Page 222 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

204 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

1) detecting the aidfuel ratio of the exhaust gases upstream and downstream of the catalytic
converter by means of an upstream and a downstream sensor
2) estimating a basic engine fuel injection quantity in function of an operating parameter of the
engine
3) determining a feedback aidfuel ratio correction coefficient based on the output signal of the
upstream aidfuel sensor
4) correcting the basic fuel injection quantity by means of the feedback correction coefficient
5) comparing the oscillation state of the output signals of the aidfuel sensors from rich to lean
and vice versa with decision standards, and assessing the performance of the catalytic
converter from this comparison. The ratio of oscillation frequencies or the phase shift
between the upstream and downstream sensor output signals are the criteria for judging the
performance of the catalytic converter.

The method of 085557929 (1 996) comprises the steps of
1) diagnosing the deterioration of the catalytic converter (any of the above mentioned methods
can be used)
2) detecting a predetermined engine operation condition at which the temperature of the
catalytic converter becomes high
3) calculating a first time period at which a control for stopping fuel to be supplied to the
engine is made
4) calculating a second time period at which a control for increasing an amount of fuel to be
supplied to the engine is made
5) avoiding an operation of diagnosing of step 1, when a deviation between the first and
second time periods is not less than a predetermined value under the predetermined engine
operating condition of step 2.

The method of JP8246853 (1996) comprises the following steps:
1) operating the engine with a rich air/hel ratio
2) switching the air/hel ratio from the rich value to a lean one
3) measuring a first delay time, that is the time needed for the downstream oxygen sensor
output signal to be reversed from the rich to the lean state, after the upstream sensor output
signal has been reversed from the rich to the lean state
4) switching the air/fuel ratio from the lean value to the previous rich one
5) measuring a second delay time, that is the time needed for the downstream oxygen sensor
output signal to be reversed from the lean to the rich state, after the upstream sensor output
signal has been reversed from the lean to the rich state
6) calculating the dispersion of a difference in response of first and second delay times
7) assessing the efficiency of the catalytic converter by comparing the dispersion with a
predetermined threshold