# US 2014/0197602 A1 · Piston ring with localized nitrided coating > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2014/0197602 A1 - Document ID: US20140197602A1 - Status: Published application - Kind: A1 - Application number: 13/741,814 - Filed: 2013-01-15 - Published: 2014-07-17 - Earliest claimed: 2013-01-15 - Assignees: Mahle International GmbH - Applicants: Mahle International GmbH - Inventors: John C. Lahrman - Web page: https://patentgrep.com/patent/US20140197602A1 ## CPC - F16J 9/26: characterised by the use of particular materials - F16J 9/20: Rings with special cross-section (L-section rings F16J9/02); Oil-scraping rings {(F16J9/06 takes precedence)} - F16J: PISTONS {(specially adapted for dampers F16F9/32)}; CYLINDERS; SEALINGS ## Abstract A piston ring comprising upper face, a lower face, an inner perimeter wall, and an outer perimeter wall that extends around the piston ring from the upper face to the lower face, where the outer perimeter wall has upper corner region disposed adjacent the upper face, a lower corner region disposed adjacent the lower face, and a band of a nitrided conversion layer extending between the upper corner region and the lower corner region, and where a PVD nitride layer is disposed on the upper corner region and on the lower corner region. ## Claims ### Claim 1 A piston ring comprising: an upper face; a lower face; an inner perimeter wall; and an outer perimeter wall that extends around the piston ring from the upper face to the lower face; wherein the outer perimeter wall has upper corner region disposed adjacent the upper face, a lower corner region disposed adjacent the lower face, and a band of a nitrided conversion layer extending along the outer perimeter wall between the upper corner region and the lower corner region, wherein the nitrided conversion layer penetrates an exterior layer of the outer perimeter wall; and wherein the upper corner region and the lower corner regions have outer surfaces that coincide with the outer perimeter wall. ### Claim 2 (depends on 1) The piston ring of claim 1, wherein the piston ring is made from stainless steel. ### Claim 3 (depends on 1) The piston ring of claim 1, wherein the nitrided conversion layer has an exterior surface that is generally coplanar with the surfaces of the upper corner region and the lower corner region that coincide with the outer perimeter wall. ### Claim 4 (depends on 1) The piston ring of claim 1, wherein a PVD nitride layer is formed by physical vapor deposition and is disposed on the upper corner region and on the lower corner region. ### Claim 5 (depends on 4) The piston ring of claim 4, wherein the PVD nitride layer is one of chromium nitride and titanium nitride. ### Claim 6 (depends on 4) The piston ring of claim 4, wherein the PVD nitride layer is further disposed on the nitrided conversion layer in the outer perimeter wall. ### Claim 7 (depends on 6) The piston ring of claim 6, wherein the PVD nitride layer has a surface profile of one of a symmetric barrel profile or an asymmetric barrel profile. ### Claim 8 (depends on 4) The piston ring of claim 4, wherein the PVD nitride layer extends into a portion of at least one of the upper face and the lower face. ### Claim 9 (depends on 6) The piston ring of claim 6, wherein the PVD nitride layer is generally thinner than the nitrided conversion layer in the outer perimeter wall. ### Claim 10 A method of making a crack-resistant piston ring, comprising: providing a piston ring, wherein the piston ring has an upper face, a lower face, an inner perimeter wall, and an outer perimeter wall that extends around the piston ring from the upper face to the lower face; the outer perimeter wall having upper corner region disposed adjacent the upper face, a lower corner region disposed adjacent the lower face, and an annular cavity in the central portion of the outer perimeter wall extending between the upper corner region and the lower corner region along the length of the outer perimeter wall; forming a nitrided conversion layer penetrating an exterior layer of the piston ring; performing a grinding process on the piston ring, thereby removing some of the nitrided conversion layer; and depositing a PVD nitride layer on the outer perimeter wall of the piston ring. ### Claim 11 (depends on 10) The method of claim 10, wherein the piston ring is stainless steel. ### Claim 12 (depends on 10) The method of claim 10, further comprising performing a keystone grind on the upper face and the lower face of the piston ring. ### Claim 13 (depends on 10) The method of claim 10, wherein performing the grinding process includes removing the nitrided conversion layer from the upper corner region and the lower corner region, thereby exposing the underlying piston ring. ### Claim 14 (depends on 10) The method of claim 10, wherein the PVD nitride layer is one of chromium nitride and titanium nitride. ### Claim 15 (depends on 10) The method of claim 10, wherein depositing the PVD nitride layer on the surface includes depositing the PVD nitride layer on the nitrided conversion layer disposed in the central portion of the piston ring between the upper and the lower corner regions, and on the underlying piston ring at the upper corner region and the lower corner regions of the piston ring. ### Claim 16 (depends on 10) The method of claim 10, further comprising forming one of a symmetric barrel profile and an asymmetric barrel profile on the PVD nitride layer. ### Claim 17 A piston ring comprising: upper face; a lower face; an inner perimeter wall; and an outer perimeter wall that extends around the piston ring from the upper face to the lower face, the outer perimeter wall comprising an upper corner region disposed adjacent the upper face along the length of the outer perimeter wall and having an outer surface that coincides with the outer perimeter wall, a lower corner region disposed adjacent the lower face along the length of the outer perimeter wall and having an outer surface that coincides with the outer perimeter wall, and a band of nitrided conversion layer disposed between the upper corner region and the lower corner region, the nitrided conversion layer penetrating an exterior layer of the outer perimeter wall, the band of nitrided conversion layer extending along the length of the outer perimeter wall and having an outer surface that is generally coplanar with the outer surfaces of the upper and lower corner regions; and a PVD nitride layer disposed on and extending along the length of the outer perimeter wall from the upper face to the lower face, and covering the outer surfaces of the upper and lower corner regions and the nitrided conversion layer. ### Claim 18 (depends on 10) The method of claim 10, wherein forming the nitrided conversion layer includes exposing the piston ring to a nitrogenous gas. ### Claim 19 (depends on 13) The method of claim 13, wherein performing the grinding process includes removing an outer layer of the nitrided conversion layer from the annular cavity thereby forming a band of nitrided conversion layer between the upper corner region and the lower corner region, and wherein an exterior surface of the band is generally coplanar with surfaces of the upper corner region and the lower corner region.