| 摘要 |
PURPOSE:To keep the safety of operation by providing a detecting means for a hydraulic defect of a hydraulic rear wheel steering mechanism and a means for setting a steering angle ratio to naught on a signal sent from the detecting means. CONSTITUTION:When hydraulic pressure detected to a hydraulic sensor 37 to detect a hydraulic defect of a hydraulic rear wheel steering mechanism 21 becomes lower than fixed value, a steering angle ratio is kept at its present value. When a front wheel steering angle detected by a steering angle sensor 32 becomes lower than fixed value, a step motor 44 of a steering angle ratio control mechanism 14 is driven to set the steering angle ratio to naught. Namely, a sliding pin 59 to connect an output link 51 to a control lever 57 is locked at a position where the pin 59 lies on a supporting shaft 53 of the control lever 57 or the steering angle ratio is naught. The rear wheel steering mechanism is thereby returned to a neutral position to change a four wheel steering state into a two wheel steering state formed by a front wheel steering mechanism. Thus the safety of operation can be kept. |
