Page 183 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Mazda Motor Corporation 165

Engines with multiple cylinder groups

In US5228287 (1993) a method to monitor a catalytic converter is presented for an engine
with two cylinder banks as the one of US5357753 (1994) (see chapter 1.3). The arrangement
of the sensors is similar to the one of fig. 38 except for the fact that the sensor placed between
the junction of the two exhaust gas branches and the catalytic converter is removed.
The method consists of the following steps:
I) detecting an airlfiel ratio based on an emission level of exhaust gas by means of the oxygen
sensors disposed in each individual exhaust passage upstream of the catalytic converter and
upstream of the common junction point of the individual exhaust gas passages
2) detecting an oxygen level of exhaust gas passed through the catalytic converter by means of
the downstream oxygen sensor
3) feedback-controlling air/hel ratios for the cylinder groups independently based on emission
levels detected by the upstream oxygen sensors
4) detecting vehicle driving conditions
5) monitoring a difference between phases in change of air/fiel ratios for both said groups of
said cylinders based on an emission level of exhaust gas detected by said upstream oxygen
sensors only when detecting a specific vehicle driving condition
6) feedback-controlling an air/hel ratio for the cylinder groups all together based on either one
of the upstream oxygen sensors during detection of the deterioration of the catalytic
converter
7) detecting deterioration of the catalytic converter based on a reversal frequency of the signal
provided from the downstream oxygen sensor and a reversal frequency of a signal
representative of an emission level detected by one of the upstream oxygen sensors, only
when detecting no difference between said phases
8) determining a critical deterioration of said catalytic converter based on a ratio between the
reversal frequencies of the signals of the downstream and upstream sensor

The method of US5233829 (1993) refers to a V-type internal combustion engine (fig. 75).
The intake system of the V-engine is endowed with a common upstream intake pipe connected
to the surge tank. The common upstream intake pipe is provided with an air flow sensor for
detecting an air flow rate and a throttle valve for regulating the amount of intake air and hence
the engine output.
Each branch intake pipe is provided with a fie1 injection valve located at a downstream portion
thereof The exhaust system of engine is endowed with a pair of upstream exhaust manifold
pipes, which extend from the exhaust ports, respectively, and a common downstream exhaust
pipe, into which the upstream exhaust pipes converge.

The common downstream exhaust pipe is provided with a main catalytic converter for
purifying exhaust gas. Each upstream exhaust pipe is provided with a secondary catalytic
converter (or pre-catalyst or light-off catalytic converter). Each of the secondary catalytic