Patent ID: 7863903

Claim:
A combustion state detection apparatus for an internal combustion engine, comprising: electrodes which are disposed within a combustion chamber of the internal combustion engine; voltage application means for applying a voltage across said electrodes in order to detect an ionic current which appears in a case where a mixture combusts within the combustion chamber; ionic current detection means for detecting the ionic current which appears across said electrodes at the application of the voltage; data extraction means including detection interval setting means for setting a detection interval for detecting preignition or a premonitory phenomenon thereof from the detected ionic current, said data extraction means serving to extract ionic current data correspondent to a change of the ionic current in the detection interval; convexity detection means for detecting that domain within the detection interval in which a change shape of the ionic current is upwardly convex, on the basis of the extracted ionic current data; and preignition decision means for finding an appearance position and a peak position of the ionic current by comparing the ionic current in the upwardly convex domain detected by said convexity detection means with a predetermined threshold value, and then deciding occurrence of the preignition or the premonitory phenomenon thereof on the basis of the appearance position and the peak position of the ionic current obtained; wherein said convexity detection means includes leak current judgment means for judging existence or nonexistence of appearance of a leak current across said electrodes, and it enables the detection of the upwardly convex domain in a case where the appearance of the leak current has been judged.