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1JGHardt，DWSheaDriveaxle/differentialAllvehicleshavesometypeofdriveaxle/differentialassemblyincorporatedintothedriveline.Whetheritisfront,rearorfourwheeldrive,differentialsarenecessaryforthesmoothapplicationofenginepowertotheroad.PowerflowThedriveaxlemusttransmitpowerthrougha90°angle.Theflowofpowerinconventionalfrontengine/rearwheeldrivevehiclesmovesfromtheenginetothedriveaxleinapproximatelyastraightline.However,atthedriveaxle,thepowermustbeturnedatrightangles(fromthelineofthedriveshaft)anddirectedtothedrivewheels.Thisisaccomplishedbyapiniondrivegear,whichturnsacircularringgear.Theringgearisattachedtoadifferentialhousing,containingasetofsmallergearsthataresplinedtotheinnerendofeachaxleshaft.Asthehousingisrotated,theinternaldifferentialgearsturntheaxleshafts,whicharealsoattachedtothedrivewheels.2Fig1DriveaxleRear-wheeldriveRear-wheel-drivevehiclesaremostlytrucks,verylargesedansandmanysportscarandcoupemodels.Thetypicalrearwheeldrivevehicleusesafrontmountedengineandtransmissionassemblieswithadriveshaftcouplingthetransmissiontothereardriveaxle.Driveinthroughthelayoutofthebridge,thebridgedriveshaftarrangedverticallyinthesameverticalplane,andnotthedriveaxleshaft,respectively,intheirownsub-actuatorwithadirectconnection,buttheactuatorislocatedatthefrontorthebackoftheadjacentshaftofthetwobridgesisarrangedinseries.Vehiclebeforeandafterthetwoendsofthedrivingforceofthedriveaxle,isthesub-actuatorandthetransmissionthroughthemiddleofthebridge.Theadvantageisnotonlyareductionofthenumberofdriveshaft,andraisethedrivingaxleofthecommonpartsofeachother,andtosimplifythestructure,reducesthevolumeandquality.3Fig2Rear-wheel-driveaxleSomevehiclesdonotfollowthistypicalexample.SuchastheolderPorscheorVolkswagenvehicleswhichwererearengine,reardrive.Thesevehiclesusearearmountedtransaxlewithhalfshaftsconnectedtothedrivewheels.Also,somevehicleswereproducedwithafrontengine,reartransaxlesetupwithadriveshaftconnectingtheenginetothetransaxle,andhalfshaftslinkingthetransaxletothedrivewheels.DifferentialoperationInordertoremovethewheelaroundinthekinematicsduetothelackofco-ordinationaboutthewheeldiameterarisingfromadifferentorthesamerollingradiusofwheeltravelrequired,inter-wheelmotorvehiclesareequippedwithaboutdifferential,thelattertoensurethatthecardriverBridgeonbothsidesofthewheelwheninrangewithatriptothecharacteristicsofrotatingatdifferentspeedstomeettherequirementsofthevehiclekinematics.4Fig3PrincipleofdifferentialTheaccompanyingillustrationhasbeenprovidedtohelpunderstandhowthisoccurs.1.Thedrivepinion,whichisturnedbythedriveshaft,turnstheringgear.2.Theringgear,whichisattachedtothedifferentialcase,turnsthecase.3.Thepinionshaft,locatedinaboreinthedifferentialcase,isatrightanglestotheaxleshaftsandturnswiththecase.4.Thedifferentialpinion(drive)gearsaremountedonthepinionshaftandrotatewiththeshaft.5.Differentialsidegears(drivengears)aremeshedwiththepiniongearsandturnwiththedifferentialhousingandringgearasaunit.6.Thesidegearsaresplinedtotheinnerendsoftheaxleshaftsandrotatetheshaftsasthehousingturns.57.Whenbothwheelshaveequaltraction,thepiniongearsdonotrotateonthepinionshaft,sincetheinputforceofthepiniongearsisdividedequallybetweenthetwosidegears.8.Whenitisnecessarytoturnacorner,thedifferentialgearingbecomeseffectiveandallowstheaxleshaftstorotateatdifferentspeeds.Open-wheeldifferentialoneachgeneralusethesameamountoftorque.Todeterminethesizeofthewheeltorquetobeartwofactors:equipmentandfriction.Indryconditions,whenalotoffriction,thewheelbearingtorquebyenginesizeandgearrestrictionsarehoursinthefriction(suchasdrivingonice),isrestrictedtoamaximumtorque,sothatvehicleswillnotspinround.Soevenifthecarcanproducemoretorque,butalsoneedtohavesufficienttractiontotransfertorquetotheground.Ifyouincreasethethrottleafterthewheelsslip,itwillonlymakethewheelsspinfaster.Fig4ConventionaldifferentialLimited-slipandlockingdifferentialoperation6Fig5Limited-slipdifferentialDifferentialsettlementofacarintheunevenroadsurfaceandsteeringwheel-drivenspeedataboutthedifferentrequirements;butisfollowedbytheexistenceofdifferentialinthesidecarwheelskidcannotbeeffectivewhenthepowertransmission,thatis,thewheelslipcannotproducethedrivingforce,ratherthanspinthewheelanddoesnothaveenoughtorque.Goodnon-slipdifferentialsettlementofthecarwheelsskidonthesideofthepowertransmissionwhentheissue,thatis,lockingdifferential,sothatnolongerserveausefuldifferentialrightandleftsidesofthewheelcanbethesametorque.Limited-slipandlockingdifferentialoperationcanbedividedintotwomajorcategories：(1)mandatorylockingtypeinordinarydifferentiallockingenforcementagenciestoincrease,whenthesideofthewheelskidoccurs,thedrivercanbeelectric,pneumaticormechanicalmeanstomanipulatethelockingbodymeshingsetsofDIPShellwillbewiththeaxledifferentiallockintoone,thusthetemporarylossofdifferentialrole.Relativelysimplestructureinthisway,butitmustbeoperatedbythedriver,andgoodroadstostoplockingandrestoretheroleofdifferential.(2)self-lockingdifferentialinstalledintheoilviscosityorfrictionclutchcoupling,whenthesideofthewheelskidoccurswhenbot