Functional fluids lubricating oil compositions

Abstract

Provided is a lubricating oil composition comprising a major amount of an oil of lubricating viscosity and a detergent system, and a method of improving brake and clutch capacity while maintaining low torque variation at low speed of a tractor hydraulic system.

What is claimed is: 
     
         1 . A tractor hydraulic fluid composition comprising:
 (a) a major amount of an oil of lubricating viscosity, and   (b) a detergent system comprising:
 (i) a low overbased sulfonate detergent; 
 (ii) a high overbased sulfonate detergent; and 
 (iii) a high overbased phenate detergent having an alkyl group derived from an isomerized normal alpha olefin having from about 10 to about 40 carbon atoms per molecule. 
   
     
     
         2 . The lubricating oil composition of  claim 1  wherein the high overbased phenate detergent is a calcium phenate detergent. 
     
     
         3 . The lubricating oil composition of  claim 2  wherein the calcium phenate detergent is derived from C20 to C24 isomerized olefins. 
     
     
         4 . The lubricating oil composition of  claim 1  wherein the composition comprises from 0.005 to 0.08 wt. % Ca from the high overbased phenate detergent. 
     
     
         5 . The lubricating oil composition of  claim 1  wherein the composition comprises from 0.01 to 0.06 wt. % Ca from the high overbased phenate detergent. 
     
     
         6 . The lubricating oil composition of  claim 1  wherein the composition comprises a zinc diakyl dithioposphate detergent. 
     
     
         7 . A method of improving brake and clutch capacity while maintaining low torque variation at low speed of a tractor hydraulic system, the method comprising lubricating said tractor hydraulic system with a lubricating oil composition comprising:
 (a) a major amount of an oil of lubricating viscosity, and   (b) a detergent system comprising:
 (i) a low overbased sulfonate detergent; 
 (ii) a high overbased sulfonate detergent; and 
 (iii) a high overbased phenate detergent having an alkyl group derived from an isomerized normal alpha olefin having from about 10 to about 40 carbon atoms per molecule. 
   
     
     
         8 . The method of  claim 7 , wherein the high overbased phenate detergent is a calcium phenate detergent. 
     
     
         9 . The method of  claim 8 , wherein the calcium phenate detergent is derived from C20 to C24 isomerized olefins. 
     
     
         10 . The method of  claim 7 , wherein the composition comprises from 0.005 to 0.08 wt. % Ca from the high overbased phenate detergent. 
     
     
         11 . The method of  claim 10 , wherein the composition comprises from 0.01 to 0.06 wt. % Ca from the high overbased phenate detergent. 
     
     
         12 . The method of  claim 7 , wherein the composition comprises a zinc diakyl dithioposphate detergent.