Lubricating oil composition

Abstract

The present invention provides a lubricating oil composition having a low traction coefficient that can reduce the friction between parts such as gear teeth surfaces, exposed to elastohydrodynamic lubrication conditions to attain energy saving properties and high efficiency, suitable for use in manual, automatic and continuously variable transmissions of automobiles or industrial gear systems. The low traction coefficient lubricating oil composition comprises a lubricating base oil containing (A) a partial ester of a polyhydric alcohol and a carboxylic acid in an amount of 0.1 to 80 percent by mass on the basis of the total mass of the base oil and having a kinematic viscosity at 100° C. of 1 to 15 mm2 / s, the composition having a kinematic viscosity at 100° C. of 1 to 20 mm2 / s.

Description

TECHNICAL FIELD [0001]The present invention relates to a lubricating oil composition, more specifically to such a lubricating oil composition having a low traction coefficient, excellent energy saving properties, and high efficiency, which is suitable for use in manual, automatic or continuously variable transmissions of automobiles, or in industrial gear systems.BACKGROUND ART [0002]Recently, energy saving in automobiles and construction or agricultural machinery, i.e., fuel saving has become an urgent need in order to deal with environmental issues such as reduction in carbon dioxide emissions, and units such as engines, transmissions, final reduction gears, compressors, or hydraulic power units have been strongly demanded to contribute to energy saving. Consequently, the lubricating oils used in these systems are required to be reduced in stir resistance and frictional resistance more than before.[0003]Reducing the viscosity of a lubricating oil can be pointed out as an effective...

AI Technical Summary

Benefits of technology

[0016]The lubricating oil composition of the present invention is low in traction coefficient and thus can maintain characteristics required for gear oil and attain energy saving properties and high efficiency when applied to manual, automatic or continuously variable transmissions of automobiles, or in industrial gear systems.DESCRIPTION OF EMBODIMENT

[0017]A lubricating oil composition according to the present invention will be described below.

[0018]The lubricating oil composition of the present invention comprises an ester-based base oil comprising (A) a partial ester of a polyhydric alcohol and a carboxylic acid.

[0019]The alcohol constituting the ester-based base oil is a polyhydric alcohol. The carboxylic acid constituting the ester-based base oil may be a monobasic or polybasic acid. However, the ester-based base oil is necessarily a partial ester where at least part of the hydroxyl groups of the polyhydric alcohol remains unesterified.

[0020]The polyhydric alcohols may be those of usually dihydric to decahydric, preferably dihydric to hexahydric. Specific examples of the polyhydric alcohols of dihydric to decahydric include dihydric alcohols such as ethylene glycol, diethylene glycol, polyethylene glycol (trimer to pentadecamer of ethylene glycol), propylene glycol, dipropylene glycol, polypropylene glycol (trimer to pentadecamer of propylene glycol), 1,3-propanedioil, 1,2-propanediol, 1,3-butanediol, 1,4-butanediol, 2-methyl-1,2-propanediol, 2-methyl-1,3-propanediol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 1,5-pentanediol, and neopentyl glycol; polyhydric alcohols such as glycerin, polyglycerin (dimer to octamer thereof, such as diglycerin, triglycerin, and tetraglycerin), trimethylolalkanes (trimethylolethane, trimethylolpropane, trimethylolbutane) and dimers to octamers thereof, pentaerythritol and dimers to tetramers thereof, 1,2,4-butanetriol, 1,3,5-pentanetriol, 1,2,6-hexanetriol, 1,2,3,4-butanetetrol, sorbitol, sorbitan, sorbitol-glycerin condensate, adonitol, arabitol, xylitol, and mannitol; saccharide such as xylose, arabinose, ribose, rhamnose, glucose, fructose, galactose, mannose, sorbose, cellobiose, maltose, isomaltose, trehalose, and sucrose; and mixtures thereof.

[0021]Among these polyhydric alcohols, preferable examples include those of dihydric to hexahydric, such as ethylene glycol, diethylene glycol, polyethylene glycol (trimer to decamer of ethylene glycol), propylene glycol, dipropylene glycol, polypropylene glycol (trimer to decamer of propylene glycol), 1,3-propanedioil, 2-methyl-1,2-propanediol, 2-methyl-1,3-propanediol, neopentyl glycol, glycerin, diglycerin, triglycerin, trimethylolalkanes(trimethylolethane, trimethylolpropane, trimethylolbutane) and dimers to tetramers thereof, pentaerythritol, dipentaerythritol, 1,2,4-butanetriol, 1,3,5-pentanetriol, 1,2,6-hexanetriol, 1,2,3,4-butanetetrol, sorbitol, sorbitan, sorbitol-glycerin condensate, adonitol, arabitol, xylitol, and mannitol, and mixtures thereof. More preferable examples include ethylene glycol, propylene glycol, neopentyl glycol, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, and sorbitan, and mixtures thereof. Particularly preferable examples include neopentyl glycol, trimethylolethane, trimethylolpropane and pentaerythritol, and mixtures thereof with the objective of attaining more excellent thermal / oxidation stability, and most preferable example is trimethylolpropane.

Problems solved by technology

However, reducing the viscosity of the lubricating oil used in these transmissions may cause the above-described units and mechanisms thereof to be significantly shortened in fatigue life and may generate seizure resulting in some malfunctions in the transmissions.

In particular when a low viscosity lubricating oil is blended with a phosphorus-based extreme pressure additive to enhance the extreme pressure properties, the fatigue life will be extremely shortened.

In general it is thus difficult to reduce the viscosity of the lubricating oil.

Although a sulfur-based extreme pressure additive can improve the fatigue life, the oxidation stability of a lubricating oil is deteriorated and thus a large amount of an anti-oxidant must be blended.

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