机动车转向系统外文原文及其翻译

本文摘于《RaceCarVehicleDynamics》作者：WilliamF.MilikenandDouglasL.MilikenSteeringsystemsIntroductionThischapterbeginswithadiscussionofsteeringgeometry—casterangle,trail,kingpininclination,andscrubradius.ThenextsectiondiscussAckermanngeometryfollowedbysteeringracksandgears.Ridesteer(bumpsteer)androllsteerarecloselyrelatedtoeachother;withoutcompliancetheywouldbethesame.Finally,wheelalignmentisdiscussed.thischapteristiedtochapter17onsuspensiongeometry-whendesigninganewchassis,steeringandsuspensiongeometryconsiderationsarehighpriorities.19.1steeringgeometryThekingpininasolidfrontaxleisthesteeringpivot.Inmodernindependentsuspensions,introducedbyMauriceolleyatCadillacin1932,thekingpinisreplacedbytwo(ormore)balljointsthatdefinethesteeringaxis.Thisaxisisnotverticalorcenteredonthetirecontactpatchforanumberofreason.seefigure19.1toclarifyhowkingpinlocationismeasured.Infrontview,theangleiscalledkingpininclinationandtheoffsetofthesteeringaxisfromthecenterofthetireprintmeasuredalongthegroundiscalledscrub(orscrubradius).Thedistancefromthekingpinaxistothewheelcenterplane,measuredhorizontallyataxleheight,isthespindlelength.Insideviewthekingpinangleiscalledcasterangle;ifthekingpinaxisdoesnotpassthroughthewheelcenterthensideviewkingpinoffsetispresent,asinmostmotorcyclefrontends.Thedistancemeasuredonthegroundfromthesteeringaxistothecenterofthetireprintisthetrail(calledcasteroffsetinref.1)〜Kingpinl.nclna:ionh—KingpinAxsHighL.BJTypicalTic御Location(RearStoor)I睇31TieRodLc^aticn(FrurtS〜Kingpinl.nclna:ionh—KingpinAxsHighL.BJTypicalTic御Location(RearStoor)I睇31TieRodLc^aticn(FrurtS翌己0—iSdtjViewKincpi-^Caster(+)—MflohanicafTrii：UBJ777777///_J_FOSWARD'Whes：OffsetUpperBellJoint(High)ySpndleLength〔+)BFakeDiscLower-BallJo；nlFlange"77^^77777777777777777ecnibF.ndiua(-■shewn)UpoerDallJoint(L&wjFigure19.1Kih耍ingeametry.KingpinfrontviewgeometryAsmentionedinchapter17,kingpininclination,spindlelength,andscrubareusuallyacompromisebetweenpackagingandperformancerequirements.Somefactorstoconsiderinclude:Withapositivespindlelength(virtuallyeverycarispositiveasshowninfigure19.1)thecarwillberaisedupasthewheelsaresteeredawayfromcenter.Themorethekingpininclinationistiltedfromverticalthemorethecarwillberaisedwhenthefrontwheelsaresteered.Thiseffectalwaysraisesthecar,regardlessofwhichdirectionthewheelissteered,unlessthekingpininclinationistruevertical.theeffectissymmetricsidetosideonlyifthereisnocasterangle.Seethefollowingsectiononcasterangle.Foragivenkingpininclination,alongerpositivespindlelengthwillincreasetheamountofliftwithsteer.Theeffectofkingpininclinationandspindlelengthinraisingthefrontend,byitself,istoaidcenteringofthesteeringatlowspeed.Athighspeedanytrailwillprobablyswampouttheeffectthatraiseadfallhaveoncentering.Kingpininclinationaffectsthesteer-cambercharacteristic.whenawheelissteered,itwillleanoutatthetop,towardpositivecamber,ifthekingpinisinclinedinthenormaldirection(towardthecenterofthecarattheupperend).Positivecamberresultsforbothleft-andright-handsteer.theamountofthiseffectissmall,butsignificantifthetrackincludestightturns.Whenawheelisrollingoverabumpyroad,therollingradiusisconstantlychanging