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.
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.
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.
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.
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.
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.
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.
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.
> 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.
> 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.
A historical pioneer in the complex technology of electric motors without magnets
Those who know the history of electric machines will find the title and verbiage very amusing. Motors with no permanent magnets were the first practical ones, and at this point wound-rotor motors are over a century old.
It's worth noting that some of the biggest motors have always been designed this way, because the size of magnets required would make them both too expensive and dangerous, and still not powerful enough for their size; a field coil can generate a field that's only limited by the current and resistive heating of the winding, but rare earth magnets have fixed limits on field strength.
Long ago, when I was in Cub Scouts, one of the projects was to build an electric motor. The parts list was:
1. a plank to form the base
2. several 6 inch nails
3. wire
4. a tin can (as a source of sheet metal)
5. tape
No magnets. But it worked perfectly fine when connected to a dry cell. Adventurous science lad that I was, I decided it would work better when connected to AC. So I attached a power cord and plugged it in.
A loud vibration ensued, and then it burst into flames. My mom wasn't happy.
P.S. I still use tin cans as a source of sheet metal. There was a big storm a while ago, with tree branches whistling by at high speed. (Not a good time to be outside.)
Three holes were punched in the house by the branches, 1-2 inches in diameter. What to do, what to do. I took a coke can, slit it and unrolled it into sheet metal. Then cut a disk bigger than the hole, and epoxied it into place. Worked like a charm, and cost nothing.
I've used coke can metal for shingles and flashing, too. They don't rust.
In other words: it rusts, but it doesn't rust like iron. It rusts in a much less destructive way because the aluminum oxide protects the rest of the aluminum from oxygen
The Cub Scouts in the 1960s were a lot of fun. Each den meeting involved a project. The other one I remember was we each built a kite from scratch.
Mine was a bit fragile, and the first gust of wind shredded the sticks and plastic film.
But it was still fun!
As a teen I built a flame thrower. No, I'm not going to explain how to build one. My dad told me that God looks out for little boys, because otherwise they'd never survive to adulthood.
When I was 9, I found a book of his "Rocket Manual for Amateurs". The opening sentence was something like "if you're fascinated by things that burn and explode, this book is not for you." Who could resist a teaser like that? I promptly read it cover to cover. He wouldn't let me buy any of the necessary materials.
"Rocket Manual for Amateurs" was my favorite book after I found it in 8th grade. In high school I had a chem teacher who would give me chemicals so I could experiment with what I'd read. A great book for budding Raketenkinder.
All big generators have an exciter coil that is used to generate the magnetic field. It has the advantage of allowing voltage regulation through adjustment of the field, rather than after the fact, which would be far less efficient.
In both motors and generators, there is an efficiency hit related to the need to supply power in order to generate the field, but when you scale up the system, it actually becomes more efficient to use the electromagnet. With the rare-earth mineral shortage, it makes even more sense.
> field. It has the advantage of allowing voltage regulation through adjustment of the field, rather than after the fact, which would be far less efficient
That and not having huge strong magnets is nice when doing maintenance.
A permanent magnet motor uses permanent magnets on the rotor, but an electrically excited synchronous motor has an electromagnet on the rotor. This requires a rotating electrical contact which has normally been made with slip rings and carbon brushes. These wear over time and need replacement.
Most large electric generators are externally excited synchronous generators using carbon slip rings, so it's a well understood field.
This can be made contactless using inductive coupling and a rectifier - since inductive coupling needs AC but the excitation coil needs DC - at the expense of some efficiency.
You can see the efficiency difference - Renault claim 92% efficiency but permanent magnet motor EVs have touted efficiency over 95% in the motor.
I am a little surprised that Renault is only claiming a drive cycle efficiency of 92% (unclear for which drive cycle). It is possible to design EESM with brushless high frequency rotating transformers and rectifiers for WLPT drive cycles with greater than 94% almost 95% efficiency.
In most EVs motors are watercooled, so that energy can indeed be scavenged – problem is, during low-speed driving, the heat output is not high enough to get noticeably above ambient temperature.
It's a small difference, but if you had a choice between "more efficient AND less maintenance" and "less efficient and more maintenance" then it's easy to see why the permanent-magnet solution is preferred.
The actual alternative is induction motors, which are just a bit less efficient than PMSM and otherwise basically the same. Except that the frequency fed to them isn't exactly proportional to speed.
They've been used to great success since we had the needed power electronics to drive the electric trains of Europe.
You can also make squirrel-cage rotors that are auto-inductive in the sense that they resist slip from the rotating field of the stator. This is also extremely simple to manufacture and doesn't require driving separate fields or anything similar.
This is mentioned in the parent page, where it is also mentioned that their disadvantage is a lower energy efficiency than either electrically-excited synchronous motors or permanent-magnet motors.
The lower efficiency means a lower range for the same battery, which is why the companies that have used them in the past, like Tesla, have abandoned them.
Permanent-magnet motors have the highest possible energy efficiency, followed by electrically-excited synchronous motors, than by the induction motors mentioned by you.
Both permanent-magnet motors and induction motors do not contain parts that need frequent maintenance, while this property is more difficult to achieve for electrically-excited synchronous motors.
Not quite true: you're also limited by the mechanical strength of your windings and core (this is the upper limit on superconducting magnets like at CERN and in fusion plants).
BMW also makes rare-earths-free motors for their EVs and - at this very moment - theirs are far more advanced. They offer almost twice the power (up to 300kW vs 160kW) and are on a 800v architecture.
I assume you’re talking about the n52 vs n20. I’ve had both engines as daily drivers, and they’re both fine. The n20 has a bad rap due to early models failing from a timing chain guides breaking.
They suffer from some of the same problem your likely modern fridge does, and then kick it up two notches.
In the name of "safety", they have made design decisions such as integrating fuses directly into the very large and expensive control boards and making them non-replacable. Just in case this wasn't enough, they also tend to blow an OTP so that in the event that you have the know how to replace the fuses anyways, nothing will work. Naturally you also cannot just swap in a replacement board, as it needs to go through the same pairing process to the ECU as things like the car doors, which in most cases requires an active certificate/license on the ecu programmer that only dealerships/oem have.
In theory they should be, but EVs also tend to be more computerised, proprietary and locked down than ICE cars, so in practice I think it's not as simple as that.
For example there was that case of the car that needed an entire new sealed €5k battery controller because it was in a minor crash and blew a fuse.
My garage charges 50% more for labour on EVs. I'm sure part of that is price discrimination but I bet part is also because working on them is more difficult. I would not be surprised if they need to pay more for access to the manufacturer's diagnostic tools too, which are becoming increasingly required.
If you take care of the car it’s just brake pads, tires, rotors. Pads and rotors are really simple to DIY. Tires are more expensive than like… an Elantra, but if you’re buying a 60k car you can afford 1.2k in tires… otherwise don’t buy the car.
If you get into an accident or let the bmw get into disrepair via neglect, yeah it’s not cheap to clean up. Body work is expensive on any car though, and I don’t have sympathy for people who own higher-end cars and don’t take care of them, they deserve to pay the price for it.
It's more than that though. Any repairs due to wear and tear or whatever, ends up being really expensive. Although you can probably reduce the costs a bit if you get the non-branded OEM part or potentially the same part from another manufacturer (e.g. the toyota supra uses a lot of bmw parts so if the toyota part might be cheaper than the same bmw part).
That was my whole point actually, the wear and tear is really minimal if you get regular oil changes. Things don’t just break and need replacing. Tires, rotors, brakes, those wear out. The tires are not cheap, rotors and pads aren’t crazy expensive and super easy to DIY.
Owned a BMW. Had the audacity to use non-BMW windshield washer fluid. The fluid sensor broke; because in a BMW it’s a fancy sensor that is only compatible with specific washing fluids. Sums up my experience with that car. It was nice to sit in, though.
If you had bought a 7 or 5 Series at that time, you would not have had that experience. The 2001 7 Series had something like a 25% roadside breakdown rate.
So like... One in four cars would break down at the side of the road before it was otherwise EOL? One roadside breakdown every 800,000 miles or so? That really doesn't sound bad.
Mostly just tires and minor maintenance. You're unlikely to need pad and rotor replacements unless you're driving as if you were on a racetrack every single day.
With daily EV driving you have the opposite problem - regen means you rarely, if ever, actually activate the brakes, so you get rust on them that you need to clean out.
The cheapest Minis are made by GWM in China, and are using different motors and batteries.
However, comparing prices between cars nowadays is a complicated matter. BMW's iX1 and iX2 (they use the BMW EESM motors) theoretically cost about €55k, but they have been very recently available to lease for about €250 euro per month - so pretty much for the same price as the cheapest electric Renault if leased.
They share the same OEMs, and both are following the same ex-China automotive strategy.
Renault has also been thumbing China recently for undermining EU manufacturing as well [0] while China has returned to using Wolf Warrior diplomacy against Europe [1][2][3][4] using the same rhetoric that the Trump admin uses.
Of course, under the Xi admin China's foreign policy has always viewed the EU as inferior and a has-been [5] and has become an active participant in the Ukraine War [6][7].
Europe might not be able to trust the US, but it can't trust China either.
It is, but the PRC has been pushing back against sourcing from within Europe and only intends to use CDKs to assemble EVs. This is what the EU is pushing back against.
