| 摘要 |
PROBLEM TO BE SOLVED: To restrict generation of off-flavor due to the sulfur (S) compound included in exhaust gas by fluctuating the exhaust air-fuel ratio of an internal combustion engine around the rich air-fuel ratio as a reference, when sulfur poisoning of the NOx catalyst is detected by a S-poisoning detecting means. SOLUTION: When storage quantity of NOx of the NOx catalyst, namely, the quantity of S-poisoning is detected (S1), a discrimination as to whether or not the NOx catalyst is being regenerated is done (S2), and if it is 'YES', a fuel injector performs two-stage injection of the fuel so as to raise the temperature of the exhaust gas, namely, the temperature of the NOx catalyst (S5). Thereafter, a discrimination whether or not temperature rise of the NOx catalyst is concluded or not, namely, temperature of the NOx catalyst achieves the SOx activating temperature is done, and if it is 'YES', fluctuation control of the exhaust air-fuel ratio is carried out (S7). The fluctuation control is performed by alternately switching the exhaust air-fuel ratio between the theoretical air- fuel ratio as a lean side of the reference air-fuel ratio and the predetermined rich air-fuel ratio as a richer air-fuel ratio. At the time of switching the air-fuel ratio, detecting signal of an O2 sensor is used. |
