Use of dialkylene glycol ester to reduce friction in vehicles with hybrid engines

Abstract

The present invention relates to the use of a diester of formula (I) in a lubricant composition for a vehicle equipped with a hybrid engine, to reduce friction when the engine is used at low speed and/or when cold.

1 - 7 . (canceled) 
     
     
         8 . A method for reducing friction when using a hybrid engine at low speed and/or when cold comprising the addition, to the lubricant composition of said engine, of a diester of formula (I)
   R a —C(O)—O—([C(R) 2 ] a —O) b —C(O)—R b    (I)
   where:   R, each independently, are a hydrogen atom or a linear or branched alkyl group having 1 to 5 carbon atoms;   s is 1 or 2;   n is 1, 2 or 3, on the understanding that when s differs from 1, the n values can be the same or different;   R a  and R b , the same or different, are each independently linear or branched, saturated or unsaturated hydrocarbon groups, having a linear sequence of 6 to 18 carbon atoms;   provided that when s is 2 and n all the same are 2, at least one of the R groups is a linear or branched alkyl group having 1 to 5 carbon atoms; and   provided that when s is 1 and n is 3, at least one of the R groups linked to the carbon at beta position of the oxygen atoms of the ester functions, is a hydrogen atom.   
     
     
         9 . The method according to  claim 8 , wherein the diester is a diester of formula (I), where when s differs from 1, all the n values are the same. 
     
     
         10 . The method according to  claim 8 , wherein the diester is a diester of formula (I) where n is 2 or 3. 
     
     
         11 . The method according to  claim 8 , wherein the diester is a diester of formula (I) where at least one of the R groups is a linear or branched alkyl group having 1 to 5 carbon atoms. 
     
     
         12 . The method according to  claim 8 , wherein the diester of formula (I) is a diester of following formula (I′):
   R a —C(O)—O—([C(R) 2 ] n —O)—([C(R′) 2 ] m —O) b-1 —C(O)—R b    (I′)
 
 where: 
 R and R′, each independently, are a hydrogen atom or a linear or branched alkyl group having 1 to 5 carbon atoms; 
 s is 1 or 2; 
 n is 2; 
 m is 2; 
 R a  and R b , the same or different, are each independently linear or branched, saturated or unsaturated hydrocarbon groups having a linear sequence of 6 to 18 carbon atoms; 
 provided that when s is 2, at least one of the groups R or R′ is a linear or branched alkyl group having 1 to 5 carbon atoms. 
 
     
     
         13 . The method to  claim 8 , wherein the diester is a compound of formula (I″a)
   R a —C(O)—O—CHR 1 —CHR 2 —O—CHR 3 —CHR 4 —O—C(O)—R b    (I″a)
 
 where:
 one of the groups R 1  and R 2  is a linear or branched alkyl group having 1 to 5 carbon atoms, the other being a hydrogen atom; 
 one of the groups R 3  and R 4  is a linear or branched alkyl group having 1 to 5 carbon atoms, the other being a hydrogen atom, 
 R a  and R b , the same or different, are such as defined in  claim 8 . 
 
 
     
     
         14 . The method according to  claim 8 , wherein the diester of formula (I) is added in a proportion of 1 to 40% by weight relative to the total weight of the lubricant composition.