1、汽車工程專業英語,李俊玲羅永革版（原文與翻譯）,todaysaveragecarcontainsmorethan15000separate,individualpartsthatmustworktogether.thesepartscanbegroupedintofourmajorcategories:body,engine,chassisandelectricalsystem.,現在的汽車一般都由15000多個分散、獨立且相互配合的零部件組成。這些零部件只要分為,四類：車身、發動機、底盤和電氣設備。,anautomobilebodyisasheetmetalshellwithwindows,

2、ahoodandatrunkdeckbuiltintoit.itprovidesaprotectivecoveringfortheengine,passengersandcargo.thebodyisdesignedtokeeppassengerssafeandcomfortable.thebodystylingprovidesanattractive,colorfulmodernappearanceforthevehicle.,轎車車身是一個鈑金件殼體，它上面有車窗、車門、發動機罩和行李艙門等部件，它給發動機、乘客和行李提供防護。車身設計是為了確保乘客乘坐的安全和舒適。車身造型設計使得汽車有

3、一個華美、現代、吸引人的外觀。,asedanhasanenclosedbodywithamaximumof4doorstoallowaccesstothepassengercompartment.thedesignalsoallowsforstorageofluggageorothergoods.asedancanalsobereferredtoasasaloonandtraditionallyhasafixedroof.therearesoft-topversionsofthesamebodydesignexceptforhaving2doors,andtherearecommonlyref

4、erredtoasconvertibles.轎車車身為封閉式，轎車最多有4個車門，乘員通過車門進出。另外車身的設計還應考慮行,李和貨物的存放。傳統的轎車都是硬頂車身?；铐敵擞密嚕ǔㄅ褴嚕┑能図斒擒涰?，車身設計與普通轎車類似，但只有兩個車門。,theutilityorpick-upcarriesgoods.usuallyithasstrongerchassiscomponentsandsuspensionthanasedantosupportgreatergrossvehiclemass.,皮卡一般用來運載貨物。為能承載更大的總質量，皮卡的底盤部件和懸架比轎車更結實。,lightvehiclev

5、anscanbebasedoncommonsedandesignsorredesignssothatmaximumcargospaceisavailable.,輕型貨車一般是基于普通轎車設計的，或是重新設計使可用載貨空間最大化。,thebodiesofcommercialvehiclesthattransportgoodsaredesignedforthatspecificpurpose.tankerstransportfluids,tipperscarryearthorbulkgrains,flatbedsandvansareusedforgeneralgoodstransport.,用于運

6、輸貨物的商用車車身必須滿足具體要求，例如運輸液體的油罐車、運輸泥土或散裝谷物的自卸車、運輸一般貨物的平板車或貨車。,busesandcoachesareusually4-wheelrigidvehices,butalargenumberofwheelsandaxlescanbeused.sometimesarticulatedbusesareusedtoincreasecapacity.busesandcoachescanbesingle-deckordouble-deck.busesarecommonlyusedincitiesascommutertransportswhilecoaches

7、aremoreluxurioususedforlongdistances.,客車和長途汽車一般是有4個車輪的整體式車輛，也能配備更多的車輪和車橋。為了增加客,車的載客量往往使用由鉸鏈連接的客車。公共汽車和長途汽車有單層和雙層兩種。公共汽車一般用城市內公共交通，而長途汽車一般用于長距離的旅行。,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.發動機作為動力設備，常見的類型是內燃

9、機，其原理是通過發動機缸內的液體燃料燃燒而產生能量。發動機可分為兩類：汽油機（點燃式）和柴油機（壓燃式），都屬于熱力發動機。燃料燃燒產生熱量使缸內氣體氣壓上升，從而產生能量，驅動與動力傳動系相連接的軸旋轉。Thewayenginecylindersarearrangediscalledengineconfiguration.In-lineengineshavethecylindersinaline.Thisdesigncreatesasimplycastengineblock.Invehicleapplications,thenumberofcylindersisnormallyfrom2up

