Patent ID: 8525382

Claim:
An electric motor comprising: a stator having a stator core and 2P field windings; wherein the stator core comprises a yoke, 2P primary poles on which the 2P field windings are wound, and 2P auxiliary poles, and wherein the 2P primary poles and 2P auxiliary poles extending inwardly from the yoke, are alternately arranged in the circumferential direction of the yoke; a rotor having a shaft, a rotor core fixed to the shaft, a commutator fixed to the shaft, and rotor windings wound about teeth of the rotor and connected to the commutator; brush gear having a plurality of brushes arranged to make sliding electrical contact with the commutator; a control device for controlling the electrical connecting state of the 2P field windings and the brushes to selectively form on the stator with 2P magnetic poles via the 2P primary poles, respectively, in one state and 4P magnetic poles via the 2P primary poles and 2P auxiliary poles, respectively, in another state when the 2P field windings are electrified, the connecting state of the 2P field windings and the brushes being changeable by the control device to allow the stator to form different magnetic poles in different states when the 2P field windings are electrified, and P is an integer equal to or greater than 1.