Abstract: In a method for identifying the state of an NOx storage catalyst which is cyclically loaded with NOx in the exhaust stream of an internal combustion engine and regenerated, two electrical defining quantities, independent of each other, of the electrically complex impedance of the NOx storage catalyst are detected, one of the two electrical quantities being a measure of the degree of loading of the NOx storage catalyst, and from the second electrical quantity the point in time being identifiable for the end of the regeneration process of the NOx storage catalyst.

Abstract: A method for determining the reducing agent concentration (NH3) in the exhaust-gas flow of an internal combustion engine, using a zeolitic NH3 gas sensor that supplies a base measuring value, which is initially corrected by an offset value and a correction value that depends on the H2O concentration of the exhaust gas to form an intermediate value. The intermediate value is subsequently corrected by an additional value that depends on the NOx and NH3 concentration of the exhaust gas. In particular at or above the limits for the operating range, the accuracy of the method increases for one of the following conditions: gas compositions with NOx concentrations >500 ppm, extremely low NH3 concentrations <20 ppm or high NH3 concentrations >100 ppm.

Abstract: A method for determining the reducing agent concentration (NH3) in the exhaust-gas flow of an internal combustion engine, using a zeolitic NH3 gas sensor that supplies a base measuring value, which is initially corrected by an offset value and a correction value that depends on the H2O concentration of the exhaust gas to form an intermediate value. The intermediate value is subsequently corrected by an additional value that depends on the NOx and NH3 concentration of the exhaust gas. In particular at or above the limits for the operating range, the accuracy of the method increases for one of the following conditions: gas compositions with NOx concentrations >500 ppm, extremely low NH3 concentrations <20 ppm or high NH3 concentrations >100 ppm.

Abstract: In a method for identifying the state of an NOx storage catalyst which is cyclically loaded with NOx in the exhaust stream of an internal combustion engine and regenerated, two electrical defining quantities, independent of each other, of the electrically complex impedance of the NOx storage catalyst are detected, one of the two electrical quantities being a measure of the degree of loading of the NOx storage catalyst, and from the second electrical quantity the point in time being identifiable for the end of the regeneration process of the NOx storage catalyst.