To enhance exhaust control in enrichment for reducing a lean NOx catalyst.
This electronic controller for controlling an air-fuel ratio of an engine having the lean NOx catalyst in an exhaust system is provided with an estimating means for estimating an amount of NOx captured in the lean NOx catalyst, a means for enriching the air-fuel ratio in response to the fact that the NOx amount estimated by the estimating means exceeds a prescribed value, a means for calculating an integrated value of exhaust flow rates, and a means for releasing the enrichment in response to the fact that the integrated value of the exhaust flow rates exceeds a threshold value. The NOx captured in the lean NOx catalyst can be accurately reduced since the rich air-fuel ratio is released using the integrated value of the flow rates correlated to a reductant amount (HC and CO discharge amounts), and exhaust control action of high order is provided thereby.
SHIMAOKA MINORU
INAGAWA WATARU
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