| 摘要 |
PROBLEM TO BE SOLVED: To accurately detect the combustion ion current regardless of a certain amount of a lag in the detecting timing. SOLUTION: An ignition plug 10 is mounted in a combustion chamber of a first cylinder, and an ignition plug 20 is mounted in a combustion chamber of a fourth cylinder. An oscillator 33 generates a rectangular wave signal of a frequency of about 30 kHz, whereby the AC voltage is applied between the counter electrodes of the ignition plugs 10, 20. The electric current flowing between the counter electrodes of each of the ignition plugs 10, 20 is detected by current detecting resistors 16, 26. A differential amplifying circuit 40 takes the detected current of the cylinder (for example, first cylinder) in a combustion stroke and the detected current of the cylinder (for example, forth cylinder) not in a combustion stroke, and an absolute value circuit 50 takes the output of the differential amplifying circuit 40 to provide its absolute value. An S/H circuit 60 samples and holds the output of the absolute value circuit 50 with a phase to maximize the AC voltage, and outputs the same as a current signal.
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