Control unit for turbocharged internal combustion engine

A control unit for a turbocharged internal combustion engine, comprising:

• a turbocharger that compresses intake air;
• a first exhaust passage that is communicated with a turbine of the turbocharger;
• a first exhaust valve that opens and closes the first exhaust passage;
• a second exhaust passage that bypasses the turbine;
• a second exhaust valve that opens and closes the second exhaust passage;
• a post-junction exhaust passage which joins the first exhaust passage and the second exhaust passage;
• a catalyst that is arranged in the post-junction exhaust passage and purifies exhaust gas;
• a first air-fuel ratio sensor that is provided in the first exhaust passage to detect an air-fuel ratio of exhaust gas in the first exhaust passage;
• a second air-fuel ratio sensor that is provided either upstream or downstream of the catalyst in the post-junction exhaust passage to detect an air-fuel ratio of exhaust gas in the post-junction exhaust passage,
• an electronic control unit programmed to include a scavenging control execution section that controls at least one of a closing timing of the second exhaust valve and an opening timing of an intake valve to secure a valve overlap period between an opening period of the second exhaust valve and an opening period of the intake valve when the internal combustion engine operates under high load, and the electronic control unit is programmed to include an air-fuel ratio control section that controls an air-fuel ratio of gas that is filled in a cylinder to an output air-fuel ratio and that controls the air-fuel ratio of gas flowing into the catalyst to a theoretical air-fuel ratio when the internal combustion engine operates under high load,
• wherein the air-fuel ratio control section of the electronic control unit includes
• a first air-fuel ratio feedback control execution section that controls to keep the air-fuel ratio of gas that is filled in the cylinder to the output air-fuel ratio based on the output of the first air-fuel ratio sensor, and
• a second air-fuel ratio feedback control execution section that controls to keep the air-fuel ratio of gas flowing into the catalyst to the theoretical air-fuel ratio based on the output of the second air-fuel ratio sensor.