Page 252 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

234 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

efficiency. Heating systems raise the temperature of an aged catalytic converter to reduce this
deterioration in emission conversion (see [22]).

The diagnosis of catalytic converters by measuring the temperature of the exhaust gases
becomes very important nowadays. In [22], temperature sensors are used to verie catalytic
converter efficiency diagnosis evaluated by means of the dual-oxygen sensor technique. The
results have shown that dual oxygen-sensor measurements for catalytic converter efficiency
become questionable with introduction of ULEV standards.

In W09420738 (1994) it is claimed that it is difficult to produce a signal qualitatively
representative of the efficiency of a catalytic converter based on the output signals of an
upstream and a downstream airhe1 sensor and this presents the vehicle manufacturer with a
serious dilemma. If a high efficiency threshold is set, then the driver will be frequently given
false warnings of failure of the catalytic converter and apart from the nuisance to the driver this
could result in the warning signals being totally disregarded when the alarm is genuine. On the
other hand, if a low threshold is set and the vehicle should fail to comply with the legislative
requirements then the manufacturer could face serious financial penalties. For these reasons, it
is proposed to use temperature measurement techniques to assess the fimctionality of a
catalytic converter.