A multi-piece oil ring includes an oil ring main member in which two rails are connected together by a columnar part and which has a roughly I-shaped cross section; and a coil expander disposed in an inner circumferential groove formed on the inner circumferential surface of the columnar. Each rail in the oil ring main member possesses a sliding section protuberance whose tip possesses a jutting portion. The axial length of the jutting portion is 0.02-0.18 mm. The change rate of the axial length of the individual jutting portion is in the range of 0 to 80% at least in a region of from its sliding surface to be faced to a cylinder, which is positioned at the tip of the jutting portion, to a position of 0.03 mm away from the aforementioned sliding surface in the radial direction of the oil ring main member.

There is provided a seal device having a seal ring structure assemblable without lowering the assembling efficiency of CVT, and free from oil leakage when an oil pump is not operated with an engine stopped, namely when oil pressure is not applied to the seal ring, which comprises a combined seal ring comprising an endless resin ring having an outer peripheral surface in slidable contact with an inner peripheral surface of an outer member, and a coil expander pushing the resin ring toward its outer peripheral surface and side surface, the coil expander being arranged in a corner recess portion of the resin ring between its pressure-receiving side surface and its inner peripheral surface, and an inner peripheral side of the combined seal ring being separate from a bottom of the seal ring groove.

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).

An oil control ring comprises: an oil ring having a pair of land parts arranged in a sliding direction and connected to each other by a web part; and a coil expander that biases the oil ring toward the outer circumferential side in the radial direction. The web part of the oil ring is provided with a plurality of window holes. In the axial cross-sectional view of the largest opening portion of the window hole in the axial direction of the oil ring, a width H1 in the sliding direction of the oil ring and a length L1 of a combustion chamber-side non-window hole part, which excludes the window hole, in the outer circumferential surface of the web part, satisfy the condition of 0.15>L1/H10.

A piston for an internal combustion engine having an improved oil control ring is provided. The piston has a piston body providing an upper combustion surface and an annular outer wall depending therefrom. A ring belt region including a plurality of ring grooves is formed in the annular outer wall. A first compression ring is disposed in one of the ring grooves and the oil control ring is disposed in another of the ring grooves. The oil control ring has generally parallel, planar upper and lower surfaces, with the upper and lower surfaces having an annular groove recessed therein. A through opening can be formed to bring the annular grooves into fluid communication with one another. The annular grooves collect oil scraped from a cylinder wall and return oil to the crank sump and reduce the contact area between the oil control ring and the wall of the ring groove.

A piston ring for a piston, the piston ring having a circumferential surface configured to engage an inner surface of a cylinder, the inner surface having at least one recess indented into the inner surface, the engagement of the circumferential surface of the piston ring with the inner surface of the cylinder defining a contact zone therebetween, wherein the circumferential surface of the piston ring is configured such that the ratio of the dimension of the contact zone the direction of travel of the piston to the dimension of the recess in the direction of travel of the piston is in the range of approximately 5:1 to 5:3.

An oil ring is a multi-piece-type oil ring provided on a piston of an internal combustion engine including a ring body having a rail, and an expander. In the oil ring, the rail of the ring body is provided with a film formed by physical vapor deposition. An outer peripheral face of the rail formed by the film includes: an actual land face formed to have a strip shape extending in a circumferential direction and abutting against and sliding on an inner wall face of a cylinder of the internal combustion engine; and an inclined face continuing from an edge of the actual land face in an axial direction to an outside and having a larger distance from the inner wall face on a further outside in the axial direction. The inclined face includes a face obtained by polishing or grinding a surface of the film along the circumferential direction.

An oil control ring includes: a main body portion having an annular shape, that includes an inner peripheral surface and an outer peripheral surface, and one side surface and an other side surface; and a coil expander installed along the inner peripheral surface. The main body portion includes a pair of first rail portion and second rail portion each having an annular shape, and a pillar portion connecting the first rail portion and the second rail portion. The outer peripheral surfaces of the first rail portion and the second rail portion each include a protruding surface having a cross-sectional shape protruding convexly outward in a radial direction. The protruding surface is an arcuate surface having a radius of curvature of 0.30 mm or less in a sliding contact region including a vertex that is a radially outermost point of the first rail portion or the second rail portion.