EXHAUST EMISSION CONTROL DEVICE FOR DIESEL ENGINE

摘要

PROBLEM TO BE SOLVED: To prevent deterioration of fuel consumption and exhausting performance in a diesel engine.

SOLUTION: An exhaust emission control device for a diesel engine includes: an NOx deposition amount computing means for computing the amount of NOx to be deposited on an NOx trap catalyst 12 in the lean combustion condition; an NOx desorption rate computing means for computing the desorption rate of NOx to be desorbed from the NOx trap catalyst 12 in the rich combustion condition; and an exhaust air-fuel ratio rich control means for raising air-fuel ratio of the exhaust to a theoretical air-fuel ratio or more by performing post injection to reduce the excess air ratio of the exhaust. This exhaust emission control device executes the exhaust air-fuel ratio rich control based on the deposition amount of NOx deposited on the NOx trap catalyst. When computing the NOx desorption rate, the exhaust emission control device performs a first correction based on the excess air ratio detected by an exhaust sensor 20 in the exhaust air-fuel ratio rich control and a second correction considering unburned HC which is not detected by the exhaust sensor 20 in the exhaust air-fuel ratio rich control.

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