Development of Next-Generation Automatic Transmission Fluid Technology

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. Low Velocity Friction Apparatus (LVFA), SAE #2, and FZG pitting tester were used to develop the technology. Also a test using current transmission was developed to measure the fuel economy of test fluids. The technology developed provides excellent fuel economy, measured by actual transmissions, while providing superior gear and bearing protection, optimized friction characteristics and excellent shear stability.