车辆工程专业 毕业设计外文翻译4Word文档下载推荐.docx

车辆工程专业 毕业设计外文翻译4Word文档下载推荐.docx

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Thereisnoclutchpedalinanautomatictransmissioncar.

Thereisnogearshiftinanautomatictransmissioncar.Onceyouputthetransmissionintodrive,everythingelseisautomatic.

Boththeautomatictransmission（plusitstorqueconverter）andamanualtransmission（withitsclutch）accomplishexactlythesamething,buttheydoitintotallydifferentways.Itturnsoutthatthewayanautomatictransmissiondoesitisabsolutelyamazing!

Inthisarticle,we'

llworkourwaythroughanautomatictransmission.We'

llstartwiththekeytothewholesystem:

planetarygearsets.Thenwe'

llseehowthetransmissionisputtogether,learnhowthecontrolsworkanddiscusssomeoftheintricaciesinvolvedincontrollingatransmission.

SomeBasics

Justlikethatofamanualtransmission,theautomatictransmission'

sprimaryjobistoallowtheenginetooperateinitsnarrowrangeofspeedswhileprovidingawiderangeofoutputspeeds.

Withoutatransmission,carswouldbelimitedtoonegearratio,andthatratiowouldhavetobeselectedtoallowthecartotravelatthedesiredtopspeed.Ifyouwantedatopspeedof80mph,thenthegearratiowouldbesimilartothirdgearinmostmanualtransmissioncars.

You'

veprobablynevertrieddrivingamanualtransmissioncarusingonlythirdgear.Ifyoudid,you'

dquicklyfindoutthatyouhadalmostnoaccelerationwhenstartingout,andathighspeeds,theenginewouldbescreamingalongnearthered-line.Acarlikethiswouldwearoutveryquicklyandwouldbenearlyundriveable.

Sothetransmissionusesgearstomakemoreeffectiveuseoftheengine'

storque,andtokeeptheengineoperatingatanappropriatespeed.

Thekeydifferencebetweenamanualandanautomatictransmissionisthatthemanualtransmissionlocksandunlocksdifferentsetsofgearstotheoutputshafttoachievethevariousgearratios,whileinanautomatictransmission,thesamesetofgearsproducesallofthedifferentgearratios.Theplanetarygearsetisthedevicethatmakesthispossibleinanautomatictransmission.

Gears

Thisautomatictransmissionusesasetofgears,calledacompoundplanetarygearset,thatlookslikeasingleplanetarygearsetbutactuallybehavesliketwoplanetarygearsetscombined.Ithasoneringgearthatisalwaystheoutputofthetransmission,butithastwosungearsandtwosetsofplanets.

Let'

slookatsomeoftheparts:

FirstGear

Infirstgear,thesmallersungearisdrivenclockwisebytheturbineinthetorqueconverter.Theplanetcarriertriestospincounterclockwise,butisheldstillbytheone-wayclutch（whichonlyallowsrotationintheclockwisedirection）andtheringgearturnstheoutput.Thesmallgearhas30teethandtheringgearhas72,sothegearratiois:

Ratio=-R/S=-72/30=-2.4:

1

Sotherotationisnegative2.4:

1,whichmeansthattheoutputdirectionwouldbeoppositetheinputdirection.Buttheoutputdirectionisreallythesameastheinputdirection--thisiswherethetrickwiththetwosetsofplanetscomesin.Thefirstsetofplanetsengagesthesecondset,andthesecondsetturnstheringgear;

thiscombinationreversesthedirection.Youcanseethatthiswouldalsocausethebiggersungeartospin;

butbecausethatclutchisreleased,thebiggersungearisfreetospinintheoppositedirectionoftheturbine

SecondGear

Thistransmissiondoessomethingreallyneatinordertogettherationeededforsecondgear.Itactsliketwoplanetarygearsetsconnectedtoeachotherwithacommonplanetcarrier.

Thefirststageoftheplanetcarrieractuallyusesthelargersungearastheringgear.Sothefirststageconsistsofthesun（thesmallersungear）,theplanetcarrier,andthering（thelargersungear）.

Theinputisthesmallsungear;

theringgear（largesungear）isheldstationarybytheband,andtheoutputistheplanetcarrier.sotheformulais:

1+R/S=1+36/30=2.2:

Theplanetcarrierturns2.2timesforeachrotationofthesmallsungear.Atthesecondstage,theplanetcarrieractsastheinputforthesecondplanetarygearset,thelargersungear（whichisheldstationary）actsasthesun,andtheringgearactsastheoutput,sothegearratiois:

1/（1+S/R）=1/（1+36/72）=0.67:

Togettheoverallreductionforsecondgear,wemultiplythefirststagebythesecond,2.2x0.67,togeta1.47:

1reduction.Thismaysoundwacky,butitworks.

ThirdGear

Mostautomatictransmissionshavea1:

1ratiointhirdgear.You'

llrememberfromtheprevioussectionthatallwehavetodotogeta1:

1outputislocktogetheranytwoofthethreepartsoftheplanetarygear.Withthearrangementinthis