Page 157 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Honda Motor Co. Ltd. 139

5) detecting a value of an inversion period Thch or Tlcan with which the output from the
downstream sensor is inverted from rich to lean and vice versa
6) determining a value of the delay time period Atrich or Atlean in function of the flow rate of the
exhaust gases e.g. by setting the value of the delay time period to a large value for a large
value of the flow rate of the exhaust gases. This happens because normally for large exhaust
flow rates the inversion time period becomes shorter causing inaccuracies to the
determination of the deterioration of the catalytic converter. So by adjusting the delay time
period the inversion time period is also adjusted to make the determination of the catalytic
converter deterioration independent from the exhaust gas flow rate
7) comparing between the value of the detected inversion period ThEh or Tlean and a
predetermined value, and determining that the catalytic converter is deteriorated, when the
detected value of the inversion period is shorter than the predetermined value.

The method of US5386695 (1995) comprises the following steps:
1) calculating an aidfuel ratio correction amount, based on an output from the upstream
aidfuel ratio sensor
2) correcting the aidfuel ratio correction amount, based on the output from the downstream
aidfuel ratio sensor
3) measuring an inversion period with which the output from the downstream air/f%el ratio
sensor is inverted from a rich to a lean state and vice versa
4) detecting deterioration of the catalytic converter, based on the measured inversion period
5) inhibiting deterioration-detecting operation of the catalytic converter when the aidfuel ratio
correction amount falls outside a predetermined range
6) permitting the deterioration-detecting operation of the catalytic converter after a
predetermined time period elapses from a time the air/f%el ratio correction amount returns
into said predetermined range
The method may also comprise a limitation of the aidfuel ratio correction amount within a
first predetermined range when the air/hel ratio correction amount falls outside the first
predetermined range. and inhibiting the deterioration detecting operation of the catalytic
converter when the aidfuel ratio correction amount falls outside a second predetermined range
included within the first predetermined range.

In US5396766 (1995) a method is described to detect abnormalities of an internal combustion
engine based on the detection of a deterioration of the catalytic converter. The method
comprises the following steps:
1) feedback controlling the air/hel supplied to said engine, in response to the output from the
downstream oxygen concentration sensor
2) detecting a repetition period of inversion of the output from the upstream oxygen sensor
3) detecting a degree of deterioration of the catalytic converter, based on: I) detecting a
response time lag of the output of the downstream oxygen sensor (a time interval from the
moment a predetermined control term is generated during the aidfuel ratio feedback control
to the moment the output from the downstream oxygen sensor is correspondingly inverted)
or 11) detecting a repetition period of inversion of the output of the downstream sensor