Throttle-by-Wire

[Orin]

> Simple scenario: twisty mountain road, nighttime, foggy, slick.
> Few drivers in the world would be using cruise control. The TBW
> controller sees full voltage from the throttle potentiometer,
> did the driver floor it, or did the ground wire fall off from
> hitting a pothole? The lives of the occupants probably depends
> on how it reacts, 'cuz if you can turn the ignition key to just
> the right spot where the engine stops but the steering wheel isn't
> locked in such a situation, you're much better than 99 and 44/100ths
> percent of the drivers on the road.
> 
> Another simple scenario: the butterfly feedback pot says the blade
> angle is less than the TBW controller thinks it should be, is it
> because the driver commanded more throttle, is the shaft binding,
> did the voltage droop due to the AC compressor engaging, or did
> the positive wire fall off? Each situation requires a different
> response from the controller.

This is why the VW/Audi system uses two pots on both throttle and
butterfly, wired so that as the voltage from one pot increases, the
voltage from the other decreases.  Loss of the ground wire pegs
the output from both - an obvious error.  Similarly, loss of the
positive wire would give a ground output from both.

Orin
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