Patent ID: 8375920

Claim:
An apparatus adapted to determine a cylinder deactivation state of an internal combustion engine configured to deactivate one or more cylinders among a plurality of cylinders in accordance with an instruction from a program-controlled electronic control unit, said apparatus comprising: detection means for producing a signal representing intake air amount into the internal combustion engine; the electronic control unit comprising Fourier transformation means configured to perform Fourier transformation on the signal from the detection means relative to a plurality of fundamental frequencies, wherein the plurality of fundamental frequencies includes a first fundamental frequency corresponding to 720 degrees of crank angle, a second fundamental frequency corresponding to 360 degrees of crank angle, and a third fundamental frequency corresponding to 240 degrees of crank angle; and threshold value supply means for providing a threshold value for determining cylinder deactivation state in accordance with a predetermined relationship between each spectrum obtained from the Fourier transformation means at each of the plurality of fundamental frequencies and the cylinder deactivation state of the internal combustion engine, and determining deactivation state of the cylinder based on whether or not each of the spectrums obtained from the Fourier transformation exceeds a corresponding threshold value.