Lubricating oil composition for internal-combustion engine, and method for reducing friction in gasoline engine

Abstract

Provided is a lubricating oil composition for internal combustion engines capable of exhibit a sufficient friction-reducing effect from a low-temperature range assuming engine starting to a practical temperature range of 80° C. or higher. The lubricating oil composition for internal combustion engines contains a surfactant having an alkylene oxide as the constituent unit and having an HLB value of 7 or more and less than 15, and a lubricant base oil.

1 . A lubricating oil composition for internal combustion engines, the composition comprising:
 a surfactant having an alkylene oxide as the constituent unit and having an HLB value of 7 or more and less than 15, and   a lubricant base oil.   
     
     
         2 . The lubricating oil composition for internal combustion engines according to  claim 1 , wherein the surfactant has a molecular weight in a range of 350 to 950 g/mol. 
     
     
         3 . The lubricating oil composition for internal combustion engines according to  claim 1 , wherein the surfactant is an amine compound. 
     
     
         4 . The lubricating oil composition for internal combustion engines according to  claim 3 , wherein the amine compound is a tertiary amine. 
     
     
         5 . The lubricating oil composition for internal combustion engines according to  claim 1 , wherein the surfactant is a polyoxyalkylene fatty acid ester. 
     
     
         6 . The lubricating oil composition for internal combustion engines according to  claim 1 , wherein a content of the surfactant in the lubricating oil composition is 0.01 to 2.0% by mass. 
     
     
         7 . The lubricating oil composition for internal combustion engines according to  claim 1 , further comprising:
 a boron-modified succinimide.   
     
     
         8 . The lubricating oil composition for internal combustion engines according to  claim 7 , wherein a boron atom-equivalent content of the boron-modified succinimide in the lubricating oil composition is 0.2% by mass or less. 
     
     
         9 . The lubricating oil composition for internal combustion engines according to  claim 7 , wherein a ratio by mass of a content of boron-modified succinimide/a content of the surfactant is 100 or less. 
     
     
         10 . The lubricating oil composition for internal combustion engines according to  claim 7 , wherein a ratio by mass of a content of boron atom-equivalent content of the boron-modified succinimide/a content of the surfactant is 20 or less. 
     
     
         11 . The lubricating oil composition for internal combustion engines according to  claim 1 , further comprising:
 a poly(meth)acrylate.   
     
     
         12 . The lubricating oil composition for internal combustion engines according to  claim 1 , wherein the lubricant base oil is at least one of a mineral oil and a synthetic oil classified in Group 3 and Group 4 in base oil classification by American Petroleum Institute. 
     
     
         13 . The lubricating oil composition for internal combustion engines according to  claim 1 , which has a kinematic viscosity at 100° C. of 3.8 to 12.5 mm 2 /s. 
     
     
         14 . The lubricating oil composition for internal combustion engines according to  claim 1 , which is adapted to function as a lubricating oil composition for gasoline engines. 
     
     
         15 . A friction reducing method for gasoline engines, the method comprising adding the lubricating oil composition of  claim 1  to a gasoline engine.