Controller and control method for internal combustion engine

A method for controlling an internal combustion engine, wherein the internal combustion engine is installed in a vehicle and includes an exhaust gas purifier that purifies exhaust gas discharged from a plurality of cylinders and a plurality of fuel injection valves that are respectively provided for the cylinders, the method comprising:

• executing a dither control process for operating the fuel injection valves to set at least one of the cylinders as a rich combustion cylinder and to set at least another one of the cylinders that differs from the at least one of the cylinders as a lean combustion cylinder, wherein the rich combustion cylinder has an air-fuel ratio that is richer than a stoichiometric air-fuel ratio, and the lean combustion cylinder has an air-fuel ratio that is leaner than the stoichiometric air-fuel ratio;
• executing the dither control process in a first mode when the vehicle is driven in a normal manner by the user;
• executing the dither control process in a second mode on condition that a command signal for performing a temperature raising process on the exhaust gas purifier is input from a device outside the vehicle at a repair shop;
• executing a process for setting an absolute value in the second mode to be greater than an absolute value set in the first mode, wherein the absolute value is an absolute value of a difference between the air-fuel ratio of the lean combustion cylinder and the air-fuel ratio of the rich combustion cylinder resulting from the dither control process.

A non-transitory computer readable recording medium that records a program that has a processing device execute a control process on an internal combustion engine, wherein the internal combustion engine is installed in a vehicle and includes an exhaust gas purifier that purifies exhaust gas discharged from a plurality of cylinders and a plurality of fuel injection valves that are respectively provided for the cylinders, the control process comprising:

• executing a dither control process for operating the fuel injection valves to set at least one of the cylinders as a rich combustion cylinder and to set at least another one of the cylinders that differs from the at least one of the cylinders as a lean combustion cylinder, wherein the rich combustion cylinder has an air-fuel ratio that is richer than a stoichiometric air-fuel ratio, and the lean combustion cylinder has an air-fuel ratio that is leaner than the stoichiometric air-fuel ratio;
• executing the dither control process in a first mode when the vehicle is driven in a normal manner by the user;
• executing the dither control process in a second mode on condition that a command signal for performing a temperature raising process on the exhaust gas purifier is input from a device outside the vehicle at a repair shop;
• executing a process for setting an absolute value in the second mode to be greater than an absolute value set in the first mode, wherein the absolute value is an absolute value of a difference between the air-fuel ratio of the lean combustion cylinder and the air-fuel ratio of the rich combustion cylinder resulting from the dither control process.