Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – With indicator or control of power plant
Reexamination Certificate
2000-11-09
2002-11-05
Vo, Hieu T. (Department: 3754)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
With indicator or control of power plant
C123S692000, C060S276000, C060S285000
Reexamination Certificate
active
06477458
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for controlling the air-fuel ratio of an internal combustion engine.
2. Description of the Related Art
Generally, catalytic converters such as three-way catalytic converters are disposed in the exhaust passages of internal combustion engines for purifying gas components including HC (hydrocarbon), NOx (nitrogen oxides), etc. contained in the exhaust gas emitted from the internal combustion engines. There have been proposed techniques of controlling the air-fuel ratio of an air-fuel mixture to be combusted by an internal combustion engine in order to maximize the purification rate at which gas components such as HC, NOx are purified by the catalytic converter.
For example, the applicant of the present application has proposed a system for achieving an optimum exhaust gas purifying capability of a catalytic converter by sequentially determining a target value for the air-fuel ratio of an exhaust gas upstream of the catalytic converter according to a feedback control process in order to converge an output (detected value of oxygen concentration) of an O
2
sensor (oxygen concentration sensor) disposed downstream of the catalytic converter to a predetermined target value (constant value), and manipulating the air-fuel ratio of an air-fuel mixture to be combusted by an internal combustion engine to equalize the air-fuel ratio of the exhaust gas upstream of the catalytic converter with the target air-fuel ratio. See, for example, Japanese laid-open patent publication No. 9-324681 and U.S. Pat. No. 5,852,930, for details. The air-fuel ratio of the exhaust gas upstream of the catalytic converter specifically represents the air-fuel ratio recognized from the oxygen concentration of the exhaust gas that enters the catalytic converter, i.e., the air-fuel ratio of the air-fuel mixture which has been combusted by the internal combustion engine to produce the exhaust gas. This air-fuel ratio will hereinafter be referred to as the air-fuel ratio of the internal combustion engine.
By controlling the air-fuel ratio of the internal combustion engine at an air-fuel ratio state to converge (set) the output of the O
2
sensor disposed downstream of the catalytic converter to the predetermined target value, it is possible to achieve the optimum capability of the catalytic converter to purify HC, NOx, etc., i.e., the purifying capability to maximize the purification rate of HC, NOx, etc., irrespective of the deteriorated state of the catalytic converter.
In recent years, there have been developed exhaust gas sensors, specifically HC sensors and NOx sensors, capable of detecting relatively accurately the concentrations of various gas components, including HC, NOx, etc., to be purified by catalytic converters. Some of these exhaust gas sensors generally have their output levels increasing substantially linearly as the concentrations of the detected gas components increase. The output levels of other exhaust gas sensors decrease as the concentrations of the detected gas components increase. The output characteristics of the exhaust gas sensors of the former type will hereinafter be referred to as positive characteristics, and the output characteristics of the exhaust gas sensors of the latter type will hereinafter be referred to as negative characteristics.
If such exhaust gas sensors are used, then it may be possible to control the purification of a gas component by a catalytic converter at a desired state while the concentration of the gas component purified by the catalytic converter is being observed.
For example, such an exhaust gas sensor may be disposed downstream of the catalytic converter, and a target air-fuel ratio for the internal combustion engine may be determined in order to equalize the output of the exhaust gas sensor or the concentration of the gas component recognized from the output of the exhaust gas sensor, i.e., the detected value of the concentration, with a desired value, and the air-fuel ratio of the air-fuel mixture combusted by the internal combustion engine may be controlled based on the target air-fuel ratio.
According to the inventor's finding, however, the purification rate of a gas component such as HC, NOx, etc. by the catalytic converter is basically maximum when the air-fuel ratio of the internal combustion engine is of a certain value, basically a value near a stoichiometric air-fuel ratio, and is reduced when the air-fuel ratio of the internal combustion engine is shifted into an air-fuel ratio range that is either leaner or richer than that certain value of the air-fuel ratio. Therefore, the concentration of the gas component recognized from the output of the exhaust gas sensor disposed downstream of the catalytic converter has a minimum value as the air-fuel ratio of the internal combustion engine changes. The output of the exhaust gas sensor which has the positive characteristics has a minimum value as the air-fuel ratio of the internal combustion engine changes, and the output of the exhaust gas sensor which has the negative characteristics has a maximum value as the air-fuel ratio of the internal combustion engine changes.
When the output of the exhaust gas sensor or the concentration of the gas component recognized from the output of the exhaust gas sensor differs from a desired value, it is difficult to identify which of the leaner and richer air-fuel ratio ranges the air-fuel ratio of the internal combustion engine should be changed into in order to eliminate the difference. Therefore, it is difficult according to the conventional feedback control process which employs the O
2
sensor disposed downstream of the catalytic converter to determine a target air-fuel ratio for controlling the output of the exhaust gas sensor at the desired value.
There has been a demand for a new technique of controlling, at a desired value, the output of an exhaust gas sensor that is disposed downstream of a catalytic converter, for detecting the concentration of a gas component to be purified by the catalytic converter, such as HC, NOx, etc.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an apparatus for controlling the air-fuel ratio of an internal combustion engine to control, well at a desired value, the output of an exhaust gas sensor that is disposed downstream of a catalytic converter, for detecting the concentration of a gas component to be purified by the catalytic converter, such as HC, NOx, etc., or the concentration of the gas component recognized from the output of the exhaust gas sensor.
To accomplish 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 for detecting the concentration of a particular component in an exhaust gas purified by a catalytic converter which is disposed in an exhaust passage of the internal combustion engine, the exhaust gas sensor being disposed downstream of the catalytic converter, identifying means for identifying the values of parameters of a nonlinear function representing correlating characteristics of the detected concentration of the particular component with respect to an air-fuel ratio of the particular component upstream of the catalytic converter, using data representing the air-fuel ratio of the exhaust gas upstream of the catalytic converter and output data of the exhaust gas sensor, target air-fuel ratio calculating means for determining the value of an air-fuel ratio at which the concentration of the particular component that is represented by a function value of the nonlinear function whose parameters are identified by the identifying means is of a value satisfying a predetermined condition, using the identified values of the parameters of the non-linear function, and obtaining the determined value of the air-fuel ratio as a target air-fuel ratio for the exhaust gas upstream of the catalytic converter, and air-fuel ratio manipulating means fo
Oshima Yoshikazu
Yasui Yuji
Honda Giken Kogyo Kabushiki Kaisha
Squire Sanders & Dempsey LLP
Vo Hieu T.
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