Patent ID: 8336305

Claim:
A hydraulic drive device including a hydraulic pump and a hydraulic actuator, the hydraulic actuator being supplied with working oil from the hydraulic pump and being operated by discharging the working oil present in the interior thereof, the hydraulic drive device, comprising: a regenerating motor, said regenerating motor being connected to the hydraulic pump so as to be able to drive the hydraulic pump and being driven by being supplied with the working oil from the hydraulic pump; a supply and discharge circuit, said supply and discharge circuit including a supply oil passage for supplying the working oil from the hydraulic pump to the hydraulic actuator, a return oil passage for conducting return oil discharged from the hydraulic actuator to a tank, and a supply and discharge adjusting section capable of adjusting the flow rate of working oil flowing through said supply oil passage and that of the working oil flowing through said return oil passage simultaneously; an outlet oil passage branching from said return oil passage so as to conduct the return oil to a tank without going through said supply and discharge adjusting section; a regeneration oil passage for conducting the return oil to said regenerating motor without going through said supply and discharge adjusting section; distribution flow rate adjusting means capable of adjusting the flow rate of the return oil flowing through said outlet oil passage and that of the return oil flowing through said regeneration oil passage; and a control section which, during an external force applying period in which the pressure of the return oil exceeds a discharge pressure of the hydraulic pump, specifies a regenerating flow rate capable of being conducted to said regeneration oil passage and a surplus flow rate other than the regenerating flow rate, out of the return oil other than the return oil conducted to said tank through said supply and discharge adjusting section, on the basis of power required of the hydraulic pump, then conducts the return oil of the regenerating flow rate to said regeneration oil passage and controls said distribution flow rate adjusting means so that the return oil of the surplus flow rate is conducted to said outlet oil passage.