Six-SpeedAutomaticTransmissionsandCVTstoSupportFuelEconomyAbstractTheimprovementinfueleconomyandinCO2emissionlevelshasahighpriorityinthedevelopmentworkofnewpassengercarsandnewmodels.Newlydeveloped6-speedautomatictransmissionsandcontinuouslyvariabletransmissions(CVT)willbeavailableinvehiclesinthenearfuture.Thesetransmissionswillfulfilltherequirementstoreducefuelconsumptionandemissionsandwillincreasedrivingcomfortatthesametime.Acomparisonwiththestateoftheartsolutions,i.e.5-speedautomatictransmissionsforrearwheeldrivenand4-speedautomaticsforfrontwheeldrivencars,showstheadvantageofthenewtransmissionsystems.ThenewdesignsleadtoafuelconsumptionreductionintheNewEuropeanDrivingCycle(NEDC)of6to8%.Inparallelthereisanincreaseinaccelerationfrom0to60mphof4to10%.1IntroductionCurrentlyinpassengercardevelopment,areductioninfuelconsumptionisoneofthekeycriteriathatanewvehicleoranewmodelismeasuredfor.InEurope,themotivatingforcebehindthisisthe1991self2adoptedmissionofGermanautomotivemanufacturerstoreducefuelconsumptionby25%bytheyear2005andtheproposalsentbytheAassociationofEuropeanAutomotiveIndustry(ACEA)totheEuropeanComm.issionin1995callingforareductionoffleetconsumptionforthevehicleslicensedinEurope.Theself2adoptedmissionofGermanautomotivemanufacturers(VDAconsent)predict,onaveragefortheindustry,areductioninaverageconsumptionfrom8l/100kmto6l/100kmoveraperiodof14years.Thiscorrespondstoanincreasefrom56.8mpgto75.7mpg.TheACEAagreementisbasedonareductioninCO2emissionsfrom180g/km(112g/mi)to140g/km(87g/mI)bytheyear2008.Thisisanextremelyambitioustargetachievedonlythroughagreatnumberofimprovementmeasures.Inadditiontoimprovementsontheengine,thedrivelinealsohastocontributetowardstheattainmentofthisobjective.Thetransmission,asthemainunitinthedriveline,isofparticularimportance.Whencallingforareductioninfuelconsumption,othercriteriademandedofthedrivelinemustbetakenintoconsideration.Inparticular,performanceshouldbementionedhere.Fuelreductionandperformanceoptimaisationrepresentconflictingobjectivesfordrivelinedevelopmentsandaretypicalofmanytechnicaltasks.Anappropriatecompromisemustbefoundfortheindividualapplications.Inadditiontomminimumfuelconsumptionandgoodperformancevalues,drivecomfortalsoplaysanincreasinglyimportantroleasanevaluationcriterionforassessingpassengercars.WwithinEurope,thisisalsoresultinginanincreasingproportionofautomatictransmissions(seeFigure1).Duetothesettingofelementsfittedasstandardinautomatictransmissions,thehydrodynamictorqueconverter,oilpump,hydraulicunitanddraglossesinshiftelementsresultinautomatictransmissionsexperiencinghigherlevelsofpowerlossescomparedtomanualtransmissions.Satisfyingtherequirementsoffuelreductionisthereforeaparticularlydifficultchallengewhencombinedwwithanincreaseintheuseofautomatictransmissions.Inordertoavoidthesystem-relateddisadvantagesofclassicmulti-ratioautomatictransmissions,continuouslyvariabletransmissionarenowavailableonthemar-ket.Othertransmissionsystems,primarilybasedonmanualtransmissionconcepts,arecurrentlyunderdevelopment.Fig.1DevelopmentoftheautomatictransmissionspenetrationinpassengercarsinWesternEuropeSincedifferenttransmissionsystemsareappropriatefordifferentapplicationsinpassengercars,ageneralcomparisonofhowthetransmissionimpactsfuelconsumptionisoflimiteduse.Thispaperwillnotprovidedetailsofhowallthenamedsystemsimpactfuelconsumption,butitwillconsiderthepotentialforimprovingfuelconsumptionforselectedtransmissionsystems.Thepaperwillfocusonsystems,whicharebeinglaunchedasvolumeproductionmodels.Afewcommentsregardingthe5and62speedmanualtransmissionswillbefollowedbyareviewofthe5and6-speedautomatictransmissionsforstandarddrivelines.The4,5and6-speedautomatictransmissionsandcontinuouslyvariabletransmissionsusedinfrontwheeldrive(FWD)vehicleswillalsobereviewed.2FuelsavingsandperformanceTheEuropeanECEdrivingcycleconsistsofonethirdurbantravelandtwothirdsconstanttravelat90and120km/hrespectivelyandhasbeenusedasabasisforcomparingfuelconsumptionformanyyearsinEurope.CurrentlytheNewEuropeanDrivingCycle(NEDC=NEFZ=“NeueEuropaischeFahrzyklus”)orMVEG(MotorVehicleEmissionsGroup)forvehiclesofupto2.5tonsdefinesthebasisforevaluatingfuelconsumptionandexhaustemissions(seeFigure2).Thisoveralldrivingcycleillcharacterizethebasisforcomparisonsinthispaperwhenevaluatingtransmissionsystems.Usageinothercountriesillbebasedonotherdrivingcycles,forexample,theEPAintheUS.Simsearly,differentautomotivemanufacturersandtestinstitutionsusespecifictestprocedures,whichwillnotbeconsideredhere.Consumptioncomparisonsarerepresentedintheformofabsolutevaluesinlitersper100kmormilespergallon(mpg)and/orasrelativedeviationsin%,wheretransmissionsrepresentingpreviousstate2of2the2arttechnologyserveatthebasisforcomparison.Takeoffacceleration(distancereachedafter4seconds),fullloadacceleration(timetoreach100km/hor60mphfrom0km/h)andelasticity(timetakentoincreasefrom80to120km/h),whichrepresentimportantparametersinthecustomersevaluationofavehicletodayhavebeenestablishedastheassessmentcriteriaforperformance.Assessmentsmadeinthispaperwillfocusonfullloadacceleration,whichwillbespecifiedastimeinseconds.Fig.2Europeandrivingcycle(NEDC)Theconsumption2acceleration2diagram(seeFigure6)isatooltodescribeconsumptionandperformanceinonediagram.Basedonfullthrottleacceleration,thisdepictsthefuelconsumptionofavehiclewithoneparticularengineanddifferenttransmissions.Anotherparameteristheaxleratiowhichinfluencesfuelconsumptionandacceleration.Theconsumption-accelerationdiagramwillvaryif,forexample,mpg(milespergallon)isappliedtotheconsumptionaxisinsteadofl/100km(litresper100kilometres)orifthesettingofaccelerationasdistanceafter4secondsisusedastheperformanceparameter.Theaxleratioparametercanalsobemodifiedbyotherinfluencingparameterssuchasvehicleweight.Theconsumptionandaccelerationvaluesshowninthispaperaremainlybasedonsimulationcalculations.Inthesimulationmodel,thelossesofdifferenttransmissionsystemsasmeasuredvaluesfromtransmissiontestsaretakenintoconsiderationsotheinfluenceofthetransmissionisdepictedrealistically.Inordertoissueastatementregardingtheaccuracyofthesimulationresults,someofthecalculatedresultswerecomparedwitthemeasuredvalues.Thisshowedtheabsolutevaluesarenotalwayscalculatedpreciselyduringsimulationbutthecomparativevaluescorrelateverywell.Arelativecomparativereviewwillprovideaccuratestatements.3TransmissionconceptsInthepast,4-and5-speedmanualtransmissions(MT)werethemaintransmissionsfoundontheEuropeanmarket.Thankstotheirmechanicalstructure,theyareefficientbutasaresultofincreasedtrafficandgreateremphasisoncomfort,theynolongersatisfytherequirementsofmanycustomers.Therefore4-and5-speedautomatictransmissions(AT)arealsoused.Currentlytheseofferaveryhighlevelofdrivecomfort,buthavethedisadvantageofhigherpowerlossesandgenerallyresultinhigherfuelconsumption.Inadditiontothisandalongsidethetwoclassictransmissionsystems(manualandmulti-ratioautomatictransmissions),thereareothertransmissionsystemsonthemarketandunderdevelopment,whichthemainobjectiveistocontributetowardsareductioninfuelconsumptionforpassengercars.Manualtransmissionsareexperiencingatrendtowards6gears,shiftandclutchautomation.Thisresultsinautomatedmanualtransmissions(AMT).Usinghydraulicallyorelectro-mechanicallyactuatedAMTsystems,whicharebasedonthemechanicsofmanualtransmissions,shiftscanbeimplementedusingtheautomaticcontrolofashiftprogram.Apowershiftprocesscharacterizesshiftsinautomatictransmissionsystemswithnointerruptiontotraction.In2001thefirst6-speedautomatictransmissionwasintroducedinthemarket.Inadditionto62speedautomatictransmissions,therearealsocontinuouslyvariabletransmissions(CVT)onthemarketwithpushbeltsandchainsservingasthetorquetransmittingelementandcontinuouslyvariabletoroidaldriveswhicharedevelopedasroller-typetransmissions.Dualclutchtransmissionsbasedonmanualtransmissionsareunderdevelopment.Sincepowershiftscanbeimplementedwiththesesystems,theyshouldbeclassifiedasautomatictransmissions.Aspreviouslymentioned,thefollowingcomparisonoffuelconsumptionanddrivingperformanceislimitedtotransmissionsystemswhicharebeinglaunchedasvolumeproductionmodelsorwillbeavailableonthemarketinthenearfuture.Forsta