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英文.docx
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英文
DiaphragmSpringClutchDynamicCharacteristicTestBench
M.Velardocchia,G.Ercole,G.MattiazzoandS.Mauro
DepartmentofMechanics,PolitecnicodiTorino
F.Amisano
MagnetiMarelli–EngineControlDivision
Copyright©1999SocietyofAutomotiveEngineers,Inc.
ABSTRACT
Acrucialproblemindesigningaservoactuatedmanualtransmissionisposedbytheclutchtorquevariationswhichdependonoperatingconditionswithequalclutchpedalpositionandclutchslip.Anexperimentalstudyofthephenomenathatdeterminetorquevariationscanbeparticularlyusefulincopingwiththisproblem.Tothisend,theauthorsdevelopedapowertraintestbench.The
benchmakesitpossibletomeasurethemainmagnitudes(disctemperature,clutchslip,clamploadandclutchdiscdisplacement)whichcaninfluencetransmittedtorque.Testbenchlayoutisdescribed.Someexperimentalresultsarepresentedanddiscussed,withparticularattentiontotheproblemsconnectedwithclutchcontrollerdesign.
INTRODUCTION
Diaphragmspringclutchesarecommonlyusedinpassengercarsandlighttruckstocontroldrivelinedynamicsduringmanualsynchromeshgearshifts.Themanualtransmissionclutchsystemdataindicatedbymanufacturerssatisfythemaincustomerneedsregardingtransmissibletorqueandpower,clampload,dimensions,andsoon.Unfortunately,thesedataareincompleteasregardstheextenttowhichclutchsystemperformancedependsoncertainoperatingconditions(e.g.slippingvelocity,shiftingspeed,temperatureinsideclutchhousing,etc.)andcertainclutchparameters(e.g.frictioncoefficientdependenceonslippingandwear).Thislackofinformationisnotimportantinconventionalsynchromeshtransmissions,wherethedrivercancompensateforchangesintransmittedtorque.Bycontrast,athoroughknowledgeofthesefactorsisneededinordertodesigneffectivecontrollersforservoactuateddrivelineswhichretaintheconventionalpowertrainlayout,butwheretheclutchpedalisreplacedbyaservoactuator.Asthecontrollermustoperateinopenloopconditions,itmustcorrectlyforecasthowclutchtorquevarieswithoperatingconditions(transmissibilityfunction).Severalstudieshaveshownbysimulationthattheclutchoperatingstrategyusedtoimproveengagementqualitycanchangesignificantly
withclutchtransmissibility[1][2][3].Thisconsiderationhasattractedmanyauthors'attentiontoinvestigatingthetransmissibilityfunction.Thestateoftheartfordiaphragmspringdryclutchsystemsiswelldescribedin[4].Osanai[5],Pacey[6]andWeaver[7]studiedeffectsoftemperatureontransmissibilitycapabilityandheattransferinwetclutches.Zhi-pengHan[8]analyzedthetemperaturedistributiononclutchdiscs.Hiromichi[9]addressedtheproblemofclutchperformanceprediction.
Theaimoftheresearchcarriedoutbytheauthorsistodesignandtestacontrollerforaservoactuatedtransmission.Suchacontrollercanbeconsideredeffectiveifitprovidesperformanceequaltothatachievedbyahighlycompetentdriverwiththesamekindofcarineachpossibleoperatingcondition.Itshouldbeborneinmindthathowoptimalperformanceisdefinedwilldependontherequireddrivingmode,i.e.,sport,comfort,etc.Indesigningacontrollerofthistype,itisnecessarytobeabletocarryoutseveralkindsofexperimentaltests,bothtomeasuretransmittedclutchtorqueandtoassesscontrollerperformance.Thispaperdescribesthetestbenchdevelopedforthispurposeandtheresultsobtainedduringthefirsttests.Thetestbenchmakesitpossibletomeasureshaftspeeds,clampload,pushplatedisplacement,clutchdisctemperature,pedalpositionandtransmittedtorque.Thetransmissionshaftcanbeconnectedbyatorquecontrolledhydraulicmotor(dynamictests)orconstrainedtotheframe(statictests).
Thepaperpresentstheresultsofaninitialseriesofstatictestscarriedoutwithanearlierversionofthetestbenchwhichwasnotcapableofmeasuringclamploadandactualclutchdiscdisplacement.Uncertaintyininterpretingresultsmadeitnecessarytoimprovethebenchpriortocarryingoutnewtestswhichwillbethefirststepinthefuturedevelopmentoftheresearch.
TESTBENCHDESCRIPTION
Thetestbenchwasdesignedsothatthediaphragmspringclutchcanbetestedwhilesimulatingthemostcommonoperatingconditions,i.e.standingstartsandgearshifting.Thedrivenshaftisthusconnectedtoanhydraulictorquecontrolledmotorusedasabrakeandcontrolledinordertosimulatevehicleinertialload.Thedriveshaftispoweredbya45kWhydraulicmotorwhosespeedcanrange,throughareducer,from30to300rpm.
