Dampening knock sensor

[amichie]

Has anyone tried this.

A search on the web will find many links describing how teflon tape on the threads can dampen or desensitize a knock sensor giving less knock retard under load.

[CrUZida]

Does the knock sensor earth through the block ?

[amichie]

Does the knock sensor earth through the block ?

Yes it does. I had mine out over the weekend with a scope on the output and it was rubbish unless the case was grounded.

A light tap with a screw driver gives a huge signal. Many volts peak to peak at about 7kHz.

I'm sure a spring washer would provide a good earth.

[CrUZida]

Surely using a spring washer would almost defeat the purpose of isolating it from the block?

Perhaps drill a small hole into the side of it and screw an earth directly to it.

[oldcorollas]

or... filter it electronically


do you knwo what the criteria for detecting knock that the ECU uses?
is it time windowed? is it frequency and amplitude or just amplitude?

[JetspeedCamry]

If it uses amplitude, then creating a simple attenuator would be easy as.
If it's frequency then that becomes more of a problem, but there are circuits that can subtract either a set frequency, or a percentage based on the input frequency.

[LeeRoy]

Shouldnt the engine not knock to begin with? So if thats the case your merely speeding up the inevitable.

Spose its better to get broken engines out of the way sooner rather than later though

[oldeskewltoy]

Hmmmmmm... major manufacturers can deal with knock... but many of the aftermarket systems don't use a knock sensor.

The reasoning I was told.... once you begin building an engine, and you go outside the stock parameters, you change the frequeny of the knock, and so the sensor must either be changed, or calibrated to the new frequency.

[amichie]

Toyota mostly uses a knock sensor with mechanical resonance( with a Q of about 7). Others use broad band sensors.

Knock frequency is determined primarily by bore diameter and the sensor resonance is tuned to this frequency.

Toyota use a gating approach where the knock is sampled for a short period after ignition only. The signal I have is saturating the first amplifier stage in the ECU and I am planning on just attenuating it inside my spare ECU.

I also have a bosch broadband that I plan to mount somewhere on the block and build a simply 2 stage bandpass filter with some gain adjustment and then tweak it until it looks roughly like the factory knock sensor signal.

Cruzida. I think I will try something like that with a separate ground. Maybe just one of those loop style connector things underneath the sensor with a teflon washer.

[510rob]

The Toyota sensor I measured (Gen2 3S-GE) was very obviously mechanically filtered, and quite accurately tuned to react most sensitively at a frequency that corresponded to the motor's ~86mm bore. For the electrical measurement of the sensor, I used a NIST calibrated HP 4195A Network/Spectrum Analyzer, and the plot showed a well defined inflexion, characteristic of a tuned piezoceramic resonator. I would assume all Toyota sensors from the same period are mechanically filtered / resonant tuned type.

RickyB of MRControls hosted the plot of the sensor, if you are interested to see what it looks like

http://www.mrcontrols.com/images/knock-sensor-toy-2.jpg

Here's a link to a GM sensor I measured. The part number is listed in the bottom left corner of the plot.

http://www.mrcontrols.com/images/knock-sensor-gm-2.jpg

[amichie]

The Toyota sensor I measured (Gen2 3S-GE) was very obviously mechanically filtered, and quite accurately tuned to react most sensitively at a frequency that corresponded to the motor's ~86mm bore. For the electrical measurement of the sensor, I used a NIST calibrated HP 4195A Network/Spectrum Analyzer, and the plot showed a well defined inflexion, characteristic of a tuned piezoceramic resonator. I would assume all Toyota sensors from the same period are mechanically filtered / resonant tuned type.

RickyB of MRControls hosted the plot of the sensor, if you are interested to see what it looks like

http://www.mrcontrols.com/images/knock-sensor-toy-2.jpg

Here's a link to a GM sensor I measured. The part number is listed in the bottom left corner of the plot.

http://www.mrcontrols.com/images/knock-sensor-gm-2.jpg

Thank you

I have an HP spectrum analyser in my lab also but I just used my portable tektronix digital scope as it does FFTs etc . It also does a peak frequency function and thats all I used.

I have the ECU at work today and I will put a simple voltage divider on the knock sensor input. Thankfully its capacitively coupled into the first Op Amp stage that buffers the signal. I will make variable from about 100% down to about 20% and see when I start to get error codes or my engine goes bang.

[TERRA Operative]

What's the difference between a 7MGTE and a 4AGZE knock sensor?