| 摘要 |
PROBLEM TO BE SOLVED: To accurately detect a combusting condition from a result of the detection of the combustion ion current to accurately detect the abnormality of a current detecting system. SOLUTION: An ignition plug 10 is mounted in a combustion chamber of an internal combustion engine, and is provided with counter electrodes 11, 12. An oscillator 25 generates a rectangular wave signal of a frequency of about 30 kHz, whereby the AC voltage is applied between the counter electrodes 11, 12. The current flowing between the counter electrodes 11, 12, is detected by a current detecting resistor 15. An S/H circuit 31 takes the detected current by the current detecting resistor 15 with a phase maximizing the AC voltage, and outputs the same as a current signal. A comparator 33 determines the combusting condition of the internal combustion engine on the basis of the output of the S/H circuit 31. An S/H circuit 32 takes the detected current with a phase making the AC voltage zero and outputs the same as a current signal. The comparators 37, 38 detect the abnormality of the current detecting system on the basis of the output of the S/H circuit 32.
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