Improving the traction coefficient of a traction drive system is a key factor in obtaining a smaller, lighter unit and also greater torque capacity. This study focused on the micro-surface texture of the rolling elements, and an attempt was made to improve the traction coefficient by raising the condition of the viscous traction fluid to the plastic region. Circumferential grooves were provided on the rolling elements as the micro-surface texture. Tests were conducted on these rolling elements using a four-roller tester that allowed high surface pressures and high rolling speeds. The test results made it clear that the groove depth, groove pitch and also the radius of curvature of the convex portion of the rolling elements are important parameters of the micro-surface structure of the circumferential grooves for improving the traction coefficient while assuring high durability at the same time.
