MS2/Extra Non-linear Injector Dead-time Voltage Correction

[motthomas]

This is one for the developers. I had been of the understanding that the injector deadtime calculation on MS2 Extra was a simple linear relationship against battery voltage.
However, I have been going through some bench testing experiments to understand the full impact of different settings on injector PW and I have found that the actual correction against battery voltage is distinctly non-linear. Looks to me like a 3rd order polynomial? See attached image. Now I welcome this as the actual response follows the physical relationship more closely than a pure linear relationship.

The only thing is that there is nothing that I can see in the documentation that suggests that the actual correction is anything other than linear. That means that when anyone measures the behaviour of their own injectors they will likely compromise the relationship by choosing a best fit linear relationship against battery voltage. However if the firmware is then creating its own polynomial relationship, the demanded behaviour is likely to be even more compromised from the measured behaviour.

Can we get some details on how the code determines injector open time correction against voltage so that a sensible “linear” relationship can be chosen to provide the most accurate correction for a particular set of injectors? How does the linear correction which is input in TS influence the curve? It would also be very useful if a note could be added in TS to warn users that the code does not actually implement the linear correction.

This was measured on a Microsquirt V3 running MS2E_3.4.2 firmware.

[racingmini_mtl]

This is the thread that resulted in changing the voltage correction to a non-linear correction: http://www.msextra.com/forums/viewtopic ... 91&t=40798

Jean

[motthomas]

Aha! Thanks Jean.

Can I assume that the code ended up using Matt's equation in the first post of that thread? It looks like a good fit when I add it to my earlier graph anyway.

opening_time(batt_volt) = opening_time(13.2v) + ( 13.2 - batt_volt ) * batt_corr_factor * (13.2 / batt_volt)

It is certainly a much better approximation of what the injector actually does but it requires a slightly different batt_corr_factor to fit than one would choose for a best linear fit. Would it be possible to document this equation in the manual and in a note in TS for other users?