Lubricating oil composition for automatic transmissions

Abstract

The present invention relates to a lubricating oil composition comprising a major amount of base oil of lubricating viscosity and the following additives in the following amounts based on a total amount of the lubricating oil composition: (A) 0.1 to 10 wt.% of a succinic acid ester, (B) 0.01 to 2 wt.% of a phosphorous acid ester, (C) 0.1 to 5 wt.% of an amide compound which is a reaction product obtained by reaction of a linear or branched, saturated or unsaturated monovalent aliphatic acid having 8 to 22 carbon atoms, urea, and polyalkylenepolyamine, (D) 0.0 1 to 2 wt.% of an overbased metal containing detergent, and (E) 0.01 to 1 wt.% of a corrosion inhibitor.

Description

[0001] The present invention relates to a lubricating oil composition, In particular, the invention relates to a lubricating oil composition for automatic transmissions of internal combustion engines, in which the lubricating oil composition shows a high torque transmission capacity and a prolonged shudder inhibition. BACKGROUND OF THE INVENTION [0002] Automatic transmissions in automobiles comprise a torque converter, a wet multi-plate clutch, a gear mechanism, and a mechanism controlling these elements. The torque transmission capacity is automatically set according to the speed of automobile and the degree of load. Modern automatic transmissions further comprise a lockup clutch mounted to the torque converter so as to improve fuel economy. The use of thee lockup clutch enables engine torque to be transmitted to the automatic transmission according to driving conditions in addition to the driving force transmitted through a lubricating oil. However, since the torque variation prod...

AI Technical Summary

Benefits of technology

[0017] It is desirable that an automatic transmission fluid not only should show a high shudder inhibiting ability when the transmission fluid is first used, but also should keep the high shudder inhibiting ability for a prolonged period of time without substantial decrease of the inhibiting ability and further should show a high torque transmission capacity.

[0026] Among other factors, the present invention is based on the surprising discovery that the lubricating oil composition of the present invention provides high transmission torque capacity and prolonged shudder inhibition when employed in an automatic transmission of an internal combustion engine. The lubricating oil composition is useful as a method for reducing shudder when used as an automatic transmission fluid. Accordingly the present invention is also directed to the use of the present additive compound in an automatic transmission fluid to reduce shudder in an automatic transmission of an internal combustion engine. The lubricating oil composition of the present invention has high stability with respect to the shudder inhibition, the torque transmission capacity and the shift performance, which are important properties of an automatic transmission fluid.

Problems solved by technology

However, since the torque variation produced by the operation of the lockup clutch sometimes disturbs passengers due to shudder, the lockup clutch is generally set to operate only under high speed driving conditions giving less torque variation.

Therefore, enough improvement of fuel economy is not attained.

At low road speeds vehicle operation is rough and engine vibration is transmitted through the drive train.

Rough operation and engine vibration are not acceptable to drivers.

However, if too much friction modifier is incorporated into a lubricating oils the friction coefficient of the wet clutch extremely decreases and hence enough torque transmission capacity cannot be obtained.