Robert Boschgmbh

Ernst Kaller

Christian Zimmermann

Karl-Heinz Kugler

Hans Koehnle

In order to protect catalytic converters from damage caused by continued engine operation with a malfunctioning ignition system, a monitoring circuit checks current in the ignition coil primary winding. Primary winding current (i) is transformed by a measuring circuit (11) into a test primary voltage (U.sub.pr) which is fed to an evaluation circuit for comparison with ignition system supply voltage (U.sub.v) from the battery. During each primary current pulse, an instantaneous value is sampled, preferably during the earlier half of the pulse, and when the instantaneous test voltage (U.sub.pr) exceeds the supply voltage (U.sub.v) by more than a predetermined amount, the evaluation circuit (10) generates an error or malfunction indication. The ignition system can then be serviced before the catalytic converter is ruined.

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Tamm, Germany

Ernst Kaller