Patent ID: 8739753

Claim:
An oil ring for an internal combustion engine having outer peripheral surface covered with at least one material selected from the group consisting of hard carbon, CrN and TiN, the oil ring comprising: a first side rail, a second side rail, and a spacer sandwiched between the first side rail and the second side rail, wherein a radius of curvature at an outermost portion of the oil ring in a sliding direction is greater than or equal to 0.3 mm and less than or equal to 2 mm, wherein the radius of curvature is obtained when a radial difference is measured within a width of 200 μm in the sliding direction of the oil ring centered on a maximum outer diameter point, the maximum outer diameter point being an outermost portion of the outer peripheral surface, wherein the radius of curvature denoted by R is expressed in terms of the radial difference denoted by Z according to the following equation in units of μm: R=Z/2+(2+10 4 )/4Z.