Patent ID: 7990017

Claim:
A dc motor comprising: a yoke forming a magnetic circuit; an array of permanent magnets disposed along an inner circumference of said yoke; an armature disposed inside said array of permanent magnets to be rotatable; a commutator provided to be rotatable together with said armature, said commutator having an outer circumferential surface; a brush riding on a commutator surface that is the outer circumferential surface of said commutator, said brush being urged elastically in a given direction into constant engagement with the commutator surface; and a plurality of protrusions that are arrayed on the commutator surface in a first direction perpendicular to a second direction that is a direction in which said commutator is to be rotated and extend over a whole of a circumference of the commutator surface, each of the protrusions being defined by two side walls arrayed adjacent to each other in the first direction, at least one of the two side walls of each of the protrusions being oriented to be inclined at a preselected angle to the given direction in which said brush is urged elastically, the preselected angle lying in a range of 30° to 55°.