Provided is a lubricating oil composition to be used in an internal combustion engine having a sliding mechanism including a piston ring and a liner, the lubricating oil composition including: a base oil; (A) a poly(meth)acrylate; and (B) an organic molybdenum compound, in which: (A) the poly(meth)acrylate contains a polymer (A1) including a repeating unit derived from a (meth)acrylate represented by the following formula (1) and having a mass-average molecular weight of from 1,000 to 500,000; and a content of (B) the organic molybdenum compound in a total amount of the composition is from 0.01 mass % to 0.2 mass % in terms of a molybdenum atom: wherein R.sup.1 represents a hydrogen atom or a methyl group, and X represents a hydrogen atom, a hydrocarbon group having 1 to 60 carbon atoms, or a functional group-containing hydrocarbon group having 1 to 60 carbon atoms.

Provided is a lubricating oil composition to be used in an internal combustion engine having a sliding mechanism including a piston ring and a liner, the lubricating oil composition including: a base oil; (A) a poly(meth)acrylate; and (B) an organic molybdenum compound, in which: (A) the poly(meth)acrylate contains a polymer (A1) including a repeating unit derived from a (meth)acrylate represented by the following formula (1) and having a mass-average molecular weight of from 1,000 to 500,000; and a content of (B) the organic molybdenum compound in a total amount of the composition is from 0.01 mass % to 0.2 mass % in terms of a molybdenum atom: wherein R.sup.1 represents a hydrogen atom or a methyl group, and X represents a hydrogen atom, a hydrocarbon group having 1 to 60 carbon atoms, or a functional group-containing hydrocarbon group having 1 to 60 carbon atoms.

To provide a wire for a taper-faced compression ring, which can be provided with a running-in surface (contact surface) uniformly and rapidly in the production process of the taper-faced compression ring, a surface of the wire corresponding to an outer peripheral surface of the ring is provided with adjacent outward inclined first and second tapered portions, the inclination angle θ2 of the second tapered portion being larger than the inclination angle θ1 of the first tapered portion, and an outer end of the second tapered portion being located radially outward than an outer end of the first tapered portion by 0.005-0.05 mm. A long-life taper-faced compression ring with reduced friction and improved fuel efficiency is formed by the above wire, the second tapered portion having a lapped surface located radially outward than an outer end of the first tapered portion by 0.001-0.048 mm.

To provide a wire for a taper-faced compression ring, which can be provided with a running-in surface (contact surface) uniformly and rapidly in the production process of the taper-faced compression ring, a surface of the wire corresponding to an outer peripheral surface of the ring is provided with adjacent outward inclined first and second tapered portions, the inclination angle θ2 of the second tapered portion being larger than the inclination angle θ1 of the first tapered portion, and an outer end of the second tapered portion being located radially outward than an outer end of the first tapered portion by 0.005-0.05 mm. A long-life taper-faced compression ring with reduced friction and improved fuel efficiency is formed by the above wire, the second tapered portion having a lapped surface located radially outward than an outer end of the first tapered portion by 0.001-0.048 mm.

A fluid actuator includes housing defining a cylinder bore and first and second fluid passages. A circumferential detent groove extends into the housing from the cylinder bore. The cylinder bore receives a piston having a top face and a skirt in sliding engagement. A circumferential detent ring groove extends radially inwardly into the skirt. The detent ring groove has a first portion of a first depth and a second portion of a second, greater depth. An o-ring is at least partially received in the second portion. A wear ring is at least partially received in the first portion and overlies the o-ring. The o-ring biases the wear ring outwardly of the detent ring so that the wear ring may be selectively engaged with the detent groove.

A fluid actuator includes housing defining a cylinder bore and first and second fluid passages. A circumferential detent groove extends into the housing from the cylinder bore. The cylinder bore receives a piston having a top face and a skirt in sliding engagement. A circumferential detent ring groove extends radially inwardly into the skirt. The detent ring groove has a first portion of a first depth and a second portion of a second, greater depth. An o-ring is at least partially received in the second portion. A wear ring is at least partially received in the first portion and overlies the o-ring. The o-ring biases the wear ring outwardly of the detent ring so that the wear ring may be selectively engaged with the detent groove.

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.

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 scraper ring for a piston includes a top surface, a bottom surface, an inner surface, and an outer surface. The top surface has a first planar portion and a first angled portion. The bottom surface has a second planar portion and a second angled portion. The second angled portion is configured to slidably contact the first angled portion to adjust a diameter of the scraper ring. The inner surface connects the top surface to the bottom surface. The outer surface is opposite to the top surface and is configured to form 360 degrees of contact with a wall of a cylinder to substantially limit an amount of oil entering a combustion chamber of the cylinder.

A method for producing a piston ring for a cylinder that moves in a sliding direction includes providing a piston ring base material having an upper surface, a lower surface and an outer circumferential surface having a first recess between the upper surface and the lower surface, forming a hard film in the first recess and on a cylindrical surface at a predetermined thickness, and removing, by performing a polishing process on the sliding surface, the hard film formed on the cylindrical surface and a part of the piston ring base material disposed adjacent to the removed hard film, to form a second recess. The second recess is formed by removing an area of the removed part of the piston ring base material as a result of polishing the sliding surface due to a difference in the hardness of the hard film and the piston ring base material.