10、to6.Usually,thecylindersarevertical.Asthenumberofthecylindersincrease,thelengthoftheblockandcrankshaftcanbecomeaproblem.OnewaytoavoidthisiswithaVconfiguration.Thisdesignmakestheenginesblockandcrankshaftshorterandmorerigid.發動機的布置即發動機氣缸的排列方式。發動機缸體按直線排列的即直列式，這種布置使得發動機缸體結構簡單。汽車發動機一般為26缸，通常氣缸是垂直放置的，但氣缸數量

11、的增加會導致缸體和曲軸的長度過大，解決問題的措施之一就是采用V型布置，這種布置方式可以使發動機缸體和曲軸長度尺寸更短，從而大大增加剛度。Anenginelocatedatthefrontcanbemountedlongitudinallyandcandriveeitherthefrontortherearwheels.Rearenginevehicleshavetheenginemountedbehindtherearwheels.Theenginecanbetransverseorlongitudinalandusuallydrivestherearwheelsonly.前置發動機可以縱向布

12、置，能夠驅動前輪或后輪。后置發動機布置在后輪后側，發動機即可縱向布置又可橫向布置，一般只能驅動后輪。1.3chassis底盤thechassisisanassemblyofthosesystemsthatarethemajoroperatingpartsofavehicle.thechassisincludesthepowertrain,steering,suspension,andbrakingsystems.底盤由汽車的主要操作系統組裝而成。包括傳動系、行駛系、轉向系和制動系四部分。1）Powertrainsystemconveysthedrivetothewheels.傳動系-將驅動力傳

13、遞到車輪。2）Steeringsystemcontrolsthedirectionofmovement.轉向系-控制汽車的行駛方向。3）Suspensionandwheelsabsorbstheroadshocks.懸掛系-吸收路面震動4）Brakeslowsdownthevehicle.制動系-使汽車減速緩行。1.3.1powertrainsystem動力傳動系統Thepowertraintransfersturningeffortfromtheenginetothedrivingwheels.apowertraincanincludeaclutchmanualtransmissionora

14、torqueconverterforautomatictransmission,adriveshaft,finaldriveanddifferentialgearsanddrivingaxles.Alternatively,atransaxlemaybeused.Atransaxleisaself-containedunitwithatransmission,finaldrivegearsanddifferentiallocatedinonecasing.傳動系把發動機輸出的扭矩傳遞給驅動輪。傳動系包括離合器（對應機械變速器）或液力變矩器（對應液力自動變速器）、變速器、驅動軸、主減速器、差速器

15、和驅動橋。另外有些傳動系采用由變速器、主減速器和差速器組成的一體式的變速驅動橋。（或者采用一個獨立的變速驅動橋，即變速器在同一個箱體內。）Avehiclewithamanualtransmissionusesaclutchtoengageanddisengagetheenginefromthepowertrain.Enginetorqueistransmittedthroughtheclutchtothetransmissionortransaxle.thetransmissioncontainssetsofgearsthatincreaseordecreasethetorquebeforei

16、tistransmitted,totherestofthepowertrain.thelowerthegearratioselected,thehigherthetorquetransmissioned.avehiclestartingfromrestneedsalotoftorque,butonceitismoving,itcanmaintainspeedwithonlyarelativelysmallamountoftorque.ahighergearratiocanthenbeselected,andenginespeedisreduced.,對于采用機械變速器的汽車，其發動機扭矩由離合

17、器傳遞給變速器或變速驅動橋，并通過離合器來控制發動機和傳動系的嚙合或分離。變速器包含了不同傳動比的齒輪副，能夠增加或減小扭矩。選擇的齒輪速比越小，傳遞的扭矩最大。汽車起步時需要較大的扭矩，一旦起動后，僅需要較小的扭矩就可維持速度，此時應該換用較高的檔位，以降低發動機轉速。,aconventionalvehiclewiththeengineatthefrontanddrivingwheelsattherearusesadriveshaft,calledapropellershaft,totransmittorquefromtransmissiontothefinaldrive.,傳統的汽車采用前

