Among the many numerous challenges of decarbonizing transportation, probably the most compelling entails electrical motors. In laboratories all around the world, researchers are actually chasing a breakthrough that would kick into excessive gear the transition to electrical transportation: a rugged, compact, highly effective electrical motor that has excessive energy density and the flexibility to face up to excessive temperatures—and that doesn’t have rare-earth everlasting magnets.

It’s an enormous problem at the moment preoccupying a number of the greatest machine designers on the planet. Quite a lot of of them are at
ZF Friedrichshafen AG, one of many world’s largest suppliers of elements to the automotive business. In reality, ZF astounded analysts late final 12 months when it introduced that it had constructed a 220-kilowatt traction motor that used no rare-earth parts. Furthermore, the corporate introduced, their new motor had traits akin to the rare-earth permanent-magnet synchronous motors that now dominate in electrical automobiles. Most EVs have rare-earth-magnet-based motors starting from 150 to 300 kilowatts, and energy densities between 1.1 and three.0 kilowatts per kilogram. In the meantime, the corporate says they’ve developed a rare-earth-free motor proper in the midst of that vary: 220 kW. (The comany has not but revealed its motor’s particular energy—its kW/kg score.)

The ZF machine is a sort referred to as a separately-excited (or doubly-excited) synchronous motor. It has electromagnets in each the stator and the rotor, so it does away with the rare-earth everlasting magnets used within the rotors of almost all EV motors on the street at the moment. In a separately-excited synchronous motor, alternating present utilized to the stator electromagnets units up a rotating magnetic area. A separate present utilized to the rotor electromagnets energizes them, producing a area that locks on to the rotating stator area, producing torque.

“As a matter of truth, 95 % of the uncommon earths are mined in China. And because of this if China decides nobody else could have uncommon earths, we are able to do nothing towards it.”
—Otmar Scharrer, ZF Friedrichshafen AG

To this point, these machines haven’t been used a lot in EVs, as a result of they require a separate system to switch energy to the spinning rotor magnets, and there’s no splendid method to try this. Many such motors use sliders and brushes to make electrical contact to a spinning floor, however the brushes produce mud and ultimately put on out. Alternatively, the ability might be transferred through inductance, however in that case the equipment is usually cumbersome, making the unit sophisticated and bodily giant and heavy.

Now, although, ZF says it has solved these issues with its experimental motor, which it calls
I²SM (for In-Rotor Inductive-Excited Synchronous Motor). In addition to not utilizing any uncommon earth parts, the motor affords a couple of different benefits as compared with permanent-magnet synchronous motors. These are linked to the truth that this sort of motor know-how affords the flexibility to exactly management the magnetic area within the rotor—one thing that’s not doable with everlasting magnets. That management, in flip, permits various the sphere to get a lot increased effectivity at excessive velocity, for instance.

With headquarters in Baden-Württemberg, Germany, ZF Friedrichshafen AG is thought for a
wealthy R&D heritage and many commercially profitable improvements courting again to 1915, when it started supplying gears and different elements for Zeppelins. Immediately, the corporate has some 168,000 workers in 31 international locations. Among the many prospects for its motors and electrical drive trains are Mercedes-Benz, BMW, and Jaguar Land Rover. (Late final 12 months, shortly after asserting the I²SM, the corporate introduced the sale of its 3,000,000^th motor.)

Has ZF simply proven the way in which ahead for rare-earth-free EV motors? To study extra in regards to the I
²SM and ZF’s imaginative and prescient of the way forward for EV traction motors, Spectrum reached out to Otmar Scharrer, ZF’s Senior Vice President, R&D, of Electrified Powertrain Expertise. Our interview with him has been edited for concision and readability.

Otmar Scharrer on…

IEEE Spectrum: Why is it essential to get rid of or to cut back using rare-earth parts in traction motors?

ZF Friedrichshafen AG’s Otmar Scharrer is main a staff discovering methods to construct motors that don’t rely on everlasting magnets—and China’s rare-earth monopolies. ZF Group

Otmar Scharrer: Nicely, there are two causes for that. One is sustainability. We name them “uncommon earth” as a result of they are surely uncommon within the earth. It is advisable to transfer quite a lot of soil to get to those supplies. Due to this fact, they’ve a comparatively excessive footprint as a result of, normally, they’re dug out of the earth in a mine with excavators and big vehicles. That generates some environmental air pollution and, after all, a change of the panorama. That’s one factor. The opposite is that they’re comparatively costly. And naturally, that is one thing we at all times deal with cautiously as a tier one [automotive industry supplier].

