Zinc-Free Farm Tractor Fluid

Abstract

A lubricating composition comprising an oil of lubricating viscosity; an amine salt of a phosphorus acid ester; a thiadiazole copper corrosion inhibitor; an overbased metal detergent; a boron compound; and at least one friction modifier provides good lubrication of a mechanical device such as a farm tractor, even though such composition is substantially free from zinc dialkyldithiophosphate.

1 . A method for lubricating the hydraulic system of a farm tractor, comprising supplying thereto a lubricating composition comprising:
 (a) an oil of lubricating viscosity;   (b) at least one amine salt of a phosphorus acid ester;   (c) at least one thiadiazole compound;   (d) at least one overbased metal detergent;   (e) at least one boron compound other than an overbased metal detergent;   (f) at least one friction modifier other than a boron compound;   said composition being substantially free from zinc dialkyldithiophosphate.   
   
   
       2 . The method of  claim 1  wherein the amine salt of (b) comprises a C 8  to C 20  alkylamine salt of a mono- or di-alkyl phosphate ester or mixtures thereof. 
   
   
       3 . The method of  claim 1  wherein the amount of the amine salt of (b) is about 0.04 to about 4 percent by weight. 
   
   
       4 . The method of  claim 1  wherein the thiadiazole compound of (c) is selected from the group consisting of 2-alkyldithio-5-mercapto-[1,3,4]-thiadiazoles, 2,5-bis(alkyldithio)-[1,3,4]-thiadiazoles, 2-alkylhydroxyphenyl-methylthio-5-mercapto-[1,3,4]-thiadiazoles, and mixtures thereof. 
   
   
       5 . The method of  claim 1  wherein the thiadiazole compound of (c) comprises the reaction product of 2,5-dimercapto-[1,3,4]-thiadiazole with a nitrogen-containing dispersant. 
   
   
       6 . The method of  claim 1  wherein the amount of the thiadiazole compound of (c) is about 0.01 to about 5 percent by weight. 
   
   
       7 . The method of  claim 1  wherein the overbased metal detergent (d) comprises a carbonated overbased metal sulfonate. 
   
   
       8 . The method of  claim 1  wherein the amount of the overbased metal detergent is about 0.05 to about 6 percent by weight. 
   
   
       9 . The method of  claim 1  wherein the boron compound of component (e) comprises the reaction product of a dialkanolamine and boric acid, further reacted with a C 8  to C 20  fatty acid. 
   
   
       10 . The method of  claim 1  wherein component (e) comprises a borated nitrogen-containing dispersant. 
   
   
       11 . The method of  claim 1  wherein component (e) comprises a borated ethoxylated amine. 
   
   
       12 . The method of  claim 1  wherein the amount of component (e) is about 0.05 to about 2 percent by weight. 
   
   
       13 . The method of  claim 1  wherein the amount of component (e) is sufficient to provide about 40 to about 4000 ppm B to the composition. 
   
   
       14 . The method of  claim 1  wherein the friction modifier of (f) is selected from the group consisting of fatty acid glycerides, fatty acid amides, fatty alkyl amines, polyoxyalkylene fatty alkyl amines, fatty alkyl hydrogen phosphites, pentaerythritol monooleate, and mixtures thereof. 
   
   
       15 . The method of  claim 1  wherein the amount of the friction modifier is about 0.1 to about 10 weight percent. 
   
   
       16 . The method of  claim 1  further comprising at least one additional additive selected from the group consisting of viscosity modifiers, pour point depressants, antioxidants, rust inhibitors, seal swell compositions, and anti-foam agents. 
   
   
       17 . The method of  claim 1 , wherein the lubricating composition is prepared by admixing the components of  claim 1 .