18、置發動機、后輪驅動，因此需要傳動軸把動力從變速器傳遞給主減速器。,thefinaldriveprovidesafinalgearreductiontomultiplythetorquebeforeapplyingtothedrivingaxles.onfrontenginerearwheeldrivevehicles,thefinaldrivechangesthedirectionofdriveby90degrees.insidethefinaldrive,adifferentialgearsetdividesthetorquetotheaxlesandallowsforthedifferen

19、ceinspeedofeachwheelWhencornering.axlesshaftstransmitthetorquetothedrivingwheels.inarear-wheeldrivevehicle,theaxlescanbesolidorcontainjointstoallowformovementofsuspension.forafront-wheeldrivevehicle,thedriveshafthasuniversaljointstoallowforsuspensionandsteeringmovement.,主減速器的作用就是在把動力傳遞給驅動輪之前，降低轉速并增加

20、扭矩。對于前置后驅的汽,車，主減速器還將驅動的旋轉方向改變了90度。主減速器內的差速器齒輪副，把動力分給,兩個驅動軸，并允許兩邊車輪在轉向時具有不同的轉速。動力最終由驅動軸傳遞給車輪。后輪驅動汽車的驅動橋應能滿足懸架的運動，可以是剛性的或包含運動副。為滿足懸架和轉向的要求，前輪驅動汽車驅動軸上需安裝萬向節。,anautomatictransmissionortransaxleperformssimilarfunctionstoamanualtransmissionortransaxleexceptthatgearselectioniscontrolledeitherhydraulicallyo

21、relectronically.theautomatictransmissionusesatorqueconverter,whichactsasahydrauliccouplingtotransferthedrive.,自動變速器或自動變速驅動橋的功能和機械式基本類似，區別在于檔位的選擇是液力或電力控制的。液力自動變速器采用液力變矩（耦合）器作為連接器以傳遞動力。,1.3.2steeringsystem轉向系統,Thedirectionalmotionofvehicleiscontrolledbyasteeringsystem.Abasicsteeringsystemhas3mainparts

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

23、Thetie-rodsmovethefrontwheelstoturnthevehiclerightorleft.,轉向系控制汽車行駛方向，一般由三部分組成：與轉向盤相連的轉向器、連接車輪和轉向器的傳動結構、允許車輪轉動的前懸架部件。當駕駛員轉動方向盤時，轉向柱內的軸帶動轉向器運動，然后通過轉向傳動機構來轉動車輪，從而使得汽車向左或向右行駛。,1.3.3suspensionsystem懸架系統,Thepurposeofthecompletesuspensionsystemistoisolatethevehiclebodyfromroadshocksandvibrations,whichwill

24、otherwisebetransferredtothepassengersandload.Itmustalsokeepthetiresincontactwiththeroadregardlessofroadsurface.Abasicsuspensionsystemconsistsofsprings,axles,shockabsorbers,arms,rodsandballjoints.,整個懸架系統的作用是隔離來自路面的沖擊和振動對車身的影響，防止傳遞給乘員和貨物。另外不論路面如何，懸架系統都應該保持輪胎和路面接觸。懸架系統的基本組成包括彈性元件、車橋、減震器、桿系（臂、桿）和球副組成的導向

25、機構。,thespringistheflexiblecomponentofthesussuspension.basictypesare:leafspring,coilspringandtorsionbars.modernpassengervehiclesandcanhavecoilspringsatthefrontandleafspringsattherear.heavycommercialvehiclesusuallyuseleafspringsorairsuspension.,彈簧是懸架的彈性元件，常見的彈簧類型有：鋼板彈簧、螺旋彈簧和扭桿彈簧?，F代汽車大多采用小的螺旋彈簧，輕型商用車常采

26、用的螺旋彈簧比一般乘用車的大得多，或者前懸架采用螺旋彈簧，后懸架采用鋼板彈簧。重型商用車則通常采用鋼板彈簧或空氣彈簧。,wheelsmustbestrongenoughtosupportthevehicleandwithstandtheforcescausedbynormaloperation.atthesametime,theymustbeaslightaspossibletohelpkeepunsprungweighttoaminimum.,車輪必須能支撐整車重量，并能承受正常工況下的載荷。同時車輪必須盡可能地輕，有助于最小化簧下質量。,wheelscanbemadefrompressed

