Romax汽车自动变速箱建模分析

MODELLINGANDANALYSISOFAMODERNAUTOMATICTRANSMISSIONGEARBOXMODELLINGANDANALYSISOFAMODERNAUTOMATICTRANSMISSIONGEARBOXYSong,ATylee-Birdsall,ERoeloffzenRomaxTechnologyLtd,RutherfordHouse,HighfieldSciencePark,NottinghamNG72PZ,UKSUMMARYAnewapproachfor3Dmodellingandanalysisofamodernautomatictransmissionsystemispresentedinthispaper.Thegearpairs,planetarygearsystem,bearings,shaftsandclutchesarerepresentedasanalysisobjectsandtheplanetarycarriersandhousingarerepresentedasstiffnessqualityfiniteelementcomponents.TheyareallcombinedtogetherintoonewholehyperstaticsysteminRomaxDesigner.ThecomplexplanetarygearcarriersandgearboxhousingaremodelledbymeansofreducedstiffnessmatricescreatedinafiniteelementanalysispackageNastran.A6-speedautomaticgearboxwasmodelledinRomaxDesignerbasedonabovemethodandthefulloperatingdutycycleofthetransmissionhasbeeninputandusedfortheanalysis.Thismethodallowstodramaticallyreducethesizeofthemodelandcanthusbecarriedouttoatimescalethatenablesquickconceptdesignsaswellasresponsiveproblemsolvinginexistinggearboxes.1:CURRENTISSUESOFMODELLINGTRANSMISSIONSYSTEMAnautomatictransmissiongearboxisaverycomplexmechanicalsystemwhichincludesplanetarygeartrain,shafts,bearings,clutches,shiftingmechanismandgearboxhousing[1,2].Allthesecomponentsareconnectingwitheachotherthroughgearmeshing,bearingmountingandotherconnections.Thedifferentgearsareselectedbyswitchingonoroffacombinationofdifferentclutchesontheplanetarygeartrains.Thehousingisnormallymountedontheengineorchassisorboth.Allthosecomponentsareinteractingwitheachotherandhencewhenchangingcertainparametersinanycomponentwillinevitablyaffectothercomponents.Intheprocessoftransmissiondesign,itisimportanttooptimiseitconsideringthechangesintheseparametersbutatthesametimetomaintainornottocompromisetheperformanceofthetransmission’sinternalcomponents.ItisdifficulttoachieveMODELLINGANDANALYSISOFAMODERNAUTOMATICTRANSMISSIONGEARBOXthosetargetsusingconventionaltransmissionanalysismethodsinwhichthegearsandthehousingareanalysedseparatelyandtheinfluenceofhousingflexibilityongearmeshmisalignmentisobtainedbymakingaseriesofapproximations.Theseapproximations,e.g.linearbearings,rigidhousings,resultinaconsiderablereductioninaccuracy.Analternativewouldbetouseafullfiniteelement(FE)modelofthewholetransmissionsystem.However,eventhemostsophisticatedFEmodel,whichrequiresgreatexpertiseandinvolvesimmensetimeandsolvingcost,thereisnoguaranteethattheresultscanbereliedupon[3,4].Forafullmodeltoberealistic,itrequiresextensivemodelcorrelationforallcomponents.Atpresentitisarequirementtocorrelateindividualtransmissioncomponentinisolationwithexperimentedmodalanalysistechniques.Thishasseveraldisadvantages,forexample,aprototypeisrequiredforeachcomponent,andwhenthecorrelatedcomponentsareconnected,assumptionsaremadeabouttheirboundaryconditions.Thiscanresultinamodelwhichisnotanalogoustorealityandwouldrequirealargeamountof‘modelcorrelation’toyieldacceptableresults.TosimulatetheloadedFEcontactanalysisofasetofgearsusingsurface-to-surfacecontactelementsincurrentFEtechnologywillrequireagreatdealofeffort.Inordertoachieveanacceptableaccuracy,theelementsusedindefiningthetoothsurfaceshouldbesmallenoughtocapturethegearmeshingcharacteristics.Thusitrequiresaconsiderablesizemodelandagreatdealofcomputerresourcetosolvethenonlineartoothcontactanalysis.Imaginehalfadozenofgearpairsinsimultaneousmeshinginamodernautomatictransmission,themodellingeffortandthesolutionexpensearereallyabigchallenge,nottomentionthecomplexgearboxhousing,differenttypesofnonlinearbearingsandclutchcomponents.Inthispaper,anewapproachto3DmodellingandanalysisofamodernautomaticgearboxusingspecialisedtransmissionsoftwareRomaxDesigner,acommercialsoftwaredevelopedbyRomaxTechnologyLtd,ispresented.RomaxDesignerallowsmodellingandanalysisofacompleteautomatictransmissioninwhichgears,planetarygearsystem,bearingsandshaftsaremodelledasanalysisobjectswithcorrelationtovalidatedtests.RomaxDesignercancalculateallthegearmeshingpoints,forces,loaddistributionandtakeintoaccountalltheboundaryconnections.TheplanetarycarriersandhousingaremeshedinacommercialfiniteelementpackageVisual/Nastran.Thehousingfiniteelementmodeliscondensedtoareducedstiffnessmatrixandcoupledwiththeinternaltransmissionthroughthebearingnodes.Thetransmissionsystemmodelbuiltbythisapproachisverycompactcomparedtoconventionalfiniteelementmodels.Sincethegears,shafts,MODELLINGANDANALYSISOFAMODERNAUTOMATICTRANSMISSIONGEARBOXbearingsandclutchesarealldefinedasobjectsinRomaxDesigner,itismucheasierandfastertoobtainthese3Dcomponentsbyjustkeyinginthedesignparametersandeditingtheirattributes.Themodellingtimeforthosecomponentsandassembliesaresignificantlyreducedandanypossiblemistakes,whichmayinevitablyhappeninaconventionalmodellingprocess,canbeavoided.Theabovemodellingmethodisillustratedbyacasestudy.A6-speedmodernautomatictransmissionismodelledinRomaxDesigner(SeeFigure1)andafulldutycycleinaseriesofdifferentgearselectionsisanalysed.Figure2showsagraphicalrepresentationofthegearboxsystemdeflectionunderload.Thecasestudywasmodelledtodete