Among the many numerous challenges of decarbonizing transportation, some of the compelling entails electrical motors. In laboratories all around the world, researchers at the moment are 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 among 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 components to the automotive business. In truth, 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 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 sort 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 right now. 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 p.c of the uncommon earths are mined in China. And because of this if China decides nobody else can have uncommon earths, we will do nothing towards it.” —Otmar Scharrer, ZF Friedrichshafen AG
Up to now, 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 manner to try 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 could be transferred through inductance, however in that case the equipment is usually 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 presents just a few different benefits compared with permanent-magnet synchronous motors. These are linked to the truth that this type of motor know-how presents the power to exactly management the magnetic discipline within the rotor—one thing that’s not potential with everlasting magnets. That management, in flip, permits various the sector 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 lots of commercially profitable improvements relationship again to 1915, when it started supplying gears and different components 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 yr, 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 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 essential to get rid of or to scale back using rare-earth components 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: 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. That you must transfer a number 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 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 tackle 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 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 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 you probably have a continuing enterprise and also you’re simply changing these models 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 identical as for a permanent-magnet machine, as a result of we produce each. And I can let you know 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 metallic does a typical traction motor include? I needed to ask my engineers. That is an fascinating query. Most of our electrical motors are within the vary of 150 to 300 kilowatts. That is the primary vary of energy for passenger vehicles. 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 often, energy era is completed with this type of electrical machine. So you probably 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 functions due to their weight and measurement. And a few of that weight-and-size downside comes immediately from the necessity to generate a magnetic discipline within the rotor, to exchange the [permanent] magnets. That you must set copper coils beneath electrical energy. So it’s good to 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 could have, sometimes, carbon brushes touching a metallic ring as a way to conduct the electrical energy.
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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 you then want a fourth section to impress the rotor. And this can be a second impediment. Many OEMs or e-mobility corporations don’t have this know-how 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 possibly can change off and change 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. If you’re transferring and the generator is spinning, related to the wheel, then it’s producing electrical energy.
“Now we have an effectivity of roughly 98 p.c, 99 p.c. So, little or no loss.” —Otmar Scharrer, ZF Friedrichshafen AG
The identical is occurring in an electrical machine within the automobile. If you’re 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’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 might be simply switched off. So it’s self-secure. It is a good characteristic.
And the second characteristic 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 frequent in most international locations. But it surely’s a German phenomenon, crucial right here.
Individuals prefer to drive quick. Then it’s good to tackle the world of discipline weakening as a result of [at high speed], the magnetic discipline can be too robust. That you must weaken the sector. And in the event 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 velocity?
Scharrer: That you must weaken the magnetic discipline with a view to hold the operation steady. 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.
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What are essentially 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 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 executed by rivals 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 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 dimensions 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 remaining outcome, you already know the motor shrinks, the housing will get smaller, you could have 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 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.
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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 case you 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’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 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’s an air hole in between. All the pieces 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 p.c, 99 p.c. So, little or no loss. And for the magnetic discipline, you don’t want a number of power. You want one thing between 10 and 15 kilowatts for the electrical discipline. So that you lose 1 p.c of that. That 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 is cooled, however the inductive unit will not be cooled.
“An excellent invention is all the time simple. In case you 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 may 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 measurement, the identical energy stage of electrical motors as with the everlasting magnets.
You could possibly do 150- or 300-kilowatt motors?
Scharrer: Completely.
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What have you ever executed thus far? 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 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 sincere. It’s arduous to check, as a result of it all the time depends upon 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 facility density is identical as for a permanent-magnet machine as a result of we produce each. And I can let you know 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. The [Mercedes] EQA, -B, and -C are geared up by us, for instance, these three vehicles. And we’re, after all, in growth with a number of different functions. And I feel 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 top-of-the-line hybrid transmissions as a result of you may 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 response to our greatest data, this by no means occurred earlier than.” —Otmar Scharrer, ZF Friedrichshafen AG
What had been the foremost challenges you needed to overcome, to transmit the facility contained in the rotor shaft?
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Scharrer: The key problem is, all the time, it must be very small. On the similar time, it must be tremendous dependable, and it must be simple.
An excellent invention is all the time simple. Whenever you see it, in the event 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 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 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 fascinating 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.
Now we have a number 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 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 basic 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 response to our greatest data, this by no means occurred earlier than.
Do you suppose the motor will likely be obtainable earlier than the tip of this yr or maybe subsequent yr?
Scharrer: You imply obtainable 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 yr, 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 business, you could have A, B, or C. For A-sample, you could have 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 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, 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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