Page 95 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

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6) indicating degradation in efficiency of the converter when at least both said first monitoring
ratio and said second monitoring ratio are beyond pre-selected values during said test period
7) by hrther generating a third monitoring ratio related to a ratio of an integration of said
feedback variable to an integration of the downstream exhaust gas oxygen sensor output
during this test period and wherein said indicating step 6 is also responsive to said third
monitoring signal.

In US5404718 (1995) the method consists of the following steps:
1) providing a test cycle each time the engine has completed operation within each of a
plurality of inducted air flow ranges for at least a minimum duration in each of said air flow
ranges. Said minimum duration comprises a pre-selected number of transitions from a first
state to a second state of the output signal of the upstream sensor while the engine operates
in one of said flow ranges.
2) integrating an output of the upstream oxygen sensor over said test cycle to generate a
feedback variable
3) controlling fuel delivery to the engine in response to this feedback variable
4) integrating an absolute value of the feedback variable over said test cycle to generate a first
control signal
5) integrating a rectified output of the downstream sensor over said cycle to generate a second
control signal
6) calculating a ratio of said second control signal to said first control signal to determine
catalytic efficiency by comparing this ratio to a predetermined one.

In US5390490 (1995) the method follows the steps mentioned below:
1) detecting the oxygen content of the exhaust gases by means of the upstream sensor
2) detecting the oxygen content downstream of the catalytic converter by means of the
downstream sensor
3) maintaining the airlfhel mixture fed to the engine at a first bias value
4) calculating a first time value, which is indicative of the time required for the upstream
sensor to detect the exhaust gas produced from the combustion of the aidfuel mixture
maintained at the first bias value
5) calculating a second time value, which is indicative of the time required for the downstream
sensor to detect the exhaust gas produced fiom the combustion of the airltiel mixture
maintained at the first bias value
6) estimating the efficiency of the catalytic converter from pre-stored data by making use of
these first and second time values. If the efficiency is outside a predetermined range then the
catalytic converter is considered as exhausted.
Additionally, the method allows a repetition of steps 4 and 5 for calculating a third and a fourth
time value when the exhaust gas produced from the combustion of the aidfuel mixture is
maintained at a second bias value. Then the efficiency of the catalytic converter is additionally
responsive to said second bias value and to said third and fourth time values. In this case the
aidfuel mixture is altered abruptly from the first to the second bias value.