Method and apparatus for detecting friction coefficient of road surface, and method and system for four-wheel steering of vehicles using the detected friction coefficient of road surface.
An method for detecting a friction coefficient ( mu ) of the road surface according to the present invention comprises a detection step of detecting an operating angle ( theta H) of the steering wheel (4) of the vehicle, a vehicle speed (V) and an operating pressure ( DELTA P) of the hydraulic power steering unit (1) for the front wheels (FW), and a calculation step of calculating the friction coefficient of the road surface on turning of the vehicle by considering relationships among a slip angle (ss f) of the front wheel, the friction coefficient of the road surface and a cornering force (CF) of the front wheels. The method according to the present invention further includes a step of prohibiting the execution of the calculation step when the steering wheel is turned back, whereby the calculation step is executed only when the direction of the operating pressure of the power steering unit is in the equiphase with the operating direction of the steering wheel. Also, the four-wheel steering system according to the present invention has a rear steering actuator (11) for steering the rear wheels (RW) so as to increase the steering angle of the rear wheels as the friction coefficient of the road surface calculated by the above-described method decreases. <IMAGE>
