AUTOMATIC TRANSMISSION FLUIDS THAT DELIVER EFFICIENCY AND PROTECTION
Well-formulated, low-viscosity transmission fluids are helping OEMs to improve fuel economy levels and ensure enhanced hardware protection
The need for automatic transmission fluids (ATFs) to contribute to vehicle fuel economy performance is growing. As a result, our engineers have been exploring how the right combination of ATF viscosity and additive technology are able to yield breakthrough efficiency gains.
In recent years, a variety of end-user requirements – including improved fuel economy, increased vehicle performance, greater power requirements and an enhanced driving experience – have driven tremendous changes and developments in automotive transmission systems and fluids.
But right now in the passenger car market, fuel economy is by far the biggest impetus for transmission hardware evolution, as car makers work to meet ever-tightening CO2 emissions mandates and targets.
This has resulted in a real diversification in transmission technology as OEMs each take different approaches to improving fuel economy. One approach, adopted by a number of car makers, is to increase the number of gears in conventional stepped automatic transmissions. While 6-speed transmissions have been a workhorse unit for many OEMs, some are now moving to 8-, 9- and 10-speed setups. Other approaches include continuously variable, dual-clutch and hybrid technologies..
Fluid contribution to economy
Today, ATFs are increasingly expected to have an impact on fuel economy performance. ATF viscosity, for example, has a direct effect on pumping, drag and churning losses. And, with the oil pump thought to account for about 30% of the total amount of energy lost in the transmission, these sources of inefficiency can’t be underestimated or ignored either. In addition, ATF viscosity and boundary film chemistries can have a direct effect on gear and bearing efficiency.
To gain the most fuel efficiency, the new formulation trend is for transmission fluids to have lower and lower viscosities over a wider range of operating conditions. A number of OEMs have moved from conventional viscosity fluids of more than 6.8cSt at 100°C to low viscosity – typically 5.5cSt – for their automatic transmissions. But there are already 4.5cSt fluids in use, and there may be a demand to move to even lower viscosities in the future. While it is possible to get a key improvement in fuel economy from transmission fluids, it involves far more than lowering viscosity at 100°C – low-temperature viscosityis also critical. In addition, because there is more tendency for mixed and boundary lubrication as viscosity is lowered, gear and bearing losses can also increase.
However, it is clear that the careful selection of friction modifier and film former additives, combined with the most appropriate base stock, can reduce these losses. Carefully designed research methodology has been used to evaluate the fuel economy performance of fluids, while ensuring they also deliver sufficient hardware protection.
Evaluating fuel economy
Formulation challenges are expected to come in the future in the form of further requirements for improved durability, longer drain interval and fuel economy in transmission hardware that is increasingly complex. This will put even more stress on the fluid and result in the development of even higher-performing ATFs.
As the formulation landscape becomes more complex, lubricant and hardware co-engineering is increasingly essential to get the right balance between economy gains and friction durability to ensure continued hardware protection
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