最新汽车专业英语原文及翻译课件PPT

1、汽车工程专业英语,李俊玲罗永革版（原文与翻译）,todaysaveragecarcontainsmorethan15000separate,individualpartsthatmustworktogether.thesepartscanbegroupedintofourmajorcategories:body,engine,chassisandelectricalsystem.,现在的汽车一般都由15000多个分散、独立且相互配合的零部件组成。这些零部件只要分为,四类：车身、发动机、底盘和电气设备。,anautomobilebodyisasheetmetalshellwithwindows,

2、ahoodandatrunkdeckbuiltintoit.itprovidesaprotectivecoveringfortheengine,passengersandcargo.thebodyisdesignedtokeeppassengerssafeandcomfortable.thebodystylingprovidesanattractive,colorfulmodernappearanceforthevehicle.,轿车车身是一个钣金件壳体，它上面有车窗、车门、发动机罩和行李舱门等部件，它给发动机、乘客和行李提供防护。车身设计是为了确保乘客乘坐的安全和舒适。车身造型设计使得汽车有

3、一个华美、现代、吸引人的外观。,asedanhasanenclosedbodywithamaximumof4doorstoallowaccesstothepassengercompartment.thedesignalsoallowsforstorageofluggageorothergoods.asedancanalsobereferredtoasasaloonandtraditionallyhasafixedroof.therearesoft-topversionsofthesamebodydesignexceptforhaving2doors,andtherearecommonlyref

4、erredtoasconvertibles.轿车车身为封闭式，轿车最多有4个车门，乘员通过车门进出。另外车身的设计还应考虑行,李和货物的存放。传统的轿车都是硬顶车身。活顶乘用车（敞篷车）的车顶是软顶，车身设计与普通轿车类似，但只有两个车门。,theutilityorpick-upcarriesgoods.usuallyithasstrongerchassiscomponentsandsuspensionthanasedantosupportgreatergrossvehiclemass.,皮卡一般用来运载货物。为能承载更大的总质量，皮卡的底盘部件和悬架比轿车更结实。,lightvehiclev

5、anscanbebasedoncommonsedandesignsorredesignssothatmaximumcargospaceisavailable.,轻型货车一般是基于普通轿车设计的，或是重新设计使可用载货空间最大化。,thebodiesofcommercialvehiclesthattransportgoodsaredesignedforthatspecificpurpose.tankerstransportfluids,tipperscarryearthorbulkgrains,flatbedsandvansareusedforgeneralgoodstransport.,用于运

6、输货物的商用车车身必须满足具体要求，例如运输液体的油罐车、运输泥土或散装谷物的自卸车、运输一般货物的平板车或货车。,busesandcoachesareusually4-wheelrigidvehices,butalargenumberofwheelsandaxlescanbeused.sometimesarticulatedbusesareusedtoincreasecapacity.busesandcoachescanbesingle-deckordouble-deck.busesarecommonlyusedincitiesascommutertransportswhilecoaches

7、aremoreluxurioususedforlongdistances.,客车和长途汽车一般是有4个车轮的整体式车辆，也能配备更多的车轮和车桥。为了增加客,车的载客量往往使用由铰链连接的客车。公共汽车和长途汽车有单层和双层两种。公共汽车一般用城市内公共交通，而长途汽车一般用于长距离的旅行。,1.2Engine,Theengineactsasthepowerunit.Theinternalcombustionengineismostcommon:this,obtainsitspowerbyburningaliquidfuelinsidetheenginecylinder.Therearetwo

8、typesof,engine:gasoline,(also,called,a,spark-ignition,engine),and,diesel(also,called,a,compression-ignitionengine).Bothenginesarecalledheatengines;theburningfuelgeneratesheatwhichcausesthegasinsidethecylindertoincreaseitspressureandsupplypowertorotateashaftconnectedtothepowertrain.发动机作为动力设备，常见的类型是内燃

9、机，其原理是通过发动机缸内的液体燃料燃烧而产生能量。发动机可分为两类：汽油机（点燃式）和柴油机（压燃式），都属于热力发动机。燃料燃烧产生热量使缸内气体气压上升，从而产生能量，驱动与动力传动系相连接的轴旋转。Thewayenginecylindersarearrangediscalledengineconfiguration.In-lineengineshavethecylindersinaline.Thisdesigncreatesasimplycastengineblock.Invehicleapplications,thenumberofcylindersisnormallyfrom2up

