This article originally appeared in the September, 2017 issue of Transmission Technology International (TTI) magazine
It is common knowledge that an increasing part of the vehicle parc, especially in mature markets, is being made up of electrified vehicles. This is a direct response from automotive manufacturers who are looking for maximum efficiency as part of achieving a low carbon long term future. According to some estimates, by 2023 around three-quarters of all cars produced globally will have some element of electrification enablement. These range from stop-start systems, simply shutting off the engine at idle, through the various iterations of hybridization, to full electric vehicles. This is clearly a very large proportion of the new vehicles that are entering the market, but it should be noted that, despite all the column inches and attention they attract, full electric vehicles, will still only be less than 3% of global production by 2023.
As Hybrid Electric Vehicles (HEVs) continue to advance in market-share and technology, the development of their drivetrain hardware towards increasingly efficient technologies starts to raise three areas of concern around the role and the nature of the lubricating fluids, especially as hardware solutions become more extreme and complex and drivetrain engineers look for that next level of efficiency.
The first is around the electrical properties of the fluids and their compatibility with an increasing number of electrical components, wires and sensors. The second is just how low can you go in terms of viscosity, with some current Automatic Transmission Fluids (ATFs) at near 4 cSt and many projected to go much lower. The final area is about thermal conductivity properties, as fluids need to be able to cool things such as electric motors used inside drivetrains that produce localized areas of extreme high temperature.
As Monica Beyer, commercial lead for HEV drivetrain strategy at Lubrizol explains, “All these factors are raising questions that cannot be answered by current lube testing and evaluation methodologies. The different aspects of lubricant function and protection are becoming more numerous and broadening even compare to the existing fluids in the marketplace. In addition to the traditional hardware, such as gears and bearings, fluids need to work with and protect an increasing numbers of sensors, the polymer systems and resins used to coat or hold in place wiring and in some cases exposed copper wiring and contacts. It’s a whole new area of investigation that requires more sophisticated ways of looking at things”.
Lubrizol have been active in seeking to understand the potential impacts of this increased exposure of lubricating fluids to electrical components and are working on developing new testing protocols that are more productive and relevant for the industry. One area of development is an improvement in the test for copper corrosion, while other work allows for a better understanding of oil conditions under a variety of temperatures, as opposed to traditional tests that rely on constant temperatures that are not necessarily reflective of real-world operating conditions. Getting as close as possible to real-world conditions is a vital objective as controlling the integrity of fluid throughout the life of the fluid remains a key factor in preventing potential issues, especially as viscosities drop and operating environments get more variable and extreme.
A new class of fluids?
All this is indicating that the industry may be at a turning point in terms of lubricating fluid requirements. There is an emerging class of required performance attributes, such as wire coating compatibility and electrical conductivity, which are not inherent in, nor tested for in current transmission fluids.
So, are current transmission fluids still suitable, or the best fit for these new environments? The answer is ‘it depends’. Currently, existing fluids are being used in hybridized versions of both Manual and Automatic Transmissions, but as can be seen from the prior paragraphs, these fluids may not always be the best solution. In the same way that different OEMs and tier suppliers are using different hardware solutions for HEVs, they are also using different lubricating fluids, with the default position being the use of whatever is readily at hand today. This in itself has the potential to be a limiting factor too as potential hardware development could be being held back by the use of traditional fluids in the thinking and development process.
To help evaluate the suitability of today’s fluids, create space for potential new hardware and define and develop tomorrow’s fluids, collaboration within the industry will be key (fig 3). The lubricant base oil and the lubricant additives all play a role in 
determining what these new fluids will look like and how they need to enable HEVs to perform at their best. To further reinforce this need for collaboration, any adjustments in lubricant technology may also have knock-on effects elsewhere. For example, seal compatibility is critical performance attribute of drivetrain lubricants. The increasing use of polyalphaolefins (PAO) to achieve lower viscosities and potential adjustments in additive chemistry to improve electrical component compatibility may compromise seal performance, so a holistic approach to fluid development and evaluation is needed.
Looking to the relatively near future, it is possible to imagine that across the entire drivetrain, a whole new class of lubricating fluids may emerge. Specialized fluids that demonstrate performance in electrical compatibility at extremely low viscosities, in speeds in excess of 20,000 rpm and in an operating environment of sustained high temperature.
Beyer concludes, “As HEVs trend more mainstream, their performance and reliability will gain greater exposure and become more apparent to a greater number of consumers. Of course, the drivetrain plays in critical role in the driver experience as it central to how a car ‘feels’ when driven. Working together, the stakeholders in the automotive industry can get ahead of any emerging issues in lubricant-related performance and continue to deliver reliable and durable new drivetrain technology to the market”.
For more information on Hybrid driveline fluids, contact your Lubrizol representative.
