Automatic transmission fluids with improved anti-shudder properties

Abstract

Automatic transmission fluids are described which contain at least 0.2 wt % of a metal-containing detergent, a dispersant, and a mixture of friction modifiers. The transmission fluids according to the present invention exhibit excellent initial anti shudder properties, excellent anti-shudder durability, and excellent friction durability.

We claim:  
     
         1 . An automatic transmission fluid, comprising: 
 (1) a major amount of a base oil, and    (2) a minor amount of an additive comprising 
 (A) at least about 0.10 weight % of a metal-containing detergent,  
 (B) a dispersant, and  
 (C) a mixture of at least two different friction modifiers.  
   
     
     
         2 . An automatic transmission fluid as claimed in  claim 1 , wherein component (A) is a calcium containing detergent.  
     
     
         3 . An automatic transmission fluid as claimed in  claim 2 , wherein component (A) is a calcium phenate, calcium sulfonate, or a mixture thereof.  
     
     
         4 . An automatic transmission fluid as claimed in  claim 1 , wherein component (A) is overbased.  
     
     
         5 . An automatic transmission fluid as claimed in  claim 1 , wherein component (A) is present in an amount of from 0.25 to abou t 1.5 wt %.  
     
     
         6 . An automatic transmission fluid as claimed in  claim 1 , wherein component (A) is present in an amount of from about 0.75 wt % to about 1.00 wt %.  
     
     
         7 . An automatic transmission fluid as claimed in  claim 1 , wherein component (B) is a succinimide dispersant.  
     
     
         8 . An automatic transmission fluid as claimed in  claim 7 , wherein the succinimide is boronated, phosphorylated, or boronated and phosphorylated.  
     
     
         9 . An automatic transmission fluid as claimed in  claim 1 , wherein the dispersant has a total nitrogen to phosphorus mass ratio of between about 3:1 and about 10:1.  
     
     
         10 . An automatic transmission fluid as claimed in  claim 1 , where in the mixture of friction modifiers comprises a mixture of an ethoxylated amine and a fatty polyamine.  
     
     
         11 . An automatic transmission fluid as claimed in  claim 1 , wherein component C is selected from the group consisting of ethoxylated fatty amines, aliphatic fatty alkanol amides, aliphatic primary amines, aliphatic secondary amines, and aliphatic fatty imidazolines.  
     
     
         12 . An automatic transmission fluid as claimed in  claim 1 , wherein component C is selected from the group consisting of glycerol esters, aliphatic carboxylic ester amides, aliphatic carboxylic acids, aliphatic phosphonates, aliphatic phosphates, aliphatic thiophosphonates, and aliphatic thiophosphates.  
     
     
         13 . An automatic transmission fluid as claimed in  claim 1 , further comprising at least one viscosity index improver, antioxidant, anti rust, or anti foam agent.  
     
     
         14 . An automatic transmission fluid as claimed in  claim 1 , further comprising an additional phosphorus source.  
     
     
         15 . An automatic transmission fluid as claimed in  claim 12 , wherein the phosphorus source is dibutyl hydrogen phosphate.  
     
     
         16 . An automatic transmission fluid as claimed in  claim 1 , further comprising a shear stable viscosity index improver.  
     
     
         17 . An automatic transmission fluid composition having good initial anti-shudder performance and anti-shudder durability, comprising: 
 (1) a major amount of a base oil and    (2) a minor amount of an additive composition comprising: 
 (A) at least about 0.25 wt % of a metal-containing detergent,  
 (B) a dispersant, and  
 (C) a mixture of at least two amine-based friction modifiers.  
   
     
     
         18 . An automatic transmission fluid as claimed in  claim 16 , wherein the metal containing detergent is an overbased calcium sulfonate.  
     
     
         19 . An automatic transmission fluid as claimed in  claim 17 , wherein the dispersant has a total nitrogen to phosphorus mass ratio of between about 3:1 and about 10:1.  
     
     
         20 . The automatic transmission fluid as claimed in  claim 17 , wherein the friction modifier comprises a mixture of ethoxylated amine and fatty polyamine.  
     
     
         21 . The automatic transmission fluid of  claim 15  further comprising at least one additive selected from the group consisting of extreme pressure/antiwear agents, seal swell agents, foam inhibitors, rust inhibitors, viscosity index improvers, lubricity agents, and dyes.  
     
     
         22 . The automatic transmission fluid of  claim 15 , wherein the fluid has a friction durability of at least 200 hours on the ECCC friction durability test as measured on the SAE #2 low speed rig.  
     
     
         23 . A method of improving friction durability and anti-shudder performance of an automatic transmission said method comprising adding to, and operating in, said automatic transmission an automatic transmission fluid as set forth in claim  17 .