What EU states are now lobbying for is if BYD wants to sell an EV in the EU, it should include European originated parts. Just assembling a knockdown kit in Hungary whose parts were all manufactured in China is not "Made in Europe". If BYD or MG wants to sell a BYD or MG car in the EU, they should source the battery pack and powertrain from the EU.
Alternatively, the PRC can drop similar origination requirements from it's domestic market.
The reality is the PRC won't back down, so they will be tariffed by the EU, especially as the EU has lost patience with the PRC due to their active involvement in the Russia-Ukraine War [0], attempting to use diplomatic immunity to kidnap a French national [1], and attempting to embargo the EU's rare earth imports [2].
Additionally, it's easier for the EU to push back against China versus the US while also winning brownie points in the US.
Why do you think the R5 was developed in China? Renault have been quite open about all the improvements they had to make to their processes, development centres and factories in France to make it. The Twingo was partially developed in China.
The EV batteries are sourced from Ampere and LG (in the EU) and the EESM from Valeo (in the EU).
Sharing platforms isn't something EU manufacturers are opposed to, but they do not want to be dependent on Chinese supply chains. That is the crux of ExChina, especially as the majority of an EV's value is derived from the battery and powertrain.
Which is quite the contrast to Mercedes new axial flux electric motor, which goes all in on rare earths- the design relies on the highest end high-grade permanent magnets.
Still, presumably Mercedes ambitions are for few motors than BMW or Renault.
Vastly different target market and/or features there. Mercedes are chasing maximum power density, minimum weight for high performance deployments, with seemingly little concern for cost or supply chain.
Renault is going after the consumer market with these motors, where minimising cost and maximising availability is more important than pushing past 95% efficiency or cramming a 700kW power output in a motor that is small and light enough to fit inside of a wheel hub.
Tesla had invented a kind of two-phase induction motor, but the three-phase induction motor that is the ancestor of the modern induction motors was invented in 1891 by Mikhail Dolivo-Dobrovolsky (working in Germany at AEG), who had also invented in 1888 the three-phase grid, the three-phase generator and the three-phase synchronous motor.
The Dolivo-Dobrovolsky motor is the ancestor of all high-power induction motors, while the Tesla motor can be considered the ancestor of the single-phase induction motors that have been used (more frequently in the past than today) for several household appliances, like washing machines (or reel-to-reel magnetic tape recorders, a half of century ago).
Other way round. He invented the induction motor (1887) which the three-phase grid was then demonstrated to drive (1891). That's how influential it was. There are other reasons a three-phase grid is handy but being able to drive these brushless contraptions must have seemed utterly wild at the time.
A three-phase grid cannot drive a two-phase induction motor, like that invented by Tesla.
In 1891, the three-phase induction motor was invented by Mikhail Dolivo-Dobrovolsky, combining the principles of the three-phase synchronous motor previously invented by Mikhail Dolivo-Dobrovolsky with the principle of the induction motors invented by Nikola Tesla and Galileo Ferraris.
Like any inventions, the induction motors of Nikola Tesla and Galileo Ferraris had not sprung out of nothing, but they were based on the experimental observation that had been known for many decades that if you rotate some magnets around a disk of copper, the disk will rotate, even if the magnets do not have any action on the disk when stationary.
Because of the symmetry, it is easier to generate electromechanically three-phase currents than two-phase currents where the phase difference must be precisely of one right angle.
Rare earth magnet motors require software too if you want them to be maximally efficient. You could embody that software in e.g. an FPGA of course, but it's still software.
Broader point is this: Middle East created oil crisis back in 70s. Since then US economy has grown enormously while it's still using pretty much same amount of oil, imported or otherwise. They shot themselves in their foot. Iran is doing this now, telling the world to avoid Hormuz. They will learn to do that.
China is doing that by blackmailing countries with rare earth.
Answers will be found. Especially as some of finest brains across 2 continents + Japan are very interested in doing it. In the past, China could flood market at right time to make alternatives unviable. But that trick has worn off.
In this context, 92% or even 80% efficiency of permanent magnets is no big deal. It'll not be the answer to every use case but will satisfy many and limit demand.
I don't know. Europe had the opportunity to make themselves energy independent multiple times; instead they doubled down on Russian oil, and in response to the latest invasion, they instead doubled down on Qatar natural gas...
Germany spent enough on solar to have nuclear power for winter heating and instead they get nearly nothing from it when energy (note I said Energy not Electricity) demand is the highest: winter heating.
Now, if they had put that solar in North Africa and ran cables, sure, but they didn't. Or if they did Drake's landing solar storage, that would also work. But they spent a fortune only to still be completely dependent on fossil fuels and are destroying the economic base because of the cost.
In the long term solutions will be found, but in the short term they can gain an enormous bargaining chip. If food prices double because we've burnt the last drop from the Strategic Petroleum Reserve, the administration will give them just about anything they want to avoid utter political destruction.
The game theoretic definition of a threat is something that harms you, but harms them so much that they will avoid forcing you to trigger the threat. It's a different matrix from the Prisoner's Dilemma, but still leaves you guessing about the personality of your opponent. The personality of Iran seems reasonably consistent. The US, less so.
Clearly making a motor with induced magnetic fields both for the stator and rotor isn't the innovation here, since a large fraction of industrial motors do not have permanent magnets.
I would assume the innovation here would need to be making it small and efficient for any meaningful torque output? Usually when you see claims of a 93% efficient electrical motor its the result of taking an absolute beast of a 2kW machine and operating it at 400W. Does anyone have insights into what Renault are doing here?
It's interesting that this is a brushed design. In the RC car community, brushless motors are generally regarded as superior, but those of course have the rare earth magnet problem.
Technically the brushes can wear out, although there are claims they are good for 150,000-250,000 miles it seems.
It's technically not a brush but a slip-ring. The design of these motors is very similar to automotive alternators, just scaled up 100x (in terms of power).
Brushes are used everywhere for transmitting electrical current between two parts that have an unlimited relative motion.
Brushes are typically made of graphite mixed with some binder. The graphite conducts the electrical current, but it also acts as a lubricant.
The metallic part that is in contact with the brush is called a slip ring, if it is continuous, like in synchronous motors, or a collector ring if it is segmented, like in DC motors or single-phase motors with brushes.
yeah I misspoke, I meant to say that it's a brush riding on a slip-ring (continuous contact, no arcing, lasts long) rather than a bunch of contacts in a cylinder (commutator, arcing, wears out).
Because it's the discontinuities in the commutator where the sparks fly (with much help from self-induction of the motor's coils) and erode the ring and brushes.
"Brushless DC motors" are good because brushed DC motors are constantly switching polarity, which causes arcing of the brushes, which causes wear. The brushes are not there to energize the rotor; the rotor is just magnets after all. The brushes are there to tell the stator to change polarity.
Brushless DC motors don't arc -- because they switch stator polarity with electronics that sense the position of the rotor without rubbing parts. (They can also fine-tune the stator current spikes to make the motor very efficient over a wide speed range, which brushed DC motors cannot do.) The lack of arcing is more important than the fact that they don't have rotating contact points.
Brushed AC motors have rotating contact points (slip rings) but they don't arc (ideally), so the contact points don't degrade as fast as brushed DC motors do. But they do carry a lot of current because their purpose is to energize the rotor. Brushed AC motors are not ideal, but making an AC motor "brushless" is not nearly as big a win as making a DC motor brushless.
Wait. You're saying DC motors require current that's constantly switching polarity? So they're sort of really AC internally?
Yep. All motors require constantly changing current. The distinction between AC and DC motors is whether you feed the motor externally with current that is already alternating sinusoidally, or whether the motor itself turns external DC into some kind of AC.
Really sounds promising. The question is will the French have the will to build it in bulk on shore in France or Europe? There’s no point if they want to sub it out to the world to build cheaper somewhere else?
This technology does show that you should never give up on industry, research, development and building on shore.
Could be wrong, but AFAIK the CATL Sodium batteries haven't yet hit LFP pricing.
You are unlikely to see a vehicle with sodium batteries until after that happens, and it needs to be significantly less than LFPs as you Na batteries have more weight per Wh. I believe they also have a shorter lifespan (but not NMC short). Edit correction, looks like CATL is promising 15000 cycles, which is much longer than LFPs which usually come in at 7000 to 10000.
It seems far more likely to me that if the Na prices tank, you'll probably first see them deployed as grid and home battery solutions.
The energy density of LFP batteries are also 30-50% higher than sodium based battery chemistries. Even if sodium battery prices drop, the lower energy density is a big disadvantage. My understanding is that sodium batteries are aimed at stationary use-cases, like battery buffers for fast charging.
At the cell level yes. But at the pack level, you need less/no cooling and there is virtually no risk of runaway fires. This means the cells can be packed more densely and you get some weight benefits for all the stuff you no longer need for fire safety.
CATL already put sodium ion in cheap cars. And there are other benefits to this type of battery like a wider range of operating temperatures that cover essentially all of the extreme temperatures you'd find in the arctic and the hottest deserts.
I would not be surprised to find some of these batteries in big semis a few years down the line when the cost benefits make the space/weight sacrifices worth the trade off.
But you are right that domestic and grid storage are also going to be huge use cases.
