汽车专业英语读译教程 第3版 课件 2-U2TA Operation,Main Components and Classification of the Engine

UNIT2

ENGINEMECHANICAL

TEXTA

Operation,MainComponentsandClassification

oftheEnginePROFESSIONALENGLISH

UNIT2

ENGINEMECHANICAL

TEXTA

Operation,MainComponentsandClassification

oftheEngine

PrincipleofOperation

MainEngineComponents

EngineClassification本次课学习内容本次课学习目标掌握发动机主要部件的英文名称掌握各中发动机的英文名称掌握常用术语（phrasesandexpressions）了解相关术语（relatedterms）较熟练翻译与发动机工作原理相关的英文文章NEWWORDScombustion[kəm'bʌs∫ən]n.燃烧stroke[strouk]n.冲程piston['pistən]n.活塞cylinder['silində]n.气缸valve[vælv]n.气门，阀门，阀exhaust[ig'zɔ:st]n.排气，废气intake['inteik]n.进气，进（引，吸）入compression[kəm'pre∫ən]n.压缩crankshaft['kræŋk∫ɑ:ft]n.曲轴swirl[swə:l]n.漩涡，涡流，紊流；v.涡动churn[t∫ə:n]v.搅拌，搅动NEWWORDSfoundation[faun'dei∫ən]n.基础，基地，基金，机座camshaft['kæm∫ɑ:ft]n.凸轮轴accessory[æk'sesəri]n.附属品，附件，辅助装置clutch[klʌt∫]n.离合器housing['hauziŋ]n.外壳bolt[boult]n.螺栓；v.用螺栓连接core[kɔ:]n.芯，核心，铁心，型芯，沙芯，（电缆）芯线aluminum['əlju:minəm]n.铝liner['lainə]n.衬套，衬里，衬板oversize['ouvə'saiz]n.&a.加大尺寸heavy-duty['hevi'dju:ti]a.重型的，重载的NEWWORDSoscillate['ɔsileit]v.振荡，振动，波动，动摇bearing['b

əriŋ]n.轴承journal['ʤə:nəl]n.轴颈throw[

rou]n.&v.投掷，扔；n.投掷距离，偏心距离，摆幅；（pl.）曲柄attach[ə'tæt∫]v.附着，连接，固定（to）reciprocating[ri'siprəkeitiŋ]a.往复的mount[mɑunt]v.安装，固定；n.安装件，支架，机座rim[rim]n.边缘，轮缘，轮辋，齿圈heat-resistant[hi:tri'zistənt]a.耐热的clearance['kliərəns]n.间隙lifter['liftə]n.挺杆NEWWORDSharden['hɑ:dn]v.硬化，变硬，淬硬revolution[ֽrevə'lu:∫ən]n.转，回转，大变革inline['in'lain]a.直列式的，在一条直线上的bank[bæŋk]n.（气缸）列，排，银行rigidity[ri'ʤiditi]n.刚性profile['proufail]n.外形，轮廓conducive[kən'dju:siv]a.有助于…的，促进…的（to）sacrifice['sækrifais]n.牺牲（品），损失liquefy['likwifai]v.液化propane['proupein]n.丙烷carburetion[ֽkɑ:bju're∫ən]n.汽化carburetor[kɑ:bju'retə]n.化油器

PHRASESANDEXPRESSIONS

internalcombustionengine内燃机four-strokecycle四冲程循环sparkplug火花塞intakestroke进气行程powerstroke作功行程compressionstroke压缩行程exhauststroke排气行程connectingrod连杆automatictransmission自动变速器torqueconverter液力变矩器PHRASESANDEXPRESSIONSinsertbearing镶入式轴承valveseat气门座valveguide气门导管valvetrain气门机构，气门组hydraulicvalvelifter液力挺杆Theautomotiveengineisessentiallyaheatengine.Theheatenginesusedinautomobilesareinternalcombustionengines.1.PrincipleofOperationThespark-ignitionengineisaninternal-combustionenginewithexternallysuppliedinignition.Thegasolineengineisakindofspark-ignitionengines.Thefour-stroke-cyclegasolineenginecycleisspreadoverfourpistonstrokes.Theoperationstrokesare(figure2-1):

