Page 144 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

126 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

1) detecting whether an aidfuel ratio is rich or lean with respect to the stoichiometric ratio by
means of the upstream and downstream oxygen sensors
2) establishing certain conditions of engine operation
3) detecting whether the amplitude of the output signal of the downstream oxygen sensor is
higher than a reference value
4) determining whether deterioration of the catalytic converter is likely to be present on the
basis of the amplitude detection results of step 3 and then
5) adjusting the response of the upstream sensor to a preset value by adjusting the aidfuel
feedback control frequency to a target setting (slower response than the one at non-testing
conditions)
6) summing a response delay time occurring within a specified period in the downstream
sensor after adjusting the response of the upstream sensor
7) finally determining whether deterioration is present in the catalytic converter by comparing
the sum of step 6 with a reference value

The method of GB2297847 (1996) comprises the following steps:
1) feedback-controlling the engine airhiel ratio by means of the upstream h sensor
2) checking whether the period of inversion of the downstream oxygen sensor exceeds a
predetermined time and determining then from this check that the three-way converter is
activated
3) estimating the quantity of heat required from the start-up of the engine to the time of
activation of the catalytic converter. The quantity of heat is obtained from the accumulated
engine intake air quantity during the period of step 2 or from the quantity of fuel injected
4) determining whether the catalytic converter has deteriorated from the calculated quantity of
heat

The method of US5622047 (1997) comprises the following steps:
1) detecting the aidfuel ratio upstream of the catalytic converter by means of an upstream
air/hel sensor
2) detecting the airhel ratio downstream of the catalytic converter by means of a downstream
air/hel sensor
3) controlling a rate of fuel injection into the engine in response to a result of the detected
upstream aidfuel ratio, and varying the aidfuel ratio of the exhaust gas flowing into the
catalytic converter around a predetermined aidfuel ratio at an amplitude and a period
4) correcting and increasing at least one of the amplitude and the period of said varying of the
aidfuel ratio
5) increasing a degree of said increasing of at least one of the amplitude and the period in
cases where the detected downstream aidtiel ratio does not vary although at least one of
the amplitude and the period is corrected and increased, and when the detected
downstream aidfuel ratio varies
6) determining a condition of deterioration of the catalytic converter in response to the
amplitude and the period which occur as result of said variation