Page 203 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Suzuki Motor Corporation 185

where:
a) the lean response delay time Ta elapses fiom the beginning of a
decrease (point “b) in an upstream feedback control-corrected
quantity to a lean inversion time (point “e”) of the downstream
detection signal in response to rich and lean inversions of the
upstream detection signal (fig. 82)
b) the rich response delay time T1.K elapses fiom the beginning of an
increase (point “f ’) in an upstream feedback control-corrected
quantity to a rich inversion time (point “g”) of the downstream
detection signal in response to rich and lean inversions of the
upstream detection signal (figs. 82a-c)
c) the rich determination delay time ATLR and the lean determination
delay time ATm, are defined in the above mentioned method of
US5379587 (1 995).
4) repeating previous step for a certain number of times
5) calculating the standard deviation of TDLY and if the dispersion is smaller than a preset
value then
6) calculating an average value of TDLY and correcting it in fbnction of the engine air intake
quantity and the period of feedback control Tw (fig. 82b) and comparing the average value
of TDLY to a predetermined value
7) considering the catalytic converter as deteriorated when the corrected average value of
TDLY is equal or less than the predetermined value.

The method of CAt153606 (1996) comprises the following steps:
1) feedback-controlling the engine aidfbel ratio in accordance with the signal of the upstream
sensor (first feedback control) to achieve a target value
2) feedback-controlling the engine air/fbel ratio so as to correct the first feedback control in
accordance with the signal of the downstream sensor (second feedback control)
3 ) establishing predetermined catalytic converter deterioration-determining conditions
4) measuring the number of successive oscillations of the upstream and downstream sensor
signals within a predetermined operation time and calculating the ratio N of the downstream
signal oscillations it2 to the upstream signal oscillations n1

5) measuring the upstream and downstream voltage signal surrounding areas (AI, A2) within
the predetermined operation time in accordance with respective areas which are surrounded
by loci of periods of time during which the upstream and downstream voltage signals are
inverted (fig. 83), thereby calculating an area ratio A