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DesignconsiderationsforanautomotivemagnetorheologicalbrakeKeremKarakoca,EdwardJ.Park,a,andAfzalSulemanaaDepartmentofMechanicalEngineering,UniversityofVictoria,P.O.Box3055,STNCSC,Victoria,BC,CanadaV8W3P6Received10October2007;accepted22February2008.Availableonline11April2008.AbstractInthispaper,designconsiderationsforbuildinganautomotivemagnetorheological(MR)brakearediscussed.TheproposedbrakeconsistsofmultiplerotatingdisksimmersedinaMRfluidandanenclosedelectromagnet.Whencurrentisappliedtotheelectromagnet,theMRfluidsolidifiesasitsyieldstressvariesasafunctionofthemagneticfieldapplied.Thiscontrollableyieldstressproducesshearfrictionontherotatingdisks,generatingthebrakingtorque.Inthiswork,practicaldesigncriteriasuchasmaterialselection,sealing,workingsurfacearea,viscoustorquegeneration,appliedcurrentdensity,andMRfluidselectionareconsideredtoselectabasicautomotiveMRbrakeconfiguration.Then,afiniteelementanalysisisperformedtoanalyzetheresultingmagneticcircuitandheatdistributionwithintheMRbrakeconfiguration.Thisisfollowedbyamultidisciplinarydesignoptimization(MDO)proceduretoobtainoptimaldesignparametersthatcangeneratethemaximumbrakingtorqueinthebrake.AprototypeMRbrakeisthenbuiltandtestedandtheexperimentalresultsshowagoodcorrelationwiththefiniteelementsimulationpredictions.However,thebrakingtorquegeneratedisstillfarlessthanthatofaconventionalhydraulicbrake,whichindicatesthataradicalchangeinthebasicbrakeconfigurationisrequiredtobuildafeasibleautomotiveMRbrake.Keywords:Mechatronicdesign;Magnetorheologicalfluid;Automotivebrake;Magneticcircuit;Finiteelementanalysis;Multidisciplinarydesignoptimization;Brake-by-wireArticleOutline1.Introduction2.AnalyticalmodelingofMRbrake3.DesignofMRbrake3.1.Magneticcircuitdesign3.2.Materialselection3.2.1.Magneticproperties3.2.2.Structuralandthermalproperties3.3.Sealing3.4.Workingsurfacearea3.5.Viscoustorquegeneration3.6.Appliedcurrentdensity3.7.MRfluidselection4.FiniteelementmodelingoftheMRBrake5.Designoptimization6.Overviewofexperimentalsetup7.Experimentalresults7.1.Discussions8.ConclusionReferences1.IntroductionTheautomotiveindustryhasdemonstratedacommitmenttobuildsafer,cheaperandbetterperformingvehicles.Forexample,therecentlyintroduced“drivebywire”technologyhasbeenshowntoimprovetheexistingmechanicalsystemsinautomobiles.Inotherwords,thetraditionalmechanicalsystemsarebeingreplacedbyimprovedelectromechanicalsystemsthatareabletodothesametasksfaster,morereliablyandmoreaccurately.Inthispaper,anelectromechanicalbrake(EMB)prototypesuitablefor“brake-by-wire”applicationsispresented.Theproposedbrakeisamagnetorheologicalbrake(MRB)thatpotentiallyhassomeperformanceadvantagesoverconventionalhydraulicbrake(CHB)systems.ACHBsysteminvolvesthebrakepedal,hydraulicfluid,transferlinesandbrakeactuators(e.g.diskordrumbrakes).Whenthedriverpressesonthebrakepedal,themastercylinderprovidesthepressureinthebrakeactuatorsthatsqueezethebrakepadsontotherotors,generatingtheusefulfrictionforces(thusthebrakingtorque)tostopavehicle.However,theCHBhasanumberlimitations,including:(i)delayedresponsetime(200–300ms)duetopressurebuildupinthehydrauliclines,(ii)bulkysizeandheavyweightduetoitsauxiliaryhydrauliccomponentssuchasthemastercylinder,(iii)brakepadwearduetoitsfrictionalbrakingmechanism,and(iv)lowbrakingperformanceinhighspeedandhightemperaturesituations.TheMRBisapureelectronicallycontrolledactuatorandasaresult,ithasthepotentialtofurtherreducebrakingtime(thus,brakingdistance),aswellaseasierintegrationofexistingandnewadvancedcontrolfeaturessuchasanti-lockbrakingsystem(ABS),vehiclestabilitycontrol(VSC),electronicparkingbrake(EPB),adaptivecruisecontrol(ACC),aswellason-boarddiagnosticfeatures.Furthermore,reducednumberofcomponents,simplifiedwiringandbetterlayoutarealladditionalbenefits.Intheautomotiveindustry,companiessuchasDelphiCorp.andContinentalAutomotiveSystemshavebeenactivelyinvolvedinthedevelopmentofcommerciallyavailableEMBsasnextgenerationbrake-by-wiretechnology.Theseareaimedatpassengervehicleswithconventionalpowertrains,aswellasvehicleswithadvancedpowersources,likehybridelectric,fuelcellandadvancedbatteryelectricpropulsion(e.g.42Vplatform).Forexample,Delphihasrecentlyproposedaswitchedreluctance(SR)motor[1]asonepossibleactuationtechnologyforEMBapplications.AnothertypeofpassengervehicleEMBsthatanumberresearchgroupsandcompanieshavebeendevelopingiseddycurrentbrakes(ECBs),e.g.[2].WhileanECBisacompletelycontactlessbrakethatisperfectlysuitedforbrakingathighvehiclespeeds(asitsbrakingtorqueisproportionaltothesquareofthewheelspeed),however,itcannotgenerateenoughbrakingtorqueatlowvehiclespeeds.AbasicconfigurationofaMRBwasproposedbyParketal.[3]forautomotiveapplications.AsshowninFig.1,inthisconfiguration,arotatingdisk(3)isenclosedbyastaticcasing(5),andthegap(7)betweenthediskandcasingisfilledwiththeMRfluid.Acoilwinding(6)isembeddedontheperimeterofthecasingandwhenelectricalcurrentisappliedtoit,magneticfieldsaregenerated,andtheMRfluidinthegapbecomessolid-likeinstantaneously.TheshearfrictionbetweentherotatingdiskandthesolidifiedMRfluidprovi