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Electric motors with no rare earths

660 points by bestouff

by adrian_b

11 subcomments

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.

by userbinator

5 subcomments

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.

by bgarbiak

2 subcomments

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.

by kopirgan

1 subcomments

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.

by Danox

0 subcomment

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.

by willXare

1 subcomments

"Replace the magnet with a controllable magnet" is probably the most automotive-engineering sentence possible.

by dcanelhas

1 subcomments

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?

by giobox

3 subcomments

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.

by latentframe

0 subcomment

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

by ZedZark

0 subcomment

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.

by E-Reverance

0 subcomment

"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

by delfugal

2 subcomments

How soon to see rare-earth-free paired with CATL Sodium batteries? Seems a price war, range war is imminent.

by ipbrown

2 subcomments

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.

by RobotToaster

1 subcomments

Why not just use an induction motor with VFD?

by derac

1 subcomments

https://youtu.be/FHufjrP0xDI?is=xmFQrXGa1dBHM67I
This is a helpful explanation of what this technology is and looks like. (Munro)

by numpad0

0 subcomment

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.

by PowerElectronix

0 subcomment

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.

by MrDrMcCoy

1 subcomments

It's a bummer they are not really available in the US.

by isopede

2 subcomments

Does regenerative braking work with a motor like this?

by general_error

1 subcomments

I own a Zoe for that reason

by alephnerd

5 subcomments

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/

by dmitrygr

3 subcomments

Seems to be: replace permanent Nd magnet with an electromagnet.

by hijinks

1 subcomments

let me guess.. but its 2x the price?

by Onavo

1 subcomments

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).

by teiji-tango

0 subcomment

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by aaron695

0 subcomment

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by letmutt

0 subcomment

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by GreenSalem

0 subcomment

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