前轮驱动-------外文翻译.docx

1.6Front-wheeldriveTheengine,differentialandgearboxformoneunit,whichcansitinfrontof,over,orbehindthefrontaxle.Thedesignisverycompactand,unlikethestandarddesign,meansthatthevehiclecaneitherbearound100-300mmshorter,orthespaceforpassengersandluggagecanbelarger.Theseareprobablythemainreasonswhy,worldwide,moreandmorecarmanufacturershavegoneovertothisdesign.Inrecentyearsonlyafewsaloonsofupto21capacitywithoutfront-wheeldrivehavecomeontothemarket.Nowadays,front-wheeldrivevehiclesaremanufacturedwithV6andV8enginesandperformancesinexcessof150kW.However,thistypeofdriveisnotsuitableforcommercialvehiclesastherearwheelsarehighlyloadedandthefrontwheelsonlyslightly.Nevertheless,somelightcommercialvehiclemanufacturersacceptthisdisadvantagesotheycanlowertheloadareaandoffermorespaceorbetterloadingconditions(Fig.1.47).Thepropshaftsnecessaryonstandardpassengercarswouldnotallowthis.Fig. 1 -47 The low cargo area on the Peugeot light commercial vehicle J 5/J 7 is achieved due to frontwheel drive and a semitrailing link axle to the rear (similar to the one in Fig. 1.63).16.1Typesofdesign161.1Enginemountedlongitudinally4North-South,infrontoftheaxleIn-lineorVenginesmountedinfrontoftheaxle-regardlessofthewheelbase-giveahighfrontaxleload,wherebythevehiclecentreofgravityispushedaIongwayforwards(Fig.1.48).Goodhandlinginsidewindsandgoodtraction,especiallyinthewinter,confirmthemeritsofahighfrontaxleload,whereastheheavysteeringfromstanding(whichcanberectifiedbypower-assistedsteering),distinctundersteeringduringcorneringandpoorbrakingforcedistributionwouldbeevidenceagainstit.Thistypeofdesign,asopposedtotransversemounting,ispreferredinthelargersaloonsasitallowsforrelativelylargein-lineengines.ThefirstvehiclesofthistypeweretheAudi80and100.Incliningthein-lineengineandplacingtheradiatorbesideitmeansthefrontoverhanglengthcanbereduced.Automaticgearboxesneedmorespacebecauseofthetorqueconverter.Thisspaceisreadilyavailablewithalongitudinallymountedengine.Adisadvantageoflongitudinalenginesistheunfavourablepositionofthesteeringgear:thisshouldbesituatedoverthegearbox.Dependingontheaxledesign,thisresultsinlongtierodswithspringstmt(McPherson)frontaxles(Fig.1.57).1.6.1.2TransverseenginemountedinfrontoftheaxleInspiteoftheadvantageoftheshortfrontoverhang,onlylimitedspaceisavailablebetweenthefrontwheelhousings(Figs1.49and1.50).Thisrestrictionmeansthatengineslargerthananin-linefourcylinderorV6cannotbefittedinamedium-sizedpassengercar.Transverse,asymmetricmountingoftheengineandgearboxmayalsocausesomeperformanceproblems.Theunequallengthofthedriveshaftsaffectsthesteering.Duringaccelerationthevehiclerisesandthedriveshaftstakeondifferentangularpositions,causingunevenmomentsaroundthesteeringaxes.Thedifferencebetweenthesemomentstotheleftandtotherightcausesunintentionalsteeringmovementsresultinginanoticeablepulltooneside(Fig.3.88);driveshaftsofequallengtharethereforedesirable.Thisalsopreventsdifferentdrillinganglesinthedriveshaftcausingtimingdifferencesindrivetorquebuild-up.ThelargearticulationangleoftheshortaxleshaftcanalsolimitthespringFig-，-48Infront-wheeldrivevehiclestheenginecanbemountedlongitudinallyinfrontofthefrontaxlewiththemanualgearboxbehind.Theshaftgoesoverthetransversedifferential(illustration:Renault).Fig.1.49CompactpowertrainunitontheVauxhallCorsa(1997).Theengineistransversemountedwiththegearboxontheleft.TheMcPhersonfronta×leandsafetysteeringcolumncanbeseenclearly.Fig.1.50Layoutoftransverseengine,manualgearboxanddifferentialontheVWPolo.Becausethearrangementisoffset,theaxleshaftleadingtotheleftfrontwheelisshorterthanthatleadingtotherightone.Theshiftershaftbetweenthetwocanbeseenclearly.Thetotalmechanicalefficiencyshouldbearoundn0.9.travelofthewheel.Toeliminatetheadverseeffectofunequallengthshafts,passengercarswithmorepowerfulengineshaveanadditionalbearingnexttotheengineandanintermediateshaft,theendsofwhichtakeoneofthetwoslidingCVjointswithangularmobility(Figs1.51and1.17),Moreover,tflexingvibration*ofthelongdriveshaftcanoccurinthemaindrivingrange.Itsnaturalfrequencycanbeshiftedbyclampingonasuppressionweight(Fig.4.1).1.6.2 Advantagesanddisadvantagesoffront-wheeldriveRegardlessoftheengineposition(seeFig.1.52),front-wheeldrivehasnumerousadvantages: thereisloadonthesteeredanddrivenwheels; goodroad-holding,especiallyonwetroadsandinwintryconditions-thecarispulledandnotpushed(Fig.1.35);Fig.1.51GearboxunitontheLanciaThema,locatedbesidethetransverseengineandbetweenthefrontaxleMcPhersonstruts.Owingtothehighengineperformance,thedesignfeaturestwoequal-lengthaxleshaftsjoinedbyanintermediateshaft.Therearealsointernallyventilateddiscbrakes. gooddrive-offandsufficientclimbingcapacitywithonlyfewpeopleinthevehicle(Fig.6.22); tendencytoundersteerincornering; insensitivetosidewind(Fig.3.125); althoughthefrontaxleisloadedduetotheweightofthedriveunit,thesteeringisnotnecessarilyheavier(incomparisonwithstandardcars)duringdriving; axleadjustmentvaluesarerequiredonlytoalimiteddegreeforsteeringalig