초록 ▼

When the pump pressure detected through a pressure detecting line 48 is raised higher than a first predetermined pressure Pd1, a recovery switching valve 44 is shifted to a valve-closed position to cease the recovery function. At this time, the pump delivery pressure detected through a pressure dete

When the pump pressure detected through a pressure detecting line 48 is raised higher than a first predetermined pressure Pd1, a recovery switching valve 44 is shifted to a valve-closed position to cease the recovery function. At this time, the pump delivery pressure detected through a pressure detecting line 51 is higher than a second predetermined pressure Pd1* close to the first predetermined pressure Pd1, and an engine speed increasing device 52 controls an engine controller 11 to increase the rotational speed of an engine 10, thereby increasing the pump delivery rate. Thus, it is possible to make small speed change of an actuator and to increase working efficiency with no deterioration in operability, even when a recovery function is ceased.

대표청구항 ▼

A hydraulic control system for construction machines, comprising an engine, engine control means for controlling a rotational speed of said engine, a hydraulic pump driven by said engine, a hydraulic actuator driven by a hydraulic fluid delivered from said hydraulic pump, a directional control valve

A hydraulic control system for construction machines, comprising an engine, engine control means for controlling a rotational speed of said engine, a hydraulic pump driven by said engine, a hydraulic actuator driven by a hydraulic fluid delivered from said hydraulic pump, a directional control valve for controlling a flow of the hydraulic fluid supplied from said hydraulic pump to said hydraulic actuator, and recovery means for recovering a return fluid from the hydraulic actuator to the supply side of said hydraulic actuator when the pressure of the hydraulic fluid supplied to said hydraulic actuator is smaller than a first predetermined value, wherein said hydraulic control system further comprises: detecting means for detecting the pressure of the hydraulic fluid supplied to said hydraulic actuator, and engine speed increasing means for controlling said engine control means to approximately simultaneously increase the rotational speed of said engine when the detected pressure is higher than said first predetermined pressure and a cessation of the recovering action of the recovery means is detected.