Design and Performance of Low-Viscosity ATF 2007-01-3974

Low-viscosity automatic transmission fluids (ATF) have advantages in terms of lower churning losses and lower drag resistance in the automatic transmission (AT) and higher transmission efficiency. While a low viscosity is effective to the improvement of fuel economy, there is a risk of degraded fatigue prevention performances or anti-wear properties of the ATF, which can have an adverse effect on the reliability of the AT. Consequently, the use of current low-viscosity ATFs were limited to AT units that were specially developed to use them. The aim of our study was to resolve these problems and improve the general versatility of low-viscosity ATFs. We developed a low-viscosity ATF having high reliability by designing its viscosity based on the field test data involving conventional commercial fluids of normal viscosity design (7.4mm²/s@100°C), and by optimizing the blend of base stocks and viscosity index improvers (VI improvers). Various laboratory tests and DEXRON® specification tests showed that the newly developed low-viscosity ATF provides fatigue resistance and anti-wear protection as good or better than conventional ATF. Moreover, this developed ATF showed better fuel economy than a conventional ATF in fuel economy tests using a chassis dynamometer.