Electric motors and power tools.

摘要

A hand power tool comprises an electric motor 40 having a rare earth permanent magnet rotor 3 and a polyphase wound stator 4 within a totally enclosed body 5, which in turn is mounted within a housing 2 of the hand tool. The rotor 3 is covered with a thermally and electrically insulative sleeve 12. Primary and secondary output shafts 42 and 49 rotate in the same sense, but one at twice the speed of the other. Thus, no bearings in the motor have to deal with an angular speed greater than half the actual rotor speed. Associated with the motor 1 is electronic control circuitry arranged to generate a polyphase alternating supply and to connect that supply to the stator 4, thereby to produce a rotating magnetic field. Means are disclosed of cooling the rotor, and various electronic circuit configurations are disclosed, for the motor control.