Power plants – Internal combustion engine with treatment or handling of... – By means producing a chemical reaction of a component of the...
Reexamination Certificate
2001-12-03
2003-07-22
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...
C060S276000
Reexamination Certificate
active
06594988
ABSTRACT:
This application is based on Application No.2001-196363, field in Japan on Jun. 28, 2001, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an air/fuel ratio control apparatus for an internal combustion engine, and more specifically, to an air/fuel ratio control apparatus for an internal combustion engine that removes poisonous components present in an exhaust gas using a catalytic purifying device provided in an exhaust system path.
2. Related Background Art
Conventionally, there has been well known an air/fuel ratio control apparatus for an internal combustion engine that has an exhaust gas purifying function of removing poisonous components, such as NOx, HC, and CO, emitted from the internal combustion engine. To achieve this function, a three-way catalyst for removing such poisonous components in an exhaust gas is provided in an exhaust system of the internal combustion engine.
If a fuel cut is performed, however, a large amount of oxygen is absorbed by the three-way catalyst, so that even if the fuel cut is reset afterward, the air/fuel ratio does not immediately return to the state before the fuel cut is started. This causes an excess oxygen state, in which an NOx reduction action becomes inactive and the three-way catalyst cannot fully exert its effect. As a result, there is the danger of poisonous components being discharged into the air.
In view of this problem, a technique of suppressing the amount of NOx discharged after the reset of the fuel cut is disclosed in Japanese Patent Application Laid-open No. Hei 8-193537 (hereinafter, the “first prior art”). With this technique, the amount of oxygen absorbed by a three-way catalyst during a fuel cut is obtained based on an intake air amount or a period of time of the fuel cut. When the fuel cut is reset, an air/fuel ratio is controlled to be on a rich side close to a theoretical air/fuel ratio for a very short time period according to the amount of the absorbed oxygen. In this manner, the amount of NOx discharged after the reset of a fuel cut is suppressed.
Another technique of solving the stated problem is disclosed in Japanese Patent Application Laid-open No. Hei 11-280457 (hereinafter, the “second prior art”). With this technique, the amount of oxygen absorbed by a three-way catalyst during a fuel cut is obtained based on an intake air amount or period of the fuel cut. When the fuel cut is reset, an air/fuel ratio is enriched in a step-by-step manner using an initial value corresponding to the amount of the absorbed oxygen, and then the enriched air/fuel ratio is brought back to an theoretical air/fuel ratio at a predetermined speed, thereby suppressing the amount of NOx discharged after the reset of the fuel cut. Also, after the enrich processing is temporarily suspended by acceleration, it is judged whether the three-way catalyst returns to the state before the fuel cut according to the output of an oxygen concentration sensor arranged downstream of the catalyst. If it is judged that the catalyst returns to the original state, re-enrich processing is not performed.
Even in the case of a fuel cut where the same amount of oxygen is supplied according to the amount of oxygen absorbed by a catalyst before the fuel cut, there may occur a phenomenon where the amount of oxygen absorbed varies after the fuel cut and therefore the deterioration degree of an NOx purification rate changes. For instance, if the oxygen absorption amount of a catalyst before a fuel cut is small and the catalyst is in a rich state, this may result in a situation where the fuel cut does not increase the amount of absorbed oxygen to a level where the NOx purification rate is decreased. Conversely, if the catalyst oxygen absorption amount before a fuel cut is large and the catalyst is in a lean state, this may cause a situation where the NOx purification rate is significantly decreased even by a fuel cut performed for a short time.
As described above, there are variations in the amount of oxygen absorbed by a catalyst before fuel cuts and therefore there occur variations in the oxygen absorption amount of the catalyst when the fuel cuts are reset. This creates the necessity to appropriately perform enrich processing according to the oxygen absorption amounts of the catalyst after the fuel cuts.
In the first and second prior arts, however, enrich processing is performed only according to the amount of oxygen supplied during a fuel cut and the oxygen absorption state of a catalyst after the fuel cut is not taken into account during the enrich processing. This causes variations in the catalyst oxygen absorption amount after the rich processing. As a result, there may occur a problem that too enriched catalyst reduces a THC purification rate, or a problem that enrich processing is not sufficiently performed and the Nox purification rate does not return to an adequate level.
Also, there has been recently devised a catalyst system that increases a purification efficiency by providing two three-way catalysts (hereinafter respectively referred to as a “front three-way catalyst” and a “rear three-way catalyst”), with the rear three-way catalyst being arranged at a position downstream of the front three-way catalyst. In this system, poisonous components in an exhaust gas are purified as much as possible (about 90% or more of the components are removed, for instance) by the front three-way catalyst and the poisonous gas that is not purified by the front three-way catalyst is purified by the rear three-way catalyst with reliability. This makes it possible to raise the exhaust gas purification rate to around 100% in total using the front and rear three-way catalysts. To achieve this high purification rate, it is required to always maintain both of the front and rear three-way catalysts in conditions where optimal exhaust purification capacities are obtained.
If a fuel cut is performed in such a catalyst system where a front three-way catalyst and a rear three-way catalyst are provided, however, a phenomenon may occur where there is a difference in oxygen absorption amount between the front and rear three-way catalysts.
If most of oxygen supplied by a fuel cut is absorbed by a front three-way catalyst, for instance, a rear three-way catalyst hardly absorbs oxygen, so that it is sufficient that enrich processing is performed only for the front three-way catalyst after the fuel cut is reset.
Also, if a large amount of oxygen exceeding the absorption capacity of a front three-way catalyst is supplied by a fuel cut, the oxygen absorption amount of a rear three-way catalyst is also increased, so that it becomes necessary to perform enrich processing for both of the front and rear three-way catalysts after the fuel cut is reset.
Such a variation in the amount of oxygen supplied to a rear three-way catalyst by a fuel cut is caused by the oxygen absorption state of a front three-way catalyst during the fuel cut.
Even in the case of the fuel cut, as described above, where the same amount of oxygen is supplied, the oxygen absorption state of the front three-way catalyst before the fuel cut causes a variation in the oxygen absorption state of the front three-way catalyst during the fuel cut, so that the supply of oxygen to the rear three-way catalyst is also affected.
That is, to accurately detect the amount of oxygen absorbed by a rear three-way catalyst during a fuel cut, it is required to detect the oxygen absorption amount of a front three-way catalyst during the fuel cut and to estimate the amount of oxygen flowing to the rear three-way catalyst.
In the first and second prior arts, however, enrich processing is performed only according to the amount of oxygen supplied by a fuel cut and therefore the oxygen absorption amounts of a front three-way catalyst before and during the fuel cut are not taken into account during the enrich processing. This causes variations in the oxygen absorption amounts of the front and rear three-way catalysts after the rich processing. As a result, ther
Azuma Tadahiro
Takubo Hideki
Denion Thomas
Mitsubishi Denki & Kabushiki Kaisha
Sughrue & Mion, PLLC
Tran Diem
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