Development of a New Fuel-Efficient Manual Transmission Oil

Reducing the viscosity of a manual transmission oil is the most effective way to obtain a fuel economy effect with the lubricant. However, there are concerns that a lower viscosity may result in a thinner oil film, causing a decline in extreme pressure performance (anti-seizure and anti-wear performance) and anti-pitting performance at the high temperature condition. Therefore, a method for maintaining sufficient oil film thickness is needed for oils with reduced viscosity.

In this study, attention was focused on the effects of the base oil and the viscosity index improver. As a result, a new manual transmission oil has been developed that provides an oil film thickness equal to that of current oil even though its viscosity has been reduced by half compared with the level of current oil. Specifically, the base oil is formulated with a high-viscosity mineral oil (Group I) and the molecular weight of the viscosity index improver has been reduced. In addition, the use of a special poly-methacrylate in the formulation has substantially improved the oil film thickness. The results of laboratory tests conducted with actual manual transmissions confirmed that the new oil provides performance equal to that of current oil. There was no sign that the reduction of viscosity caused any decline in extreme pressure performance or anti-pitting performance. In tests conducted with actual transmissions, it was found that lower viscosity had the effect of reducing friction by 10-20% in an actual operating temperature range of -10° to 80°C. Evaluations conducted with actual transmissions also showed that the new oil improved low-temperature shiftability by 40% at -5°C.