Lubricating oil composition for automatic transmission

Abstract

A lubricating oil composition provides enhanced anti-wear and anti-seizure properties, even though reduced in viscosity, suitable for use as an automatic transmission oil, particularly as a metal belt continuously variable transmission oil. The lubricating oil composition contains a base oil and the following based on the total mass of the composition: (A) a boron-containing ashless dispersant in an amount of 300 to 1000 ppm by mass on a boron basis, (B) a metallic detergent having a total base number of at least 200 mgKOH/g in an amount of 100 to 1200 ppm by mass on a metal basis, and (C) a friction modifier in an amount of 0.01 to 5 percent by mass. The ratio (Bo/M) of the content of Component (A) on a boron basis (Bo:ppm by mass) to the content of Component (B) on a metal basis (M:ppm by mass) being from 0.5 to 4.

1 . A lubricating oil composition for automatic transmissions comprising a base oil, and on the basis of the total mass of the composition:
 (A) a boron-containing ashless dispersant in an amount of 300 to 1000 ppm by mass on a boron basis;   (B) a metallic detergent with a total base number of 200 mgKOH/g or greater in an amount of 100 to 1200 ppm by mass on a metal basis; and   (C) a friction modifier in an amount of 0.01 to 5 percent by mass,   the ratio (Bo/M) of the content of Component (A) on a boron basis (Bo:ppm by mass) to the content of Component (B) on a metal basis (M:ppm by mass) being from 0.5 to 4.   
     
     
         2 . The lubricating oil composition for automatic transmissions according to  claim 1  wherein the lubricating base oil comprises one type of base oil or a mixture of two or more types of base oils, at least one type of base oil is a mineral base oil or synthetic base oil having a 40° C. kinematic viscosity of 8 to 14 mm 2 /s, the base oil is blended in an amount of 20 percent by mass or more, and the composition has a 40° C. kinematic viscosity of 10 to 30 mm 2 /s and a viscosity index of 160 or greater. 
     
     
         3 . The lubricating oil composition for automatic transmissions according to  claim 1  further comprising (D) a phosphorus-containing additive in an amount of 50 to 2000 ppm by mass on a phosphorus basis on the basis of the total mass of the composition and (E) a viscosity index improver in an amount of 0.1 to 40 percent by mass on the basis of the total mass of the composition. 
     
     
         4 . The lubricating oil composition for automatic transmissions according to  claim 1  wherein (A) the boron-containing ashless dispersant contains one percent by mass more of boron and 3 percent by mass or more of nitrogen. 
     
     
         5 . The lubricating oil composition for automatic transmissions according to  claim 1  wherein (B) the metallic detergent consists of calcium sulfonate. 
     
     
         6 . The lubricating oil composition for automatic transmissions according to  claim 1  wherein the composition is used for a continuously variable transmission with a metal belt.