混合动力电动汽车机械和再生制动的整合mechanical and regenerative braking integration for a hybrid ele.docx
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混合动力电动汽车机械和再生制动的整合mechanicalandregenerativebrakingintegrationforahybridele
外文文献原稿和译文
原稿
MechanicalandRegenerativeBrakingIntegrationforaHybridElectricVehicle
Abstract
Hybridelectricvehicletechnologyhasbecomeapreferredmethodfortheautomotiveindustrytoreduceenvironmentalimpactandfuelconsumptionoftheirvehicles.Hybridelectricvehiclesaccomplishthesereductionsthroughtheuseofmultiplepropulsionsystems,namelyanelectricmotorandinternalcombustionengine,whichallowtheeliminationofidling,operationoftheinternalcombustionengineinamoreefficientmannerandtheuseofregenerativebraking.However,theaddedcostofthehybridelectricsystemhashinderedthesalesofthesevehicles.
Amorecosteffectivedesignofanelectro-hydraulicbrakingsystemispresented.Thesystemelectro-mechanicallycontrolledtheboostforcecreatedbythebrakeboosterindependentlyofthedriverbrakingforceandwithadequatetimeresponse.Thesystemallowedfortheblendingofthemechanicalandregenerativebrakingtorquesinamannertransparenttothedriverandallowedforregenerativebrakingtobeconductedefficiently.
Asystematicdesignprocesswasfollowed,withemphasisplacedondemonstratingconceptualdesignfeasibilityandpreliminarydesignfunctionalityusingvirtualandphysicalprototyping.Thevirtualandphysicalprototypeswerethenusedincombinationasapowerfultooltovalidateanddevelopthesystem.Theroleofprototypinginthedesignprocessispresentedanddiscussed.
Throughtheexperiencesgainedbytheauthorduringthedesignprocess,itisrecommendedthatstudentscreatephysicalprototypestoenhancetheireducationalexperience.Theseexperiencesareevidentthroughoutthethesispresented.
1.1ModernHybridElectricVehicles
Withrisinggaspricesandtheoverwhelmingconcernfortheenvironment,consumersandthegovernmenthaveforcedtheautomotiveindustrytostartproducingmorefuelefficientvehicleswithlessenvironmentalimpact.Onepromisingmethodthatiscurrentlybeingimplementedisthehybridelectricvehicle.
Hybridvehiclesaredefinedasvehiclesthathavetwoormorepowersources[25].Therearealargenumberofpossiblevariations,butthemostcommonlayoutofhybridvehiclestodaycombinesthepowerofaninternalcombustionengine(ICE)withthepowerofanelectricmotorandenergystoragesystem(ESS).Thesevehiclesareoftenreferredtoashybridelectricvehicles(HEV’s)[25].Thesetwopowersourcesareusedinconjunctiontooptimizetheefficiencyandperformanceofthevehicle,whichinturnwillincreasefueleconomyandreducevehicleemissions,allwhiledeliveringtheperformancetheconsumerrequires.In1997,theToyotaPriusbecamethefirsthybridvehicleintroducedintomassproductioninJapan.Ittookanotherthreeyearsforthefirstmassproducedhybridvehicle,theHondaInsight,tobeintroducedintotheNorthAmericanmarket.ThereleaseoftheHondaInsightwascloselyfollowedbythereleaseoftheToyotaPriusinNorthAmericaacoupleofmonthslater[35].
Hybridelectricvehicleshavethedistinctadvantageofregenerativebraking.Theelectricmotor,normallyusedforpropulsion,canbeusedasageneratortoconvertkineticenergyofthevehiclebackintoelectricalenergyduringbraking,ratherthanwastingenergyasheat.ThiselectricalenergycanthenbestoredinanESS(e.g.batteriesorultracapacitors)andlaterreleasedtopropelthevehicleusingtheelectricmotor.
Thisprocessbecomesevenmoreimportantwhenconsideringtheenergydensityofbatteriescomparedtogasolineordieselfuel.Energydensityisdefinedastheamountofenergystoredinasystemperunitvolumeormass[44].Toillustratethispoint,4kilograms(4.5litres)ofgasolinewilltypicallygiveamotorvehiclearangeof50kilometres.Tostorethesameamountofusefulelectricenergyitrequiresaleadacidbatterywithamassofabout270kilograms[25].Thisdemonstratestheneedforefficientregenerativebrakingtostoreelectricalenergyduringdriving,whichinturnwillkeepthemassoftheenergystoragesystemdownandimprovetheperformanceandefficiencyoftheHEV.
1.2ResearchScope-RegenerativeBrakingSystems
Thescopeoftheresearchpresentedistocreatealowcostregenerativebrakingsystemtobeusedonfutureeconomicalhybridvehiclestostudytheinteractionbetweenregenerativeandmechanicalbrakingofthesystem.Thissystemshouldbeabletocontrolthecombinationofbothregenerativeandmechanicalbrakingtorquedependingondriverdemandandshouldbeabletodososmoothlyandsafely.Controllingtheregenerativebrakingtorquecanbedoneusingcontrolalgorithmsandvectorcontrolforinductionmotors.However,controllingthemechanicalbrakingtorqueindependentlyofthedriverpedalforce,whilemaintainingpropersafetyback-ups,provedtobemoreofachallenge.Toovercomethisproblem,asystemwasdevelopedthatwouldattenuatethepressureinthebrakeboosterinordertocontroltheamountofmechanicaltorquedevelopedbythebrakingsystem.
