What sort of signal is the knock sensor?

[Don.F.Broadus at ucm.com]

 I have been experimenting with ESC modules and knock sensors and have found
that both detect a wide range of frequencies. 
By using the output of a HP3324A function generator connected to  DR 562
knock sensor coupled with a 1/4 pipe to another DR 562 knock sensor I was
able to track the freq. curve of the sensor. The sensor responds to
sine,square and triangle waveforms with no
loss of signal output. With 1 V-PP sine wave in and monitoring the output
with a scope the DR 562 sweet spot was 6KHZ. A loud tone could be heard at
6KHZ indicating resonance.  7-10KHZ had good outputs. The voltage dropped
off at 12 KHZ . An output was observed up to 50KHZ very small amplitude  4
MV-PP.   The ESC modules that I have tested so far are  HKD,HKM,HKR,BLN,AFWB
and ANRZ. With the DR562 det sensor all ESC modules responded at 6,9,10 KHZ.
The ESC output is approx. 10 VDC with no knock and goes to 0 VDC for Millsec
then back to 10 VDC with knock. All ESC testing was at 10 VPP sine wave
input into the first DR 562. the second DR 562 outputs to the ESC module.
The ESC output toggles low/high with each knock like a one shot
multivibrator and never has a continuous low output. When I find some more
knock sensors I'll run a profile on them.   

 
Don



 

> -----Original Message-----
> From:	Bruce Plecan [SMTP:nacelp at bright.net]
> Sent:	Saturday, November 20, 1999 7:10 AM
> To:	gmecm at efi332.eng.ohio-state.edu
> Subject:	Re: What sort of signal is the knock sensor?
> 
> 
> ----- Original Message -----
> From: Paul Blackmore <paul_blackmore at hotmail.com>
> Subject: What sort of signal is the knock sensor?
> 
> Much easier way to remember it is noise sensor.  Only after filtering is
> it
> somewhat a knock sensor.   Exhaust rattles, fan belt, alt bearings, all of
> these can mimick the sound of knock as far as the gm sensor/system goes.
>   The knock between gear changes is why I beleive they came up with a
> burst
> knock contol during rapid TPS changes (if anyone knows better feel free to
> correct me).
> Grumpy
> The above mentioned filtering is to reduce the signal to a specific
> frequency that the engineers were worring about (Maybe more than 1, I've
> found two in one application).
> 
> 
> | Hi all,
> |
> | I've been looking at some ALDL info of VS Holden Commodores taken while
> | doing some very hard driving around Winton raceway. (Its hard to type
> while
> | coming out of a corner sidways)
> |
> | The signal is graphed and appears as a spike varying in height (well
> value
> | actually) from 10 to 255(max).
> |
> | The signal rarely appears under normal driving conditions but when we
> were
> | pushing the cars hard around the race track at WOT the spikes were
> coming
> | high and often (four or five times while accelerating per gear change).
> | The signal also usually appears (only once) when blipping the throttle
> for
> | downchange while braking.
> | It also appears (only once) when the car is stationary and the engine is
> | spun up to redline with a WOT.
> | It appears more so when the engine is warm and less so when the engine
> is
> | cold.
> |
> | I have been told that the knock sensor would not "go off" that often.
> | However, could it be that the knock sensor is probably going off more
> than
> | we think but it is just "ignored" by the ECM if it is just a small knock
> and
> | that only big knocks cause the spark to be retarded?
> |
> | Cheers
> | Paul Blackmore
> |
> |
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