To eliminate inconvenience according to a rapid change of a pump discharge amount by making the speed for returning an actuator piston for operating a discharge flow rate variable means for a pump device to a neutral position gentle up to the return midway by improving an actuator spring for energizing the actuator piston to the neutral position.
An actuator piston 63 for operating a swash plate 37 for a variable displacement pump device 33 is energized to a neutral position by an actuator spring 64 and pilot hydraulic pressure for displacing the actuator piston 63 against the actuator spring 64 is supplied to a signal pressure chamber 78. By fitting a plurality of coil springs 73, 74 of different lengths into the actuator spring 64, a spring constant variable means 75 is formed. When the displacement amount of the actuator piston 63 is large, the spring constant becomes large and when the displacement amount of the actuator piston 63 is small, the spring constant becomes small.
TANEMURA HIDEAKI
TAKAHASHI YUICHI
RON BIYAAKI
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