BMW magnetless motors

3073 Views 22 Replies 5 Participants Last post by brian_, 11 mo ago

57Chevy

Discussion Starter · Feb 18, 2022

Interesting idea, do away with rare earth magnets so vehicle price isn't tied to the commodities price and then instead of an old induction motor like Tesla, power the rotor via brushes and achieve a motor with adjustable BEMF. The extra thermal load from the rotor electromagnet is well made up by being able to turn down the magnet at light loads and at high speeds. Quite clever really. Can't wait till people start crashing these

1 - 20 of 23 Posts

remy_martian

· #2 · Feb 18, 2022

Meh...it's slip rings and ecommutation, not a slotted copper commutator they coyly imply which is what produces wear and dust.

Unless they're using superconductors, they'll have iron losses and joule heating in the copper.

Dr's Faraday and Lenz don't make free lunches...you can turn stuff down, but then you're not doing work.

Meh...PR bs by a company that publicly stated ICE is their focus.

Call me a luddite or skeptic, but the reality is that permanent magnets vs induction motors, much like cobalt in batteries is a a few percent increase in efficiency as bragging rights by a big mouth cartoon character that sells a lot of EV's. So succesfully that everybody and his dog wants to put a Tesla motor in their conversion when they write their noob intro here.

The reality is we could go back to simply swapping out rotors (and taking a few minor precautions that Tesla didn't do in very early Model S) to induction, we could take all the cobalt out of the battery, and nobody would notice.

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57Chevy

Discussion Starter · #3 · Feb 18, 2022

remy_martian said:
Call me a luddite or skeptic,

I'd call you a lot of things before either of those terms based on the way you interact with people here. Rude, impulsive, attention deprived... But then I also need to recognise that as part of an inclusive society we have to accept that some people don't have awareness of or control over their behavior.

The design is not new in any way, car alternators have used this principle since the 1960s. What is new is the realisation that China holds almost all of the raw materials to make magnet motors and this is a risk to productivity if China decided to change the price or availability for reasons that suit their desires. I wonder if the chip shortage has made OEMs take a harder look at their supply weaknesses and act accordingly.

What is new, and quite clever, is the holistic approach to making a drive unit that meets more than just the basic requirements of being efficient.

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brian_

· #4 · Feb 19, 2022 (Edited)

Until this announcement from BMW, as far as I know the only modern production EVs using DC-excited wound rotors were the Renault Zoe and related models, with Continental motors.

The Interesting Engineering article, and others quoting it, erroneously say that the motor uses a commutator, and of course it does not - it has brushes and slip rings. Judging from this and other articles from Interesting Engineering, there is no one associated with the site with any significant technical knowledge: it is better to just read the releases from BMW.

57Chevy said:
What is new, and quite clever, is the holistic approach to making a drive unit that meets more than just the basic requirements of being efficient.

I don't think that's new at all, but it is good.

After all, Renault considered the same factors and made the same decision - a decade ago - and has since switched to PM motors.

57Chevy

Discussion Starter · #5 · Feb 19, 2022

I did notice the use of commutator, which it obviously isn't. I guess their writer and editor aren't electric motor specialists.

Mahle are claiming to be developing an induction coupled system to eliminate the brushes which is basically what truck alternators have done for decades

remy_martian

· #6 · Feb 19, 2022

China doesn't hold all the materials. China has caved world prices on strategic minerals (gee, how do they do that...) to where neodymium and other materials mining has been mothballed.

Including the Nd mine near Los Angeles, which was being turned on a short while ago.

They did buy up many of these Western "unprofitable" mines, but nothing stops Western governments from seizing them should the strategic need arise.

Ironically, round eyes play checkers while the Chinese government play chess.

57Chevy

Discussion Starter · #7 · Feb 19, 2022

brian_ said:
After all, Renault considered the same factors and made the same decision - a decade ago - and has since switched to PM motors.

Tesla also, and also now have PM motors. I guess there is nothing new, just new reasons

The simplest reason from a DIY perspective is that magnet motors are virtually impossible to disassemble safely without a very strong jig

brian_

· #8 · Feb 19, 2022

57Chevy said:
I did notice the use of commutator, which it obviously isn't. I guess their writer and editor aren't electric motor specialists.

That's more generous than I would be...

57Chevy said:
Mahle are claiming to be developing an induction coupled system to eliminate the brushes which is basically what truck alternators have done for decades

It's a little different from the truck alternators. The traditional system uses an auxiliary three-phase radial stator winding to induce current in an auxiliary three-phase radial rotor winding, which is rectified to power the rotor main rotor winding. The Mahle design uses high-frequency AC power to a stationary axial auxiliary winding, inducing current in a rotating auxiliary, which is rectified to power the rotor main rotor winding; this axial coupling approach relieves the rotor excitation system of any effect of changing rotational speed.

Any inductive coupling system for rotor excitation power is more complex than brushes and slip rings, but avoids any wear components (and the mechanical drag).

brian_

· #9 · Feb 19, 2022

57Chevy said:
Tesla also, and also now have PM motors. I guess there is nothing new, just new reasons

Yes, except that Tesla went from induction asynchronous to PM synchronous, while Renault went from DC-excited synchronous to PM synchronous.

57Chevy said:
The simplest reason from a DIY perspective is that magnet motors are virtually impossible to disassemble safely without a very strong jig

True, but as long as the motor is complete with end housings (like a Leaf, for instance, but unlike a Tesla) there's no reason for the DIY conversion builder to disassemble the motor.

