Page 304 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

286 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

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CATALYST TEMPERATURE

Fig. 128 (from EP0498598)

In JP5202735 (1993), when the engine starts up, a heater is turned on to heat the catalytic
converter. The temperature of the catalyst bed is then detected and when the temperature of
the bed remains lower than a threshold for a certain time, the heater is turned off and a
malfbnction signal is produced.

In US5447696 (1995), a method is presented to assess the efficiency of a plurality of
electrically heated catalytic converters (EHC) of the heater-converter type located upstream of
a plurality of main catalytic converters. Each electrically heated catalytic converter and each
main catalytic converter are located in the exhaust passage of a corresponding cylinder bank.
For simplicity reasons only two cylinder banks will be used further in the presentation of the
method (fig. 129).

As shown in fig. 129, each catalytic converter comprises a cylindrical casing, a heater-
converter and a main converter, both disposed in said cylindrical casings. The heater-
converters are electrically heated converters having metal substrates, which also act as electric