Patent ID: 8307633

Claim:
An exhaust gas purification apparatus for an internal combustion engine, the apparatus comprising: a NOx (nitrous oxides) catalyst device installed in an exhaust passage of said internal combustion engine for deoxidizing NOx contained in an exhaust gas, a catalyst regeneration apparatus, control circuitry for controlling said catalyst regeneration apparatus to execute regeneration of said NOx catalyst device from sulfur poisoning by reducing an A/F (air-to-fuel) ratio of said exhaust gas to value that is lower than a stoichiometric A/F ratio, an upstream A/F ratio sensor for obtaining measured values of A/F ratio of said exhaust gas, disposed in said exhaust gas passage at a location which is upstream from said NOx catalyst device, with respect to a flow direction of said exhaust gas, a downstream A/F ratio sensor for obtaining measured values of A/F ratio of said exhaust gas, disposed in said exhaust gas passage at a location which is downstream from said NOx catalyst device, a flow rate sensor for detecting a flow rate of said exhaust gas through said exhaust gas passage, and a temperature sensor for detecting a temperature of said NOx catalyst device; wherein said control circuitry is configured to operate during execution of said regeneration to: acquire measured values of A/F ratio from said downstream A/F ratio sensor and said upstream A/F ratio sensor respectively, and calculate a difference between said respective A/F ratio values from said upstream A/F ratio sensor and said downstream A/F ratio sensor; wherein said control circuitry is configured to: compare said difference with a predetermined difference value, attainment of said predetermined difference value corresponding to a condition whereby a residual amount of sulfur contained in said NOx catalyst device attains a predetermined threshold value of residual amount, and terminate said regeneration when said difference is judged to be less than said predetermined difference value while also said flow rate of said exhaust gas is lower than a predetermined flow rate value and said temperature of said NOx catalyst device is higher than a predetermined temperature value.