System for controlling the exhaust gas return rate by means of virtual NOx sensors with adaptation via a NOx sensor

1. A method for adjusting a mass flow of an exhaust gas recirculation system of an internal combustion engine under consideration of a NOx behavior, said method comprising:

providing a controlling system which provides a coupling of a virtual NOx determination with a real NOx control by:

providing a virtual oxygen quantity (Ψ O2, Virtual ) from virtual EGR and air mass sensors;

providing a desired value of an oxygen quantity (Ψ O2,0 ) and a desired value of a NOx quantity (Ψ NOx,0 ) from an engine characteristic map and as a function of engine rotational speed (N engine ) and load (q);

determining a first model-based NOx quantity difference (ΔΨ NOx,fast,model ) from the virtual oxygen quantity (Ψ O2, Virtual ) and the desired value of an oxygen quantity (Ψ O2,0 );

determining a second NOx quantity difference (ΔΨ NOx, fast ) from the desired value of a NOx quantity (Ψ NOx,0 ) and a NOx sensor value (Ψ NOx );

comparing the first model-based NOx quantity difference (ΔΨ NOx,fast,model ) to the second NOx quantity difference (ΔΨ NOx, fast ) and providing the comparison to a learning function, the learning function providing an adapted NOx value (Ψ NOx, adapt );

providing the adapted NOx value (Ψ NOx, adapt ) to an inverse correlation that provides an oxygen difference quantity (ΔΨ O2,adapt );

comparing the virtual oxygen quantity (Ψ O2, Virtual ) with the oxygen difference quantity (ΔΨ O2,adapt ) and providing a corrected virtual oxygen quantity (Ψ O2, Virtual,corrected ); and

providing the corrected virtual oxygen quantity (Ψ O2, Virtual,corrected ) to a NOx model that produces a virtual NOx quantity (Ψ NOx,virtual ),

for the purpose of coupling a virtual NOx determination with a real NOx control in order to allow a quick and precise setting of the mass flow in the exhaust-gas recirculation system to be performed.

2. The method according to claim 1 , wherein a control parameter of the NOx control is determined by means of a virtual NOx sensor.

3. The method according to claim 1 , wherein a virtual NOx-dependent control parameter is compared with a NOx desired value determined from an engine characteristic map.

4. The method according to claim 1 , wherein an AGR mass flow is used as a control parameter for a virtually determined NOx control parameter.

5. The method according to claim 1 , wherein the NOx control reverts back to an exhaust gas recirculation model.

6. The method according to claim 1 , wherein an exhaust gas recirculation model of the controlling system in a quasi-stationary operating state of the internal combustion engine is calibrated by means of a signal of a real NOx sensor.

7. The method according to claim 1 , wherein the controlling system uses a PID regulator for regulating a virtually determined NOx value.

8. The method according to claim 1 , wherein a virtually determined NOx control parameter is adapted in the scope of an adaptive control.

9. The method according to claim 8 , wherein the adaptive control uses a real NOx sensor.

10. The method according to claim 1 , wherein the controlling system operates an inner and an outer cascade, wherein the inner cascade reverts back to a lambda probe, while the outer cascade reverts back to a real NOx sensor.

11. The method according to claim 10 , wherein the inner cascade performs a calibration of an air determination.

12. The method according to claim 10 , wherein the outer cascade performs a calibration of a NOx determination.

13. The method according to claim 8 further including the step of testing whether a prerequisite for an application of an adaptation of the controlling system is still present and if it is determined that the prerequisite has been eliminated, the adaptation of the controlling system is discontinued.

14. The method according to claim 1 , wherein the virtual NOx determination is performed more quickly than the determination of a NOx value by means of a real NOx sensor.

15. The method according claim 1 , wherein a parameter characterizing a particulate stream is determined under the use of a virtually determined oxygen content.

16. The method according to claim 1 , further including determining a virtual oxidation air ratio (λ Ox,virtual ), supplying the virtual oxidation air ratio (λ Ox,virtual ) to a particulate model that determines a particulate concentration (C PM ) in an exhaust gas passing through the exhaust gas recirculation system.