| 摘要 |
PURPOSE:To keep the NOx purification efficiency of a lean NOx catalyst high even if the lean NOx catalyst is deteriorated. CONSTITUTION:An internal combustion engine 2 includes a lean NOx catalyst 6 provided in an exhaust system 4 thereof, a catalyst deterioration judging means and an HC quantity increasing means for increasing the HC quantity in the exhaust gas when the catalyst deterioration judging means judges the deterioration of the catalyst 6. When the lean NOx catalyst 6 is deteriorated, the NOx purification efficiency is lowered, and the temperature range of the NOx purification efficiency peak is shifted to the high temperature side. According to the above shifting, the HC quantity increasing means increases the HC quantity, so that the NOx purification efficiency of the lean NOx catalyst 6 can be always kept high. If the catalyst floor temperature is shifted to the high temperature side at the same time, a large effect of improving the NOx purification efficiency is produced.
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