EXHAUST PURIFICATION SYSTEM OF INTERNAL COMBUSTION ENGINE

摘要

An exhaust purification system of an internal combustion engine comprises an upstream side catalyst, a downstream side catalyst, a downstream side air-fuel ratio sensor provided between the upstream side catalyst and the downstream side catalyst, and a control device able to control an air-fuel ratio of exhaust gas flowing into the upstream side catalyst as air-fuel ratio control. In the air-fuel ratio control, the control device switches the air-fuel ratio of the exhaust gas to the lean air-fuel ratio when the output air-fuel ratio of the downstream side air-fuel ratio sensor becomes the rich judged air-fuel ratio or less and switches the air-fuel ratio of the exhaust gas to the rich air-fuel ratio when the oxygen storage amount of the upstream side catalyst becomes the switching reference storage amount or more. During the air-fuel ratio control, the control device increases the concentration of NOX in the exhaust gas flowing into the upstream side catalyst when the oxygen storage amount of the downstream side catalyst becomes the limit storage amount or less as control for increasing NOX. As a result, NOX is kept from flowing out from the downstream side catalyst.

主权项

1. An exhaust purification system of an internal combustion engine comprising:
an upstream side catalyst provided in an exhaust passage of the internal combustion engine; a downstream side catalyst provided at a downstream side from the upstream side catalyst in a direction of exhaust flow in the exhaust passage; a downstream side air-fuel ratio sensor provided between the upstream side catalyst and the downstream side catalyst in the exhaust passage; and a control device configured to be able to control an air-fuel ratio of an exhaust gas flowing into the upstream side catalyst as air-fuel ratio control, wherein the control device is further configured to: switch the air-fuel ratio of the exhaust gas flowing into the upstream side catalyst to a lean air-fuel ratio leaner than a stoichiometric air-fuel ratio if an output air-fuel ratio of the downstream side air-fuel ratio sensor becomes a constant rich judged air-fuel ratio richer than the stoichiometric air-fuel ratio or becomes less and switch the air-fuel ratio of the exhaust gas flowing into the upstream side catalyst to a rich air-fuel ratio richer than the stoichiometric air-fuel ratio if an oxygen storage amount of the upstream side catalyst becomes a switching reference storage amount smaller than a maximum storable amount of oxygen or becomes more in the air-fuel ratio control; and make the concentration of NOX in the exhaust gas flowing into the upstream side catalyst increase without making the concentration of oxygen in the exhaust gas flowing out from the upstream side catalyst increase as control for increasing NOX if the oxygen storage amount of the downstream side catalyst becomes a predetermined limit storage amount smaller than the maximum storable amount of oxygen or becomes less during the air-fuel ratio control.