Method of providing high coefficients of friction across oil-lubricating friction clutches

Abstract

The invention concerns a method of increasing the dynamic coefficient of friction in an oil-lubricated friction clutch by using a lubricating oil containing at least one specific copolymer, the presence of which develops higher dynamic friction levels in the clutch.

What is claimed is: 
     
         1 . A method of increasing the friction in an oil-lubricated friction clutch having a cellulose-based friction lining, or in a power-transmission device utilising said clutch, the method comprising:
 (i) preparing or otherwise obtaining a lubricant composition comprising
 (i.a) a major amount of oil of lubricating viscosity, and 
 (i.b) one or more copolymers of ethylenically unsaturated esters present in an amount effective to increase the dynamic coefficient of friction of the lubricant composition when used in said clutch or device; and 
   (ii) lubricating said clutch or device with the lubricant composition resulting from step (i);   
       wherein at least one copolymer (i.b) is a statistical copolymer derived essentially from the following co-monomers (a) and (b): 
       (a) at least one ethylenically unsaturated ester compound of the formula (I): 
       
         
           
           
               
               
           
         
       
       in which R is hydrogen or methyl, R 1  is a linear or branched chain alkyl group having from 6 to 36 carbon atoms, and R 2  and R 3  are each independently hydrogen or a group of the formula —COOR′ in which R′ is hydrogen or a linear or branched chain alkyl group having from 6 to 36 carbon atoms; and 
       (b) at least one ethylenically unsaturated ester compound of the formula (II): 
       
         
           
           
               
               
           
         
       
       in which R is hydrogen or methyl, X is oxygen, sulfur or an amino group of the formula —NH— or —NR a — in which R a  is an alkyl radical having from 1 to 40 carbon atoms, R 4  is a radical comprising from 2 to 100 carbon atoms and contains at least 2 oxygen, sulfur or nitrogen atoms, R 5  and R 6  are each independently hydrogen or a group of the formula —COX′R 7  in which X′ is oxygen or an amino group of the formula —NH— or —NR a′ — in which R a′  is an alkyl radical having from 1 to 40 carbon atoms, and R 7  is a radical comprising from 1 to 100 carbon atoms; 
       wherein the co-monomer units originating from co-monomer (b) constitute from 0.1 to 30 weight percent of the total weight of said statistical copolymer. 
     
     
         2 . The method of  claim 1 , wherein the monomer units originating from co-monomer (b) constitute from 1 to 10 weight percent of the total weight of said statistical copolymer. 
     
     
         3 . The method of  claim 2 , wherein the co-monomer units originating from co-monomer (b) constitute from 4 to 8 weight percent of the total weight of said statistical copolymer. 
     
     
         4 . The method of  claim 2 , wherein the co-monomer units originating from monomer (a) constitute at least 90 weight percent of the total weight of said statistical copolymer. 
     
     
         5 . The method of  claim 1 , wherein the co-monomer units originating from monomer (a) constitute the remainder of said statistical copolymer. 
     
     
         6 . The method of  claim 1 , wherein said statistical copolymer has a weight-average molecular weight, Mw, as measured by GPC within the range of 10,000 to 100,000 g/mol. 
     
     
         7 . The method of  claim 6 , wherein said statistical copolymer has a weight-average molecular weight, Mw, as measured by GPC within the range of 10,000 to 60,000 g/mol. 
     
     
         8 . The method of  claim 1 , wherein the co-monomer units originating from co-monomer (b) constitute from 1 to 6 weight percent of the total weight of said statistical copolymer, and wherein said statistical copolymer has a weight-average molecular weight, Mw, as measured by GPC within the range of 40,000 to 60,000 g/mol. 
     
     
         9 . The method of  claim 1 , wherein the lubricant composition resulting from step (i) additionally comprises (i.c) an ashless dispersant, wherein said dispersant is present in an amount that is effective in combination with the copolymer (i.b) to increase the dynamic coefficient of friction of the lubricant composition when used in said clutch or device. 
     
     
         10 . The method of  claim 9 , wherein the co-monomer units originating from co-monomer (b) constitute from 6 to 10 weight percent of the total weight of said statistical copolymer, and wherein said statistical copolymer has a weight-average molecular weight, Mw, as measured by GPC within the range of 10,000 to 40,000 g/mol. 
     
     
         11 . The method of  claim 9 , wherein the ashless dispersant comprises one or more alkenyl- or polyalkenyl-substituted succinimide or succinamide compounds. 
     
     
         12 . The method of  claim 10 , wherein the ashless dispersant comprises one or more alkenyl- or polyalkenyl-substituted succinimide or succinamide compounds. 
     
     
         13 . The method of  claim 11 , wherein the ashless dispersant consists of one or more alkenyl- or polyalkenyl-substituted succinimide or succinamide compounds derived from polyalkylene polyamines. 
     
     
         14 . The method of  claim 12 , wherein the ashless dispersant consists of one or more alkenyl- or polyalkenyl-substituted succinimide or succinamide compounds derived from polyalkylene polyamines. 
     
     
         15 . The method of  claim 1 , wherein, in said statistical copolymer, the R 4  radical in the co-monomer units originating from at least one co-monomer (b) comprises at least one nitrogen atom and at least one oxygen atom. 
     
     
         16 . The method of  claim 1 , wherein, in said statistical copolymer, the R 4  radical in the co-monomer units originating from at least one co-monomer (b) comprises at least one urea group. 
     
     
         17 . The method of  claim 16 , wherein, in said statistical copolymer, the R 4  radical in the co-monomer units originating from at least one co-monomer (b) is a group of the formula (III) 
       
         
           
           
               
               
           
         
       
       in which A is a hydrocarbylene connecting group containing from 1 to 50 carbon atoms. 
     
     
         18 . The method of  claim 17 , wherein said statistical copolymer is derived essentially from at least one co-monomer (b) of the formula (IV): 
       
         
           
           
               
               
           
         
       
     
     
         19 . The method of  claim 1 , wherein said statistical copolymer is derived essentially from at least one co-monomer (a) of the formula (I) wherein the R 1  radical is a straight chain alkyl group having between 12 and 15 carbon atoms. 
     
     
         20 . The method of  claim 19 , wherein, in said statistical copolymer, the R 4  radical in the co-monomer units originating from at least one co-monomer (b) is a group of the formula (III) 
       
         
           
           
               
               
           
         
       
       in which A is a hydrocarbylene connecting group containing from 1 to 50 carbon atoms. 
     
     
         21 . The method of  claim 1 , wherein said clutch is utilised in a power-transmission device, and said device is a vehicular automatic transmission. 
     
     
         22 . The method of  claim 21 , wherein said automatic transmission is of a type selected from the group consisting of stepped automatic transmissions, automated manual transmissions, continuously variable transmissions and dual clutch transmissions. 
     
     
         23 . The method of  claim 1 , wherein the lubricant composition resulting from step (i) additionally comprises one or more performance enhancing additive packages.