Unfortunately, their Web page does not say a single word about the important problems of their motors.
The electrically excited synchronous motors have been known forever, but they had not been used in EVs because of 2 disadvantages.
The first is that traditional EESMs require brushes, i.e. sliding electrical contacts, which are worn out by friction, so such motors require frequent maintenance for changing the brushes.
It is possible to make brushless EESMs, but they require a rotating transformer and a semiconductor rectifier inside the rotor.
The second disadvantage is a lower efficiency than with permanent magnets, which cannot be improved so much as to match PM motors, because the electrical currents that circulate through the rotor windings must generate heat. The lower efficiency also makes cooling more difficult.
Renault says that their EESMs have an efficiency of 92%. This is a good efficiency, even if not as good as attainable with permanent magnets. Losing a few percents in efficiency is an acceptable compromise for avoiding the use of expensive and supply-constrained chemical elements.
What I wonder is whether Renault reaches this 92% efficiency with EESMs having brushes, or with brushless EESMs, and this is what I would have liked to read on the parent Web page.
Brushless EESMs usually had a lower efficiency, so 92% would be impressive for them, while it would look normal for EESMs with brushes.
If Renault has succeeded to make a brushless EESM (i.e. maintenance-free) with an efficiency of 92%, that is something worth to brag about. Otherwise, making a traditional EESM would not be great news, because everybody has avoided those because of the maintenance problem.
> such motors require frequent maintenance for changing the brushes.
"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.
150kkm - wouldn't that be 150 Mm?
Yes, you are correct. As the SI brochure states: "Compound prefix symbols, i.e. prefix symbols formed by the juxtaposition of two or more prefix symbols, are not permitted."
Unfortunately, almost no one uses SI units and/or prefixes correctly.
Sure, also 1 mAU and 0.5 light seconds, but treating km as a base unit and prefixing it with another k isn't too uncommon a misuse.
Munro took apart a Nissan Ariya which has this exact kind of motor. The maintenance is basically removing a tiny cover and replacing the tiny and cheap carbon brushes every 100k km or more. It's basically cabin filter level maintenance.
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.
> [...] but their coils get saturated at higher RPMs meaning they lose efficiency at highway speeds (which actually affect the range number people car about).
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.
Interesting question, it looks like they are / will be brushelss:
> 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. :-/
All sources point that their 2025 models are still using brushed rotors. Here is a teardown video it's from Nisan car but it's using a Renault electric motor https://www.youtube.com/watch?v=BFmp9ODkCA8 .
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.
Compared to an ICE, maintenance of brushes is still quite an improvement.
TFA does specifically call out the lower efficiency of eesm. I guess it was edited after you wrote your comment.
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.
Efficiency varies according to the load and RPM.
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.
> so such motors require frequent maintenance for changing the brushes.
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.
If the desired location for this is a car, then a few years of life that requires half disassembly of a motor isn’t going to work.
That does not sound worse than replacing the spark plugs in a Subaru engine.
The slip rings are not in the middle of the motor, they're on the butt. I know car makers don't always try to make things serviceable, but it'll be hard to make it hard to replace. Probably the only issue will be needing to remove other parts first to get to it, if anything.
Not sure how familiar you are with Renault, but “maintenance problems” pretty much sums up a lot of older Renaults.
There were models with tons of problems, other that were bullet proof really.
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.
What does older mean in this context? Because some people still think the year 1996 wasn't that long ago. Modern Renault cars are fine and reliable enough. I've had 4 in my life time and had zero issues myself. I see a ton of them here in the UK and, again, they're fine.
As the old saying goes - better a naughty French than boring German...
Which "older" ones? The original 5 is kind of a tank.
I didn't know tank have regular problems with starting, especially in cold weather, regardless of whether the choke is open or not :)
Yeah, if we are talking about cars with choke we can say with confidence that most of the original engineering team is in retirement.
> electrically excited synchronous motors
So hold on, their amazing technological innovation is... <drum roll please>
a washing machine motor?
> The second disadvantage is a lower efficiency than with permanent magnets, which cannot be improved so much as to match PM motors, because the electrical currents that circulate through the rotor windings must generate heat. The lower efficiency also makes cooling more difficult.
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.
Amazing breakdown for someone (me) who knows literally nothing about how motors work.
> The second disadvantage is a lower efficiency than with permanent magnets, which cannot be improved so much as to match PM motors, because the electrical currents that circulate through the rotor windings must generate heat. The lower efficiency also makes cooling more difficult.
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.
That just means lower net voltage => lower current => lower torque right? When you do need torque you need current and the losses that come with it.