EXHAUST EMISSION CONTROL DEVICE FOR INTERNAL COMBUSTION ENGINE

摘要

PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion device sufficiently maintaining exhaust emission control performance of an NOx storage catalyst while inhibiting deterioration of fuel economy due to purge treatment.

SOLUTION: NOx conversion rate Rp is operated (S14) from flow in quantity of NOx to an NOx reduction catalyst detected by an upstream side NOx sensor and flow put quantity of NOx from the NOx reduction catalyst detected by a downstream side NOx sensor. Period from start of lean air-fuel ratio operation in which the air-fuel ratio of exhaust gas is made lean until NOx conversion rate Rp gets to a predetermined value or less is established as execution period Tp of lean air-fuel ratio operation (S16). The lean air-fuel ratio operation and rich air-fuel ratio operation are repeated to perform lean air-fuel ratio operation based on the execution period Tp of the lean air-fuel ratio operation (S20, S30).

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