Photo: Ton Aarts via Twitter | Edited
In a petition sent to the NHTSA, Ronald Belt claimed that the sudden unintended acceleration (SUA) cases reported by many owners were caused by a faulty inverter design. Since autoevolution broke the story, Tesla hackers have offered their own side of this story, and I believe you should read it.
On Tuesday, autoevolution discovered that the NHTSA reopened the investigation into the SUA cases. New evidence at the Office of Defects Investigation (ODI) showed that a faulty inverter design might have triggered sudden unintended acceleration events. Specifically, intermittent high electrical current demands on the vehicles' 12-volt systems may have caused some or all of the incidents. The petition cites open-source research into the intricate electronics that control the drive units in a Tesla Model 3 and other models.
To make the matter worse, the condition that triggers an SUA event is perceived by the car as a genuine accelerator press. This would explain why the logs analyzed by Tesla and the NHTSA show that drivers pressed the accelerator pedal all the way down, although many were convinced they did not touch the accelerator.
The explanation for this condition has to do with the way Tesla uses a voltage reference derived from the 12-volt system to calibrate the accelerator pedal position (APP) sensor. The paper also claims that the researchers have been able to replicate the problem, although they did not have a Tesla EV to test it on a real vehicle. Several solutions to eliminate the issue were also offered. Since I've already summarized the petition, please read the details in the original article.
There's one thing that the paper doesn't talk about: the failsafe measures Tesla implemented to prevent this kind of problem. Everyone Tesla owner knows that simultaneously pressing the accelerator and brake will cut the electric motors' power. Sadly, the petition doesn't take this into consideration. Tesla logs supplied to the NHTSA show the brakes were not applied, which, together with the accelerator pedal pressed all the way down, led to the conclusion the SUA events were caused by driver error.
There's more to it, as the autoevolution article caused ripples in the Teslasphere. People with knowledge of Tesla's internal circuitry have expressed doubt that the inverter design cited in the petition is similar to what Tesla uses. Jason Hughes (@wk057) is well-known for his work on Tesla, especially its battery packs, the infotainment system, and other hardware. Hughes has often criticized Tesla but praised the inverter controller design, which he said was already excellent in 2012 and has only improved since then.
Hughes doesn't believe a drop in the 12-volt rail voltage, as described in the petition, will cause a calibration error leading to an SUA event. The 12-volt rail is monitored by dozens of modules, which would log any low-voltage conditions. Hughes has personally analyzed logs resulting from SUA crashes and thinks a situation like the one described in Ronald Belt's petition is impossible. No log he examined suggests an associated 12-volt drop of any kind, and the NHHTSA had the same information when it decided to close the SUA investigation.
"Tesla's accelerator pedal power, while derived from the 12-volt system, is using two independent isolated 5-volt supplies," writes Hughes. "There is no way for a fault in that system to create the correct signals for full acceleration. It's not possible. If somehow the 12-volt system were so low it caused the isolated 5-volt supplies and their capacitors to drop below the expected voltages, that'd sag the entire curve of the dual sensors, leading to a pedal fault, not full acceleration."
Another known Tesla hacker, Green (@greentheonly), thinks that the claims in the paper should be easy to validate if anyone with a spare inverter controller PCB is willing to try. Still, this should be the first task on the NHTSA's experts' agenda. Hopefully, they will get to the bottom of this issue and clear the waters regarding Tesla's sudden unintended acceleration.
To make the matter worse, the condition that triggers an SUA event is perceived by the car as a genuine accelerator press. This would explain why the logs analyzed by Tesla and the NHTSA show that drivers pressed the accelerator pedal all the way down, although many were convinced they did not touch the accelerator.
The explanation for this condition has to do with the way Tesla uses a voltage reference derived from the 12-volt system to calibrate the accelerator pedal position (APP) sensor. The paper also claims that the researchers have been able to replicate the problem, although they did not have a Tesla EV to test it on a real vehicle. Several solutions to eliminate the issue were also offered. Since I've already summarized the petition, please read the details in the original article.
There's one thing that the paper doesn't talk about: the failsafe measures Tesla implemented to prevent this kind of problem. Everyone Tesla owner knows that simultaneously pressing the accelerator and brake will cut the electric motors' power. Sadly, the petition doesn't take this into consideration. Tesla logs supplied to the NHTSA show the brakes were not applied, which, together with the accelerator pedal pressed all the way down, led to the conclusion the SUA events were caused by driver error.
There's more to it, as the autoevolution article caused ripples in the Teslasphere. People with knowledge of Tesla's internal circuitry have expressed doubt that the inverter design cited in the petition is similar to what Tesla uses. Jason Hughes (@wk057) is well-known for his work on Tesla, especially its battery packs, the infotainment system, and other hardware. Hughes has often criticized Tesla but praised the inverter controller design, which he said was already excellent in 2012 and has only improved since then.
Hughes doesn't believe a drop in the 12-volt rail voltage, as described in the petition, will cause a calibration error leading to an SUA event. The 12-volt rail is monitored by dozens of modules, which would log any low-voltage conditions. Hughes has personally analyzed logs resulting from SUA crashes and thinks a situation like the one described in Ronald Belt's petition is impossible. No log he examined suggests an associated 12-volt drop of any kind, and the NHHTSA had the same information when it decided to close the SUA investigation.
"Tesla's accelerator pedal power, while derived from the 12-volt system, is using two independent isolated 5-volt supplies," writes Hughes. "There is no way for a fault in that system to create the correct signals for full acceleration. It's not possible. If somehow the 12-volt system were so low it caused the isolated 5-volt supplies and their capacitors to drop below the expected voltages, that'd sag the entire curve of the dual sensors, leading to a pedal fault, not full acceleration."
Another known Tesla hacker, Green (@greentheonly), thinks that the claims in the paper should be easy to validate if anyone with a spare inverter controller PCB is willing to try. Still, this should be the first task on the NHTSA's experts' agenda. Hopefully, they will get to the bottom of this issue and clear the waters regarding Tesla's sudden unintended acceleration.
Just sent this in a DM reply and will c/p here:
— Jason Hughes (@wk057) July 5, 2023
Howdy. The open source "research" into the Tesla inverters is flawed... which is why the open source controllers always damage the units when used.
Tesla's accelerator pedal power, while derived from the 12V system, is using two…
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