Page 154 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

I36 Methods for Monitoring and Diagnosing the Eficiency of Catalytic Converters

The method of US5325664 (1994) comprises the following steps:
1) sensing concentration of oxygen contained in exhaust gases emitted from the engine by
means of an upstream sensor
2) sensing concentration of oxygen contained in the exhaust gases downstream of the catalytic
converter by means of a downstream sensor
3) controlling the aidfuel ratio of a mixture supplied to the engine by means of an aidfuel ratio
feedback correction value, the control being responsive to the outputs of the upstream and
downstream sensors (first control)
4) controlling the aidfbel ratio of the mixture by means of the air/fbel ratio feedback correction
value, the control being responsive to the output of the downstream sensor (second control)
5) detecting the temperature of the catalytic converter by means of a temperature sensor
mounted inside the catalytic converter body, or estimating the temperature of the catalytic
converter from an amount of intake air supplied to the engine or from a rotational speed and
a load on the engine
6) effecting changeover fiom the first air/fiel ratio control to the second air/fuel ratio control
for controlling the aidfuel ratio of the mixture, when the detected temperature or the
estimated temperature of the catalytic converter falls outside a predetermined range
7) determining whether the output from the downstream oxygen sensor has been inverted from
a lean side to a rich side or vice versa with respect to a stoichiometric air/hel ratio
8) measuring a first time period elapsed from the time the second air/fbel ratio control causes a
change in the value of the aidfuel ratio feedback correction value from the rich side to the
lean side to the time the output from the downstream oxygen sensor is inverted tiom the
rich side to the lean side, after the changeover has been effected
9) measuring a second time period elapsed from the time the second air/fiel ratio control
causes a change in the value of the aidfie1 ratio feedback correction value from the lean
side to the rich side to the time the output from the second oxygen concentration sensor is
inverted from the lean side to the rich side, after the changeover has been effected
10) comparing the sum of the first and second time periods or an average value thereof with a
predetermined time period and determining that the catalytic converter is deteriorated, when
the sum or the average value is shorter than the predetermined time period. The
predetermined time period is extracted from a table as function of the in oxygen storage
capacity (OX) and the temperature of the catalytic converter.

Fig. 65 shows the change in oxygen storage capacity (OSC) of the catalytic converter with
respect to the temperature of the converter for a new, a qualified and a deteriorated converter.
For new converters the oxygen storage capacity reaches the maximum value at approximately
300 "C, and at higher values of catalytic converter temperatures, it remains unchanged. For a
progressively degraded converter the oxygen storage capacity becomes smaller. The qualified
and the deteriorated converters show a change in the oxygen storage capacity within a
temperature range A-B defined between 300 and 550 "C.