To provide a piston ring comprising a hard carbon film that is easy to form and exhibits excellent wear resistance. The above-described problem is solved by having a hard carbon film 4 formed on at least an outer peripheral sliding surface 11 of a piston ring base material 1, wherein the hard carbon film 4 is a laminated film comprising a plurality of layers, and is configured so as to contain boron within a range of an atomic density of 0.210.sup.22 atoms/cm.sup.3 to 2.010.sup.22 atoms/cm.sup.3 inclusive. This hard carbon film 4 may be configured to have an sp.sup.2 component ratio within a range of 40% to 80% inclusive, measured in a TEM-EELS spectrum formed by combining electron energy loss spectroscopy (EELS) with a transmission electron microscope (TEM), and a hydrogen content within a range of 0.1 atom % to 5 atom % inclusive. Further, a total thickness of this hard carbon film 4 may be configured to be within a range of 0.5 m to 20 m inclusive.

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; each intermediate portion opposing the side rail has at least one groove extending in a substantially circumferential direction is recessed when viewed along a radial direction.

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 h.sub.1 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.h.sub.1)/W0.151 (1)

A sliding assembly for utilization in an internal combustion engine may include at least one piston ring and a cylinder head provided with a through cavity defining an internal surface. The internal surface may define a TDC portion in a proximity of a top dead center, a central portion, and a BDC portion in a proximity of bottom dead center. The TDC portion, central portion, and BDC portion may present surface finishes having a first roughness, a second roughness, and a third roughness, respectively, each defined by a structure of recesses and projections, at least one of which may be substantially uniform. The second roughness may be less than the first roughness value. The piston ring may present at least part of a contact surface upon which a ceramic coating may be applied by a physical vapor deposition.

A sliding assembly for utilization in an internal combustion engine may include at least one piston ring and a cylinder head provided with a through cavity defining an internal surface. The internal surface may define a TDC portion in a proximity of a top dead center, a central portion, and a BDC portion in a proximity of bottom dead center. The TDC portion, central portion, and BDC portion may present surface finishes having a first roughness, a second roughness, and a third roughness, respectively, each defined by a structure of recesses and projections, at least one of which may be substantially uniform. The second roughness may be less than the first roughness value. The piston ring may present at least part of a contact surface upon which a ceramic coating may be applied by a physical vapor deposition.

A side rail (1) is formed in a sprit ring shape with an opening (10) and to be mounted on a space expander (2) in an annular shape to constitute, together with the space expander (2), a multi-piece oil ring (3) used in an internal combustion engine. The side rail (1) includes an outer peripheral surface (14) facing radially outward, an inner peripheral surface (13) facing radially inward, a first axial surface (11) facing a crankcase, a second axial surface (12) facing a combustion chamber and parallel to the first axial surface (11), and a protrusion (20) formed on the outer peripheral surface (14) in a position offset from an intermediate position between the first axial surface (11) and the second axial surface (12) toward the first axial surface (11) and protruding radially outward from the outer peripheral surface (14).

An oil ring (1) includes an oil ring body (10) and a coil expander (20). The oil ring body (10) includes a pair of rail portions (12) each including an end portion of an outer periphery having a land (30) formed protruding radially outward from each rail portion (12). The land (30) includes an upper axial portion (31) and a lower axial portion (32) facing opposite to each other in an axial direction, a tapered portion (33) having one axial end contiguous to the upper axial portion (31) via a first curved portion (35), and a protruding portion (34) having one of axial ends contiguous to the tapered portion (33) and the other axial end contiguous to the lower axial portion (32) via a second curved portion (36). The protruding portion (34) is protruding in a direction perpendicular to the tapered portion (33).

A piston ring includes an annular main body 2 having a side surface 2a and a side surface 2b, and an inner peripheral surface 2c and an outer peripheral surface 2d, wherein in the main body 2, a cutout section 21 is provided in a corner section 31 formed by the side surface 2b and the outer peripheral surface 2d. The cutout section 21 has a first surface 21a and a second surface 21b. An angle 1 formed by the first surface 21a and the side surface 2b is an obtuse angle, and a corner section 32 formed by the second surface 21b and the outer peripheral surface 2d is located between the side surface 2b and the side surface 2a in a width direction of the main body 2.

A piston ring includes an annular main body 2 having a side surface 2a and a side surface 2b, and an inner peripheral surface 2c and an outer peripheral surface 2d, wherein in the main body 2, a cutout section 21 is provided in a corner section 31 formed by the side surface 2b and the outer peripheral surface 2d. The cutout section 21 has a first surface 21a and a second surface 21b. An angle 1 formed by the first surface 21a and the side surface 2b is an obtuse angle, and a corner section 32 formed by the second surface 21b and the outer peripheral surface 2d is located between the side surface 2b and the side surface 2a in a width direction of the main body 2.