DIYbanter - View Single Post - Accelerator stuck wide open while car is going fast: what should you do?

TMS320

On 29/07/18 09:16, wrote:
On Thu, 26 Jul 2018 11:29:14 +0100 TMS320 wrote:
On 26/07/18 09:38, wrote:

It has to lock up or at least considerably slow down first, the
ABS isn't psychic. I imagine the algorithm simply takes the
average of the wheel speeds

and then operates on any wheel going much slower or much faster.
Of course
that
has a number of potential issues, eg on snow or ice the ABS has
no way of knowing if the car is skidding or parked, if 1 wheel is
going much faster than the other 3 is that wheel spinning or are
the others skidding etc. I'm sure car manufacturers have written
some clever algorithms that remember the speed up until now and
cross check against engine rpm and gear but
there's
only so much it can do.

This was discussed in control theory at university. Part of the
algorithm is double or triple differentiation of rotation speed. In
the days before cheap microprocessors easy to do with phase lock
loops.

I assumed ABS systems had always been microcontroller controlled,
didn't realise there were analogue versions. Interesting to know.

The electronics industry didn't make a quantum leap from analogue to
microcontroller. There was an intervening period with boards full of
logic chips, plenty of which would have been part analogue, such as
monostables. Then, not all of it could instantly be mopped up by micros.

I guess they have put many more deductions in modern systems.
Clever people have been working on it for 40 years and no doubt
they have covered any eventuality people on news groups can
imagine.

No doubt, but the more complex ian algorithm becomes the more likely
it is that there's some nasty undisovered edge cases lurking in there
either due to the implementation or the algorithm itself which might
cause serious problems. In aviation they do formal proof checking,
multiple implementations of the same algorithm by different teams and
god knows what else to mitigate this, but I doubt the automotive
industry is quite so thorough simply due to cost.

Formal proof has limits. Test, test and test again on real product.