机械手外文翻译(英).docx

《机械手外文翻译(英).docx》由会员分享，可在线阅读，更多相关《机械手外文翻译(英).docx（21页珍藏版）》请在淘文阁 - 分享文档赚钱的网站上搜索。

1、机械手外文翻译(英)TheEffectofaViscousCouplingUsedasaFront-WheelDriveLimited-SlipDifferentialonVehicleTractionandHandling1ABCTRACTTheviscouscouplingisknownmainlyasadrivelinecomponentinfourwheeldrivevehicles.Developmentsinrecentyears,however,pointtowardtheprobabilitythatthisdevicewillbecomeamajorplayerinmains

2、treamfront-wheeldriveapplication.ProductionapplicationinEuropeanandJapanesefront-wheeldrivecarshavedemonstratedthatviscouscouplingsprovidesubstantialimprovementsnotonlyintractiononslipperysurfacesbutalsoinhandingandstabilityevenundernormaldrivingconditions.Thispaperpresentsaseriousofprovinggroundtes

3、tswhichinvestigatetheeffectsofaviscouscouplinginafront-wheeldrivevehicleontractionandhanding.Testingdemonstratessubstantialtractionimprovementswhileonlyslightlyinfluencingsteeringtorque.Factorsaffectingthissteeringtorqueinfront-wheeldrivevehiclesduringstraightlinedrivingaredescribed.Keyvehicledesign

4、parametersareidentifiedwhichgreatlyinfluencethecompatibilityoflimited-slipdifferentialsinfront-wheeldrivevehicles.Corneringtestsshowtheinfluenceoftheviscouscouplingontheselfsteeringbehaviorofafront-wheeldrivevehicle.Furthertestingdemonstratesthatavehiclewithaviscouslimited-slipdifferentialexhibitsan

5、improvedstabilityunderaccelerationandthrottle-offmaneuversduringcornering.2THEVISCOUSCOUPLINGTheviscouscouplingisawellknowncomponentindrivetrains.Inthispaperonlyashortsummaryofitsbasicfunctionandprincipleshallbegiven.Theviscouscouplingoperatesaccordingtotheprincipleoffluidfriction,andisthusdependent

6、onspeeddifference.AsshowninFigure1theviscouscouplinghasslipcontrollingpropertiesincontrasttotorquesensingsystems.Thismeansthatthedrivetorquewhichistransmittedtothefrontwheelsisautomaticallycontrolledinthesenseofanoptimizedtorquedistribution.Inafront-wheeldrivevehicletheviscouscouplingcanbeinstalledi

7、nsidethedifferentialorexternallyonanintermediateshaft.TheexternalsolutionisshowninFigure2.Thislayouthassomesignificantadvantagesovertheinternalsolution.First,thereisusuallyenoughspaceavailableintheareaoftheintermediateshafttoprovidetherequiredviscouscharacteristic.Thisisincontrasttothelimitedspacele

8、ftintodaysfront-axledifferentials.Further,onlyminimalmodificationtothedifferentialcarrierandtransmissioncaseisrequired.In-houseproductionofdifferentialsisthusonlyslightlyaffected.Introductionasanoptioncanbemadeeasilyespeciallywhentheshaftandtheviscousunitissuppliedasacompleteunit.Finally,theintermed

9、iateshaftmakesitpossibletoprovideforsideshaftsofequallengthwithtransverselyinstalledengineswhichisimportanttoreducetorquesteer(shownlaterinsection4).Thisspecialdesignalsogivesagoodpossibilityforsignificantweightandcostreductionsoftheviscousunit.GKNViscodriveisdevelopingalowweightandcostviscouscoupli

10、ng.Byusingonlytwostandardizedouterdiameters,standardizedplates,plastichubsandextrudedmaterialforthehousingwhichcaneasilybecuttodifferentlengths,itispossibletoutilizeawiderangeofviscouscharacteristics.AnexampleofthisdevelopmentisshowninFigure3.3TRACTIONEFFECTSAsatorquebalancingdevice,anopendifferenti

11、alprovidesequaltractiveefforttobothdrivingwheels.Itallowseachwheeltorotateatdifferentspeedsduringcorneringwithouttorsionalwind-up.Thesecharacteristics,however,canbedisadvantageouswhenadhesionvariationsbetweentheleftandrightsidesoftheroadsurface(split-)limitsthetorquetransmittedforbothwheelstothatwhi

12、chcanbesupportedbythelow-wheel.Withaviscouslimited-slipdifferential,itispossibletoutilizethehigheradhesionpotentialofthewheelonthehigh-surface.ThisisschematicallyshowninFigure4.Whenforexample,themaximumtransmittabletorqueforonewheelisexceededonasplit-surfaceorduringcorneringwithhighlateralaccelerati

