| 摘要 |
PURPOSE:To maintain a parking brake in release condition for a long time when pressure in the piping between a brake control valve and a parking brake cylinder goes down to less than a specified limit, by supplying pressure oil from a hydraulic pressure source in the other hydraulic circuit to the parking brake cylinder by switching over a selector valve. CONSTITUTION:When the pressure in the piping 22 is over a specified limit by the pressure of a hydraulic pump 1, a selector valve 32 is switched over to A position to feed oil discharged from a hydraulic pump 31 for working to the piping 23 only, and a selector valve 33 is set at the A position. Accordingly, the oil discharged from the hydraulic pump 1 is led to a brake cylinder 2 to release a brake. On the other hand, if the hydraulic pump 1 fails and the pressure in the piping 22 is lowered to a specified level, for example, the selector valve 32 is switched over to B position by the spring force of a spring 32a to lead the oil discharged from the hydraulic pump 31 for working to the piping 24. Then, the selector valve 33 is switched over to the B position due to pressure in the piping 24 to lead the oil discharged from the hydraulic pump 31 to the brake cylinder 2 through a check valve 34 and the piping 22, thus the brake is maintained in release condition. |
