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1、书名：汽车专业英语ISBN：978-7-111-42342-3作者：卢晓春出版社：机械工业出版社本书配有电子课件 Task 1 The Operation Cycle of an EngineParagraphAt present,the most automobile uses an internal combustion engine in the world.What is an internal combustion engine?How does the internal combustion engine work?Engine Construction Four strokesT
2、he most common engine is the fourstroke piston engineThese four strokes are intake stroke,compression stroke，power stroke and exhaust stroke.Intake Stroke The intake stroke of a fourstroke engine begins with the piston at top dead center(TDC)The starter causes the crankshaft to rotate in a clockwise
3、 direction（Fig.23）The crankshaft，through the connecting rod，forces the piston to move downwardThis downward movement of the piston creates a vacuum，a difference in pressure，in the space above the pistonThe engine manufacturer times the intake valve action so that it opens automatically at or slightl
4、y before the piston starts downTherefore,a mixture of gasoline and air，pushed by the atmospheric pressure outside the engine,rushes through the intake manifold and into the engine cylinderAt the same time,the exhaust valve remains closed during this downward stroke of the piston.This valve closure p
5、revents the entering airfuel charge from escaping through the exhaust port.After the piston reaches the bottom of its first stroke,the cylinder is practically full of an airfuel chargeThe drawing of an airfuel charge into the cylinder in this manner，during the downward movement of the piston，constit
6、utes the intake stroke of the piston Compression Stroke After the piston reaches bottom dead center(BDC)，it moves upward again as the starter continues to turn the crankshaft in a clockwise directionAs the piston is beginning to move upward，the intake valve closes，and the exhaust valve remains close
7、dSince both valves are closed，the piston compresses the airfuel mixture in the small space between the top of the piston and the cylinder headAs the piston reaches TDC again during its upward travel，the compression stroke of the piston is overThe airfuel charge is now under compression so that it wi
8、ll produce a great deal of power when the spark plug ignites it Power StrokeJust as or slightly before the piston reaches TDC on the compression stroke with the airfuel mixture fully compressed，a timed electrical spark appears at the spark plugThis spark ignites the compressed airfuel mixtureThe bur
9、ning mixture begins to expand；the pressure in the combustion chamber above the piston immediately increasesThis results in a high pressure applied to the top of the pistonNow，both valves remain closed during the power strokeThis assures that the total force of the expanding gas applies itself to the
10、 head of the pistonThis tremendous force pushes the piston downward on the power stroke，causing the connecting rod to rotate the crankshaft.In other words，the force resulting from the expansion of the burning airfuel mixture is turning the crankshaft Exhaust Stroke Near the end of the downward movem
11、ent of the piston on the power stroke，the camshaft opens the exhaust valve，but the intake valve remains closedAlthough much of the gas pressure has expended itself driving the piston downward，some pressure still remains when the exhaust valve opensThis remaining pressurized gas flows comparatively f
12、reely from the cylinder through the passage(port)opened by the exhaust valve.Then，as the piston again moves up in the cylinder，it drives any remaining gases out of the cylinder past the open exhaust valveAs the piston travels through the TDC position and starts downward again in the cylinder，a new o
13、perating cycle beginsThe four strokes are continuously repeated in every cylinder as long as the engine remains runningIntake ValvePistonExhaust ValveSpark PlugFig.2-5 Exhaust StrokeWords&expressionsvehicle：交通工具，车辆 charge：充气，装料engine：发动机，引擎，draw：吸引，吸人stroke：冲程，行程 constitute：组成，构成piston：活塞 ignite：点火，
14、点燃crankshaft：曲轴 spark：火花intake：入口，进口，吸入 combustion：燃烧clockwise：顺时针方向 port：通道，港口，端口gasoline：汽油 internal combustion engine：内燃机manifold：进、排气歧管 intakestroke：进气行程remain：保持，逗留，剩余 compression stroke：压缩行程airfuel mixture：空气燃油混合物(可燃混合气exhaust stroke：排气行程power stroke：作功行程 connecting rod：连杆top dead center(TDC)：
15、上止点 atmospheric pressure：大气压力intake valve：进气门 bottom dead center(BDC)：下止点exhaust valve：排气门 spark plug：火花塞Task 2 Connecting Rod and CrankshaftParagraphConnecting rod and crankshaftConnecting rod and crankshaft is very important framework of the engine,which converts the heat energy of fuel into mecha
16、nical energy for moving the vehicleHow does it is achieve?PistonThe engine manufacturer fits a piston into each cylinder of the engineThe piston is a movable part or plug that receives the pressure from the burning airfuel mixture and converts this pressure into reciprocating(upanddown)motion.Manufa
17、cturers make most engine pistons from aluminum,which is less than half the weight of iron.Iron pistons were common in early automotive engines.Piston Rings Some operating clearance must exist between the piston and the cylinder wall；however，some form of seal is necessary between the piston and the c
