汽車(chē)轉(zhuǎn)向系統(tǒng)外文原文及翻譯

1、本文摘于Race Car Vehicle Dynamics 作者：William F. Miliken and Douglas L. MilikenSteering systemsIntroduction This chapter begins with a discussion of steering geometrycaster angle ,trail ,kingpin inclination ,and scrub radius .The next section discuss Ackermann geometry followed by steering racks and gear

2、s .Ride steer (bump steer ) and roll steer are closely related to each other ;without compliance they would be the same .Finally ,wheel alignment is discussed .this chapter is tied to chapter 17 on suspension geometry when designing a new chassis ,steering and suspension geometry considerations are

3、high priorities . steering geometry The kingpin in a solid front axle is the steering pivot .In modern independent suspensions , introduced by Maurice olley at Cadillac in 1932,the kingpin is replaced by two (or more ) ball joints that define the steering axis .This axis is not vertical or centered

4、on the tire contact patch for a number of reason .see figure to clarify how kingpin location is measured .In front view ,the angle is called kingpin inclination and the offset of the steering axis from the center of the tire print measured along the ground is called scrub (or scrub radius ). The dis

5、tance from the kingpin axis to the wheel center plane , measured horizontally at axle height ,is the spindle length .In side view the kingpin angle is called caster angle ; if the kingpin axis does not pass through the wheel center then side view kingpin offset is present ,as in most motorcycle fron

6、t ends .The distance measured on the ground from the steering axis to the center of the tire print is the trail (called caster offset in ref .1 )Kingpin front view geometry As mentioned in chapter 17, kingpin inclination ,spindle length ,and scrub are usually a compromise between packaging and perfo

7、rmance requirements .Some factors to consider include : a positive spindle length (virtually every car is positive as shown in figure the car will be raised up as the wheels are steered away from center .The more the kingpin inclination is tilted from vertical the more the car will be raised when th

8、e front wheels are steered .This effect always raises the car , regardless of which direction the wheel is steered ,unless the kingpin inclination is true vertical .the effect is symmetric side to side only if there is no caster angle .See the following section on caster angle .For a given kingpin i

9、nclination ,a longer positive spindle length will increase the amount of lift with steer . effect of kingpin inclination and spindle length in raising the front end ,by itself ,is to aid centering of the steering at low speed .At high speed any trail will probably swamp out the effect that raise ad

10、fall have on centering .3. Kingpin inclination affects the steer camber characteristic .when a wheel is steered ,it will lean out at the top ,toward positive camber ,if the kingpin is inclined in the normal direction (toward the center of the car at the upper end ). Positive camber results for both

11、left and right-hand steer .the amount of this effect is small ,but significant if the track includes tight turns.4. When a wheel is rolling over a bumpy road ,the rolling radius is constantly changing ,resulting in changes of wheel rotation speed . This gives rise to longitudinal forces at the wheel

12、 center .The reaction of these forces will introduce kickback into the steering in proportion to the spindle length .If the spindle length is zero then there will be no kick from this source .Design changes made in the last model of the GM “P ”car (fiero ) shortened the spindle length and this resul

13、ted in less wheel kickback on rough roads when compared to early model “P ”cars.5. The scrub radius shown in figure is negative ,as used on front-wheel drive cars (see below ) . driving or braking forces (at the ground ) introduce steer torques proportional to the scrub radius . If the driving or br

14、aking force is different on left and right wheels then there will be a net steering torque felt by the driver (assuming that the steering gear has good enough rev erse efficiency ).The only time that this is not true is with zero scrub (centerpoint steering ) because there is no moment arm for the d

15、rive (or brake ) force to generate torque about the kingpin .With very wide tires the tire forces often are not centered in the wheel center plane due to slight changes in camber ,road surface irregularities ,tire nonuniformity (conicity ),or other asymmetric effects .These asymmetries can cause ste

16、ering kickback regardless of the front view geometry .Packaging requirements often conflict with centerpoint steering and many race cars operate more or less okay on smooth tracks with large amounts of scrub .6. For front drive ,a negative scrub radius has two strong stabilizing effects :first ,fixe

17、d steering wheel if one drive wheel loses traction ,the opposing wheel will toe out an amount determined by the steer compliance in the system .This will tend to steer the car in a straight line ,even though the tractive force is not equal side-to side and the unequal tractive force is applying a ya

18、w moment to the vehicle .Second ,with good reverse efficiency the drivers hands never truly fix the steering wheel . In this case the steering wheel may be turned by the effect of uneven longitudinal tractive forces ,increasing the stabilizing effect of the negative scrub radius .Under braking the s

