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Among the many numerous challenges of decarbonizing transportation, some of the compelling includes 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 flexibility to resist excessive temperatures—and that doesn’t have rare-earth everlasting magnets.
It’s an enormous problem at present 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 actual fact, 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 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 in the present day. 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 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 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 very best method 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 facility 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 just a few different benefits compared with permanent-magnet synchronous motors. These are linked to the truth that this type of motor expertise affords the flexibility to exactly management the magnetic area within the rotor—one thing that’s not attainable with everlasting magnets. That management, in flip, permits various the sphere to get a lot greater effectivity at excessive velocity, for instance.
With headquarters in Baden-Württemberg, Germany, ZF Friedrichshafen AG is understood 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. At this time, 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 12 months, shortly after asserting 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 be taught extra concerning 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 vital 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: Effectively, 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 good 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 large 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 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] 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’ve got a continuing 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 similar 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 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 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 rationale 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 often, energy era is finished with this type of electrical machine. So when you’ve got an enormous energy plant, for instance, a gasoline energy plant, then you definitely would usually 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 straight from the necessity to generate a magnetic area within the rotor, to switch the [permanent] magnets. It’s good to set copper coils below electrical energy. So that you must carry electrical present contained in the rotor. That is often executed 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 then you definitely want a fourth section to affect the rotor. And it is a second impediment. Many OEMs or e-mobility firms shouldn’t have this expertise 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 type 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. In case you are shifting and the generator is spinning, related to the wheel, then it’s producing electrical energy.
“We’ve got 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. In case you are driving on the freeway at 75 miles an hour, after which all of the sudden your complete 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 frequent in most international locations. But it surely’s a German phenomenon, crucial right here.
Individuals wish to drive quick. Then that you must deal with the realm of area weakening as a result of [at high speed], the magnetic area can be too sturdy. It’s good 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 ends in a lot greater effectivity at excessive speeds.
You referred to as this area weakening at excessive velocity?
Scharrer: It’s good to weaken the magnetic area in an effort to preserve the operation steady. And this weakening occurs by extra 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 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 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 executed by rivals as nicely, 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 had been shrinking the inductive unit to the scale of the rotor shaft, after which we put it contained in the shaft. And subsequently, we decreased this 50-to-90-millimeter progress in axial size. And subsequently, as a ultimate outcome, you realize 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 just transmit electrical energy with out touching something. You do it with a magnetic area. 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 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’ve got 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.
So you utilize coils, specifically designed, and also you induce voltage from one to the opposite?
Scharrer: Sure. And we have now 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 possibly can put it contained in the rotor shaft.
So after all, when you’ve got two coils, they usually’re spaced subsequent to one another, you’ve got a niche. 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 sphere may very well be transferred. In different phrases, they might couple regardless that considered one of them was spinning.
Scharrer: We’ve got a coil within the rotor shaft, which is rotating with the shaft. After which we have now 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’ve got an effectivity of roughly 96 %. So, little or no loss. And for the magnetic area, you don’t want loads 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 vital as a result of we don’t cool the unit actively and subsequently 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 constructions.
“ invention is all the time simple. For those who look as an engineer on good IP, then you definitely 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 possibly can construct, in kilowatts?
Scharrer: We don’t suppose that there’s a limitation with this expertise. We’re satisfied that we will construct the identical dimension, the identical energy stage of electrical motors as with the everlasting magnets.
You might do 150- or 300-kilowatt motors?
Scharrer: Completely.
What have you ever executed to date? What prototypes have you ever constructed?
Scharrer: We’ve got a prototype with 220 kilowatts. And we will simply improve it to 300, for instance. Or we will 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 let you know, to be fairly trustworthy. It’s exhausting to match, as a result of it all the time is determined by the place the borderline is. You by no means have a motor by itself. You all the time want a housing as nicely. 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 similar 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 at present 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 improvement with loads 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 top-of-the-line 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 accordance with our greatest information, this by no means occurred earlier than.”
—Otmar Scharrer, ZF Friedrichshafen AG
What had been the key challenges you needed to overcome, to transmit the facility contained in the rotor shaft?
Scharrer: The foremost problem is, all the time, it must be very small. On the similar time, it must be tremendous dependable, and it must be simple.
invention is all the time simple. While you see it, should you look as an engineer on good IP [intellectual property], then you definitely 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 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 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 minimize the extra size out of the magnet-free motor.” Okay. That’s a very good reply.
We’ve got loads of IP right here. That is vital as a result of when you’ve got the concept, I imply, the concept is the principle factor.
What had been the precise financial savings in weight and rotor shaft and so forth?
Scharrer: Effectively, 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 in accordance with our greatest information, this by no means occurred earlier than.
Do you suppose the motor will likely be out there earlier than the tip of this 12 months or maybe subsequent 12 months?
Scharrer: You imply out there for a severe utility?
Sure. If Volkswagen got here to you and mentioned, “Look, we need to use this in our subsequent automobile,” might you try this earlier than the tip of this 12 months, or wouldn’t it 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 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’re producing near a presumably severe manufacturing line. C-sample means you’re 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 %.
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