18、ylinder wall to prevent blowbyConsequently，piston rings are used to provide the necessary seal to eliminate blowby and to control oil consumption.Automotive pistons have two kinds of rings：compression and oil controlThe compression rings primarily seal against the loss of airfuel mixture as the pist
19、on compresses it and also the combustion pressure as the mixture burnsWhile the function of the oil control ring is to prevent excessive amounts of oil from working up into the combustion chamber Compression RingCompressionOil RingPistonPistonConnecting RodConnecting Rod BearingConnecting Rod CapFig
20、.2-7 PistonConnecting RodsAs mentioned earlier，the piston moves up and down in the cylinder，in a reciprocating motionIn order to rotate the drive wheels，a connecting rod and crankshaft must change reciprocating motion to rotaryThe connecting rod itself attaches at one end to the piston and on the ot
21、her end to the crankpin section of the crankshaft Crankshaft The crankshaft is the main rotating member，or shaft，of the engineIts function，along with the connecting rod，is to change the reciprocating motion of the piston to rotaryIn addition，the crankshaft is responsible for driving the camshaft thr
22、ough timing gears,plus operating the accessories via a system of belts and pulleysLastly，the crankshaft Carries the total torqueturning or twisting effort and delivers it to the flywheelFrom the flywheel the torque then passes either to the friction clutch assembly or to the torque converter Designe
23、d into the onepiece crankshaft are areas for main bearing journals，crankpins，counterweights，flywheel flange，and driving hub Flywheel The flywheel is a comparatively heavy wheel，bolted to the flange on the rear end of the crankshaftIts function is to keep the engine running smoothly between power str
24、okesIts inertia tends to keep the flywheel rotating at a constant speedThe flywheel also has several other functionsFor example，the flywheel has gear teeth around its outer circumferenceThese teeth mesh with teeth located on the starting motor drive pinion in order to crank the engine overIn additio
25、n,the rear surface of the flywheel serves as the driving member of the clutch assemblyWords&expressionsreciprocating 往复的 Crankpin 曲柄销，连杆轴颈Plus 加上，以及 Counterweight 平衡物，平衡重Blowby 窜气 Flange 凸缘，边缘，轮缘Via 经，通过，经由 flywheel飞轮Clutch 离合器 Circumference 周围;圆周piston ring 活塞环 bearing cap 轴承盖 compression ring 气环 t
26、hrust washer 推力垫片 oil control ring 油环 main bearing 主轴承 connecting rod 连杆 connecting rod cap 连杆盖 connecting rod bearing 连杆轴承 Task 3Valve GearValve gearWhen the engine is running,the valve opened and closed frequently,that controls fuel entry and exhaust emissions.Valve Modem engines have cylinder hea
27、ds that contain valvesThese valves open and close ports to allow or stop the flow of gases into or from the combustion chamberEach cylinder requires at least two：an intake and exhaustCamshaftThe camshaft is another rotating shaft within the engine；it serves usually three functionsFirst，the camshaft
28、has a series of cams that can change rotary motion to straightline motion which cause the intake and exhaust valves to openThe camshaft will have one cam for each valve，or，in most engines，two cams per cylinderSecond,the camshaft has an eccentric，or special cam，designed to operate the fuel pumpFinall
29、y，the camshaft has a gear that drives the oil pump and ignition distributorLifter(Tappet)A lifter is a cylindrical part within an engine that rests on a cam of the camshaftAs the camshaft rotates，the cam raises the lifter，and the lifter in turn opens a valveThe lifter may be in direct contact with t
30、he tip of the valve stem，or it may bear against a push rod that functions along with a rockerarm assembly to open a valvePush Rods and Rocker ArmsAlong with the camshaft，valves，valve seats，and valve springs，some valve trains have several other componentsthe push rods and rocker armsThe push rod is a
31、 metal rod that fits between the lifter and the rocker arm.Its function is to transmit cam lobe lift from the camshaft to the rocker arm assemblyThe rocker arm is nothing more than a precisiondesigned leverIts function is to convert the upward motion of a push rod into downward motion that compresse
32、s the spring and opens the valveValve TimingDuration is the length of time a valve is openThe measurement of this open period is not in units of time because the actual time a valve remains open varies with engine speed Therefore，this measurement is in degrees of crankshaft rotation，which does not c
33、hange with speed To lengthen the time and to accelerate the air/fuel mixture flow into the cylinders,both the intake and exhaust valves must be open at the same time for a short periodThe overlap is provided in order to take advantage of the inertial forces in the escaping exhaust gases.These gases
