Lubricating oil composition for internal combustion engines

#This invention relates to a lubricant oil composition for internal combustion engines and a friction reducing method for internal combustion engines and, more specifically, relates to a lubricant oil composition useful for reduction of friction loss and improvement in fuel economy in automotive internal combustion engines, particularly a lubricant oil composition for internal combustion engines suitable for lubrication of diesel engines equipped with an exhaust gas recirculation system (hereinafter often referred to as “EGR”).

#Lubricant oils are used for sliding parts of internal combustion engines, for example, piston rings, cylinder liners, crankshafts, bearings for connecting rods, valve system mechanisms including cams and valve lifters, and the like. However, because of their large energy loss by friction, in general, various techniques have been developed to reduce the friction loss and improve the fuel economy. As a friction reducing agent to be added to lubricant oils to reduce the friction coefficients of lubricant oils, for example, attention is paid to organic molybdenum compounds, and a combination of organic molybdenum compound with metallic detergent (e.g., Kokoku publication No. 6-62933), a combination of organic molybdenum compound with sulfur compound (e.g., Kokoku publication No. 5-83599) and the like have been proposed. As a friction reducing agent different from the organic molybdenum compounds, further, a combination of glycerol partial ester of fatty acid with organic copper compound (e.g., Kokoku publication No. 3-77837), a combination of pentaerythritol with -succinimide or zinc dithiophosphate (Kokoku publication No. 55-80494), and the like have also been proposed.

#However, the production of soot resulting from incomplete combustion of diesel fuel cannot be avoided in a diesel engine, unlike a gasoline engine, and the engine oil is contaminated with the produced soot. Accordingly, conventional friction reducing agents such as organic molybdenum compound, amine compounds, amide compounds and the like involve a difficulty in that a sufficient effect cannot be exhibited due to the influence of the soot in oil. To improve the fuel economy of diesel engines, only the mixing with alkali metal borate hydrate (e.g., Kokoku publication No. 1-48319) has been proposed.

#This invention is described further in detail by the following non-limiting Examples and Comparative Examples.

#The coefficient of friction and soot content in oil of the prepared lubricant oil compositions were measured according to the following method.

#The alkylene oxide-added nonionic surfactant used in Examples and Comparative Examples is as follows.