Patent ID: 8436505

Claim:
An electric motor comprising: a yoke whose number of pole pairs is 2; an armature rotationally journalled to the yoke, the armature including: a rotary shaft journalled to the yoke; an armature core attached to the rotary shaft and having a plurality of teeth extending in a radial fashion toward the radial direction; coils wound around the plurality of teeth; a plurality of slots formed between the teeth and extending along the axial direction; and a commutator provided at the rotary shaft so as to be adjacent to the armature core, and having a plurality of segments arranged in the circumferential direction; and brushes which supply electric power to the coils via the segments come into sliding contact with the segments, wherein the commutator is provided with short-circuit members which short-circuit equipotential segments, wherein the brushes are constituted by three brushes of a low-speed brush, a high-speed brush, and a common brush used in common by the low-speed and high-speed brushes and juxtaposed along the circumferential direction, wherein the circumferential width of the high-speed brush is set to be smaller than the circumferential width of the low-speed brush, and the high-speed brush and the low-speed brush are formed so that simultaneous sliding contact with the equipotential segments can be avoided, and wherein the armature core is provided such that the plurality of teeth is point-symmetrical about the rotary shaft at equal intervals in the circumferential direction, and the teeth and the slots are formed so a tooth and a slot exist alternately at intervals of 90 degrees in the circumferential direction.