INTERNAL COMBUSTION ENGINE EXHAUST PURIFYING DEVICE AND EXHAUST PURIFYING METHOD

摘要

Provided is an internal combustion engine exhaust purifying device capable of avoiding surging which occurs when the exhaust A/F is enriched. The device is equipped with a high-pressure EGR passage (6) which recirculates a portion of the upstream exhaust from a turbine (81) into a manifold (3), a high-pressure EGR control unit (43), a low-pressure EGR passage (10) which recirculates a portion of the downstream exhaust from the turbine (81) into an air intake tube (2), a low-pressure EGR control unit (44), a NOx purification catalyst (31) which is provided inside an exhaust pipe (4), captures NOx in an oxidizing atmosphere and purifies the captured NOx in a reducing atmosphere, a NOx purification catalyst reduction control unit (41) for controlling reduction of the exhaust air-fuel ratio, a prediction unit for predicting the occurrence of surging in a supercharger (8), and an EGR switching unit (45) which selects recirculation control of the exhaust by the high-pressure EGR control unit (43) when a prediction is made that no surging will occur in the supercharger (8) while reduction control is being executed, and which selects recirculation control of the exhaust by the low-pressure EGR control unit (44) when a prediction is made that surging will occur.