| 摘要 |
According to the present invention, discharge ports of each of closed-circuit hydraulic pumps (2a, 2b) are connected to the head-side chambers and the rod-side chambers of arm/boom cylinders (7a, 7b). On-off valves (12a, 12b) are disposed between the cylinder head-side chambers and the discharge ports of the open-circuit hydraulic pumps (1a, 1b). Proportional control valves (14a, 14b) are disposed between the cylinder head-side chambers and an oil tank. When the cylinder is extending, both the closed-circuit pumps and the open-circuit pumps, and the on-off valves, are controlled so that the flow discharged from both types of pumps is channeled into the head-side chamber. When the cylinder is retracting, the closed-circuit pumps and the proportional control valves are controlled so that a part of the flow channeled from the head-side chamber is returned to the closed-circuit pumps and the other part is returned to the oil tank. |