10、to6.Usually,thecylindersarevertical.Asthenumberofthecylindersincrease,thelengthoftheblockandcrankshaftcanbecomeaproblem.OnewaytoavoidthisiswithaVconfiguration.Thisdesignmakestheenginesblockandcrankshaftshorterandmorerigid.发动机的布置即发动机气缸的排列方式。发动机缸体按直线排列的即直列式，这种布置使得发动机缸体结构简单。汽车发动机一般为26缸，通常气缸是垂直放置的，但气缸数量

11、的增加会导致缸体和曲轴的长度过大，解决问题的措施之一就是采用V型布置，这种布置方式可以使发动机缸体和曲轴长度尺寸更短，从而大大增加刚度。Anenginelocatedatthefrontcanbemountedlongitudinallyandcandriveeitherthefrontortherearwheels.Rearenginevehicleshavetheenginemountedbehindtherearwheels.Theenginecanbetransverseorlongitudinalandusuallydrivestherearwheelsonly.前置发动机可以纵向布

12、置，能够驱动前轮或后轮。后置发动机布置在后轮后侧，发动机即可纵向布置又可横向布置，一般只能驱动后轮。1.3chassis底盘thechassisisanassemblyofthosesystemsthatarethemajoroperatingpartsofavehicle.thechassisincludesthepowertrain,steering,suspension,andbrakingsystems.底盘由汽车的主要操作系统组装而成。包括传动系、行驶系、转向系和制动系四部分。1）Powertrainsystemconveysthedrivetothewheels.传动系-将驱动力传

13、递到车轮。2）Steeringsystemcontrolsthedirectionofmovement.转向系-控制汽车的行驶方向。3）Suspensionandwheelsabsorbstheroadshocks.悬挂系-吸收路面震动4）Brakeslowsdownthevehicle.制动系-使汽车减速缓行。1.3.1powertrainsystem动力传动系统Thepowertraintransfersturningeffortfromtheenginetothedrivingwheels.apowertraincanincludeaclutchmanualtransmissionora

14、torqueconverterforautomatictransmission,adriveshaft,finaldriveanddifferentialgearsanddrivingaxles.Alternatively,atransaxlemaybeused.Atransaxleisaself-containedunitwithatransmission,finaldrivegearsanddifferentiallocatedinonecasing.传动系把发动机输出的扭矩传递给驱动轮。传动系包括离合器（对应机械变速器）或液力变矩器（对应液力自动变速器）、变速器、驱动轴、主减速器、差速器

15、和驱动桥。另外有些传动系采用由变速器、主减速器和差速器组成的一体式的变速驱动桥。（或者采用一个独立的变速驱动桥，即变速器在同一个箱体内。）Avehiclewithamanualtransmissionusesaclutchtoengageanddisengagetheenginefromthepowertrain.Enginetorqueistransmittedthroughtheclutchtothetransmissionortransaxle.thetransmissioncontainssetsofgearsthatincreaseordecreasethetorquebeforei

16、tistransmitted,totherestofthepowertrain.thelowerthegearratioselected,thehigherthetorquetransmissioned.avehiclestartingfromrestneedsalotoftorque,butonceitismoving,itcanmaintainspeedwithonlyarelativelysmallamountoftorque.ahighergearratiocanthenbeselected,andenginespeedisreduced.,对于采用机械变速器的汽车，其发动机扭矩由离合

17、器传递给变速器或变速驱动桥，并通过离合器来控制发动机和传动系的啮合或分离。变速器包含了不同传动比的齿轮副，能够增加或减小扭矩。选择的齿轮速比越小，传递的扭矩最大。汽车起步时需要较大的扭矩，一旦起动后，仅需要较小的扭矩就可维持速度，此时应该换用较高的档位，以降低发动机转速。,aconventionalvehiclewiththeengineatthefrontanddrivingwheelsattherearusesadriveshaft,calledapropellershaft,totransmittorquefromtransmissiontothefinaldrive.,传统的汽车采用前