19、ame is true .Negative scrub radius tends to keep the car traveling straight even when the braking force is not equal on the left and right side front tiresome (due to differences in the roadway or the brakes).Caster angle and trail With mechanical trail ,shown in figure ,the tire print follows behin

20、d the steering axis in side view .Perhaps the simplest example is on an office chair caster with any distance of travel ,the wheel aligns itself behind the point .More trail means that the tire side force has a large moment arm to act on the kingpin axis .This produces more self-centering effect and

21、 is the primary source of self-centering moment about the kingpin axis at speed .Some considerations for choosing the caster angle and trail are : trail will give higher steering force .with all cars ,less trail will lower the steering force .In some cases ,manual steering can be used on heavy sedan

22、s (instead of power steering ) if the trail is reduced to almost zero . angle ,like kingpin inclination ,cause the wheel to rise and fall with steer .unlike kingpin inclination ,the effect is opposite from side to side .With symmetric geometry (including equal positive caster on left and right wheel

23、s ) ,the effect of left steer is to roll the car to the right ,causing a diagonal weight shift .In this case ,more load will be carried on the LF RR diagonal ,an oversteer effect in a left-hand turn .The diagonal weight shift will be larger if stiffer springing is used because this is a geometric ef

24、fect .The distance each wheel rises (or falls ) is constant but the weight jacking and chassis roll angle are functions of the front and rear roll stiffness. This diagonal load change can be measured with the car on scales and alignment ( weaver ) plates .Keep in mind that the front wheels are not s

25、teered very much in actual racing , except on the very tightest hairpin turns . For example , on a 100-ft .radius (a 40-50 mph turn ), a 10-ft. wheelbase neutral steer car needs only about .of steer at the front wheels (with a 16:1steering ratio this is about 90degree at the steering wheel ).For car

26、s that turn in one direction only , caster stagger (differences in left and right caster ) is used to cause the car to pull to one side due to the car seeking the lowest ride height . caster stagger will also affect the diagonal weight jacking effect mentioned above . If the caster is opposite (posi

27、tive on one side and negative the same number of degrees on the other side ) then the front of the car will only rise and fall with steer , no diagonal weight jacking will occur .3. Caster angle affects steer-camber but ,unlike kingpin inclination ,the effect is favorable . With positive caster angl

28、e the outside wheel will camber in a negative direction (top of the wheel toward the center of the car ) while the inside wheel cambers in a positive direction , again learning into the turn .In skid recovery , “opposite lock ” (steer out of the turn ) is used and in this case the steercamber result

29、ing from caster angle is in the “wrong ” direction for increased front tire grip . conveniently ,this condition results from very low lateral force at the rear so large amounts of front grip are not needed .4. As discussed in chapter 2, tires have pneumatic trail which effectively adds to (and at hi

30、gh slip Angles subtracts from ) the mechanical trail . This tire effect is nonlinear with lateral force and affects steering torque and driver feel .In particular , the fact that pneumatic trail approaches zero as the tire reaches the limit will result in lowering the self-centering torque and can b

31、e s signal to the driver that the tire is near breakaway .The pneumatic trail “breakaway signal” will be swamped out by mechanical trail if the mechanical trail is large compared to the pneumatic trail . the trail is measured in a direction perpendicular to the steering axis (rather than horizontal

32、as shown in figure because this more accurately describes the lever (moment ) arm that connects the tire lateral forces to the kingpin .Tie rod location Note that in figure a shaded area is shown for the steering tie rod location . Camber compliance under lateral force is unavoidable and if the tie

33、rod is located as noted ,the effect on the steering will be in the understeer ( steer out of the turn ) direction becomes much more complex than can be covered here . Ackerman steering geometry As the front wheels of a vehicle are steered away from the straight-ahead position ,the design of the stee

34、ring linkage will determine if the wheels stay parallel or if one wheel steers more than the other .This difference in steer Angles on the left and right wheels should not be confused with toe-in or toe-out which are adjustments and add to ( or subtract from ) Ackerman geometric effects .For low lat

35、eral acceleration usage (street cars) it is common to use Ackerman geometry . as seen on the left of figure , this geometry ensures that all the wheels roll freely with no slip Angles because the wheels are steered to track a common turn center . Note that at low speed all wheels are on a significan