And as a matter of truth, 95 % of the uncommon earths are produced in China. And because of this if China decides nobody else could have uncommon earths, we are able to do nothing towards it. The recycling circle [for rare earth elements] won’t work as a result of there are simply not sufficient electrical motors on the market. They nonetheless have an energetic lifetime. When you find yourself ramping up, when you might have a steep ramp up when it comes to quantity, you by no means can fulfill your calls for with recycling. Recycling will solely work when you have a continuing enterprise and also you’re simply changing these items that are failing. I’m positive it will come, however we see this a lot later when the steep ramp-up has ended.

“The facility density is identical as for a permanent-magnet machine, as a result of we produce each. And I can let you know that there isn’t any distinction.”
—Otmar Scharrer, ZF Friedrichshafen AG

You had requested an excellent query: How a lot rare-earth steel does a typical traction motor include? I needed to ask my engineers. That is an fascinating query. Most of our electrical motors are within the vary of 150 to 300 kilowatts. That is the principle vary of energy for passenger vehicles. And people motors sometimes have 1.5 kilograms of magnet materials. And 0.5 % to 1 % out of this materials is pure [heavy rare-earth elements]. So this isn’t an excessive amount of. It’s solely 5 to fifteen grams. However, sure, it’s a really difficult-to-get materials.

That is the explanation for this [permanent-] magnet-free motor. The idea itself just isn’t new. It has been used for years and years, for many years, as a result of normally, energy era is finished with this sort of electrical machine. So when you have an enormous energy plant, for instance, a gasoline energy plant, you then would sometimes discover such an externally-excited machine as a generator.

We didn’t use them for passenger vehicles or for cellular purposes due to their weight and dimension. And a few of that weight-and-size downside comes straight from the necessity to generate a magnetic area within the rotor, to exchange the [permanent] magnets. It is advisable to set copper coils beneath electrical energy. So you must carry electrical present contained in the rotor. That is normally achieved with sliders. And people sliders generate losses. That is the one factor as a result of you might have, sometimes, carbon brushes touching a steel ring so that you could conduct the electrical energy.

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These brushes are what make the unit longer, axially, within the course of the axle?

Scharrer: Precisely. That’s the purpose. And also you want an inverter which is ready to excite the electrical machine. Regular inverters have three phases, and you then want a fourth part to impress the rotor. And it is a second impediment. Many OEMs or e-mobility corporations do not need this know-how prepared. Surprisingly sufficient, the primary ones who introduced this into severe manufacturing had been [Renault]. It was a really small automobile, a Renault. [Editor’s note: the model was the Zoe, which was manufactured from 2013 until March of this year.]

It had a comparatively weak electrical motor, simply 75 or 80 kilowatts. They determined to do that as a result of in an electrical car, there’s an enormous benefit with this sort of externally excited machine. You’ll be able to swap off and swap on the magnetic area. It is a nice security benefit. Why security? Give it some thought. In case your bicycle has a generator [for a headlight], it really works like an electrical motor. If you’re transferring and the generator is spinning, linked to the wheel, then it’s producing electrical energy.

“We now have an effectivity of roughly 96 %. So, little or no loss.”
—Otmar Scharrer, ZF Friedrichshafen AG

The identical is going on in an electrical machine within the automobile. If you’re driving on the freeway at 75 miles an hour, after which all of the sudden your entire system breaks down, what would occur? In a everlasting magnet motor, you’ll generate huge voltage as a result of the rotor magnets are nonetheless rotating within the stator area. However in a permanent-magnet-free motor, nothing occurs. You’re simply switched off. So it’s self-secure. It is a good characteristic.

And the second characteristic is even higher should you drive at excessive velocity. Excessive velocity is one thing like 75, 80, 90 miles an hour. It’s not too widespread in most international locations. Nevertheless it’s a German phenomenon, crucial right here.

