Patent ID: 7322186

Claim:
An exhaust gas purifying apparatus for an internal combustion engine comprising: a diesel particulate filter provided in an exhaust pipe of the engine for trapping and accumulating diesel particulates contained in exhaust gas emitted from the engine; an electronic control unit for controlling a compulsory re-generating operation of the diesel particulate filter, wherein the compulsory re-generating operation is performed when an accumulated amount of the diesel particulates in the diesel particulate filter reaches at a predetermined threshold value, so that the diesel particulates are combusted and removed; a pressure loss detecting means for detecting pressure loss at the diesel particulate filter; an accumulated amount calculating means for calculating accumulated amount of the diesel particulates in the diesel particulate filter based on the pressure loss and a first accumulation pattern, the accumulation pattern having a first accumulation characteristic line for a smaller amount range of the accumulated amount and a second accumulation characteristic line for a larger amount range of the accumulated amount, each of the first and second accumulation characteristic lines being formed as a straight line and representing a relationship between the pressure loss and the accumulated amount of the diesel particulates in the diesel particulate filter, wherein a ratio of the first accumulation characteristic line for an increase of the pressure loss with respect to an increase of the accumulated amount of the diesel particulates is larger than that of the second accumulation characteristic line, the first accumulation characteristic line passes over an initial point, and the first and second accumulation characteristic lines cross each other at a predetermined transition point; and a threshold value correcting means for calculating a correction amount and making the threshold value to a smaller value based on the correction amount during a transitional period, in which the amount of the pressure loss is decreased depending on natural combustion of the diesel particulates in the diesel particulate filter from a point on the second accumulation characteristic line to a point on a line of a second accumulation pattern, the line of the second accumulation pattern having the same ratio for the increase of the pressure loss with respect to the increase of the accumulated amount of the diesel particulates to that of the second accumulation characteristic line, and line of the second accumulation pattern passing over the initial point.