Ashless additive formulations suitable for hydraulic oil applications

Abstract

An ashless additive formulation, particularly suited for hydraulic oil applications, comprising a particular concentration of a monothiophosphate ester and a dithiophosphate ester was found to have improved performance properties and good compatibility with calcium containing packages. Lubricating compositions employing these monothiophosphate and dithiophosphate esters allow for low phosphorous content lubricating oil compositions.

1 . A metal free low phosphorous content lubricating oil composition comprising 
 a) an oil of lubricating viscosity;    b) a mixture of ashless, sulfur containing organo phosphorous compounds comprising 
 i) from 0.2 to 0.4 weight percent based upon the total mass of the lubricating oil composition of a monothiophosphate ester of the formula 
   (RO) 3 —P═S 
   wherein R is independently selected from phenyl, alkylphenyl, aryl, alkaryl, aralkyl, and alkoxyaryl; and    ii) from 0.01 to 0.03 weight percent based upon the total mass of the lubricating oil composition of a dithiophosphate ester of the formula                        wherein each R 1  is an independently selected hydrocarbyl from 3 to 20 carbon atoms; alk is a straight or branched chain alkylene group of 2 to 6 carbon atoms; R 2  is hydrogen or alkyl from 1 to 4 carbons atoms;    wherein the total phosphorous content of the composition is less than 350 parts per million phosphorous.      
     
     
         2 . The lubricating oil composition of  claim 1 , wherein the oil of lubricating viscosity is a hydraulic fluid.  
     
     
         3 . The lubricating oil composition of  claim 1 , wherein at least one R substituent of the monothiophosphate ester is selected from alkylphenyl, alkaryl and alkoxyaryl.  
     
     
         4 . The lubricating oil composition of  claim 3 , wherein R is selected from phenyl and alkylphenyl of 7 to 18 carbon atoms.  
     
     
         5 . The lubricating oil composition of  claim 1 , wherein the monothiophosphate ester is present at less than about 0.3 weight percent.  
     
     
         6 . The lubricating oil composition of  claim 1 , wherein R 1  is selected from the group consisting of propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, isopentyl, hexyl, 2-ethylbutyl, 1-methylpentyl, 1,3 dimethylbutyl, and 2 ethylhexyl.  
     
     
         7 . The lubricating oil composition of  claim 1  wherein R 2  is hydrogen.  
     
     
         8 . The lubricating oil composition of  claim 1 , wherein -(alk)- is selected from the group consisting of —CH 2 CH 2 —, —CH 2 CH(CH 3 )—, —CH 2 CH(CH 2 CH 3 )— and —CH 2 CH(CH 2 CH 2 CH 3 )—.  
     
     
         9 . The lubricating oil composition of  claim 1 , wherein the dithiophosphate ester is present at less than about 0.02 weight percent.  
     
     
         10 . The lubricating oil composition of  claim 9 , wherein the dithiophosphate ester is present at less than about 0.015 weight percent.  
     
     
         11 . The lubricating oil composition of  claim 1 , wherein the weight ratio of component i) to component ii) is in the range from 10:1 to 25:1.  
     
     
         12 . The lubricating oil composition of  claim 11 , wherein the weight ratio of component i) to component ii) is in the range from 15:1 to 25:1.  
     
     
         13 . The lubricating oil composition of  claim 1 , further comprising a rust preventing agent.  
     
     
         14 . The lubricating oil composition of  claim 13 , wherein the rust preventing agent is the reaction product of a carboxylic acid having from 4 to 30 carbon atoms and an amino acid.  
     
     
         15 . The lubricating oil composition of  claim 14 , wherein the rust preventing agent is N-acyl sarcosine of the formula  
       
         
           
           
               
               
           
         
       
       wherein R 3  represents an alkyl or alkenyl group from 8 to 18 carbon atoms.  
     
     
         16 . The lubricating oil composition of  claim 15  wherein the N-acyl sarcosine is selected from the group consisting of lauroyl sarcosine, cocyl sarcosine, oleoyl sarcosine, stearoyl sarcosine and tall oil sarcosine.  
     
     
         17 . The lubricating oil composition of  claim 1  further with the proviso that no phosphorous content in the lubricating oil is attributable to an amine phosphate.