36、tly different radius , the inside front wheel must steer more than the outer front wheel . A reasonable approximation to this geometry may be as shown in figure .According to ref .99, Rudolf Ackerman patented the double pivot steering system in 1817 and in 1878, Charles Jeantaud added the concept me

37、ntioned above to eliminate wheel scrubbing when cornering . Another reason for Ackermann geometry ,mentioned by Maurice olley , was to keep carriage wheels from upsetting smooth gravel driveways .High lateral accelerations change the picture considerably . Now the tires all operate at significant sl

38、ip Angles and the loads on the inside track are less than on the outside track . Looking back to the tire performance curves ,it is seen that less slip angle is required at lighter loads to reach the peak of the cornering force to a higher slip angle than required for maximum side force . Dragging t

39、he inside tire along at high slip Angles ( above for peak lateral force ) raise the tire temperature and slows the car down due to slip angle ( induced ) drag .For racing , it is common to use parallel steering or even reverse Ackermann as shown on the center and right side of figure .It is possible

40、 to calculate the correct amount of reverse Ackermann if the tire properties and loads are known . In most cases the resulting geometry is found to be too extreme because the car must also be driven (or pushed ) at low speeds , for example in the pits .Another point to remember is that most turns in

41、 racing have a fairly large radius and the Ackermann effect is very small . In fact , unless the steering system and suspension are very stiff ,compliance (deflection ) under cornering loads may steer the wheels more than any Ackermann (or reverse Ackermann ) built into the geometry .The simplest co

42、nstruction that generates Ackermannn geometry is shown in figure for “rear steer ” . Here ,the rack (cross link or relay rod in steering box systems ) is located behind the front axle and lines staring at the kingpin axis , extended through the outer tie rod ends , intersect in the center of the rea

43、r axle . The angularity of the steering knuckle will cause the inner wheel to steer more than the outer (toe-out on turning ) and a good approximation of “perfect Ackermann ” will be achieved . The second way to design-in differences between inner and outer steer Angles is by moving the rack (or cro

44、ss link ) forward or backward so that it is no longer on a line directly connecting the two outer tie rod ball joints .This is shown in figure . with “rear steer ” , as shown in the figure ,moving the rack forward will tend more toward parallel steer (and eventually reverse Ackermann ), and moving i

45、t toward the rear of the car will increase the toe-out on turning .A third way to generate toe with steering is simply to make the steering arms different lengths . A shorter steering arm (as measured from the kingpin axis to the outer tie rod end ) will be steered through a larger angle than one wi

46、th a longer knuckle. Of course this effect is asymmetric and applies only to cars turning in one directionoval track cars .Recommendation With the conflicting requirements mentioned above , the authors feel that parallel steer or a bit of reverse Ackermann is a reasonable compromise . With parallel

47、steer , the car will be somewhat difficult to push through the pits because the front wheels will be fighting each other . at racing speeds , on large-radius turns , the front wheels are steered very little , thus any ackermann effects will not have a large effect on the individual wheel slip angles

48、 , relative to a reference steer angle , measured at the centerline of the car . 文獻(xiàn)翻譯 摘自Race Car Vehicle Dynamics第19章 轉(zhuǎn)向系統(tǒng)序言：本章以轉(zhuǎn)向幾何參數(shù)的討論為開(kāi)始，包括主銷后傾角，后傾拖距，主銷內(nèi)傾角，主銷偏置量。接下來(lái)的部分討論了轉(zhuǎn)向齒輪齒條以及阿克曼轉(zhuǎn)向幾何關(guān)系。跳動(dòng)轉(zhuǎn)向和側(cè)傾轉(zhuǎn)向之間是緊密相關(guān)的，如果沒(méi)有柔性這兩種情況是等同的。最后討論了車(chē)輪的調(diào)整。這一章與第17章的懸架幾何形狀密切相關(guān)，在設(shè)計(jì)新的底盤(pán)系統(tǒng)時(shí)，轉(zhuǎn)向和懸架幾何參數(shù)是優(yōu)先考慮的因素。 轉(zhuǎn)向幾何關(guān)系（定位參數(shù)）

