Lubricating composition for a hybrid electric vehicle transmission

Abstract

The disclosed technology relates to a lubricant composition for use in an automatic transmission of a hybrid electric vehicle, containing an oil of lubricating viscosity, at least one borate ester, and at least one phosphorus containing compound.

What is claimed is: 
     
         1 . A lubricant composition for lubricating a transmission in a vehicle with an electric motor comprising
 a. an oil of lubricating viscosity   b. 0.2 to 2.0 wt % of at least one borate ester of formula I,   
       
         
           
           
               
               
           
         
         
           wherein each R, independently, is a C 3  to C 12  alkyl, 
         
         c. at least one phosphorous containing compound present in an amount to deliver 100 to 450 ppm of phosphorus to the lubricating composition comprising a phosphite ester composition that comprises the reaction product of a monomeric phosphorous acid or an ester thereof with at least two alkylene diol, 
         d. a dispersant at a total amount of 1.8 wt. % or less and delivering less than 100 ppm boron to the lubricant composition comprising at least one of a carboxylic dispersant prepared by the reaction of a hydrocarbyl-substituted carboxylic acid or reactive equivalent thereof with an amine; amine dispersants prepared by the reaction of high molecular weight aliphatic or alicyclic halides and amines; Mannich dispersants prepared by the reaction of alkyl phenols in which the alkyl group contains at least 30 carbons atoms with aldehydes and amines; and ester dispersants prepared by reaction of a hydrocarbyl acylating agent and a polyhydric aliphatic alcohol, and 
         e. optionally a calcium containing sulfonate or salicylate detergent or mixtures thereof present in an amount to deliver 300 ppm or less calcium to the lubricating composition,
 wherein the lubricant composition has a kinematic viscosity at 40° C. of from 8 cSt to 18 cSt, and 
 wherein the ratio of phosphorous from the phosphite ester of (c) and the boron from the borate ester of (b) is greater than 0.7. 
 
       
     
     
         2 . The lubricant composition of  claim 1 , where the phosphorous containing compound additionally comprises a C 3-8  hydrocarbyl phosphite. 
     
     
         3 . The lubricant composition of  claim 1  further comprising 0.01 to 1.0 wt % of an ester of (1) a polyol, and 2) an aliphatic carboxylic acid containing about 12 to about 24 carbon atom. 
     
     
         4 . The lubricant composition of  claim 1 , wherein the ester is glycerol monooleate. 
     
     
         5 . The lubricant composition of  claim 1 , further comprising 0.1 to 3.0 wt % of an ester of (1) an alcohol, and 2) an aliphatic carboxylic acid containing about 4 to about 8 carbon atoms. 
     
     
         6 . The lubricant composition of  claim 1 , wherein the ester is a C 8-13  adipate ester. 
     
     
         7 . The lubricant composition of  claim 1  further comprising 0.01 wt % to 0.5 wt % of a dimercaptothiadiazole or derivative thereof. 
     
     
         8 . The lubricant composition of  claim 1  further comprising 0.1 wt % to 5 wt % of a poly(meth)acrylate ester polymer viscosity modifier. 
     
     
         9 . The lubricant composition of  claim 8 , wherein the poly(meth)acrylate ester polymer has a weight average molecular weight of 5,000 to 25,000. 
     
     
         10 . The lubricant composition of  claim 1  further comprising 0.05 wt % to 1.0 wt % of a C 12  to C 24  hydrocarbyl phosphite. 
     
     
         11 . The lubricant composition of  claim 1  further comprising 0.01 wt % to 1.0 wt % of a C 12-24  borated epoxide. 
     
     
         12 . The lubricant composition of  claim 1  further comprising 0.1 wt % to 3.0 wt % of a mixture of at least two antioxidants selected from hindered phenols, aryl amines, and sulfur containing antioxidants. 
     
     
         13 . The lubricant composition of  claim 1  wherein the lubricant composition exhibits an electrical conductivity of up to 7.0×10 −10  S/cm as measured by ASTM D2624 at 100° C. and 500 V. 
     
     
         14 . A method of lubricating a transmission comprising supplying to the automatic transmission a composition of  claim 1 , and operating the transmission. 
     
     
         15 . The method of  claim 14 , wherein the transmission does not include a shifting clutch.