Page 132 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

114 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

Two fuel injection valves are installed, one for each bank. The control of the fuel injection is
similar to this of fig. 40. The difference is that there are two control units, each comprising a
down counter, a flip-flop and a drive circuit. Each of these control units controls one of the
fbel injection valves.

The method of US5207057 (1993) comprises the following steps:
1) individually controlling the air/fbel ratio of each cylinder group in accordance with the
output of the upstream aidfuel ratio sensor corresponding to the respective cylinder group
2) controlling the air/fbel ratio of all cylinder groups simultaneously, in accordance with an
output of one of the upstream sensors, when the engine is operated under a predetermined
operating condition. The output of said one of the upstream airhel ratio sensors alternates
between a rich aidfuel ratio side and a lean air/fbel ratio side periodically, compared with
the stoichiometric aidfuel ratio.
3) determining whether or not said catalyst converter has deteriorated, when the ratio of
periods of the oscillating outputs of said upstream sensor and said downstream sensor
becomes larger than a predetermined value.

The method of EP0595044 (1 994) comprises the following steps:
1) individually controlling the aidfuel ratio of each cylinder group in accordance with control
parameters defined from the output signals of the upstream airhe1 ratio sensors so that the
aidfbel ratio of each cylinder group oscillates periodically between a rich air/fbel ratio and a
lean airhe1 ratio
2) detecting phases of the airhe1 ratio oscillations of exhaust gases flowing into said common
exhaust passage from said respective individual exhaust passages
3) determining whether or not conditions in which the above mentioned phases of airhe1 ratio
oscillations spontaneously synchronize, are satisfied. A spontaneous synchronization can
exist due to slight differences of the periods of the cycle of the airhel ratio feedback
controls in the respective cylinder groups. The conditions for the spontaneous
synchronization of these phases are satisfied when
a) the phases of the airhel ratio oscillations of the respective cylinder
groups synchronize, or
b) the differences in the phases of the airlfkel oscillations of the
respective cylinder groups become predetermined time periods (e.g.
constant time periods regardless of the operating conditions of the
engine)
4) determining the condition of the catalytic converter based on the output signal of the
downstream sensor, when the conditions for the spontaneous synchronization of these
phases are satisfied. Three different methods are used to determine the deterioration of the
catalytic converter by using

a) the number of reversals of the output signal of the downstream
oxygen sensor, or