Page 145 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Nippon Denso Co. 127

start of detection
of deterioration condition deterioration
+
determination
- TO
lean
AA

target
ai rifuel
ratio A

ratio A

(rich) high
$.- nv, >=€
umer rich limit , - I

downstream
sensor output
voltage V2
lower lean limit _- ----.
dl
(lean) low
time (msec --+

Fig. 60 (from US5622047)

As shown in fig. 60, during deterioration detection of the catalytic converter the target air/fiel
ratio of the engine varies at a greater amplitude and a longer period in response to a corrected
increased dither amplitude AA and dither period AT than the ones during a normal engine
operation. The correction takes place according to the expressions:

AR=AR+P
AT=AT+y

where
P.y: corrective quantities