Patent ID: 8236740

Claim:
A lubricating oil composition comprising: a lubricating base oil having % C A of not more than 2, % C P /% C N of not less than 6, % C N of 7 to 13, a sulfur content of not more than 100 ppm by mass, and an iodine value of not more than 2.5, wherein the content of the saturated components in the lubricating base oil is not less than 95% by mass based on the total amount of the lubricating base oil and wherein the ratio M A /M B of the mass of monocyclic saturated components M A to the mass of bi- or more cyclic saturated components M B in the saturated cyclic components is not more than 3; and an ashless antioxidant containing no sulfur as a constituent element, wherein the content of the ashless antioxidant is 0.3 to 5% by mass, based on the total amount of the composition; and at least one alkyl group-substituted aromatic hydrocarbon compound containing one or two alkyl groups having 8 to 30 carbon atoms selected from alkylbenzenes, alkylnaphthalenes, alkylbiphenyls and alkyldiphenylalkanes; wherein the lubricating oil composition comprises both a phenyl-α-naphthylamine compound and an alkylated diphenylamine compound as the ashless antioxidant; and wherein the ratio of the alkylated diphenylamine compound to the total amount of the phenyl-α-naphthylamine compound and the alkylated diphenylamine compound is from 0.1 to 0.9 by mass ratio.