Four wheel steering system with speed-dependent phase reversal

Claim 1

In a vehicle steering system having a pair of front wheels which are steered by operator rotation of a handwheel to initiate a steering maneuver, and a pair of rear wheels which are steered in accordance with a rear wheel steering command, a method for developing the rear wheel steering command, comprising the steps of: developing a steady state rear wheel steering command as a function of vehicle speed and front wheel steering angle for producing steady state rear wheel steering which is in phase with the front wheel steering angle when the vehicle is relatively high; obtaining and temporarily storing samples of the front wheel steering angle at periodic intervals; computing differences between samples taken at consecutive periodic intervals to produce a measure of the change of front wheel steering angle during a respective sample interval; determining a front wheel steering rate by summing a specified number of said computed differences; modifying the steady state command in accordance with the determined front wheel steering rate so as to increase yawing of said vehicle upon initiation of the steering maneuver, such modification having a time response which is variable with the number of computed differences summed in such determination; and varying said specified number of computed differences as a function of vehicle speed to thereby vary the time response of said modification with vehicle speed.