Power plants – Internal combustion engine with treatment or handling of... – By means producing a chemical reaction of a component of the...
Reexamination Certificate
2003-02-25
2004-06-22
Denion, Thomas E. (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
By means producing a chemical reaction of a component of the...
Reexamination Certificate
active
06751950
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application is based on Japanese Patent Application No. 2002-47908 filed on Feb. 25, 2002, contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an emission control apparatus for engine, specifically to an air-fuel ratio control after a lean air-fuel ratio has continued longer than a predetermined period, especially resuming from a fuel cut operation.
2. Description of Related Art
Heretofore there has been known a technique wherein when an accelerator pedal is released by a driver during operation of an internal combustion engine, a fuel injection control is stopped or significantly decreased to reduce the amount of fuel consumed on condition that the engine speed is higher than a predetermined engine speed. This kind of control is hereinafter referred to as a fuel cut operation or fuel cut. It is generally known that if fuel cut is performed during operation of an internal combustion engine, the amount of oxygen capable of being occluded by a catalyst, e.g., a three-way catalyst, reaches saturation, the catalyst being provided in an exhaust passage of the internal combustion engine for the purification of exhaust gas.
A purification rate of a three-way catalyst indicates a maximum exhaust gas purifying characteristic in the vicinity of a stoichiometric air-fuel ratio. Therefore, there arises an inconvenience such that, even if fuel is fed so as to give a stoichiometric air-fuel ratio after the return from fuel cut, an air-fuel ratio after passing through the three-way catalyst becomes lean with oxygen occluded by the same catalyst.
As techniques for eliminating such an inconvenience there have been proposed a technique disclosed in Japanese Patent No. 2604840 and a technique disclosed in JP-A-8-193537. These techniques employ a system configuration comprising a catalytic converter disposed in an exhaust passage of an engine and a sensor, e.g., an oxygen sensor, disposed downstream of the catalytic converter to detect an oxygen concentration of exhaust gas discharged from an engine.
According to the technique disclosed in Japanese Patent No. 264840, the amount of fuel injected by an injector is increased, or enriched, by a preset amount for prompt consumption of oxygen which has been occluded by the catalytic converter after the return from fuel cut. When the output of the oxygen sensor disposed downstream of the catalytic converter has become rich, the increase, or enriching, of the amount of fuel injected is stopped assuming that the oxygen occluded by the catalytic converter has been consumed.
The system configuration according to the technique disclosed in the JP-A-8-193537 is further provided with a linear A/F sensor for detecting an air-fuel ratio of exhaust gas, the linear A/F sensor being positioned in front of the catalytic converter disposed on the engine side. In such a system, for the consumption of oxygen occluded by the catalyst after the return from fuel cut, the amount of fuel injected by the injector is increased so that an output value of the linear A/F sensor becomes a desired value. According to the technique in question, first in fuel cut, the amount of oxygen occluded by the catalytic converter is estimated. Hereinafter, the amount of oxygen occluded is referred to as an occluded oxygen quantity. Then, at the time of increasing the amount of fuel injected after the return from fuel cut, there is calculated a deoccluded oxygen quantity based on enriching of the air-fuel ratio relative to the estimated occluded oxygen quantity, and the increase of the injected fuel quantity is stopped when the occluded oxygen quantity has reached a level not requiring any further consumption of oxygen.
In the above system configuration, the number of the catalytic converter disposed in the engine exhaust passage is one. But recently, for the purpose of diminishing the emission when an engine is started in the cold, it has been known that a catalytic converter smaller in capacity than the conventional catalytic converter which permits quick warm-up of catalyst is disposed upstream of the exhaust passage. That is, there has been known a system which is provided in the engine exhaust gas passage with a linear A/F sensor, an upstream-side catalyst small in capacity, an oxygen sensor, and a downstream-side catalyst larger in capacity than the upstream-side catalyst, successively from the upstream side.
However, if the foregoing techniques disclosed in Japanese Patent No. 2604840 and the JP-A-8-193537 are applied to such a system, there is a fear that the following inconvenience may occur.
According to the technique disclosed in Japanese Patent No. 2604840, a stop timing of the increase of the fuel injection quantity is determined by the oxygen sensor disposed downstream of catalyst, so in a system not provided with an oxygen sensor downstream of a downstream-side catalyst, it is impossible to determine a stop timing of the increase of the fuel injection quantity. Consequently, there sometimes is a case where a return is made to an ordinary feedback control in a state in which oxygen occluded by the downstream-side catalyst is not consumed to a sufficient degree. Therefore, the increase of the fuel injection quantity is not performed thereafter and it takes time for consumption of the oxygen occluded by the downstream-side catalyst. If the increase of the fuel injection quantity is performed in an actually completely consumed state of the oxygen occluded by the downstream-side catalyst, a rich gas will be released to the atmosphere, with a consequent likelihood of deteriorated emission.
On the other hand, according to the technique disclosed in the JP-A-8-193537, the amount of oxygen occluded in the catalytic converter is estimated. Therefore, it is here assumed that the amount of oxygen occluded by two catalytic converters is estimated and that an increase of the fuel injection quantity is executed on the basis of the estimated value. In the JP-A-8-193537, it is described that an increase of the fuel injection quantity is executed by setting the air-fuel ratio to a value richer by 0.5% to 2.0% than a stoichiometric air-fuel ratio.
However, even if an increase of the fuel injection quantity is set to a 0.5% richer value in terms of air-fuel ratio, it is likely that a long time will be required for the consumption of oxygen occluded by the catalytic converter, making a quick return to the ordinary feedback control impossible. A description will now be given of the case where an increase of the fuel injection quantity is set to a 2.0% richer value in terms of air-fuel ratio. Also in this case, since the amount of oxygen occluded by the catalytic converter is an estimated value, there is the possibility that a 2.0% richer exhaust gas will be released to the atmosphere despite the actual consumption of oxygen, that is, the emission will be deteriorated.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an emission control apparatus for engine capable of rapidly consuming oxygen occluded by a catalytic converter and diminishing emission released to the atmosphere even if an estimated value of the amount of oxygen occluded is deviated from an actual value.
For achieving the above-mentioned object, according to a first aspect of the present invention, an emission control apparatus for engine is applied to an engine control system that has a fuel supply stop means for stopping the supply of fuel injected by a fuel injection valve during operation of the engine. The emission control apparatus comprises a first occluded oxygen quantity estimating means for estimating a total amount of oxygen occluded by an upstream-side catalyst and oxygen occluded by a downstream-side catalyst, a first air-fuel ratio enriching means for enriching the air-fuel ratio of exhaust gas when a return is made from the state in which the supply of fuel is stopped by the fuel supply stop means, and a second air-fuel ratio enriching means which
Iida Hisashi
Ikemoto Noriaki
Denion Thomas E.
Denso Corporation
Nixon & Vanderhye P.C.
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