JSAE 20077280 SAE 2007-01-1975 Advanced ATF Technology Meets Future Global OEM Needs Hyun-Soo Hong, William D. Abraham, M asahiko Ikeda, and Craig D. Tipton The Lubrizol Corporation, USA ABSTRACT Fuel economy is a well known driver of change in transmission and automatic transmission fluid (ATF) technology. It has led to reducing transmission components’ size and weight and also to adding continuously slipping torque converter clutches and other refinements. Resulting ATF performance improvements include: 1) reduced viscosity to lessen churning losses and improve fuel economy [1,2,3]; 2) high shear stability to ensure adequate fluid film thickness throughout the life of the vehicle; 3) high viscosity index (VI) to improve fuel economy; 4) improved gear and bearing protection due to lower viscosity[4]; 5) high static friction to improve clutch holding capacity; 6) high dynamic friction for good clutch engagement performanc e; and, 7) long-term anti- shudder performance to enable aggressive use of controlled slip torque converter clutches for fuel economy. Our paper reports on the development of new ATF technology specifically design ed to meet all seven of the ATF fluid performance areas mentioned above. Data is presented from the JASO LVFA (Low Velocity Friction Apparatus), shear stability and film thickness, and FZG pitting testing to establish gear protection properties for lower viscosity formulations with fuel-saving properties. We conducted friction testing on a wide range of composite materials from various suppliers. Results show that the new fluid technology is superior to existing commercial fluid technology worldwide and can address all the major concerns enumerated above. INTRODUCTION Over the past 20 years, increases in crude oil costs globally along with legislative initiatives such as the North American requirements for Corporate Average Fuel Economy (CAFE) have driven change in automatic transmission fluid (ATF) technology. Although the Continuously Variable Transmission (CVT), Traction Drives or Infinitely Variable Transmission (IVT), and Dual Clutch Transmission (DCT) have been designed for smaller passenger vehicles, the conventional automatic transmission continues to dominate the marketplace, particularly in North America. This is partly due to such improvements as the continuously slipping torque converter clutch (CSTCC), electronic controls, and gear ratios of 6, 7, or 8 forward speeds using the efficient Lepelletier gear set arrangement. Additionally, in order to achieve fuel economy goals, the size and weight of transmissions has decreased while power density through the units has increased. These changes have led to the development of ATFs with improved CSTCC anti-shudder performance, lower viscosity for less power-robbi ng, churning resistance and clutch drag, better anti-wear and bearing performance for durability with lower viscosity fluids, and higher static friction to enable high capacity in smaller clutches. These trends are seen across Asia, North America, and Europe. While it would be simpler to address each transmission need individually, there are multiple trade-offs when formulating a complete ATF. For example, a lower viscosity may result in improved fuel economy but at the cost of film thickness for bearing protection. A static friction increase makes it more difficult to provide durable positive μ/v friction curve slope performance for proper CSTCC performance. A negative slow-speed μ/v curve can result in shudde r, an objectionable oscillation or stick-slip phenomenon t hat vehicle occupants can feel. Another driver is that several OEMs have included friction composites for clutches made by different suppliers in their specifications. For example, Ford MERCON ® V [8] requires two 30,000-cycle friction durability tests, one using clutches su rfaced with BorgWarner SD1777 and one using