Systems and methods for monitoring catalyst deactivation and controlling an air/fuel ratio

1. A method for controlling an air/fuel ratio in an engine, the method comprising:

operating the engine,

generating a gas stream from the engine;

passing the gas stream through a three way catalyst, and then passing the gas stream through a NH 3 sensor;

determining, at the NH 3 sensor, whether an actual value of NH 3 concentration downstream from the three way catalyst is lower than a nominal value for NH 3 concentrations produced at rich operating conditions;

if the actual value of NH 3 concentration is lower than the nominal value for NH 3 concentrations produced at rich operating conditions then, at an air/fuel control subsystem, adjusting the air/fuel ratio based on estimated CO concentrations.

2. The method for controlling an air/fuel ratio in an engine of claim 1 , wherein determining whether an actual value of NH 3 concentration is lower than a nominal value for NH 3 concentrations produced at rich operating conditions comprises:

establishing the nominal value for NH 3 concentrations produced at rich operating conditions;

detecting the actual value of NH 3 concentration downstream from the three way catalyst; and

comparing the actual value of NH 3 concentration downstream from the three way catalyst with the nominal value for NH 3 concentrations produced at rich operating conditions.

3. The method for controlling an air/fuel ratio in an engine of claim 1 , wherein adjusting the air/fuel ratio based on estimated CO concentrations comprises:

determining an actual air/fuel ratio;

determining whether an actual CO concentration is greater than a reference CO concentration; and

changing the air/fuel ratio when the actual CO concentration is greater than the reference CO concentration.

4. The method for controlling an air/fuel ratio in an engine of claim 3 , wherein determining whether an actual CO concentration is greater than a reference CO concentration comprises:

establishing a reference CO concentration value;

estimating an actual CO concentration value; and

comparing the actual CO concentration value to the reference CO concentration value.

5. The method for controlling an air/fuel ratio in an engine of claim 4 , wherein estimating an actual CO concentration value comprises calculating the actual CO concentration value using a model-based estimator.

6. The method for controlling an air/fuel ratio in an engine of claim 3 , wherein changing the air/fuel ratio comprises:

adjusting the air/fuel ratio to an adjusted air/fuel ratio that is leaner than the actual air/fuel ratio.

7. The method for controlling an air/fuel ratio in an engine of claim 6 , further comprising:

establishing a lower threshold value for NH 3 concentrations;

comparing the actual value of NH 3 concentration downstream from the three way catalyst with the lower threshold value for NH 3 concentrations;

adjusting the air/fuel ratio to an air/fuel ratio that is richer than the adjusted air/fuel ratio if the actual value of NH 3 concentration downstream from the three way catalyst is lower than the lower threshold value for NH 3 concentrations; and

if the actual value of NH 3 concentration downstream from the three way catalyst is greater than the lower threshold value for NH 3 concentrations then detecting actual value of NH 3 concentration downstream from a three way catalyst.

8. A method for detecting deactivation of a catalyst, the method comprising:

operating an engine,

generating a gas stream from the engine;

passing the gas stream through a three way catalyst, and then passing the gas stream through an NH 3 sensor;

determining, at the NH 3 sensor, whether an actual value of NH 3 concentration downstream in the gas stream from the three way catalyst is lower than a nominal value for NH 3 concentrations produced at rich operating conditions;

if the actual value of NH 3 concentration is lower than the nominal value for NH 3 concentrations produced at rich operating conditions then determining an estimated CO concentration value;

comparing the estimated CO concentration value to a reference CO concentration value for detecting deactivation of the three way catalyst; and

sending one or more control signals to an air/fuel control subsystem based on the comparison of the estimated CO concentration value to the reference CO concentration value, wherein the air/fuel control subsystem is configured to adjust an air/fuel ratio based on the received control signals.

9. The method for detecting deactivation of a catalyst of claim 8 , wherein determining an estimated CO concentration value comprises determining the estimated CO concentration value using a model-based estimator.

10. The method for detecting deactivation of a catalyst of claim 9 , wherein the model-based estimator comprises an observer based on a physical model of the three way catalyst.

11. The method for detecting deactivation of a catalyst of claim 10 , wherein the observer based on the physical model of the three way catalyst is a linear observer.

12. The method for detecting deactivation of a catalyst of claim 10 , wherein the observer based on the physical model of the three way catalyst is a non-linear observer.

