BMW using brushed motors
- Thread starter Vercingetorix
- Start date
I did read the article and call BS on that too. My exp with motor control also tells me the only way to get better power / perf vs brushless is switch between brushed and brushless half way to take less compromise on high vs low speed of each motor type. I do think they would be cheaper if they use less rare earth but then they need to pay it back somehow in the compromise, but then using brushes means they either limit to low rpm high torque application, or they have to find a way to clutch in and out of the brushes to reduce high rpm drag.
Maybe they should have an electrical engineer wrote this article instead of a mechanical engineer, IMO they would ask the question better than the author here?
Or maybe, just maybe, they have the mechanical people and this is a very mechanical solution to address what they don't have (electrical or control people) quickly? This happens a lot in real life.
I prefer the term fine German engineering.
agreed, most guys don't know how things work.
We see it all the time in the questions and statements people make.
In many ways this is a rehash of the timing belt v chain discussion.
edyvw
$50 site donor 2025
It is not problem at all.
BMW is experimenting. They don’t even have EV specific platform. Now it is time to experiment.
edyvw
$50 site donor 2025
It is not. It comes assemble like a tank, has potent brakes and suspension without speed limits.
I know some companies that still cannot figure that out.
Brakes and suspension - can be changed if the owner wishes to do so.
The drivetrain cannot be changed.
This drivetrain deviates from industry practice and introduces a maintenance point with no timeframe or cost along with it.
I read somewhere it is speed limited - did I get that wrong?
edyvw
$50 site donor 2025
So basically what you saying is that Tesla is IKEA? Assemble after purchase?
Yes, it is acceleration and speed limited to M3 competition.
Also, BMW, MB, Audi come speed limited bcs. gentleman's agreement not bcs their suspension cannot handle speed, again, unlike some other IKEA products.
Surely everyone here knows how an alternator works?? It's much the same - the current flow is low through the brushes and they engage slip rings rather than a segmented commutator so wear is minimal. It's a not a forklift motor.
How often do you change the brushes on your alternator? Does the fact that alternators have brushes affect your acceptance of ICE technology?
As for EV efficiencies in general, a li-po pack typically has 98% cycle efficiency, motor typically 95%, driver electronics perhaps 92-98%.
How often do you change the brushes on your alternator? Does the fact that alternators have brushes affect your acceptance of ICE technology?
As for EV efficiencies in general, a li-po pack typically has 98% cycle efficiency, motor typically 95%, driver electronics perhaps 92-98%.
No Eddy you are making that claim, and the binary claims the car has no suspension or brakes. This is of course -your opinion.
I'm simply pointing out what an owners options are - and changing the drivetrain isnt one.
edyvw
$50 site donor 2025
No it’s not. You have Plaid that is limited bcs. suspension cannot handle speed. Any car that is limited in speed 40-50mph from what could develop bcs. suspension cannot handle it is junk.
Any car that doesn’t have brakes for that speed in 2022 is junk. Cars could go 200mph 20yrs ago, and didn’t have problem stopping.
So please, either Tesla doesn’t know how to make car or they don’t want bcs. as long as there is sheep there will be wool.
edyvw
$50 site donor 2025
And as I pointed earlier, BMW doesn’t even use platform that is specific to EV. It uses CLAR platform which is ICE platform.
If this engine is junk, nothing stops them to make engine like others when new generation comes out that will have modular platform supporting both EV and ICE. They sell ICE, a lot. They can afford to experiment when EV’s are in “keeping up with Joneses” phase.
If this engine is junk, nothing stops them to make engine like others when new generation comes out that will have modular platform supporting both EV and ICE. They sell ICE, a lot. They can afford to experiment when EV’s are in “keeping up with Joneses” phase.
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Your opinion has done nothing to slow the sales of the product. The clients disagree.
As mine opinion has no effect on BMW' sales.
edyvw
$50 site donor 2025
I never mentioned clients. They are anyway buying ticket to social club, not vehicle.
Changing worn brushes is one thing, changing a worn commutator is another.
Brushes on a slip ring don`t see the wear a brush on commutator sees.
Brushes on a slip ring don`t see the wear a brush on commutator sees.
Read the article or at the very least this section I'll quote in since no one wants to actually read it then wrongly say it will last forever like an alternator and that any worries are invalid. The bmw motor has a commutator. Alternators don't have commutators.
"This fifth-generation BMW motor has no magnets. It operates as a three-phase AC synchronous motor using brushes and a commutator to provide power to the rotor windings, meaning that AC brushed motors aren't just for third-world electric locomotives any more. We asked BMW about the life expectancy of those brushes and commutators, and what happens to the dust as they wear. While they couldn't give us a lifetime estimate for the brushes"
Lol, don't rely on journalists for your technical education. He's used the wrong terminology. Guess what "Schleifring" means in German?
The brushes provide a fixed magnetic field at the rotor to replace permanent magnets. It uses slip rings to transfer the current. There is no commutation needed or provided.
The photograph is clear, there are three brushes to share current provided to each slip ring. There are no segments in the slip ring as a commutator would have. The other three brushes have the same arrangement on the back of the plastic bracket.
The field windings operate exactly the same as in a brushless PM motor, 3-phase currents provide a rotating magnetic field.
The brushes provide a fixed magnetic field at the rotor to replace permanent magnets. It uses slip rings to transfer the current. There is no commutation needed or provided.
The photograph is clear, there are three brushes to share current provided to each slip ring. There are no segments in the slip ring as a commutator would have. The other three brushes have the same arrangement on the back of the plastic bracket.
The field windings operate exactly the same as in a brushless PM motor, 3-phase currents provide a rotating magnetic field.
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The "slip ring" still has some friction, yes the amount can be reduced by making the sliding speed low (i.e. on a narrow shaft), but it is still there. Yes it can be controlled and wear minimized. However, the bigger problem IMO is the cooling of the coil would be impossible. On a permanent magnet and AC motor usually you don't need to cool the stator or the magnet, but you can cool the coil on the outside, stationary part, of the motor. I wonder how they solve that problem.
It doesn't indicate in the docs what parts of the motor are cooled, or by what method.
