外文翻译外文原文：PASSAGEAPowerTrainThepowertrainservestwofunctions：ittransmitspowerfromtheenginetothedrivewheels,anditvariestheamountoftorque.Thepowertrainincludes：1.engine：thatproducespower；2.transmission：eithermanualorautomatic；3.clutch：usedonlyonmanualtransmission,ortorqueconverter.：usedonlyonautomatictransmission;4.driveshaft：thattransmitsthepowerfromtransmissiontodifferential；5.thatcarriesthepowertothetwowheelaxles.SeeFig.5-1.ManualtransmissionThefunctionofamanualtransmission,showninFig.5-2,istotransferenginepowertothedriveshaftandrearwheels.Gearsinsidethetransmissionchangethecar’sdrive-wheelspeedandtorqueinrelationtoenginespeedandtorque.Thiskeepstheengine’soutputmatchedascloseaspossibletovaryingroadspeedsandloads.Amanualtransaxle，shownintheFig.5-3.,isasingleunitcomposedofamanualtransmission,differential,anddriveaxles.Mostfront-wheel-drive（FWD）carsareequippedwithatransaxle.Suchtransaxlearealsofoundonsomefront-enginedorrear-wheel-drive（RWD）,four-wheel-drive（4WD）carsandonrear-enginedandrear-wheel-drivecars.Amanualtransmissionrequiresuseofaclutchtoapplyandremoveenginetorquetothetransmissioninputshaft.Theclutchallowsthistohapppengraduallysothatthecarcanbestartedfromacompletestop.Manualtransmissionusuallyhavefourorfivespeeds,andoftenhave“overdrive”,whichmeansthattheoutputshaftcanturnfasterthantheinputShaftforfueleconomyonthehighway.Whenyouuseit,itwillreducetheenginespeedbyone-third,whilemaintainingthesameroadspeed.ClutchDrivingacarwithamanualtransmission,youdepresstheclutch,selectagear,andreleasetheclutchwhileapplyingpowertogetthecartomove.Theclutchallowsenginepowertobeappliedgraduallywhenavehicleisstartingout,andinterruptspowertoavoidgearcrunchingwhenshifting.Engagingtheclutchallowspowertotransferfromtheenginetotransmissionanddrivewheel.Disengagingtheclutchstopsthepowertransferandallowstheenginetocontinueturningwithoutforcetothedrivewheels.Theclutchbasiccomponentsare：theflywheel,clutchdisk,pressureplate,releasebearingandlinkage.SeeFig.5-4.Theflywheelisboltedtothecrankshaftoftheengine.Itsmainfunctionistotransferenginetorquefromtheenginetothetransmission.Theclutchdiskisbasicallyasteelplate,coveredwithafrictionalmaterialthatgoesbetweentheflywheelandthepressureplate.Apressureplateisboltedtotheflywheel.Itincludesasheetmetalcover,heavyreleasesprings,ametalpressureringthatprovidesafrictionsurfacefortheclutchdisk.Thereleasebearingistheheartofclutchoperation.Whentheclutchpedalisdepressed,thethrow-outbearingmovestowardtheflywheel,pushinginthepressureplate’sreleasefingersandmovingthepressureplatefingersorleversagainstpressureplatespringforce.Thelinkagetransmitsandmultipliesthedriver’slegforcetotheforkoftheclutchpressureplate.Amechanicalclutchlinkageusuallyconsistsoftheclutchpedal,aseriesoflinkagerodsandarms,oracable.Ahydraulicclutchlinkagetypicallyincludesaclutchmastercylinderandreservoir,ahydrauliclineandaslavecylinder.AutomatictransmissionBothanautomatictransmissionandamanualtransmissionaccomplishexactlythesamething,buttheydoitintotallydifferentways.Thekeydifferencebetweenamanualandanautomatictransmissionsisthatthemanualtransmissionlocksandunlocksanddifferentsetsofgearstotheoutputshafttoachievethevariousgearratios,whileinanautomatictransmission,thesamesetofgearsproducesallofdifferentgearratios.Theplanetarygear-setisthedevicethatmakesthispossibleinanauto...
