Technical Question - Lambda to Voltage Formula

Ask for and share advice on using the PicoScope kit to fix vehicles here.
Post Reply
User avatar
Posts: 377
Joined: Thu Dec 13, 2012 11:26 am
Location: London, UK

Technical Question - Lambda to Voltage Formula

Post by FioranoCars » Mon Nov 07, 2016 10:57 am

Sorry folks, a bit of a nerd question, I was idling playing with a thought, sadly they do happen occassionally :shock:

We're all familiar with this little graphic, but I wanted to get the formula or a table of values for it:

So first things, yes of course narrow and wide band behave completely differently, so lets stick to narrow band sensors, as per the graphic ...

From a load of google searches I'm sure the Bosch employee Bauman, who invented the sensor, produced a formulae, but the ones I've found are a bit abstract even for me! Serves me right eh! :oops: ... and yes, I have googled loads, I'm not lazy, but need a reliable source, and plenty of the stuff I've found is plain wrong or missing key parts, so thought I'd ask some knowledgeable people here :D

Also I'm confident that the formula is temperature dependant, so for simplicity I was only going to use a single value of say 400°C, but the formula with temparature bit in it would be good to have, although if in lookup table form I'd take any reasonable temperature value, it's not critical for my needs.

Lambda was was the goal, but if the AirFlow ratio was there too/conversion all the better. I have a conversion rough table, again appears non-lineer, not searched too hard for this, but if anyone can point, please poke a finger at the keyboard for me ...

Alternative views on best Temperature base for a "at Temperature" normally aspirated petrol engine (95-97Ron fuel) "pre cat sensor" also be pleased to hear views ...

As a by-product of this I'm happy to create and post back here a custom probe file of both Lambda and Airflow, for those interested, as think they've not been done as yet?

Thanks in advance

Richard Lukins
Fiorano Cars
Ferrari Maserati Lamborghini and Porsche Independent Specialists

User avatar
Posts: 790
Joined: Sun Sep 13, 2015 2:10 am

Re: Technical Question - Lambda to Voltage Formula

Post by STC » Mon Nov 07, 2016 11:28 pm

From a load of google searches I'm sure the Bosch employee Bauman, who invented the sensor, produced a formulae, but the ones I've found are a bit abstract even for me!
Bosch refer to it as a "2 Step" sensor. Above or below Lambda 1. It only needs to be accurate at one point, "stoichiometry"
With a need for incremented & accurate values above or below it was necessary to design and build the "Wideband" Counterpart. Particularly for Stratified and Homogeneous modes. (Which are soon to be a thing of the past along with the Wideband Sensor)
Lambda was the goal,
If Lambda "1" was "the goal" then there in no doubt that the ECU could achieve and maintain that very easily. An engine spinning at 6000rpm, fast in human conception, is still quite slow for an Electronic ECU. It can maintain very accurate Spark, Injector, Valve Timing etc. ..... and not break into a sweat. In fact a Con Rod will probably let go first !?

In the late 80's we had "Lean Burn" engines, the ECU of that era could hold the mixture above Lambda and hold it there all day long and indeed it did.

With the introduction of the Catalyst the "Lean Burn" became obsolete. It wouldn't work.

The reasons behind modern engines switching "Rich" -"Lean" - "Rich" are very intentional and essential for the Catalyst to function. Oxygen Storage Capacity "OSC" being just one of many.

The setting strategy of P0420 is a reasonably good insight and starting point into that.

The catalyst is the reason why our 4/5 gas analyser is now redundant for Engine Diagnostic purposes, unless we take the gas sample upstream of the Catalyst. (I have seen Ferraris that have a port for that purpose)

Post Reply