Controller and control method for internal combustion engine

A method of controlling an internal combustion engine that includes a filter configured to trap particulate matter in exhaust gas discharged from a plurality of cylinders and fuel injection valves provided for the respective cylinders, the internal combustion engine including an electronic control unit programmed to execute control of each step of the method, the method comprising:

• executing a dither control process of operating the fuel injection valves such that at least one of the cylinders is a lean combustion cylinder, in which an air-fuel ratio is leaner than a stoichiometric air-fuel ratio, and at least another one of the cylinders is a rich combustion cylinder, in which an air-fuel ratio is richer than the stoichiometric air-fuel ratio;
• and
• executing an enlarging process, which includes at least one of the following two processes
• a process of causing an operation region of the internal combustion engine in which the dither control process is executed to be larger in a case in which an amount of particulate matter trapped by the filter is large than in a case in which the amount is small, and
• a process of causing a degree of richness of the rich combustion cylinder and a degree of leanness of the lean combustion cylinder to be greater in a case in which the amount of particulate matter trapped by the filter is large than in a case in which the amount of particulate matter trapped by the filter is small.

A controller for an internal combustion engine, the controller being configured to control an internal combustion engine that includes a filter configured to trap particulate matter in exhaust gas discharged from a plurality of cylinders and fuel injection valves provided for the respective cylinders, wherein

• the controller comprises processing circuitry, and
• the processing circuitry is configured to execute
• a dither control process of operating the fuel injection valves such that at least one of the cylinders is a lean combustion cylinder, in which an air-fuel ratio is leaner than a stoichiometric air-fuel ratio, and at least another one of the cylinders is a rich combustion cylinder, in which an air-fuel ratio is richer than the stoichiometric air-fuel ratio, and
• an enlarging process, which includes at least one of the following two processes
• a process of causing an operation region of the internal combustion engine in which the dither control process is executed to be larger in a case in which an amount of particulate matter trapped by the filter is large than in a case in which the amount is small, and
• a process of causing a degree of richness of the rich combustion cylinder and a degree of leanness of the lean combustion cylinder to be greater in a case in which the amount of particulate matter trapped by the filter is large than in a case in which the amount of particulate matter trapped by the filter is small.