Exhaust gas purification apparatus of internal combustion engine

Abstract

An adding time a of a fuel addition to an exhaust system is limited to a guard value G or less during an adding period A of a concentrated intermittent fuel of a catalyst recovery control. Accordingly, a one-time fuel adding amount from an adding valveis limited to be equal to or less than a predetermined value, and it is possible to prevent such a great amount of unburned fuel component that cannot be fully purified by a NOx catalyst from being supplied to the NOx catalyst during the adding period A. Further, if a total amount (GF+Q)·t of the unburned fuel component supplied to the NOx catalyst during the adding period A reaches an allowable upper limit value UL, the concentrated intermittent fuel addition is canceled and a suspend period B is forcibly started. Accordingly, it is possible to prevent a total amount of such a great amount of unburned fuel component that cannot be fully purified by the NOx catalyst from being supplied to the NOx catalyst during the adding period A. Therefore, generation of white smoke in exhaust gas of the internal combustion engine by an excessive supply of the unburned fuel component to the NOx catalyst at a time of executing catalyst recovery control can be prevented.