| 摘要 |
PURPOSE:To satisfy the high responsiveness and stability of steering by reducing the opening of the throttle part of a by-pass during low speed travel and the stop time whereas enlarging the opening of the throttle part of the by-pass during high speed travel. CONSTITUTION:The upper reaches of the throttle parts A, C of the high pressure side inter-valve passage 27 of a passage for communicating a pump 70, a tank 71 and a hydraulic cylinder 20 is communicated with the low pressure side tank 71 side by a by-pass 80. In this case, an operating condition sensing throttle valve 81 is provided to change the throttle opening of the by-pass 80 according to the operating condition, and a circuit pressure sensing throttle valve 81 is provided to change the throttle opening of the by-pass 80 according to the upstream pressure of the throttle parts A, C. During low speed travel or the stop time, the high responsiveness of steering is satisfied by reducing the throttle opening of the by-pass 80 by the operating condition sensing throttle valve 81. During high speed travel, the steering stability is satisfied unless steering input torque is enlarged, by enlarging the throttle opening of the by-pass 80 by the operating condition sensing throttle valve 81. |
