Page 122 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

I04 Methods for Monitoring and Diagnosing the Eficiency of Catalytic Converters

In a second embodiment of the method the following further steps are considered:
a) calculating a first integral value obtained by a temporal integration of the difference between
the maximum and minimum values in each cycle of fluctuation of the output signal of the
upstream air/hel sensor
b) calculating a second integral value obtained by a temporal integration of the difference
between the maximum and minimum values in each cycle of fluctuation of the output signal
of the downstream aidfuel sensor
c) calculating lengths of the output signal response curves of the two sensors
d) estimating the length of the output signal response curve of the downstream sensor in an
imaginary condition in which the catalytic converter is considered to be removed from the
exhaust pipe by multiplying the length of the output of the upstream sensor (step (c)) and
the ratios between the calculated first and second integral values (steps (a) and (b))
e) calculating the degree of deterioration of the catalytic converter based on the estimated
length of the output signal of the downstream sensor and the length of the output signal of
the downstream sensor as calculated in step (d).

The method of EP0748927 (1996) comprises the following steps:
1) detecting the aidfuel ratio upstream of the catalytic converter by means of an upstream
air/fuel sensor
2) detecting the air/fUel ratio downstream of the catalytic converter by means of a downstream
aidfuel sensor
3) feedback controlling the engine airhel by means of the output of the upstream sensor in
such a manner, that the aidfuel ratio of the exhaust gas flowing into the catalytic converter
becomes a predetermined ratio
4) determining the deterioration of the catalytic converter based on the output signal of the
downstream air/fUel sensor during the feedback control
5) detecting the flow rate of the intake air drawn to the engine
6) inhibiting the operation for determining the deterioration of the catalytic converter of step 4
when the flow rate of intake air drawn to the engine is out of a predetermined allowable
range
7) setting the allowable air flow range in accordance with:
a) the temperature of the catalytic converter, or
b) the engine speed
In this way the method takes into account the fact that a catalytic converter has different
oxygen storage capacities at e.g. different temperatures of the catalytic converter.

The method of EP0756072 (1 997) comprises the following steps:
1) grasping an ability value in relation with a current purification ability of the catalytic
converter. The ability value can be based a) on a current oxygen storage ability or b) on a
current HC purification ability of the converter
2) grasping a varying amount of the ability value grasped in step 1. The varying amount of the
ability value can be expressed