汽车车辆类悬架和框架设计外文文献翻译.docx
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汽车车辆类悬架和框架设计外文文献翻译.docx
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汽车车辆类悬架和框架设计外文文献翻译
附录A
FormulaSAEisastudentcompetitionsponsoredbySocietyofAutomotiveEngineers(SAE),werestudentsdesign,build,andcompetewithasmallformulastyleracecar.Thebasisofthecompetitionisthatafictitiouscompanyhascontractedagroupofengineerstobuildasmallformulacar.Sincethecarisintendedfortheweekendautocrossracer,thecompanyhassetamaximumpriceof$8,500.Theracecarisalsolimitedtoasingle610ccdisplacementenginewithasingleinletrestrictor.Othermajorrulesrequirethatthecarmusthaveasuspensionsystemwithaminimumwheeltravelof50mmandawheelbasegreaterthan1524mm.Theremainderoftherulesdefinesafetyrequirementssuchassideimpactprotection.
Thecompetitionisseparatedintostaticanddynamicevents.Thestaticeventsincludethecostnalysis,salespresentation,andengineeringdesign.Thedynamicportionsofthecompetitionarethe15.25mdiameterskid-pad,91.44maccelerationevent,0.8kmautocross,44kmendurancerace,andfueleconomy.
TheFSAEcompetitionhasbeenestablishedtoprovideaneducationalexperienceforcollegestudentsthatisanalogoustothetypeofprojectstheywillfaceintheworkforce.ToparticipateinFSAE,studentgroupsworkwithaprojectfromtheabstractdesignuntilitiscompleted.Theaspectsofengineeringdesign,teamwork,projectmanagement,andfinancehavebeenincorporatedintothebasicrulesofFormulaSAE.
ThispaperisintendedtocoversomeofthebasicconceptsofsuspensionandframedesignandalsohighlightstheapproachUM-Rollausedwhendesigningtheir1996suspensionandframe.Thesuspensionsectionaddressesthebasicdesignparametersandpresentsspecificexamples.Next,theframesectiondiscusseshowtoachieveacompromisewiththeFSAEdesignconstraints.Finally,thedesignsectiongivesabriefoverviewofthedesignmethodologyusedbyUM-Rollaforthe1996racecar.
1.SuspensionGeometry
FSAEsuspensionsoperateinanarrowrealmofvehicledynamicsmainlyduetothelimitedcorneringspeedswhicharegovernedbytheracetracksize.Therefore,FSAEsuspensiondesignshouldfocusontheconstraintsofthecompetition.Forexample,vehicletrackwidthandwheelbasearefactorsgoverningthesuccessofthecar'shandlingcharacteristics.Thesetwodimensionsnotonlyinfluenceweighttransfer,buttheyalsoaffecttheturningradius.
NotonlydothekinematicshavetobeconsideredforFSAEsuspension,butthecomponentsmustalsobereasonablypricedforthecostanalysisandmarketableforthesalespresentation.Forexample,inboardsuspensioncouldbeamoremarketabledesign,whileoutboardsuspensionmightcostlessandbeeasiertomanufacture.ThesuspensiongeometrysectionconcentratesonsomeofthebasicareasofsuspensiondesignandhighlightswhattheUM-Rolladesignteamselectedfortheir1996racecarsuspensiongeometry.UM-Rollachosetouseafourwheelindependentsuspensionsystemwithpushrodactuatedinboardcoilovershocks.Thisdecisionwasmainlybecauseofpackagingconstraints.Furthermore,theappearanceofinboardsuspensionwasconsideredimportantforboththedesignjudgingandthesalespresentationbecauseofitssimilaritytomodernracecars.Also,thissectionofthepaperwaswrittenwithshort-longarmsuspensionsystemsinmind.However,manyoftheconceptsarevalidforothersuspensiontypes.
2.TrackWidthandWheelbase
ThedefinitionoftrackwidthisthedistancebetweentherightandleftwheelcenterlineswhichisillustratedinFigure1.Thisdimensionisimportantforcorneringsinceitresiststhe
Figure1.TrackWidth
overturningmomentduetotheinertiaforceatthecenterofgravity(CG)andthelateralforceatthetires.Forthedesigner,trackwidthisimportantsinceitisonecomponentthataffectstheamountoflateralweighttransfer.Also,thedesignersmustknowthetrackwidthbeforekinematicanalysisofthesuspensiongeometrycanbegin.
Whenselectingthetrackwidth,thefrontandreartrackwidthsdonotnecessarilyhavetobethesame.Forexample,trackwidthistypicallywiderinthefrontforarearwheeldriveracecar.Thisdesignconceptisusedtoincreasereartractionduringcornerexitbyreducingtheamountofbodyrollresistedbythereartiresrelativetothefronttires.BasedonthecornerspeedsandhorsepowertoweightratioofFSAEcars,thisconceptshouldbeconsideredbythedesigner.
