To judge normal combustion state/misfiring state or an abnormal state of wire harness, or the like, correctly for every cylinder of an internal combustion engine, and to specify a failed cylinder and a failed part at the time of inspection, repair or maintenance.
After an ignition coil 10 is driven based on an ignition command signal IGt from an ECU(electronic control unit for internal combustion engine), an ion current flowing between an ignition plug 12 and the ground is detected by means of an ion current detecting resistor 17, an operational amplifier 20, and the like, and converted through a comparator 30 into a signal which is fed through an offset means, i.e., resistors 31, 32, to produce a signal within a specified range corresponding to the ECU 40. Since the ion current signal is not fixed to the power supply voltage or the ground potential when an internal combustion engine is in normal combustion state or misfiring state, normality/abnormality of circuit can be distinguished surely and thereby a failed cylinder and a failed part can be specified easily at the time of inspection, repair or maintenance.
KATO YUKIHIRO
NOMURA TOKUYUKI
TOYOTA MOTOR CORP