Patent attributes
A hydraulic motor (52) is arranged in a control hydraulic line (51) connecting a second hydraulic fluid supply line (4a) (for supplying the hydraulic fluid delivered from the main pump (2) to flow control valves (26a to 26h)) to a tank (T). A generator (53) connected with the rotating shaft (52a) of the hydraulic motor (52). Maximum load pressure (PLmax) is detected by a pressure sensor (54). Power generation control of the generator (53) is performed by a second control device (55) so that the hydraulic motor (52) rotates when the delivery pressure of the main pump (2) exceeds target control pressure (Pun) determined by adding a preset value (Pb) to the maximum load pressure (PLmax). AC power generated by the generator (53) is stored in a battery (41).
