Lubricating oil composition for continuously variable transmission

Abstract

A lubricating oil composition for a continuously variable transmission including: (A) a lubricant base oil; (B) a borate ester compound in an amount of 25 to 500 mass ppm in terms of boron on the basis of the total mass of the composition; (C) phosphoric acid in an amount of 100 to 750 mass ppm in terms of phosphorus on the basis of the total mass of the composition; (D) a poly(meth)acrylate having a weight average molecular weight of no more than 100,000, wherein the lubricating oil composition has a kinematic viscosity at 40° C. of no more than 25 mm 2 /s.

1 . A lubricating oil composition for a continuously variable transmission comprising:
 (A) a lubricant base oil;   (B) a borate ester compound in an amount of 25 to 500 mass ppm in terms of boron on the basis of the total mass of the composition;   (C) phosphoric acid in an amount of 100 to 750 mass ppm in terms of phosphorus on the basis of the total mass of the composition;   (D) a poly(meth)acrylate having a weight average molecular weight of no more than 100,000,   wherein the lubricating oil composition has a kinematic viscosity at 40° C. of no more than 25 mm 2 /s.   
     
     
         2 . The lubricating oil composition for a continuously variable transmission according to  claim 1 , further comprising:
 (E) a thiadiazole compound in an amount of 180 to 900 mass ppm in terms of sulfur on the basis of the total mass of the composition,   wherein a ratio (B+P)/S of a sum of a boron content B (unit: mass ppm) in the composition derived from the component (B) and a phosphorus content P (unit: mass ppm) in the composition to a sulfur content S (unit: mass ppm) in the composition derived from the component (E) is 1 to 3.   
     
     
         3 . The lubricating oil composition for a continuously variable transmission according to  claim 1 ,
 the (A) lubricant base oil comprising:   (Al) a base oil having a kinematic viscosity at 100° C. of no more than 2.8 mm 2 /s, a viscosity index of no less than 110, and % C P  of no less than 90, in an amount of 30 to 100 mass % on the basis of the total mass of the lubricant base oil,   the (A) lubricant base oil optionally comprising:   (A2) an API group III base oil or group IV base oil or mixture thereof, having a kinematic viscosity at 100° C. of 3 to 10 mm 2 /s, in an amount of no more than 70 mass % on the basis of the total mass of the lubricant base oil; and   a base oil other than the base oils (Al) and (A2), in an amount of no more than 4 mass % on the basis of the total mass of the lubricant base oil,   wherein the (A) lubricant base oil has a kinematic viscosity at 100° C. of no more than 3.4 mm 2 /s.   
     
     
         4 . The lubricating oil composition for a continuously variable transmission according to  claim 1 ,
 wherein the component (B) is at least one borate ester compound represented by the following general formula (1):   
       
         
           
           
               
               
           
         
         wherein in the formula (1), R 1  is a hydrocarbyl group having a carbon number of 1 to 30; and R 2  and R 3  are each independently a hydrogen atom or a hydrocarbyl group having a carbon number of 1 to 30. 
       
     
     
         5 . The lubricating oil composition for a continuously variable transmission according to  claim 2 ,
 the (A) lubricant base oil comprising:   (A 1 ) a base oil having a kinematic viscosity at 100° C. of no more than 2.8 mm 2 /s, a viscosity index of no less than 110, and % C P  of no less than 90, in an amount of 30 to 100 mass % on the basis of the total mass of the lubricant base oil,   the (A) lubricant base oil optionally comprising:   (A2) an API group III base oil or group IV base oil or mixture thereof, having a kinematic viscosity at 100° C. of 3 to 10 mm 2 /s, in an amount of no more than 70 mass % on the basis of the total mass of the lubricant base oil; and   a base oil other than the base oils (Al) and (A2), in an amount of no more than 4 mass % on the basis of the total mass of the lubricant base oil,   wherein the (A) lubricant base oil has a kinematic viscosity at 100° C. of no more than 3.4 mm 2 /s.   
     
     
         6 . The lubricating oil composition for a continuously variable transmission according to  claim 2 ,
 wherein the component (B) is at least one borate ester compound represented by the following general formula (1):   
       
         
           
           
               
               
           
         
         wherein in the formula (1), R 1  is a hydrocarbyl group having a carbon number of 1 to 30; and R 2  and R 3  are each independently a hydrogen atom or a hydrocarbyl group having a carbon number of 1 to 30. 
       
     
     
         7 . The lubricating oil composition for a continuously variable transmission according to  claim 3 ,
 wherein the component (B) is at least one borate ester compound represented by the following general formula (1):   
       
         
           
           
               
               
           
         
         wherein in the formula (1), R 1  is a hydrocarbyl group having a carbon number of 1 to 30; and R 2  and R 3  are each independently a hydrogen atom or a hydrocarbyl group having a carbon number of 1 to 30.