Among the many numerous challenges of decarbonizing transportation, one of the vital compelling entails electrical motors. In laboratories everywhere in the world, researchers are actually 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 resist excessive temperatures—and that doesn’t have rare-earth everlasting magnets.
It’s an enormous problem at the moment preoccupying a number of the greatest machine designers on the planet. Quite a lot of of them are at
ZF Friedrichshafen AG, one of many world’s largest suppliers of elements to the automotive trade. In truth, 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 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 midst of that vary: 220 kW. (The comany has not but revealed its motor’s particular energy—its kW/kg ranking.)
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 practically all EV motors on the street at this time. 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 reality, 95 % of the uncommon earths are mined in China. And which means that if China decides nobody else could 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 splendid approach 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 usually cumbersome, making the unit difficult 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). In addition to not utilizing any uncommon earth parts, the motor provides a number of different benefits as compared with permanent-magnet synchronous motors. These are linked to the truth that this sort of motor know-how provides the power to exactly management the magnetic discipline within the rotor—one thing that’s not doable with everlasting magnets. That management, in flip, permits various the sphere to get a lot larger effectivity at excessive velocity, 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 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 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 Expertise. Our interview with him has been edited for concision and readability.
Otmar Scharrer on…
IEEE Spectrum: Why is it essential to get rid of or to cut 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 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. You might want to transfer loads 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 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 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 could 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 lively lifetime. If you find yourself ramping up, when you could have 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 relentless 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 ability 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 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 shouldn’t be new. It has been used for years and years, for many years, as a result of often, energy technology is completed with this sort of electrical machine. So when you’ve got an enormous energy plant, for instance, a fuel 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 functions due to their weight and measurement. And a few of that weight-and-size drawback comes instantly from the necessity to generate a magnetic discipline within the rotor, to interchange the [permanent] magnets. You might want to set copper coils beneath electrical energy. So you have to carry electrical present contained in the rotor. That is often performed with sliders. And people sliders generate losses. That is the one factor as a result of you could have, usually, 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 route 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 this can be a second impediment. Many OEMs or e-mobility firms wouldn’t 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 sort of externally excited machine. You may change off and change 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.
“Now we have 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. If you’re driving on the freeway at 75 miles an hour, after which out of the blue your complete 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 discipline. 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 the event you drive at excessive velocity. Excessive velocity is one thing like 75, 80, 90 miles an hour. It’s not too widespread in most international locations. However it’s a German phenomenon, crucial right here.
Folks prefer to drive quick. Then you have to deal with the world of discipline weakening as a result of [at high speed], the magnetic discipline could be too robust. You might want to weaken the sphere. And in the event you don’t have [permanent] magnets, it’s straightforward: 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 known as this discipline weakening at excessive velocity?
Scharrer: You might want to weaken the magnetic discipline as a way to hold 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 after we do an externally excited motor. We thought loads 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 performed by opponents as properly, 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 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 decreased this 50-to-90-millimeter development in axial size. And due to this fact, as a last end result, you understand 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 discipline. And we’re doing it inside 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 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 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’ve a really neat, small package deal, which has a diameter of lower than 30 millimeters. In the event you can shrink it to that worth, then you may put it contained in the rotor shaft.
So after all, when you’ve got 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 may very well be transferred. In different phrases, they may couple regardless that one in all them was spinning.
Scharrer: Now we have a coil within the rotor shaft, which is rotating with the shaft. After which we’ve 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. Every part 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 96 %. So, little or no loss. And for the magnetic discipline, you don’t want loads 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 essential 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.
“ invention is all the time straightforward. In the event you 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 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 would do 150- or 300-kilowatt motors?
Scharrer: Completely.
What have you ever performed to date? What prototypes have you ever constructed?
Scharrer: Now we have 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 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 sincere. It’s exhausting to check, 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 properly. What a part of the housing are you together with within the calculation? However I can let you know one factor: The ability 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 at the moment 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 functions. 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 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 the most effective hybrid transmissions as a result of you may drive totally 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 keeping with our greatest data, this by no means occurred earlier than.”
—Otmar Scharrer, ZF Friedrichshafen AG
What have 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 straightforward.
invention is all the time straightforward. Whenever you see it, in the event 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 complicated 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 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. Straightforward 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 will lower the extra size out of the magnet-free motor.” Okay. That’s reply.
Now we have loads of IP right here. That is essential as a result of when you’ve got the concept, I imply, the concept is the principle factor.
What have been the particular financial savings in weight and rotor shaft and so forth?
Scharrer: Nicely, once more, I’d simply reply in a really normal approach. 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.
Do you assume the motor shall be accessible earlier than the tip of this 12 months or maybe subsequent 12 months?
Scharrer: You imply accessible for a severe software?
Sure. If Volkswagen got here to you and stated, “Look, we need to use this in our subsequent automobile,” might you do this earlier than the tip of this 12 months, or would it not need to 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 trade, 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 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, which 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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