13、on,aspeeddifferencebetweenthetwodrivingwheelsoccurs.Theresultingself-lockingtorqueintheviscouscouplingresistsanyfurtherincreaseinspeeddifferenceandtransmitstheappropriatetorquetothewheelwiththebettertractionpotential.ItcanbeseeninFigure4thatthedifferenceinthetractiveforcesresultsinayawingmomentwhich

14、triestoturnthevehicleintothelow-side,Tokeepthevehicleinastraightlinethedriverhastocompensatethiswithoppositesteeringinput.Thoughthefluid-frictionprincipleoftheviscouscouplingandtheresultingsofttransitionfromopentolockingaction,thisiseasilypossible,Theappropriateresultsobtainedfromvehicletestsareshow

15、ninFigure5.Reportedaretheaveragesteering-wheeltorqueTsandtheaveragecorrectiveoppositesteeringinputrequiredtomaintainastraightcourseduringaccelerationonasplit-trackwithanopenandaviscousdifferential.Thedifferencesbetweenthevalueswiththeopendifferentialandthosewiththeviscouscouplingarerelativelylargein

16、comparisontoeachother.However,theyaresmallinabsoluteterms.Subjectively,thesteeringinfluenceisnearlyunnoticeable.Thetorquesteerisalsoinfluencedbyseveralkinematicparameterswhichwillbeexplainedinthenextsectionofthispaper.4FACTORSAFFECTINGSTEERINGTORQUEAsshowninFigure6thetractiveforcesleadtoanincreasein

17、thetoe-inresponseperwheel.Fordifferingtractiveforces,Whichappearwhenacceleratingonsplit-withlimited-slipdifferentials,thetoe-inresponsechangesperwheelarealsodifferent.Unfortunately,thiseffectleadstoanundesirableturn-inresponsetothelow-side,i.e.thesameyawdirectionascausedbythedifferenceinthetractivef

18、orces.Reducedtoe-inelasticityisthusanessentialrequirementforthesuccessfulfront-axleapplicationofaviscouslimited-slipdifferentialaswellasanyothertypeoflimited-slipdifferential.GenerallythefollowingequationsapplytothedrivingforcesonawheelVTFF=With=TFTractiveForce=VFVerticalWheelLoad=UtilizedAdhesionCo

19、efficientThesedrivingforcesresultinsteeringtorqueateachwheelviathewheeldisturbancelevelarm“eandasteeringtorquedifferencebetweenthewheelsgivenbytheequation:eT=()loHhiHFFe-?cosWhere=eTSteeringTorqueDifferencee=WheelDisturbanceLevelArm=KingPinAnglehi=high-sidesubscriptlo=low-sidesubscriptInthecaseoffro

20、nt-wheeldrivevehicleswithopendifferentials,Tsisalmostunnoticeable,sincethetorquebias(loHhiTFF-/)isnomorethan1.35.Forapplicationswithlimited-slipdifferentials,however,theinfluenceissignificant.Thusthewheeldisturbanceleverarmeshouldbeassmallaspossible.DifferingwheelloadsalsoleadtoanincreaseinTesothedi

21、fferenceshouldalsobeassmallaspossible.WhentorqueistransmittedbyanarticulatedCV-Joint,onthedriveside(subscript1)andthedrivenside(subscript2),differingsecondarymomentsareproducedthatmusthaveareactioninaverticalplanerelativetotheplaneofarticulation.Themagnitudeanddirectionofthesecondarymoments(M)arecal

22、culatedasfollows(seeFigure8):DrivesideM1=vvTTtan/)2/tan(2-?DrivensideM2=vvTTtan/)2/tan(2+?WithT2=dynTrF?T=()systemJoTfint,2Wherev=VerticalArticulationAngle=ResultingArticulationAngledynr=DynamicWheelRadiusT=AverageTorqueLossThecomponentcos2?Mactsaroundtheking-pinaxis(seefigure7)asasteeringtorqueperw

23、heelandasasteeringtorquedifferencebetweenthewheelsasfollows:)tan/2/tan()sin/2/tan(cos22liwhiwTTTTT-+=?where=?TSteeringTorqueDifferenceW=WheelsidesubscriptItisthereforeapparentthatnotonlydifferingdrivingtorquebutalsodifferingarticulationscausedbyvariousdriveshaftlengthsarealsoafactor.Referringtothemo

24、ment-polygoninFigure7,therotationaldirectionofM2orTrespectivelychange,dependingonthepositionofthewheel-centertothegearboxoutput.ForthenormalpositionofthehalfshaftshowninFigure7(wheel-centerbelowthegearboxoutputjoint)thesecondarymomentsworkinthesamerotationaldirectionasthedrivingforces.Foramodifiedsu

