EXHAUST EMISSION CONTROL DEVICE OF INTERNAL COMBUSTION ENGINE

摘要

PROBLEM TO BE SOLVED: To absorb moisture and restrain worsening of afterward NOx trap efficiency in an operation condition with little NOx in exhaust or in an operation condition with much moisture in the exhaust when trapping NOx in the exhaust from a low temperature by using a zeolite catalyst. SOLUTION: The zeolite catalyst 18, a bypass passage 19 for bypassing the catalyst 18 and a selector valve 20 for selectively letting the exhaust to the catalyst 18 or the passage 19 are provided with an exhaust system of an engine 1. The selector valve 20 is controlled according to a ratio of NOx and moisture in the exhaust. More specifically, the passage 19 is selected when the NOx/moisture ratio in the exhaust is at or below a predetermined value and the catalyst 18 is selected when the ratio is over the predetermined value.