logalinipoo

https://www.rx8club.com/engine-tunin...epower-139278/

I was reading this old thread and it made me think.

Our WBO2 uses O2 in the air and in the exhaust to get a AFR or Lambda. If Lambda is complete combustion of all O2 in the air how can it read lower then 1.0?

olddragger

iTrader: (3)

It is important to remember that the O2 sensor is comparing the amount of Oxygen inside and outside the engine. If the outside of the sensor should become blocked, or coated with oil/grease etc--then it will not be accuate.

TeamRX8

iTrader: (25)

I'm getting that facepalm kind of feeling again ...

logalinipoo

Mine is brand new and the engine compartment was clean when I installed it.

I was just reading old threads and it made me think. If they measure oxygen and calculate AFR based on that measurement then They can only measure down to zero Oxygen.

After there is no oxygen left in the Exhaust(In theory that is 14.7 to 1) how could it read 13:1 or 10:1?

logalinipoo

Flame on Team

logalinipoo

As a side note

O2 sensors consume Oxygen as they process it.

So you would have little to no oxygen outside the sensor(depending on how clogged it is) and some oxygen inside the engine so it would see it is lean and then go rich as hell. Probably so rich that you would flood the engine.

Brettus

iTrader: (2)

AFR = air fuel RATIO .

So 13:1 is 13 parts air to 1 part fuel .

Lambda is another way of measuring the same thing taking out the fuel stoichometric value as a variable so is actually a more accurate measurement because you don't always know the exact number for the fuel. Guages assume a value for the fuel of 14.65 (I think) and do the calculation before displaying AFR.

so 13:1 for a fuel of 14.65 = 13/14.65 =0.887 lambda
What's the question again ?

logalinipoo

Stoichometry is the Ideal ratio for a chemical reaction. With a Stioch fuel mixture there should be no Oxygen left in the exhaust to measure.

In that case how does the car measure anything richer then stichometric?

olddragger

iTrader: (3)

From Innovate:
Wideband sensors

For many years manufacturers sought a method to extend the range of exhaust gas sensors to cover the entire range of engine operations. In the early 1990's NTK patented the pump-cell sensor now known as WBO2 or UEGO sensor. The first ones (NTK L1H1) were used on lean-burn Honda engines because engine operation could not be controlled by a NBO2 signal on the lean side of 14.7 (see curve).
It was quickly discovered that these sensors also work in a rich gas environment. Many modern turbo engines require tight control over the air/fuel ratio to keep emissions at minimum but nevertheless produce enough power. These applications keep the engines just shy of the onset of knock. The Bosch LSU4 series sensors were designed with that application in mind and are widely used by OEM's in turbo engines.

WBO2 sensors combine a regular NBO2 sensor and what's called a pump cell in one package. The pump cell is kind of the opposite of a NBO2 sensor. It can pump oxygen ions in or out of the sensor cavity. An electrical current through the pump cell transports the oxygen ions. If the current flows in one direction, oxygen ions are transported from the outside air into the sensor, in the other direction oxygen ions are transported out of the sensor to the outside air. The magnitude of the current determines how many oxygen ions/second are transported, just like the electrical current through a fuel pump determines the fuel transport rate.

Both, the NBO2 part and the pump cell, are mounted in a very small measurement chamber open with an orifice to the exhaust gas. The pumping rate of the pump cell is very temperature dependent. Therefore the sensor head temperature must be tightly regulated through a built in heater. A WBO2 controller (like the LM-1) monitors and regulates the heater to keep it at a constant temperature. In a rich condition the WBO2 controller regulates the pump cell current such that just enough oxygen ions are pumped into the chamber to consume all oxidizable combustion products. This basically produces a stochiometric condition in the measurement chamber. In that condition the NBO2 sensor part produces 0.45V. In a lean condition the controller reverses the pump current so that all oxygen ions are pumped out of the measurement chamber and a stochiometric condition again exists there. The pump cell is strong enough to pump all oxygen out of the measurement chamber even if it was filled with free air.

The task of the WB controller is then to regulate the pump current such that there is never any oxygen nor oxidizable combustion products in the measurement chamber. The required pump current is then a measure for the Air/Fuel ratio.

A basic diagram of a WBO2 controller is shown below:


The PID part in the WB controller regulates the pump current based on the NB-Signal, trying to hold it at a steady 0.45 Volts by varying the pump current. PID stands for Proportional/Integral/Differential and is a commonly used method for a feedback regulation system. Because of manufacturing tolerances the pump current can't be used directly as AFR measurement. For the same AFR different sensors require different currents. Therefore every sensor has built into its connector a calibration resistor called RCal in the diagram. The voltage drop over this resistor is actually measured by the controller (V = I*R). The sensor manufacturers trim this resistor during the manufacturing process so that the controller sees the same voltage drop for a given AFR.

This is how analog WB meters work. They are called analog because the input/output signals of the controller are smoothly varying voltages/currents. The PID controller can be implemented in a microprocessor or as analog electronic circuit using amplifiers, transistors and so on. Implementing it in a microcontroller does not make it a digital system. The LM-1 operates the WBO2 sensor differently. Its (pat. pend.) working principle will be explained in a future article.

Until next time... Keep On Tuning!

-Innovate Motorsports

logalinipoo

Thank you OD, That was it exactly. I did a couple of searches before asking, but I'm at work and the internet is real slow.

TeamRX8

iTrader: (25)

There's this thing called the Internet and believe it or not it has all kinds of information where people who are motivated to learn can educate themselves to undrstand the basics of almost anything. It's truly amazing.

http://ngkntk.co.uk/index.php/techni...a-sensor-work/

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