Page 87 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Ford Motor Co. - Ford France SA - Ford Werke AG - Ford Motor Co. Ltd. 69

as finctions of engine speed/load conditions. If the measured frequency is higher than the
stored one, the catalytic converter is considered to be degraded.

In W09303358 (1 993) two differentially catalyzed EGO sensors replace the conventional
EGO sensor downstream of the catalytic converter (fig. 32). One of the sensors is highly-
catalyzed while the other one is low or non-catalyzed. As it can be noticed from fig. 32, there
is an important change of the downstream highly-catalyzed sensor signal depending on whether
the catalytic converter is good or bad.

The low or non-catalyzed sensor signal shows smaller amplitude variations, because the sensor
cannot equilibrate the gases in the case of a bad converter and the sensor is consequently
saturated.

%iICrt+Y ' ' 6lGHLY bW10 NDN
CATAL TIC CATALYTIC CATAWTIC
UPSTREAM EGO DOWNSTREAM DWNSREAM
SENSOR EGO SENSOR EGOSENSOR

Fig. 32 (from W09303358)

ffhe engine is operated under closed-loop control by making use first of the downstream
highly-catalyzed sensor and then by making use of the downstream low or non-catalyzed