Ignition Controllers - knock detection

[Steven Arnold]

> I remember reading a formula somewhere that relates the knock
> frequency to the engine bore. It was a simple thing like Knock
> Freq=Constant/Bore. I'd guess that the frequency would change with a
> turbo engine as the speed of sound would change with gas pressure.

In the sillicon chip engine knock indicator article, they quote the
formula -

F=900/(pi*r)
r=cylinder radius in metres 

However, I think they proceed to do some calculations that seem to be
based bore diameter, rather than radius - which seen to be incorrect.

I have also read that the knock frequency reduces the later the knock
occurs or is measured - due to the increasing volume of the cylinder.
So positioning of the knock detection window will have some effect on
the freq - however this probably wouldn't matter, as the bandwidth of
your bandpass filter would be wider than this freq variation.

-- 
sarnold at iname.com
http://www.geocities.com/MotorCity/1309
RE - That is all, there is no more.