Page 140 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

I22 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

The method of US5097700 (1992) allows accurate detection of the catalytic converter
irrespective of the deterioration of the downstream oxygen sensor itself. This can be achieved
as follows:
1) detecting a concentration of oxygen of the exhaust gas by means of the downstream sensor
2) comparing a predetermined judgment threshold with an amplitude of the output signal
therefrom to detect, on the basis of the comparison result, whether the catalytic converter is
in a deteriorated state
3) relatively correcting said predetermined judgment threshold with respect to the output
signal from said gas concentration sensor means I) on the basis of the output signal
therefrom under a predetermined rich or lean aidfuel ratio state or 11) on the basis of the
difference between the output signal therefrom under the condition that an aidfuel ratio for
said internal combustion engine is in a predetermined rich state and the output signal
therefrom under the condition that the aidfuel ratio is in a predetermined lean state.

The predetermined rich state is taken when an output of the internal combustion engine is
increasing and the predetermined lean state is taken when supply of a fuel to said internal
combustion engine is stopped.

In the method of DE4322341 (1994) the saturation of a gas (e.g. CO or HC) entering the
catalytic converter is checked and comprises the following steps:
1) monitoring the exhaust gases with an oxygen sensor installed downstream of the catalytic
converter
2) driving the engine with a h sensor installed upstream of the catalytic converter. The sensor
drives the engine with a correction feedback amount in a given direction away fiom the
stoichiometric value (h= 1 )
3) increasing the correction feedback amount andlor the correction feedback time interval, in
order to execute a variation process of the airhel ratio towards saturation of the catalytic
converter
4) judging whether the catalytic converter is saturated and when saturation is detected by
means of the downstream sensor then
5) calculating the saturation amount of a gas absorbed from the catalytic converter (e.g. CO or
HC) and checking if this saturation amount is out of a predefined range indicating the need
of replacement of the catalytic converter

The method of US5280707 (1994) comprises the steps:
1) measuring the airhel ratio of the exhaust gases upstream of the catalytic converter
2) measuring the aidfuel ratio of the exhaust gases downstream of the catalytic converter
3) calculating, in accordance with an output signal from the upstream and/or downstream
oxygen sensors, an air/fbel ratio correction coefficient with which the aidfbel ratio is
corrected so as to be in the neighborhood of the theoretical air/fbel ratio