Controller and control method for internal combustion engine

A controller for an internal combustion engine that is provided with an intake path and an exhaust path, a throttle valve for opening and closing the intake path, an EGR path for recirculating exhaust gas from the exhaust path to an intake manifold that is part of the intake path and is at the downstream side of the throttle valve, and an EGR valve for opening and closing the EGR path, the controller for the internal combustion engine comprising:

• a driving-condition detector that detects a manifold pressure, which is a pressure of gas in the intake manifold, a manifold temperature, which is a temperature of gas in the intake manifold, a manifold humidity, which is a humidity of gas in the intake manifold, an intake-air pressure, which is a pressure of intake air to be taken into the intake path, an intake-air temperature, which is a temperature of the intake air, an intake-air humidity, which is a humidity of the intake air, an intake air flow rate, which is a flow rate of the intake air, and an opening degree of the EGR valve;
• a humidity detecting EGR rate calculator that calculates a humidity detecting EGR rate, which is a ratio of a recirculation exhaust gas, which is the exhaust gas recirculated into the intake manifold, to the intake air, based on the intake-air temperature, the intake-air humidity, the intake-air pressure, the manifold temperature, the manifold humidity, and the manifold pressure;
• an opening area learning value calculator that calculates a humidity detecting recirculation flow rate which is a flow rate of the recirculation exhaust gas based on the humidity detecting EGR rate and the intake air flow rate, calculates a humidity detecting opening area, which is an opening area of the EGR valve which realizes the humidity detecting recirculation flow rate, and calculates a learning value of the opening area of the EGR valve based on the humidity detecting opening area;
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• a recirculation exhaust gas calculator for control that calculates a learned opening area of the EGR valve corresponding to the present opening degree of the EGR valve using the learning value of the opening area, and calculates a flow rate of the recirculation exhaust gas for control used for controlling the internal combustion engine based on the learned opening area.