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ExTuner: AFR + EGT meter. Exhaust gas tuning

We did not stop at real-time ECU programming and decided to start expanding our narrow specialization in the field of devices for tuning ICE control systems, and the next product was ExTuner - a system for measuring and monitoring the parameters of the air-fuel mixture (A / F Ratio) and temperature exhaust gases (EGT), as well as additional functions, such as connecting most of the sensors to monitor additional parameters (for example, boost pressure, coolant temperature, oil, etc.); signal emulation of a narrow-band oxygen sensor (0-1V); support Innovate serial protocol (LC-1 / LM-1,2) for the ability to output AFR readings to any software that supports this protocol and others.

Background. What attention was paid to when creating

It took more than a year to develop this device, when the release dates were outlined in half a year after writing the first line of code. Why? The fact is that most of the time was spent on creating a competent controller for a wideband oxygen sensor (hereinafter AFR), namely, great attention was paid to the accuracy of readings and reliability. The fact is that initially the accuracy of the AFR controller system was based on the use of the internal calibration resistance of the sensor, the resistance of which is selected during production, depending on the individual characteristics of the sensor, and during operation, the controller automatically takes into account this resistance to correct the readings. This approach is the simplest, but with its own nuances, which we will discuss below.

Bosch LSU sensor calibration resistor (source wbo2.com)

AFR controller of the device

During operation, the sensor "grows old" and when used as a reference of the calibration resistance, the readings begin to differ from the true ones, due to irreversible processes in the sensor's sensitive element, which can also be caused by the "poisoning" of the sensor with a too rich ratio. Also, we have not achieved accurate and adequate readings of even new sensors manufactured by Bosch, it seems that recently the manufacturer began to save on the process of selecting the exact parameters of the calibration resistance of each sensor during production.
We used as a reference Innovate LM-2 famous American company which has patented AFR controller algorithms.
About a dozen sensors have been tested Bosch LSU 4.2 and 4.9, both new and used, which were installed in the same exhaust pipe environment in test vehicles. The first problem we encountered was a significant deviation of readings from LM-2, and the nature of the deviation was significantly different on different sensors, even within the same version (4.2 or 4.9), so it would be impossible to simply "fit" the values by some universal coefficient, which could be acceptable for marketing reasons.
We sought not just readings that would be acceptable at the level of budgetary "display meters", but readings that look almost indistinguishable against the background of a well-known brand. But this was achieved only when we implemented our own calibration algorithm using air as a reference.
Having done research and numerous tests, we can confidently answer for the readings of our device!

free air calibration
Calibration result
extuner calibration
Air oxygen reading after calibration process

This, as well as testing, took a significant part of the development time of the entire project.

Diagnostic system. More than just a "show meter"

The second step in the development approach was the implementation of a system for diagnosing the state of the oxygen sensor and the main systems of the device. The widebandband oxygen sensor is not very simple in structure, which is an electrochemical system consisting of a narrow-band Nernst cell; oxygen ion Pump and heating element. At the same time, it should be noted that the failure of the sensor is not always obvious - the AFR sensor can continue to work with a significant change in the properties of its structure, which may affect the readings! We talked about one of the reasons for such phenomena above. Overheating and mechanical shock can also deteriorate the sensor performance.
For these reasons, it was decided to introduce a diagnostic system for the oxygen sensor and not only, which constantly monitors the sensor parameters, and if they are deviated, the device warns about this in the form of separate codes on the display, each of which has a description and solution methods.

Устройство ШДК
Bosch sensor device

Exhaust gas temperature monitoring

Every seasoned tuner knows that controlling the temperature of the exhaust gases during tuning is more important than it might seem at first glance.
Measuring the temperature of the exhaust gases is more trivial. For this we use a ready-made company controller Maxim Integrated  for K-type thermocouples with cold junction compensation. The temperature range is quite sufficient for most solutions - from 0 to 1024 ° C, with an error of + -2 degrees.

EGT контроллер
egt meter

Emulation of Innovate Serial Protocol

In order to "make friends" the device with various third-party tuning programs, we decided to use an open Innovate serial protocolwhich is available in almost any modern program that uses AFR readings. Of course, you can blame us for this, and say that we just "stole" the work of others, but on the other hand, we have our own protocol for working with our own software ExTuner Utility, which is also available to third-party developers, but so that other developers can use or add to existing programs, it will take years.
A common USB interface is used to connect to a PC.

ExTuner Utility

As for the CobraRTP emulators, we have developed a separate utility. At the time of this writing, ExTuner Utility allows you to:

  • Display parameters to virtual devices in real time
  • Logging parameters and save in CSV format for further analysis
  • Updating device firmware
  • Configuring the analog input (AUX) for your own needs
  • Setting the analogue AUX outputs
  • Check for updates on the server online
  • there are 2 interface languages: Russian and English

To connect, you need to connect the device via USB and in the program. 

extuner software
Main
extuner
Settings of Analog input

Not enough AFR + EGT? There is an output: AUX

As an additional option, the device has a general purpose analog input (0-5V), with which you can connect various sensors to display readings on the display in the form of a physical quantity and more.
Most sensors with an output signal in the range of 0 ... 5V are suitable for connection. But how to make the voltage signal converted into human-readable values? The answer is simple, for this you need to know 2 operating points for the system to build a linear function. These parameters are set in the ExTuner Utility graphical interface:

extuner
Settings of Analog input
Показания с ДАД (MAP)

Thus, the device already has 3 independent measured values, which can be very useful, rather than using a separate device for this.

Analog outputs (AUX)

If, for example, you need to use ExTuner as an SDK controller, which must be connected to the analog inputs of the ECU to obtain the composition of the "mixture", then for this we have provided analog outputs to which the AFR and EGT readings (0-5V) are displayed.
With LSU 4.9, the range is 7.7: 1 to 20.0: 1.

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