Lubrication of an automatic transmission with reduced wear on a needle bearing

Abstract

A lubricant composition comprising (a) an oil having a kinematic viscosity at 100° C. of 2.2 to 3.7 mm2/s; at least one borate ester having an alkyl group of 4 to 18 carbon atoms in an amount to provide 25 to 150 parts per million by weight boron to the composition; and (c) at least one phosphorus ester in an amount to provide 150 to 650 parts per million by weight phosphorus to the composition, wherein the kinematic viscosity at 100° C. of the lubricant composition is less than or equal to 4.7 mm2/s, provides wear resistance to a needle bearing in an automatic transmission.

1 . A lubricant composition comprising:
 (a) an oil having a kinematic viscosity at 100° C. of about 2.2 to about 3.7 mm 2 /s;   (b) at least one borate ester having an alkyl group of 4 to about 18 carbon atoms in an amount to provide about 25 to about 100, parts per million by weight boron to the composition; and   (c) at least one phosphorus ester in an amount to provide about 150 to about 650 parts per million by weight phosphorus to the composition;   (d) the viscosity index modifier comprise a linear polymer viscosity modifier having dispersant functionality, wherein the linear polymer has aweight average molecular weight of 5,000 to 25,000, and wherein said linear polymer is present in an amount of about 0.1 to about 4 weight percent.   wherein the kinematic viscosity at 100° C. of the lubricant composition is less than or equal to about 4.7 mm 2 /s.   
     
     
         2 . The lubricant composition of  claim 1  wherein:
 the amount of the at least one borate ester (b) is about 0.1 to about 1.1 percent by weight, or 0.15 to about 0.7 percent by weight; and 
 the amount of the at least one phosphorus ester (c) is about 0.05 to about 0.40 percent by weight. 
 
     
     
         3 . The lubricant composition of  claim 1  wherein the composition comprises about 100 to about 500 parts per million boron and about 150 to about 1000 parts per million phosphorus. 
     
     
         4 . The lubricant composition of  claim 1  wherein the oil of component (a) comprises an API Group II or Group III oil or mixtures thereof 
     
     
         5 . The lubricant composition of  claim 1  wherein (b) the at least one borate ester component comprises a borate ester containing an alkyl group of 4 to 12 carbon atoms and a borate ester containing an alkyl group of 14 to about 18 carbon atoms. 
     
     
         6 . The lubricant composition of  claim 1  wherein (b) the at least one borate ester component comprises a borated epoxide having about 12 to about 18 carbon atoms. 
     
     
         7 . The lubricant composition of  claim 1  wherein (b) the at least one borate ester component comprises the reaction product of boric acid with an alcohol of about 6 to about 12 carbon atoms. 
     
     
         8 . The lubricant composition of  claim 1  wherein (c) the phosphorus ester comprises a C4 to C6 alkyl phosphite such as dibutylphosphite or an oligomeric phosphite which is the reaction product of a monomeric phosphorous acid or ester with an alkylene diol. 
     
     
         9 . (canceled) 
     
     
         10 . The lubricant composition of  claim 8  wherein (d) the viscosity index modifier comprises a poly(meth)acrylate containing a nitrogen-containing dispersant monomer. 
     
     
         11 . (canceled) 
     
     
         12 . The lubricant composition of  claim 1  further comprising (e) a succinimide dispersant. 
     
     
         13 . The lubricant composition of  claim 10  wherein (e) the succinimide dispersant comprises a borated succinimide dispersant. 
     
     
         14 . The lubricant composition of  claim 10  wherein (e) the succinimide dispersant is further treated with a dimercaptothiadiazole. 
     
     
         15 . The lubricant composition of  claim 10  wherein some or all of (e) the succinimide dispersant is borated and treated with a dimercaptothiadiazole. 
     
     
         16 . The composition of  claim 12  wherein the amount of (e) the boron-containing succinimide dispersant is about 1.0 to about 3.5 percent by weight. 
     
     
         17 . The lubricant composition of  claim 10  wherein (e) the boron-containing succinimide dispersant component provides about 10 to about 250 parts per million by weight sulfur to the composition by means of the presence of a dimercaptothiadiazole moiety present therewith. 
     
     
         18 . The lubricant composition of  claim 12  wherein (e) the boron-containing succinimide dispersant has a boron content of about 0.6 to about 0.9 weight percent, or 0.54 to 0.85, or 0.56 to 0.83 weight percent. 
     
     
         19 . The lubricant composition of  claim 1  further comprising at least one of a friction modifier, an antioxidant, a detergent, a corrosion inhibitor, an extreme pressure/antiwear agent, a foam inhibitor, or a seal swell agent. 
     
     
         20 . A lubricant composition comprising:
 (a) about 50 to about 98 percent by weight of an oil having a kinematic viscosity at 100° C. of about 2.2 to about 3.7 mm 2 /s;   (b-1) about 0.1 to about 1.0 percent by weight of a borate ester containing a C4 to C12 alkyl group;   (b-2) about 0.15 to about 0.40 percent by weight of a borate ester containing a C14 to about a C18 alkyl group;   (c) at least one phosphorus ester in an amount to provide about 150 to about 650 parts per million by weight phosphorus to the composition;   (e-1) about 1.0 to about 4.0 percent by weight of a borated succinimide dispersant not treated with a dimercaptothiadiazole; and   (e-2) about 0.1 to about 1.5 percent by weight of a borated succinimide dispersant that is treated with a dimercaptothiadiazole;   wherein the amount of boron provided by components (b-1), (b-2), (e-1) and (e-2) is at least 180 parts per million by weight of the composition; and wherein the kinematic viscosity at 100° C. of the lubricant composition is less than or equal to about 4.7 mm 2 /s.   
     
     
         21 . A method of lubricating an automatic transmission comprising supplying thereto the lubricant composition of  claim 1 . 
     
     
         22 . The method of  claim 20  wherein the automatic transmission contains a bearing that is lubricated by said lubricant composition.