Amainmotor
(1)isconnectedtoareducer
(2)andfinallytoadriveshaft(3).Theclutchiscontainedinitshousing(4),whichalsoprovidesitsdrivingmechanism.Thedrivenshaft(5)islinkedtoabrakingmotor(6).Thebrakingmotorcanbereplacedwithafixedleverlinkedtotheframeiftestsaretobecarriedoutwiththedrivenshaftrestrained.Theclutchspringisoperatedbyapneumaticcylinderwhichsubstitutesthepedal.
Thebenchisequippedwithsensorstomeasurethemagnitudesthatcandefineandinfluencetheclutchtransmissibilityfunction.Thisfunctionisusuallyconsideredtobetheproductofthefrictioncoefficient,theclamploadandthemeanclutchdiscradius.Thefrictioncoefficient,thoughusuallyconsideredconstant,canactuallydependontemperatureandrelativespeed,whilethemeanradiuscanvarywithdiscwearandtemperature.Sensorswerethusarrangedinordertomeasuretransmittedtorque,relativespeed,actualcontactpressurebetweenclutchdiscandflywheelandtemperatureofthecontactsurfaces.
Thetransmittedtorqueismeasuredbystraingaugesinstalledonthedriveanddrivenshafts,andwhichthusmeasurethetorquetransmittedbyeachshaft.Ifthedrivenshaftisrestrainedbythelever,thetorquecanbemeasuredbyaloadcell.Relativespeediscomputedfromtheshafts’speed,measuredbytwopickupsfacingtheflywheelringgearandatonewheelshrink-fitonthe
transmissionshaftrespectively.
Clamploadcanbemeasuredbystraingaugesinstalledintheshanksofthescrewssecuringtheclutchdisctotheflywheel.Astheseboltsprovidethereactiontodiaphragmspringforce,theirtensionisproportionaltotheforceactingontheclutch.Toensureaccuratemeasurementandreducepossibleerror,threeboltslocated120°apartweresensorized,whilethreeadditionalunloadedsensorizedboltsinstalledinthesamepositionrelativetotheclutchdiscareusedforthermalcompensation.
Contactpressurebetweenthefrictionsurfacesismeasuredbyflatpiezoresistivesensorsinsertedbetweenthetwoclutchdiscs.Theroundsensorsare12mmindiameterand0.1mmthick.Sixsensorsarearrangedonthediscsurfaceatdifferentdistancesfromitscenterinordertoevaluatecontactpressureanddistribution.Unfortunately,thesesensorsshowhighhysteresisandlowaccuracy,andthemeasuredvaluesmustthusbecheckedagainstthetotalforcemeasuredbythesensorizedbolts.However,theycanprovideusefulinformationaboutcontactpressuredistribution.
Flywheelandclutchdisctemperatureismeasuredbythermocouplesplacedinspeciallyproducedseatsdistributedacrossthefrictionsurfaces.Threethermocouplesareinstalledontheclutchdiscatdifferentdistancesfromitscenterinordertoevaluatetemperaturedistributionalongtheradius.Similarly,threethermocouplesarelocatedalongtheradiusoftheflywheel.Afinalthermocoupleisplacedintheclutchhousingtomeasureambienttemperature.
Alaserdisplacementsensormeasuresthepositionofareflectingdiscrigidlyconnectedtothepushplateouterring.Displacementismeasuredrelativetothetransmissioncover.
Duetothelimitednumberofchannelsprovidedbyremotemeasurementhardware,itisnotcurrentlypossibletoacquireallthemeasurablemagnitudesduringeachtest.Accordingly,atestpolicywasselectedwherebytransmittedtorqueisalwaysmeasured,andsignalsregardingclamploadorflywheeltemperatureareacquiredinalternatetests.Similarly,signalsprovidedbycontactpressuresensorsmustbeacquiredinalternationwithsignalsfromclutchdiscthermocouples.Finally,themainmotorsupplypressureandthepositionofthepneumaticcylinderusedtooperatetheclutcharerecorded.
TESTPROCEDURE
Differentproceduresmaybeusedaccordingtotheaimofthetest.Specifically,itispossibletoteststandingstartsorgearshiftoperation.Testscanalsobecarriedoutwiththedrivenshaftconstrained,withthemainadvantageofprovidingawiderrangeofsignalsgiventhatremotemeasurementhardwareisnotneededonthedrivenshaftside.
Testscarriedoutwiththerotatingtransmissionshaftcanbedirectlyrelatedtoactualdrivingconditions,andareparticularlyusefulinstudyingclutchcontrolstrategies.
Bothstandingstartandgearshiftmaneuverscanbesimulated.Inbothcases,thebrakingtorquereferencevalueiscomputedinordertosimulatethevehicleinertialloadandthestaticloadsaccordingtothegearratio.Inparticular,thebrakingmotorcanbeusedasapowermotorfor
simulatingroadslopeduringuphillstandingstarts.
Themainmotortorquecanberegulatedthroughitspressurereducingvalve.
Bycontrast,testscarriedoutwiththeshaftconstrainedareusefulforclutchtransmissibilityfunctionidentification.Unfortunately,testscarriedoutwiththislayoutmaybeaffectedbyerrorsresultingfromthebuild-upofwearmaterialonthefrictionsurface,whichcansignificantlyinfluencethefrictioncoefficient.Whentheclutchdiscrotates,asinactualservice,particlesareejectedbycentrifugalforc
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