Lubricating oil composition

Abstract

[Problem] To provide a lubricating oil composition capable of attaining high-level fuel efficiency, durability and piston detergency in internal-combustion engines. [Means for Resolution] The lubricating oil composition according to the present invention contains a viscosity index improver and a metallic detergent in at least one base oil selected from mineral oils and synthetic oils therein, wherein the viscosity index improver contains a polymethacrylate viscosity index improver and an olefin copolymer viscosity index improver, the polymethacrylate viscosity index improver is contained in an amount of from 3.0% by mass to 9.5% by mass based on the total amount of the lubricating oil composition, the metallic detergent is at least one selected from calcium sulfonate, calcium phenate and calcium salicylate, the calcium amount derived from the metallic detergent is from 500 ppm to 1500 ppm based on the total amount of the lubricating oil composition, the high-temperature high-shear viscosity at 150° C. of the lubricating oil composition is 2.6 mPa·s or more, the high-temperature high-shear viscosity at 80° C. of the lubricating oil composition is 7.8 mPa·s or less, and the ratio of the high-temperature high-shear viscosity at 100° C. of the lubricating oil composition to the high-temperature high-shear viscosity at 150° C. thereof is 2.05 or less.

1 . A lubricating oil composition comprising a viscosity index improver and a metallic detergent in at least one base oil selected from mineral oils and synthetic oils therein:
 wherein the viscosity index improver contains a polymethacrylate viscosity index improver and an olefin copolymer viscosity index improver,   the polymethacrylate viscosity index improver is contained in an amount of from 3.0% by mass to 9.5% by mass based on the total amount of the lubricating oil composition,   the metallic detergent contains at least one selected from calcium sulfonate, calcium phenate and calcium salicylate,   the calcium amount derived from the metallic detergent is from 500 ppm to 1500 ppm based on the total amount of the lubricating oil composition,   the high-temperature high-shear viscosity at 150° C. of the lubricating oil composition is 2.6 mPa·s or more, the high-temperature high-shear viscosity at 80° C. of the lubricating oil composition is 7.8 mPa·s or less,   and the ratio of the high-temperature high-shear viscosity at 100° C. of the lubricating oil composition to the high-temperature high-shear viscosity at 150° C. thereof is 2.05 or less.   
     
     
         2 . The lubricating oil composition according to  claim 1 , wherein the NOACK value, as measured in the NOACK test at 250° C. for 1 hour according to ASTM D 5800, is 13% by mass or less. 
     
     
         3 . The lubricating oil composition according to  claim 1 , wherein the polymethacrylate viscosity index improver is a non-dispersant type polymethacrylate viscosity index improver. 
     
     
         4 . The lubricating oil composition according to  claim 1 , wherein the content of the olefin copolymer viscosity index improver is from 30 parts by mass to 250 parts by mass relative to 100 parts by mass of the polymethacrylate viscosity index improver. 
     
     
         5 . The lubricating oil composition according to  claim 1 , wherein the weight-average molecular weight of the polymethacrylate viscosity index improver is from 100,000 to 500,000. 
     
     
         6 . The lubricating oil composition according to  claim 1 , which comprises an antioxidant selected from a phenol-based antioxidant and an amine-based antioxidant in an amount of from 0.5% by mass to 10% by mass based on the total amount of the lubricating oil composition. 
     
     
         7 . A method for producing a lubricating oil composition, which comprises:
 incorporating a viscosity index improver that contains a polymethacrylate viscosity index improver and an olefin copolymer viscosity index improver so that the amount of the polymethacrylate viscosity index improver is from 3.0% by mass to 9.5% by mass based on the total amount of the lubricating oil composition,   and a metallic detergent containing at least one selected from calcium sulfonate, calcium phenate and calcium salicylate,   in at least one base oil selected from mineral oils and synthetic oils:   so that the calcium amount derived from the metallic detergent is from 500 ppm to 1500 ppm based on the total amount of the lubricating oil composition,   that the high-temperature high-shear viscosity at 150° C. of the lubricating oil composition is 2.6 mPa·s or more, that the high-temperature high-shear viscosity at 80° C. of the lubricating oil composition is 7.8 mPa·s or less,   and that the ratio of the high-temperature high-shear viscosity at 100° C. of the lubricating oil composition to the high-temperature high-shear viscosity at 150° C. thereof is 2.05 or less.