Page 88 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

70 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

sensor and the change in the engine aidfuel ratio feedback signal is observed while doing so.
Since the two sensors will produce the same output voltage at a different aidfuel ratio value,
there will be a difference in the aidfie1 feedback signal of the engine depending on which
sensor is in control. The magnitude of the change in aidfuel feedback signal is used as an
indicator of the condition of the catalytic converter.

In fig. 33 a preferred embodiment of the current method is presented. The feedback signal of
aidfuel ratio using a low or non-catalyzed downstream sensor, gradually increases to a new
higher level over a period 5-10 sec in the case of a degraded catalytic converter. This period is
enough for an accurate, clear comparison of the signals to be made. In case of a good catalytic
converter this signal remains essentially the same as for the highly-catalyzed sensor. The
method does not require any comparisons to pre-stored data for the evaluation of the condition
of the catalytic converter.

(BAD MAIN

(GOOD MAIN
airfluel
..
H fGHLY I LOW TO NON
CATALYZED CATALYZED
ELECTRODE ELECTRODE
SENSOR IN i SENSOR IN
FEEDBACk

0 15 30
time (sec)

Fig. 33 (from W09303358)

The oxygen sensors used in the method of W09303358 (1993) are described in detail in
W09303357 (1 993).