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Fuel economy is well known as the main driver for change in transmission and automatic transmission fluid (ATF) technology. This driver has led to the reduction in size and weight of transmission components and also advancements in transmission design. Some of the key transmission design changes include the addition of continuously slipping torque converter clutches, the increase in the number of speeds, the use of more thermally stable friction materials, and other refinements.

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 performance; and, 7) long-term anti-shudder performance to enable aggressive use of controlled slip torque converter clutches for fuel economy.

Driven by global demands for improved fuel economy and reduced emissions, significant improvements have been made to engine designs and control systems, vehicle aerodynamics, and fuel quality. Improvements, such as the continuously slipping torque converter, have also been made to automatic transmissions to increase vehicle efficiency. Recently, belt-continuously variable transmissions (b-CVTs) have been commercialized with the promise of significant fuel economy improvements over conventional automatic transmissions. Automotive traction drive transmissions may soon join belt-CVTs as alternative automatic transmission technology. Much of the information reported in technical and trade publications has been on the mechanics of these traction drive systems. As automotive traction drives move closer to commercial reality, more attention must be given to the performance requirements of the automotive traction fluid.

New technologies are being commercialized across the automotive industry to address demands for improved fuel economy, emissions reductions, and improved customer satisfaction. Push-belt continuously variable transmissions (b-CVTs) are beginning to command a significant percentage of the market now dominated by manual and conventional automatic transmissions. In addition, automobile manufacturers plan to introduce the first traction drive toroidal-CVTs to the market place within the next five years. A review of the relative benefits and limitations of each of these automatic transmissions exists in the literature. In this paper we consider how the performance requirements of each of these automatic transmission systems impact automatic transmission fluid technology. The physical characteristics and screen test performance of two commercial ATFs, a b-CVTF, and two traction fluids were examined.