Lubricating oil composition

Abstract

A lubricating oil composition comprising a lubricating base oil having a kinematic viscosity at 100° C. of 1 to 10 mm 2 /s, and a poly(meth)acrylate viscosity index improver containing a structural unit represented by the formula (1) in a proportion of 30 to 90 mol % and having a hydrocarbon main chain ratio of 0.18 or less: wherein R 1 represents hydrogen or a methyl group, and R 2 represents a linear or branched hydrocarbon group having a carbon number of 6 or less.

1 . A lubricating oil composition comprising:
 a lubricating base oil having a kinematic viscosity at 100° C. of 1 to 10 mm 2 /s; and   a poly(meth)acrylate viscosity index improver containing a structural unit represented by the following formula (1) in a proportion of 30 to 90 mol % and having a hydrocarbon main chain ratio of 0.18 or less:   
       
         
           
           
               
               
           
         
       
       wherein R 1  represents hydrogen or a methyl group, and R 2  represents a linear or branched hydrocarbon group having a carbon number of 6 or less. 
     
     
         2 . The lubricating oil composition according to  claim 1 , wherein the poly(meth)acrylate viscosity index improver is a poly(meth)acrylate viscosity index improver containing the structural unit represented by the formula (1) in the proportion of 30 to 90 mol % and a structural unit represented by the following formula (2) in a proportion of 0.1 to 50 mol %, and having a hydrocarbon main chain ratio of 0.18 or less: 
       
         
           
           
               
               
           
         
       
       wherein R 3  represents hydrogen or a methyl group, and R 4  represents a linear or branched hydrocarbon group having a carbon number of 16 or more. 
     
     
         3 . The lubricating oil composition according to  claim 1 , wherein the viscosity index improver is a viscosity index improver having a PSSI of 10 or less and a ratio of a molecular weight to the PSSI (Mw/PSSI) of 1×10 4  or more. 
     
     
         4 . The lubricating oil composition according to  claim 2 ,
 wherein R 4  in the formula (2) is a linear or branched hydrocarbon group having a carbon number of 16 or more and 19 or less, and   in the viscosity index improver, the proportion of the structural unit represented by the formula (2) in which R 4  is a linear or branched hydrocarbon group having a carbon number of 18 is 0.1 to 40 mol %.   
     
     
         5 . The lubricating oil composition according to  claim 1 ,
 wherein an aromatic content of the lubricating base oil is 5.0% or less,   a kinematic viscosity at 100° C. of the lubricating oil composition is 6 to 9 mm 2 /s,   a viscosity index of the lubricating oil composition is 180 or more,   an HTHS viscosity at 150° C. of the lubricating oil composition is 2.6 mPa·s or more, and   an HTHS viscosity at 100° C. of the lubricating oil composition is 5.0 mPa·s or less.   
     
     
         6 . The lubricating oil composition according to  claim 1 , further comprising a friction modifier. 
     
     
         7 . The lubricating oil composition according to  claim 6 , wherein the friction modifier is an organic molybdenum friction modifier. 
     
     
         8 . The lubricating oil composition according to  claim 1 , further comprising a second viscosity index improver which is a dispersive viscosity index improver. 
     
     
         9 . The lubricating oil composition according to  claim 1 , further comprising a metallic detergent, wherein the metallic detergent has a linear or branched hydrocarbon group having a carbon number of 20 or more. 
     
     
         10 . The lubricating oil composition according to  claim 1 , further comprising a metallic detergent, wherein the metallic detergent is an overbased metallic detergent having a metal ratio of 3.4 or less. 
     
     
         11 . The lubricating oil composition according to  claim 9 , wherein the metallic detergent is an overbased alkaline earth metal salicylate prepared by overbasing an alkaline earth metal salicylate with an alkaline earth metal borate.