Lubrication oil composition

Abstract

The present invention provides a lubricating oil composition having an extremely high viscosity index and a low coefficient of traction as a low coefficient of fluid friction in an elastohydrodynamic lubrication which is excellent in saving of energy and reduction in fuel consumption. The lubricating oil composition according to the present invention includes the following components (A) and (B): (A) a low-viscosity synthetic oil comprising a compound containing ether bond(s) in a molecule thereof and having a kinematic viscosity of less than 10 mm 2 /s as measured at 40° C., in which a ratio of the number of oxygen atoms to the number of carbon atoms as constituents of the compound (O/C ratio) and the kinematic viscosity (mm 2 /s) of the compound as measured at 40° C. satisfy the following formula (1); Kinematic Viscosity at 40° C.≦12−[(O/C ratio)×30] (1); and (B) a high-viscosity synthetic oil as a hydrocarbon-based synthetic oil having a kinematic viscosity of 40 mm 2 /s or more as measured at 100° C. which includes at least one compound selected from the group consisting of an α-olefin oligomer, a hydrogenated α-olefin oligomer and an ethylene-propylene co-oligomer.

1 . A lubricating oil composition, comprising:
 (A) a low-viscosity synthetic oil comprising a compound comprising an ether bond in a molecule thereof and having a kinematic viscosity of less than 10 mm 2 /s as measured at 40° C., in which a ratio of number of oxygen atoms to number of carbon atoms as constituents of the compound (O/C ratio) and the kinematic viscosity (mm 2 /s) of the compound as measured at 40° C. satisfy formula (1):
   Kinematic Viscosity at 40° C.≦12−[(O/C ratio)×30]  (1);
 
   
       and
 (B) a high-viscosity synthetic oil as a hydrocarbon-based synthetic oil having a kinematic viscosity of 40 mm 2 /s or more as measured at 100° C. which comprises at least one compound selected from the group consisting of an α-olefin oligomer, a hydrogenated α-olefin oligomer and an ethylene-propylene co-oligomer. 
 
     
     
         2 . The lubricating oil composition according to  claim 1 , wherein the component (A) is at least one compound selected from the group consisting of:
 (a-1) a dialkyl ether of di- or tri-ethylene glycol, wherein two alkyl groups in the dialkyl ether may be the same or different from each other;   (a-2) di- or tri-ethylene glycol comprising an alkyl ether at one terminal end thereof and an alkyl ester at the other terminal end thereof; and   (a-3) an alkoxyalkyl ester of a saturated or unsaturated fatty acid.   
     
     
         3 . The lubricating oil composition according to  claim 1 , wherein the component (B) is the α-olefin oligomer, hydrogenated α-olefin oligomer, or both, which have a kinematic viscosity of from 100 to 150 mm 2 /s as measured at 100° C. 
     
     
         4 . The lubricating oil composition according to  claim 1 , wherein the component (B) is the α-olefin oligomer, hydrogenated α-olefin oligomer, or both, which are produced with a metallocene catalyst. 
     
     
         5 . The lubricating oil composition according to  claim 1 , further comprising as a component (C), at least one lubricating oil additive selected from the group consisting of an antioxidant, an extreme pressure agent an anti-wear agent, a dispersant and a metal-based detergent.