researchers may have found a way to speed up the shift to electric vehicles worldwide.
by rick richardson
technology this week
currently, 95 percent of the rare earths come from china. today, electric vehicle (ev) motors include rare-earth magnets, and if china decides not to share their supply, it will be catastrophic for the ev marketplace.
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of all the obstacles to transportation decarbonization, electric motors present one of the most compelling. researchers are currently working on a development that could speed up the shift to electric vehicles worldwide: a tough, small, strong electric motor without rare-earth permanent magnets that can withstand high temperatures and has a high power density.
this enormous issue currently concerns some of the world’s top machine designers, many of whom work at zf friedrichshafen ag, one of the world’s biggest auto parts manufacturers.
when zf unveiled its groundbreaking achievement last year – the successful construction of a 220-kilowatt traction motor without the use of rare-earth elements – it sent shockwaves through the industry. this remarkable feat of engineering not only showcases the company’s technical prowess but also underscores its commitment to sustainable innovation.
the company declared that the features of their new motor were like those of the rare-earth permanent-magnet synchronous motors that are currently the industry standard in electric cars. most evs are powered by 150- to 300-kilowatt rare-earth magnet motors, with power densities varying from 1.1 to 3.0 kw per kilogram. in the meantime, zf claims to have created a 220 kw rare-earth-free motor that falls squarely in the middle of that range.
a separately excited (or doubly excited) synchronous motor is the kind of motor that the zf machine is. it replaces the rare-earth permanent magnets found in the rotors of almost all ev motors on the road today with electromagnets in both the stator and the rotor. a rotating magnetic field is created in a separately excited synchronous motor by applying alternating current to the stator electromagnets. the rotor electromagnets are energized by a separate current that applies to them. this creates a field that locks onto the rotating stator field, producing torque.
because there isn’t a perfect method for transferring power to the rotating rotor magnets, these devices haven’t been used very often in evs up to now. these motors create electrical contact with a spinning surface using sliders and brushes. however, the brushes eventually wear out and emit dust. an alternative method of transferring power is by inductance, although in that scenario, the apparatus is typically cumbersome, making the unit complicated and physically large and heavy.
however, zf now claims that its experimental motor, the i2sm (for in-rotor inductive-excited synchronous motor), has resolved these issues. in contrast to permanent-magnet synchronous motors, the motor has a few more benefits besides not using rare-earth materials. these are related to the fact that, unlike permanent magnets, this type of motor technology allows for exact control of the magnetic field in the rotor. this control thus allows the field to be varied to achieve, for example, substantially higher efficiency at high speeds.
zf friedrichshafen ag was founded in 1915 and is based in baden-württemberg, germany. it is renowned for its extensive r&d history and many commercially successful inventions. the company first started providing gears and other parts for zeppelins in 1915. currently, the corporation employs about 168,000 people across 31 countries. customers for its electric drivetrains and motors include jaguar land rover, mercedes-benz and bmw. late last year, shortly after announcing the i2sm, the company announced the sale of its 3,000,000th motor.