Page 93 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Ford Motor Co. - Ford France SA - Ford Werke AG - Ford Motor Co. Ltd. 75

In US5363646 (1994) the following steps are applied:
1) integrating an output of the upstream oxygen sensor to generate a feedback variable
2) controlling he1 delivery to the engine in response to this feedback variable
3) providing a test period each time the engine has completed operation within each of a
plurality of inducted air flow ranges for at least a minimum duration in each of said air flow
ranges. Said minimum duration comprises a pre-selected number of transitions of the
feedback variable per air flow range.
4) generating a monitoring ratio related to a ratio of frequency of transitions in the feedback
variable to frequency of transitions from the downstream sensor output for each of said test
periods
5) providing a weighted average of the monitoring ratio over a plurality of test periods
6) indicating degradation in efficiency of the converter when the weighted average of step 5
exceeds a predetermined value (for a pre-selected number of times).
The weighted average of the monitoring ratio of step 5 is reset to the monitoring ratio itself
after the monitoring ratio exceeds the weighted average by a pre-selected amount A.

I r--- 7
1 .) A

4 I I I I I
I 1 I I
TPI TP2 TP3 TP4 TP5 TP6 TP7
Time Period

Fig. 36 (from US53636463