Patent ID: 8291747

Claim:
An internal combustion engine combustion state detection apparatus, comprising: a control device that generates a spark signal in an internal combustion engine; an ignition device that ignites and burns a combustible mixture taken into a combustion chamber in a cylinder of the internal combustion engine; an ion current detection device that detects ions generated in the combustion chamber by combustion of the combustible mixture; an end detection device that detects end timing of an ion signal obtained from the ion current after spark timing obtained from the ion current detection device; and a combustion diagnosis device that sets comparative timing to be compared with the end timing of the ion signal and determines that combustion is abnormal when the end timing of the ion signal is advanced from the comparative timing, wherein the combustion diagnosis device sets a smoothed value smoothed using values of various end timings of the ion signal to detect a relation between the smoothed value and the spark timing and sets the comparative timing that varies according to the relation at predetermined timing corresponding to a combustion state with respect to the smoothed value.