Lubricating oil composition

Abstract

A lubricating oil composition contains: a first base oil with a kinematic viscosity at 100 degrees C. in a range from 1.5 mm 2 /s to 3.5 mm 2 /s; a second base oil with a kinematic viscosity at 100 degrees C. in a range more than 3.5 mm 2 /s but not more than 100 mm 2 /s; polymethacrylate with a mass average molecular weight in a range from 1×10 4 to 4×10 4 ; and a sulfur compound. The lubricating oil composition has a kinematic viscosity at 100 degrees C. in a range from 5 mm 2 /s to 6 mm 2 /s and a viscosity index of 200 or more.

1 . A lubricating oil composition, comprising:
 a first base oil with a kinematic viscosity at 100 degrees C. in a range from 1.5 mm 2 /s to 3.5 mm 2 /s;   a second base oil with a kinematic viscosity at 100 degrees C. in a range more than 3.5 mm 2 /s but not more than 100 mm 2 /s;   a polymethacrylate with a mass average molecular weight in a range from 1×10 4  to 4×10 4 ; and   a sulfur compound,   wherein:   the lubricating oil composition has having a kinematic viscosity at 100 degrees C. in a range from 5 mm 2 /s to 6 mm 2 /s and a viscosity index of 200 or more;   when a blending amount (mass %) of the first base oil based on a total composition amount is represented by A, and a blending amount (mass %) of the second base oil with the reference to the total composition amount is represented by B, the blending amount A and the blending amount B satisfy a formula [1]:
   0.6≦ A /( A+B )<1  [1];
 
   the blending amount B of the second base oil is 10 mass % or more based on the total composition amount;   a blending amount of the polymethacrylate ranges from 1 mass % to 16 mass % based on the total composition amount;   a blending amount of the sulfur compound is 0.03 mass % or more based on the total composition amount; and   the sulfur compound comprises sulfur in an amount of 20 mass % or more based on the sulfur compound.   
     
     
         2 - 6 . (canceled) 
     
     
         7 . The lubricating oil composition according to  claim 1 , further comprising at least one of a detergent dispersant, an antiwear agent, a friction modifier, a rust inhibitor, a metal deactivator, an antifoaming agent and an antioxidant. 
     
     
         8 . A lubricating method, comprising lubricating an automatic transmission with the lubricating oil composition of  claim 1 . 
     
     
         9 . The lubricating oil composition according to  claim 1 , wherein the sulfur compound is selected from the group consisting of a thiadiazole compound, a mono-olefin sulfide, a di-olefin sulfide, a dihydrocarbyl mono-sulfide, a dihydrocarbyl di-sulfide, a dithiocarbamate compound and an ester compound with a di-sulfide structure. 
     
     
         10 . The lubricating oil composition according to  claim 1 , wherein the sulfur compound is at least one selected from the group consisting of 2,5-bis(n-hexyldithio)-1,3,4-thiadiazole, 2,5-bis(n-octyldithio)-1,3,4-thiadiazole, 2,5-bis(n-nonyldithio)-1,3,4-thiadiazole, 2,5-bis[(1,1,3,3-tetramethylbutyl)dithio]-1,3,4-thiadiazole, 3,5-bis(n-hexyldithio)-1,2,4-thiadiazole, 3,6-bis(n-octyldithio)-1,2,4-thiadiazole, 3,5-bis(n-nonyldithio)-1,2,4-thiadiazole, 3,5-bis[(1,1,3,3-tetramethylbutyl)dithio]-1,2,4-thiadiazole, 4,5-bis(n-octyldithio)-1,2,3-thiadiazole, 4,5-bis(n-nonyldithio)-1,2,3-thiadiazole and 4,5-bis[(1,1,3,3-tetramethylbutyl)dithio]-1,2,3-thiadiazole. 
     
     
         11 . The lubricating oil composition according to  claim 1 , wherein:
 the blending amount B of the second base oil is 10 mass % or more;   the blending amount of the polymethacrylate ranges from 7 mass % to 13 mass % based on the total composition amount; and   the blending amount of the sulfur compound is 0.05 mass % or more based on the total composition amount.   
     
     
         12 . The lubricating oil composition according to  claim 1 , wherein the blending amount of the sulfur compound is 0.5 mass % or more based on the total composition amount. 
     
     
         13 . The lubricating oil composition according to  claim 1 , wherein:
 the first base oil is at least one of a mineral oil and a synthetic oil;   the second base oil is at least one of the mineral oil and the base oil;   the mineral oil is at least of a paraffin-based mineral oil, an intermediate-based mineral oil and a naphthalene-based mineral oil; and   the synthetic oil is at least one of a polybutene, a polyolefin, a polyol ester, a dibasic acid ester, a phosphate, a polyphenyl ether, a polyglycol, an alkylbenzene and an alkylnaphthalene.   
     
     
         14 . The lubricating oil composition according to  claim 13 , wherein the synthetic oil is at least one of an alpha-olefin homopolymer and an alpha-olefin copolymer.