Piston ring

Abstract

A piston ring which is provided with a carbon-based coating which has a low friction property and wear resistance, that is, a piston ring which has a carbon-based coating formed over its sliding surface, in which piston ring, the coating is a multilayer coating comprised of two types of layers having different hardnesses laminated in at least two layers, a hardness difference between the two types of layers is 500 to 1700 HV, a high hardness layer has the same or greater thickness than a low hardness layer, and the coating as a whole has a thickness of 5.0 μm or more. The high hardness layer has a thickness of 5 to 90 nm. The surface on which the coating is formed has a base material roughness of 1.0 μmRz or less.

1 . A piston ring which has a carbon-based coating formed over its sliding surface, in which piston ring, said coating is a multilayer coating comprised of two types of layers having different hardnesses laminated in at least two layers, a hardness difference between said two types of layers is 500 to 1700 HV, a high hardness layer has the same or greater thickness than a low hardness layer, and the coating as a whole has a thickness of 5.0 μm or more. 
     
     
         2 . A piston ring as set forth in  claim 1 , wherein said high hardness layer has a thickness of 5 to 90 nm. 
     
     
         3 . A piston ring as set forth in  claim 1 , wherein the surface on which said coating is formed has a base material roughness of 1.0 μmRz or less. 
     
     
         4 . A piston ring as set forth in  claim 1 , wherein a surface-most layer of said coating is a high hardness layer. 
     
     
         5 . A piston ring as set forth in  claim 1 , wherein a low hardness layer of said coating contains carbon alone or carbon and also Cr or Ti.