Method for detecting combustion knock from the ionic current in an

Abstract

A method of recognizing knocking combustion in an internal combustion engine involves sensing an ionic current in the combustion chamber and providing a corresponding ionic current signal, detecting the signal during a pertinent time window and band-pass filtering the signal for a pertinent frequency range characteristic of knocking phenomena, integrating the signal to provide a present integral value, and then comparing the present integral value to a lower knocking threshold and a higher knocking threshold. If the present integral value exceeds the lower knocking threshold but does not exceed the higher knocking threshold, the combustion is identified as a knocking combustion. If the present integral value exceeds the higher knocking threshold, the value is essentially disregarded as being implausible, and the combustion is identified either as non-knocking, or as the same combustion condition, i.e. either knocking or non-knocking, that had been determined in the previous combustion cycle. The knocking thresholds are updated to follow variations in the integral values that do not exceed the existing lower knocking threshold. Especially the higher knocking threshold is adjusted dependent on the present operating condition of the engine, as represented by a plurality of respectively differently weighted prior integral values. Whenever a knocking combustion is recognized, the higher knocking threshold is maintained at the previously determined value.