A piston ring that is pre-treated by grit blasting to a defined roughness, followed by PVD coating with a metal nitride to a thickness of at least 10 m, leaving peaks and valleys in the coated piston ring. The coated piston ring is then lapped to remove the peaks without penetrating the coating, so that valleys and plateaus remain in the coated surface. The resulting piston ring exhibits superior coating retention due to the increased surface area created by the grit blasting, and yet also superior performance, as the cavities remaining increase the porosity of the coating and thus enhance the lubrication of the ring.

A piston ring that is pre-treated by grit blasting to a defined roughness, followed by PVD coating with a metal nitride to a thickness of at least 10 m, leaving peaks and valleys in the coated piston ring. The coated piston ring is then lapped to remove the peaks without penetrating the coating, so that valleys and plateaus remain in the coated surface. The resulting piston ring exhibits superior coating retention due to the increased surface area created by the grit blasting, and yet also superior performance, as the cavities remaining increase the porosity of the coating and thus enhance the lubrication of the ring.

A piston ring is made from a copper-beryllium alloy. This material permits the top compression ring of a piston to be moved closer to the piston crown, reducing crevice volume and reducing the tendency for pre-ignition. Ignition timing advance can be realized by installing the rings and letting the ECU advance the timing as the sensors allow, increasing efficiency. Also, shorter pistons and longer connecting rods are possible. The shorter pistons reduces the reciprocated mass in the engine and the longer connecting rods reduce the frictional loss caused by radial forces pushing the piston against the liner. Both reducing volume and tendency for pre-ignition increase engine efficiency.

A piston ring is made from a copper-beryllium alloy. This material permits the top compression ring of a piston to be moved closer to the piston crown, reducing crevice volume and reducing the tendency for pre-ignition. Ignition timing advance can be realized by installing the rings and letting the ECU advance the timing as the sensors allow, increasing efficiency. Also, shorter pistons and longer connecting rods are possible. The shorter pistons reduces the reciprocated mass in the engine and the longer connecting rods reduce the frictional loss caused by radial forces pushing the piston against the liner. Both reducing volume and tendency for pre-ignition increase engine efficiency.

To provide a piston ring having a hard laminate coating having excellent scuffing resistance, wear resistance and peeling resistance, which can be used in an environment of high mechanical and thermal load in engines, the piston ring is provided on its outer peripheral sliding surface with a CrN-type hard coating as thick as 10-60 m and comprising a CrN/CrCN laminate coating having hardness Hv of 1000 or more and residual compression stress of 1500 MPa or less, a laminate unit composed of a CrN layer and a CrCN layer being as thick as 30 nm or more; the CrN/CrCN laminate coating being formed by alternately laminating CrN layers and CrCN layers containing C dissolved in CrN by ion plating.

To provide a piston ring having a hard laminate coating having excellent scuffing resistance, wear resistance and peeling resistance, which can be used in an environment of high mechanical and thermal load in engines, the piston ring is provided on its outer peripheral sliding surface with a CrN-type hard coating as thick as 10-60 m and comprising a CrN/CrCN laminate coating having hardness Hv of 1000 or more and residual compression stress of 1500 MPa or less, a laminate unit composed of a CrN layer and a CrCN layer being as thick as 30 nm or more; the CrN/CrCN laminate coating being formed by alternately laminating CrN layers and CrCN layers containing C dissolved in CrN by ion plating.

A compression ring, has a ring running surface (2) on a first butt end region, a ring running surface (2) on a second butt end region, a ring inner surface (4), a top ring flank surface (6) and a bottom ring flank surface (8), wherein the ring has overlapping first and second butt end regions. The first butt end region has at least one protrusion (10) in the circumferential direction, and the second butt end region has at least one recess (12) in the circumferential direction. The at least one protrusion (10) forms at least one axial and/or radial overlap surface, and the at least one recess (12) forms at least one parallel surface, which lies at least partially opposite to the axial and/or radial overlap surface in order to shift parallel to one another in response to a change of the butt play. At least one of the surfaces, which can be shifted parallel to one another, is provided with an axial wear element (14) and/or with a radial wear element (14).

A method of coating all surfaces of a plurality of piston rings in a single run by a chemical vapor deposition (CVD) process is provided. The method can include providing a coil formed of an iron-based material; heating the coil; and depositing a coating on all surfaces of the coil during a single continuous period of time, without having to move the coil during the CVD process. The coil is maintained in a fixed position during the depositing step. The method next includes splitting the coil into a plurality of separate coated piston rings. Alternatively, the method can include providing a plurality of stacked keystone piston ring bodies; and disposing a cylinder around the stack to maintain the keystone piston ring bodies in position while depositing the CVD coating on all surfaces of the keystone piston ring bodies during the single coating run.

A piston ring includes a generally circular open ring having a generally cylindrical outer diameter surface and an inner diameter surface having a plurality of radially outwardly extending arcuate recesses. A method of making the piston ring includes extruding a rectangle cross-section steel wire to include at least two recesses in a side edge thereof. The extruded steel wire is wound in a ring-shape with the arcuate recesses being on an inner diameter surface of the wound ring.

Exemplary piston rings are disclosed, comprising a base portion formed of a metallic material, and an outer contact surface extending between opposing side faces of the piston ring. The piston ring may include a coating layer applied to the outer contact surface, with the coating layer including an inner layer and an outer layer. Exemplary methods of making a piston ring are also disclosed, comprising providing a base portion formed of a metallic material, applying an inner layer to an outer surface of the base portion, and applying an outer layer on top of the inner layer.