Patent ID: 7853400

Claim:
A knock control apparatus for an internal combustion engine, comprising: a knock sensor for detecting knock of an internal combustion engine; a signal processing section for performing frequency analysis using discrete Fourier transform on a knock sensor signal output from the knock sensor for each cylinder and each ignition cycle to calculate a knock intensity; and a knock determination level setting section: for calculating an average value of the knock intensity; for calculating, based on the average value, an overall variance corresponding to a variance of the knock intensity of an entirety of a frequency distribution, a higher variance corresponding to a variance of the knock intensity above the average value, and a lower variance corresponding to a variance of the knock intensity below the average value; for calculating a standard deviation of the knock intensity from the overall variance; for presetting a value allowing the frequency distribution of the knock intensity to be a predetermined confidence interval as a confidence coefficient and correcting the confidence coefficient based on the higher variance and the lower variance to calculate a corrected confidence coefficient; and for setting a sum of the average value and a value obtained by multiplying the standard deviation by the corrected confidence coefficient as a knock determination level.