Page 230 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

212 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

Plurality of catalytic converters arranged in series in the exhaust pipe

The method of US5509267 (1996) refers to the monitoring of two catalytic converters
mounted in series in an exhaust pipe like the one of fig. 72. Three sensors are also used as in
method of fig. 72. The method comprises the following steps:
I) sensing the oxygen content of the exhaust gas between the engine and the upstream
converter by means of a first oxygen sensor
2) sensing the oxygen content of the exhaust gas between the upstream and the downstream
converter by means of a second oxygen sensor
3) sensing the oxygen content of the exhaust downstream of the downstream converter by
means of a third oxygen sensor
4) during non-diagnostic periods, sensing a first untreated oxygen content of the exhaust gas
before this gas has been treated in one of the two converters by means of the first oxygen
sensor
5) during a diagnostic period, sensing a second treated oxygen content of the exhaust gas after
the gas has been treated by the upstream catalytic converter by means of the second oxygen
sensor
6) during a diagnostic period, sensing a third treated oxygen content of the exhaust gas after
the gas has been treated by the downstream catalytic converter by means of the third
oxygen sensor
7) controlling engine aidfuel ratio in response to the second oxygen content during the
diagnostic period
8) controlling engine air/fiel ratio in response to the first oxygen content during the non-
diagnostic periods
9) determining the condition of the upstream catalytic converter by
a) comparing an estimated oxygen storage capacity of the converter (as
predetermined function of the sensed second treated oxygen content) with
predetermined threshold or
b) comparing the frequency variation of the sensed second oxygen content with
a predetermined threshold
10) determining the condition of the downstream catalytic converter by
a) comparing an estimated oxygen storage capacity of the converter (as
predetermined function of the sensed third treated oxygen content) with
predetermined threshold or
b) comparing the amplitude of the sensed third oxygen content with a
predetermined threshold