Patent ID: 7849733

Claim:
A misfire judging device judging misfire of an internal combustion engine having a plurality of cylinders with an output shaft connected to a post-stage via a spiral element, said misfire judging device comprising: a rotational position detecting module detecting a rotational position of the output shaft of said internal combustion engine; a unit rotation angle rotation speed calculating module calculating a unit rotation angle rotation speed which is a rotation speed of each predetermined unit rotation angle of the output shaft of said internal combustion engine based on said detected rotational position; and a misfire judging module judging whether or not misfire occurs to any of cylinders of said internal combustion engine based on a variation in the rotation speed after calculation obtained by adding or subtracting a sine wave component with a time in which the output shaft of said internal combustion engine rotates 720 degrees as a period, to or from a variation in said calculated unit rotation angle rotation speed, when an operation point of said internal combustion engine belongs in a resonance region in a post-stage including said spiral element.