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In Mahle's Contact-Free Electric Motor, Power Reaches the Rotor Wirelessly
- mjb 5y agoThe 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.
- aetherspawn 5y agoI 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.
- tjpd 5y agoThe 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. https://en.m.wikipedia.org/wiki/Rare_earth_industry_in_China https://en.m.wikipedia.org/wiki/Rare_earth_industry_in_China
- elihu 5y agoYeah, it sounds like they're saying they get the efficiency of a permanent magnet motor (which can be around 95% or so) without using magnets. Induction motors I think tend to be in the high 80's. 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=469 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.
- slashdot2008 5y agothe contacts they are referring to are brushes to tranfer energy to the rotating shaft not bolted connections for stator leads
- Animats 5y agoThat'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.
- aetherspawn 5y agoI 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]. [1]: https://en.wikipedia.org/wiki/Squirrel-cage_rotor https://en.wikipedia.org/wiki/Squirrel-cage_rotor
- amluto 5y agoTesla used induction motors and even got funding from Toyota to develop them as a rare earth free design. But permanent magnet motors can be more efficient, and newer Tesla motors use permanent magnets. (Unless I’m very much mistaken, Tesla’s PM motor has no windings in the rotor.) There are plenty of motor designs with neither slip rings nor brushes. I don’t see what’s special about this supposedly new design.
- jabl 5y agoThere seems to be plenty of R&D around these days for developing rare earth free motors which are better than the standard induction motor (which, per se, isn't bad, but if you can do better, why not). 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 http://www.refreedrive.eu
- kumarvvr 5y agoThis 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.
- hinkley 5y agoPermanent 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.
- londons_explore 5y agoMany induction generators are 'self starting' - even a tiny bit of the earth's magnetic field is enough to get them generating something, which in turn makes them generate more, etc.
- jbay808 5y agoWould it really be the earth's magnetic field? Residual magnetization of the steel laminations seems more likely.
- robocat 5y agoStarting up power grids from zero is called black start[1]. Synchronous generators can have external exciter systems, or be self+excited[2]. [1] https://en.wikipedia.org/wiki/Black_start https://en.wikipedia.org/wiki/Black_start [2] https://en.wikipedia.org/wiki/Excitation_(magnetic) https://en.wikipedia.org/wiki/Excitation_(magnetic)
- londons_explore 5y agoCarbon 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.
- notRobot 5y agoHaha, I like the wording in the URL
- baybal2 5y agoSoo.... They invented an induction motor? They are at least 100 years too late.
- jbay808 5y agoIt's actually not an induction motor. It's likely synchronous, with the wound rotor actively energized.
- baybal2 5y agoOh, bingo https://player.admiralcloud.com/?v=34a065e8-47e7-4a52-b679-fc46edea94f5 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.
- Gibbon1 5y agoThis pdf of a thesis covers the design. https://core.ac.uk/download/pdf/20328622.pdf 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.
- adrian_b 5y agoThanks for the link, it is interesting. 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.
- Ice_cream_suit 5y agoSeems 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.
- heisenbit 5y agoThe 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.
- rkangel 5y agoWe'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.
- himinlomax 5y agoI'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.
- adrian_b 5y agoWhat 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.
- himinlomax 5y agoThat's what I eventually figured. But the angle really made the writer sound like they had no fucking clue about electric motors in the first place.
- 4ad 5y ago> Unlike internal-combustion engines, electric motors have practically no moving parts. 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 5y agobrushless 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.
- 4ad 5y agoElectric motors, just like any other motor have moving parts. End of discussion. Their purpose is to move things. 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.
- SigmundA 5y agoI believe the difference in moving parts between a combustion engine and electric motor is about two orders of magnitude (20 vs 2000). 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.
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- robbmorganf 5y agoThere is a video here that explains the concept: https://www.mahle.com/en/news-and-press/press-releases/mahle-develops-highly-efficient-magnet-free-electric-motor--82368 https://www.mahle.com/en/news-and-press/press-releases/mahle... 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.
- xg15 5y agoDumb 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.
- CRConrad 5y agoNice 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.