ION CURRENT SENSING DEVICE FOR AN INTERNAL COMBUSTION ENGINE WITH SPURIOUS VOLTAGE PREVENTING FILTER

摘要

An ion current sensing device for an internal combustion engine is able to accurately sense an ion current generated between electrodes of a spark plug during combustion of a mixture even when the electrodes have been smeared by carbon or other combustion products deposited or accumulated thereon. A power source 14 supplies a bias voltage to the electrodes of the spark plug. An ion current sensing resistor 15 is connected between the elecrodes of the spark plug and the power source for sensing an ion current as generated between the electrodes of the spark plug each time a mixture in the combustion chamber is combusted. A comparator 11 compares the voltage across the ion current sensing resistor with a reference voltage and generates an output signal when the voltage is higher than the reference voltage. A filter comprising a capacitor 22 and a resistor 23 is connected between the ion current sensing resistor and the comparator for passing only AC components of the voltage across the ion current sensing resistor to the comparator while blocking a DC component thereof.