Advancements of tribological performance of carbon brushes in electrical motors

In electrical motors electrical energy is transformed into mechanical energy or vice versa. Electrical energy has to be transferred from a stationary component into a moving one, which is done by a copper commutator in sliding contact with carbon brushes. Wear occurs at surfaces of both components during dry sliding. To reduce friction and wear rate, solid lubricants are added to the carbon brush compositions. It was observed that, during sliding, a solid lubricant film is formed on the surface of the copper commutator. This transfer film has a limited life. After failure of the layer a new film is formed from the reservoir of the carbon brushes. Various solid lubricants in carbon brushes were tested. It was found that certain solids form very thin layers with good adhesion on commutator surfaces, which improves tribological performance of both moving components. In particular, wear rate, friction and noise are reduced significantly. This resulted in much longer service life of electrical motors for automotive applications.