Robert Boschgmbh

Hans Koehnle

Christian Zimmermann

Karl-Heinz Kugler

Walter Viess

Ernst Kaller

An exhaust-gas recirculation system includes means for diagnosing the system based upon temperature values measured in the exhaust-gas return duct when certain conditions exist. A differential value between the actual temperature in the exhaust-gas return duct and a reference temperature, which indicates the possible beginning of diagnosis, is provided for a flow-through test. The differential value is then fed to a low-pass filter. If the conditions for a diagnosis are satisfied, it is determined whether the recirculation system is in order based upon a comparison of the differential value to a threshold value. A leak test of the exhaust-gas return valve can likewise be performed based upon the differential value of the two temperatures.

Exhaust-gas recirculation system for an internal combustion engine

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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Schwieberdingen, Germany

Hans Koehnle