| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for controlling an engine exhaust system which can efficiently decrease the concentration of NOx in exhaust gas from an internal combustion engine and a method for detecting the deterioration of the catalyst which is used in the above method correctly. SOLUTION: A method for controlling an engine exhaust system including a NOx reduction catalyst 30 which is set in the exhaust system of an engine operated principally in lean conditions and can adsorb nitrogen oxides in atmosphere and a NOx sensor 40 which is set at least downstream from the NOx reduction catalyst. When an air/fuel ratio (A/F) control circuit part 50 detects the output value of the NOx sensor 40 corresponding to a NOx discharge concentration and compares it with a prescribed value, and the output value reaches the prescribed value, a fuel injection control part 60 controls the injection of fuel based on a signal from the A/F control circuit part 50 so that the air/fuel ratio (A/F) of the mixture to be supplied to an engine 20 is stoichimetric or rich. By the control, NOx adsorbed on the NOx reduction catalyst 30 is desorbed or decomposed, and the engine 20 is operated again in lean conditions. |