For about a half of year there have been cars with sodium-ion batteries, in China. As you say, for now they are more expensive, but it is expected that the price will drop quickly in the following years.
Because they lose neither capacity nor charging speed at low temperatures, like the lithium-ion batteries, they expect that in the future sodium-batteries will be the best choice in the countries with cold climates.
And high temperatures, too. Meaning they don't require cooling nor heating, basically matching the per kg capacity of ready modules with LFP while being significantly safer and less complex.
They're promising to start selling a Qiyuan A06 variant with Sodium batteries sometime this year... so if you went looking you could probably see one... or will be able to soon.
EESMs are primarily manufactured by European OEMs (ZF, MAHLE, Schaffler, AEM) and their Indian JV partners (Sona Comstar, Sterling, and the India branches of the OEMs listed). Both have been blocked via export controls from accessing battery tech from China over the past few years, and a major reason for the push for EESMs was for an ex-China supply chain, especially after China began export controlling rare earths to the EU [6].
Additonally, Chinese and American EVs tend to use PMSMs unlike European and now Indian EVs. Also, the EU is cracking down on automotive exports (cars and OEMs) from non-FTA states as part of the EU Industrial Accelerator Act (which btw has made China go ballistic [2][3][4][5]).
On the other hand, they will most likely use Japanese or Korean solid-state batteries as Idemetsu Kosan is in the process of mass producing them [0][1] as is LG [7], and both Japan+SK are FTA partners with the EU.
Say all you want about the inferior efficiency and so on, but if nothing else they have proven that it's viable, even commercially. So the rare earths are really not as vital as they have been made out to be.
One of the most interesting thing about commodity bottlenecks is that they often accelerate substitution ; scarcity can end up by making a material being less important
Electrically excited synchronous machines (EESMs), also known as wound field synchronous machines (WFSMs) have a number of potential advantages and disadvantages compared to interior permanent magnet synchronous machines (IPMSMs). IPMSMs are the dominant motor topology currently in use for North American electric vehicles.
Advantages:
- Not subject to the price and supply chain volatility of rare earth permanent magnets.
- For highway dominant drive cycles, the cycle efficiency of EESMs can be higher than state of the art IPMSMs. EESMs tend to have their best efficiency at moderate torques and high speeds because of their excellent field weakening characteristics. I tend to think that they would be a good fit for application in class 8 trucks or as auxiliary motors in automobiles with two powered axles.
- The output torque doesn't necessarily decrease with rotor temperature. In IPMSMs the permanent magnet flux linkage decreases with rotor temperature.
- At least theoretically, with proper control, it is possible to operate EESMs with unity power factor and decrease the kVA rating of the stator inverter.
- If there is a stator inverter fault, there are schemes to denergize the rotor which have some safety implications.
Disadvantages:
- DC current needs to be transferred to the rotating field winding. For automotive applications this tends to be done either with brushes and slip rings or brushlessly using a high frequency transformer with a rotating rectifier. In either case additional power electronics and other components are needed for the field power transfer and control which reduces some of the potential cost savings of the elimination of the permanent magnets. If brushes and slip rings are used with oil spray/oil jet cooling of the rotor they need to be sealed in a separate compartment. I am a little surprised that Renault has stuck with brushes and slip rings versus an inductive high frequency transformer solution. I think this has limited their power density.
- For very torque dense machines, cooling the rotor field winding is challenging, and in my opinion is best accomplished by oil spray/oil jet cooling.
- It is difficult to reach the same maximum speeds as IPMSMs in an automotive package size. The rotor field winding retention system to keep the field turns from moving into the airgap at high speeds needs considerable attention during the design.
- The overall axial length of the non-active region of EESMs is typically longer than IPMSMs because of the field winding end turns and field excitation system.
- EESM efficiency is dominated by the manufacturable slot fill of the field winding.
- High performance current/torque regulation is considerably more difficult.
High performance EESMs have been used in aerospace generator applications for decades, albeit with a different rotor excitation system than what is used in automotive applications. Renault (and their supplier Continental) really led the commercialization of EESMs into automotive mass production. Now BMW has followed suit and multiple suppliers have EESM designs (Mahle, ZF, etc.) GM had a really nice EESM design and high frequency transformer excitation which they published back in 2014. My colleagues and I built several generations of EESMs as part of U.S. Dept. of Energy projects (https://www.osti.gov/servlets/purl/1837809) and I think they have their place as EV traction motors for certain applications.
You can switch a motor without permanent magnets to "idle mode".
I understand in Tesla dual motor configurations, the front motor is without magnets. The excitation field will be turned on when you need extra power, but at crusing speed it does not cause extra "drag".
From one teardown I've seen, they even went so far to use cheaper and less efficient IGBTs for the front drive, and more efficient SiC Mosfets for the rear motor (in the same vehicle!). If you need extra acceleration briefly, lower efficiency can be accepted.
It’s interesting that EESMs can be more efficient at high/highway speeds, and it’s something I had read before. This seems to me to be a key advantage of EESMs, because when people worry about EV range, they worry mainly about range on long-distance, high-speed journeys.
(I have a Renault EV and it’s excellent. Aside from the motor technology, it’s relatively light, has a heat pump as standard, and a good-sized battery).
As said in the parent Web page, lower energy efficiency, thus shorter range with the same battery.
Another poster has mentioned that BMW also uses EESMs instead of permanent-motor magnets.
BMW uses EESMs as the main motors, on the rear axle, while they use induction motors as auxiliary motors on the front axle.
Besides being cheaper, the induction motors have the advantage that if they are used only as auxiliary motors, you can cut the power supply to them at any time, in which case they will consume nothing.
So their lower efficiency does not matter, because most of the time they are turned off.
> Besides being cheaper, the induction motors have the advantage that if they are used only as auxiliary motors, you can cut the power supply to them at any time, in which case they will consume nothing.
EESMs have this advantage too, you can simply cut power to the field winding.
It was a dude with motors on a table with a flip board. No animations. No diagrams. When it got to the point about having one of each motor, and using the best, he then said that you use the permanent motor even when the other makes sense. Ok, well then why have the two different kinds of motors? No answer. Just handwaved. If you can't use the induction motor when its most efficient, because thats when the permanent motor is causing spin loss, why have the induction motor at all? No answer.
So. Analog presentation. Actual motors on a desk with a flip chart. No animations. No internal visualizations. One page had diagrams that would have been better super-imposed (or hey, animated). Then one page the begs questions with no answers given.
Weren't Tesla ACIM drive unit motors before Model 3 also magnet-free? I thought they used passive isolated bundles of copper wires and their reluctance as magnets.
Rare earth magnets are just too good for electric motors to go this way. Europe and the US just need to get the rare earth manufacturing going and stop being reliant on china for this stuff.
They're also used by Nissan [1], BMW [2], and Indian EVs [3].
European firms like ZF, Valeo, MAHLE, and Schaffler along with British firms like AEM have been working with their Indian JVs as well as Indian players like Sona Comstar and Sterling for a couple years now to integrate supply chains for mass-producing EESMs.
EESMs as well as the larger OEM story played a role in helping land the EU-India and the UK-India FTAs because the supply chains for French+Italian (Renault, Stellantis), Japanese (Toyota, Honda, Suzuki), Korean (Hyundai-Kia), and Indian automotive manufacturers merged.
On the other hand, EESM EVs aren't a thing here in North America nor China yet as both primarily use PMSMs (edited typo).
> does Nissan still use these motors, the car in the linked article has been discontinued
Yes. The Ariya was discontinued in North America (EDIT: USA, TIL still sold in Canada) but is still manufactured and sold in Asia.
> European and Indian manufacturers/engineering are definitely not in the same category though
It's the same manufacturers and supply chain now.
Renault and their OEMs are the biggest driver for EESM, and Renault's largest markets and manufacturing hubs are France, India, and Romania. Heck, Renault is now going to start exporting it's Made in India cars and parts back to the EU [0] becuase of the EU-India FTA.
And the European OEMs have transferred the IP for EESMs to Indian JVs as I mentioned. It's the same style of tech transfer as Samsung did for BYD and TDK for CATL for battery chemistry in the 2000s. Heck, Valeo [1], MAHLE [2], ZF [3], and Schaffler [4] are opening and expanding factories and R&D hubs dedicated to EV transmission manufacturing in India for domestic and export usecases.
Also, if you've ever driven a Japanese (Toyota, Honda, Suzuki) or Korean (Hyundai, Kia) make care in the EU, Australia, Middle East, Africa, or Asia outside of their home countries their parts sourcing and even the entire manufactured car would have come from India, such as the Toyota Urban Cruiser EV [5].
No, and it was mentioned by the consortium of European cars manufacturers after the joint press release with Der Leyen herself: the implementation of factories and research centers in India is solely to be able to sell on that market. It is the exact same process that happened with China in the past. The exact same also happened with Airbus.
You are also wrong on the market importance for Renault. For 2024, France was the biggest, followed by Italy, Turkey, Spain, Germany, Brazil, UK, Morocco, BENELUX, Romania, Poland, Netherlands and... #13 India with 0.9% market share...
Supply chains didn't change at all, in fact it did the opposite, and Europeans won't rely on anything Indian made for the near future, as local re-industrialization is already acted on and even accelerated since the pandemic.
