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外文翻译--汽车悬架如何工作.doc

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外文翻译--汽车悬架如何工作.doc

英文原文HowCarSuspensionWorkByWilliamHarrisUniversityofMichiganWhenpeoplethinlyofautomobileperformance,theynormallythinkofhorsepower,torqueandzeroto60acceleration.Butallofthepowergeneratedbyapistonengineisuselessifthedriercantcontrolthecar.ThatswhyautomobileengineersturnedtheirattentiontothesuspensionsystemalmostassoonastheyhadmasteredthefourStrokeinternalcombustionengine.DoublewishbonesuspensiononHondaAccord2005CoupeThejobofacarsuspensionistomaximizethefrictionbetweenthetiresandtheroadsurface,toprovidesteeringstabilitywithgoodhandlingandtoensurethecomfortofthepassengers.Inthisarticle,wellexplorehowcarSuspensionswork,howtheyreevolvedovertheyearsandwherethedesignofsuspensionsisheadedinthefuture.1.VehicleDynamicsIfaroadwereperfectlyt1at,withnoirregularities,suspensionswouldntbenecessary.Butroadsarefarfromt1at.Evenfreshlypavedhighwayshavesubtleimperfectionsthatcaninteractwiththewheelsofacar.Itstheseimperfectionsthatapplyforcestothewheels.AccordingtoNewtonslawsofmotion,allforceshavebothmagnitudeanddirection.Abumpintheroadcausesthewheeltomoveupanddownperpendiculartotheroadsurface.Themagnitude,ofcourse,dependsonwhetherthewheelisStrikingagiantbumporatinyspeck.Eitherway,theca.rwheelexperiencesaverticalaccelerationasitpassesoveranimperfection.Withoutaninterveningstructure,allofwheelsverticalenergyistransferredtotheframe,whichmovesintheSamedirection.Insuchasituation,thewheelscanlosecontactwiththeroadcompletely.Then,underthedownwardforceofgravity,wheelscanslambackintotheroadsurface.Whatyouneedisasystemthatabsorbtheenergyoftheverticallyacceleratedwheel,allowingtheframeandbodytorideundisturbedwhilethewheelsfollowbumpsintheroad.TheStudyofthefarcesatworkanamovingcariscalledvehicledynamics,andyouneedtosuspensionisnecessaryofneedtounderstandsameoftheseconceptsinordertoappreciatewhyanecessaryinthefirstplace.MastautomobileengineersconsiderthemovingcarPramtwoperspectives1Rideacarsabilitytosmoothoutabumpyroad2Handlingacarsabilitytosafelyaccelerate,brakeandcornerThesetwocharacteristicscanbefurtherdescribedinthreeimportantprinciplesroadisolation,roadholdingandcornering.Thetablebelowdescribestheseprinciplesandhowengineersattempttosolvethechallengesuniquetoeach.Acarssuspension,withitsvariouscomponents,providesalloftheSolutionsdescribed.2.TheChassisSystemThesuspensionofacarisactuallypartofthechassis,whichcomprisesalloftheimportantsystemslocatedbeneaththecarsbody.figure21ChassisThesesystemsinclude1Theframestructural,loadcarryingcomponentthatsupportsthecarsengineandbody,whichareinturnsupportedbythesuspension2TheSuspensionsystemsetupthatsupportsweight,absorbsanddampensshockandhelpsmaintaintirecontact3Thesteeringsystemmechanismthatenablesthedrivertoguideanddirectthevehicle4Thetiresandwheelscomponentsthatmakevehiclemotionpossiblebywayofgripand/orfrictionwiththeroadSothesuspensionisjustoneofthemajorsystemsinanyvehicle.Withthisbigpictureoverviewinmind,itstimetolookatthethreefundamentalcomponentsofanysuspensionsprings,dampersandantiswaybars.3.springsTodaysspringingsystemsarebasedononeoffourbasicdesign1CoilspringThisisthemastcommontypeofspringandis,inessence,aheavydutytorsionbarcoiledaroundanaxis.Coilspringscompressandexpandtoabsorbthemotionofthewheels.2LeafspringThistypeofspringconsistsofseverallayersofmetalcalledleavesboundtogethertoactasasingleunit.LeafspringswerefirstusedonhorsedrawncarriagesandwerefoundanmostAmericanautomobilesuntil1985.Theyarestillusedtodayonmosttrucksandheavydutyvehicles.3TorsionbarsTorsionbarsusethetwistingpropertiesofasteelGartoprovidecoilspringlikeperformance.ThisishowtheyworkOneendofabarisanchoredtothevehicleframe.Theotherendi5attachedtoawishbone,whichactslikealeverthatmaresperpendiculartothetorsionbar.Whenthewheelhitsabump,verticalmotionistransferredtothewishboneandthen,throughtheleveringaction,tothetorsionbar.Thetorsionbarthentwistsalongitsaxistoprovidethespringfarce.Europeancaretakersusedthissystemextensively,asdidPackardandChryslerintheUnitedStates,throughthe1950sand1960s.4AirspringsAirSprings,whichconsistofacylindricalchamberofairpositionedbetweenthewheelandthecarsbody,usethecompres5irequalitiesofairtoabsorbwheelvibrations.Theconceptisactuallymorethanacenturyoldandcouldbefoundanhorsedrawnbuggies.Airspringsfromthiseraweremadefromairfilled,leatherdiaphragms,muchlikeabellowstheywerereplacedwithmoldedrubberairspringsinthe1930s.Basedonwherespringsarelocatedonacari.e.,betweenthewheelsandtheframeengineersoftenfinditconvenienttotalkaboutthesprungmassandtheunsprungmass.4.SprungandUnsprungMassThesprungmassisthemassofthevehiclesupportedanthesprings,whiletheunsprungmassislooselydefinedasthemassbetweentheroadandthesuspensionSprings.Thestiffnessofthespringsaffectshowthesprungmassrespondswhilethecarisbeingdriven.Looselysprungcars,suchasluxurycars{thinkLincolnTawsCard,canSwallowbumpsandprovideasupersmoothridehowever,suchacarisprunetodiveandsquatduringbrakingandaccelerationandtendstoexperiencebodyawayorrollduringcornering.Tightlysprungcars,suchassportscarsthinkMazdaMiata,arelessforgivingonbumpyroads,buttheyminimizebodymotionwell,whichmeanstheycanbedrivenaggressively,evenaroundcorners.So,whilespringsbythemselvesseemlikesimpledevices,designingandimplementingthemonacartobalancepassengercomfortwithhandlingisacomplextask.Andtomakemattersmorecomplex,springsalonecantprovideaperfectlysmoothride.WhyBecauseSpringsaregreatatabsorbingenergy,butnotsogoodatdissipatingit.Otherstructures,knownasdampers,arerequiredtodothis.5.ShackAbsorbersUnlessadampeningstructureispresent,acarspringwillextendandreleasetheenergyitabsorbsfromabumpatanuncontrolledrate.Thespringwillcontinuetobounceatitsnaturalfrequencyuntilalloftheenergyoriginallyputintoitisusedup.Asuspensionbuiltanspringsalonewouldmakeforanextremelybouncyrideand,dependingantheterrain,anuncontrollablecar.Entertheshackabsorber,orsnubber,adevicethatcontrolsunwantedspringmotionthroughaprocessknownasdampening.Shockabsorbersslowdownandreducethemagnitudeofvibratorymotionsbyturningthekineticenergyofsuspensionmovementintoheatenergythatcanliedissipatedthroughhydraulicfluid.Tounderstandhowthisworks,itsbesttolookinsideashackabsorbertoseeitsstructureandfunction.Ashockabsorberisbasicallyanoilpumpplacedbetweentheframeofthecarandthewheels.Theuppermountoftheshockconnectstotheframei.e.,thesprungweight,whilethelowermountconnectstotheaxle,nearthewheeli.e.,theunsprungweight.Inatwintubedesign,oneofthemostcommontypesofshockabsorbers,theuppermountisconnectedtoapistonrod,whichinturnisconnectedtoapiston,whichinturnsitsinatubefilledwithhydraulicfluid.Theinnertubeisknownasthepressuretube,andtheoutertubeisknownasthereservetube.Thereservetubestoresexcesshydraulicfluid.Whenthecarwheelencountersabumpintheroadandcausesthespringytocoilanduncoil,theenergyofthespringistransferredtotheshockabsorberthroughtheuppermount,downthroughthepistonrodandintothepistonOrificesperforatethepistonandallowfluidtoleakthroughasthepistonmovesupanddowninthepressuretube.Becausetheorificesarerelativelytiny,onlyasmallamountoffluid,undergreatpressure,passesthrough.Thisslowsdownthepiston,whichinturnslowsdownthespring.Shockabsorbersworldintwocyclesthecompressioncycleandtheextensioncycle.Thecompressioncycleoccursasthepistonmovesdownward,compressingthehydraulicfluidinthechamberbelowthepiston.Theextensioncycleoccursasthepistonmovestowardthetopofthepressuretube,compressingthefluidinthechamberabovethepiston.Atypicalcarorlighttruckwillhavemareresistanceduringitsextensioncyclethanitscompressioncycle.Withthatinmind,thecompressioncyclecontrolsthemotionofthevehiclesunsprungweight,whileextensioncontrolstheheavier,sprungweight.Allmodernshockabsorbersarevelocitysensitivethefasterthesuspensionmoves,themoreresistancetheshockabsorberprovides.Thisenablesshackstoadjusttoroadconditionsandtocentralalloftheunwantedmotionsthatcanoccurinamovingvehicle,includingbounce,sway,brakediveandaccelerationsquat.6.StrutsandAntiswayBars

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