Automatic transmission fluids with improved anti-wear properties

Abstract

Automatic transmission fluids are described which contain at least 0.05 weight percent of a dialkyl thiadiazole and sulfurized fat, sulfurized fatty acid, sulfurized fatty acid ester, up to about 0.15 weight % of a metal-containing detergent, and/or a mixture thereof. The transmission fluids according to the present invention exhibit improved anti-wear and extreme pressure performance.

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 0.05 wt %, based on the fluid, of an ashless dialkyl thiadiazole,  
 (B) a sulfurized fat, sulfurized fatty acid, sulfurized fatty acid ester or a mixture thereof, and  
 (C) up to about 0.15 wt %, based on the fluid, of a metal-containing detergent.  
   
     
     
         2 . An automatic transmission fluid as claimed in  claim 1 , wherein component (A) is a compound of the formula:  
       
         
           
           
               
               
           
         
       
       wherein R 1  is a hydrocarbyl substituent having from 6 to 18 carbon atoms; and R 2  is a hydrocarbyl substituent having from 6 to 18 carbon atoms and may be the same as or different from R 1 .  
     
     
         3 . An automatic transmission fluid as claimed in  claim 2 , wherein R 1  and R 2  are about 9-12 carbon atoms.  
     
     
         4 . An automatic transmission fluid as claimed in  claim 3 , wherein R 1  and R 2  are the same, and are each 9 carbon atoms.  
     
     
         5 . An automatic transmission fluid as claimed in  claim 1 , wherein component (B) comprises at least one sulfurized fatty acid ester.  
     
     
         6 . An automatic transmission fluid as claimed in  claim 1 , wherein component (C) comprises at least one calcium-containing detergent.  
     
     
         7 . An automatic transmission fluid as claimed in  claim 1 , wherein component (A) is present in an amount of from 0.05 to about 0.75 weight percent, based on the transmission fluid.  
     
     
         8 . An automatic transmission fluid as claimed in  claim 7 , wherein component (A) is present in an amount of from 0.075 to about 0.25 weight percent, based on the transmission fluid.  
     
     
         9 . An automatic transmission fluid as claimed in  claim 7 , wherein component (A) is present in an amount of about 0.10 weight percent, based on the transmission fluid.  
     
     
         10 . An automatic transmission fluid as claimed in  claim 1 , wherein component (B) is present in an amount of from about 0.10 to about 1.00 weight %, based on the transmission fluid.  
     
     
         11 . An automatic transmission fluid as claimed in  claim 1 , wherein component (B) is present in an amount of from about 0.25 to about 0.75 weight %, based on the transmission fluid.  
     
     
         12 . An automatic transmission fluid as claimed in  claim 1 , wherein component (B) is present in an amount of about 0.50 weight %, based on the transmission fluid.  
     
     
         13 . An automatic transmission fluid as claimed in  claim 1 , further at least one inhibitor selected from the group consisting of foam inhibitors, corrosion inhibitors, rust inhibitors, and oxidation inhibitors.  
     
     
         14 . An automatic transmission fluid as claimed in  claim 1 , further comprising at least one viscosity index improver, dispersant, or friction modifier.  
     
     
         15 . An automatic transmission fluid as claimed in  claim 14 , wherein there is a mixture of viscosity index improvers present.  
     
     
         16 . An automatic transmission fluid as claimed in  claim 14 , wherein there is at least one dispersant present, and the at least one dispersant has a total nitrogen to phosphorus mass ratio of between about 3:1 and about 10:1.  
     
     
         17 . An automatic transmission fluid composition comprising: 
 (1) a major amount of a base oil and    (2) a minor amount of an additive composition comprising: 
 (A) at least 0.05 wt %, based on the fluid, of a dialkyl thiadiazole,  
 (B) a sulfurized fatty acid ester,  
 (C) up to about 0.15% of a metal containing detergent,  
 (D) a dispersant having a total nitrogen to phosphorus mass ratio of between about 3:1 and about 10:1,  
 (E) a diphenylamine antioxidant, and  
 (K) a mixed viscosity index improver system containing 
 (i) a nondispersant polymethacrylate, and  
 (ii) a dispersant polymethacrylate.  
 
   
     
     
         18 . The automatic transmission fluid of  claim 16  further comprising at least one additive selected from the group consisting of seal swell agents, foam inhibitors, lubricity agents, and dyes.  
     
     
         19 . A method of improving automatic transmission antiwear and extreme pressure performance, said method comprising adding to, and operating in, said automatic transmission an automatic transmission fluid as set forth in  claim 17 .  
     
     
         20 . An automatic transmission fluid composition, which exhibits good anti wear and extreme pressure performance and stability, obtained by combining (1) a major amount of a base oil and (2) a minor amount of an additive composition comprising: 
 (A) at least 0.10 weight % dialkyl thiadiazole,    (B) at least 0.10 weight % of at least one sulfurized fatty acid ester, and    (C) up to about 0.15 weight % of a metal-containing detergent.    
     
     
         21 . The automatic transmission fluid of  claim 19  further comprising at least one additive selected from the group consisting of seal swell agents, foam inhibitors, lubricity agents, and dyes.