Page 96 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

78 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

The method of US5499500 (1996) comprises the following steps:
1) adjusting the he1 delivered to the engine (responsive to the upstream oxygen sensor) to
maintain the engine aidhe1 ratio at a desired value
2) pumping electric current at a gradually increasing amplitude into an electrode of the
downstream exhaust gas oxygen sensor having a non-catalytic electrode until the output of
the sensor changes output states
3) providing an indication of the converter efficiency in relation to the pumping current
amplitude occurring at the change of the downstream sensor output state

The method also allows checking of the condition of the downstream sensor and to retard the
engine ignition timing when the efficiency of the catalytic converter is less than a
predetermined efficiency.

The method of US5522219 (1996) allows the monitoring of the condition of an auxiliary
catalytic converter installed in a bypass channel upstream of the main catalytic converter and
the monitoring of the main catalytic converter as well (fig. 37).

The exhaust gases are enabled to flow through the auxiliary catalytic converter when the
temperature of the exhaust gases is lower than a predetermined value and the exhaust gases are
enabled to flow only through the main catalytic converter when the temperature is over the
predetermined value. This switching of the exhaust gases flow takes place by means an
electronic control of two bypass valves, one installed in the bypass channel and one installed in
the main channel. The method comprises the following steps:
1) establishing test conditions based on the air flow inducted to the engine (see the description
of any of the methods mentioned above)
2) adjusting the engine aidfuel ratio in response to a feedback variable derived from the
oxygen sensor installed upstream of the main catalytic converter
3) correcting the feedback variable in response to a correction signal derived from the oxygen
sensor downstream of the main catalytic converter
4) allowing flow of the exhaust gas through the main catalytic converter at high temperatures
of the gases
5) providing a first ratio of transitions in outputs of exhaust gas oxygen sensors respectively
positioned downstream and upstream of the main catalytic converter
6) allowing flow of the exhaust gas through the auxiliary catalytic converter at low
temperatures of the gases
7) providing a second ratio of transitions in outputs of exhaust gas oxygen sensors respectively
positioned downstream and upstream of the auxiliary catalytic converter
8) indicating degraded operation of the main catalytic converter when the first ratio exceeds a
first predetermined ratio
9) indicating degraded operation of the auxiliary converter when both the second ratio exceeds
a second predetermined ratio and an indication of the air flow inducted into the engine
exceeds a predetermined air flow