US Patent 7554239 Dynamo-electric machine and vehicular air blower having the same

Each brush box, which receives a corresponding brush, has a contact wall. The contact wall becomes deformable when the temperature of the contact wall reaches a predetermined temperature. A radially outer end surface of the brush is tilted relative to the contact wall, so that the brush is urged against the contact wall by a compression coil spring, which urges the brush against a commutator of an armature. Upon energization of the armature, when the temperature of the brush reaches a predetermined temperature, an urging force of the spring, which is conducted to the contact wall through the brush, causes deformation of the contact wall to disengage a radially inner end of the brush from the commutator.