Lubricating oil composition for continuously variable transmission

Abstract

A lubricating oil composition for a continuously variable transmission has low viscosity to exhibit fuel savings, higher metal-to-metal friction coefficient to ensure high power transmission, wet clutch friction characteristics and anti-shudder properties required for transmissions, and low traction coefficient to achieve fuel savings. The composition contains a base oil adjusted so the product (EC×V40) of the mass % (ECmass %) of saturated cyclic component based on the total base oil and the 40° C. kinematic viscosity (V40 mm2 / s) is 500 or less and the 100° C. kinematic viscosity is 3.6 to 4.1 mm2 / s, (B) a phosphorus compound, (C) a calcium salicylate and / or a calcium sulfonate, (D) a boron-modified ashless dispersant in an amount of 0.001 to 0.008 mass % as boron, and (E) a friction modifier, each in a specific amount, the lubricating oil composition having a 100° C. kinematic viscosity of 5.2 to 5.6 mm2 / s and a viscosity index of 165 or greater.

Description

TECHNICAL FIELD[0001]The present invention relates to lubricating oil compositions for continuously variable transmissions, more specifically to the lubricating oil compositions with enhanced fuel saving properties, suitable for metal belt type continuously variable transmissions of automobiles.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 systems such as engines, transmissions, final reduction gears, compressors, or hydraulic power units have been strongly demanded to contribute to energy saving.[0003]As one of means for saving fuel by transmissions, the use of continuously variable transmissions has been growingly expanding. This is for maximizing the fuel economy by driving an internal combustion engine under the most efficient driving conditions.[0004]Furthermore, continuously variable t...

AI Technical Summary

Benefits of technology

The continuously variable transmission lubricating oil composition described in this patent has the unique ability to save fuel while maintaining its viscosity during use. It also provides high power transmitting capacity and the necessary wet clutch friction characteristics and anti-shudder properties for a transmission. Additionally, this oil has a low traction coefficient, which further improves fuel saving.

Problems solved by technology

However, since the lubricating oil used in continuously variable transmissions is also used as a medium for a hydraulic control system, excess reduction of the viscosity causes some defects such as poor lubricity by wear or seizure due to insufficient oil film thickness, and failure of generation of sufficient hydraulic pressure caused by oil leakage from the control valves or oil pumps.

However, even though the oil retain a proper viscosity when it is fresh, addition of the high molecular weight additive causes a problem that the additive cannot retain a proper viscosity because it is subjected to shear and is reduced in viscosity as the lubricating oil is used.

However, the oil has been unable to meet the recent further fuel saving demand.

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