Diagnostic method and device for operating an internal combustion engine

1. A method of operating an internal combustion engine comprising a catalytic converter, a first exhaust gas sensor that is disposed in such a way that it may be used in a lambda closed-loop control operation, and a second exhaust gas sensor that is disposed in such a way that it may be used in a trim closed-loop control operation, the method comprising the steps of:

modulating a forced excitation upon an air-fuel ratio setpoint value in order to adjust a lambda variation for optimizing an efficiency of the catalytic converter,

using a second exhaust gas sensor to generate a measuring signal responsive to a controlled air-fuel ratio of the internal combustion engine,

a controller determining an HC quality value that is representative of an oxygen storage capacity of the catalytic converter by:

increasing the forced excitation amplitude applied to the air-fuel ratio setpoint value,

comparing an oscillation of the measuring signal generated by the second exhaust gas sensor with respect to a predefined reference value for the measuring signal, and

determining the HC quality value based on the results of the comparison, the controller determining a NOx correction value by:

comparing the measuring signal generated by the second exhaust gas sensor to one or more threshold values, each having a predetermined factor assigned thereto,

determining durations during which the measuring signal crosses each of the one or more threshold values,

for each determined duration, calculating a product of a determined air mass flow for the internal combustion engine and the factor assigned to the threshold value crossed during that duration, and

summing the calculated products for the durations,

the controller multiplying or adding the HC quality value and the NOx correction value to determine an NOx quality value representing a level of current NOx emissions from the engine.

2. The method according to claim 1 , comprising comparing the NOx quality value with a preselected NOx quality limit value, and generating a fault indicator if the NOx quality value exceeds the preselected NOx quality limit value.

3. The method according to claim 1 , wherein the NOx correction value is determined in dependence upon signal components that are representative of the presence of residual oxygen.

4. The method according to claim 1 , wherein the HC quality value is determined by increasing the forced excitation amplitude and over a preselected number of cycles of the forced excitation, determining the HC quality value in dependence upon an amplitude of an oscillation of the measuring signal of the second exhaust gas sensor in relation to a reference value of the measuring signal of the second exhaust gas sensor.

5. The method according to claim 4 , wherein the preselected number of cycles is approximately 20 cycles.

6. The method according to claim 1 , wherein the HC quality value is determined by means of a corresponding oxygen balance calculation in dependence upon the measuring signal of the first exhaust gas sensor and the second measuring signal of the second exhaust gas sensor.

7. An electronic control device for of an internal combustion engine comprising a catalytic converter, a first exhaust gas sensor that is disposed in such a way that it may be used in a lambda closed-loop control operation, and a second exhaust gas sensor that is disposed in such a way that it may be used in a trim closed-loop control operation, the electronic control device being communicatively coupled to the first and second exhaust sensors, the electronic control device comprising:

a memory storing data and programs, the programs when executed:

determines an HC quality value, which is representative of an oxygen storage capacity of the catalytic converter, in dependence upon a measuring signal of the second exhaust gas sensor,

determines a NOx correction value by:

comparing the measuring signal to one or more threshold values, each having a predetermined factor assigned thereto,

determining durations during which the measuring signal crosses each of the one or more threshold values,

for each determined duration, calculating a product of a determined air mass flow for the internal combustion engine and the factor assigned to the threshold value crossed during that duration, and

summing the calculated products for the durations, and

multiplies or adds the HC quality value and the NOx correction value to determine a NOx quality value.

8. The device according to claim 7 , further being operable to compare the NOx quality value with a preselected NOx quality limit value, and generate a fault indicator if the NOx quality value exceeds the preselected NOx quality limit value.

9. A system for operating an internal combustion engine comprising:

a catalytic converter,

a control device,

a first exhaust gas sensor that is disposed in such a way that it may be used in a lambda closed-loop control operation, and

a second exhaust gas sensor that is disposed in such a way that it may he used in a trim closed-loop control operation,

wherein the second exhaust gas sensor feeds a measuring signal to the control device which:

determines an HC quality value that is representative of an oxygen storage capacity of the catalytic converter from the measuring signal by:

increasing a forced excitation amplitude applied to an air-fuel ratio setpoint value,

comparing an oscillation of the measuring signal generated by the second exhaust gas sensor with respect to a predefined reference value, and

determining the HC quality value based on the results of the comparison,

determines an NOx correction value by:

comparing the measuring signal generated by the second exhaust gas sensor to one or more threshold values, each having a predetermined factor assigned thereto,

determining durations during which the measuring signal crosses each of the one or more threshold values,

for each determined duration, calculating a product of a determined air mass flow for the internal combustion engine and the factor assigned to the threshold value crossed during that duration, and

summing the calculated products for the durations,

multiplies or adds the HC quality value and the NOx correction value to determine an NOx quality value representing a level of current NOx emissions from the engine.

10. The system according to claim 9 , wherein the control device further compares the NOx quality value with a preselected NOx quality limit value, and generates a fault indicator if the NOx quality value exceeds the preselected NOx quality limit value.

11. The system according to claim 9 , wherein the control device comprises a plurality of functional blocks.

12. The system according to claim 11 , wherein a functionality of each block is stored in the form of programs which are executed during operation of the internal combustion engine.

13. The system according to claim 9 , wherein the control device modulates a forced excitation upon a basic setpoint value of an air-fuel ratio in order to adjust a lambda variation for optimizing an efficiency of the catalytic converter.

14. The system according to claim 13 , wherein the control device determines the HC quality value by increasing the forced excitation amplitude and over a preselected number of cycles of the forced excitation, determining the HC quality value in dependence upon an amplitude of an oscillation of the measuring signal of the second exhaust gas sensor in relation to a reference value of the measuring signal of the second exhaust gas sensor.

15. The system according to claim 14 , wherein the preselected number of cycles is approximately 20 cycles.

16. The system according to claim 9 , wherein the control device determines the HC quality value by means of a corresponding oxygen balance calculation in dependence upon the measuring signal of the first exhaust gas sensor and the second measuring signal of the second exhaust gas sensor.