27、-steelingtwosections,andalsobemadefromcastaluminiumalloy.alloywheelsarepopularbecauseoftheirappearanceandbecausetheyarelighterthansimilarsteelwheels.aluminiumisabetterconductorofheat,soalloywheelscandissipateheatfrombrakeesandtiresmoreeffectivelythansteelones.,車輪可采用雙面鋼化板壓制而成，也可采用鑄造的鋁合金材料。除了外觀漂亮之外，鋁合

28、金比鋼更輕，因此鋁合金車輪應用較廣。另外鋁合金導熱性更好，因此相比鋼制車輪，制動器和車輪產生的熱量更容易被鋁合金車輪散發。,thetireprovidesacushionbetweenthevehicleandtheroadtoreducethetransmissionofroadshocks.italsoprovidesfrictiontoallowthevehicletoperformitsnormaloperations.moderntiresaremanufacturedfromarangeofmaterials.therubberismainlysynthetic.twotypeso

29、ftireconstructionarecommon:cross-plyandradial.mostpassengercarsnowuseradialtires,andradialsarereplacingcross-plytireson4-wheeldrivesandheavyvehicles.,輪胎在汽車和路面之間起緩沖作用，能減小路面沖擊。同時輪胎也提供了車輪正常行駛所需的摩擦力。輪胎是由多種材料加工而成，橡膠多是人工合成的。最常見的輪胎類型是子午線輪胎和斜交輪胎?，F在大部分乘用車都采用子午線輪胎，在四輪驅動和商用車上，子午線輪胎也正在取代斜交胎。,tubetiresrequireani

30、nnertubetosealairinsidethetire.tubelesstiresareeliminatingtheinnertubebymakingthecompletewheelandtireassemblyairtight.aspecialairtightvalveassemblyisneeded.thiscanbetightfitintotherimorcanbeheldwithanutandsealingwashers.,有內胎的輪胎用內胎來密封內部氣體。無內胎的輪胎則要求車輪和輪胎具有很好的密封性，這就需要專用的密封件，可以緊固在輪緣上，也可用螺釘和密封圈來固定。,1.3.4

31、Brakingsystem制動系統,Drumbrakeshaveadrumattachedtothewheelhub,andbrakingoccursbymeansofbrakeshoesexpandingagainsttheinsideofthedrum.Withdiscbrakes,adiscattachedtothewheelhubisclenchedbetweentwobrakepads.onlightvehicles,bothofthesesystemsarehydraulicallyoperated.thebrakepedaloperatesamastercylinder.hydr

32、auliclinesandhousesconnectthemastercylindertobrakecylindersatthewheels.mostmodernlightvehicleshaveeitherdiscbrakesonthefrontwheelsanddrumbrakesontherearordiscbrakesonall4wheels.discbrakesrequiregreaterforcestooperatethem.abrakeboosterassistthedriverbyincreasingtheforceappliedtothemastercylinderwhent

33、hebrakeisoperated.,鼓式制動器的制動鼓和輪轂連接，制動蹄張開壓緊制動鼓內側從而產生制動。在盤式制動器上，連著輪轂的制動盤被緊緊夾在兩個制動塊之間。輕型汽車上都采用液壓制動系統，制動踏板控制制動主缸，通過液壓管路與車輪上的制動輪缸相連。現在輕型汽車上的制動器，前輪采用盤式，后輪采用鼓式，或全部采用盤式。相比鼓式制動器，盤式制動器需要更大的作用力。在制動時采用增壓器輔助駕駛員提高施加在主缸上的制動力。,pressedairoperatingonlargediameterdiaphragmsprovidesthelargeforcestothebrakeassemblythatar

