Page 68 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

50 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

where:

Aa -- a-i
kr. k2 : constants

Fig. 20 shows the case of a deteriorated catalytic converter at different operating conditions.
An idealized time-dependent variation of AI from lean to rich state and vice-versa is shown,
which is symmetrical around “1”. This means that for a new catalytic converter so much
oxygen is stored in the catalytic converter in the lean phase as taken therefrom in the following
rich phase for oxidizing non-combusted exhaust gas components. The thick line corresponds to
the corresponding measured A2 value, which, as it can be noticed at time point T1, changes
indicating that at this point the catalytic converter is exhausted (deteriorated catalytic
converter). At To the catalytic converter is emptied of stored oxygen. The ratio of the
maximum amplitudes of these two E. values defines the variable AZ.

As shown in fig. 20b. the reduction of storage capacity of the catalytic converter leads to a
shift of TI to the let? and consequently to an increase ofA2,,,,x and ofAZ.
Figs. 20c-e show different AZ values which depend on the operating conditions of the catalytic
converter and not necessarily to a change of the state of the catalytic converter. Fig. 20c shows
the case of a low E.lmax due to a long time period of work of the catalytic converter in the lean
region. In fig. 20d the control position is shifted towards rich, while in fig. 20e a higher control
frequency of aidfuel ratio oscillation is used than that of fig. 20a.

In DE4112480 (1992) the engine is first brought into a forced inertia and idling condition. It is
then operated with a lean aidfuel ratio mixture @=I .05) for a certain time (e.g. 5 sec) until
the catalytic converter is completely filled with oxygen and the rotation speed is stabilized (fig.
21a). Then from time point TI onwards, the engine is operated with a A varied in the opposite
sense (rich) so that the upstream E.1 value changes in the corresponding direction. The time
taken between the starting time instant TI till a time instant T3 is measured. T? is the time
instant at which the signal E.2 of the downstream probe changes in the same sense as the
upstream one and exceeds a certain threshold E (figs. 2labc). The aging state is defined by the
parameter AZ which is calculated as follows:

where

At 7:v -7;
k: constant