Page 192 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

174 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

In EPO634567 (1995) two oxygen sensor probes with different response times are used for the
determination of the deterioration state of the catalytic converter. The response times of the
probes may be altered by varying the material of the probes, or by using a catalytic active
mantle which surrounds the probe, or by using different protective sleeves or by changing the
thickness of the sensor elements.
During feedback control the output signals of the two probes oscillate. By comparing the
oscillations of the two signals usehl conclusions about the deterioration state of the catalytic
converter may be drawn when compared to predetermined values. The method allows the
evaluation of the efficiency of the catalytic converter over a wider efficiency range than other
methods.

In the method of DE19506012 (1996), the second (downstream) h probe is installed inside the
catalytic converter at a position close to the inlet of the converter. The volume of the converter
between the inlet of the converter and the second h probe is greater than the volume of the
converter which is necessary for the conversion of the pollutants when the internal combustion
engine is in a stationary mode. In a second embodiment, the downstream h probe is installed
between two monoliths which form the catalytic converter. The method of EPO634567 (1995)
is used for the evaluation of the condition of the converter.

In the method of GB2307557 (1997) an exhaust sensor with a substrate with two sensor
elements for measuring the oxygen partial pressure is installed in or downstream of the
catalytic converter. The exhaust gas in the region of the first sensor element is activated by a
catalytic layer to produce a chemical reaction. The exhaust gas environment of the first sensor
element is separated from the exhaust gas environment of the second sensor element in such a
way that the exhaust gas environment of the second sensor element is not catalytically
activated. The voltage obtained between the first and second sensor elements is used for
monitoring the conversion capability of the catalytic converter.

The method of DE19540673 (1997) uses a downstream oxygen sensor which has a layer of
metal-oxide with slightly catalytic or non-catalytic properties. The electric resistance of the
sensor layer is measured for a value of the aidfuel ratio parameter h that is lower than one and
for a value of the aidfuel ratio parameter h that is higher than one. When the difference of
these resistance values is greater than a reference value, then the converter is considered to be
deteriorated,
The oxygen sensor can be installed downstream of the converter or inside the converter.
The metal-oxide used as a sensor layer is Strontium Titanate (SrTiO3) or Cerium-oxide (Ce02)
or Gallium-oxide (Ga203) or Titanium-oxide (Ti02).