Lubricating oil compositions

Abstract

A lubricating oil composition formulated with a viscosity index (VI) improver composition including a combination of an ethylene α-olefin copolymer having no greater than 66 mass % of units derived from ethylene, and a linear diblock copolymer including at least one block derived primarily from a vinyl aromatic hydrocarbon monomer, and at least one block derived primarily from diene monomer.

1 . A lubricating oil composition comprising a major amount of an oil of a Group II or higher base oil of lubricating viscosity and a minor amount of a polymer composition comprising at least a first polymer that is an ethylene α-olefin copolymer comprising no greater than 66 mass % of units derived from ethylene; and a second polymer comprising a linear diblock copolymer comprising at least one block derived primarily from a vinyl aromatic hydrocarbon monomer, and at least one block derived primarily from diene monomer.  
     
     
         2 . A lubricating oil composition as claimed in  claim 1 , wherein the first polymer and the second polymer are present in a mass % ratio of from about 80:20 to about 20:80.  
     
     
         3 . A lubricating oil composition as claimed in  claim 2 , wherein said ethylene α-olefin copolymer is an ethylene-propylene copolymer and said linear diblock copolymer is at least one diblock copolymer comprising at least one polystyrene block, and at least one block derived from isoprene, butadiene, or a mixture thereof.  
     
     
         4 . A lubricating oil composition as claimed in  claim 3 , wherein said ethylene α-olefin copolymer is an ethylene-propylene copolymer and said linear diblock copolymer is at least one diblock copolymer selected from the group consisting of hydrogenated styrene/butadiene block copolymers and hydrogenated styrene/isoprene block copolymers.  
     
     
         5 . A lubricating oil composition as claimed in  claim 3 , wherein said ethylene-propylene copolymer comprises from about 20 to about 66 mass % of units derived from ethylene.  
     
     
         6 . A lubricating oil composition as claimed in  claim 3 , wherein said ethylene-propylene copolymer has a Shear Stability Index (SSI) value of from about 20% to about 50% (30 cycles), and the polydiene block of the diblock copolymer comprises from about 40 mass % to 90 mass % derived from isoprene and from about 10 mass % to about 60 mass % derived from butadiene.  
     
     
         7 . A lubricating oil composition as claimed in  claim 1 , wherein said base oil of lubricating viscosity has a saturates content of at least about 80.  
     
     
         8 . A lubricating oil composition as claimed in  claim 1 , containing less than about 30 mass % of Group I base oil.  
     
     
         9 . A lubricating oil composition as claimed in  claim 1 , further comprising a nitrogenous dispersant derived from a polyalkene having a number average molecular weight (M n ) of greater than about 1500, wherein said base oil of lubricating viscosity has a saturates content of at least about 80%, and wherein said lubricating oil composition contains less than about 0.4 mass % of sulfur, less than about 0.12 mass % phosphorus and less than about 1.2 mass % of sulfated ash.  
     
     
         10 . A method of operating an internal combustion engine, said method comprising lubricating said engine with a lubricating oil composition as claimed in  claim 1 , and operating the lubricating engine.  
     
     
         11 . A method of operating an internal combustion engine, said method comprising lubricating said engine with a lubricating oil composition as claimed in  claim 9 , and operating the lubricating engine.  
     
     
         12 . The method as claimed in  claim 11 , wherein said engine is a heavy duty diesel (HDD) engine.  
     
     
         13 . A method of improving the soot-handling properties of a lubricating oil composition for the lubrication of an internal combustion engine, which method comprises formulating said lubricating oil composition with a polymer composition comprising at least a first polymer that is an ethylene α-olefin copolymer comprising no greater than 66 mass % of units derived from ethylene; and a second polymer comprising a linear diblock copolymer comprising at least one block derived primarily from a vinyl aromatic hydrocarbon monomer, and at least one block derived primarily from diene monomer.  
     
     
         14 . The method as claimed in  claim 13 , wherein said lubricating oil composition is further formulated with a nitrogenous dispersant derived from a polyalkene having a number average molecular weight (M n ) of greater than about 1500, and a base oil of lubricating viscosity having a saturates content of at least about 80%, and wherein said lubricating oil composition contains less than about 0.4 mass % of sulfur, less than about 0.12 mass % phosphorus and less than about 1.2 mass % of sulfated ash.