Jo SOCIETY OF AUTOMOTIVE ENGINEERS, INC. 485 Lexington Avenue, New York 17, N. Y. Technical Considerations of Automatic Transmission Fluid Formulation D. Borden, N. R. Roux, and C. M. Stendahl Enjay Laboratories OF A U TO MOTIVE ENGINEERS National Farm, Construction & Industrial Machinery Meeting Milwaukee, Wise. Sept. 10-13, 1962 574B Downloaded from SAE International by University Of Newcastle, Thursday, October 04, 2018Technical Considerations of Automatic Transmission Fluid Formulation D. Borden, N. R. Roux, and C. M. Stendahl Enjay Laboratories AUTOMATIC TRANSMISSIONS HAVE made a considerable impact on the automotive industry as well as the motoring public. Since the end of World War II, the number of new cars equipped with automatic transmissions has risen from less than 5°Jo to approximately 70%. This surge of popularity can be accredited to one primary reason--ease of operation. It is becoming increasingly evident that a similar trend is occurring—albeit on a reduced scale—in the farm and con­ struction equipment industry. It is not the automatic trans­ mission that is becoming more prevalent, but rather, the automatic transmission's first cousin—the manually selected, power shift transmission. Ease of operation plays a large role in the acceptability of this type of transmission also; how­ ever, the major reason for its acceptance is that the presence of the hydrodynamic unit between the engine and the drive- shaft protects the engine from the severe shocks normally encountered in heavy-duty operation. This increases engine life and reduces engine maintenance. In the last 15 years, cooperative work between the auto­ motive and petroleum industries and the additive suppliers to the petroleum industry has solved a number of problems associated with fluid-transmission operation. During this pe­ riod, automatic transmission fluids (ATF's) have evolved from products closely resembling straight mineral oils to fluids composed of as many as 10 or more components that satisfy the most stringent requirements of today's automatic trans­ missions. Some of the technological advancements associated with the development of ATF's may have application to hydraulic fluids currently used by the farm and construction equipment industry. Admittedly, the needs of this industry are not iden­ tical to those of the automotive industry; however, there are enough similarities in fluid requirements to make a general discussion of automatic transmission fluids worth while. This paper will discuss the more important properties of automatic transmission fluids and will then elaborate on the techniques that have been developed to achieve and evalu­ ate these desirable properties. The authors hope that from this paper the farm and construction equipment manufactur­ ers will gain greater insight into automatic transmission fluid technology. Moreover, it is hoped that the lubricant sup­ pliers and equipment manufacturers can utilize this tech­ nology to further improve fluid-equipment design. WHAT PROPERTIES MUST AN AUTOMATIC TRANSMISSION FLUID HAVE Before discussing the many varied properties an automatic transmission fluid should have, we must first determine what functions the ATF must serve in a transmission. These func­ tions are to: 1. Transmit power in the fluid member of the transmis­ sion. 2. Serve as a hydraulic medium for the hydraulic control system. 3. Serve as a medium to transfer heat to coolers where the heat is dissipated. 4. Lubricate a variety of critical transmission parts, for example, gears, clutches, and bearings. In order for a fluid, then, to satisfy these functions suc­ cessfully over the wide temperature ranges (-40-+350 F) to which it is subjected, it must have certain special properties. Acceptable Viscosity Properties at High and Low Tem­ peratures - The fluid must have a sufficiently high viscosity at elevated temperatures to ensure that excessive