Commercial VI improvers with dispersant properties are typically made with a particular amine that is selected to disperse soot, or with a particular amine that is selected to disperse sludge and varnish. However, unless all deleterious materials in an engine oil are effectively dispersed, oil filter plugging may occur. Combining two different amine dispersants may not always be effective for dispersing all of the deleterious materials that may cause filter plugging.
Additionally, certain commercial VI improvers with dispersant properties may be highly effective for dispersing soot at the levels generated in today's modem engines in Group I and Group II base oils. However, the treat rate for such VI improvers in high viscosity index base stocks, i.e., base stocks having a viscosity index of greater than 120, is too low to provide effective dispersant performance and relatively high shear stability.
Accordingly, there continues to be a need for lubricant formulations and additives that provide wider dispersant properties for modern engines and are effective at relatively lower treat rates than commercial VI improvers having dispersant properties.
In accordance with exemplary embodiments, the disclosure provides a lubricating oil composition and methods of operating an internal combustion engine to provide improved engine operational performance. The lubricating composition includes a major amount of oil of lubricating viscosity; and a minor amount of at least one highly grafted, multi-functional olefin copolymer made by reacting an acylating agent with an olefin copolymer having a number average molecular weight greater than about 10,000 up to about 50,000 in the presence of a free radical initiator to provide an acylated olefin copolymer having a degree of grafting (DOG) of the acylating agent on the olefin copolymer of from above about 1.5 to about 3.0 wt. %. The acylated olefin copolymer is then reacted with an amine to provide the highly grafted, multi-functional olefin copolymer.
In another exemplary embodiment, the disclosure provides a method for extending an oil drain interval for an internal combustion engine. The method includes lubricating the engine with a lubricant composition including a major amount of oil of lubricating viscosity, and a minor amount of at least one highly grafted, multi-functional olefin copolymer made by reacting an acylating agent with an olefin copolymer having a number average molecular weight greater than about 10,000 and less than about 50,000 in the present of a free radical initiator to provide an acylated olefin copolymer having a degree of grafting (DOG) of the acylating agent on the olefin copolymer ranging from about 1.5 to about 3.0 wt. %. The acylated olefin copolymer is then reacted with an amine to provide the highly grafted, multi-functional olefin copolymer, and the engine is operated using the lubricant composition.
Yet another exemplary embodiment of the disclosure provides a method of reducing oil filter plugging for an oil filter of an internal combustion engine. The method includes lubricating the engine with a lubricant composition including a major amount of oil of lubricating viscosity, and a minor amount of at least one highly grafted, multi-functional olefin copolymer made by reacting an acylating agent with an olefin copolymer having a number average molecular weight greater than about 10,000 and less than about 50,000 in the present of a free radical initiator to provide an acylated olefin copolymer having a degree of grafting (DOG) of the acylating agent on the olefin copolymer ranging from about 1.5 to about 3.0 wt. %. The acylated olefin copolymer is then reacted with an amine to provide the highly grafted, multi-functional olefin copolymer, and the engine is operated using the lubricant composition.
Accordingly, a primary advantage of the exemplary embodiments may be an increased in oil change intervals due to a lower viscosity increase in the lubricating oil for an engine operating with the lubricating oil composition. Another advantage is that a copolymer dispersant VI improver made with a certain mixture of amines may provide synergistic performance for handling a wider range of deleterious materials that may accumulate in a lubricant during engine operation.