Page 61 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey
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Chapter 1.1
Robert Bosch GmbH
In DE2328459 (1975) the company Robert Bosch GmBH proposed one of the earliest
methods for monitoring a catalytic converter by installing two oxygen sensors, one upstream
and one downstream of the converter. A warning signal is produced when a voltage difference
indication between the downstream and the upstream sensors of the oxygen concentration in
the exhaust gases as a function of aidfuel ratio 1 passes over a predetermined threshold (fig.
15, lines 28,29), showing that the catalyst cannot oxidize anymore the impurities and must be
replaced.
The indication of the sensor can also be corrected for differences in temperature between the
upstream and the downstream side of the catalytic converter (US4007589 (1977)). The
disadvantage of the method is that it is accurate only in certain operational domains, which are
quite difficult to define.
In DE2444334 (1976) an oxygen concentration sensor upstream of the catalytic converter
sends a voltage change signal to a monitoring electronic system at certain operating conditions.
If within a predetermined time interval a similar downstream sensor also changes its output
voltage, then that is an indication of a too short time difference in this change, meaning that the
catalytic converter is defective.
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