Controller for internal combustion engine

A controller for an internal combustion engine, wherein the internal combustion engine includes a fuel injection valve, a catalyst provided in an exhaust passage and capable of storing oxygen, and an air-fuel ratio sensor provided downstream of the catalyst in the exhaust passage, the controller comprising:

• processing circuitry, wherein
• the processing circuitry is configured to execute an air-fuel ratio control process that operates the fuel injection valve to control an air-fuel ratio of a mixture in a combustion chamber of the internal combustion engine to a target value,
• the processing circuitry is configured to execute a rich control process that is triggered when a detection value of the air-fuel ratio sensor is greater than or equal to a lean determination value,
• the detection value of the air-fuel ratio sensor being equal to the lean determination value indicates that an air-fuel ratio is leaner than a stoichiometric air-fuel ratio,
• the rich control process includes setting the target value to be richer than the stoichiometric air-fuel ratio,
• the processing circuitry is configured to execute a lean control process that is triggered when the detection value of the air-fuel ratio sensor is less than or equal to a rich determination value,
• the detection value of the air-fuel ratio sensor being equal to the rich determination value indicates that the air-fuel ratio is richer than the stoichiometric air-fuel ratio,
• the lean control process includes setting the target value to be leaner than the stoichiometric air-fuel ratio,
• the processing circuitry is configured to execute a deviation amount calculation process when an execution condition of a process that calculates a deviation amount indication value indicating a deviation amount of a detection value of the air-fuel ratio sensor is satisfied,
• the deviation amount calculation process includes calculating the deviation amount indication value based on a detection value of the air-fuel ratio sensor obtained during an execution of the rich control process,
• the processing circuitry is configured to execute a variable process that variably sets at least one of the target value set by the rich control process or the target value set by the lean control process, and
• the target value variably set when the execution condition is satisfied differs from the target value variably set when the execution condition is not satisfied.