Daimler-benz Ag

Temic Telefunken Microelectronic Gmbh

Jens Schirmer

Peter Hohner

Method for identifying knocking combustion in an internal combustion

With a transistor ignition system, in order to generate an ion current measurement signal at the secondary end, the ignition transistor, following an ignition triggering impulse, will be driven such that a saw-toothed collector current results as a primary current, and whose rate of increase is selected such that the quasi-stationary direct voltage generated hereby at the secondary end will not trigger any ignition process. The advantage is that for generating such a measurement signal as well as for its evaluation only a few components are required.

Circuit layout for ion current measurement

An alternating current ignition system which can be used in one of two ways for ion current measurement. On the one hand, an oscillating circuit at the primary end of the ignition coil can be driven such that, after ignition has taken place, an alternating current signal is generated at the primary end; the amplitude of the alternating current signal must be sufficiently low so as not to cause any sparks at the secondary end, but lead to an alternating voltage signal which is modulated in relation to the ionisation degree of the ignition spark gap and thus represents an ion current measurement signal. On the other hand, however, if an auto transformer is used as an ignition coil, the intermediate circuit voltage applying at the primary end will be modulated in the medium-high voltage range of, e.g, 180 V in relation to the degree of ionisation, so that this supply voltage is used as a measurement signal.

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Heilbronn, Germany

Jens Schirmer