Tribological Characteristics of Electric Sliding Contacts With Oil-Impregnated Porous Materials

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The electric sliding contacts are widely used in electrical components such as for automobiles. The purpose of the present study is to improve the performance characteristics of the electric sliding contacts and to extend their lifetime by applying the porous materials used in conventional sintered metal bearings to the surface materials of the sliding contacts.The effects of the permeability of porous materials on the electrical conductivity and the frictional characteristics have been investigated theoretically and experimentally. The sliding contacts used in the present study consist of a nonporous rider (stator) having convex surface and a rotating porous disk (slider). The experimental analysis is conducted with a pin-on-disk friction tester to measure the frictional force and the contact voltage between the sliding contacts. The numerical analysis yields the oil-film pressure distributions, the oil-film force and the frictional force at the contact area between the rider and the … More rotating disk. These characteristics are calculated by simultaneously solving the modified Reynolds equation, which includes the filter term and the effect of tangential velocity slip, and the Laplace equation derived from Darcy's law.The results show that the numerical and the experimental results agree qualitatively. An increase in the permeability of the porous materials extends the operating conditions under the continuous metal contact to a higher value of the dimensionless bearing characteristic number S defined by ηU_0L/w_f (η : oil viscosity, U_0 : sliding speed, B : width of rider, w_f : applied load), and also decreases the frictional force at the maximum value of S where the rider could make electrical contacts with the disk surface. This suggests that the porous materials yield a lower frictional loss and a longer lifetime than the conventional nonporous sliding contacts.Consequently, the oil-impregnated porous materials have superiority over the conventional nonporous ones as sliding contact materials from the viewpoint that the rider and the disk could operate under continuous metal contact condition with a lower frictional force for a wide range of S. Less