Control system of internal combustion engine

A control system of an internal combustion engine controlling an internal combustion engine comprising:

• a variable valve timing mechanism able to change an amount of valve overlap between an intake valve and an exhaust valve,
• an exhaust purification catalyst arranged in an exhaust passage and able to store oxygen, and
• an upstream side air-fuel ratio sensor arranged at an upstream side of the exhaust purification catalyst in a direction of exhaust flow and detecting an air-fuel ratio of exhaust gas flowing into the exhaust purification catalyst, wherein
• the control system further comprises an electronic control unit (ECU) controlling an air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst,
• the ECU is configured to alternately set a target air-fuel ratio between a rich air-fuel ratio richer than a stoichiometric air-fuel ratio and a lean air-fuel ratio leaner than the stoichiometric air-fuel ratio and controls the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst so that an output air-fuel ratio of the upstream side air-fuel ratio sensor becomes the target air-fuel ratio,
• the ECU is configured to correct a parameter relating to the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst under conditions of (1) when scavenging occurs so that air blows from an intake passage through a cylinder to the exhaust passage due to an occurrence of the valve overlap, (2) the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst changes to a rich side wherein the changing amount is more than an amount of deviation from the actual air-fuel ratio expected to occur in the output air-fuel ratio of the upstream side air-fuel ratio sensor due to the occurrence of the scavenging, and
• the ECU is configured to increase a lean degree of the target air-fuel ratio when setting the target air-fuel ratio to the lean air-fuel ratio when the scavenging occurs compared with when the scavenging does not occur.