机械毕业设计钢筋切断机外文翻译Word格式文档下载.docx
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BrianD.Kilmartin
SiemensVDOAutomotiveCorporation
ABSTRACT
AMagnetoelasticbasedNon-Contacting,Non-CompliantTorqueSensorisbeingdevelopedbySiemensVDOforautomotivetransmissionapplications.Suchasensorwouldbenefittheautomotiveindustrybyprovidingthefeedbackneededforprecisecomputercontroloftransmissiongearshiftingunderawiderangeofroadconditionsandwouldalsofacilitatecross-platformusageofacommontransmissionunit.
SiemensVDOhasprototypedtransmissiontorquesensorsoperatingontheprincipleofInverse-magnetostriction,alsoreferredtoastheInverse-JouleEffectandtheVillariEffect.Magnetostriction,firstdocumentedinthemid1800’s,isastructuralpropertyofmatterthatdefinesamaterial’sdimensionalchangesasaresultofexposuretoamagneticfield.Magnetostrictioniscausedwhentheatomsthatconstituteamaterialreorientinordertoaligntheirmagneticmomentswithanexternalmagneticfield.Thiseffectisquantifiedforaspecificmaterialbyitssaturationmagnetostrictionconstant,whichisavaluethatdescribesamaterial’smaximumchangeinlengthperunitlength.
Inverse-magnetostriction,conversely,defineschangesinamaterial’smagneticpropertiesinresponsetoappliedmechanicalforces.Materialthatishighlymagnetostrictiveandelasticinnatureisreferredtoasbeingmagnetoelastic.ThepremiseoftheSiemensVDOtorquesensordesignisthatamagnetoelasticmaterialcanbebondedtoacylindricalshaftandmagnetizedinitsmechanicalquiescentstatetocreateasense-element.Whileundertorque,principletensileandcompressivestressvectorsintheformofcounter-spiraling,mutuallyorthogonalhelicesdevelopintheshaftandareconveyedtothemagnetoelasticsense-elementgivingrisetoameasurablemagneticfieldchange.Themagneticfielddeviationthatarisesfromthemagnetoelasticsense-elementisdirectlyproportionaltothemagnitudeoftheimposedtorque.Ineffect,themagneticfieldismodulatedbytorque.Asensitivemagnetometerthentranslatesthefieldstrengthintoananalogvoltagesignal,therebycompletingthetorque-to-voltagetransducerfunction.
CriticaltothesuccessoftheSiemensVDOtorquesensordesignisanintimateattachmentofthesense-elementtothetorque-bearingmember.Inconsistenciesintheboundarybetweenthesense-elementandthetorque-bearingmemberwillresultinaberrantcouplingofstressesintothesense-elementmanifestinginperformancedegradation.Boundaryinconsistenciescanincludesuchimperfectionsasvoids,contaminates,lateralshearing,andlocalizedzonesofstresspre-load.Suchinhomogeneitiesmaybeinherenttoanattachmentmethoditselformaysubsequentlybecausedbysystemicallyrenderedmalformations.
Thermalspray,theprocesswheremetalparticlesaredepositedontoasubstratetoformacoating,wasusedtoaddresstheissueofsecurelyaffixingmagneticmaterialtoatorque-bearingmember.Inadditiontoachievingtheprerequisiteofanintimateandsecurebond,thethermalsprayprocesscanberegulatedsuchthatthedepositedmagneticmaterialispre-loadedwiththeinternalstressesneededtoinvoketheinverse-magnetostrictioneffect.
Summarizing,thepassivenatureofthemagneticsense-elementprovidesanintrinsicallysimplekernelfortheSiemensVDOtorquesensorthatmakesforahighlyreliableandstabledesign.Thethermalsprayprocessaddsrobustnesstothemechanicalaspectbypermittingtorqueexcursionstoanunprecedented±
2000%offullscale(perprototypevalidationtestingofcertainconstructs)withouttheneedforancillarytorquelimitingprotectiondevices.Furthermore,accuracy,repeatability,stability,lowhysteresis,rotationalpositionindifference,lowcostandamenabilitytothehigh-volumemanufacturingneedsoftheautomotivemarketplaceareallattributesofthistorquesensingtechnique.Whencoupledwithamagnetometerthatisgroundedinwell-establishedfluxgatetechnology,theresultantsensorisinherentlydependableandcanpotentiallyestablishanewstandardfortorquemeasuringsensors.
INTRODUCTION
Asiswellknown,automotivetransmissionsaredesignedtoalterthepowertransferratiobetweentheengineandthedrivewheelseffectivelyoptimizingengineloading.Theenginetherebyrunsinanarrowandefficientoperatingbandeventhoughthevehicletravelsoverawiderangeofspeeds.Forautomatictransmissions,shiftvalvesselectthegearratiobasedgenerallyonthethrottleposition,enginevacuumandtheoutputshaftgovernorvalvestate.Withtheadventofelectronicsensorsandcomputerizedenginecontrollers,transmissionshiftfunctionshavebeenmigratingtowardsclosed-loopoperationundersoftwareprocessingcontrol.Alongwiththisprogressioncametherealizationthatthetransmissionoutputtorquewouldprovideavaluablefeedbackparameterforshiftandtractioncontrolalgorithms.Themeasurementofoutputtorque,however,provedelusiveduetotheextremelyharshoperatingconditions.OneparticularSUVapplicationunderconsiderationrequired1%accuracyinmeasurementsofroughly2700Nmwithpossibletorqueexcursionof4700Nm;
allwhileexposedtotemperatureextremes-45to+160oC.