Production numbers across all manufacturers even Volkswagen (which was unexpected) show the number of cars manufactured in Europe increased in the past 2 years.
Electric cars in Europe mostly come from China, the US and European brands. Nothing Indian-made, not even parts.
Not sure why this was voted down, it was the most useful comment here.
does Nissan still use these motors, the car in the linked article has been discontinued, and then only real info I can find on their site about the leaf is about their ROCKIN' bose sound system/s
Niron is not developing an EESM. They are developing Iron Nitride permanent magnets. These magnets can be used in a variable flux permanent magnet synchronous machine (VFPMSM). Variable flux machines have some similar characteristics to EESMs in terms of their ability to change the field excitation, but they are fundamentally different than EESM in terms of how they do so. EESM change their field excitation and VFPMSMs change the magnetization state through stator current pulses. Their current/torque regulation control is also quite different.
There are other startup companies developing EESMs but not Niron to my knowledge.
Not just some, approximately all of them. It greatly complicates the logistics of a black start. † Of course that situation has additional complexity due to the need for substantial additional power in order for the various fuel supply systems to operate but I digress.
Generator excitation is not the hard part of a black start. You have to run coal feeders, blowers, and water pumps for an hour before you can spin the generator. Then you get power instantly upon applying power to the field windings.
And even that's not the hard part of a black start. The plant control is relatively easy. What's hard is grid coordination.
All generation and consumption have to be almost perfectly balanced every second of every day. And the power company doesn't have good addressability of load. Worse when you restore power to an area all their stuff turns on in parallel giving an inrush that could be 3x or more the steady state.
A black start is a very drawn out process of bringing generation and load online in a balanced way and with wait times between load increases for stabilization.
After watching a Munro video about it, I see your point. In the motor shown, the rotor gets its magnetic field simply by inducing a current and a field in it in reaction to the stator's field. There are no electromagnets in the rotor like I expected. In that case, I'm not sure either... I'd say more likely than not but it's complicated since the stator basically needs to induce a field and at the same time recover energy from the field that comes back from the rotor. I would further guess that the phase shift between the two components makes it possible to treat them separately.
Previous comment: Don't see why not - the "field" coils (the ones that replace the permanent magnets) need to be energized, which can initially come from the batteries if necessary.
There is something... weird about this. this tech has existed.... a long time. And I am not familiar with what is common in electric cars so may be missing something obvious but thought this was already how it was done. let me explain my limited understanding.
With ac motors electromagnets can be used in the rotor. there is even a super clever way to do it where the electromagnet in the rotor is driven wirelessly via induction. there are some downsides but having no physical sliding electrical connection to the rotor is a huge upside. The ac can be dynamically formed from DC via high speed switching(transistors, in industry often called a VFD).
Due to the upsides of ac induction motors I sort of assumed this was already what was found in cars. I am a bit surprised to find out there were rare earth magnets in the first place.
Permanent magnet motors are simpler and cheaper to make, at least in the small (yes, small --- there are electric motors in the MW range in industrial applications, which are themselves larger than an average car) sizes found in EVs.
AC motors are not magic. The core is essentially just a coil with one turn, so it can generate only a very limited magnetic field. So they have to be bulkier for a given power density and generally slightly less efficient.
I don't think car owners have to worry about this the first half million miles or so with these motors. Electrical motors last a long time. We'll know for sure in a few decades, I guess. That's how long it will take for a significant number of their cars to actually drive that far.
Also, compare this to ICE engines which experience continuous explosions, lots of mechanical parts, extreme temperature swings, etc. and still manage pretty decent durability. There's simply no base for assuming that parts like this wearing out and needing to be replaced is going to be a common thing.
The Continental and Renault motors like those in my Kangoo ZE and Zoe have so far proven fairly reliable, with the occasional exception being shaft bearings. The Q210 is particularly robust. I'm not aware of anybody having brush/slip ring issues yet.
Cars already have lots of wear items and a mature service industry for them. If I can reliably get at least 50k miles out of it, then I wouldn't be all that bothered, as this is not likely to be an expensive part or service.
The main difference between this and your typical AC induction motors (also magnet free) is that this is a DC motor so you need a commutator. Your AC induction magnet free motors are very similar to drone motors in that you don't have any electrically active moving parts like slip rings and commutators. But for AC induction there will be a slight lag (known as slip).
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.
A historical pioneer in the complex technology of electric motors without magnets
Those who know the history of electric machines will find the title and verbiage very amusing. Motors with no permanent magnets were the first practical ones, and at this point wound-rotor motors are over a century old.
It's worth noting that some of the biggest motors have always been designed this way, because the size of magnets required would make them both too expensive and dangerous, and still not powerful enough for their size; a field coil can generate a field that's only limited by the current and resistive heating of the winding, but rare earth magnets have fixed limits on field strength.
Long ago, when I was in Cub Scouts, one of the projects was to build an electric motor. The parts list was:
1. a plank to form the base
2. several 6 inch nails
3. wire
4. a tin can (as a source of sheet metal)
5. tape
No magnets. But it worked perfectly fine when connected to a dry cell. Adventurous science lad that I was, I decided it would work better when connected to AC. So I attached a power cord and plugged it in.
A loud vibration ensued, and then it burst into flames. My mom wasn't happy.
P.S. I still use tin cans as a source of sheet metal. There was a big storm a while ago, with tree branches whistling by at high speed. (Not a good time to be outside.)
Three holes were punched in the house by the branches, 1-2 inches in diameter. What to do, what to do. I took a coke can, slit it and unrolled it into sheet metal. Then cut a disk bigger than the hole, and epoxied it into place. Worked like a charm, and cost nothing.
I've used coke can metal for shingles and flashing, too. They don't rust.
I like that story. I fixed a microwave door latch with a beer-can shim and some decorative ribbon; we used it another 11 years.
there's also a plastic liner on them that I'm sure helps.
It also helps that they are made from aluminum which doesn’t rust like iron does.
It rusts just like iron, but the rust (AlOx, or alumina) stays bonded to the metal and actually protects it.
Rust being literal Fe2O3 makes a convincing argument that aluminium sure oxidises but doesn't rust pretty much by definition ;)
In other words: it rusts, but it doesn't rust like iron. It rusts in a much less destructive way because the aluminum oxide protects the rest of the aluminum from oxygen
it does not rust, it corrodes :)
And epoxy binds to aluminum just fine ? Epoxy is weird. What solid material does it NOT bond to ?
Polyethylene, like they use in food containers. Virtually nothing sticks to it unless specifically designed.
It does not bond to polypropylene and other low surface energy plastics
Terminology question - I understood those to be "high-energy" surfaces, because the chains are strongly bound. Is it a typo, or am I wrong?
Teflon.
Yummy, my favorite!
Actually should be mostly fine since it’s pretty inert, unless you eat the stuff used to make it.
That 60Hz sound is a sure sign we did something very wrong. By the time you hear it it’s usually too late to say “Uh oh”
One of my favorite sayings:
"Good judgement comes from experience; experience comes from bad judgement."
I commend your excellent use of bad judgement there, WalterBright (despite your mom's lack of enthusiasm)!
Username checks out.
Been there. Im gonna guess that 90% of HN folk have similar stories to tell.
The Cub Scouts in the 1960s were a lot of fun. Each den meeting involved a project. The other one I remember was we each built a kite from scratch.
Mine was a bit fragile, and the first gust of wind shredded the sticks and plastic film.
But it was still fun!
As a teen I built a flame thrower. No, I'm not going to explain how to build one. My dad told me that God looks out for little boys, because otherwise they'd never survive to adulthood.
When I was 9, I found a book of his "Rocket Manual for Amateurs". The opening sentence was something like "if you're fascinated by things that burn and explode, this book is not for you." Who could resist a teaser like that? I promptly read it cover to cover. He wouldn't let me buy any of the necessary materials.
"Rocket Manual for Amateurs" was my favorite book after I found it in 8th grade. In high school I had a chem teacher who would give me chemicals so I could experiment with what I'd read. A great book for budding Raketenkinder.
> if you're fascinated by things that burn and explode, this book is not for you.
Translation… ‘read me now!’
You're right about the verbiage being amusing.
All big generators have an exciter coil that is used to generate the magnetic field. It has the advantage of allowing voltage regulation through adjustment of the field, rather than after the fact, which would be far less efficient.
In both motors and generators, there is an efficiency hit related to the need to supply power in order to generate the field, but when you scale up the system, it actually becomes more efficient to use the electromagnet. With the rare-earth mineral shortage, it makes even more sense.
> field. It has the advantage of allowing voltage regulation through adjustment of the field, rather than after the fact, which would be far less efficient
That and not having huge strong magnets is nice when doing maintenance.
What advantage do permanent magnets provide that it isn't the case that all motors are made without them?
A lack of wear components.
A permanent magnet motor uses permanent magnets on the rotor, but an electrically excited synchronous motor has an electromagnet on the rotor. This requires a rotating electrical contact which has normally been made with slip rings and carbon brushes. These wear over time and need replacement.
Most large electric generators are externally excited synchronous generators using carbon slip rings, so it's a well understood field.
This can be made contactless using inductive coupling and a rectifier - since inductive coupling needs AC but the excitation coil needs DC - at the expense of some efficiency.
