Page 123 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Toyota Motor Co. Ltd. 105

a) as a ratio of a varying amount of the ability value to a varying
amount of time or
b) as a ratio of a varying amount of the ability value to a varying
amount of the temperature of the catalytic converter
3) determining that the catalytic converter is deteriorated when said varying amount grasped in
step 2 is smaller than a predetermined value

The test takes place when the temperature of the catalytic converter is within a predetermined
state and/or the engine operation is steady and/or when an amount of intake air is within a
predetermined range.

The method of EP0756073 (1997) comprises the following steps:
I) feedback-controlling the air/hel ratio of the exhaust gases flowing into the catalytic
converter so that the aidfuel ratio of the exhaust gases fluctuates around a center value on
the lean air/fbel ratio side compared to the stoichiometric air/fhel ratio (fig. 52a)
2) determining whether the catalytic converter has absorbed oxygen to its maximum oxygen
storage capacity (saturation) during the period in which the airhel ratio of the exhaust gas
flowing into the catalytic converter is on a lean side (step 1) (figs. 52b,d)
3) prohibiting the determination of deterioration of the catalytic converter when the
determination of step 2 does not indicate a saturated catalytic converter whereas allowing
the determination of deterioration of the catalytic converter when the determination of step
2 indicates a saturated catalytic converter
4) calculating the amount of CO and HC in the exhaust gas flowing into the catalytic converter
based on the output of the upstream air/fbel sensor, when the aidhel ratio of the exhaust
gas is feedback-controlled
5) calculating the amount of CO and HC in the exhaust gas flowing out from the catalytic
converter based on the output of the downstream aidfuel sensor, when the air/fhel ratio of
the exhaust gas is feedback-controlled
6) determining the deterioration of the catalytic converter based on the inflow and outflow
amounts of HC and CO as calculated in steps 4 and 5
The curves of figs. 52b,c illustrate the change in the amount of oxygen stored in the catalytic
converter and the response of the output V2 of the downstream air/hel sensor, respectively,
when the converter is normal. The curves of figs. 52d,e illustrate the change in the amount of
oxygen stored in the catalytic converter and the response of the output V2 of the downstream
air/fhel sensor, respectively, when the converter is deteriorated.
As shown in curves of figs. 52b,d, the converter absorbs oxygen up to its saturation point.
When the air/fhel ratio of the exhaust gases temporarily largely fluctuates to the rich side (point
A, fig. 52a), the catalytic converter releases all the absorbed oxygen (point B, fig. 52b).
Therefore the reversal of V2 occurs even though the catalytic converter is normal (point C, fig.
52c). However, if the portion A of the curve of fig. 52c is compared with the portion 3 of the
curve of fig. 52e, the amount of fluctuation of Vz to the rich side and the length of the period
in which Vz stays on the rich side become smaller for the case of a normal converter than that
of a deteriorated converter (point E, fig. 52e). Namely, even if the air/fbel ratio of the exhaust
gas flowing into the catalytic converter fluctuates to the rich side in the same manner, the