Among the many numerous challenges of decarbonizing transportation, probably the most compelling entails electrical motors. In laboratories everywhere in the world, researchers at the moment are chasing a breakthrough that might kick into excessive gear the transition to electrical transportation: a rugged, compact, highly effective electrical motor that has excessive energy density and the power to face up to excessive temperatures—and that doesn’t have rare-earth everlasting magnets.
It’s an enormous problem presently preoccupying a few of the greatest machine designers on the planet. Various of them are at
ZF Friedrichshafen AG, one of many world’s largest suppliers of components to the automotive trade. In actual fact, ZF astounded analysts late final yr when it introduced that it had constructed a 220-kilowatt traction motor that used no rare-earth components. Furthermore, the corporate introduced, their new motor had traits corresponding 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 course 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 kind known 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 highway in the present day. In a separately-excited synchronous motor, alternating present utilized to the stator electromagnets units up a rotating magnetic subject. A separate present utilized to the rotor electromagnets energizes them, producing a subject that locks on to the rotating stator subject, producing torque.
“As a matter of reality, 95 % of the uncommon earths are mined in China. And which means that if China decides nobody else may have uncommon earths, we will do nothing in opposition to it.”
—Otmar Scharrer, ZF Friedrichshafen AG
To date, 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 very best means to try this. Many such motors use sliders and brushes to make electrical contact to a spinning floor, however the brushes produce mud and finally put on out. Alternatively, the facility will be transferred through inductance, however in that case the equipment is often 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). Moreover not utilizing any uncommon earth components, the motor affords a couple of different benefits compared with permanent-magnet synchronous motors. These are linked to the truth that this sort of motor know-how affords the power to exactly management the magnetic subject within the rotor—one thing that’s not attainable with everlasting magnets. That management, in flip, permits various the sector to get a lot increased effectivity at excessive pace, for instance.
With headquarters in Baden-Württemberg, Germany, ZF Friedrichshafen AG is thought for a
wealthy R&D heritage and many commercially profitable improvements relationship again to 1915, when it started supplying gears and different components for Zeppelins. As we speak, the corporate has some 168,000 staff in 31 international locations. Among the many clients for its motors and electrical drive trains are Mercedes-Benz, BMW, and Jaguar Land Rover. (Late final yr, shortly after saying the I2SM, the corporate introduced the sale of its 3,000,000th 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 Know-how. Our interview with him has been edited for concision and readability.
Otmar Scharrer on…
IEEE Spectrum: Why is it necessary to remove or to cut back using rare-earth components 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: Properly, 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. You want 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, often, they’re dug out of the earth in a mine with excavators and large vans. 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 handle cautiously as a tier one [automotive industry supplier].
And as a matter of reality, 95 % of the uncommon earths are produced in China. And which means that if China decides nobody else may have uncommon earths, we will do nothing in opposition to 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’re ramping up, when you will 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 in case you have a relentless enterprise and also you’re simply changing these items that are failing. I’m certain 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 a distinction.”
—Otmar Scharrer, ZF Friedrichshafen AG
You had requested an excellent query: How a lot rare-earth steel does a typical traction motor comprise? 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 automobiles. And people motors usually 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 will not be new. It has been used for years and years, for many years, as a result of often, energy era is finished with this sort of electrical machine. So in case you have an enormous energy plant, for instance, a gasoline energy plant, then you definately would usually discover such an externally-excited machine as a generator.
We didn’t use them for passenger automobiles or for cell purposes due to their weight and measurement. And a few of that weight-and-size drawback comes instantly from the necessity to generate a magnetic subject within the rotor, to switch the [permanent] magnets. You want to set copper coils below electrical energy. So you want to carry electrical present contained in the rotor. That is often accomplished with sliders. And people sliders generate losses. That is the one factor as a result of you will have, usually, carbon brushes touching a steel ring so as to conduct the electrical energy.
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 then you definately want a fourth part to affect the rotor. And this can be a second impediment. Many OEMs or e-mobility firms should not have this know-how prepared. Surprisingly sufficient, the primary ones who introduced this into severe manufacturing had been [Renault]. It was a really small automotive, 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 change off and change on the magnetic subject. This can be 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. In case you are shifting and the generator is spinning, related to the wheel, then it’s producing electrical energy.
“We’ve an effectivity of roughly 96 %. So, little or no loss.”
—Otmar Scharrer, ZF Friedrichshafen AG
The identical is occurring in an electrical machine within the automotive. In case you are driving on the freeway at 75 miles an hour, after which abruptly your complete system breaks down, what would occur? In a everlasting magnet motor, you’d generate monumental voltage as a result of the rotor magnets are nonetheless rotating within the stator subject. However in a permanent-magnet-free motor, nothing occurs. You’re simply switched off. So it’s self-secure. This can be a good function.
And the second function is even higher in case you drive at excessive pace. Excessive pace is one thing like 75, 80, 90 miles an hour. It’s not too frequent in most international locations. However it’s a German phenomenon, crucial right here.