25、spensionlayout(wheel-centerabovegearboxoutputjoint,i.e.vnegative)thesecondarymomentscounteractthemomentscausedbythedrivingforces.Thusforgoodcompatibilityofthefrontaxlewithalimited-slipdifferential,thedesignrequires:1)verticalbendingangleswhicharecenteredaround0=vornegative(0()loloDWhihiDWfLMLMfT/cos

26、-?=?Where=fTSteeringTorqueperWheel=?fTSteeringTorqueDifference=fJointDisturbanceLever=LConnectionshaft(halfshaft)LengthForsmallvaluesoff,whichshouldbeideallyzero,fT?isofminorinfluence.5EFFECTONCORNERINGViscouscouplingsalsoprovideaself-lockingtorquewhencornering,duetospeeddifferencesbetweenthedriving

27、wheels.Duringsteadystatecornering,asshowninfigure10,theslowerinsidewheeltendstobeadditionallydriventhroughtheviscouscouplingbytheoutsidewheel.Figure10:Tractiveforcesforafront-wheeldrivevehicleduringsteadystatecorneringThedifferencebetweentheTractiveforcesDfrandDflresultsinayawmomentMCOG,whichhastobe

28、compensatedbyahigherlateralforce,andhencealargerslipangleafatthefrontaxle.Thustheinfluenceofaviscouscouplinginafront-wheeldrivevehicleonself-steeringtendstowardsanundersteeringcharacteristic.Thisbehavioristotallyconsistentwiththehandlingbiasofmodernvehicleswhichallundersteerduringsteadystatecornerin

29、gmaneuvers.Appropriatetestresultsareshowninfigure11.Figure11:comparisonbetweenvehiclesfittedwithanopendifferentialandviscouscouplingduringsteadystatecornering.Theasymmetricdistributionofthetractiveforcesduringcorneringasshowninfigure10improvesalsothestraight-linerunning.Everydeviationfromthestraight

30、-linepositioncausesthewheelstorollonslightlydifferentradii.Thedifferencebetweenthedrivingforcesandtheresultingyawmomenttriestorestorethevehicletostraight-linerunningagain(seefigure10).Althoughthesedirectionaldeviationsresultinonlysmalldifferencesinwheeltravelradii,therotationaldifferencesespeciallya

31、thighspeedsarelargeenoughforaviscouscouplingfrontdifferentialtobringimprovementsinstraight-linerunning.Highpoweredfront-wheeldrivevehiclesfittedwithopendifferentialsoftenspintheirinsidewheelswhenacceleratingoutoftightcornersinlowgear.Invehiclesfittedwithlimited-slipviscousdifferentials,thisspinningi

32、slimitedandthetorquegeneratedbythespeeddifferencebetweenthewheelsprovidesadditionaltractiveeffortfortheoutsidedrivingwheel.thisisshowninfigure12Figure12:tractiveforcesforafront-wheeldrivevehiclewithviscouslimited-slipdifferentialduringaccelerationinabendTheaccelerationcapacityisthusimproved,particul

33、arlywhenturningoracceleratingoutofaT-junctionmaneuver(i.e.acceleratingfromastoppedpositionata“Tintersection-rightorleftturn).Figures13and14showtheresultsofaccelerationtestsduringsteadystatecorneringwithanopendifferentialandwithviscouslimited-slipdifferential.Figure13:accelerationcharacteristicsforaf

34、ront-wheeldrivevehiclewithanopendifferentialonwetasphaltataradiusof40m(fixedsteeringwheelanglethroughouttest).Figure14:AccelerationCharacteristicsforaFront-WheelDriveVehiclewithViscousCouplingonWetAsphaltataRadiusof40m(Fixedsteeringwheelanglethroughouttest)Thevehiclewithanopendifferentialachievesana

35、verageaccelerationof2.02/smwhilethem(limitedby/svehiclewiththeviscouscouplingreachesanaverageof2.32engine-power).Inthesetests,themaximumspeeddifference,causedbyspinningoftheinsidedrivenwheelwasreducedfrom240rpmwithopendifferentialto100rpmwiththeviscouscoupling.Duringaccelerationinabend,front-wheeldr

36、ivevehiclesingeneraltendtoundersteermorethanwhenrunningatasteadyspeed.Thereasonforthisisthereductionofthepotentialtotransmitlateralforcesatthefront-tiresduetoweighttransfertotherearwheelsandincreasedlongitudinalforcesatthedrivingwheels.Inanopenloopcontrol-circle-testthiscanbeseeninthedropoftheyawing

37、speed(yawrate)afterstartingtoaccelerate(Time0inFigure13and14).ItcanalsobetakenfromFigure13andFigure14thattheyawrateofthevehiclewiththeopendifferentialfalls-offmorerapidlythanforthevehiclewiththeviscouscouplingstartingtoaccelerate.Approximately2secondsafterstartingtoaccelerate,however,theyawratefall-

