Lubricating oil composition

Abstract

A lubricating oil composition includes: a lubricant base having a kinematic viscosity at 100° C. of 1.0 to 10 mm 2 /s and % C P of no less than 70; (A) 0.1 to 30 mass % of a poly(meth)acrylate viscosity index improver having a PSSI of no more than 5, a weight average molecular weight of 10,000 to 500,000, a ratio A/B of less than 2.4 and a ratio C/B of less than 1.4, the ratio A/B being a ratio of a viscosity increase effect A on kinematic viscosity at 100° C. to a viscosity increase effect B on HTHS viscosity at 150° C., and the ratio C/B being a ratio of a viscosity increase effect C on kinematic viscosity at 150° C. to the viscosity increase effect B on HTHS viscosity at 150° C.; and (B) 0.01 to 2.0 mass % of a friction modifier.

1 . A lubricating oil composition comprising:
 a lubricant base oil comprising one or more base oil, the lubricant base oil having a kinematic viscosity at 100° C. of 1.0 to 10 mm 2 /s and % C P  of no less than 70;   (A) 0.1 to 30 mass % of a poly(meth)acrylate viscosity index improver having a PSSI of no more than 5, a weight average molecular weight of 10,000 to 500,000, a ratio A/B of less than 2.4 and a ratio C/B of less than 1.4, the ratio A/B being a ratio of a viscosity increase effect A on kinematic viscosity at 100° C. represented by the following formula (1) to a viscosity increase effect B on HTHS viscosity at 150° C. represented by the following formula (2), and the ratio C/B being a ratio of a viscosity increase effect C on kinematic viscosity at 150° C. represented by the following formula (3) to the viscosity increase effect B on HTHS viscosity at 150° C. represented by the following formula (2); and   (B) 0.01 to 2.0 mass % of a friction modifier,
     A=X−X   0   (1)
 
   
       wherein in the formula (1), A represents the viscosity increase effect of the viscosity index improver on kinematic viscosity at 100° C.; X represents kinematic viscosity at 100° C. (unit: mm 2 /s) of a mixture consisting of a reference base oil and 6 mass % of the viscosity index improver, the reference base oil being a hydrocracked base oil YUBASE™ 4 manufactured by SK Lubricants Co., Ltd.; and X 0  represents kinematic viscosity at 100° C. (unit: mm 2 /s) of the reference base oil;
     B=Y−Y   0   (2)
 
 
       wherein in the formula (2), B represents the viscosity increase effect of the viscosity index improver on HTHS viscosity at 150° C.; Y represents HTHS viscosity at 150° C. (unit: mPa·s) of the mixture consisting of the reference base oil and 6 mass % of the viscosity index improver; and Y 0  represents HTHS viscosity at 150° C. (unit: mPa·s) of the reference base oil; and
     C=Z−Z   0   (3)
 
 
       wherein in the formula (3), C represents the viscosity increase effect of the viscosity index improver on kinematic viscosity at 150° C.; Z represents kinematic viscosity at 150° C. (unit: mm 2 /s) of the mixture consisting of the reference base oil and 6 mass % of the viscosity index improver; and Z 0  represents kinematic viscosity at 150° C. (unit: mm 2 /s) of the reference base oil. 
     
     
         2 . The lubricating oil composition according to  claim 1 ,
 wherein the lubricant base oil has a NOACK evaporation loss at 250° C. of less than 15 mass %.   
     
     
         3 . The lubricating oil composition according to  claim 2 ,
 wherein the (A) viscosity index improver has a ratio (Mw/PSSI) of the weight average molecular weight (Mw) to the PSSI of no less than 1×10 4 .   
     
     
         4 . The lubricating oil composition according to  claim 2 ,
 wherein the (B) friction modifier is a molybdenum-based friction modifier.   
     
     
         5 . The lubricating oil composition according to  claim 2 ,
 wherein the lubricating oil composition has a NOACK evaporation loss at 250° C. of no more than 15 mass %.   
     
     
         6 . The lubricating oil composition according to  claim 1 ,
 wherein the lubricant base oil has a NOACK evaporation loss at 250° C. of no less than 15 mass %; and   the poly(meth)acrylate viscosity index improver has a weight average molecular weight of 10,000 to 400,000.   
     
     
         7 . The lubricating oil composition according to  claim 6 ,
 wherein the (A) viscosity index improver has a ratio (Mw/PSSI) of the weight average molecular weight (Mw) to the PSSI of no less than 1×10 4 .   
     
     
         8 . The lubricating oil composition according to  claim 6 ,
 wherein the (B) friction modifier is a molybdenum-based friction modifier.   
     
     
         9 . The lubricating oil composition according to  claim 6 ,
 wherein the lubricating oil composition has a NOACK evaporation loss at 250° C. of no less than 15 mass %.   
     
     
         10 . The lubricating oil composition according to  claim 6 ,
 wherein the lubricant base oil is a wax isomerized base oil having a kinematic viscosity at 100° C. of 2.0 to 4.5 mm 2 /s, % C P  of no less than 85, and a NOACK evaporation loss at 250° C. of no less than 15 mass %.