Page 126 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

108 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

5) interrupting the calculation of the response curve length of step 4 for a predetermined
length of time when the output of the upstream sensor or the amount of change of said
output exceeds a preset value, or/and
6) imposing an upper limit on an absolute value of the integral term or on a gain of the integral
term of step 3 during the deterioration determination, or/and
7) inhibiting the correction of the output of the upstream sensor (step 3) when the
determination of deterioration takes place, orland
8) imposing a limit so that the determination of deterioration is carried out only when the
response curve length or variation amplitude of the output of the upstream sensor is within
a prescribed range, or/and
9) changing the deterioration determination reference value according to the response curve
length or variation amplitude of the output of the upstream sensor.

Fig. 53 shows the principle of embodiment i). If the output VI of the upstream sensor exceeds
a limit value (limits “a”, “b’, fig. 53a) that can cause an excessive response of the output of the
downstream sensor, then the summation of data for determination of the deterioration of the
catalytic converter is interrupted for a prescribed duration of time considering the distance
between the two sensors (the time required until the gas detected by the upstream sensor
reaches the downstream sensor) (fig. 53b).

The method of EP0793009 (1997) comprises the following steps:
1) measuring the oxygen content of the exhaust gas upstream of the catalytic converter by
means of an upstream oxygen sensor
2) measuring the oxygen content of the exhaust gas downstream of the catalytic converter by
means of a downstream oxygen sensor
3) feedback-controlling the engine aidfuel ratio so as to bring the engine aidfuel ratio to a
target air/fuel ratio on the basis of a difference between an output of the upstream oxygen
sensor and a target output corresponding to said target aidfuel ratio
4) determining the lengths of the response curves of the output signals of the upstream and
downstream oxygen sensors respectively for a prescribed period during the aidfuel ratio
feedback control of step 3
5) calculating
a) an amplitude of the output of the upstream sensor, measured in
reference to the target output
b) a period from the time the output of the upstream sensor crosses the
target output to the time this output returns to the target output,
each time an inversion occurs in the output of the upstream sensor
with respect to the target output during the aidfuel ratio feedback
control
6) correcting on the basis of the calculated amplitude and period in step 7 the output response
curve length of the upstream sensor
7) judging deterioration of the catalytic converter on the basis of the lengths of the response
curves of the output signals of the two sensors determined in steps 4 and 6.