汽车电子稳定程序的分层协调控制策略研究

JUN2013机床与液压HYDR0MECHATR0NICSENGINEERINGVO141NO12DOI103969JISSN10013881201312020ASTUDYONHIERARCHICALCOORDINATIONCONTROLSTRATEGYOFVEHICLEELECTRONICSTABILITYPROGRAMZHANGYONG，OUJIAN，YANWEN，PANGTONGCHONGQINGAUTOMOBILEINSTITUTE，CHONGQINGUNIVERSITYOFTECHNOLOGY，CHONGQING400054，CHINA1INTRODUETIONABSTRACTTODECREASEMUTUALINTERFERENCEBETWEENSYSTEMSANDIMPROVETHECONTROLEFFECTOFESPSYSTEM，TAKINGYAWANGULARVELOCITYASCONTROLVARIABLE，AKINDOFHIERARCHICALCOORDINATIONCONTROLLERISDESIGNEDBYADOPTINGFUZZYCONTROLANDPIDCONTROLALGORITHMTHETYREMODEL，ENTIREAUTOMODELANDREFERENCEMODELAREESTABLISHEDINMATLABSJMULINKANDAFOURWAYHYDRAULICBRAKEMODELAREESTABLISHEDINAMESIM；ANDALLOFTHEMODELSARECONNECTEDTOCOMBINEDSIMU1ATIONMODELFORAUTODYNAMICSBYUTILIZINGINTERFACESHARDWAREISEMBEDDEDINTOTHEENTIRESIMU1ATIONSYSTEMTOCONDUCTHARDWAREINTHELOOPSIMULATIONTESTRESULTSOFOFF1INEANDREA1TIMESIMULATIONSHOWTHAT，ITCANIMPROVEOPEMTIONSTABILITYANDSAFETYOFAUTOSEFFECTIVELYBYADOPTINGHIERARCHICALCOORDINATIONCONTROLSTRATEGYKEYWORDSELECTRONICSTABILITYPROGRAM，COORDINATIONCONTROL，HYDRAULICBRAKINGSYSTEMHARDWAREINTHELOOPSIMULATIONVEHICLEELECTRONICSTABILITYPROGRAMESP，ASAKINDOFVEHICLEACTIVESAFETYTECHNOLOGYDEVELOPEDINRECENTYEARS，HASBECOMESTANDARDAUTOCONFIGURATIONGRADUALLYBYACTIVELYCONTROLLINGVEHICLEBRAKINGSYSTEM，DRIVINGSYSTEMANDCONTROLSYSTEMETC，ITADJUSTSAMPLITUDEANDDISTRIBUTIONOFWHEELSLONGITUDINALFORCEANDTRANSVERSEFORCETOEONTROLTHEDYNAMICSMODEOFAUTOUNDERANYCASETOIMPROVETHESAFETYPROPERTYANDTHECONTROLSTABILITYOFAUTO12ESPISAMULTIPLENON1INEARSYSTEMWHICHINCLUDESDRIVING，BRAKINGANDTRANSVERSESTABILIZINGETCCONTROLFUNCTIONS，ANDADOPTSSTATUSCONTROLOROPTIMUMCONTROLBASEDONMATHEMATICALMODELTHEREAREMANYPARAMETERSWHICHSHOULDBEMEASURED，EVALUATEDANDIDENTIFIEDSOTHEAMOUNTOFCALCULATIONRECEIVED20130216SUPPOSEDBYNATURALSCIENCEFOUNDATIONPROJECTOFCHONGQINGCSTC，2008BB6338ZHANGYONGEMAILCAMZY163COMISVERYGREAT，ANDTHEROBUSTNESSISNOTSTRONGRRLEMOTIONCONDITIONSANDTHEPARAMETERSOFAUTOCHANGEINEVERYMOMENTDURINGTHEMOTION，ANDITISVERYDI伍CULTTOFINDOUTAKINDOFOPTIMUMCONTROLSTRATEGY34THEREFORE，BASEDONANALYZINGMUTUALINFLUENCEAMONGSYSTEMS，THETHESISPROPOSESAKINDOFHIERARCHICALCOORDINATIONCONTROLSTRATEGYTAKINGYAWANGULARVELOCITYASCONTRO1VARIABLEANDADOPTINGFUZZYCONTROLANDPIDCONTROLALGORITHM，THEADOPTINGFUZZYCONTROLANDPIDCONTROLALGORITHMAREDESIGNEDTHERESULTSOFTHESIMULATIONSHOWTHATTHEHIERARCHICAICOORDINATIONCONTROLSTRATEGYCANDECREASEMUTUALINTERFERENCEAMONGSYSTEMSANDIMPROVESTABILITYCONTROLLINGEFFECT2CONTROLLERDESIGNBASEDONTHEMETHODOFACTIVEBRAKINGONWHEELSINORDERTOOBTAINCOMPENSATEDYAWINGMOMENTTOIMPROVETHEVEHICLEHANDLINGSTABILITY，SELECTINGTHEYAWANGULARVELOCITYASTHECONTROLVARIABLE，ANDUSINGHIERARCHICALCOORDINATIONCONTROLSTRATEGYFUZZVCONTROLANDPIDCONTROLALGORITHMTHEVEHICLEELECTRONICSTA96HYDROMECHATRONICSENGINEERINGBILITYPROGRAMMODELISESTABLISHED21THEOVERALLSTRUCTUREOFTHEHIERARCHICALCOORDINATIONCONTROLSTRATEGYASSHOWNINFIG，1，THEWHOLEVEHICLEELECTRONICSTABILITYPROGRAMISDIVIDEDINTOTHREECONTROLLEVELS5THEFIRSTLEVE1TAKESTHEPOSTUREOFENTIREAUTOASCONTROLOBJECT，TAKESYAWANGULARVELOCITYANDNOMINALYAWANGULARVELOCITYOFAUTOMODELASINPUTVALUESOFCONTROLLER，ANDTAKESOBJECTIVEYAWINGMOMENTASINPUTVALUETOTRANSFERTOTHESECONDCONTROLLEVELTHESECONDCONTROLLEVELTAKESWHEELSASCONTROLLEDOBJECTS，TAKESOBJECTIVEYAWINGMOMENTVALUEANDTURNINGANGLEOFFRONTWHEELSASINPUTVALUESTOCONDUCTTHEDISTRIBUTIONOFYAWINGMOMENTANDTHECALCULATIONOFBRAKINGPRESSURETOTRANSFERTO出ETHIRDCONTROLLEVELTHETHIRDLEVELTAKESELECTROMAGNETICVALVESANDDUMPPUMPMOTORASCONTROLLEDOBJECTSBYCOMPARINGTHEOBJECTIVEBRAKINGPRESSUREANDTHEAETUA1BRAKINGTOTURNONTURNOFFELECTROMAGNETICVALVE，ITREALIZESTHEPRESSUREADJUSTMENTOFBRAKINGWHEELCYLINDERFIG1OVERALLSTRUCTUREOFTHEHIERARCHICALCOORDINATIONCONTROLSTRATEGY22OBJECTIVEYAWINGMOMENTALGORITHMTHEOBJECTIVEYAWINGMOMENTADOPTSFUZZYCONTROLALGORITHM，ANDTAKESYAWANGULARVELOCITYASCONTROLVARIABLE，OBJECTIVEYAWINGMOMENTASOUTPUTTOESTABLISHTHECONTROLLER6ASSHOWNINFIG2，THETHEVARIABLEERROREISSETAS一E，E；THEUNIVERSERANGEOFTHEERRORCHANGINGRATEECISSETAS一EC，EC；THEUNIVERSERANGEOFCONTROLQUANTITYUISSETAS一，OFWHICH，E，ECANDUVALUESAREDETERMINEDACCORDINGTOERRORVALUEBETWEENVEHICLEACTUALYAWANGULARVELOCITYGOTTENBYCOLLECTINGANDREFERENCEMODELSNOMINALYAWANGULARVELOCITYGOTTENBYCALCULATINGFRONTWHEELSTECONTROL】ERFIG2YAWRATECONTROLBLOCKDIAGRAMTHEFUZZYSETSANDTHEUNIVERSERANGEOFNORMALIZEDVARIABLEERRORE，THEERRORCHANGINGECANDTHECONTROLQUANTITYUAREDEFINEDASFOLLOWSTHEFUZZYSETSOFE，ECANDUAREDEFINEDASNB，NS，Z，PS，PBHEREARETHEUNIVERSEOFFUZZYSETSWHICHTHEVBELONGTOEANDEC一1，一08，一06，一04，一02，0，02，04，06，08，1一1，一08，一06，一04，一02，0，02，04，06，08，I；THEMEMBERSHIPFUNCTIONISSHOWNINFIG，34ANDTHEFUZZYCONTROLRULESARESHOWNINTAB1010080604O20O204O60810INPUTVARIABLEEFIG3E，ECMEMBERSHIPFUNCTION1005O1008060402002040608I0INPUTVARIABLE“E”FIG4CONTROLQUANTITYUSMEMBERSHIPFUNCTION23DISTRIBUTIONOFYAWINGMOMENTANDEALCULATIONOFBRAKINGFORCETHEYAWINGMOMENTADOPTSMATLABSTATEFLOWZHANGYONG，ETALASTUDYONHIERARCHICALCOORDINATIONCONTROLSTRATEGYOFVEHICLEELECTRONICSTABILITY97TODISTRIBUTESTATEFLOWJUDGESTHEVEHICLEMOTIONSTATEACCORDINGTOTHEFRONTWHEELSTURNINGANGLEANDTHEDIFFERENCEVALUEOFYAWANGULARVELOCITYAYA1一ID1，ANDTHENDECIDESHOWTOCONTROLWHEELS，ASSHOWNINTAB2ITISREGULATEDTHATTHEVALUEDIFFERFRAMEISSHOWNINFIG5FIG5PIDCONTROLBLOCKDIAGRAMENCEISPOSITIVEIFTHEYAWANGULARVELOCITYISCOUNTER。CLOCKWISE，ANDTHETURNINGANGLEOFSTEERINGWHEELIS3ESPCOMBINEDSIMULATIONMODELPOSITIVEIFTHEFRONTWHEELTURNSLEFTTAB1FUZZYCONTROLRULESTHEGOALOFTHEPRESSURENEEDOFPRODUCINGEERRAINYAWINGMOMENTOFBRAKEWHEELCYLINDERIS苦1WHERE，D一WHEELCYLINDERDIAMETER；NNUMBEROFUNILATERALBRAKECYLINDER；CBRAKEEFFECTIVENESSFACTOR；R6一BRAKEWORKINGRADIUS；RDTYREDYNAMICLOADRADIUSTAB2CONTRO1WHEEISELECTRULES24VALVEANDMOTORCONTROLALGORITHMINBRAKINGSYSTEM，DERPRESSUREINCREASINGTHEPRESSURESOFWHEELCYLINANDPRESSUREDECREASINGVALVESADOPTPWMTOADJUST，ANDTHEVALUEDIFFERENCEBETWEENTHEWHEELCYLINDERSOBJECTIVEPRESSUREANDTHEREALPRESSURECOLLECTEDISTAKENASTHEINPUTVALUES；AFTERPIDCONTROLLING，THEDUTYRATIOOFPWMISOUTPUTTEDTOREALIZETHEPRESSUREINCREASINGANDPRESSUREDECREASINGOFTHEWHEELEYLINRANDITSCONTROL31VEHICLEDYNAMICSSIMULATIONMODELMATIABSIMULINKSOFTWAREHASALLKINDSOFLINEARANDNONLINEARMODULEANDCONTROLMODULE，ETCITCANBEUSEDTOESTABLISHTHEVEHICLEDYNAMICSMODELINTHECONTROLSYSTEMMODEL，ANDCANALSOBEUSEDINTHESTUDYOFTHEVEHICLEELECTRONICSTABILITYPROGRAMTHEREFORE，BASEDONTHEMATLABSIMULINKPLATFORM，THETYREMODEL，SEVENDEGREESOFFREEDOMVEHICLEMODE1ANDTHETWODEGREESOFFREEDOMLINEARREFERENCEMODELWHICHCANREFLECTTHERELATIONSHIPBETWEENTHEDRIVERSTEERINGINPUTANDTHEYAWANGULARVELOCITYAREESTABLISHEDSEEFIG6FIG6VEHICLEDYNAMICSSIMULATIONMODEL311TYREMODELMAGICFORMULAOFTYREMODELISASEMIEMPIRICALTYREMODELBASEDONTESTDATA，WHICHUTILIZESTRIGONOMETRICFUNCTIONCOMBINATIONALFORMULATOEXPRESSIONGITUDINALFORCE，TRANSVERSEFORCEANDALIGNINGTORQUE，ANDTHEEXPRESSIONIS7YDSINCARCTANB1一DXSEBARCTANBXSH51WHERETHELONGITUDINALFORCEORLATERALFORCEOFTYRE；一THESLIPRATEORLATERALDECLINATIONOFTYRE；DCUIVEPEAKVALUEFACTOR，SHOWSTHEMAXIMUMVALUEOFTHECURVE；CCUI、，ESHAPEFACTOR，DETERMINESBASICSHAPEOFTHECURVEBSTIFFNESSFACTOR；ECURVATUREFACTOR，SHOWSTHESHAPEOFPARTCLOSETOTHEMAXIMUMVALUESHTHEDRIFTONHORIZONTALDIRECTIONOFTHECUNES。，一THEDRIFTONVERTICALDIRECTIONOFTHEC1】RVE98HYDROMECHATRONICSENGINEERINGUNDERTHECOMBINEDOPERATINGCONDITIONSOFTHEBRAKINGDRIVINGANDTHESTEERING，THELONGITUDINALFORCEFANDTHELATERALFORCEFYNEEDTOADOPTTHESLIPRATEAANDTHELATERALDECLINATIONOTTOCORRECTORY；ORY2WHERE，厢，一，一312SEVENDEGREESOFFREEDOMVEHICLEMODELAUTODYNAMICSMODELWHICHINCLUDESLONGITUDINALMOTION，TRANSVERSEMOTION。YAWMOTIONANDTURNINGMOTIONOFFOURWHEELS，WASESTABLISHEDBASEDONNEWTONSLAWLONGITUDINALDYNAMICSEQUATIONM一秽COS一SI硒“FTRANSVERSEDYNAMICSEQUATIONMSIN6FXAF毋E0S8FDFYAWINGMOTIONEQUATION34。SIN6D一C。NFYRC。一SI硒一BFL一一5TURNINGKINEMATICEQUATIONOFWHEELS，一R6，一F矿R7DO一F,RLR8，一9WHERE，MISTHEMASSOFENTIREAUTO；IS山ELATERALVELOCITY；ISTHELONGITUDINALVELOCITY；ISTHEYAWANGULARVELOCITYFM，F，F试ANDFRARETHEIONGITUDINALFORCEOFFRONTLEFTWHEEL，THEFRONTRIGHTWHEE1THEBACK1EFTWHEELANDTHEBACKRIGHTWHEELRESPECTIVELY；6ISTHETURNINGANGLEOFFRONTWHEELS；ISTHEYAWINGMOMENTOFINERTIA；AISTHEDISTANCEFROMMASSCENTERTOFRONTSHAFTANDBISTHEDISTANCEFROMMASSCENTERTOBACKSHAFT；DISTHEWHEELTRACKOFAUTO；JSHOWSTHEMOMENTOFINERTIAOFTYRES；ISTHEANGULARVELOCITYOFWHEELS；TBIISTHEBRAKEMOMENTONEACHWHEELRISTHERADIUSOFWHEE1313REFERENCEMODELLINEARTWOFREEDOMAUTOMODELISUTILIZEDTOCA1CU|ATETHEIDEALYAWANGULARVELOCITYANDMASSCENTERLATERA1DECLINATIONOFAUTOANDITSMOTIONDIFFERENTIALEQUATIONIS8K1K2口0K1一BK2K16MU。_6N10THEIDEALYAWANGULARVELOCITYWILLBELIMITEDBYADHESIONCONDITIONSOFROADSURFACE，IELAIG，OTHERWISE，SIDESLIPPINGWILLOCCURIFTHELATERALDECLINATIONISSMALIAM，SO，IFTHEAUTOLQLNSONTHEROADSURFACEWITHLOWADHESION，THEMAXIMUMNOMINALYAWANGULARVELOCITYOFAUTOISEXPRESSEDAS11TOSATISFYDIFFERENTRUNNINGCONDITIONS，THESMALLERNOMINALYAWANGULARVELOCITYSHOULDBETAKENYNOMINII，F。