You can see the efficiency difference - Renault claim 92% efficiency but permanent magnet motor EVs have touted efficiency over 95% in the motor.
I am a little surprised that Renault is only claiming a drive cycle efficiency of 92% (unclear for which drive cycle). It is possible to design EESM with brushless high frequency rotating transformers and rectifiers for WLPT drive cycles with greater than 94% almost 95% efficiency.
To a layman that seems like a really small efficiency tax if you can't get your hands on the magnets for some reason.
It’s a near-doubling of energy loss - probably a healthier way to understand it when the efficiencies are all 90%+
Funnily enough if enough of that energy loss (heat) can be scavange, this wouldn't be nearly that bad for us living up here in the cold.
In most EVs motors are watercooled, so that energy can indeed be scavenged – problem is, during low-speed driving, the heat output is not high enough to get noticeably above ambient temperature.
You can get about 2/3 as much output power for a given amount of waste heat and cooling capacity.
It's like how laptop power bricks used to be big and get hot, and now they aren't and don't.
It's a small difference, but if you had a choice between "more efficient AND less maintenance" and "less efficient and more maintenance" then it's easy to see why the permanent-magnet solution is preferred.
The actual alternative is induction motors, which are just a bit less efficient than PMSM and otherwise basically the same. Except that the frequency fed to them isn't exactly proportional to speed.
They've been used to great success since we had the needed power electronics to drive the electric trains of Europe.
Another comment said they're not using brushes, so they shouldn't need more maintenance.
You can also make squirrel-cage rotors that are auto-inductive in the sense that they resist slip from the rotating field of the stator. This is also extremely simple to manufacture and doesn't require driving separate fields or anything similar.
This is mentioned in the parent page, where it is also mentioned that their disadvantage is a lower energy efficiency than either electrically-excited synchronous motors or permanent-magnet motors.
The lower efficiency means a lower range for the same battery, which is why the companies that have used them in the past, like Tesla, have abandoned them.
Permanent-magnet motors have the highest possible energy efficiency, followed by electrically-excited synchronous motors, than by the induction motors mentioned by you.
Both permanent-magnet motors and induction motors do not contain parts that need frequent maintenance, while this property is more difficult to achieve for electrically-excited synchronous motors.
> The lower efficiency means a lower range for the same battery,
And some heat which must be dissipated or else they will dethrone the BMW as the leading burning car. /s
Not quite true: you're also limited by the mechanical strength of your windings and core (this is the upper limit on superconducting magnets like at CERN and in fusion plants).
And if you also ignore iron saturation.
BMW also makes rare-earths-free motors for their EVs and - at this very moment - theirs are far more advanced. They offer almost twice the power (up to 300kW vs 160kW) and are on a 800v architecture.
The cheapest EV model Renault sells is around €20K, the cheapest BMW EV is around €65K.
It's safe to say the companies are not in the market bracket, no?
The bit the gets me more than the sale price is servicing.
BMWs have a terrible record for needing expensive repairs.
I know you shouldn’t rely on anecdote, but it seems I do.
The only way I would buy a BMW is if it were an EV. I’m just not brave (or rich) enough to buy their ICEs.
The BMW inline 6 were the best engines ever. Their inline 4 and other are a strong contender for the worst engines ever.
I assume you’re talking about the n52 vs n20. I’ve had both engines as daily drivers, and they’re both fine. The n20 has a bad rap due to early models failing from a timing chain guides breaking.
I miss my E39 530 every time I drive. My next 90s Jag is also going to be a straight-six; the V12 is glorious but heavy.
They suffer from some of the same problem your likely modern fridge does, and then kick it up two notches.
In the name of "safety", they have made design decisions such as integrating fuses directly into the very large and expensive control boards and making them non-replacable. Just in case this wasn't enough, they also tend to blow an OTP so that in the event that you have the know how to replace the fuses anyways, nothing will work. Naturally you also cannot just swap in a replacement board, as it needs to go through the same pairing process to the ECU as things like the car doors, which in most cases requires an active certificate/license on the ecu programmer that only dealerships/oem have.
This is a company intentionally making sure EVs didn’t erode service revenues
Simpler != more reliable. Electronics fail quite often too. Just ask SSDs.
Also new EVs fail often too due to being cost cut to the extreme with the "move fast and break things".
In theory they should be, but EVs also tend to be more computerised, proprietary and locked down than ICE cars, so in practice I think it's not as simple as that.
For example there was that case of the car that needed an entire new sealed €5k battery controller because it was in a minor crash and blew a fuse.
My garage charges 50% more for labour on EVs. I'm sure part of that is price discrimination but I bet part is also because working on them is more difficult. I would not be surprised if they need to pay more for access to the manufacturer's diagnostic tools too, which are becoming increasingly required.
If you take care of the car it’s just brake pads, tires, rotors. Pads and rotors are really simple to DIY. Tires are more expensive than like… an Elantra, but if you’re buying a 60k car you can afford 1.2k in tires… otherwise don’t buy the car.
If you get into an accident or let the bmw get into disrepair via neglect, yeah it’s not cheap to clean up. Body work is expensive on any car though, and I don’t have sympathy for people who own higher-end cars and don’t take care of them, they deserve to pay the price for it.
It's more than that though. Any repairs due to wear and tear or whatever, ends up being really expensive. Although you can probably reduce the costs a bit if you get the non-branded OEM part or potentially the same part from another manufacturer (e.g. the toyota supra uses a lot of bmw parts so if the toyota part might be cheaper than the same bmw part).
That was my whole point actually, the wear and tear is really minimal if you get regular oil changes. Things don’t just break and need replacing. Tires, rotors, brakes, those wear out. The tires are not cheap, rotors and pads aren’t crazy expensive and super easy to DIY.
What other wear and tear things are expensive?
Owned a BMW. Had the audacity to use non-BMW windshield washer fluid. The fluid sensor broke; because in a BMW it’s a fancy sensor that is only compatible with specific washing fluids. Sums up my experience with that car. It was nice to sit in, though.
After 22 years, my z4 has needed batteries and a starter.
Recently, there was a problem with the engine misfiring but it was $200.
LA, California
If you had bought a 7 or 5 Series at that time, you would not have had that experience. The 2001 7 Series had something like a 25% roadside breakdown rate.
25% every journey, or 25% over the lifetime of the car? Neither seems really believable but I don't understand how else you would measure this.
25% of cars. It was... not good.
So like... One in four cars would break down at the side of the road before it was otherwise EOL? One roadside breakdown every 800,000 miles or so? That really doesn't sound bad.
Mostly just tires and minor maintenance. You're unlikely to need pad and rotor replacements unless you're driving as if you were on a racetrack every single day.
With daily EV driving you have the opposite problem - regen means you rarely, if ever, actually activate the brakes, so you get rust on them that you need to clean out.
It's still good to know that SOTA is further, and we can expect the more advanced designs to seep into more affordable segments.
BMW also produces Mini EVs, which start at £26,840
The cheapest Minis are made by GWM in China, and are using different motors and batteries.
However, comparing prices between cars nowadays is a complicated matter. BMW's iX1 and iX2 (they use the BMW EESM motors) theoretically cost about €55k, but they have been very recently available to lease for about €250 euro per month - so pretty much for the same price as the cheapest electric Renault if leased.
They share the same OEMs, and both are following the same ex-China automotive strategy.
Renault has also been thumbing China recently for undermining EU manufacturing as well [0] while China has returned to using Wolf Warrior diplomacy against Europe [1][2][3][4] using the same rhetoric that the Trump admin uses.
Of course, under the Xi admin China's foreign policy has always viewed the EU as inferior and a has-been [5] and has become an active participant in the Ukraine War [6][7].
Europe might not be able to trust the US, but it can't trust China either.
[0] - https://www.reuters.com/world/china/renault-ceo-asks-eu-enco...
[1] - https://www.globaltimes.cn/page/202605/1361926.shtml
[2] - https://www.chinausfocus.com/finance-economy/dear-brussels-d...
[3] - https://www.globaltimes.cn/page/202605/1362161.shtml
[4] - http://news.china.com.cn/2026-06/10/content_118541873.shtml
[5] - https://fddi.fudan.edu.cn/_t2515/57/f8/c21257a743416/page.ht...
[6] - https://www.reuters.com/business/aerospace-defense/russians-...
[7] - https://www.pravda.com.ua/eng/news/2026/06/12/8039041/
only replying to the first link: isn't sourcing (buying or manufacturing locally) parts for Chinese cars made in Europe a good thing?
It is, but the PRC has been pushing back against sourcing from within Europe and only intends to use CDKs to assemble EVs. This is what the EU is pushing back against.
What EU states are now lobbying for is if BYD wants to sell an EV in the EU, it should include European originated parts. Just assembling a knockdown kit in Hungary whose parts were all manufactured in China is not "Made in Europe". If BYD or MG wants to sell a BYD or MG car in the EU, they should source the battery pack and powertrain from the EU.
Alternatively, the PRC can drop similar origination requirements from it's domestic market.
The reality is the PRC won't back down, so they will be tariffed by the EU, especially as the EU has lost patience with the PRC due to their active involvement in the Russia-Ukraine War [0], attempting to use diplomatic immunity to kidnap a French national [1], and attempting to embargo the EU's rare earth imports [2].
