外文翻译自动变速器如何工作Word格式.docx
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外文翻译自动变速器如何工作Word格式.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.Withthearrangementinth
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