Page 282 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

264 Methods for Monitoring and Diagnosing the Efkiency of CataIytic Converters

In the method of DE4338547 (1995) a temperature sensor element is installed in the
longitudinal direction of the catalytic converter (fig. 116). The sensor has an electrical
resistance with defined temperature dependence. The electrical resistance of the sensor is
measured at two, at least, regions of the sensor (fig. 11 6). The knctionality of the catalytic
converter is evaluated by comparing the ratio of the resistance of the fiont part of the catalytic
converter over the resistance of the rear part of the catalytic converter with a predetermined
value. When the ratio is bigger than the predetermined value then the catalytic converter is
considered as deteriorated. The method is based on the fact that in a new converter the major
conversion of pollutants takes place in the front part (F) of the converter, whereas for a
deteriorated converter the conversion region moves towards the rear part (R).

The method of DE4426020 (1996) comprises the following steps:
1) measuring the temperature downstream of the catalytic converter
2) estimating the temperature downstream of the catalytic converter by means of a theoretical
model
3) calculating the difference between the measured and the estimated temperature at certain
operating conditions
4) judging that the catalytic converter is deteriorated when this difference is bigger than a
predetermined value.