Page 208 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

190 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

1) calculating individual integration values (S) corresponding to areas enclosed by output
signals of the upstream and downstream oxygen sensors and designated signals (fig. 85),
wherein a designated signal for the upstream sensor is variable in accordance with the
output signal of the downstream sensor, and the integration values are calculated for areas
both above and below an associated designated signal. The designated signals are corrected
by a hysteresis factor
2) determining variable, individual time periods (T) between which the output signals reverse
polarity with respect to the designated signals
3) calculating a parameter (C) for determining deterioration of the catalytic converter based on
one of mean values and summation values of one of the integration values and the polarity
reversal time periods in a predetermined time
4) determining deterioration of the catalytic converter by comparing said parameter with a
predetermined value (CS,)
5) issuing an alarm when the catalytic converter is determined as deteriorated

More specifically the parameter (C) can be calculated by one of the following methods:
1) The sum of individual areas SZ of fig. 85 is calculated within a time interval for the signal of
the downstream sensor. The sum of individual periods TZ within the above mentioned time
interval is calculated as well. The average value of areas Sz and periods TZ is formed and the
parameter (C) is defined as

2) The parameter (C) is calculated as the ratio of area SI of the upstream sensor to the area SZ
of the downstream sensor

3) In a third case the following equation defines the deterioration parameter

4) The deterioration of the catalytic converter is also checked by the formula