| 摘要 |
A catalyst recovery method is capable of maintaining NOx purification performance by efficiently releasing SOx occluded in a NOx catalyst in an exhaust system of an internal combustion engine. The air fuel ratio of exhaust gas in a fuel supply period (Deltat 1 ) is made further richer (C 2 ) than a predetermined rich air fuel ratio (C 0 ) with increasing length of a set stop period (Deltat 2 ). Provided within a stop period (Deltat 2 ) is an excessively lean period (Deltat 3 ) in which the air fuel ratio of the exhaust gas becomes higher (C 3 ) with increasing length of the stop period (Deltat 2 ), whereby an amount of reducing agent to be added is increased, thus making it possible to ensure a sufficient amount of SOx released from the NOx catalyst. As a result, the length of the stop period (Deltat 2 ') is shortened, so the SOx occluded in the NOx catalyst can be efficiently released.
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