Patent Document ID: 20160265465
Application ID: 15066089
Patent Flag: 0

Claim One:
1. An exhaust purification system of an internal combustion engine which has a plurality of cylinders comprising: an exhaust purification catalyst which is arranged in an engine exhaust passage and which can store oxygen; a downstream side air-fuel ratio sensor which is arranged at a downstream side of the exhaust purification catalyst in a direction of flow of exhaust; and a control device which is to control by feedback the fuel feed amounts to combustion chambers so that combustion air-fuel ratios when combustion is performed at the cylinders become target air-fuel ratios, wherein the control device is configured to be able to: perform an average air-fuel ratio control which alternately controls an average value of the target air-fuel ratios for all cylinders, constituting a target average air-fuel ratio, between a rich air-fuel ratio which is richer than a stoichiometric air-fuel ratio and a lean air-fuel ratio which is leaner than the stoichiometric air-fuel ratio and an inter-cylinder air-fuel ratio control which controls the target air-fuel ratios of the cylinders so that the target air-fuel ratio becomes the rich air-fuel ratio at least at one cylinder among the plurality of cylinders including if the target average air-fuel ratio is set to the lean air-fuel ratio by the average air-fuel ratio control; and calculate an amount of excess oxygen or an amount of deficiency in oxygen when trying to make the exhaust gas which flows into the exhaust purification catalyst the stoichiometric air-fuel ratio, constituting a cumulative oxygen excess/deficiency, and wherein the control device is further configured to perform a learning control which uses an absolute value of the cumulative oxygen excess/deficiency in a first time period from when switching the target average air-fuel ratio from the rich air-fuel ratio to the lean air-fuel ratio to when again switching it to the rich air-fuel ratio, constituting a cumulative value of a first oxygen amount, and an absolute value of the cumulative oxygen excess/deficiency in a second time period from when switching the target average air-fuel ratio from the lean air-fuel ratio to the rich air-fuel ratio to when again switching it to the lean air-fuel ratio, constituting a cumulative value of a second oxygen amount, as the basis to correct a parameter relating to the air-fuel ratio so that a difference between the cumulative value of the first oxygen amount and cumulative value of the second oxygen amount becomes smaller.