In the antilock braking system ( ABS) test for four-wheel-drive vehicle equipped with viscous coupler, when traditional disposal ( making failure of one axle's braking) is adopted, the adhesion coefficient obtained of low-adhesion lane far exceeds the real value. The reason is revealed through the in-depth analyses in this paper that when one axle's braking fails, there is a significant difference between the rotation speeds of front and rear axles caused by the variation of tires slip ratio, leading to the occurrence of hump phenomena in viscous coupler, then the front and rear axles become quasi-rigid connected and all the wheels involve in braking. Therefore it is suggested that in the ABS test for four-wheel-drive vehicle equipped with viscous coupler, the input shaft of viscous coupler should be dismounted for making only one axle involved in braking, so that a right adhesion coefficient can be obtained.%装备黏性联轴器的四驱车辆在进行防抱死制动系统的试验中,按照传统的使单轴制动失效的办法获得的低附路面附着系数远高于试验路面实际的附着系数.文中通过分析揭示了其原因是:单轴制动失效时前、后轴轮胎滑移率变化造成转速差过大而产生驼峰现象,前、后轴形成准刚性连接而共同参与制动.因此,装备黏性联轴器的四驱车辆在进行ABS路面附着系数试验时应将黏性联轴器输入轴拆除,使之仅有单轴参与制动,才能获得正确的路面附着系数.
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