Exhaust gas purification system for internal combustion engine

An exhaust gas purification system, comprising:

• a NOx catalyst arranged in the exhaust path;
• an exhaust gas purification catalyst arranged in the exhaust path upstream of said NOx catalyst;
• calculation means for calculating a value associated with the amount of at least one component flowing out from said exhaust gas purification catalyst into said NOx catalyst;
• and
• rich spike execution means for executing a rich spike operation based on a value associated with the amount of the component calculated by said calculation means,
• wherein said component includes NOx absorbed into said NOx catalyst when a rich spike operation is not executed and a reducing component for reducing the NOx absorbed into said NOx catalyst when the rich spike operation is executed, and said value associated with the amount of said component calculated by said calculation means is a value obtained by accumulating the amounts of NOx flowing into said NOx catalyst when the rich spike operation is not executed and by subtracting said value associated with the amount of said reducing component flowing into said NOx catalyst when the rich spike operation is executed.

An exhaust gas purification system comprising:

• a NOx catalyst arranged in the exhaust path;
• an exhaust gas purification catalyst arranged in the exhaust path upstream of said NOx catalyst;
• first calculation means for calculating the amount of the component flowing out from said exhaust gas purification catalyst and absorbed into each area of a plurality of areas of said NOx catalyst per unit time;
• second calculation means for calculating the total amount of said component absorbed into said NOx catalyst by totaling the amounts of said component for the plurality of areas of said NOx catalyst each calculated by said first calculation means;
• and
• rich spike execution means for executing the rich spike operation based on the amount of said component calculated by said second calculation means.