Internal-combustion engines – Charge forming device – Exhaust gas used with the combustible mixture
Reexamination Certificate
2002-04-11
2003-12-16
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Charge forming device
Exhaust gas used with the combustible mixture
C251S129120
Reexamination Certificate
active
06662790
ABSTRACT:
TECHNICAL FIELD
This invention relates to a method of controlling an exhaust gas recirculation valve (hereinafter referred to as an EGR valve) disposed in an exhaust gas recirculation system.
BACKGROUND ART
FIG. 1
is a conventional schematic diagram showing an arrangement of a control valve
11
as an EGR valve disposed in an exhaust gas recirculation passage c which communicates an exhaust passage “a” of an engine E with an intake passage b.
The method of controlling the EGR valve involves driving and controlling a stepping motor M of a hybrid PM type 4-phase construction or the like by an engine control unit (hereinafter referred to as ECU)
51
, and controlling the opening and closing of the control valve
11
by this stepping motor M. An open-loop control of the stepping motor M by a stepping angle contributes to control over the degree of the opening of the control valve
11
.
Such a control method using this kind of stepping motor M imposes restrictions on the control over the degree of the opening of the control valve
11
because the degree of the opening of the control valve
11
can be controlled only by the stepping angle of the stepping motor M. The control valve
11
has a limited resolution for the controllable opening. In addition, the stepping motor M has a limited open-loop control response characteristic due to the possible occurrence of a stepping-out phenomenon. Once the stepping-out has occurred, the reliability falls as an error is still contained uncompensated in the control amount.
To this end, the conventional control method of an EGR valve involves giving a predetermined return torque to the control valve
11
in the control valve closing direction and, by a unidirectional driving of a direct current (DC) motor M (hereinafter referred to as a motor M), giving a motor torque to vary the control valve
11
in the opening direction, and opening and closing the control valve
11
by the balance of these torque.
An arrangement is described in Japanese Published Patent Feeding No. 159405/1999. This arrangement includes an open loop control system for controlling an open loop of the motor M such that a motor torque is generated in correspondence with the target opening and closing position of the above control valve
11
; and a feedback control system for feedback-controlling the motor M based on a deviation between input data corresponding to the target opening and closing position of the above control valve
11
and detected data of the current opening and closing position of the control valve
11
.
FIG. 2
is a characteristic diagram showing the relationship between a motor torque and an opening and closing position of a control valve in an EGR valve of torque balance drive system.
First, the driving system using this motor M will be described. In case the degree of the opening of the control valve
11
is feedback-controlled by the motor M, the generated torque of the motor M is continuously controlled by feeding back the degree of the opening of the control valve
11
through unintermitted detection with a position sensor such as a sliding resistor type. Theoretically, the continuous control over the generated torque of the motor M promotes infinite reduction of the resolution of the controllable opening of the control valve
11
.
This kind of method of controlling the EGR valve using the motor M adopted a so-called torque balance method. The method involves giving a predetermined return torque in the closing direction by means of a spring as urging means, giving a motor torque variable in the opening direction by driving the motor M in the opening direction, and determining the valve opening position by the balance of these torque.
In case this kind of control method is adopted, since the EGR valve is constantly given the return torque, the opening and closing positions (shift amount) vary in correspondence with the inclination of lines A, B having a hysteresis characteristics due to friction as shown in FIG.
2
.
Here, line A indicates an operating characteristic when the control valve
11
is opened by increasing the motor torque, and line B an operating characteristic when the control valve
11
is closed by reducing the motor torque. The inclination of the operating characteristics A, B varies depending on the spring constant of the spring to give the return torque, and the operating characteristics A, B shift to the right or left in
FIG. 2
depending on the magnitude of the set torque.
Now, in order to control the control valve
11
having this kind of operating characteristics, suppose that a method is admitted, in which the motor is under the control of a P(proportional) I(integral) control based on a deviation between the input data corresponding to the target opening and closing position of the control valve
11
and the detected data of the current opening and closing position of the control valve. In this case, owing to the relation of the operating characteristics A, B as shown in
FIG. 2
, it becomes difficult to stabilize the control valve
11
at the target opening position.
In other words, in order to open the control valve
11
to the target opening position by increasing the motor torque, the P gain and the I gain must be increased to take control along the operating characteristic A shown in FIG.
2
. However, when the motor torque is increased by the PI control under the control of this kind, the deviation of the opening position of the control valve becomes “0” as soon as the control valve
11
is opened to the target opening position. The P component thus becomes “0” and the I component is cleared, with the result that the control valve
11
begins to close by the return torque.
FIG. 3
is a characteristic diagram showing the relationship between the time and the operating position of a motor shaft.
At an initial stage in which the control valve
11
begins to close (at the time the deviation is small), the P and I components are both small and therefore the motor torque cannot overwhelm the return torque, with the result that the deviation becomes large. Thereafter, even if the deviation becomes large to a certain degree, the motor torque and the return torque balance with each other, the closing operation of the control valve
11
cannot stop abruptly due to the inertia of the motor M. The control valve
11
thus cannot be opened immediately. If the gain is made large such that a relatively large motor torque is generated even at the time the deviation is small, there will be a vicious cycle that incurs an increase of the overshooting and undershooting as shown in FIG.
3
.
FIG. 4
is a longitudinal sectional view of the EGR valve.
The arrangement implementing a method of controlling the control valve
11
in a so-called torque balance drive system using the motor M will now be described, with due consideration of the above circumstance.
Referring to
FIG. 4
, reference numeral
1
denotes a valve body having therein a passage forming a part of an exhaust gas recirculation passage c which is interposed in a recirculation system of the exhaust gas. By upwardly moving the control valve
11
to contact it with a valve seat
12
as shown in
FIGS. 4
to
6
the exhaust gas recirculation passage c is closed. Conversely, by downwardly moving the control valve
11
to depart it from the valve seat
12
the exhaust gas recirculation passage c is opened.
Reference numeral
2
denotes a motor case for housing therein the motor M. Inside this motor case
2
, reference numeral
21
denotes a rotor around which a coil
22
is wound, and reference numeral
23
a yoke with a magnet
24
. The lower end of the rotor
21
is rotatably supported on the valve body
1
by a bearing
27
.
Inside the rotor
21
, a motor shaft
31
is screwed. The motor shaft
31
is prevented from rotating by a guide bush
13
in the body
1
. It therefore follows that the motor shaft
31
moves in the upward and downward direction depending on the amount of rotation of the rotor
21
. A valve shaft
14
is held in contact with the lower end of the motor shaft
31
Fujita Youichi
Kawamura Satoshi
Miyake Toshihiko
Miyoshi Sotsuo
Castro Arnold
Mitsubishi Denki & Kabushiki Kaisha
Yuen Henry C.
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