Side rail and combined oil control ring incorporated with the side rails for reduction of oil consumption

A side rail for use in an oil control ring, said side rail being formed into a ring shape having its generally rectangular section that comprises a pair of side surfaces in parallel to each other, an outer surface formed between two outer peripheries of said side surfaces for contact to an inner surface of a cylinder, and an inner surface formed between two inner peripheries of said side surfaces for contact to a spacer expander of said oil control ring,

• said outer surface comprising a pair of edge surfaces connected to said adjacent side surfaces, and an intermediate surface formed between said edge surfaces,
• each of said edge surfaces being formed with a radius substantially equal to from one fifth to eight fifth of said side rail width,
• said intermediate surface being formed by a cylindrical face formed with a substantially constant radius or by a barrel face formed with a substantially constant radius of curvature greater than radius of curvature for said edge surfaces, said barrel face forming a convex surface slightly outwardly protruding from connections between said intermediate surface and edge surfaces by a height equal to or less than about 0.01 mm, and
• axial length of said intermediate surface being in a range between about 30% and about 70% of the side rail width.