Internal-combustion engines – Charge forming device – Including exhaust gas condition responsive means
Reexamination Certificate
2003-11-25
2004-09-14
Huynh, Hai (Department: 3747)
Internal-combustion engines
Charge forming device
Including exhaust gas condition responsive means
C123S494000, C701S103000, C701S115000
Reexamination Certificate
active
06789534
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an air-fuel ratio control system and method and an engine control unit for an internal combustion engine, for controlling the air-fuel ratio of a mixture supplied to a plurality of cylinders of the engine on a cylinder-by-cylinder basis.
2. Description of the Related Art
Recently, it is demanded of internal combustion engines due to social requirements that the engines have excellent exhaust emission characteristics, that is, an excellent emission reduction rate of the catalyst. On the other hand, internal combustion engines having a plurality of cylinders can suffer variation in air-fuel ratio between the cylinders to which a mixture is supplied, due to the malfunction of an EGR system, an evaporative fuel processing system, or injectors. In such a case, there is a fear of the emission reduction rate of the catalyst being lowered. Therefore, to overcome the problem, as an air-fuel ratio control system for an internal combustion engine, which corrects (absorbs) variation in air-fuel ratio between cylinders, there has been conventionally proposed one to which is applied an observer based on the optimal control theory (see e.g. Publication of Japanese Pat. No. 3296472, pages 18-23, FIGS. 35 and 36). This air-fuel ratio control system is comprised of a LAF sensor disposed in the collecting section of an exhaust pipe, for detecting the air-fuel ratio of exhaust gases, a control unit to which a detection signal (indicative of the detected air-fuel ratio) from the LAF sensor is input, and injectors disposed in the intake manifold of the exhaust pipe for the respective cylinders and connected to the control unit.
In this control unit, the variation in the air-fuel ratio of the mixture supplied to each cylinder is corrected by calculating a cylinder-by-cylinder fuel injection amount #nTout (n=1 to 4) as the amount of fuel to be injected into each cylinder, based on the detected air-fuel ratio output from the LAF sensor, using the observer and by PID control, as described below.
That is, the control unit calculates the basic fuel injection amount Tim depending on the operating conditions of the engine, and multiplies the basic fuel injection amount by various correction coefficients to calculate the output fuel injection amount Tout. Then, as described below, the observer calculates a cylinder-by-cylinder estimated air-fuel ratio #nA/F, and a cylinder-by-cylinder estimated feedback correction coefficient #nKLAF is determined by PID control based on the estimated cylinder-by-cylinder air-fuel ratio #nA/F. The cylinder-by-cylinder fuel injection amount #nTout is calculated by multiplying the output fuel injection amount Tout by the cylinder-by-cylinder feedback correction coefficient #nKLAF.
The cylinder-by-cylinder estimated air-fuel ratio #nA/F is calculated by the observer based on the optimal control theory. More specifically, by using a model of a discrete-time system representative of the relationship between a cylinder-by-cylinder fuel-air ratio and a fuel-air ratio detected at the collecting section (where the LAF sensor is disposed), the cylinder-by-cylinder air-fuel ratio #nA/F is calculated. Further, in the PID control, a value obtained by dividing the fuel-air ratio detected at the collecting section, i.e. the detected air-fuel ratio KACT, by the average value of the respective preceding values of the feedback correction coefficients #nKLAF is set to a target value, and the cylinder-by-cylinder feedback correction coefficient #nKLAF is calculated such that the difference between the target value and the cylinder-by-cylinder estimated air-fuel ratio #nA/F calculated by the observer converges to a value of 0.
Recently, aside from the above-mentioned demand of excellent exhaust emission characteristics, internal combustion engines are demanded of higher power output and higher torque. To meet the demand, there is employed the technique of reducing the exhaust resistance by configuring the layout of the exhaust system into a complicated shape (in which exhaust passages from the cylinders are progressively combined in the exhaust manifold such that four passages, for example, are combined into two passages, and the two passages are then combined into one passage). However, when the conventional air-fuel ratio control system is applied to internal combustion engines having such an exhaust system layout, the observer can be no longer applicable based on the conventional optimal control theory, and therefore, the variation in air-fuel ratio between the cylinders cannot be properly corrected, which can lead to a lowered emission reduction rate of the catalyst. This is because according to the conventional optimal control theory, modeling errors and changes in the dynamic characteristics of a model are not considered in the simulation model and the optimal control theory itself, which makes the observer small in margin of stability and low in robustness. Therefore, the air-fuel ratio control system does not have a sufficient stability against changes in the contributions of exhaust gases from the individual cylinders to the detected air-fuel ratio of the LAF sensor caused by attachment of fuel, etc., changes in the response of the LAF sensor, and the aging of the same.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an air-fuel ratio control system and method and an engine control unit for an internal combustion engine, which are capable of appropriately and promptly correcting variation in air-fuel ratio between a plurality of cylinders and realizing a very robust air-fuel ratio control.
To attain the above object, in a first aspect of the present invention, there is provided an air-fuel ratio control system for an internal combustion engine including a plurality of cylinders and an exhaust passage through which exhaust gases from the cylinders flow, the air fuel ratio control system controlling an amount of fuel to be supplied to each of the cylinders, on a cylinder-by-cylinder basis, to thereby control an air fuel ratio of a mixture supplied to each cylinder.
The air-fuel ratio control system according to the first aspect of the present invention is characterized by comprising:
fuel amount-determining means for determining an amount of fuel to be supplied to each cylinder;
correction parameter-determining means for determining a correction parameter for correcting the amount of fuel to be supplied to each cylinder;
first fuel amount-correcting means for correcting the determined amount of fuel to be supplied to each cylinder, according to the determined correction parameter;
air-fuel ratio parameter-detecting means for detecting an air-fuel ratio parameter indicative of an air-fuel ratio of the exhaust gases flowing through the exhaust passage;
variation parameter-calculating means for calculating a variation parameter indicative of a variation in air-fuel ratio between the plurality of parameters, on a cylinder-by-cylinder basis, based on a model parameter of a model formed by modeling each cylinder and having an input of the correction parameter and an output of the air-fuel ratio parameter;
identification means for identifying the model parameter of the model based on the determined correction parameter and the detected air-fuel ratio parameter; and
second fuel amount-correcting means for further correcting the amount of fuel to be supplied to the plurality of cylinders on a cylinder-by-cylinder basis such that the variation parameter calculated on a cylinder-by-cylinder basis converges to a predetermined target value.
With the arrangement of the air-fuel ratio control system according to the first aspect of the present invention, an amount of fuel to be supplied to each cylinder is determined by the fuel amount-determining means, and corrected according to a correction parameter by the first fuel amount-correcting means. Further, a variation parameter indicative of a variation in air-fuel ratio between the plurali
Mizuno Takahide
Yasui Yuji
Honda Motor Co. Ltd.
Huynh Hai
Squire Sanders & Dempsey L.L.P.
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