In a combination oil ring, when a line passing through a center of a segment width is a first intermediate line, a length of a line segment between a position on an engine combustion chamber side and a position on a side distant from the engine combustion chamber on a contour curve at a position at a distance of 3 m from an outer peripheral vertex toward an inner peripheral side in a segment radial direction is L, and an intermediate line of the line segment L is a second intermediate line, the second intermediate line is located on the side more distant from the engine combustion chamber than the first intermediate line, and the outer periphery vertex of the segment is located on the second intermediate line or on the side more distant from the engine combustion chamber than the second intermediate line.

A piston ring having a resin-based film covering at least one of the upper and lower sides, wherein the resin-based film contains a fibrous filler with a mean fiber diameter of 50 to 500 nm and an aspect ratio of 30 to 500, wherein the fibrous filler in the resin-based film to align roughly parallel to the film surface.

A piston ring having a resin-based film covering at least one of the upper and lower sides, wherein the resin-based film contains a fibrous filler with a mean fiber diameter of 50 to 500 nm and an aspect ratio of 30 to 500, wherein the fibrous filler in the resin-based film to align roughly parallel to the film surface.

In a combination oil ring, when a line passing through a center of a segment width is a first intermediate line, a length of a line segment between a position on an engine combustion chamber side and a position on a side distant from the engine combustion chamber on a contour curve at a position at a distance of 3 m from an outer peripheral vertex toward an inner peripheral side in a segment radial direction is L, and an intermediate line of the line segment L is a second intermediate line, the second intermediate line is located on the side more distant from the engine combustion chamber than the first intermediate line, and the outer periphery vertex of the segment is located on the second intermediate line or on the side more distant from the engine combustion chamber than the second intermediate line.

A sliding element, for example a piston ring for an internal combustion engine, may include a sliding face, an adhesive layer disposed on the sliding face, and a coating disposed over the adhesive layer. The coating may be composed of an amorphous carbon material. The coating may have a ratio between sp.sup.3 bonds and sp.sup.2 bonds that indicates a predominance of sp.sup.2 bonds. The coating may have a roughness profile including a value of Rpk of 0.15 m and a value of Rz of 0.7Rz1.5 m.

Provided is a piston ring (10) comprising a sliding surface (11) covered with a CrBVN alloy film (3), wherein a B content is within a range of 0.1-1.5 mass % inclusive, a V content is within a range of 0.05-1 mass % inclusive, and a ratio [B content/V content] is within a range greater than 1 and 30 or less, thereby achieving a piston ring (10) having higher wear resistance, cracking resistance, and peeling resistance. This alloy film (3) preferably further includes Ti, the Ti content being within a range greater than 0 mass % and 8 mass % or less. Such a piston ring (10) is preferably mounted on an engine that uses an alcohol fuel or an alcohol-containing fuel.

A piston ring includes an annular main body portion having an inner peripheral surface, an outer peripheral surface, and one side surface and the other side surface. The piston ring includes a first curved surface provided on the outer peripheral surface, being convexly curved outwards in a radial direction of the main body portion, a second curved surface provided on the outer peripheral surface, being convexly curved outwards in the radial direction of the main body portion, and an intermediate surface formed to extend in a direction connecting the one side surface to the other side surface connecting the first curved surface to the second curved surface. The intermediate surface has a flat portion formed in at least a part thereof. The width of the intermediate surface in the direction connecting the one side surface to the other side surface is 0.05 mm or more and 0.30 mm or less.

A thermal spray coating for piston ring having excellent abrasion resistance, and capable of suppressing abrasion of the opposite member is provided. The thermal spray coating for piston ring according to the invention is a thermal spray coating for piston ring obtained by thermally spraying a powder composition on the outer peripheral sliding surface of a piston ring base material, and the powder composition contains molybdenum particles, nickel chromium alloy particles and chromium carbide particles, and the median diameter of the chromium carbide particles is 5 to 25 m.

A thermal spray coating for piston ring having excellent abrasion resistance, and capable of suppressing abrasion of the opposite member is provided. The thermal spray coating for piston ring according to the invention is a thermal spray coating for piston ring obtained by thermally spraying a powder composition on the outer peripheral sliding surface of a piston ring base material, and the powder composition contains molybdenum particles, nickel chromium alloy particles and chromium carbide particles, and the median diameter of the chromium carbide particles is 5 to 25 m.

Improved liquid lubricated piston ring gas seals with reduced friction and wear compared to prior art rings are disclosed for use in internal combustion engines, gas pumps, and gas compressors. These improved rings allow independent adjustment of the parameters controlling friction and wear, and eliminate the tradeoff between friction and wear typical of prior art rings.