49、 在整體式車(chē)橋上轉(zhuǎn)向節(jié)主銷是轉(zhuǎn)向時(shí)的樞軸。1932年Maurice Olley在Cadillac首次提出了現(xiàn)在的非獨(dú)立懸架，主銷因此而被兩個(gè)球絞連接定義的轉(zhuǎn)向軸線代替。因?yàn)楦鞣N原因這根軸并不是垂直的也不在輪胎接地中心處。主銷的位置表示見(jiàn)圖。在前視圖中，主銷偏轉(zhuǎn)的角度被稱為主銷內(nèi)傾角，轉(zhuǎn)向主銷與地面的交點(diǎn)至車(chē)輪中心平面與地面相交處的距離稱之為主銷偏置量。在前軸所在水平面內(nèi)，從主銷軸心到車(chē)輪中心平面的距離稱為主銷偏距（spindle length）。在側(cè)視圖中，主銷偏轉(zhuǎn)角度稱為主銷后傾角。如果主銷軸線沒(méi)有通過(guò)車(chē)輪中心那么就有了側(cè)視的主銷偏距（side view kingpin offset），就像

50、大部分的摩托車(chē)前輪一樣。在地平面內(nèi)測(cè)量從主銷到輪胎接地點(diǎn)中心的距離稱為主銷后傾拖距。前視圖中的主銷定位參數(shù)正如在17章中提到，主銷內(nèi)傾角，主銷偏距還有主銷偏置量在裝配以及性能滿足時(shí)往往是互相妥協(xié)的。一些需要考慮的因素包括以下：1. 當(dāng)主銷偏距是正的時(shí)（一般的車(chē)都是正主銷偏距，如圖中一樣）那車(chē)輪轉(zhuǎn)離中心位置的時(shí)候車(chē)會(huì)有一個(gè)抬升效果。主銷內(nèi)傾角偏離豎直平面越大前輪轉(zhuǎn)向時(shí)車(chē)被抬起的效果越明顯。不管車(chē)輪往哪個(gè)方向轉(zhuǎn)都會(huì)是一個(gè)抬升的效果，除非主銷是完全垂直的。這個(gè)效果只有在主銷后傾角為零時(shí)才是兩邊對(duì)稱的。見(jiàn)后面關(guān)于主銷后傾角部分。對(duì)于一個(gè)給定的主銷內(nèi)傾角來(lái)說(shuō)，主銷偏距越大轉(zhuǎn)向時(shí)的抬升量也越大。2. 主銷

51、內(nèi)傾角和主銷偏距將車(chē)子前端抬起的效果對(duì)于自身來(lái)說(shuō)是有助于低速轉(zhuǎn)向的。在高速轉(zhuǎn)向時(shí)，只要有主銷后傾拖距就可能會(huì)掩蓋掉轉(zhuǎn)向時(shí)抬升和下落的效果。3. 主銷內(nèi)傾角影響轉(zhuǎn)向時(shí)車(chē)輪的外傾角特性。如果主銷向內(nèi)傾斜（主銷上端傾向車(chē)輛中心）當(dāng)車(chē)輪轉(zhuǎn)向的時(shí)候，車(chē)輪上端將會(huì)向外傾斜，趨向正的車(chē)輪外傾角。左右轉(zhuǎn)向都會(huì)導(dǎo)致正的車(chē)輪外傾。如果跑道有比較緊的彎這個(gè)作用效果是比較小但卻是有重要意義的。4. 當(dāng)車(chē)輪滾過(guò)顛簸不平的路面時(shí)，滾動(dòng)半徑是不斷變化的，將會(huì)導(dǎo)致輪速的改變。這將會(huì)增加車(chē)輪中心的縱向力。這些力的反作用與主銷偏距的大小成比例，成為反沖效果進(jìn)入轉(zhuǎn)向系統(tǒng)。如果主銷偏距為零，那么將不會(huì)有由此引起的反沖。在前面提到的一

52、輛通用“P”型車(chē)（菲羅車(chē)）中做出設(shè)計(jì)改動(dòng)，與較早的一輛“P”型車(chē)模型相比，減小了主銷偏距，因此而減少了不平路面上的反沖。5. 如圖中所示的主銷偏置量是負(fù)的，正如下面這輛前輪驅(qū)動(dòng)車(chē)用的一樣。來(lái)自地面的驅(qū)動(dòng)和制動(dòng)力與主銷偏置量成比例的轉(zhuǎn)化成轉(zhuǎn)向力矩。如果左右輪的制動(dòng)或者驅(qū)動(dòng)力是不等的，那么駕駛者將會(huì)感受到的到這個(gè)轉(zhuǎn)向力矩（假設(shè)轉(zhuǎn)向器有較高的逆效率）。只有在主銷偏置量為零時(shí)才不會(huì)有這個(gè)力矩產(chǎn)生因?yàn)榇藭r(shí)制動(dòng)力或驅(qū)動(dòng)力對(duì)主銷的作用力臂為零。如果輪胎比較寬的話輪胎力通常并不是作用在輪胎中心平面內(nèi)的，因?yàn)檩p微的外傾角變化、路面不平、輪胎有一定圓錐度、或者其他的不對(duì)稱因素存在。這些不對(duì)稱因素可能導(dǎo)致轉(zhuǎn)向反沖，

