An analysis of the main factors on the wear of brushes for automotive small brush-type DC motor

Abstract

Some critical components in motors and generators have sliding electrical contacts. Electrical brushes are commonly used in those contact points to conduct current between the stationary and moving parts of a motor. Brushes are exposed both to mechanical and electrical loading. In this paper, studies on the wear of brushes against copper commutator were briefly reviewed. The main influential factors of brush wear are associated with both mechanical and electrical wear. Brush wear is affected by various factors including temperature, material properties, sliding speed, contact force, and interfacial and environmental conditions. The mechanical wear of brushes is proportional to the brush spring pressure and sliding speed, while the electrical wear of brushes is associated with current and contact voltage drop. To characterize the wear, a brush wear test machine was designed, and influential factors were measured such as electrical contact resistance, temperature, wear mass loss, and so on. The wear tests were processed using a small brush type automotive DC motor.

The main objective of this study is to investigate the effects of the wear behavior of copper-graphite brushes in a small brush-type DC motor. The variable conditions are with and without electrical current by changing the brush spring pressure and sliding speed, and the results are electrical contact resistance, voltage drop, brush surface temperature rise, and so on. Brush wear greatly changes with electrical current. This shows that the high current not only produces more Joule heating but also causes an increase in voltage drop, which will result in additional Joule heating.