Exhaust gas purification apparatus for an internal combustion engine

摘要

The sulfur poisoning of a three-way catalyst is intended to be detected with a high degree of accuracy. It is determined whether the sulfur poisoning of the three-way catalyst is made to be recovered, or a determination is made that the degree of sulfur poisoning of the three-way catalyst is higher when the concentration of NOx detected by an NOx sensor is high than when it is low, based on the concentration of NOx downstream of the three-way catalyst after the air fuel ratio of the exhaust gas flowing into the three-way catalyst has been made to change from a rich air fuel ratio to a lean air fuel ratio and before the air fuel ratio of the exhaust gas flowing out of the three-way catalyst changes to a lean air fuel ratio.

主权项

1. An exhaust gas purification apparatus for an internal combustion engine, exhaust gas purification apparatus comprising:
a three-way catalyst that is arranged in an exhaust passage of the internal combustion engine and has an oxygen storage ability; an NOx sensor that is arranged in the exhaust passage at a location downstream of the three-way catalyst, and configured to detect a concentration of NOx in exhaust gas; an air fuel ratio sensor that is arranged in the exhaust passage at a location downstream of the three-way catalyst, and configured to detect an air fuel ratio of the exhaust gas; and an electronic control unit configured to: change the air fuel ratio of the exhaust gas flowing into the three-way catalyst; determine a degree of sulfur poisoning based on the concentration of the NOx detected by the NOx sensor after the air fuel ratio of the exhaust gas has been changed from a rich air fuel ratio to a lean air fuel ratio by the electronic control unit and before the air fuel ratio detected by the air fuel ratio sensor changes to a lean air fuel ratio, the degree of sulfur poisoning is determined to be higher when the concentration of NOx detected by the NOx sensor is high compared to the degree of sulfur poisoning when the concentration of NOx detected by the NOx sensor is low; determine whether the three-way catalyst requires sulfur poisoning recovery based on degree the of sulfur poisoning of the three-way catalyst determined by the electronic control unit; and perform the sulfur poisoning recovery when it has been determined that the three-way catalyst requires sulfur poisoning recovery.