Page 161 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Honda Motor Co. Ltd 143

Engines with multiple cylinder groups

The method of US5394691 (1995) is applied to the case of a multiple cylinder bank engine
with an aidfuel sensor (1 a, 1 b) installed in each cylinder bank exhaust pipe upstream of the
catalytic converter and an aidfuel sensor (2) installed in the common exhaust pipe section
downstream of the catalytic converter (fig. 38). The general detection layout is that of fig. 62.
The method comprises the steps:
1) when the engine is in a predetermined operating condition then
I) controlling the aidfuel ratio of an aidfuel mixture supplied into the left group of
cylinders by the use of a first aidfuel ratio control amount based on outputs from
the left upstream oxygen sensor and the downstream oxygen sensor and
11) controlling the aidfuel ratio of an aidfuel mixture supplied into the right group of
cylinders by the use of a second aidfuel ratio control amount based on outputs
from the right upstream oxygen sensor and the downstream oxygen sensor
2) when the engine is in an operating condition other than the predetermined condition of the
previous step then
1) controlling the aidfuel ratio of an aidfuel mixture supplied into one of said left
and right groups of cylinders by using a third air/fiel ratio control amount based
solely on an output from the downstream oxygen sensor and
11) controlling the air/fuel ratio of an aidfuel mixture supplied into the other of said
left and right groups of cylinders by using a predetermined value
3) detecting deterioration of the left or the right catalytic converter, based on an inversion time
period of the output from the downstream oxygen sensor obtained during operation as
described in step 2.

The method of detecting alternately the deterioration of the left or right bank catalytic
converters is similar to the one of US5381657 (1995) described above.