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Among the many numerous challenges of decarbonizing transportation, probably the most compelling includes 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 present preoccupying among the finest 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 business. 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 components. Furthermore, the corporate introduced, their new motor had traits corresponding 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 ranking.)
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 street 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 truth, 95 p.c of the uncommon earths are mined in China. And which means if China decides nobody else can have uncommon earths, we are able to do nothing in opposition to 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 superb 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 finally put on out. Alternatively, the facility may be transferred by way of inductance, however in that case the equipment is often 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). Apart from not utilizing any uncommon earth components, 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 power to exactly management the magnetic area within the rotor—one thing that’s not potential 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 workers in 31 nations. 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 saying 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 concerning 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 Expertise. Our interview with him has been edited for concision and readability.
Otmar Scharrer on…
IEEE Spectrum: Why is it necessary to eradicate or to cut back the usage of rare-earth components in traction motors?
ZF Friedrichshafen AG’s Otmar Scharrer is main a workforce 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 plenty of soil to get to those supplies. Due to this fact, 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 handle cautiously as a tier one [automotive industry supplier].
And as a matter of truth, 95 p.c of the uncommon earths are produced in China. And which means if China decides nobody else can have uncommon earths, we are able to 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 lively lifetime. When you’re 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 when you have a relentless 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 ability density is similar as for a permanent-magnet machine, as a result of we produce each. And I can inform you 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 fascinating query. Most of our electrical motors are within the vary of 150 to 300 kilowatts. That is the principle vary of energy for passenger automobiles. And people motors usually 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 is just not new. It has been used for years and years, for many years, as a result of normally, energy era is completed with this type of electrical machine. So when you have an enormous energy plant, for instance, a fuel energy plant, you then would usually discover such an externally-excited machine as a generator.
We didn’t use them for passenger automobiles or for cell 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 area within the rotor, to switch the [permanent] magnets. It’s good to set copper coils below electrical energy. So it’s essential 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’ve gotten, usually, 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 part to affect 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 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 change off and change on the magnetic area. 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 transferring and the generator is spinning, linked to the wheel, then it’s producing electrical energy.
“We’ve got 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 automotive. 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 area. However in a permanent-magnet-free motor, nothing occurs. You’re simply switched off. So it’s self-secure. This can be 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 nations. But it surely’s a German phenomenon, essential right here.
Folks wish to drive quick. Then it’s essential to handle the realm of area weakening as a result of [at high speed], the magnetic area can be too robust. It’s good to weaken the sphere. And should you don’t have [permanent] magnets, it’s straightforward: 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 larger effectivity at excessive speeds.
You referred to as this area weakening at excessive velocity?
Scharrer: It’s good to weaken the magnetic area with the intention to hold the operation steady. And this weakening occurs by further 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 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 once we do an externally excited motor. We thought loads 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 opponents as nicely, however they merely changed the slider rings with inductance transmitters.
“We’re satisfied that we are able to 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 diminished this 50-to-90-millimeter progress in axial size. And due to this fact, as a last outcome, you realize the motor shrinks, the housing will get smaller, you’ve gotten 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 just transmit electrical energy with out touching something. You do it with a magnetic area. And we’re doing it inside the rotor shaft. That is the place the vitality 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’ll 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 bundle, which has a diameter of lower than 30 millimeters. In case you can shrink it to that worth, then you possibly can put it contained in the rotor shaft.
So after all, when 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 will spin independently. So that you needed to design one thing the place the sphere could possibly be transferred. In different phrases, they may couple although one in every of them was spinning.
Scharrer: We’ve got 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’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: We’ve got an effectivity of roughly 98 p.c, 99 p.c. So, little or no loss. And for the magnetic area, you don’t want plenty of vitality. You want one thing between 10 and 15 kilowatts for the electrical area. So that you lose 1 p.c of that. That 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 is cooled, however the inductive unit is just not cooled.
“A great invention is at all times straightforward. 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 most important motors you’ve constructed or what are the most important motors you assume you possibly can construct, in kilowatts?
Scharrer: We don’t assume that there’s a limitation with this know-how. We’re satisfied that we are able to construct the identical measurement, the identical energy degree of electrical motors as with the everlasting magnets.
You may do 150- or 300-kilowatt motors?
Scharrer: Completely.
What have you ever completed to this point? What prototypes have you ever constructed?
Scharrer: We’ve got 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 straightforward.
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 exhausting to match, as a result of it at all times relies on the place the borderline is. You by no means have a motor by itself. You at all times want a housing as nicely. What a part of the housing are you together with within the calculation? However I can inform you one factor: The ability density is similar as for a permanent-magnet machine as a result of we produce each. And I can inform you 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 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 automobiles. And we’re, after all, in growth with plenty of different functions. And I feel you perceive that I can not 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 computerized transmission with a hybrid electrical motor as much as 160 kilowatts. It’s probably the greatest 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 line with our greatest information, this by no means occurred earlier than.” —Otmar Scharrer, ZF Friedrichshafen AG
What have been the foremost 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 straightforward.
A great invention is at all times straightforward. If you see it, should 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 normally this isn’t a good suggestion to be carried out. 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. Simple to clarify 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 are able to lower the extra size out of the magnet-free motor.” Okay. That’s a great reply.
We’ve got plenty of IP right here. That is necessary as a result of when you have the concept, I imply, the concept is the principle factor.
What have 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 line with our greatest information, this by no means occurred earlier than.
Do you assume the motor will likely be out there earlier than the top of this 12 months or maybe subsequent 12 months?
Scharrer: You imply out there for a severe software?
Sure. If Volkswagen got here to you and mentioned, “Look, we need to use this in our subsequent automotive,” may you try this earlier than the top 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 gotten A, B, or C. For A-sample, you’ve gotten 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 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, which 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.
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