knock sensing

BrentP · Post by **BrentP** » Tue May 23, 2006 8:05 am

Seems like everything out there is tuned for frequencies, and I cannot see something made for a big automotive block working on a small single motorcycle engine.

Does anyone know where I can purchase the piezoelectric "washers" that go underneath sparkplugs for knock sensing?

Chopper · Post by **Chopper** » Wed May 24, 2006 12:35 am

Have a look here ...

http://www.sp125racing.com/BPSDetonationCounter.htm

I have other links too, if only I could find them. I'm sure I recently saw the sensors/washers for sale, probably here ...

http://www.iane.co.uk

... but his site appears to be down at the moment.

Guy.

Boris740 · Post by **Boris740** » Fri May 26, 2006 7:08 am

My product KnocksenseMS hooks up directly between the knock sensor and Megasquirt. I custom tune each unit to your cylinder bore. See my sig.

BrentP · Post by **BrentP** » Fri May 26, 2006 10:58 am

I don't recall the part about tuning to bore size last time I checked out your site, is good to know.

The Bosch sensors you work with and sell are not tuned then? The circuit is, not the sensor resonance?

Guess the last thing I need to figure out then is how to mount the sensor. It is a single-cylinder engine, almost entirely aluminum except for some magnesium. I know that this damps vibrations more than an iron block, so I imagine I should mount to the head if possible?

The only knock sensing I have ever seen successfully implemented on motorcycles is the HRC system for their 2T grand-prix bikes. It uses a piezoelectric plug washer. The detonation causes a pressure pulse which decreases the pressure on the piezo unit and sends out a pulse that is detected/counted. These buggers cost nearly US$1k and only work on one cylinder. And the piezo washer doesn't work on recessed plugs.

Last weekend was a US Grand Prix Riders Union (USGPRU) event at Porland Raceway. I helped replace a lot of piston/cylinders that really could have used a det indicator.

I know of more than a few people who are interested at a lesser cost. If you don't mind working with me on development/proving, I would like to buy a couple units and get them working.

Boris740 · Post by **Boris740** » Fri May 26, 2006 5:03 pm

Brent,
Bosch sensors that I am familiar with are flat frequency response and the knock frequency filtering is done by the circuit.

I would be interested in finding out more about under the spark plug sensor. It is not easy to design a robust housing for a piezoelectric transducer that can withstand crushing forces, extreme heat and proximity to high voltage.

Here is one manufacturer of the sensing elements.

http://www.murata.com/catalog/p19e.pdf

See pg 26. The big doughnut would fit under the plug but this is a ceramic material that has two contact electrodes, one on top and the other one on bottom. The packaging is where the effort goes. Perhaps a smaller doughnut could be held by a screw. Murata is pretty good with samples.

Marcus · Post by **Marcus** » Fri May 26, 2006 6:45 pm

Here is one system used on twostoke racebikes:
http://www.sp125racing.com/BPSDetonationCounter.htm

Sensor is mounted on a washer that goes under the plug.

BrentP · Post by **BrentP** » Fri May 26, 2006 10:39 pm

Saw this when you were kind enough to post the URL before.

Unfortunately it will not fit down a deeply recessed spark plug hole. Not a problem on a 125/250, but most modern 4T bikes have tall heads and very deep plugs.

DarrowConley · Post by **DarrowConley** » Sun May 28, 2006 10:33 am

Boris,

Is it the box of the sensor that determines the frequency or 'tunning'. I have a toyota with a 2 wire knock sensor. Do I need to get a sensor compatable with your box or can I just get the box? Since you say your system is tunned for the bore I have. In your wirte up it talks about the user tunning it themselves. Is there other tunning you do or is this the tunning you are talking about?

Thanks.

Darrow

Clifton · Post by **Clifton** » Sun May 28, 2006 2:46 pm

I was using a Toyota (7M) sensor with his box. I had to use a pot with it but it works great. I just installed MSII and haven't had a chance to try it with both sensors yet.

Boris740 · Post by **Boris740** » Sun May 28, 2006 5:20 pm

DarrowConley wrote:Boris,

Is it the box of the sensor that determines the frequency or 'tunning'. I have a toyota with a 2 wire knock sensor. Do I need to get a sensor compatable with your box or can I just get the box? Since you say your system is tunned for the bore I have. In your wirte up it talks about the user tunning it themselves. Is there other tunning you do or is this the tunning you are talking about?

Thanks.

Darrow

KnocksenseMS comes tuned to have maximum sensitivity to knock frequency for your particular cylinder bore. Your original sensor that comes with the car should work fine. Some sensors (Bosch) have flat frequency response in which case KnocksenseMS does all the filtering while others are resonate type meaning that they have maximum sensitivity to the knock signal for that specific bore that they were deigned for. These sensors will work well with KnocksenseMS as long as they are from that original block. There is no tuning by the user. All you have to do is adjust the threshold level so that it trips on a knock signal and not on the background noise.