外文翻译悬吊系统.doc

英文资料SuspensionSuspensionisthetermgiventothesystemofsprings,shockabsorbersandlinkagesthatconnectsavehicletoitswheels.Suspensionsystemsserveadualpurposecontributingtothecarsroadholding/handlingandbrakingforgoodactivesafetyanddrivingpleasure,andkeepingvehicleoccupantscomfortableandreasonablywellisolatedfromroadnoise,bumps,andvibrations,etc.Thesegoalsaregenerallyatodds,sothetuningofsuspensionsinvolvesfindingtherightcompromise.Itisimportantforthesuspensiontokeeptheroadwheelincontactwiththeroadsurfaceasmuchaspossible,becausealltheforcesactingonthevehicledosothroughthecontactpatchesofthetires.Thesuspensionalsoprotectsthevehicleitselfandanycargoorluggagefromdamageandwear.Thedesignoffrontandrearsuspensionofacarmaybedifferent.LeafspringshavebeenaroundsincetheearlyEgyptians.Ancientmilitaryengineersusedleafspringsintheformofbowstopowertheirsiegeengines,withlittlesuccessatfirst.Theuseofleafspringsincatapultswaslaterrefinedandmadetoworkyearslater.Springswerenotonlymadeofmetal,asturdytreebranchcouldbeusedasaspring,suchaswithabow.HorsedrawnvehiclesBytheearly19thcenturymostBritishhorsecarriageswereequippedwithsprings；woodenspringsinthecaseoflightone-horsevehiclestoavoidtaxation,andsteelspringsinlargervehicles.Theseweremadeoflow-carbonsteelandusuallytooktheformofmultiplelayerleafsprings.1TheBritishsteelspringswerenotwellsuitedforuseonAmericasroughroadsofthetime,andcouldevencausecoachestocollapseifcorneredtoofast.Inthe1820s,theAbbotDowningCompanyofConcord,NewHampshiredevelopedasystemwherebythebodiesofstagecoachesweresupportedonleatherstrapscalled"thoroughbraces",whichgaveaswingingmotioninsteadofthejoltingupanddownofaspringsuspension(thestagecoachitselfwassometimescalleda"thoroughbrace")AutomobilesAutomobileswereinitiallydevelopedasself-propelledversionsofhorsedrawnvehicles.However,horsedrawnvehicleshadbeendesignedforrelativelyslowspeedsandtheirsuspensionwasnotwellsuitedtothehigherspeedspermittedbytheinternalcombustionengine.In1903MorsofGermanyfirstfittedanautomobilewithshockabsorbers.In1920Leylandusedtorsionbarsinasuspensionsystem.In1922independentfrontsuspensionwaspioneeredontheLanciaLambdaandbecamemorecommoninmassmarketcarsfrom1932.2ImportantpropertiesSpringrateThespringrate(orsuspensionrate)isacomponentinsettingthevehiclesrideheightoritslocationinthesuspensionstroke.Vehicleswhichcarryheavyloadswilloftenhaveheavierspringstocompensatefortheadditionalweightthatwouldotherwisecollapseavehicletothebottomofitstravel(stroke).Heavierspringsarealsousedinperformanceapplicationswheretheloadingconditionsexperiencedaremoreextreme.Springsthataretoohardortoosoftcausethesuspensiontobecomeineffectivebecausetheyfailtoproperlyisolatethevehiclefromtheroad.Vehiclesthatcommonlyexperiencesuspensionloadsheavierthannormalhaveheavyorhardspringswithaspringrateclosetotheupperlimitforthatvehiclesweight.Thisallowsthevehicletoperformproperlyunderaheavyloadwhencontrolislimitedbytheinertiaoftheload.Ridinginanemptytruckusedforcarryingloadscanbeuncomfortableforpassengersbecauseofitshighspringraterelativetotheweightofthevehicle.Aracecarwouldalsobedescribedashavingheavyspringsandwouldalsobeuncomfortablybumpy.However,eventhoughwesaytheybothhaveheavysprings,theactualspringratesfora2000lbracecaranda10,000lbtruckareverydifferent.Aluxurycar,taxi,orpassengerbuswouldbedescribedashavingsoftsprings.Vehicleswithwornoutordamagedspringsridelowertothegroundwhichreducestheoverallamountofcompressionavailabletothesuspensionandincreasestheamountofbodylean.Performancevehiclescansometimeshavespringraterequirementsotherthanvehicleweightandload.MathematicsofthespringrateSpringrateisaratiousedtomeasurehowresistantaspringistobeingcompressedorexpandedduringthespringsdeflection.ThemagnitudeofthespringforceincreasesasdeflectionincreasesaccordingtoHookesLaw.Briefly,thiscanbestatedaswhereFistheforcethespringexertskisthespringrateofthespring.xisthedisplacementfromequilibriumlengthi.e.thelengthatwhichthespringisneithercompressedorstretched.Springrateisconfinedtoanarrowintervalbytheweightofthevehicle,loadthevehiclewillcarry,andtoalesserextentbysuspensiongeometryandperformancedesires.SpringratestypicallyhaveunitsofN/mm(orlbf/in).Anexampleofalinearspringrateis500lbf/in.Foreveryinchthespringiscompressed,itexerts500lbf.Anon-linearspringrateisoneforwhichtherelationbetweenthespringscompressionandtheforceexertedcannotbefittedadequatelytoalinearmodel.Forexample,thefirstinchexerts500lbfforce,thesecondinchexertsanadditional550lbf(foratotalof1050lbf),thethirdinchexertsanother600lbf(foratotalof1650lbf).Incontrasta500lbf/inlinearspringcompressedto3incheswillonlyexert1500lbf.Thespringrateofacoilspringmaybecalculatedbyasimplealgebraicequationoritmaybemeasuredinaspringtestingmachine.Thespringconstantkcanbecalculatedasfollows:wheredisthewirediameter,Gisthespringsshearmodulus(e.g.,about12,000,000lbf/in²or80GPaforsteel),andNisthenumberofwrapsandDisthediameterofthecoil.WheelrateWheelrateistheeffectivespringratewhenmeasuredatthewheel.Thisisasopposedtosimplymeasuringthespringratealone.Wheelrateisusuallyequaltoorconsiderablylessthanthespringrate.Commonly,springsaremountedoncontrolarms,swingarmsorsomeotherpivotingsuspensionmember.Considertheexampleabovewherethespringratewascalculatedtobe500lbs/inch,ifyouweretomovethewheel1inch(withoutmovingthecar),thespringmorethanlikelycompressesasmalleramount.Letsassumethespringmoved0.75inches,theleverarmratiowouldbe0.75to1.Thewheelrateiscalculatedbytakingthesquareoftheratio(0.5625)timesthespringrate.Squaringtheratioisbecausetheratiohastwoeffectsonthewheelrate.Theratioappliestoboththeforceanddistancetraveled.Wheelrateonindependentsuspensionisfairlystraight-forward.However,specialconsiderationmustbetakenwithsomenon-independentsuspensiondesigns.Takethecaseofthestraightaxle.Whenviewedfromthefrontorrear,thewheelratecanbemeasuredbythemeansabove.Yetbecausethewheelsarenotindependent,whenviewedfromthesideunderaccelerationorbrakingthepivotpointisatinfinity(becausebothwheelshavemoved)andthespringisdirectlyinlinewiththewheelcontactpatch.Theresultisoftenthattheeffectivewheelrateundercorneringisdifferentfromwhatitisunderaccelerationandbraking.Thisvariationinwheelratemaybeminimizedbylocatingthespringasclosetothewheelaspossible.RollcouplepercentageRollcouplepercentageistheeffectivewheelrates,inroll,ofeachaxleofthevehiclejustasaratioofthevehiclestotalrollrate.RollCouplePercentageiscriticalinaccuratelybalancingthehandlingofavehicle.Itiscommonlyadjustedthroughtheuseofanti-rollbars,butcanalsobechangedthroughtheuseofdifferentsprings.Avehiclewitharollcouplepercentageof70%willtransfer70%ofitssprungweighttransferatthefrontofthevehicleduringcornering.Thisisalsocommonlyknownas"TotalLateralLoadTransferDistribution"or"TLLTD".WeighttransferWeighttransferduringcornering,accelerationorbrakingisusuallycalculatedperindividualwheelandcomparedwiththestaticweightsforthesamewheels.Thetotalamountofweighttransferisonlyaffectedby4factors:thedistancebetweenwheelcenters(wheelbaseinthecaseofbraking,ortrackwidthinthecaseofcornering)theheightofthecenterofgravity,themassofthevehicle,andtheamountofaccelerationexperienced.