Drive Cam and Valve Operating System in Engine

Abstract

Provided are a drive cam having an improved wear resistant sliding surface that gives the drive cam enhanced durability and a valve operating system in an engine with such a drive cam. The drive cam of the present invention, made of a nitriding steel, has on its sliding surface, a hardened surface formed by nitrocarburizing wherein the hardened layer lies on top of the sliding surface. It is preferred that the driven mechanism used in combination with the drive cam has, in its sliding surface against which the drive cam slides, a chrome-plated layer and thereon a diamond-like carbon coating.

1 . A drive cam having a sliding surface and which drive cam rotates in association with rotation of a crank shaft in a valve operating system in an engine, wherein said drive cam comprises a nitriding steel and wherein said drive cam has on said sliding surface a hardened layer formed by nitrocarburizing, said hardened layer lying on top of said sliding surface. 
     
     
         2 . The drive cam as set forth in  claim 1 , wherein said drive cam is manufactured such that subsequently to forming said hardened layer and a compound layer on said sliding surface by nitrocarburizing, said compound layer is removed. 
     
     
         3 . The drive cam as set forth in  claim 1 , wherein said hardened layer is a layer having a Vickers hardness of 550HV100gf or greater and a thickness in a range of 100 to 300 micrometers. 
     
     
         4 . The drive cam as set forth in  claim 1 , wherein said nitriding steel is a nitriding steel with a bainite structure formed therein. 
     
     
         5 . A valve operating system in an engine, said valve operating system comprising:
 a drive cam as set forth in  claim 1 ; and   a driven mechanism having a sliding surface in contact with said sliding surface of said drive cam and which driven mechanism is driven by sliding against said drive cam.   
     
     
         6 . The valve operating system as set forth in  claim 5 , wherein there are formed in said sliding surface of said driven mechanism a chrome-plated layer and thereon a diamond-like carbon coating. 
     
     
         7 . The valve operating system as set forth in  claim 6 , wherein said chrome-plated layer is formed by such polishing that it has a surface roughness (Rz) of 0.5 micrometers or smaller and that its period of corrugation of 0.1 micrometers or greater is 50 micrometers or greater. 
     
     
         8 . The valve operating system as set forth in  claim 6 , wherein said diamond-like carbon coating is a metal-containing diamond-like carbon coating. 
     
     
         9 . The valve operating system as set forth in  claim 5 , wherein said driven mechanism is a mechanism having a sliding surface in contact with said sliding surface of said drive cam and another sliding surface in contact with a tappet. 
     
     
         10 . The valve operating system as set forth in  claim 9 , further comprising, in addition to said drive cam, a driven member in contact with said drive cam; a pivot member mounted to said driven member and which pivot member transmits the movement of said driven member to said tappet; and a relative position changing mechanism operable to make a change in relative position between said driven member and said pivot member.