Unlike the permanently excited synchronous motors (PSM) that are widely used today, externally excited synchronous machines (EESM) do not require rare earth elements. The reason is simple: unlike the PSM, the rotor does not have a permanent magnet with rare earth elements, but a coil. EESM is not based on a permanent magnetic field of a permanent magnet, which is driven by a magnetic field generated in the stator, but magnetic fields are generated by coils in both the stator and the rotor.
According to Vitesco, EESMs (also often referred to as current excited synchronous machines or SSMs) are more efficient than PSMs, especially at higher speeds. According to the supplier, they are particularly suitable for long distance travel with fast motorway driving. What Vitesco doesn't explicitly mention in the post: Since the rotor's magnetic field can also be simply turned off, EESMs have the same low resistance losses as induction motors (ASMs). This makes them more suitable for electric four-wheel drives than PSM, where a constant magnetic field causes losses that must be compensated by either a mechanical clutch or a sophisticated zero-torque control system.
Vitesco has not yet provided technical details for the planned EESM. The company has already created a plan "which will make EESM technology available to already successful main axle drives, including power electronics."
Vitesco is not the only one seeing the benefits of EESM: BMW's fifth generation electric drives (eg in the iX3, i4, iX, i7 and iX1) are also externally excited synchronous motors.