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That might be actually bad news. I can't speak of motors used in EV's, but on a general term a small brushed motor lasts around 1000 to 3000 hours, while a brushless kan last ten thousands of hours.
 

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I think the article incorrectly used the word "commutator" which is specific to DC motors. It appears as the brushes in the BMW 3 phase motor is a "slip ring" setup, similar to the excitation used in an alternator. The commutator setup does eat brushes and are regularly changed. Slip ring brushes last a very long time. It appears as the brushes are at the very end of the motor assembly and "expect" they are replaceable.

I've had many BMWs with well over 100K, one over 200K miles. I've never worn out an engine, nor even had one that needed oil added between changes. I would be surprised if the brushes did not last at least 100K if not 200K miles.
 

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I hope you are right. The whole idea of owning an EV is to have lower maintanance costs in the logn run. But with brushes that need to be replaced and put "in an enclosed and sealed compartment, eliminating dust contamination inside the stator/rotor wiring." That sounds for me like troubles are inevitable.
 

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"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...", I think that is a wouldn't not a couldn't. You don't go into this scale of design and manufacturing without estimating life expectancy of parts. I don't particularly see anything sinister in this, it is not in BMW's interests to manufacture something that is going to put you off the BMW brand. I suspect it is more to do with wanting to get some real world data before they commit.

I also wouldn't draw too many comparisons with technology used in other fields. If you used the same battery technology in cars that you have in mobile phones, your EV battery would be knackered after a very short time. The principle of using brushes may be old but the implementation can vary a lot.

I would hope that BMW have come up with a design that gives a reasonable (insert your own figure here) longevity but it will be a wear and tear part and being a sealed unit will probably not be particularly cheap.
 

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Here in California, the law on BEV batteries say, they must last 10 years or 150K miles whichever comes first.

I can't imagine the brushes not being able to be replaced. I replaced the brushes on my alternator in my 335i and when the car was totaled with 240K miles the alternator was still great.

I have owned BMWs for more than 30 years and I've never replaced an engine, transmission or differential from failure.

Sent from my LE2125 using Tapatalk
 

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If you look at the close-up picture, second picture below title "The Fifth Generation BMW electric motor", you can see clearly one of the brushes, with a little wire soldered to it, that contacts a circular copper ring on the motor axle, just above the label "Schleifringmodul" (Slip ring module), and pushed against the ring by a spiral spring, the smaller one of the 3 brushes circling this ring. Enlargement below. This seems to be one out of 2 slip ring modules on both sides of the circular black plate (you can see the 2nd wire connected to the terminal going through the plate to the other side), and they are indeed inside a closed section at the end of the motor, that does seem easily serviceable. The size of that brush seems to indicate that it will NOT wear too much with time (else it would be much longer), so it is likely that BMW has some self-lubrication technology that allows rotating contact with minimal wear. This aligns with the feedback of owners above that this is a technology from BMW with reliability proven over tens of years.

Automotive tire Automotive lighting Camera lens Motor vehicle Rim
 

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If you look at the close-up picture, second picture below title "The Fifth Generation BMW electric motor", you can see clearly one of the brushes, with a little wire soldered to it, that contacts a circular copper ring on the motor axle, just above the label "Schleifringmodul" (Slip ring module), and pushed against the ring by a spiral spring, the smaller one of the 3 brushes circling this ring. Enlargement below. This seems to be one out of 2 slip ring modules on both sides of the circular black plate (you can see the 2nd wire connected to the terminal going through the plate to the other side), and they are indeed inside a closed section at the end of the motor, that does seem easily serviceable. The size of that brush seems to indicate that it will NOT wear too much with time (else it would be much longer), so it is likely that BMW has some self-lubrication technology that allows rotating contact with minimal wear. This aligns with the feedback of owners above that this is a technology from BMW with reliability proven over tens of years.

View attachment 5166
@MinhSATx Thank you for comments but one day all the three brushes will be completely used and need to be changed, no? I did this experience with my central vacuum after many years, it stopped running and the Guy has changed the brushes and it's running like new. On a car of $80,000 it's look cheap no?
 

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@MinhSATx Thank you for comments but one day all the three brushes will be completely used and need to be changed, no? I did this experience with my central vacuum after many years, it stopped running and the Guy has changed the brushes and it's running like new. On a car of $80,000 it's look cheap no?
I confess, I’m a bit surprised by all of this too. What other EV manufacturers are using brushes?
 

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@MinhSATx Thank you for comments but one day all the three brushes will be completely used and need to be changed, no? I did this experience with my central vacuum after many years, it stopped running and the Guy has changed the brushes and it's running like new. On a car of $80,000 it's look cheap no?
Your vacuum cleaner has a high speed single phase motor (essentially a DC motor that can also run on AC) using commutators with all the slots, not slip rings. The commutator based A/C motor sparks when it runs, and the slots in the commutator act like rough sandpaper wearing brushes very quickly. This is absolutely no comparison (apples to elephants) to the smooth slip ring with lubricated brushes used in the BMW motor. It's the engineering tradeoff for not using rare earth magnets (from China), and gives an additional controllable parameter to operating the motor.
 

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Your vacuum cleaner has a high speed single phase motor (essentially a DC motor that can also run on AC) using commutators with all the slots, not slip rings. The commutator based A/C motor sparks when it runs, and the slots in the commutator act like rough sandpaper wearing brushes very quickly. This is absolutely no comparison (apples to elephants) to the smooth slip ring with lubricated brushes used in the BMW motor. It's the engineering tradeoff for not using rare earth magnets (from China), and gives an additional controllable parameter to operating the motor.
Thank you to clarify, I VERY like you explanation :D
 

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Your vacuum cleaner has a high speed single phase motor (essentially a DC motor that can also run on AC) using commutators with all the slots, not slip rings. The commutator based A/C motor sparks when it runs, and the slots in the commutator act like rough sandpaper wearing brushes very quickly. This is absolutely no comparison (apples to elephants) to the smooth slip ring with lubricated brushes used in the BMW motor. It's the engineering tradeoff for not using rare earth magnets (from China), and gives an additional controllable parameter to operating the motor.
However I imagine there's a dramatic difference between the 'run times' of a car's electric motor vs a vacuum cleaner...unless you're really anal about dirt in the house. ;)
 

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Hi,

I might be wrong but I believe that this construction is necessary - to build a motor than can rotate without magnetic resistance, that the i4M50 uses to reduce consumption by disabling the front motor when not needed.
 

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However I imagine there's a dramatic difference between the 'run times' of a car's electric motor vs a vacuum cleaner...unless you're really anal about dirt in the house. ;)
That's why my comparison was an alternator in a 335i.

It also isn't a smooth ring brush contact but lasted 140k miles.

If the contact was smooth I suspect my alternator would have lasted twice as long.

Sent from my LE2125 using Tapatalk
 
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