Page 108 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

90 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

rarely higher than an increase in the threshold E. As a result, it can be determined that the
condition of the catalytic converter has considerably deteriorated when the ratio of the
frequency of the voltage output of the downstream oxygen sensor to the frequency of the
voltage output by the downstream oxygen sensor is larger than a predetermined value.

converter considerably deteriorated

full 9 storage
amount
O2 storage amount ----
f'
L-
0 II d
voltage output by
downstream sensor
0
T3 T4 time

Fig. 43 (from US5 165230)

In E80536789 (1993) the criterion of deterioration of the catalytic converter is the ratio of the
lengths of the response curves of the output signal of the downstream sensor to the output
signal of the upstream sensor when the engine is feedback controlled.
When this ratio is larger than a predetermined value the catalytic converter is considered as
degraded. In another embodiment the criterion can be the ratio of the length of the response
curve of the downstream sensor to a variable determined by the operating load of the engine
during feedback control.

In DE4234102 (1993) the following steps are considered:
1) detecting the signal condition that the output signal of the downstream aidfuel ratio sensor
is being maintained at either a rich side aidfuel ratio or a lean side aidfuel ratio compared
with a stoichiometric aidfuel ratio for more than a predetermined time during the feedback
control of the engine by said feedback control means
2) calculating an area surrounded by the output signal response curve of the downstream
aidfie1 ratio sensor and a predetermined reference value line