| 摘要 |
<p>PROBLEM TO BE SOLVED: To restrain deterioration of fuel consumption performance and lowering of torque by reducing the frequency of sulfur poisoning elimination for NOx catalyst provided in an exhaust system of a lean burn engine. SOLUTION: A control unit 20 calculates temporary deterioration of the NOx catalyst due to sulfur poisoning and permanent deterioration of the NOx catalyst due to heat or phosphor poisoning, and when the total deterioration of the NOx catalyst 17 obtained by adding the above deterioration reaches a designated limit value, at least either making an air fuel ratio rich or retard of ignition timing is performed to execute sulfur poisoning elimination for the NOx catalyst 17. Not only the temporary deterioration of the NOx catalyst 17, but the permanent deterioration is taken into consideration, whereby in the condition of little permanent deterioration, the frequency of sulfur poisoning elimination is effectively reduced so as to restrain the problems of deterioration of fuel consumption performance and lowering of torque.</p> |
