WPSLPGExhaust Gas Oxygen (EGO) sensor Information

[Greg Hermann]

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.
>
>----------------------------------------------------------------------------
>To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes)
>in the body of a message (not the subject) to majordomo at lists.diy-efi.org


----------------------------------------------------------------------------
To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org