EGOR

[Walter Sherwin]

Very well stated, and YES I agree with you 100%.  REPEATABILITY and
CONSISTENCY is what you want from "your" WBEGO setup in "your" powertrain
configuration.  Not absolute accuracy, nor direct comparability to a
friend's meter in his application.  A given powertrain combo will make best
power at a specific Lambda value, under a specific set of operating points,
and the various composite RPM Lambda operating points can only be deduced
thru regimented and disciplined in-situ testing together with a decent EGT
setup.  The key is to initially determine these operating points, and then
later have the ability to return to them, from destinations unknown.

This last sentence carries a number of explicit assumptions with respect to
WBEGO meters/products, and selection thereof for your project needs.

For us non-lab-grade-DIY'ers we would want to:  1) have the confidence that
we can later replace a UEGO sensor, and get back to the same sensor curve
that we were initially using  2)have the confidence that systemic voltage
fluctuations would not throw-off our measurements  3)that UEGO heater
element temperature would not throw-off our consistency   4)that varying
pumping cell currents would not skew our results   5)that UEGO sensor aging
could be identified so that we all "knew" when our sensors had to be
replaced at or near some fixed life span   6)that improper voltages or
improper polarities weren't going to all of a sudden f**k our expensive
meter setup   7)that EGT and EBP weren't going to throw huge volumes of
uncertainty into our UEGO readings.

So, YES, while I agree with your original statement, I would retort that the
task of simply "returning" to the silver mine is fraught with many
complexities if not first robustly thought out in advance.  None of the
issues I've mentioned are insolvable, as most of them have already been
resolved in the high-end commercial WBEGO meters.  If a DIY EGOR (or anyone
else's) product is to be successful, it will have to adhere to these
criteria as a minimum.

Other special options and features would just be marketing fodder.


Walt.




> Lets say you are a bullet maker specializing in exotic loads.  You get
paid a
> visit by some Transylvanian Villagers in need of silver bullets to slay
some
> blood sucker and his evil assistants.  You zip out to your hidden silver
mine
> in the desert, scoop up the good stuff and take it back to the shop.
Mission
> accomplished.
>
> How does this relate to a wide range EGO?   When you went back to your
mine,
> you didn't care EXACTLY where it was, nor were you concerned about
PRECIOSLY
> where you dug up the silver.  The only thing you cared about was getting
back
> to the silver field.
>
> The same thing applies to using a wide range EGO for engine control.
>
> There are only three ratios of interest:
>
> Lean Best Power - the mixture where the maximum power is obtained per unit
> mass of fuel.
>
> Rich Best Power - the mixture where the maximum power is obtained per unit
> mass of air.
>
> Stoic.  The point where all available oxygen is combined with all
available
> fuel at the time and point measured.
>
> The first two are important for maximum power and economy - the last
simply to
> satisfy the catalytic converter and the rectally inserted cranium clean
air
> bureaucrats.  But, it does lay about halfway between the two best power
> points.
>
> Stoic is determined primarily by the fuel and little else.  The others
vary
> considerably from engine to engine, altitude, temperature etc.  Both are
> determined empirically from actually tuning the engine and optimizing the
> results.  In other words - they are not magic numbers.
>
> If you record the ego output at these two points, you have a nice means of
> getting back to these points.  The actual numbers are meaningless - as
long as
> they are repeatable and of usable scale.
>
> Precision is a fruitless anal exercise in futility.  At either point you
can
> vary the mixture a few percent and the difference will be lost in
statistical
> noise.
>
> There are a number of wide range EGO systems or projects in existence.
Most
> calibrate the EGO to a known output curve.  Free air calibration, trim
> resisters, or a special patch to the ECU seem to be in the lead.  All of
them
> assume an anal need to be exact.
>
> But suppose for a moment, that you reverted to the good pre-computer
> engineering practice of good enough is good enough - get on to something
else
> that matters?  It is reasonable to assume that the published output curves
are
> close to reality, and that if one were to peg some part of the curve to a
> known standard, and correct the output accordingly, the rest of the curve
> would be good enough for engine control and replacement of sensors with
> similar sensors as they deteriorated.
>
> And that can be accomplished easily with little defecation complication by
> simply used a standard EGO as a reference.  The standard EGO is highly
> accurate, repeatable and reliable at detecting Stoic crossing.  Simply by
> recording the wide range EGO actual output at each crossing, and then
applying
> a correction to the output to bring it to the standard curve, you can
> effectively continuously calibrate the wide range EGO to well within the
good
> enough limits.  And it should be tolerant of reasonable sensor aging and
> replacement.  Not much is needed.  A second standard EGO sensing the same
> exhaust stream as the wide range EGO, some minute computing power and a
> handful of silicon should do it.
>
> Good enough self calibration for engine control and getting back to the
best
> power points after they are determined by other much more accurate means.
>
> Thimk about it.
>
> ----- End of forwarded message from Robert Harris -----
> --------------------------------------------------------------------------
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