Lubricating oil composition for internal combustion engine

Abstract

A lubricating oil composition comprising a GTL (Gas to-Liquid) base oil synthesized by the Fischer-Tropsch process and a viscosity index improver, wherein the content of the viscosity index improver is 0.1 to 20 mass %, and at least HTHSV 50° C./HTHSV 150° C. is 6.50 or less and KV 50° C./HTHSV 150° C. is 8.00 or less.

1 . A lubricating oil composition for an internal combustion engine, comprising a GTL (Gas To Liquid) base oil synthesized by the Fischer-Tropsch method and a viscosity index improver, wherein the content of the viscosity index improver relative to the total amount of lubricating oil composition is 0.1 to 20 mass % by resin amount, and the lubricating oil composition satisfies the following (a) to (e):
 (a) high temperature high shear viscosity (HTHSV (ASTM D4683 or ASTM D5481)) at 150° C., 106 s-1 is 1.0 mPa·s or more;   (b) kinematic viscosity (KV (JIS K2283)) at 100° C. is 3.0 mm2/s or more;   (c) HTHSV50° C./HTHSV 150° C. is 6.50 or less;   (d) KV50° C./HTHSV150° C. is 8.00 or less; and   (e) NOACK evaporation amount (JPI-5S-41) is 15 mass % or less.   
     
     
         2 . The lubricating oil composition of  claim 1 , comprising one or more base oils having KV100° C. of 1 to 8 mm2/s, a viscosity index of 110 or more, % CA by ASTM D3238 of 5 or less, and % CP by ASTM D3238 of 60 or more, wherein: the content of the base oils relative to the total amount of the lubricating oil composition is 50 mass % or less, and a fraction of an entire base oil at 380° C. or less in gas chromatography distillation by ASTM D2887 is 10 mass % or less. 
     
     
         3 . The lubricating oil composition of  claim 1 , wherein at least one of (f) through (i), below, is satisfied:
 (f) the lubricating oil composition includes a metal-including detergent having at least one selection from Ca and Mg, and [Ca]+[Mg]=0.10 to 0.25, where [Ca], [Mg] are respectively concentrations (mass %) of calcium and magnesium in the lubricating oil composition;   (g) the lubricating oil composition contains a succinimide ashless dispersant and/or a boron modified succinimide ashless dispersant, and the dispersants are 0.01 to 0.20 mass % (based on a total amount of the lubricating oil composition) in terms of nitrogen concentration;   (h) the lubricating oil composition includes ZnDTP of 0.03 to 0.09 mass % (based on the total amount of the lubricating oil composition) in terms of phosphorus concentration; and/or   (i) the lubricating oil composition includes an organic molybdenum compound of 0.01 to 0.12 mass % (based on the total amount of the lubricating oil composition) in terms of Mo concentration.   
     
     
         4 . The lubricating oil composition of  claim 1 , including at least one selection from a corrosion inhibitor, a phenol-based antioxidant, an amine-based antioxidant, and a sulfur-containing additive. 
     
     
         5 . The lubricating oil composition of  claim 1 , wherein the viscosity index improver is a comb polymer, preferably wherein the comb polymer comprises (1) repeating units derived from polyolefin-based macro monomers, and (2) repeating units derived from low-molecular-weight monomers selected from a group comprising styrene monomers having between 8 and 17 carbon atoms, alkyl(meth)acrylates having between 1 and 10 carbon atoms in an alcohol base, vinyl esters having between 1 and 11 carbon atoms in an acyl, vinyl ethers having between 1 and 10 carbon atoms in an alcohol base, (di)alkyl fumarate having between 1 and 10 carbon atoms in an alcohol base, (di)alkyl maleates having between 1 and 10 carbon atoms in an alcohol base, and mixtures of these monomers, included in the main chain.