Evaluation of Arc Erosion of Cu-graphite Brush Used in Small DC Motors with and without Quenching Device

Many small DC motors are used for anti-lock breaking system (ABS) and other applications. It is well-known that in DC motors the commutation arc causes a high rate of erosion and wear of brush and commutator. Therefore, it is important how the commutation arc influences the erosion and wear of brush in small DC motors.The wear and erosion of brush is caused by both mechanical sliding action and arc discharge. To figure out the wear/erosion mechanism of brush, mechanical wear and arc erosion are needed to be separately evaluated. However, it is usually difficult, because arc dis charge causes not only arc erosion but also the increase of mechanical sliding wear as R. Holm said.In this study, a switching device is newly developed and arc erosion of brush material is investigated. The brush material is Cu-graphite which is generally used in small DC motors. In the test the Cu-graphite as a brush is cathode and Cu is anode as a commutator of DC motors, and fundamental characteristics of arc duration and arc energy are obtained. Furthermore, the effect of a spark quenching circuit with a Zener diode is examined. In both cases, the arc erosion is measured by a laser microscope and the arc erosion per unit energy is obtained. In addition brush wear/erosion obtained by a commutation test could be analyzed, using the above results.