Magnets Make the Motor

Magnets Make the Motor Magnets Make the Motor Magnets Make the MotorManufacturers need light, extremely strong magnets to power electric-vehicle murls, and they have long relied on the rare-earth metals neodymium and dysprosium to create them. But those metals are expensive and subject to wild price jumps and shaky supply chainsproblems that have become more acute as demand for electric cars grows.Researchers at Oak Ridge National Laboratory say theyve found a solution. They recently built a powerful EV motor that uses common ferrite magnets rather than those made from the rare earth metals, which can cost up to 30 times more per pound.The new motor achieves 75 percent higher power than comparably sized commercial EV motors, the researchers said, and it could be ready for mass production in a year.ur main target was to reach the same or higher power density, keep within the same volume, and use cheaper magnets, said Tim Burress, project leader at ORNL.Most electric motors include two main components the stator, which is stationary, and the rotor, which moves. Like most stators, ORNLs was made from thin, laminated sheets of steel that form a hollow cylinder. A series of copper coils line the cylinder and produce a magnetic field when charged. The rotor sits inside the cylinder, surrounded by a series of magnets and attached to an axle. The stator and rotor repel each other magnetically, causing the rotor and axle to spin.ORNL researcher Tim Burress works on a prototype EV motor that uses magnets made from iron. Image ORNLTo reduce costs, the researchers used ferrite magnets that are readily available from most suppliers. Their finished magnets cost $3 a pound, compared with $90 per pound for those made from neodymium and dysprosium. Back in 2010, the prices of both metals skyrocketed after China, the main supplier of the metals, limited the export of rare-earth minerals.While prices have since dropped, they are mucksmuschenstill high and subject to sudden change s. But the researchers still had a problem. Ferrite-based magnets are up to 10 times weaker than rare earth magnets. It can take up to 10 times more ferrite than neodymium to make a magnet of equal strengthand that can make a magnet so heavy it flies out of the rotor, said Jason Pries, an ORNL research associate who worked closely with Burress.ORNLs rotor, for example, includes 16 magnets. Each of them weighs 175 gramsalmost four times the weight of the neodymium-dysprosium magnets in the rotor of a 2015 Toyota Prius motor, which the researchers used for performance comparisons.To secure the heavy magnets, the researchers machined bevels into the magnets and slipped them into S-shaped slots in the rotor. An epoxy prevented the magnets from bouncing around.The team offset the extra weight of the magnets by reducing the mass of steel and copper in the rotor. The motor weighed only about one pound more than the Prius motor, a difference manufacturers can live with, Burress said. The to tal cost of the magnets in the ORNL motor was $20, compared with $150 for the Prius motor.ORNLs motor was also more powerful. It generated 103 kW (138 hp) at 9,000 rpm, compared with the Prius 60 kW (80 hp) at the same speed. The researchers attribute the performance gains to powerful modeling, simulation and design tools, and the new class of optimized ferrite compounds. Optimization was the key to making this work, Pries said.Read the latest issue of Mechanical Engineering Magazine.Our main target was to reach the same or higher power density, keep within the same volume, and use cheaper magnets.Tim Burress, ORNL