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外文翻译悬吊系统.doc

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外文翻译悬吊系统.doc

英文资料SuspensionSuspensionisthetermgiventothesystemofsprings,shockabsorbersandlinkagesthatconnectsavehicletoitswheels.Suspensionsystemsserveadualpurpose–contributingtothecarsroadholding/handlingandbrakingforgoodactivesafetyanddrivingpleasure,andkeepingvehicleoccupantscomfortableandreasonablywellisolatedfromroadnoise,bumps,andvibrations,etc.Thesegoalsaregenerallyatodds,sothetuningofsuspensionsinvolvesfindingtherightcompromise.Itisimportantforthesuspensiontokeeptheroadwheelincontactwiththeroadsurfaceasmuchaspossible,becausealltheforcesactingonthevehicledosothroughthecontactpatchesofthetires.Thesuspensionalsoprotectsthevehicleitselfandanycargoorluggagefromdamageandwear.Thedesignoffrontandrearsuspensionofacarmaybedifferent.LeafspringshavebeenaroundsincetheearlyEgyptians.Ancientmilitaryengineersusedleafspringsintheformofbowstopowertheirsiegeengines,withlittlesuccessatfirst.Theuseofleafspringsincatapultswaslaterrefinedandmadetoworkyearslater.Springswerenotonlymadeofmetal,asturdytreebranchcouldbeusedasaspring,suchaswithabow.HorsedrawnvehiclesBytheearly19thcenturymostBritishhorsecarriageswereequippedwithspringswoodenspringsinthecaseoflightonehorsevehiclestoavoidtaxation,andsteelspringsinlargervehicles.Theseweremadeoflowcarbonsteelandusuallytooktheformofmultiplelayerleafsprings.1TheBritishsteelspringswerenotwellsuitedforuseonAmericasroughroadsofthetime,andcouldevencausecoachestocollapseifcorneredtoofast.Inthe1820s,theAbbotDowningCompanyofConcord,NewHampshiredevelopedasystemwherebythebodiesofstagecoachesweresupportedonleatherstrapscalledthoroughbraces,whichgaveaswingingmotioninsteadofthejoltingupanddownofaspringsuspensionthestagecoachitselfwassometimescalledathoroughbraceAutomobilesAutomobileswereinitiallydevelopedasselfpropelledversionsofhorsedrawnvehicles.However,horsedrawnvehicleshadbeendesignedforrelativelyslowspeedsandtheirsuspensionwasnotwellsuitedtothehigherspeedspermittedbytheinternalcombustionengine.In1903MorsofGermanyfirstfittedanautomobilewithshockabsorbers.In1920Leylandusedtorsionbarsinasuspensionsystem.In1922independentfrontsuspensionwaspioneeredontheLanciaLambdaandbecamemorecommoninmassmarketcarsfrom1932.2ImportantpropertiesSpringrateThespringrateorsuspensionrateisacomponentinsettingthevehiclesrideheightoritslocationinthesuspensionstroke.Vehicleswhichcarryheavyloadswilloftenhaveheavierspringstocompensatefortheadditionalweightthatwouldotherwisecollapseavehicletothebottomofitstravelstroke.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/mmorlbf/in.Anexampleofalinearspringrateis500lbf/in.Foreveryinchthespringiscompressed,itexerts500lbf.Anonlinearspringrateisoneforwhichtherelationbetweenthespringscompressionandtheforceexertedcannotbefittedadequatelytoalinearmodel.Forexample,thefirstinchexerts500lbfforce,thesecondinchexertsanadditional550lbfforatotalof1050lbf,thethirdinchexertsanother600lbfforatotalof1650lbf.Incontrasta500lbf/inlinearspringcompressedto3incheswillonlyexert1500lbf.Thespringrateofacoilspringmaybecalculatedbyasimplealgebraicequationoritmaybemeasuredinaspringtestingmachine.Thespringconstantkcanbecalculatedasfollowswheredisthewirediameter,Gisthespringsshearmoduluse.g.,about12,000,000lbf/in²or80GPaforsteel,andNisthenumberofwrapsandDisthediameterofthecoil.WheelrateWheelrateistheeffectivespringratewhenmeasuredatthewheel.Thisisasopposedtosimplymeasuringthespringratealone.Wheelrateisusuallyequaltoorconsiderablylessthanthespringrate.Commonly,springsaremountedoncontrolarms,swingarmsorsomeotherpivotingsuspensionmember.Considertheexampleabovewherethespringratewascalculatedtobe500lbs/inch,ifyouweretomovethewheel1inchwithoutmovingthecar,thespringmorethanlikelycompressesasmalleramount.Letsassumethespringmoved0.75inches,theleverarmratiowouldbe0.75to1.Thewheelrateiscalculatedbytakingthesquareoftheratio0.5625timesthespringrate.Squaringtheratioisbecausetheratiohastwoeffectsonthewheelrate.Theratioappliestoboththeforceanddistancetraveled.Wheelrateonindependentsuspensionisfairlystraightforward.However,specialconsiderationmustbetakenwithsomenonindependentsuspensiondesigns.Takethecaseofthestraightaxle.Whenviewedfromthefrontorrear,thewheelratecanbemeasuredbythemeansabove.Yetbecausethewheelsarenotindependent,whenviewedfromthesideunderaccelerationorbrakingthepivotpointisatinfinitybecausebothwheelshavemovedandthespringisdirectlyinlinewiththewheelcontactpatch.Theresultisoftenthattheeffectivewheelrateundercorneringisdifferentfromwhatitisunderaccelerationandbraking.Thisvariationinwheelratemaybeminimizedbylocatingthespringasclosetothewheelaspossible.RollcouplepercentageRollcouplepercentageistheeffectivewheelrates,inroll,ofeachaxleofthevehiclejustasaratioofthevehiclestotalrollrate.RollCouplePercentageiscriticalinaccuratelybalancingthehandlingofavehicle.Itiscommonlyadjustedthroughtheuseofantirollbars,butcanalsobechangedthroughtheuseofdifferentsprings.Avehiclewitharollcouplepercentageof70willtransfer70ofitssprungweighttransferatthefrontofthevehicleduringcornering.ThisisalsocommonlyknownasTotalLateralLoadTransferDistributionorTLLTD.WeighttransferWeighttransferduringcornering,accelerationorbrakingisusuallycalculatedperindividualwheelandcomparedwiththestaticweightsforthesamewheels.Thetotalamountofweighttransferisonlyaffectedby4factorsthedistancebetweenwheelcenterswheelbaseinthecaseofbraking,ortrackwidthinthecaseofcorneringtheheightofthecenterofgravity,themassofthevehicle,andtheamountofaccelerationexperienced.

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