In an automotive fuel pump system, a small DC motor is widely used to drive the pump and driven by a automotive battery. Recently a bio-fuel, usually a mixture of gasoline and ethanol has been used due to shortage of gasoline and environmental aspect. It affects strongly the performances of a DC motor, especially commutation phenomena, what kind of fuel is used. Therefore the authors have started to investigate the influence of ethanol on the commutation phenomena. They have been reporting the wear of brush and carbon flat commutator in gasoline and ethanol so far. In this paper commutation period, arc duration, brush and commutator wear are examined in ethanol 50-gasoline 50%. Brush wears are very small compared with the previous results. Namely in the present test a mechanical sliding wear is predominant rather than erosion by arc due to short arc duration. Further, an area eroded by arc is observed to re-appear as a sliding surface. From these results a threshold arc energy between arc erosion and mechanical sliding wear is obtained, and a wear model is proposed to explain the above wear pattern on the sliding surface.

Automotive fuel pumps are driven by small DC motor. Commutation is carried out in gasoline, and arc voltage and duration are different from that in air. Our laboratory have analyzed commutation phenomenon in gasoline quantitatively and we have considered brush materials. To develop high power motor, we need to examine materials that are less arc abrasion and good sliding condition. In this research, we attend to characteristics of flat carbon commutator. As a result, it is possible to drive longer time, like established cylindrical copper commutator.