Patent ID: 7677375

Claim:
A device that transmits drive force through frictional engagement between a first drive force transmitting member and a second drive force transmitting member, which are rotatable relative to each other about a common rotational axis, with a lubricant oil provided between the first and second drive force transmitting members, wherein the first and second drive force transmitting members each have a sliding surface, the sliding surfaces facing each other, a diamond-like carbon film being formed on the sliding surface of the first drive force transmitting member, a fine circumferential groove being formed in the sliding surface of the second drive force transmitting member, and wherein the proportion of a sliding area to the sliding surface of the second drive force transmitting member at an initial stage of use is 55 to 90%, wherein the fine groove of the second drive force transmitting member at the initial stage of use has a depth of 15 μm or smaller and an average width of 15 to 45 μm at the surface of the sliding surface and at the depth of 1.5 μm from the surface of the sliding surface.