Among the many numerous challenges of decarbonizing transportation, one of the vital 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 among the finest 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 business. 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 similar 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 kind 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 highway at present. In a separately-excited synchronous motor, alternating present utilized to the stator electromagnets units up a rotating magnetic discipline. A separate present utilized to the rotor electromagnets energizes them, producing a discipline that locks on to the rotating stator discipline, 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 may have uncommon earths, we are able to do nothing in opposition to 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 ultimate means to do 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 may be transferred by way of inductance, however in that case the equipment is often cumbersome, making the unit difficult and bodily massive 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 just a few different benefits 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 discipline within the rotor—one thing that’s not attainable with everlasting magnets. That management, in flip, permits various the sector to get a lot larger effectivity at excessive pace, for instance.
With headquarters in Baden-Württemberg, Germany, ZF Friedrichshafen AG is understood 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. At present, the corporate has some 168,000 staff in 31 nations. Among the many prospects 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 I2SM 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 eradicate or to scale back the usage of rare-earth components in traction motors?
ZF Friedrichshafen AG’s Otmar Scharrer is main a crew discovering methods to construct motors that don’t depend upon 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’s essential to transfer loads of soil to get to those supplies. Subsequently, they’ve a comparatively excessive footprint as a result of, often, 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 all the time 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 may have uncommon earths, we are able to do nothing in opposition to it. The recycling circle [for rare earth elements] is not going to 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’ve got a steep ramp up by way of 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 certain this may come, however we see this a lot later when the steep ramp-up has ended.
“The facility density is similar as for a permanent-magnet machine, as a result of we produce each. And I can inform you 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 comprise? I needed to ask my engineers. That is an attention-grabbing query. Most of our electrical motors are within the vary of 150 to 300 kilowatts. That is the primary 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 shouldn’t be new. It has been used for years and years, for many years, as a result of often, energy era is completed with this sort of electrical machine. So when you have an enormous energy plant, for instance, a fuel energy plant, you then 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 dimension. And a few of that weight-and-size drawback comes straight from the necessity to generate a magnetic discipline within the rotor, to switch the [permanent] magnets. It’s essential to set copper coils underneath electrical energy. So you’ll want to carry electrical present contained in the rotor. That is often carried out with sliders. And people sliders generate losses. That is the one factor as a result of you’ve got, usually, carbon brushes touching a steel ring in an effort to conduct the electrical energy.
These brushes are what make the unit longer, axially, within the path 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 affect the rotor. And it is a second impediment. Many OEMs or e-mobility firms would not have this know-how prepared. Surprisingly sufficient, the primary ones who introduced this into critical 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 automobile, there’s an enormous benefit with this sort of externally excited machine. You possibly can swap off and swap on the magnetic discipline. 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. In case you are transferring and the generator is spinning, linked to the wheel, then it’s producing electrical energy.
“Now we have an effectivity of roughly 98 %, 99 %. So, little or no loss.” —Otmar Scharrer, ZF Friedrichshafen AG
The identical is going on in an electrical machine within the automobile. In case you are driving on the freeway at 75 miles an hour, after which instantly 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 discipline. However in a permanent-magnet-free motor, nothing occurs. You might be 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 pace. Excessive pace is one thing like 75, 80, 90 miles an hour. It’s not too frequent in most nations. But it surely’s a German phenomenon, crucial right here.
Individuals prefer to drive quick. Then you’ll want to deal with the world of discipline weakening as a result of [at high speed], the magnetic discipline can be too robust. It’s essential to weaken the sector. And should you don’t have [permanent] magnets, it’s simple: you simply adapt the electrically-induced magnetic discipline to the suitable worth, and also you don’t have this field-weakening requirement. And this leads to a lot larger effectivity at excessive speeds.
You referred to as this discipline weakening at excessive pace?
Scharrer: It’s essential to weaken the magnetic discipline in an effort to hold the operation secure. And this weakening occurs by further electrical energy coming from the battery. And subsequently, you’ve got a decrease effectivity of the electrical motor.
