Functional fluids with servo valve erosion resistance

Abstract

Phosphate ester based functional fluids containing novel anti-erosion additives provides enhanced results in erosion control.

What is claimed is:  
     
         1 . A hydraulic fluid composition, comprising: 
 a phosphate ester basestock and a salt or mixture of salts represented by the formula    RSO 3 M    where M is an alkali metal or ammonium; and    R is a perfluorinated hydrocarbyl group having 1 to 12 carbon atoms, wherein the hydrocarbyl group is linear or branched.    
     
     
         2 . A hydraulic fluid composition according to  claim 1 , wherein 
 the salt or mixture of salts comprises about 0.01 to about 0.5 wt % of the basestock;    the perfluorinated hydrocarbyl group has 1 to 8 carbon atoms; and    M is at least one member selected from the group consisting of lithium, sodium, potassium, and cesium.    
     
     
         3 . A hydraulic fluid composition according to  claim 1  comprising, by weight percentage based on the total hydraulic fluid composition weight: 
 a phosphate ester base fluid containing one or more trialkyl phosphate esters, wherein the alkyl groups of the phosphate ester contain 4 to 5 carbon atoms;  
 10 to 100 weight percent of trialkyl phosphates;  
 0 to 75 weight percent of dialkyl aryl phosphates, wherein the alkyl group contains from 4 to 5 carbon atoms and the aryl group is phenyl;  
 0 to 30 weight percent of alkyl diaryl phosphate, wherein the alkyl group contains from 4 to 5 carbon atoms and the aryl group is phenyl;  
 0 to 20 weight percent of alkylated triaryl phosphates, wherein the alkyl group is at least one member selected from the group consisting of isopropyl, n-butyl and tert-butyl; and  
 1 to 10 weight percent of an acid scavenger represented by the following formula:  
                     
 where R 1  is H or a C 1  to C 4  alkyl group, x is 1 or 2, y is an integer of 1 to 4, and R 2  is a C 1  to C 4  alkyl group or a phenyl group.  
 
     
     
         4 . A hydraulic fluid composition according to  claim 3 , wherein the hydraulic fluid composition comprises, by weight percentage based on the total hydraulic fluid composition weight, 20 to 90 weight percent of the trialkyl phosphates.  
     
     
         5 . A hydraulic fluid composition according to  claim 4 , wherein M is an alkali metal.  
     
     
         6 . A hydraulic fluid composition according to  claim 5  wherein M is potassium.  
     
     
         7 . A hydraulic fluid composition according to  claim 1 , wherein the formula comprises at least one member selected from the group consisting of: 
 Potassium trifluoromethanesulfonate or potassium triflate;    Lithium trifluoromethanesulfonate or lithium triflate;    Potassium 1,1,2,2,2-pentafluoroethane-1-sulfonate-;    Potassium 1,1,2,2,3,3,3-heptafluoropropane-1-sulfonate-;    Potassium 1,1,2,2,3,3,4,4,4-nonafluorobutane-1-sulfonate-;    Potassium 1,1,2,2,3,3,4,4,5,5,5-undecafluoropentane-1-sulfonate-;    Potassium 1,1,2,2,3,3,4,4,5,5,6,6,6-tridecafluorohexane-1-sulfonate;    Potassium 1,1,2,2,3,3,4,4,5,5,6,6,7,7,7-pentadecafluoroheptane- 1-sulfonate1; and    Potassium 1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-heptadecafluorooctane-1-sulfonate.    
     
     
         8 . A hydraulic fluid composition according to  claim 7 , wherein the formula comprises potassium 1,1,2,2,3,3,4,4,4-nonafluorobutane-1-sulfonate- or potassium trifluoromethanesulfonate.  
     
     
         9 . A hydraulic fluid composition according to  claim 1 , containing: 
 from 0.5 to 3 weight percent, based on the total hydraulic fluid composition weight, of an antioxidant or antioxidants mixture selected from the group consisting of: 
 2,6-di-tert-butyl-4-methyl phenol, tetrakis[methylene (3,5-di-tert-butyl-4-hydroxyhydrocinnamate)] methane,  
 octylated diphenylamine,  
 phenyl-α-naphthylamine,  
 diphenylamine,  
 ditolylamine,  
 4,4′-diaminodiphenylamine, and  
 mixtures thereof.  
   
     
     
         10 . A hydraulic fluid composition according to  claim 9 , wherein the antioxidant or antioxidants mixture is 0.5 to 2 weight percent, based on the total hydraulic fluid composition weight.  
     
     
         11 . A hydraulic fluid composition according to  claim 1  containing from about 3 to about 10 weight percent, based on the total hydraulic fluid composition weight, of a viscosity index improver, comprising: 
 an acrylate or methacrylate ester polymer where the repeating units substantially comprise n-hexyl; and  
 idodecyl acrylate or methacrylate, wherein at least 95% by weight of the polymer has a molecular weight between about 50,000 and 900,000.  
 
     
     
         12 . A hydraulic fluid composition according to  claim 11 , containing from 4 to 8 weight percent, based on the total hydraulic fluid composition weight, of the viscosity index improver.  
     
     
         13 . A method of inhibiting the erosion tendency of a phosphate ester based fluid comprising incorporating in the fluid from 0.01 to about 0.5 wt % of a salt or mixture of salts represented by the formula  
       RSO 3 M  
       where M is an alkali metal or ammonium; and 
 R is a perfluorinated hydrocarbyl group with 1 to 12 carbon atoms, wherein the hydrocarbyl group can be linear or branched.  
 
     
     
         14 . A method according to  claim 13  wherein M is an alkali metal and the hydrocarbyl group has 1 to 8 carbon atoms.