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外文翻譯--黏性連接器用作前輪驅動限制滑移差速器對汽車牽引和操縱的影響-汽車設計.doc

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外文翻譯--黏性連接器用作前輪驅動限制滑移差速器對汽車牽引和操縱的影響-汽車設計.doc

畢業設計論文外文資料翻譯 系 部 機械工程系 專 業 機械工程及自動化 姓 名 學 號 外文出處The Effect of a Viscous Coupling Used as a Front-Wheel Drive Limited-Slip Differential on Vehicle Traction and Handling 附 件1.外文資料翻譯譯文;2.外文原 文。 用外文寫 附件 1外文資料翻譯譯文 黏性連接器用作前輪驅動限制滑移差速器對汽車牽 引和操縱的影響 5 轉彎時的效應 扭轉時由于驅動輪的速度不相等,黏性連接器也提供一個自瑣的扭轉力矩。 如圖表 10 所示,在平穩轉向過程中,速度較慢的內側車輪被外側車輪黏性連接器 施加的一個附加的驅動力。 如圖表 10前輪驅動力的汽車穩定狀態下轉向時的牽引力。 不同的牽引力 和 導致一個側偏力矩 MCOG,它必須被一個較大的側偏flDrfl 力補償,因此在前軸有一個大的滑動角 af。因此前驅動輪的汽車自動轉向裝置上 黏性連接器的影響趨向一個在轉向裝置狀態下的特性。這個運動方式整體上和所 有轉向操縱下在穩定狀態下轉彎移動時的現代汽車操縱方式的偏重心相一致.合適 的試驗結果如圖表 11 所示。 如圖表 11安裝有開式差速器的汽車餓安裝有黏性連接器的汽車在穩定狀態 下轉彎時的對比 如圖表 10 所示在轉彎時不對稱的牽引力干擾也會改進汽車的直線行駛。每一 次偏離正常的直線方向都會引起車輪以輕微的不同半徑滾動。驅動力和產生的側 偏力矩差會使汽車重新回到直線行駛(如圖表 10) 。 雖然這些方向的偏離引起僅僅很小的車輪滾動半徑差,但是旋轉的偏差尤其 在高速時對于一個黏性連接器前差速器是足夠將汽車帶到直線上行駛的。 安裝有開式差速器的高動力前輪驅動汽車當以低檔加速離開緊急轉角時通常 旋轉它們的內側車輪。安裝有限制滑動黏性差速器,這個旋轉是有限的并且有不 同車輪的速度差產生的扭轉力為外側的驅動輪提供附加的牽引力效果。這顯示在 圖表 12 中。 如圖表 12裝有黏性限制滑動差速器的前輪驅動汽車在轉道上加速時的牽引 力 特別地當行駛或加速離開一個 T 形交叉路口加速能力就這樣被改善(也就是 說在 T 形路口橫切向右或向左從停止位置加速) 。 圖表 13 和 14 顯示了裝有開式差速器和裝有黏性限制滑動差速器在穩定狀態 下轉彎過程中加速試驗的結果。 如圖表 13 所示裝有一個開式差速器的前輪驅動汽車在半徑為 40m 的濕瀝青 彎曲路面上加速特性(實驗過程中安裝有轉向裝置輪角測試儀) 如圖表 14 所示裝有一個黏性連接器的前輪驅動汽車在半徑為 40m 的濕瀝青 彎曲路面上加速特性(實驗過程中安裝有轉向裝置輪角測試儀) 安裝有一個開式差速器的汽車平均加速度為 同時裝有黏性連接CSDM2.0/ms 器的汽車平均加速度達到 (被發動機功率限制) 。在這些試驗中,由內側2.3/ms 的從動輪引起的最大速度差,被從帶有開式差速器的 240rpm 減少到帶有黏性連接 器的 100rpm。 在彎道上加速行駛時,前輪驅動的汽車通常處在操縱狀態下要多于其勻速行 駛的狀態。前輪傳遞側偏力潛能降低的原理是由于重心移到后軸車輪并且在驅動 輪上增加了縱向力。在一個開式環形控制循環測試中這個能夠看出在開始加速以 后(時間為 0 在圖表 13 和 14 中)偏跑速度(跑偏率)的降低。從圖表 13 和 14 中還可以看出開始加速時裝有開式差速器汽車的跑偏率比裝有黏性連接器汽車的 下降的更快。然而,在開始加速大約 2 秒后,黏性連接的汽車的跑偏率下降斜率 增加高于裝有開式差速器 的汽車。 安裝有限制滑動前差速器的汽車在轉彎過程中加速時具有一個更穩定的最初 反應比裝有開式差速器的汽車,降低它的操縱狀態。這是因為內側驅動輪的高滑 動通過黏性連接器產生一個增加的驅動力到外側車輪,這在圖表 12 中有解釋。前 輪牽引力的不平衡導致在行駛方向上的偏跑力矩 ,反對操縱狀態。CSDM 當驅動輪的附著限制是超出的,安裝黏性連接器的汽車處于操縱狀態比安裝有 開式差速器的汽車更明顯這里,開始加速后 2 秒。在非常低的摩擦力表面,例如 雪或者冰,當裝有限制滑動差速器的汽車在曲線路面上加速時更強的操縱性被期 望因為通過黏性連接器連接的驅動輪更容易旋轉(動力轉向裝置) 。然而,這個特 性能很容易地被駕駛員或者自動節氣門調節牽引系統控制。在這些情況下比后輪 驅動的汽車更容易控制。在轉彎過程中當加速時它能夠防止動力過分操縱。考慮 到,所有的情況,裝配有一個黏性連接器的汽車在加速過程中具有穩定的加速行 動方式在光滑路面上只有小的缺點。 通過突然釋放加速器,在轉彎過程中節氣門關閉的反應,通常導致前輪驅動 的汽車改換方向(節氣門關閉超出了操縱) 。高動力的模型能得到高側偏加速度顯 示出最大規模的反應。這個節氣門關閉反應有幾個原因例如運動學上的影響,或 者,當汽車降低速度試著以一個較小的轉變半徑通過時。然而,實質上的原因, 是動力的重心從后軸轉移到前軸,這會導致前軸降低滑動角。后軸增加滑動角。 因為,后軸車輪不傳遞驅動力矩,在這種情況下在后軸上的影響比前軸上的影響 更大。在節氣門關閉之前(如圖表 10) 。前輪上的驅動力不再滾動或者以后制動力, 黏性裝置汽車這個解釋在圖表 15 中。 如圖表 15安裝有黏性限制滑動差速器前輪驅動的汽車當轉變時關閉節氣門 后移動立刻產生的制動力 隨著內側的車輪繼續比外側車輪更慢的轉動,黏性聯結器給外側車輪提供更 大的制動力 。由于前輪力的不同圍繞著汽車重量的中心會產生一個抵消正常?fB 轉向反應的側偏力矩 MCOG.。 將安裝有開式差速器的汽車和裝有黏性聯結器的在關閉節氣門的移動過程中 轉向方式進行比較時,如圖表 16 和 17 所示,安裝有黏性差速器的兩個驅動輪子 之間速度差是降低的。 圖表 16 在轉彎半徑為 40 米(不封閉的環形)的濕瀝青路面上安裝有開式差 速器前輪驅動汽車的節氣門關閉特性 如圖表 17 在轉彎半徑為 40 米(不封閉的環形)的濕瀝青路面上安裝有黏性 聯結器前輪驅動汽車的節氣門關閉特性 安裝有開式差速器的汽車側偏速度(側偏率) ,和相對的側偏角(除汽車保持 繼續在穩定狀態下轉彎的側偏角之外)在節氣門關閉后(時間為零如圖表 14 和 15)顯示一個非常明顯的增加。在安裝有一個黏性的限制滑動差速器的汽車上節 氣門關閉后側偏率的突然增加和相對側偏角的增加都有很大的降低。 例如在一個彎道上隨著半徑的增加,一上正常的駕駛一個超大號的前輪驅動 汽車的人通常僅僅的慣常的空檔的操縱裝置下的汽車操縱方式,然后駕駛員忽然 驚奇并且在節氣門突然的釋放后會有有力的操縱反應。如果駕駛員對情況的反應 不正確汽車將進一步惡化汽車離開車道到曲線的內側的事故是這個事件的驗證。 