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Vitesco presents externally excited synchronous electric motor for future EV drive systems

At the EVS Symposium in Oslo, Vitesco Technologies is presenting an externally excited synchronous electric machine (EESM) which does not require the use of rare earth metals and which is specifically designed for high ranges, faster driving on highways, and thus for future long-distance electric vehicles.

220609 VT PP EMR4_2

Permanently excited synchronous machines (PSM) are the general standard in vehicle electrification. This is due to the high efficiency of these electric motors in city traffic or at medium ranges. Permanent magnets based on rare earths are installed in the rotor of PSM motors.

However, Vitesco says, the general conditions for electric drives are changing. The ranges of battery electric vehicles are becoming longer, and on real long-distance routes with fast highway driving, externally excited synchronous machines (EESM) can show their advantages. Especially at high speeds they are more efficient than PSMs. Viteco is presenting a comparative life cycle assessment for the two technologies at EVS35.

Instead of magnets, the rotor here has coils. In addition to efficiency at high speeds, this offers the advantage of avoiding the prices for permanent magnets, which have now risen to a 10-year high. In addition, the CO2 footprint of the drive is reduced by the portion attributable to rare earth mining, which can have a positive impact on product sustainability over its life cycle.

Vitesco Technologies is therefore preparing a portfolio expansion that will make EESM technology available for its already successful axle drive including power electronics. The company has many years of field experience with this technology and thus has a certain head start in development and industrialization.


  • Comparative Life Cycle Assessment For Permanent And Externally Excited Drive Systems”, Florian UHRIG , Vitesco Technologies GmbH, Session F2, EVS35



My preferred electric motor type.
Unfortunately, only Renault and Mercedes are using them, as far as I know.

There is no real need for neodymium in the new electrified world; maybe only for aviation.


These motors have an definite advantage in that they do not require expensive magnetic materials. However, I believe that they require slip rings which are a potential wear item. they may also generate more heat in the rotor which is harder to remove than the heat from external coils.


There is the inductively coupled rotor but it still has the heat issue


Slipping rings are graphite based and seem to have a very long life (unlike brushes).
Don't know much about the heat problem; one advantage of wound rotors is you can regulate the field as you wish (unlike permanent magnets). As a consequence, they are more efficient in the lower torque area.

I have a bit of experience with forced air rotor cooling an it seems to work pretty well, although it can be noisy.

In any case, not every electric motor must have Tesla-like power specs! :D


Tesla still uses Induction motors in the front drive engine of AWD models. The BMW IX M60 also has a “magnet free motor” (

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