Page 190 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey
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172 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters
The method of Em626506 (1994) is applied during a specific time interval and comprises the
following steps:
1) determining the number of times ti, during which both the output signals of the upstream
and downstream sensors indicate a rich aidfuel ratio
2) determining the number of times ti,, during which both the output signals of the upstream
and downstream sensors indicate a lean aidfuel ratio
3) determining from both tiN and ti,. the minimum value FI,,,,, = min(tiL, n,)
4) comparing timln to a predetermined limit value E
5) judging that the catalytic converter is deteriorated when n,," > E
The method of W09420737 (1994) presents the case of monitoring during start-up the
efficiency of an electrically heated catalytic converter (EHC) placed upstream of a normal
three-way catalytic converter (fig. 78).
control
Fig. 78 (from W09420737)
The upstream oxygen sensor is placed upstream of the EHC, whereas the downstream sensor
is placed downstream of the three-way catalytic converter. The method works as follows:
