Following a conversation over the Christmas meal yesterday (why do all my products end up relating to food ?
) my brain started thinking of another possibly useful product.
The discussion was about standalone aftermarket ECU's and the almost universal lack of knock control on anything less than £1K. The only one I've personally had experience of recently bacame nearer £1.5K with the knock control added and IMO the knock control was VERY crude and unlikly to offer good protection on road style usage, only with constant hard driving in the map area prone to knock.
Anyway, it would be relatively simple to interrupt the IGT line from ECU to igniter (5V pulse) and add a variable delay to retard the ignition by a few degrees. This line would also provide and RPM measurement and a trigger for 'knock window'. Add a single analogue signal from the map sensor for load axis and the signal from the knock sensor and you have all you need to provide a very comprehensive knock control system.
In short, a small box to go next to the ECU whick will have 2x power wires and 2x signal wires to connect in to the loom at the back of the ECU, plus cut one wire at the back of the ECU and join each end to 2 further wires from the small box. The box will have a USB port to link to a PC with windows software to set it all up.
Finger in air, direct selling price likely to be about £200
What are peoples initial thoughts ?
Is there such a device already on the market that I'm unaware of ? No point re-inventing wheels.
Would it be useful to make it a 4 channel device for coil on plug ?
What knock control strategy to use ?
Initial thoughs are to split a 2D area of RPM vs load up into zones (cells) with each cell containing a 'retard value'. When knock is detected, immediately retard ignition by a few degrees depending on level and add a small figure e.g. 1/2 degree to the current cell in the map. Areas of the map where knock happens will quickly build sufficient retard to stop knock happeneing.
Also, how about advancing the cells back up again ? Do we just clear to zero on switch off, or do we gently advance back up again so we're running on the edge of kncok ? Modern cars seem to do this as there are plenty of claims of significantly increased MPG from running high octane fuels.
I think it's a given that 'knock sensed' will be based on exceeding a threshold based on RPM and load in a 2D table. This could easily be done in a 'learn mode' with ignition retarded by a couple of degrees to ensure zero det. and then run through the RPM range with zero load, medium load and full boost.
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