FSIGN61232VEHICLEHYDRAULICBRAKINGSYSTEMSIMULATIONMODELTHEVEHICLEHYDRAULICBRAKINGSYSTEMISTHEHIGHSPEEDACTUATOROFTHEELECTRONICSTABILITYPROGRAM，THEHYDRAULICCONTROLVALVESMUSTRESPONDTOTHECONTROLINSTRUCTIONSINASHORTTIME，ANDTHEDYNAMICRESPONSECHARACTERISTICSDIRECTLYDETERMINETHEVALIDITYANDRELIABILITYOFTHEELECTRONICSTABILITYPROGRAMTHEREFORE，THERESEARCHONDYNAMICRESPONSECHARACTERISTICSOFTHEHYDRAULICACTUATORS，THEDESIGNOFHIGHEFFICIENTCONTROLSYSTEM，ANDENSURINGTHERELIABILITYOFTHESYSTEMAREVERYNECESSARYINAMESIMSOFTWARE，THEHYDRAULICBRAKINGSYSTERNMODEL，INCLUDINGTHEMASTERCYLINDERMODEL，THEHYDRAULICELEMENTMODELANDTHEWHEELCYLINDERMODEL，ISESTABLISHED9THEMASTERCYLINDERADOPTSBICAVITYTANDEMTYPEMASTERMODELSUPPLIEDBYAMESIMSOFTWARE，ANDTHECHARACTERISTICPARAMETERSSHOULDBESETACCORDINGTOTHESAMPLEAUTOTOPREVENTTHATTHEHYDRAULICSYSTEMESTABLISHESTHEPRESSUREFORMUCHLONGTIMEUNDERLOWTEMPERATURECONDITION，THEPREPRESSINGELEMENTISADOPTEDTOCONDUCTPREPRESSINGONTHESYSTEMHYDRAULICELEMENTISTHECORECOMPONENTOFESPSYSTEM；EACHELECTROMAGNETICVALVECONDUCTSONANDOFFACTIONTOCONTROLLOOPACCORDINGTOECUCOMMANDTOADJUSTPRESSUREOFTHESYSTEMANDEACHBRAKINGWHEELCYLINDERTHEMOTORISDCMOTOR；THEDUMPPUMPISHIGHPRESSUREPLUNGERPUMP；THEACCUMULATORISSPRINGPISTONTYPE；THEPRESSUREINCREASINGZHANGYONG，ETALASTUDYONHIERARCHICALCOORDINATIONCONTROLSTRATEGYOFVEHICLEELECTRONICSTABILITYPROGRAMVALVE，THEPRESSDECREASINGVALVEANDTHESUCTIONVALVEARETYPICALBIBITBIWAYELECTROMAGNETICVALVESTHEHYDRAULICELEMENTMODELCANBEESTABLISHEDBYSELECTINGPROPERCOMPONENTSINCOMPONENTSTORAGETHEWHEELCYLINDERADOPTSWHEELCYLINDERSUPPLIEDBYAMESIMSOFTWARE，ANDTHECHARACTERISTICPARAMETERSSHOULDBESETACCORDINGTOTHESAMPLEAUTO33SIMULINKAMESIMCOMBINEDSIMULATIONMODELINSIMULINKTHECONTROLSYSTEMMODELISESTAB1ISHEDTOCONTROL12ELECTROMAGNETICVALVESAND1DUMPPUMPMOTOROFESPHYDRAULICELEMENT，ANDTOCONDUCTPRESSURECOLLECTIONONFOURWHEELHYDRAULICCYLINDERSASSHOWNINFIG7，THEHYDRAULICBRAKINGSYSTEMMODELESTABLISHEDINAMESIMANDTHEAUTOMODELESTABLISHEDINSIMULINKSHOULDBECONNECTEDTHROUGHSOFTWAREINTERFACESTOESTABLISHESPCOMBINEDSIMULATIONMODE1FIG7SIMULINKAMESIMCOMBINEDSIMULATIONMODEL4OFFLINESIMULATIONTESTANDANALYSISTAKINGAPASSENGERAUTOASEXAMPLE，OFFLINESIMULATIONANALYSISISCONDUCTEDONESPCOMBINEDSIMULATIONMODELUNDERTYPICALWORKINGCONDITIONSANDSIMULATIONWORKINGCONDITIONSARESHOWNINT3TAB3SIMULATIONWORKINGCONDITIONSFROMFIG810，WHENHIGHVELOCITYSNAKESHAPETESTISCONDUCTEDONROADWITHHIGHADHESION，THEYAWANGULARVELOCITYOFAUTOWITHOUTESPCONTROLCHANGESGREATLY，ANDTHEAUTOWILLPRESENTUNSTABLESTATEESPSYSTEMCANSELECTOPTIMUMWHEELTOCONDUCTBRAKINGFORCEADJUSTMENTACCORDINGTOVEHICLEMOTIONSTATETOMAKEWHEELCYLINDERFLOWANDPRESSURERAPIDRESPONSEANDTHEYAWANGULARVELOCITYCLOSETONOMINALVALUE005L0L520253O354OTSFIG8YAWANGULARVELOCITYRESPONSESUNDERWORKINGCONDITION1OO51O152O253O354OTSFIG9WHEELCYLINDERPRESSURERESPONSESUNDERWORKINGCONDITION1I吐IL_IF一FLFRRL一RR00L0203040TSFIG10WHEELCYLINDERFLOWRESPONSESUNDERWORKINGCONDITION1FROMFIG1113WHENHIGHVELOCITYSNAKESHAPETESTISCONDUCTEDONROADWITHLOWADHESION，THEADHESIONFORCECANNOTFULLYSATISFYTHESTEERINGREQUIREMENTOFAUTOTHEVEHICLEYAWANGULARVELOCITYWITHOUTESPCONTROLHASDIVERGED，ANDTHEAUTOWILLPRESENTUNSTABLESTATEANDTHEVEHICLEYAWANGULARVELOCITYWITHESPCONTROLCANFOLLOWNOMINALYAWANGULARVELOCITYBETTER，ANDTHEAUTOCANKEEPSTABLE5O505O5O5O5221LOO1122OOOOO加加加一晕。营208642O磊拿砷盆642024680OO0O加加加加一UIGR1一葛事0ZHANGYONG，ETALASTUDYONHIERARCHICALCOORDINATIONCONTROLSTRATEGYOFVEHICLEELECTRONICSTABILITYPROGRAM101TIVELYANDTHECONTROLALGORITHMISEFFECTIVEBECAUSEOFUSINGTHEBRAKESYSTEM，THEHYDRAULICUNITOBJECTSINSTEADOFTHEMATHEMATICALMODE1THEREARESOMEDIFFERENCESBETWEENTHEHARDWAREINTHE1OOPSIMULATIONTESTRESULTSANDTHEOFFLINESIMULATIONRESULTSTHEPULSEOFTHEHYDRAULICSYSTEMCANMAKETHEVEHICLETINYSWINGING，BUTITDOESNOTAFFECTTHESTABILITYOFTHEVEHICLEBOTHSENSORSIGNALANDDRIVINGSIGNALAREREALVOLTAGESIGNAL，INCLUDINGCERTAINNOISESIGNALWHICHMAKESTHETESTMUCHCLOSERTOREALCONDITIONSITSHOWSTHATESPALGORITHMHASCERTAINROBUSTNESS6CONCLUSIONSFUZZYCONTROLANDPIDCONTROLALGORITHMARE印一PLIEDINTHEVEHICLEDYNAMICSTABILITYCONTROLSYSTEMANDTHEHIERARCHICALCOORDINATIONCONTROLLERWHICHDECREASESTHEMUTUALINTERFERENCEBETWEENSYSTEMSANDIMPROVESTHEROBUSTNESSOFESPSYSTEMBYUTILIZINGMATLABSIMULINKANDAMESIMCOMBINEDSIMULATIONTECHNOLOGY，THECOMBINEDSIMULATIONMODELFORVEHICLEDYNAMICSTABILITYWASESTABLISHED，ANDTHEHIGHVELOCITYSNAKESHAPESIMULATIONTESTWASCONDUCTEDANDTHECORRECTNESSOFTHEESTABLISHEDMODELANDTHECONTROLSYSTEMHASBEENPROOFEDA1READYTHEVEHICLEHARDWAREINTHE1OOPSIMULATIONPLAFFORILLWASESTABLISHEDBASEDONDSPACEANDTHEAUTOMATICGENERATIONOFCODENUMBERWASFINISHEDTHERESULTSOFTHEHARDWAREINTHE1OOPSIMULATIONTESTSHOWTHATTHEHIERARCHICALCOORDINATIONCONTROLSTRATEGYPOSSESSESFAVORABLEREALTIMEPROPERTYANDCOULDIMPROVEVEHICLESTABILITYUNDERUTMOSTWORKINGCONDIT