Patent ID: 7138744
Filing Date: 2006-11-21
Classification: H01R

Abstract:
1. A brush to be disposed on a commutator of a dc rotary electric machine having a plurality of commutator segments, the brush comprising: a high resistance member to be positioned at a front side of the commutator in the rotation direction thereof; a low resistance member to be positioned at a back side in the rotation direction of the commutator; a medium resistance member disposed between the high resistance member and the low resistance member; wherein: a difference in content of conductive material between the low resistance member and the high resistance member is in a range from 45% to 70%; the medium resistance member has a content of conductive material to provide a thermal expansion coefficient between those of the low resistance member and the high resistance member; and the following expression is given between a total circumferential width of W of the brush, a circumferential width wa of the high resistance member, a circumferential width Sw of one commutator segment and a width δ of a gap between the commutator segments: