Lubricating oil composition

Abstract

The lubricating oil composition contains a base oil; (A) an acidic alkyl phosphate ester having a C6 to C20 alkyl group; (B) a dialkylamine and/or a trialkylamine; and (C) (c-1) a sulfur compound in an amount of 0.2 to 0.6 mass % as reduced to S, the sulfur compound containing no poly-sulfur bond which is equal to or longer than —S—S—S— in a molecule thereof and having an S content of the molecule of 15 mass % or more and (c-2) an optional thiophosphoric acid trihydrocarbyl ester in an amount of 0.1 to 1.0 mass %, the ester being represented by formula (I): (R—O—) 3 P═S  (I) (wherein R represents a C6 to C20 hydrocarbyl group) and having a P content of the composition of 150 to 500 ppm by mass The lubricating oil composition has excellent anti-seizure performance, excellent anti-fatigue performance (e.g., anti-FZG-micropitting performance), and reduced sludge formation in an oxidation test.

1 . A lubricating oil composition comprising:
 a base oil;   (A) an acidic alkyl phosphate ester having a C6 to C20 alkyl group;   (B) a dialkylamine, a trialkylamine or a combination thereof; and   (C) (c-1) a sulfur compound in an amount of 0.2 to 0.6 mass % as reduced to S, the sulfur compound containing no poly-sulfur bond which is equal to or longer than —S—S—S— in a molecule thereof and having an S content of the molecule of 15 mass % or more wherein a P content of the composition is 150 to 500 ppm by mass.   
     
     
         2 . The lubricating oil composition as described in  claim 1 , wherein component (B) is present in an amount where the ratio by mass of P contained in component (A) to N contained in component (B) is adjusted to 1.7 to 2.1. 
     
     
         3 . The lubricating oil composition as described in  claim 1 , wherein component (B) is a trialkylamine having a C6 to C20 alkyl group. 
     
     
         4 . The lubricating oil composition as described in  claim 1 , which further comprises (D) a polyol partial ester in an amount of 5 to 20 mass %. 
     
     
         5 . The lubricating oil composition as described in  claim 1 , which is used as a step-up gear oil composition for wind power generation. 
     
     
         6 . The lubricating oil composition as described in  claim 1 , further comprising (c-2) a thiophosphoric acid trihydrocarbyl ester in an amount of 0.1 to 1.0 mass %, represented by formula (I):
   (R—O—) 3 P═S  (I)   
       wherein R represents a C6 to C20 hydrocarbyl group.