Page 107 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Toyota Motor Co. Ltd. 89

output by the upstream oxygen sensor also becomes small. Accordingly, since the rate of
change of the oxygen storage amount becomes small, the time for which the oxygen storage
amount is zero becomes short, and thus the voltage output of the downstream sensor is rarely
higher than the threshold E. Accordingly, when a slight deterioration of the condition of the
catalytic converter is determined, the frequency of the voltage output by the downstream
oxygen sensor is considerably lower than the frequency of the voltage output by the upstream
oxygen sensor.

converter slightly deteriorated

voltage output by
upstream sensor 0

airfluel ratio 11 *
feedback correction
amount 1 1

1 \ I
I t $
\' I 1
> '\ '# 't full 9 storage
I $ ', 1'8
imognt
O2 storage amount
0

I I
voltage output by I E
1
downstream sensor A.
time

Fig. 42 (from US5165230)

Further, when a considerable deterioration of the catalytic converter is determined (fig. 43),
since the full oxygen storage amount becomes lower, the time (TX - T4) for which the oxygen
storage amount is zero is increased, and thus the voltage output by the downstream sensor is