According to a new petition, the National Highway Traffic Safety Administration (NHTSA) is re-investigating whether a design flaw in the Tesla Model 3 could cause the vehicle to accelerate suddenly. The application, filed by Dr. Ronald Belt, claims there is new evidence that the Model 3’s inverter design may cause the vehicle to misread the gas pedal signal even when the driver is not pressing on it.
The issue was first raised with NHTSA in 2019 by Brian Sparks, who asked the agency to force Tesla to recall all Model S, X and 3 models produced between 2013 and 2019. However, after an evaluation, NHTSA’s Office of Defect Investigations (ODI) agreed with Tesla’s conclusion that in nearly all of the 232 crashes cited in the original application, the driver stepped on the gas pedal. is derived from data collected by the vehicle. As a result, the ODI rejected Sparks’ application for 2021.
However, this conclusion did not please everyone, as in at least one incident, the driver claimed that the vehicle accelerated while they were outside. Now, based on the new information, Dr. Belt has submitted a new application to ODI to re-examine Sparks’ application.
Dr. Belt’s new allegations are based on information gleaned from enthusiasts dismantling Tesla vehicles for purposes such as electric vehicle conversions. In the case of the Tesla Model 3, Dr. Belt alleged a design flaw that could In rare cases, the vehicle mistakenly believe that random voltage fluctuations are the accelerator signal. That’s because the Model 3’s inverter uses a single 1.65-volt calibration signal to sense four ADCs (analogue-to-digital converters, or the part that converts throttle position into an electrical signal that the vehicle can read). In some cases, especially when the vehicle is moving slowly, such as when more power is needed when turning, the current on the 12-volt battery can cause relatively large voltage fluctuations within the system, causing the inverter to deduce that the gas pedal is being pressed, resulting in a sudden, unintentional acceleration.
According to Dr. Belt, the chances of this happening are low because the voltage fluctuations (which last for microseconds) have to happen at the same time as the vehicle’s ADC detection (also lasts for microseconds). However, this low probability coincides with more than 200 accidents reported between 2013 and 2019. He also claimed that due to the nature of the fault – the inverter misinterpreting voltage fluctuations as throttle inputs – it would not be recorded as an error. So while owners reported they were off the gas pedal, vehicle data was inconsistent with their claims, which may explain why the ODI rejected the application in the first place.
Dr. Belt also further tested his theory by deliberately feeding the wrong calibration voltage into the inverter. When they input 0.28 volts or less (instead of the expected 1.65 volts), which can happen when the 12 volt supply drops briefly to 2.14 volts, the accelerator pedal position (APP) sensor reads the equivalent of full throttle value. This can cause the car to accelerate out of control even when the driver is not pressing on the gas pedal.
The study also proposes two solutions. The first option is to add a second 12-volt supply line with its own battery and DC/DC converter. This power supply line is only used to provide clean power to the App sensors and ADC. The second option is to modify the calibration program software by testing the calibration voltage before use. The latter is easier and cheaper to implement in existing vehicles since only a software update is required.
According to the petition, all Tesla models are affected, although the Model S and Model X use slightly different DSP controller chips. The NHTSA investigation mentioned 1.8 million vehicles were involved in this new investigation. The discovery comes as comforting news to owners whose vehicles spun out of control and were told they were to blame, but it may be too late for some.
In addition, it is learned from Bloomberg that the National Highway Traffic Safety Administration (NHTSA) also sent a letter to Tesla on July 3, asking the automaker to update its information requirements related to its Autopilot automatic assisted driving defect investigation. In response, NHTSA asked Tesla to describe any changes made to the vehicles under investigation that could relate to driver engagement or attention.
