Page 277 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Chapter 2.3

Robert Bosch GmbH

The method of DE2643739 (1978) detects the efficiency of a catalytic converter consisting of
two parts KI and Ko (fig. 1 12 and fig. 113). Two embodiments are presented.
In the first embodiment a temperature sensor is installed upstream of KI and an additional
sensor is installed in the reaction zone of KI (fig. 112). The temperature distribution in the
catalytic converter is presented by the graph of fig. 112. For the case of a fbnctional catalytic
converter, the temperature inside K, and Kn is higher than the temperature outside the catalytic
converter due to the exothermic oxidation reaction taking place in the catalytic converter. In
the case of a degraded catalytic converter, the temperature inside the catalytic converter is
lower than the temperature upstream of the catalytic converter (dashed line). When the
difference in temperature between the value measured inside the catalytic converter minus the
temperature measured upstream of the catalytic converter is lower than a predetermined value
then the catalytic converter is considered as deteriorated. The method requires that the
catalytic converter is fully warmed-up before the detection starts.

In the second embodiment two sensors can be installed close to one another inside Kn or
downstream of the catalytic converter (fig. 113). One sensor is similar to those ones of the
previous embodiment, whereas the other sensor has a catalytic coating similar to the coating of
the catalytic bodies Kr and Kn. When the catalytic converter is functional the two sensors show
a similar temperature indication (fig. I13a). When the catalytic converter is degraded then the
non-catalytic sensor indicates a low temperature value whereas the catalytic sensor still
indicates a high temperature value because of the exothermic oxidation reaction taking place
on the sensor itself (fig. 1 13b).

259