Lubricating oil compositions with improved friction properties

Abstract

The present invention concerns friction reducers for use in lubricating oil compositions which comprise certain groups of aromatic compounds, esters, narrow mixtures of base stocks, and/or amorphous polymers such as amorphous olefin copolymers. These compositions can provide substantial reductions in the coefficient of friction and fuel economy improving benefits when admixed to lubricating oils without deleterious effects such as instability, undesirable high viscosities and deposits. In one aspect of the invention, pentaerythritol esters and optionally triol esters are added to lubricating oil compositions to provide reduced friction and improved fuel economy. In a second aspect of the invention, similar results are obtained by adding hydrocarbyl aromatics to a lubricating oil composition containing one or more of Groups II and III base stock. In a third aspect, the invention concerns a lubricating oil composition comprising an amorphous olefin copolymer and one or more of Groups II and III base stocks. In one embodiment, the third aspect also includes one or more of hydrocarbyl aromatics and polyol esters as part of the composition. In a fourth aspect, moderate concentrations of hydrocarbyl aromatics are used in a lubricating oil composition comprising paraffinic base oil stocks and preferably a borated polyisobutenyl succinimide ashless dispersant.

1 . A method for enhancing the overall fuel economy relative to SAE viscosity grade and reducing the coefficient of friction of a lubricating engine oil in use in an engine at temperatures of 60° C. or higher comprising a base oil which is one or more of a Group II base stock, Group III base stock, wax isomerate base stock and polyalphaolefins base stock by incorporating into said base oil 
 (a) between 8 to 15 wt % of a polyol ester selected from the group consisting of a pentaerythritol ester,    (b) about 4-15 wt % of a hydrocarbyl aromatic, and    (c) about 0.5 to 8 wt %, as received, of a borated polyisobutenyl succinimide ashless dispersant, wherein percentages are based on the total oil composition, the borated polyisobutenyl succinimide ashless dispersant contributing about 8 to 620 ppm boron and about 44 to 1260 ppm total nitrogen to the lubricating engine oil.    
     
     
         2 . The method of  claim 1 , wherein the borated polyisobutenyl succinimide ashless dispersant is incorporated into the base oil in an amount in the range of about 1 to 7 wt %, contributing about 15 to 540 ppm boron and about 88 to 1100 ppm total nitrogen to the lubricating engine oil.  
     
     
         3 . The method of  claim 1  wherein the borated polyisobutenyl succinimide ashless dispersant is incorporated into the base oil in an amount in the range of about 2 to 6 wt % contributing about 30-460 ppm boron and about 176 to 940 ppm total nitrogen to the lubricating engine oil.  
     
     
         4 . The method of  claim 1  wherein the borated polyisobutenyl succinimide ashless dispersant is incorporated into the base oil in an amount in the range of about 3 to 5 wt % contributing about 45 to 390 ppm boron and about 270 to 790 ppm total nitrogen to the lubricating engine oil  
     
     
         5 . The method of  claim 1  wherein in the pentaerythritol ester a substantial amount of the available —OH groups on the pentaerythritol polyol are converted to esters.  
     
     
         6 . The method of  claim 5  wherein the pentaerythritol esters are derived from mono-, di-, and polypentaerythritol polyols reacted with mixed hydrocarbyl acids of the formula RCO 2 H, wherein R comprises hydrocarbyl groups of from about C 6  to C 16  or more.  
     
     
         7 . The method of  claim 1 ,  2 ,  3 ,  4 ,  5  or  6  wherein the lubricating engine oil comprises at least about 20% of one or more base stock oils selected from Group II base stock, Group III base stock, wax isomerate base stock, and polyalphaolefins.  
     
     
         8 . The method of  claim 7  wherein the lubricating engine oil comprises at least about 30% of one or more base stock oils selected from Group II base stock, Group III base stock, wax isomerate base stock and polyalphaolefins.  
     
     
         9 . The method of  claim 7  wherein the lubricating engine oil comprises at least about 50% of one or more base stock oils selected from Group II base stock, Group III base stock, wax isomerate base stock and polyalphaolefins.  
     
     
         10 . The method of  claim 7  wherein the lubricating engine oil comprises at least about 80% of one or more base stock oils selected from Group II base stock, Group III base stock, wax isomerate base stock and polyalphaolefins.  
     
     
         11 . The method of  claim 1 ,  2 ,  3 ,  4 ,  5  or  6  wherein the enhancement in the overall fuel economy relative to SAE viscosity grade and the reduction in the coefficient of friction of the lubricating engine oil is achieved in an engine in use at temperatures of about 65° C. and higher.  
     
     
         12 . The method of  claim 11  wherein the improvements are achieved in an engine in use at temperatures of about 70° C. and higher.  
     
     
         13 . The method of  claim 11  wherein the improvements are achieved in an engine in use at temperatures between about 70 to 150° C.