Fuel control apparatus for an engine

Details Fuel control apparatus for an engine Fuel control apparatus for an engine

2001-09-27

2003-05-13

Denion, Thomas (Department: 3748)

Power plants

Internal combustion engine with treatment or handling of...

By means producing a chemical reaction of a component of the...

C060S285000, C123S399000, C123S493000

Reexamination Certificate

active

06560960

ABSTRACT:

BACKGROUD OF THE INVENTION
1. Field of the Invention
This invention relates to an engine fuel control apparatus equipped with an exhaust purification catalyst which controls an average air/fuel ratio prior to an ignition in an in-cylinder combustion chamber to be leaner than a stoichiometric air/fuel ratio in a predetermined region of low rotational speed and low load side and performs a fuel cut control under a predetermined condition.
2. Description of Related Arts
Conventionally, this kind of engine fuel control apparatus is known and is provided with a fuel injector so as to face an in-cylinder combustion chamber of the engine, causes the fuel injector to inject fuel mainly during a cylinder compression stroke to generate a stratified combustion state when the engine is in a predetermined region of low rotational speed and low load side and causes the fuel injector to inject fuel mainly during a cylinder intake stroke in a region of high rotational speed or high load side, as disclosed in Japanese publication of patent application no. 11-229856.
In the aforementioned stratified combustion state, since a mixture combusts in a state where the mixture is unevenly distributed in a proximity of a spark plug, an average air fuel ratio prior to an ignition in an in-cylinder combustion chamber, hereinafter referred to as the in-cylinder air/fuel ratio, can be set at an extremely lean state such as A/F=30-140, thereby fuel consumption rate can be substantially improved by reducing pumping loss or heat loss compared with a homogeneous combustion state.
Then, when the in-cylinder air/fuel ratio is in the extremely lean state as described above, an exhaust air/fuel state is in a lean state as well. In other words, generally, if the in-cylinder air/fuel ratio is the substantially stoichiometric air/fuel ratio, oxygen concentration remaining in the exhaust gas will become less than about 0.5% and an exhaust air/fuel state at this time will become a state corresponding to the substantially stoichiometric air/fuel ratio. On the other hand, if the in-cylinder air/fuel ratio becomes lean, the exhaust air/fuel state becomes lean, i.e. a higher oxygen concentration state. But, it is very difficult to efficiently reduce NOx in this higher oxygen concentration state.
Hence, in the aforementioned prior art, NOx catalyst is provided including NOx absorbent which absorbs NOx in an excess oxygen atmosphere and releases NOx when the oxygen concentration decreases, and in the proximity of this a three-way catalyst is disposed, wherein the aforementioned NOx catalyst is caused to absorb NOx when the exhaust air/fuel state is lean while the three-way catalyst is caused to reduce and purify NOx released from the NOx catalyst when the exhaust air/fuel state becomes the stoichiometric air/fuel ratio or richer.
In this respect, generally, such a NOx absorbent as described above has a characteristic of lower absorptive ability for NOx the greater the NOx absorptive amount. Hence, in the aforementioned prior art, when an engine operation in the stratified combustion state continues over a long period of time, it is shifted to the homogeneous combustion state and the exhaust air/fuel state is made richer by compulsorily changing the in-cylinder air/fuel ratio into the rich side prior to the substantial decrease of the NOx absorptive performance by the NOx catalyst, to release NOx from the NOx catalyst and reduce and purify it with the three-way catalyst (hereinafter referred to as a compulsory NOx purge).
Also in the aforementioned prior art, when the engine is in a decelerating operating state and when a predetermined condition is fulfilled such as no manipulation of an accelerator pedal being made, a fuel cut control is performed which stops a fuel injection supply from a fuel injector, whereby an engine brake effect can be enhanced and a fuel consumption rate can be decreased.
Meanwhile, since an exhaust temperature state generally becomes lower compared to the time of the substantially stoichiometric air/fuel ratio as the in-cylinder air/fuel ratio becomes leaner, a temperature state of catalyst tends to be lower in a spark ignited direct injection engine which is in the stratified combustion state in the lower rotational speed and lower load region as in the aforementioned prior art and a diesel engine whose in-cylinder air fuel ratio becomes lean during almost all of the operating region. Furthermore, when the fuel cut control is performed as in the aforementioned prior art, thereby the aforementioned catalyst temperature state becomes extremely low and the exhaust purification performance by this catalyst might be deteriorated.
Also if the compulsory NOx purge were performed regardless of the engine operating condition as in the aforementioned prior art, when the engine is in an operating condition where vibration or noise is inherently low such as an idle operating condition, the combustion state might be compulsorily shifted from the stratified combustion through the homogeneous combustion to the stratified combustion and an output torque might vary. Even if the torque variation at this time is small, since it occurs regardless of driver manipulation, a driver tends to get a strange feeling and a driving feeling would be deteriorated if the occurring frequency were high.
SUMMARY OF THE INVENTION
It is an object of the present invention to improve the driving feeling in the overall engine operating region while maintaining the exhaust purification performance of for example a catalyst by elaborating a control process of the exhaust air/fuel state in terminating the fuel cut control and recovering the fuel supply in an engine fuel control apparatus which operates the engine in the lean in-cylinder air/fuel state in the lower rotational speed and lower load region and performs the fuel cut control under a predetermined condition.
Preferably, a recovery timing is determined when the engine shifts from a fuel cut state to an operating condition of lean in-cylinder air/fuel ratio and then controls an exhaust air/fuel state to be a state corresponding to or richer than a substantially stoichiometric air/fuel ratio if a catalyst is in a state of lower purification performance due to being over cooled or an increase of NOx absorptive amount.
Particularly, according to an aspect of the present invention, there is provided a fuel control apparatus of an engine equipped with a catalyst which performs a three-way purification function at least when an exhaust air/fuel state is a state corresponding to a substantially stoichiometric air/fuel ratio, an in-cylinder air/fuel ratio control device for controlling an in-cylinder air/fuel ratio which is an average air fuel ratio prior to an ignition in an in-cylinder combustion chamber to be leaner than the stoichiometric air/fuel ratio at least when the engine is in a predetermined region of low rotational speed and low load side, and a fuel cut control device for performing a fuel cut control for compulsorily stopping a fuel supply to the combustion chamber under a predetermined condition during a decelerating operation of the engine. And it is configured to comprise a low catalyst temperature state determining device for determining if the catalyst is in a predetermined low temperature state where its exhaust purification performance is deteriorated; and an exhaust air/fuel ratio control device for controlling the exhaust air/fuel state to be a state corresponding to or richer than the substantially stoichiometric air/fuel ratio when the low catalyst temperature determining device determines that the catalyst is in the low temperature state and when the fuel cut control by the fuel cut control device terminates and then the engine shifts to the predetermined region. At that time, the air/fuel ratio is preferably controlled between the stoichiometric air/fuel ratio and an air fuel ratio of 12 because unburned fuel in the exhaust gas increases the temperature of the catalyst if the air/fuel ratio exceeds 12.
Accordingly, when the engine is in the predetermined r

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