EGO clogging.

Dale Ulan ulan at ee.ualberta.ca
Fri Oct 28 05:22:09 GMT 1994


> Aaahh!! Neat!

Note I said 'most'. Some ECM's actually control the temperature,
notably cars using UEGO sensors...

> So the 'trip point' is much the same but the overall voltage is lower at
> lower temperatures.. The curve is 'squashed down' if you will.
> So, with a thermocouple and an EGO you could (with some processing) find
> out the A/F ratio.

Yes and no. You could find it out right around stoich. Generally, an O2
sensor doesn't like sitting at one voltage very much. That's why the O2
sensing algorithms always oscillate the sensor a bit.

> How does a UEGO work?

It contains an additional 'pump' cell. Since the normal O2 sensor
responds to hydrogen and other gasses (except oxygen, of course),
the reverse process (applying current to the cell) will move these
same ions through the ceramic.
By combining an O2 sensor and a 'pump' cell, the O2 sensor will operate
with a shifted centre point. By pumping, say, 10 mA of current through
the cell in one direction, the trip point will go from, say, 14.7:1 to
10:1. etc. With some creative electronics, the sensor can be made to
read out the actual A:F ratio.

After a bit of testing, people have found that the O2 sensor does not
actually respond to oxygen ions until the cell reaches 800-900 deg. C.
Few exhaust systems run that hot, but at the lower temperature of
400-500 deg. C., the cell responds to other gasses, such as hydrogen.
The net result is correct, but the cell doesn't actually respond to
oxygen.

-Dale



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