this post was submitted on 04 Jul 2023
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RealTesla

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Breaking: NHTSA Petition Claims Tesla Sudden Unintended Acceleration Is Real (but Fixable) (www.autoevolution.com)
submitted 1 year ago* (last edited 1 year ago) by dragontamer to c/realtesla
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EDIT: This PDF contains very detailed electrical information for the EEs who wanna go through the complaint: https://www.autoevolution.com/pdf/news_attachements/breaking-nhtsa-petition-shows-tesla-s-sudden-unintended-acceleration-is-real-and-curable-217525.pdf

Last year at /r/RealTesla, a Chinese video of a car rocketing at full speed for 1+ minutes before crashing / killing a pedestrian made the rounds. We all recognized it as one of the weirder cases of "Sudden Unintended Acceleration", and I think that particular video really changed some minds.

https://www.republicworld.com/world-news/china/tesla-to-assist-police-probe-fatal-model-y-acceleration-incident-in-china-articleshow.html

While a lot of SUA events are from driver-error, it began a search into why Teslas seemed to be getting more SUA above-and-beyond the industry normal. This investigation (now filed under NHTSA) suggests that the ADC could be miscalibrated during a load-dump (or other electrical surge-like) scenario.

If the ADC associated with the accelerator pedal is off, then the Tesla will have the pedal at the wrong level of acceleration until the next calibration event, which is not going to happen until over a minute later.

This is extremely similar to that Chinese runaway Tesla, and perfectly seems to explain it. I'm glad that someone seems to have gotten to the bottom of this.

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[–] Abhalphiest 2 points 1 year ago (3 children)

Wow. For someone who knows nothing about EE, is this a hardware or software level problem? Would this require a physical (ie not OTA) recall?

[–] dragontamer 5 points 1 year ago* (last edited 1 year ago) (2 children)

I'm Bachelor's level EE and this PDF here is Master's level. But I guess I'm good enough to explain the problem and tell you its hardware.

So, how can a negative-going voltage spike occur on the attenuated 5V calibration voltage while it is being digitized by the ADC? First, the negative-going voltage spike can occur on the "12V' supply line because it is used by the electric power steering booster motor, which draws a whopping 100A or greater DC current in Tesla vehicles. This current load is so high because the weight of Tesla's high voltage battery makes Tesla vehicles some of the heaviest passenger vehicles on the road, requiring a power steering gystem with the greatest torque and the highest current available. Then, when the power assist motor in this system is suddenly turned on by turning the vehicle's steering wheel while making a sharp low-speed turn in a parking lot, the assist motor suddenly draws an inrush current three to five times higher than the DC current for several hundred microseconds. This higher inrush current can't be supported by the "12V' battery, which can supply a maximum current of only 100A or less, and the DC/DC converter, which can only supply about 200A or less. Therefore, the "12V" supply line is pulled down to near zero volts for several hundred microseconds. See Figures 12 and 13 which provide evidence on the existence these voltage dips.

Specifically caused by this. So large motors (and other power-level electricity) changes the voltage. Voltages, and currents, associated with motors (especially induction motors), can change the voltage on other lines.

It seems like the 12V supply line, that eventually provides the sensor's electricity, is being wrecked by the electrical motors / noise under normal operations. The only solution is to physically change the electrical lines entirely (IE: Better isolation). The electrical motor associated with turning the steering wheel, in particular.

Notice how the 12V line is... erm... not 12V anymore? No computer chip can survive this level of voltage droop.

Further note: the designs here are OpAmps and ADCs, analog electronics. The location of the pedal on the accelerator is stored as a voltage at this point of the design. ("Before" the pedal information gets to the computer, it needs to be a physical voltage, if that makes any sense). The entire criticism here is on this analog / voltage level analysis, before the (traditional) computers are involved. (Arguably, this analog-circuitry is analog-computers. OpAmps are really cool and stuff, but these voltage-droops cause issues cause it changes the physical values that these things calculates)

[–] Abhalphiest 2 points 1 year ago (1 children)

Thank you for the explanation, it helped.

This should very clearly be addressed immediately, and.. wow, what a huge bill (potentially) upcoming for Tesla.

[–] dragontamer 4 points 1 year ago* (last edited 1 year ago)

At /r/RealTesla, we've been following this SUA problem for literally years.

A lot of us thought it was just the typical "stupid driver" pedal problem (Ex: Toyota's SUA turned out to be just a bunch of people confusing the pedals). A lot of us thought it was due to one-pedal driving (training the Tesla drivers to confuse the pedals).

Turns out it was the hardware this whole time.

Given the level of detail, reverse engineering, and electrical knowledge in this .pdf, I really don't see how Tesla survives this. They're on the hook for many dozens of deaths already, if this .pdf is true.