Effects of Brush Spring Force on Brush Wear and Arc Behaviors of Small DC Motor

Many small DC commutator motors are still used especially in automobile applications such as anti-lock breaking system (ABS) and other equipment. Cu-graphite brush is popular in small DC motors because of low resistivity and high current density. And brush wear is one of important factors relating to life-time and reliability of motors. Further, arc discharge occurs often during the current commutation of the coil. As well-known, the commutation arc often causes a high rate of erosion and wear of brush and damage of commutators.Further, brush spring pressure is one of key factors for brush wear, and its high pressure sometimes increases brush wear largely, while it makes contacts between brush and commutator stable.In this paper, the effect of brush spring pressure on brush mechanical wear and wear with arc discharge is investigated with parameters of Cu contents and firing temperature. The test is carried out by an equipment using an equivalent commutation circuit instead of a real DC motor. Comparing results of three brush pressures 400, 800 and 1200 gf /cm² for Cu 30 % brush, arc duration changes from 15 μs at 400 gf/cm² to 12 μs at 1200 gf/cm², while brush wear with arc discharge is smaller, 12 mg at low pressure than 20 mg at high one. Further the effect of arc discharge on brush wear is discussed.