Tuning O2sensor Knock Sensor Engine Damage

[Tony Cooper]

bruce plecan wrote:
> 
> Well thought I just had one to go, #$%^&*(, talking too
> much and remembered a couple details.
> Preventing Engine Damage:
> The problem with totally reling on a Knock sensor is that it is
> tone deaf.  It is designed to look for a particular range of noises
> and completely ignores some.  With a SBC that is usually in
> the 2,000 to 2,600 rpm range.  Soo at 6,200rpm I would not
> beat the cost of a new engine on that.  Also I have not seen
> anyone guarantee in writting that there are no secondary
> harmonics that might dampen the tones the knock sensor
> might hear at other rpm,  TC, I would invite your comments
> on the above.

Righty Ohhhh.

Most knock sensors are either one of the following 2 types.

1. A fairly cr*p microphone, which is 'tuned' to pick up frequencies
between 1khz and 5khz.
2. An Accellerometer - which has been selected due to its natural
resonance being between 1khz and 5khz - unfortunatly it has a very
narrow frequency window 

   You will hear all sorts of engine noise while the engine is running.
The trick is to filter out all the rubbish, and only listen to the
knocking sounds. This is where a 'learning' DSP comes into the equation.
You still need a human to say 'this is knocking', so that it can learn
what to listen for. However, this task is usually a painfull one (And
need only be done on one engine!) - cause you have to run your engine
whilst detonating - very painfull to the ears. Now, detonation will
'appen and do the most damage at peak torque, however, ALL engines (read
Every and ALL) work at their best with just a little bit of detonation.
The trick is, it to let the engine detonate just a little bit, giving
peak torque, but not let it detonate so much as to do damage. The
wonders of R&D. 

Detonation at other times can happen, (and usually do). The engine speed
does not usually effect the detonation signal. Once a FFT footprint of
detonation has been learnt, the DSP can pick out detonation at any RPM.

IMHO the microphone is actually a better choice for after market
implementation, because the acceleeromter is usually very picky.
 

> Bruce          If your cone shaped hat falls off in your sleep
>                    does it make a sound???....

Just me 2p's worth
Tony
-- 
Sent By Tony Cooper.
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