Surface treated rocker arm shaft

Abstract

A shaft for a rocker arm assembly is disclosed. The shaft includes a substantially cylindrical outer surface at least a portion of which defines a bearing surface thereon and an interior core portion located radially inward of the bearing surface. The bearing surface has a hardness greater than that of the core portion, for providing wear resistance and deterring crack initiation and propagation.

1 . A shaft for a rocker arm assembly, said shaft comprising:
 a substantially cylindrical outer surface at least a portion of which defines a bearing surface thereon and an interior core portion located radially inward of said bearing surface;   said bearing surface being configured to rotatably engage a mating surface positioned in a receiving bore of a rocker arm; and   said bearing surface having a hardness greater than that of said core portion, for providing wear resistance and deterring crack initiation and propagation.   
     
     
         2 . The shaft of  claim 1 , wherein said bearing surface has a Rockwell C scale hardness of at least 59. 
     
     
         3 . The shaft  claim 1 , wherein a concentration of at least one of carbon and nitrogen at said bearing surface and extending radially inward therefrom to an effective case depth of about 0.063 inches, exceeds the concentration of at least one of said carbon and nitrogen in said core portion. 
     
     
         4 . The shaft of  claim 1 , wherein portions of said shaft outside of an area wherein said bearing surface and said mating surface engage one another, are masked prior to surface hardening said shaft to prevent surface hardening of said masked area such that said masked area has a hardness about equal to that of said core portion. 
     
     
         5 . The shaft of  claim 3 , wherein said bearing surface has an arithmetic mean roughness of less than about 2.5 micro inches. 
     
     
         6 . The shaft of  claim 1 , wherein said bearing surface is isotropic. 
     
     
         7 . The shaft of  claim 1 , wherein said bearing surface has a specular brightness. 
     
     
         8 . A shaft for a rocker arm assembly, said shaft comprising:
 a substantially cylindrical outer surface at least a portion of which defines a bearing surface thereon;   at least a portion of said bearing surface having an arithmetic mean roughness of less than about 2.5 micro inches, for providing wear resistance and deterring crack initiation and propagation.   
     
     
         9 . The shaft of  claim 8 , wherein said bearing surface is isotropic. 
     
     
         10 . The shaft of  claim 8 , wherein said bearing surface has a specular brightness. 
     
     
         11 . The shaft of  claim 8 , wherein said outer surface defines an interior core portion located radially inward of said bearing surface; and
 at least a portion of said bearing surface having a hardness greater than that of said core portion, for providing wear resistance and deterring crack initiation and propagation.   
     
     
         12 . The shaft of  claim 11 , wherein said bearing surface has a Rockwell C scale hardness of at least 59. 
     
     
         13 . The shaft  claim 10 , wherein a concentration of at least one of carbon and nitrogen at said bearing surface and extending radially inward therefrom to an effective case depth of about 0.063 inches, exceeds the concentration of at least one of said carbon and nitrogen in said core portion. 
     
     
         14 . The shaft of  claim 8 , wherein portions of said shaft are masked prior to treatment of said shaft to prevent said at least a portion of said bearing surface from having an arithmetic mean roughness of less than about 2.5 micro inches. 
     
     
         15 . A rocker arm assembly comprising:
 a substantially cylindrical shaft having an outer surface at least a portion of which defines a bearing surface thereon and an interior core portion located radially inward of said bearing surface;   a rocker arm having a receiving bore extending therethrough;   said bearing surface being configured to rotatably engage a mating surface positioned in said receiving bore; and   said bearing surface having a hardness greater than that of said core portion, for providing wear resistance and deterring crack initiation and propagation.   
     
     
         16 . The rocker arm assembly of  claim 15 , wherein a concentration of at least one of carbon and nitrogen at said bearing surface and extending radially inward therefrom to an effective case depth of about 0.063 inches, exceeds the concentration of at least one of said carbon and nitrogen in said core portion. 
     
     
         17 . The rocker arm assembly of  claim 16 , wherein said bearing surface has an arithmetic mean roughness of less than about 2.5 micro inches.