Gads Spark attack-decay

[Orin Eman]

> don't know about 'state of the art', but back in the
> eighties the Bosh Motronic ecms used to reduce the timing in
> steps of 3 degrees (maybe related to the max resolution of
> one flywheel tooth?) when knocking was detected. 

On the Audis which use the flywheel teeth, there are 135 teeth.
They can trigger the ignition off the rising or falling edge of
the signal, so the resolution is 4/3 (1.33) degrees.  IMO,
retarding this much wouldn't be enough, so they retard two steps,
or 2.67 degrees.  I'd guess that 3 deg is what they really aim
for.  In this case, advance is done in 1.33 degree steps.
I wouldn't know if they are aiming for 1 degree or half
the retard step...  they don't get a choice.

BTW, I've scoped the flywheel tooth signal inside the ECU
after conditioning.  It's pretty close to a 50% duty cycle
square wave.

This was before they used Motronic... the Motronic version
uses the same sensors, so I'm assuming that they trigger
off the teeth in the same manner.

Orin.