18、置发动机、后轮驱动，因此需要传动轴把动力从变速器传递给主减速器。,thefinaldriveprovidesafinalgearreductiontomultiplythetorquebeforeapplyingtothedrivingaxles.onfrontenginerearwheeldrivevehicles,thefinaldrivechangesthedirectionofdriveby90degrees.insidethefinaldrive,adifferentialgearsetdividesthetorquetotheaxlesandallowsforthedifferen

19、ceinspeedofeachwheelWhencornering.axlesshaftstransmitthetorquetothedrivingwheels.inarear-wheeldrivevehicle,theaxlescanbesolidorcontainjointstoallowformovementofsuspension.forafront-wheeldrivevehicle,thedriveshafthasuniversaljointstoallowforsuspensionandsteeringmovement.,主减速器的作用就是在把动力传递给驱动轮之前，降低转速并增加

20、扭矩。对于前置后驱的汽,车，主减速器还将驱动的旋转方向改变了90度。主减速器内的差速器齿轮副，把动力分给,两个驱动轴，并允许两边车轮在转向时具有不同的转速。动力最终由驱动轴传递给车轮。后轮驱动汽车的驱动桥应能满足悬架的运动，可以是刚性的或包含运动副。为满足悬架和转向的要求，前轮驱动汽车驱动轴上需安装万向节。,anautomatictransmissionortransaxleperformssimilarfunctionstoamanualtransmissionortransaxleexceptthatgearselectioniscontrolledeitherhydraulicallyo

21、relectronically.theautomatictransmissionusesatorqueconverter,whichactsasahydrauliccouplingtotransferthedrive.,自动变速器或自动变速驱动桥的功能和机械式基本类似，区别在于档位的选择是液力或电力控制的。液力自动变速器采用液力变矩（耦合）器作为连接器以传递动力。,1.3.2steeringsystem转向系统,Thedirectionalmotionofvehicleiscontrolledbyasteeringsystem.Abasicsteeringsystemhas3mainparts

22、:asteeringboxconnectedtothesteeringwheel,thelinkageconnectingthesteeringboxtothewheelassemblyatthefrontwheelsandfrontsuspensionpartstoletthewheelassembliespivot.Whenthedriverturnsthesteeringwheel,ashaftfromthesteeringcolumnturnsthesteeringgear.Thesteeringgearmovestie-rodsthatconnecttothefrontwheels.

23、Thetie-rodsmovethefrontwheelstoturnthevehiclerightorleft.,转向系控制汽车行驶方向，一般由三部分组成：与转向盘相连的转向器、连接车轮和转向器的传动结构、允许车轮转动的前悬架部件。当驾驶员转动方向盘时，转向柱内的轴带动转向器运动，然后通过转向传动机构来转动车轮，从而使得汽车向左或向右行驶。,1.3.3suspensionsystem悬架系统,Thepurposeofthecompletesuspensionsystemistoisolatethevehiclebodyfromroadshocksandvibrations,whichwill

24、otherwisebetransferredtothepassengersandload.Itmustalsokeepthetiresincontactwiththeroadregardlessofroadsurface.Abasicsuspensionsystemconsistsofsprings,axles,shockabsorbers,arms,rodsandballjoints.,整个悬架系统的作用是隔离来自路面的冲击和振动对车身的影响，防止传递给乘员和货物。另外不论路面如何，悬架系统都应该保持轮胎和路面接触。悬架系统的基本组成包括弹性元件、车桥、减震器、杆系（臂、杆）和球副组成的导向

25、机构。,thespringistheflexiblecomponentofthesussuspension.basictypesare:leafspring,coilspringandtorsionbars.modernpassengervehiclesandcanhavecoilspringsatthefrontandleafspringsattherear.heavycommercialvehiclesusuallyuseleafspringsorairsuspension.,弹簧是悬架的弹性元件，常见的弹簧类型有：钢板弹簧、螺旋弹簧和扭杆弹簧。现代汽车大多采用小的螺旋弹簧，轻型商用车常采

26、用的螺旋弹簧比一般乘用车的大得多，或者前悬架采用螺旋弹簧，后悬架采用钢板弹簧。重型商用车则通常采用钢板弹簧或空气弹簧。,wheelsmustbestrongenoughtosupportthevehicleandwithstandtheforcescausedbynormaloperation.atthesametime,theymustbeaslightaspossibletohelpkeepunsprungweighttoaminimum.,车轮必须能支撑整车重量，并能承受正常工况下的载荷。同时车轮必须尽可能地轻，有助于最小化簧下质量。,wheelscanbemadefrompressed

