pulse width / pulse granularity

[Bruce Plecan]

----- Original Message -----
From: "Carter Shore" <clshore at yahoo.com>
To: <diy_efi at diy-efi.org>
Sent: Thursday, June 01, 2000 11:00 PM
Subject: Re: pulse width / pulse granularity


> Hello DIY LM's,
> When I first connected a scope to my injectors, I was
> surprised that the actual pulsewidth did not increase
> linearly with RPM/load, even at WOT. Slowing down the
> sweep showed me why: The amount of fuel injected is
> proportional to the duty cycle, not the pulsewidth.
> A (very) broad generalization is that the difference
> in pulsewidth is due to differences in VE, not engine
> speed. This, because the amount of fuel needed is
> approximately proportional to the amount of air that
> the motor breathes at a given RPM (ie VE).
> Of course, at the extremes, as the duty cycle
> approaches 0% and 100%, this generalization falls down
> due to the physical limitations of the injectors.
>
> My point being that the most sensitive AFR tuning
> requirements for emissions occurs at lower RPM (non
> WOT operation). And since the pulsewidth will be on
> the shorter end, then finer timeslice resolution would
> be a good thing.
>
> Now, does anyone know how much 'jitter' an injector
> typically shows on delivered mass of fuel vs
> pulsewith?
> Of course in closed loop mode any non-linearity is
> compensated for, but the 'jitter' in such a closed
> loop system will show up as noise, and can cause loop
> stability problems, etc.
>
> Just wondering
>
> Carter Shore
>
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