WPSLPGExhaust Gas Oxygen (EGO) sensor Information

[Greg Hermann]

There is absolutely no way that the sensor input in the factory ecu's could
be characterized as either P, PI, or PID, or any of the various possible
permutations thereof!

 It is NOT banb-bang in the sense of fuel on--fuel off, it is bang-bang in
the sense of bang--begin reducing injector duty cycle relative to the
mapped value for the particular engine operating point if rich; bang, begin
increasing the injector duty cycle relative to the mapped value for the
particular engine operating point if lean. This is done with a multiplier
that is used, and increased or decreased progressively, on a bang-bangt
basis, across all mapped engine operating points during transient operating
conditions.

Sorry, but I thought that the part about sdjusting the duty cycle was self
evident!

Suggest you not try to throw around textbook vocabulary in an attempt to
make a point here, unless you have a _VERY _ thorough understanding of, as
well as working experience with, what you are talking about!

Greg



>Sorry, Greg, but I must disagree.
>
>The 'bang-bang' control you refer to would be fuel_on - fuel_off.  The fact
>that the EGO can only accurately report RICH or LEAN, has no bearing on the
>control algorithm.  The ECU maintains an injector DUTY CYCLE, which is
>constantly adjusted, in small increments, up and down, to keep the EGO
>crossing the stoich point.  PROPORTIONAL control, possibly with an INTEGRAL
>term, under some conditions.  That is the ONLY way it can know that the
>AVERAGE mixture is NEAR stoich.  The control algorithm has nested loops, if
>you will.  I suppose you COULD look at TPS response as a DERIVATIVE term,
>but we digress...
>
>New and interesting info:
>
>> three way CAT PERFORMS BEST if the gas coming through it
>> alternates between
>> a bit rich and a bit lean.
>
>I didn't know this!  But it has a ring of truth.
>
>Some of this is splitting hairs, and watching dozens of angels dancing on
>the head of a pin...
>
>Best,
>Steve
>
>>
>> The reasons why the oem ecu's oscillate across stoich:
>>
>> It allows use of a very cheap (in terms of ecu capability) bang/bang
>> control strategy.
>>
>> It also allows a very cheap way of checking sensor performance (I believe
>> this is an EPA requirement), by counting the frequency of crossings.
>>
>> By using such a crude control strategy, it also plays into the fact that a
>> three way CAT PERFORMS BEST if the gas coming through it
>> alternates between
>> a bit rich and a bit lean.
>>
>> Nothing at all to do with sensor performance.
>>
>> Greg
>>
>> >At 11:59 PM 8/2/00 -0500, Tom Meagher wrote:
>> >
>> >>Oscillation duty cycle, averaged with a low pass filter to produce a DC
>> >>voltage is evidently the operative parameter.  Perhaps you
>> could sample the
>> >>signal with the PIC and do FFT's on it to produce additional
>> information to
>> >>better characterize AFR.
>> >
>> >If all you wanted was an average AFR over a few seconds, go ahead.
>> >It's a waste of time imho. It still won't be any more *accurate*
>> >than an instantaneous reading due to the sensor's output being so
>> >nonlinear, and varying with EGT, backpressure, etc, none of which
>> >are compensated for by any amount of averaging over time. You'd be
>> >averaging over many many cycles, slowing response time greatly,
>> >and gaining nothing in the bargain.
>> >
>> >
>> >>Does anyone know the physics behind the oscillating output?
>> >
>> >There's no physics of it, that's the ECU adjusting AFR to try and
>> >maintain stoich, aka closed loop operation. Look at the timebase
>> >on the scope traces. The sensors can show some interesting things
>> >at much higher bandwidths, but those traces are not showing any
>> >of them.
>> >
>> >Really this has all been beat to death in the archives. People
>> >are almost lucky Gar is away for the moment. I can easily see
>> >him dispensing a brace of new bodily orifices when he returns.
>> >(And if you think I'm exaggerating, you haven't been reading
>> >the archives enough.)
>> >
>> >   Chris C.
>> >
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