In his teardown video of the Bolt drive unit, Prof. Kelly of Weber State U. shows the GM special tool for rotor removal, which his shop bought (because they provide instruction in automotive technology - they don't just tear down stuff to see the cool parts inside). In one of the Tesla Plaid motor videos the rotor is only partially removed, because the person making it was clever enough to realize that just pulling it out would not go well and he didn't want to (or couldn't) buy or build appropriate tooling.

lj516

· #10 · Feb 19, 2022

I bet they are switched reluctance. They haven't been possible until recently because of the switching and calcs needed for the micro. Alts use a field with a claw tooth rotor to provide an alternating field and are VERY rpm limited, let alone 70% efficient...

lj516

· #11 · Feb 19, 2022

57Chevy said:
The simplest reason from a DIY perspective is that magnet motors are virtually impossible to disassemble safely without a very strong jig

Not true

Automotive tire Automotive lighting Motor vehicle Gear Automotive design

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57Chevy

Discussion Starter · #12 · Feb 19, 2022

lj516 said:
Not true

lol. Getting them out is the easy(er) part, getting them back in without gacking the sleeve or tweaking a bearing is less fun. I spent more than a bit of time making rotor extraction jigs for exactly these reasons.

57Chevy

Discussion Starter · #13 · Feb 19, 2022

brian_ said:
The traditional system uses an auxiliary three-phase radial stator winding to induce current in an auxiliary three-phase radial rotor winding, which is rectified to power the rotor main rotor winding.

The ones I have seen are much simpler, just a stationary coil of wire inside the spinning claws, rather than a spinning coil of wire as part of the claws.

brian_

· #14 · Feb 19, 2022 (Edited)

lj516 said:
I bet they are switched reluctance.

No, they're not reluctance motors at all, and they're synchronous, not switched.

A reluctance motor has neither permanent magnets nor electromagnets (windings) in the rotor, only a stack of iron laminations which create preferential paths for magnetic flux (paths of different magnetic reluctance, which is analogous to electrical resistance). In a synchronous reluctance motor a typical multiphase (normally 3-phase) stator produces a rotating field and the rotor stays locked with that and rotates similar to other synchronous motors (up until the torque is to high and it breaks loose, which happens at much lower torque than a PM or wound motor of the same size). In a switched reluctance motor phases of the stator winding switch in sequence, and the rotor follows them around in jerking steps (but at least the stator phases can be crudely switched instead of sinusoidally varied).

This motor has a wound rotor producing a constant-polarity field just like permanent magnets do, but variable in intensity (by varying excitation current) and with copper instead of the materials needed to make a strong permanent magnet.

lj516 said:
... switched reluctance. They haven't been possible until recently because of the switching and calcs needed for the micro.

Switched reluctance motors have been used (with clever switching logic) for many years. They're just not smooth and don't have enough advantages in small sizes (like an electric car size) to be worth using.

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brian_

· #15 · Feb 19, 2022 (Edited)

57Chevy said:
The ones I have seen are much simpler, just a stationary coil of wire inside the spinning claws, rather than a spinning coil of wire as part of the claws.

That's sounds like a normal alternator - with the cheap-to-build claw rotor configuration excited through brushes and slip rings - but with the axial coil stationary. The magnetic coupling of the stationary rotor winding with the movig claws around it would be terrible, but apparently Delco Remy offers that. The rotor is supported and driven from one end, and the winding is supported and held non-rotating within it from the other end.

The traditional configuration with separate excitation power transfer coils may only be used on larger machines.

brian_

· #16 · Mar 25, 2022

I just realized that Nissan is going with this type of motor for the Ariya, perhaps due to the influence of their association with Renault. They are calling them "Externally Excited Synchronous Motors". I assume they're just using brushes and slip rings to get excitation current to the rotor, but I haven't seen any details on that aspect.

rishimaze

· #17 · 11 mo ago (Edited)

57Chevy said:
I'd call you a lot of things before either of those terms based on the way you interact with people here. Rude, impulsive, attention deprived... But then I also need to recognise that as part of an inclusive society we have to accept that some people don't have awareness of or control over their behavior.

Good job 57Chevy! Totally agree about Remi!

Well remi_martin, he NAILED you to the wall...Mr. Arrogant Industry Veteran! Nice to see I'm not the first person to tell you that you suck!

rishimaze

· #18 · 11 mo ago

brian_ said:
That's sounds like a normal alternator - with the cheap-to-build claw rotor configuration excited through brushes and slip rings - but with the axial coil stationary. The magnetic coupling of the stationary rotor winding with the movig claws around it would be terrible, but apparently Delco Remy offers that. The rotor is supported and driven from one end, and the winding is supported and held non-rotating within it from the other end.

The traditional configuration with separate excitation power transfer coils may only be used on larger machines.

Wait what? Did I read that right? Did you say the armature has a fixed winding in it? So does the actual armature spin around this fix winding and the fixed winding is inducing a magnetic field onto the armature...so "sort of reluctance"? Slip rings and brushes do suck and however this works with a fixed coil inside the armature (if I have that right) would probably be much more efficient.

rishimaze

· #19 · 11 mo ago

57Chevy said:
The ones I have seen are much simpler, just a stationary coil of wire inside the spinning claws, rather than a spinning coil of wire as part of the claws.

Can you guys show any diagrams of these magical motors. They sound fascinating!

rishimaze

· #20 · 11 mo ago

7

lj516 said:
Not true
View attachment 127712

Agreed...a 3 jaw puller makes extraction and insertion very controllable. Never crashed a motor yet!

C80100:

Hub motor with 65mm x 180mm stator:

Hub motor with a 65mm x 165mm stator:

Motenergy Axial flux, dual stator 3031-001 with 7" x 2" stators.

3031-001 next to a 120mm x 90mm outrunner. It's BIG!

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