Experimental evaluation of a vehicle steering assi

VehicleSystemDynamicsVol.44,No.3,March2006,223–245ExperimentalevaluationofavehiclesteeringassistcontrollerusingadrivingsimulatorLIANG-KUANGCHEN*†andA.GALIPULSOY‡†DepartmentofMechanicalEngineering,NationalTaiwanUniversityofScienceandTechnology,No.43,KeelungRoad,Section4,Taipei10672,Taiwan‡DepartmentofMechanicalEngineering,UniversityofMichigan,2350Hayward,AnnArbor,MI48109,USAHuman-in-the-loopdrivingsimulatorexperimentsareconductedtoevaluateaproposedrobuststeer-ingassistcontrollerthatisdesignedonthebasisofdriveruncertaintymodelling.Anominalcontroller(NC)thatisdesignedwithoutconsiderationofdrivermodeluncertaintyisalsotestedforcomparison.Twotypesofexperimentsareproposed:alongdrivingtaskwithnominalconfigurationsandashortdrivingtaskwithinitiallylargelateralpositionerror.Thedataareanalysedusingbothtimedomainandfrequencydomainmetrics.Inthetimedomain,thestandarddeviationoflateralpositionerrorandpercentageofroaddepartureareused.Inthefrequencydomain,thestabilitymarginsandcrossoverfrequencyareused.Thedrivingsimulatorresultsindicatethatstatistically,thedesignedrobustcon-trollershowsimprovementsintheshortdrivingexperiments.Theimprovementsinthelongdrivingexperimentsarelessevidentbecauseofdriveradaptation.Thenon-robustNCsuffersfromhighgainandshouldbeavoided.Thebenefitsofconsideringdrivermodeluncertaintyinthedesignofvehiclesteeringassistcontrollersare,therefore,justified.Keywords:Vehiclesteeringassist;Driver-controllerinteraction1.IntroductionSinglevehicleroaddeparture(SVRD)accidentsaccountfor∼20%ofallvehiclecrashesandnearly40%offatalities[1].AlthoughthecauseofSVRDvarieswidely,inmanycases,thecrashescanbeattributedtodegradationindriverperformance.Forexample,fatigue,drowsiness,orinattentionmayimpairdrivingperformance.Recently,driverdistractionduetocellphoneuseandnavigationaldisplayshasdrawnsignificantpublicattention[2–4].Thedegradationisevidencedindriverreactiontime,vigilance,attention,andinformationpro-cessing.Overall,thedegradationindriverperformancecanpotentiallyleadtoSVRDcrashes.Incontrasttopassivesafetysystemssuchasairbagsandseatbelts,activesafetysystemshavethepotentialtopreventvehiclecrashes.Steeringassistisasubsetofactivesafetysystemsfocusingonthevehiclelateralmotioncontrol.Asthesteeringassistsystemwillfunctionwhilethedriverisstillinthecontrolloop,properrepresentationofdriversteeringbehaviourisneededtodesignthecontroller.Manydriversteeringmodelsareavailableinthe*Correspondingauthor.Email:[e-mail];Tel.:[phone]VehicleSystemDynamicsISSN0042-3114print/ISSN1744-5159online©2006Taylor&Francis:10.1080/00423110500268350224L.-K.ChenandA.G.Ulsoyliterature[5–9];however,thesemodelsarenotexactandmodeluncertaintyisexpected.Anapproachtomodellingdrivermodeluncertaintyfromdrivingsimulatordatahasbeenpresentedin[10].Theuncertaintyresultsshowthatalthoughtheaveragedrivermodelexhibitsacceptableperformance,thedrivercanperformverypoorlyduringalongdrivingtask.Theperformanceisevaluatedintermsofdifferentmetricssuchasphasemargin(PM),gainmargin(GM),andcrossoverfrequency.Thedriverdegradationobservedfromtheidentifieddrivermodelsmaybeanindicationoflowalertnesslevelofthedriver.Tohelpimprovethevehicledrivingsafety,steeringassistsystemshavereceivedsignificantresearchattentioninrecentyears.Intheliterature,warninghasbeenstudiedextensivelyasameanstoassistthedriver[11–14].However,directinfluenceofvehiclemotionthroughsteeringassistisrelativelylessinvestigatedintheliterature.NaabandReichart[15]reportedonthedriverassistancesystemdevelopedbyBMWintheframeworkofPrometheus.Theyimplementedaparallellowauthoritysteeringwheelcontrolbycomparingthecalculatedsteeringwheelangle,generatedfromacomputervisionsystem,withthedriver’ssteeringangle.AsimilarapproachtoprovidesteeringassisthasbeenreportedbyHsuetal.[16].Steeringassisttoaddressdriverperformancedegradationremainsanunansweredquestion.Thedegradationofthedriverbehaviourismodelledasuncertaintyinthedrivermodel[10].Itisdesiredtoensurereasonablesteeringperformanceevenwhenthedriverperformancedegrades.Aserialsteeringassistcontroller,designedtoimprovesteeringperformanceunderthedrivermodeluncertainty,isdescribedin[17].Thecontrolleriscascadedwiththevehicledynamicsasshowninfigure1.Theanalysesin[17]showthattheproposedrobustcontroller(RC)canimprovesteeringperformanceunderdegradeddriverperformance.Moreconsistentlane-keepingperformance,despitevariationsindriverbehaviour,istheexpectedbenefitoftherobuststeeringassistcontroller.Thepurposeofthisworkistovalidatethedesignoftherobuststeeringassistcontrollerbytestingitonadesktopdrivingsimulator.Thesimulatorexperimentalresultscanverifywhethertheexpectedimprovements(improvedstabilitymar-ginsandreducedroaddepartureoccurrence)areobserved,thusprovidingsupportforfurthertestingtheproposedcontrollersusingahigherqualitydrivingsimulatororanactualvehicleonatesttrack.Inthisarticle,itwillbeshownthatforacriticalsteeringmanoeuvre,statistically,therobuststeeringassistcontrollercanimprovethesteeringperformance.However,undernormaldrivingconditions,suchasthelongdri