外文翻译--汽车悬架如何工作.doc

英文原文HowCarSuspensionWorkByWilliamHarrisUniversityofMichiganWhenpeoplethinlyofautomobileperformance,theynormallythinkofhorsepower,torqueandzero-to-60acceleration.Butallofthepowergeneratedbyapistonengineisuselessifthedriercantcontrolthecar.Thatswhyautomobileengineersturnedtheirattentiontothesuspensionsystemalmostassoonastheyhadmasteredthefour-Strokeinternalcombustionengine.Double-wishbonesuspensiononHondaAccord2005CoupeThejobofacarsuspensionistomaximizethefrictionbetweenthetiresandtheroadsurface,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.MastautomobileengineersconsiderthemovingcarPramtwoperspectives:1)Ride-acarsabilitytosmoothoutabumpyroad2)Handling-acarsabilitytosafelyaccelerate,brakeandcornerThesetwocharacteristicscanbefurtherdescribedinthreeimportantprinciples-roadisolation,roadholdingandcornering.Thetablebelowdescribestheseprinciplesandhowengineersattempttosolvethechallengesuniquetoeach.Acarssuspension,withitsvariouscomponents,providesalloftheSolutionsdescribed.2.TheChassisSystemThesuspensionofacarisactuallypartofthechassis,whichcomprisesalloftheimportantsystemslocatedbeneaththecarsbody.figure2-1ChassisThesesystemsinclude:1)Theframe-structural,load-carryingcomponentthatsupportsthecarsengineandbody,whichareinturnsupportedbythesuspension2)TheSuspensionsystem-setupthatsupportsweight,absorbsanddampensshockandhelpsmaintaintirecontact3)Thesteeringsystem-mechanismthatenablesthedrivertoguideanddirectthevehicle4)Thetiresandwheels-componentsthatmakevehiclemotionpossiblebywayofgripand/orfrictionwiththeroadSothesuspensionisjustoneofthemajorsystemsinanyvehicle.Withthisbig-pictureoverviewinmind,itstimetolookatthethreefundamentalcomponentsofanysuspension:springs,dampersandanti-swaybars.3.springsTodaysspringingsystemsarebasedononeoffourbasicdesign:1)Coilspring-Thisisthemastcommontypeofspringandis,inessence,aheavy-dutytorsionbarcoiledaroundanaxis.Coilspringscompressandexpandtoabsorbthemotionofthewheels.2)Leafspring-Thistypeofspringconsistsofseverallayersofmetal(called"leaves")boundtogethertoactasasingleunit.Leafspringswerefirstusedonhorse-drawncarriagesandwerefoundanmostAmericanautomobilesuntil1985.Theyarestillusedtodayonmosttrucksandheavy-dutyvehicles.3)Torsionbars-TorsionbarsusethetwistingpropertiesofasteelGartoprovidecoil-spring-likeperformance.Thisishowtheywork:Oneendofabarisanchoredtothevehicleframe.Theotherendi5attachedtoawishbone,whichactslikealeverthatmaresperpendiculartothetorsionbar.Whenthewheelhitsabump,verticalmotionistransferredtothewishboneandthen,throughtheleveringaction,tothetorsionbar.Thetorsionbarthentwistsalongitsaxistoprovidethespringfarce.Europeancaretakersusedthissystemextensively,asdidPackardandChryslerintheUnitedStates,throughthe1950sand1960s.4)Airsprings-AirSprings,whichconsistofacylindricalchamberofairpositionedbetweenthewheelandthecarsbody,usethecompres5irequalitiesofairtoabsorbwheelvibrations.Theconceptisactuallymorethanacenturyoldandcouldbefoundanhorse-drawnbuggies.Airspringsfromthiseraweremadefromair-filled,leatherdiaphragms,muchlikeabellows；theywerereplacedwithmolded-rubberairspringsinthe1930s.Basedonwherespringsarelocatedonacar-i.e.,betweenthewheelsandtheframe-engineersoftenfinditconvenienttotalkaboutthesprungmassandtheunsprungmass.4.SprungandUnsprungMassThesprungmassisthemassofthevehiclesupportedanthesprings,whiletheunsprungmassislooselydefinedasthemassbetweentheroadandthesuspensionSprings.Thestiffnessofthespringsaffectshowthesprungmassrespondswhilethecarisbeingdriven.Looselysprungcars,suchasluxurycarsthinkLincolnTawsCard,canSwallowbumpsandprovideasuper-smoothride；however,suchacarisprunetodiveandsquatduringbrakingandaccelerationandtendstoexperiencebodyawayorrollduringcornering.Tightlysprungcars,suchassportscars(thinkMazdaMiata),arelessforgivingonbumpyroads,buttheyminimizebodymotionwell,whichmeanstheycanbedrivenaggressively,evenaroundcorners.So,whilespringsbythemselvesseemlikesimpledevices,designingandimplementingthemonacartobalancepassengercomfortwithhandlingisacomplextask.Andtomakemattersmorecomplex,springsalonecantprovideaperfectlysmoothride.Why?BecauseSpringsaregreatatabsorbingenergy,butnotsogoodatdissipatingit.Otherstructures,knownasdampers,arerequiredtodothis.5.ShackAbsorbersUnlessadampeningstructureispresent,acarspringwillextendandreleasetheenergyitabsorbsfromabumpatanuncontrolledrate.Thespringwillcontinuetobounceatitsnaturalfrequencyuntilalloftheenergyoriginallyputintoitisusedup.Asuspensionbuiltanspringsalonewouldmakeforanextremelybouncyrideand,dependingantheterrain,anuncontrollablecar.Entertheshackabsorber,orsnubber,adevicethatcontrolsunwantedspringmotionthroughaprocessknownasdampening.Shockabsorbersslowdownandreducethemagnitudeofvibratorymotionsbyturningthekineticenergyofsuspensionmovementintoheatenergythatcanliedissipatedthroughhydraulicfluid.Tounderstandhowthisworks,itsbesttolookinsideashackabsorbertoseeitsstructureandfunction.Ashockabsorberisbasicallyanoilpumpplacedbetweentheframeofthecarandthewheels.Theuppermountoftheshockconnectstotheframe(i.e.,thesprungweight),whilethelowermountconnectstotheaxle,nearthewheel(i.e.,theunsprungweight).Inatwin-tubedesign,oneofthemostcommontypesofshock)absorbers,theuppermountisconnectedtoapistonrod,whichinturnisconnectedtoapiston,whichinturnsitsinatubefilledwithhydraulicfluid.Theinnertubeisknownasthepressuretube,andtheoutertubeisknownasthereservetube.Thereservetubestoresexcesshydraulicfluid.Whenthecarwheelencountersabumpintheroadandcausesthespringytocoilanduncoil,theenergyofthespringistransferredtotheshockabsorberthroughtheuppermount,downthroughthepistonrodandintothepiston-Orificesperforatethepistonandallowfluidtoleakthroughasthepistonmovesupanddowninthepressuretube.Becausetheorificesarerelativelytiny,onlyasmallamountoffluid,undergreatpressure,passesthrough.Thisslowsdownthepiston,whichinturnslowsdownthespring.Shockabsorbersworldintwocycles-thecompressioncycleandtheextensioncycle.Thecompressioncycleoccursasthepistonmovesdownward,compressingthehydraulicfluidinthechamberbelowthepiston.Theextensioncycleoccursasthepistonmovestowardthetopofthepressuretube,compressingthefluidinthechamberabovethepiston.Atypicalcarorlighttruckwillhavemareresistanceduringitsextensioncyclethanitscompressioncycle.Withthatinmind,thecompressioncyclecontrolsthemotionofthevehiclesunsprungweight,whileextensioncontrolstheheavier,sprungweight.Allmodernshockabsorbersarevelocity-sensitivethefasterthesuspensionmoves,themoreresistancetheshockabsorberprovides.Thisenablesshackstoadjusttoroadconditionsandtocentralalloftheunwantedmotionsthatcanoccurinamovingvehicle,includingbounce,sway,brakediveandaccelerationsquat.6.StrutsandAnti-swayBars