To control pump discharge in the same way as before the generation of a failure even in case of the failure being generated to an electric system in a hydraulic pump displacement control device performing electromagnetic proportional control of a pump discharge by electrohydraulic servo mechanism using a solenoid proportional control valve.
A shaft 4j of a solenoid 4c of a control valve 4 and a shaft 4k of a spool 4b are separated, and an input switching control chamber 4n is provided at a part where the end faces of the shafts 4j, 4k are positioned. The diameter of the shaft 4j is made larger than that of the shaft 4k, and a command pressure port 4p is formed at a casing part of the input switching control chamber 4n. A horsepower control piston 4q is arranged in series to a spring 4d on the opposite side of the solenoid 4c, and a horsepower control spring 4r is provided in such a way as to support the piston 4q. A horsepower control chamber 4t is formed at a part where the piston 4q is positioned and a horsepower control oil pressure port 4u for taking in delivery pressure of a hydraulic pump 1 is formed at a casing 4s of the horsepower control chamber 4t.
GOTO YASUHARU
KOKUBU HARUO
YUASA KAZUMASA
NAKAMURA SHIGETAKA
MOTOSAWA YUKIHIRO
SAKAIRI TETSUYA