Device for controlling vehicle four wheel drive front/rear coupling device by learning effective front/rear vehicle wheels radius discrepancy, and method of operation thereof

摘要

In a four wheel drive vehicle having two front wheels and two rear wheels driven from an engine via a central differential gear and a front/rear coupling device for selectively locking up the differentiating operation of the central differential gear, a system for controlling the front/rear coupling device calculates an actual ratio between the effective rolling radius of the front wheels and the effective rolling radius of the rear wheels from the rotational speed of the front wheels and the rotational speed of the rear wheels detected by the rotational speed sensors when the vehicle is running along a substantially straight course at a speed within a predetermined relatively moderate speed range under an engine output power less than a predetermined relatively moderate rate with no braking while the front/rear coupling device is released. Based upon the thus calculated ratio, the system calculates the difference between the peripheral speed of the front wheels and the peripheral speed of the rear wheels to detect a slippage in one of the front and rear wheels so as thereby to control the front/rear coupling device for locking up the differentiating operation of the central differential gear when more than a certain amount of slippage has occurred.