Knock Sensor Output 3

[NDSUFormulaSAE]

Does anyone know what kind of signal a knock sensor puts out?

I see MSD makes a cheezy box that you wire up to a knock sensor; it has a couple LED's, a beeper, and a sensitivity adjustment on it. And they can still sell it for $150 because nobody knows how it works.

I am wondering how difficult it would be to modify the knock sensor output to control an electronic advance distributor. Has anyone done it?

 

[jjm300zx]

Go here:

http://www.gnttype.org/techarea/projects/projectspage.html

for schematics using a gm sensor

 

[JohnAtJandS]

Hi to all. My name is John Pizzuto, and I'm the designer of the J&S SafeGuard.

For a background on knock sensors, read SAE Technical Paper Series 900488, Combustion Knock Sensing: Sensor Selection and Application Issues

Authored by Steven M. Dues, Joseph M. Adams, and George A. Shinkle: Delco Remy Div, General Motors Corp.

In the mid '90's, a GM engineer sent me a list of GM sensors, showing part numbers, resonant frequencies, parrallel load resistance, and mounting style.

At the time, they were producing sensors in these frequencies: 5.2kHz, 6.0kHz, and 7.0kHz.

A chart from the SAE paper shows that the fundamental frequency of a 75mm bore is about 7kHz, a 94mm bore is about 6.0 kHz, while that of a 110mm bore is about 5.2kHz. The chart shows a fairly linear relationship of frequency to bore diameter.

The paper terms the GM sensors to be "broadband resonant", with "bandwidths approaching one thoundsand hertz".

The detector in the J&S unit is in software, running on a 68HC11. The unit controls dwell and timing as well.

Software sets up a knock window, since knock is expected to occur around TDC. The window opens 32° after the ignition trigger, and remains open for 44°.

A load qualifier is used to disable the detector under light engine loads and decel, where piston slap can cause a large interfering signal.

The unit uses a proprietary algorithm to develop a threshold, against which the signal is compared.

jpizzuto@jandssafeguard.com

 

[JohnAtJandS]

The output of a resonant sensor is about 500mv/g, while that of a non resonant sensor is about 20mv/g.

An example of a non resonant sensor is the Bosch sensor, which requires a shielded cable.

 

[grogg]

Hi Nagy,
Check your e-mail in a few days. I wonder though, your e-mail looks like you work at magnetimarelli? You guys build ignition modules for ferrari and fiat ect... can't you get help from the people there?

Heuf, hi.
If I remember correctly the renault 5 turbo uses wet liners and a knock sensor.


Surfpac....how do I contact you, E-mail, post..?

The circuit at the turbo regal site does look like it could work on the bench but i cant see it working in the field. the output side of the circuit is ok, the trigger needs some work.

cheers grogg

 

[JohnAtJandS]

Sorry, but there is no such thing as a "simple knock detector". You might as well be looking for the Holy Grail.

Remember: You are asking a circuit to detect knock that you can't hear, while ignoring engine noise that you can hear. And the input is essentially a microphone.

It takes signal processing.

 

[Dieselpg]

I stumbled acros this page

http://www3.sympatico.ca/borism/

and thought of this thread. The page has a link or two to follow on. The starting price of 60 has to be better than 150
Cheers, D.
"If you are interested in a knock sensor monitor have a look at Knocksense

http://www3.sympatico.ca/borism/Knock

"
and
"Another approach would be to bolt a seperate knock sensor to the block. The electronics sits in a tiny box under the dash. It contains an active filter that amplifies the knock frequency signal and a comparator circuit that drives an LED which flashes on every knock event. The LED is separate from the box so that it can be mounted anywhere. There is a threshold pot in the box the you can set so that it triggers on the knock signal only.

The unit sells for $60CAD (Canadian Dollars) "

Enjoy

 

[turboice]

I found this link helpful when I was looking into understanding what the ECU was "listening" to on my WRX. Someone on a WRX board gave it to me:

http://home.netcom.com/~bsundahl/knock/sound/KnockSounds.htm

And best of all to listen into the secret conversations being had:

http://home.netcom.com/~bsundahl/knock/listen/listen.htm#Recorder

Ed.

 

[Azmio]

It is possible to use only one knock sensor for a V6, V8 or V12. However, it is preferable to have more as it will be more accurate.

For an engine, there will be a cylinder that has a knocking tendency more than the rest of the cylinder. This cylinder is generally the far from the entrance of water pump, has the poorest cooling, strongest intake mixture charge, etc.

During the development, this cylinder will be identified. Once it is identified, you can weld several M8 bosses in different locations to test for the best signal to noise ratio.

Once the best sensor location is identified, it will serve as the focal point for the knock sensing and ignition timing tuning.

Using only one knock sensor may not yield the best result. One for each bank will be much better. For me, I would prefer to have ionic sensor at the spark plug cause this will enable me to control every cylinder ignition timing.