Exhaust purification device for internal combustion engine

An exhaust gas purification device for an internal combustion engine, comprising:

• a filter that is provided in an exhaust passage of the internal combustion engine and configured to collect particulate matter included in an exhaust gas;
• an exhaust gas temperature detector at the exhaust passage upstream of the filter and configured to detect exhaust gas temperature;
• an electrostatic capacity detector configured to detect an electrostatic capacity of the filter;
• a device to introduce a supply of fuel to the filter;
• and
• a processor configured to
• estimate an amount of accumulated particulate matter, which is collected by the filter, based on the detected electrostatic capacity, and
• control the fuel supply device to supply the fuel to the filter to perform a forced regeneration that raises a temperature of the filter to a particulate matter burning temperature,
• wherein the forced regeneration is performed when the estimated amount of accumulated particulate matter has reached an accumulated-amount threshold and the detected exhaust gas temperature reaches a temperature threshold,
• wherein the accumulated-amount threshold is a value smaller than an upper particulate matter accumulation limit, and the temperature threshold corresponds to a predetermined high exhaust gas temperature at which the accumulated particulate matter up to the accumulated-amount threshold can still be burned and removed even if an amount of the supply of fuel is reduced, and
• wherein the processor is further configured to change the temperature threshold to a lower value, when the processor does not perform the forced regeneration over a predetermined period of time.