Exhaust gas purification apparatus and method for internal combustion engine

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

• a NOx storage-reduction catalyst which is disposed in an exhaust passageway of the internal combustion engine, and which selectively traps and stores a specific component that includes at least one of nitrogen oxides (NOx) and sulfur oxides (SOx) from an exhaust gas coming into the NOx storage-reduction catalyst by at least one of adsorption and absorption when the exhaust gas coming into the catalyst has an air-fuel ratio lean of stoichiometry, and which releases the specific component stored and removes the specific component through reduction when the exhaust gas coming into the catalyst has a stoichiometric or rich-of-stoichiometry air-fuel ratio;
• a estimation device that estimates an amount of storage of the specific component in the NOx storage-reduction catalyst and an amount of release of the specific component from the NOx storage-reduction catalyst;
• and
• a regeneration device that performs a regeneration operation of releasing the specific component stored in the NOx storage-reduction catalyst and removing the specific component through reduction by supplying a rich-of-stoichiometry exhaust gas to the NOx storage-reduction catalyst based on the amount of storage of the specific component estimated by the estimation device,
• wherein the estimation device estimates the amount of storage of the specific component and the amount of release of the specific component with respect to each one of at least two different portions of the NOx storage-reduction catalyst, and
• wherein the estimation device indicates the amount of storage of the specific component in each portion of the NOx storage-reduction catalyst by using a storage counter, and estimates the amount of storage of the specific component in each portion of the NOx storage-reduction catalyst by incrementing the storage counter at a rate proportional to a concentration of the specific component in the exhaust gas coming into the NOx storage-reduction catalyst when the exhaust gas coming into the catalyst has an air-fuel ratio lean of stoichiometry, and decrementing the storage counter at a predetermined rate when the exhaust gas coming into the catalyst has a stoichiometric or rich-of-stoichiometry air-fuel ratio.