Importance

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Abstract

A four-wheel drive vehicle comprises an engine and a power transmission system, including a shiftable change gear transmission having a power input shaft and a differential having front and rear output shafts and a biasing clutch, for driving the front and rear vehicle wheels. The differential, with biasing clutch disengaged, allows for differences in rotational speed between the front and rear wheels. Increased speed of one output shaft as may be caused by its' associated wheels slipping, results in decreased speed of the other output shaft. Conversely, decreased speed of one output shaft as may be caused by its' associated wheels being bogged down by mud, sand or deep snow, results in increased speed of the other output shaft. The degree of differential action may be determined from the known input shaft speed, the gear ratio engaged and an output shaft speed. A control system, which includes a microprocessor, employs sensors to directly sense the speed differences between the power input shaft of the transmission and only one of the output shafts of the differential and effects temporary biasing clutch engagement in the event of excessive slippage for a predetermined interval of time. The control system also senses the selected gear range of the transmission. The microprocessor periodically samples the speed ratio between those two shafts, compensating for the gear range selected, and compares it to a preselected (adjsutable) ratio in the microprocessor memory. If the preselected ratio band is deviated from for a selected interval of time, the microprocessor effects clutch lockup for a selected interval of time so that both output shafts of the differential (and the front and rear wheels) rotate at the same speed and wheel slippage is eliminated.

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First Claim