27、-steelingtwosections,andalsobemadefromcastaluminiumalloy.alloywheelsarepopularbecauseoftheirappearanceandbecausetheyarelighterthansimilarsteelwheels.aluminiumisabetterconductorofheat,soalloywheelscandissipateheatfrombrakeesandtiresmoreeffectivelythansteelones.,车轮可采用双面钢化板压制而成，也可采用铸造的铝合金材料。除了外观漂亮之外，铝合

28、金比钢更轻，因此铝合金车轮应用较广。另外铝合金导热性更好，因此相比钢制车轮，制动器和车轮产生的热量更容易被铝合金车轮散发。,thetireprovidesacushionbetweenthevehicleandtheroadtoreducethetransmissionofroadshocks.italsoprovidesfrictiontoallowthevehicletoperformitsnormaloperations.moderntiresaremanufacturedfromarangeofmaterials.therubberismainlysynthetic.twotypeso

29、ftireconstructionarecommon:cross-plyandradial.mostpassengercarsnowuseradialtires,andradialsarereplacingcross-plytireson4-wheeldrivesandheavyvehicles.,轮胎在汽车和路面之间起缓冲作用，能减小路面冲击。同时轮胎也提供了车轮正常行驶所需的摩擦力。轮胎是由多种材料加工而成，橡胶多是人工合成的。最常见的轮胎类型是子午线轮胎和斜交轮胎。现在大部分乘用车都采用子午线轮胎，在四轮驱动和商用车上，子午线轮胎也正在取代斜交胎。,tubetiresrequireani

30、nnertubetosealairinsidethetire.tubelesstiresareeliminatingtheinnertubebymakingthecompletewheelandtireassemblyairtight.aspecialairtightvalveassemblyisneeded.thiscanbetightfitintotherimorcanbeheldwithanutandsealingwashers.,有内胎的轮胎用内胎来密封内部气体。无内胎的轮胎则要求车轮和轮胎具有很好的密封性，这就需要专用的密封件，可以紧固在轮缘上，也可用螺钉和密封圈来固定。,1.3.4

31、Brakingsystem制动系统,Drumbrakeshaveadrumattachedtothewheelhub,andbrakingoccursbymeansofbrakeshoesexpandingagainsttheinsideofthedrum.Withdiscbrakes,adiscattachedtothewheelhubisclenchedbetweentwobrakepads.onlightvehicles,bothofthesesystemsarehydraulicallyoperated.thebrakepedaloperatesamastercylinder.hydr

32、auliclinesandhousesconnectthemastercylindertobrakecylindersatthewheels.mostmodernlightvehicleshaveeitherdiscbrakesonthefrontwheelsanddrumbrakesontherearordiscbrakesonall4wheels.discbrakesrequiregreaterforcestooperatethem.abrakeboosterassistthedriverbyincreasingtheforceappliedtothemastercylinderwhent

33、hebrakeisoperated.,鼓式制动器的制动鼓和轮毂连接，制动蹄张开压紧制动鼓内侧从而产生制动。在盘式制动器上，连着轮毂的制动盘被紧紧夹在两个制动块之间。轻型汽车上都采用液压制动系统，制动踏板控制制动主缸，通过液压管路与车轮上的制动轮缸相连。现在轻型汽车上的制动器，前轮采用盘式，后轮采用鼓式，或全部采用盘式。相比鼓式制动器，盘式制动器需要更大的作用力。在制动时采用增压器辅助驾驶员提高施加在主缸上的制动力。,pressedairoperatingonlargediameterdiaphragmsprovidesthelargeforcestothebrakeassemblythatar

34、eneeded.anaircompressorpumpsairtostoragetanks.drivercontrolledvalvesthendirectthecompressedairtodifferentwheelunitstooperatethefrictionbrakes.onarticulatedvehicles,anydelayinapplyingthetrailerbrakeshouldbeminimize.thisisachievedbyusingarelayvalveandaseparatereservoironthetrailer.thisarrangementalsoa

