Transmission fluid composition

Abstract

The invention provides a transmission fluid composition which has a kinematic viscosity as determined at 100° C. of 2 to 10 mm2/s and a viscosity index of 150 or higher and which satisfies a relationship between kinematic viscosity and NOACK evaporation loss amount represented by formula (I): X/3+Y≦6.33  (I) (wherein X represents a kinematic viscosity (mm2/s) as determined at 100° C., and Y represents a NOACK evaporation loss amount (mass %) at 200° C. for one hour), and a transmission fluid composition containing, as a base oil, at least one species selected from among α-olefin oligomers produced through oligomerization of an α-olefin through a specific method and hydrogenation products of the oligomers. Such transmission fluid compositions exhibit a very small evaporation loss despite having low viscosity, and a long metal fatigue life (e.g., pitting resistance) and have high viscosity index, good low-temperature fluidity, good extreme pressure properties, and good oxidation stability, and are suitable for transmissions, particularly automatic transmissions.

Dependencies are inferred from the claim text.