Piston ring

Abstract

A piston ring has a diamond-like carbon film formed in a thickness of 0.5 to 30 micrometers over an under film on the upper and lower surfaces. The under film is directly formed on the surfaces, or formed on a hard surface treatment layer consisting of a gas nitrided layer or a chromium plating film. The diamond-like carbon is configured with any one of an amorphous carbon structure, an amorphous carbon structure having partly a diamond structure, or an amorphous carbon structure having partly a graphite structure. The under film is comprised of one or more elements selected from the group consisting of silicon, titanium, tungsten, chromium, molybdenum, niobium and vanadium in an atomic content of 70 percent or more and below 100 percent, and the remaining content consisting of carbon, or one or more of said elements in an atomic content of 100 percent. The films may also be formed in the same way on the outer circumferential surface of the piston ring.

Dependencies are inferred from the claim text.