自动变速器的工作原理外文翻译中英文翻译外文文献翻译.docx

自动变速器的工作原理外文翻译中英文翻译外文文献翻译.docx

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自动变速器的工作原理外文翻译中英文翻译外文文献翻译

HowAutomaticTransmissionsWork

byKarimNice

IntroductiontoHowAutomaticTransmissionsWork

Ifyouhaveeverdrivenacarwithanautomatictransmission,thenyouknowthattherearetwobigdifferencesbetweenanautomatictransmissionandamanualtransmission:

Thereisnoclutchpedalinanautomatictransmissioncar.

Thereisnogearshiftinanautomatictransmissioncar.Onceyouputthetransmissionintodrive,everythingelseisautomatic.

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

AutomaticTransmissionImageGallery

Inthisarticle,we'llworkourwaythroughanautomatictransmission.We'llstartwiththekeytothewholesystem:

planetarygearsets.Thenwe'llseehowthetransmissionisputtogether,learnhowthecontrolsworkanddiscusssomeoftheintricaciesinvolvedincontrollingatransmission.

Justlikethatofamanualtransmission,theautomatictransmission'sprimaryjobistoallowtheenginetooperateinitsnarrowrangeofspeedswhileprovidingawiderangeofoutputspeeds.

PhotocourtesyDaimlerChrysler

Mercedes-BenzCLK,automatictransmission,cut-awaymodel

Withoutatransmission,carswouldbelimitedtoonegearratio,andthatratiowouldhavetobeselectedtoallowthecartotravelatthedesiredtopspeed.Ifyouwantedatopspeedof80mph,thenthegearratiowouldbesimilartothirdgearinmostmanualtransmissioncars.

You'veprobablynevertrieddrivingamanualtransmissioncarusingonlythirdgear.Ifyoudid,you'dquicklyfindoutthatyouhadalmostnoaccelerationwhenstartingout,andathighspeeds,theenginewouldbescreamingalongnearthered-line.Acarlikethiswouldwearoutveryquicklyandwouldbenearlyundriveable.

Sothetransmissionusesgearstomakemoreeffectiveuseoftheengine'storque,andtokeeptheengineoperatingatanappropriatespeed.

Thekeydifferencebetweenamanualandanautomatictransmissionisthatthemanualtransmissionlocksandunlocksdifferentsetsofgearstotheoutputshafttoachievethevariousgearratios,whileinanautomatictransmission,thesamesetofgearsproducesallofthedifferentgearratios.Theplanetarygearsetisthedevicethatmakesthispossibleinanautomatictransmission.

Let'stakealookathowtheplanetarygearsetworks.

PlanetaryGearsets&GearRatios

Whenyoutakeapartandlookinsideanautomatictransmission,youfindahuge

∙Aningeniousplanetarygearset

∙Asetofbandstolockpartsofagearset

∙Asetofthreewet-plateclutchestolockotherpartsofthegearset

∙Anincrediblyoddhydraulicsystemthatcontrolstheclutchesandbands

∙Alargegearpumptomovetransmissionfluidaround

Thecenterofattentionistheplanetarygearset.Aboutthesizeofacantaloupe,thisonepartcreatesallofthedifferentgearratiosthatthetransmissioncanproduce.Everythingelseinthetransmissionistheretohelptheplanetarygearsetdoitsthing.ThisamazingpieceofgearinghasappearedonHowStuffWorksbefore.Youmayrecognizeitfromtheelectricscrewdriverarticle.Anautomatictransmissioncontainstwocompleteplanetarygearsetsfoldedtogetherintoonecomponent.SeeHowGearRatiosWorkforanintroductiontoplanetarygearsets.

Fromlefttoright:

theringgear,planetcarrier,andtwosungears

Anyplanetarygearsethasthreemaincomponents:

∙Thesungear

∙Theplanetgearsandtheplanetgears'carrier

∙Theringgear

Eachofthesethreecomponentscanbetheinput,theoutputorcanbeheldstationary.Choosingwhichpieceplayswhichroledeterminesthegearratioforthegearset.Let'stakealookatasingleplanetarygearset.

Oneoftheplanetarygearsetsfromourtransmissionhasaringgearwith72teethandasungearwith30teeth.Wecangetlotsofdifferentgearratiosoutofthisgearset.

