Page 115 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Toyota Motor Co. Ltd. 97

2) measuring the aidfuel ratio downstream of the catalytic converter by means of a
downstream sensor
3) feedback controlling the aidfuel ratio of the engine by a feedback control based on the
output signal of the upstream air/fuel ratio sensor
4) changing over the aidfie1 ratio of the exhaust gas flowing into the catalyst, from a lean
adfuel ratio to a rich aidfuel fuel ratio hlrich (fig. 48)
5) calculating a length of time ATri,h which is necessary for the catalyst to release the oxygen
stored therein after the air/fiel ratio is changed over to said rich aidfuel ratio. During time
L\Tfich the aidfuel ratio of the downstream sensor is maintained at the stoichiometric value
&=I (fig. 48)
6) determining a degree of deterioration of the catalyst after said length of time has elapsed
7) determining said degree of deterioration of the catalyst from a difference AI.,,& between the
aidfie] ratio hlrich detected by said first aidfuel ratio sensor and the aidfie1 ratio h2rich
detected by said second aidfuel ratio sensor when compared to predetermined data

In US5282383 (1994) the method comprises the steps of
1) adjusting an air/fiel ratio correction factor in accordance with the output of the upstream-
side airhel ratio sensor so that an aidfie1 ratio is controlled at a predetermined target
aidfuel ratio that is equal to the stoichiometric aidfuel ratio, the aidfuel ratio changing from
the rich state to the lean state, or vice versa
2) monitoring fluctuations in the output of the downstream-side air/fuel ratio sensor around a
predetermined reference voltage
3) determining that the degree of deterioration of said catalyst is such that a diagnostic
procedure is required when the number of these fluctuations during a predetermined interval
is greater than a predetermined value
4) shifting the aidfie1 ratio that is controlled in accordance with said adjusting step to an
aidfuel ratio that is not equal to the stoichiometric aidfuel ratio (e.g. lean)
5) determining whether said catalyst converter has deteriorated in accordance with the output
of the downstream-side airhel ratio sensor when
a) the number of fluctuations is greater than a predetermined value, or
b) the difference between the number of upstream-side fluctuations and
the number of downstream-side fluctuations, when the number of
upstream-side fluctuations is greater than a first predetermined
value, is greater than a second predetermined value, or
c) a ratio of the number of downstream-side fluctuations to the number
of upstream-side fluctuations is greater than a predetermined value,
which is about ” 1 ‘I.

The adjusting step I comprises the step of
a) increasing the aidfuel ratio correction factor when the aidfuel ratio
changes from the lean state to the rich state, and decreasing the
airhiel ratio correction factor when the aidfuel ratio changes from
the rich state to the lean state. or