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

35、ppliesthebrakesifthetrailerdisconnectedfromtheprimemover.,重型商用車多采用氣壓制動系統，壓縮氣體作用在直徑較大的膜片上時能為制動總成提供較大的制動力。氣壓制動系統靠空氣壓縮機把氣體吸入儲氣罐。駕駛員控制閥門開啟，使壓縮氣體進入車輪制動氣室進行制動。在鉸接車輛的拖車上采用繼動閥和單獨的儲氣罐，以減小拖車制動系統的時間延遲，這種布置方式還可以在拖車失去動力時制動拖車。,allvehiclesmustbefittedwithatleast2independentsystems.theywereoncecalledtheservicebrake

36、andtheemergencybrake.nowtheyareusuallyreferredtoasthefootbrakeandtheparkbrake.mostlightvehiclesuseafootbrakethatoperatesthroughahydraulicsystemonallwheelsandahandoperatedbrakethatactsmechanicallyontherearwheelsonly.onecommonuseofthehandbrakesystemistoholdthevehiclewhenitisparked.thesystemaredesigned

37、tobeindependentSothatifonefails,theotherisstillavailable.,所有汽車必須安裝至少兩套獨立的制動系統，即行車制動系統與緊急制動系統，一般被稱之為腳制動和停車制動。大部分輕型汽車的腳制動通過液壓系統作用在四個車輪上，而其手制動則是機械式的，且僅作用在后輪。手制動的一個普通用途就是停車時對汽車進行制動。設計兩套獨立的制動系統的目的就是當一套失效時，另一套仍可工作。,1.4.1Electricalsystem電器系統,Theelectricalsystemsupplieselectricityforthestarter,ignition,ligh

38、tsandheater.Theelectricitylevelismaintainedbyachargingcircuit.,電器系統為起動機、點火系、照明和加熱設備提供電流，電流的大小由充電電路來維持。,Thechargingsystemprovideselectricalenergyforalloftheelectricalcomponentsonthevehicle.themainpartsofthechargingsysteminclude:thebattery,thealternator,thevoltageregulatorwhichisusuallyintegraltotheal

39、ternator,achargingwarningorindicatorlightandwiringthatcompletethecircuits.thebatteryprovideselectricalcomponentsofthevehicle.italsochargesthebattertoreplacetheenergyusedtostarttheengine.thevoltageregulatorpreventsovercharging.,充電系統為汽車上所有的電器系統提供電能。充電系統主要組成部分有：蓄電池、交流發電機、穩壓器（多集成在發電機中），充電指示燈和組成電路的電線。汽車起

40、動時由蓄電池提供能量，一旦發動機開始工作，交流電機為電氣設備供電，同時還對蓄電池進行充電，以補償起動所消耗的電能。穩壓器則防止過載。,1.4.2Starting啟動系統,Thestaringsystemconsistsofthebattery,cables,startermotor,flywheelringgearandtheignitionswitch.duringstarting,twoactionsoccur.thepinionofthestartermotorengageswiththeflywheelringgearandthestartermotorthenoperatestocr

41、anktheengine.thestartermotoris,anelectricalmotormountedontheengineblockandoperatedfromthebattery.,起動系統包括電池、電纜、啟動電機、飛輪齒圈和點火開工。起動需要兩個動作，啟動電機齒輪和飛輪齒圈嚙合，從而帶動發動機轉動。起動電機安裝在發動機殼體上，靠電池工作。,1.4.3Ignition點火系統,Abasicignitionsystemconsistsofthebattery,low-tensioncables,theignitioncoil,distributor,coilhigh-tension

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

43、creasedbytheignitioncoil.thesystemhastwocircuits.theprimaryorlow-tensioncircuitinitiatesthespark.thesecondaryorhigh-tensioncircuitproducesthehighvoltageanddistributesittosparkplugs.,點火系統包括電池、低壓電纜、點火線圈、分電器、高壓電纜、火花塞連線和火花塞。點火系統在火花塞處產生高壓火花，點燃發動機燃燒室內的燃油混合物。點火系統必須在恰當的時刻提供火花，并且能量滿足各種工況的要求。電池和交流發電機為點火系統供電，點

