Knock control system for internal combustion engine

摘要

A knock control system for an internal combustion engine derives a knock intensity indicative value Vpi from an output of a knock sensor and decides presence or absence of an engine knock by comparing the knock intensity indicative value Vpi and a knock decision level VKDi for controlling a knock control factor such as an ignition timing based on the decision. The system derives a value Si corresponding to a standard deviation of a distribution of a substantially logarithmic conversion value of the knock intensity indicative value Vpi, and a value VMi corresponding to a median value of the above-noted distribution. The system derives the knock decision level VKDi based on the value Si and the value VMi when the value Si is within a predetermined range. On the other hand, when the value Si deviates from the predetermined range, the system derives the knock decision level VKDi based on the value VMi and a corrected value which is set smaller or larger than the value Si so as to prevent divergence of the knock decision level VKDi.