Control device for internal combustion engine and catalyst abnormality diagnosis method

A control device for an internal combustion engine, the control device comprising:

• a catalyst located in an exhaust passage and configured to store oxygen;
• an air-fuel ratio sensor configured to detect an air-fuel ratio of exhaust gas flowing out of the catalyst;
• and
• one or more electronic control units configured to control an air-fuel ratio of incoming exhaust gas flowing into the catalyst, wherein the one or more electronic control units are configured to
• perform oxygen amount variation control in which a target air-fuel ratio for the incoming exhaust gas is switched between a rich set air-fuel ratio that is richer than a stoichiometric air-fuel ratio and a lean set air-fuel ratio that is leaner than the stoichiometric air-fuel ratio,
• set the target air-fuel ratio to the lean set air-fuel ratio when the air-fuel ratio detected by the air-fuel ratio sensor is equal to or less than a predetermined oxygen depletion determination air-fuel ratio in the oxygen amount variation control, and
• set the target air-fuel ratio to the rich set air-fuel ratio when the air-fuel ratio detected by the air-fuel ratio sensor is equal to or higher than a predetermined oxygen saturation determination air-fuel ratio in the oxygen amount variation control, wherein
• the oxygen depletion determination air-fuel ratio is an air-fuel ratio richer than the stoichiometric air-fuel ratio, and
• the oxygen saturation determination air-fuel ratio is leaner than the oxygen depletion determination air-fuel ratio and richer than the stoichiometric air-fuel ratio.