FOUR WHEEL STEERING DEVICE FOR CAR

PURPOSE:To make it possible to distinguish a malfunction of a car speed detective device as a lock of wheels in braking motion, by making such constitution in which, when a sudden drop of the car speed is regarded apparently as the malfunction of the car speed detective device, the output characteristic of the car speed detective device after that occurrence is observed in a preset time interval, then the judgement is made. CONSTITUTION:When a car speed V which is detected by a car speed detective device 102 goes down suddenly below a preset one, a malfunction judging part 104 in a steering ratio control device 103 operates, then a steering ration change device 32 is firstly controlled to operate in order to maintain a steering ratio of the front wheel to the rear wheel at the steering ratio K corresponding to the speed before the above-mentioned drop. After that, the malfunction judging part 104 observes the car speed V which is detected by the car speed detective device 102 during a preset time passes since the car speed V drops to V=0. On this occasion, if there is the rise of the car speed V to Vnot equal to 0 after the car speed has suddenly droped, it is regarded as the stop state by the wheel lock due to braking action and if the car speed V is V=0 after the preset time, it is regarded as the malfunction of the car speed detective device 102.