Piston ring arrangement (40) with a piston ring (50) encircling a main axis (X), the piston ring (50) having a sealing surface (58) directed radially outward and a contact surface (55) directed radially outward, the sealing surface (58) being radially outside of the contact surface (55). To improve the service life of piston rings for reciprocating compressors, the piston ring arrangement (40) has a retaining ring (70) encircling the main axis (X) with a retaining surface (72) directed radially inward, the piston ring (50) and the retaining ring (70) being situated such that the retaining surface (72) and the contact surface (55) are adjacent in the radial direction.

A sliding element for an internal combustion engine may include a base material having an annular external surface. The external surface may include a bonding layer, a first layer of coating, and a second layer of coating sequentially disposed thereon. The first layer of coating and the second layer of coating may include hard amorphous carbon (DLC) of a combined matrix having a plurality of sp3/sp2 bonds. The first layer of coating may include 45% sp3 bonds or less and may have a thickness of at least 10 micrometers. The second layer of coating may include at least 55% sp3 bonds and may have a thickness of at least 3 micrometers.

A sliding element for an internal combustion engine may include a base material having an annular external surface. The external surface may include a bonding layer, a first layer of coating, and a second layer of coating sequentially disposed thereon. The first layer of coating and the second layer of coating may include hard amorphous carbon (DLC) of a combined matrix having a plurality of sp3/sp2 bonds. The first layer of coating may include 45% sp3 bonds or less and may have a thickness of at least 10 micrometers. The second layer of coating may include at least 55% sp3 bonds and may have a thickness of at least 3 micrometers.

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 piston ring assembly includes an inner ring, a first outer ring, and a second outer ring. The inner ring has an outer surface and an inner surface that extends between a first inner ring face and a second inner ring face. The first outer ring has a first outer ring outer surface disposed opposite a first outer ring inner surface, each extends between a first outer ring face and a first outer ring second face. The first outer ring inner surface engages the outer surface. The second outer ring has a second outer ring outer surface disposed opposite a second outer ring inner surface, each extends between a second outer ring first face and a second outer ring second face.

A piston ring assembly includes an inner ring, a first outer ring, and a second outer ring. The inner ring has an outer surface and an inner surface that extends between a first inner ring face and a second inner ring face. The first outer ring has a first outer ring outer surface disposed opposite a first outer ring inner surface, each extends between a first outer ring face and a first outer ring second face. The first outer ring inner surface engages the outer surface. The second outer ring has a second outer ring outer surface disposed opposite a second outer ring inner surface, each extends between a second outer ring first face and a second outer ring second face.

A piston of a cylinder of an internal combustion engine includes: a piston skirt; a grooved ring belt on a first axial side of the piston skirt, the ring belt grooves being limited by, and separated from one another by, ring lands, the ring grooves for receiving a piston ring; and an oil collection channel between the piston skirt and the ring belt. The oil collection channel has a greater depth than in the circumferential position of a coupling side of the piston and/or in the circumferential position of a coupling opposite side of the piston. The oil collection channel has a gradient, the gradient emanating from an axial depth in a region of the coupling side and/or of the coupling opposite side in the direction of the axial depth in the region of the pressure side and/or of the pressure opposite side.

A piston of a cylinder of an internal combustion engine includes: a piston skirt; a grooved ring belt on a first axial side of the piston skirt, the ring belt grooves being limited by, and separated from one another by, ring lands, the ring grooves for receiving a piston ring; and an oil collection channel between the piston skirt and the ring belt. The oil collection channel has a greater depth than in the circumferential position of a coupling side of the piston and/or in the circumferential position of a coupling opposite side of the piston. The oil collection channel has a gradient, the gradient emanating from an axial depth in a region of the coupling side and/or of the coupling opposite side in the direction of the axial depth in the region of the pressure side and/or of the pressure opposite side.

A guide ring for a pump element of a hydraulic unit of a vehicle brake system is configured to guide a pump piston in a pump housing when the pump piston is displaced along the axis thereof in the pump housing. On the inner side of the guide ring facing the pump piston, the guide ring includes a first step that has a first inner diameter and a second inner diameter.