Exhaust gas purification system for internal combustion engine

An exhaust gas purification system of an internal combustion engine having a particulate filter located in an exhaust passage of the engine for collecting exhaust particulate matters, the exhaust gas purification system regenerating the particulate filter by eliminating the exhaust particulate matters collected by the particulate filter, the exhaust gas purification system comprising:

• a flowing state sensing device that senses a flowing state of exhaust gas at the particulate filter;
• a first accumulation quantity estimation device that estimates an accumulation quantity of the exhaust particulate matters in the particulate filter based on the flowing state of the exhaust gas;
• an operating state sensing device that senses an operating state of the engine;
• a second accumulation quantity estimation device that estimates the accumulation quantity of the exhaust particulate matters in the particulate filter based on the operating state of the engine;
• an employment condition determination device that determines whether employment conditions to employ the first accumulation quantity estimation device including a condition that a flow rate of the exhaust gas flowing through the exhaust passage is equal to or greater than a predetermined flow rate are satisfied;
• a regeneration determination device that selects the first accumulation quantity estimation device when the employment conditions of the first accumulation quantity estimation device are satisfied and selects the second accumulation quantity estimation device when the employment conditions are not satisfied, wherein the regeneration determination device compares the accumulation quantity estimated by the selected accumulation quantity estimation device with a predetermined quantity to determine whether regeneration operation of the particulate filter should be performed;
• a continuing state sensing device that senses a continuing state of the accumulation quantity estimation performed by the second accumulation quantity sensing device;
• and
• an exhaust gas flow rate increasing device that increases the exhaust gas flow rate if the accumulation quantity estimation by the second accumulation quantity estimation device continues for a predetermined period or longer.