Method of improving the efficiency of automotive transmissions

Abstract

A method for improving the fuel economy of an automobile is disclosed. The method involves lubricating an automotive transmission system with a lubricant composition containing (a) an oil of lubricating viscosity; (b) a viscosity modifying polymer comprising linear polymers characterized by the formula: D′-PA-D″; and star polymers characterized by the formula: (D′-PA-D″)n-X; wherein D′, PA, D″ are polymer blocks as defined herein; and (c) a performance additive package.

What is claimed is:: 
     
         1 . A method for improving the fuel economy of an automobile, comprising the following steps:
 (a) lubricating an automotive transmission system with a lubricant composition comprising (a) an oil of lubricating viscosity;   (b) a viscosity modifying polymer comprising linear polymers characterized by the formula:
   D′-PA-D″;
 
   
       and star polymers characterized by the formula:
   p 1  (D′-PA-D″)n-X;
 
 wherein D′ represents a block derived from diene; PA represents a block derived from monoalkenyl arene; D″ represents a block derived from diene; n represents the average number of arms per star polymer formed by the reaction of 2 or more moles of a polyalkenyl coupling agent per mole of arms; and X represents a nucleus of a polyalkenyl coupling agent; 
 wherein at least one of diene blocks D′ and D″ is a copolymer block derived from mixed diene monomer, in which from 65 wt. % to 95 wt. % of the incorporated monomer units are from isoprene and from 5 wt. %, up to 35 wt. % of the incorporated monomer units are from butadiene, and wherein at least 80 wt. % of the butadiene is incorporated in a 1,4-configuration; and 
 wherein D′ has a number average molecular weight of from 10,000 to 120,000 daltons; PA has a number average molecular weight of from 10,000 to 50,000 daltons; and D″ has a number average molecular weight of from 5,000 to 60,000 daltons; and 
 (c) a performance additive package. 
 
     
     
         2 . The method of  claim 1  wherein at least 50% by weight of the oil of lubricating viscosity is a polyalphaolefin. 
     
     
         3 . The method of  claim 1  wherein the lubricant composition is an automatic transmission fluid and the additive package comprises one or more of the following components: an ashless dispersant; an anti-wear agent; an anti-oxidant; a corrosion inhibitor; a friction modifier; a seal swell agent; an anti-foamant; and/or a viscosity modifier. 
     
     
         4 . The method of  claim 1  wherein D′ has a number average molecular weight of from 20,000 to 60,000 daltons. 
     
     
         5 . The method of  claim 1  wherein D″ has a number average molecular weight of from 10,000 to 30,000 daltons. 
     
     
         6 . The method of  claim 1  wherein PA has a number average molecular weight of from 12,000 to 35,000 daltons. 
     
     
         7 . The method of  claim 1  wherein D′ has a number average molecular weight of from 20,000 to 60,000 daltons; D″ has a number average molecular weight of from 10,000 to 30,000 daltons; and PA has a number average molecular weight of from 12,000 to 35,000 daltons 
     
     
         8 . The method of  claim 1  wherein the ratio between the number average molecular weight of D′ and the number average molecular weight of D″ is at least 1.4:1. 
     
     
         9 . The method of  claim 1  wherein the ratio between the number average molecular weight of PA and the number average molecular weight of D″ is at least 0.75:1. 
     
     
         10 . The method of  claim 1  wherein the polymer is a star polymer and n is, on average, from 4 to 25. 
     
     
         11 . The method of  claim 1  wherein the polymer is a star polymer having a total number average molecular weight of from 100,000 daltons to 1,000,000 daltons. 
     
     
         12 . The method of  claim 1  wherein the polymer is a linear polymer having a total number average molecular weight of from 40,000 daltons to 1,000,000 daltons. 
     
     
         13 . A lubricant composition capable of enabling an automobile to exhibit improved fuel efficiency comprising:
 (a) an oil of lubricating viscosity;   (b) a viscosity modifying polymer comprising linear polymers characterized by the formula:
   D′-PA-D″;
 
   
       and star polymers characterized by the formula:
   (D′-PA-D″)n-X;
 
 wherein D′ represents a block derived from diene; PA represents a block derived from monoalkenyl arene; D″ represents a block derived from diene; n represents the average number of arms per star polymer formed by the reaction of 2 or more moles of a polyalkenyl coupling agent per mole of arms; and X represents a nucleus of a polyalkenyl coupling agent; 
 wherein at least one of diene blocks D′ and D″ is a copolymer block derived from mixed diene monomer, in which from 65 wt. % to 95 wt. % of the incorporated monomer units are from isoprene and from 5 wt. %, up to 35 wt. % of the incorporated monomer units are from butadiene, and wherein at least 80 wt. % of the butadiene is incorporated in a 1, 4- configuration; and 
 wherein D′ has a number average molecular weight of from 10,000 to 120,000 daltons; PA has a number average molecular weight of from 10,000 to 50,000 daltons; and D″ has a number average molecular weight of from 5,000 to 60,000 daltons; and 
 (c) a performance additive package.