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An exhaust gas purification system determines a deposited state of particulate matters based on a differential pressure across a diesel particulate filter (DPF) sensed by a differential pressure sensor. An electronic control unit (ECU) of the system prohibits the determination of the deposited stat

An exhaust gas purification system determines a deposited state of particulate matters based on a differential pressure across a diesel particulate filter (DPF) sensed by a differential pressure sensor. An electronic control unit (ECU) of the system prohibits the determination of the deposited state of the particulate matters, which is performed based on the differential pressure, when uniformity of temperature distribution inside the DPF is low. The ECU estimates temperatures at multiple points inside the DPF distant from an inlet along a direction of a flow of exhaust gas based on the temperature at the inlet sensed by an exhaust gas temperature sensor disposed immediately upstream of the DPF. The ECU determines the uniformity of the temperature distribution inside the DPF based on a range of the temperatures at the multiple points.

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What is claimed is: 1. A method of purifying exhaust gas of an internal combustion engine, which includes a particulate filter disposed in an exhaust passage for collecting particulate matters contained in exhaust gas, the method comprising: calculating a value of a deposited amount of the particul

What is claimed is: 1. A method of purifying exhaust gas of an internal combustion engine, which includes a particulate filter disposed in an exhaust passage for collecting particulate matters contained in exhaust gas, the method comprising: calculating a value of a deposited amount of the particulate matters deposited on the particulate filter based on a state of the exhaust gas including a differential pressure between an inlet and an outlet of the particulate filter; measuring a temperature distribution inside the particulate filter; and invalidating the calculated value of the deposited amount of the particulate matters when uniformity of the temperature distribution inside the particulate filter is low; wherein the uniformity of the temperature distribution decreases as a range of temperatures at multiple points inside the particulate filter increases, and the multiple points are arranged on a central axis of the particulate filter or on a plane perpendicular to the central axis. 2. The method as in claim 1, wherein the temperature distribution is uniform when a difference between the temperatures at the multiple points inside the particulate filter resides in a range from minus 50�� C. to plus 50�� C. 3. The method as in claim 1, wherein the multiple points include the inlet or the outlet of the particulate filter. 4. The method as in claim 1, wherein measuring the temperature distribution includes: sensing the temperature at a certain point of the particulate filter; and estimating the temperature at another point, which is distant from the certain point along a direction of a flow of the exhaust gas, by using a transfer function of a first-order delay model or an inverse transfer function of the first-order delay model, based on the temperature at the certain point. 5. The method as in claim 4, wherein the multiple points include the inlet and the outlet of the particulate filter, and the temperature in a certain area downstream of the inlet of the particulate filter with respect to the flow of the exhaust gas is estimated based on the temperature at the inlet of the particulate filter, and the temperature in the other area extending to the outlet is estimated based on the temperature at the outlet. 6. An exhaust gas purification system of an internal combustion engine, which includes a particulate filter disposed in an exhaust passage for collecting particulate matters contained in exhaust gas and calculates a deposited amount of the particulate matters deposited on the particulate filter based on a state of the exhaust gas including a differential pressure between an inlet and an outlet of the particulate filter, the exhaust gas purification system comprising: measuring means for measuring temperature distribution inside the particulate filter; and invalidating means for invalidating the calculated value of the deposited amount of the particulate matters when uniformity of the temperature distribution inside the particulate filter is low; wherein the measuring means determines that the uniformity of the temperature distribution decreases as a range of temperatures at multiple points inside the particulate filter increases, and the multiple points are arranged on a central axis of the particulate filter or on a plane perpendicular to the central axis. 7. The exhaust gas purification system as in claim 6, wherein the measuring means determines that the temperature distribution is uniform when a difference between the temperatures at the multiple points inside the particulate filter resides in a range from minus 50�� C. to plus 50�� C. 8. The exhaust gas purification system as in claim 6, wherein the multiple points include the inlet or the outlet of the particulate filter. 9. The exhaust gas purification system as in claim 6, wherein the measuring means includes: sensing means for sensing the temperature at a certain point of the particulate filter; and estimating means for estimating the temperature at another point, which is distant from the certain point along a direction of a flow of the exhaust gas, by using a transfer function of a first-order delay model or an inverse transfer function of the first-order delay model, based on the temperature at the certain point. 10. The exhaust gas purification system as in claim 9, wherein the multiple points include the inlet and the outlet of the particulate filter, and the estimating means estimates the temperature in a certain area downstream of the inlet of the particulate filter with respect to the flow of the exhaust gas based on the temperature at the inlet of the particulate filter, and estimates the temperature in the other area extending to the outlet based on the temperature at the outlet. 11. An exhaust gas purification system of an internal combustion engine, which includes a particulate filter disposed in an exhaust passage for collecting particulate matters contained in exhaust gas and calculates a deposited amount of the particulate matters deposited on the particulate filter based on a state of the exhaust gas including a differential pressure between an inlet and an outlet of the particulate filter, the exhaust gas purification system comprising: measuring means for measuring temperature distribution inside the particulate filter; and invalidating means for invalidating the calculated value of the deposited amount of the particulate matter when uniformity of the temperature distribution inside the particulate filter is low, wherein the measuring means determines that the uniformity of the temperature distribution decreases as a difference between temperatures as multiple points inside the particulate filter increases, and the temperature difference inside the particulate filter is larger than a temperature difference caused by a heat capacity difference of the particulate matters unevenly existing inside the particulate filter. 12. The exhaust gas purification system as in claim 11, wherein the measuring means determines that the temperature distribution is uniform when a difference between the temperatures at the multiple points inside the particulate filter resides in a range from minus 50�� C. to plus 50�� C. 13. The exhaust gas purification system as in claim 11, wherein the multiple points include the inlet or the outlet of the particulate filter. 14. The exhaust gas purification system as in claim 11, wherein the measuring means includes: sensing means for sensing the temperature at a certain point of the particulate filter; and estimating means for estimating the temperature at another point, which is distant from the certain point along a direction of a flow of the exhaust gas, by using a transfer function of a first-order delay model or an inverse transfer function of the first-order delay model, based on the temperature at the certain point. 15. The exhaust gas purification system as in claim 14, wherein the multiple points include the inlet and the outlet of the particulate filter, and the estimating means estimates the temperature in a certain area downstream of the inlet of the particulate filter with respect to the flow of the exhaust gas based on the temperature at the inlet of the particulate filter, and estimates the temperature in the other area extending to the outlet based on the temperature at the outlet.