Onemethodformeasuringtorqueistoexaminethephysicalstressesthatdevelopinashaftwhenitissubjectedtoanend-to-endtwistingforce.Theprinciplestressesarecompressiveandtensileinnatureanddevelopalongthetwocounter-spiraling,mutuallyorthogonal45ohelices.Theyaredefinedbytheequation:
t=Tr/J
WhereTisthetorqueappliedtotheshaft,ristheshaftradiusandJisthepolarmomentofinertia.
Settingpr4/2=Jforasolidcylindricalshaftandr=d/2yields:
t=16T/pd
Onceagain,Tisthetorqueappliedtotheshaftanddistheshaftdiameter.
Furthermore,thedegreeoftwistexperiencedbytheshaftforagiventorqueisgivenby2:
q=32(LT)/(pd4G)
WhereListhelengthoftheshaft,Tistheappliedtoque,disthediameteroftheshaftandGisthemodulusofrigidityoftheshaft.Themodulusofrigiditydefinesthelevelofelasticityoftheshaftmaterial,thus,alowerGvaluewouldmanifestinashaftwithahigherdegreeoftwistforanygivenappliedtorque.
Torqueinducedstressesthatoccurintheshaftmaterialaretransferredintoanaffixedmagneticcoatingandgiverisetomeasurablechangesinitssurroundingmagneticfieldthataredirectlyproportionaltothemagnitudeoftheappliedtorque;
withthepolarityofthemagneticfield,i.e.,northorsouth,governedbythedirectionoftheappliedtorque.Inessence,thisisthepremiseoftorquesensingbymeansofinversemagnetostriction.
TORQUESENSOREMBODIMENT
Toeffectivelyinvoketheinverse-magnetostrictioneffect,themagneticmaterialmustbecorrectlypre-loadedwithstressanisotropyinitsquiescentstate.Inthecaseofacylindricallyshapedmagneticelement,theanisotropicforcesmustbecircumferential(i.e.,tangential)innatureandcanbeeithercompressiveortensile–dependingonthepolarityorsignofthematerial’ssaturationmagnetostrictionconstant.Achievingahomogenouspre-loadthroughoutthemagneticmaterialiscrucialifthesensoristoaccuratelyinterprettorqueregardlessofitsrotationalpositionwithinastationarymagnetometer.
POSITIVEMAGNETOELASTICDEVICES
Earliereffortstocreatesuchatorquesensingelementreliedonasenseelementmadeofmaterialwithapositivesaturationmagnetostrictionconstant.Thisembodimentwasrealizedwitharing-shapedmagnetoelasticelementmadefrom18%nickel-ironalloythatintrinsicallyrequirestensilecircumferentialpre-loading3.Suchapre-loadwasachievedbypressingtheringontoataperedareaofthebaseshaft–effectivelystretchingit.TheeffectoftensilestressonthemagnetichysteresisbehaviorisshowninFigure1wheretheremnantinductance,Br,nearlytriples.The“easy-axes”ofthemagneticdomainsaligncircumferentiallyduetotheanisotropydefinedbytheprincipaltensilestressvector.Whenmagneticallybiased,thesystemineffectoperatesasacircumferentiallyshortedmagnetwithBapproachingBrandHapproachingzero.
NEGATIVEMAGNETOELASTICDEVICES
Toadvancethestateoftheart,SiemensVDOAutomotivehasoptedforamagnetoelasticelementwithanegativesaturationmagnetostrictionconstant.Inthiscase,thealloyisveryhighinnickelcontentexhibitingasaturationmagnetostriction,ls,intherangeof-3e-5dl/landrequiresthestresspre-loadtobetangentiallycompressiveinnature.Toachievethisembodiment,themagnetoelasticmaterialthatconstitutesthesenseelementis“deposited”ontothebaseshaftusingahigh-velocity-oxygen-fuel(HVOF)thermalsprayprocess.Thecoatingthicknessisonly0.5mmwithanaxiallengthof25mm.Thesenseelementmaterialisendowedwithcompressivestressbymeansofprecisecontrolofthethermalsprayprocessparameters.Thisproprietaryproceduretransformsadepositionprocessthatnormallyconfersisotropicmaterialpropertiesintoonethatrenderstherequisitestressanisotropy.
PrototypeFabrication
MagnetoelasticElement
Thespecificationfortheshaftrequiresthemeasurementoftorquelevelsof2700Nmwithnodeleteriouseffectsfollowingexposuresofupto4700Nm.Operatingtemperatureis-45oCto160oC.
Byconvertingfromtheearliertorquesensor“pressed-onring”concepttoonebasedonamagnetoelasticmaterialwithanegativesaturationmagnetostrictionconstant,ls,thedesignisadvancedinseveralrespects.Primarily,itsresiliencyagainststress/corrosioncrackingisenhancedby1)