Influence of Arc Discharge on Carbon Commutator and Brush Wear in DC Motor Driving Fuel Pump

A small DC motor is used to drive an automotive fuel pump. 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. To evaluate the wear of commutator and brush, mechanical wear and arc erosion have to be separated respectively. In this paper, to examine the erosion only by arc a switching device system is developed and the arc discharge almost equivalent to the commutation arc is realized by it. Using this system the mass change of carbon contacts is examined in air, gasoline, ethanol and methanol to evaluate the arc erosion of commutator and brush. Tests with switching operation of 30,000 times are carried out in various fuels, and after the tests the mass loss is evaluated by a 3D laser microscope. Consequently, it can be made clear that mass loss per unit arc energy is a little bit larger in ethanol and methanol than in air and gasoline, but it is around 0.92 m3/J for the cathode. In addition the mass change of the anode is also loss and the loss per arc energy is smaller than that of the cathode. Further, the mass loss per arc energy is somewhat dependent on the circuit inductance.