Low viscosity gear lubricants

Abstract

A lubricant composition of 40 to 95% of an oil having a kinematic viscosity at 100° C. of 3 to 7.5; 0.3 to 2% of an amine salt of a phosphorus compound obtained by reacting phosphorus pentasulfide with one or more alcohols having 4 to about 13, or 4 to 8, or 6, carbon atoms, with an alkylene oxide, and further with phosphorus pentoxide, and salting the resulting material with one or more amines having 2 to 20 or 12 to 24 carbon atoms; and an active-sulfur containing agent in an amount to provide 0.5 to 7% sulfur to the composition provides good wear protection to gears at a relatively low viscosity of the composition.

1 . A lubricant composition comprising:
 (a) about 40 to about 95 percent by weight, or about 58 to about 80 percent by weight, of an oil having a kinematic viscosity at 100° C. by ASTM D445 of about 3 to about 7.5, or about 3.6 to about 6, or about 3.5 to about 5 mm 2/ s;   (b) about 0.3 to about 2 percent by weight of an amine salt of a phosphorus compound, or mixtures thereof, obtained by reacting phosphorus pentasulfide with one or more alcohols having 4 to about 13, or 4 to 8, or 6, carbon atoms, with an alkylene oxide, and further with phosphorus pentoxide, and salting the resulting material with one or more amines having 2 to 20 or 12 to 24 carbon atoms; and   (c) a sulfurized olefin in an amount to provide about 0.5 to about 7, or about 0.5 to about 1.5, or about 1.5 to about 2, or about 3 to about 5, or about 2 to about 3, percent by weight sulfur to the composition;   wherein said composition has a kinematic viscosity at 100° C. by ASTM D445 of up to about 7.5 mm 2 /s.   
     
     
         2 . The lubricant composition of  claim 1  wherein the oil comprises a polyalpha olefin having a kinematic viscosity at 100° C. of about 3 to about 7.5. 
     
     
         3 . The lubricant composition of  claim 1  wherein the oil comprises an API Group III oil or a Group III+ oil. 
     
     
         4 . The lubricant composition of  claim 1  wherein the alkylene oxide comprises 1,2-propylene oxide. 
     
     
         5 . The lubricant composition of  claim 1  wherein the alcohol has 6 carbon atoms. 
     
     
         6 . The lubricant composition of  claim 1  wherein the alcohol is 4-methylpentan-2-ol. 
     
     
         7 . The lubricant composition of  claim 1  having a phosphorus content of or about 0.02 to about 0.20 weight percent phosphorus supplied by the material of component (b). 
     
     
         8 . The lubricant composition of  claim 1  wherein the total phosphorus content of the lubricant is about 0.08 to about 0.30 weight percent. 
     
     
         9 . The lubricant composition of  claim 1  further comprising an overbased alkaline earth metal detergent in an amount to provide 1 to about 500 50 parts by million by weight alkaline earth metal. 
     
     
         10 . The lubricant composition of  claim 1  being substantially free from alkaline earth metal detergent. 
     
     
         11 . The lubricant composition of  claim 1  further comprising 5 to about 30 percent by weight of a polymeric viscosity index modifier. 
     
     
         12 . A composition prepared by admixing the components of  claim 1 . 
     
     
         13 . A method of lubricating a gear or a bearing, comprising supplying thereto the lubricant composition of  claim 1 . 
     
     
         14 . The method of  claim 13  comprising lubricating a gear wherein the gear is located in an axle assembly. 
     
     
         15 . The method of  claim 13  comprising lubricating a gear wherein the gear is a hypoid gear. 
     
     
         16 . The method of  claim 13  wherein the lubricant composition is employed in a lubricated axle assembly characterized by a λ value of less than 2.0, or 1.1 to 1.5, where λ is defined as the ratio of elastohydrodynamic film thickness of the lubricant to the composite surface roughness of the gear surface.