第5页共13页编号：时间：2021年x月x日书山有路勤为径，学海无涯苦作舟页码：第5页共13页HowAutomaticTransmissionsWorkIfyouhaveeverdrivenacarwithanautomatictransmission,thenyouknowthattherearetwobigdifferencesbetweenanautomatictransmissionandamanualtransmission:Thereisnoclutchpedalinanautomatictransmissioncar.Thereisnogearshiftinanautomatictransmissioncar.Onceyouputthetransmissionintodrive,everythingelseisautomatic.Boththeautomatictransmission(plusitstorqueconverter)andamanualtransmission(withitsclutch)accomplishexactlythesamething,buttheydoitintotallydifferentways.Itturnsoutthatthewayanautomatictransmissiondoesitisabsolutelyamazing!Inthisarticle,we'llworkourwaythroughanautomatictransmission.We'llstartwiththekeytothewholesystem:planetarygearsets.Thenwe'llseehowthetransmissionisputtogether,learnhowthecontrolsworkanddiscusssomeoftheintricaciesinvolvedincontrollingatransmission.SomeBasicsJustlikethatofamanualtransmission,theautomatictransmission'sprimaryjobistoallowtheenginetooperateinitsnarrowrangeofspeedswhileprovidingawiderangeofoutputspeeds.Withoutatransmission,carswouldbelimitedtoonegearratio,andthatratiowouldhavetobeselectedtoallowthecartotravelatthedesiredtopspeed.Ifyouwantedatopspeedof80mph,thenthegearratiowouldbesimilartothirdgearinmostmanualtransmissioncars.You'veprobablynevertrieddrivingamanualtransmissioncarusingonlythirdgear.Ifyoudid,you'dquicklyfindoutthatyouhadalmostnoaccelerationwhenstartingout,andathighspeeds,theenginewouldbescreamingalongnearthered-line.Acarlikethiswouldwearoutveryquicklyandwouldbenearlyundriveable.Sothetransmissionusesgearstomakemoreeffectiveuseoftheengine'storque,andtokeeptheengineoperatingatan第6页共13页第5页共13页编号：时间：2021年x月x日书山有路勤为径，学海无涯苦作舟页码：第6页共13页appropriatespeed.Thekeydifferencebetweenamanualandanautomatictransmissionisthatthemanualtransmissionlocksandunlocksdifferentsetsofgearstotheoutputshafttoachievethevariousgearratios,whileinanautomatictransmission,thesamesetofgearsproducesallofthedifferentgearratios.Theplanetarygearsetisthedevicethatmakesthispossibleinanautomatictransmission.GearsThisautomatictransmissionusesasetofgears,calledacompoundplanetarygearset,thatlookslikeasingleplanetarygearsetbutactuallybehavesliketwoplanetarygearsetscombined.Ithasoneringgearthatisalwaystheoutputofthetransmission,butithastwosungearsandtwosetsofplanets.Let'slookatsomeoftheparts:FirstGearInfirstgear,thesmallersungearisdrivenclockwisebytheturbineinthetorqueconverter.Theplanetcarriertriestospincounterclockwise,butisheldstillbytheone-wayclutch(whichonlyallowsrotationintheclockwisedirection)andtheringgearturnstheoutput.Thesmallgearhas30teethandtheringgearhas72,sothegearratiois:Ratio=-R/S=-72/30=-2.4:1Sotherotationisnegative2.4:1,whichmeansthattheoutputdirectionwouldbeoppositetheinputdirection.Buttheoutputdirectionisreallythesameastheinputdirection--thisiswherethetrickwiththetwosetsofplanetscomesin.Thefirstsetofplanetsengagesthesecondset,andthesecondsetturnstheringgear;thiscombinationreversesthedirection.Youcanseethatthiswouldalsocausethebiggersungeartospin;butbecausethatclutchisreleased,thebiggersungearisfreetospinintheoppositedirectionoftheturbineSecondGearThistransmissiondoessomethingreallyneatinordertogettherationeededforsecondgear.Itactsliketwoplanetarygearsetsconnectedtoeachotherwithacommonplanetcarrier.Thefirststageofthe...
