| 摘要 |
<P>PROBLEM TO BE SOLVED: To optimally maintain the amount of exhaust emission circulating in a NOX catalyst when a reducing agent is supplied from a reducing agent supplying valve. <P>SOLUTION: A NO<SB>x</SB>catalyst 81 is arranged in an exhaust passage of an internal combustion engine where combustion is carried out continuously under a lean air-fuel ratio. The reducing agent supplying valve 77 is arranged in the exhaust passage at the upstream of the NO<SB>x</SB>catalyst 81. When the amount of accumulated NOX in the NOX catalyst 81 should be reduced, the amount of the exhaust emission circulating in the NOX catalyst 81 is reduced positionally by changing a change-over valve from a down-flow position to an up-flow position or vice versa. The reducing agent is supplied only after the predetermined elapsed time from the time when a signal for changing the change-over valve 61 is generated. When the reducing agent is supplied, oxygen concentration in the exhaust emission exhausted from the NO<SB>X</SB>catalyst 81 is detected with an oxygen concentration sensor 48, and the elapsed time is corrected so as to conform a peak value generated in the oxygen concentration to a target value. <P>COPYRIGHT: (C)2004,JPO |
