Power plants – Internal combustion engine with treatment or handling of... – Having means analyzing composition of exhaust gas
Reexamination Certificate
1999-08-23
2001-05-08
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Having means analyzing composition of exhaust gas
C060S277000, C060S285000, C060S274000
Reexamination Certificate
active
06226982
ABSTRACT:
The present invention relates to a method for controlling the strength of the air/fuel. mixture supplied to an internal-combustion engine.
In particular, the present invention relates to a method for controlling the strength of the mixture after the engine has been in an operating condition known as the “cut-off” condition, during which the supply of fuel to the engine cylinders is interrupted.
During cut-off conditions, the catalytic converter which is arranged along the exhaust pipe of the engine is acted on by a flow of pure air and, acting in the manner of a lung, stores oxygen.
BACKGROUND OF THE INVENTION
As is known, the maximum efficiency of the catalytic converter, namely the capacity to eliminate successfully the polluting substances present in the combusted gases, depends both on the strength of the mixture supplied to the engine and on the existing state of the converter itself, namely on the quantity of oxygen which it has stored. In particular, the catalytic converter performs the catalytic action with the maximum efficiency if the strength of the mixture supplied to the engine is within a given range centered around the value of one and if the quantity of oxygen stored is any case less than a predefined threshold value.
During the cut-off condition, the catalytic converter, being acted on by the intake air of the engine, stores a quantity of oxygen which is far greater than the threshold value and therefore is made to operate in a low-efficiency zone.
At the end of the cut-off condition, despite the fact that a target strength close to the value of one is defined, the catalytic converter is unable to eliminate correctly the polluting substances on account of the excess oxygen stored.
Therefore, for the whole of the time required by the converter to dispose of this excess oxygen, the polluting emissions are not minimized.
At present, at the end of the cut-off condition, the target strength is corrected in a way which tends to enrich the mixture supplied to the engine in order to prevent the engine from stalling.
Enrichment of the mixture is performed independently of the state of the catalytic converter. This enrichment has a beneficial effect on the converter in that it allows it to dispose of part of the stored oxygen, but, being independent of the state of the converter itself (i.e. of the quantity of stored oxygen), it may sometimes be excessive to the detriment of the fuel consumption and the emission of polluting substances or, alternatively, it may be insufficient to the detriment of the time during which the converter is not operating at high efficiency.
SUMMARY OF THE INVENTION
The object of the present invention is that of providing a method for controlling the strength which, depending on the state of the catalytic converter (i.e. the quantity of stored oxygen), minimizes the time during which the catalytic converter is not operating at high efficiency at the end of the fuel cut-off condition.
According to the present invention a method for controlling the strength of the air/fuel mixture supplied to an internal-combustion engine of the type described in claim
1
is provided.
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Ceccarini Daniele
Poggio Luca
Secco Marco
Denion Thomas
Liniak Berenato Longacre & White
Magneti Marelli S.p.A.
Tran Diem
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