Patent ID: 8333061

Claim:
An exhaust gas purifying apparatus for an internal combustion engine, comprising: a particulate filter provided in an exhaust passage of said engine; pressure difference detecting means for detecting a pressure difference between an upstream side pressure and a downstream side pressure of said particulate filter; an upstream side passage, connecting said pressure difference detecting means and an upstream side of said exhaust passage relative to said particulate filter; a downstream side passage connecting said pressure difference detecting means and a downstream side of said exhaust passage relative to said particulate filter; exhaust gas flow rate calculating means for calculating an exhaust gas flow rate according to an operating condition of said engine; change characteristic detecting means for detecting a characteristic of change in the pressure difference, which is detected by said pressure difference detecting means, relative to a change in the exhaust gas flow rate; and abnormality determining means for determining an abnormality of said downstream side passage based on the characteristic of change in the pressure difference, wherein said change characteristic detecting means calculates a change degree parameter indicative of a degree of a change in the pressure difference relative to a change in the exhaust gas flow rate by performing a statistical processing with respect to a plurality of data of the exhaust gas flow rate and the corresponding detected pressure difference, and said abnormality determining means determines that said downstream side passage is abnormal when said change degree parameter is greater than a determination threshold value.