Page 200 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

182 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

3) correcting a specific execution timirg by means of the standard comparison value
4) calculating an average value of the standard comparison value measured in a specific
number of cycles
5) judging the deterioration of the catalytic converter from the average value of the standard
comparison value

The method of US5379587 (1 995) comprises the following steps:
1) fdback-controlling the engine airhe1 ratio by detecting signals of the upstream and
downstream exhaust sensors (dual feedback control)
2) judging if certain conditions of engine load and rotational speed are filfilled and in case they
do
3) setting a feedback correction amount to be larger than that in a non-deteriorated state
4) stopping the dual exhaust sensor feedback control
5) setting a rich judgment (or determination) delay time ATLR and a lean judgment (or
determination) delay time ATRI. (fig. 82a) in accordance with a ratio at the time of the dual
exhaust sensor feedback control so as to set a richllean judgment delay time to a
predetermined value, where
a) the rich determination delay time AT~,R elapses from a rich
inversion time (point “a”) of the upstream detection signal (fig.
82a) to the beginning of the decrease (point “b) in the feedback
control-corrected quantity (fig. 82b)
b) the lean determination delay time ATm. elapses from a lean
inversion time (point “c”) of the upstream detection signal (fig.
82a) to the beginning of the increase (point “f’) in the feedback
control-corrected quantity (fig. 82b)
6) setting the upstream sensor feedback correction amount to a deterioration judgment value
by a skip correction amount Ks and an integration correction amount KI (gradient) (fig.
82b)
7) measuring a downstream sensor response delay time. This delay time is the time from the
moment the upstream sensor switches e.g. from rich to lean aidfuel ratio till the time the
downstream sensor switches in the same direction
8) repeating the measurement of the downstream sensor delay time for a certain number of
times and calculating an average value of the delay time
9) checking if the average value of the delay time is stable and in case it is stable
10) correcting the downstream exhaust sensor response delay time by an engine load and an
exhaust temperature
I 1) comparing the downstream exhaust sensor response delay time after completion of the
correction with the deterioration judgment value defined in step 6
12) determining whether the catalytic converter has deteriorated (fig. 83c) or not (fig. 83b),
depending if the measured delay time of the downstream sensor is bigger or not than said
deterioration judgment value