Next-Generation Fluid Technology for CVT and AT 2011-01-2122

Globally, greater emphasis has been placed on vehicles to reduce carbon dioxide emission and fuel consumption. In light of this, Original Equipment Manufacturers (OEMs) have been developing various automatic transmissions such as the step automatic transmission (AT) and the continuously variable transmission (CVT) to improve both fuel consumption and drivability.

Step AT and belt-CVT's are very popular with Japanese OEMs and in particular, recent market trends show CVT use is expanding rapidly due to its potential for improved fuel efficiency. Since the fluid performance requirements for both AT's and CVT's are different depending on transmission design, AT and CVT fluids are currently used separately, with no single fluid technology currently available on the market. The desire for high belt-pulley capacity has driven studies concentrating on metal-on-metal friction for the development of CVT fluids, whereas the desire for anti-shudder durability has been the primary driver for ATF development. As those parameters are typically trade-offs, it is very difficult to achieve both in one fluid.

We herein report on the development of new fluid technologies that show high metal-on-metal friction coefficient with good anti-shudder durability and higher static friction coefficient. As such, the authors were able to develop a Next-Generation Fluid Technology for both CVT and AT applications. The technology has been developed by understanding the function and activity of each component, while further enhancing our understanding of the control of the friction characteristics of the fluid. This enabled the optimization of the whole formulation designed for both CVTF and ATF performance in the areas mentioned above.

Benchmark studies such as static and dynamic friction coefficient in SAE No.2 (JASO 348:2002), anti-shudder durability in LVFA (JASO M349:2001), metal-on-metal friction coefficient in the Block on Ring (JASO M358:2005) and SRV, Shell-4-ball (ASTM D2783), Foaming (ASTM D892), Oxidation stability (JIS K2514)… etc. were carried out in order to confirm the applicability of our fluid technology to Japanese CVTF and ATF applications. Based on the benchmark results, our developed fluid technologies are applicable for both CVTF and ATF performance applications.