Internal-combustion engines – Charge forming device – Exhaust gas used with the combustible mixture
Reexamination Certificate
2002-04-11
2004-01-13
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Charge forming device
Exhaust gas used with the combustible mixture
C251S129110
Reexamination Certificate
active
06675783
ABSTRACT:
TECHNICAL FIELD
This invention relates to an apparatus for controlling an exhaust gas recirculation valve (hereinafter referred to as an EGR valve) which is disposed in an exhaust gas recirculation system.
BACKGROUND ART
FIG. 1
is a conventional schematic explanation diagram of an engine exhaust system.
In this apparatus for controlling the EGR valve, the opening and closing of the control valve
11
is controlled by, for example, a stepping motor M of a hybrid PM type 4-phase construction or the like. An open-loop control of the stepping motor M by a stepping angle contributes to a control over the degree of the opening of the control valve
11
.
Such a control apparatus using this kind of stepping motor M imposes a restriction on the control over the degree of the control 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 of 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 phenomenon has occurred, the reliability falls as an error is still contained uncompensated in the control amount.
To this end, the conventional apparatus for controlling an EGR valve gives a predetermined return torque to the control valve
11
in the opening or closing direction by urging means and, by the application of a unidirectional current to a direct current (DC) motor (hereinafter referred to also as a DC motor) gives a motor torque to vary the control valve
11
in the closing direction, and opens and closes the control valve
11
by the balance of these torque. An arrangement is described in Japanese Published Unexamined Patent Application No. 122059/1998. This arrangement includes an open loop control system for controlling an open loop of the DC motor such that a motor torque is generated in corresponding with a target opening and closing positions of the above control valve
11
; and a feedback control system for feedback-controlling the DC motor based on a deviation between input data corresponding to the target opening and closing positions of the control valve
11
and detected data of the current opening and closing positions 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 DC motor will be described. In case the degree of the opening of the control valve
11
is feedback-controlled in a DC servo motor system, the generated torque of the DC motor 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 continuos control over the generated torque of the motor M promotes infinite reduction of the resolution. Further, the DC motor does not cause the control error due to the stepping-out as with the stepping motor M and, therefore, the response can be improved accordingly as compared with the case where the stepping motor M is used, thereby improving reliability.
This kind of apparatus for controlling the EGR valve using the DC motor adopted a so-called torque balance system. The apparatus gives a predetermined return torque in the closing direction (or in the opening direction) by means of a spring as urging means, gives a variable motor torque in the opening direction (or in the closing direction) by unidirectional power feeding to the DC motor and controls the valve opening and closing by the balance of these torque.
In case this kind of driving system is adopted, since the EGR valve is constantly given the return torque, there occurs a hysteresis, due to friction, as shown in
FIG. 2
between the operating characteristic A when the control valve
11
is opened by increasing the motor torque and the operating characteristic B when the control valve
11
is closed by decreasing the motor torque. The inclination of the operating characteristics A, B varies depending on the spring constant of the spring which gives the return torque, and the operating characteristics A, B shift to the right or to the 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 DC motor is under the control of a PI (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 as shown in
FIG. 2
, it becomes difficult to stabilize the control valve
11
in 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 the control along the operating characteristic A in FIG.
2
. However, when the motor torque is increased under the control of this kind, the deviation of the opening position of the control valve
11
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 opening and closing position in the EGR valve.
At an initial stage, the control valve
11
begins to close (at the time the deviation is small), since the P and I components are both small, 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, and therefore the closing operation of the control valve
11
cannot stop abruptly due to the inertia of the DC motor M. The control valve
11
thus cannot be operated in the opening direction immediately. If the gain is made large such that generate a relatively large motor torque is generated even when 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 longitudinal sectional view of the RGR valve.
An apparatus for controlling the control valve
11
in a so-called torque balance drive system using the DC motor M will be made in consideration of the above situation with reference to
FIGS. 4
to
7
.
Referring to
FIG. 4
, reference numeral
1
denotes a valve body having formed therein a passage which forms a part of an exhaust gas recirculation passage c interposed in a recirculation system of the exhaust gas. By moving upwardly the control valve
11
as illustrated to contact a valve seat
12
, the exhaust gas recirculation passage c is closed and, by moving downwardly the control valve
11
to apart from the valve seat
12
, the exhaust gas recirculation passage c is opened.
Reference numeral
2
denotes a motor case for housing therein a DC motor
20
. In the DC motor
20
, reference numeral
21
denotes a rotor around which a coil
22
is wound, and reference numeral
23
denotes a yoke provided with a magnet
24
. The upper end of the rotor
21
is rotatably supported on the motor case
2
by a sliding-ball
25
and a rotor shaft
26
, and the lower end of the rotor
21
is rotatably supported on the valve body
1
by a bearing
27
. A commutator
28
is attached to the upper end of the rotor
21
, and a motor brush
30
provided on the motor case
2
is urged by a brush spring
29
into contact with the commutator
28
.
Reference numeral
40
denotes a position sensor for detecting the rotati
Fujita Youichi
Kawamura Satoshi
Miyake Toshihiko
Miyoshi Sotsuo
Ali Hyder
Mitsubishi Denki & Kabushiki Kaisha
Sughrue & Mion, PLLC
Yuen Henry C.
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