Without rare earths: New engine should make electric cars cheaper and cleaner

With a new electric motor for battery-electric vehicles, the Japanese supplier Astemo wants to avoid the use of rare earths in the future. Conventional electric car motors usually use permanent magnets made from rare earths such as neodymium – materials that can generate strong magnetic fields but are considered critical due to geopolitical dependencies.

Astemo, a joint venture between Hitachi and the Japanese car manufacturer Honda, relies on a so-called synchronous reluctance motor system that is intended to achieve comparable performance to today’s permanent magnet motors. The system does not rely on permanent magnets, but rather on specifically generated magnetic fields in the iron core of the rotor: The motor generates its rotational force by using differences in magnetic resistance (reluctance) that result from the shape of the rotor core.

Special rotor shape makes it possible to avoid critical raw materials

By developing a so-called “multi-layer flux” structure, the path of magnetic force transmission is divided into several layers. At the same time, the current is controlled so precisely that magnetic poles are formed in the rotor core. In this way, the strong magnetic force of neodymium magnets can be compensated for, according to a statement from the company. The formation of magnetic poles in the rotor core requires a higher current flow through the stator coils. This poses a challenge because the coils also heat up more – however, Astemo has developed a structure in which the grooves and ends of the coils are immersed in cooling oil. This should effectively reduce the additional heat generated in the engine.

For the main drive, the company combines this principle with ferrite magnets, which also do not contain rare earths. The motor should be able to achieve a continuous output of 180 kW, but this is also accompanied by an increase in size of around 30 percent compared to conventional permanent magnet motors. The drive is supplemented by a magnet-free secondary motor with up to 135 kW of power, which is only switched on when necessary and should not cause any energy losses when freewheeling. Together, the main and auxiliary drive have a system output of 315 kW. According to Astema, series use of the electric motor is planned from 2030.

BMW has also been building its engines without rare earths for years

The absence of rare earths is not a brand new concept: BMW has been relying on separately excited synchronous motors for years, in which the magnetic field in the rotor is generated by an electrically excited coil. However, this also requires the use of additional copper in the rotor and the possibility of separate excitation.

Astemo’s approach differs significantly from that of the Munich car manufacturer: the magnetic field here is largely created by the shape of the rotor itself, the motor does without additional excitation coils and thus the costly additional use of copper. However, whether the concept becomes established in the mass market will likely depend on the efficiency, economy and longevity of the engine – values ​​that Astemo still has to prove.