In Mahle's Contact-Free Electric Motor, Power Reaches the Rotor Wirelessly
spectrum.ieee.org
spectrum.ieee.org
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.
There are plenty of motor designs with neither slip rings nor brushes. I don’t see what’s special about this supposedly new design.
Here's an EU project that designed and compared induction, synchronous reluctance, and synchronous reluctance with ferrite magnets in the rotor: http://www.refreedrive.eu
There is plenty of real world data from tesla model S owners showing that the batteries easily last more than 200k miles, which is about how long cars in the US last before getting scrapped. https://maartensteinbuch.com/2015/01/24/tesla-model-s-batter...
The same is more or less true for Priuses, their batteries last around 150-200k miles.
Fun fact: cars are commonly designed to be operated for 8h in reverse gear over lifetime.
Another fun fact: Electric drills are used for an _average_ of 8 minutes over their lifetime.
I did see that somewhere, and I think it was in the context that every home has an electric drill, but most might only get used for 1 or 2 projects a year.
You would hope though that this might be only a design guide for one of those $30 stocking stuffers.
I'm an owner builder and I am pretty sure my drills and impact drivers have racked up many tens of hours.
I'll guess that each spin took about 3 seconds (because that makes the math easy), so 2 minutes total. I couldn't exactly share the drill with a neighbor in the approximate hour that I spent measuring and repositioning the jig between uses.
In the context of duty cycle lifetime, maybe 8 minutes isn't that low -- but I am definitely using it for more than 8 minutes.
Then there's the grit wheel or flap disc, which might have me axially loading the drill for 30 minutes at a time (such as for stripping paint or sanding rust off an iron engine block).
I think they must be including a lot of people who buy or receive a drill as a gift and never use it at all, to get to 8 minutes average. I do find it believable that the cheaper ones might have a design life of 8 minutes, but that's a sad state of affairs.
You're probably right about the stat including people who never use the drill at all, or only ever use it to tighten screws.
https://en.wikipedia.org/wiki/Alternator#Brushless_alternato...
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.
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.
https://en.m.wikipedia.org/wiki/Rare_earth_industry_in_China
I don't entirely buy the rare earths thing. You can buy permanent magnet EV motors without rare earths, like the Netgain Hyper9 [1] (which I'm using in a conversion I've been working on for awhile). The hyper9 is kind of heavy for its power density, though, so maybe that's the advantage of rare earth magnets. If this company can get the efficiency of a permanent magnet motor but without rare earths and at a high power density, maybe they've got something new and interesting.
[1] https://www.evwest.com/catalog/product_info.php?products_id=...
edit: another advantage of avoiding magnets is that they tend to demagnetize if they get too hot. Not having magnets means you might be able to run the motor hotter without damage. Though, a 95% efficient motor should be pretty easy to keep cool.
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.
Synchronous generators can have external exciter systems, or be self+excited[2].
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.
And that is why their reported efficiency of 95% is significant.
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.
They are at least 100 years too late.
https://player.admiralcloud.com/?v=34a065e8-47e7-4a52-b679-f...
That's a rotary transformer excited synchronous motor. A bit better, they are now only 90-80 years too late.
https://core.ac.uk/download/pdf/20328622.pdf
Here and elsewhere found two issues.
A problem is efficiently driving the rotary transformer due to losses in the drive circuit because air gapped transformers have a lot of leakage inductance. I take that to mean they throw a lot of reactive power back at the drive electronics.
Hidden problem they are trying to solve is these motors are typically/often oil cooled. Oil and slip rings don't play well together.
However the conclusion about the low efficiency of the electronic converter for the rotary transformer is no longer valid.
With modern switches of silicon carbide or gallium nitride and with resonant soft switching techniques, the converter should operate at much higher frequencies and at much lower losses.
This is what has probably enabled today the manufacturing of a high-efficiency synchronous motor with a rotary transformer by Mahle.
I'm on this train of thought that the service life of electric power trains is 2 to 5 times that of gasoline ones. There is a potential to design cars that last 30-50 years. Which potentially reduces the environmental impact of vehicles. I've noticed though that people in the automotive industry look at you like an moron when you suggest that the service life of cars may double or triple. I think it's so ingrained they can't think around it.
Not to mention the fact that EVs sparked an interest in rediscovering existing motor technology.
It's not hypothesized and prototyped 100 years ago, it's the most common type of medium power electric motor in the world.
Find me a brush-less, magnet-less electric motor like this with a 95% transfer efficiency.
https://ouc.bizenergyadvisor.com/article/ac-induction-motors
Turntide gets to about that level with their high-rotor-pole switched reluctance motors, I think:
One of my old jobs holds (software) patents on my work. I built some pretty clever software, but I wouldn't have said that I "invented" anything.
The actual content of the patents is absolutely ridiculous too. Here's an excerpt from one of the patents on my work:
> There is also provided a system for identifying software capable of capturing personally identifiable information, comprising a module arranged to connect to a remote server via a local device, the module further being arranged to send at least one request for data and retrieve at least one packet of data in response to the request, and an identification module arranged to receive the retrieved at least one packet of data and determine whether the received data originated from a third party server other than the remote server, and if so, determine whether the received data received contains evidence of the presence of personally identifiable information
It's almost indistinguishable from nonsense claims generated by GPT-2 [1].
Also, half the claims in the patents were for features that, in the end, were never even implemented.
But worst of all, I'm not even credited as one of the inventors. I don't care one iota about the intellectual property, they can keep all claims to that, I just want the bragging rights.
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.
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.
Less moving parts doesn't mean "practically no moving parts", as the idiotic article claims.
Coincidentally, the brushes which wear out on DC engines are not moving, it's the commutators that move and wear out the brushes...
...but cars use BLDC motors (which are induction motors or variants thereof) and not DC motors anyway... Brushed DC motors are only used by forklifts and similar equipment (although more recently they started to move to brushless designs too).
A DC motor and an induction motor have the same number of moving parts. It's not the number of moving parts that matter, but the fact that moving parts don't have to touch each other.
I would say "practically no moving parts" is an ok term in relative comparison but thats just my opinion.
There isn't really a debate, as far as size, weight, complexity and maintenance electric motors win over combustions engines.
The problem of course is the battery size cost and weight compared to a gas tank.
Bottom line though electric cars have much less maintenance and much of that can be attributes to much less moving parts.