NTK Sensor Article

[David LaRoe]

Hi Brian;

Very informative article.  Does the SAE have a web site that this paper may
be ordered from?  If not, how would one order one?  Thanks in advance.

David LaRoe


----- Original Message -----
From: "Brian L Massey" <blocklm at juno.com>
To: <diy_efi at diy-efi.org>
Sent: Friday, November 09, 2001 8:51 AM
Subject: NTK Sensor Article


> Late as usual, but here's the outline & comments I promised.
>
> A few remarks first: this about SAE #920234, and the sensor discussed in
> this article isn't exactly the same as the Honda sensor; you can see that
> from the pictures. But judging from other people's observations, it has
> to be very close, so everyone assumes that most material applies to both.
>
> First to David Harris, who asked about the portion where it talks about
> temp range of these sensors, here's the important quotation:
>
> "The usable range of the element temperature is from 700C to 950C."
>
> Another:
>
> "It should be noted that the problem of carbon accumulation can occur in
> a temperature range less than 700C and there is danger of the element
> blackening in a temperature range less than 600C." This is one reason I
> guess why everybody says don't operate or leave the sensor in the exhaust
> without the heater running.
>
> Here's a rough outline, and then I will mention some juicy bits:
>
> Construction & Mechanism         (how it's built and works)
> UEGO Sensor Construction         (goes into the chemistry; some important
> things here)
> Output Characteristic                 (shows how the pumping current
> relates to AFR; also
>                                                 discusses mfg. variations
> and how output varies with T & P)
> Engine Operation                        (discuss results under diff.
> engine conditions)
> Response Time                        (shows measurements of how quickly
> the sensor responds;
>                                                  compares to a
> conventional HEGO sensor)
> Warm-up Properties                  (talks about warm-up and some great
> graphs on what
>                                                 the sensor output does
> during warmup, interesting)
> Durability                                (about lifetime variations, not
> bad for hot gas exposure)
> Futher Applications                (discusses other uses like determining
> cat deterioration,
>                                                misfire detection)
>
> Now for the tidbits: the sensor construction part reveals that with rich
> AFR, the sensor is sensitive to...CO (carbon monoxide), HC (unburned
> hydrocarbons), and H2 (hydrogen). I didn't realize the significance of
> this until I read in the Heywood book about a typical exhaust gas mix
> under rich afr. There apparently is a measurable amount of hydrogen.
> These three sensor sensitivities have to be taylored to a representative
> component mix of exhaust gas. Interesting.
>
> One of the graphs shows changes in pump current (and therefore measured
> AFR) based on temp changes: 3.0% per 100C change in the measurement
> element, which of course will depend on how well the heater controls that
> temperature. Also of interest is a graph regarding same, based on
> pressure changes: 3.7% per 0.1atm, but they only give a graph for lean
> mixtures, not for rich ones. One thing I noticed in the Bosch LSU
> datasheet recently published (thanks Bert & Jorgen!) is that the LSU
> looks like it's more than twice as sensitive to temperature changes (6-7%
> per 100C), which might explain why Bosch has a more elaborate heater
> control mechanism.
>
> On this same subject, another graph suggests that temp is controlled to
> within +-0.2 AFR if the heater is simply held at a constant *voltage*!
> This has to be due to the sensor's temp coefficient being tuned to
> compensate for exhaust gas temps (at a given voltage, the heater heats up
> if the gas is cold, and cools off if the gas is hot). They also show the
> heater being supplied with a range of fixed voltages from 10 to 14.5V,
> and remaining within +-0.2 AFR over the full range of exhaust gas temps
> and over the full spread of lean to rich AFRs (well, at least from 12 to
> 18 AFR). I am fairly impressed with this. As a controls guy, this looks
> like a very well-tempered sensor over temperature.
>
> Last, as others have mentioned in the archives, they do show how the
> sensor is fast enough to pick up misfires on individual cylinders. Nice
> article; for me at least, it was worth the $13.
>
> HTH,
> Brian
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