To enhance the responsiveness of a hydraulic pressure control device by reducing the torque of a servomotor and miniaturizing the servomotor.
When a flow-rate command is output from a controller 3 to a servomotor driver 2, the rotating speed of an a.c. servomotor 1 is regulated, so that flow control is carried out by combining both the flow rate of a pressure-controlling hydraulic pressure pump 5 and that of a hydraulic pump 4 other than the coaxial pressure-controlling hydraulic pressure pump. At the time of pressure control, a directional changeover valve 7 is changed over, and the discharge port of the hydraulic pump 4 is communicated with a tank 10 so that an unload condition is attained, and the shock at the time of unload is reduced by a throttle valve 6. At that time, the a.c. servomotor 1 is rotated at a very low speed for compensating the amount of leakage in a load circuit and the hydraulic pump 5, and at the same time since it is sufficient to produce the torque required for only the hydraulic pump 5, the device can be miniaturized to be small in its output.
ISHIKAWA HIROYUKI
NAKAO HIROTOSHI
KIHARA KAZUYUKI
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