专业英语ppt课件汽车专业英语ppt课件-与汽车专业英语读译教程配套-宋进桂制作2-U2TA

UNIT2ENGINEMECHANICALTEXTAOperation,MainComponentsandClassificationoftheEngine,PROFESSIONALENGLISH,UNIT2ENGINEMECHANICALTEXTAOperation,MainComponentsandClassificationoftheEnginePrincipleofOperationMainEngineComponentsEngineClassification,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,NEWWORDS,combustionkmbsnn.燃烧strokestroukn.冲程pistonpistnn.活塞cylindersilindn.气缸valvevlvn.气门，阀门，阀exhaustigz:stn.排气，废气intakeinteikn.进气，进（引，吸）入compressionkmprenn.压缩crankshaftkrk:ftn.曲轴swirlsw:ln.漩涡，涡流，紊流；v.涡动churnt:nv.搅拌，搅动,foundationfaundeinn.基础，基地，基金，机座camshaftkm:ftn.凸轮轴accessoryksesrin.附属品，附件，辅助装置clutchkltn.离合器housinghauzin.外壳boltboultn.螺栓；v.用螺栓连接corek:n.芯，核心，铁心，型芯，沙芯，（电缆）芯线aluminumlju:minmn.铝linerlainn.衬套，衬里，衬板oversizeouvsaizn.&a.加大尺寸heavy-dutyhevidju:tia.重型的，重载的,oscillatesileitv.振荡，振动，波动，动摇bearingbrin.轴承journal:nln.轴颈throwroun.&v.投掷，扔；n.投掷距离，偏心距离，摆幅；（pl.）曲柄attachttv.附着，连接，固定（to）reciprocatingrisiprkeitia.往复的mountmuntv.安装，固定；n.安装件，支架，机座rimrimn.边缘，轮缘，轮辋，齿圈heat-resistanthi:t-rizistnta.耐热的clearanceklirnsn.间隙lifterliftn.挺杆,hardenh:dnv.硬化，变硬，淬硬revolutionrevlu:nn.转，回转，大变革inlineinlaina.直列式的，在一条直线上的bankbkn.（气缸）列，排，银行rigidityriiditin.刚性profileproufailn.外形，轮廓conducivekndju:siva.有助于的，促进的（to）sacrificeskrifaisn.牺牲（品），损失liquefylikwifaiv.液化propaneproupeinn.丙烷carburetionk:bjurenn.汽化carburetork:bjuretn.化油器,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,PHRASESANDEXPRESSIONS,insertbearing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,TEXTAOperation,MainComponentsandClassificationoftheEngineTheautomotiveengineisessentiallyaheatengine.Theheatenginesusedinautomobilesareinternalcombustionengines.1.PrincipleofOperationThespark-ignitionengineisaninternal-combustionenginewithexternallysuppliedinignition.Thegasolineengineisakindofspark-ignitionengines.Thefour-stroke-cyclegasolineenginecycleisspreadoverfourpistonstrokes.Theoperationstrokesare(figure2-1):,Fig.2-1Theoperationofafour-stroke-cyclegasolineengine,Thefirststrokeinyourengineiscalledtheintakestroke.Insteadofopeningtheintakevalveafteryouhavedrawnthepistondown,youwillfinditbettertoopentheintakevalveasthepistonstartsdown1.Thisallowstheairtodrawfuelintheentiretimethepistonismovingdown.Remember,theintakestrokestartswiththepistonatthetopofthecylinder(intakevalveopenandexhaustvalveclosed)andstopswiththepistonatthebottomofitstravel2.Thisrequiresone-halfturnofthecrankshaft.,1Insteadofopeningtheintakevalveafteryouhavedrawnthepistondown,youwillfinditbettertoopentheintakevalveasthepistonstartsdown.Insteadof的意思是“而不是”，“代替着”。drawdown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。2Remember,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。,Asthecrankshaftcontinuestomove,thepistonisforcedupthroughthecylinder.Ifyoukeepbothvalvesclosed,thefuelmixturewillbesqueezed,orcompressed,asthepistonreachesthetop.Thisiscalledthecompressionstroke.It,too,requiresahalfturnofthecrankshaft.Thecompressionstrokeservestobreakupthefuelintoevensmallerparticles.Thishappensduetothesuddenswirlingandchurningofthemixtureasitiscompressed.Whentheair-fuelmixtureissubjectedtoasuddensharpcompressionforce,itstemperaturerises.Thisincreaseintemperaturemakesthemixtureeasiertoigniteandcausesittoexplodewithgreaterforce.