Input

Output

Stationary

Calculation

GearRatio

A

Sun（S）

PlanetCarrier（C）

Ring（R）

1+R/S

3.4:

1

B

PlanetCarrier（C）

Ring（R）

Sun（S）

1/（1+S/R）

0.71:

1

C

Sun（S）

Ring（R）

PlanetCarrier（C）

-R/S

-2.4:

1

Also,lockinganytwoofthethreecomponentstogetherwilllockupthewholedeviceata1:

1gearreduction.Noticethatthefirstgearratiolistedaboveisareduction--theoutputspeedisslowerthantheinputspeed.Thesecondisanoverdrive--theoutputspeedisfasterthantheinputspeed.Thelastisareductionagain,buttheoutputdirectionisreversed.Thereareseveralotherratiosthatcanbegottenoutofthisplanetarygearset,butthesearetheonesthatarerelevanttoourautomatictransmission.Youcantrytheseoutintheanimationbelow:

Sothisonesetofgearscanproduceallofthesedifferentgearratioswithouthavingtoengageordisengageanyothergears.Withtwoofthesegearsetsinarow,wecangetthefourforwardgearsandonereversegearourtransmissionneeds.We'llputthetwosetsofgearstogetherinthenextsection.

CompoundPlanetaryGearset

Thisautomatictransmissionusesasetofgears,calledacompoundplanetarygearset,thatlookslikeasingleplanetarygearsetbutactuallybehavesliketwoplanetarygearsetscombined.Ithasoneringgearthatisalwaystheoutputofthetransmission,butithastwosungearsandtwosetsofplanets.

Let'slookatsomeoftheparts:

Howthegearsinthetransmissionareputtogether

Lefttoright:

theringgear,planetcarrier,andtwosungears

Thefigurebelowshowstheplanetsintheplanetcarrier.Noticehowtheplanetontherightsitslowerthantheplanetontheleft.Theplanetontherightdoesnotengagetheringgear--itengagestheotherplanet.Onlytheplanetontheleftengagestheringgear.

Planetcarrier:

Notethetwosetsofplanets.

Nextyoucanseetheinsideoftheplanetcarrier.Theshortergearsareengagedonlybythesmallersungear.Thelongerplanetsareengagedbythebiggersungearandbythesmallerplanets.

Insidetheplanetcarrier:

Notethetwosetsofplanets.

AutomaticTransmissionGears

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（counterclockwise）.

SecondGear

Thistransmissiondoessomethingreallyneatinordertogettherationeededforsecondgear.Itactsliketwoplanetarygearsetsconnectedtoeachotherwithacommonplanetcarrier.

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

Theinputisthesmallsungear;theringgear（largesungear）isheldstationarybytheband,andtheoutputistheplanetcarrier.Forthisstage,withthesunasinput,planetcarrierasoutput,andtheringgearfixed,theformulais:

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

1

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

1/（1+S/R）=1/（1+36/72）=0.67:

1

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

1reduction.Thismaysoundwacky,butitworks.

ThirdGear

Mostautomatictransmissionshavea1:

1ratiointhirdgear.You'llrememberfromtheprevioussectionthatallwehavetodotogeta1:

1outputislocktogetheranytwoofthethreepartsoftheplanetarygear.Withthearrangementinthisgearsetitiseveneasier--allwehavetodoisengagetheclutchesthatlockeachofthesungearstotheturbine.

Ifbothsungearsturninthesamedirection,theplanetgearslockupbecausetheycanonlyspininoppositedirections.Thislockstheringgeartotheplanetsandcauseseverythingtospinasaunit,producinga1:

1ratio.

Overdrive

Bydefinition,anoverdrivehasafasteroutputspeedthaninputspeed.It'saspeedincrease--theoppositeofareduction.Inthistransmission,engagingtheoverdriveaccomplishestwothingsatonce.IfyoureadHowTorqueConvertersWork,youlearnedaboutlockuptorqueconverters.Inordertoimproveefficiency,somecarshaveamechanismthatlocksupthetorqueconvertersothattheoutputoftheenginegoesstraighttothetransmission.

Inthistransmission,whenoverdriveisengaged,ashaftthatisattachedtothehousingofthetorqueconverter（whichisboltedtotheflywheeloftheengine）isconnectedbyclutchtotheplanetcarrier.Thesmallsungearfreewheels,andthelargersungearisheldbytheoverdriveband.Nothingisconnectedtotheturbine;theonlyinputcomesfromtheconverterhousing.