因此黏性聯結器為一個正常的駕駛員改善節氣門關閉的行為方式當保持可控制, 可預言的并且安全駕駛時。 雖然這也許會被認為是一個負面影響而且對于一輛安裝有前黏性聯結器的汽 車來說當安裝 YMR 計算程序就能很容易地被修正,但是汽車試驗已經證明這個影 響是很小的,實際上不需要專門的新的 ABS/YMR 計算程序的開發。一些典型的求 平均的測試結果被總結如圖表 19。 如圖表 19結果構成了帶有 YMR 在滑動系數為 (V 050mph,三檔,閉環)上? 的 ABS 自動測試在圖表 19 的左側顯示了在制動過程中有第一個 ABS 控制循環產生 的最大速度差的比較。很明顯,黏性聯結器減小了速度差。當黏性聯結器抵消 YMR 時,要求操縱車輪角在制動第一秒鐘從 39 度增加到 51 度保持汽車在直線方向上 (圖表 19,中部) 。由于大多數汽車和 ABS 制造廠家認為 90 度是達到臨界狀態的 限制,所以這能被接受。最后,在高 值的一側通過黏性聯結器產生的一個增加? 的自鎖扭轉力。車輪制動力,一輛稍稍的高一些的汽車保持減速(圖表 19 右側) 6 總結 總之,黏性聯結器在前軸差速器的試用能被證實。它也明確地影響整個汽車 的控制和穩定,只是稍微地,但是可以接受的在扭轉力操縱上的影響。 為了減小不想要的扭轉力操縱的影響一個基本的設計準則被給出 1 由于縱向載荷改變產生的警覺反應必須盡可能的小 2 主銷軸線和車輪中心之間的距離必須盡可能的小 3 垂直彎曲角變化范圍應該接近零(或者為負值) 4 兩側的垂直彎曲角應該一樣 5 側軸應該等長 在扭轉力操縱上小的影響是聯結處的干擾常數不管什么理由這個常數的理想 值是零。帶有和不帶有 ABS 的制動系統僅僅是黏性聯結器不重要的影響。在前輪 驅動的汽車上通過黏性的限制滑動差速器牽引力有著很重要的改善。 前輪驅動汽車獨立的轉向裝置的行動方式在操縱狀態的方向下被黏性限制滑 動差速器稍稍地影響。在轉彎過程中節氣門關閉和加速改進的反應使前軸安裝有 黏性聯結器的汽車更穩定,更可預見而且更安全。 附件 2外文原文(復印件) 5.EFFECT ON CORNERING Viscous couplings also provide a self-locking torque when cornering, due to speed differences between the driving wheels. During steady state cornering, as shown in figure 10, the slower inside wheel tends to be additionally driven through the viscous coupling by the outside wheel. Figure 10 Tractive forces for a front-wheel drive vehicle during steady state cornering The difference between the Tractive forces Dfr and Dfl results in a yaw moment MCOG, which has to be compensated by a higher lateral force, and hence a larger slip angle af at the front axle. Thus the influence of a viscous coupling in a front-wheel drive vehicle on self-steering tends towards an understeering characteristic. This behavior is totally consistent with the handling bias of modern vehicles which all under steer during steady state cornering maneuvers. Appropriate test results are shown in figure 11. Figure 11 comparison between vehicles fitted with an open differential and viscous coupling during steady state cornering. The asymmetric distribution of the tractive forces during cornering as shown in figure 10 improves also the straight-line running. Every deviation from the straight-line position causes the wheels to roll on slightly different radii. The difference between the driving forces and the resulting yaw moment tries to restore the vehicle to straight-line running again see figure 10. Although these directional deviations result in only small differences in wheel travel radii, the rotational differences especially at high speeds are large enough for a viscous coupling front differential to bring improvements in straight-line running. High powered front-wheel drive vehicles fitted with open differentials often spin their inside wheels when accelerating out of tight corners in low gear. In vehicles fitted with limited-slip viscous differentials, this spinning is limited and the torque generated by the speed difference between the wheels provides additional tractive effort for the outside driving wheel. this is shown in figure 12 Figure 12 tractive forces for a front-wheel drive vehicle