Abstract: A hydraulic apparatus for a construction machine, which is adapted to prevent the number of revolutions of an engine from increasing when the flow of the fluid discharged by a variable displacement hydraulic pump driven by the engine is cut off. The hydraulic apparatus comprises a proportional solenoid (11) connected to a fuel supply control lever (13) so as to vary the horsepower characteristics of the engine, which are set by the action of a governor (12) based on manipulated variable of the fuel supply control lever (13) when the flow of the fluid discharged by said pump is cut off, and a controller (10) for controlling the proportional solenoid (11). In this apparatus, a decrement (.DELTA.Nr) in a target number of revolutions per minute (Nr) of the engine, which can be obtained by subtracting a target number of revolutions per minute (Nrb) of the engine at the desired engine horsepower characteristics (l.sub.

Abstract: Disclosed is a hydraulic control system mounted in a hydraulic circuit of a hydraulic excavator and adapted to increase the relief hydraulic pressure and the flow rate. In accordance with one aspect of the invention, a hydraulic control system for a hydraulic excavator having power constant control and cut-off control comprises: a variable relief valve (60) for increasing the pressure upon receipt of a pilot signal (Pc7), a solenoid valve (80) for connecting or disconnecting the pilot signal (Pc7), a variable cut-off control valve 10A which, upon receipt of a pilot signal (Pc6), cancels the cut-off control, a solenoid valve (70) for connecting or disconnecting the pilot signal (Pc6) and an electric circuit (X01) in which a switch (90) for opening or closing the solenoid valves (70, 80) is provided. In accordance with a second aspect of the invention, a timer is provided in the electric circuit (X02) used in the first aspect of the invention.

Abstract: An operation control device is disclosed. According to a drive command value generated depending on the manipulated amount of a plurality of operating means (11, 12, 13, 14, 15, 16), the operation control device controls the drive amount of actuators (BMS, AMS, BKS, LDM, RDM, TNM) associated with the operated actuator. In the drive amount control, the operation control device changes a ratio of the manipulated amount and the drive amount command value by work accuracy flow rate data (41), weights the drive command values based on the same manipulated values of said operating means by priority mode weight data (42), and/or controls the timing of supply of the drive energy from at least two separate energy sources (FFP, RP) as a drive energy source for the respective actuators, and the supply amount of the drive energy, under control of pump utilization data (43) and pump swash plate control data (44).