| 摘要 |
The present invention is to provide a technique which can detect the level of degradation of a precatalyst in an exhaust gas purification system for an internal combustion engine that includes a NOx catalyst arranged on an exhaust passage of the internal combustion engine, and the precatalyst arranged on the exhaust passage at a location upstream of the NOx catalyst and having an oxidation function. In the present invention, the level of degradation of the precatalyst is detected based on the width of change in temperature of the NOx catalyst at the time when a reducing agent is intermittently supplied from an upstream side of the precatalyst to the precatalyst and the NOx catalyst. At this time, it is determined that the larger the width of change in temperature of the NOx catalyst, the higher the level of degradation of the oxidation catalyst is.
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