PURPOSE: To improve working efficiency by gearing two two-speed type hydraulic motors with a ring gear for driving an auger screw, and regulating the feed quantity of pressure oil to each hydraulic motor to switch it to three high, middle and low speeds.
CONSTITUTION: The pinion gears 41, 42 of two-speed type hydraulic motors 31, 32 set on an auger driving device raised and lowered along a leader 2 in which large or small capacity is selected by a capacity switching valve so that the output of an auger can be switched to high speed or low speed are geared with a ring gear 5. The capacity switching valve is set so that both the hydraulic motors 31, 32 have a small capacity (high rotation, low torque) when the output of the auger is set to high speed, and both the motors have a large capacity (low rotation, high torque) when the output is set to low speed. When middle speed is set, one motor 31 is set to the small capacity (high speed, low torque), the other motor 32 is set to the large capacity (low speed, high torque), and the ring gear 5 is driven. Thus, the speed suitable for the property of the ground and the working content can be selected.
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