Additionally, it's easier for the EU to push back against China versus the US while also winning brownie points in the US.
[0] - https://www.reuters.com/business/aerospace-defense/russians-...
[1] - https://www.lemonde.fr/societe/article/2024/07/02/deux-espio...
[2] - https://www.reuters.com/business/autos-transportation/china-...
> Alternatively, the PRC can drop similar origination requirements from it's domestic market.
Can you share any details on this? Is something I've rarely seen discussed
> following the same ex-China automotive strategy
Is that why Renault EVs (R5, Twingo) are wholesale developed in China? Doesn't seem very ex-to me, more an in- type of strategy.
Why do you think the R5 was developed in China? Renault have been quite open about all the improvements they had to make to their processes, development centres and factories in France to make it. The Twingo was partially developed in China.
The EV batteries are sourced from Ampere and LG (in the EU) and the EESM from Valeo (in the EU).
Sharing platforms isn't something EU manufacturers are opposed to, but they do not want to be dependent on Chinese supply chains. That is the crux of ExChina, especially as the majority of an EV's value is derived from the battery and powertrain.
same order of magnitude :)
Which is quite the contrast to Mercedes new axial flux electric motor, which goes all in on rare earths- the design relies on the highest end high-grade permanent magnets.
Still, presumably Mercedes ambitions are for few motors than BMW or Renault.
Vastly different target market and/or features there. Mercedes are chasing maximum power density, minimum weight for high performance deployments, with seemingly little concern for cost or supply chain.
Renault is going after the consumer market with these motors, where minimising cost and maximising availability is more important than pushing past 95% efficiency or cramming a 700kW power output in a motor that is small and light enough to fit inside of a wheel hub.
"Replace the magnet with a controllable magnet" is probably the most automotive-engineering sentence possible.
Also known as: “we removed the rare earths and added software.”
Synchronous motors: running on software since the 1880s. Nikola really was ahead of his time!
He invented the induction motor which runs right off the grid.
Tesla had invented a kind of two-phase induction motor, but the three-phase induction motor that is the ancestor of the modern induction motors was invented in 1891 by Mikhail Dolivo-Dobrovolsky (working in Germany at AEG), who had also invented in 1888 the three-phase grid, the three-phase generator and the three-phase synchronous motor.
The Dolivo-Dobrovolsky motor is the ancestor of all high-power induction motors, while the Tesla motor can be considered the ancestor of the single-phase induction motors that have been used (more frequently in the past than today) for several household appliances, like washing machines (or reel-to-reel magnetic tape recorders, a half of century ago).
Other way round. He invented the induction motor (1887) which the three-phase grid was then demonstrated to drive (1891). That's how influential it was. There are other reasons a three-phase grid is handy but being able to drive these brushless contraptions must have seemed utterly wild at the time.
A three-phase grid cannot drive a two-phase induction motor, like that invented by Tesla.
In 1891, the three-phase induction motor was invented by Mikhail Dolivo-Dobrovolsky, combining the principles of the three-phase synchronous motor previously invented by Mikhail Dolivo-Dobrovolsky with the principle of the induction motors invented by Nikola Tesla and Galileo Ferraris.
Like any inventions, the induction motors of Nikola Tesla and Galileo Ferraris had not sprung out of nothing, but they were based on the experimental observation that had been known for many decades that if you rotate some magnets around a disk of copper, the disk will rotate, even if the magnets do not have any action on the disk when stationary.
Because of the symmetry, it is easier to generate electromechanically three-phase currents than two-phase currents where the phase difference must be precisely of one right angle.
Rare earth magnet motors require software too if you want them to be maximally efficient. You could embody that software in e.g. an FPGA of course, but it's still software.
Broader point is this: Middle East created oil crisis back in 70s. Since then US economy has grown enormously while it's still using pretty much same amount of oil, imported or otherwise. They shot themselves in their foot. Iran is doing this now, telling the world to avoid Hormuz. They will learn to do that.
China is doing that by blackmailing countries with rare earth.
Answers will be found. Especially as some of finest brains across 2 continents + Japan are very interested in doing it. In the past, China could flood market at right time to make alternatives unviable. But that trick has worn off.
In this context, 92% or even 80% efficiency of permanent magnets is no big deal. It'll not be the answer to every use case but will satisfy many and limit demand.
I don't know. Europe had the opportunity to make themselves energy independent multiple times; instead they doubled down on Russian oil, and in response to the latest invasion, they instead doubled down on Qatar natural gas...
Germany spent enough on solar to have nuclear power for winter heating and instead they get nearly nothing from it when energy (note I said Energy not Electricity) demand is the highest: winter heating.
Now, if they had put that solar in North Africa and ran cables, sure, but they didn't. Or if they did Drake's landing solar storage, that would also work. But they spent a fortune only to still be completely dependent on fossil fuels and are destroying the economic base because of the cost.
In the long term solutions will be found, but in the short term they can gain an enormous bargaining chip. If food prices double because we've burnt the last drop from the Strategic Petroleum Reserve, the administration will give them just about anything they want to avoid utter political destruction.
The game theoretic definition of a threat is something that harms you, but harms them so much that they will avoid forcing you to trigger the threat. It's a different matrix from the Prisoner's Dilemma, but still leaves you guessing about the personality of your opponent. The personality of Iran seems reasonably consistent. The US, less so.
Clearly making a motor with induced magnetic fields both for the stator and rotor isn't the innovation here, since a large fraction of industrial motors do not have permanent magnets.
I would assume the innovation here would need to be making it small and efficient for any meaningful torque output? Usually when you see claims of a 93% efficient electrical motor its the result of taking an absolute beast of a 2kW machine and operating it at 400W. Does anyone have insights into what Renault are doing here?
The real innovation is in making them brushless and essentially maintenance free while still being efficient enough.
It's interesting that this is a brushed design. In the RC car community, brushless motors are generally regarded as superior, but those of course have the rare earth magnet problem.
Technically the brushes can wear out, although there are claims they are good for 150,000-250,000 miles it seems.
It's technically not a brush but a slip-ring. The design of these motors is very similar to automotive alternators, just scaled up 100x (in terms of power).
Brushes are used everywhere for transmitting electrical current between two parts that have an unlimited relative motion.
Brushes are typically made of graphite mixed with some binder. The graphite conducts the electrical current, but it also acts as a lubricant.
The metallic part that is in contact with the brush is called a slip ring, if it is continuous, like in synchronous motors, or a collector ring if it is segmented, like in DC motors or single-phase motors with brushes.
I've probably taken apart 10 automotive alternators. Every single one had brushes.
yeah I misspoke, I meant to say that it's a brush riding on a slip-ring (continuous contact, no arcing, lasts long) rather than a bunch of contacts in a cylinder (commutator, arcing, wears out).
Slip rings have brushes.
Yes but they wear less than DC brushed motors exactly because it's a slip ring and not a commutator
Because it's the discontinuities in the commutator where the sparks fly (with much help from self-induction of the motor's coils) and erode the ring and brushes.
It's brushless: https://www.evspecifications.com/images/news/6ec9484/additio...
Makes me wonder why they made that choice, if what your parent commenter said is true.
"Brushless DC motors" are good because brushed DC motors are constantly switching polarity, which causes arcing of the brushes, which causes wear. The brushes are not there to energize the rotor; the rotor is just magnets after all. The brushes are there to tell the stator to change polarity.
Brushless DC motors don't arc -- because they switch stator polarity with electronics that sense the position of the rotor without rubbing parts. (They can also fine-tune the stator current spikes to make the motor very efficient over a wide speed range, which brushed DC motors cannot do.) The lack of arcing is more important than the fact that they don't have rotating contact points.
Brushed AC motors have rotating contact points (slip rings) but they don't arc (ideally), so the contact points don't degrade as fast as brushed DC motors do. But they do carry a lot of current because their purpose is to energize the rotor. Brushed AC motors are not ideal, but making an AC motor "brushless" is not nearly as big a win as making a DC motor brushless.
Wait. You're saying DC motors require current that's constantly switching polarity? So they're sort of really AC internally?
Yep. All motors require constantly changing current. The distinction between AC and DC motors is whether you feed the motor externally with current that is already alternating sinusoidally, or whether the motor itself turns external DC into some kind of AC.
Really sounds promising. The question is will the French have the will to build it in bulk on shore in France or Europe? There’s no point if they want to sub it out to the world to build cheaper somewhere else?
This technology does show that you should never give up on industry, research, development and building on shore.
"At the same time, China is also the world's leading producer of electric cars..."
Kind of interesting for a professionally branded company to use "..." like that
How soon to see rare-earth-free paired with CATL Sodium batteries? Seems a price war, range war is imminent.
Could be wrong, but AFAIK the CATL Sodium batteries haven't yet hit LFP pricing.
You are unlikely to see a vehicle with sodium batteries until after that happens, and it needs to be significantly less than LFPs as you Na batteries have more weight per Wh. I believe they also have a shorter lifespan (but not NMC short). Edit correction, looks like CATL is promising 15000 cycles, which is much longer than LFPs which usually come in at 7000 to 10000.
It seems far more likely to me that if the Na prices tank, you'll probably first see them deployed as grid and home battery solutions.
