Page 238 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

220 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

driver about the malhnctioning of the catalytic converter. The data can also be handled in a
garage by a specialized person in order to decide whether or not the catalytic converter must
be replaced.

FIA T A Ut0 S.P. A.

In the method of EP0588123 (1994) and US5627757 (1997) the following steps are
comprised:
1) detecting the aidfuel ratio content of the exhaust gases upstream and downstream of the
catalytic converter by means of two lambda sensors
2) calculating the moving average of each of the two signals VI, V2. The variable moving
average v of a signal C’ is obtained from three successive values of the variable measured
at the points, or at the moments k-2, k-1 and k:

where k = [2 - 001
3) calculating the differences I),, 1j2 between the instantaneous values of the sensor output
signals and the values of the moving averages

D, = VI - v, I), = v, - v,

4) generating signals.f(D) relating to the difference between the instantaneous values and the
moving averages. These signals f(D) are generated by squaring and integrating the
differences I1 and by calculating their mean quadratic deviations for the period in question
5) calculating an output signal A k’ indicative of the efficiency of the catalytic converter on the
basis of the difference signals or signals derived therefrom. This signal can be one of the
ratio and the difference between the difference signals or signals derived therefrom

or AV= f(D,) - f(D,)