Method for processing measured values from a nitrogen oxide sensor
View Patent ↗A method for processing measured values two nitrogen oxide sensors, one of which is arranged upstream of a nitrogen oxide reduction catalytic converter in the exhaust gas system of a motor vehicle and the other of which is arranged downstream of the nitrogen oxide reduction catalytic converter, involves recording and comparing measured values from the two nitrogen oxide sensors at least approximately at the same time. A sensitivity of the first nitrogen oxide sensor and/or of the second nitrogen oxide sensor is changed depending on the result of the comparison.
1. A method, comprising:
measuring, by a first nitrogen oxide sensor arranged upstream of a nitrogen oxide reduction catalytic converter in an exhaust gas system of a motor vehicle, a nitrogen oxide content of exhaust gas;
measuring, by a second nitrogen oxide sensor arranged downstream of the nitrogen oxide reduction catalytic converter, the nitrogen oxide content of the exhaust gas,
wherein the measurements of the nitrogen oxide content of the exhaust gas by the first and second nitrogen oxide sensors occur at least approximately at a same time and at a time at which conditions exist such that a same measured value of the nitrogen oxide content of the exhaust gas should be measured by both the first and second nitrogen oxide sensors;
comparing the measurements of the nitrogen oxide content of the exhaust gas by the first and second nitrogen oxide sensors; and
adjusting a sensitivity of the first nitrogen oxide sensor or of the second nitrogen oxide sensor if the comparison indicates that respective measured values of the nitrogen oxide content of the exhaust gas by the first and second nitrogen oxide sensors differ by more than a specified amount, wherein the sensitivity of the first nitrogen oxide sensor or of the second nitrogen oxide sensor is changed in such a way that the first nitrogen oxide sensor and the second nitrogen oxide sensor have at least approximately equal sensitivities with respect to NO and/or NO 2 .
2. The method of claim 1 , wherein the sensitivity of the first nitrogen oxide sensor or of the second nitrogen oxide sensor is changed in such a way that the sensitivity of the first nitrogen oxide sensor or of the second nitrogen oxide sensor is adapted to the sensitivity of the respective other nitrogen oxide sensor that is left unchanged.
3. The method of claim 1 , wherein the sensitivity of the first nitrogen oxide sensor or of the second nitrogen oxide sensor is changed in such a way that the sensitivity of the nitrogen oxide sensor, the measured value from which deviates more strongly from a calculated NOx raw emission value, is adapted to the sensitivity of the other nitrogen oxide sensor.
4. The method of claim 1 , wherein the sensitivity of the first nitrogen oxide sensor and of the second nitrogen oxide sensor are changed in such a way that the measured values from the nitrogen oxide sensors correspond to a mean value of the measured values from the nitrogen oxide sensors before carrying out the sensitivity change.
5. The method of claim 1 , wherein the measurements are carried out at a time at which at least approximately equal concentrations of hydrocarbons or NOx are present in the exhaust gas at a point where the first nitrogen oxide sensor is installed and at a point where the second nitrogen oxide sensor is installed.
6. The method of claim 5 , wherein the measurements are carried out at a time at which the concentrations of hydrocarbons and/or ammonia in the exhaust gas do not exceed specified limits of, in each case, less than 20 ppm at the point where the first nitrogen oxide sensor is installed and at the point where the second nitrogen oxide sensor is installed.
7. The method of claim 5 , wherein the measurements are carried out at a time at which a temperature of the exhaust gas exceeds 450° C. at the point where the first nitrogen oxide sensor is installed and at the point where the second nitrogen oxide sensor is installed.
8. The method of claim 1 , wherein the measurements are carried out at a time at which concentrations of hydrocarbons and/or ammonia in the exhaust gas do not exceed specified limits of, in each case, less than 6 ppm at a point where the first nitrogen oxide sensor is installed and at a point where the second nitrogen oxide sensor is installed.
9. The method of claim 8 , wherein the measurements are carried out at a time at which a temperature of the exhaust gas exceeds 450° C. at the point where the first nitrogen oxide sensor is installed and at the point where the second nitrogen oxide sensor is installed.
10. The method of claim 1 , wherein the measurements are carried out at a time at which a temperature of the exhaust gas exceeds 450° C. at a point where the first nitrogen oxide sensor is installed and at a point where the second nitrogen oxide sensor is installed.
11. The method of claim 1 , wherein an error signal is output when the measured values from the nitrogen oxide sensors deviate from one another by more than a predefinable amount.
12. The method of claim 1 , wherein the measurements take place immediately following a thermal regeneration of a particulate filter arranged in the exhaust gas system.
13. The method of claim 1 , wherein an oxidation catalytic converter, a particulate filter and the nitrogen oxide reduction catalytic converter are arranged in the exhaust gas system one after the other in a direction of the exhaust gas flow, and the first nitrogen oxide sensor is arranged on an input side of the oxidation catalytic converter and the second nitrogen oxide sensor is arranged downstream of the nitrogen oxide reduction catalytic converter.