EPS传感器010939.docx

EPS传感器010939.docx

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EPS传感器010939

2006-01-0939DevelopmentofaContactlessHalleffecttorquesensorforElectricPowerSteering

DidierANGLEVIELMovingMagnetTechnologiesS.A.DidierFRACHON,GéraldMASSONMovingMagnetTechnologiesS.A.

Copyright©2005SAEInternational

ABSTRACT

Inthispaper,wewillpresentaninnovativetorquesensordesignwhichcouldbepreferablyusedinElectricPowerAssistedSteering（EPASapplication.Thistorquesensorisanon-contactHalleffectdesign.Thespecificityofthisstructureisitsabilitytomeasuretheshiftanglebetweentworotatingshaftslinkedbyatorsionbar.Thismeasurementisdonewithstationaryelectroniccomponents.Thisuniquestructuregeneratesenoughmagneticfluxvariationtomeasureangularshiftsfrom+/-1°to+/-8°withlow-coststandardHallASICsavailablefromvarioussuppliers.Thistorquesensorhasconvincedautomotiveindustryduetoitsgoodperformances,itscompactdimensionandapricecompatiblewiththemarketexpectationforthisapplication.

Thispaperwillexplainthebasicmagneticprincipleofthistorquesensor,theimprovementswhichhaveleadtoastructurecompatiblewithautomotiveindustryrequirements,somemeasurementresultsandpossiblesensorintegrationintheapplication.

INTRODUCTION

Nowadays,forcostandpollutionreasons,thedevelopmentofnewvehiclesisstronglydrivenbyaresearchoffuelconsumptionreduction.OneinterestingwayforsuchfueleconomiesisthereplacementofcurrenthydraulicpowersteeringbyEPASusinghighpowerBrushlessDC（BLDCmotors.ThetypicalfueleconomyrealizedbyshiftingfromahydraulicpowersteeringtoanEPASisabout5percent.WiththeimprovementoftheBLDCmotorstructuresandtheincreaseoftheelectricpoweravailablewithbatteries,themarketsharesofEPASshouldgrowquicklyinthenextfewyears[1].

InordertodriveefficientlytheBLDCmotor,theECUrequiresaccurateinformationonthetorqueappliedbythedrivertothesteeringwheel.Thistorquesignalusuallycomesfromtheshiftmeasurementbetweentwoshaftslinkedbyalineartorsionbar.Themainconcerninthismeasurementisduetothefactthattheseshaftsarealsorotatingwiththesteeringwheelandtheintegrationofelectroniconrotatingpartsisdefinitelyablockingpoint.AnexampleofBLDCmotorandtorquesensortypicalintegrationonthesteeringcolumnisshownonthefollowingdrawing.TheBLDCexertsitstorquetothesteeringcolumnthroughawormgearmechanism.

Figure1:

ElectricPowerSteering

MovingMagnetTechnologies（MMThasdevelopedaninnovativelowcoststructureansweringalltherequirementsoftorquesensingforEPAS.Thistorquesensorisbasedonanon-contactHalleffectprincipleandusesstandardprogrammableHallASICsavailableonthemarket.MMThasappliedfortwopatentsregardingfirstabasicstructureofthistorquesensorandthenanoptimizeddesign[2][3].Thesetorquesensordesignsarepresentedhereafter.

Torquesensor

housing

BLDCmotor

BASICDESIGNANDSENSORPRINCIPLE

TheMMTtorquesensorbasicstructureisshownhereafter.

Figure2:

ExplodedviewoftheMMTtorquesensorThissensorismadeupofthefollowingsub-assemblies:

•Therotor（greyandredparts,fixedonone

rotaryshaftofthesteeringcolumn,ismadebyapluralityofpermanentmagnetsfixedonasoftferro-magneticyoke.

•Thestators（blueandyellowpartsarefixedon

thesecondrotaryshaftofthesteeringcolumn,linkedtothefirstonebyatorsionbar.Thesestatorsarefixedonetowardtheother.Theyaremadeofsoftferro-magneticmaterial.

•Oneortwo（forredundancyHallASICsfixed

stationaryonthehousing.TheHallprobeisinsertedinameasurementslotcreatedbetweenthetwostators.WiththeMMTdesign,wegenerateenoughfluxvariationtousetheHallASICsavailablefromMelexis（MLX90251orredundantMLX90277orMicronas（HAL8XX.

Thefollowingfigureshowsthesensorinaworking

configuration.

Figure3:

MMTtorquesensorbasicstructure

Onthesetwofirstviewsofthetorquesensor,therotorisrealizedwithmagnetsofthesamepolarity（redpartsalternatedwithferro-magneticareasfromtheyoke.Thismagnetconfigurationcouldbereplacedbyamoreindustrialringmagnetwithalternatednorthandsouth

polesonitssurfaceasshownbelow.

Figure4:

RotormadewithmultipolarringmagnetOnecoupleofnorthandsouthpolesofthemagnetisassociatedtoonetoothoneachstatortocreateanelementarysensorasshownbelow.

