Saturday, January 3, 2015

Toyota CTS pedal flexing - interaction of mechanical and electronic problems

Toyota's pedal supplied by CTS, with Hall sensors in left center

Looped video of CTS pedal flexing when pressed

This video was shared by Dr. Antony Anderson some time ago. I understand that he made it himself. The looped video clearly shows how the pedal assembly flexes when pressed in a way that mimics the pressure from a driver's foot.

This is the pedal that was recalled for "sticky pedal" and the fix was to insert a shim to reinforce it. It is not the tin whiskers pedal. It is the slightly more robust replacement for the tin whiskers pedal of the 2002-2006 MY Camry, which had a potentiometer sensor.

Not being an engineer, I cannot comment with any authority, but I think it is plain to anyone that the pedal is not strong enough to remain completely rigid under typical use conditions, and even more under more extreme conditions such as someone jamming the "pedal to the metal."

This mechanical weakness links to potential electronics problems because there is a very close clearance between the pedal's sensor housing, that narrowly encloses the pedal sensor assembly, and the magnets that slide up and down next to the sensors, outside the sensor housing. The pedal works because the sensors inside pick up the varying strength of the magnetic field and covert it to a digital signal. When the pedal flexes, as seen in the video, the magnet housing can rub direcly along the sides of the sensor assembly housing and scrape it when the pedal is pressed. Over time the wear from this scraping can create unforseeen problems like roughness or holes in the sides of the sensor housing. Then the pedal can catch at a certain position and the pedal signal ceases to reflect driver intent, and sometimes the ETCS does not notice, and the driver loses control of the speed. Worse, the sensor housing might eventually wear through and expose the sensors to the outer environment, admitting moisture and salts, and anyone knows that either or both can lead to short circuits, or corrosion that could also lead to unpredictable results. When the ETCS has incomplete failsafes that cannot distinguish the erroneous signals sent by short circuits, sudden acceleration can result.

This is my guesswork about what is happening, based on a limited understanding gleaned from various engineering sources. I am just presenting it because I found it interesting (horrifying) that the interaction between the mechanical and electronic elements in the design is what causes the unpredicable vehicle behavior. To me, this is logically quite similar to both the GM and Takata defects in the sense that the integration of electronic controls in a fundamentally mechanical machine, when coupled with a save-money attitude, can lead to all kinds of mechanical-electronic interactions that are not fully predicted by engineers.

I despise defense lawyers who write millions of words for legal defense filings that in effect obscure the plain truth about such physical realities.