PURPOSE: To reduce responsive delay as for both changeover from the neutral condition to the working condition and from the working condition to the neutral condition of an oil pressure changeover valve.
CONSTITUTION: A pilot oil pressure source 16 is connected to the pilot ports 10a, 10b of a main control valve 10 through an electromagnetic proportional pressure reducing valve 20 and an electromagnetic changeover valve 24, and when an operation lever 39 is at neutral, very small current is let flow in a variable solenoid 20a and given by dither, while holding the electromagnetic changeover valve 24 at neutral position. When the operation lever 39 is operated, the electromagnetic changeover valve 24 is changed over according to the operated direction, and current corresponding to the operated quantity is let flow in the variable solenoid 20a.
KUSAKABE TOSHIBUMI
KINUKAWA HIDEKI
YOKOYAMA SHOZO
