Control apparatus for internal combustion engine and method for controlling internal combustion engine

A control apparatus for an internal combustion engine including an exhaust purifying device configured to purify an exhaust gas discharged from a plurality of cylinders, a fuel injection valve provided for each of the plurality of cylinders, a canister that collects fuel vapor in a fuel tank, which stores fuel injected by the fuel injection valves, and an adjusting device configured to adjust a flow rate of a fluid from the canister to an intake air passage, wherein the control apparatus comprises hardware circuitry configured to perform acts comprising:

• a dither control process that operates the fuel injection valves so that at least one of the plurality of cylinders is set as a lean combustion cylinder, which has an air-fuel ratio that is leaner than a theoretical air-fuel ratio, and so that at least a further one of the plurality of cylinders is set as a rich combustion cylinder, which has an air-fuel ratio that is richer than the theoretical air-fuel ratio;
• a purge control process that operates the adjusting device to control the flow rate of the fluid from the canister to the intake air passage;
• an update process that updates a learning value of a concentration of fuel vapor in the fluid based on a detection value of the air-fuel ratio, the learning value being a correction rate per percentage of a purge rate, the correction rate being a value for correcting a deviation of a base injection amount from an injection amount calculated based on a feedback operation amount, the purge rate being a value obtained by dividing the flow rate of the fluid that flows into the intake air passage from the canister by an intake air amount;
• and
• a limit process that limits a change in the learning value updated by the update process to a smaller amount in a second period during which the dither control process is performed as compared to an amount of a change in the learning value in a first period during which the dither control process is not performed.

A method for controlling an internal combustion engine including an exhaust purifying device configured to purify an exhaust gas discharged from a plurality of cylinders, a fuel injection valve provided for each of the plurality of cylinders, a canister that collects fuel vapor in a fuel tank, which stores fuel injected by the fuel injection valves, and an adjusting device configured to adjust a flow rate of a fluid from the canister to an intake air passage,

• the method comprising:
• operating the fuel injection valves in a dither control process so that at least one of the plurality of cylinders is set as a lean combustion cylinder, which has an air-fuel ratio that is leaner than a theoretical air-fuel ratio, and so that at least a further one of the plurality of cylinders is set as a rich combustion cylinder, which has an air-fuel ratio that is richer than the theoretical air-fuel ratio;
• operating the adjusting device to control the flow rate of the fluid from the canister to the intake air passage;
• updating a learning value of a concentration of fuel vapor in the fluid based on a detection value of the air-fuel ratio, the learning value being a correction rate per percentage of a purge rate, the correction rate being a value for correcting a deviation of a base injection amount from an injection amount calculated based on a feedback operation amount, the purge rate being a value obtained by dividing the flow rate of the fluid that flows into the intake air passage from the canister by an intake air amount;
• and
• limiting a change in the learning value when updating the learning value to a smaller amount in a second period during which the dither control process is performed as compared to an amount of a change in the learning value in a first period during which the dither control process is not performed.