Products and ser vices / AF TON CHEMICAL
E-axle performance
Bearing wear Oxidation
Synchro friction
The result of extensive development, the first dedicated lubricant additive for direct oil-cooled multispeed e-axles paves the way for new technology
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ELECTRICAL PROPERTIES E-axle lubricant can be formulated from a wide range of base stocks, depending on the application’s viscometric and performance needs. E-axle fluids formulated with Afton’s wet multispeed additive demonstrate electrical properties equivalent to or better than commercially available fluids. “Even the choice of viscosity modifier plays a part. It can enhance – or detract – from the fluid’s electrical and oxidation properties,” Cleveland says. Also crucial is that the lubricant does not attack any of the wide range of insulation materials and wire coatings used by OEMs
7 8 Transmission Technology International / 2021
According to Afton, the dedicated team behind this breakthrough will look to apply this ‘nocompromise’ approach in the next challenge
Copper (extended testing)
Copper vapor phase
Plate friction
Aged electrical resistivity HiTEC 35701 ETF Additive
ombining the e-motor, reduction gearing, shifting device, differential and power electronics into one efficient e-axle module was a necessary step to increase the driving range and appeal of electric vehicles. However, these diverse systems don’t make easy bedfellows; their proximity adds layers of complexity to lubricant requirements. “Conventional transmission fluids may have properties that appear suitable for e-axles, but testing has shown that using these fluids inevitably compromises some areas of e-axle performance,” says Zhang Yun, senior OEM manager at Afton Chemical. “OEMs are also looking for long durability and efficiency in any solution.” A dedicated additive was needed to avoid the inherent compromises of traditional fluids and unlock the full potential of e-axle hardware. Afton collaborated closely with OEMs during development and testing to ensure the latest technology is supported. “It’s been a demanding journey to arrive at this dedicated additive package,” notes Dr Chris Cleveland, director of R&D at Afton. “We had a long list of performance targets.’’ Initially the focus was on cooling. E-motors run hot, so effective heat transfer is critical for optimizing motor efficiency and dynamics. Wet cooling, where the lubricant comes into direct contact with the e-motor, is the most efficient method. It also helps to protect heat-sensitive parts, such as permanent magnets. However, direct oil contact with electrical components brings additional challenges. “The start point has to be a dielectric fluid, one with excellent thermal capacity and resistance to oxidation. Not only does it need to cool effectively, it must mitigate changes to electrical properties as it ages,” explains Cleveland.
Gear protection
Electrical resistivity Asian ATF
MTF
EU ATF
DCTF
globally. “Our main priority was compatibility with copper and nylon,” explains Dr Atanu Adhvaryu, senior R&D scientist at Afton. E-axles include numerous sources of copper, from e-motor windings to electronic sensors and controls. “In gaseous form, the lubricant can come into contact with sensitive electronic systems,” he adds, “so we have developed and carried out extensive testing to ensure our additive really delivers on compatibility.” Then there’s the multispeed transmission. This helps electric vehicles to achieve the desired balance of responsiveness and top speed, but incorporating a shifting device into an e-axle turns the spotlight onto another area – friction control. Afton’s multispeed additive also had to deliver good all-round friction for the transmission clutches and synchronizers, while keeping gears and bearings free from wear. “Formulation development is about balance, to ensure that excellent performance in one area does not compromise others. Our formulation for wet e-axles takes the very best of axle and automatic transmission fluid development to create an entirely new paradigm,” says Cleveland. “For example, in traditional transmission fluids, extreme pressure and anti-wear additives can be known to attack copper. We have to ensure compatibility isn’t compromised, even when extreme pressure and anti-wear properties are boosted. There can be similar antagonism between friction performance and electrical properties.” For the challenging combination of a wet, multispeed e-axle, the final additive package developed by Afton Chemical offers a strong balance of performance, rather than compromises. Delivering cooling, compatibility and conductivity, the additive also provides the all-round friction and strong anti-wear performance that the hardware demands. “By enabling the most advanced e-axle technology, this additive also offers engineers the simplicity of catering for all their e-axle needs with one premium fluid. Whether wet or dry e-axle, single or multispeed, the performance benefits will be obvious – including the excellent gear and bearing protection that is specified by Chinese OEMs,” says Zhang.
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