Control device for internal combustion engine

A control device for an internal combustion engine for controlling an internal combustion engine provided with:

• an engine body;
• a first catalyst arranged in an exhaust passage of the engine body and having an oxygen storage ability;
• a second catalyst arranged in the exhaust passage at the further downstream side in the direction of flow of exhaust from the first catalyst and having an oxygen storage ability;
• a first air-fuel ratio sensor arranged in the exhaust passage at the further upstream side in the direction of flow of exhaust from the first catalyst for detecting an air-fuel ratio of the exhaust flowing into the first catalyst;
• a second air-fuel ratio sensor arranged in the exhaust passage between the first catalyst and the second catalyst for detecting an air-fuel ratio of the exhaust flowing out from the first catalyst;
• and
• a third air-fuel ratio sensor arranged in the exhaust passage at a further downstream side in the direction of flow of exhaust of the second catalyst for detecting an air-fuel ratio of the exhaust flowing out from the second catalyst,
• the control device comprising:
• an air-fuel ratio control part configured to control an air-fuel ratio of the exhaust discharged from the engine body so that the output air-fuel ratio of the first air-fuel ratio sensor becomes a target air-fuel ratio;
• and
• a target air-fuel ratio setting part configured to set the target air-fuel ratio,
• the target air-fuel ratio setting part comprising:
• a first setting control part configured to perform normal control alternately switching the target air-fuel ratio between a predetermined first lean air-fuel ratio larger than a stoichiometric air-fuel ratio and a predetermined first rich air-fuel ratio smaller than the stoichiometric air-fuel ratio;
• and
• a second setting control part configured to perform control for restoration of the storage amount stopping the normal control and increasing the oxygen storage amount of the second catalyst when the output air-fuel ratio of the third air-fuel ratio sensor becomes a predetermined rich judgment air-fuel ratio smaller than the stoichiometric air-fuel ratio and larger than the first rich air-fuel ratio or becomes less,
• the second setting control part:
• configured to set the target air-fuel ratio at a predetermined second lean air-fuel ratio larger than the first lean air-fuel ratio when starting the control for restoration of the storage amount;
• and
• configured to set the target air-fuel ratio to a predetermined third lean air-fuel ratio smaller than the second lean air-fuel ratio after exhaust larger in air-fuel ratio than the stoichiometric air-fuel ratio flows out from the first catalyst in the time period when setting the target air-fuel ratio to the second lean air-fuel ratio.