The energy density of LFP batteries are also 30-50% higher than sodium based battery chemistries. Even if sodium battery prices drop, the lower energy density is a big disadvantage. My understanding is that sodium batteries are aimed at stationary use-cases, like battery buffers for fast charging.
At the cell level yes. But at the pack level, you need less/no cooling and there is virtually no risk of runaway fires. This means the cells can be packed more densely and you get some weight benefits for all the stuff you no longer need for fire safety.
CATL already put sodium ion in cheap cars. And there are other benefits to this type of battery like a wider range of operating temperatures that cover essentially all of the extreme temperatures you'd find in the arctic and the hottest deserts.
I would not be surprised to find some of these batteries in big semis a few years down the line when the cost benefits make the space/weight sacrifices worth the trade off.
But you are right that domestic and grid storage are also going to be huge use cases.
For about a half of year there have been cars with sodium-ion batteries, in China. As you say, for now they are more expensive, but it is expected that the price will drop quickly in the following years.
Because they lose neither capacity nor charging speed at low temperatures, like the lithium-ion batteries, they expect that in the future sodium-batteries will be the best choice in the countries with cold climates.
One of the most interesting features of sodium batteries is that they still perform good in cold temperatures.
And high temperatures, too. Meaning they don't require cooling nor heating, basically matching the per kg capacity of ready modules with LFP while being significantly safer and less complex.
They're promising to start selling a Qiyuan A06 variant with Sodium batteries sometime this year... so if you went looking you could probably see one... or will be able to soon.
Looks ideal for a power wall at home.
Superior temperature range in cold weather as well IIRC.
Unlikely.
EESMs are primarily manufactured by European OEMs (ZF, MAHLE, Schaffler, AEM) and their Indian JV partners (Sona Comstar, Sterling, and the India branches of the OEMs listed). Both have been blocked via export controls from accessing battery tech from China over the past few years, and a major reason for the push for EESMs was for an ex-China supply chain, especially after China began export controlling rare earths to the EU [6].
Additonally, Chinese and American EVs tend to use PMSMs unlike European and now Indian EVs. Also, the EU is cracking down on automotive exports (cars and OEMs) from non-FTA states as part of the EU Industrial Accelerator Act (which btw has made China go ballistic [2][3][4][5]).
On the other hand, they will most likely use Japanese or Korean solid-state batteries as Idemetsu Kosan is in the process of mass producing them [0][1] as is LG [7], and both Japan+SK are FTA partners with the EU.
[0] - https://www.chiyodacorp.com/en/projects/solidelectrolytefaci...
[1] - https://battery-tech.net/battery-markets-news/idemitsu-kosan...
[2] - https://www.globaltimes.cn/page/202605/1361926.shtml
[3] - https://www.globaltimes.cn/page/202605/1362200.shtml
[4] - https://www.globaltimes.cn/page/202605/1362161.shtml
[5] - https://www.ft.com/content/5903318c-319b-426e-b05d-062f7620f...
[6] - https://www.reuters.com/world/china/eu-lawmakers-rebuke-chin...
[7] - https://blog.lgchem.com/en/2026/03/25_solid_state_battery/
Say all you want about the inferior efficiency and so on, but if nothing else they have proven that it's viable, even commercially. So the rare earths are really not as vital as they have been made out to be.
One of the most interesting thing about commodity bottlenecks is that they often accelerate substitution ; scarcity can end up by making a material being less important
Electrically excited synchronous machines (EESMs), also known as wound field synchronous machines (WFSMs) have a number of potential advantages and disadvantages compared to interior permanent magnet synchronous machines (IPMSMs). IPMSMs are the dominant motor topology currently in use for North American electric vehicles.
Advantages:
- Not subject to the price and supply chain volatility of rare earth permanent magnets.
- For highway dominant drive cycles, the cycle efficiency of EESMs can be higher than state of the art IPMSMs. EESMs tend to have their best efficiency at moderate torques and high speeds because of their excellent field weakening characteristics. I tend to think that they would be a good fit for application in class 8 trucks or as auxiliary motors in automobiles with two powered axles.
- The output torque doesn't necessarily decrease with rotor temperature. In IPMSMs the permanent magnet flux linkage decreases with rotor temperature.
- At least theoretically, with proper control, it is possible to operate EESMs with unity power factor and decrease the kVA rating of the stator inverter.
- If there is a stator inverter fault, there are schemes to denergize the rotor which have some safety implications.
Disadvantages:
- DC current needs to be transferred to the rotating field winding. For automotive applications this tends to be done either with brushes and slip rings or brushlessly using a high frequency transformer with a rotating rectifier. In either case additional power electronics and other components are needed for the field power transfer and control which reduces some of the potential cost savings of the elimination of the permanent magnets. If brushes and slip rings are used with oil spray/oil jet cooling of the rotor they need to be sealed in a separate compartment. I am a little surprised that Renault has stuck with brushes and slip rings versus an inductive high frequency transformer solution. I think this has limited their power density.
- For very torque dense machines, cooling the rotor field winding is challenging, and in my opinion is best accomplished by oil spray/oil jet cooling.
- It is difficult to reach the same maximum speeds as IPMSMs in an automotive package size. The rotor field winding retention system to keep the field turns from moving into the airgap at high speeds needs considerable attention during the design.
- The overall axial length of the non-active region of EESMs is typically longer than IPMSMs because of the field winding end turns and field excitation system.
- EESM efficiency is dominated by the manufacturable slot fill of the field winding.
- High performance current/torque regulation is considerably more difficult.
High performance EESMs have been used in aerospace generator applications for decades, albeit with a different rotor excitation system than what is used in automotive applications. Renault (and their supplier Continental) really led the commercialization of EESMs into automotive mass production. Now BMW has followed suit and multiple suppliers have EESM designs (Mahle, ZF, etc.) GM had a really nice EESM design and high frequency transformer excitation which they published back in 2014. My colleagues and I built several generations of EESMs as part of U.S. Dept. of Energy projects (https://www.osti.gov/servlets/purl/1837809) and I think they have their place as EV traction motors for certain applications.
I see another advantage..
You can switch a motor without permanent magnets to "idle mode".
I understand in Tesla dual motor configurations, the front motor is without magnets. The excitation field will be turned on when you need extra power, but at crusing speed it does not cause extra "drag". From one teardown I've seen, they even went so far to use cheaper and less efficient IGBTs for the front drive, and more efficient SiC Mosfets for the rear motor (in the same vehicle!). If you need extra acceleration briefly, lower efficiency can be accepted.
It’s interesting that EESMs can be more efficient at high/highway speeds, and it’s something I had read before. This seems to me to be a key advantage of EESMs, because when people worry about EV range, they worry mainly about range on long-distance, high-speed journeys.
(I have a Renault EV and it’s excellent. Aside from the motor technology, it’s relatively light, has a heat pump as standard, and a good-sized battery).
EESMs generally are not great at city driving cycles compared to IPMSMs. They do really excel in field weakening at moderate torques.
Why not just use an induction motor with VFD?
As said in the parent Web page, lower energy efficiency, thus shorter range with the same battery.
Another poster has mentioned that BMW also uses EESMs instead of permanent-motor magnets.
BMW uses EESMs as the main motors, on the rear axle, while they use induction motors as auxiliary motors on the front axle.
Besides being cheaper, the induction motors have the advantage that if they are used only as auxiliary motors, you can cut the power supply to them at any time, in which case they will consume nothing.
So their lower efficiency does not matter, because most of the time they are turned off.
> Besides being cheaper, the induction motors have the advantage that if they are used only as auxiliary motors, you can cut the power supply to them at any time, in which case they will consume nothing.
EESMs have this advantage too, you can simply cut power to the field winding.
https://youtu.be/FHufjrP0xDI?is=xmFQrXGa1dBHM67I
This is a helpful explanation of what this technology is and looks like. (Munro)
It was a dude with motors on a table with a flip board. No animations. No diagrams. When it got to the point about having one of each motor, and using the best, he then said that you use the permanent motor even when the other makes sense. Ok, well then why have the two different kinds of motors? No answer. Just handwaved. If you can't use the induction motor when its most efficient, because thats when the permanent motor is causing spin loss, why have the induction motor at all? No answer.
So. Analog presentation. Actual motors on a desk with a flip chart. No animations. No internal visualizations. One page had diagrams that would have been better super-imposed (or hey, animated). Then one page the begs questions with no answers given.
Weren't Tesla ACIM drive unit motors before Model 3 also magnet-free? I thought they used passive isolated bundles of copper wires and their reluctance as magnets.
Rare earth magnets are just too good for electric motors to go this way. Europe and the US just need to get the rare earth manufacturing going and stop being reliant on china for this stuff.
Mentioned in another HN thread [0]:
They're also used by Nissan [1], BMW [2], and Indian EVs [3].
European firms like ZF, Valeo, MAHLE, and Schaffler along with British firms like AEM have been working with their Indian JVs as well as Indian players like Sona Comstar and Sterling for a couple years now to integrate supply chains for mass-producing EESMs.
EESMs as well as the larger OEM story played a role in helping land the EU-India and the UK-India FTAs because the supply chains for French+Italian (Renault, Stellantis), Japanese (Toyota, Honda, Suzuki), Korean (Hyundai-Kia), and Indian automotive manufacturers merged.
