Reference information about Knock Sensors

[robert dingli]

Steve Buchholz asks,
> 
> I would appreciate it if one of you in the know can point me to a 
> good reference work that covers the function of the knock sensor.
> I am interested in knowing if they are tuned for particular freq-
> uencies, and such.  They appear to be very much like ceramic ele-
> ment microphones ... is there any signal processing circuitry on 
> the sensor, or is the processing done in the ECU?  
> 

There are several SAE references on the topic although you may have to
go back a few years to find references to articles about products which
have been available for many years now.  A relatively recent article
(SAE 940146) describes various signal processing methods within the ECU
and comes to the conclusion that a band pass filter coupled with a time
window for sampling is the best choice.  Determining a suitable reference
or threshold to distinguish between background noise and dangerous knock
is the difficult part.

You could try contacting Bosch and/or Nippondenso to get technical 
information on their products.  I know that Bosch, at least, make sensors
which inherently band pass filter the signal mechanically as well as
broad band sensors.  In either case, further filtering would be required
within the ECU.

regards,

Robert

-- 
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             Robert Dingli           r.dingli at ee.mu.oz.au

Power and Control Systems                 Thermodynamics Research Lab
Electrical Engineering                    Mechanical Engineering
   (+613) 9344 7966                          (+613) 9344 6728
  University of Melbourne, Parkville, 3052, Victoria, AUSTRALIA
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