5 ms·

Wow. A wonderful article. The real question is, just how in-control is the computer. And how much has to go wrong such that uncontrollable acceleration happens

Wow. A wonderful article. The real question is, just how in-control is the computer. And how much has to go wrong such that uncontrollable acceleration happens and nothing can override that acceleration such that no matter what you do the computer makes the car go into "drive" and accelerate to the max, without responding to other parts of the system like the breaks and such.

kolosy 17y ago
short answer - the brake system has to suffer a mechanical failure. read the part where "brakes always win over engines".
- deleted 17y ago
  [deleted]
sliverstorm 17y ago
The accelerator pedal would have to be immovable, frozen in place. The ignition switch would have to lock or otherwise malfunction The shift lever or clutch or automatic shift lever would have to malfunction The brakes would have to overheat (does not really happen much in a production car). It is not 100% true that brakes will always overpower the engine, but the cases in which they don't are the ones with massive 700hp engines with big 'ol turbos and stock drum brakes, and in that situation it's the owner's responsibility. There would also have to be no runaway truck exits. If you were creative and knew something about cars, you could pull one of many fuses from the fuse box. On cars I've serviced, the computer fuse is always in the driver kick panel, so just rip off that panel and start yanking fuses while watching the road. It should be noted that the e-brake on fwd cars is not your best choice (though still a decent choice); while a locked up wheel provides drag, it does not apply as much drag as a rolling wheel with maximum braking (which can easily be obtained cause of ABS). Also at extreme speeds you run the risk of a spin, which puts you possibly at risk for a roll.
- lanstein 17y ago
  There is about a .000000001% chance you just saved my life. Thank you. (edited math)
- jonknee 17y ago
  > The accelerator pedal would have to be immovable, frozen in place. In recent Toyota vehicles the pedal isn't connected to the throttle--it's drive by wire. In theory the computer could continue accelerating regardless of the gas pedal's position.
  - cryptnoob 17y ago
    I've designed systems like this. You use redundant potentiometers to sense throttle position. If they don't match within 5%, you power down. You also toggle bits in your code. One in the main loop, another in any interrupt service routine that you are dependent upon. These bits then go to a GPIO so that the GPIO toggles. If the ISR freezes or the main loop freezes, the GPIO quits toggling. You then have an hardware, RC-Diode type circuit, that stays high if it's input toggles, but goes low, if it's input goes low and stays low, or goes high and stays high. The output of this circuit drives a relay, so that if the CPU quits toggling the GPIO, the relay clicks off. The output of that relay is a dead-man's switch that powers down the vehicle. The end result is a hardware fail-safe if the CPU misbehaves. There are other tests to confirm that the relay isn't frozen, that the RC-Diode circuit isn't frozen, etc. So, in theory, if a high-school sophomore designed the vehicle, you might have a problem. Otherwise, I think you don't give the engineers that design these systems enough credit.
    - jonknee 17y ago
      ... And yet there are out of control cars without the pedal being stuck. "Well, I have many models of Prius that got recalled, but I have a new model that didn't get recalled. This new model has an accelerator that goes wild, but only under certain conditions of cruise control. And I can repeat it over and over and over again--safely." "This is software. It's not a bad accelerator pedal. It's very scary, but luckily for me, I can hit the brakes," he said. -- Steve Wozniak http://news.cnet.com/8301-13924_3-10445564-64.html http://news.cnet.com/8301-13924_3-10445564-64.html

kolosy 17y ago

short answer - the brake system has to suffer a mechanical failure. read the part where "brakes always win over engines".

deleted 17y ago
[deleted]

sliverstorm 17y ago

The accelerator pedal would have to be immovable, frozen in place. The ignition switch would have to lock or otherwise malfunction The shift lever or clutch or automatic shift lever would have to malfunction The brakes would have to overheat (does not really happen much in a production car). It is not 100% true that brakes will always overpower the engine, but the cases in which they don't are the ones with massive 700hp engines with big 'ol turbos and stock drum brakes, and in that situation it's the owner's responsibility. There would also have to be no runaway truck exits. If you were creative and knew something about cars, you could pull one of many fuses from the fuse box. On cars I've serviced, the computer fuse is always in the driver kick panel, so just rip off that panel and start yanking fuses while watching the road. It should be noted that the e-brake on fwd cars is not your best choice (though still a decent choice); while a locked up wheel provides drag, it does not apply as much drag as a rolling wheel with maximum braking (which can easily be obtained cause of ABS). Also at extreme speeds you run the risk of a spin, which puts you possibly at risk for a roll.

lanstein 17y ago
There is about a .000000001% chance you just saved my life. Thank you. (edited math)
jonknee 17y ago
> The accelerator pedal would have to be immovable, frozen in place. In recent Toyota vehicles the pedal isn't connected to the throttle--it's drive by wire. In theory the computer could continue accelerating regardless of the gas pedal's position.
- cryptnoob 17y ago
  I've designed systems like this. You use redundant potentiometers to sense throttle position. If they don't match within 5%, you power down. You also toggle bits in your code. One in the main loop, another in any interrupt service routine that you are dependent upon. These bits then go to a GPIO so that the GPIO toggles. If the ISR freezes or the main loop freezes, the GPIO quits toggling. You then have an hardware, RC-Diode type circuit, that stays high if it's input toggles, but goes low, if it's input goes low and stays low, or goes high and stays high. The output of this circuit drives a relay, so that if the CPU quits toggling the GPIO, the relay clicks off. The output of that relay is a dead-man's switch that powers down the vehicle. The end result is a hardware fail-safe if the CPU misbehaves. There are other tests to confirm that the relay isn't frozen, that the RC-Diode circuit isn't frozen, etc. So, in theory, if a high-school sophomore designed the vehicle, you might have a problem. Otherwise, I think you don't give the engineers that design these systems enough credit.
  - jonknee 17y ago
    ... And yet there are out of control cars without the pedal being stuck. "Well, I have many models of Prius that got recalled, but I have a new model that didn't get recalled. This new model has an accelerator that goes wild, but only under certain conditions of cruise control. And I can repeat it over and over and over again--safely." "This is software. It's not a bad accelerator pedal. It's very scary, but luckily for me, I can hit the brakes," he said. -- Steve Wozniak http://news.cnet.com/8301-13924_3-10445564-64.html http://news.cnet.com/8301-13924_3-10445564-64.html