Internal combustion engine system

An internal combustion engine system comprising:

• a first exhaust gas cleaning catalyst disposed in an exhaust passage of an internal combustion engine;
• a second exhaust gas cleaning catalyst disposed downstream of the first exhaust gas cleaning catalyst in an exhaust gas flow direction;
• a first air-fuel ratio sensor disposed upstream of the first exhaust gas cleaning catalyst in the exhaust gas flow direction in the exhaust passage;
• a second air-fuel ratio sensor disposed downstream of the first exhaust gas cleaning catalyst in the exhaust gas flow direction and upstream of the second exhaust gas cleaning catalyst in the exhaust gas flow direction in the exhaust passage;
• and
• a control device configured to control the internal combustion engine, wherein the control device is configured to execute
• feedback processing of performing feedback control of an air-fuel ratio of exhaust gas exhausted from the internal combustion engine such that a first air-fuel ratio detected by the first air-fuel ratio sensor reaches a target air-fuel ratio,
• target air-fuel ratio switching processing of alternately switching the target air-fuel ratio between a lean setting value leaner than a stoichiometric air-fuel ratio and a rich setting value richer than the stoichiometric air-fuel ratio,
• parameter calculation processing of calculating, based on an operating condition of the internal combustion engine, a gas impingement parameter indicating a degree of gas impingement to which unclean gas in the exhaust gas exhausted from the first exhaust gas cleaning catalyst impinges on the second air-fuel ratio sensor, and
• switching cycle change processing of lengthening a switching cycle of the target air-fuel ratio in the target air-fuel ratio switching processing as the gas impingement parameter is a value indicating that the degree of gas impingement is high.