Wideband O2 sensor output graph

Wideband O2 One

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The Oxygen sensor is critical to any engine management system. Especially today, Wideband controllers have become the goto standard in good engine management. Why? Simply because they have a wider range of monitoring. See, older sensors could only manage rich or lean diagnosis.

The latest Bosch LS 4.9 controllers have a much wider range of oxygen sensing capabilities. However this comes at a cost. See, with the features from the new sensors comes the cost of keeping them in the proper range.

Wideband Require Special Controllers

First, it is important to understand how the Bosch LS 4.9 controller works. Below, is a diagram of its layout. As shown, it has three main critical parts

Bosch LS 4.0 Oxygen Sensor Layout.
  1. Pump Cell – holds the critical components within the correct tolerances.
  2. Diffusion Bar – Accepts the exhaust gas and pull the o2 towards the actual o2 sensor.
  3. O2 sensor – reads the o2 concentration and compares it to the reference pump current. This comparison signal is then sent to the controller for processing.

Requires Accurate Heater Control

Second, the O2 sensor requires a very specific heat of 720 C to properly diffuse the O2 from the exhaust gases. Further, this must be maintained very specifically and at high tolerances.

Also, heating the sensor has to be done at the correct rate and time. If not, the sensor can be damage or at least not read accurate results. So, it is critical to use a controller that properly reads the sensor to know how hot the heater actually is and not just blindly apply 12 volts to the heater and pray for the best.

Requires Proper Reference Pump Current

Third, comes the reference pump current. As, this is critical to getting accurate results from the sensor. See, previous versions of the LS models like the 4.2 used reference air. However, due to the harsh environment involved in a car the reference air is often contaminated and unreliable. So, LS 4.9 sensors change to reference pump current.

This known value allows the op amp to have a accurate reference point to go off. Thus, allows for accurate readings. See, this is similar to ref voltages use in voltage regulators. Fundamentally, a comparison is done against the existing oxygen content current and compared against a known quantity of oxygen current.

Then, the sensor signal is moved in the direction and magnitude by comparing the referenced current to the measured current. Finally, this is fed back to the controller and then the microcontroller calculate the variance from 14.7 lambda.

So, proper fuel combustion results in 14.7 lambda or stoichiometric air fuel ratio.That is, lower values of lambda is rich condition and there is too much fuel is in combustion chamber. Where as, higher lambda is leaner and there is more oxygen in the combustion chamber. Remember, improper engine tuning will result in less power, worse gas mileage, or even worse catastrophic engine failure.

Wideband Are Not Linear

Wideband O2 sensor output graph
Wideband O2 sensor output

Also, as if control was not enough the output from the sensor is very non linear. So, to get accurate results proper scaling of the output signal must be done. Currently, my controller will use tables to approximate the point on the graph. Ultimately, I will calculate the actual point on the graph rather than approximate. So, that is the ultimate goal. For now, I will rely on the tables for speed and simplicity of code around air to fuel ratio.

CJ125 Chip To The Rescue

First, Wideband O2 One is based on Bosch’s CJ125 chip. Ultimately, this chip simplifies overall design. Also, I can use this controller as a reference since the chip is designed to work with the O2 sensor. So, starting with a somewhat known quantity should result in better accuracy. As such, this proof of concept project is making great progress.

Prototype Done (4-28-2022)

Yes, more progress on this project as of 4-28-2022 I have wired the initial prototype breadboard. Well, now it is time to write the software. Oh, here is a post on the programmer for the ATTiny1626 chip that I am using. Wow, by the end of next week I should be ready to fire up Wideband o2 One and control an actual Bosch LS 4.9 sensor with it! Stay tuned!!!

Wideband O2 One Prototype Breadboard

Schematics

Below, is the Wideband O2 One schematic I have built. Also, I used ByLund Lamba Shield as the basis of this code.

Get the latest schematics from github.

PDF Files

Also, more to come in the near future! Finally, thanks for visiting!

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