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TheZFASTronicFamilyAutomotiveTransmissionsforAllCommercialVehicleClasses1RequirementsforCommercialVehicleTransmissionsCustomersdemandhighefficiencyalongwithincreasingvehiclecomfortandsafety.Asanindependenttransmissionmanufacturer,ZFcustomerneedsincludetheneedsofdrivers,forwardingcompanies,andvehiclemanufacturers.Therefore,ZFconsidersthemanyrequirementsthatanewtransmissionconceptmustfulfillwhendevelopingatransmission,Figure1.Keepingcostslowisaconsiderablechallenge,initiallyintermsofacquisitionandlaterduringoperation.Thatiswhyfuelconsumptionisincreasinglyoneofthedecisivevehiclefeaturesthatseparatethecompetition.Amoderntransmissioncanmakeanimportantcontributionhere:Ontheonehandbyimprovingefficiencyandontheotherhandinautomatictransmissionsbytheoptimalselectionofthegearratiodependentonthedrivingsituation.Reducingthetransmission,sweightalsoleadstoreducedcosts:Usinglessmaterialreducesacquisitioncostsandenablingahigherpayloadreducesoperatingcosts.Ontheonehand,decreasedoilconsumptioncontributestoenvironmentalprotection;additionally,ithasanimmediateinfluenceonthecosts,however,thataccruethroughoutthevehicle’sservicelife.Thedemandforsystemcomfortincreasinglyapproachesthestandardsetbycartechnology,whereasinthiscaselimitsaresetbymassratiosandcostconstraints.图1商用车辆的需求Fig.1RequirementsforcommercialvehiclesLownoiseemissionsarearesultoflegalregulationsontheonehandbutalsocontributetomorecomfortabledriverworkplaceswhenmet.Furthermore,electronicsystemsincreasinglysupportthedriverandrelievehim/herfromroutinetasks.Thisbenefitssafetyintraffic.2AdvanceswithAutomaticTransmissionsAutomatictransmissionscansatisfymanyofthedemandsthatcustomersmakeoncommercialvehiclesconsiderablybetterthanmanualtransmissions.Despitethefactthatautomatictransmissionsaregenerallymoreexpensive,ifonetakesthecompleteinstalledmanualtransmissionsystemincludingthegearshiftsystemintoaccount,thedifferenceinacquisitioncostsisnolongerasgreat.Moreover,thegoaloffuturedevelopmentsistofurtherreducethecostsforautomatictransmissions.Eventodaythehigheracquisitioncostsarealreadypayingforthemselvesrelativelyquicklyduetoloweroperatingcostssothatautomatictransmissionsareeconomicallyadvantageousinthelongrun.TheefficiencyoftheASTronicfamilyoftransmissionsiscomparabletoamanualtransition;however,asarule,theshiftingpointselectionisbetterduetotheapplicationofanautomaticdrivingstrategy,whichpositivelyaffectsfuelconsumption.AlongtermstudyconductedbyZFandDEKRAfoundthattheautomaticshiftingpointselectionrepresentstheconsumptionperformanceofaverygood,concentrateddriver.Thus,averagingalldriversanddrivingsituationsinacommercialfleet,consumptionisreducedontheorderof3percentsincetheengineoperatesreliablyintheoptimumspeedrangewithregardtofuelconsumption;aprocessthatiscontrolledindependentlyofthedriver,squalification.Anadditionaladvantageintermsofoperatingcostsisreducedclutchwear.Reduceddifferentialspeedsduringstartingandshiftingoperationslengthentheservicelifeoftheclutch,whichhasalsobeenproveninlongtermtests.ManyvehiclemanufacturerstakethisintoaccountandofferasignificantlylongerwarrantycoverontheclutchinASTronictransmissions.Byautomatingtheclutch,theclutchpedalisnolongerneeded,whichclearlysimplifiesoperationforthedriver,particularlyinstopandgotrafficorwhenmaneuvering.Theautomaticgearselectionrelievesthedriverfromshiftingaswell,wherebyhe/shecanconcentratebetteronroadtraffic.However,atthesametime,thedrivercanengagemanuallyatanytime,forinstanceindrivingsituationswherethedriver'sforwardfieldofvisionisinquestion.ThistakesplaceaccordingtoShiftbyWireviaanelectromechanicalcontrolswitchsothatonlyverylittleactuatingforcesareappliedwhenmanuallyselectinggears.Therapidautomaticshiftingandtheprotectionagainstoperatingerroralsocontributetotheincreaseindrivercomfortwhileatthesametimeprotectingthetransmissionanddriveline.Inaddition,theabsenceofamechanicallinkbetweenshiftleverandtransmissionreducescabinnoise.Usinganautomatictransmissionalsohasadvantagesforvehiclemanufacturers.Liketheclutchcontrol,thecompleteshiftlinkageisnolongerneeded,whichmakesbothleftandrighthandsteeringvehicleseasytomanufacture.Whendesigningthedriverworkplace,anythingispossibleintermsofoperatingthetransmission.3TheZFASTronicFamilyZFbegandevelopingautomatedmanualtransmissionsforcommercialvehiclesearly.Thefirstproductwasapartiallyautomatedtransmissionwithautomaticpreselection,whichwasintroducedintothemarketin1984.Tenyearslater,anautomatedtransmissionfollowedwiththeintroductionofthefirstASTronic;however,thedriverstillhadtoselectgears.Itssuccessormodelwasfirstequippedwithanintelligentshiftprogram,whichhasbeeninproductionsince1998.Thus,afullyautomaticsolutionwasofferedinaheavycommercialvehicleforthefirsttime.ThechosentransmissionconceptforASTronicresultedinthemostefficientsolutionpossibleforlargervolumes.Extensiveintegrationandremovalofunnecessarycomponentsopeneduppotentialcostsavings.Asagroupdrive,ASTronicisdesignedwithanunsynchronizedbasictransmissionandsynchronizedsplitterandrangechangegroup,Figure2.图2ZFASTronic的3D剖示图Fig.2ZFASTronic:3Dsectionc