Patent ID: 7776805

Claim:
A lubricating oil composition comprising a copolymer containing a constituent unit derived from ethylene, and a constituent unit derived from an α-olefin having 3 to 20 carbon atoms, wherein the copolymer improves low-temperature properties of the lubricating oil composition and the copolymer has the following (1) to (6): (1) the copolymer has a melting point (Tm) measured by DSC of −20° C. to 100° C.; (2) the copolymer has a molecular weight distribution (Mw/Mn) measured by GPC of 1.6 to 5.0; (3) the copolymer has a half-width (ΔThalf) of a melting peak measured by DSC of 90° C. or less; (4) the half-width (ΔThalf) and the melting point (Tm) satisfy the relationship shown by the expression: ΔThalf≦−0.71×Tm+101.4 (5) the copolymer has a heat of melting (ΔH) measured by DSC of 100 J/g or less; and (6) the heat of melting (ΔH), a crystallization temperature Tc measured by DSC, and a crystallization temperature Tcrystaf measured by a CRYSTAF method satisfy the relationship shown by the expression: Tc−Tcrystaf≧0.028×ΔH+25.3 wherein the amount of the copolymer is 0.1 to 30 percent by weight based on the lubricant oil composition.