with viscous limited-slip differential during acceleration in a bend The acceleration capacity is thus improved, particularly when turning or accelerating out of a T-junction maneuver i.e. accelerating from a stopped position at a “T” intersection-right or left turn . Figures 13 and 14 show the results of acceleration tests during steady state cornering with an open differential and with viscous limited-slip differential . Figure 13 acceleration characteristics for a front-wheel drive vehicle with an open differential on wet asphalt at a radius of 40m fixed steering wheel angle throughout test. Figure 14 Acceleration Characteristics for a Front-Wheel Drive Vehicle with Viscous Coupling on Wet Asphalt at a Radius of 40m Fixed steering wheel angle throughout test The vehicle with an open differential achieves an average acceleration of 2.0 while the2/sm vehicle with the viscous coupling reaches an average of 2.3 limited by engine-power. In these tests, the maximum speed 2/ difference, caused by spinning of the inside driven wheel was reduced from 240 rpm with open differential to 100 rpm with the viscous coupling. During acceleration in a bend, front-wheel drive vehicles in general tend to understeer more than when running at a steady speed. The reason for this is the reduction of the potential to transmit lateral forces at the front- tires due to weight transfer to the rear wheels and increased longitudinal forces at the driving wheels. In an open loop control-circle-test this can be seen in the drop of the yawing speed yaw rate after starting to accelerate Time 0 in Figure 13 and 14. It can also be taken from Figure 13 and Figure 14 that the yaw rate of the vehicle with the open differential falls-off more rapidly than for the vehicle with the viscous coupling starting to accelerate. Approximately 2 seconds after starting to accelerate, however, the yaw rate fall-off gradient of the viscous-coupled vehicle increases more than at the vehicle with open differential. The vehicle with the limited slip front differential thus has a more stable initial reaction under accelerating during cornering than the vehicle with the open differential, reducing its understeer. This is due to the higher slip at the inside driving wheel causing an increase in driving force through the viscous coupling to the outside wheel, which is illustrated in Figure 12. the imbalance in the front wheel tractive forces results in a yaw moment acting in direction of the turn, countering the understeer.CSDM When the adhesion limits of the driving wheels are exceed, the vehicle with the viscous coupling understeers more noticeably than the vehicle with the open differential here, 2 seconds after starting to accelerate. On very low friction surfaces, such as snow or ice, stronger understeer is to be expected when accelerating in a curve with a limited slip differential because the driving wheels-connected through the viscous coupling-can be made to spin more easily power-under-steering. This characteristic