TEXTAOperation,MainComponentsandClassificationoftheEngine

TEXTAOperation,MainComponentsandClassificationoftheEngineFig.2-1Theoperationofafour-stroke-cyclegasolineengineTEXTAOperation,MainComponentsandClassificationoftheEngineThefirststrokeinyourengineiscalledtheintakestroke.Insteadofopeningtheintakevalveafteryouhavedrawnthepistondown,youwillfinditbettertoopentheintakevalveasthepistonstartsdown[1].Thisallowstheairtodrawfuelintheentiretimethepistonismovingdown.Remember,theintakestrokestartswiththepistonatthetopofthecylinder(intakevalveopenandexhaustvalveclosed)andstopswiththepistonatthebottomofitstravel[2].Thisrequiresone-halfturnofthecrankshaft.[1]Insteadofopeningtheintakevalveafteryouhavedrawnthepistondown,youwillfinditbettertoopentheintakevalveasthepistonstartsdown.Insteadof…的意思是“而不是…”，“代替着…”。draw…down的意思是“将…向下移”。better为副词，意思为“更好”，“更多”，“更加”，修饰动词不定式短语toopentheintakevalve。本句译为：在活塞下行之后，进气门不只是已经打开，而是随着活塞的下移，开度还在进一步增大。TEXTAOperation,MainComponentsandClassificationoftheEngine[2]Remember,theintakestrokestartswiththepistonatthetopofthecylinder(intakevalveopenandexhaustvalveclosed)andstopswiththepistonatthebottomofitstravel.With后面的宾语接有现在分词、过去分词、形容词,甚至是副词，with后面的宾语与现在分词、过去分词、形容词之间具有“主谓”关系。这时整个with短语说明附带情况，或者交待细节。本句译为：记住，进气行程在活塞位于气缸顶部（进气门开启，排气门关闭）时开始，在活塞到达其行程的底部时结束。TEXTAOperation,MainComponentsandClassificationoftheEngineTEXTAOperation,MainComponentsandClassificationoftheEngineAsthecrankshaftcontinuestomove,thepistonisforcedupthroughthecylinder.Ifyoukeepbothvalvesclosed,thefuelmixturewillbesqueezed,orcompressed,asthepistonreachesthetop.Thisiscalledthecompressionstroke.It,too,requiresahalfturnofthecrankshaft.Thecompressionstrokeservestobreakupthefuelintoevensmallerparticles.Thishappensduetothesuddenswirlingandchurningofthemixtureasitiscompressed.Whentheair-fuelmixtureissubjectedtoasuddensharpcompressionforce,itstemperaturerises.ThisincreaseintemperaturemakesthemixtureeasiertoigniteandcausesittoexplodewithgreaterforceTEXTAOperation,MainComponentsandClassificationoftheEngine

Asthepistonreachesthetopofitstravelonthecompressionstroke,ithasreturnedtotheproperpositiontobepushedbackdownbytheexplosion.Remember,thecompressionstrokestartswiththepistonatthebottomofthecylinder(bothvalvesclosed)andstopswiththepistonatthetopofthecylinder.Thisrequiresanadditionalhalfturnofthecrankshaft.Asthepistonreachesthetopofthecompressionstroke,themixtureisbrokenintotinyparticlesandheatedup.Whenignited,itwillexplodewithgreatforce.Thisistherighttimetoexplodethemixture.Asparkplugprovidesasparkinsidethecombustionchamber.Thesparkproducedattheplugisformedbytheignitionsystem.ThiswillbediscussedinUnit6.

Justimaginethatahotsparkhasbeenprovidedinthefuelmixture.Themixturewillexplodeand,inturn,forcethepistondownintothecylinder.Thisgivesthecrankshaftaquickandforcefulpush.Thisisthepowerstroke.Bothvalvesmustbekeptclosedduringthepowerstrokeorthepressureoftheburningfuelwillsquirtoutthroughthevalvepods.Remember,thepowerstrokestartswiththepistonatthetopofthecylinder(bothvalvesclosed)andstopswiththepistonatthebottomofthecylinder.Thisrequiresanotherhalfturnofthecrankshaft.

TEXTAOperation,MainComponentsandClassificationoftheEngineWhenthepistonreachesthebottomofthepowerstroke,theexhaustvalveopens.Thespinningcrankshaftforcesthepistonupthroughthecylinder,pushingburnedgasesout.Thisistheexhauststroke.Remember,theexhauststrokestartswiththepistonatthebottomofthecylinder(exhaustvalveopenandintakevalveclosed).Itstopswiththepistonatthetopofthecylinder.Thisrequiresonemorehalfturnofthecrankshaft.Ifyoucountthenumberofhalfturnsintheintake,compression,power,andexhauststrokes,youwillfindyouhaveatotaloffour.Thisgivesyoutwocompleteturns,orrevolutions,ofthecrankshaft.TEXTAOperation,MainComponentsandClassificationoftheEngineTEXTAOperation,MainComponentsandClassificationoftheEngineWhilethecrankshaftisturningaroundtwice,itisreceivingpoweronlyduringonehalfturn,oronefourthofthetime.Assoonasthepistonreachesthetopoftheexhauststroke,itstartsdownonanotherintake,compression,power,andexhaustcycle.Thiscycleisrepeatedoverandover.

