Lubricating oil composition for internal combustion engine

Abstract

A lubricating oil composition for an internal combustion engine including: (A) a lubricant base oil having a kinematic viscosity at 100° C. of 2 to 8 mm 2 /s and having an aromatic content of no more than 10 mass %; (B) a metallic detergent including: (B1) a metallic detergent overbased with calcium carbonate; and (B2) a metallic detergent overbased with magnesium carbonate; and (C) a molybdenum sulfide dithiocarbamate or a molybdenum oxysulfide dithiocarbamate, wherein the composition has, on the basis of the total mass of the composition, a calcium content of no more than 1500 mass ppm, a magnesium content of no less than 300 mass ppm, and a molybdenum content of no less than 600 mass ppm; and the composition has an HTHS viscosity at 150° C. of no more than 2.7 mPa·s.

1 . A lubricating oil composition for an internal combustion engine comprising:
 (A) a lubricant base oil having a kinematic viscosity at 100° C. of 2 to 8 mm 2 /s and having an aromatic content of no more than 10 mass %;   (B) a metallic detergent comprising:
 (B1) a metallic detergent overbased with calcium carbonate; and 
 (B2) a metallic detergent overbased with magnesium carbonate; and 
   (C) a molybdenum sulfide dithiocarbamate or a molybdenum oxysulfide dithiocarbamate,   wherein the composition has a calcium content of 1400 to 1500 mass ppm on the basis of the total mass of the composition;   the composition has a magnesium content of 350 to 600 mass ppm on the basis of the total mass of the composition;   the composition has a molybdenum content of no less than 600 mass ppm on the basis of the total mass of the composition;   the composition has a boron content of 200 to 300 mass ppm on the basis of the total mass of the composition;   the composition has an HTHS viscosity at 150° C. of no more than 2.7 mPa·s, and   the composition has a parameter r s ′ represented by the following mathematical formula (2) of 1.15 to 1.50:
     r   s ′=([S]′+[Mo]+[Zn])/([Mg]+2×[Ca])  (2)
 
   wherein in the mathematical formula (2), [S]′ represents a sulfur content derived from additives other than any sulfonate detergent (unit: mass ppm); [Mo] represents the molybdenum content of the composition (unit: mass ppm); [Zn] represents a zinc content of the composition (unit: mass ppm); [Mg] represents the magnesium content of the composition (unit: mass ppm); and [Ca] represents the calcium content of the composition (unit: mass ppm).   
     
     
         2 . The lubricating oil composition according to  claim 1 , comprising:
 (D) an amine antioxidant and/or a phenol antioxidant.   
     
     
         3 . The lubricating oil composition according to  claim 1 , comprising:
 (D) an amine antioxidant,   wherein the composition has a ratio (X 100 /X 150 ) of an HTHS viscosity at 100° C. (X 100 ) to the HTHS viscosity at 150° C. (X 150 ) of no more than 2.0.   
     
     
         4 . (canceled) 
     
     
         5 . The lubricating oil composition according to  claim 3 ,
 wherein the composition has the molybdenum content of 700 to 800 mass ppm on the basis of the total mass of the composition.   
     
     
         6 . The lubricating oil composition according to  claim 3 , comprising:
 (E) a zinc dialkyldithiophosphate,   wherein the composition has a sulfur content of 0.20 to 0.30 mass % on the basis of the total mass of the composition.   
     
     
         7 . The lubricating oil composition according to  claim 3 ,
 wherein the composition has the ratio (X 100 /X 50 ) of the HTHS viscosity at 100° C. (X 100 ) to the HTHS viscosity at 150° C. (X 150 ) of 1.8 to 2.0.   
     
     
         8 . A method for suppressing LSPI of an internal combustion engine, the method comprising:
 operating an internal combustion engine, while lubricating a cylinder of the internal combustion engine by means of the lubricating oil composition as in  claim 1 .