Folks wish to drive quick. Then you must deal with the realm of area weakening as a result of [at high speed], the magnetic area could be too robust. It is advisable to weaken the sphere. And should you don’t have [permanent] magnets, it’s simple: you simply adapt the electrically-induced magnetic area to the suitable worth, and also you don’t have this field-weakening requirement. And this leads to a lot increased effectivity at excessive speeds.

You referred to as this area weakening at excessive velocity?

Scharrer: It is advisable to weaken the magnetic area with a view to preserve the operation secure. And this weakening occurs by further electrical energy coming from the battery. And subsequently, you might have a decrease effectivity of the electrical motor.

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What are probably the most promising ideas for future EV motors?

Scharrer: We imagine that our idea is most promising, as a result of as you identified a few minutes in the past, we’re rising in precise size after we do an externally excited motor. We thought so much what we are able to do to beat this impediment. And we got here to the conclusion, let’s do it inductively, by electrical inductance. And this has been achieved by opponents as effectively, however they merely changed the slider rings with inductance transmitters.

“We’re satisfied that we are able to construct the identical dimension, the identical energy stage of electrical motors as with the everlasting magnets.”
—Otmar Scharrer, ZF Friedrichshafen AG

And this didn’t change the scenario. What we did, we had been shrinking the inductive unit to the dimensions of the rotor shaft, after which we put it contained in the shaft. And subsequently, we decreased this 50-to-90-millimeter development in axial size. And subsequently, as a remaining end result, the motor shrinks, the housing will get smaller, you might have much less weight, and you’ve got the identical efficiency density as compared with a PSM [permanent-magnet synchronous motor] machine.

What’s an inductive exciter precisely?

Scharrer: Inductive exciter means nothing else than that you simply transmit electrical energy with out touching something. You do it with a magnetic area. And we’re doing it inside the rotor shaft. That is the place the power is transmitted from outdoors to the shaft [and then to the rotor electromagnets].

So the rotor shaft, is that completely different from the motor shaft, the precise torque shaft?

Scharrer: It’s the identical.

The factor I do know with inductance is in a transformer, you might have coils subsequent to one another and you may induce a voltage from the energized coil within the different coil.

Scharrer: That is precisely what is going on in our rotor shafts.

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So you utilize coils, specifically designed, and also you induce voltage from one to the opposite?

Scharrer: Sure. And we’ve got a really neat, small bundle, which has a diameter of lower than 30 millimeters. If you happen to can shrink it to that worth, then you may put it contained in the rotor shaft.

So after all, when you have two coils, they usually’re spaced subsequent to one another, you might have a spot. In order that hole allows you to spin, proper? Since they’re not touching, they will spin independently. So that you needed to design one thing the place the sphere may very well be transferred. In different phrases, they might couple regardless that considered one of them was spinning.

Scharrer: We now have a coil within the rotor shaft, which is rotating with the shaft. After which we’ve got one other one that’s stationary contained in the rotor shaft whereas the shaft rotates round it. And there’s an air hole in between. All the pieces occurs contained in the rotor shaft.

What’s the effectivity? How a lot energy do you lose?

Scharrer: We now have an effectivity of roughly 96 %. So, little or no loss. And for the magnetic area, you don’t want quite a lot of power. You want one thing between 10 and 15 kilowatts for the electrical area. Let’s assume a transmitted energy of 10 kilowatts, we’ll have losses of about 400 watts. This [relatively low level of loss] is essential as a result of we don’t cool the unit actively and subsequently it wants this sort of excessive effectivity.

The motor isn’t cooled with liquids?

Scharrer: The motor itself is actively cooled, with oil, however the inductive unit is passively cooled, with warmth switch to close by cooling buildings.

“A great invention is at all times simple. If you happen to look as an engineer on good IP, you then say, ‘Okay, that appears good.’”
—Otmar Scharrer, ZF Friedrichshafen AG

What are the most important motors you’ve constructed or what are the most important motors you assume you may construct, in kilowatts?

Scharrer: We don’t assume that there’s a limitation with this know-how. We’re satisfied that we are able to construct the identical dimension, the identical energy stage of electrical motors as with the everlasting magnets.

You can do 150- or 300-kilowatt motors?

Scharrer: Completely.

