Control apparatus for an internal combustion engine

A control apparatus for an internal combustion engine in which an exhaust gas purification device including an NOx storage reduction (NSR) catalyst and a measuring device for measuring an amount of NOx flowing out from said NSR catalyst are arranged in an exhaust passage, comprising:

• a regeneration unit configured to carry out regeneration processing which is processing of regenerating the NOx storage capacity of said NSR catalyst;
• a diagnostic unit configured to carry out NSR diagnostic processing which is processing of diagnosing an abnormality in said NSR catalyst, based on a measured value of said measuring device at a predetermined NSR diagnostic time after said regeneration processing ended;
• and
• a control unit configured to control an engine air fuel ratio which is an air fuel ratio of a mixture to be supplied to said internal combustion engine;
• wherein in cases where said NSR diagnostic processing is carried out, said control unit controls, in a period of time from a predetermined weak lean operation start time after an end time of said regeneration processing to said NSR diagnostic time, the engine air fuel ratio to a weak lean air fuel ratio which is lower than a lean air fuel ratio according to an operating condition of the internal combustion engine and which is higher than a stoichiometric air fuel ratio, and changes, after said NSR diagnostic time, the engine air fuel ratio from said weak lean air fuel ratio to a rich air fuel ratio which is lower than the stoichiometric air fuel ratio.