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 Post subject: Re: Dead (compesation) time
PostPosted: Tue Jun 09, 2015 10:46 pm 
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You could just literally measure dead time. Feed small pulses and then increment the size until you see some fuel flowing. I think you need a different interface than Tuner Studio to make this easy though

A bench test mode for the firmware would be a help with development in general.Having a good model for generic injectors is the first step to having models for specific individual injectors...


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 Post subject: Re: Dead (compesation) time
PostPosted: Wed Jun 10, 2015 8:25 am 
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Horizenjob wrote:
You could just literally measure dead time. Feed small pulses and then increment the size until you see some fuel flowing. I think you need a different interface than Tuner Studio to make this easy though


Not exactly. While you can certainly measure when the injector starts flowing that is not what's meant by "deadtime". Deadtime is a theoretical point which represents the intercept on the time axis of a plot of flow vs time, is b in y=mx+b equations. Its theoretical becasue the injector flow is not linear at short duration so the physically measured actual deadtime will be about double the theoretical point you're looking for.

So, change voltage and deadtime changes because it takes long for the injector to open, easy.

Change fuel pressure and deadtime changes mostly because you've changed the slope of the flow curve, so you've also change the intercept point aka deadtime.

Horizenjob wrote:
A bench test mode for the firmware would be a help with development in general.Having a good model for generic injectors is the first step to having models for specific individual injectors...


o5e already has a bench test / development mode that lets you simulate pretty much any set of inputs.

The current injector model is a simple and completely generic y=mx+b model. there is a generic correction for voltage but I think it still needs pressure correction and a way to better characterize the non-linear range from 0ms to 2-3ms depending on the injector and this is what the GM system does pretty well.

Ford developed a system years ago that basically defines 2 linear equations for short and normal regions and its better than nothing, but it's not as complete as the newer GM system.

On a running engine you can mostly figure out the dead time by changing the pulse width and looking at the reaction on the O2 sensor. If 3ms+ deadtime gets to 1.0 lamdba then 3.3ms+deadtime should get you 0.9 lambda and if it doesn't your deadtime is wrong.

The difficulty is ECUs don't let you set pulsewidth directly, they calculate it for you based on all kinds of things so you have to play a bit with say the VE table or coolant correction to force a pulsewidth change then plug the pulse width, dset deadtime and 02 readings into a spreadsheet and calculate what the actual deadtime should be.....or trial and error it to close enough.

You can sort out the non-linear region using this same method once you have the deadtime right. It just takes patience

...or you order a set of injectors from injector dynamics that are fully characterized and fully matched and just plug in the info and be done with it :)


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