Page 94 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

76 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

This operation is described in fig. 36, where TPI to TP7 correspond to 7 test periods. Lines
630,632,634 and 638 correspond to a hypothetical selected monitoring ratio, a corresponding
weighted average ratio, a deviation A from the weighted average ratio and a reference ratio
indicating a faulty catalytic converter respectively. Selected ratios are shown at the end of each
test period.
At the end of TPl the selected ratio (line 630) is higher than the reference ratio (638). This
seems to be a casual fluctuation and is not an indication of catalytic converter failure because
the corresponding weighted average ratio (line 632) is below reference line 638. At the end of
TP6 the selected ratio (line 630) exceeds weighted average ratio (line 632) by more than A.
Accordingly, the weighted average ratio (line 632) is reset to selected ratio (line 630) as shown
at TP6. The reset weighted average (line 632) at TP6 exceeds reference line 638 indicating a
degraded catalytic converter.

In US5381656 (1995) the following mentioned steps are followed:
1) generating a feedback variable by integrating an output of the upstream oxygen sensor
2) trimming said integration by a signal derived from the output of the downstream oxygen
sensor
3) cycling the above mentioned variable above and below a nominal value
4) adjusting fuel delivered to the engine by the feedback variable
5) generating a first test signal by squaring the peak amplitude of said feedback variable for
each cycle of a plurality of cycles of step 3 and summing the squares
6) generating a second test signal by squaring the peak amplitude of the downstream sensor
output for each cycle of a plurality of cycles of step 3 and summing the squares
7) completing a test cycle generated when the engine has operated during a plurality of
inducted air flow ranges each for a predetermined duration. This duration comprises a pre-
selected number of cycles of the feedback variable.
8) after completion of test cycle, indicating degraded catalytic converter when a ratio of the
second test signal over the first test signal exceeds a predetermined ratio

In US5386693 (1995) the following steps are applied
1) integrating an output of the upstream oxygen sensor to generate a feedback variable
2) controlling fuel 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 first 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) generating a second monitoring ratio related to a ratio of amplitude of transitions in the
feedback variable to amplitude of transitions fiom the downstream sensor output for each
of said test periods