13. The method for detecting deactivation of a catalyst of claim 8 , wherein determining whether an actual value of NH 3 concentration downstream from the three way catalyst is lower than a nominal value for NH 3 concentrations produced at rich operating conditions comprises determining whether a time averaged value of NH 3 concentration downstream from the three way catalyst is lower than the nominal value for NH 3 concentrations produced at rich operating conditions.

14. The method for detecting deactivation of a catalyst of claim 8 , wherein the one or more control signals indicate that the three way catalyst is deactivated if the estimated CO concentration value is greater than the reference CO concentration value.

15. A system for controlling an air/fuel ratio in an engine, the system comprising:

a three way catalyst;

an NH 3 sensor disposed downstream from the three way catalyst;

a control subsystem that compares a measured value of NH 3 concentration with a nominal value of NH 3 concentration at rich operating conditions; and

an air/fuel control subsystem that adjusts the air/fuel ratio to the engine based on the measured value of NH 3 concentration and estimated CO concentrations.

16. The system for controlling an air/fuel ratio in an engine of claim 15 , wherein the subsystem that adjusts the air/fuel ratio comprises:

a subsystem that estimates a CO concentration downstream of the three way catalyst.

17. The system for controlling an air/fuel ratio in an engine of claim 16 wherein the subsystem that estimated a CO concentration comprises an observer based on a physical model of the three way catalyst.

18. The system for controlling an air/fuel ratio in an engine of claim 17 wherein the observer is a linear observer.

19. The system for controlling an air/fuel ratio in an engine of claim 17 wherein the observer is a non-linear observer.

20. The system for controlling an air/fuel ratio in an engine of claim 15 , wherein the subsystem that adjusts the air/fuel ratio comprises:

a subsystem that compares an estimated value of CO concentration to a reference value of CO concentration.

21. A method for controlling an air/fuel ratio in an engine, the method comprising:

operating the engine;

generating a gas stream from the engine;

passing the gas stream through a three way catalyst, and then passing the gas stream through a NH 3 sensor;

determining, at the NH 3 sensor, whether an actual value of NH 3 concentration downstream from a three way catalyst is lower than a nominal value for NH 3 concentrations produced at rich operating conditions;

if the actual value of NH 3 concentration is lower than the nominal value for NH 3 concentrations produced at rich operating conditions then, at an air/fuel control subsystem, adjusting the air/fuel ratio based on estimated CO concentrations; wherein adjusting the air/fuel ratio based on estimated CO concentrations comprises:

determining an actual air/fuel ratio;

determining whether an actual CO concentration is greater than a reference CO concentration; and changing the air/fuel ratio when the actual CO concentration is greater than the reference CO concentration;

wherein determining whether an actual CO concentration is greater than a reference CO concentration comprises:

establishing a reference CO concentration value;

estimating an actual CO concentration value; and comparing the actual CO concentration value to the reference CO concentration value,

wherein estimating an actual CO concentration value comprises calculating an actual CO concentration using a model based estimator.

22. A method for detecting deactivation of a catalyst, the method comprising:

operating an engine,

generating a gas stream from the engine;

passing the gas stream through a three way catalyst, and then passing the gas stream through an NH 3 sensor;

determining, at the NH 3 sensor, whether an actual value of NH 3 concentration downstream in the gas stream from the three way catalyst is lower than a nominal value for NH 3 concentrations produced at rich operating conditions;

if the actual value of NH 3 concentration is lower than the nominal value for NH 3 concentrations produced at rich operating conditions then determining an estimated CO concentration value;

comparing the estimated CO concentration value to a reference CO concentration value for detecting deactivation of the three way catalyst; and

sending one or more control signals to an air/fuel control subsystem based on the comparison of the estimated CO concentration value to the reference CO concentration value, wherein the air/fuel control subsystem is configured to adjust an air/fuel ratio based on the received control signals,

wherein determining an estimated CO concentration value comprises determining an estimated CO concentration value using a model-based estimator.

23. A system for controlling an air/fuel ratio in an engine, the system comprising:

a three way catalyst;

an NH 3 sensor disposed downstream from the three way catalyst;

a control subsystem that compares a measured value of NH 3 concentration with a nominal value of NH 3 concentration at rich operating conditions; and

an air/fuel control subsystem that adjusts the air/fuel ratio to the engine based on the measured value of NH 3 concentration and estimated CO concentrations;

wherein the subsystem that adjusts the air/fuel ratio comprises:

a subsystem that estimates a CO concentration downstream of the three way catalyst, and

wherein the subsystem that estimates a CO concentration comprises an observer based on a physical model of the three way catalyst.