,resultinginchangesofwheelrotationspeed.Thisgivesrisetolongitudinalforcesatthewheelcenter.Thereactionoftheseforceswillintroducekickbackintothesteeringinproportiontothespindlelength.Ifthespindlelengthiszerothentherewillbenokickfromthissource.DesignchangesmadeinthelastmodeloftheGM“P”car(fiero)shortenedthespindlelengthandthisresultedinlesswheelkickbackonroughroadswhencomparedtoearlymodel"P”cars.Thescrubradiusshowninfigure19.1isnegative,asusedonfront-wheel-drivecars(seebelow).drivingorbrakingforces(attheground)introducesteertorquesproportionaltothescrubradius.Ifthedrivingorbrakingforceisdifferentonleftandrightwheelsthentherewillbeanetsteeringtorquefeltbythedriver(assumingthatthesteeringgearhasgoodenoughreverseefficiency).Theonlytimethatthisisnottrueiswithzeroscrub(centerpointsteering)becausethereisnomomentarmforthedrive(orbrake)forcetogeneratetorqueaboutthekingpin.Withverywidetiresthetireforcesoftenarenotcenteredinthewheelcenterplaneduetoslightchangesincamber,roadsurfaceirregularities,tirenonuniformity(conicity),orotherasymmetriceffects.Theseasymmetriescancausesteeringkickbackregardlessofthefrontviewgeometry.Packagingrequirementsoftenconflictwithcenterpointsteeringandmanyracecarsoperatemoreorlessokayonsmoothtrackswithlargeamountsofscrub.Forfrontdrive,anegativescrubradiushastwostrongstabilizingeffects:first,fixedsteeringwheel-ifonedrivewheellosestraction,theopposingwheelwilltoe-outanamountdeterminedbythesteercomplianceinthesystem.Thiswilltendtosteerthecarinastraightline,eventhoughthetractiveforceisnotequalside-to-sideandtheunequaltractiveforceisapplyingayawmomenttothevehicle.Second,withgoodreverseefficiencythedriver’shandsnevertrulyfixthesteeringwheel.Inthiscasethesteeringwheelmaybeturnedbytheeffectofunevenlongitudinaltractiveforces,increasingthestabilizingeffectofthenegativescrubradius.Underbrakingthesameistrue.Negativescrubradiustendstokeepthecartravelingstraightevenwhenthebrakingforceisnotequalontheleftandrightsidefronttiresome(duetodifferencesintheroadwayorthebrakes).CasterangleandtrailWithmechanicaltrail,showninfigure19.1,thetireprintfollowsbehindthesteeringaxisinsideview.Perhapsthesimplestexampleisonanofficechaircaster-withanydistanceoftravel,thewheelalignsitselfbehindthepoint.Moretrailmeansthatthetiresideforcehasalargemomentarmtoactonthekingpinaxis.Thisproducesmoreself-centeringeffectandistheprimarysourceofself-centeringmomentaboutthekingpinaxisatspeed.Someconsiderationsforchoosingthecasterangleandtrailare:Moretrailwillgivehighersteeringforce.withallcars,lesstrailwilllowerthesteeringforce.Insomecases,manualsteeringcanbeusedonheavysedans(insteadofpowersteering)ifthetrailisreducedtoalmostzero.Casterangle,likekingpininclination,causethewheeltoriseandfallwithsteer.unlikekingpininclination,theeffectisoppositefromsidetoside.Withsymmetricgeometry(includingequalpositivecasteronleftandrightwheels),theeffectofleftsteeristorollthecartotheright,causingadiagonalweightshift.Inthiscase,moreloadwillbecarriedontheLF-RRdiagonal,anoversteereffectinaleft-handturn.Thediagonalweightshiftwillbelargerifstifferspringingisusedbecausethisisageometriceffect.Thedistanceeachwheelrises(orfalls)isconstantbuttheweightjackingandchassisrollanglearefunctionsofthefrontandrearrollstiffness.Thisdiagonalloadchangecanbemeasuredwiththecaronscalesandalignment(weaver)plates.Keepinmindthatthefrontwheelsarenotsteeredverymuchinactualracing,exceptontheverytightesthairpinturns.Forexample,ona100-ft.radius(a40-50mphturn),a10-ft.wheelbaseneutralsteercarneedsonlyabout0.1rad.