E-Mobility Engineering 016 l Aurora Powertrains eSled dossier l In Conversation: Thomas de Lange l Automated manufacturing focus l Torque sensing insight l Battery Show Europe 2022 report l Sodium batteries insight l User interfaces focus

validated the high structural support that our carbon and metal hybrid wheels achieve. “Wanting stiffness might sound counterintuitive – people see Formula One cars shattering their carbon fibre shells all the time – but those front wings and other bits are deliberately designed to splinter and fall off. That’s how they dissipate energy. The bits that actually protect the driver, such as the wheels and the halo, are actually really stiff and hence good at absorbing energy. “Aluminium wheels tend to deform permanently or shatter from impacts, bleeding air thereafter. Carbon wheels have fewer and much safer failure modes and stand to really aid the safety case for EVs, and help protect onboard components such as batteries.” The carbon sections of the rims and wheels are made using a resin infusion process known as resin transfer moulding. This begins with wrapping dry fibres around a cylindrical mandrel to form the multiple layers of carbon comprising each rim. Then, a high- end resin system is injected – this is a product from Henkel that de Lange notes has very desirable thermal properties, in addition to being extremely UV-stable and hence long-lived. After that, the rim goes through a post-curing phase in an oven to ensure the desired structural and mechanical properties. De Lange adds, “In essence, it’s a simple process but the devil is in the details, and there’s some IP to our manufacturing techniques that we can’t reveal publicly.” Use in EVs Naturally, the drivetrains, bodies, chassis and so on in EVs need to be lighter than those of conventional IC- engined vehicles in order to make best use of the electric powertrain. At the same time, however, automotive consumers (in both the EV and IC- engined markets) are tending towards bigger and heavier vehicles. It’s a trend that has been going on for some time, with the result that designers and consumers alike want larger and larger wheels in their cars. “It’s not unusual to see 22-23 in- diameter wheels on cars now, and bigger wheels than that are becoming more and more common,” de Lange says “When you get to these sizes, you are looking at an incredibly heavy wheel – a conventional 22 or 23 in wheel made from cast aluminium will weigh well over 20 kg.” That means the mass saving to be gained from switching to carbon- hybrid wheels is around 50% of the conventional wheel’s weight – around 10 kg per wheel. Naturally, shaving 40 kg off any vehicle is worthy of note to EV engineers, but there is still more to the story in terms of automotive physics. “Losing 40 kg of rotating mass is very different from cutting out non-rotating or ‘sprung’ mass,” de Lange explains. “Different automotive authorities will have slightly different takes on that, but the approximate figure in terms of the force on the vehicle from saving rotating mass in the wheels versus sprung mass elsewhere on the vehicle is about five to one. “So in real terms, saving 40 kg in the wheels is equivalent to saving 200 kg in the sprung mass of the car. Granted, our wheels cost more than cast aluminium ones, but if you compare the weight saved from switching to Dymag wheels and the impact of that on an EV’s range – and compare that with the staggering sums spent on r&d, and the material and assembly costs some OEMs face when upgrading their batteries’ specific energy for comparable increases in range – The hydrogen-electric Apricale hypercar from Viritech is one of several EVs using the Dymag wheel 18 Winter 2022 | E-Mobility Engineering