44、火線圈提高電壓。點火系統由兩級電路組成，初級電路（低壓電路）初始化火花，次級電路（高壓電路）產生高壓電，并分到各個火花塞。,2.1principleofoperation工作原理2.1.1energyandpower能源和動力,Engineisusedtoproducepower.Thechemicalenergyinfuelisconvertedtoheatbytheburningofthefuelatacontrolledrate.Thisprocessiscalledcombustion.Ifenginecombustionoccurswiththepowerchamber.,theen

45、gineiscalledinternalcombustionengine.Ifcombustiontakesplaceoutsidethecylinder,theengineiscalledanexternalcombustionengine.,能源用于產生動力。燃料以控制的速率燃燒，燃料中的化學能轉換為熱能。這個過程叫做燃燒。如果發動機燃燒發生在動力室內，這種發動機叫做內燃機。如果燃燒發生在氣缸外，這樣的發動機叫做外燃發動機。,Engineusedinautomobilesareinternalcombustionheatengines.Heatenergyreleasedinthecomb

46、ustionchamberraisesthetemperatureofthecombustiongaseswithinthechamber.Theincreaseingastemperaturecausesthepressureofthegasestoincrease.Thepressuredevelopedwithinthecombustionchamberisappliedtotheheadofapistontoproduceausablemechanicalforce,whichisthenconvertedintousefulmechanicalpower.,汽車使用的發動機是內燃發動

47、機。在燃燒室內釋放的熱能提高了室內燃燒氣體的溫度。氣體溫度的增肌使氣體的壓力增加。在燃燒室內產生的壓力作用于活塞的頂部，產生機械力，這個力轉換成有用的機械動力。,2.1.2EngineTerms,Linkingthepistonbyaconnectingrodtoacrankshaftcausesthegastorotatetheshaftthroughhalfaturn.Thepowerstroke“usesup”thegas,someansmustbeprovidedtoexpeltheburntgasandrechargethecylinderwithafreshpetrol-airmi

48、xture:thiscontrolofgasmovementisthedutyofthevalves；aninletvalveallowsthenewmixturetoenterattherighttimeandanexhaustvalveletsouttheburntgasafterthegashasdoneitsjob.Enginetermsare：,活塞通過連桿和曲軸連接，使得氣體帶動曲軸旋轉半圈。作功沖程耗盡了所以的氣體，這樣就必須采取相應的措施排出廢氣以及向氣缸內充入新鮮的可燃混合氣：氣體的運動由氣門來控制。進氣閥允許新的混合氣體在適當的時間進入，排氣閥在作功完成后，可以放出燃燒后的

49、氣體。引擎術語：,TDC(TopDeadCenter):thepositionofthecrankandpistonwhenthepistonisfartherawayfromt,hecrankshaft.,上止點：活塞處于離曲軸最遠處時，曲柄和活塞所處的位置。,BDC(BottomDeadCenter):thepositionofthecrankandpistonwhenthepistonisnearesttothe,crankshaft.,下止點：活塞處于離曲軸最近處時，曲柄和活塞所處的位置。,Stroke:thedistancebetweenBDCandTDC;strokeiscontr

50、olledbythecrankshaft.行程：上止點和下止點間的距離;行程由曲軸控制。,Bore:theinternaldiameterofthecylinder.,缸徑：氣缸的內徑,Sweptvolume:thevolumebetweenTDCandBDC.有效容積：上止點和下止點間的容積Enginecapacity:thisisthesweptvolumeofallthecylinders.e.g.afour-cylinderenginehavingacapacityoftwoliters(2000cm3)hasacylindersweptvolumeof500cm3.發動機排量：所有氣

51、缸的有效容積之和.例如一四缸發動機有能力兩升（2000cm3）有一個氣缸排量500cm3。Clearancevolume:thevolumeofthespaceabovethepistonwhenitisatTDC.燃燒室容積：活塞處于上止點時，活塞上方的體積Compressionratio=(sweptvol+clearancevol)(clearancevol)壓縮比：（有效容積+燃燒室容積）/燃燒室容積Two-stroke:apowerstrokeeveryrevolutionofthecrank.兩沖程：曲柄旋轉一圈作功一次。Four-stroke:apowerstrokeeveryo

