汽車專業(yè)英語讀譯教程 第3版 教案 UNIT 6 ENGINE ELECTRICAL SYSTEMS

授課題目UNIT9

AUTOMATICTRANSMISSIONS

TEXTA

AutomaticTransmission(AT)授課類型理論課首次授課時(shí)間學(xué)時(shí)2學(xué)時(shí)教學(xué)目標(biāo)1、自動(dòng)變速箱扭矩變矩器的組成和原理的英文表達(dá)；2、液壓控制系統(tǒng)和電子控制系統(tǒng)。重點(diǎn)與難點(diǎn)重點(diǎn)：自動(dòng)變速箱扭矩變矩器的組成和原理的英文難點(diǎn)：液壓控制系統(tǒng)和電子控制系統(tǒng)。教學(xué)手段與方法多媒體教學(xué)教學(xué)過程：（包括授課思路、過程設(shè)計(jì)、講解要點(diǎn)及各部分具體內(nèi)容、時(shí)間分配等）1.授課思路在學(xué)習(xí)了前置課程之后，通過專業(yè)英語的學(xué)習(xí)，進(jìn)行與汽車相關(guān)技術(shù)結(jié)構(gòu)原理的中文英文對(duì)接，培養(yǎng)和提高英文專業(yè)資料（信息）的閱讀能力，從而為與專業(yè)英語密切相關(guān)的后續(xù)課程奠定了必要的基礎(chǔ)。2.過程設(shè)計(jì)：（1）課程內(nèi)容簡(jiǎn)介（5分鐘）（2）導(dǎo)入新課（15分鐘）。（3）新課內(nèi)容（75分鐘）教師根據(jù)學(xué)生學(xué)習(xí)的情況，對(duì)課程內(nèi)容的重點(diǎn)和難點(diǎn)進(jìn)行講解。（4）課程小結(jié)（5分鐘）3.授課內(nèi)容：Intoday'sautomobile,theautomatictransmissionisbyfarthemostcomplicatedmechanicalcomponent.Itisatypeoftransmissionthatshiftsitself.Automatictransmissionortransaxlehasfourbasicsystems-atorqueconverter,agearsystem,ahydraulicsystemandanelectronicsystem(Fig.9-1).TORQUECONVERTERThetorqueconverterreplacestheconventionalclutch.Ithasthreefunctions:1.Itallowstheenginetoidlewiththevehicleatastandstill,evenwiththetransmissionortransaxleingear[1].2.Itallowsthetransmissionortransaxletoshiftfromrange-to-rangesmoothly,withoutrequiringthatthedriverclosethethrottleduringtheshift.3.Itmultipliesenginetorquetoanincreasingextentasvehiclespeeddropsandthrottleopeningisincreased.Thishastheeffectofmakingthetransmissionortransaxlemoreresponsiveandreducestheamountofshiftingrequired.Thetorqueconverterisametalcasewhichisshapedlikeaspherethathasbeenflattenedonoppositesides,itisboltedtotherearendoftheengine'scrankshaft.Generally,theentiremetalcaserotatesatenginespeedandservesastheengine'sflywheel.Thecasecontainsthreesetsofblades(Fig.9-2).Onesetisattacheddirectlytothecase.Thissetformsthetorusorpump.Anothersetisdirectlyconnectedtotheoutputshaft,andformstheturbine.Thethirdsetismountedonahubwhich,inturn,ismountedonastationaryshaftthroughaone-wayclutch.Thisthirdsetisknownasthestator.Apump,whichisdrivenbytheconverterhubatenginespeed,keepsthetorqueconverterfullofautomatictransmissionfluidatalltimes.Fluidflowscontinuouslythroughtheunittoprovidecooling.Underlowspeedacceleration,thetorqueconverterfunctionsasfollows:Thetorusisturningfasterthantheturbine.Itpicksupfluidatthecenteroftheconverterand,throughcentrifugalforce,slingsitoutward.Sincetheouteredgeoftheconvertermovesfasterthantheportionsatthecenter,thefluidpicksupspeed.Thefluidthenenterstheouteredgeoftheturbineblades;itthentravelsbacktowardthecenteroftheconvertercasealongtheturbineblades.Inimpingingupontheturbineblades,thefluidlosestheenergypickedupinthetorus.Ifthefluidwasnowreturneddirectlyintothetorus,bothhalvesoftheconverterwouldhavetoturnatapproximatelythesamespeedatalltimes,andtorqueinputandoutputwouldbothbethesame.Inflowingthroughthetorusandturbine,thefluidpicksuptwotypesofflow,orflowintwoseparatedirections.Itflowsthroughtheturbineblades,anditspinswiththeengine.Thestator,whosebladesarestationarywhenthevehicleisbeingacceleratedatlowspeeds,convertsonetypeofflowintoanother[2].Insteadofallowingthefluidtoflowstraightbackintothetorus,thestator'scurvedbladesturnthefluidalmost90°towardthedirectionofrotationoftheengine.Thusthefluiddoesnotflowasfasttowardthetorus,butisalreadyspinningwhenthetoruspicksitup.Thishastheeffectofallowingthetorustoturnmuchfasterthantheturbine.Thisdifferenceinspeedmaybecomparedtothedifferenceinspeedbetweenthesmallerandlargergearsinanygeartrain.Theresultisthatenginepoweroutputishigher,andenginetorqueismultiplied.Asthespeedoftheturbineincreases,thefluidspinsfasterandfasterinthedirectionofenginerotation.Asaresult,theabilityofthestatortoredirectthefluidflowisreduced.Undercruisingconditions,thestatoriseventuallyforcedtorotateonitsone-wayclutchinthedirectionofenginerotation.Undertheseconditions,thetorqueconverterbeginstobehavealmostlikeasolidshaft,withthetorusandturbinespeedsbeingalmostequal.PLANETARYGEARTheabilityofthetorqueconvertertomultiplyenginetorqueislimited.Also,theunittendstobemoreefficientwhentheturbineisrotatingatrelativelyhighspeeds.Therefore,aplanetarygearboxisusedtocarrythepoweroutputoftheturbinetothedriveshaft.Planetarygearsfunctionverysimilarlytoconventionaltransmissiongears.However,theirconstructionisdifferentinthatthreeelementsmakeuponegearsystem,and,inthatallthreeelementsaredifferentfromoneanother[3].Thethreeelementsare:anoutergearthatisshapedlikeahoop,withteethcutintotheinnersurface;asungear,mountedonashaftandlocatedattheverycenteroftheoutergear;andasetoffourplanetgears,heldbypinsinaring-likeplanetcarrier,meshingwithboththesungearandtheoutergear（Fig.9-3）.Eithertheoutergearorthesungearmaybeheldstationary,providingmorethanonepossibletorquemultiplicationfactorforeachsetofgears.Also,ifallthreegearsareforcedtorotateatthesamespeed,thegearsetforms,ineffect,asolidshaft.Mostautomaticsusetheplanetarygearstoprovidevariousreductionsratios.Bandsandclutchesareusedtoholdvariousportionsofthegearsetstothetransmissioncaseortransaxlecaseortotheshaftonwhichtheyaremounted[4].Shiftingisaccomplished,then,bychangingtheportionofeachplanetarygearsetwhichisheldtothecaseortotheshaft.Thehydraulicpressureusedtooperatetheservoscomesfromthemainoilpump.Thisfluidischanneledtothevariousservosthroughtheshiftvalves.Thereisgenerallyamanualshiftvalvewhichisoperatedbytheselectorleverandanautomaticshiftvalveforeachautomaticupshiftthetransmissionortransaxleprovides.Therearetwopressureswhichaffecttheoperationofthesevalves.Oneisthegovernorpressurewhichisaffectedbyvehiclespeed.Theotheristhemodulatorpressurewhichisaffectedbyintakemanifoldvacuumorthrottleposition.Governorpressureriseswithanincreaseinvehiclespeed,andmodulatorpressurerisesasthethrottleisopenedwider.Byrespondingtothesetwopressures,theshiftval