Lubricant composition for automatic transmission

Abstract

The invention provides a lubricant composition for automatic transmissions excellent in sustainability of anti-shudder property, low-temperature viscosity characteristics, and oxidation stability, and excellent and well-balanced in durability of friction characteristics, energy-conserving performance, and anti-fatigue performance on gears. The composition contains a base oil having a kinematic viscosity at 100° C. of 3.7-4.1 mm2 / s, and composed of base oil having the viscosity of 2.5-4.5 mm2 / s, and base oil having the viscosity of 10-40 mm2 / s; 1-20 mass % poly(meth)acrylate viscosity index improver having Mw of 15000-300.00; 2-4 mass % imide friction modifier having a C8-C30 hydrocarbon group; 0.01-0.04 mass % phosphorus extreme pressure agent in terms of phosphorus; and 0.01-0.04 mass % ashless dispersant having at least one alkyl or alkenyl group of a number average molecular weight of ≧2000 in terms of nitrogen, all with respect to the total amount of the composition, and has the viscosity of 5.6-5.8 mm2 / s.

Description

FIELD OF ART [0001] The present invention relates to a lubricant composition for automatic transmissions, in particular, to a lubricant composition for automatic transmissions, particularly for vehicles, which prolongs fatigue life of gears irrespective of its low viscosity, and which is excellent and well-balanced in sustainability of anti-shudder property, low-temperature viscosity characteristics, oxidation stability, and durability of friction characteristics. BACKGROUND ART [0002] There is recently a pressing need for saving energy consumption of vehicles, or energy conservation, in order to address environmental issues, for example, by reduction of CO2 emission. Engines and automatic transmissions are strongly demanded to contribute to energy-saving, and lubricants therefor are desired to have lower agitation resistance and friction resistance. [0003] One means for making automatic transmissions energy-conserving is to lower the viscosity of a lubricant used therein. By loweri...

AI Technical Summary

Benefits of technology

[0007] It is an object of the present invention to provide a lubricant composition for automatic transmissions which has excellent sustainability of anti-shudder property, low-temperature viscosity characteristics, and oxidation stability, and is excellent and well-balanced in durability of friction characteristics, energy-conserving performance, and anti-fatigue performance on gears, in particular a lubricant composition for automatic transmissions, particularly suitable for vehicle automatic transmissions, having both energy-conserving performance and anti-fatigue performance on gears.

[0008] The present inventors have made intensive studies for solving the above problems to find out that a low-viscosity lubricant composition for automatic transmissions wherein particular base oils and particular additives are combined, may solve the above problems, thereby completing the present invention.

[0016] The present composition is capable of prolonging fatigue life of gears irrespective of its low viscosity, has excellent sustainability of anti-shudder property, low-temperature viscosity characteristics, and oxidation stability, and is excellent and well-balanced in durability of friction characteristics, energy-conserving performance, and anti-fatigue performance on gears. The present composition is particularly suitable for vehicle automatic transmissions, has both energy-conserving performance and anti-fatigue performance on gears, and is capable of achieving energy conservation of vehicles.

Problems solved by technology

However, the lowered viscosity of lubricants used in these parts may remarkably shorten their fatigue life, causing seizure or the like to result in troubles in the transmission.

In particular, when a phosphorus extreme pressure agent is used for improving extreme pressure property of a low-viscosity lubricant, fatigue life of gears is remarkably impaired, so that it is usually hard to lower the viscosity of such lubricant.

On the other hand, a sulfur extreme pressure agent may improve fatigue life of gears, but impairs oxidation stability, so that a large amount of antioxidants is required.

These compositions, however, are not intended to improve fuel efficiency, and thus have a high kinematic viscosity.

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