Page 240 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

222 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

of times in this diagnostic region. The mean value of this ratio is then calculated and the
deterioration of the catalytic converter is based on the comparison of this mean value to a
predetermined threshold .

In JP8303233 (1996) a predetermined diagnostic region for assessing the fbnctionality of the
catalytic converter is defined, which is based on operation parameters of the engine. During
operation of the engine, this region is changed according to the outside air temperature.

In JP8303234 (1996) the diagnosis takes place within a predetermined diagnostic region. The
engine aidfie1 ratio is feedback-controlled by performing weighed averaging of the output
signal of the downstream sensor in accordance with an assumed temperature of the catalytic
converter. The catalytic converter performance is based on the inversion ratio of the output
signals of the upstream and downstream oxygen sensors. The wrong diagnosis of degradation
of the catalytic converter is prevented in the case of chattering.

Other methods of Unisia Jecs Corp.: JP8303235 (1996), JP9033478 (1997).

Engines with multiple cylinder groups

In JP7063045 (1995) a method to monitor a catalytic converter is presented for an engine with
two cylinder banks as the one of fig. 38. The arrangement of the oxygen sensors is similar to
the one of fig. 38 except for the fact that the oxygen sensor placed between the junction of the
two exhaust branches and the catalytic converter is removed. The aidfuel ratio for each bank
of cylinders is feedback-controlled based on the corresponding output of the sensor installed
downstream of the corresponding bank. The deterioration of the catalytic converter is based on
a comparison of the output signals of the downstream sensor and the upstream sensors. When
the output signal of one of the oxygen sensors fluctuates with an amplitude greater than a
specified threshold, then the degradation diagnosis is prohibited in order to avoid an erroneous
diagnosis.

The method of JP7238824 (1995) is applied to the case of a multiple cylinder bank engine
with an air/fbel sensor installed in each cylinder bank exhaust pipe upstream of the catalytic
converter and an aidfuel sensor installed in the common exhaust pipe section downstream of
the catalytic converter. The general layout is this of fig. 56. The degradation of the secondary
catalytic converters and the main catalytic converter is evaluated. During the evaluation, one
group of cylinders (e.g. the left bank) is feedback-controlled by the left bank upstream oxygen
sensor, whereas the aidfuel ratio of the right bank of cylinders is controlled to be fixed at a
control value equivalent to a specified target value. The variation of aidfuel ratio detected by
the downstream sensor corresponds then to the variations provoked by the feedback control of