To constitute a drive circuit for hydraulic motor so that the rotating speed range of an auger screw is increased.
As a pair of hydraulic motors 23 and 24 for driving the auger screw 12, multi-stroke type motors are used, so that the motor discharge capacities M1 and M2 thereof are changeable by switching selector valves 31-34. A circuit selector valve 26 is provided between a hydraulic pump 21 and the hydraulic motors 23 and 24, so that the motor circuit is switchable to a parallel circuit and serial circuit by switching the circuit selector valve 26. When a low-speed command is given by a speed setter 51, the motor discharge capacities M1 and M2 of the hydraulic motors 23 and 24 are changed to large q, and the motor circuit is switched to the parallel circuit. When a high-speed command is given, the motor discharge capacities M1 and M2 are changed to small 1/2q, and the motor circuit is switched to the serial circuit.
FUKUSHIMA KATSUJI
YOSHIDA KUNIHIKO
OBARA ATSUSHI
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