Page 221 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Nissan Motor Co. Ltd. 203

5) calculating an amplitude threshold in accordance with a judging result of the engine
operating conditions
6) judging deterioration of the catalytic converter based on the comparison result of the
amplitude ratio and the threshold value

The method JP7310536 (1995) comprises the following steps:
1) judging if the operating condition of the engine is within a domain of deterioration
diagnosis of the catalytic converter
2) comparing the output signals of the upstream and downstream oxygen sensors
3) weight-averaging the comparison result of step 2 by a weight averaging means
4) reducing the weight of the weight averaging means to a prescribed time after the result of
judgment attains the domain of deterioration diagnosis of the catalytic converter (step 1)
5) calculating the reduced weighted mean value
6) determining the efficiency of the catalytic converter based on the calculated result of step 5,
even if the operating condition of step 1 is short.

In the method of JP8128317 (1996), the total quantity of heat of the exhaust system is
calculated from the starting of the engine. The engine aidfbel ratio is feedback-controlled
based on the output of the upstream oxygen sensor. The feedback-control is krther corrected
based on the output signal of the downstream sensor. The ratio of periods of oscillation of the
output signals of the upstream and downstream output signals is calculated. If the total
quantity of heat reaches a prescribed value and the above mentioned ratio of periods does not
decrease, it is judged that the catalytic converter is degraded.

In the method of JP8377468 (1996), the judgment of the deteriorated of the catalytic
converter is prohibited when the measured temperature of the exhaust gases upstream of the
catalytic converter has a value lower than a specified threshold.

The method of JP8177469 (1996) performs the deterioration diagnosis of the catalytic
converter by a first diagnostic means, that is, by comparing the output signals of the two
sensors, during a forced variation of the engine air/fbel ratio from rich to lean and vice versa.
When for any reason this first diagnostic means does not provide reliable results, a second
means is activated to perform the diagnosis. That is, the engine air/fbel ratio is forcibly made
lean, and this state is detected by the upstream and downstream oxygen sensors. Then the
aidfie1 ratio is inverted into a rich state. The time from the moment the rich inversion is
detected by the upstream oxygen sensor to the moment the rich inversion is detected by the
downstream sensor (delay time) is measured and compared with a specific threshold in order to
determine the degradation of the converter.

The method of DE1 9539024 (I 996) comprises the following steps: