Page 171 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

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where maM(@;) represents the M largest values of @i within the designated time interval.

This calculation achieves greater diagnostic accuracy than a straight mean value calculation
because the maximum deterioration index occurs at a time when the air-fuel ratio, as detected
and indicated by the output signal of the downstream 02 sensor (fig. 70b), varies about the
stoichiometric point, as shown in fig. 70d.

In the patent application DE4412191 (1994), a method similar to the one described in
DE4243339 (1993) is presented in order to assess the performance of a catalytic converter.
The main difference between the two methods is that in the current method, the deterioration
index a, is corrected for possible abnormalities of the finction of the engine. Such
abnormalities are provoked by misfiring or malfunctioning of a secondary air supply system.
The assessment of the deterioration of the catalytic converter is interrupted in the event of an
important abnormality of the fhction of the engine being logged.

The method of EP0626507 (1994) and US5649420 (1997) comprises the following steps:
I) estimating the temperature of the catalytic converter in function of an engine physical
parameter e.g. the engine intake air mass flow, by means of a map stored in the control unit
of the system
2) suspending the decision ofjudgment on condition that the temperature of the catalytic
converter is outside a predetermined range
3) obtaining a value of conversion efficiency of the catalytic converter by means of two oxygen
sensors installed upstream and downstream of the catalytic converter
4) correcting the conversion efficiency value to a value in a standard state of the catalytic
converter previously set as to the temperature of the catalytic Converter estimated in step 1
5) deciding the deterioration state of the catalytic converter by comparing the corrected
conversion eficiency value with a threshold value
6) deciding that the catalytic converter is deteriorated when the corrected conversion
efficiency value is smaller than the threshold value

The method of EP0641920 (1995) diagnoses the degradation of the catalytic converter and the
upstream airhe1 sensor with high accuracy. The method comprises the following steps:
1) sampling data of an output signal from the upstream and downstream aidfuel sensors at a
rate dependent on engine speed by means of an angular-based data sampler e.g. a sampler
sampling data at a constant rotation angle of the crank shaft
2) judging that the conditions of the catalytic converter monitoring zone are satisfied when the
rotational speed of the internal combustion engine is higher than or equal to a
predetermined rotational speed value, and a catalytic converter temperature estimated from
the rotational speed, and intake air flow rate of the internal combustion engine is higher than
or equal to a predetermined temperature