Hydraulic recovery device

A hydraulic recovery device equipped in a hydraulic drive system comprising a plurality of actuators (4, 5) operated by a hydraulic fluid supplied from a variable displacement type hydraulic pump (1), and a plurality of directional control valves (2, 3) disposed between said hydraulic pump and said plurality of actuators for controlling respective flows of the hydraulic fluid supplied to the associated actuators, said hydraulic recovery device comprising variable resistance means (6;

• 60) disposed in a first line (12) communicating a reservoir port (23) of at least one (2) of said plurality of directional control valves and a reservoir (9) for controlling a flow rate passing from said reservoir port to said reservoir in accordance with a control signal (Px), a third line (14) communicating a portion of said first line upstream of said variable resistance means and a second line (10C) connected to a pump port (24) of said one directional control valve, and a check valve (7) disposed in said third line for allowing the hydraulic fluid to flow only in a direction from said first line toward said second line, wherein said hydraulic recovery device further comprises:
• (a) detecting means (101;
• 106;
• 102a, 102b;
• 103a, 103b) for detecting a condition variable (Pd;
• Ph;
• Pia1, Pia2;
• Pib1, Pib2) related to an operation of said actuator (4);
• (b) control means (100;
• 100A-100H) for receiving a signal from said detecting means and producing a drive signal (i;
• i*) corresponding to said condition variable based on a relationship stored therein in advance;
• and
• (c) control signal generating means (105) for receiving said drive signal and producing said control signal (Px) corresponding to said drive signal.