Exhaust purification system for internal combustion engine

An exhaust purification system for an internal combustion engine, the exhaust purification system comprising:

• a particulate filter for trapping particulate matter which is contained in exhaust gas in an engine exhaust passage, where the particulate filter is provided with alternately arranged exhaust gas inflow passages and exhaust gas outflow passages and porous partition walls which separate these exhaust gas inflow passages and exhaust gas outflow passages from each other, micropore zones being defined at upstream sides of the partition walls, and macropore zones being defined at downstream sides of the partition walls, wherein:
• a pore size of the partition walls in the micropore zones is set so that particulate matter and ash can be trapped by the partition walls at the micropore zones,
• a pore size of the partition walls in the macropore zones is set so that ash can pass through the partition walls at the macropore zones, and
• the partition walls at the micropore zones and the partition walls at the macropore zones are integrally formed;
• a fuel valve configured to supply fuel for increasing a temperature of the particulate filter;
• and
• an electronic control unit configured to:
• determine a quantity of particulate matter which flows into the particulate filter per unit time:
• calculate a difference between the quantity of the particulate matter which is trapped on the partition walls at the micropore zones and the quantity of particulate matter which is trapped on the partition walls at the macropore zones based on the quantity of particulate matter which flows into the particulate filter per unit time, and
• execute PM removal control when the difference between the quantity of the particulate matter which is trapped on the partition walls at the micropore zones and the quantity of particulate matter which is trapped on the partition walls at the macropore zones exceeds a predetermined threshold value by increasing the temperature of the particulate filter to a PM removal temperature and maintaining the PM removal temperature using the fuel valve while maintaining the particulate filter in an oxidizing atmosphere in order to remove the particulate matter on the particulate filter.