Patent ID: 9518593
Filing Date: 2016-12-13
CPC Classification: E02F,F04B,F15B

Claim Text:
1. A hydraulic drive system for a construction machine including a prime mover, a main pump of the variable displacement type driven by the prime mover, a plurality of actuators driven by hydraulic fluid delivered from the main pump, a plurality of flow control valves that respectively control the flow of the hydraulic fluid supplied from the main pump to the actuators, and a pump control device that performs load sensing control for a delivery flow rate of the main pump in such a manner that a delivery pressure of the main pump becomes higher than a maximum load pressure of the actuators by a target differential pressure, comprising: a hydraulic motor arranged in a control hydraulic line connecting a hydraulic fluid supply line for supplying the hydraulic fluid from the main pump to the flow control valves, to a tank, the hydraulic motor being drivable by the hydraulic fluid delivered from the main pump; a generator connected with a rotating shaft of the hydraulic motor; a control device that performs power generation control of the generator in such a manner that the hydraulic motor is driven by the hydraulic fluid delivered from the main pump when the delivery pressure of the main pump becomes higher than a target control pressure; a pressure sensor that detects the maximum load pressure; and an electricity storage device that stores electric power generated by the generator, wherein the control device calculates the target control pressure by adding a preset value to the maximum load pressure detected by the pressure sensor, calculates a power generation torque of the generator having a magnitude overcoming a rotating torque of the hydraulic motor caused by the target control pressure, and performs the power generation control of the generator in such a manner that the power generation torque is achieved.