摘要 |
Provided is a hydraulic closed circuit system with hydraulic pumps which maintains a well-balanced flow rate by automatically controlling the flow rate, even if an imbalance of a flow rate during extension/retraction of a hydraulic cylinder device is caused by a pump capacity error. In this system, a first hydraulic pump 12 is connected to the hydraulic cylinder device 11 in such a manner that a hydraulic closed circuit is made, a second hydraulic pump 13 is connected at one of paired delivery ports to a bottom side of the hydraulic cylinder device 11 and at the other of the ports to a tank 16, and a prime mover 20 drives the first and second hydraulic pumps 12, 13 and recovers motive power from these pumps. A pump capacity control unit 100 detects a moving direction of the hydraulic cylinder device 11, and a pressure in a lower-thrust side of the device 11, and controls a capacity of the second hydraulic pump 13 so that the flow rate during the extension/retraction of the hydraulic cylinder device becomes balanced between the first and second hydraulic pumps and the hydraulic cylinder device. |