Page 159 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Honda Motor Co. Ltd. 141

this output signal is inverted from a lean (rich) side to a rich (lean) side in a prescribed
reference voltage and a time point at which this output signal is inverted in a reverse direction,
is detected (inversion cycles). The deterioration judgment of the catalytic converter is based on
these inversion cycles.

The method described in JP8144745 (1996) is based on the phase difference of the output
signals of the upstream and downstream sensor during a forced oscillation of the engine aidhel
ratio.

The method of JP8296482 (1996) prevents a deterioration misjudgment of a catalytic
converter due to sulfbr poisoning of the converter. The sulhr poisoning is determined by the
fact that the larger the content of sulhr is, the smaller the maximum output of the downstream
oxygen sensor becomes. If poisoning is detected then the aidfuel ratio feedback is stopped and
the air/fuel ratio is maintained to a rich side for a predetermined time. The sulfbr then is
discharged as oxygen sulfide. After the predetermined time has passed the ordinary detection
of the efficiency of the catalytic converter starts.

The methods of JP9041952 (1997), JP9041953 (1997) and JP9041954 (1997) interrupt the
deterioration judgment of the catalytic converter when respectively
a) an operation parameter of the engine varies beyond a predefined value
b) the amplitude of the output signal of the downstream oxygen sensor is below a
predetermined value
c) the density of oxygen in evaporated fbel discharged from a purge tank to the intake suction
system is high.

The method of US5636514 (1997) comprises the following steps:
1) detecting concentration of oxygen in the exhaust gases by means of an oxygen sensor
installed downstream of the catalytic converter
2) feedback-controlling the engine airhel ratio amount based on the output of the downstream
oxygen sensor
3) detecting deterioration of the catalytic converter based on a value of a catalytic converter
deterioration parameter indicative of a degree of deterioration of the catalytic converter,
and an amount of variation in the air/fbel ratio control amount. The catalytic converter
deterioration parameter is a time period from execution of the proportional term control to
inversion of the output from the downstream oxygen sensor. The amount of variation in the
aidhe1 ratio control amount is:
a) a cumulative value of a difference between two adjacent values of
the air/fkel ratio control amount measured immediately after
proportional term control carried out by the aidfuel ratio control
means, or