Kock Sensor

[ChrisH]

Hi All,

Knock sensors have been asked about before but they don't seem to have been discussed much by anyone. Anyhow I'm really keen to implement something so I can push the timing up with the knowledge some level of protection exists.

My thought at the moment is to use a standard knock sensor which when triggered cuts the signal from MegaJolt to EDIS (SAW is it, I forget which) which would (after 4 ignition events) take the timing back to a safe 10 deg BTDC. This assumes that that MegaJolt and EDIS wouldn’t mind being ‘HotSwaped/Unplugged’ during operation – comments Brent?

Main prob I see with this is that it would be after 4 ign events so the potential detonation damage would be extended a bit. Anyone have any thoughts by how much this may be – is the 4 event delay significant or not?

Obviously the only other aspect of the circuit would be 'extending' the signal from the knock sensor such that it stayed on for a length of time long enough for the driver to notice a warning light of some kind.

Any thoughts ideas comments would be good. For the sake of £5 worth of bits something like this could make tuning a lot easier as you could safely keep increasing the advance until this circuit cut in. On which note, does anyone have a good understanding of any times when the engine may develop max power at an advance significantly less than the point just prior to detonation?

Chris

[ChrisH]

See previous message.

[brentp]

The key to kock sensing lies in more than the sensor- since the sensor is basically a microphone, you need conditioning/filtering circuitry to distinguish a real knock from regular engine noise. This can range in compexity from simple analog filters to sophisticated DSP technqiues.

The MJLJ could be modified to accept a digital signal indicating a 'knock' condition and then take the appropriate remedy. More elaborate, it could accept an analog signal indicating knock severity and pull back the ignition advance accordingly.

Bottom line, it's a worthwhile feature addition, but it would take some research on my part to come up with an effective knock filtering circuit. What complicates things is that each engine's "knock" will sound different to knock sensors.

[4600cc]

I don't think MJLJ is powerful enough for an elaborate knock detection. And since it is ran on a multitude of engines, it will be impossible to create a routine that will work with all. A much better idea is to have knock detection in configuration software. A laptop would hook up to a microphone, or an actual knock sensor. While tuning is done, tuner would see knock locations in the ignition map, and adjust timing accordigly. This is one of my original ideas and I have some plans to implement it. It is seriously complex!

What should be implemented in megajolt is acceleration dependant timing.