Power regeneration device for operating machine

A power regeneration device for an operating machine equipped with an engine (50), a hydraulic pump (6) driven by the engine (50), a control valve (2) for switching the flow of hydraulic fluid from the hydraulic pump (6) and supplying the hydraulic fluid to a hydraulic cylinder (3a), and an operating device (4) for controlling the control valve (2), comprising:

• a hydraulic line (31) which is connected to a bottom-side hydraulic chamber of the hydraulic cylinder (3a) and through which returning fluid returning to a tank (6A) flows when the hydraulic cylinder (3a) contracts;
• a branching part (32) which is provided in the hydraulic line (31) to separate the hydraulic line (31) into a plurality of hydraulic lines;
• a regeneration line (33) which is connected to the branching part (32) and leads the returning fluid to the tank (6A) via a hydraulic motor (11) that is connected with a generator (12) controlled by an inverter (13);
• a control valve line (34) which is connected to the branching part (32) and leads the returning fluid to the tank (6A) via the control valve (2);
• operation amount detection means (16) which detects the operation amount of the operating device (4);
• an electricity storage device (15) which stores electric power generated by the generator (12);
• electric amount detection means (17) which detects the electric amount of the electricity storage device (15);
• flow rate calculation means (9) which calculates the flow rate of the returning fluid flowing through the regeneration line (33) and the flow rate of the returning fluid flowing through the control valve line (34) depending on an electric amount signal from the electric amount detection means (17);
• first flow rate control means (8) which controls the flow rate through the control valve line (34) based on the result of the calculation by the flow rate calculation means (9);
• and
• second flow rate control means (13) which controls the flow rate through the regeneration line (33) based on the result of the calculation by the flow rate calculation means (9).