| 摘要 |
PROBLEM TO BE SOLVED: To provide an ion current to accurately reflect the combustion state of an internal combustion engine despite of a fluctuation of atmosphere humidity by a method wherein an ion current responding to an amount of ion generated occasioned by combustion of air-fuel mixture in the cylinder of an internal combustion engine is measured, and the measured value of the ion current is corrected according to detected atmosphere humidity. SOLUTION: Since along with turning ON and OFF of the transistor 51a of an igniter 51, a high voltage is induced at the primary winding 52a and the secondary winding 52b of an ignition coil 52, spark discharge is generated between the central electrode 50a and the outside electrode 50b of an ignition plug 50 and air-fuel mixture is ignited and burnt and ionized. An ion current flows from the positive electrode of a constant voltage source 116 to the negative electrode of the constant voltage source 116 through an ion current measuring resistor 118, the ignition plug 50, and a diode 114. In this case, an ion output detected under given humidity is converted into an ion output under standard humidity, and an ion current value excluding the influence of a humidity fluctuation is detected. Further, by using a map determining a humidity sensitivity factor, an ion output is corrected.
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