Page 65 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey
P. 65
Robert Bosch GmbH 47
k = constant
The deviation M upstream of the catalytic converter compared to value “1” is determined.
This deviation is positive for lean he1 mixture and negative for rich fuel mixture. The oxygen
flow into the catalytic converter is determined then as the product of the computed oxygen
flow to the engine and the above mentioned 1 deviation.
The oxygen storage of the catalytic converter is defined as that oxygen quantity from a
continuous additive oxygen flow being able to be stored by the catalytic converter from an
oxygen free empty state up to an overflow limit, at which the concentration of oxygen in the
exhaust gas leaving the catalytic converter is above a predetermined value.
A simulated downstream value of 1 is then set to “1” for as long as the catalytic converter is
disposed in a filling (emptying) state below (above) an overflow (a depletion) threshold or it is
set to the upstream 1 value when either of the thresholds is crossed. The method thus utilizes a
model of the temporal behavior of oxygen flows.
The method can be extended in measuring the actual 12 value, modifying the defined oxygen
storage volume of the converter until the simulated temporal mean value of 12 corresponds
with the actual 1, value and utilizing the modified oxygen storage volume as a measure of the
state of aging of the converter.
In DE41 12478 (I 992) a controlled oscillation of the 11 value from rich to lean and vice-versa
takes place (fig. 19a). When the downstream probe shows a significant variation of 12 (fig.
19b,c), then the time integrals of the products of the exhaust gas flow through the catalytic
converter times 1, and times 12 are formed:
T2
As a measure of the performance loss of the catalytic converter, either the difference between
said integrals or the quotient of said difference and one of said integrals is used:
