To provide a piston ring for an internal combustion engine, particularly a second compression ring, which has excellent wear resistance and can achieve both lower fuel consumption and efficient combustion. The above-described problem is solved by a piston ring (1) for an internal combustion engine formed so as to have a tapered shape by a peripheral surface (14) that gradually projects outward from a top to a bottom, and a radial cross-sectional shape of a Napier ring. The peripheral surface (14) is constituted by an outer edge end portion (14b) that has a non-tapered shape and comes into sliding contact, as a peripheral sliding surface, with a mating material, an outer peripheral tapered part (14a) formed at a predetermined taper angle (α) above the outer edge end portion (14b), a curved surface part (14c) having a diameter that gradually decreases inward from the outer edge end portion (14b) to a lower end in an axial direction, and a lower end portion (14d) forming a section of the curved surface part (14c). A distance (d2) between a position (A) of the outer edge end portion (14b) and a position (C) of the lower end portion (14d) in a ring axial direction is within a range of 0.001 mm to 0.05 mm, and a contact width (d1) of the outer edge end portion (14b) in the ring axial direction is within a range of 0.01 mm to 0.3 mm.

A sliding member having a hard carbon coating that has a thickness of 3 μm or more and demonstrates high peeling resistance and high wear resistance is provided. A sliding member 100 according to the present disclosure includes a base member 10 and a hard carbon coating 12 that is formed on the base member 10 and has the hydrogen content of 3 atomic % or less and a thickness of 3 μm or more. When HM represents a Martens hardness of the hard carbon coating 12 and HIT represents an indentation hardness, the ratio HM/HIT is 0.40 or more.

A method for manufacturing a piston ring includes the following steps: (A) a step of supplying an arc current to a cathode formed of a carbon material having a density of 1.70 g/cm.sup.3 or more, to ionize the carbon material; and (B) a step of applying a bias voltage in an environment where hydrogen atoms are substantially absent to form a DLC film on a surface of a base material for a piston ring. The step (A) is continuously carried out, subsequently the step (A) is interrupted, and then the step (A) is restarted, which sequence is repeated thereby to form the DLC film having an extinction coefficient of 0.1 to 0.4 as measured using light having a wavelength of 550 nm and a nanoindentation hardness of 16 to 26 GPa.

An engine comprises a housing and a combustion assembly carried by the housing. The combustion assembly comprises an annular bore defined by the housing, at least one combustion piston disposed within the annular bore, and a sealing mechanism configured to selectively seal the at least one combustion piston relative to at least one corresponding wall of the annular bore. The engine comprises at least one rotary valve configured to move between a first position within the annular bore to allow the at least one combustion piston to travel within the annular bore from a first location proximate to the at least one valve to a second location distal to the at least one rotary valve and a second position within the annular bore to define a combustion chamber relative to the at least one combustion piston at the second location.

An engine comprises a housing and a combustion assembly carried by the housing. The combustion assembly comprises an annular bore defined by the housing, at least one combustion piston disposed within the annular bore, and a sealing mechanism configured to selectively seal the at least one combustion piston relative to at least one corresponding wall of the annular bore. The engine comprises at least one rotary valve configured to move between a first position within the annular bore to allow the at least one combustion piston to travel within the annular bore from a first location proximate to the at least one valve to a second location distal to the at least one rotary valve and a second position within the annular bore to define a combustion chamber relative to the at least one combustion piston at the second location.

An engine includes a housing and a combustion assembly. The combustion assembly includes an annular bore and a combustion piston assembly disposed within the annular bore. The combustion piston assembly includes a set of pistons, a first sealing ring connected to each piston and a second sealing ring connected to each piston. The second sealing ring is configured to provide selective access between the annular bore and at least one fluid conduit carried by the engine. The engine includes at least one valve configured to move between a first position within the annular bore to allow the combustion piston assembly to travel within the annular bore from a first location proximate to the at least one valve to a second location distal to the at least one valve and a second position within the annular bore to define a combustion chamber.

An engine includes a housing and a combustion assembly. The combustion assembly includes an annular bore and a combustion piston assembly disposed within the annular bore. The combustion piston assembly includes a set of pistons, a first sealing ring connected to each piston and a second sealing ring connected to each piston. The second sealing ring is configured to provide selective access between the annular bore and at least one fluid conduit carried by the engine. The engine includes at least one valve configured to move between a first position within the annular bore to allow the combustion piston assembly to travel within the annular bore from a first location proximate to the at least one valve to a second location distal to the at least one valve and a second position within the annular bore to define a combustion chamber.

Provided is a side rail 1 having an outer peripheral surface 14, an inner peripheral surface 13, a first axial side surface 11, and a second axial side surface 12 parallel to the first axial side surface 11, in which, a beveled portion 30 is provided between the outer peripheral surface 14 and the second axial side surface 12, the beveled portion 30 is formed in a tapered surface having a diameter gradually decreasing from the first axial side surface 11 toward the second axial side surface in an axial direction; a tapered surface 30a is provided between a first tapered surface portion 30a1 with an angle of 10° or more to the axial direction and a second tapered surface portion 30a2 provided between the first tapered surface portion 30a1 and the outer peripheral surface 14 and having a smaller angle of inclination to the axial direction than that of the first tapered surface portion.

A piston ring (10) has a running surface (12) and a flank surface (14) which are coated. The uppermost layer of the running surface (12) is a hydrogen-containing or a hydrogen-free DLC layer, and the uppermost layer of at least one flank surface (14) is a chromium layer. A method of producing a piston ring (10) includes forming a DLC layer as the uppermost layer of the running surface (12), and forming a chromium layer as the uppermost layer of at least one flank surface (14).

A sliding mechanism of the present invention includes a cylinder bore having a thermally sprayed iron-based coating and includes a piston with a piston ring covered with a hard coating composed mainly of carbon.

The thermally sprayed coating has diamond abrasive grains.

An area ratio of the diamond abrasive grains to a surface of the thermally sprayed coating is 0.3 to 1.8%, which enables suppressing wear of the piston ring having the hard coating composed mainly of carbon.