Piston ring

Abstract

The second compression ring is formed such that the outer peripheral surface shape has a tapered face, and the radial cross-sectional shape is a rectangular ring, a scraper ring, or a Napier ring, and has a piston ring base and a hard film provided at least on an outer peripheral sliding surface thereof. The piston ring base is composed of a low-alloy steel or carbon steel having a Vickers hardness of Hv 350 Hv 550. The outer peripheral sliding surface is formed so that the axial length is from 0.01 to 0.30 mm between the outer edge end part of the tapered outer peripheral sliding surface and an imaginary line contacting with a lower end surface where a curved surface having a diameter that decreases gradually inward from the outer edge end part toward the lower end in the axial direction is parallel to a ring underside.

1 - 4 . (canceled) 
     
     
         5 . A piston ring used as a second pressure ring for an internal combustion engine, the piston ring having the outer peripheral surface shape that is tapered face, and the radial cross-sectional shape that is one of a rectangular ring, a scraper ring, and a Napier ring, the piston ring comprising:
 a piston ring base; and   a hard film provided at least on an outer peripheral sliding surface thereof, wherein   the piston ring base is composed of a low-alloy steel or carbon steel having a Vickers hardness (Hv) of 350 to 550,   the outer peripheral sliding surface is formed in a tapered shape gradually expanding outward from the upper end of the piston ring base toward the lower end thereof, and is formed so that the axial length is from 0.01 to 0.30 mm between the outer edge end part of the tapered outer peripheral sliding surface and an imaginary line contacting with a lower end surface or a lower end part where a curved surface having a diameter that decreases gradually inward from the outer edge end part toward the lower end in the axial direction is parallel to a ring underside, and   the hard film is composed of an ion plating coat having a film thickness of from 5 μm to 30 μm, a porosity of from 0.5% to 1.5% and a Vickers hardness (Hv) of from 800 to 2300, the hard film being formed on the surface of the piston ring base.   
     
     
         6 . The piston ring according to  claim 5 , wherein a Cr film or Cr—B film is formed as a base film of the hard film. 
     
     
         7 . The piston ring according to  claim 5 , wherein a hard carbon film is formed on the hard film. 
     
     
         8 . The piston ring according to  claim 6 , wherein a hard carbon film is formed on the hard film. 
     
     
         9 . The piston ring according to  claim 5 , wherein the piston ring base has a surface that is irradiated with a metal ion which is an ionized metal target while being maintained at a temperature at which decrease in the hardness of the piston ring base does not occur is cleaned. 
     
     
         10 . The piston ring according to  claim 6 , wherein the piston ring base has a surface that is irradiated with a metal ion which is an ionized metal target while being maintained at a temperature at which decrease in the hardness of the piston ring base does not occur is cleaned. 
     
     
         11 . The piston ring according to  claim 7 , wherein the piston ring base has a surface that is irradiated with a metal ion which is an ionized metal target while being maintained at a temperature at which decrease in the hardness of the piston ring base does not occur is cleaned. 
     
     
         12 . The piston ring according to  claim 8 , wherein the piston ring base has a surface that is irradiated with a metal ion which is an ionized metal target while being maintained at a temperature at which decrease in the hardness of the piston ring base does not occur is cleaned.