Lubricant composition

Abstract

Provided is a lubricant composition containing a lubricant base oil and 0.5 to 10 mass % of (A) an ethylene / α-olefin copolymer having a number average molecular weight of 2,800 to 8,000, in which the lubricant base oil used here has a kinematic viscosity at 100° C. of 1.5 to 40 mm2 / s, a viscosity index of 100 or more, a pour point of −25° C. or lower, and a sulfur content of 0.01 mass % or less, and the lubricant composition has low viscosity and a long metal fatigue life, while being excellent in low-temperature fluidity and oxidation stability, thereby being particularly suitable as a lubricant for automobile transmissions or the like.

Description

TECHNICAL FIELD[0001]The present invention relates to a lubricant composition, and more specifically, to a lubricant composition having low viscosity and has a long metal fatigue life, while being excellent in low-temperature fluidity and oxidation stability, thereby being particularly suitable as a lubricant for automobile transmissions or the like.BACKGROUND ART[0002]Energy savings, that is, fuel savings in, for example, construction machines, agricultural machines and automobiles have recently become urgent matters with the advent of the need to cope with environmental issues, so an apparatus such as an engine, a transmission, a final reduction gear, a compressor, or a hydraulic system has been strongly requested to contribute to the energy savings. Accordingly, a lubricant to be used in any such apparatus has been requested to reduce the stirring resistance or frictional resistance of the apparatus to a larger extent than a conventional lubricant does.[0003]For example, a reduct...

AI Technical Summary

Benefits of technology

[0008]The present invention has been made in view of such circumstances, and an object of the present invention is to provide a lubricant composition having low viscosity and a long metal fatigue life, while being excellent in low-temperature fluidity and oxidation stability, and hence is particularly suitable as a lubricant for automobile transmissions.Means for Solving the Problems

[0009]The inventors of the present invention have made extensive studies with a view to developing a lubricant composition having the foregoing excellent performance. As a result, the inventors have found that the object can be achieved by blending a base oil having specific properties with an ethylene / α-olefin copolymer having a molecular weight in a specific range at a predetermined ratio. The present invention has been completed on the basis of such finding.

[0011]According to the present invention, there can be provided a lubricant composition having low viscosity and a long metal fatigue life, while being excellent in low-temperature fluidity and oxidation stability, and hence is particularly suitable as a lubricant for automobile transmissions or the like.

Problems solved by technology

However, a lubricant with its viscosity reduced is apt to be lost by evaporation particularly when used in a high-humidity environment.

Moreover, a problem such as an increase in coefficient of friction of a film composed of the lubricant arises in association with the reduction in viscosity.

As a result, the lubricant has a significantly reduced fatigue life to cause seizing or the like, so a transmission or the like may undergo malfunctions.

In particular, when a phosphorus-based extreme pressure agent is blended for improving the extreme-pressure property of a low-viscosity oil, the fatigue life of the oil remarkably deteriorates, so it is generally difficult to reduce the viscosity of the oil.

However, no investigation has been conducted on an influence of any such composition on the fatigue life of a lubricant when the viscosity of the lubricant is reduced.