1ElectronicpowersteeringsystemWhatitisElectricallypoweredsteeringusesanelectricmotortodriveeitherthepowersteeringhydraulicpumporthesteeringlinkagedirectly.Thepowersteeringfunctionisthereforeindependentofenginespeed,resultinginsignificantenergysavings.Howitworks:Conventionalpowersteeringsystemsuseanengineaccessorybelttodrivethepump,providingpressurizedfluidthatoperatesapistoninthepowersteeringgearoractuatortoassistthedriver.Inelectro-hydraulicsteering,oneelectricallypoweredsteeringconceptusesahighefficiencypumpdrivenbyanelectricmotor.Pumpspeedisregulatedbyanelectriccontrollertovarypumppressureandflow,providingsteeringeffortstailoredfordifferentdrivingsituations.Thepumpcanberunatlowspeedorshutofftoprovideenergysavingsduringstraightaheaddriving(whichismostofthetimeinmostworldmarkets).Directelectricsteeringusesanelectricmotorattachedtothesteeringrackviaagearmechanism(nopumporfluid).Avarietyofmotortypesandgeardrivesispossible.Amicroprocessorcontrolssteeringdynamicsanddrivereffort.Inputsincludevehiclespeedandsteering,wheeltorque,angularpositionandturningrate.WorkingInDetail:Asteeringsensorislocatedontheinputshaftwhereitentersthegearboxhousing.Thesteeringsensorisactuallytwosensorsinone:atorquesensorthatconvertssteeringtorqueinputanditsdirectionintovoltagesignals,andarotationsensorthatconvertstherotationspeedanddirectionintovoltagesignals.Aninterfacecircuitthatsharesthesamehousingconvertsthesignalsfromthe2torquesensorandrotationsensorintosignalsthecontrolelectronicscanprocess.Inputsfromthesteeringsensoraredigestedbyamicroprocessorcontrolunitthatalsomonitorsinputfromthevehiclesspeedsensor.Thesensorinputsarethencomparedtodeterminehowmuchpowerassistisrequiredaccordingtoapreprogrammedforcemapinthecontrolunitsmemory.Thecontrolunitthensendsouttheappropriatecommandtothepowerunitwhichthensuppliestheelectricmotorwithcurrent.Themotorpushestheracktotherightorleftdependingonwhichwaythevoltageflows(reversingthecurrentreversesthedirectionthemotorspins).Increasingthecurrenttothemotorincreasestheamountofpowerassist.Thesystemhasthreeoperatingmodes:anormalcontrolmodeinwhichleftorrightpowerassistisprovidedinresponsetoinputfromthesteeringtorqueandrotationsensorsinputs；areturncontrolmodewhichisusedtoassiststeeringreturnaftercompletingaturn；andadampercontrolmodethatchangeswithvehiclespeedtoimproveroadfeelanddampenkickback.Ifthesteeringwheelisturnedandheldinthefull-lockpositionandsteeringassistreachesamaximum,thecontrolunitreducescurrenttotheelectricmotortopreventanoverloadsituationthatmightdamagethemotor.Thecontrolunitisalsodesignedtoprotectthemotoragainstvoltagesurgesfromafaultyalternatororchargingproblem.Theelectronicsteeringcontrolunitiscapableofself-diagnosingfaultsbymonitoringthesystemsinputsandoutputs,andthedrivingcurrentoftheelectricmotor.Ifaproblemoccurs,thecontrolunitturnsthesystemoffbyactuatingafail-saferelayinthepowerunit.Thiseliminatesallpowerassist,causingthesystemtorevertbacktomanualsteering.AdashEPSwarninglightisalsoilluminatedtoalertthedriver.Todiagnosetheproblem,atechnicianjumpstheterminalsontheservicecheckconnectorandreadsoutthetroublecodes.3clickheretoseeabiggerElectricpowersteeringsystemspromiseweightreduction,fuelsavingsandpackageflexibility,atnocostpenalty.Europeshighfuelpricesandsmallervehiclesmakeafertiletestbedforelectricsteering,atechnologythatpromisesautomakersweightsavingsandfueleconomygains.Andinashorttime,electricsteeringwillmakeittotheU.S.,too.Itsjustjustamatteroftime,saysAlyBadawy,directorofresearchanddevelopmentforDelphiSaginawSteeringSystemsinSaginaw,Mich.Theissuewascostandthatsbehindusnow.By2002hereintheU.S.thecostofelectricpowersteeringwillabsolutelybeawashoverhydraulic.Today,electricandhybrid-poweredvehicles(EV),includingToyotasPriusandGMsEV-1,aretheperfectdomainforelectricsteering.Butby2010,aTRWIernalstudyestimatesthatoneoutofeverythreecarsproducedintheworldwillbeequippedwithsomeformofelectrically-assistedsteering.TheCleveland-basedsupplierclaimsitsnewsteeringsystemscouldimprovefueleconomybyupto2mpg,whileenhancinghandling.Therearetruebottom-linebenefitsaswellforautomakersbyreducingoverallcostsanddecreasingassemblytime,sincetheresnoneedforpumps,hosesandfluids.Anotherclaimedadvantageisshorteneddevelopmenttime.Forinstance,aDelphigroupdevelopedE-TUNE,aride-and-handlingsoftwarepackagethatcanberunoffalaptopcomputer.Theycantakethatcomputerandplugitin,attachittothecontrollerandchangeallthehandlingparameters-effortlevel,returnability,damping-onthefly,Badawysays.Itusedtotakemonths.DelphihasoneOEMcustomerthatshouldstartlow-volumeproductionin99.Electricsteeringunitsarenormallyplacedinoneofthreepositions:column-drive,pinion-driveandrack-drive.Whichsystemwillbecomethenormisstillunclear.Shortterm,OEMswillchoosethesteeringsystemthatiseasiesttointegrateintoanexistingplatform.Obviously,4greaterpotentialcomesfromdesigningthesystemintoanall-newplatform.Wehaveallthreedesignsunderconsideration,saysDr.HermanStrecker,groupvicepresidentofsteeringsystemsdivisionatZFinSchwaebischGmuend,Germany.ItsuptothemarketandOEMswhichversionfinallywillbeusedandmanufactured.Thelargemanufacturershaveallgrabbedholdofwhattheyconsideracoretechnology,explainsJamesHandysides,TRWvicepresident,electricallyassistedsteeringinSterlingHeights,Mich.Hiscompanyoffersaportfolioofelectricsteeringsystems(hybridelectric,rack-,pinion-,andcolumn-drive).TRWoriginallyconcentratedonwhatitstillbelievesisthepurestengineeringsolutionforelectricsteering-therack-drivesystem.Thesystemissometimesreferedtoasdirectdriveorball/nutdrive.Still,thiswinterTRWhedgeditsbet,formingajointventurewithLucasVarity.TheBritishsupplierreceived$50millioninexchangeforitselectriccolumn-drivesteeringtechnologyandassets.InitialproductionofthecolumnandpiniondriveelectricsteeringsystemsisexpectedtobegininBirmingham,England,in2000.Whatwelackisthecredibilityinthesteeringmarket,saysBrendanConner,managingdirector,TRW/LucasVarityElectricSteeringLtd.ThecombinationwithTRWprovidesuswithagoodopportunityforustobridgethatgap.LucasVaritycurrentlyhasexperimentalsystemson11differentvehicletypes,mostlyEuropean.TRWiscurrentlysupplyingitsEASsystemsforFordandChryslerEVsinNorthAmericaandforGMsnewOpelAstra.In1995,accordingtoDelphi,traditionalhydraulicpowersteeringsystemswereon7596ofallvehiclessoldglobally.That37-millionvehiclepoolconsumesabout10milliongallonsinhydraulicfluidthatcouldbesuperfluous,ifelectricsteeringreallytakesoff.Thepresentinventionrelatestoanelectricallypowereddrivemechamsmforprovidingpoweredassistancetoavehiclesteeringmechanism.Accordingtooneaspectofthepresentinvention,thereisprovidedanelectricallypowereddrivenmechanismforprovidingpoweredassistancetoavehiclesteeringmechanismhavingamanuallyrotatablememberforoperatingthesteeringmechanism,thedrivemechanismincludingatorquesensoroperabletosensetorquebeingmanuallyappliedtotherotatablemember,anelectricallypowereddrivemotordrivinglyconnectedtotherotatablememberandacontrollerwhichisarrangedtocontrolthespeedanddirectionofrotationofthedrivemotorinresponsetosignalsreceivedfromthetorqu