To provide a high torque in a wide rotation speed range by changing a pole based on a frequency in an intersection point of the maximum output torques of respective poles according to frequencies in driving an inverter of a pole-change electric motor.
An inverter circuit 21 is added to a pole change motor 10 for a drive of an electric earth auger. It can be changed between an ordinary driving and an inverter driving by a drive mode change means 11 by the operation of a driver. A pole of the pole change motor 10 can be changed by a pole change device 12. In the inverter driving, the frequency can be changed by operating a rotation speed setting device 23 by this constitution. When the frequency exceeds the reference frequency with the reference set to the preset frequency, the pole is so set to be automatically changed. That is to say, the pole is kept in a large number till the frequency is within the reference frequency and when it exceeds the reference frequency, the pole is changed to the small number side. This constitution can automatically provide the high torque in a wide rotation range from the inverter driving low rotation speed to the high rotation speed.
| JP3119467 | SOIL DISCHARGE DEVICE |
| JPS61176788 | DRILLING AND/OR LIFTING MACHINE |
ISOGAI TAKAAKI
OMI MASARU
YOSHIDA ICHIRO
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