Characteristics of carbon and copper flat commutator on DC motor for automotive fuel pump

Many small motors are used in automobile. In an automotive fuel pump system, a small DC motor is widely used to drive the pump. The motor is installed in a gasoline tank, so that the current is commutated in gasoline, and arc voltage and duration differ from that in air. In this research, we use carbon brush and carbon flat commutator, replacing a cylindrical copper commutator, and investigate relationship between arc duration and sliding condition. Under small commutation current, arc duration is short and sliding condition is good, but under high commutation current, arc duration is long and black parts damaged by arcing on commutator rapidly invade from the edge of segments. Unstable sliding or abnormal wear occurs when a black part width reaches a brush width. Then, effective commutation interval becomes very short, and arc duration and residual current increase rapidly. Experimental results of a copper flat commutator are also described, compared with the carbon commutator.