The invention provides a lubricating composition comprising a low viscosity base oil and a synergistic mixture of a functionalized ethylene-α-olefin copolymer, a poly(meth)acrylate polymer, and a metal-free anti-wear agent. The invention also provides a method of lubricating an internal combustion engine using such a lubricating composition.

Lubricant compositions comprising a base oil, one or more antioxidants selected from a group consisting of N-α-naphthyl-N-phenylamine antioxidants and diphenylamine antioxidants; and a sulfur-containing additive comprising up to seven carbon atoms exhibit outstanding oxidative stability and non-corrosion properties. The N-α-naphthyl-N-phenylamine antioxidants plus diphenylamine antioxidants in total may be present from about 0.2 wt % to about 0.8 wt %, based on the total weight of the lubricant composition. The sulfur provided by the sulfur-containing additive may be present from about 50 ppm to about 1000 ppm by weight, based on the total weight of the lubricant composition.

A lubricant additive capable of imparting various functions to a lubricant base oil contains an ester compound (A) represented by formula (1) and an ester compound (B) represented by formula (2). (A):(B) being a mass ratio of the ester compound (A) to the ester compound (B) is 99:1 to 80:20.

A lubricant additive includes a monoester carboxylic acid salt (A) represented by formula (1). ##STR00001## In formula (1), R.sup.1 represents a single bond between carbon atoms of carbonyl groups, or a divalent hydrocarbon group having 1 to 4 carbon atoms, and R.sup.2 represents a hydrocarbon group having 1 to 22 carbon atoms. AO represents an oxyalkylene group of one type selected from oxyalkylene groups having 2 to 4 carbon atoms, or a mixed oxyalkylene group of two or more types selected from oxyalkylene groups having 2 to 4 carbon atoms, and n is an average number of added moles of the oxyalkylene group represented by AO and is 0 to 5. M represents organic ammonium.

A lubricant additive capable of imparting various functions to a lubricant base oil contains an ester compound (A) represented by formula (1) and an ester compound (B) represented by formula (2). (A):(B) being a mass ratio of the ester compound (A) to the ester compound (B) is 99:1 to 80:20.

A lubricant additive includes a monoester carboxylic acid salt (A) represented by formula (1).

##STR00001##

In formula (1), R.sup.1 represents a single bond between carbon atoms of carbonyl groups, or a divalent hydrocarbon group having 1 to 4 carbon atoms, and R.sup.2 represents a hydrocarbon group having 1 to 22 carbon atoms. AO represents an oxyalkylene group of one type selected from oxyalkylene groups having 2 to 4 carbon atoms, or a mixed oxyalkylene group of two or more types selected from oxyalkylene groups having 2 to 4 carbon atoms, and n is an average number of added moles of the oxyalkylene group represented by AO and is 0 to 5. M represents organic ammonium.

A quaternary ammonium compound of formula (I): wherein R.sup.0, R.sup.1, R.sup.2 and R.sup.3 is each independently an optionally substituted hydrocarbyl group, X is a linking group, R.sup.4 is an optionally substituted alkylene group, R.sup.5 is hydrogen or an optionally substituted alkyl, alkenyl or aryl group, and n is 0 or a positive integer, provided that n is not 0 when R.sup.5 is hydrogen. ##STR00001##

A quaternary ammonium salt of formula (I): (I) where in X is a linking group; Y is O, NH or NR.sup.1 wherein R.sup.1 is H or an optionally substituted hydrocarbyl group; Q.sup.+ is a moiety that includes a quaternary ammonium cation; A.sup.− is an anion; R.sup.2 is an optionally substituted alkylene group; R.sup.3 is hydrogen or an optionally substituted hydrocarbyl group; and n is 0 or a positive integer; provided that n is not 0 when R.sup.3 is hydrogen. ##STR00001##

A quaternary ammonium compound of formula (I): (I) wherein R.sup.0, R.sup.1, R.sup.2 and R.sup.3 is each independently an optionally substituted hydrocarbyl group, X is a linking group, R.sup.4 is an optionally substituted alkylene group, R5 is hydrogen or an optionally substituted alkyl, alkenyl or aryl group, and n is 0 or a positive integer, provided that n is not 0 when R5 is hydrogen. ##STR00001##

A lubricating composition which, when used with a device for clamping an article, such as a chuck, produces excellent lubricating properties whilst remaining strongly adhered to metal parts in a clamping mechanism of the device and showing enhanced chemical and physical resistance to fluids such as cutting fluids.