Page 51 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Chapter I

Catalytic Converter Functionality Diagnosis by Means of
Oxygen or Air/Fuel Ratio Sensors

This chapter comprises methods of diagnosing degradation of the hnctionality of catalytic
converters by making use of two oxygen or lambda (h) sensors placed upstream and
downstream of a catalytic converter (fig. 12). For reasons of simplicity the two sensors will be
called from here onwards just tpstream and downstream sensor.

Before explaining the principles used by these methods, a few definitions used hrther in the
chapter are given followed by a short explanation of how the injection system of modern
vehicle engines is controlled.
The composition of the combustible airhel mixture fed to the engine must be right to within
close limits. The criterion is the ratio lambda (h)

existing oxygeit cmterrt ac tima1 errgitre air I jtel ratio
A= -
-
stoichiometric oxygen coiiteirt 14.7

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