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.

A process for obtaining a piston ring may include providing a piston ring of an internal combustion engine and submitting a surface of the piston ring to a laser surface heat treatment. The surface may be a sliding surface of the piston ring. The piston ring may be a one piece piston ring and/or a scrapper ring.

A piston ring has a running surface, an inner surface, a lower ring flank, and an upper ring flank. A recess, extending across the perimeter in the shape of an internal angle, is located at the transition between the inner surface and the upper ring flank. The recess defines a conical first surface and a conical second surface at the piston ring. The first surface lies farther outward, when viewed in the radial direction, and farther above, when viewed in the axial direction, than the second surface. In an axial cross section, a first angle between the axial direction and the first surface lies in the range between 10° and 50°, and a second angle between the radial direction and the second surface lies in the range between 5° and 30°. A piston having a piston ring groove includes a projection on the groove bottom. A combination made from an above-mentioned piston ring and an above-mentioned piston are adapted to one another, so that the projection projects into the recess.

A piston ring has a running surface, an inner surface, a lower ring flank, and an upper ring flank. A recess, extending across the perimeter in the shape of an internal angle, is located at the transition between the inner surface and the upper ring flank. The recess defines a conical first surface and a conical second surface at the piston ring. The first surface lies farther outward, when viewed in the radial direction, and farther above, when viewed in the axial direction, than the second surface. In an axial cross section, a first angle between the axial direction and the first surface lies in the range between 10° and 50°, and a second angle between the radial direction and the second surface lies in the range between 5° and 30°. A piston having a piston ring groove includes a projection on the groove bottom. A combination made from an above-mentioned piston ring and an above-mentioned piston are adapted to one another, so that the projection projects into the recess.

A piston for an internal combustion engine may include a ring belt, a groove, and an additional groove. The ring belt may extend along an axial direction. The groove may be arranged on the outer circumference of the ring belt and may be configured to receive an oil scraper ring. The additional groove may be arranged on the outer circumference spaced apart from the groove with respect to the axial direction. The additional groove may include a first groove side axially facing away from the groove and a second groove side axially facing the groove. The first groove side may include an axial step.

A piston ring includes a body portion presenting a running surface, and a spring member disposed between the body portion and a ring groove of a piston. A running surface of the piston ring presents an upper rail, a lower rail, and a fulcrum disposed between the rails and each extending radially outwardly. An outermost tip of the fulcrum is disposed radially outwardly relative to an outermost surface of the rails, and the running surface presents a convex shape along the fulcrum. The fulcrum contacts an oil film applied to a cylinder wall as the piston reciprocates along the cylinder wall. The spring member presses the body portion of the piston ring toward the cylinder wall and causes the body portion to pivot about the fulcrum to provide for improved control of the oil film, less friction, and reduced oil consumption.

An oil ring to be attached to a ring groove of a piston for an engine is provided. The oil ring includes two annular ring bodies having a common axis and arranged in tandem, and an expander for biasing the ring bodies radially outward. A sliding surface is formed at an outer circumference of each ring body to bulge radially outward and slides on a cylinder inner circumferential surface. The sliding surface of one of the ring bodies has a tip portion and first and second curved surfaces. In cross sections of the first and second curved surfaces, the first and second curved surfaces are connected while tangent lines to the cross sections at the tip portion align with each other, and when positional change rates are compared between points on the first and second curved surfaces, a change rate of the first curved surface is lower.

When a laminated gasket product is demolded from a mold in production thereof by a conventional production process, the gasket product is rubbed against the mold and, therefore, minute scratches are formed on a surface of the gasket product. The minute scratches may impair the reliable sealability of a liquid drug. A method for producing a gasket (13) for use in a prefilled syringe (10) includes the steps of: preparing a gasket forming mold; molding a gasket (13) in the mold, the gasket having a surface laminated with a lamination film (15) and including a circumferential surface portion (17); demolding the gasket (13) from the mold, and then simultaneously forming a groove (22) and a projection (24) each extending circumferentially of the gasket in a portion of the lamination film (15) present in the circumferential surface portion (17) of the gasket.

When a laminated gasket product is demolded from a mold in production thereof by a conventional production process, the gasket product is rubbed against the mold and, therefore, minute scratches are formed on a surface of the gasket product. The minute scratches may impair the reliable sealability of a liquid drug. A method for producing a gasket (13) for use in a prefilled syringe (10) includes the steps of: preparing a gasket forming mold; molding a gasket (13) in the mold, the gasket having a surface laminated with a lamination film (15) and including a circumferential surface portion (17); demolding the gasket (13) from the mold, and then simultaneously forming a groove (22) and a projection (24) each extending circumferentially of the gasket in a portion of the lamination film (15) present in the circumferential surface portion (17) of the gasket.

A piston for an internal combustion engine includes a cylindrical piston body defining a longitudinal axis and having a top end and an outer cylindrical surface. A first piston ring groove is formed in the outer cylindrical surface and includes a groove root, an upper surface and a lower surface. The groove root has a variable depth about a circumference of the cylindrical piston body.