Lubricating oil composition

Abstract

A lubricating oil composition which comprises a lubricant base oil and, incorporated therein, (A) from 0.01 to 0.2 mass % of a polyol compound having from 2 to 20 carbon atoms, (B) from 0.03 to 0.05 mass %, in terms of the amount of boron, of an alkali metal borate, (C) from 0.05 to 0.2 mass %, in terms of the amount of nitrogen, of an ashless dispersant, and (D) from 0.1 to 0.4 mass %, in terms of the amount of an alkaline earth metal, of an alkaline earth metal sulfonate having a total base number of 250 mg-KOH/g or more, the percentages being based on the total amount of the composition. The lubricating oil composition can simultaneously enhance the dynamic and the static friction coefficients in a wet clutch, and is suitable for use particularly in an automatic transmission.

1 . A lubricating oil composition which comprises a lubricant base oil and, incorporated therein, 
 (A) from 0.01 to 0.2 mass % of a polyol compound having from 2 to 20 carbon atoms,    (B) from 0.03 to 0.05 mass %, in terms of the amount of boron, of an alkali metal borate,    (C) from 0.05 to 0.2 mass %, in terms of the amount of nitrogen, of an ashless dispersant, and    (D) from 0.1 to 0.4 mass %, in terms of the amount of an alkaline earth metal, of an alkaline earth metal sulfonate having a total base number of 250 mg-KOH/g or more, the percentages being based on the total amount of the composition.    
     
     
         2 . The lubricating oil composition according to  claim 1 , wherein the polyol compound (A) is an alcohol having three or more hydroxyl groups.  
     
     
         3 . The lubricating oil composition according to  claim 1 , wherein the polyol compound (A) has from 3 to 10 carbon atoms.  
     
     
         4 . The lubricating oil composition according to  claim 1 , wherein the ashless dispersant (C) is a mixture of non-modified succinimide and a boric acid modified succinimide.  
     
     
         5 . The lubricating oil composition according to  claim 4 , wherein it is a lubricating oil composition for use in an automatic transmission.  
     
     
         6 . The lubricating oil composition according to  claim 2 , wherein the polyol compound (A) has from 3 to 10 carbon atoms.  
     
     
         7 . The lubricating oil composition according to  claim 2 , wherein the ashless dispersant (C) is a mixture of non-modified succinimide and a boric acid modified succinimide.  
     
     
         8 . The lubricating oil composition according to  claim 3 , wherein the ashless dispersant (C) is a mixture of non-modified succinimide and a boric acid modified succinimide.  
     
     
         9 . The lubricating oil composition according to  claim 2 , wherein it is a lubricating oil composition for use in an automatic transmission.  
     
     
         10 . The lubricating oil composition according to  claim 3 , wherein it is a lubricating oil composition for use in an automatic transmission.  
     
     
         11 . The lubricating oil composition according to  claim 4 , wherein it is a lubricating oil composition for use in an automatic transmission.  
     
     
         12 . The lubricating oil composition according to  claim 6 , wherein the ashless dispersant (C) is a mixture of non-modified succinimide and a boric acid modified succinimide.  
     
     
         13 . The lubricating oil composition according to  claim 12 , wherein it is a lubricating oil composition for use in an automatic transmission.