Page 128 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

1 10 Methods for Monitoring and Diagnosing the EEciency of Catalytic Converters

Conversely, when the airlfuel ratio of the exhaust gas supplied to the converter deviates largely
to the rich state at time ts, the length of the response curve of the oxygen sensor becomes long
because the output of the oxygen sensor also deviates largely to the rich state from the lean
state.

That is, the accuracy for detecting the deterioration of the converter may become worst
because the deviation of the oxygen sensor is affected by the fluctuation of the airhel ratio of
the exhaust gas exhausted from the converter, even when the fluctuation of the exhaust gas
supplied to the converter is kept constant.

lean
stoichiometric
rich

lean
stoichiometric
rich

time

Fig. 54 (from EP0796985)

The object of the method of EPO801215 (1997) is to avoid misjudgment of a catalytic
converter deterioration detection even though the balance between the oxygen absorbing and
releasing power disappears. The met hod comprises the following steps:
1) feedback-controlling the amount of fuel supplied to the engine at least in accordance with
the output of the upstream air/fbel sensor