Abstract: An ion current detection device is disclosed that is designed to hold an ion current output voltage within a prescribed limit to ensure proper operation of a processing device connected to the output side thereof, while, at the same time, shortening the decay time of the LC resonance associated with an ignition coil. An ion current flows from one end of a capacitor and back to the other end thereof passing through an ignition coil secondary winding, a spark plug, an ion current detecting resistor, and a load resistor. A voltage equal to -(ion current value).times.detecting resistor value appears at a node between the ion current detecting resistor and the load resistor. This voltage is inverted by an inverting circuit and supplied as an ion current output to the processing circuit.

Abstract: A device for controlling knocking includes a first unit which applies a voltage across a pair of electrodes installed in a combustion chamber of the internal combustion engine, detects an ionic current flowing between said pair of electrodes through ions generated when a gas mixture in the combustion chamber burns, and discriminates whether the knocking is occurring or not based upon the ionic current that is detected. The device for controlling knocking further includes a second unit which detects vibration of the cylinder block by using a vibration sensor installed in the cylinder block of the internal combustion engine, and discriminates whether the knocking is occurring or not based upon the vibration of the cylinder block that is detected. The device for controlling knocking controls the ignition timing of the internal combustion engine based upon the result of discrimination of either the first unit or the second unit depending upon the operation region of the internal combustion engine.

Abstract: A preignition detecting method which prevents preignition (PI) from being misjudged as having occurred when an ignition plug is fouling. It is determined whether or not the ignition plug fouls in accordance with a voltage, developed across a detecting resistor which is fetched into a microcomputer 18 at a relatively early timing after an ignition command signal is outputted from an ignition device. Further it is determined whether or not preignition occurs in accordance with another voltage fetched at a relatively late timing after the ignition command signal is outputted. When it is determined that the ignition plug is fouling, it is inhibited to fetch the another voltage at a relatively late timing to prevent a misjudgment that preignition occurs due to a leakage current from being caused though preignition does not actually occur.