JSAE 20077133 SAE 2007-01-1986 Automatic Transmission Fluid Development: Reaching New Levels of Friction Durability Samuel H. Tersigni, Lee D. Saathoff and Christopher Cleveland R&D Laboratory, Afton Chemical, Inc., Richmond, Virginia, USA Mark S. Jones R&D Laboratory, Afton Chemical, Ltd., Bracknell, Berkshire, United Kingdom Kenji Yatsunami R&D Laboratory, Afton Chemical Japan Corp., Tsukuba, Japan ABSTRACT This paper reports development of a new automatic transmission (AT) fluid (ATF) with enhanced durability for the Asian marketplace. The authors contend the new step-automatic transmission hardware, such as wet starting clutches, new friction materials, dual clutches and six- and seven-speed ATs, create the need for enhanced levels of friction durability from the ATF. The new challenge from such hardware for the fluid developer lies in simultaneously meeting more stringent wear, extreme pressure (EP), friction durability and torque capacity requirements. The new additive chemistry, when used in a mineral oil base fluid, is capable of 1000+ hours in JASO M349 LVFA durability testing, a 16-fold increase over the JASO M349 reference ATF Toyota T-III. This performance easily doubles that of the currently most durable Asian ATFs, while offering better anti-wear and EP performance. INTRODUCTION Automobile manufacturers expect some corporate average vehicle fuel economy (CAFÉ) benefits by employing lower viscosity automatic transmissions fluids (ATFs). Previous generations of ATFs had a 100C kinematic viscosity (Kv100C) in the range of 7.0 to 8.0 cSt; the new generation of ATFs has a fresh oil Kv100C between 5.4 and 6.4 cSt. [1] Accordingly, low temperature (-40C) and start-up viscosities (0 to 25C) are also lower with the new ATFs. Lower viscosity (thinner) fluids reduce transmission churning (or spin) energy losses in the transmission, the extent to which depends on the test protocol and specifically thetemperature range used to evaluate fuel economy benefits. In most testing, the magnitude of the fuel economy benefit is roughly equivalent to the precision of the test being used to measure it, so careful test operation, statistical design of experiments and numerical analysis of the results are necessary. [2] Lower viscosity ATFs can be a challenge for the transmission hardware, especially with respect to pump losses and gear and bearing durability. Thinner fluids leak easier through pumps and seals. Likewise, a lower viscosity fluid usually means thinner protective films for bearings and gears, unless fluid design is specifically altered to compensate for the drop in kinematic viscosity. [3] Higher quality base oils may be needed for the lower viscosity fluids to ensure their robustness with respect to volatility, which affects oil volume within the transmission during operating life. Meanwhile, in addition to the ATF changes, most automakers have moved to new hardware, including additional gears (i.e., six- and seven-speeds) and start- up devices, to further enhance fuel economy in their automatic transmissions (ATs). The additional shifting energy can affect the durability of the transmission, particularly in the clutch packs (friction plates), and the oil. Along with more clutch applications, the new AT hardware designs typically offer smaller sumps that allow less fluid volume and less time in the sump for the ATF to release air and reduce foam. The combination of new hardware and less ATF requires an increased level of additive performance. Many ATFs on the Asian market contain additives over a decade old, designed well before the release of the new transmission hardware. For reasons discussed above, the optimum performance additive and fluid design for the new step-AT hardwareCopyright © 2007 Society of Automotive Engineers of Japan, Inc. and Copyright © 2007 SAE International -883-Downloaded from SAE International by Univ of Nottingham - Kings Meadow Campus, Monday, September 17, 2018may require a significant increase