump,，,fuel filter,，,fuel delivery pipe(fuel rail),，,fuel injector,，,fuel pressure regulator,，,and fuel return pipe.,Fuel is delivered from the tank to the injector by means of an electric fuel pump.The pump is typically located in or near the fuel tank.Contaminants are filtered out by a high capacity in line fuel filter.,Fuel is maintained at a constant pressure by means of a fuel pressure regulator.Any fuel which is not delivered to the intake manifold by the injector is returned to the tank through a fuel return pipe.,2,Air induction system,The air induction system consists of the air cleaner,，,air flow meter,，,throttle valve,，,air intake Chamber,，,intake manifold runner,，,and intake valve.When the throttle valve is opened,，,air flows through the air cleaner,through the air flow meter(on L type systems),，,past the thrott