Knock detecting device

Abstract

Provided is a knock detecting device capable of ensuring knock detection accuracy irrespective of fuel injection conditions even when a period during which injection-valve noise occurs overlaps with a knock determination period. An ECUsubjects signals output from a knock sensor, which detects vibrations of an internal combustion engine, to frequency analysis to calculate frequency components (). The ECUcalculates a background level that indicates the average of the frequency components (). The ECUstores, in association with each other, the number of fuel injections, which indicates the number of fuel injections in a predetermined time period during one combustion cycle, with a learning value, which indicates a frequency-component correction amount (). The ECUdetermines the presence or absence of a knock () on the basis of a knock index, which indicates the ratio of the difference between each frequency component and the learning value corresponding to the number of fuel injections, to the background level ().