ABNORMALITY DETECTION DEVICE AND ABNORMALITY DETECTION METHOD FOR EGR SYSTEM

An object of the present invention is to more preferably detect the abnormal situation of an EGR system of an internal combustion engine provided with a high pressure EGR apparatus and a low pressure EGR apparatus. In the present invention, the flow rate ratio allowable range, which is such a range that the degree of deterioration of the exhaust characteristic of the internal combustion engine falls in an allowable level, is calculated for the EGR gas flow rate ratio as the ratio between the high pressure EGR gas amount and the low pressure EGR gas amount (S103 to S107). If the estimated value of the EGR gas flow rate ratio is deviated from the flow rate ratio allowable range, it is judged that the EGR system is in an abnormal situation (S109 to S112).