Lubricating oil composition

Abstract

The present invention provides a lubricating oil composition having a low traction coefficient that can reduce the friction between parts such as gear teeth surfaces, exposed to elastohydrodynamic lubrication conditions to attain energy saving properties and high efficiency, suitable for use in manual, automatic and continuously variable transmissions of automobiles or industrial gear systems. The low traction coefficient lubricating oil composition comprises a lubricating base oil containing (A) a partial ester of a polyhydric alcohol and a carboxylic acid in an amount of 0.1 to 80 percent by mass on the basis of the total mass of the base oil and having a kinematic viscosity at 100° C. of 1 to 15 mm 2 /s, the composition having a kinematic viscosity at 100° C. of 1 to 20 mm 2 /s.

1 . A lubricating oil composition having a low traction coefficient, comprising a lubricating base oil containing (A) a partial ester of a polyhydric alcohol and a carboxylic acid in an amount of 0.1 to 80 percent by mass on the basis of the total mass of the base oil and having a kinematic viscosity at 100° C. of 1 to 15 mm 2 /s, the composition having a kinematic viscosity at 100° C. of 1 to 20 mm 2 /s. 
     
     
         2 . The lubricating oil composition according to  claim 1  wherein (A) the partial ester of a polyhydric alcohol and a carboxylic acid is a partial ester of trimethylolpropane and a monovalent carboxylic acid. 
     
     
         3 . The lubricating oil composition according to  claim 1 , further comprising (B) a poly(meth)acrylate compound composed of a structural unit represented by formula (I) below, in an amount of 0.01 to 20 percent by mass: 
       
         
           
           
               
               
           
         
         wherein R 1  is hydrogen or methyl and R 2  is a hydrocarbon group having 1 to 30 carbon atoms. 
       
     
     
         4 . The lubricating oil composition according to  claim 1 , wherein the composition has a traction coefficient of 0.013 or less. 
     
     
         5 . The lubricating oil composition according to  claim 1 , wherein the composition has a ratio of the traction coefficient to the 100° C. kinematic viscosity (mm 2 /s) which is 1.2E-03 or less. 
     
     
         6 . The lubricating oil composition according to  claim 1 , wherein the composition has a −40° C. Brookfield viscosity of 40,000 mPa·s or less.