Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – With indicator or control of power plant
Reexamination Certificate
2002-02-01
2004-01-27
Wolfe, Willis R. (Department: 3747)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
With indicator or control of power plant
C701S109000, C700S029000, C060S276000, C060S285000
Reexamination Certificate
active
06684150
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for and a method of controlling a plant.
2. Description of the Related Art
The applicant of the present application has proposed a technique for controlling the air-fuel ratio of an air-fuel mixture to be combusted in an internal combustion engine, and hence the air-fuel ratio of an exhaust gas that enters a catalytic converter (hereinafter referred to as “upstream-of-catalyst air-fuel ratio”) in order to converge the output of an exhaust gas sensor (oxygen concentration sensor) to a given target value (constant value), the oxygen concentration sensor being disposed downstream of the catalytic converter for detecting the concentration of a certain component, e.g., the concentration of oxygen, in the exhaust gas that has passed through the catalytic converter, in order to enable the catalytic converter disposed in the exhaust passage of the internal combustion engine to perform its desired exhaust gas purifying capability, as disclosed in Japanese laid-open patent publication No. 11-93740 and U.S. Pat. No. 6,079,205. The upstream-of-catalyst air-fuel ratio is specifically the air-fuel ratio of a combusted air-fuel mixture that enters the catalytic converter, as recognized from the concentration of oxygen in the exhaust gas.
According to the disclosed system, an exhaust system ranging from an upstream side of the catalytic converter to the oxygen concentration sensor disposed downstream of the catalytic converter is used a system to be controlled. A manipulation variable for determining the upstream-of-catalyst air-fuel ratio as an input quantity for the exhaust system, e.g., a target air-fuel ratio for the exhaust gas, is successively generated in order to converge the output of the oxygen concentration sensor as an output variable from the exhaust system to the target value. By manipulating the air-fuel ratio of the air-fuel mixture combusted in the internal combustion engine depending on the target air-fuel ratio, the upstream-of-catalyst air-fuel ratio is manipulated into the target air-fuel ratio, and hence the output of the oxygen concentration sensor is converged to the target value.
The exhaust system has a relatively long dead time owing to the catalytic converter included in the exhaust system. While the internal combustion engine is operating in a low rotational speed range, e.g., is idling, the dead time of a system for generating the upstream-of-catalyst air-fuel ratio from the target air-fuel ratio, which system includes the internal combustion engine and will be referred to as “air-fuel ratio manipulating system”) is also relatively long. These dead times tend to adversely affect the process of converging the output of the oxygen concentration sensor to the target value. According to the above technique, therefore, data representing an estimated value for the output of the oxygen concentration sensor after the dead time of the exhaust system or the sum of the dead time of the exhaust system and the dead time of the air-fuel ratio manipulating system is sequentially generated according to an algorithm which is constructed based on a predetermined model of the exhaust system. The target air-fuel ratio is generated using the above estimated value. The target air-fuel ratio is generated according to a sliding mode control process (specifically, an adaptive sliding mode control process) which is one type of feedback control process.
The air-fuel ratio of the exhaust gas while the output of the oxygen concentration sensor is being converged to the target value is an air-fuel ratio close to a stoichiometric air-fuel ratio.
According to the above technique, the control process of converging the output of the oxygen concentration sensor to the target value can stably be carried out while compensating for the effect of the dead times of the exhaust system and the air-fuel ratio manipulating system, and the good purifying capability of the catalytic converter can be maintained irrespectively of a degraded state of the catalytic converter.
In the above technique, if the exhaust system is regarded as a plant, then the internal combustion engine can be regarded as an actuator for generating the upstream-of-catalyst air-fuel ratio as an input to the plant and the oxygen concentration sensor as a detecting means for detecting the concentration of oxygen as an output of the plant.
Generally, internal combustion engines mounted on automobiles or the like are not always operated at an air-fuel ratio close to a stoichiometric air-fuel ratio in a mode referred to as “stoichiometric operation mode”. Depending on the operating conditions, the internal combustion engine may be operated with the fuel supply being cut off or operated in a lean air-fuel ratio range in a mode referred to as “lean operation mode”. The control process of converging the output of the oxygen concentration sensor to the target value is carried out in the stoichiometric operation mode.
The output of the oxygen concentration sensor exhibits substantially linear characteristics with respect to the concentration of oxygen in a range close to the target value, i.e., in an air-fuel ratio range close to a stoichiometric air-fuel ratio. However, the output of the oxygen concentration sensor is nonlinear with respect to the concentration of oxygen out of the range close to the target value (see the solid-line curve “a” in
FIG. 2
of the accompanying drawings). Therefore, the output of the oxygen concentration sensor is nonlinear with respect to the concentration of oxygen when the internal combustion engine is operated with the fuel supply being cut off or operated in the stoichiometric operation mode immediately after the lean operation mode.
However, when the output of the oxygen concentration sensor varies in the nonlinear range, according to the above technique, the accuracy of the estimated value for the output of the oxygen concentration sensor tends to be lowered, and it is difficult to keep the accuracy of the estimated value at the same level as when the output of the oxygen concentration sensor is in the linear range. In addition, the catalyst has different responses when the catalyst exhibits a reducing action based on its chemical reaction, i.e., when the air-fuel ratio changes from a lean side to a rich side, and when the catalyst exhibits an oxidizing action based on its chemical reaction, i.e., when the air-fuel ratio changes from a rich side to a lean side, and the nonlinearity of the oxygen concentration sensor also increases with the different responses of the catalyst. The sliding mode control process (specifically, the adaptive sliding mode control process) which is a stable control process for generating the target air-fuel ratio may be used to prevent the stability of the process of controlling the output of the oxygen concentration sensor from being impaired. However, the quick response of the control process of converging the output of the oxygen concentration sensor may be impaired due to the reduction in the accuracy of the estimated value for the output of the oxygen concentration sensor.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an apparatus for and a method of controlling a plant so as to be able to perform, with a highly quick response, a control process of converging an output of a detecting means for detecting the output of the plant to a predetermined target value irrespective of the output state of the detecting means even if the output of the detecting means is nonlinear.
Another object of the present invention is to provide an apparatus for and a method of controlling a plant so as to be able to perform, with a highly quick response, a control process of converging an output of a an exhaust gas sensor (detecting means) such as an oxygen concentration sensor disposed downstream of a catalytic converter in the exhaust passage of an internal combustion engine to a predetermined target value irrespective of the output state of the exhaust gas sen
Iwaki Yoshihisa
Morishita Kunihiro
Tagami Hiroshi
Yasui Yuji
Honda Giken Kogyo Kabushiki Kaisha
Lahive & Cockfield LLP
Wolfe Willis R.
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