Page 63 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Robert Bosch GmbH 45

The ratio Ji is used as an indication of the conversion rate of the catalytic converter (fig. 17).
The catalytic converter is considered operational for a value of R<0.6. Mer this point the
catalytic converter is considered as aged. The measured value of the ratio R is also used for
controlled modification (reduction) of the amplitude of controlled oscillation with decreased
conversion rate of the catalytic converter (compensation of aging of catalytic converter).

I -

0.6 -

0.2
time

Fig. 17 (from DE4024210)

In DE4039762 (1992) the evaluation of the catalytic converter is based on the signal overshoot
of the downstream sensor when the air/fbel ratio supplied to the engine changes from lean to
rich within a predetermined time period. Fig. 18a (leR part) shows the course of the upstream
sensor output signal during this change, while fig. 18b shows the corresponding output signal
of the downstream sensor. When the overshoot OS exceeds a predetermined amplitude the
catalytic converter is considered as aged. Alternatively when the air/t%el ratio is regulated from
rich to lean within a predetermined time period (fig. 18% right part), the amplitude of the back-
shoot BS of the output signal of the downstream sensor is used as the evaluation parameter of
catalytic converter aging (fig. 1812).