O2 sensor response times

[Garfield Willis]

On Mon, 27 Mar 2000 07:32:21 -0700, bearbvd at cmn.net (Greg Hermann)
wrote:

>On Mon, 27 Mar 2000 14:26:30 +0100, Corner Paul <Paul.Corner at icl.com>
>wrote:
>
>>> This has probably been asked before - but as I can't access the archives
>>> at the moment, so...
>>> what is the typical response time for these lambda sensors ?

>One of the NTK WBO2 pump type sensors is generally capable of picking up a
>misfire on a V-8 at 3000 rpm---so pretty quick for these!

This is an interesting question.

As Dr. Pelican and Greg have mentioned (in the original NTK article,
they give these same numbers for misfire detection on an I-4), there are
some "varying claims". If you add in the high-end meter mfg's specs for
response time (I remember seeing one claim 0.05secs!; ECM Inc says their
NTK-based boxe$ response time is "<150ms", while curiously NTK doesn't
spec the response time of their own blue box system/interface), so
you've got all kinds of all-over-the-place specs. Even in the NTK
article, there seem to be potentially conflicting numbers; in one place,
they show the response time for AFR deltas/excursions of around +-4AFR,
and show these response times in the several hundreds of milliseconds!
Then, in discussing the ability to detect misfires (seeing the lean
excursion that occurs from one cyl's mix not burning), they show blips
in the sensor's outputs that are as narrow as say <100ms, and conclude
from that "...by using the lean signal [the lean excursion blips I
mentioned prior] with the ign timing signal, the misfired cylinder also
can be distinquished". How this all corresponds to picking out misfires
at 3-4kRpm I'm still unclear on. The numbers just don't seem to match
up. Add to this, the diagram they (NTK) give for their misfire test
setup shows all four exhausts collected and then the AFR being measured
*downstream* just prior to the cat. Thus, there is definitely some gas
mixing. Remember that mass transport (exh gas movement) occurs at a much
slower speed than pressure wave propagation, so just because the exhaust
puffs indeed have a distinct and sharp delineation in pressure, gotta
consider that in a manner akin to waves propagating in the ocean, the
pressure phenom may be very distinct along with considerable
mixing/diffusion of the mass of the media taking place as it transports
downstream. As an extreme example of this phenom, consider the flow at
the end of the tailpipe, where even tho the pressure pulses from each
cylinder are still clearly distinct, the individual mixture packets from
each cylinder are by then pretty thoroughly mixed/averaged.

Having given all those caveats, what seems to be universally accepted is
that these sensors are indeed noticeably faster than say the older HEGOs
like the LSM-11s (Frank Parker showed me an example where his NTK box
caught a funny rich blip/excursion on his Typhoon when you quickly
released the throt, but IIRC, his LSM-based equipment misses that
excursion...correct me if I err here FP). And what's probably most
important, they DO seem to be fast enough to catch any possible mixture
excursions that present EFI controllers can produce. Hardly a "spec",
but reassuring nevertheless. We just haven't had time to set up an
apparatus to do our own response time testing, but I can tell you that
EGOR does absolutely NO smoothing or averaging of the sensor output, so
whatever the bandwidth of the sensor itself is, you're getting/seeing
all of it at the output of our electrics. I have no way of knowing if
this is true for other mfgs.

If I had to guess from the mongrel mix of specs, the response time is
probably somewhere between 100-200ms. Just a swag, tho.

Gar


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