EVs Need Different Lubes

STUTTGART, Germany - The number of hybrid electric and electrically chargeable vehicles is on the rise, particularly in the European Union, and this should begin to affect lubricant technology, an official from an additive supplier told an industry conference here last week.

In Germany, the largest car market on the continent, registrations of hybrids and EVs grew by and 54.8 percent and 39 percent, respectively in 2017. Across the EU, 431,504 hybrids and 216,566 electric vehicles joined the car parc, according to the European Automobile Manufacturers Association.

Alternatively powered vehicles, including cars running on liquefied petroleum gas and natural gas vehicles, only accounted for 5.7 percent of new car sales in the region. French market research firm IHS Markit, however, predicts vehicles utilizing some form of electrification will hold a market share of roughly 40 percent by 2028.

This has implications for lubricant technology, as explained by Lubrizols Michael Gahagan, the companys global manager for transmission lubricants, at the Mineral Oil Technology Forum.

While hybrids can and often do use traditional driveline fluids, manufactures would do well to adopt new, dedicated fluids that are better able to protect and ensure the smooth functioning of the electrified drivetrain parts. Gahagan highlighted three main considerations: electrical conductivity of fluids and related safety concerns, corrosion protection and, finally, thermal transfer and material compatibility.

The drivetrain of the Toyota Prius hybrid, arguably the worlds best known hybrid, uses power split architecture, allowing the petrol engine to operate independently of the cars speed. The power split unit, which doubles as the transmission, consists of a planetary gear set, generator, electric motor and an oil pump. The aforementioned novel fluid considerations come into play due to higher system voltage, a greater presence of copper and electronics, higher temperatures and speeds and varying friction requirements.

Fluids tailored to hybrids and EVs would, therefore, have to have the right electrical properties, ensure corrosion protection and be compatible with insulating materials. They also need to have appropriate thermal transfer characteristics, offer high-speed bearing protection and provide oxidation and sludge control.

There are two considerations Gahagan highlights when it comes to the electrical conductivity of fluids. If the electrical conductivity of fluids is too high, there is a risk of current leaking. But if it is too low, static charge can build up, resulting in electrical arcing in oil. This leads to the degradation of the fluid, compromising its protective features.

Lubricants are not conductive, but rather dissipative, though additives can affect the level of dissipativity. Conductivity increases, however, as oxidation causes an oil to deteriorate. Lubrizols testing suggests oils susceptible to oxidation are potentially problematic, Gahagan told the audience.

According to Lubrizol, its is not just the lubricant that needs to adapt to hybrid and electric vehicles; the same applies to lubricant test methods. Given the presence of electrical components and wires in the hybrid architecture, and given the potential for changes in the level of conductivity and a greater variation in temperatures, corrosion deposition tests need to be made more sophisticated.

About 20 kilograms of copper are used in a regular vehicle, compared to as much as 80 kg for an EV, noted Gahagan. For example, he suggested, the industry should consider adopting a wire corrosion test since stray voltage or energized circuits promote corrosion that would normally not occur.

Another technological development that lubricants and fluid producers must take note of is the introduction of the efficient dual clutch transmission, a multiple-speed automatic gearbox for EVs that draws on the example of the dual clutch transmission. The e-DCT utilizes an e-motor in addition to the twin clutch for seamless shifting. Because of the electrical components and wiring involved, a gearbox fluid would have to offer copper corrosion protection while at the same time being compatible with the insulation and other materials of construction.

Cars charging on street in Amsterdam.

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