That's a common trick in large generators. The field winding rotates, and the armature winding produces the output. So the heavy power doesn't flow through brushes.
So how is the field winding energized? There's a second smaller generator on the same shaft, with the armature winding rotating and the field winding stationary. This generates AC for the field. You want DC for the main field winding, so there are also diodes in the rotating system to convert the AC to DC.
The shaft floats on a self-pumping oil film. So there's no moving metal to metal contact in the machine. That's a good thing in something that's expected to run 24/7 for decades.
So now this power-station sized technology has been downsized to car size. Unclear if it's worth it, since the lifespan of cars is only a few thousand operating hours, not the hundreds of thousands of hours of a power station generator.
I don't think that's the concept used. It's more likely to be a salient pole synchronous machine with the field winding supplied by an rotating transformer and diodes (the second illustration in the linked article seems to corroborate that). This concept has been proposed at least since the 1960s, to the best of my knowledge, but is only viable with modern power semiconductors. The hyped-up style is typical of american "technical" articles about electrical machinery.
I don't think they would have used brushes in this application. I'm quite certain that the most popular choice in this space is a squirrel cage induction motor [1].
I'm sure there's gotta be something new here, but what the title and intro describe could apply to induction motors, which date back to the 19th century. That makes the whole thing sound rather silly.
What is new is that it has a high efficiency similar to the permanent magnet motors, i.e. a higher efficiency than induction motors.
The reason for the high efficiency is because the motor seems to be some kind of synchronous motor, where the rotor is not supplied by wearable brushes but by a contactless transformer and a rectifier.
Besides the permanent-magnet motors and the induction motors, there are 2 other kinds of electrical motors without supply contacts on the rotor: variable-reluctance motors and hysteresis motors. However these other 2 share the disadvantage of the induction motors of having a lower efficiency.
The highest efficiency with no contacts to the rotor can be reached with either permanent-magnet motors or with designs similar to this Mahle motor.
If you're like me, and thought this was basically a squirrel-cage motor, then they key point is that this is a synchronous motor which replaces the typical permanent magnets with electromagnets.
But I wonder whether the poles in the rotor (which would ordinarily be permanent magnets) are DC or alternating field. If DC, then perhaps the rotor has a built-in rectifier? If alternating, then the stator coils must be doing some interesting compensation.
The experience curve for electric motors, power electronics, and batteries is going to be extremely interesting to watch over the next decade or two. The change over the last fifteen years has been incredible already.
I don't really understand what problem they're trying to solve. Contacts don't really wear out if they are tightened correctly and there was definitely no need for this on the 3-phase side of the driveline.
But you add induction coils like this and you're nearly going to need a medium as big as the motor itself to transfer that energy over an air gap.
It's also dumb to say 'no wear, we removed the last interface!!'. The motor is full of bearings. It actually seems to have twice as many bearings as a normal motor. So yes, you will need to replace all those bearings and it will be a right pain compared to just tightening a bolt for each of the phases.
The article states another benefit of the motor is that it doesn’t require rare earth elements, so presumably they’re trying to solve the ecological and supply problems presented by rare earth mining.
This is a common tech, with many variations of such induction used.
What is important is that the wireless power transfer is lossy. It's not very efficient.
Designs that do not require permanent magnets are good, but I believe that using good quality carbon brushes reduces the complexity of power transfer and is reliable enough for use case of cars.
Carbon brushes also have isolation issues. If your motor is to be air cooled, you will be blowing outdoor air through it, complete with fog/condensation. In brushed motors, that fog will cause a leakage current from the motor brushes to ground. The leakage current may be tiny, but in a system where you want 10's of megaohms between the high voltage system and the chassis for human safety, it becomes a problem.
Or you could try to hermetically seal your brushes in to stop moisture getting in, but now you have the difficulty of a spinning moisture seal and build up of carbon dust which is probably going to start to get warm/hot.
We have DC-Motors with brushes on work (50kW-500kW). Brushes really need a bit care all the time. And if something happened, you have to rework the whole thing on a turning machine.
Permanent magnets are handy for spinning up a power grid from zero, are they not? Many generators need power to produce power, so they’re useless if the grid is down, until they get fed some power by something else.
Dumb question: Couldn't you also reduce wear-and-tear considerably by placing the contacts at both ends of the axle, so they lie in the center of rotation?
This would mean you have to transmit mechanical energy from the motor using a gear or a belt - but that has to be done anyway if there is a transmission, as I understand it.
Nice to see that Mahle, which at least to me is known mostly as a supplier of pistons (and possibly other ICE parts), is preparing for a post-ICE future.
This was my first thought too. And then I remembered reading so many entries at the USPTO's website where they simply wrote about a 100-year old technology, obfuscated the heck out of it with convoluted language, and got the patent through. The odds that this company is doing the same thing are pretty good.
Seems that a journalist got sucked in by marketing hype.
I had expected better of the IEEE.
Actually, now that I look at other articles from IEEE Spectrum, most of them seem full of uncorrobrated and unwarrented hype.
