programming for a MAF based system

[Perry Harrington]

Hello,

I'm new to the list, so if you're perplexed as to who I am, that's why.

For a MAF system you want MAF, TPS, ACT, BAP, ECT, ISV, and RPM.
Here's the reason:

You want to reference MAF to RPM to infer VE.  Once you know VE,
you can key in a table, just like MAP does.  The other reason is
because you can make an even simpler inference:  Have a global
that defines your lb/hr per HP.  With the MAF vs RPM you can calulate
realtime HP and use that to simply find your base fuel pulswidth.

This makes for very simple integer math with table lookups if you
want.

Then add the O2 sensor to fine tune the mixture.

The other sensors I'd use are BAP (baro), constantly to adjust for
altitude, ACT for additional spark advance and air density, and
ECT for input to lean/richen the mixture so as to obtain the desired
engine temp. The BAP is important especially on turbo cars, because
turbos were intended for altitude compensators.

Ford uses the ACT for advance, ECT vs VE for AFR, and BAP to compensate
for altitude.

I postulate that it is possible to design a fuel injection computer and
program that will tune an engine without user input, just give it gross
values and it'll fine tune it.  The only thing I'd add to do that is an
engine mounted accelerometer and MAP sensor.

The accelerometer would be used to sense the roughness of the engine,
and the MAP to sense vacuum; so you can adjust the mixture like you would
with a conventional vacuum gauge.  Find the mixture that provides the smoothest
idle and highest vacuum.

--Perry

On Thu, Mar 21, 2002 at 03:15:38PM -0500, Eric Fahlgren wrote:
> les wrote:
> > 
> > Can someone point me to any hints for how to approach the
> > algorithms for fuel calculations, as they apply to a mass air
> > flow measuring fuel system?
> > 
> > At first look, it seems that all the 'normal' variables needed for
> > MAP systems just drop out of the equation. I suppose that I still need
> > a 2d map , to allow for richening under boost, but it just seems too
> > simple. I mean, other that for idle speed needs, rpm doesn't even seem
> > to enter the equation. Air mass is air mass.
> > I understand that the MAF is not linear, but a simple lookup table
> > should
> > fix that.
> 
> Les,
> 
> Are you working with a true _MASS_ air meter, not an AFM which
> produces some uncorrected value?  In that case, just have a 1D
> map which relates mass to AFR and from that calculate a pulse
> width.  If not, you need temperature correction (at least) to
> get mass, then use the table.  Should be pretty simple compared
> to the 2d VE tables usually used with speed density.
> 
> All the usual gamma terms still apply same as with MAP systems,
> acceleration enrichment, cold start/warmup and so on.
> 
> Eric
> 
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-- 
Perry Harrington             Linux rules all OSes.               APSoft      ()
perry at apsoft dot com 			                 Think Blue. /\

Those who would give up essential liberty to purchase a little temporary safety
deserve neither liberty or safety. Nor, are they likely to end up with either.
                             -- Benjamin Franklin

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