Friction modifier composition for lubricants

Abstract

Combining a metal based friction modifier, such as a molybdenum dialkyldithiocarbamate, and certain esters of hydroxy carboxylic acids, such as short chain alkyl esters of citric or tartaric acid, e.g., tributyl citrate, has a synergistic effect on lowering the friction coefficient of lubricating oils allowing one to reduce the amount of metal based friction modifier needed to adequately formulate a lubricant with low friction characteristics.

What is claimed: 
     
         1 . A lubricant composition comprising:
 A) 70 wt % or more of a automotive motor lubricating oil, and   B) from about 1.5 to about 4.5 wt %, based on the weight of the lubricant composition, of a mixture of
 i) from about 0.75 to about 1.5 wt % a friction modifier selected from the group of molybdenum dialkyldithiocarbamates, and 
 ii) from 0.75% to about 3% a hydroxy carboxylic ester selected from the group consisting of triethyl citrate, tripropyl citrate and tributyl citrate; 
   wherein i) and ii) are present in a weight ratio of metal based friction modifier i) to hydroxy carboxylic ester ii) of about 1:1 to about 1:4 based on the total weight of metal based friction modifier i) and hydroxy carboxylic ester ii).   
     
     
         2 . The lubricant composition according to  claim 1  further comprising one or more additional lubricant additive selected from the group consisting of dispersants, detergents, corrosion/rust inhibitors, antioxidants, anti-wear agents, anti-foamants, friction modifiers, seal swell agents, demulsifiers, V.I. improvers and pour point depressants. 
     
     
         3 . The lubricant composition according to  claim 1  wherein the automotive motor lubricating oil is a natural petroleum based automotive motor lubricating oil. 
     
     
         4 . The lubricant composition according to  claim 3  further comprising one or more additional lubricant additive selected from the group consisting of dispersants, detergents, corrosion/rust inhibitors, antioxidants, anti-wear agents, anti-foamants, friction modifiers, seal swell agents, demulsifiers, V.I. improvers and pour point depressants. 
     
     
         5 . The lubricant composition according to  claim 1  wherein i) and ii) are present in a weight ratio of metal based friction modifier i) to hydroxy carboxylic ester ii) of about 1:1 to about 1:3 based on the total weight of metal based friction modifier i) and hydroxy carboxylic ester ii). 
     
     
         6 . The lubricant composition according to  claim 3  wherein i) and ii) are present in a weight ratio of metal based friction modifier i) to hydroxy carboxylic ester ii) of about 1:1 to about 1:3 based on the total weight of metal based friction modifier i) and hydroxy carboxylic ester ii). 
     
     
         7 . The lubricant composition according to  claim 4  wherein i) and ii) are present in a weight ratio of metal based friction modifier i) to hydroxy carboxylic ester ii) of about 1:1 to about 1:3 based on the total weight of metal based friction modifier i) and hydroxy carboxylic ester ii). 
     
     
         8 . The lubricant composition according to  claim 1  wherein the natural petroleum based automotive motor lubricating oil is present from about 95 to about 99 wt %. 
     
     
         9 . The lubricant composition according to  claim 3  wherein the natural petroleum based automotive motor lubricating oil is present from about 95 to about 99 wt %. 
     
     
         10 . The lubricant composition according to  claim 4  wherein the natural petroleum based automotive motor lubricating oil is present from about 95 to about 99 wt %. 
     
     
         11 . The lubricant composition according to  claim 5  wherein the natural petroleum based automotive motor lubricating oil is present from about 95 to about 99 wt %. 
     
     
         12 . The lubricant composition according to  claim 6  wherein the natural petroleum based automotive motor lubricating oil is present from about 95 to about 99 wt %. 
     
     
         13 . The lubricant composition according to  claim 7  wherein the natural petroleum based automotive motor lubricating oil is present from about 95 to about 99 wt %.