35、ppliesthebrakesifthetrailerdisconnectedfromtheprimemover.,重型商用车多采用气压制动系统，压缩气体作用在直径较大的膜片上时能为制动总成提供较大的制动力。气压制动系统靠空气压缩机把气体吸入储气罐。驾驶员控制阀门开启，使压缩气体进入车轮制动气室进行制动。在铰接车辆的拖车上采用继动阀和单独的储气罐，以减小拖车制动系统的时间延迟，这种布置方式还可以在拖车失去动力时制动拖车。,allvehiclesmustbefittedwithatleast2independentsystems.theywereoncecalledtheservicebrake

36、andtheemergencybrake.nowtheyareusuallyreferredtoasthefootbrakeandtheparkbrake.mostlightvehiclesuseafootbrakethatoperatesthroughahydraulicsystemonallwheelsandahandoperatedbrakethatactsmechanicallyontherearwheelsonly.onecommonuseofthehandbrakesystemistoholdthevehiclewhenitisparked.thesystemaredesigned

37、tobeindependentSothatifonefails,theotherisstillavailable.,所有汽车必须安装至少两套独立的制动系统，即行车制动系统与紧急制动系统，一般被称之为脚制动和停车制动。大部分轻型汽车的脚制动通过液压系统作用在四个车轮上，而其手制动则是机械式的，且仅作用在后轮。手制动的一个普通用途就是停车时对汽车进行制动。设计两套独立的制动系统的目的就是当一套失效时，另一套仍可工作。,1.4.1Electricalsystem电器系统,Theelectricalsystemsupplieselectricityforthestarter,ignition,ligh

38、tsandheater.Theelectricitylevelismaintainedbyachargingcircuit.,电器系统为起动机、点火系、照明和加热设备提供电流，电流的大小由充电电路来维持。,Thechargingsystemprovideselectricalenergyforalloftheelectricalcomponentsonthevehicle.themainpartsofthechargingsysteminclude:thebattery,thealternator,thevoltageregulatorwhichisusuallyintegraltotheal

39、ternator,achargingwarningorindicatorlightandwiringthatcompletethecircuits.thebatteryprovideselectricalcomponentsofthevehicle.italsochargesthebattertoreplacetheenergyusedtostarttheengine.thevoltageregulatorpreventsovercharging.,充电系统为汽车上所有的电器系统提供电能。充电系统主要组成部分有：蓄电池、交流发电机、稳压器（多集成在发电机中），充电指示灯和组成电路的电线。汽车起

40、动时由蓄电池提供能量，一旦发动机开始工作，交流电机为电气设备供电，同时还对蓄电池进行充电，以补偿起动所消耗的电能。稳压器则防止过载。,1.4.2Starting启动系统,Thestaringsystemconsistsofthebattery,cables,startermotor,flywheelringgearandtheignitionswitch.duringstarting,twoactionsoccur.thepinionofthestartermotorengageswiththeflywheelringgearandthestartermotorthenoperatestocr

41、anktheengine.thestartermotoris,anelectricalmotormountedontheengineblockandoperatedfromthebattery.,起动系统包括电池、电缆、启动电机、飞轮齿圈和点火开工。起动需要两个动作，启动电机齿轮和飞轮齿圈啮合，从而带动发动机转动。起动电机安装在发动机壳体上，靠电池工作。,1.4.3Ignition点火系统,Abasicignitionsystemconsistsofthebattery,low-tensioncables,theignitioncoil,distributor,coilhigh-tension

42、cable,sparkplukcablesandsparkplugs.theignitionsystemprovideshighintensesparkstosparkplugstoignitethefuelchargesinthecombustionchambers.thesparksmustbesuppliedattherighttimeandtheymusthavesufficientenergyoverarangeofconditionstoignitethecharges.theenergycomesfromthebatteryandalternator,andvoltageisin

43、creasedbytheignitioncoil.thesystemhastwocircuits.theprimaryorlow-tensioncircuitinitiatesthespark.thesecondaryorhigh-tensioncircuitproducesthehighvoltageanddistributesittosparkplugs.,点火系统包括电池、低压电缆、点火线圈、分电器、高压电缆、火花塞连线和火花塞。点火系统在火花塞处产生高压火花，点燃发动机燃烧室内的燃油混合物。点火系统必须在恰当的时刻提供火花，并且能量满足各种工况的要求。电池和交流发电机为点火系统供电，点

