Page 191 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Siemens Automotive SA - Siemens AG 173

1) controlling the aidfuel ratio of the engine by means of an open loop feedback control during
a cold start-up of the engine (rich air/fbel ratio)
2) heating the EHC by means of a heater during the cold start-up of the engine
3) measuring the temperature of the EHC
4) controlling the engine with a closed-loop feedback control when the temperature of the
EHC passes a certain limit e.g. 350-400 degrees C (fig. 79a)
5) checking the condition of the three-way catalytic converter by using the method of
W09309335 (1993) described above, and if the condition of the catalytic converter is good
then
6) measuring the output signal of the upstream sensor (fig. 79b)
7) measuring the output signal of the downstream sensor (figs. 79c,d)
8) judging whether the EHC is deteriorated (fig. 79d) or not (fig. 79c) depending on the
oscillations present on the signal of the downstream sensor. Significant oscillations of the
signal means that the EHC is in a deteriorated state, taking into account that the three-way
catalytic converter has been already checked to be in good condition.

sensor
voltage
c-
L

I
downstream f I deteriorated EHC
sensor
voltage -
~
time

Fig. 79 (from W09420737)