Patent ID: 7127887

Claim:
A hydraulic circuit for a working machine comprising a first hydraulic pump for supplying a hydraulic fluid to a plurality of actuators including a particular actuator, a plurality of directional control valves including a particular directional control valve, which are connected in parallel with respect to said first hydraulic pump and control respective flows of the hydraulic fluid supplied to said plurality of actuators, a second hydraulic pump for supplying a hydraulic fluid to another actuator separate from said plurality of actuators, another directional control valve for controlling a flow of the hydraulic fluid supplied from said second hydraulic pump, and a hydraulic recovery system comprising throttle means disposed in a line connecting a reservoir port of said particular directional control valve and a reservoir, and a check valve disposed in a line connecting a reservoir-side line and a pump-side line of said particular directional control valve and allowing the hydraulic fluid to flow from the reservoir-side line to the pump-side line when the pressure in the reservoir-side line is higher than the pressure in the pump-side line, wherein said control circuit further comprises joining means for introducing the hydraulic fluid delivered from said second hydraulic pump to said particular actuator when said particular directional control valve is driven, and wherein said throttle means constituting said hydraulic recovery system is variable throttle means changing an opening area thereof in accordance with a control signal, and said hydraulic recovery system further comprises control signal generating means for generating the control signal supplied to said variable throttle means, first pressure detecting means for detecting the delivery pressure of said first hydraulic pump, second pressure detecting means for detecting the delivery pressure of said second hydraulic pump, and control means for receiving pressure signals from said first and second pressure detecting means, executing predetermined arithmetic processing, and outputting a drive signal to said control signal generating means.