Page 241 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Other Methods 223

the left bank of cylinders. The detected output signals of the downstream sensor and the left
bank upstream oxygen sensor are then used for the assessment of the secondary catalytic
converter installed in the left exhaust branch as well as of the main catalytic converter. The
same procedure is repeated for the right bank of cylinders.

The method of JP8135432 (1996) is applied in an engine layout with two cylinder banks
similar to the one described in the JP7063045 (1995) (fig. 38). First it is evaluated which of
the two upstream sensors has the fastest response (e.g. the left bank upstream oxygen sensor).
The ratio of the number of reversals of the output signal of the upstream sensor with the fastest
response and of the number of reversals of the output signal of the downstream sensor is then
formed. The deterioration diagnosis of the catalytic converter is carried out by judging whether
this ratio is lower than a specific threshold.

FE V Motorentechnik GmbN & Co.

The method of DE4019572 (1992) monitors the fknctionality of a catalytic converter, engine
misfiring and/or variable injection. It uses two sensors placed in the exhaust path. One of the
sensors has a catalytic activity. The difference in the outputs of the signals of the two sensors,
provoked by the change in temperature when the HC/air mixtures react with the catalyst of one
of the sensors, gives an indication of the condition of the converter and the misfiring of the
engine. Oxygen sensors can be installed upstream and downstream of the converter.

Hyundai Motor Co.

The method of W09628646 (1996) comprises the following steps:
1) determining if a certain time of operation of the engine has elapsed, in order to prevent an
erroneous judgment
2) setting rich and lean adjusting parameters ki for an engine aidfuel ratio after the certain
time has elapsed
3) calculating virtual oxygen content sensing signals relevant to a predetermined period of time
by using the formula:

where,
AM: amplitude of the signals set in accordance with an automobile state,
.f: frequency of the signals set in accordance with the automobile state
11: a time variable and