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In an exhaust gas cleaning system of an internal combustion engine having a diesel particulate filter (DPF), measuring accuracy of a collection quantity of particulate matters collected by the DPF is estimated based on an accelerator position change rate and an exhaust gas flow rate. When the measur

In an exhaust gas cleaning system of an internal combustion engine having a diesel particulate filter (DPF), measuring accuracy of a collection quantity of particulate matters collected by the DPF is estimated based on an accelerator position change rate and an exhaust gas flow rate. When the measuring accuracy is high, the collection quantity is calculated based on a pressure difference and the exhaust gas flow rate at the DPF. If the measuring accuracy is low, an increment value of the collection quantity is calculated based on a quantity of the particulate matters discharged from an engine main body. Then, the collection quantity is calculated by adding the collection quantity increment value to the previous collection quantity calculated based on the pressure difference and the exhaust gas flow rate while the measuring accuracy is high.

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1. An exhaust gas cleaning system for an internal combustion engine having a particulate filter, which is disposed in an exhaust pipe for collecting exhaust particulate matters included in the exhaust gas discharged from cylinders of an engine main body and is regenerated at a predetermined timing b

1. An exhaust gas cleaning system for an internal combustion engine having a particulate filter, which is disposed in an exhaust pipe for collecting exhaust particulate matters included in the exhaust gas discharged from cylinders of an engine main body and is regenerated at a predetermined timing by eliminating the collected exhaust particulate matters, the system comprising:passing state detecting means for detecting a passing state of the exhaust gas through the particulate filter;operating state detecting means for detecting an operating state of the engine main body;measuring accuracy determination value calculating means for calculating a measuring accuracy determination value based on the detected operating state or the detected passing state;measuring accuracy determining means for determining whether the measuring accuracy of a collection quantity of the collected exhaust particulate matters is higher than a threshold measuring accuracy or not by comparing the measuring accuracy determination value with a predetermined value;first collection quantity calculating means for calculating the collection quantity based on the detected passing state of the exhaust gas when the measuring accuracy is determined to be higher than the threshold measuring accuracy;collection quantity increment value calculating means for calculating a discharge quantity of the exhaust particulate matters discharged from the engine main body per unit time based on the detected operating state of the engine main body and for calculating a collection quantity increment value per unit time from the calculated discharge quantity per unit time when the measuring accuracy is determined to be lower than the threshold measuring accuracy;second collection quantity calculating means for calculating the collection quantity by adding the collection quantity increment value to the previous collection quantity when the measuring accuracy is determined to be lower than the threshold measuring accuracy;regeneration determining means for determining whether the collection quantity, which is calculated by the first or second collection quantity calculating means, is greater than a threshold collection quantity or not; andregeneration performing means for performing the regeneration of the particulate filter if the collection quantity is determined to be greater than the threshold collection quantity. 2. The exhaust gas cleaning system as in claim 1, wherein;the collection quantity increment value calculating means calculates concentration of the exhaust particulate matters included in the exhaust gas discharged from the engine main body based on the detected operating state of the engine main body, and calculates the discharge quantity of the exhaust particulate matters discharged from the engine main body per unit time by multiplying a flow rate of the exhaust gas by the concentration of the exhaust particulate matters. 3. The exhaust gas cleaning system as in claim 1, wherein;the collection quantity increment value calculating means calculates the collection quantity increment value per unit time by multiplying the discharge quantity of the exhaust particulate matters per unit time by predetermined collection efficiency. 4. The exhaust gas cleaning system as in claim 2, wherein;the collection quantity increment value calculating means selects the concentration of the exhaust particulate matters from a group of discrete values. 5. The exhaust gas cleaning system as in claim 1, wherein;the measuring accuracy determination value calculating means calculates a rate of change with time of a state quantity representing the operating state of the engine main body as the measuring accuracy determination value. 6. The exhaust gas cleaning system as in claim 1, wherein;the first collection quantity calculating means calculates the collection quantity based on pressure of the exhaust gas, which changes in accordance with the collection quantity of the exhaust particulate m atters, and a flow rate of the exhaust gas passing through the particulate filter, andthe measuring accuracy determination value calculating means calculates the flow rate of the exhaust gas passing through the particulate filter as the measuring accuracy determination value.