Please kindly explain oxygen sensor
Please kindly explain oxygen sensor
(OP)
I am a materials engineer and curious about automotive oxygen sensor. I understand the principle of oxygen sensor. Actually, I was involved in research on oxygen pumping using zirconia. What I don't understand is signal fluctuation. According to internet, it cycles up and down about once a second. Why?





RE: Please kindly explain oxygen sensor
RE: Please kindly explain oxygen sensor
hope this helps
RE: Please kindly explain oxygen sensor
RE: Please kindly explain oxygen sensor
By the way, these O2 sensors are OEM Rich/Lean sensors, when mounted closer to the exhaust valve flange.
Franz
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RE: Please kindly explain oxygen sensor
The real reason this cyclic behaviour occurs and is desirable is, as follows: -
As rightly said above the controller determines the position of Lambda=1 by correcting the rich/lean signal of the 2 point lambda sensor (adding fuel when the sensor reports lean and removing when it reports rich). However, it is not a sinusoidal behaviour.
The operating band of a three-way catalyst is quite narrow and located between a little richer than stoic and a little leaner.
Since the catalyst has two reactions occurring in it, oxidization (to remove HC & CO) & reduction (to remove NOx) both an excess of O2 and a lack of O2 are required – which can be achieved by the cycling the AFR.
To ensure that these two conditions occur, and emissions are efficiently reduced, a closed loop fuelling controller introduces a delay time in the switch over from rich/lean & lean/rich to bias toward one or other of the reactions (hence the behaviour is not sinusoidal). The aim is to efficiently remove all pollutants from the tailpipe gases, to aid this the cat is also designed to store O2 to better aid oxidization reactions.
The rear lambda sensor determines the amount of O2 that is stored in the cat by reporting lean when the cat is full of O2 and rich when it is empty and adjusts the amount of time bias that the fuelling will remain rich or lean.
Since O2 storage is a measure of the cats effectiveness rich & lean excursions can be used for catalyst diagnostic purposes - but that’s another story altogether.
MS
RE: Please kindly explain oxygen sensor