Among the many numerous challenges of decarbonizing transportation, one of the crucial compelling entails electrical motors. In laboratories everywhere in 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 power 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 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 similar to the rare-earth permanent-magnet synchronous motors that now dominate in electrical autos. 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 corporate has not but revealed its motor’s particular energy—its kW/kg score.)
The ZF machine is a sort 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 practically all EV motors on the highway immediately. 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 which means if China decides nobody else can have uncommon earths, we will 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 excellent manner to do 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 ability might be transferred through inductance, however in that case the equipment is often cumbersome, making the unit sophisticated 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). In addition to not utilizing any uncommon earth parts, the motor affords a couple of different benefits compared with permanent-magnet synchronous motors. These are linked to the truth that this type of motor know-how affords the power 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 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 courting again to 1915, when it started supplying gears and different elements for Zeppelins. Right now, the corporate has some 168,000 staff 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 3,000,000th motor.)
Has ZF simply proven the best way ahead for rare-earth-free EV motors? To be taught 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 necessary to remove or to scale back the usage of 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 upon 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 have to transfer lots 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 large vans. That generates some environmental air pollution and, in fact, 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 tackle cautiously as a tier one [automotive industry supplier].
And as a matter of truth, 95 % of the uncommon earths are produced in China. And which means if China decides nobody else can have uncommon earths, we will do nothing towards 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. If you end up ramping up, when you’ve gotten a steep ramp up by way of 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 positive this may 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 inform you that there is no such thing as 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 attention-grabbing 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 rationale for this [permanent-] magnet-free motor. The idea itself is just not new. It has been used for years and years, for many years, as a result of often, energy technology is finished with this type of electrical machine. So in case 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 drawback comes immediately from the necessity to generate a magnetic discipline within the rotor, to exchange the [permanent] magnets. You have to set copper coils underneath electrical energy. So you might want to carry electrical present contained in the rotor. That is often finished with sliders. And people sliders generate losses. That is the one factor as a result of you’ve gotten, sometimes, carbon brushes touching a steel ring as a way 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 you then want a fourth section 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 critical manufacturing have 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 automobile, there’s an enormous benefit with this type of externally excited machine. You possibly can swap off and swap on the magnetic discipline. 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. If you’re shifting and the generator is spinning, linked to the wheel, then it’s producing electrical energy.
“We have now 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. 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’d generate monumental 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. This can be a good characteristic.
And the second characteristic 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. But it surely’s a German phenomenon, crucial right here.
Individuals prefer to drive quick. Then you might want to tackle the realm of discipline weakening as a result of [at high speed], the magnetic discipline can be too robust. You have to weaken the sector. And in case 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 increased effectivity at excessive speeds.
You known as this discipline weakening at excessive pace?
Scharrer: You have to weaken the magnetic discipline with a purpose to preserve the operation steady. And this weakening occurs by extra electrical energy coming from the battery. And due to this fact, you’ve gotten a decrease effectivity of the electrical motor.
What are essentially 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 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 finished by opponents as properly, however they merely changed the slider rings with inductance transmitters.
“We’re satisfied that we will 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 have been shrinking the inductive unit to the scale 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 progress in axial size. And due to this fact, as a last consequence, you already know the motor shrinks, the housing will get smaller, you’ve gotten 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 just transmit electrical energy with out touching something. You do it with a magnetic discipline. And we’re doing it within 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’ve gotten 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 utilize 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. For those who can shrink it to that worth, then you’ll be able to put it contained in the rotor shaft.
So in fact, in case you have two coils, they usually’re spaced subsequent to one another, you’ve gotten a spot. In order that hole allows you to spin, proper? Since they’re not touching, they’ll spin independently. So that you needed to design one thing the place the sector may very well be transferred. In different phrases, they may couple though considered one of them was spinning.
Scharrer: We have now 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. Every part occurs contained in the rotor shaft.
What’s the effectivity? How a lot energy do you lose?
Scharrer: We have now an effectivity of roughly 96 %. So, little or no loss. And for the magnetic discipline, you don’t want lots of power. You want one thing between 10 and 15 kilowatts for the electrical discipline. 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 type 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.
“An excellent invention is at all times simple. For those who look as an engineer on good IP, you then say, ‘Okay, that appears good.’”
—Otmar Scharrer, ZF Friedrichshafen AG
What are the biggest motors you’ve constructed or what are the biggest motors you suppose you’ll be able to construct, in kilowatts?
Scharrer: We don’t suppose that there’s a limitation with this know-how. We’re satisfied that we will 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.
What have you ever finished up to now? What prototypes have you ever constructed?
Scharrer: We have now 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 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 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 properly. What a part of the housing are you together with within the calculation? However I can inform you one factor: The facility density is identical as for a permanent-magnet machine as a result of we produce each. And I can inform you that there is no such thing as a 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, in fact, in improvement with lots of different purposes. And I believe you perceive that I can’t discuss that.
So for BMW, Land Rover, Mercedes-Benz, you’re offering electrical motors and drivetrain parts?
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 the most effective hybrid transmissions as a result of you’ll be able to 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 keeping with our greatest data, this by no means occurred earlier than.”
—Otmar Scharrer, ZF Friedrichshafen AG
What have been the main challenges you needed to overcome, to transmit the ability contained in the rotor shaft?
Scharrer: The foremost problem is, at all times, it must be very small. On the identical time, it must be tremendous dependable, and it must be simple.
An excellent invention is at all times simple. While you see it, in case 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 may 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. Straightforward 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 will lower the extra size out of the magnet-free motor.” Okay. That’s an excellent reply.
We have now lots of IP right here. That is necessary as a result of in case you have the thought, I imply, the thought is the principle factor.
What have been the particular financial savings in weight and rotor shaft and so forth?
Scharrer: Properly, once more, I’d simply reply in a really basic manner. We achieved the identical values, for energy density and different traits, as for a [permanent] magnet motor. And that is actually a breakthrough as a result of in keeping with our greatest data, this by no means occurred earlier than.
Do you suppose the motor can be obtainable earlier than the tip of this 12 months or maybe subsequent 12 months?
Scharrer: You imply obtainable for a critical utility?
Sure. If Volkswagen got here to you and stated, “Look, we need to use this in our subsequent automotive,” might you try this earlier than the tip of this 12 months, or wouldn’t it need to be 2025?
Scharrer: It must be 2025. I imply, technically, the electrical motor may 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 gotten A, B, or C. For A-sample, you’ve gotten 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 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 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 %.
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