hallcp said:
This article
https://electrek.co/2020/06/12/when-an-out-of-warranty-ev-fails-who-you-gonna-call/ in Electrek has a nice discussion of the fatal motor problems afflicting some Model B's. Tony Williams of "QC Charge" in California gives the best explanation I've seen of this problem. I believe Tony has been mentioned before in this forum, but some years ago (correct me if I'm wrong).
I've reread the article because some of the technical "facts" just don't make sense to me. This may be due to overzealous editing for the article, or some glossing over of details by the author and his source.
For some reason that link no longer works tonight, I wonder if someone else challenged the piece?
My observation is that there are two distinct failure modalities for MY2014 MUs. Firstly, we have the flooded coolant problem, where electrically conductive coolant shorts out the inverter, basically an electrical fault. This seems to be the majority of failures reported here. Secondly, there's the Motor Whine problem, where the vehicle makes a progressively louder noise until it quits. From MBUSA's point of view, where they do module-level diagnosis and swapping, either case requires a completely new MU.
However, the motor whining is caused by failure of the main bearings that support the rotor inside the motor. While it is the only part of the motor that spins, it does drive the transmission gearing, so its wrong to say there's only one moving part. One reason for the failure of MY2014 Tesla made motor units was reported as incorrect tolerance on the machining for the bearing supports, leading to binding and eventual failure.
Another factor with an AC induction motor (the type used by Tesla and other EV drive trains, but not the Tesla Model 3 which uses a Permanent Magnet Synchronous Reluctance Motor or “PMSRM") is the electrical charge formed on the rotor itself.
Here's a scholarly paper explaining the problem.
This results in electrical arcing between the rotor and stator or motor frame. Which leads to premature failure of the bearings, as they are the only electrical path between the two. Tesla uses a high-tech electrically conductive brush to provide low electrical resistance and direct the current to bypass the bearings. Obviously, bearings could still fail due to other mechanical issues. Other solutions include electrostatic shielding, as cited in the paper above.
Collectively, we are early adopters of EVs, particularly the MB B250e. The price for being first in is often we are the first to find bugs.
Peter,