can, however, be easily controlied by the driver or by an automatic throttle modulating traction control system. Under these conditions a much easier to control than a rear-wheel drive car. Which can exhibit power-oversteering when accelerating during cornering. All things, considered, the advantage through the stabilized acceleration behavior of a viscous coupling equipped vehicle during acceleration the small disadvantage on slippery surfaces. Throttle-off reactions during cornering, caused by releasing the accelerator suddenly, usually result in a front-wheel drive vehicle turning into the turn throttle-off oversteering . High-powered modeles which can reach high lateral accelerations show the heaviest reactions. This throttle-off reaction has several causes such as kinematic influence, or as the vehicle attempting to travel on a smaller cornering radius with reducing speed. The essential reason, however, is the dynamic weight transfer from the rear to the front axle, which results in reduced slip-angles on the front and increased slip-angles on the rear wheels. Because the rear wheels are not transmitting driving torque, the influence on the rear axle in this case is greater than that of the front axle. The driving forces on the front wheels before throttle-off see Figure 10 become over running or braking forces afterwards, which is illustrated for the viscous equipped vehicle in Figure 15. Figure 15Baraking Forces for a Front-Wheel Drive Vehicle with Viscous Limited-Slip Differential Immediately after a Throttle-off Maneuver While Cornering As the inner wheel continued to turn more slowly than the outer wheel, the viscous coupling provides the outer wheel with the larger braking force . The force difference between the front-wheels applied around the center fB of gravity of the vehicle causes a yaw moment that counteracts the GCM0 normal turn-in reaction. When cornering behavior during a throttle-off maneuver is compared for vehicles with open differentials and viscous couplings, as shown in Figure 16 and 17, the speed difference between the two driving wheels is reduced with a viscous differential. Figure 16 Throttle-off Characteristics for a Front-Wheel Drive Vehicle with an open Differential on Wet Asphalt at a Radius of 40m Open Loop Figure 17Throttle-off Characteristics for a Front-Wheel Drive Vehicle with Viscous Coupling on Wet Asphalt at a Radius of 40m Open Loop The yawing speed yaw rate, and the relative yawing angle in addition to the yaw angle which the vehicle would have maintained in case of continued steady state cornering show a pronounced increase after throttle- off Time0 seconds in Figure 14 and 15 with the open differential. Both the sudden increase of the yaw rate after throttle-off and also the increase of the relative yaw angle are significantly reduced in the vehicle equipped with a viscous limited-slip differential. A normal driver os a front-wheel drive vehicle is usually only accustomed to neutral and understeering vehicle handing