【正文】 在非常低的摩擦力表面，例如 雪或者冰，當(dāng)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(qū)動輪更容易旋轉(zhuǎn)（動力轉(zhuǎn)向裝置）。前輪傳遞側(cè)偏力潛能降低的原理是由于重心移到后軸車輪并且在驅(qū)動輪上增加了縱向力。 安裝有 開式差速器的高動力前輪驅(qū)動汽車當(dāng)以低檔加速離開緊急轉(zhuǎn)角時通常旋轉(zhuǎn)它們的內(nèi)側(cè)車輪。 如圖表 10：前輪驅(qū)動力的汽車穩(wěn)定狀態(tài)下轉(zhuǎn)向時的牽引力。由于改進的懸掛裝置設(shè)計（車輪中心高于變速箱輸出點，也就是說， v? 為負值）第二個力矩抵消了由驅(qū)動力引起的力矩。 c o s ( )ioe H h H lT e F F? ??? ? ? ? ? 這里 eT? — 扭轉(zhuǎn)力矩差值 e— 車輪干擾常數(shù) ? — 主銷傾角 ih — 高滑動系數(shù)一側(cè)下標(biāo) ol — 低滑動系數(shù)一側(cè)下標(biāo) 9 在帶有開式差速器前輪驅(qū)動汽車的情況下， ST? 是很不明顯的，因為扭轉(zhuǎn)力基數(shù) ( / )H hi H loFF??是不大于 。然而，在絕對條件下它們是小的。 3 牽引力的影響 作為一個扭轉(zhuǎn)力平衡裝置，一個開的差速器提供相等的力到兩個驅(qū)動輪上。其次，差速器架和轉(zhuǎn)送軸套只需要很小的修改。 黏性連接器是根據(jù)液體摩擦的原理和依靠速度差來運轉(zhuǎn)的。在歐洲和日本前輪驅(qū)動轎車產(chǎn)量的施用已經(jīng)證明黏性連接器不僅對于光滑路面的汽車牽引，而且在正常行駛條件下對于操縱性和穩(wěn)定性都有所改善。 1 The Effect of a Viscous Coupling Used as a FrontWheel Drive LimitedSlip Differential on Vehicle Traction and Handling 1 ABCTRACT The viscous coupling is known mainly as a driveline ponent in four wheel drive vehicles. Developments in recent years, however, point toward the probability that this device will bee a major player in mainstream frontwheel drive application. Production application in European and Japanese frontwheel drive cars have demonstrated that viscous couplings provide substantial improvements not only in traction on slippery surfaces but also in handing and stability even under normal driving conditions. This paper presents a serious of proving ground tests which investigate the effects of a viscous coupling in a frontwheel drive vehicle on traction and handing. Testing demonstrates substantial traction improvements while only slightly influencing steering torque. Factors affecting this steering torque in frontwheel drive vehicles during straight line driving are described. Key vehicle design parameters are identified which greatly influence the patibility of limitedslip differentials in frontwheel drive vehicles. Cornering tests show the influence of the viscous coupling on the self steering behavior of a frontwheel drive vehicle. Further testing demonstrates that a vehicle with a viscous limitedslip differential exhibits an improved stability under acceleration and throttleoff maneuvers during cornering. 2 THE VISCOUS COUPLING The viscous coupling is a well known ponent in drivetrains. In this paper only a short summary of its basic function and principle shall be given. The viscous coupling operates according to the principle of fluid friction, and is thus dependent on speed difference. As shown in Figure 1 the viscous coupling has slip controlling properties in contrast to torque sensing systems. This means that the drive torque which is transmitted to the front wheels is automatically controlled in the sense of an optimized torque distribution. In a frontwheel drive vehicle the viscous coupling can be installed inside the differential or externally on an intermediate shaft. The external solution is shown in Figure 2. This layout has some significant advantages over the internal solution. First, there is usually enough space available in the area of the intermediate shaft to provide the required viscous characteristic. This is in contrast to the limited space left in today’s frontaxle differentials. Further, only minimal modification to the differential carrier and transmission case is required. Inhouse production of differentials is thus only slightly affected. Introduction as an option can be made easily especially when the shaft and the viscous unit is supplied as a plete unit. Finally, the intermediate shaft makes it possible to provide for sideshafts of equal length with transversely installed engines which is important to reduce torque steer (shown later in section 4). This special design also gives a good possibility for significant weight and cost reductions of the viscous unit. GKN Viscodrive is developing a low weight and cost viscous coupling. By using only two standardized outer diameters, standardized plates, plastic hubs and extruded material for the housing which can easily be cut to different lengths, it is possible to utilize a wide range of viscous characteristics. An example of this development is shown in Figure 3. 3 TRACTION EFFECTS As a torque balancing device, an open differential provides equal tractive effort to both driving wheels. It allows each wheel to rotate at different speeds during cornering without torsional windup. These characteristics, however, can be disadvantageous when adhesion variations between the left and right sides of the road surface (splitμ ) limits the torque transmitted for both wheels to that which can be supported by the lowμ wheel. With a viscous limitedslip differential, it is possible to utilize the higher adhesion potential of the wheel on the highμ surface. This is schematically shown in Figure 4. When for example, the maximum transmittable torque for one wheel is exceeded on a splitμ surface or during cornering with high lateral acceleration, a speed difference between the two driving wheels occurs. The resulting selflocking torque in the viscous coupling resists any further increase in speed difference and transmits the appropriate torque to the wheel with the better traction potential. It can be seen in Figure 4 that the difference in the tractive forces results in a yawing moment which tries to turn the vehicle in to the lowμ side, To keep the vehicle in a straight line the driver has to pensate this with opposite steering input. Though the fluidfriction principle of the viscous coupling 2 and the resulting soft transition from open to locking action, this is easily possible, The appropriate results obtained from vehicle tests are shown in Figure 5. Reported are the average steeringwheel torque Ts and the average corrective opposite steering input required to maintain a straight course during acceleration on a splitμ track with an open and a viscous differential. The differences between