Bimodal gear lubricant formulation

Abstract

The present invention provides a hypoid axle bimodal gear lubricant formulation comprising: (a) a base oil of lubricating viscosity, (b) at least one viscosity index improver, (c) a friction modifier, and (d) an antiwear additive; wherein said bimodal gear lubricant formulation produces a gel permeation chromatogram having at least a first peak representative of the base oil and at least a second peak representative of the viscosity index improver, and wherein said base oil has a viscosity at 100° C. in the range of from about 2 centistokes to about 8 centistokes, and wherein said undilute viscosity index improver has a viscosity in the range of from about 600 centistokes to about 45,00 centistokes.

What is claimed is:  
     
         1 . A hypoid axle bimodal gear lubricant formulation comprising: 
 (a) a base oil of lubricating viscosity,    (b) at least one viscosity index improver,    (c) a friction modifier, and    (d) an antiwear additive;    wherein said bimodal gear lubricant formulation produces a gel permeation chromatogram having at least a first peak representative of the base oil and at least a second peak representative of the viscosity index improver, and wherein said base oil has a viscosity in the range of from about 2 centistokes to about 8 centistokes at 100° C., and wherein said undiluted viscosity index improver has a viscosity in the range of from about 600 centistokes to about 45,00 centistokes at 100° C.    
     
     
         2 . The formulation of  claim 1  wherein said friction modifier is selected from the group consisting of: the reaction products of a C 5  to C 60  carboxylic acid and at least one amine selected from the group consisting of (i) guanidine, urea and thiourea compounds, (ii) C 1  to C 20  hydrocarbyl or hydroxy-substituted hydrocarbyl (a) mono-amines, (b) alkylene diamines, and (c) polyalkylene polyamines; and (iii) N-alkyl glycine.  
     
     
         3 . The formulation of  claim 1  wherein said antiwear additive is an amine derivative salt of dialkyldithiophosphoric acid.  
     
     
         4 . The formulation of  claim 3  wherein said amine is selected from the group consisting of primary alkyl amines, tertiary alkyl amines, heterocyclic amines, anilines, alkoxy amines, amides, and derivatives of amine compounds produced by reaction of the amine compound with an additional oil soluble acidic organic compound.  
     
     
         5 . The formulation of  claim 4  wherein said derivative of an amine compound is selected from the group consisting of an oil-soluble ashless dispersant having a basic nitrogen, an oil-soluble ashless dispersant having at least one hydroxyl group, and an oil soluble ashless dispersant having a basic nitrogen and at least one hydroxyl group.  
     
     
         6 . The formulation of  claim 5  wherein said dispersant is selected from the group consisting of alkenyl succinimides, alkenyl succinic ester-amides, Mannich bases, hydrocarbyl polyamines, and polymeric polyamines.  
     
     
         7 . The formulation of  claim 3  wherein said dialkyldithiophosphoric acid is the reaction product of diphosphorous pentasulfides and at least one alcohol selected from the group consisting of a primary alcohol, a secondary alcohol, a phenol and mixtures thereof  
     
     
         8 . The formulation of  claim 1 , wherein the viscosity of the formulation is from about 13 centistokes to about 24 centistokes at 100° C.  
     
     
         9 . The formulation of  claim 8 , wherein the viscosity of the formulation is from about 15 centistokes to about 19 centistokes at 100° C.  
     
     
         10 . The formulation of  claim 9 , wherein the viscosity of the formulation is about 17 centistokes at 100° C.  
     
     
         11 . A lubricating oil comprising a formulation of  claim 1 .  
     
     
         12 . A gear lubricated with a formulation of  claim 1 .  
     
     
         13 . A gear lubricated with the oil of  claim 11 .  
     
     
         14 . A vehicular transmission lubricated with a formulation of  claim 1 .  
     
     
         15 . A vehicular transmission lubricated with the oil of  claim 11 .  
     
     
         16 . A vehicle comprising the gear of  claim 12 .  
     
     
         17 . A vehicle comprising the gear of  claim 13 .  
     
     
         18 . A vehicle comprising the transmission of  claim 14 .  
     
     
         19 . A vehicle comprising the transmission of  claim 15 .  
     
     
         20 . A method of lubricating a gear box, differential, or transmission comprising adding to a gear box, differential, or transmission the lubricant formulation of  claim 1 .  
     
     
         21 . A method for reducing operating temperatures during green axle break-in comprising adding to said axle the lubricant formulation of  claim 1 , whereby the operating temperature in said axle is reduced relative to the operating temperature in a comparable axle not lubricated with the lubricant formulation of  claim 1 .  
     
     
         22 . A method to improve fuel economy of a vehicle with an axle and gear assembly, said method comprising lubricating the axle or gear with the lubricant formulation of  claim 1 .  
     
     
         23 . A method to improve axle efficiency of a vehicle with an axle and gear assembly, said method comprising lubricating the axle or gear with the lubricant formulation of  claim 1.