53、即使沒(méi)有前輪的各個(gè)定位參數(shù)作用。裝配要求通常會(huì)與中心點(diǎn)轉(zhuǎn)向要求沖突因而很多賽車(chē)在較平整的賽道上是采用較大的主銷偏置量也是可以的。6. 對(duì)于前輪驅(qū)動(dòng)來(lái)說(shuō)，一個(gè)負(fù)的主銷偏置量有兩個(gè)重要的穩(wěn)定作用：第一， 固定方向盤(pán)，如果一個(gè)驅(qū)動(dòng)輪打滑，另外一個(gè)輪將會(huì)外張一定角度，因?yàn)?轉(zhuǎn)向系統(tǒng)內(nèi)有變形。即使兩側(cè)的牽引力不等，不同的牽引力使車(chē)輛產(chǎn)生一個(gè)偏航角，這個(gè)負(fù)的主銷偏置量作用也會(huì)使車(chē)輛回復(fù)到直線行駛。第二， 有良好的反饋?zhàn)饔们闆r下駕駛員從來(lái)不會(huì)真正的固定住方向盤(pán)。在這種情況下方向盤(pán)可能在不等的車(chē)輪縱向牽引力作用下而轉(zhuǎn)動(dòng)，因此而增加了負(fù)主銷偏置量的穩(wěn)定效果。制動(dòng)的情況同樣適用。負(fù)的主銷偏置量能使車(chē)子回正，即使是

54、在左右輪制動(dòng)力不等的情況下（左右輪的制動(dòng)情況或者路面情況不同時(shí)）。(fsae沒(méi)人用吧)主銷后傾角和后傾拖距如圖中所示，在有后傾拖距時(shí)，側(cè)視圖中輪胎接地點(diǎn)是在主銷之后的?；蛟S最簡(jiǎn)單的例子就是辦公室座椅上的小腳輪（？）不管移動(dòng)多遠(yuǎn)，輪子總會(huì)校正使其自身在樞軸之后。主銷拖距越大意味著輪胎側(cè)向力在主銷軸上作用有更大的力臂。這會(huì)產(chǎn)生更明顯的回正作用，并且是作用在主銷上最主要的回正力矩。在選擇主銷后傾角和主銷拖距時(shí)需要考慮的因素如下：1. 主銷后傾拖距越大轉(zhuǎn)向力也越大。對(duì)于所有的車(chē)來(lái)說(shuō)，小的后傾拖距都將會(huì)減小轉(zhuǎn)向力。在某些情況下，如果后傾拖距減小接近零的話，人力轉(zhuǎn)向也可能被用于重型轎車(chē)（代替助力轉(zhuǎn)向）。2

55、. 像主銷內(nèi)傾角一樣，主銷后傾角伴隨著轉(zhuǎn)向過(guò)程也會(huì)引起車(chē)輪的抬起和回落。與內(nèi)傾角不同的是，后傾角對(duì)兩側(cè)的影響是相反的。在有對(duì)稱定位參數(shù)時(shí)（包括左右輪有相等的正的主銷后傾角），左轉(zhuǎn)的效應(yīng)是使車(chē)向右側(cè)傾，導(dǎo)致一個(gè)對(duì)角線的重量轉(zhuǎn)移。在這種情況下，左前右后對(duì)角線會(huì)承受更大的載荷，有一個(gè)左轉(zhuǎn)時(shí)的過(guò)度轉(zhuǎn)向效應(yīng)。使用的彈簧越硬對(duì)角線的重量轉(zhuǎn)移效果也會(huì)越明顯因?yàn)檫@個(gè)是幾何效應(yīng)。每個(gè)車(chē)輪被抬起（或者下落）的距離是恒定的但是重量抬起量和底盤(pán)側(cè)傾角是前后側(cè)傾剛度的作用結(jié)果。這個(gè)對(duì)角線的載荷轉(zhuǎn)移可以通過(guò)把車(chē)放在秤上和定位板上來(lái)測(cè)量。記住在實(shí)際比賽中前輪并沒(méi)有轉(zhuǎn)過(guò)很大的角度，除非是非常緊的發(fā)夾彎。例如，在一個(gè)半徑是100英尺（時(shí)速在40-50英