FOUR-WHEEL STEERING DEVICE

PURPOSE:To obtain a proper rear wheel steering state by applying the constitution wherein a control valve and a bypass valve provided in a hydraulic piping system to a power cylinder for rear wheel steering, are actuated and controlled with a front wheel steering angle, a rear wheel steering angle, a vehicle speed signal and the like. CONSTITUTION:With the operation of a steering handle 5, a hydraulic fluid supply amount corresponding to a steering amount is fed from a totally hydraulic steering unit 21 to one of the chambers 7a and 7b of a rear wheel steering power cylinder 7 via a control valve 24 actuated and controlled with a controller 11, depending upon a running condition such as a front and rear wheel steering angle, a vehicle speed or the like, while the valve 24 being selectively connected to an auxiliary pump 28. Rear wheels 4 are thereby steered and controlled. In this case, when the vehicle speed becomes equal to or above the predetermined value, a bypass valve 27 is opened, thereby keeping the rear wheel steering power cylinder 7 in a non-steering state. According to the aforesaid construction, a proper rear wheel steering state can be obtained.