2.1HybridElectricVehicleOverview
Hybridvehicleshaveemergedasoneoftheshorttermsolutionsforreducingvehicle emissionsandimprovingfueleconomy.Overthepast10yearsalmostallofthemajor automotive companieshavedevelopedandreleasedforsaletheirownhybridelectric vehiclestothepublic.Thepopularityofhybridelectricvehicleshasgrownconsiderablysincetheturnof thecentury.Withenormouspressuretobecomemoreenvironmentallyfriendlyandwith unpredictablegasprices,thesalesofhybridelectricvehicleshaveincreaseddramatically inrecentyears.
2.1.1HybridConfigurations
Forthepast100yearstheobjectiveofthehybridhasbeentoextendtherangeofelectric vehiclesandtoovercometheproblemoflongrechargingtimes[35].Therearethree predominanthybridelectricvehicleconfigurationscurrentlyonthemarkettoday.Theseconfigurationsareknownasserieshybrids,parallelhybridsandseries/parallelhybrids.
Eachconfigurationhasitsadvantagesanddisadvantageswhichwillbediscussedinthefollowingsections.
SeriesHybrids
Inserieshybridsthemechanicaloutputfromtheinternalcombustionengineisusedto driveageneratorwhichproduceselectricalpowerthatcanbestoredinthebatteriesor usedtopoweranelectricmotoranddrivethewheels.Thereisnodirectmechanical connectionbetweentheengineandthedrivenwheels.Serieshybridstendtobeusedin highpowersystemssuchaslargetrucksorlocomotivesbutcanalsobeusedforlowerpowerpassengervehicles[18].Themechanicallygeneratedelectricalpoweriscombinedwiththepowerfromthebatteryinanelectroniccontroller.Thiscontrollerthencomparesthedriverdemandwiththevehiclespeedandavailabletorquefromtheelectricmotortodeterminetheamountofpowerrequiredfromeachsourcetodrivethevehicle.Duringbraking,thecontrolleralsoswitchesthepowerelectronicstoregenerativemode,anddirectsthepowerbeingregeneratedtothebatteries[55].
Therearemanyadvantagesmadepossiblebythearrangementdescribedabove.ItispossibletoruntheICEconstantlyatitsmostefficientoperatingpointandshareitselectricaloutputbetweenchargingthebatteryanddrivingtheelectricmotor.Byoperatingtheengineatitsmostefficientoperatingpoint,emissionscanbegreatlyreducedandthemostelectricalpowercanbegeneratedpervolumeoffuel.Thisconfigurationisalsoeasiertoimplementintoavehiclebecauseitislesscomplexwhichmakesthismethodmorecosteffective.
ParallelHybrids
InparallelhybridconfigurationsthemechanicalenergyoutputfromtheICEistransmittedtoagearbox.InthisgearboxtheenergyfromtheICEcanbemechanicallycombinedwithaseconddrivefromanelectricmotor.Thecombinedmechanicaloutputisthenusedtodrivethewheels[35].Inthisconfigurationthereisadirectconnectionbetweentheengineandthedrivenwheels.Asinserieshybridsthecontrollercomparesthedriverdemandwiththevehiclespeedandoutputtorqueanddeterminestheamountofpowertobeusedfromeachsourcetomeetthedemand,whileobtainingthebestpossibleefficiency.Aparallelhybridalsocontrolsregenerativebrakingsimilarlytoaserieshybrid.Parallelhybridsareusuallyusedinlowerpowerelectricvehiclesinwhichbothdrivescanbeoperatedinparalleltoprovidehigherperformance[18].
Thereareanumberofadvantagesofaparallelhybridoveraserieshybrid.Themostimportantadvantageisthatsinceonlyoneconversionbetweenelectricalandmechanicalpowerismade,efficiencywillbemuchbetterthantheserieshybridinwhichtwoconversionsarerequired.Sincetheparallelhybridhastheabilitytocombineboththeengineandelectricmotorpowerssimultaneously,smallerelectricmotorscanbeusedwithoutsacrificingperformance,whilegettingthefuelconsumptionandemissionreductionbenefits.Lastly,parallelhybridsonlyneedtooperatetheenginewhenthevehicleismovinganddonotneedasecondgeneratortochargethebatteries.
Series/ParallelHybrids
Combinedhybridshavethefeaturesofbothseriesandparallelconfigurations.Theyuseapowersplitdevicetodrivethewheelsusingdualsourcesofpower(e.g.electricmotoronly,ICEonlyoracombinationofboth).Whiletheaddedbenefitsofbothserieshybridsandparallelhybridsareachievedforthisconfiguration,controlalgorithmsbecomeverycomplexbecauseofthelargenumberofdrivingpossibilitiesavailable.
2.1.2DegreeofHybridization
SincemostHEV’sontheroadtodayareeitherparallelorseries/parallel,itisusefultodefineavariablecalledthe‘degreeofhybridization’toquantifytheel