"Frequent" is all relative.
The Renault Zoe, 10y ago, was already using a synchronous engine with wired rotor. And most were going over 150kkm without any issues nor brush changes.
> because the electrical currents that circulate through the rotor windings must generate heat
Currently stator heat in wired synchronous engine is less a problem than in SynRMs with permanent magnets.
Most neodymium based permanent magnets start to be irreversibly damaged id they heat up beyond 100°C. That's currently why Tesla has such a good cooling system in their engine.
Wired rotor are bunch of copper coil, as such they are much more resistant to temperature gradients.
Unfortunately, almost no one uses SI units and/or prefixes correctly.
And they said that PMSM motors are more efficient at low RPM, but their coils get saturated at higher RPMs meaning they lose efficiency at highway speeds (which actually affect the range number people car about).
So overall not such a bad tradeoff, if it makes cars less expensive.
This seems like a big disadvantage. Highway is exactly where EVs fare worst compared to ICE cars.
I wonder if this could be solved by introducing a gearbox?
I know the new Mercedes CLA (EV) has two gears, the second gear being optimized for highway speeds. But I don't know whether it's related to this.
> Group will gradually embed new technological improvements from 2024 on its EESM: stator hairpin, glued motor stack, *brushless* and hollow rotor shafts.
[0] https://www.evspecifications.com/en/news/6ec9484
That said, what sibling says about the maintenance problems is very true. :-/
In the picture at Renault website (section describing their next gen 2027 motors) you can clearly see the 2 slip rings on right side. That might be just a placeholder using their last gen motor, but I would expect that they would mention it if their next gen was brushless while the current one has brushes.
Brushless seems to be a thing that they have described as future work for at least 5 years but it's not there yet.
Efficiency schmischiency. I see your 3% and raise you the abolition of SUVs.
I see your motor-brush maintenance burden with my washer fluid, tyres, brakes, seals bearings bulbs filters etc etc. Then I raise you control modules that send your car to three garages and the scrapyard. Cars have wear items, you heard it here first.
Permanent magnet motors have higher peak efficiency but EESMs are better in non ideal conditions, particularly low torque high RPM i.e. highway cruising where efficiency is more critical than at low speeds.
Define frequent. I maintain machinery with brushes so I have a decent idea of what life span should be depending on the environment. If the housing for the slip ring setup is well protected from dirt and the slip rings aren't cleaned by a cave man you can get a few years of life from the brushes.
I think if we take french cars (Renault/Peugeot/Citroen) in general, most major reliability issues have been on diesel cars exhaust gas recirculation systems due to strict european emissions and they are far from the only brands suffering from that.
German cars were known for their great reliability in the early 90's but in later decades had all sort of electronical gremlins.
Also I think regardless of their actual current reliability, some brands or models attract on average different kind of owners which impact how actual services are followed, if the car is stored inside or outside, if the owner take care or not of warming up the engine in the morning or floor it while cold, and the general care they apply to it.
It depends.
With PM motors if you exceed the Curie temperature, the magnets lose their magnetism. Also one can control the rotor excitation current on EESMs so core saturation is less of an issue compared to PMSMs.
The brushes are also quite long lasting and easy to change on a good design so maintenance is not as a big of an issue.
ASMs are even more robust but they have lower power density and efficiency but are better for coasting.
There is also the SynRM which uses an unwound rotor with flux barriers (cutouts) that aligns with the stator flux, no magnets needed. It's basically as robust as the ASM but without its lower efficiency disadvantages and also no brushes, at the cost of more complex power electronics and lower speed noise.
Wouldn't the back EMF help here? In brushed DC motor it surely does, reducing losses way below what full voltage over winding resistance would incur.