Fundamental Study on No-lubricating Friction Characteristics Due to Anisotropy of Surface Properties Applied to Differential Gear

The solid frictional characteristics of surface roughness in combination with anisotropy were systematically investigated through linear reciprocating sliding tests on planar surfaces with no lubrication. Four types of test pieces with anisotropy and varying amounts of surface roughness controlled by polishing were prepared. For test pieces #800 and #3000, their friction coefficients did not change significantly based on anisotropic combination conditions and remained relatively constant at 0.35. In contrast, for test pieces #80 and #150, their friction coefficients changed significantly based on anisotropic combination conditions. Their friction coefficients were approximately 0.45 when their crease directions were parallel and sliding directions were orthogonal, approximately 0.3 when their crease directions and sliding directions were both parallel, and approximately 0.15 when their crease directions were orthogonal and sliding direction were parallel. Therefore, the anisotropic combination conditions in which test pieces #80 and #150 had orthogonal crease directions and parallel sliding directions yielded the smallest friction coefficient.