(5.7)ofsteeratthefrontwheels(witha16:1steeringratiothisisabout90degreeatthesteeringwheel).Forcarsthatturninonedirectiononly,casterstagger(differencesinleftandrightcaster)isusedtocausethecartopulltoonesideduetothecarseekingthelowestrideheight.casterstaggerwillalsoaffectthediagonalweightjackingeffectmentionedabove.Ifthecasterisopposite(positiveononesideandnegativethesamenumberofdegreesontheotherside)thenthefrontofthecarwillonlyriseandfallwithsteer,nodiagonalweightjackingwilloccur.Casterangleaffectssteer-camberbut,unlikekingpininclination,theeffectisfavorable.Withpositivecasterangletheoutsidewheelwillcamberinanegativedirection(topofthewheeltowardthecenterofthecar)whiletheinsidewheelcambersinapositivedirection,againlearningintotheturn.Inskidrecovery,“oppositelock”(steeroutoftheturn)isusedandinthiscasethesteer-camberresultingfromcasterangleisinthe“wrong"directionforincreasedfronttiregrip.conveniently,thisconditionresultsfromverylowlateralforceattherearsolargeamountsoffrontgriparenotneeded.Asdiscussedinchapter2,tireshavepneumatictrailwhicheffectivelyaddsto(andathighslipAnglessubtractsfrom)themechanicaltrail.Thistireeffectisnonlinearwithlateralforceandaffectssteeringtorqueanddriverfeel.Inparticular,thefactthatpneumatictrailapproacheszeroasthetirereachesthelimitwillresultinloweringtheself-centeringtorqueandcanbessignaltothedriverthatthetireisnearbreakaway.Thepneumatictrail“breakawaysignal”willbeswampedoutbymechanicaltrailifthemechanicaltrailislargecomparedtothepneumatictrail.5.Sometimesthetrailismeasuredinadirectionperpendiculartothesteeringaxis(ratherthanhorizontalasshowninfigure19.1)becausethismoreaccuratelydescribesthelever(moment)armthatconnectsthetirelateralforcestothekingpin.TierodlocationNotethatinfigure19.1ashadedareaisshownforthesteeringtierodlocation.Cambercomplianceunderlateralforceisunavoidableandifthetierodislocatedasnoted,theeffectonthesteeringwillbeintheundersteer(steeroutoftheturn)directionbecomesmuchmorecomplexthancanbecoveredhere.19.2AckermansteeringgeometryAsthefrontwheelsofavehiclearesteeredawayfromthestraight-aheadposition,thedesignofthesteeringlinkagewilldetermineifthewheelsstayparallelorifonewheelsteersmorethantheother.ThisdifferenceinsteerAnglesontheleftandrightwheelsshouldnotbeconfusedwithtoe-inortoe-outwhichareadjustmentsandaddto(orsubtractfrom)Ackermangeometriceffects.Forlowlateralaccelerationusage(streetcars)itiscommontouseAckermangeometry.asseenontheleftoffigure19.2,thisgeometryensuresthatallthewheelsrollfreelywithnoslipAnglesbecausethewheelsaresteeredtotrackacommonturncenter.Notethatatlowspeedallwheelsareonasignificantlydifferentradius,theinsidefrontwheelmuststeermorethantheouterfrontwheel.Areasonableapproximationtothisgeometrymaybeasshowninfigure19.3.Accordingtoref.99,RudolfAckermanpatentedthedoublepivotsteeringsystemin1817andin1878,CharlesJeantaudaddedtheconceptmentionedabovetoeliminatewheelscrubbingwhencornering.AnotherreasonforAckermanngeometry,mentionedbyMauriceolley,wastokeepcarriagewheelsfromupsettingsmoothgraveldriveways.Highlateralaccelerationschangethepictureconsiderably.NowthetiresalloperateatsignificantslipAnglesandtheloadsontheinsidetrackarelessthanontheoutsidetrack.Lookingbacktothetireperformancecurves,itisseenthatlessslipangleisrequiredatlighterloadstoreachthepeakofthecorneringforcetoahigherslipanglethanrequiredformaximumsideforce.DraggingtheinsidetirealongathighslipAngles(aboveforpeaklateralforce)raisethetiretemperatureandslowsthecardownduetoslipangle(induced)drag.Forracing,itiscommontouseparallelsteeringorevenreverseAckermannasshownonthecenterandrightsideoffigure19.2.ItispossibletocalculatethecorrectamountofreverseAckermannifthetirepropertiesandloadsareknown.Inmostcasestheresultinggeometryisfoundtobetooextremebecausethecarmustalsobedriven(orpushed)atlowspeeds,forexampleinthepits.AnotherpointtorememberisthatmostturnsinracinghaveafairlylargeradiusandtheAckermanneffectisverysmall.Infact,unlessthesteeringsystemandsuspensionareverystiff,compliance(deflection)undercorneringloadsmaysteerthewheelsmorethananyAckermann(orreverseAckermann)builtintothegeometry.ThesimplestconstructionthatgeneratesAckermannngeometryisshowninfigure19.3for“rearsteer".Here,therack(crosslinkorrelayrodinsteeringboxsystems)islocatedbehindthefrontaxleandlinesstaringatthekingpinaxis,extendedthroughtheoutertierodends,intersectinthecenteroftherearaxle.Theangularityofthesteeringknucklewillcausetheinnerwheeltosteermorethantheouter(toe-outonturning)andagoodapproximationof“perfectAckermann”willbeachieved.iigareJ2Ackemicirmsteermg£en朋etry.SteeringRae*TitRudOulfc?rBell!JujritSteeringArmFigure193Ac:ke.rmanu^GmeTryiigareJ2Ackemicirmsteermg£en朋etry.SteeringRae*TitRudOulfc?rBell!JujritSteeringArmFigure193Ac:ke.rmanu^GmeTry1withsBeringr^ckbehindtheaxleRj*Thesecondwaytodesign-indifferencesbetweeninnerandoutersteerAnglesisbymovingtherack(orcrosslink)forwardorbackwardsothatitisnolongeronalinedirectlyconnectingthetwooutertierodballjoints.Thisisshowninfigure19.4.with“rearsteer”，asshowninthefigure,movingtherackforwardwilltendmoretowardparallelsteer(andeventuallyreverseAckermann),andmovingittowardtherearofthecarwillincreasethetoe-outonturning.Athirdwaytogeneratetoewithsteeringissimplytomakethesteeringarmsdifferentlengths.Ashortersteeringarm(asmeasuredfromthekingpinaxistotheoutertierodend)willbesteeredthroughalargeranglethanonewithalongerknuckle.Ofcoursethiseffectisasymmetricandappliesonlytocarsturninginonedirection—ovaltrackcars.RecommendationWiththeconflictingrequirementsmentionedabove,theauthorsfeelthatparallelsteerorabitofreverseAckermannisareasonablecompromise.Withparallelsteer,thecarwillbesomewhatdifficulttopushthroughthepitsbecausethefrontwheelswillbefightingeachother.atracingspeeds,onlarge-radiusturns,thefrontwheelsaresteeredverylittle,thusanyackermanneffectswillnothavealargeeffectontheindividualwheelslipangles,relativetoareferencesteerangle,measuredatthecenterlineofthecar.