Eachcompletecycleconsistsoffourstrokesofthepiston,hencethenamefour-strokecycle.TEXTAOperation,MainComponentsandClassificationoftheEngine2.MainEngineComponentsEngineblockTheengineblockservesasarigidmetalfoundationforallpartsofanengine.Itcontainsthecylindersandsupportsthecrankshaftandcamshaft.Inolderengines,thevalveseats,ports,andguidesarebuiltintotheblock.Accessoryunitsandtheclutchhousingareboltedtoit.Blocksaremadeofeithercastironoraluminum.Thelightertheblock(providingithassufficientstrength),thebetter.Themodernthin-wallcastingprocesscontrolscoresizeandplacementmuchmoreaccuratelythantheoldercastingprocess.TEXTAOperation,MainComponentsandClassificationoftheEngineThispermitscastingtheblockwallsmuchthinner,reducingtheweightoftheblock.Sincetheblockwallthicknessismoreuniform,blockdistortionduringserviceislesssevere.TEXTAOperation,MainComponentsandClassificationoftheEngineCylindersThecylinderisaroundholeformedintheblock.Itformsaguideforthepistonandactsasacontainerfortakingin,compressing,firing,andexhaustingtheair-fuelcharge.Cylindershavebeenmadeofbothsteelandcastiron.Castironisbyfarthemostpopular.Whensteelcylindersaredesiredinanaluminumblock,theyareinstalledintheformofcylindersleeves(round,pipe-likeliners),Thesesleevesmaybeeithercastorpressedintotheblock.Someenginesuseremovablecylindersleeves.Whenthecylinderbecomesworn,theoldsleevescanbepulledoutandnewsleevescanbepressed

in.TEXTAOperation,MainComponentsandClassificationoftheEngineThesleevesarepressedintooversizecylinderholes.Cylindersleevesarewidelyusedinheavy-dutytruckandindustrialengines.Sleevescanalsobeusedtorepairawornorcrackedcylinderinacastironblock.TEXTAOperation,MainComponentsandClassificationoftheEnginePistonsThepistonmustmovedownthroughthecylindertoproduceavacuumtodrawafuelchargeintothecylinder.Itthentravelsupinthecylinderandcompressesthemixture.Whenthemixtureisfired,thepressureoftheexpandinggasistransmittedtothetopofthepiston.Thisdrivesthepistonbackdownthroughthecylinderwithgreatforce,transmittingtheenergyoftheexpandinggastothecrankshaft.Thepistonthentravelsupthroughthecylinderandexhauststheburnedfuelcharge.

TEXTAOperation,MainComponentsandClassificationoftheEnginePistonsareusuallymadeofaluminum.Often,aluminumpistonsaretin-platedtoallowproperbreak-inwhentheengineisstarted.Aluminumpistonscanbeforged,buttheyaremorecommonlycast.Castironisagoodmaterialforpistonsusedinaslow-speedengine.Ithasexcellentwearcharacteristicsandwillprovidegoodperformance.TEXTAOperation,MainComponentsandClassificationoftheEngineConnectingRodsAsthenameimplies,connectingrodsareusedtoconnectpistonstothecrankshaft.Theupperendoftherodoscillates(swingsbackandforth),whilethelower,orbigend,bearingrotates(turns).Becausethereisverylittlebearingmovementintheupperend,thebearingareacanbereasonablysmall.Thelowerendrotatesveryfast,andthecrankshaftbearingjournalturnsinsidetheconnectingrod.Thisrotationalspeedtendstoproduceheatandwear.Tomaketherodwearwell,alargerbearingareaisrequired.