behavior, the driver can then be surprised by sudden and forceful oversteering reaction after an abrupt release of the throttle, for example in a bend with decreasing radius. This vehicle reaction is further worsened if the driver over-corrects for the situation. Accidents where cars leave the road to the inner side of the curve is proof of this occurrence. Hence the viscous coupling improves the throttle-off behavior while remaining controllable, predictable, and safer for an average driver. Although this might be considered as a negative effect and can easily be corrected when setting the YMR algorithm for a vehicle with a front viscous coupling, vehicle tests have proved that the influence is so slight that no special development of new ABS/YMR algorithms are actually needed. Some typical averaged test results are summarized in Figure 19. figure 19 results form ABS braking tests with YMR on split-μVo50 mph, 3rd Gear, closed loop in figure 19 on the left a comparison of the maximum speed difference which occurred in the first ABS control cycle during braking is shown. It is obvious that the viscous coupling is reducing this speed difference. As the viscous coupling counteracts the YMR, the required steering wheel angle to keep the vehicle in straight direction in the first second of braking increased from 39 to 51 figure 19,middle. Since most vehicle and ABS manufacturers consider 90 to be the critical limit, this can be tolerated. Finally, as the self-locking torque produced by the viscous coupling causes an increase in high-. Wheel braking force, a slightly higher vehicle deceleration was maintainedfigure 19,right. 6.SUMMARY in conclusion,it can be established that the application of a viscous coupling in a front-axle differential. It also positively influences the complete vehicle handling and stability , with only slight, but acceptable influence on torques-steer. To reduce unwanted torque-steer effects a basic set of design rules have been established ? Toe-in response due to longitudinal load change must be as small as possible . ? Distance between king-pin axis and wheel center has to be as small as possible. ? Vertical bending angle-rang should be centered around zeroor negative. ? vertical bending angles should be the same for both sides. ? Sideshafts should be of equal length. Of minor influence on torque-steer is the joint disturbance lever arm which should be ideally zero for other reasons anyway. Braking with and without ABS is only negligibly influenced by the viscous coupling. Traction is significantly improved by the viscous limited slip differential in a front-wheel drive vehicle. The self-steering behavior of a front-wheel drive vehicle is slightly influenced by a viscous limited slip differential in the direction of understeer. The improved reactions to throttle-off and acceleration during cornering make a vehicle with viscous coupling in the front-axle considerably more stable, more pre

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