Thewheelbasealsoneedstobedetermined.Wheelbaseisdefinedasthedistancebetweenthefrontandrearaxlecenterlines,andalsoinfluencesweighttransfer,butinthelongitudinaldirection.Exceptforanti-diveandanti-squatcharacteristics,thewheelbaserelativetotheCGlocationdoesnothavealargeeffectonthekinematicsofthesuspensionsystem.However,thewheelbaseshouldbedeterminedearlyinthedesignprocesssincethewheelbasehasalargeinfluenceonthepackagingofcomponents.Fortrackwidthandwheelbasestartingpoints,thedesignersshouldresearchtheopposition'sdimensionstoserveasabaselinefortheirowncalculations.FSAEcarspecificationsforthecompetingteams,includingtrackwidthandwheelbase,areavailableintheeventprogrampublishedbySAE.
The1996designteamselecteda1727mmwheelbase,1270mmfronttrackwidth,anda1219mmreartrackwidth,whichwerebasedonpreviousUM-Rollacars.AlthoughthiswheelbasewasadequatefortheFSAEcompetitionsizecourses,theUM-Rolladesignteamhasdecidedtoincreasethewheelbaseforthenextcarto1854.2mm.Thisincreaseinwheelbaseisanattempttoimprovestabilityforhighspeedcornerentryatthecompetition.
3.TireandWheel
Aftertrackwidthandwheelbaseconsiderationshavebeenaddressed,tireandwheelselectionisthenextstepinthedesignprocess.Sincethetireisimportanttothehandlingofthevehicle,thedesignteamshouldthoroughlyinvestigatethetiresizesandcompoundsavailable.Thetiresizeisimportantatthisstageofthedesignsincetheheightofthetiremustbeknownbeforethegeometrycanbedetermined.Forexample,thetireheightforagivenwheeldiameterdetermineshowclosethelowerballjointcanbetothegroundifpackagedinsidethewheel.
TireSize-Thedesignersshouldbeawarethatthenumberoftiresizesofferedforagivenwheeldiameterislimited.Therefore,consideringtheimportanceofthetiretohandling,thetireselectionprocessshouldbeamethodicalprocess.Sincetheamountoftireonthegroundhasalargeinfluenceongrip,itissometimesdesirabletousewidetiresforincreasedtraction.However,itisimportanttorememberthatwidetiresaddrotatingmasswhichmustbeacceleratedbyarestrictedFSAEengine.Thisaddedmassmightbemoredetrimentaltotheoverallperformancethantheincreaseintractionfromthewidertires.Notonlydoesawidertireaddmass,butitalsoincreasestheamountofrubberthatmustbeheated.Sinceracingtiresaredesignedtooperatemostefficientlyinaspecifictemperaturerange,thisaddedmaterialmaypreventthetiresfromreachingtheoptimumtemperaturerange.TheUM-Rollateamusedtiresforthe1996competitionthatweredesignedtoworkmostefficientlyataminimumof71°.
Duringtheselectionprocessthedesignersmustconsiderhowthetireswillinfluencetheperformanceoftheentirepackage.Forexample,theweatherconditionsfortheFSAEdynamiceventsmightdeterminewhichtirecompoundandtiresizeshouldbeusedforthecompetition.Anotherimportantconsiderationisthepriceofthetiressincethecostcanbealargeportionofateam'sbudget.
Forthe1996competition,UM-Rollaselecteda20by6-13racingtireforboththefrontandrearofthecar.Becauseofthelowvehiclemass,anarrowtirewasselectedsotiretemperatureswouldbegreaterthanpreviousUM-Rolladesigns.Thistireselectionincreasedtheoperatingtemperaturefrom48oto60oC.Forthecompetition,theweatherwaspredictedtobecool,sotheteambroughtasetofhardandsoftcompoundtires.Theteamchosetousethehardercompoundsincetheweatherfortheendurancewaspredictedtobeclearandwarm.
WheelSelection-Onceadecisionhasbeenmadeastowhichtiresizestouse,thewheelselectionshouldbenext.Usually,thewheeldimensionsarefixedandallowforlittlemodification.Therefore,itisimportanttohavesomedesigngoalsinmindbeforeinvestinginwheels.Generally,theupright,brakecaliper,androtorareplacedinsidethewheelwhichrequireswheeloffsetforclearance.Itisusuallyeasiertodesignthesuspensiongeometryifthewheelprofileisknown.Forexample,theballjointlocationislimitedtotheareadefinedbythewheelprofile.SomepackagingconstraintsareshowninFigure2.Otherconsiderationsforwheelselectioninclude:
cost,availability,boltcircle,andweight.Forexample,three-piecerims,althoughexpensive,havethedistinctadvantageofofferingmanyoffsetsandprofilesthatcanbechangedduringthedesignprocess.
Figure2.1996FrontSuspension
UM-Rolladesignedthe1996suspensiongeometryaroundawheelprofilefromapreviouscarandthenacquiredasetofthree-piecerimstomeetthedesignspecifications.Allfourwheelsselectedforthe1996competitionweresize6by13.Thiswheelselectionallowedfortirerotations,reducedcost,andawideselectionoftiresizes,compounds,andmanufacturers.
4.Geometry
Thedesignercannowsetsomedesiredparametersforthesuspensionsystem.Theseusuallyincludecambergain,rollcenterplacement,andscrubradius.Thechoiceoftheseparametersshouldbebasedonhowthevehicleisexpectedtoperform.Byvisualizingtheattitudeofthecarinacorner,thesuspensioncanbedesignedtokeepasmuchtireontheg
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