双离合器-变速器系统-外文文献翻译

黑龙江工程学院本科生毕业设计PAGEPAGE68附录附录A外文文献原文7-SpeedDualClutchTransmissionSystemforSportyApplicationABSTRACT:Withits7-speeddualclutchtransmission,ZFhasintroducedaninnovativetransmissionforsportyapplications.Thecloseratioscombinedwithextremelyspontaneousdrivebehaviormakesitanidealtransmissionforsportyapplications.Thisarticledescribesthecompactgearsetwithlubricationbyinjectionforimprovingthelevelofefficiencyandincreasingtheengine-speed-strength,thedualclutchunitaswellasthehydrauliccontrolunit,whichisbasedonthepre-controlprinciple,arealsodescribedindetail.Thehy-drauliccontrolprincipleprovidestheoptionofahydrauliccruisemodeintheeventofanelectronicsfailure.Inadditiontothetransmissiondesign,functionalfeaturesthatalsohighlightthesportycharacterofthetransmissionaredescribedindetail.Keywords:Automatictransmission;Dualclutch;Vehicleconnection;Efficiency1IntroductionWhenitcomestothefieldofautomatictransmissions,dualclutchsystemscurrentlyrepresentthebenchmarkintermsofspontaneityandsportiness.Inthistypeoftransmission,whichisbasedonacountershafttransmission,theseadvantagesarecombinedwithaverydirect"vehicleconnection",highrpmperformance,andexcellenttransmissionefficiency.The7-speeddualclutchtransmissionforthestandarddrivelinepresentedhereisdesignedforatorquecapacityofupto520Nmandrotationalspeedsofupto9250rpms.Inordertobeabletoachievetheseperformancedataintheexistinginstallationspace,aconceptwasdevelopedinwhichanoilchamberaswellaslubricationbyinjectionareused.Beforeintroducingthetransmission′sseveraluniquefeaturesinmoredetailbelow,anoverviewofthebasictransmissiondesignwillbepresented,Fig.1.Theenginetorqueisintroducedtothedualclutchviaatorsiondamper(notshowninFig.1).Themultidiskclutchesinthedualclutchareradiallynestedinoneanotherandtransferthetorquetobothinputshaftsinthecountershafttransmissiongearset.Inthiscase,duetotheinstallationspace,thecountershaftisnotlocatedunderthemainshaft,butistiltedlaterally.Thisbecomespossiblebecausetheconceptisbasedonlubricationbyinjectionwithadrysump.Ontheonehand,lubricationbyinjectionimprovesheatremoval,ontheother,therearenonoticeablelossesduetothegearssplashingintheoilpan.Theoilissuppliedtothetransmissionviaaninternalgearpumpwhichisdrivenbyaspurgeartrainbehindthedualclutch.Withthehelpofaspurgeartrain,thedriveunithastheadvantagethat,viadifferentgearratiophasesanddependingontheintendeduse,theflowrateandthemax.speedofthepumpcanbeadapted.AnadditionaladvantageisthatbasedontheresultingIprovedinstallationspace,anoptimalratiobetweenthepumpwidthandthepumpdiametercanbeachievedforthepump′slevelofefficiency.Thehydrauliccontrolunitisarrangedunderthegearset.Thehydraulicunitsuppliestheclutch,basedonneed,withpressureandcoolingoilaswellasshiftactuators.Thelatterarearrangedlaterallytothegearsetandworkwithdouble-actingcylinders.Thesensorfordetectingthepositionofthegearshiftsisattacheddirectlyontothefourgearshifts.Thetransmissionhasanexternalcontrolunit.Fig.1Overviewdualclutchtransmission(DCT)2Sevenspeedswithsophisticatedstepping-aconceptforextrmesporti-nessThegearsetconceptofthedualclutchtransmissionintroducedherewasdevelopedinhousetakingintoconsiderationthefollowingrequirements:HighpowerdensityHighspeedendurancestrengthupto9250rpmVariabilityandmodulardesignRepresentationoftransmission-ratiospreadsofabout4.7and6.8with7speedsUseofexistingsynergiesformanualtransmissionsAfterextensivesystematicdevelopmentofthegearsetinwhichmanythousandsofvariantswereproducedandcompared,thegearsetconceptthatisillustratedinFig.2isthefinalvariantandtheidealconceptforachievingthegoalsspecified.ThegearsetselectedisbasedontheconstantdriveconceptandconsistsoftwoconcentricdriveshaftseachofwhicharedrivenbyoneofthetwomultidiskclutchesintheFig.2Gearsetschemeof7Dvariantdualclutch,twocountershaftsalsoconcentrictooneanother,amainshaftandanoutputshaft.ThegearratiosareengagedbythefoursynchronizerunitsA/B,C/D,E/F,andG/H,whicharearrangedonthemainshaftandonthehollowcountershaftandtheseareconnectedtotheloosewheelsortheadjacentshafts.AnimportantfeatureinthegearsetistheconnectabilityofbothcountershaftsthroughtheC/Dsynchronizerunit.IntheDshiftposition,thegearratiosselectedinthiswaycanbedoublyusedwhichreducesconstructioncostscomparedtoconventionaldualclutchgearsets.Similarly,thisfeatureisusedinfirstgearbecausethenthevehicleisstartedupusingthemorepowerfulK1clutch.Becauseofthisdualuseofthelastgearlevelinthetransmissionforthefirstandsecondgear,thedesiredratiostep1-2isachievedthroughthetransmissionratiosofbothconstantdrivephases.TheuseoftheK1clutchforstartingupinfirstgearresultsinevitablyinthedirectgearalsobeingassignedtotheoddsubsection.Inthiscase,thefifthandseventhgearscanbeselectedasadirectdrive.Withthisfeature,itwaspossibletodevelopamodulargearsetwhich,onjustafewchanges,containstwodifferenttransmissiongearratiovariantswithfundamentallydifferentcharacters.Forthefirstversion,withanoverallspreadofabout4.7,theseventhgearisselectedasadirectgear(calledthe7Dvariant).Fig.2showstherelevantgearsetdiagramwiththeperformanceflowsinallspeeds.Duetoitssophisticatedgearsteps,thistransmissionishighlysuitableforverysportyvehiclesthatneedonlya"little"transmissionsteppingduetothehighrotatingengine.Optimaltractivepowercanbeprovidedatanytimeduringvehicleoperation.Thesecondversionisbasedonthe7Dvariant,however,fifthgearwasselectedasthedirectdrive.Whenmaintainingthetorquemultiplicationratioandinadaptingthetransmissionratioofseverallowergearlevels,yougetthe5Dvariantwithaconsiderablyhighertransmission-ratiospreadforvehicleswithincreasedcomfortdemandsandsimultaneouslyreducedconsumption.Fig.3illustratesthedesignofthe7Dvariant.Themainsimilaritywithexistingmanualtransmissionsforstandardtransmissionsisnoticeable.Duetothecompactgearsetdesign,thesufficientshaftdimensioningandthefavorablearrangementinproximityofthebearingofthehightransmittingratios,centralbearingglasseswerenotnecessarydespitetheproportionallylargebearingclearance.Overall,onlytwohousingbearinglevelsarenecessarywherethefrontlevelislocatedbehindbothconstantgears.Inaddition,averycompactandinexpensivetransmissiondesigncouldbeimplementedbasedonthebearingconceptselected,especiallyintheareaofthehollowshaft.Fig.3SectionalDrawingof7Dvariant3ThedualclutchThecentralmoduleofthishighlytopicaltransmissionconceptisthewetdualclutch.Withabroadspectrumoftechnicalfeatures,itimplementsthefunctionalprovisionsofthetransmissioncontrolunitandthusdistinguishesthespecialcharacterofthistransmissionconcept.Veryfastdelaytimes,lowinertiaandgood,comfortablefrictionvalueprogressionsfacilitate,verysportyhandlingwithhighlydynamicgearshiftingandcomfortablecruisingatahighlevelofefficiency.Thedualclutchplaceddirectlyonthetransmissioninputacceptstheenginetorquefromthtorsiondamperandfeedsittooneofthetwosubsections,dependingonthesituation.Safetyconsiderationshaveledtoa"normallopen"design.Theradialarrangementofthemultidiskpackagerepresentsthebestcombinationofperformancandinstallationspaceneed,Fig.4.Fig.4DualclutchCarefulliningandoilselectionaswellasintensiveenhancementofthistribologicalsystemaretherequirementsforcomfortandperformanceofthisclutchthroughoutitsservicelife.Throughintensetestinganddetailedcalculations,itwaspossibletoachieveaveryhighthermaloadingcapacity.Aspartoftheprocess,theliningtype,dimensioning,andgroovingaswellasequaldistributionofthermalloadandoilflowinthemultidiskpackagearedecisivedesignfeatures.Lowtorquedragevenwithlowtemperaturesaswellashighspeedendurancestrengthsupportcomfortandahighlevelofsportiness,butarealsoimportantsafetyrequirements.Rotating,centrifugalforce-compensatingclutchcylinderswithhysteresisoptimizedgasketsmaketheclutcheseasytocontrol.Integratedplatespringsreliablyacceptrapidpistonresettingevenathighspeeds.Inthecaseofanopenclutch,onlytransmissioninputshaftswithverylowadditionalmassinertiaareused.Thissupportsrapidsynchronizingsequencesandalongservicelifeofthesynchronizerunits.4ThehydrauliccontrolunitInthepresentdualclutchtransmission,thehydrauliccontrolunitfulfillsthefollowingtasks:ActuatingthedualclutchShiftingthegearshifts,i.e.engaging/synchronizingthegearCoolingthedualclutchGearlubricationEmergencystopfunctionincaseofcompletefailureoftransmissionelectronicsSeveralfeaturesinthehydrauliccontrolunitaswellascriteriafortheselectionofthecontrolconceptaregoingtobedescribedinmoredetailbelow.4.1PerformanceTheuseofthedualclutchtransmissioninsportyvehiclesdemandshighperformancefromthehydrauliccontrolunit,especiallywithregardtothefirsttwotasksbecausethetimely"handling"ofthesetaskscomeintoplayingearshiftingandgearshiftingtimes.Thatiswhyparticularvalueisplacedontheselectionoftherightcontrolunitconceptaspartofthesystemdesign.Duringthedecisionprocess,thechoicewasmade,inprinciple,betweentwoconcepts,Fig.5.Fig.5Controlconceptdirectcontrol/precontrolPrecontrolofthevalvesDirectcontrolofthevalves(so-calledcartridgevalves)Incaseofdirectcontrol,thevalvethatisusedforpressurecontrol,e.g.aclutch,isdirectlyconnectedtothepower-generatingproportionalsolenoidsandprovidesthemainpressuretothecorrespondingclutchpressure.Theprecontrolusesthepressurethatissuppliedbyapressurecontroller,forexample,toactuateanadditionalvalvethatsuppliestheclutchpressurefromthemainpressure.Toassesstheperformanceofbothconcepts,alargernumberofcomparedmeasurementswereperformedwithdifferentsystems,ofwhichtwosystemsshallbeconsideredhere:ZFhydrauliccontrolunitwithprecontrolforDCTstandarddriveComparativehydrauliccontrolunitwithdirectcontrolAreferenceclutchwasusedastheclutchtoengage.Criteriaforassessingtheperformancewere(seealsoFig.6):Fig.6Delay,increase/rise,andfalltimes.Redcurve:Power/Electriccurrent.Greencurve:ClutchpressureDelaytime,1to4Timeofstepresponseuntilclutchinflationpressure,1to2Timeofthestepresponseupto90%ofthemainpressure1to3Timeofpressuredrop(emptyingtimes),5to6Fig.6shows,asanexample,thetimesforatransmissionoiltemperatureof+20°Ctobereached.Onenoticesthatthedirectcontrolfirstindicatesalowerdelaytime(14.3ms)comparedtotheprecontrol(30.1ms),seealsotimeofbrand1to4.Forincreasetoclutchinflationpressureorto90%ofthemainpressureshows,however,theadvantageoftheprecontrolledsystem(seealsosummarizingtab1).Emptyingtimes,alsopresentadisadvantagefordirectcontrol.Trans-missionoiltemperatureof-20°Calsoshowcomparableresultsforstepresponsesandfalltimes.Allofthetestssupportthestatementthatdirectcontrolhasanadvantageouseffectwithsmalloilvolumes.However,iflargeoilvolumeshavetobetransported,precontrolvalvesaretobepreferredduetolargeropeningcross-sections.4.2OperationalsafetyOperationalsafetyisdeterminedessentiallyduetothesoilingtendencybecausetheso-calledsiltingcanleadtothevalvesgettingjammed.Provocationtestswithtransmission-specificenvironmentalconditions(dirtyoil)demonstratedtheinfluencesofsoilingonthecharacteristiccurves.Technical,trouble-freecharacteristiccurveprogressionscouldbeillustratedonlywithahighditheramplitudeinvalveactuation,whichleads,inturn,toincreasedvalvewear-and-tearduetothemicromovementsthatitcauses.Theincreasedtendencytowardsoilingcanresultneedingafinefilter.4.3CostsInadditiontothedelaytimecomparisonaswellasassessingtheoperationalsafety,thecostswererelevantforafinalevaluation.Thecomparisonwithregardtothehydraulicandelectro-magneticcomponentsshowsthataprecontrolsystemhascostbenefitscomparedtoadirectcontrolsystem.Addedtothisarethehigherflowswiththeactuationofdirectcontrolvalves,which,inturn,resultinamoreexpensiveTCU.Furthermore,inoptingforprecontrol,ZFisableto"pool"togetherpressurecontrollersinlargequantitiesbecausethese,too,areusedintheautomaticZFplanetarygearset.4.4EmergencystopfunctionIncasethereisacompleteoutageinthetransmissionelectronics,ahydraulicemergencystopfunctionisactuatedinthetransmission.Theclutchthatispressurizedwithalargeramountofpressureintheeventofasystemoutagewillcontinuetobepressurized.Thisconditionismaintaineduntilanadjustableenginespeedthresholdisachieved,thentheclutchopensinordertopreventtheenginefrombeingchoked.Itisnotpossibletore-startthissystem.5SportyfunctionsForfunctiondevelopers,thedualclutchtransmissionofferstheopportunitytocombinethecomfortofasteppedautomatictransmissionwiththedynamicsandsportinessofacountershafttransmission.Connected,therefore,aretypical"catalogvalues,"suchastimefromzeroto100kilometersperhourorthetimefrom80to120kilometersperhourwithcorrespondinglyfastkick-downshifting,butalsosubjectiveaccelerationsensitivityduringashiftingsequencewherethepuristamongthemanualtransmissiondriversstillwantstofeelthatjoltofacceleration.Onefunctionespeciallydesignedforthedualclutchtransmissioninsportscarsisthe"racestart"function.Theracestartisafunctionusedtoachieveoptimalaccelerationfromastandstill,i.e.intheshortesttimefrom0to100km/h.Thesequenceprogressesasfollows:Theengineisbroughttoasuitablyhighrpmwiththeclutchengagedinfirstgear.Thedriversimultaneouslyactuatesthebrakeswiththeleffootsothattheclutchcanalreadybelightlyengagedandthegaspedal(fullthrottle)inordertobringthevehicleuptothetargetspeed.Bysimultaneouslypressingandholdinganoperatingelement,suchastheselectorleverorapushbuttononthesteeringwheel,theracestartintentionisconveyedtothesystem,theenginespeedadjustedandthestartuppreventeduntilthedriverreleasesthebrake.Duringtheracestart,theclutchisclosedunderthecontrolofthewheelslipwithwhichtheoptimalaccelerationisachievedandbyexploitingthedynamicenginetorque(inertiatorque).Theentireprocedureprogressesautomaticallyoncethedriverreleasessothatevenaninexperienceddrivercanachievethebestpossibledriveperformancefigures.Obviously,thedrivercancanceltheprocedurebyremovinghis/herfootfromthegaspedalortouchingthebrakes.Also,thesystemrecognizeswhenthestreetconditionsdonotpermitaracestart,suchaswetroads,forexample.Duetotheoptimalstart-upandashiftingsequenceintosecondgearfreeoftractioninterruption(seealsosportsshifting),theracestartfunctionenablestheaccelerationtimeof0to100km/htobeimprovedbyanaverageof0.2seccomparedtoacarwithamanualtransmission.Atthesametime,thisfunctionalityhelpsavoidimproperuseandresultingclutchoverload.ThetopchartinFig.7illustratestheengineandtransmissioninputshaftspeed,thelowerchartshowsthevehicle′slongitudinalacceleration.Startingwithacrankingspeedof6,800rpm,theclutchbeginstoclose,whichleadstoanenginepressureuptoabout4,000rpm.Thedynamicenginetorqueusedtoachievethisresultsinanaccelerationof0.7-0.9g.Intheprocess,noticeablevibrationsinthetransmissioninputshaftspeedsignaldevelopduetothewheelslipregulation.Afterabout1.2sec,thevehicleisacceleratedonlybytheenginetorquewithapprox.0.5g.Itmustbementionedherethatthistestwasperformedusingavehiclewithveryhightraction.Inmostcases,astartingspeedofonlyuptoabout4,000rpmisreasonable.Afurtherfunctiondevelopedforthedualclutchtransmissionisso-calledsportsshifting.Thisisdescribedinmoredetailbelow.Ingeneral,agear-shiftchangebythedriverisonlyperceivedacousticallybythechangeintheenginespeed.ThetransitionfromtheaccelerationleveloftheoriginalgeartoFig.7Measurementofaracestarthenewgearshouldbemadesmoothlyandcontinuously.Thisalsocorrespondstothestandardshiftingsequencesinauto-maticanddualclutchtransmissions.However,manydriversofsportycarswishthattheyhadtheoptionofbothdistinctivecomfortshiftingsequencesaswellassportyshiftingsequences,which,besidesthehapticresponse(accelerationjolt),alsohaveanaccelerationadvantageasaresult.Tothisend,thedynamicenginetorquecanalsobeusedagain.Therequirementforthisisthetorquecapacityofthedualclutchwhichhastobeabletotransmitthistorqueincrease.Asthepossibletorqueincreasedependsonthegradientsoftheenginespeed,thiscanbeusedparticularlyeffectivelyinshiftinggearswithalargespeeddifferencewiththetargetgear(largeratiospread/ratiostep),whichiswhythegearchanges1-2,2-3,and3-4areoffered.Intheprocess,sportsshiftingfromthefrsttosecondgearcanserveasasupplementtotheacestartforimprovingtheaccelerationtimefromto100km/h.Astheuseofthedynamictorqueispureapplicationtopic,wedistinguish,asarule,betweenthreeshiftingsystems.Fig.8illustrateshestylizeddifferencesandfeaturesbetweenthehiftingsystems,Fig.9showsanoriginalmeasurementfromaprototypevehicle.Thetopchartshowstherespectiveengineandransmissionspeed,thebottomchartshowstheorquesfrombothclutches.Thebottomlineinthehartrepresentstheclutchfromthetargetgearthatisusedtoachievethetorqueincreaseduringenginespeedadjustmentandtherebyaccelerationgains.Fig.8SimplifieddepictionofaccelerationprocedureswithFig.9Measurementofsportsshift2-3inthevehicle附录B外文文献翻译运动型7速双离合器变速器系统摘要：ZF公司的7速双离合器变速器是一款创新型的、适用于运动型车辆的变速器。精密的速比和自然拥有的极佳驾驶性能使得它成为运动型车辆理想的变速装置。本文对该变速器紧凑的齿轮机构、可改善效率和提高发动机-速度-强度的直接喷射润滑系统,双离合器系统及基于预先控制原理的液压控制单元等作了详细介绍。在出现电气故障时液压控制系统可选用液压巡航模式。另外,变速器设计、功能特性等也都体现出变速器具有鲜明的运动特征。关键词：自动变速器;双离合器;车辆连接;效率1.前言提及自动变速器时,双离合器系统被普遍认为是运动型的标杆。基于中间轴结构的该类变速器的优点是非常直接的“车辆连接”、高转速性能和及其优越的变速器效率。本文介绍的用于标准型传动系统的7速双离合器变速器的最大转矩可达520Nm、最高转速为9250rpm。为在现有安装空间内实现这些性能数据,创造性的引入了储油室和润滑油直接喷射概念。在详细介绍变速器各特点之前,首先对变速器给出一个总的描述,见图1。图1双离合器变速器(DCT)剖视图发动机转矩经过扭转减振器(未在图1中表示)传递给双离合器。双离合器中的多片式离合器沿径向互相嵌套并将转矩通过两输入轴传递给中间轴齿轮装置。这里,因为安装空间的缘故,中间轴并不位于主轴下方,而是横向斜置。用于采用了带干油箱的直接喷射润滑,才有这样的可能。一方面,直接喷射改善了热传递,另一方面不会在油底壳中出现明显的飞溅损失。向变速器供给的润滑油由内啮合齿轮泵提供,利用齿轮机构驱动的该泵安装在双离合器后面。借助于该齿轮机构,驱动装置的优点是可根据不同的齿轮速比和预期的需要获得适合的流速和油泵最高转速。另一优点是改善了安装空间,可根据油泵效率实现油泵宽度和直径之间的最佳比例。液压控制单元安装在齿轮机构的下方。液压控制单元根据需要向离合器和换档执行机构提供压力和冷却润滑油。而采用双向作用油缸的换档执行机构则安装在齿轮机构的侧面。检测档位位置的传感器直接安装在四根换档轴上。变速器具有一个外部控制单元。2.七个精密档位-极具运动性的概念这里引入的双离合器变速器齿轮机构考虑了以下需求：高动力密度；高达9250rpm的高速耐久强度；可变性和模块化设计；变速特性-速比范围从4.7到6.8；源于现有的手动变速器。据此对齿轮机构进行了广泛的系统开发,引入并比较了数以千计的变量,图2所示的齿轮机构是最终形式,是一个满足各项目标的理想概念。所选择的齿轮机构是基于常规传动概念,变速器由各由双离合器中的一组多片式离合器驱动的两根同心传动轴、两根同心的副轴、主轴和输出轴组成。齿轮速比的变化由4组同步器A/B、C/D、E/F和G/H实现,这些同步器布置在主轴和中空的中间轴上并连接到自由轮或相邻轴上。齿轮机构的一个主要特征是两中间轴通过C/D同步器连接。在D位置可两次选择齿轮速比,与常规双离合器变速器相比降低了成本。同样,该特征也被应用在1档齿轮上,因此当车辆起步时可利用更强有力的K1离合器。由于变速器1档和2档均使用了最后一对齿轮,1-2档之间的速比是由两常啮合齿轮副确定。利用K1离合器和1档起步不可避免的会导致直接档齿轮设定成奇数。这时,5档和7档齿轮可选作直接档传动。据此可开发一模块化齿轮机构,仅需少量改变而获得两种具有不同特性的齿轮速比。第一种结构的总速比是4.7,7档齿轮作为直接档(称为7D型)。图2给出了齿轮机构的动力流。借助于精密的速比间隔,该变速器非常适用于高发动机转速和“小”速比间隔的运动型车辆。可在车辆的各种工况下获得最佳的牵引力。第二种结构基于7D型,但将5档作为直接档。当维持转矩放大倍数和稍稍减少变速器档位数时,5D型仍具有相当高的变速器总速比范围并且提高了舒适性同时也降图27D型齿轮机构简图低了油耗。图3是7D变速器的设计图。和现有标准的手动变速器的相似之处是显见的。由于齿轮机构设计紧凑,各轴具有足够的尺寸并且有利于在大速比处布置轴承,中央轴承罩无需顾及大的轴承间隙。由于前轴承座位于两常啮合齿轮后部,因此仅需两个轴承座即可。另外,非常紧凑和廉价的变速器设计也是基于对轴承的选择,特别在空心轴方面。图37D型变速器剖面图3.双离合器该变速器的核心模块是湿式双离合器。该离合器具有一个宽型谱的技术特征,能实现变速器控制单元的功能和辨别该变速器的专有特征。离合器延迟时间短、惯量小、动作过程中具有良好和舒适的摩擦系数、极具运动性的高动态换档特性、行驶舒适以及高效率。双离合器直接安装在变速器的输入端,发动机转矩经扭转减振器后根据具体情况传递给两离合器中的任一个。出于安全考虑,离合器设计成“常开”状态。沿径向布置的多片离合器具有最佳的性能和安装空间,见图4。图4双离合器确保离合器在使用寿命中其性能和舒适性取决于摩擦片衬里、润滑油的选择和提高该摩擦学系统的性能。经过大量试验和详细计算,获得了相当高的热负载特性。作为其中的一部分,摩擦片衬里的类型、尺寸、沟槽以及在离合器壳体中热负荷耗散和润滑油流动等都是决定性的设计特点。离合器甚至在低温情况下也具有低的牵引转矩,并具有高速疲劳强度、运动舒适性和高水平的运动性,同时也能满足安全性方面需要。装有滞后优化垫圈和配备有离心力补偿的离合器主缸使得离合器操控更容易。板簧能确保高速时活塞的快速回位。在离合器断开情况下,变速器输入轴仅有非常低的附加转动惯量。这样可确保快速同步和同步器的长寿命。4.液压控制单元在现有的双离合器变速器中,液压控制单元应完成下列任务:操纵双离合器；换档,即齿轮的结合/同步；冷却双离合器；变速器电子系统完全失效时的应急停车功能；液压控制单元的几个特征和控制概念的选择标准详见以下各小节。（1）性能在