LUBRICANT OIL COMPOSITION FOR TRANSMISSIONS

摘要

As a lubricant oil composition having improved fuel consumption saving performance and also having an excellent metal fatigue preventing property and excellent heat resistance, a lubricant oil composition for transmissions is provided, which comprises: a lubricant oil base oil comprising (A) 50 to 97% by mass of a mineral-oil-type base oil having a kinematic viscosity of 1.5 to 3.5 mm2/s at 100˚C, a pour point of -25˚C or lower, a viscosity index of 105 or more, a %CP value of 85 or more, a %CN value of 2 to 20 and a %CA value of 3 or less and (B) 3 to 10% by mass of a monoester-type base oil having a kinematic viscosity of 2 to 10 mm2/s at 100˚C; (C) phosphorous acid ester in such an amount that the phosphorous content in the composition becomes 250 to 350 ppm by mass in terms of phosphorous atom content; and (D) a boronated ashless dispersant in an amount of 30 to 120 ppm by mass in terms of boron atom content relative to the whole amount of the lubricant oil composition. In the oil composition, the ratio of the amount (% by mass) of boron atoms to the amount (% by mass) of phosphorus atoms (i.e., B/P) is 0.07 to 0.42, and the kinematic viscosity of the composition is 2.5 to 4.0 mm2/s at 100˚C.