Individuals wish to drive quick. Then you want to handle the realm of subject weakening as a result of [at high speed], the magnetic subject can be too robust. You want to weaken the sector. And in case you don’t have [permanent] magnets, it’s straightforward: you simply adapt the electrically-induced magnetic subject to the suitable worth, and also you don’t have this field-weakening requirement. And this ends in a lot increased effectivity at excessive speeds.
You known as this subject weakening at excessive pace?
Scharrer: You want to weaken the magnetic subject so as to preserve the operation steady. And this weakening occurs by extra electrical energy coming from the battery. And due to this fact, you will have a decrease effectivity of the electrical motor.
What are essentially 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 rather a lot what we will do to beat this impediment. And we got here to the conclusion, let’s do it inductively, by electrical inductance. And this has been accomplished by rivals as effectively, however they merely changed the slider rings with inductance transmitters.
“We’re satisfied that we will construct the identical measurement, the identical energy degree of electrical motors as with the everlasting magnets.”
—Otmar Scharrer, ZF Friedrichshafen AG
And this didn’t change the state of affairs. 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 due to this fact, we diminished this 50-to-90-millimeter development in axial size. And due to this fact, as a ultimate consequence, you realize the motor shrinks, the housing will get smaller, you will have much less weight, and you’ve got the identical efficiency density 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 subject. And we’re doing it within the rotor shaft. That is the place the vitality is transmitted from exterior to the shaft [and then to the rotor electromagnets].
So the rotor shaft, is that totally 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 will 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 occurring in our rotor shafts.
So you employ coils, specifically designed, and also you induce voltage from one to the opposite?
Scharrer: Sure. And we now have a really neat, small package deal, which has a diameter of lower than 30 millimeters. When you can shrink it to that worth, then you may put it contained in the rotor shaft.
So after all, in case you have two coils, and so they’re spaced subsequent to one another, you will have a spot. In order that hole lets you spin, proper? Since they’re not touching, they will spin independently. So that you needed to design one thing the place the sector might be transferred. In different phrases, they might couple regardless that one among them was spinning.
Scharrer: We’ve a coil within the rotor shaft, which is rotating with the shaft. After which we now have 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. The whole lot occurs contained in the rotor shaft.
What’s the effectivity? How a lot energy do you lose?
Scharrer: We’ve an effectivity of roughly 96 %. So, little or no loss. And for the magnetic subject, you don’t want quite a lot of vitality. You want one thing between 10 and 15 kilowatts for the electrical subject. Let’s assume a transmitted energy of 10 kilowatts, we’ll have losses of about 400 watts. This [relatively low level of loss] is necessary as a result of we don’t cool the unit actively and due to this fact 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 constructions.
“A superb invention is at all times straightforward. When you look as an engineer on good IP, then you definately 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 will construct the identical measurement, the identical energy degree of electrical motors as with the everlasting magnets.
You could possibly do 150- or 300-kilowatt motors?
Scharrer: Completely.
What have you ever accomplished thus far? What prototypes have you ever constructed?
Scharrer: We’ve a prototype with 220 kilowatts. And we will simply improve it to 300, for instance. Or we will shrink it to 150. That’s at all times straightforward.
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 match, as a result of it at all times depends upon 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 a distinction.
What automakers do you presently have agreements with? Are you offering electrical motors for sure automakers? Who’re a few of your clients 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’t discuss 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 automated transmission with a hybrid electrical motor as much as 160 kilowatts. It’s probably the greatest hybrid transmissions as a result of you may drive totally electrically with 160 kilowatts, which is kind 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 in accordance with our greatest information, this by no means occurred earlier than.”
—Otmar Scharrer, ZF Friedrichshafen AG
What had been the foremost challenges you needed to overcome, to transmit the facility contained in the rotor shaft?
Scharrer: The key problem is, at all times, it must be very small. On the identical time, it must be tremendous dependable, and it must be straightforward.
A superb invention is at all times straightforward. Once you see it, in case you look as an engineer on good IP [intellectual property], then you definately say, “Okay, that appears good”—it’s fairly apparent that it’s a good suggestion. If the concept is advanced and it must be defined and also you don’t perceive it, then often this isn’t a good suggestion to be carried out. And this one could be very straightforward. Simple. It’s a good suggestion: Shrink it, put it into the rotor shaft.
So that you imply very straightforward 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 will lower the extra size out of the magnet-free motor.” Okay. That’s a great reply.
We’ve quite a lot of IP right here. That is necessary as a result of in case you have the concept, I imply, the concept is the principle factor.
What had been the particular financial savings in weight and rotor shaft and so forth?
Scharrer: Properly, once more, I’d simply reply in a really normal means. 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 in accordance with our greatest information, this by no means occurred earlier than.
Do you assume the motor shall be obtainable earlier than the top of this yr or maybe subsequent yr?
Scharrer: You imply obtainable for a severe utility?
Sure. If Volkswagen got here to you and stated, “Look, we wish to use this in our subsequent automotive,” might you do this earlier than the top of this yr, or wouldn’t it should 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 trade, you will have A, B, or C. For A-sample, you will have all of the features, 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 might 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 %.
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