Page 117 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Toyota Motor Co. Ltd 99

The method can be better explained by making use of fig. 49. In fig. 49a the upstream oxygen
sensor output is denoted while in fig. 49b the corresponding airhe1 correction amount is
presented that is changed in order to shift the actual airhe1 ratio to the lean side. Figs. 49c,d
and e correspond to the voltage signal of the downstream sensor for the cases of a normal
converter, a 20% deteriorated converter and a 50% deteriorated converter respectively. In the
case of fig. 49e the number of reversals per unit time period of the downstream sensor output
is larger than in the cases of figs. 49c and d and can be easily distinguished.

The method of EP0602468 (1994) comprises the steps of
1) detecting an air/fbel ratio of the exhaust gas upstream of the catalytic converter
2) detecting the air/fbel ratio of the exhaust gas downstream of the catalytic converter
3) controlling the air/fbel ratio of the engine by a feedback control based on the output of the
upstream air/fbel ratio sensor
4) calculating the ratio of the length of the output signal response curve of the downstream
air/fbel ratio sensor and the length of the output signal response curve of the output signal
response curve of the upstream aidfirel ratio sensor, when the engine is controlled by said
feedback control means
5) calculating the ratio of the area bounded by the output signal response curve of the
downstream aidfie1 ratio sensor and a reference line thereof and the area bounded by the
output signal response curve of the upstream air/fbel ratio sensor and a reference line
thereof
6) determining the degree of transition of the operating condition of the engine and correcting
the value of said ratio of areas of the output signal response curves in accordance with said
degree of transition of the operating condition of the engine
7) detecting deterioration of the catalytic converter based on the ratio of the lengths, the
corrected ratio of the areas and the degree of transition of the operating condition of the
engine, The catalytic converter has deteriorated when the relationship between said ratio of
the lengths of the output response curves and said corrected value of the ratio of the areas
satisfies predetermined conditions.

The determination of transition of step 6 comprises:
a) detecting the number of reversals between a rich aidfuel ratio side and a lean air/fbel ratio
side of the output signal of said upstream airhe1 ratio sensor over a predetermined time,
and determining the degree of transition in such a manner that the degree of transition
becomes larger as said number of reversals decreases, or
b) detecting whether the number of occurrences of
the rate of change of the pressure in the intake manifold, or
8 the rate of change of the intake air flow, or
the rate of change of the degree of opening of the throttle valve, or
rn the rate of change of the traveling speed of the vehicle driven by the engine
exceeds a predetermined rate or not over a predetermined time and determining the degree of
transition in such a manner that the degree of transition becomes larger as said number of
occurrences increases.