46 Simple conversion This simplicity makes the conversion process fairly quick, but it will vary depending on how much, if any, refurbishment needs to be carried out. “The estimated time is in days or weeks, not months,” says Lambert. Perhaps surprisingly, the suspension mostly escaped the need for modification, despite the extra weight inside the wheels. “What we have learned is that the unsprung mass isn’t that big an issue. Some small modifications to the suspension can help, but really, it’s only in high-performance vehicles where you’re ever going to notice anything. To some extent, higher unsprung mass can help with damping down the effects of pothole strikes or curb strikes, for example,” Lambert explains. “Equally, it’s about the ratio of sprung mass to unsprung mass, so if you’ve got a commercial vehicle weighing 3 t or 3.5 t, adding a few kilos to the unsprung mass isn’t going to make much difference.” The conversions are not limited to front-wheel-drive vans, but at the moment they are offered for the Citroen Jumper, Fiat Ducato, Opel Movano and Peugeot Boxer, with the Renault Master and Mercedes Sprinter coming soon. As with most hybrids, the RE-100’s battery pack has a fairly modest capacity of 37 kWh, giving the van a range of 117 m on electric power, plus 600 km with the range extender when measured according to the Worldwide Harmonised Light Vehicles Test Procedure (WLTP). It is based on a lithium nickel manganese cobalt oxide (NMC) cathode chemistry and designed for commercial vehicles. “Battery technology is at a level now where you don’t have to push the boundaries to meet the majority of user requirements,” Lambert says. The priorities for the battery technology were led by value for money for the customer, he says. In performance terms, meeting the gradability requirements for a fully loaded commercial vehicle was the most important thing. Cooled by a standard 50/50 water/ glycol mix, Protean’s motors (EME 003, Summer 2019) are permanent magnet synchronous radial-flux AC machines with an external rotor. This architectural choice was the result of a lot of engineering analysis, Lambert says. “It is really about trying to come up with the highest power density that can fit in the wheel space at an acceptable cost. There are other machine topologies that might give you a higher torque density or a higher power density; you could look at an axial-flux machine, for example. The problem is that starts to increase the cost because of the amount of magnetic material you need, so we really think we are in the sweet spot for cost and performance for in-wheel motors,” he adds. Sealing challenge The main technical challenges during development involved sealing and making sure the motor worked reliably in all use cases. “It’s quite a harsh environment down there by the wheel, so we do a lot of testing, wading through water, running in ice, exposing it to extremes of temperature and vibration as well,” he says. “In the wheels, there is a lot of high-frequency as well as low-frequency, high-amplitude vibration that you have to take account of. Now, we have a reliable product that can survive in that environment.” In addition to the vibration, sealing the motors against the ingress of contaminants such as water and dust is critical. Part of the challenge here, says Lambert, was designing a seal that would keep contaminants out while keeping any drag torque that it imposes on the motor to a minimum to preserve energy efficiency. “You’re going to put some additional drag torque on the motor with any part that has to seal against a rotating surface, but we have been quite successful with our low-resistance seal,” he adds. EVD | Protean van conversion March/April 2024 | E-Mobility Engineering The Pd18 motor’s compatibility with standard wheels and tyres is an important feature, and one that is central to the conversion’s practicality for commercial vehicles (Image courtesy of Protean)
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