Patent ID: 7480591

Claim:
A misfire detecting apparatus for an internal combustion engine, having rotational speed parameter detecting means for detecting a rotational speed parameter indicative of a rotational speed of said engine, and detecting a misfire of said engine based on the detected rotational speed parameter, the misfire detecting apparatus comprising: moving averaging means for performing a moving averaging calculation with respect to data of the detected rotational speed parameter to calculate an averaged speed parameter, wherein a number of the data is equal to a sampling number (NTDC); reference value calculating means for calculating a reference value of the averaged speed parameter; relative speed parameter calculating means for calculating a relative speed parameter, which is a deviation of the averaged speed parameter corresponding to the rotational speed parameter detected at every predetermined crank angle from the reference value; integrated value calculating means for calculating an integrated value of the relative speed parameter; and misfire determining means for performing a misfire determination based on the integrated value, wherein the sampling number (NTDC) is determined by an equation: NTDC= 720/( N×D θ) where (N) is a number of cylinders of said engine, and (Dθ) is a sampling angular period (degree) of the rotational speed parameter.