Exhaust gas purification apparatus and exhaust gas purification method for internal combustion engine

Abstract

In an exhaust gas purification apparatus for an internal combustion engine () equipped with independent exhaust passages () provided one for each cylinder group () with a catalyst () having a NOx trapping ability being arranged in each exhaust passage, the present invention is intended to provide a technique that can independently control the flow rates of exhaust gases flowing into the respective catalysts. To this end, the exhaust gas purification apparatus according to the present invention provides a communication passage () connecting mutually portions of said exhaust passages () at upstream of said catalysts (), an upstream side switching valve () openning and closing said upstream side communication passage (), a plurality of flow rate regulation valves () being arranged at downstream of connecting portions of said exhaust passages with said upstream side communication passage, respectively, and a control section () controlling said upstream side switching valve () and said respective flow rate regulation valves () in accordance with the states of said respective catalysts (). When the NOx trapping ability of one of the plurality of catalysts () is regenerated, the control section () opens the upstream side switching valve (), fully closes one flow rate regulation valve () in one of the exhaust passages () in which the one catalyst () is arranged, and operates a reducing agent addition valve () in such a manner that the reducing agent arrives at the one catalyst () when the actual degree of opening of the one flow rate regulation valve () becomes fully closed.