Afton Chemical presents The Power of Cool

November 2020

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The power of cool The latest research from Ricardo and Afton Chemical highlights the benefits of effective cooling for e-axles, multispeed transmissions and beyond Recent simulations carried out

by Ricardo, in collaboration with Afton Chemical, have explored the potential benefits of three areas of emerging e-axle technology: direct oil-cooling of e-motors, multispeed transmissions and battery immersion cooling.

E-motors generate a formidable amount of heat, so direct oil-cooling – as used in Tesla vehicles – is increasingly seen as a way to optimize performance. Depending on OEM priorities, direct cooling can be used to extend the range or decrease the cost of batteries.

Multispeed transmission solutions are also growing in popularity, with suggested advantages for efficiency, responsiveness and speed. First seen in the premium segment – for example, GKN’s two-speed e-axle featured in the BMW i8, which was launched in 2014 – multispeed transmissions and e-axles are now being developed or considered for various higher-volume applications.

“Through our OEM partnerships we understand how crucial efficiency is to the e-mobility equation,” explains Walter Bunting, Asia Pacific OEM relationship director at Afton. “We reached out to Ricardo to develop greater insight into the potential for advanced lubricants to drive increased efficiency; in representative vehicles and in a real-world context.”

Compared with indirect cooling, Ricardo found that direct oil-cooling gave e-motors greater flexibility to operate within higher efficiency zones. Ricardo’s analysis indicated an overall 1.2% efficiency improvement for the WLTC cycle, with a note that under more thermally challenging cycles, that benefit would likely increase to 2-3%. “That is an impressive efficiency gain from a lubricant,” notes Bunting. “As higher efficiency

Results from Afton Chemical and Ricardo research comparing the efficiency of direct (top) and indirect (above) cooling concepts

generally results in lower thermal stress, this would also have a positive impact on component life.”

Permanent magnet temperatures were calculated to be 60°C (140°F) lower with direct oil-cooling, with a gain of around 25% in continuous e-motor performance. “A further expected benefit for e-motors that are directly cooled with a dedicated electrified transmission fluid (ETF) is the opportunity to reduce mass and packaging by integrating the e-motor cooling system with existing oil circuits,” adds Bunting.

Afton and Ricardo then looked at transmissions, comparing efficiency and performance benefits for one, two and three speeds across different vehicle segments.

They found that for both premium and sports vehicles, a multispeed solution with dedicated ETF enabled greater performance and efficiency than a single-speed solution. At the same performance level, two-speed transmissions were 2-3% more efficient and three-speed transmissions were 3-4% more efficient than single-speed solutions.

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“The results of this analysis are in line with ZF’s announcement in 2019 that its new two-speed e-axle offers improved efficiency, translating into a 5% greater driving range,” comments Dr Harald Maelger, European OEM relationship manager at Afton.

When considering C-segment SUVs, Ricardo found that efficiency improvements gained from using a multispeed transmission would support a net reduction in e-motor and battery costs.

“Based on a typical 2020 battery price of US$190 [€161] per kWh, Ricardo estimated the overall cost benefit to be in the range of US$250-375 [€212-318] per vehicle,” reports Dr Maelger. “That’s a significant saving – which would more than compensate for additional cost in the transmission.”

As the degree of electrification increases and technology is refined, requirements for lubricants are becoming more specific and severe.

“Our data points toward dedicated fluids being necessary to unleash the full power and benefits of the latest e-motors, e-axles and multispeed transmissions,” comments Dr Maelger.

Following extensive development and taking advantage of powerful new test methodologies, Afton recently launched a dedicated ETF product that it believes has the potential to spawn a whole new generation of EV lubricants.

An analysis by Afton and Ricardo into the efficiency and performance of single and multispeed transmissions in the premium/sports vehicle sector

Afton Chemical and Ricardo compared immersion versus cold-plate battery cooling when charging at 4.5C-rate at a 1 l/min (0.26 gal/min) coolant fl ow rate

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“By protecting critical parts from wear and other damage and being compatible with sensitive electric components, as well as offering the right friction performance for the specific shift device, our new additive package delivers excellent support for e-axles with multispeed,” states Dr Maelger. “This works effectively with low-viscosity base oils, enabling the advanced ETF to avoid the compromises inherent in using traditional fluids, while enhancing efficiency.”

Afton and Ricardo also explored the emerging technology of battery immersion cooling. Installed in the recently launched hybrid McLaren Speedtail, this system involves immersing battery cells in specialized coolant fluid. The technology is posited to offer more effective and uniform cooling, helping to meet growing demand for shorter charging times, a higher discharge rate and greater efficiency. In particular, Ricardo analyzed fluid performance under the most challenging circumstances of ultra-fast charging.

It was found that direct immersion cooling would maintain battery core

cell temperature 13°C (55.4°F) lower than indirect (cold-plate) cooling.

“This indicated to Ricardo that battery life could be prolonged and cell requirements better balanced, with the battery life – the number of full cycles – estimated to increase by 5-10%,” says Bunting.

Using immersion-cooled cells, the battery could also be charged to 80% capacity 20-25% faster.

Although specialist immersion battery technology and coolants are not yet mainstream, Afton is already considering how its chemistry could enhance such fluids. “Our focus is always on future developments, figuring out how best to unlock the potential of new hardware,” says Bunting. “Our work with OEM partners already demonstrates the value that advanced lubricants can bring to every tier of the rapidly evolving EV market.”

While the market will certainly continue to evolve, EV lubrication is also coming of age – bringing with it the power of cool.

FREE READER INQUIRY SERVICE To learn more about Afton Chemical, visit: www.magupdate.co.uk/PEHV

The people that make the additives that go into the oil that lubricates the transmission that drives the wheels smoothly in electrified passenger and commercial vehicles. www.aftonchemical.com © 2020. Afton Chemical Corporation is a wholly owned subsidiary of NewMarket Corporation (NYSE:NEU) www.aftonchemical.com

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