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.,Whenthepistonreachesthebottomofthepowerstroke,theexhaustvalveopens.Thespinningcrankshaftforcesthepistonupthroughthecylinder,pushingburnedgasesout.Thisistheexhauststroke.Remember,theexhauststrokestartswiththepistonatthebottomofthecylinder(exhaustvalveopenandintakevalveclosed).Itstopswiththepistonatthetopofthecylinder.Thisrequiresonemorehalfturnofthecrankshaft.Ifyoucountthenumberofhalfturnsintheintake,compression,power,andexhauststrokes,youwillfindyouhaveatotaloffour.Thisgivesyoutwocompleteturns,orrevolutions,ofthecrankshaft.Whilethecrankshaftisturningaroundtwice,itisreceivingpoweronlyduringonehalfturn,oronefourthofthetime.Assoonasthepistonreachesthetopoftheexhauststroke,itstartsdownonanotherintake,compression,power,andexhaustcycle.Thiscycleisrepeatedoverandover.,Eachcompletecycleconsistsoffourstrokesofthepiston,hencethenamefour-strokecycle.2.MainEngineComponentsEngineblockTheengineblockservesasarigidmetalfoundationforallpartsofanengine.Itcontainsthecylindersandsupportsthecrankshaftandcamshaft.Inolderengines,thevalveseats,ports,andguidesarebuiltintotheblock.Accessoryunitsandtheclutchhousingareboltedtoit.Blocksaremadeofeithercastironoraluminum.Thelightertheblock(providingithassufficientstrength),thebetter.Themodernthin-wallcastingprocesscontrolscoresizeandplacementmuchmoreaccuratelythantheoldercastingprocess.Thispermitscastingtheblockwallsmuchthinner,reducingtheweightoftheblock.Sincetheblockwallthicknessismoreuniform,blockdistortionduringserviceislesssevere.,CylindersThecylinderisaroundholeformedintheblock.Itformsaguideforthepistonandactsasacontainerfortakingin,compressing,firing,andexhaustingtheair-fuelcharge.Cylindershavebeenmadeofbothsteelandcastiron.Castironisbyfarthemostpopular.Whensteelcylindersaredesiredinanaluminumblock,theyareinstalledintheformofcylindersleeves(round,pipe-likeliners),Thesesleevesmaybeeithercastorpressedintotheblock.Someenginesuseremovablecylindersleeves.Whenthecylinderbecomesworn,theoldsleevescanbepulledoutandnewsleevescanbepressedin.Thesleevesarepressedintooversizecylinderholes.Cylindersleevesarewidelyusedinheavy-dutytruckandindustrialengines.Sleevescanalsobeusedtorepairawornorcrackedcylinderinacastironblock.,PistonsThepistonmustmovedownthroughthecylindertoproduceavacuumtodrawafuelchargeintothecylinder.Itthentravelsupinthecylinderandcompressesthemixture.Whenthemixtureisfired,thepressureoftheexpandinggasistransmittedtothetopofthepiston.Thisdrivesthepistonbackdownthroughthecylinderwithgreatforce,transmittingtheenergyoftheexpandinggastothecrankshaft.Thepistonthentravelsupthroughthecylinderandexhauststheburnedfuelcharge.Pistonsareusuallymadeofaluminum.Often,aluminumpistonsaretin-platedtoallowproperbreak-inwhentheengineisstarted.Aluminumpistonscanbeforged,buttheyaremorecommonlycast.Castironisagoodmaterialforpistonsusedinaslow-speedengine.Ithasexcellentwearcharacteristicsandwillprovidegoodperformance.,ConnectingRodsAsthenameimplies,connectingrodsareusedtoconnectpistonstothecrankshaft.Theupperendoftherodoscillates(swingsbackandforth),whilethelower,orbigend,bearingrotates(turns).Becausethereisverylittlebearingmovementintheupperend,thebearingareacanbereasonablysmall.Thelowerendrotatesveryfast,andthecrankshaftbearingjournalturnsinsidetheconnectingrod.Thisrotationalspeedtendstoproduceheatandwear.Tomaketherodwearwell,alargerbearingareaisrequired.Theupperendoftherodhasaholethroughitforthepistonpin.Thebottomofthelargeendoftheconnectingrodmustberemovedsotherodcanbeinstalledonthecrankshaftjournal.Thesectionthatisremovediscalledtheconnectingrodcap.Connectingrodsarenormallymadeofalloysteel.Theyaredrop-forgedtoshapeandthenmachined.,CrankshaftTheenginecrankshaftprovidesaconstantturningforcetothewheels.Ithasthrowstowhichconnectingrodsareattached,anditsfunctionistochangethereciprocatingmotionofthepistontoarotarymotiontodrivethewheels.Crankshaftsaremadeofalloysteelorcastiron.Thecrankshaftisheldinpositionbyaseriesofmainbearings.Themaximumnumberofmainbearingsforacrankshaftisonemorethanthenumberofcylinders.Itmayhavefewermainbearingsthancylinders.Mostenginesuseprecisioninsertbearingsthatareconstructedliketheconnectingrodbearings,butaresomewhatlarger.Inadditiontosupportingthecrankshaft,oneofthemainbearingsmustcontroltheforwardandbackwardmovement.,FlywheelAheavyflywheelisattachedtotherearofthecrankshaftwithbolts.Thefunctionoftheflywheelistosmoothoutenginespeedandkeepthecrankshaftspinningbetweenpowerstrokes,insomeengines,theflywheelalsoservesasamountingsurfacefortheclutch.Theouterrimoftheflywheelhasalargeringattachedwithgearteethcutintoit.Theteethofthestartermotorengagetheseteethandspintheflywheeltocranktheengine.Whenanautomatictransmissionisused,thetorqueconverterassemblyworkswiththeflywheel.CamshaftThecamshaftisusedtoopenandclosethevalves.Thereisonecamonthecamshaftforeachvalveintheengine.Generallyonlyonecamshaftisusedinmostengines.Newerenginesareincreasinglyequippedwithtwoormorecamshafts(figure2-2).,Figure2-2Dualoverheadcamshaft（DOHC）drivenbyatootheddrivebelt,ValvesEachenginecylinderordinarilyhastwovalves.However,modernenginesoftenusefourvalvespercylinder(twointakeandtwoexhaust).Afewenginesusedinsmallervehicleshavethreeorfivevalvespercylinder:twointakevalvesandoneexhaustvalveorthreeintakevalvesandtwoexhaustvalves.Becausetheheadofanexhaustvalveoperatesattemperaturesupto1300(704),valvesaremadeofheat-resistantmetal.Inordertopreventburning,thevalvemustgiveoffheattothevalveseatandtothevalveguide.Thevalvemustmakegoodcontactwiththeseatandmustrunwithminimumclearanceintheguide.,ValveLiftersMechanicalvalveliftersareusuallymadeofcastiron.Thebottompartthatcontactsthecamshaftishardened.Someliftersarehollowtoreduceweight.Mostvalvetrainsthatcontainmechanicalliftershavesomeprovisionforadjustingclearance.Mechanicalvalvelifterswereusedinolderengines.Hydraulicvalveliftersperformthesamejobasmechanicallifters.However,hydraulicliftersareself-adjusting,operatewithnolifter-to-rockerarmclearance,andusesengineoilunderpressuretooperate.Hydraulicliftersarequietinoperation.3.EngineClassificationCycleClassificationEnginesareoftenclassifiedaccordingtocycle.Mostinternalcombustionpistonenginesuseatwo-orfour-strokecycle.Allmodernautomobileenginesusethefour-strokecycleengine.Thetwo-strokecycleengineperformstheintake,compression,firing,andexhaustsequenceinonerevolutionofthecrankshaft.,CylinderClassificationTheinlineenginehasitscylindersarrangedoneaftertheotherinastraightline.Theyareinavertical,ornearverticalposition.Mostmoderninlineenginesarefourcylinders.AV-typeengineplacestwobanksorrowsofcylindersatanangletoeachothergenerallyat60or90.TheV-typeenginehasseveraladvantages:shortlength,extrablockrigidity,ashort,heavycrankshaft,andlowprofilethatisconducivetolowhoodlines.Theshorterblockpermitsareductioninvehiclelengthwithnosacrificeinpassengerroom.ThehorizontalopposedengineislikeaV-typeengine,exceptthatbothbankslieinahorizontalplane.Theadvantagehereisanextremelylowoverallheight,whichmakesthisengineideallysuitedtoinstallationswherespaceislimited.,CoolingClassificationAsyouhavelearned,enginesareeitherliquid-cooledorair-cooled.Mostvehiclesuseliquid-coo