A cylinder of an internal combustion engine, having a cylinder liner and a cylinder piston guided in the cylinder liner The cylinder piston has multiple ring grooves delimited by ring webs and are separated by the ring webs. Each ring grooves receives a compression ring or an oil scraping ring. Each ring groove is delimited by an upper groove flank, a lower groove flank and a groove base, and each piston ring has a lower ring flank, an upper ring flank a ring back and a section which rests against a radially inner running surface of the cylinder liner. A depression is introduced into the lower groove flank of the at least one ring groove or each ring groove which receives a compression ring and/or into the lower ring flank of the piston ring designed as a compression ring.

Provided are an oil ring for an internal combustion engine and a piston assembly including the same, in which the oil ring for an internal combustion engine includes: a compression portion protruding from an upper portion of a body, in close contact with a cylinder inner wall and effectively limiting explosive gas generated in a combustion chamber; a scraper portion protruding from a lower portion of the body, in close contact with the cylinder inner wall and including a nose scraping off oil oversupplied to cylinder inner wall; and an oil suction portion being a space formed between the compression portion and the scraper portion to collect and discharge the oil oversupplied to cylinder inner wall, thereby reducing leakage of high-temperature and high-pressure gas generated in the combustion chamber, and preventing incomplete combustion caused by oil leaked into the combustion chamber.

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.

In this piston ring combination, a second outer peripheral surface, which is the outer peripheral surface of a second ring, has a second protruding surface curved into a convex shape, and a pair of third outer peripheral surfaces, which are the outer peripheral surfaces of a pair of segments, each have a third outer peripheral area in which a third protruding surface is formed, the third protruding surfaces being curved into convex shapes. In at least one of the pair of third outer peripheral surfaces, the peripheral edge on a crank-chamber side is positioned farther outward in the diametrical direction than the peripheral edge on a combustion-chamber side, and a peak of the third protruding surface is positioned nearer to the crank chamber than the center of the third outer peripheral surface.

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 piston assembly for an internal combustion engine includes a cylinder bore and a piston having exactly two ring grooves, a scraper ring positioned in the upper ring groove, and an oil control ring positioned in the lower ring groove. A constant twist occurs in the scraper ring about a rotational center of the cross-section, the constant twist occurring at each cross-sectional location of the scraper ring about the circumference of the ring and between adjacent free ends of the ring. The oil control ring can be of a multi-segmented U-flex design, with a coil spring mounted in a channel thereof. The combination of the two rings leads to improved sealing and oil control so that the piston can be manufactured with only two rings, thus reducing overall weight and cost.

A scraper ring is provided with a plurality of sealing sections on the radially inner circumferential surface, each including a scraping edge, wherein the sealing sections are spaced axially apart from each other by inner circumferential grooves, with at least one recess provided on the circumference of the scraper ring which extends at least partially from a first axial ring end to a second axial ring end and extends at least partially in a direction different from the axial direction of the scraper ring. At least one drainage opening is provided on the outer circumferential surface of the scraper ring, which is connected to at least one inner circumferential groove for removing scraped oil from the inner circumferential grooves.

A combination of piston rings assembled to a piston includes a first compression ring, a second compression ring, a third compression ring and an oil ring. When an axial width of the first compression ring is h1(1), an axial width of the second compression ring is h1(2), an axial width of the third compression ring is h1(3) and an axial width of the oil ring is h1(4), h1(1)≥h1(2) and h1(1)≥h1(3), and when h1(TOTAL)=h1(1)+h1(2)+h1(3)+h1(4), h1(TOTAL)≥3.1 mm.

Provided are an oil ring for an internal combustion engine and a piston assembly including the same, in which the oil ring for an internal combustion engine includes: a compression portion protruding from an upper portion of a body, in close contact with a cylinder inner wall and effectively limiting explosive gas generated in a combustion chamber; a scraper portion protruding from a lower portion of the body, in close contact with the cylinder inner wall and including a nose scraping off oil oversupplied to cylinder inner wall; and an oil suction portion being a space formed between the compression portion and the scraper portion to collect and discharge the oil oversupplied to cylinder inner wall, thereby reducing leakage of high-temperature and high-pressure gas generated in the combustion chamber, and preventing incomplete combustion caused by oil leaked into the combustion chamber.

A three-piece piston oil control ring 2 has an upper, disc-shaped scraping ring 4, a lower, disc-shaped stabilising ring 6, and a circular expander 8 which has projections 10 protruding in the axial direction on an inner face. The circular expander 8 is arranged between the upper scraping ring 4 and the lower stabilising ring 6, wherein the projections 10 each bear inwardly against an inner face 14 of the scraping ring 4 or against an inner face 16 of the stabilising ring 6. An outer radius 18 of the scraping ring 4 is greater than an outer radius 20 of the lower stabilising ring 6, so that there is a radius difference δ between the scraping ring 4 and the stabilising ring 6.