Closed loop lambda control in fuel injection

Mary's picture

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Joined: Nov 23, 2020

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Closed loop lambda control in fuel injection
November 23, 2020 - 4:26pm

Hi, I got a project and I have no idea what to do...I have to do a diagnostic circuit of a lambda closed loop fuel injection that has the corect fill factor of the signal from the lambda sensor : 40%÷60%.

Under 40%, the engine will work on poor mixture and will set a code of 2 digits(between 40...49)

Over the 60%, the engine will work on rich mixture, and will set another code, different from the first one (still between 40...49).

The signaling of the emergency situation will be done with a signaling lamp with 1 Hz frequency and a 0.5 filling factor.

      - I have to use a microcontroller, make a proteus simulation, and solve this using functions in C

  Until now, I only understood what closed loop lambda is, found some theories in general and learned that 16 bytes microcontrollers are best for engines applications,  but I really don't know how to do the circuit or the code....I don't have any knowledge about power electronics or automotive, just some C/C++ and some basic electronics. Any help is useful. Thank you!

Sourav Gupta's picture

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First find out whether the sensor is available in proteus? Or its library for proteus? Otherwise it is useless to write code and then test it.

Mary's picture

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Proteus has a gas sensor, but I'm not sure if it's ok to use it, lambda sensor refers to air/fuel ratio, and I can't find something clear related to this.

I think it can be MQ-4, that has high sensitivity to CH4, Natural gas, but i am not sure.

Sourav Gupta's picture

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lambda sensor works different way than the preheated resistive sensors. You need to find proper sensor or need to create a dummy one by hardcoded values.

Mary's picture

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I found a circuit for  an O2 sensor build with a 555timer, maybe it will be good enough?

From what I read about it, it has the same purpose as lambda sensor.

Michal Podmanický's picture

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It is a relatively simple task regarding to writing a code for uC, harder make finished product to be usefull, especially if you are going to use PID regulator.

The lambda sensor I saw has output signal in range 0.1 - 0.8V so this can be easy measured by integrated ADC. Then you need to create a timed loop in uC, I would use a period about 1ms. In this loop you have to:

1.Read new data from lambda

2.Calculate the error from previous lambda reading

3.Recalculate the PID equations with new error

4.Set the mixture according the output from PID

 

This part is easy, but the problem is if you are going to use it real system, where you cant effort mistake (damage of engine and others)  and  cant measure the efectivness of system easy way(fuel to power ratio). Tune the PID in this example is a task when you have to know what you do. Also, it is hard to find the constants of the controlled system, you probably will have to measure it by some methods.

 

Sourav Gupta's picture

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Michal is absolutely right. You can test the available sensor. Make sure everything is correct before the dummy run.