| 摘要 |
PROBLEM TO BE SOLVED: To suppress NOx reduction treatment to the minimum, and improve fuel consumption performance while achieving an intended NOx purifying performance by estimating a NOx absorbing quantity of a NOx absorbing catalyst on a downstream side of an exhaust system in an internal combustion engine capable of operating in a lean condition with a good efficiency on the basis of a purifying ratio of a selective reduction catalyst of the upstream side, in a device wherein the selective reduction catalyst is arranged on the upstream side and the NOx absorbing catalyst is disposed on the downstream side. SOLUTION: A NOx delivery quantity X of an engine, and an FNOMPL (D) are calculated from engine rotating speed by a map retrieval (S16, S18), a NOx purifying ratio is calculated from a catalyst temperature TCAT by a table retrieval (S22), it is corrected by a target air-fuel ratio KCMD (S24), a NOx adsorbing quantity Q. NOx is calculated (S26), an integrated value ΣQ.NOx is calculated (S28), it is compared with a prescribed value, and then, it is judged whether a NOx reduction treatment is carried out or not (S30 to S34). |
