Method for monitoring the efficiency of a catalytic converter for treating exhaust gases from an internal combustion engine

A method for monitoring the efficiency of a catalytic converter for treating exhaust gases from an internal combustion engine, wherein the engine is equipped with at least one fuel injector and a device for regulating an engine inlet air/fuel mixture and an opening time of the fuel injector, the method which comprises:

• a) disposing an oxygen probe in a gas flow leaving a catalytic converter, wherein the oxygen probe provides an output signal which switches between two levels;
• b) measuring an injector opening time suitable for ensuring stoichiometry of an air/fuel mixture during regulation and at substantially stabilised speed, and choosing a base injection time from the measured injector opening time;
• c) subsequently, during a predetermined time interval, imposing on the opening time a time variation of symmetric deviation having a predetermined amplitude and shape about the base injection time;
• d) progressively and monotonically modifying the base opening time during successive time intervals, so as to pass through a centering of the deviation of the opening time on that of an oxygen storage capacity of the catalytic converter;
• and
• e) evaluating an efficiency of the catalytic converter by determining the resulting oscillation of the output signal.