HYDRAULIC DRIVE SYSTEM FOR CONSTRUCTION MACHINE

摘要

Pressure compensating valves not fully closing at the stroke end are employed, and upon the operators operation for the traveling, pilot primary pressure is reduced and supplied to remote control valves 34c-34h of non-travel operating devices. Thus, the inflow of the hydraulic fluid into non-travel actuators is suppressed and a necessary amount of hydraulic fluid for travel motors is secured in travel combined operation. Accordingly, when saturation occurs in a construction machine's hydraulic drive system performing the load sensing control due to combined operation with a great load pressure difference between two actuators, deceleration/stoppage of an actuator on the low load pressure side is prevented by preventing full closure of the pressure compensating valve on the low load pressure side, while also preventing deceleration/stoppage of a high load pressure actuator by securing a necessary amount of hydraulic fluid for the high load pressure actuator.

主权项

1. A hydraulic drive system for a construction machine, comprising:
a variable displacement type hydraulic pump; a plurality of actuators which are driven by hydraulic fluid delivered from the hydraulic pump; a plurality of flow control valves which control flow rates of the hydraulic fluid supplied from the hydraulic pump to the actuators; a plurality of operating devices provided corresponding to the actuators and including remote control valves for generating operation pilot pressures for driving the flow control valves; a plurality of pressure compensating valves which respectively control differential pressures across the flow control valves; and a pump control system which performs load sensing control on displacement of the hydraulic pump so that delivery pressure of the hydraulic pump becomes higher than maximum load pressure of the actuators by a target differential pressure, the pressure compensating valves being of the type in which full closing of the valves is not attained at the stroke end in the direction of decreasing the opening area, wherein: the hydraulic drive system comprises a pilot primary pressure circuit which supplies pilot primary pressure, as pressure of a pilot hydraulic pressure source, to the remote control valves of the operating devices, and the pilot primary pressure circuit includes a first circuit which supplies the pilot primary pressure to the remote control valves of one or more specific operating devices among the plurality of operating devices corresponding to one or more specific actuators and a second circuit which supplies the pilot primary pressure to the remote control valves of operating devices other than the specific operating devices, and when the specific operating devices are not operated, the second circuit supplies the pilot primary pressure directly to the remote control valves of the operating devices other than the specific operating devices, and when the specific operating devices are operated, the second circuit reduces the pilot primary pressure and supplies the reduced pilot primary pressure to the remote control valves of the operating devices other than the specific operating devices.