Ferrite Magnets Replace Rare-earths in EV Motor
Yaskawa says it has developed an electric vehicle (EV) motor that avoids the need for neodymium magnets, using much cheaper and easier-to-obtain ferrite magnets instead. The development is intended to reduce the company’s dependence on rare-earth materials, such as neodymium and dysprosium, whose prices have fluctuated widely in recent years, with China dominating and controlling their supply.
Yaskawa has used the new design to build a prototype motor with a continuous output of 45kW (80kW peak) and a maximum torque rating of 200Nm. The motor, which weighs about 60kg, is designed to operate at a top speed of 1,200 rpm.
The IPM (interior permanent magnet) motor has ferrite magnets embedded in its rotor. Its stator coil density has been increased by using rectangular wires, and the rotor’s magnetic circuit has been optimised to produce a motor with comparable external dimensions to a similarly-rated machine based on neodymium magnets. The motor has been designed for automated manufacturing.
Yaskawa says that optimising the form and placement of the magnet and core in the IPM structure using the ferrite magnets enhances the motor’s torque characteristics and tackles the problem of low-temperature demagnetisation. The stator’s lamination factor is claimed to be about 30% higher than usual.
Most conversations about EVs pretty soon turn towards battery technology and charging times, but the electric motors that actually drive an EV rarely catch the limelight. That’s a shame, because the beating heart of a car, the engine, has traditionally been something drivers get excited about, so why should electric motors be any different?
An EV’s electric machine (to use the motor’s proper name – it works as a generator as well) is just as important as the battery in achieving the best possible range. Range directly relates to one crucial characteristic of electric motors: their phenomenal efficiency (ie how good they are at converting electrical energy into mechanical energy). Even the best combustion engines don’t do a great job in converting the energy in the fuel into torque, with only around one third of the fuel you put in the tank contributing to actually getting you down the road. Ouch. In contrast, a sophisticated EV’s electric machine can be more than 90% efficient.
The three main types of electric machine used for EVs are brushless asynchronous induction (Tesla Model S), brushed externally excited synchronous (Renault Zoe) and, by far the most common, brushless permanent magnet synchronous (Nissan Leaf, Tesla Model 3).