Ignition Controllers

[Seth]

On Fri, 25 Jul 1997, Rob Skala wrote:

> 
> Hi All,
> 
> I am contemplating constructing a digital igniton system (similar to the
> one designed by Tim Drury). based on a Hc11 microcontroller. I want to
> incorporate a few additional features one of which in knock control. 
> 
> Does anyone out there have any advice as to the best method to implement
> this ? Ideally what I would like to do is advance the timing to the onset
> of knock and then retard it slightly back into the safe zone. The
> controller will be used on a fuel injected 12A turbo rotary engine.
> 
> I welcome all ideas and comments about this.
> 
> Thanks to all in advance for your help
> 
> Regards,
> 
> Rob
> 
> 
> 
> Robert D Skala

Robert-  somewhere I have either an SAE paper on VW's knock sensor 
ignition, or a book with it in it.  From what I remember, the knocking 
rings the belock like a bell and the knock sensor is placed at a node of 
great intensity.  The piezo electric microphone output is filtered with a 
high and lo pass filter to diminish all input other than the knocking 
frequency.  Then the computer (which also has a manifold absolute 
pressure sender) determines the map and listens for knock.  If it hears 
it , then it iterates through advance and retard cycles.  The 1985 VW 
system wasn't adaptive, and is often accused of being too sensitive. If I 
can find technical documentation, I will post it.  I used to have 3d 
plots of ignition maps, and some sort of photographic technique that 
showed the ringing of the block.

Seth Allen

PS this topic wwas discussed a while back, at least as far as knock 
sensor placement, with suggestions like bolting the sensor the edge of 
the block near the oil pan, if I remember correctly.