52、therrevolutionofthecrank.四沖程：曲柄旋轉兩圈作功一次。2.1.3TheFour-strokeSpark-ignitionEngineCycleThespark-ignitionengineisaninternal-combustionenginewithexternallysuppliedinignition,whichconvertstheenergycontainedinthefueltokineticenergy.Thecycleofoperationsisspreadoverfourpistonstrokes.Tocompletethefullcycleitt

53、akestworevolutionsofthecrankshaft.火花點火式發動機是由外部提供點火的內燃機，從而將含在燃料內的能量轉化成動能。發動機的一個工作循環分布在活塞的四個行程中，一個完整的工作循環曲軸需要轉動兩圈。Thedownward-movingpistonincreasesthevolumeinthecylinderanddrawsinfreshair-fuelmixturethroughtheopenintakevalve.向下運動的活塞使氣缸里的體積增大，并且將新的空氣燃料混合物通過節氣門吸進氣缸。Theupward-movingpistonreducesthevolume

54、inthecylinderandcompressestheair-fuelmixture.ShortlybeforeTDCisreached,thesparkplugignitesthecompressedair-fuelmixtureandthusinitiatesthecombustionprocess.Ahighercompressionratiomeansbetterutilizationofthefuel.Theextentofcompressionisrestrictedbytheknocklimit.向上運動的活塞使氣缸里的體積減小，從而壓縮空氣燃料混合物。在活塞即將到達上止點的

55、瞬間，火花塞點燃壓縮的空氣燃油混合氣，從而燃燒過程開始了。壓縮比越高，燃料利用率越高，但是壓縮的程度受到爆震極限的限制。Aftertheignitionsparkatthesparkplughasignitedthecompressedair-fuelmixture,thetemperatureincreasesastheresultofcombustionofthemixture.Thepressureinthecylinderincreasesandforcesthepistondownwards.Thepistontransferspowertothecrankshaftviatheco

56、nnectingrod.當火花塞噴出的火花點燃壓縮的空氣燃料混合物后，空氣燃料混合物開始然后，隨之氣缸內的溫度開始升高。氣缸里的壓力也隨之增加，使得活塞向下運動。這樣活塞就把動力通過連桿傳遞給曲軸。,Theupward-movingpistonexpelsthecombustedgases（exhaustgas）throughtheopenexhaustvalve.Afterthis4thstroke,thecycleisrepeated.,向上運動的活塞使燃燒后的氣體（廢氣）通過排氣門排出氣缸。在這第四個行程后，整個工作工程將重復進行。,2.1.4EngineOverallMechanics

57、發動機的總體構造,Theenginehashundredsofotherparts.Themajorpartsofengineareengineblock,engineheads,pistons,connectingrods,crankshaftandvalves.Theotherpartsarejoinedtomakesystems.Thesesystemsarethefuelsystem,intakesystem,ignitionsystem,coolingsystem,lubricationsystemandexhaustsystem.Eachofthesesystemshasadefi

58、nitefunction.Thesesystemswillbediscussedindetaillater。,發動機有上百個其它部件。發動機的主要部件是發動機缸體、發動機頭、活塞、連桿、曲軸和閥門。其他部分也加入到系統中。這些的系統是燃油系統、進氣系統、點火系統、冷卻系統、潤滑系統和排氣系統。這些系統中的每一個都有一個明確的功能。這些系統以后將進行詳細論述。,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.,氣缸體是發動機的基本框架。發動機的其他零件都安裝在它里面或者固定在它上。缸體里有,氣缸，水套和油道。曲軸也固定在氣缸體底部。除了頂置凸輪(OHC)發動機以外，凸輪軸都安裝在氣缸體里面。在大多數汽車里，氣缸體由灰鑄鐵或者一種灰鑄鐵和其他金屬的合金(混合物)做成，例如鎳或鉻。氣缸體是鑄件。,Someengineblocks,especiallythoseinsmallercars,aremadeofcastaluminum.Thismetalismuchlighterthaniron.However,ironwearsbetterth