差速器和后轴

DifferentialandRearAxlesThedifferentialispartoftherear-axle-housingassembly,whichincludesthedifferential,rearaxles,wheels,andbearings.Ifthecarweretobedriveninastraightlinewithouthavingtomaketurns,thennodifferentialwouldbenecessary.However,whenthecarroundsaturn,theouterwheelmusttravelfartherthantheinnerwheel.Thedifferentialpermitsthetworearwheelstorotatedifferentamountswhenthecargoesaroundaturn,whilestilldeliveringpowertobothrearwheels.Therearaxlesareattachedtothewheelsandhavebevelsidegearsontheirinnerends.Thedifferentialcaseisassembledontheleftaxlebutcanrotateonabearingindependentlyoftheaxle.Thedifferentialcasesupportsthedifferential-piniongearonashaft,andthisgearmesheswiththetwobevelgears.Theringgearisattachedtothedifferentialcasesothatthecaserotateswiththeringgearwhenthelaterisdrivenbythedrivepinion.Thedrivingpowerentersthedifferentialthroughthedrivepinionontheendofthepropellershaft.Thedrivepinionismeshedwithalargeringgearsothattheringgearrevolveswiththepinion.Attachedtotheringgear(throughthedifferentialcase)isadifferential-pinionshaftonwhichareassembledtwodifferential-piniongears.Eachrearcarwheelhasaseparateaxle,andtherearetwosidegearssplinedtotheinnerendsofthetwowheelaxles.Thetwodifferential-piniongearsmeshwiththesetwosidegears.Whenthecarisonastraightroad,thetwodifferential-piniongearsdonotrotateonthepinionshaft,buttheydoexertpressureonthetwosidegearssothatthesidegearsturnatthesamespeedastheringgear,causingbothrearwheelstoturnatthesamespeed,also.Thedifferentialcaseissupportedinthecarrierbytwotapered-rollersidebearings.Thisassemblycanbeadjustedfromsidetosidetoprovidetheproperbacklashbetweentheringgearandpinionandtherequiredsidebearingpreload.Thisadjustmentisachievedbythreadedbearingadjustersonsomeunitsandtheplacementofselectiveshimsandspacersonothers.Thedifferentialcaseissupportedinthecarrierbytwotapered-rollersidebearings.Thisassemblycanbeadjustedfromsidetosidetoprovidetheproperbacklashbetweentheringgearandpinionandtherequiredsidebearingpreload.Thisadjustmentisachievedbythreadedbearingadjustersonsomeunitsandtheplacementofselectiveshimsandspacersonothers.Transaxlefinaldrivegearsprovidethemeansfortransmittingtransmissionoutputtorquetothedifferentialsectionofthetransaxle.ThedifferentialsectionofthetransaxlehasthesamecomponentsasthedifferentialgearsinaRWDaxleandbasicallyoperateinthesameway.Thepowerflowintransverselymountedpowertrainsisinlinewiththewheelsandthereforethedifferentialunitdoesnotneedtoturnthepower90degrees.Whenthecarroundsacurve,theouterwheelmustturnfasterthantheinnerwheel.Topermitthis,thetwopiniongearsrotateontheirpinionshaft,transmittingmoreturningmovementtotheoutersidegearthantotheinnersidegear.Thus,thesidegearontheouter-wheelaxleturnsmorerapidlythanthesidegearontheinner-wheelaxle.Thispermitstheouterwheeltoturnmorerapidlywhilethecarisroundingthecurve.Therearetwobasictypesofaxle:deadaxlesandliveaxle.Thedeadaxledoesnotrotate;thewheelrotatesonit.Acommonexampleistheaxleonahorse-drawnwagon.Liveaxlesareattachedtothewheelsothatboththewheelandtheaxlerotatetogether.Liveaxlesareclassifiedaccordingtothemannerinwhichtheyaresupported:semi-floating,three-quarter-floating,andfull-floating.PropellerShaftandUniversalJointThepropellershaftisadriveshafttocarrythepowerfromthetransmissiontotherear-wheelaxles.Itconnectsthetransmissionmain,shaftcarriesthroughthepropellershafttothedifferentialattherearaxles.Rotarymotionofthetransmissionmainshaftcarriesthroughthepropellershafttothedifferential,causingtherearwheelstorotate.Thepropeller-shaftdesignmusttaketwofactsintoconsideration.First,theengineandtransmissionaremoreorlessrigidlyattachedtothecarframe.Second,therear-axlehousing(withwheelsanddifferential)isattachedtotheframebysprings.Astherearwheelsencounterirregularitiesintheroad,thespringscompressorexpand.Thischangestheangleofdriveandthedistancebetweenthetransmissionandthedifferential,andthepropellershaftmaytakecareofthesetwochanges.Thatistosay,astherearaxlehousing,withdifferentialandwheels,movesupanddown,theangelbetweenthetransmissionoutputshaftchanges.Thereasonthepropellershaftshortensastheangelincreasesisthattherearaxleanddifferentialmoveinashorterarcthanthepropellershaft.Thecenterpointoftheaxle-housingarcistherear-springorcontrol-armattachmenttotheframe.Inorderthatthepropellershaftmaytakecareofthesetwochanges,itmustincorporatetwoseparatetypesofdevice.Theremustbeoneormoreuniversaljointstopermitvariationsintheangelofdrive.Theremustalsobeaslipjointthatpermitstheeffectivelengthofthepropellershafttochange.Thepropellershaftmaybesolidorhollow,protectedbyanoutertubeorexposed.Someapplicationsincludebearingsatornearthepropellershaftcentertosupporttheshaft.Thetwo-sectionpropellerissupportedbyacenterbearingandcoupledtogetherbyuniversaljoints.Auniversaljointisessentiallyadouble-hingedjointconsistingoftwoY-shapedyokes,oneonthedrivingshaftandtheotheronthedrivenshaft,andacross-shapedmembercalledthespider.Thefourarmsofthespider,knownastrunnions,areassembledintobearingsintheendsofthetwoshaftyokes.Thedrivingshaftcausesthespidertorot