Page 234 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

2 I6 Methods for Monitoring and Diagnosing the Eficiency of Catalytic Converters

1) perturbing the oxygen concentration of the exhaust gas entering the catalytic converter such
that the concentration repeatedly alternates between a rich and a lean value
2) counting the number of transitions of the gas leaving the catalytic converter in response to a
predetermined number of transitions of the gas entering the catalytic converter and if a
faulty catalytic converter is indicated then
3) integrating the oxygen concentration of gas leaving the catalytic converter while the oxygen
concentration of gas entering the catalytic converter is less than a first predetermined
oxygen concentration
4) repeating the previous step for a predetermined number of transitions of the oxygen
concentration of the gas leaving the catalytic converter
5) summing the integrals E(AA.)i calculated at steps 3 and 4 to form a first sum
6) correcting the first sum for engine load and for gas flow entering the catalytic converter so
as to form a corrected value
7) subtracting the corrected value from a first predetermined threshold E] to form a first
difference
8) repeating steps 3 to 7 a predetermined number of times and forming a second sum of the
first differences
9) comparing the second sum with a second predetermined threshold EZ and
10) indicating the catalytic converter to be faulty when the second sum exceeds the second
predetermined threshold ~2

Magneti Marelli S.p.A.

The method of EP0715063 (1996) comprises the following steps:
1) detecting the output signals of the A. sensors installed upstream and downstream of the
catalytic converter
2) performing a high-pass filtering of the signals
3) calculating signal time averages (E , E) by means of an integration operation and a
subsequent division for the duration of an integration window of the filtered output signals
4) multiplying the time averages by scaling factors (F,. F2) indicative of the excursions of the
output signals
5) calculating a difference between the time averages multiplied by the scaling factors so as to
generate a deviation signal AZ between the time averages

6) calculating, starting from the deviation signal AZ, an output signal indicative of the
efficiency of the catalytic converter