Gear

Abstract

A gear comprised of a tooth surface and a hard carbon film formed on at least a part of the tooth surface. When the gear is used in lubricant including a specific component, a friction of a tooth surface of the gear is largely decreased, and therefore the gear performs an excellent power transmission efficiency. Further, when the gear is employed in a planetary gear mechanism or speed reducing mechanism which has a plurality of meshing portions of gears, the power transmission efficiency of the mechanism is also improved.

1 . A gear comprising: 
 a tooth surface; and    a hard carbon film formed on at least a part of the tooth surface.    
     
     
         2 . The gear as claimed in  claim 1 , wherein a hydrogen amount in the hard carbon film is smaller than or equal to 1 atomic percent.  
     
     
         3 . The gear as claimed in  claim 2 , wherein a hydrogen amount in the hard carbon film is smaller than or equal to 0.3 atomic percent.  
     
     
         4 . The gear as claimed in  claim 1 , wherein the gear is used as a gear of a planetary gear mechanism.  
     
     
         5 . The gear as claimed in  claim 1 , wherein the gear is used as a gear of a speed reduction mechanism.  
     
     
         6 . The gear as claimed in  claim 1 , wherein the gear is used in a lubricant.  
     
     
         7 . The gear as claimed in  claim 6 , wherein the lubricant includes a mixture employing poly-alfa-olefin (PAO) as a base oil.  
     
     
         8 . The gear as claimed in  claim 6 , wherein the lubricant includes an additive including a hydroxyl group.  
     
     
         9 . The gear as claimed in  claim 8 , wherein the additive includes two or more hydroxyl groups in a molecule.  
     
     
         10 . The gear as claimed in  claim 6 , wherein an additive in the lubricant includes ester.  
     
     
         11 . The gear as claimed in  claim 6 , wherein an additive in the lubricant includes monoester of glycerin.  
     
     
         12 . The gear as claimed in  claim 6 , wherein a main component of the lubricant is a hydroxy-compound.  
     
     
         13 . The gear as claimed in  claim 12 , wherein the hydroxy-compound includes alcohol.  
     
     
         14 . The gear as claimed in  claim 13 , wherein the alcohol includes glycerin.  
     
     
         15 . The gear as claimed in  claim 13 , wherein the alcohol includes ethylene glycol.