Exhaust emission control system for internal combustion engine and exhaust emission control method

An exhaust emission control method for an internal combustion engine, in which a filter provided in an exhaust passage of the internal combustion engine is used to trap a particulate matter and ash contained in exhaust gas, comprising:

• estimating an amount of the particulate matter trapped and accumulated on the filter;
• estimating an amount of the ash trapped and accumulated on the filter;
• and
• starting a filter recovery process by controlling a temperature of the filter to a target temperature to bring an inside of the filter into an oxidizing atmosphere such that the particulate matter trapped and accumulated on the filter is removed through oxidization when the estimated amount of the particulate matter trapped and accumulated on the filter exceeds a predetermined amount,
• wherein the target temperature is set based on the estimated amount of the ash trapped and accumulated on the filter.

An exhaust emission control system for an internal combustion engine, comprising:

• a filter provided in an exhaust passage of the internal combustion engine so as to trap a particulate matter and ash contained in exhaust gas;
• accumulated particulate matter amount estimating means for estimating an amount of the particulate matter trapped and accumulated on the filter;
• accumulated ash amount estimating means for estimating an amount of the ash trapped and accumulated on the filter, and filter recovery processing means for issuing a command to start a filter recovery process by controlling a temperature of the filter to a target temperature to bring an inside of the filter into an oxidizing atmosphere such that the particulate matter trapped and accumulated on the filter is removed through oxidization when the estimated amount of the particulate matter trapped and accumulated on the filter exceeds a predetermined amount,
• wherein the filter recovery processing means includes target temperature setting means for setting the target temperature, and
• wherein the filter recovery processing means sets the target temperature based on the estimated amount of the ash trapped and accumulated on the filter by the accumulated ash amount estimating means.