Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – With indicator or control of power plant
Reexamination Certificate
2003-02-14
2004-11-09
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
C060S276000, C060S285000, C123S697000, C701S115000, C701S109000
Reexamination Certificate
active
06816774
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an O
2
sensor for use in the exhaust system of an internal combustion engine, an apparatus for and a method of controlling the air-fuel ratio in a system where an O
2
sensor is incorporated in the exhaust system of an internal combustion engine, and a recording medium which stores an air-fuel ratio control program for such a system.
2. Description of the Related Art
There has been proposed by the applicant of the present application a system for controlling the air-fuel ratio of an exhaust gas, i.e., the air-fuel ratio represented by the concentration of oxygen in an exhaust gas, supplied from an internal combustion engine to a catalytic converter for keeping the output voltage of an O
2
sensor disposed downstream of the catalytic converter at a predetermined target value (a constant value) in order to give a required exhaust gas purifying capability to the catalytic converter, which comprises a three-way catalyst or the like disposed in the exhaust system (passage) of the internal combustion engine (see, for example, Japanese laid-open patent publication No. 11-324767 and U.S. Pat. No. 6,188,953).
The proposed system is based on the phenomenon that when the air-fuel ratio of the exhaust gas supplied from the internal combustion engine to the catalytic converter is controlled at an air-fuel ratio state for settling the output voltage of the O
2
sensor disposed downstream of the catalytic converter at a predetermined constant value, the rates of purification of CO (carbon monoxide), HC (hydrocarbon), NOx (nitrogen oxide), etc. by the catalytic converter are kept well, i.e., substantially maximum, irrespective of the deteriorated state of the catalytic converter.
A further study made by the inventors of the present invention has revealed the following findings:
An O
2
sensor has its output characteristics changed when the temperature of an active element of the O
2
sensor, i.e., a sensitive element of the O
2
sensor which is held in contact with an exhaust gas, is changed by factors that affect the temperature of the active element of the O
2
sensor, such as the layout of the exhaust system of the internal combustion engine, the temperature of the exhaust gas, etc. A change in the output characteristics of the O
2
sensor tends to affect the control properties (control response and stability) of the air-fuel control process for keeping the output voltage of the O
2
sensor disposed downstream of the catalytic converter at a predetermined target value. This is because such a change in the output characteristics of the O
2
sensor varies the sensitivity of the output voltage of the O
2
sensor with respect to an air-fuel ratio change in the vicinity of the target value. The change in the output characteristics of the O
2
sensor also varies the value of the output voltage of the O
2
sensor disposed downstream of the catalytic converter for making well the exhaust gas purifying capability of the catalytic converter, i.e., the value of the output voltage of the O
2
sensor to be used as a target value for maintaining the good exhaust gas purifying capability of the catalytic converter.
Therefore, the control properties of the air-fuel control process for keeping the output voltage of the O
2
sensor at the target value may possibly be lowered depending on the temperature of the active element of the O
2
sensor or the operating conditions or environmental conditions of the internal combustion engine which affect the temperature of the active element of the O
2
sensor. Furthermore, if factors that affect the temperature of the O
2
sensor, e.g., the temperature of the exhaust gas, are likely to vary while the internal combustion engine is in operation, then it tends to be difficult to keep the desired exhaust gas purifying capability of the catalytic converter even when the output voltage of the O
2
sensor is controlled at the constant target value.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an O
2
sensor having adequate output characteristics for maintaining the required exhaust gas purifying capability of a catalytic converter.
Another object of the present invention is to provide an apparatus for and a method of controlling an air-fuel ratio to reliably maintain the required exhaust gas purifying capability of a catalytic converter.
Still another object of the present invention is to provide a recording medium which stores a program for enabling a computer to control an air-fuel ratio to reliably maintain the required exhaust gas purifying capability of a catalytic converter.
Prior to describing the present invention in detail, the output characteristics of an O
2
sensor will first be described below. An O
2
sensor which is disposed in the exhaust passage of an internal combustion engine generates an output voltage depending on the concentration of oxygen in an exhaust gas which is brought into contact with an active element (sensitive element) of the O
2
sensor. The active element of the O
2
sensor is usually made of a material containing or coated with lead, silver, platinum, etc. (e.g., zirconia (ZrO
2
+Y
2
O
3
)). The O
2
sensor has output characteristics (specifically, the characteristics of an output voltage of the O
2
sensor with respect to the air-fuel ratio in the exhaust gas which is represented by the concentration of oxygen sensed by the active element) generally referred to as a Z curve.
More specifically, as indicated by the solid-line curve “a” in
FIG. 3
of the accompanying drawings, the output characteristics of the O
2
sensor have a segment e
1
where the output voltage changes substantially linearly at a relative large gradient with respect to a change in the air-fuel ratio in the exhaust gas (hereinafter referred to as “large-gradient segment e
1
”), and segments e
2
, e
3
where the gradient of a change in the output voltage with respect to a change in the air-fuel ratio is smaller than the large-gradient segment e
1
(hereinafter referred to as “small-gradient segments e
2
, e
3
”). The small-gradient segments e
2
, e
3
are present respectively on both sides of the large-gradient segment e
1
, i.e., respectively in regions that are richer and leaner than an air-fuel ratio range &Dgr; corresponding to the large-gradient segment e
1
. The air-fuel ratio range &Dgr; corresponding to the large-gradient segment e
1
is a narrow range near a stoichiometric air-fuel ratio. The gradients of the small-gradient segments e
2
, e
3
are much smaller than the gradient of the large-gradient segment e
1
. The small-gradient segments e
2
, e
3
are joined to the large-gradient segment e
1
by respective boundary segments e
4
, e
5
that provide inflection points across which the gradient changes greatly. The output characteristics shown in
FIG. 3
are general output characteristics of the O
2
sensor. The air-fuel ratio in the exhaust gas according to the above output characteristics, i.e., the air-fuel ratio represented by the concentration of oxygen that is sensed by the active element of the O
2
sensor, becomes richer, i.e., the ratio of fuel to air being larger, as the concentration of oxygen is lower, and becomes leaner, i.e., the ratio of fuel to air being smaller, as the concentration of oxygen is higher.
According to the inventors' knowledge, when the air-fuel ratio in the exhaust gas supplied to the catalytic converter is controlled to keep the output voltage of the O
2
sensor with the above output characteristics at a certain constant target value, it is preferable for the purpose of improving the control properties of such an air-fuel ratio control process to have the target value at a level substantially equal to an output voltage at the inflection point e
4
at a richer air-fuel ratio, of the two inflection points e
4
, e
5
, or specifically to have the target value in an output voltage range in at the inflection point e
4
.
The above target value control is preferable for the following reasons: At
Iwaki Yoshihisa
Yasui Yuji
Hoang Johnny H.
Honda Giken Kogyo Kabushiki Kaisha
Squire Sanders & Dempsey L.L.P.
Wolfe Willis R.
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