Patent attributes
A dc motor is provided which is equipped with brushes each of which is urged by a spring pressure into constant abutment with a commutator surface. A plurality of protrusions are arrayed on the commutator surface in a direction perpendicular to a direction in which a commutator is to be rotated and extend over a whole of a circumference of the commutator surface. Each of the protrusions is defined by two side walls arrayed adjacent each other. At least one of the two side walls of each of the protrusions is oriented to be inclined at a preselected angle to the orientation of the spring pressure. The preselected angle lies within a range of 20° to 70°. This ensures the stability of the abutment of the brush with the commutator surface, thus enhancing the startability of the dc motor.
