Exhaust gas purification apparatus for an internal combustion engine

An exhaust gas purification apparatus for an internal combustion engine which performs lean burn operation, the apparatus comprising:

• a first NOx storage reduction catalyst that is arranged in an exhaust passage of the internal combustion engine;
• a post-stage catalyst that is arranged in the exhaust passage at the downstream side of the first NOx storage reduction catalyst, and reduces NOx in an exhaust gas by a supplied reducing agent;
• a reducing agent supply device that is arranged in the exhaust passage between the first NOx storage reduction catalyst and the post-stage catalyst, and supplies the reducing agent into the exhaust passage;
• a controller comprising at least one processor is configured to carry out rich spike to temporarily change an air fuel ratio of an exhaust gas flowing into the first NOx storage reduction catalyst from a lean air fuel ratio higher than a stoichiometric air fuel ratio into a rich air fuel ratio lower than the stoichiometric air fuel ratio;
• wherein
• the controller carries out supply control to supply the reducing agent to the post-stage catalyst by using the reducing agent supply device, wherein in cases where a temperature of the first NOx storage reduction catalyst becomes less than a predetermined determination temperature in at least a part of a determination period of time from the completion of the execution of the last rich spike to a request for the execution of the current rich spike, the controller carries out the supply control according to the execution of the current rich spike;
• and
• the controller calculates a storage amount of NOx which is an amount of NOx stored in the first NOx storage reduction catalyst;
• wherein in cases where the storage amount of NOx is the same, the controller carries out supply amount control to make an amount of supply of the reducing agent in the supply control larger as a period of time in which the temperature of the first NOx storage reduction catalyst is less than the predetermined determination temperature becomes longer.