Electrical brush assembly

An electrical brush assembly for use with a d.c. dynamoelectric machine including a commutator (44) having a substantially cylindrical commutator contact surface (46), comprising:

• an elongate electrical brush element (48) having a sliding contact surface (50) at one end engageable with said contact surface of said commutator, and a side support surface;
• a brush holder (54) for slidably supporting said brush element such that said side support surface of said brush element is slidably supported for a sliding movement of said brush element relative to said commutator of the d.c. dynamoelectric machine substantially along a diameter of said commutator, and such that said contact surface of said brush element can be disposed in sliding contact with said contact surface of said commutator;
• and
• means (58) for urging said sliding contact surface of said brush element against said contact surface of said commutator;
• wherein said sliding contact surface of said brush element is a single, continuous, concave cylindrical surface having a central axis (62) substantially parallel to a central axis (45) of said commutator contact surface, and has a radius (R2) of from 1.2 to 2.5 times larger than a radius (R1) of said commutator contact surface to establish a partial surface contact between said commutator contact surface and said brush element contact surface, and wherein a longitudinal axis (60) of said brush element substantially lies in a plane including said central axes of said commutator contact surface and said sliding contact surface of said brush element.