A piston ring is formed from a steel substrate consisting of the carbon in a range of 0.80-0.95 wt. %, silicon in a range of 0.30-0.55 wt. %, manganese in a range of 0.25-0.5 wt. %, phosphorus in a range of up to 0.04 wt. %, sulfur in a range of up to 0.04 wt. %, chromium in a range of 17-18 wt. %, molybdenum in a range of 0.70-1.25 wt. %, vanadium in a range of 0.05-0.15%, the remainder iron. The ring has been through hardened and tempered so that it has a hardness of 46-54 HRC. A coating is then applied via PVD or other suitable methods onto the ring surface to create the finished piston ring.

A pressure ring includes a first pressure ring fitted in a first ring groove of a piston; and a second pressure ring fitted in a second ring groove of the piston, and positioned between the first pressure ring and an oil ring. The second pressure ring is provided with a groove that extends across a surface of the second pressure ring from an inner peripheral side to an outer peripheral side. The groove is configured such that at least one of a width and a depth of the groove becomes larger toward the outer peripheral side from the inner peripheral side.

A pressure ring includes a first pressure ring fitted in a first ring groove of a piston; and a second pressure ring fitted in a second ring groove of the piston, and positioned between the first pressure ring and an oil ring. The second pressure ring is provided with a groove that extends across a surface of the second pressure ring from an inner peripheral side to an outer peripheral side. The groove is configured such that at least one of a width and a depth of the groove becomes larger toward the outer peripheral side from the inner peripheral side.

The present invention provides a piston ring having excellent abrasion resistance to an aluminum alloy cylinder or cylinder liner formed of a mating material and is therefore capable of decreasing abrasion of the mating material. An exemplary piston ring has a hard carbon coating formed on an outer peripheral surface, and the hard carbon coating contains 0.5 atom % or more to less than 5 atom % of tungsten (W).

A combination of piston rings assembled to a piston of an internal combustion engine includes four compression rings. An outer peripheral surface of a first compression ring includes a barrel surface, an outer peripheral surface of a second compression ring includes an outer peripheral end portion and a taper surface, an outer peripheral surface of a third compression ring includes an outer peripheral end portion and a taper surface, and an outer peripheral surface of a fourth compression ring includes an outer peripheral end portion and a taper surface.

An internal combustion engine is disclosed. The engine may have a cylinder that defines a combustion chamber for combusting an air/fuel mixture. The engine may also have a piston reciprocally movable within the cylinder between a top dead center (TDC) and a bottom dead center (BDC). The piston may have an uppermost piston ring configured to sealingly contact the cylinder. The engine may have an annular crevice facing the combustion chamber. The crevice may be defined by the cylinder, the piston, and the uppermost piston ring. The engine may also have a flow channel fluidly connected to the combustion chamber. The flow channel may direct unburned air/fuel-mixture out of the combustion chamber. The at least one flow channel may be fluidly connected to the annular crevice for a crank angle range of about 85 to 95 and about 265 to 275 after the top dead center (TDC).

An internal combustion engine is disclosed. The engine may have a cylinder that defines a combustion chamber for combusting an air/fuel mixture. The engine may also have a piston reciprocally movable within the cylinder between a top dead center (TDC) and a bottom dead center (BDC). The piston may have an uppermost piston ring configured to sealingly contact the cylinder. The engine may have an annular crevice facing the combustion chamber. The crevice may be defined by the cylinder, the piston, and the uppermost piston ring. The engine may also have a flow channel fluidly connected to the combustion chamber. The flow channel may direct unburned air/fuel-mixture out of the combustion chamber. The at least one flow channel may be fluidly connected to the annular crevice for a crank angle range of about 85 to 95 and about 265 to 275 after the top dead center (TDC).

A piston for an internal combustion engine including a piston crown and a combustion chamber recess recessed therein, the combustion chamber recess including a recess edge. The piston may also include a ring groove for receiving a piston ring. The piston may further include a cooling duct having a smaller spacing from the piston crown than that of a flank of the ring groove, the cooling duct defining a minimum spacing from the piston crown at a first location, and a minimum spacing from the combustion chamber recess at a second location. The cooling duct may have a rounded portion between the first location and the second location. The cooling duct may have a maximum spacing from the recess edge at a third location. The rounded portion may have a rounding radius defined at least at the third location that is greater than 4% of a piston diameter.

An example of a cylinder liner according to the present disclosure includes a first portion having a first end and a second end and a second portion having a first end and a second end. The second portion is separate from the first portion and the second end of the first portion overlays the first end of the second portion. The first portion and the second portion are configured to receive a piston slideably disposed within the first portion and the second portion.

Provided is a sliding member capable of achieving excellent wear resistance and high coating adhesion under harsh sliding conditions without subjecting a base member to nitriding treatment. The sliding member includes a base member made of a steel material and a hard coating that is formed on the base member and having a surface serving at least as a sliding surface. The hard coating has a Young's modulus having a distribution to increase first in a depth direction directed from an interface between the hard coating and the base member to the surface, to become maximum at a predetermined depth, and then to decrease in the depth direction directed from the interface to the surface.