Characteristics of carbon flat commutator for high-inductance DC motor driving automotive fuel pump

Many small motors are used in automobiles. 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 coil current is commutated in gasoline, and arc voltage and duration differ from those in air. In this research, the authors use carbon brush and carbon flat commutator, and investigate relationship between surface morphology of commutator and commutation waveform. Under high inductance and large commutation current, effective commutation interval becomes very short, because black parts damaged by arcing on the commutator invade from the edge of segments. Then, effective commutation interval becomes very short, and arc duration and residual current increase rapidly. Observing surfaces of tested commutator by a laser microscope, the depth of arcing part maybe becomes larger with operations. Commutator and brush lifetimes are short with large commutation current, but the process of wear is similar to the result at small commutation current. Then, relationship between arc duration and surface morphology of commutator is investigated by a laser microscopy. The results show that arc duration affects both width and depth of black parts damaged by arcing.