Lubricating Composition Containing a Dispersant

Abstract

The invention provides a lubricating composition containing a lubricating composition comprising an oil of lubricating viscosity and a polyester. The invention further relates to a method of lubricating a mechanical device (such as an internal combustion engine) with the lubricating composition. The invention further relates to the use of the polyester as a dispersant.

What is claimed is: 
     
         1 . A lubricating composition comprising:
 an oil of lubricating viscosity,   0.05 wt % to 10 wt % of a polyester which comprises a self-condensation product of a C 8-22  fatty carboxylic acid containing at least one hydroxyl group,   0.1 wt % to 15 wt % of a dispersant, and   0.1 wt % to 10 wt % of an overbased calcium- or magnesium-containing detergent.   
     
     
         2 . The lubricating composition of  claim 1 , wherein the fatty carboxylic acid is represented by the formula: 
       
         
           
           
               
               
           
         
       
       where R 1  is a hydrogen or a hydrocarbyl group containing from 1 to 20 carbon atoms and R 2  is a hydrocarbylene group containing from 1 to 20 carbon atoms, with the proviso that the total number of carbon atoms present from R 1  and R 2  is 6 or more. 
     
     
         3 . The lubricating composition of  claim 1 , wherein the self-condensation product of the C 8-22  fatty carboxylic acid containing at least one hydroxyl group produces a polyester with 2 to 10 repeat units. 
     
     
         4 . The lubricating composition of  claim 1 , wherein the polyester is present at 1 wt % to 8 wt % of the lubricating composition. 
     
     
         5 . The lubricating composition of  claim 1 , wherein the dispersant is a succinimide dispersant or mixtures thereof. 
     
     
         6 . The lubricating composition of  claim 1 , wherein the dispersant is a polyisobutylene succinimide, wherein the polyisobutylene from which the polyisobutylene succinimide is derived has a number average molecular weight in the range of 750 to 2200. 
     
     
         7 . The lubricating composition of  claim 1 , wherein the dispersant is a polyisobutylene succinimide derived from an aliphatic polyamine selected from the group consisting of ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyamine still bottoms, and mixtures thereof. 
     
     
         8 . The lubricating composition of  claim 1 , wherein the dispersant is a polyisobutylene succinimide derived from an aliphatic polyamine selected from tetraethylenepentamine, pentaethylenehexamine, polyamine still bottoms, and mixtures thereof. 
     
     
         9 . The lubricating composition of  claim 1 , wherein the dispersant is a polyisobutylene succinimide having a carbocyclic ring present on less than 50 mole % of the dispersant molecules. 
     
     
         10 . The lubricating composition of  claim 1 , wherein the dispersant is a polyisobutylene succinimide having a carbocyclic ring present on 50 mole % or more of the dispersant molecules. 
     
     
         11 . The lubricating composition of  claim 1 , wherein the dispersant is present at 1 wt % to 8.5 wt % of the lubricating composition. 
     
     
         12 . A method of lubricating an internal combustion engine comprising supplying to the internal combustion engine a lubricating composition of  claim 1 . 
     
     
         13 . The method of  claim 12 , wherein the internal combustion engine has a steel surface on a cylinder bore, cylinder block, or piston ring. 
     
     
         14 . The method of  claim 12 , wherein the internal combustion engine has a surface of steel, or an aluminium alloy, or an aluminium composite.