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外文翻译-- 汽车黏性连接器.doc

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外文翻译-- 汽车黏性连接器.doc

1TheEffectofaViscousCouplingUsedasaFrontWheelDriveLimitedSlipDifferentialonVehicleTractionandHandling1ABCTRACTTheviscouscouplingisknownmainlyasadrivelinecomponentinfourwheeldrivevehicles.Developmentsinrecentyears,however,pointtowardtheprobabilitythatthisdevicewillbecomeamajorplayerinmainstreamfrontwheeldriveapplication.ProductionapplicationinEuropeanandJapanesefrontwheeldrivecarshavedemonstratedthatviscouscouplingsprovidesubstantialimprovementsnotonlyintractiononslipperysurfacesbutalsoinhandingandstabilityevenundernormaldrivingconditions.Thispaperpresentsaseriousofprovinggroundtestswhichinvestigatetheeffectsofaviscouscouplinginafrontwheeldrivevehicleontractionandhanding.Testingdemonstratessubstantialtractionimprovementswhileonlyslightlyinfluencingsteeringtorque.Factorsaffectingthissteeringtorqueinfrontwheeldrivevehiclesduringstraightlinedrivingaredescribed.Keyvehicledesignparametersareidentifiedwhichgreatlyinfluencethecompatibilityoflimitedslipdifferentialsinfrontwheeldrivevehicles.Corneringtestsshowtheinfluenceoftheviscouscouplingontheselfsteeringbehaviorofafrontwheeldrivevehicle.Furthertestingdemonstratesthatavehiclewithaviscouslimitedslipdifferentialexhibitsanimprovedstabilityunderaccelerationandthrottleoffmaneuversduringcornering.2THEVISCOUSCOUPLINGTheviscouscouplingisawellknowncomponentindrivetrains.Inthispaperonlyashortsummaryofitsbasicfunctionandprincipleshallbegiven.Theviscouscouplingoperatesaccordingtotheprincipleoffluidfriction,andisthusdependentonspeeddifference.AsshowninFigure1theviscouscouplinghasslipcontrollingpropertiesincontrasttotorquesensingsystems.Thismeansthatthedrivetorquewhichistransmittedtothefrontwheelsisautomaticallycontrolledinthesenseofanoptimizedtorquedistribution.Inafrontwheeldrivevehicletheviscouscouplingcanbeinstalledinsidethedifferentialorexternallyonanintermediateshaft.TheexternalsolutionisshowninFigure2.Thislayouthassomesignificantadvantagesovertheinternalsolution.First,2thereisusuallyenoughspaceavailableintheareaoftheintermediateshafttoprovidetherequiredviscouscharacteristic.Thisisincontrasttothelimitedspaceleftintodaysfrontaxledifferentials.Further,onlyminimalmodificationtothedifferentialcarrierandtransmissioncaseisrequired.Inhouseproductionofdifferentialsisthusonlyslightlyaffected.Introductionasanoptioncanbemadeeasilyespeciallywhentheshaftandtheviscousunitissuppliedasacompleteunit.Finally,theintermediateshaftmakesitpossibletoprovideforsideshaftsofequallengthwithtransverselyinstalledengineswhichisimportanttoreducetorquesteershownlaterinsection4.Thisspecialdesignalsogivesagoodpossibilityforsignificantweightandcostreductionsoftheviscousunit.GKNViscodriveisdevelopingalowweightandcostviscouscoupling.Byusingonlytwostandardizedouterdiameters,standardizedplates,plastichubsandextrudedmaterialforthehousingwhichcaneasilybecuttodifferentlengths,itispossibletoutilizeawiderangeofviscouscharacteristics.AnexampleofthisdevelopmentisshowninFigure3.3TRACTIONEFFECTSAsatorquebalancingdevice,anopendifferentialprovidesequaltractiveefforttobothdrivingwheels.Itallowseachwheeltorotateatdifferentspeedsduringcorneringwithouttorsionalwindup.Thesecharacteristics,however,canbedisadvantageouswhenadhesionvariationsbetweentheleftandrightsidesoftheroadsurfacesplitμlimitsthetorquetransmittedforbothwheelstothatwhichcanbesupportedbythelowμwheel.Withaviscouslimitedslipdifferential,itispossibletoutilizethehigheradhesionpotentialofthewheelonthehighμsurface.ThisisschematicallyshowninFigure4.Whenforexample,themaximumtransmittabletorqueforonewheelisexceededonasplitμsurfaceorduringcorneringwithhighlateralacceleration,aspeeddifferencebetweenthetwodrivingwheelsoccurs.Theresultingselflockingtorqueintheviscouscouplingresistsanyfurtherincreaseinspeeddifferenceandtransmitstheappropriatetorquetothewheelwiththebettertractionpotential.ItcanbeseeninFigure4thatthedifferenceinthetractiveforcesresultsinayawingmomentwhichtriestoturnthevehicleintothelowμside,Tokeepthevehicleinastraightlinethedriverhastocompensatethiswithoppositesteeringinput.Thoughthefluidfrictionprincipleoftheviscouscouplingandtheresultingsoft3transitionfromopentolockingaction,thisiseasilypossible,TheappropriateresultsobtainedfromvehicletestsareshowninFigure5.ReportedaretheaveragesteeringwheeltorqueTsandtheaveragecorrectiveoppositesteeringinputrequiredtomaintainastraightcourseduringaccelerationonasplitμtrackwithanopenandaviscousdifferential.Thedifferencesbetweenthevalueswiththeopendifferentialandthosewiththeviscouscouplingarerelativelylargeincomparisontoeachother.However,theyaresmallinabsoluteterms.Subjectively,thesteeringinfluenceisnearlyunnoticeable.Thetorquesteerisalsoinfluencedbyseveralkinematicparameterswhichwillbeexplainedinthenextsectionofthispaper.4FACTORSAFFECTINGSTEERINGTORQUEAsshowninFigure6thetractiveforcesleadtoanincreaseinthetoeinresponseperwheel.Fordifferingtractiveforces,Whichappearwhenacceleratingonsplitμwithlimitedslipdifferentials,thetoeinresponsechangesperwheelarealsodifferent.Unfortunately,thiseffectleadstoanundesirableturninresponsetothelowμside,i.e.thesameyawdirectionascausedbythedifferenceinthetractiveforces.Reducedtoeinelasticityisthusanessentialrequirementforthesuccessfulfrontaxleapplicationofaviscouslimitedslipdifferentialaswellasanyothertypeoflimitedslipdifferential.GenerallythefollowingequationsapplytothedrivingforcesonawheelVTFFWithTFTractiveForceVFVerticalWheelLoadUtilizedAdhesionCoefficientThesedrivingforcesresultinsteeringtorqueateachwheelviathewheeldisturbancelevelarmeandasteeringtorquedifferencebetweenthewheelsgivenbytheequation△eTloHhiHFFecosWhere△eTSteeringTorqueDifferenceeWheelDisturbanceLevelArmKingPinAngle4hihighμsidesubscriptlolowμsidesubscriptInthecaseoffrontwheeldrivevehicleswithopendifferentials,△Tsisalmostunnoticeable,sincethetorquebiasloHhiTFF/isnomorethan1.35.Forapplicationswithlimitedslipdifferentials,however,theinfluenceissignificant.Thusthewheeldisturbanceleverarmeshouldbeassmallaspossible.Differingwheelloadsalsoleadtoanincreasein△Tesothedifferenceshouldalsobeassmallaspossible.WhentorqueistransmittedbyanarticulatedCVJoint,onthedrivesidesubscript1andthedrivensidesubscript2,differingsecondarymomentsareproducedthatmusthaveareactioninaverticalplanerelativetotheplaneofarticulation.ThemagnitudeanddirectionofthesecondarymomentsMarecalculatedasfollowsseeFigure8DrivesideM1vvTTtan/2/tan2DrivensideM2vvTTtan/2/tan2WithT2dynTrFTsystemJoTfint,,2WherevVerticalArticulationAngleResultingArticulationAngledynrDynamicWheelRadiusTAverageTorqueLossThecomponentcos2Mactsaroundthekingpinaxisseefigure7asasteeringtorqueperwheelandasasteeringtorquedifferencebetweenthewheelsasfollowstan/2/tansin/2/tancos22liwhiwTTTTTwhereTSteeringTorqueDifferenceWWheelsidesubscriptItisthereforeapparentthatnotonlydifferingdrivingtorquebutalsodiffering

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