| 摘要 |
<P>PROBLEM TO BE SOLVED: To accurately measure, when measuring an oxygen storage ability of an exhaust purifying catalyst by using an exhaust sensor provided downstream of the exhaust emission control catalyst, the oxygen storage ability even when a condition occurs in which exhaust gas around the exhaust sensor is not sufficiently mixed. Ž<P>SOLUTION: After deriving an oxygen discharging amount Or, the derived oxygen discharging amount Or is determined whether or not being deviated downward from an oxygen discharging predicted range within which the amount Or is predicted to fall this time (S230). When the derived oxygen discharging amount Or is not deviated downward from the oxygen discharging predicted range, a target air-fuel ratio is immediately set to a lean air-fuel ratio (S250). On the other hand, when the derived oxygen discharging amount Or is deviated downward from the oxygen discharging predicted range, the target air-fuel ratio is set to a lean air-fuel ratio (S250) after an excessive injection amount Pn becomes a required fuel amount Pnref or more so that oxygen remaining in an exhaust purifying catalyst 31 may be used up (negative determination in S310). Ž<P>COPYRIGHT: (C)2010,JPO&INPIT Ž
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