COPYRIGHT - / 7f/ SOCIETY OF AUTOMOTIVE ENGINEERS, INC. ABSTRACT Automatic transmission fluids are specially designed to meet the many different require­ ments of automatic transmissions. This paper describes the properties of such fluids, the types of additives used to formulate them, and the tests used to evaluate ATF's. Also described are the powershift transmission fluids, Allison C-3 and Caterpillar TO-2, which are used in truck, bus, and heavy equipment transmissions. I. INTRODUCTION Automatic transmission fluids (ATF's) are recognized as the most complex lubricants in the petroleum industry. Containing as many as 15 components, ATF's represent a careful balance of properties needed to meet the unique requirements of automatic trans­ missions. In terms of viscosity, they may be described as SAE 20 grade oils with exceptionally good low temperature proper­ ties. They contain some of the same types of additives used in engine oils, but may have in addition additives to provide special friction properties, and improved oxidation stability. Because of their excellent low temperature viscosity and antiwear properties, automatic transmission H. E. Deen and J. Ryer Exxon Chemical Co. fluids often find applications as hydraulic fluids in industrial equipment and air compressors. There are two types of fluids widely marketed in the U.S., DEXR0N®-II, and Type F. The former fluids are friction modified and are recommended for service fill by most major automotive companies for current pro­ duction vehicles. Type F fluids are non- friction modified and are designed for some 1978 and earlier Ford vehicles. Appendix Table I lists the typical properties of automatic transmission fluids. These are discussed in more detail in the following sections of this report. Powershift transmission fluids meeting the SAE J1285 classification are designed for users of heavy duty transmission. Includ­ ing the targets of the Allison C-3 and Caterpillar TO-2 specification, this class­ ification is met by fluids including heavy duty engine oils, DEXR0N®-II fluids and lower cost fluids designed specifically for these applications. II. FUNCTIONS OF MODERN ATF'S The fluid used in passenger car, light truck, and school bus automatic trans­ missions must perform in five distinct functions. These are: 1. Hydrodynamic energy transmission medi­ um for use in the torque converter. 2. Hydrostatic energy transmission medium for use in the hydraulic control logic circuits and for servomechanisms. Downloaded from SAE International by Columbia Univ, Monday, August 20, 20183o Lubricating medium for shaft bearings, thrust bearings, and involute or spur gear load surfaces. 4. Sliding friction energy transmission medium for use with lubricated bands and clutches. 5. Heat transfer medium with liquid or air cooled systems for maintenance of a suitable automatic transmission temperature range. Table I summarizes these functions and includes other important requirements of ATF's which will be discussed in more detail later* TABLE I REQUIREMENTS OF AN ATF o Transmit power in torque converter,, o Act as a hydraulic fluido o Lubricate gears and bushings. o Function as a heat transfer medium., o Maintain seal performance with a variety of elastomers. o Operate over a -40°C to 175°C. wide temperature range, o High oxidation resistance. o Noncorrosive towards all transmission componentso o Provide special friction properties for clutch operations. o Prevent foaming. cooling by the oil that is absorbed. This is particularly important since the instant­ aneous temperature of the mating steel plates can reach almost 600°C. Also, paper plates have high coefficients of friction and have excellent resilience and resistance to wear. All these properties are important in enabling designers to use a minimum number of clutch plate surfaces and thus design compact transmissions. Sintered bronze' or