38、offgradientoftheviscous-coupledvehicleincreasesmorethanatthevehiclewithopendifferential.Thevehiclewiththelimitedslipfrontdifferentialthushasamorestableinitialreactionunderacceleratingduringcorneringthanthevehiclewiththeopendifferential,reducingitsundersteer.Thisisduetothehigherslipattheinsidedriving

39、wheelcausinganincreaseindrivingforcethroughtheviscouscouplingtotheoutsidewheel,whichisillustratedinFigure12.theimbalanceinthefrontwheeltractiveforcesresultsinayawmomentMactingindirectionoftheturn,counteringtheCSDundersteer.Whentheadhesionlimitsofthedrivingwheelsareexceed,thevehiclewiththeviscouscoup

40、lingundersteersmorenoticeablythanthevehiclewiththeopendifferential(here,2secondsafterstartingtoaccelerate).Onverylowfrictionsurfaces,suchassnoworice,strongerundersteeristobeexpectedwhenacceleratinginacurvewithalimitedslipdifferentialbecausethedrivingwheels-connectedthroughtheviscouscoupling-canbemad

41、etospinmoreeasily(power-under-steering).Thischaracteristiccan,however,beeasilycontroliedbythedriverorbyanautomaticthrottlemodulatingtractioncontrolsystem.Undertheseconditionsamucheasiertocontrolthanarear-wheeldrivecar.Whichcanexhibitpower-oversteeringwhenacceleratingduringcornering.Allthings,conside

42、red,theadvantagethroughthestabilizedaccelerationbehaviorofaviscouscouplingequippedvehicleduringaccelerationthesmalldisadvantageonslipperysurfaces.Throttle-offreactionsduringcornering,causedbyreleasingtheacceleratorsuddenly,usuallyresultinafront-wheeldrivevehicleturningintotheturn(throttle-offoverste

43、ering).High-poweredmodeleswhichcanreachhighlateralaccelerationsshowtheheaviestreactions.Thisthrottle-offreactionhasseveralcausessuchaskinematicinfluence,orasthevehicleattemptingtotravelonasmallercorneringradiuswithreducingspeed.Theessentialreason,however,isthedynamicweighttransferfromthereartothefro

44、ntaxle,whichresultsinreducedslip-anglesonthefrontandincreasedslip-anglesontherearwheels.Becausetherearwheelsarenottransmittingdrivingtorque,theinfluenceontherearaxleinthiscaseisgreaterthanthatofthefrontaxle.Thedrivingforcesonthefrontwheelsbeforethrottle-off(seeFigure10)becomeoverrunningorbrakingforc

45、esafterwards,whichisillustratedfortheviscousequippedvehicleinFigure15.Figure15:BarakingForcesforaFront-WheelDriveVehiclewithViscousLimited-SlipDifferentialImmediatelyafteraThrottle-offManeuverWhileCorneringAstheinnerwheelcontinuedtoturnmoreslowlythantheouterwheel,theviscouscouplingprovidestheouterwh

46、eelwiththelargerbrakingforcefB.Theforcedifferencebetweenthefront-wheelsappliedaroundthecenterofgravityofthevehiclecausesayawmomentGCM0thatcounteractsthenormalturn-inreaction.Whencorneringbehaviorduringathrottle-offmaneuveriscomparedforvehicleswithopendifferentialsandviscouscouplings,asshowninFigure1

47、6and17,thespeeddifferencebetweenthetwodrivingwheelsisreducedwithaviscousdifferential.Figure16:Throttle-offCharacteristicsforaFront-WheelDriveVehiclewithanopenDifferentialonWetAsphaltataRadiusof40m(OpenLoop)Figure17:Throttle-offCharacteristicsforaFront-WheelDriveVehiclewithViscousCouplingonWetAsphalt

48、ataRadiusof40m(OpenLoop)Theyawingspeed(yawrate),andtherelativeyawingangle(inadditiontotheyawanglewhichthevehiclewouldhavemaintainedincaseofcontinuedsteadystatecornering)showapronouncedincreaseafterthrottle-off(Time=0secondsinFigure14and15)withtheopendifferential.Boththesuddenincreaseoftheyawrateafte

49、rthrottle-offandalsotheincreaseoftherelativeyawanglearesignificantlyreducedinthevehicleequippedwithaviscouslimited-slipdifferential.Anormaldriverosafront-wheeldrivevehicleisusuallyonlyaccustomedtoneutralandundersteeringvehiclehandingbehavior,thedrivercanthenbesurprisedbysuddenandforcefuloversteeringreactionafteranabruptreleaseoft