Ignition module

Steve Baldwin steveb at kcbbs.gen.nz
Tue May 16 07:40:03 GMT 1995


> 
> ...
> > Knock detection.
> > I'm interested in hearing more on this. The recent discussions on spark
> ...
> > My understanding of 'knock sensors' is that they rely on the resonant
> > frequency characteristics of the block. How make specific is this ?
> ...
> 
> I have no hands on experience whith these, but I can tell how VW developed
> their knock sensing DGIFANT EFI. They used an instrumented engine block
> for the development. In the combustion chamber they installed a piezo
> pressure transducer to verify the knock condition. 

This is an approach I have considered in the past too. Putting a strain
gauge on the head next to the plug and looking for deflection in the
casting. One area where a flathead has an advantage, I guess.


> production version. For finding the placement of this sensor they
> used holographic photo techniques to find the vibrational node points on the
> block. That was the place where they put the sensor. When the engine was

Damn !  I just threw mine out. :-)

> I would imagine, that the 7.5 KHz would be the resonant freaquency of the
> block with everything on it, and knocking would give the exitation of
> the system. Would be interesting to hook up a DSO to the output of a
> knock sensor on a VW, and hit the block with something, and analyze the
> output to see if this is the case.
> 

This would be interesting to know. If the resonant frequency off a knock
is the same as, or related to, the frequency of ringing with a good bash
from a hammer. I can imagine some rather puzzled looking car salesmen if
you wonder around the lot with a large hammer, banging on the engines
and then loading the engine up until it knocks. :-)

Steve.



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