Lubricating oil composition for internal combustion engines

Abstract

Provided is a lubricant oil composition for an internal combustion engine which is characterized by including a base oil having a viscosity index of 125 or higher and a Noack evaporation amount (250° C.×1 h) of 15% by mass or less, and, based on a total amount of the composition, from 0.1 to 10% by mass of (A) a C₂ to C₂₀ olefin polymer having a mass average molecular weight of 500 or more and 10,000 or less and/or (B) a polymeric compound having a mass average molecular weight of 10,000 or more and less than 100,000, wherein a content of (C) a polymeric compound having a mass average molecular weight of 100,000 or more is less than 1.0% by mass. The lubricant oil composition can, despite of its low viscosity, reduce noise during running, prevent fatigue damage such as gear pitting, reduce the consumption of the oil, and provide excellent fuel saving performance.

Description

TECHNICAL FIELD[0001]The present invention relates to a lubricant oil composition for internal combustion engines and, more specifically, to a lubricant oil composition for internal combustion engines which can reduce noise during running, improve fatigue life, reduce lubricating oil consumption and provide excellent fuel saving performance and which is useful as a lubricating oil for four-cycle engines for motorcycles.BACKGROUND ART[0002]Because of demand for energy saving and reduction of carbon dioxide (CO2), fuel saving performance is strongly desired in the field of lubricating oils for internal combustion engines (engine oils) as one of required properties thereof.[0003]In the case of engine oils for automobiles, it has been a conventional practice to reduce the viscosity thereof for the purpose of improving their fuel saving performance.[0004]In the case of engine oils for motorcycles, however, various problems arise, when the viscosity thereof is reduced to improve the fuel ...

AI Technical Summary

Benefits of technology

[0010]With the foregoing circumstance in view, it is an object of the present invention to provide a lubricant oil composition for internal combustion engines which can, despite of its low viscosity, reduce noise during running, prevent fatigue damage such as gear pitting, reduce the consumption of the oil and provide excellent fuel saving performance.

Problems solved by technology

In the case of engine oils for motorcycles, however, various problems arise, when the viscosity thereof is reduced to improve the fuel saving performance thereof although both are equally called engine oils, due to differences in mechanical structure between automobiles and motorcycles.

When an engine oil, whose viscosity has been reduced in order to improve fuel saving performance, is used in a motorcycle having the above structure, fatigue damage such as gear pitting is caused in a transmission thereof.

Additionally, in the motorcycle, since the engine is installed in an exposed state, engine noise is big to cause noise pollution problems.

It follows that oil consumption is increased due to oil evaporation.

Thus, because the conventional multi-grade engine oil (lubricating oil containing a polymeric compound) cannot maintain sufficient high temperature high shear viscosity, the metal fatigue resistance thereof tends to be reduced.

This is an obstacle against reduction of the viscosity of engine oils for motorcycles.

Therefore, the foregoing problems, encountered when the viscosity of an engine oil for use in motorcycles is reduced so as to improve the fuel saving performance thereof, have not yet been solved at present.

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