| 摘要 |
A hydraulic control apparatus 1 includes a switch valve 11, a valve support chamber 35, a flow control valve 12 movable within the valve support chamber 35, an on-off valve 13 movable within the communication path chamber 12a, and a valve control device 14. The flow control valve 12 has a communication path chamber 12a and a back pressure chamber 12d. The on-off valve 13 is capable of opening and shutting off a communication path X between a cylinder line 32 and a switch valve line 33. A restrictor is formed between the flow control valve 12 and a wall defining the valve support chamber 35. The restrictor connects the cylinder line 32 and the communication path chamber 12a to each other. The opening degree of the restrictor is changed in correspondence with movement of the flow control valve 12. When the switch valve 11 is located at the neutral position or the supply position, the valve control device 14 applies a fluid pressure in the cylinder line 32 to the back pressure chamber 12d for urging the on-off valve 13 in a direction for shutting off the communication path 12a. When the switch valve 11 is located at the drainage position, the valve control device 14 applies a pilot pressure lower than the fluid pressure in the cylinder line 32 to the back pressure chamber 12d, thereby moving the on-off valve 13 in a direction for opening the communication path X. |