The innovation here is not pure concept but having designed a product with 95% efficiency and low cost, low pollution components. As one of the major automotive part suppliers Mahle presumably has developed that with some consultation to the closely located Porsche and Mercedes engineers and has the manufacturing capabilities to scale this up. This does not seem to be a toy effort and the newsworthy bit is that the broader automotive supply chain seems to be seriously pivoting away from ICE new.
We're talking engineering here not physics. It doesn't have to be a radical new concept for it to be interesting and useful. Across many fields, new applications of existing concepts have proven revolutionary and disruptive.
brushless electric motors spin using magnets rather than pistons, so there are less required moving parts to get the one moving part (the shaft) that you actually want.
[+] [-] Animats|4 years ago|reply
So how is the field winding energized? There's a second smaller generator on the same shaft, with the armature winding rotating and the field winding stationary. This generates AC for the field. You want DC for the main field winding, so there are also diodes in the rotating system to convert the AC to DC.
The shaft floats on a self-pumping oil film. So there's no moving metal to metal contact in the machine. That's a good thing in something that's expected to run 24/7 for decades.
So now this power-station sized technology has been downsized to car size. Unclear if it's worth it, since the lifespan of cars is only a few thousand operating hours, not the hundreds of thousands of hours of a power station generator.
[+] [-] alexshendi|4 years ago|reply
[+] [-] CapitalistCartr|4 years ago|reply
[+] [-] aetherspawn|4 years ago|reply
[1]: https://en.wikipedia.org/wiki/Squirrel-cage_rotor
[+] [-] thescriptkiddie|4 years ago|reply
https://en.wikipedia.org/wiki/Alternator#Brushless_alternato...
[+] [-] himinlomax|4 years ago|reply
[+] [-] adrian_b|4 years ago|reply
The reason for the high efficiency is because the motor seems to be some kind of synchronous motor, where the rotor is not supplied by wearable brushes but by a contactless transformer and a rectifier.
Besides the permanent-magnet motors and the induction motors, there are 2 other kinds of electrical motors without supply contacts on the rotor: variable-reluctance motors and hysteresis motors. However these other 2 share the disadvantage of the induction motors of having a lower efficiency.
The highest efficiency with no contacts to the rotor can be reached with either permanent-magnet motors or with designs similar to this Mahle motor.
[+] [-] robbmorganf|4 years ago|reply
If you're like me, and thought this was basically a squirrel-cage motor, then they key point is that this is a synchronous motor which replaces the typical permanent magnets with electromagnets.
But I wonder whether the poles in the rotor (which would ordinarily be permanent magnets) are DC or alternating field. If DC, then perhaps the rotor has a built-in rectifier? If alternating, then the stator coils must be doing some interesting compensation.
[+] [-] mjb|4 years ago|reply
[+] [-] unknown|4 years ago|reply
[deleted]
[+] [-] newyankee|4 years ago|reply
[+] [-] aetherspawn|4 years ago|reply
It's also dumb to say 'no wear, we removed the last interface!!'. The motor is full of bearings. It actually seems to have twice as many bearings as a normal motor. So yes, you will need to replace all those bearings and it will be a right pain compared to just tightening a bolt for each of the phases.
[+] [-] tjpd|4 years ago|reply
https://en.m.wikipedia.org/wiki/Rare_earth_industry_in_China
[+] [-] slashdot2008|4 years ago|reply
[+] [-] kumarvvr|4 years ago|reply
What is important is that the wireless power transfer is lossy. It's not very efficient.
Designs that do not require permanent magnets are good, but I believe that using good quality carbon brushes reduces the complexity of power transfer and is reliable enough for use case of cars.
[+] [-] londons_explore|4 years ago|reply
Or you could try to hermetically seal your brushes in to stop moisture getting in, but now you have the difficulty of a spinning moisture seal and build up of carbon dust which is probably going to start to get warm/hot.
[+] [-] heisenbit|4 years ago|reply
And that is why their reported efficiency of 95% is significant.
[+] [-] _trampeltier|4 years ago|reply
[+] [-] hinkley|4 years ago|reply
[+] [-] miskin|4 years ago|reply
[+] [-] xg15|4 years ago|reply
This would mean you have to transmit mechanical energy from the motor using a gear or a belt - but that has to be done anyway if there is a transmission, as I understand it.
[+] [-] CRConrad|4 years ago|reply
[+] [-] notRobot|4 years ago|reply
[+] [-] baybal2|4 years ago|reply
They are at least 100 years too late.
[+] [-] qart|4 years ago|reply
[+] [-] jbay808|4 years ago|reply
[+] [-] Ice_cream_suit|4 years ago|reply
I had expected better of the IEEE. Actually, now that I look at other articles from IEEE Spectrum, most of them seem full of uncorrobrated and unwarrented hype.
[+] [-] heisenbit|4 years ago|reply
[+] [-] rkangel|4 years ago|reply
[+] [-] 4ad|4 years ago|reply
WAT. If they have no moving parts, why even have a motor at all?
As other commenters have already said, terrible, terrible article. I expected more from IEEE.
[+] [-] beaconstudios|4 years ago|reply