Patent ID: 9732691
Date: 2017-08-15
CPC Classifications: F01N,F02D

Claim:
1. A control system of an internal combustion engine, the engine comprising an upstream side catalyst which is provided in an exhaust passage of the internal combustion engine, and a downstream side catalyst which is provided in said exhaust passage at a downstream side, in the direction of flow of exhaust, from said upstream side catalyst, said control system comprising: a downstream side air-fuel ratio sensor which is provided in said exhaust passage between said upstream side catalyst and said downstream side catalyst; an inflow air-fuel ratio control device which controls an air-fuel ratio of exhaust gas flowing into said upstream side catalyst so that said air-fuel ratio of the exhaust gas becomes a target air-fuel ratio; and an electronic control unit (ECU) configured to perform: an estimation of an oxygen storage amount of said downstream side catalyst; a normal period lean control for setting said target air-fuel ratio of exhaust gas flowing into said upstream side catalyst continuously or intermittently to leaner than a stoichiometric air-fuel ratio, when an air-fuel ratio detected by said downstream side air-fuel ratio sensor becomes a rich judged air-fuel ratio, which is richer than the stoichiometric air-fuel ratio, or less, until an oxygen storage amount of the upstream side catalyst becomes a given upstream side judged reference storage amount smaller than a maximum oxygen storage amount; a normal period rich control for setting said target air-fuel ratio continuously or intermittently to richer than a stoichiometric air-fuel ratio, when said oxygen storage amount of the upstream side catalyst becomes said upstream side judged reference storage amount or more so that said oxygen storage amount decreases toward zero without reaching the maximum oxygen storage amount; and a storage amount recovery control for setting said target air-fuel ratio continuously or intermittently to leaner than the stoichiometric air-fuel ratio, when the estimated oxygen storage amount of said downstream side catalyst becomes a given downstream side lower limit storage amount, which is smaller than the maximum storage amount, or less, so that the air-fuel ratio of the exhaust gas flowing out from said upstream side catalyst never becomes richer than the stoichiometric air-fuel ratio but continuously or intermittently becomes leaner than the stoichiometric air-fuel ratio, without performing said normal period rich control and normal period lean control.