34、create strong suction as they rush out of the combustion chamber Timing GearsThe manufacturer machines a cam lobe into a given shape that produces a given amount of alveopen duration and overlap.Furthermore，meshing the timing gears or installing the chain onto the sprockets at a specific place will
35、time the valves to open and close at the proper moment in the engines cycleWords&expressionsFunction 功能，作用Component 部分，部件，零件，元件Cam 凸轮 Lever 杆，杠杆Eccentric 偏心轮 Duration 持续时间Gear 齿轮，传动装置Suction 吸入，吸引1ifter 挺杆 Mesh 啮合，相啮合Assembly 安装，装配，部件，装置，组合体push rod 气门推杆 cam lobe 凸轮凸起部，凸轮工作部分valve spring 气门弹簧 valve
36、timing 气门正时 rocker arm 气门摇臂 Sprocket 链轮齿 Task 4Engine Lubricating SystemEngine Lubricating SystemLubrication Principles Reducing friction to minimize wear and loss of power is the primary job a lubrications system must perform.Residual oil on engine parte also provides lubrication for engine startup
37、.The engine oil forms a seal among the pistons,rings and cylinders.It also helps to cool engine parts.Without the cleaning action of the lubricating system,carbon and varnish buildup would be excessive.The engine oil also absorbs the shock and dampens the noise of moving parts.How successful the lub
38、rication system is in performing all these functions depends on a number of factors and conditions.There must be an adequate supply of goodquality lubricant delivered to all moving engine parts under sufficient pressure to provide hydrodynamic lubrication of rotating parts and oil adhesion to surfac
39、e subject to sliding friction.Parts of the Pressure-Lubrication SystemOil pan The oil pan bolts under the engine block,where it seals off the bottom of engine.Shaped like trough,this sheetmetal pan serves as the reservoir for about 5 quarts of oil.As oil flows from the engine,it drains downward into
40、 the oil pan.The oil pump sucks oil from the lowest part of the oil panthe oil sump.Many oil pans have baffles,which are thin metal partition.These baffles keep the oil in the sump when the car corners heard of brakes suddenly.A drain plug at the bottom of the sump allows oil to be drained from the
41、engine.The oilpan gasket fits between the oil pand and the bottom of the engine block.In most time,the oil circulates in the engine,and then returns to the pan.It stays in the pan until drawn back into the engine by the oil pump.During operation,the sump usually holds 2 to 3 quarts of oil.The rest o
42、f the oil moves through the passageways of the lubrication system.With the engine off,the pan holds about four quarts of oil.The fifth quart is in the oil filter.Because a pool of oil always rests in the sump,the type of lubrication system is called a wetsump oiling system.A drysump oil system is us
43、ed in many racing engines.This system has a separate storage tank for the oil.A second oil pump draws oil from the oil pan as soon as the oil drains from the engine.As a result,a drysump system can circulate more oil through the engine than a wetsump system.Oil Pump In most cars,the oil pump is in t
44、he crankcase above the sump.It draws oil through a tube that extends downward into the sump.This tube,called the oil-pump pickup tube,has a filter screen over its bottom end.Ten screen keeps large pieces of sludge and dirt from being drawn into the pump.The tube may be hinged on the pump end so that
45、 it can move up and down as the oil level changes in the sump.Thus,the pump always always draws oil from the top of the sump,not from the bottom where the dirt and sludge tend to settle.Modern cars have two common types of oil pumps-the gear-type and rotor-type.Oil FiltersA modern engine uses a full
46、-flow filtering system.In this system,the output of the oil pump flows through the oil filter before moving through the engine.In other words,the oil is filtered and cleaned before each trip through the engine.When an engine rens at 3,000 rpm,its entire five quarts of oil pass through the filter at
47、least once every minute.Thus the oil filter ensures that only clean oil enters the engine.Modern engine use replaceable oil filters.When dirty,such a screw-on filter is replaced with a new one.Inside the steel outer casing of the unit,a special pater acts as a filter.Folded and tightly packed,this p
48、aper has just the right porosity.These tiny holes in the paper allow oil to pass through,but filter out dirt and sludge.The paper is treated to protect it from acid or water in the oil.Normally,oil enters the oil filter from the outside.Oil enters the filter around the outer edge of the base.The oil
49、 flows through the paper to the center of the container.It thenflows out to the engine.Most filters also have a pressure-relief valve,or bypass valve.Such a valve allows oil to flow to the engine with out going through the filter.This is necessary when the filter becomes too clogged for oil to pass
50、through.Thus,a plugged filter allows dirty oil to circulate through the engine.To prevent this,the oil and oil filter should be changed regularly.Engine Lubrication An internal combustion engine would not run for even a few minutes if the moving parts were allowed to make metal-to-metal contact.The