Patent ID: 8129319

Claim:
A lubricating composition comprising: a base oil; a phenolic antioxidant; an aminic antioxidant; and an ester compound having a disulfide structure according to the following general formula (I): (R 1 OOC) n -A 1 -S—S-A 2 -(COOR 2 ) m (I) wherein R 1 and R 2 each independently represent a hydrocarbyl group having 1-30 carbon atoms; A 1 and A 2 each independently represent a divalent or trivalent hydrocarbon group; and m and n each independently represent 1 or 2, wherein the base oil has a sulfur content of 50 ppm by weight or less, a % CA of 3.0 or less as determined by ring analysis, and a kinematic viscosity of 1-500 mm 2 /s at 40° C., wherein the phenolic antioxidant is selected from the group consisting of a monocyclic phenol and a biscyclic phenol, wherein the aminic antioxidant is a dialkyldiphenylamine, wherein the ester compound having a disulfide structure according to the general formula (I) is present in an amount of 0.05-3.0 wt. %, based on a total weight of the lubricating composition, wherein the ester compound having a disulfide structure according to the general formula (I) includes one or more ester compounds selected from the group consisting of: a dimer of an alkyl ester of thioglycolic acid, wherein the alkyl group has 4-18 carbon atoms; a dimer of an alkyl ester of mercaptomaleic acid, wherein the alkyl group has 4-18 carbon atoms; a dimer of an alkyl ester of thiosalicylic acid, wherein the alkyl group has 4-18 carbon atoms; and a dimer of an alkyl ester of mercaptopropionic acid, wherein the alkyl group has 4-18 carbon atoms, and wherein a weight ratio of the phenolic and aminic antioxidants to the ester compound having a disulfide structure according to the general formula (I) is 20-80:80-20.