TOPVIEWTOPVIEWAppmximalelyParallelSteer'MoreTOPVIEWTOPVIEWAppmximalelyParallelSteerFigureJ9.4Modifiedsteecgeometry—movingsteeringrackforwardandbackward.文献翻译摘自《RaceCarVehicleDynamics》第19章转向系统序言：本章以转向几何参数的讨论为开始，包括主销后倾角，后倾拖距，主销内倾角，主销偏置量。接下来的部分讨论了转向齿轮齿条以及阿克曼转向几何关系。跳动转向和侧倾转向之间是紧密相关的，如果没有柔性这两种情况是等同的。最后讨论了车轮的调整。这一章与第17章的悬架几何形状密切相关，在设计新的底盘系统时，转向和悬架几何参数是优先考虑的因素。19.1转向几何关系（定位参数）在整体式车桥上转向节主销是转向时的枢轴。1932年MauriceOlley在Cadillac首次提出了现在的非独立悬架，主销因此而被两个球绞连接定义的转向轴线代替。因为各种原因这根轴并不是垂直的也不在轮胎接地中心处。主销的位置表示见图19.1。

—主销轴线匕球头接点（高）—、主销内倾角厂-上球头接点（高）主销偏距（+）典型的横拉杆位置（后置梯形）车轮偏置距~上球头接点（低）一d典型的横拉—主销轴线匕球头接点（高）—、主销内倾角厂-上球头接点（高）主销偏距（+）典型的横拉杆位置（后置梯形）车轮偏置距~上球头接点（低）一d典型的横拉•杆位置（前一4。置梯形）下球头接点—侧视主销偏距轮辆挡边主销4倾角H）制动盘匕球头接点（低）下球头接点777777777777777777777777777777771■前进方向77777777777777777777777777777777777??^主情后倾拖距T卜主销偏置量（示图为负值）•在前视图中，主销偏转的角度被称为主销内倾角，转向主销与地面的交点至车轮中心平面与地面相交处的距离称之为主销偏置量。在前轴所在水平面内，从主销轴心到车轮中心平面的距离称为主销偏距（spindlelength）。•在侧视图中，主销偏转角度称为主销后倾角。如果主销轴线没有通过车轮中心那么就有了侧视的主销偏距（sideviewkingpinoffset），就像大部分的摩托车前轮一样。在地平面内测量从主销到轮胎接地点中心的距离称为主销后倾拖距。前视图中的主销定位参数正如在17章中提到，主销内倾角，主销偏距还有主销偏置量在装配以及性能满足时往往是互相妥协的。一些需要考虑的因素包括以下：当主销偏距是正的时（一般的车都是正主销偏距，如图19.1中一样）那车轮转离中心位置的时候车会有一个抬升效果。主销内倾角偏离竖直平面越大前轮转向时车被抬起的效果越明显。不管车轮往哪个方向转都会是一个抬升的效果，除非主销是完全垂直的。这个效果只有在主销后倾角为零时才是两边对称的。见后面关于主销后倾角部分。对于一个给定的主销内倾角来说，主销偏距越大转向时的抬升量也越大。主销内倾角和主销偏距将车子前端抬起的效果对于自身来说是有助于低速转向的。在高速转向时，只要有主销后倾拖距就可能会掩盖掉转向时抬升和下落的效果主销内倾角影响转向时车轮的外倾角特性。如果主销向内倾斜（主销上端倾向车辆中心）当车轮转向的时候，车轮上端将会向外倾斜，趋向正的车轮外倾角。左右转向都会导致正的车轮外倾。如果跑道有比较紧的弯这个作用效果是比较小但却是有重要意义的。当车轮滚过颠簸不平的路面时，滚动半径是不断变化的，将会导致轮速的改变。这将会增加车轮中心的纵向力。