Page 106 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

88 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

In US5134847 (1992) the technique proposed comprises the following steps:
1) adjusting an aidfuel ratio in accordance with the outputs of the upstream and downstream
oxygen sensors
2) detecting whether the catalytic converter is deteriorated in accordance with an output of the
downstream sensor while the aidfuel ratio is adjusted by an air/fbel correction amount. The
criteria of deterioration proposed are:
a) when the amplitude of the output signal from the downstream oxygen sensor is
larger than a predetermined value, or
b) when the period of the output signal of the downstream oxygen sensor is smaller
than a predetermined value, or
c) when the ratio of periods of the output of the upstream oxygen sensor to the
period of the output of the downstream oxygen sensor is larger than a
predetermined value.
3) detecting whether the upstream sensor is a normal state in accordance with the output of
said sensor
4) prohibiting the detection of state of the catalytic converter efficiency when the upstream
oxygen sensor is in an abnormal state.

In US5165230 (1992) the following steps are comprised:
I) calculating an aidfuel ratio feedback correction amount in accordance with an output of the
upstream sensor. The correction procedure skips down said aidfuel ratio feedback
correction amount by a leati skip amount when an output of the upstream sensor is switched
from a lean side to a rich side, gradually decreases the aidfuel ratio feedback correction
amount by a lean integration amount when the output of said upstream sensor is on the rich
side, skips up the air/fbel ratio feedback correction amount by a rich skip amount when the
output of said upstream sensor is switched from the rich side to the lean side, and gradually
increases said aidfuel ratio feedback correction amount by a rich integration amount when
the output of said upstream sensor is on the lean side. The correction procedure may also
include rich and lean delay means for delaying the output of the upstream sensor when
switched from lean to rich aidfuel and from rich to lean air/fuel respectively.
2) controlling the air/fbel ratio to a predetermined target aidfuel ratio on the basis of said
aidfuel ratio feedback correction amount
3) determining whether or not an engine running state is a predetermined engine running state
4) reducing a rate of change of said aidfuel ratio feedback correction amount when it is
determined that the engine running state is said predetermined engine running state. The
reduction procedure reduces the lean and rich skip amounts and/or the lean and rich
integration amounts by multiplying them with certain coefficients.
5) determining that the condition of the three-way catalyst has deteriorated by utilizing an
output of the downstream aidfuel ratio sensor when the engine runs in said predetermined
state. The criterion of deterioration is whether the number of reversions of the output of the
downstream sensor per unit time is larger than a predetermined number.
As shown in fig. 42 for the case of a slightly deteriorated converter, since the rate of change of
the aidfuel ratio feedback correction amount becomes small, the rate of change of the voltage