Page 110 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

92 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

When only the area of the downstream sensor is used in order to determine the efficiency of
the catalytic converter, then the predetermined reference value, based on which said area of the
output signal response curve of the downstream aidfuel ratio sensor is calculated, is:

1) a minimum value of the output signal of the downstream aidhe1 ratio sensor during
each oscillation cycle thereof and the three-way catalyst has deteriorated when said
area is more than a predetermined value, or
2) a predetermined constant value, and the three-way catalyst has deteriorated when
said area is larger than a predetermined first value and smaller than a predetermined
second value

Similar predetermined reference values are calculated for the upstream sensor when the ratio of
areas is used as a criterion of efficiency detection.
An embodiment of this method is shown in fig. 44. Fig. 44e shows the forced voltage
oscillation around h=l of the upstream sensor fiom rich to lean and vice versa, whereas figs.
44a-d show the corresponding variations of the downstream sensor for different efficiencies of
the catalytic converter. The mean value of the downstream sensor does not oscillate around
h=l by influencing the operation characteristics of the sensor or by influencing the fuel
injection properties of a certain engine cylinder.
In this case the zero voltage line is considered as the predetermined reference value of step 2.
The area under the oscillation line of the sensor becomes maximum when the catalytic
converter works normally and the sensor works towards the rich side region (fig. 44c). The
area under the oscillation line becomes minimum when the catalytic converter works normally
and the sensor works towards the lean side region (fig. 44d). When the catalytic converter is
degraded (figs. 44a,b) the area under the oscillation curve always lies between the maximum
value of fig. 44c and the minimum value of fig. 44d.

In EP0547326 (1993) the following steps are considered:
1) generating an output signal corresponding to m airlfuel ratio of the exhaust gas upstream of
the catalytic converter by means of the upstream sensor
2) generating an output signal corresponding to an aidfuel ratio of the exhaust gas
downstream of the catalytic converter by means of the downstream sensor
3) feedback controlling the aidfuel ratio of the engine by a feedback control based on the
output signal of the upstream aidfuel ratio sensor
4) calculating the lengths of the output signal response curves of the upstream and
downstream aidtire1 ratio sensors when the engine is feedback controlled
5) forming the ratio of the length of the downstream sensor signal to the length of the
upstream sensor signal
6) calculating the areas surrounded by the output signal response curves and reference lines of
said upstream and downstream air/fuel ratio sensors when the engine is controlled by said
feedback control means
7) forming the ratio of the area of the downstream sensor signal to the area of the upstream
sensor signal