Page 295 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Chapter 2.6

Siemens AG - Siemens Automotive SA - Bayerische

Motoren Werke AG - Mercedes Benz AG

In the method of EP0262558 (1988), which is applied to a series of catalytic converters used
in the exhaust system of industrial applications, a reducing gas (NH? or CO) is injected in the
exhaust gases to promote NO, reduction on the catalytic converters. Temperature sensors are
provided upstream and downstream of individual layers of the catalytic converters, and a
differential amplifier coupled with the sensor reads the difference in temperature among the
layers to provide information about the efficiency of the catalytic layers by comparing the
actual readings with predetermined values.

In the method of FR2690203 (1993) a sharp enrichment of the exhaust gases with unburned
fuel is produced by releasing the accelerator pedal without cutting the fie1 feed to the engine.
This produces an exothermic reaction of the oxidation of the hydrocarbons present in the
exhaust and a release of heat in the catalytic converter. The detection of this heat upstream and
downstream of the catalytic converter is a measure of the deterioration state of the catalytic
converter. In order to measure the temperature downstream of the catalytic converter a special
oxygen sensor is used. The sensor has a film of dioxide of titanium deposited on a support and
it is equipped with a heating resistance and means of regulation of its temperature to a
predetermined temperature. The intensity of the electric current used for heating the resistance
permits measurement of the temperature of the exhaust gases.

277