| abstract |
An object of the present invention is to reduce the amount of sulfate discharged into the atmosphere. A place particulate filter in an exhaust passage of an internal combustion engine air-fuel ratio of the mixture burned in the combustion chamber is maintained lean, supporting the NO X catalyst on the particulate filter. When the engine back pressure P, which indicates the amount of accumulated particulates on the particulate filter, becomes higher than the first threshold value P1, the air-fuel ratio of the exhaust gas flowing into the particulate filter is maintained lean while maintaining the leanness of the particulate filter. The temperature is raised to the target temperature TPM, and a fine particle oxidizing action for maintaining the target temperature TPM for the target time tPM is performed. Determine the amount of SO X are stored in the NO X catalyst without forming sulfates, than when small when the large amount of SO X are stored in the NO X catalyst without forming sulfates Thus, the target temperature TPM is lowered and the target time tPM is lengthened. [Selection diagram] Fig. 4 |