【正文】 ditions a much easier to control than a rearwheel drive car. Which can exhibit poweroversteering when accelerating during cornering. All things, considered, the advantage through the stabilized 5 acceleration behavior of a viscous coupling equipped vehicle during acceleration the small disadvantage on slippery surfaces. Throttleoff reactions during cornering, caused by releasing the accelerator suddenly, usually result in a frontwheel drive vehicle turning into the turn (throttleoff oversteering ). Highpowered modeles which can reach high lateral accelerations show the heaviest reactions. This throttleoff 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 slipangles on the front and increased slipangles 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 throttleoff (see Figure 10) bee over running or braking forces afterwards, which is illustrated for the viscous equipped vehicle in Figure 15. Figure 15:Baraking Forces for a FrontWheel Drive Vehicle with Viscous LimitedSlip Differential Immediately after a Throttleoff 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 fB . The force difference between the frontwheels applied around the center of gravity of the vehicle causes a yaw moment GCM0 that counteracts the normal turnin reaction. When cornering behavior during a throttleoff maneuver is pared 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: Throttleoff Characteristics for a FrontWheel Drive Vehicle with an open Differential on Wet Asphalt at a Radius of 40m (Open Loop) Figure 17:Throttleoff Characteristics for a FrontWheel 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 throttleoff (Time=0 seconds in Figure 14 and 15) with the open differential. Both the sudden increase of the yaw rate after throttleoff and also the increase of the relative yaw angle are significantly reduced in the vehicle equipped with a viscous limitedslip differential. A normal driver os a frontwheel 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 overcorrects 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 throttleoff behavior while remaining controllable, predictable, and safer for an average driver. 6. EFFECT ON BRAKING The viscous coupling in a frontwheel drive vehicle without ABS (antilock braking system) has only a very small influence on the braking behavior on splitμ surfaces. Hence the frontwheels are connected partially via the frontwheel on the lowμ side is slightly higher than in an vehicle with an open differential. On the other side ,the brake pressure to lock the frontwheel on the highμ side is slightly lower. These differences can be measured in an instrumented test vehicle but are hardly noticeable in a subjective assessment. The locking sequence of front and rear axle is not influenced by the viscous coupling. Most ABS offered today have individual control of each front wheel. Electronic ABS in frontwheel drive vehicles must allow for the considerable differences in effective wheel inertia between braking with the clutch engaged and disengaged. Partial coupling of the front wheels through the viscous unit does not therefore promise the action of the ABS a fact that has been confirmed by numerous tests and by several independent car manufacturers. The one theoretical exception to this occurs on a splitμ — surface if a yaw moment buildup delay or Yaw Moment Reduction(YMR) is included in the ABS control unit. Figure 18 shows typical brake pressure sequences, with and without YMR. figure 18: brake pressure buildup characteristics for the front brakes of a vehicle braking on splitμ with ABS. In vehicles with low yaw inertia and a short wheelbase, the yaw moment buildup can be delayed to allow an average driver enough reaction time by slowing the brake pressure buildup over the ABS for the 6 highμ wheel. The wheel on the surface with the higher friction coefficient is therefore, particularly at the beginning of braking, underbraked and runs with less slip. The lowμ wheel, in contrast, can at the same time have a very high slip, which results in a speed difference across the viscous differential. The resulting selflocking torque then appears as an extra braking force at the highμ wheel which counteracts the YMR. 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 1