Here's one for you tekkies:

What does the Lambda sensor actually measure in the exhaust gases?
And how does it convert this to a voltage that equates to an AFR?

I know lambda sensors are often referrred to as Oxygen sensors, but are they actually measuring oxygen? And if so, how do they do that exactly.

Just wondering as I've been faffing around with a Lambda Link this weekend and it got me thinking.

Cheers

Rich

 

Try the URL bellow its good and easy to understand...


http://www.howstuffworks.com/question257.htm


Dan...

 

The lambda sensor measures the amount of oxygen left after combustion, and at stoichiometric mix for petrol (14.7:1 AFR) it displays a characteristic almost vertical response from 0.3 to 0.7 V. Outside these ranges it is not used by the ECU, but can be used by us lot to get an estimate of the wide open throttle air fuel ratio.

 

Cheers John and Dan,

How does it actually detect the oxygen though? Chemically I mean.

Cheers

Rich

 

From the link above:
"The oxygen sensor is positioned in the exhaust pipe and can detect rich and lean mixtures. The mechanism in most sensors involves a chemical reaction that generates a voltage (see the patents below for details). The engine's computer looks at the voltage to determine if the mixture is rich or lean, and adjusts the amount of fuel entering the engine accordingly."

Additional link explaining one of the patents on the how, also from howstuffworks:
http://www.howstuffworks.com/framed.htm?parent=question257.htm&url=http://www.delphion.com/details?&pn10=US03933028

 

Hi,

Cheers for that but the link is only available to premier subscribers, any chance you can print it up here?

Just wanted to know what chemical reaction is actually going on in the lambda probe to detect the oxygen, i.e. what chemical elements/compounds or whatever are used.

Cheers Rich

 

RICH,

Found this for you...!!

The oxygen sensor relies on another scientific fact, the "Nernst effect." Nernst's law gives a way to measure the voltage between two materials in close contact, one of which is a known constant. When the zirconium dioxide ceramic sensor reaches the high temperatures generated by the car's engine, typically 617 to 662 degrees F, it registers a difference between the oxygen content of outside air (the known constant) and the exhaust gas oxygen content. This difference is emitted as a voltage signal, proportionate to the difference between exhaust gas oxygen content and that of outside air, and is sent to the ECU (Electronic Control Unit) which measures the electrical switching points of the oxygen sensor voltage as the exhaust gas oxygen content changes. The engine computer reads this signal and adjusts the fuel mixture accordingly in order to maintain the perfect ratio.

So, as the engine runs, the output voltage changes as the fuel mixtures fluctuates between rich and lean. The type of engine determines the switching speed of the O2 sensor: (1) carburetor systems switch 1/second at 2,500 rpm, (2) throttle body injection systems switch 2-3/second at 2,500 rpm, and (3) multipoint injection systems switch 5-7/second at 2,500 rpm.

Dan

 

Dan,

You are a star

Cheers m8

Rich