US Patent 7265475 Electric motor having convex high-speed brush

A two speed direct current electric motor comprising: an armature having a commutator assembly that is adapted to receive an electromotive force to cause the armature to operatively rotate. A brush assembly having a common brush and a low-speed brush is disposed about and in electrical communication with the commutator to provide a first electromotive force to cause the armature to provide a low-speed rotational output. The brush assembly further includes a high-speed brush having a convex shaped end in physical and electrical communication with the commutator to provide a second electromotive force to cause the armature to provide a high-speed rotational output. The convex shaped end of the high-speed brush is further adapted to wear to take the shape of the commutator such that as the high-speed brush wears the high-speed rotational output decreases.