ISSUE 011 Autumn 2021 Candela C-7 hydrofoil speedboat dossier l In conversation: Robert Hoevers l Battery recycling focus l Vehicle dynamics insight l ZeroAvia hydrogen-electric aircraft digest l Motor materials

for developers, 50EH provides more magnetic performance, at 1.4 T for 15-20% more power but with more rare earth material, so that costs 30% more. “We are also developing 52EH and 55UH grades.” These will have a higher magnetic performance but the higher cost of the material itself might not translate into a higher motor cost. “If you have 15% more performance in the same volume you can make the entire magnet stack shorter, which means the rotor and the machine can be 15% shorter,” he says. “That compensates for the small increase in price. Using rare earths at the surface of the magnet will see only a 5% price increase but it will save a lot on the rest of the motor.” The magnets also have to be glued onto the rotors and held in place by fixtures, and the coating material used on a magnet is key for the adhesion. “For the fixtures we try to get the best glue adhesion possible,” Stienen says. “We have slightly altered the coating process to get a coating adhesion of over 40 MPa – if we are going higher than that the forces will pull the magnet apart.” Non-rare earth designs Motor designs that avoid the use of rare earth elements are now coming to market. These designs require higher levels of optimisation of the motor with the control controller. “We want to produce simple e-machines at lower cost,” says Paul Price, CTO at motor designer IRP Systems. “For that we need to bend the rules of controls, which means making them more sophisticated. Without rare earths there are issues with control, power electronics, size and weight, all of which need to be optimised, so we are doing both control and e-machine design.” The issue of sourcing rare earths has even driven automotive parts manufacturer Mahle to develop a new kind of electric motor that does not use magnets. Dr Martin Berger, head of r&d and advanced engineering at Mahle, says, “Our traction motor does not use magnets but generates the JL Mag. “Some elements such as cobalt improve the structural integrity, and from a magnet performance point of view we want to add as much cobalt as possible, yet from the pricing and availability viewpoints we don’t want to do that. “The drive in eliminating HREs is mostly tied to volatility in their prices,” he adds. “There was a price hike in 2011, from 100 to 200%, in 2014 from 100 to 130%, while in 2019 their scarcity from a trade war pushed prices from 100 to 115%, so the spikes are getting smaller. Customers are also pushing for stronger magnets that they can use as a construction part and that use less cobalt, so they are not as strong. “We use HREs where they are needed, which is only in the grain boundaries of the magnet, so you can save a lot on the elements you need. “Automotive applications tend to use the SH, UH and EH grades, which are stable up to 200 C, and the grade used depends on the cooling of the motor. The 35EH 1.2 Tesla (T) grade material is the sweet spot Table showing the range of JL Mag neodymium-iron-boron e-motor alloys and their properties (Courtesy of JL Mag) Autumn 2021 | E-Mobility Engineering 57 Deep insight | E-motor materials