| 摘要 |
A NOx catalyst (14) is attached to an engine exhaust pipe (12), an A/F sensor (26) is disposed upstream of the NOx catalyst (14), and an O2 sensor (27) is disposed downstream of the NOx catalyst (14). A CPU (31) in an ECU (30) executes a lean combustion control so that NOx in exhaust gases discharged at the time of the lean combustion is occluded by the NOx catalyst (14). The CPU (31) further executes a rich combustion control temporarily, so that the occluded NOx to be discharged from the NOx catalyst (14). The CPU (31) checks if the NOx catalyst (14) deteriorates. When occurrence of deterioration is detected, the CPU (31) increases the proportion of the rich combustion to the lean combustion, thereby increasing the temperature of the NOx catalyst (14). After the catalyst temperature increases, the air-fuel ratio is controlled to the stoichiometric air-fuel ratio ( lambda = 1) to regenerate the NOx catalyst (14). <IMAGE> |
