Knock sensing

[Roy]

Hi there

On the subject of knock detection,  I have looked into
this for a company I was doing some work for a few
years ago.  There was an integrated device from I
believe Harris semiconductors that processed the data
from a knock sensor and interfaced with a
microprocessor.  I will see if I have the part numbers
still and let you know.

Knock detection is done normally using acelerometers
attached to the engine.  You need to seperate normal
background noise and clean combustion from knock. 
What is often done is to create a window during which
a cylinder is on the power stroke and knock is deemed
to occur when the signal exceeds a baseline of normal
acceptable noise, then the engine controler responds
by retarding the ignition timing by a set ammount that
prevents knock.  Following this the timing is advanced
towards the correct value in steps over a period of
time.

A more accurate method of knock detection involves
using cylinder pressure transducers and a scope to
actually watch the variation in cylinder pressure,
knock occurs as sharp pressure spikes.

This is a simple overview and there are often many
software variables associated  with knock detection
algorithms but I would say that is is feasible to
produce a basic system that could prevent engine
destruction based around a fast PIC chip.  Ideally a
DSP would be more suited.

               Roy ( Spectric's Ltd ) 

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