Page 246 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

228 Methods for Monitoring and Diagnosing the Eficiency of Catalytic Converters

0 VDO A dolfschindling A C

The method of DE19545693 (1997) compensates for the uncertainties due to manufacturing
tolerances and aging of the 1-probes used and comprises the following steps:
1) determining the oscillation amplitudes of the output signals of the upstream and
downstream h-probes respectively when the engine airfuel ratio oscillates from lean to rich
and back to lean during a testing period
2) calculating the ratio of the oscillation amplitude of the downstream probe to the oscillation
amplitude of the upstream sensor
3) determining for each probe, after the probe has been changed, an extreme value of its
corresponding output signal. The extreme values for each probe are calculated by
continuously forming differences of subsequent discrete samples of the output signal. The
extreme value becomes a maximum when the sign of a difference changes from positive to
negative and the extreme value becomes a minimum when the sign of a difference changes
from negative to positive
4) correcting the calculated ratio of amplitudes of step 2 by means of the extreme values of
step 3
5) comparing the corrected calculated ratio value to a predetermined threshold
6) determining that the converter is deteriorated when the corrected calculated ratio is greater
than the predetermined threshold

0 Regie Nationale des Usines Renault SA

The method of FR2746142 (1997) comprises the following steps:
1) measuring the rotation speed (N) of the engine and the admission pressure (P) of the engine
airlfkel mixture
2) calculating the flow velocity (V) of the exhaust gas in the catalytic converter in hnction of a
model describing the gas flow in the exhaust pipe, the rotational speed (N) of the engine and
admission pressure (P)
3) measuring the oxygen content of the exhaust gas upstream (u) and downstream (v) of a
catalytic converter by means of an upstream and a downstream oxygen sensor. The values
(u, v) are normalized in a way to be negative or positive depending on whether the engine
air/fbel ratio is lean or rich
4) determining at every time point (t) the maximum quantity of oxygen (y) that can be stored
in the catalytic converter and the quantity of oxygen (x) that is effectively stored in the
catalytic converter. (x) and (y) are determined by making use of mathematical models of the
chemical reactions taking place inside the catalytic converter. The models take into
consideration the kinetics (CI, c2) of the reactions, which depend on the concentrations of
oxidants (Ox) and reducers (Red) of the chemical species that participate in the reactions