Page 262 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

244 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

configuration of fig. 103 is used. An essential feature is that after reaching its maximum, the
temperature does not remain substantially constant. Instead, it decreases again downstream of
the zone of the catalytic converter in which the catalytic reaction primarily occurs (reaction
zone). Downstream of this zone there is no catalytic activity on the jacket anymore and the
temperature drops. As the catalytic converter deteriorates the region of high temperature
moves towards the outlet end of the catalytic converter (broken line),

The second method of DE4027207(1992), also described in US5428956 (1995) comprises the
following steps:
1) measuring a temperature at least at two temperature measuring locations associated to the
catalytic converter by means of two sensors. A deviation over time of at least one of the
temperature sensor signals is formed and the measurement is inhibited if the deviation over
time differs substantially from zero
2) periodically repeatedly determining a temperature measuring variable from signals issued
by the sensors during operation of the engine with an engine monitoring system. The
temperature measuring variable is defined
I) as a difference between the temperatures measured by the two temperature
measuring sensors or
11) by monitoring the signal of a first one of the temperature measuring sensors for
discontinuous changes i.e. changes from a first steady operating state of the
engine to a second steady operating time within a brief time. If such a
discontinuous change occurs, then observing the signal of a second one of the
temperature measuring sensors over a short period of time (1-3 seconds), and
finally forming the temperature measuring variable from the changes over time
of the signal of the second temperature measuring sensor
3) determining hrther measuring variables characterizing an applicable operating state of the
engine. Variables of this kind include engine speed, exhaust gas temperature, exhaust gas
pressure etc.
4) determining a temperature limit value from the fbrther measuring variables and from at
least one temperature measuring variable ascertained in an earlier measurement. The
activity of the catalytic converter is recorded and it is taken into account for the applicable
determination of the temperature limit value, over a period of time sufficiently long for
averaging out special strains in each case
5) determining catalytic activity by comparing the temperature measuring variable with the
temperature limit value
6) issuing a report if the temperature measuring variable is lower than the temperature limit
value

The judgment of the catalytic activity of the catalytic converter in the method of W09203643
(1992) is executed as follows:
1) measuring the temperature of the catalytic converter honeycomb body at a plurality of
measurement points along the flow direction
2) performing each temperature measurement continuously during a time interval