PURPOSE: To reduce delivery pressure changes of a fixed displacement pump despite of a simple and inexpensive structure, by amplifying output signals of a filter circuit which passes only frequency signal components of the delivery pressure changes originated from the fixed displacement pump, converting the amplified output signals into binary values, and selecting a voltage value according to the binary signals.
CONSTITUTION: A pressure gage 3 is provided downstream from the delivery opening of a fixed displacement pump 2 which is driven by a motor 1 and only frequency signal components of delivery pressure changes originated from the fixed displacement pump 2 out of its output signals are made to pass through a filter circuit 4. The signals passed through the filter circuit are amplified 5 and then compared with a prescribed reference voltage in a comparison circuit 6 so as to be converted into binary values and voltage values (b), (c) (b>c), which are set in an additional value set circuit 8, are selected and output according to the binary signals by a selector 9. Next, the output voltage of the selector 9 and the output voltage (a) of a rotation speed set circuit 7 are added 10, and the output after addition is output 11 to a motor 1 by converted into a voltage value or a current value drivable of the motor.
AMAKAWA TAKEAKI
OKAMOTO MASAJI
NAKAMURA KAZUMI
MURO MAKOTO