汽车悬架如何工作毕业设计外文翻译外文翻译Word格式.docx
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汽车悬架如何工作毕业设计外文翻译外文翻译Word格式.docx
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Thejobofacarsuspensionistomaximizethefrictionbetweenthetiresandtheroadsurface,toprovidesteeringstabilitywithgoodhandlingandtoensurethecomfortofthepassengers.Inthisarticle,we'
llexplorehowcarsuspensionswork,howthey'
veevolvedovertheyearsandwherethedesignofsuspensionsisheadedinthefuture.
1.VehicleDynamics
Ifaroadwereperfectlyflat,withnoirregularities,suspensionswouldn'
tbenecessary.Butroadsarefarfromflat.Evenfreshlypavedhighwayshavesubtleimperfectionsthatcaninteractwiththewheelsofacar.It'
stheseimperfectionsthatapplyforcestothewheels.AccordingtoNewton'
slawsofmotion,allforceshavebothmagnitudeanddirection.Abumpintheroadcausesthewheeltomoveupanddownperpendiculartotheroadsurface.Themagnitude,ofcourse,dependsonwhetherthewheelisstrikingagiantbumporatinyspeck.Eitherway,thecarwheelexperiencesaverticalaccelerationasitpassesoveranimperfection.
Withoutaninterveningstructure,allofwheel'
sverticalenergyistransferredtotheframe,whichmovesinthesamedirection.Insuchasituation,thewheelscanlosecontactwiththeroadcompletely.Then,underthedownwardforceofgravity,thewheelscanslambackintotheroadsurface.Whatyouneedisasystemthatwillabsorbtheenergyoftheverticallyacceleratedwheel,allowingtheframeandbodytorideundisturbedwhilethewheelsfollowbumpsintheroad.
Thestudyoftheforcesatworkonamovingcariscalledvehicledynamics,andyouneedtounderstandsomeoftheseconceptsinordertoappreciatewhyasuspensionisnecessaryinthefirstplace.Mostautomobileengineersconsiderthedynamicsofamovingcarfromtwoperspectives:
1)Ride-acar'
sabilitytosmoothoutabumpyroad
2)Handling-acar'
sabilitytosafelyaccelerate,brakeandcorner
Thesetwocharacteristicscanbefurtherdescribedinthreeimportantprinciples-roadisolation,roadholdingandcornering.Thetablebelowdescribestheseprinciplesandhowengineersattempttosolvethechallengesuniquetoeach.
Acar'
ssuspension,withitsvariouscomponents,providesallofthesolutionsdescribed.
2.TheChassisSystem
Thesuspensionofacarisactuallypartofthechassis,whichcomprisesalloftheimportantsystemslocatedbeneaththecar'
sbody.
Thesesystemsinclude:
1)Theframe-structural,load-carryingcomponentthatsupportsthecar'
sengineandbody,whichareinturnsupportedbythesuspension
2)Thesuspensionsystem-setupthatsupportsweight,absorbsanddampensshockandhelpsmaintaintirecontact
3)Thesteeringsystem-mechanismthatenablesthedrivertoguideanddirectthevehicle
4)Thetiresandwheels-componentsthatmakevehiclemotionpossiblebywayofgripand/orfrictionwiththeroad
Sothesuspensionisjustoneofthemajorsystemsinanyvehicle.
Withthisbig-pictureoverviewinmind,it'
stimetolookatthethreefundamentalcomponentsofanysuspension:
springs,dampersandanti-swaybars.
figure2-1Chassis
3.Springs
Today'
sspringingsystemsarebasedononeoffourbasicdesigns:
1)Coilsprings-Thisisthemostcommontypeofspringandis,inessence,aheavy-dutytorsionbarcoiledaroundanaxis.Coilspringscompressandexpandtoabsorbthemotionofthewheels.
2)Leafsprings-Thistypeofspringconsistsofseverallayersofmetal(called"
leaves"
)boundtogethertoactasasingleunit.Leafspringswerefirstusedonhorse-drawncarriagesandwerefoundonmostAmericanautomobilesuntil1985.Theyarestillusedtodayonmosttrucksandheavy-dutyvehicles.
3)Torsionbars-Torsionbarsusethetwistingpropertiesofasteelbartoprovidecoil-spring-likeperformance.Thisishowtheywork:
Oneendofabarisanchoredtothevehicleframe.Theotherendisattachedtoawishbone,whichactslikealeverthatmovesperpendiculartothetorsionbar.Whenthewheelhitsabump,verticalmotionistransferredtothewishboneandthen,throughtheleveringaction,tothetorsionbar.Thetorsionbarthentwistsalongitsaxistoprovidethespringforce.Europeancarmakersusedthissystemextensively,asdidPackardandChryslerintheUnitedStates,throughthe1950sand1960s.
4)Airsprings-Airsprings,whichconsistofacylindricalchamberofairpositionedbetweenthewheelandthecar'
sbody,usethecompressivequalitiesofairtoabsorbwheelvibrations.Theconceptisactuallymorethanacenturyoldandcouldbefoundonhorse-drawnbuggies.Airspringsfromthiseraweremadefromair-filled,leatherdiaphragms,muchlikeabellows;
theywerereplacedwithmolded-rubberairspringsinthe1930s.
