Among the many numerous challenges of decarbonizing transportation, one of the vital compelling includes 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 resist excessive temperatures—and that doesn’t have rare-earth everlasting magnets.
It’s an enormous problem at present preoccupying a number of 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. Actually, 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 corresponding to the rare-earth permanent-magnet synchronous motors that now dominate in electric vehicles. Most EVs have rare-earth-magnet-based motors starting from 150 to 300 kilowatts, and energy densities between 1.1 and 3.0 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 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 at present. 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 p.c 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 towards 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 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 facility will be transferred by way of 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). Moreover 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 type of motor know-how affords the flexibility 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 sphere to get a lot larger effectivity at excessive pace, for instance.
With headquarters in Baden-Württemberg, Germany, ZF Friedrichshafen AG is thought for a
rich R&D heritage and many commercially successful innovations courting again to 1915, when it started supplying gears and different elements for Zeppelins. At present, 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 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 essential to eradicate or to scale back the usage of rare-earth parts in traction motors?
ZF Friedrichshafen AG’s Otmar Scharrer is main a group 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. You have to transfer quite a lot of soil to get to those supplies. Subsequently, 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 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 deal with cautiously as a tier one [automotive industry supplier].
And as a matter of reality, 95 p.c 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 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. If you find yourself ramping up, when you could 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 you probably have a relentless enterprise and also you’re simply changing these items that are failing. I’m certain this can 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 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 include? 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 sometimes have 1.5 kilograms of magnet materials. And 0.5 p.c to 1 p.c 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 will not be new. It has been used for years and years, for many years, as a result of normally, energy technology is completed with this type of electrical machine. So you probably have an enormous energy plant, for instance, a gasoline energy plant, then you definitely would sometimes 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 downside comes straight from the necessity to generate a magnetic subject within the rotor, to switch the [permanent] magnets. You have to set copper coils beneath electrical energy. So it’s worthwhile to carry electrical present contained in the rotor. That is normally completed with sliders. And people sliders generate losses. That is the one factor as a result of you could have, sometimes, carbon brushes touching a steel ring with the intention 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 definitely want a fourth part to impress the rotor. And it is a second impediment. Many OEMs or e-mobility corporations would not have this know-how prepared. Surprisingly sufficient, the primary ones who introduced this into severe manufacturing have 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 possibly can swap off and swap 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 have now an effectivity of roughly 96 p.c. So, little or no loss.”
—Otmar Scharrer, ZF Friedrichshafen AG
The identical is occurring in an electrical machine within the automobile. In case you are driving on the freeway at 75 miles an hour, after which out of the blue your entire system breaks down, what would occur? In a everlasting magnet motor, you’d generate huge 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 if you happen to drive at excessive pace. Excessive pace 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 it’s worthwhile to deal with the realm of subject weakening as a result of [at high speed], the magnetic subject could be too robust. You have to weaken the sphere. And if you happen to don’t have [permanent] magnets, it’s simple: 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 larger effectivity at excessive speeds.
You known as this subject weakening at excessive pace?
Scharrer: You have to weaken the magnetic subject to be able to preserve the operation secure. And this weakening occurs by further electrical energy coming from the battery. And due to this fact, you could have 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 rather a lot 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 completed 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 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 dimensions of the rotor shaft, after which we put it contained in the shaft. And due to this fact, we decreased this 50-to-90-millimeter progress in axial size. And due to this fact, as a last consequence, the motor shrinks, the housing will get smaller, you could 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 subject. 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 could 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 utilize coils, specifically designed, and also you induce voltage from one to the opposite?
Scharrer: Sure. And we’ve got 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 may put it contained in the rotor shaft.
So after all, you probably have two coils, and so they’re spaced subsequent to one another, you could 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 sphere could possibly be transferred. In different phrases, they might couple though one among them was spinning.
Scharrer: We have now 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 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: We have now an effectivity of roughly 96 p.c. So, little or no loss. And for the magnetic subject, you don’t want quite a lot of power. 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 essential 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.
“A superb invention is at all times simple. If you happen to look as an engineer on good IP, then you definitely 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 suppose you may construct, in kilowatts?
Scharrer: We don’t suppose 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.
What have you ever completed to this point? What prototypes have you ever constructed?
Scharrer: We have now 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 inform you, to be fairly sincere. 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 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 is no such thing as 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 quite a lot of different purposes. And I believe you perceive that I can’t speak about 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 probably the greatest hybrid transmissions as a result of you may 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 line 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 facility contained in the rotor shaft?
Scharrer: The most important problem is, at all times, it must be very small. On the similar time, it must be tremendous dependable, and it must be simple.
A superb invention is at all times simple. Whenever you see it, if you happen to 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 normally 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 clarify?
Scharrer: Sure. Simple to clarify as a result of it’s clearly an attention-grabbing 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 a very good reply.
We have now quite a lot of IP right here. That is essential as a result of you probably have the concept, I imply, the concept is the primary factor.
What have been the particular financial savings in weight and rotor shaft and so forth?
Scharrer: Effectively, once more, I might simply reply in a really common manner. 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 line with our greatest data, this by no means occurred earlier than.
Do you suppose the motor might 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 stated, “Look, we need to use this in our subsequent automobile,” may you do this earlier than the tip of this 12 months, 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 business, you could have A, B, or C. For A-sample, you could 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’re producing near a probably 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 traditional SOP [“Start of Production”] with our buyer. So we could possibly 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 p.c, not 98 or 99 p.c.
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