CONTROLLER FOR INTERNAL COMBUSTION ENGINE AND METHOD FOR CONTROLLING INTERNAL COMBUSTION ENGINE

A controller for an internal combustion engine includes processing circuitry. The processing circuitry performs a dither control process. The dither control process includes a first mode in which a cylinder serving as a rich combustion cylinder is sequentially changed and a second mode in which a specified cylinder is fixed as one of a rich combustion cylinder and a lean combustion cylinder. The processing circuitry selects the first mode or the second mode based on an operating point of the internal combustion engine.