EXHAUST EMISSION CONTROL DEVICE FOR INTERNAL COMBUSTION ENGINE

摘要

PROBLEM TO BE SOLVED: To quickly change over an air-fuel ratio in exhaust gas to be rich while suppressing the occurrence of misfire when rich control should be started.SOLUTION: An internal combustion engine includes an exhaust turbocharger, a high pressure side EGR passage 26H and a high pressure side EGR control valve 27H, and a low pressure side EGR passage 26L and a low pressure side EGR control valve 27L. When rich control should be started to hold an air-fuel ratio in exhaust gas from a combustion chamber 2 temporarily rich, the low pressure side EGR control valve is closed, a throttle opening is reduced, and then additional fuel injection is started. Besides, the opening of the high pressure side EGR control valve is controlled so that an actual exhaust EGR rate corresponds to a target EGR rate during the rich control.