前轮驱动-------外文翻译.docx

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1、1.6Front-wheeldriveTheengine,differentialandgearboxformoneunit,whichcansitinfrontof,over,orbehindthefrontaxle.Thedesignisverycompactand,unlikethestandarddesign,meansthatthevehiclecaneitherbearound100-300mmshorter,orthespaceforpassengersandluggagecanbelarger.Theseareprobablythemainreasonswhy,worldwid

2、e,moreandmorecarmanufacturershavegoneovertothisdesign.Inrecentyearsonlyafewsaloonsofupto21capacitywithoutfront-wheeldrivehavecomeontothemarket.Nowadays,front-wheeldrivevehiclesaremanufacturedwithV6andV8enginesandperformancesinexcessof150kW.However,thistypeofdriveisnotsuitableforcommercialvehiclesast

3、herearwheelsarehighlyloadedandthefrontwheelsonlyslightly.Nevertheless,somelightcommercialvehiclemanufacturersacceptthisdisadvantagesotheycanlowertheloadareaandoffermorespaceorbetterloadingconditions(Fig.1.47).Thepropshaftsnecessaryonstandardpassengercarswouldnotallowthis.Fig. 1 -47 The low cargo are

4、a 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-regardlessofthewheel

5、base-giveahighfrontaxleload,wherebythevehiclecentreofgravityispushedaIongwayforwards(Fig.1.48).Goodhandlinginsidewindsandgoodtraction,especiallyinthewinter,confirmthemeritsofahighfrontaxleload,whereastheheavysteeringfromstanding(whichcanberectifiedbypower-assistedsteering),distinctundersteeringdurin

6、gcorneringandpoorbrakingforcedistributionwouldbeevidenceagainstit.Thistypeofdesign,asopposedtotransversemounting,ispreferredinthelargersaloonsasitallowsforrelativelylargein-lineengines.ThefirstvehiclesofthistypeweretheAudi80and100.Incliningthein-lineengineandplacingtheradiatorbesideitmeansthefrontov

7、erhanglengthcanbereduced.Automaticgearboxesneedmorespacebecauseofthetorqueconverter.Thisspaceisreadilyavailablewithalongitudinallymountedengine.Adisadvantageoflongitudinalenginesistheunfavourablepositionofthesteeringgear:thisshouldbesituatedoverthegearbox.Dependingontheaxledesign,thisresultsinlongti

8、erodswithspringstmt(McPherson)frontaxles(Fig.1.57).1.6.1.2TransverseenginemountedinfrontoftheaxleInspiteoftheadvantageoftheshortfrontoverhang,onlylimitedspaceisavailablebetweenthefrontwheelhousings(Figs1.49and1.50).Thisrestrictionmeansthatengineslargerthananin-linefourcylinderorV6cannotbefittediname

9、dium-sizedpassengercar.Transverse,asymmetricmountingoftheengineandgearboxmayalsocausesomeperformanceproblems.Theunequallengthofthedriveshaftsaffectsthesteering.Duringaccelerationthevehiclerisesandthedriveshaftstakeondifferentangularpositions,causingunevenmomentsaroundthesteeringaxes.Thedifferencebet

10、weenthesemomentstotheleftandtotherightcausesunintentionalsteeringmovementsresultinginanoticeablepulltooneside(Fig.3.88);driveshaftsofequallengtharethereforedesirable.Thisalsopreventsdifferentdrillinganglesinthedriveshaftcausingtimingdifferencesindrivetorquebuild-up.Thelargearticulationangleoftheshor

11、taxleshaftcanalsolimitthespringFig-，-48Infront-wheeldrivevehiclestheenginecanbemountedlongitudinallyinfrontofthefrontaxlewiththemanualgearboxbehind.Theshaftgoesoverthetransversedifferential(illustration:Renault).Fig.1.49CompactpowertrainunitontheVauxhallCorsa(1997).Theengineistransversemountedwithth

12、egearboxontheleft.TheMcPhersonfrontaleandsafetysteeringcolumncanbeseenclearly.Fig.1.50Layoutoftransverseengine,manualgearboxanddifferentialontheVWPolo.Becausethearrangementisoffset,theaxleshaftleadingtotheleftfrontwheelisshorterthanthatleadingtotherightone.Theshiftershaftbetweenthetwocanbeseenclearl

13、y.Thetotalmechanicalefficiencyshouldbearoundn0.9.travelofthewheel.Toeliminatetheadverseeffectofunequallengthshafts,passengercarswithmorepowerfulengineshaveanadditionalbearingnexttotheengineandanintermediateshaft,theendsofwhichtakeoneofthetwoslidingCVjointswithangularmobility(Figs1.51and1.17),Moreove

14、r,tflexingvibration*ofthelongdriveshaftcanoccurinthemaindrivingrange.Itsnaturalfrequencycanbeshiftedbyclampingonasuppressionweight(Fig.4.1).1.6.2 Advantagesanddisadvantagesoffront-wheeldriveRegardlessoftheengineposition(seeFig.1.52),front-wheeldrivehasnumerousadvantages: thereisloadonthesteeredanddr

15、ivenwheels; goodroad-holding,especiallyonwetroadsandinwintryconditions-thecarispulledandnotpushed(Fig.1.35);Fig.1.51GearboxunitontheLanciaThema,locatedbesidethetransverseengineandbetweenthefrontaxleMcPhersonstruts.Owingtothehighengineperformance,thedesignfeaturestwoequal-lengthaxleshaftsjoinedbyanin

16、termediateshaft.Therearealsointernallyventilateddiscbrakes. gooddrive-offandsufficientclimbingcapacitywithonlyfewpeopleinthevehicle(Fig.6.22); tendencytoundersteerincornering; insensitivetosidewind(Fig.3.125); althoughthefrontaxleisloadedduetotheweightofthedriveunit,thesteeringisnotnecessarilyheavier(incomparisonwithstandardcars)duringdriving; axleadjustmentvaluesarerequiredonlytoalimiteddegreeforsteeringalig