EXHAUST EMISSION CONTROL SYSTEM

摘要

PROBLEM TO BE SOLVED: To make a temperature of an NOx occlusion reduction type catalyst appropriate in regeneration processing of an NOx reduction type catalyst.SOLUTION: An exhaust emission control system includes: an NOx reduction type catalyst 32 provided in an exhaust passage of an internal combustion engine 10; an NOx/lambda sensor (excess air factor sensor) 45 for detecting an excess air factor of exhaust gas that has passed through the NOx reduction type catalyst 32; and a control section 50 for executing regeneration processing for recovering NOx purification capacity of the NOx reduction type catalyst by switching an exhaust air-fuel ratio from a lean state to a rich state by using both of air system control for reducing intake air amount and injection system control for increasing fuel injection amount. When a learning prohibition condition is not satisfied, the control section 50 acquires a learning value corresponding to a difference between an estimated excess air factor and an actual excess air factor detected by the excess air factor sensor and corrects the fuel injection amount in the injection system control on the basis of the acquired learning value. When the learning prohibition condition is satisfied, the control section does not acquire the learning value.SELECTED DRAWING: Figure 1