[jonknee]

... 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

[cryptnoob]

This is more believable to me, as the "set-point" for cruise control is not dependent upon throttle position, but instead, is remembered by the computer. There's nothing to check against to insure believability.

More suspect, in my opinion, is that in a cruise control, you have a feedback system, based on car speed. The car speed is almost certainly redundantly sensed, so that's no worries, but the feedback loop itself could potentially go oscillatory if there were other variables introduced that hadn't been designed for. Those variables could be pretty subtle. For example, maybe the gear motor that you use to mechanically control the engine gets sourced from another distributor, and they give you a better one, that has more torque. Perhaps that throws off the stability analysis that you had done. Tons of things could change somewhere between the 500K's car and 1M's car you produced, lots of different vendors and permutations could come into play that could throw off the stability of a cruise control, I would think.

EDIT: They're probably using feedback in the control motors as well (servos), so that's a non-realistic example, but it illustrates the problem.

[CamperBob]

To be fair, Woz's account seems to be limited to the case where someone uses the cruise control above 80 MPH, far from what the control loop was optimized for. I didn't see anything in what he wrote that could possibly have any bearing on the cases being examined.

Brain-dead cruise control behavior is nothing new. My '92 Porsche 968 would cheerfully redline the engine if you disengaged the clutch with cruise active.