Lubricant oil composition and internal-combustion-engine friction reduction method

Abstract

A lubricating oil composition which exhibits an excellent friction-reducing effect and excellent fuel consumption reducing properties is provided. The lubricating oil composition includes a lubricating base oil (A), a molybdenum compound (B), and an ashless friction modifier (C), wherein the lubricating oil composition includes a binuclear organic molybdenum compound represented by the following general formula (I) as the molybdenum compound (B), with the content of the binuclear organic molybdenum compound as converted into molybdenum atoms being 0.030 mass % or more and 0.140 mass % or less based on the total amount of the lubricating oil composition; and an ester-based ashless friction modifier (C1) and/or an amine-based ashless friction modifier (C2) as the ashless friction modifier (C), with the total content of the ester-based ashless friction modifier (C1) and the amine-based ashless friction modifier (C2) being more than 0.1 mass % and 1.8 mass % or less based on the total amount of the lubricating oil composition: in the general formula (I), R 1 to R 4 each represents a hydrocarbon group having 4 to 22 carbon atoms, R 1 to R 4 may be the same as or different from each other, and X 1 to X 4 each represents a sulfur atom or an oxygen atom.

1 . A lubricating oil composition, comprising:
 a lubricating base oil (A);   a molybdenum compound (B); and   an ashless friction modifier (C),   
       wherein the lubricating oil composition includes:
 a binuclear organic molybdenum compound represented by the following general formula (I) as the molybdenum compound (B): 
 
       
         
           
           
               
               
           
         
       
       with a content of the binuclear organic molybdenum compound as converted into molybdenum atoms being 0.030 mass % or more and 0.140 mass % or less based on a total amount of the lubricating oil composition; and
 an ester-based ashless friction modifier (C1), an amine-based ashless friction modifier (C2), or both, as the ashless friction modifier (C), with a total content of the ester-based ashless friction modifier (C1) and the amine-based ashless friction modifier (C2) being more than 0.1 mass % and 1.8 mass % or less based on the total amount of the lubricating oil composition, 
 wherein: 
 R 1  to R 4  each represents a hydrocarbon group having 4 to 22 carbon atoms, and R 1  to R 4  may be the same as or different from each other; and 
 X 1  to X 4  each represents a sulfur atom or an oxygen atom. 
 
     
     
         2 . The lubricating oil composition according to  claim 1 , comprising, as the ester-based ashless friction modifier (C1), an ester compound having one or more hydroxyl groups in a molecule thereof. 
     
     
         3 . The lubricating oil composition according to  claim 2 , wherein the ester compound having one or more hydroxyl groups in a molecule thereof is glycerin monooleate. 
     
     
         4 . The lubricating oil composition according to  claim 1 , comprising the ester-based ashless friction modifier (C1) and the amine-based ashless friction modifier (C2), as the ashless friction modifier (C). 
     
     
         5 . The lubricating oil composition according to  claim 4 , wherein a mass ratio between a content of the amine-based ashless friction modifier (C2) and a content of the ester-based ashless friction modifier (C1) [the content of the amine-based ashless friction modifier (C2)/the content of the ester-based ashless friction modifier (C1)] is less than 1.00. 
     
     
         6 . The lubricating oil composition according to  claim 1 , further comprising a boratad succinimide (D). 
     
     
         7 . The lubricating oil composition according to  claim 6 , wherein a content of the boratad succinimide (D) as converted into boron atoms is 0.050 mass % or less based on the total amount of the lubricating oil composition. 
     
     
         8 . The lubricating oil composition according to  claim 6 , comprising the ester-based ashless friction modifier (C1) and the amine-based ashless friction modifier (C2), as the ashless friction modifier (C),
 wherein a mass ratio of a total content of the ester-based ashless friction modifier (C1) and the amine-based ashless friction modifier (C2) to a content of the boratad succinimide (D) as converted into boron atoms [the content of the boratad succinimide (D) as converted into boron atoms/(the content of the ester-based ashless friction modifier (C1)+the content of the amine-based ashless friction modifier (C2))] is 0.011 or more.   
     
     
         9 . The lubricating oil composition according to  claim 1 , further comprising a poly(meth)acrylate (E). 
     
     
         10 . The lubricating oil composition according to  claim 1 , further comprising a metal-based detergent (F). 
     
     
         11 . The lubricating oil composition according to  claim 1 , further comprising zinc dithiophosphate (G). 
     
     
         12 . The lubricating oil composition according to  claim 1 , wherein the lubricating base oil (A) is one or more selected from mineral oils or synthetic oils classified into Group 3 and Group 4 in the base oil classification of the American Petroleum Institute. 
     
     
         13 . The lubricating oil composition according to  claim 1 , which is adapted to function as a lubricating oil for an internal combustion engine. 
     
     
         14 . A method for reducing friction of an internal combustion engine, the method comprising adding the lubricating oil composition of  claim 1  to an internal combustion engine.