Page 285 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Volkswagen AG 267

5) comparing the calculated and the measured temperature values downstream of the catalytic
converter
6) judging that the catalytic converter is deteriorated when the difference of the two
temperatures is higher than a certain value

The method of G62295033 (1996) comprises the following steps:
I) measuring the temperature of the exhaust gases upstream and downstream of the catalytic
converter by means of two temperature sensors
2) filtering the output signal of one of these temperature sensors
3) forming an actual temperature difference value ATlzf between the filtered signal of one of
the sensors and the unfiltered signal of the other sensor
4) reading out a desired temperature difference AT12 from a predetermined map. The map uses
the engine speed, the exhaust gas temperature and the current fuel injection quantity of the
engine as input variables
5) filtering value AT12 read out in a desired value filter and receiving value (ATlzf)’
6) reading out a current time window from a time characteristic map as a function of the
exhaust gas temperature
7) triggering a monitoring signal when the value (AT12f)’ becomes higher than AT12f for the
duration of the current time window.

temperature

time

Fig. 1 I8 (from GB2295033)

Fig. I I8 shows the variation of temperature TI measured upstream of the catalytic converter,
the variation of temperature T2 measured downstream of the catalytic converter and the
variation Tlf of the filtered variation of temperature TI.