Knock sensors

[Terry Sare]

     The TI web page has a app note on building a DSP based knock detection 
     system. The web page is www.ti.com and to get to the app notes you 
     have to request a password. The app note is spra039.pdf and has the 
     formulas  etc. No code though.
     
     TS

Remember the Reichstag

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> From: Todd Knighton <knighton at net-quest.com>
> To: diy_efi at coulomb.eng.ohio-state.edu
> Subject: Re: Knock sensors
> Date: Monday, September 02, 1996 4:01 AM
>
> Tom,
>      My first question is, how tall are you really?!? ha, ha.
>
>      I've found that if I run the ignition timing too close to the limit on
> the dyno that the knock sensors hit, the runs will be very
> inconsistent.  But if the engine is set up properly, and the knock
> sensors never need to do any thing then the engine performs well and
> consistently.
>      Knock sensors are for worst case scenario's.  Bad gas, carbon buildup,
> impropper octane, exceedingly high temperatures.  I've never found a
> system that works well enough to let it run on the sensors.
>      We use the knock sensors with the monitor from J&S to tune the engine
> till there is no more knock showing, not to leave it run on it.  A
> properly calibrated engine should never see knock anyway!
>
> Todd Knighton
> Protomotive Engineering
>
> >
> >   I did a Corvette with a turbo on it and used a old buick spark retard
> > system, and while it worked, I wasn't really very happy with it. It
would
> > retard 3 degrees for every clatter it didn't like, and hold it for
20-60
> > seconds. The problem was that it was inconsistent, back to back runs
would

Dumb Idea forming - maybe.  By knock sensor, I assume we mean
the knock caused by the fuel air mixture igniting prior to the timed
spark - generally at medium load and rpm.  Since this occurs before
the timed spark, nothing you can do to the timed spark directly
affects the knock.  Retarding the spark lowers power thereby
lowering the temp/pressure part of the equation - eliminates
knock.

Why not use the sensor to directly change a parameter that
controls knock - temperature?    Instead of retarding timing and
losing power - why not richen mixture?  More fuel - more  evaporative
cooling - lower temp - rat noww

Richening mixture small amount has no negative effect on power.
Early turbos (pre EFI and intercoolers) often ran as high as 40% rich
to cool the charge to keep from detonating.

Simple algorithm -  already have feedback loop for O2 sensor.  Step
bang the correction a fixed ammout richer.  O2 sensor corrects back
over time.  No more knock, no power loss, far less critical to tune,
no need to f with ignition timing and if it false alarms - worst effect is
lowered fuel mileage.

Just a thought for what its worth