这些力的反作用与主销偏距的大小成比例，成为反冲效果进入转向系统。如果主销偏距为零，那么将不会有由此引起的反冲。在前面提到的一辆通用“P”型车（菲罗车）中做出设计改动，与较早的一辆『”型车模型相比，减小了主销偏距，因此而减少了不平路面上的反冲。如图19.1中所示的主销偏置量是负的，正如下面这辆前轮驱动车用的一样。来自地面的驱动和制动力与主销偏置量成比例的转化成转向力矩。如果左右轮的制动或者驱动力是不等的，那么驾驶者将会感受到的到这个转向力矩（假设转向器有较高的逆效率）。只有在主销偏置量为零时才不会有这个力矩产生因为此时制动力或驱动力对主销的作用力臂为零。如果轮胎比较宽的话轮胎力通常并不是作用在轮胎中心平面内的，因为轻微的外倾角变化、路面不平、轮胎有一定圆锥度、或者其他的不对称因素存在。这些不对称因素可能导致转向反冲，即使没有前轮的各个定位参数作用。装配要求通常会与中心点转向要求冲突因而很多赛车在较平整的赛道上是采用较大的主销偏置量也是可以的。对于前轮驱动来说，一个负的主销偏置量有两个重要的稳定作用：第一，固定方向盘，如果一个驱动轮打滑，另外一个轮将会外张一定角度，因为转向系统内有变形。即使两侧的牵引力不等，不同的牵引力使车辆产生一个偏航角，这个负的主销偏置量作用也会使车辆回复到直线行驶。第二，有良好的反馈作用情况下驾驶员从来不会真正的固定住方向盘。在这种情况下方向盘可能在不等的车轮纵向牵引力作用下而转动，因此而增加了负主销偏置量的稳定效果。制动的情况同样适用。负的主销偏置量能使车子回正，即使是在左右轮制动力不等的情况下（左右轮的制动情况或者路面情况不同时）。（fsae没人用吧）主销后倾角和后倾拖距如图19.1中所示，在有后倾拖距时，侧视图中轮胎接地点是在主销之后的。或许最简单的例子就是办公室座椅上的小脚轮（？）一一不管移动多远，轮子总会校正使其自身在枢轴之后。主销拖距越大意味着轮胎侧向力在主销轴上作用有更大的力臂。这会产生更明显的回正作用，并且是作用在主销上最主要的回正力矩。在选择主销后倾角和主销拖距时需要考虑的因素如下：主销后倾拖距越大转向力也越大。对于所有的车来说，小的后倾拖距都将会减小转向力。在某些情况下，如果后倾拖距减小接近零的话，人力转向也可能被用于重型轿车（代替助力转向）。像主销内倾角一样，主销后倾角伴随着转向过程也会引起车轮的抬起和回落。与内倾角不同的是，后倾角对两侧的影响是相反的。在有对称定位参数时（包括左右轮有相等的正的主销后倾角），左转的效应是使车向右侧倾，导致一个对角线的重量转移。在这种情况下，左前一一右后对角线会承受更大的载荷，有一个左转时的过度转向效应。使用的弹簧越硬对角线的重量转移效果也会越明显因为这个是几何效应。每个车轮被抬起（或者下落）的距离是恒定的但是重量抬起量和底盘侧倾角是前后侧倾刚度的作用结果。这个对角线的载荷转移可以通过把车放在秤上和定位板上来测量。记住在实际比赛中前轮并没有转过很大的角度，除非是非常紧的发夹弯。例如，在一个半径是100英尺（时速在40-50英里）的弯，一个10英尺的轴距的中性转向车辆转弯时前轮只需要转过0.1rad（5.7°）（转向传动比是16：1时方向盘的转角大概在90°）。对于只往一个方向转的车来说，因为整车为了寻求最低的最小离地间隙，可以使主销后倾角交错（左右主销后倾角不同）来把车拉到一边。主销后倾角的交错也会影响上面提到的对角线重量抬升效应。如果两侧主销后倾角是相反的（一侧为正一侧为负且两侧角度大小相等）那么在转向时车的前端只会抬升和下落，而不会有对角线的重量抬升主销后倾角也会影响转向外倾角，但是