Basedonwherespringsarelocatedonacar--i.e.,betweenthewheelsandtheframe--engineersoftenfinditconvenienttotalkaboutthesprungmassandtheunsprungmass.
4.SprungandUnsprungMass
Thesprungmassisthemassofthevehiclesupportedonthesprings,whiletheunsprungmassislooselydefinedasthemassbetweentheroadandthesuspensionsprings.Thestiffnessofthespringsaffectshowthesprungmassrespondswhilethecarisbeingdriven.Looselysprungcars,suchasluxurycars(thinkLincolnTownCar),canswallowbumpsandprovideasuper-smoothride;
however,suchacarispronetodiveandsquatduringbrakingandaccelerationandtendstoexperiencebodyswayorrollduringcornering.Tightlysprungcars,suchassportscars(thinkMazdaMiata),arelessforgivingonbumpyroads,buttheyminimizebodymotionwell,whichmeanstheycanbedrivenaggressively,evenaroundcorners.
So,whilespringsbythemselvesseemlikesimpledevices,designingandimplementingthemonacartobalancepassengercomfortwithhandlingisacomplextask.Andtomakemattersmorecomplex,springsalonecan'
tprovideaperfectlysmoothride.Why?
Becausespringsaregreatatabsorbingenergy,butnotsogoodatdissipatingit.Otherstructures,knownasdampers,arerequiredtodothis.
5.ShockAbsorbers
Unlessadampeningstructureispresent,acarspringwillextendandreleasetheenergyitabsorbsfromabumpatanuncontrolledrate.Thespringwillcontinuetobounceatitsnaturalfrequencyuntilalloftheenergyoriginallyputintoitisusedup.Asuspensionbuiltonspringsalonewouldmakeforanextremelybouncyrideand,dependingontheterrain,anuncontrollablecar.
Entertheshockabsorber,orsnubber,adevicethatcontrolsunwantedspringmotionthroughaprocessknownasdampening.Shockabsorbersslowdownandreducethemagnitudeofvibratorymotionsbyturningthekineticenergyofsuspensionmovementintoheatenergythatcanbedissipatedthroughhydraulicfluid.Tounderstandhowthisworks,it'
sbesttolookinsideashockabsorbertoseeitsstructureandfunction.
Ashockabsorberisbasicallyanoilpumpplacedbetweentheframeofthecarandthewheels.Theuppermountoftheshockconnectstotheframe(i.e.,thesprungweight),whilethelowermountconnectstotheaxle,nearthewheel(i.e.,theunsprungweight).Inatwin-tubedesign,oneofthemostcommontypesofshockabsorbers,theuppermountisconnectedtoapistonrod,whichinturnisconnectedtoapiston,whichinturnsitsinatubefilledwithhydraulicfluid.Theinnertubeisknownasthepressuretube,andtheoutertubeisknownasthereservetube.Thereservetubestoresexcesshydraulicfluid.
Whenthecarwheelencountersabumpintheroadandcausesthespringtocoilanduncoil,theenergyofthespringistransferredtotheshockabsorberthroughtheuppermount,downthroughthepistonrodandintothepiston.Orificesperforatethepistonandallowfluidtoleakthroughasthepistonmovesupanddowninthepressuretube.Becausetheorificesarerelativelytiny,onlyasmallamountoffluid,undergreatpressure,passesthrough.Thisslowsdownthepiston,whichinturnslowsdownthespring.
Shockabsorbersworkintwocycles--thecompressioncycleandtheextensioncycle.Thecompressioncycleoccursasthepistonmovesdownward,compressingthehydraulicfluidinthechamberbelowthepiston.Theextensioncycleoccursasthepistonmovestowardthetopofthepressuretube,compressingthefluidinthechamberabovethepiston.Atypicalcarorlighttruckwillhavemoreresistanceduringitsextensioncyclethanitscompressioncycle.Withthatinmind,thecompressioncyclecontrolsthemotionofthevehicle'
sunsprungweight,whileextensioncontrolstheheavier,sprungweight.
Allmodernshockabsorbersarevelocity-sensitive--thefasterthesuspensionmoves,themoreresistancetheshockabsorberprovides.Thisenablesshockstoadjusttoroadconditionsandtocontrolalloftheunwantedmotionsthatcanoccurinamovingvehicle,includingbounce,sway,brakediveandaccelerationsquat.
6.StrutsandAnti-swayBars
figure6-1Commonstrutdesign
Anothercommondampeningstructureisthestrut--basicallyashockabsorbermountedinsideacoilspring.Strutsperformtwojobs:
Theyprovideadampeningfunctionlikeshockabsorbers,andtheyprovidestructuralsupportforthevehiclesuspension.Thatmeansstrutsdeliverabitmorethanshockabsorbers,whichdon'
tsupportvehicleweight--theyonlycontrolthespeedatwhichweightistransferredinacar,nottheweightitself.
Becauseshocksand
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