Page 220 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

202 Methods for Monitoring and Diagnosing the Eficiency of Catalytic Converters

range, it is judged that the temperature of the converter is low and deterioration diagnosis
should be repeated.

The method of JP7189664 (1995) comprises feedback-control of the engine aidfie1 ratio
based on the output signal of the upstream sensor. The feedback-control is corrected by means
of a correction value based on the output of the downstream oxygen sensor. The deterioration
of the converter is derived by comparing the number of inversions of the output of the
downstream oxygen sensor with a threshold value. This threshold may be adjusted by
increasing or decreasing its value and this adjustment depends on said correction value.

The method of JP7189781 (1995) comprises a first feedback-control mode of the engine
aidfuel ratio based on the output signal of the upstream sensor. When it is judged that certain
diagnosis conditions are satisfied the feedback-control switches to a second feedback-control
mode based on the output signal of the downstream sensor. The inversion frequencies of the
oxygen sensors are counted for both feedback-control modes and the deterioration of the
converter is judged by comparing these inversion fiequencies with predetermined values.

The method of JP7243342 (1995) comprises feedback-control of the engine aidfie1 ratio
based on the output signal of the upstream sensor. When certain operating conditions are
achieved, the signal outputs of the two sensors are compared. Whenever the comparison result
reaches a prescribed number, the comparison result is updated and it is weight averaged. The
deterioration of the catalytic converter is detected based on the result of the weighted average.

The method of JP7247830 (1995) comprises feedback-control of the engine aidfie1 ratio
based on the output signal of the upstream sensor. It is judged whether or not the operating
condition of the engine is in one or plural pre-stored catalytic converter diagnosis areas
according to the operating conditions. When the judged result is in such a catalytic converter
diagnosis region then the efficiency of the catalytic converter is assessed by comparing the
output signals of the upstream and downstream sensors. The converter is considered as
deteriorated when the comparison of the output signals shows deterioration in a plurality of
such diagnosis areas.

The method of JP7305623 (1995) comprises the following steps:
1) checking if certain operating conditions are satisfied
2) feedback-controlling the engine air-fuel ratio
3) filtering the output signal of the downstream oxygen sensor based on the signal frequency of
the upstream sensor output signal
4) calculating an amplitude ratio between the amplitude of the filtered signal of the
downstream sensor and the amplitude of the signal of the upstream sensor