44、火线圈提高电压。点火系统由两级电路组成，初级电路（低压电路）初始化火花，次级电路（高压电路）产生高压电，并分到各个火花塞。,2.1principleofoperation工作原理2.1.1energyandpower能源和动力,Engineisusedtoproducepower.Thechemicalenergyinfuelisconvertedtoheatbytheburningofthefuelatacontrolledrate.Thisprocessiscalledcombustion.Ifenginecombustionoccurswiththepowerchamber.,theen

45、gineiscalledinternalcombustionengine.Ifcombustiontakesplaceoutsidethecylinder,theengineiscalledanexternalcombustionengine.,能源用于产生动力。燃料以控制的速率燃烧，燃料中的化学能转换为热能。这个过程叫做燃烧。如果发动机燃烧发生在动力室内，这种发动机叫做内燃机。如果燃烧发生在气缸外，这样的发动机叫做外燃发动机。,Engineusedinautomobilesareinternalcombustionheatengines.Heatenergyreleasedinthecomb

46、ustionchamberraisesthetemperatureofthecombustiongaseswithinthechamber.Theincreaseingastemperaturecausesthepressureofthegasestoincrease.Thepressuredevelopedwithinthecombustionchamberisappliedtotheheadofapistontoproduceausablemechanicalforce,whichisthenconvertedintousefulmechanicalpower.,汽车使用的发动机是内燃发动

47、机。在燃烧室内释放的热能提高了室内燃烧气体的温度。气体温度的增肌使气体的压力增加。在燃烧室内产生的压力作用于活塞的顶部，产生机械力，这个力转换成有用的机械动力。,2.1.2EngineTerms,Linkingthepistonbyaconnectingrodtoacrankshaftcausesthegastorotatetheshaftthroughhalfaturn.Thepowerstroke“usesup”thegas,someansmustbeprovidedtoexpeltheburntgasandrechargethecylinderwithafreshpetrol-airmi

48、xture:thiscontrolofgasmovementisthedutyofthevalves；aninletvalveallowsthenewmixturetoenterattherighttimeandanexhaustvalveletsouttheburntgasafterthegashasdoneitsjob.Enginetermsare：,活塞通过连杆和曲轴连接，使得气体带动曲轴旋转半圈。作功冲程耗尽了所以的气体，这样就必须采取相应的措施排出废气以及向气缸内充入新鲜的可燃混合气：气体的运动由气门来控制。进气阀允许新的混合气体在适当的时间进入，排气阀在作功完成后，可以放出燃烧后的

49、气体。引擎术语：,TDC(TopDeadCenter):thepositionofthecrankandpistonwhenthepistonisfartherawayfromt,hecrankshaft.,上止点：活塞处于离曲轴最远处时，曲柄和活塞所处的位置。,BDC(BottomDeadCenter):thepositionofthecrankandpistonwhenthepistonisnearesttothe,crankshaft.,下止点：活塞处于离曲轴最近处时，曲柄和活塞所处的位置。,Stroke:thedistancebetweenBDCandTDC;strokeiscontr

50、olledbythecrankshaft.行程：上止点和下止点间的距离;行程由曲轴控制。,Bore:theinternaldiameterofthecylinder.,缸径：气缸的内径,Sweptvolume:thevolumebetweenTDCandBDC.有效容积：上止点和下止点间的容积Enginecapacity:thisisthesweptvolumeofallthecylinders.e.g.afour-cylinderenginehavingacapacityoftwoliters(2000cm3)hasacylindersweptvolumeof500cm3.发动机排量：所有气

51、缸的有效容积之和.例如一四缸发动机有能力两升（2000cm3）有一个气缸排量500cm3。Clearancevolume:thevolumeofthespaceabovethepistonwhenitisatTDC.燃烧室容积：活塞处于上止点时，活塞上方的体积Compressionratio=(sweptvol+clearancevol)(clearancevol)压缩比：（有效容积+燃烧室容积）/燃烧室容积Two-stroke:apowerstrokeeveryrevolutionofthecrank.两冲程：曲柄旋转一圈作功一次。Four-stroke:apowerstrokeeveryo

52、therrevolutionofthecrank.四冲程：曲柄旋转两圈作功一次。2.1.3TheFour-strokeSpark-ignitionEngineCycleThespark-ignitionengineisaninternal-combustionenginewithexternallysuppliedinignition,whichconvertstheenergycontainedinthefueltokineticenergy.Thecycleofoperationsisspreadoverfourpistonstrokes.Tocompletethefullcycleitt

53、akestworevolutionsofthecrankshaft.火花点火式发动机是由外部提供点火的内燃机，从而将含在燃料内的能量转化成动能。发动机的一个工作循环分布在活塞的四个行程中，一个完整的工作循环曲轴需要转动两圈。Thedownward-movingpistonincreasesthevolumeinthecylinderanddrawsinfreshair-fuelmixturethroughtheopenintakevalve.向下运动的活塞使气缸里的体积增大，并且将新的空气燃料混合物通过节气门吸进气缸。Theupward-movingpistonreducesthevolume

54、inthecylinderandcompressestheair-fuelmixture.ShortlybeforeTDCisreached,thesparkplugignitesthecompressedair-fuelmixtureandthusinitiatesthecombustionprocess.Ahighercompressionratiomeansbetterutilizationofthefuel.Theextentofcompressionisrestrictedbytheknocklimit.向上运动的活塞使气缸里的体积减小，从而压缩空气燃料混合物。在活塞即将到达上止点的

55、瞬间，火花塞点燃压缩的空气燃油混合气，从而燃烧过程开始了。压缩比越高，燃料利用率越高，但是压缩的程度受到爆震极限的限制。Aftertheignitionsparkatthesparkplughasignitedthecompressedair-fuelmixture,thetemperatureincreasesastheresultofcombustionofthemixture.Thepressureinthecylinderincreasesandforcesthepistondownwards.Thepistontransferspowertothecrankshaftviatheco

56、nnectingrod.当火花塞喷出的火花点燃压缩的空气燃料混合物后，空气燃料混合物开始然后，随之气缸内的温度开始升高。气缸里的压力也随之增加，使得活塞向下运动。这样活塞就把动力通过连杆传递给曲轴。,Theupward-movingpistonexpelsthecombustedgases（exhaustgas）throughtheopenexhaustvalve.Afterthis4thstroke,thecycleisrepeated.,向上运动的活塞使燃烧后的气体（废气）通过排气门排出气缸。在这第四个行程后，整个工作工程将重复进行。,2.1.4EngineOverallMechanics

57、发动机的总体构造,Theenginehashundredsofotherparts.Themajorpartsofengineareengineblock,engineheads,pistons,connectingrods,crankshaftandvalves.Theotherpartsarejoinedtomakesystems.Thesesystemsarethefuelsystem,intakesystem,ignitionsystem,coolingsystem,lubricationsystemandexhaustsystem.Eachofthesesystemshasadefi

58、nitefunction.Thesesystemswillbediscussedindetaillater。,发动机有上百个其它部件。发动机的主要部件是发动机缸体、发动机头、活塞、连杆、曲轴和阀门。其他部分也加入到系统中。这些的系统是燃油系统、进气系统、点火系统、冷却系统、润滑系统和排气系统。这些系统中的每一个都有一个明确的功能。这些系统以后将进行详细论述。,2.2EngineBlockandCylinderHead2.2.1EngineBlock,Theengineblockisthebasicframeoftheengine.Allotherenginepartseitherfitinsi

59、deitorfastentoit.Itholdsthecylinders,waterjackets,andoilgalleries.Theengineblockalsoholdsthecrankshaft,whichfastenstothebottomoftheblock.Thecamshaftalsofitsinsidetheblock,exceptonoverhead-camengines(OHC).Inmostcars,thisblockismadeofgrayiron,oranalloy(mixture)ofgrayironandothermetals,suchasnickelorch

60、romium.Engineblocksarecastings.,气缸体是发动机的基本框架。发动机的其他零件都安装在它里面或者固定在它上。缸体里有,气缸，水套和油道。曲轴也固定在气缸体底部。除了顶置凸轮(OHC)发动机以外，凸轮轴都安装在气缸体里面。在大多数汽车里，气缸体由灰铸铁或者一种灰铸铁和其他金属的合金(混合物)做成，例如镍或铬。气缸体是铸件。,Someengineblocks,especiallythoseinsmallercars,aremadeofcastaluminum.Thismetalismuchlighterthaniron.However,ironwearsbetterth