Brake Overrides: The Devil in the Details

Why Toyota does not install brake overrides of the throttle control system on all their recalled cars and future models is a topic of considerable discussion.   Toyota has indeed announced that they will have such ‘smart brakes’, which prioritize braking actions over throttle actions’, in future models.  In addition, some but also past models will be upgraded with a software patch.

Let’s look at some details of what this means.  In a fully throttle-by-wire system like Toyota’s ETCS-i, the override mechanism can be made completely electronic as well.  If the brake pedal is pressed, that information can be communicated to the throttle control system (using a message over a wire/communication bus), which in turn can close the throttle in response, and independent of the position of the gas pedal.   Cost: a software update.  But, this solution makes several assumptions:

  1. There exists a communication medium between the braking system and the throttle control system.   This may or may not be true.
  2. There exists enough bandwidth/message slots in this communication medium that do not disrupt other messages.  Probably true, if the medium by itself is present.
  3. The ECU (Electronic Control Unit, i.e. computer) and software are all functioning correctly so that the brake override message is both received and processed correctly.  If the root of the problem is that the ECU and/or software has failed in some way, the override will not work.  However, an electronic override would be better than having no override at all.
  4. The throttle mechanism continues to work correctly under electronic control.  This aspect too would depend on whether the root of the problem lies at the interface between the ECU and the throttle control.

An override mechanism that is better and stronger than the electronic mechanism would be mechanical in nature.  In this solution, when the brake pedal is pressed, it mechanically (or electro-mechanically) pushes the throttle to close.    The link from the brake pedal to this mechanical override could be mechanical or electronic (but must be completely independent of the throttle control electronics).

Yes, this superior fail-safe alternative would be costlier. Nevertheless, such independent fail-safe mechanisms should be deemed necessary in all future vehicles particularly for the safety-critical subsystems for acceleration, braking, steering and transmission control.   Using laws of physics (such as gravity or Maxwell’s Laws for Electro-magnetism) so that the fail-safe mechanisms will be guaranteed to kick in is a ripe area of innovation as electronics and software take on more and more functionality in automobiles.


3 Responses to “Brake Overrides: The Devil in the Details”

  1. Kate Hall Says:

    I have a 2006 Toyota Corolla. While I haven’t experienced any problems with unintentional acceleration, I do have a Sym Tech Elctronic Corrosion Control device installed for rust protection on my vehicle. I recently read an article in Maclean’s magazine that talked about “random, intermittent electronic faults” that could be caused by electromagnetic interferenence. I’m wondering if this device could interfer with the functionality of the ECU. Mine recently failed and had to be replaced. Could there be a connection here??

    • safetransportation Says:

      You may want to check with the manufacturer. The location of the device relative to the ECU, the material used by the enclosure of the device, and shielding used on cables could make a difference in principle.

  2. Mandatory brake overrides are not a panacea! « Blog on Automotive Safety Says:

    […] The question is not whether there should be a brake override mechanism, but what kind of brake override should be in place.   A fully electronic override may not even be recognized if implemented in the wrong subsystem within an automobile.  A mechanical override on the other hand will have independent failure characteristics.   I have made this argument in a previous blog posting here. […]

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