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

Claim 1

For a four wheel drive vehicle with two front wheels, two rear wheels, a four wheel drive device, and an engine, rotational power from said engine being provided via said four wheel drive device to a combination of the front wheels of said vehicle and also to a combination of the rear wheels of said vehicle, and further comprising a front/rear coupling device fitted to said four wheel drive device for selectively coupling together the rotation of said combination of said front wheels and the rotation of said combination of said rear wheels, a system for controlling said front/rear coupling device, comprising: (a) a means for detecting the rotational speed of said combination of the front wheels of said vehicle; (b) a means for detecting the rotational speed of said combination of the rear wheels of said vehicle; (c) a calculating means for calculating a ratio between an effective rolling radius of the front wheels and an effective rolling radius of the rear wheels from the rotational speed of said combination of the front wheels and the rotational speed of said combination of the rear wheels as they are detected by said rotational speed detecting means when the vehicle is running along a substantially straight course at a speed within a predetermined speed range under an engine output power less than a predetermined rate with no braking while said front/rear coupling device is released; and (d) a control means for controlling said front/rear coupling device according to a discrepancy between the detected rotational speed of said combination of the front wheels and the detected rotational speed of said combination of the rear wheels, as corrected by said calculated ratio between the effective rolling radius of the front wheels and the effective rolling radius of the rear wheels.