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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.

Global original equipment manufacturers (OEMs) have requested lower viscosity automatic transmission fluid (ATF) for use in conventional and 6-speed automatic transmissions (AT) to meet growing demands for improved fuel economy. While lower-viscosity ATF may provide better fuel economy by reducing churning losses, other key performance attributes must be considered when formulating lower viscosity ATF(1,2). Gear and bearing performance can be key concerns with lower-viscosity ATFs due to reduced film thickness at the surfaces. Long-term anti-shudder performance is also needed to enable the aggressive use of controlled slip torque converter clutches that permit better fuel economy. And, friction characteristics need to be improved for higher clutch holding capacity and good clutch engagement performance. This paper covers the development of next-generation, low-viscosity ATF technology, which provides optimum fuel economy along with wear and friction durability.

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.

Public concern and increasing regulations surrounding environmental issues, such as CO₂ emissions, are making it important for car makers to improve the fuel efficiency of the vehicles they manufacture and sell. A wide array of transmission technologies are being employed towards this end including, but not limited to, 6, 7, and 8 speeds stepped automatic transmissions, dual clutch transmissions (DCT) and continuously variable transmissions (CVT). The number of passenger cars equipped with CVTs has been increasing and push belt CVT types (b-CVT) are widely used. Since engine torque is transferred to the wheels via friction between the steel elements of the belt and the steel pulleys in a b-CVT, having a high metal on metal friction is required. As the CVT fluid is a key part of the CVT system, using a special CVT Fluid (CVTF) is critical in order to provide and maintain the required high metal-on-metal friction performance.