Patent ID: 6845702

Claim:
A hydraulic control unit for use in a several-directional-control-valves-assembled-type hydraulic control system having a plurality of actuators to be controlled by a variable displacement pump and provided with a load sensing function to detect a maximum load pressure, which is the highest one of load pressures working at the respective actuators, and to control a delivery pressure of the variable displacement pump so that the delivery pressure becomes higher by a predetermined value than the maximum load pressure detected, the hydraulic control unit having a maximum load pressure port to which the maximum load pressure in the hydraulic control system is supplied, the hydraulic control unit being characterized by comprising: a compensator including an input port connected to a first flow path communicating with a pump port through a variable orifice, an output port connected to a second flow path communicating with an output port of the hydraulic control unit connected to a predetermined one of the actuators, and a metering orifice having a variable opening for controlling a pressure in the first flow path according to a pressure in the second flow path, and a pressure chamber operative to exert a force in such a direction as to close the metering orifice; and a directional control valve which operates independently of the variable orifice and the compensator, and which reduces the pressure in the first flow path to the pressure in the second flow path and guides the pressure thus reduced to the maximum load pressure port when the pressure in the second flow path is higher than a maximum load pressure working at other hydraulic control units in the hydraulic control system, wherein: the directional control valve is incorporated in the compensator, and the directional control valve has a function of sliding due to a deviation between the pressure at the maximum load pressure port and the pressure in the second flow path and guiding the pressure in the first flow path to the maximum load pressure port for use as the maximum load pressure by the sliding thereof, and a function of guiding the pressure at the maximum load pressure port to the pressure chamber of the compensator to close the metering orifice by the sliding thereof.