What are probably the most promising ideas for future EV motors?
Scharrer: We consider 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 once we do an externally excited motor. We thought quite a bit 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 carried out by rivals 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 degree 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 last consequence, the motor shrinks, the housing will get smaller, you’ve got 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 discipline. And we’re doing it inside 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 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’ve got coils subsequent to one another and you’ll induce a voltage from the energized coil within the different coil.
Scharrer: That is precisely what is going on 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. If you happen to can shrink it to that worth, then you possibly can put it contained in the rotor shaft.
So after all, when you have two coils, and so they’re spaced subsequent to one another, you’ve got a spot. In order that hole lets you spin, proper? Since they’re not touching, they’ll spin independently. So that you needed to design one thing the place the sector might be transferred. In different phrases, they might couple despite the fact that one in every of them was spinning.
Scharrer: Now we have 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 may be 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: Now we have an effectivity of roughly 98 %, 99 %. So, little or no loss. And for the magnetic discipline, you don’t want loads of vitality. You want one thing between 10 and 15 kilowatts for the electrical discipline. So that you lose 1 % of that. That is necessary 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 is cooled, however the inductive unit shouldn’t be cooled.
“An excellent invention is all the time 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 possibly can 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 degree of electrical motors as with the everlasting magnets.
You possibly can do 150- or 300-kilowatt motors?
Scharrer: Completely.
What have you ever carried out up to now? What prototypes have you ever constructed?
Scharrer: Now we 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 all the time simple.
And what’s your particular energy of this motor?
Scharrer: You imply kilowatts per kilogram? I can’t inform you, to be fairly trustworthy. It’s onerous to match, as a result of it all the time is dependent upon the place the borderline is. You by no means have a motor by itself. You all the time want a housing as effectively. What a part of the housing are you together with within the calculation? However I can inform you one factor: The facility density is similar as for a permanent-magnet machine as a result of we produce each. And I can inform you 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. The [Mercedes] EQA, -B, and -C are outfitted by us, for instance, these three automobiles. And we’re, after all, in improvement with loads of different purposes. And I believe you perceive that I can not 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 computerized transmission with a hybrid electrical motor as much as 160 kilowatts. It’s the most effective hybrid transmissions as a result of you possibly can drive absolutely 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 in response to our greatest information, this by no means occurred earlier than.” —Otmar Scharrer, ZF Friedrichshafen AG
What had been the main challenges you needed to overcome, to transmit the ability contained in the rotor shaft?
Scharrer: The key problem is, all the time, it must be very small. On the identical time, it must be tremendous dependable, and it must be simple.
An excellent invention is all the time simple. While 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 often this isn’t a good suggestion to be applied. And this one could be very simple. Simple. It’s a good suggestion: Shrink it, put it into the rotor shaft.
So that you imply very simple to elucidate?
Scharrer: Sure. Simple to elucidate as a result of it’s clearly an attention-grabbing thought. 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 minimize the extra size out of the magnet-free motor.” Okay. That’s a very good reply.
Now we have loads of IP right here. That is necessary as a result of when you have the thought, I imply, the thought is the primary factor.
What had been the particular financial savings in weight and rotor shaft and so forth?
Scharrer: Nicely, once more, I’d simply reply in a really common 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 response to our greatest information, this by no means occurred earlier than.
Do you assume the motor will likely be out there earlier than the tip of this yr or maybe subsequent yr?
Scharrer: You imply out there for a critical software?
Sure. If Volkswagen got here to you and mentioned, “Look, we wish to use this in our subsequent automobile,” may you do this earlier than the tip of this yr, or would it not must 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 implies we’re…
What sort of standing?
Scharrer: A-sample. Within the automotive business, you’ve got A, B, or C. For A-sample, you’ve got 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 critical manufacturing line. C-sample means you might be producing on critical 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 traditional SOP [“Start of Production”] with our buyer. So we might be very quick.
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