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What have you ever achieved thus far? What prototypes have you ever constructed?

Scharrer: We now have a prototype with 220 kilowatts. And we are able to simply improve it to 300, for instance. Or we are able to shrink it to 150. That’s at all times simple.

And what’s your particular energy of this motor?

Scharrer: You imply kilowatts per kilogram? I can’t let you know, to be fairly trustworthy. It’s exhausting to check, as a result of it at all times will depend on the place the borderline is. You by no means have a motor by itself. You at all times want a housing as effectively. What a part of the housing are you together with within the calculation? However I can let you know one factor: The facility density is identical as for a permanent-magnet machine as a result of we produce each. And I can let you know that there isn’t any distinction.

What automakers do you at the moment have agreements with? Are you offering electrical motors for sure automakers? Who’re a few of your prospects now?

Scharrer: We’re offering our devoted hybrid transmissions to BMW, to Jaguar Land Rover, and our electric-axle drives to Mercedes-Benz and Geely Lotus, for instance. And we’re, after all, in growth with quite a lot of different purposes. And I feel you perceive that I can not speak about that.

So for BMW, Land Rover, Mercedes-Benz, you’re offering electrical motors and drivetrain elements?

Scharrer: BMW and Land Rover. We offer devoted hybrid transmissions. We offer an eight-speed computerized transmission with a hybrid electrical motor as much as 160 kilowatts. It’s the most effective hybrid transmissions as a result of you may drive totally electrically with 160 kilowatts, which is sort of one thing.

“We achieved the identical values, for energy density and different traits, for as for a [permanent] magnet motor. And that is actually a breakthrough as a result of based on our greatest data, this by no means occurred earlier than.”
—Otmar Scharrer, ZF Friedrichshafen AG

What had been the most important challenges you needed to overcome, to transmit the ability contained in the rotor shaft?

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Scharrer: The most important problem is, at all times, it must be very small. On the identical time, it must be tremendous dependable, and it must be simple.

A great invention is at all times simple. Whenever you see it, should you look as an engineer on good IP [intellectual property], you then say, “Okay, that appears good”—it’s fairly apparent that it’s a good suggestion. If the thought is advanced and it must be defined and also you don’t perceive it, then normally this isn’t a good suggestion to be carried out. And this one could be very simple. Easy. It’s a good suggestion: Shrink it, put it into the rotor shaft.

So that you imply very simple to clarify?

Scharrer: Sure. Simple to clarify as a result of it’s clearly an fascinating concept. You simply say, “Let’s use a part of the rotor shaft for the transmission of the electrical energy into the rotor shaft, after which we are able to reduce the extra size out of the magnet-free motor.” Okay. That’s reply.

We now have quite a lot of IP right here. That is essential as a result of when you have the thought, I imply, the thought is the principle factor.

What had been the particular financial savings in weight and rotor shaft and so forth?

Scharrer: Nicely, once more, I might simply reply in a really common method. We achieved the identical values, for energy density and different traits, for as for a [permanent] magnet motor. And that is actually a breakthrough as a result of based on our greatest data, this by no means occurred earlier than.

Do you assume the motor can be out there earlier than the tip of this 12 months or maybe subsequent 12 months?

Scharrer: You imply out there for a severe software?

Sure. If Volkswagen got here to you and stated, “Look, we need to use this in our subsequent automobile,” might you do this earlier than the tip of this 12 months, or would it not need to be 2025?

Scharrer: It must be 2025. I imply, technically, the electrical motor could be very far alongside. It’s already in an A-sample standing, which suggests we’re…

What sort of standing?

Scharrer: A-sample. Within the automotive business, you might have A, B, or C. For A-sample, you might have all of the capabilities, and you’ve got all of the options of the product, and people are secured. After which B- is, you aren’t producing any longer within the prototype store, however you might be producing near a probably severe manufacturing line. C-sample means you might be producing on severe fixtures and instruments, however not on a [mass-production] line. And so that is an A-sample, that means it’s about one and a half years away from a standard SOP [“Start of Production”] with our buyer. So we may very well be very quick.

This text was up to date on 15 April 2024. An earlier model of this text gave an incorrect determine for the effectivity of the inductive exciter used within the motor. This effectivity is 96 %, not 98 or 99 %.