A piston ring includes an annular body having: an inner circumferential surface and an outer circumferential surface; one side surface and the other side surface substantially orthogonal to the inner circumferential surface; and a pair of joint ends. The outer circumferential surface includes an inclined surface and an abutment surface. In a direction connecting the one side surface and the other side surface, a maximum width W1 of the abutment surface at the joint end is 80% to 150% of a maximum width W2 of the abutment surface in a portion other than the joint end. In the body, a two-axis difference (d2d1) between a diameter d1 in a first axis direction passing through a central position of the joint and a diameter d2 in a second axis direction orthogonal to the first axis direction is greater than 0.25 mm and less than +0.36 mm.

A piston ring includes an annular body having: an inner circumferential surface and an outer circumferential surface; one side surface and the other side surface substantially orthogonal to the inner circumferential surface; and a pair of joint ends. The outer circumferential surface includes an inclined surface and an abutment surface. In a direction connecting the one side surface and the other side surface, a maximum width W1 of the abutment surface at the joint end is 80% to 150% of a maximum width W2 of the abutment surface in a portion other than the joint end. In the body, a two-axis difference (d2d1) between a diameter d1 in a first axis direction passing through a central position of the joint and a diameter d2 in a second axis direction orthogonal to the first axis direction is greater than 0.25 mm and less than +0.36 mm.

There is provided a highly heat conductive piston ring for an internal combustion engine capable of exhibiting a gas seal function and a heat transfer function for a long period of time in a stable manner when used in an automobile gasoline engine having a high compression ratio. The highly heat conductive piston ring for an internal combustion engine is a piston ring for an internal combustion engine having an MnCr steel as a base material, the MnCr steel including C in the range of from 0.52 to 0.65 mass %, Si in the range of from 0.15 to 0.35 mass %, Mn in the range of from 0.60 to 1.00 mass %, Cr in the range of from 0.60 to 1.00 mass %, P in the range of 0.04 mass % or less, S in the range of 0.04 mass % or less, a slight amount of components (total content of Al, Ni, and Cu) in the range of from 0.05 to 3.0 mass %, and a remnant being Fe and unavoidable impurities.

There is provided a highly heat conductive piston ring for an internal combustion engine capable of exhibiting a gas seal function and a heat transfer function for a long period of time in a stable manner when used in an automobile gasoline engine having a high compression ratio. The highly heat conductive piston ring for an internal combustion engine is a piston ring for an internal combustion engine having an MnCr steel as a base material, the MnCr steel including C in the range of from 0.52 to 0.65 mass %, Si in the range of from 0.15 to 0.35 mass %, Mn in the range of from 0.60 to 1.00 mass %, Cr in the range of from 0.60 to 1.00 mass %, P in the range of 0.04 mass % or less, S in the range of 0.04 mass % or less, a slight amount of components (total content of Al, Ni, and Cu) in the range of from 0.05 to 3.0 mass %, and a remnant being Fe and unavoidable impurities.

A piston ring has an annular body including an inner circumferential surface, an outer circumferential surface and first and second side surfaces connecting the inner circumferential surface and the outer circumferential surface, and a joint section. The joint section includes a first protrusion portion, a first reception portion, a second protrusion portion, a second reception portion, a first male portion, a first female portion, a second male portion and a second female portion. The first male portion includes a first mating surface and a first contact surface located adjacent the first mating surface and including either an inclined surface or a curved surface. The second male portion includes a second mating surface and a second contact surface located adjacent the second mating surface including either an inclined surface or a curved surface.

A multi-piece oil ring includes an oil ring main member in which two rails are connected together by a columnar part and which has a roughly I-shaped cross section; and a coil expander disposed in an inner circumferential groove formed on the inner circumferential surface of the columnar. Each rail in the oil ring main member possesses a sliding section protuberance whose tip possesses a jutting portion. The axial length of the jutting portion is 0.02-0.18 mm. The change rate of the axial length of the individual jutting portion is in the range of 0 to 80% at least in a region of from its sliding surface to be faced to a cylinder, which is positioned at the tip of the jutting portion, to a position of 0.03 mm away from the aforementioned sliding surface in the radial direction of the oil ring main member.

Provided is a piston ring excellent in peeling resistance, wear resistance, and thermal conductivity. A piston ring 1 includes: an annular main body 2 having a pair of side faces 2a and 2b, an outer peripheral face 2d, and an inner peripheral face 2c; and a hard coating 11 provided on the outer peripheral face 2d. When a width of the main body 2 in a first direction D1 perpendicular to the pair of side faces 2a and 2b is set to h1 mm, a width of the hard coating 11 in the first direction D1 is set to W mm, and a thickness of the hard coating 11 in a second direction D2 perpendicular to the outer peripheral face 2d is set to L mm, the following Formula (1) is satisfied: 0.003(L.Math.h1)/W0.151.

Provided is a piston ring excellent in peeling resistance, wear resistance, and thermal conductivity. A piston ring 1 includes: an annular main body 2 having a pair of side faces 2a and 2b, an outer peripheral face 2d, and an inner peripheral face 2c; and a hard coating 11 provided on the outer peripheral face 2d. When a width of the main body 2 in a first direction D1 perpendicular to the pair of side faces 2a and 2b is set to h1 mm, a width of the hard coating 11 in the first direction D1 is set to W mm, and a thickness of the hard coating 11 in a second direction D2 perpendicular to the outer peripheral face 2d is set to L mm, the following Formula (1) is satisfied: 0.003(L.Math.h1)/W0.151.

To provide a combined oil control ring comprising a pair of upper and lower side rails and an axially corrugated spacer expander having upper and lower portions for automobile engines, which is capable of keeping an excellent oil-controlling function without sticking between a spacer expander and side rails even in a long period of engine operation, the upper and lower portions of the spacer expander have tabs pushing inner peripheral surfaces of the side rails, projections supporting the side rails, and intermediate portions between the tabs and the projections; and each intermediate portion opposing the side rail has a center-raised bottom having a center-raised shape when viewed along a substantially circumferential direction center-raised shape and a radial direction.

To provide a combined oil control ring comprising a pair of upper and lower side rails and an axially corrugated spacer expander having upper and lower portions for automobile engines, which is capable of keeping an excellent oil-controlling function without sticking between a spacer expander and side rails even in a long period of engine operation, the upper and lower portions of the spacer expander have tabs pushing inner peripheral surfaces of the side rails, projections supporting the side rails, and intermediate portions between the tabs and the projections; and each intermediate portion opposing the side rail has a center-raised bottom having a center-raised shape when viewed along a substantially circumferential direction center-raised shape and a radial direction.