Page 218 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

200 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

comprise corresponding reference values to which the outputs of the air/fbel ratio sensors
are compared
12)counting the number of inversions of the upstream sensor output signal across the
stoichiometric aidfuel ratio
13) counting the number of inversions of the downstream sensor signal across the set catalytic
converter diagnosing slice levels
14) checking whether the ratio of the downstream sensor counted value to the upstream sensor
counted value exceeds a predetermined value
15) determining that the catalytic converter has been degraded when the ratio exceeds a
predetermined value

deteriorated catalyst

rich
.T

downstrea
sensor
voltage

J
lean

Fig. 90 (from US5 1 19628)

In the method of JP5312025 (1993), at the time of the diagnosis procedure, the mean engine
air/fuel ratio is shifted to a rich value by means of a suitable feedback control. When the
catalytic converter is deteriorated, then the output signal of the downstream sensor crosses a
predefined slice level (as defined in US5119628 (1992)). The same procedure can be repeated
by shifting the mean engine aidfuel ratio to a lean value.

The method of JP5098945 (1993) inhibits the deterioration diagnosis of the catalytic converter
when during feedback-control of the engine, engine cooling water temperature, car speed,
engine speed and basic fuel injection quantity are not in predetermined ranges. Namely, the
diagnosis takes place only when the converter is activated under ordinary operating
conditions.