Lubricant oil composition

Abstract

A lubricating oil composition of the invention contains: a lubricating base oil; a component (A) that is a polymethacrylate having a mass average molecular weight in a range from 30,000 to 600,000; and a component (B) that is an olefin copolymer having a 95% weight-loss temperature of 500 degrees C. or less as calculated by differential thermal analysis and having 40 or less of SSI (Shear Stability Index).

I/We claim: 
     
         1 . A lubricating oil composition, comprising:
 a lubricating base oil;   a component (A) that is a polymethacrylate having a mass average molecular weight in a range of from 30,000 to 600,000; and   a component (B) that is an olefin copolymer having a 95% weight-loss temperature of 500 degrees C. or less as calculated by differential thermal analysis and having a shear stability index of 40 or less.   
     
     
         2 . The lubricating oil composition according to  claim 1 , wherein
 the component (A) is a polymethacrylate having a mass average molecular weight in a range of from 200,000 to 600,000, and   the shear stability index of the component (B) is 30 or less.   
     
     
         3 . The lubricating oil composition according to  claim 1 , wherein
 when the lubricating oil composition has a kinematic viscosity at 100 degrees C. in a range of from 9.3 mm 2 /s to less than 12.5 mm 2 /s, the kinematic viscosity at 100 degrees C. of the lubricating oil composition after a shear stability test is 9.3 mm 2 /s or more.   
     
     
         4 . The lubricating oil composition according to  claim 3 , wherein
 the kinematic viscosity at 100 degrees C. of the lubricating oil composition after the shear stability test is 10 mm 2 /s or less.   
     
     
         5 . The lubricating oil composition according to  claim 1 , wherein
 when the lubricating oil composition has a kinematic viscosity at 100 degrees C. in a range of from 5.6 mm 2 /s to less than 9.3 mm 2 /s, the kinematic viscosity at 100 degrees C. of the lubricating oil composition after a shear stability test is 5.6 mm 2 /s or more.   
     
     
         6 . The lubricating oil composition according to  claim 1 , wherein
 the lubricating oil composition has a viscosity index of 120 or more.   
     
     
         7 . The lubricating oil composition according to  claim 1 , wherein
 the lubricating oil composition has a phosphorus content of 0.12 mass % or less, based on a total amount of the composition.   
     
     
         8 . The lubricating oil composition according to  claim 1 , further comprising:
 a metal detergent in a content of from 0.05 mass % to 0.3 mass %, based on a total amount of the composition in terms of metals.   
     
     
         9 . The lubricating oil composition according to  claim 1 , further comprising:
 at least one ashless dispersant selected from the group consisting of polybutenyl succinimide and polybutenyl succinimide borate.   
     
     
         10 . An internal combustion engine, comprising:
 the lubricating oil composition according to  claim 1 .