| 摘要 |
PURPOSE:To automatically stop the rotation of a hydraulic motor to aim at ensuring the safety of working even if any abnormality occurs in an electrical control section, by providing a bypass circuit in parallel with a servo-pressure circuit, and by disposing change-over valves which may be changed over upon emergency, in the bypass circuit and the servo-pressure circuit, respectively. CONSTITUTION:Upon occurrence of abnormality such as, for example, disturbance, in a control section 1, a signal is automatically generated so that a first change-over valve 22 disposed in a servo-pressure circuit 4 is turned into its isolating position while a second change-over valve 24 disposed in a bypass circuit 23 in parallel with the servo-pressure circuit 4 is turned into its communicating position. When a servo- device 5 is returned into its neutral position by servo-liquid fed from the bypass circuit 23, a neutral return valve 25 takes its neutral position so that the communication of the bypass passage 23 is isolated. At this time a discharge amount adjusting lever 7 for a hydraulic pump 8 is returned to its neutral position, and a piston 5C does not move further so that the discharge of hydraulic liquid from the hydraulic pump 8 is interrupted. Accordingly, the rotation of a hydraulic motor 10 in a closed hydraulic circuit 9 is stopped, thereby it is possible to avoid a run-away condition such as, for example, sustaining of turn of a shovel arm. |
