| 摘要 |
PROBLEM TO BE SOLVED: To correct shift in the output originating from degradation, etc., of an NOx sensor. SOLUTION: An NOx occluding/reducing catalyst 7 is installed in the exhaust passage 2 of an internal combustion engine 1, and the NOx concentration in the exhaust gas after passage of catalyst 7 is detected by an NOx sensor 33. An electronic control unit(ECU) 30 of an engine 1 operates the engine with the rich air-fuel ratio for a short time each time the sensed NOx concentration increases to a prescribed value and performs the regenerative process of the NOx occluding/reducing catalyst 7. Also the ECU learns the shift of the NOx sensor output from the reference value (output corresponding to the NOx concentration being zero) and the NOx sensor output, when the engine is operated in the condition that the NOx emission in the low-load operation, etc., at a lean air-fuel ratio is less and also the NOx occluding/reducing catalyst is functioning normally, i.e., in the condition that the NOx concentration in the exhaust gas reaching the NOx sensor becomes approx. zero and then corrects the NOx sensor output on the basis of the learnt value. |
