Page 256 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

238 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

activate them as fast as possible. A failure of the heating system of such converters might take
place (e.g. due to corrosion of the lead wires of an electric heater) and contributes to the
complexity of detecting deterioration of a heated converter. So, more sophisticated methods
than just measuring the temperature difference between the two sensors are necessary to assess
the hnctionality of a catalytic converter.

In the methods of the ~O’S, simple temperature sensors are used to monitor deterioration of the
catalytic converter. The signals are fed to simple instrumentation that can calculate the
difference in temperature between inlet and outlet and produce a warning signal when this
difference exceeds certain ranges.
In most modern OBD methods a control unit (computer) is used to assess the functionality of
the catalytic converter. The control unit receives the output signal(s) of the temperature
sensor(s) plus information concerning the operation conditions of the engine e.g. engine load,
cooling water temperature, intake air flow etc. The control unit processes all the input and
produces a warning signal in case a degraded catalytic converter is detected (fig. 100). The
control unit may comprise calculation means, integrators, comparators, storage means etc.
Signal filtering means, A/D converters and other necessary equipment may be included in the
monitoring system.

For simplicity reasons, the two temperatures sensors mounted upstream and downstream of
the catalytic converter will be called from here onwards just upstream and downstream
temperature sensor.

In the case of indirect measurement of the temperature of the exhaust gases, the control unit
receives different engine parameters and calculates the temperature of the catalytic converter
based on this piece of information.