On the other hand, EESM EVs aren't a thing here in North America nor China yet as both primarily use PMSMs (edited typo).
[0] - https://news.ycombinator.com/item?id=48510402
[1] - https://leandesign.com/nissan-ariya-magnet-free-motor-teardo...
[2] - https://www.bmwblog.com/2025/02/20/bmw-gen6-electric-motors-...
[3] - https://www.reuters.com/world/china/india-revs-up-alternate-...
---
Edit: can't reply
> does Nissan still use these motors, the car in the linked article has been discontinued
Yes. The Ariya was discontinued in North America (EDIT: USA, TIL still sold in Canada) but is still manufactured and sold in Asia.
> European and Indian manufacturers/engineering are definitely not in the same category though
It's the same manufacturers and supply chain now.
Renault and their OEMs are the biggest driver for EESM, and Renault's largest markets and manufacturing hubs are France, India, and Romania. Heck, Renault is now going to start exporting it's Made in India cars and parts back to the EU [0] becuase of the EU-India FTA.
And the European OEMs have transferred the IP for EESMs to Indian JVs as I mentioned. It's the same style of tech transfer as Samsung did for BYD and TDK for CATL for battery chemistry in the 2000s. Heck, Valeo [1], MAHLE [2], ZF [3], and Schaffler [4] are opening and expanding factories and R&D hubs dedicated to EV transmission manufacturing in India for domestic and export usecases.
Also, if you've ever driven a Japanese (Toyota, Honda, Suzuki) or Korean (Hyundai, Kia) make care in the EU, Australia, Middle East, Africa, or Asia outside of their home countries their parts sourcing and even the entire manufactured car would have come from India, such as the Toyota Urban Cruiser EV [5].
[0] - https://m.economictimes.com/industry/auto/auto-news/india-eu...
[1] - https://www.valeo.com/en/valeo-inaugurates-new-electric-powe...
[2] - https://auto.economictimes.indiatimes.com/news/auto-technolo...
[3] - https://press.zf.com/press/en/releases/release_66050.html
[4] - https://www.basispointinsight.com/Story/schaeffler-india-ope...
[5] - https://newsroom.toyota.eu/the-all-new-toyota-urban-cruiser/
No, and it was mentioned by the consortium of European cars manufacturers after the joint press release with Der Leyen herself: the implementation of factories and research centers in India is solely to be able to sell on that market. It is the exact same process that happened with China in the past. The exact same also happened with Airbus.
You are also wrong on the market importance for Renault. For 2024, France was the biggest, followed by Italy, Turkey, Spain, Germany, Brazil, UK, Morocco, BENELUX, Romania, Poland, Netherlands and... #13 India with 0.9% market share...
Supply chains didn't change at all, in fact it did the opposite, and Europeans won't rely on anything Indian made for the near future, as local re-industrialization is already acted on and even accelerated since the pandemic.
Production numbers across all manufacturers even Volkswagen (which was unexpected) show the number of cars manufactured in Europe increased in the past 2 years.
Electric cars in Europe mostly come from China, the US and European brands. Nothing Indian-made, not even parts.
Not sure why this was voted down, it was the most useful comment here.
does Nissan still use these motors, the car in the linked article has been discontinued, and then only real info I can find on their site about the leaf is about their ROCKIN' bose sound system/s
Because it's grossly untrue and backed with propaganda slop articles. I suspect this is a bot.
European and Indian manufacturers/engineering are definitely not in the same category though.
> The Ariya was discontinued in North America but is still manufactured and sold in Asia.
The Nissan Ariya is NOT discontinued in North America. Nissan no longer sells it in the USA because of Trump's tariff war.
The Nissan Ariya is still sold in Canada.
what is a prsm? Do you mean pmsm?
It's a bummer they are not really available in the US.
EVs in the US and China tend to use PMSMs, though GM, Stellantis, the DoE, and the DoD are funding an EESM startup [0]
[0] - https://nironmagnetics.com/
Niron is not developing an EESM. They are developing Iron Nitride permanent magnets. These magnets can be used in a variable flux permanent magnet synchronous machine (VFPMSM). Variable flux machines have some similar characteristics to EESMs in terms of their ability to change the field excitation, but they are fundamentally different than EESM in terms of how they do so. EESM change their field excitation and VFPMSMs change the magnetization state through stator current pulses. Their current/torque regulation control is also quite different.
There are other startup companies developing EESMs but not Niron to my knowledge.
Does regenerative braking work with a motor like this?
Yes: IIRC some large generators work exactly like this, as the energized rotor gives a lot more flexibility in managing frequency and power output.
Not just some, approximately all of them. It greatly complicates the logistics of a black start. † Of course that situation has additional complexity due to the need for substantial additional power in order for the various fuel supply systems to operate but I digress.
† https://en.wikipedia.org/wiki/Black_start
Generator excitation is not the hard part of a black start. You have to run coal feeders, blowers, and water pumps for an hour before you can spin the generator. Then you get power instantly upon applying power to the field windings.
And even that's not the hard part of a black start. The plant control is relatively easy. What's hard is grid coordination.
All generation and consumption have to be almost perfectly balanced every second of every day. And the power company doesn't have good addressability of load. Worse when you restore power to an area all their stuff turns on in parallel giving an inrush that could be 3x or more the steady state.
A black start is a very drawn out process of bringing generation and load online in a balanced way and with wait times between load increases for stabilization.
> You have to run coal feeders, blowers, and water pumps for an hour before you can spin the generator.
That's probably the reason most grid black start facilities in my country (Brazil) are hydroelectric dams, which need none of these.
After watching a Munro video about it, I see your point. In the motor shown, the rotor gets its magnetic field simply by inducing a current and a field in it in reaction to the stator's field. There are no electromagnets in the rotor like I expected. In that case, I'm not sure either... I'd say more likely than not but it's complicated since the stator basically needs to induce a field and at the same time recover energy from the field that comes back from the rotor. I would further guess that the phase shift between the two components makes it possible to treat them separately.
Previous comment: Don't see why not - the "field" coils (the ones that replace the permanent magnets) need to be energized, which can initially come from the batteries if necessary.
There are electromagnets in the rotor, it is directly energized.
I own a Zoe for that reason
I also have a Zoé (an R135). Wonderful little machine.
Seems to be: replace permanent Nd magnet with an electromagnet.
There is something... weird about this. this tech has existed.... a long time. And I am not familiar with what is common in electric cars so may be missing something obvious but thought this was already how it was done. let me explain my limited understanding.
With ac motors electromagnets can be used in the rotor. there is even a super clever way to do it where the electromagnet in the rotor is driven wirelessly via induction. there are some downsides but having no physical sliding electrical connection to the rotor is a huge upside. The ac can be dynamically formed from DC via high speed switching(transistors, in industry often called a VFD).
Due to the upsides of ac induction motors I sort of assumed this was already what was found in cars. I am a bit surprised to find out there were rare earth magnets in the first place.
Permanent magnet motors are simpler and cheaper to make, at least in the small (yes, small --- there are electric motors in the MW range in industrial applications, which are themselves larger than an average car) sizes found in EVs.
AC motors are not magic. The core is essentially just a coil with one turn, so it can generate only a very limited magnetic field. So they have to be bulkier for a given power density and generally slightly less efficient.
They even use regular carbon brushes to supply power to the magnet. Munro has a teardown video for a similar motor for Nissan: https://www.youtube.com/watch?v=BFmp9ODkCA8
So does it consume significantly more electricity?
Not really. The excitation power is a small fraction of the total.
The problem is that it makes the rotor far less mechanically robust and also heavier. That's why these motors are less powerful.
let me guess.. but its 2x the price?
no, but requires introduces brushes (slip-rings really) which is a wear item
I don't think car owners have to worry about this the first half million miles or so with these motors. Electrical motors last a long time. We'll know for sure in a few decades, I guess. That's how long it will take for a significant number of their cars to actually drive that far.
Also, compare this to ICE engines which experience continuous explosions, lots of mechanical parts, extreme temperature swings, etc. and still manage pretty decent durability. There's simply no base for assuming that parts like this wearing out and needing to be replaced is going to be a common thing.
The Continental and Renault motors like those in my Kangoo ZE and Zoe have so far proven fairly reliable, with the occasional exception being shaft bearings. The Q210 is particularly robust. I'm not aware of anybody having brush/slip ring issues yet.
Cars already have lots of wear items and a mature service industry for them. If I can reliably get at least 50k miles out of it, then I wouldn't be all that bothered, as this is not likely to be an expensive part or service.
> mature service industry for them
The car service industry is a scam, and I am glad that EVs require minimal to no servicing that cannot be easily DIY like tires and brakes.
Yet they still charge me the same price as my ICE to service! What a scam.
so apparently on the BMW i4s it requires a rear subframe drop which isn't going to be cheap (10s of hours).
The main difference between this and your typical AC induction motors (also magnet free) is that this is a DC motor so you need a commutator. Your AC induction magnet free motors are very similar to drone motors in that you don't have any electrically active moving parts like slip rings and commutators. But for AC induction there will be a slight lag (known as slip).
They are electronically commutated. The stator field is more or less variable AC.
The inductance ones yes, not these ones.