Page 158 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

140 Methods for Monitoring and Diagnosing the EWciency of Catalytic Converters

4) setting a reference value for determining an abnormality in the engine, based on the degree
of deterioration of the catalytic converter e.g. by setting this reference value to a value
capable of detecting a lower degree of the abnormality in the engine as the detected degree
of deterioration of the catalytic converter is higher
5) comparing between the reference value and a value based on the repetition period of the
output of the upstream oxygen concentration sensor detected in step 2.
6) determining the abnormality in the engine, based on a result of said comparison

The method of US5416710 (1995) comprises the following steps:
1) obtaining a first signal and a second signal based on respective signal outputs fiom the
upstream and downstream aidfuel ratio sensors when the fuel supply to the engine is
increased (high load)
2) obtaining a third signal and a fourth signal based on respective signal outputs from the
upstream and downstream aidfuel ratio sensors when the fuel supply to the engine is
interrupted (fUel cut)
3) calculating
a) a first area defined between the waveform of the signal outputted
from the upstream aidfuel ratio sensor and the first and third signals
with
b) a second area defined between the waveform of the signal outputted
from the downstream air/fbel ratio sensor and the second and fourth
signals
4) correcting at least one of the first and second areas by a ratio calculated between a
difference between the first and third signals and a difference between the second and fourth
signals while the engine is steadily cruising
5) comparing
a) a difference between the first area and the second area with a
predetermined reference value or
b) a ratio between the first area and the second area with a
predetermined reference value
6) determining deterioration of the three-way catalyst when said difference or said ratio of
areas are smaller than said predetermined reference values

The explanation of the method is similar to the one of fig. 63.

The method of US5437154 (1995) is similar to the one of US5396766 (1995) described
above. The method detects misfiring (abnormality) of an internal combustion engine based on
the detection of a deterioration of the catalytic converter. All steps of US5395766 (1995) are
also applied in this method so they are not repeated here

In JP8144744 (1996) the judgment of deterioration of the catalytic converter is based on the
output signal of the downstream oxygen sensor only. A time between a time point at which