Page 202 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

184 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

upstream a)
sensor

output lean

downstream
sensor
output non-deteriorated

rich T2
downstream c)

sensor time
output lean deteriorated

Fig. 83 (from US5379587)

The method of US5448886 (1995) comprises the following steps:
1) feedback-controlling the engine aidfuel ratio for matching the aidfuel ratio with a desired
value in accordance with upstream and downstream detection signals respectively from the
upstream and downstream exhaust sensors
2) judging if certain conditions of engine load and rotational speed are fblfilled and in case they
do
3) determining a deterioration-determined time value TDLY from a calculation based on a rich
determination delay time AT,.K, a lean determination delay time ATN,, a lean response delay
time Tw, and a rich response delay time Tr,~ (fig. 82)