Patent ID: 6209321
Filing Date: 2001-04-03
Classification: E02F,F15B

Abstract:
A hydraulic controller for a working machine, comprising:a tank for holding hydraulic oil;a lever for operating the working machine;an actuator for driving the working machine;a hydraulic pump for supplying pressurized oil to said actuator;a directional control valve having a pilot portion and a bleed-off opening, said directional control valve being disposed in a line connecting said hydraulic pump and said actuator, said directional control valve for causing an entire flow of pressurized oil from said hydraulic pump to be supplied to said actuator;proportional pressure control valve for generating hydraulic pressure according to a position of said lever and for supplying a pilot hydraulic pressure to said pilot portion of said directional control valve;a back pressure relief valve, disposed in a bleed-off line connecting the bleed-off opening and the tank, for adding a back pressure to said bleed-off opening;a proportional solenoid valve for supplying a control pressure to said back pressure relief valve;a pilot hydraulic sensor for detecting a generated pilot hydraulic pressure; anda controller for receiving a pilot hydraulic signal from said pilot hydraulic sensor, and for outputting a control signal to said proportional solenoid valve to control said back pressure relief valve.