Power plants – Internal combustion engine with treatment or handling of... – Having sensor or indicator of malfunction – unsafeness – or...
Reexamination Certificate
2002-10-28
2004-03-02
Tran, Binh (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Having sensor or indicator of malfunction, unsafeness, or...
C060S276000, C060S285000, C060S286000, C123S679000, C701S103000, C701S115000, C073S118040
Reexamination Certificate
active
06698186
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an apparatus for controlling the air-fuel ratio of an internal combustion engine, and more particularly to an air-fuel ratio control apparatus which is capable of evaluating the deteriorated state of a catalytic converter for purifying exhaust gases.
BACKGROUND ART
Conventional processes of determining the deteriorated state of a catalytic converter for purifying exhaust gases which is disposed in the exhaust passage of an internal combustion engine are known from Japanese patent publication No. 2,526,640 and Japanese laid-open patent publication No. 7-19033, for example.
The disclosed techniques are based on the fact that when the air-fuel ratio of an air-fuel mixture to be combusted by an internal combustion engine is changed from a leaner value to a richer value or from a richer value to a leaner value, the outputs from oxygen concentration sensors that are positioned respectively upstream and downstream of a catalytic converter combined with the internal combustion engine are inverted. More specifically, under certain operating conditions of the internal combustion engine, i.e., when the power output of the internal combustion engine is increased or the fuel supplied to the internal combustion engine is cut off as disclosed in Japanese patent publication No. 2,526,640 or when certain conditions are satisfied, e.g., the load and rotational speed of the internal combustion engine are in predetermined ranges as disclosed in Japanese laid-open patent publication No. 7-19033, the air-fuel ratio is positively changed from a leaner value to a richer value or from a richer value to a leaner value. At this time, the time consumed after the output of the upstream oxygen concentration sensor is inverted until the output of the downstream oxygen concentration sensor is inverted, and the period at which output of the downstream oxygen concentration sensor is inverted are measured, and the deteriorated state of the catalytic converter is evaluated based on the measured values.
According to these techniques, when the internal combustion engine is operating under ordinary conditions, i.e., conditions without estimating the deteriorated state of the catalytic converter, the air-fuel ratio is feedback-controlled depending on the inversion of the outputs from the oxygen concentration sensors in order to keep the air-fuel ratio of the internal combustion engine in the vicinity of a stoichiometric air-fuel ratio, for thereby allowing the catalytic converter to keep an appropriate purifying capability.
According to the above process of evaluating the deteriorated state of the catalytic converter, however, it is necessary to positively change the air-fuel ratio from a leaner value to a richer value or from a richer value to a leaner value in order to evaluate the deteriorated state of the catalytic converter. Consequently, as long as the air-fuel ratio of the internal combustion engine is feedback-controlled so as to allow the catalytic converter to keep an appropriate purifying capability, it is impossible to evaluate the deteriorated state of the catalytic converter. Therefore, at the time of evaluating the deteriorated state of the catalytic converter, it is difficult for the catalytic converter to keep an appropriate purifying capability.
The applicant of the present application has proposed another technique for achieving an appropriate purifying capability of a catalytic converter (see, for example, Japanese laid-open patent publication No. 9-324681, Japanese laid-open patent publication No. 11-153051, U.S. Pat. No. 5,852,930, and U.S. patent application Ser. No. 09/153,300). According to the proposal, an exhaust gas sensor for detecting the concentration of a certain component, e.g., oxygen, of exhaust gases is positioned downstream of the catalytic converter, and the air-fuel ratio of an air-fuel mixture to be combusted by an internal combustion engine is manipulated in order to converge the output of the exhaust gas sensor to a predetermined target value.
More specifically, in order to converge the output (the detected value of the oxygen concentration) of the exhaust gas sensor to a predetermined target value (constant value), a target value (target air-fuel ratio) for the air-fuel ratio of the exhaust gases that enter the catalytic converter, or specifically the air-fuel ratio recognized from the oxygen concentration of the exhaust gases, is successively calculated according to a sliding mode control process. The air-fuel ratio of the air-fuel mixture to be combusted by an internal combustion engine is then manipulated depending on the target air-fuel ratio to achieve the appropriate purifying capability of the catalytic converter.
Since the above proposed technique is capable of stably keeping the appropriate purifying capability of the catalytic converter by controlling the air-fuel ratio as described above, it is desirable to be able to evaluate the deteriorated state of the catalytic converter while performing the above air-fuel control process.
It is therefore an object of the present invention to provide an apparatus for controlling the air-fuel ratio of an internal combustion engine, which is capable of appropriately evaluating the deteriorated state of a catalytic converter while keeping a desired purifying capability of the catalytic converter that is disposed in the exhaust passage of the internal combustion engine.
DISCLOSURE OF THE INVENTION
To achieve the above object, there is provided in accordance with the present invention an apparatus for controlling the air-fuel ratio of an internal combustion engine, comprising an exhaust gas sensor disposed downstream of a catalytic converter which is disposed in an exhaust passage of an internal combustion engine, for detecting the concentration of a particular component of a exhaust gas emitted from the internal combustion engine and having passed through the catalytic converter, air-fuel ratio manipulated variable generating means for sequentially generating a manipulated variable to determine the air-fuel ratio of the exhaust gas entering the catalytic converter to converge an output of the exhaust gas sensor to a predetermined target value, air-fuel ratio manipulating means for manipulating the air-fuel ratio of an air-fuel mixture to be combusted in the internal combustion engine depending on the manipulated variable, and deteriorated state evaluating means for sequentially determining the value of a deterioration evaluating linear function from time-series data of the output of the exhaust gas sensor, the deterioration evaluating linear function having variable components represented by the time-series data of the output of the exhaust gas sensor, and evaluating a deteriorated state of the catalytic converter based on the determined value of the deterioration evaluating linear function, while the air-fuel ratio of the air-fuel mixture is being manipulated by the air-fuel ratio manipulating means.
The inventors of the present invention have found that while a manipulated variable for the air-fuel ratio (e.g., a target value for the air-fuel ratio) of the exhaust gas entering the catalytic converter to converge the output of the exhaust gas sensor downstream of the catalytic converter to a given target value is being sequentially generated and the air-fuel ratio of the air-fuel mixture is being manipulated depending on the manipulated variable, when an appropriate linear function whose variable components are represented by time-series data of the output of the exhaust gas sensor, i.e., a linear function expressed as a linear coupling of the time-series data of the output of the exhaust gas sensor, is determined from the time-series data of the output of the exhaust gas sensor, the value of the linear function has a tendency to exhibit a characteristic correlation between itself and the degree to which the deterioration of the catalytic converter progresses.
For example, when the catalytic converter is substantially brand-new, the value of the linear function tends to be accum
Akazaki Shusuke
Iwaki Yoshihisa
Kitagawa Hiroshi
Ueno Masaki
Arent Fox Kintner Plotkin & Kahn
Honda Giken Kogyo Kabushiki Kaisha
Tran Binh
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