Figure5:

ViewofanelementarysensorinabeginningofthestrokepositionwithfluxlinesAmagneticfluxvariationisgeneratedinthestatorteethwhenthemagnettransitionsaremovinginfrontofthem.Thisfluxvariationisalinearfunctionofthemagnetangularpositionandwehavedemonstratedthefollowinganalyticalequation:

Where:

•Bmisthefluxmeasuredintheslotbetweentwo

statorteeth

•Bristhemagnetremanence

•Daistheaveragediameteroftheairgap•Listhemagnetthickness

•Θistheangularpositionofthemagnettransition•α1istheangularlengthofonestatorteeth•Fisthethicknessoftheslotbetweenthetwo

statorteeth

•σisthefluxleakagecoefficient•Eistheradialairgaplength•Histheteethradiallength

2stators（ferromagneticpartsfixed

onarotaryshaft

Rotor（ferro-magneticyoke+magnetsfixedona

rotaryshaft

Hallprobe+Electronic（fixedstationaryonthehousing

Statorteeth（oneofeach

stator

Magnetpolesoftherotor

Asshownonthepreviousfigures,inthissensor,wemultiplythenumberofelementarysensorsinordertoincreasethefluxvariationinthemeasurementslot.Thefluxvariationsgeneratedineachelementarysensorareintegratedinanexternaldisconeachstator.Thesetwodiscscreatearadialmeasurementslotinbetweenthestators.Bydesign,theinductiononagivenradiusinthemeasurementslotisconstantasshownonthe3D

simulationresultshereafter:

Figure6:

3Dsimulationresultshowingtheinductioninthemeasurementslot

MMThasdemonstratedthatananalyticalequationofthefluxvariationinthemeasurementslotis:

Where:

•Nisthenumberofelementarysensors

•Zistheaxialdimensionofthepermanent

magnet

•Smisthemeasurementsurface.

MMThasalsodevelopedsomerulesinordertosizetheangularlengthofthestatorteethaccordingtothestroketomeasureandthediameterofthesteeringcolumnonwhichwewillmountthesensor.

ThisfirststructurehasconvincedsomeautomotivepartnersofMMTwithitsperformancesandwehavestartedanewdevelopmentphaseinordertoimprovethesensorperformancesandusesomelower-costparts.

DESIGNIMPROVEMENTTOANOPTIMIZEDAUTOMOTIVESENSORDESIGN

Inordertoincreasethefluxinthemeasurementslot,agoodsolutionistocollectthefluxfromthestatorwithstationaryferro-magneticparts,andthenconcentratethisfluxontheHallASICwithareducedsurfacemeasurementslot.Thesepartsareshowninthefigurebelow.

Figure7:

Fluxcollector/concentrator

Theuseofthesefluxcollectors/concentratorsallowsasimplificationofthestatordesigntoL-shapestator.Theaxialcollectionofthemagneticfluxonthestatorcouldbedoneontheoutsideortheinsideofthediscfluxintegratingareaofthestator.Evenifanoutercollectionofthefluxleadstoalittleincreaseoftheaxiallengthofthesensor,MMTstronglyadvisesthissolution.Indeed,thisoutercollectionofthefluxdecreasesthefluxleakagebetweenthefluxcollector（18%increaseonthefluxvariationandthesensitivitytomagnettransitionrotatinginfrontoftheHallASICisalsodecreased.Thesestatormodificationsleadtothedesigninthefollowingfigure.

Figure8:

MMTdesignwithsimplifiedstatorsandexternalfluxcollector

Thesecondmodificationonthestatorshapehasbeendoneontheshapeoftheteeth.Indeed,inourfirstdesign,thestatorteethwereoverlappingthemagnetontheiraxialdirection.Inordertooptimizetheaxialdimensionofthesensor,thecollectionareaofonestator（discareawasaxiallyclosetotheendoftheteethoftheotherstator.Inthisproximityareabetweenbothstators,fluxleakagewasoccurring.Some3Dsimulationsandprototypemeasurementshaveshownthatshorteningtheteethofthestatorinvolvesanincreaseofthefluxvariationinthemeasurementslotwithoutanydeteriorationofothersensorperformances.3Dsimulationhasalsoshownthatthecloserwearefromthestatorfluxintegrationdiscarea,thehigheristheinductionandsotheleakagefromonetoothtothenextoneontheotherstator.Inordertoincreasethecrosssectionoftheteethwhenthefluxdensityincreases（decreaseoftheinductionintheteeth,wehavedesignedsometrapezoidalshapeteeth.Wehavealsovalidatedthisshapemodificationoftheteethwith3Dmagneticsimulationsandprototypemeasurements.Fluxcollectionarea

Fluxconcentrationareas

（redundantdesign

L-shapestators

Externalfluxcollection

Thecombinationofthesetwomodificationsoftheteethshapeleadstoa12%outputsignalincreaseinthemeasurementslot.Figurebelowshowstheevolutionof

thestatorshape.

Figure9:

Teethshapemodification

Thesestatorshapemodificationsleadtoapartwhichcouldbestampedandformedeasilyandwhichallowsalargesavinginweightascomparedwithpreviousdesign（typicallyabout50%.

Today,MMToptimizedtorquesensordesignforsteering

columnapplicationisshownonthefigurebelow:

Figure10:

OptimizedMMTtorquesensormagnetic

structure

PROTOTYPESMEASUREMENTRESULTS

Basedonthisoptimizedtorquesensor,MMThasdevelopedafamilyofdesignswiththesameoveralldimensions（magnet:

OD=37.5mm,ID=34.75mm,L=8mmforstrok