Ion-current-measuring circuit for knock detection in combustion chamber of IC engine

摘要

The circuit employs the sparking plug (Zk) in the secondary circuit of the ignition coil (Tr) as an ion current probe. With every successful spark a signal is generated in the secondary circuit which depends upon the degree of ionisation in the spark gap. A resonant circuit formed by the primary circuit and a capacitor (C) is controlled by a regulator (1) so as to provide bipolar ignition current. The ion current signal is picked off by e.g. a series double Zener diode circuit (4), demodulated and filtered (3) to produce e.g. a knock warning for retardation of the ignition without recourse to an acoustic knock detector.