Erosion by Arc Discharge at Carbon Contacts in Various Automotive Fuels

A small DC motor is used to drive an automotive fuel pump. It is one of its features that brush and commutator work in gasoline or other fuels. In the DC motor the commutation arc causes a high rate of wear of brush and commutator. Therefore, it is important how the commutation arc influences the erosion and wear of commutator and brush in various fuels. The wear of commutator and brush is caused by both mechanical sliding action and arc discharge. In the previous paper, a switching device system was developed to realize the arc discharge almost equivalent to the commutation arc. Using this system the mass change of carbon contacts was examined in air, gasoline, ethanol and methanol to evaluate the arc erosion of commutator and brush. In this paper the arc erosion is examined in Butanol and MTBE besides fuels of the previous paper by the switching device. Further, based on the previous and present results the lifetime is predicted and compared with the experimental results of the commutation tests. Consequently, the predicted lifetimes are generally shorter than the experimental ones. The reason is guessed as follows; mechanical wear takes place together with arc erosion. Then, arc-eroded part is sometimes changed again to sliding surface. A model is discussed.