| 摘要 |
PROBLEM TO BE SOLVED: To keep favorable exhaust gas characteristic over a long period of time by providing a SOx emit means for emitting SOx absorbed in a NOx purifying means, which is constructed by a rich means for an air-fuel mixture air-fuel ratio and an ignition timing control means for controlling the ignition timing to the side where the engine exhaust temperature rises. SOLUTION: During the operation of an engine 1, when the lean operation is discriminated in an ECU 5, an increment value is determined according to the engine rotating speed NE and the intake pipe internal absolute pressure PBA, and a NOx quantity counter and a SOx quantity counter are incremented by using the increment value. When the SOx quantity counter value exceeds an allowable value, SOx quantity reduction rich is executed so that SOx absorbed in NOx absorbent is emitted as SO. At this time, the ignition timing is lag-corrected to raise the exhaust gas temperature. On the other hand, when the NOx quantity counter value exceeds an allowable value, NOx reduction rich is executed so that NOx absorbed in the NOx absorbent is emitted as nitrogen gas.
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