Oil composition for power steering with excellent load carrying capacity and wear resistance

Abstract

An oil composition for power steering, includes: a) 75 to 85 weight percent (wt %) of a paraffinic base oil; b) 5 to 15 wt % of a dioctyl adipate plasticizer; c) 1 to 5 wt % of a polymethacrylate viscosity modifier; d) 0.01 to 1 wt % of an overbased calcium sulfonate detergent/dispersant; and e) 1 to 5 wt % of a load-carrying and wear resistant additive package.

What is claimed is: 
     
         1 . An oil composition for power steering, the oil composition comprising:
 a) 75 to 85 weight percent (wt %) of a paraffinic base oil;   b) 5 to 15 wt % of a dioctyl adipate plasticizer;   c) 1 to 5 wt % of a polymethacrylate viscosity modifier;   d) 0.01 to 1 wt % of an overbased calcium sulfonate detergent/dispersant; and   e) 1 to 5 wt % of a load-carrying and wear resistant additive package.   
     
     
         2 . The oil composition of  claim 1 , wherein the load-carrying and wear resistant additive package comprises at least one additive selected from the group consisting of e1) thiophene, tetrahydro 1,1-dioxide, and 3-(C9-11-isoalkyloxy) derivatives, e2) 1-(tert-dodecylthio)propan-2-ol, and e3) 1,3,4-thiadiazolidine-2,5-dithione. 
     
     
         3 . The oil composition of  claim 1 , wherein the paraffinic base oil comprises a hydrotreated heavy paraffinic distillate. 
     
     
         4 . The oil composition of  claim 1 ,
 wherein the paraffinic base oil comprises a mixture of a first base oil and a second base oil in a mixing ratio of 6:4 to 8:2,   wherein the first base oil has:
 a specific gravity of 0.83 to 0.84; 
 a kinematic viscosity of 4 cSt to 5 cSt, at a temperature of 100° C.; 
 a viscosity index of 120 or higher; and 
 a flash point of 210° C. or higher, and 
   wherein the second base oil has:
 a specific gravity of 0.84 to 0.85; 
 a kinematic viscosity of 8 cSt to 9 cSt, at a temperature of 100° C.; 
 a viscosity index of 130° C. or higher, and 
 a flash point of 230° C. or higher. 
   
     
     
         5 . The oil composition of  claim 1 , wherein the plasticizer has:
 a specific gravity of 0.92 to 0.93;   a kinematic viscosity of 7.5 cSt to 8.5 cSt, at a temperature of 40° C.; and   a saponification value of 299 to 305.   
     
     
         6 . The oil composition of  claim 1 , wherein the viscosity modifier has:
 a specific gravity of 0.875 to 0.905; and   a kinematic viscosity of 650 cSt to 750 cSt, at a temperature of 100° C.   
     
     
         7 . The oil composition of  claim 1 , wherein the overbased calcium sulfonate detergent/dispersant has:
 a kinematic viscosity of 50 cSt to 100 cSt at a temperature of 100° C.; and   a total base number (TBN) of 290 or more.   
     
     
         8 . The oil composition of  claim 1 , wherein the oil composition has a load-carrying capacity of 200 kgf or more, corresponding to a measurement of the load-carrying capacity in accordance with an ASTM D 2783 Standard test method. 
     
     
         9 . The oil composition of  claim 8 , wherein the ASTM D 2783 Standard test method comprises a four-ball load carrying capacity test. 
     
     
         10 . The oil composition of  claim 1 , wherein the oil composition has a wear resistance of 0.4 mm or less, corresponding to a measurement of the wear resistance in accordance with an ASTM D 4172 Standard test. 
     
     
         11 . The oil composition of  claim 1 , wherein the oil composition has a corrosion resistance rating of Grade 1a, corresponding to a measurement of corrosion resistance in accordance with an ASTM D 130 Standard test. 
     
     
         12 . The oil composition of  claim 1 , wherein the oil composition lubricates a power steering gearbox of a vehicle. 
     
     
         13 . The oil composition of  claim 1 , wherein the oil composition has an aniline point of 90° C. or higher, corresponding to a measurement of the aniline point in accordance with an ASTM D 61 Standard test method.