An internal combustion may include a cylinder having a first combustion chamber at one end and a second combustion chamber at an opposing end, first and second cylinder heads located at an end of the first and second combustion chambers, respectively, and a double-faced piston slidably mounted therein. The piston may be configured to move in a first stroke that includes an expansion stroke portion and a non-expansion stroke portion. The engine may further include first and second piston rod portions extending from opposite faces of the piston. A recess in the piston rod portions may be configured to communicate gases between a combustion chamber and locations outside the cylinder. There may also be a chamber surrounding the first or second piston rod portion, the chamber configured to be supplied with gas and the chamber being isolated from the first combustion chamber and the second combustion chamber.

A piston ring assembly includes an inner ring, a first outer ring, and a second outer ring. The inner ring has an outer surface and an inner surface that extends between a first inner ring face and a second inner ring face. The first outer ring has a first outer ring outer surface disposed opposite a first outer ring inner surface, each extends between a first outer ring face and a first outer ring second face. The first outer ring inner surface engages the outer surface. The second outer ring has a second outer ring outer surface disposed opposite a second outer ring inner surface, each extends between a second outer ring first face and a second outer ring second face.

A piston ring assembly includes an inner ring, a first outer ring, and a second outer ring. The inner ring has an outer surface and an inner surface that extends between a first inner ring face and a second inner ring face. The first outer ring has a first outer ring outer surface disposed opposite a first outer ring inner surface, each extends between a first outer ring face and a first outer ring second face. The first outer ring inner surface engages the outer surface. The second outer ring has a second outer ring outer surface disposed opposite a second outer ring inner surface, each extends between a second outer ring first face and a second outer ring second face.

A combined oil control ring comprising a pair of annular side rails each having a gap, and an axially corrugated spacer expander arranged between the side rails; the corrugated spacer expander having on the inside seating tabs for pushing inner peripheral surfaces of the side rails; the side-rail-pushing surface of each seating tab being provided with a nitrided layer; an entire surface of each spacer expander except for those provided with the nitrided layer being coated with a plating film; and the plating film having Vickers hardness HV0.01 of 300 or less.

A combined oil control ring comprising a pair of annular side rails each having a gap, and an axially corrugated spacer expander arranged between the side rails; the corrugated spacer expander having on the inside seating tabs for pushing inner peripheral surfaces of the side rails; the side-rail-pushing surface of each seating tab being provided with a nitrided layer; an entire surface of each spacer expander except for those provided with the nitrided layer being coated with a plating film; and the plating film having Vickers hardness HV0.01 of 300 or less.

The piston ring assembly having a first and a second endless sealing ring and an elastic ring carrier, the first and the second sealing ring extending in a circumferential direction (U) and each having an outer circumferential surface, the first sealing ring having a first center point (M1) with respect to its outer circumferential surface and the second sealing ring having a second center point (M2 ) with respect to its outer circumferential surface, the first and second sealing rings each having a longitudinal axis (L) running perpendicular to the circumferential direction (U), wherein the ring carrier runs in the circumferential direction (U), and wherein the ring carrier and the first and second sealing rings are designed to be mutually adapted in such a way that the first and second sealing rings are arranged one after the other in the ring carrier in the direction of the longitudinal axis (L), and in that their first and second centers (M1, M2) are arranged at a distance from one another radially with respect to the longitudinal axis (L), the sealing rings being pressed in opposite directions against the inner wall of a cylinder when the piston ring assembly is used in accordance with the invention.

The piston ring assembly having a first and a second endless sealing ring and an elastic ring carrier, the first and the second sealing ring extending in a circumferential direction (U) and each having an outer circumferential surface, the first sealing ring having a first center point (M1) with respect to its outer circumferential surface and the second sealing ring having a second center point (M2 ) with respect to its outer circumferential surface, the first and second sealing rings each having a longitudinal axis (L) running perpendicular to the circumferential direction (U), wherein the ring carrier runs in the circumferential direction (U), and wherein the ring carrier and the first and second sealing rings are designed to be mutually adapted in such a way that the first and second sealing rings are arranged one after the other in the ring carrier in the direction of the longitudinal axis (L), and in that their first and second centers (M1, M2) are arranged at a distance from one another radially with respect to the longitudinal axis (L), the sealing rings being pressed in opposite directions against the inner wall of a cylinder when the piston ring assembly is used in accordance with the invention.

A piston ring has an annular base body 2, which is preferably open at a joint, with a U-shaped cross section, the open side of which faces inwards in the radial direction. A ring spring 4 is provided which runs in a meandering manner in the axial direction, and which pretensions the base body 2 outwards in the radial direction. In one section of the ring spring 4, which is located inside the base body, meandering loops 5 bear alternately against the shanks 3 of the U-shaped cross section. In one section of the ring spring 4, which protrudes out of the base body 2, meandering loops 6 bear alternately against the radially inwardly facing edges of the shanks 3 of the U-shaped cross section.

A piston ring has an annular base body 2, which is preferably open at a joint, with a U-shaped cross section, the open side of which faces inwards in the radial direction. A ring spring 4 is provided which runs in a meandering manner in the axial direction, and which pretensions the base body 2 outwards in the radial direction. In one section of the ring spring 4, which is located inside the base body, meandering loops 5 bear alternately against the shanks 3 of the U-shaped cross section. In one section of the ring spring 4, which protrudes out of the base body 2, meandering loops 6 bear alternately against the radially inwardly facing edges of the shanks 3 of the U-shaped cross section.

A piston ring includes a body portion presenting a running surface, and a spring member disposed between the body portion and a ring groove of a piston. A running surface of the piston ring presents an upper rail, a lower rail, and a fulcrum disposed between the rails and each extending radially outwardly. An outermost tip of the fulcrum is disposed radially outwardly relative to an outermost surface of the rails, and the running surface presents a convex shape along the fulcrum. The fulcrum contacts an oil film applied to a cylinder wall as the piston reciprocates along the cylinder wall. The spring member presses the body portion of the piston ring toward the cylinder wall and causes the body portion to pivot about the fulcrum to provide for improved control of the oil film, less friction, and reduced oil consumption.