Page 211 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Mitsubishi Motors Corporation - Mitsubishi Electric Corporation 193

with
The downstream sensor signal VOZ is converted to the filtered signal V~Z a delay in the
response time, which corresponds to a time constant of the filtering means (e.g. 100-300
milliseconds).

a) normal converter
4
downstream

0 time

b) deteriorated converter

downstream
sensor output
(VI

0 time

Fig. 86 (from US5425234)

When the catalytic converter is normal (fig. 86a), the filtered signal Vmz follows the signal Vo2
even when the level of the signal VOz shifts from a solid line curve a to a curve b. The two
signals Vo2 and Vn,2 essentially coincide because of the large time constant.
When the catalytic converter is deteriorated (fig. 86b), the level of the filtered signal Vf02
differs significantly from the non-filtered signal Voz and intersects a downstream target value
VR~~ a large delay in the response time to the signal V02 of a large amplitude. The
due
to
difference between the filtered and non-filtered signal increases beyond a predetermined value
and indicates a deteriorated catalytic converter.