Page 121 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Toyota Motor Co. Ltd. 103

The method of EP0690213 (1996) comprises the following steps:
1) temporarily changing the aidfuel ratio of the exhaust gases from rich to lean for a
predetermined fixed time to
2) detecting the variation of the air/fuel ratio of the exhaust gases by means of an oxygen
concentration sensor installed downstream of the catalytic converter
3) detecting a peak value of the level of the output of the downstream oxygen sensor within
the predetermined fixed time during which the aidfuel ratio of the exhaust gases flowing
into the catalytic converter is temporarily maintained at a lean or at a rich aidhe1 ratio
4) judging a degree of deterioration of the catalytic converter on the basis of the peak value of
the output of the downstream sensor

Fig. 51a shows the feedback fuel correction coefficient for a predetermined fixed time to, that
is, when the air/hel ratio is made rich for the predetermined fixed time to. Figs. 51b and c show
the corresponding measured air fuel ratio and current I, (mA) of the downstream sensor for
the cases of a new (I), a slightly deteriorated (II), a much deteriorated (111) and a completely
deteriorated (IV) catalytic converter. The higher the deterioration of the catalytic converter the
shorter the time during which the aidfuel ratio of the exhaust gases is maintained substantially
at the stoichiometric air/hel ratio (fig. 5 1 b).

The corresponding peak of the current I, becomes smaller the larger the degree of
deterioration of the catalytic converter (fig. 51c). The value of current I, becomes zero for a
completely deteriorated converter (case IV).
The method is also applied to NO, adsorbents.

In the method of E330743433 (1996) the following steps are considered:
I) detecting the air/fuel ratio upstream of the catalytic converter by means of an upstream
sensor
2) detecting the airhe1 ratio downstream of the catalytic converter by means of a downstream
sensor
3) feedback controlling the engine air/hel ratio between a rich and a lean value by means of
the upstream sensor
4) calculating the amount of oxygen released from the catalytic converter when the air/fhel
ratio of the exhaust gas flowing into the catalytic converter is rich, based on the value
obtained by a temporal integration of the amount of the deviation of the aidfuel ratio
flowing into the catalytic converter from the stoichiometric aidfuel ratio
5) controlling the length of the time period in which the aidfuel ratio of the exhaust gas
flowing into the catalytic converter becomes a rich aidfuel ratio in such a manner that the
amount of oxygen released from the catalytic converter becomes a predetermined value

In a first embodiment of the method the following hrther steps are considered:
a) controlling the length of the output signal response curve of the downstream airhe1 sensor
b) determining the degree of deterioration of the catalytic converter based on this length of the
output signal response curve of the downstream airhe1 sensor