TEXTAOperation,MainComponentsandClassificationoftheEngineTheupperendoftherodhasaholethroughitforthepistonpin.Thebottomofthelargeendoftheconnectingrodmustberemovedsotherodcanbeinstalledonthecrankshaftjournal.Thesectionthatisremovediscalledtheconnectingrodcap.Connectingrodsarenormallymadeofalloysteel.Theyaredrop-forgedtoshapeandthenmachined.TEXTAOperation,MainComponentsandClassificationoftheEngineCrankshaftTheenginecrankshaftprovidesaconstantturningforcetothewheels.Ithasthrowstowhichconnectingrodsareattached,anditsfunctionistochangethereciprocatingmotionofthepistontoarotarymotiontodrivethewheels.Crankshaftsaremadeofalloysteelorcastiron.Thecrankshaftisheldinpositionbyaseriesofmainbearings.Themaximumnumberofmainbearingsforacrankshaftisonemorethanthenumberofcylinders.Itmayhavefewermainbearingsthancylinders.Mostenginesuseprecisioninsertbearingsthatareconstructedliketheconnectingrodbearings,butaresomewhatlarger.Inadditiontosupportingthecrankshaft,oneofthemainbearingsmustcontrolthe

forwardandbackwardmovement.TEXTAOperation,MainComponentsandClassificationoftheEngineFlywheelAheavyflywheelisattachedtotherearofthecrankshaftwithbolts.Thefunctionoftheflywheelistosmoothoutenginespeedandkeepthecrankshaftspinningbetweenpowerstrokes,insomeengines,theflywheelalsoservesasamountingsurfacefortheclutch.Theouterrimoftheflywheelhasalargeringattachedwithgearteethcutintoit.Theteethofthestartermotorengagetheseteethandspintheflywheeltocranktheengine.Whenanautomatictransmissionisused,thetorqueconverterassemblyworkswiththeflywheel.TEXTAOperation,MainComponentsandClassificationoftheEngineCamshaftThecamshaftisusedtoopenandclosethevalves.Thereisonecamonthecamshaftforeachvalveintheengine.Generallyonlyonecamshaftisusedinmostengines.Newerenginesareincreasinglyequippedwithtwoormorecamshafts(figure2-2).TEXTAOperation,MainComponentsandClassificationoftheEngineFigure2-2Dualoverheadcamshaft（DOHC）drivenbyatootheddrivebeltTEXTAOperation,MainComponentsandClassificationoftheEngineValvesEachenginecylinderordinarilyhastwovalves.However,modernenginesoftenusefourvalvespercylinder(twointakeandtwoexhaust).Afewenginesusedinsmallervehicleshavethreeorfivevalvespercylinder:twointakevalvesandoneexhaustvalveorthreeintakevalvesandtwoexhaustvalves.Becausetheheadofanexhaustvalveoperatesattemperaturesupto1300℉(704℃),valvesaremadeofheat-resistantmetal.Inordertopreventburning,thevalvemustgiveoffheattothevalveseatandtothevalveguide.Thevalvemustmakegoodcontactwiththeseatandmust

runwithminimumclearanceintheguide.TEXTAOperation,MainComponentsandClassificationoftheEngineValveLifters

Mechanicalvalveliftersareusuallymadeofcastiron.Thebottompartthatcontactsthecamshaftishardened.Someliftersarehollowtoreduceweight.Mostvalvetrainsthatcontainmechanicalliftershavesomeprovisionforadjustingclearance.Mechanicalvalvelifterswereusedinolderengines.Hydraulicvalveliftersperformthesamejobasmechanicallifters.However,hydraulicliftersareself-adjusting,operatewithnolifter-to-rockerarmclearance,andusesengineoilunderpressuretooperate.Hydraulicliftersarequietinoperation.TEXTAOperation,MainComponentsandClassificationoftheEngine3.EngineClassificationCycleClassificationEnginesareoftenclassifiedaccordingtocycle.Mostinternalcombustionpistonenginesuseatwo-orfour-strokecycle.Allmodernautomobileenginesusethefour-strokecycleengine.Thetwo-strokecycleengineperformstheintake,compression,firing,andexhaustsequenceinonerevolutionofthecrankshaft.TEXTAOperation,MainComponentsandClassificationoftheEngineCylinderClassificationTheinlineenginehasitscylindersarrangedoneaftertheotherinastraightline.Theyareinavertical,ornearverticalposition.Mostmoderninlineenginesarefourcylinders.AV-typeengineplacestwobanksorrowsofcylindersatanangletoeachother—generallyat60°or90°.TheV-typeenginehasseveraladvantages:shortlength,extrablockrigidity,ashort,heavycrankshaft,andlowprofilethatisconducivetolowhoodlines.Theshorterblockpermitsareductioninvehiclelengthwithnosacrificeinpassengerroom.

TEXTAOperation,MainComponentsandClassificationoftheEngineThehorizontalopposedengineislikeaV-typeengine,exceptthatbothbankslieinahorizontalplane.Theadvantagehereisanextremelylowoverallheight,