Patent ID: 9593635
Date: 2017-03-14
CPC Classifications: F02D

Claim:
1. A control system of an internal combustion engine, the engine comprising an exhaust purification catalyst which is arranged in an exhaust passage of the internal combustion engine and which can store oxygen, the system comprising: a downstream side air-fuel ratio detection device which is arranged at a downstream side, in the direction of flow of exhaust, of said exhaust purification catalyst and which detects the air-fuel ratio of the exhaust gas which flows out from said exhaust purification catalyst, and an air-fuel ratio control system which controls said air-fuel ratio of the exhaust gas so that said air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst becomes a target air-fuel ratio, the air-fuel ratio control system including an electronic control unit (ECU) having an air-fuel ratio lean switching control, a lean degree lowering control, an air-fuel ratio rich control, and a rich degree lowering control, the ECU configured to: change said target air-fuel ratio to a lean set air-fuel ratio which is leaner than a stoichiometric air-fuel ratio, when an exhaust air-fuel ratio detected by said downstream side air-fuel ratio detection device becomes a rich air-fuel ratio with the air-fuel ratio lean switching control; change said target air-fuel ratio to a lean air-fuel ratio with a smaller difference from the stoichiometric air-fuel ratio than said lean set air-fuel ratio with the lean degree lowering control, at a timing after said air-fuel ratio lean switching control changes the air-fuel ratio and before the exhaust air-fuel ratio detected by said downstream side air-fuel ratio detection device becomes the lean air-fuel ratio; change said target air-fuel ratio to a rich set air-fuel ratio which is richer than the stoichiometric air-fuel ratio with the air-fuel ratio rich switching control, when the exhaust air-fuel ratio detected by said downstream side air-fuel ratio detection device becomes the lean air-fuel ratio; and change said target air-fuel ratio to a rich air-fuel ratio with a smaller difference from the stoichiometric air-fuel ratio than said rich set air-fuel ratio with the rich degree lowering control, at a timing after said air-fuel ratio lean switching control changes the air-fuel ratio and before the exhaust air-fuel ratio detected by said downstream side air-fuel ratio detection device becomes the rich air-fuel ratio.