Valves and valve actuation – With means to increase head and seat contact pressure – With positive reduction
Reexamination Certificate
1999-12-13
2001-05-01
Shaver, Kevin (Department: 3754)
Valves and valve actuation
With means to increase head and seat contact pressure
With positive reduction
C251S124000, C251S129120, C251S124000, C123S568230
Reexamination Certificate
active
06224034
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a control valve device which opens and closes a valve by driving a stepper motor.
BACKGROUND ART
FIG. 12
is a cross section of a conventional exhaust gas recirculation control valve device (hereinafter simply “EGR valve”),
FIG. 13
is a cross section along line XIII—XIII of
FIG. 12
,
FIG. 14
is a cross section along line XIV—XIV of
FIG. 12
,
FIG. 15
is a cut away perspective view of part of the stepper motor in
FIG. 12
, and
FIG. 16
is a schematic of the interior of the stepper motor in FIG.
15
. Further,
FIG. 14
is expanded to twice the size of FIG.
13
.
This EGR valve is provided with a valve main body
1
and a stepper motor
2
mounted on the upper portion of the valve main body
1
.
The valve main body
1
is provided with a valve body
5
having an exhaust gas inflow passage
3
and an exhaust gas outflow passage
4
, a valve seat
6
disposed between the exhaust gas inflow passage
3
and the exhaust gas outflow passage
4
, a valve
7
in direct contact with the valve seat
6
, a valve shaft
8
, one end of which is fixed to the valve
7
, a shaft bushing
9
disposed between the valve body
5
and the valve shaft
8
so as to slidably support the valve shaft
8
, a spring bracket
10
fixed to the other end of the valve shaft
8
, and a coil spring
11
compressed and disposed between the valve body
5
and the spring bracket
10
.
The stepper motor
2
is provided with a motor case
20
, a motor cap
21
fixed to the motor case
20
, a rotor
28
disposed within the motor case
20
and rotatably supported by a shaft bushing
27
, and a stator
32
disposed on the outside of the rotor
28
to turn the rotor
28
.
The rotor
28
is provided with a shaft bushing
22
fixed to the motor cap
21
, a motor shaft
23
having a shaft portion
24
supported by the shaft bushing
22
so as to slide freely along the direction of the shaft and a male thread portion
25
, a female thread portion
26
screwing the male thread portion
25
, and a cylindrical magnet portion
30
consisting of an array of alternating north pole magnets and south pole magnets disposed outside the female thread portion
26
.
As shown in
FIG. 13
, the cross section of the shaft portion
24
of the motor shaft
23
is a segmented circle, so that the motor shaft
23
can only move along the direction of the shaft axis. Also, as shown in
FIG. 14
, protruding shaft portion positioning portions
29
are formed in the upper portion of the shaft portion
24
. A pair of rotor positioning portions
31
, which come into direct contact with the shaft portion positioning portions
29
, are formed on the inner surface of the lower portion of the female thread portion
26
. The upper positional limit of the motor shaft
23
is regulated by the rotor positioning portions
31
coming into contact with the shaft portion positioning portions
29
. In other words, as the female thread portion
26
rotates, the motor shaft
23
, which has a thread screwing that of the female thread portion
26
, may move upwards, but once the rotor positioning portions
31
come into contact with the shaft portion positioning portions
29
, the female thread portion
26
can no longer rotate, and so the motor shaft
23
cannot move upwards any further (the motor shaft
23
cannot rotate; it can only move along the direction of the shaft axis because of the shaft bushing
22
).
The aforementioned stator
32
is provided with an upper coil
41
, a lower coil
42
disposed below the upper coil
41
, a first phase stator portion
43
mounted on the upper surface of the upper coil
41
, a second phase stator portion
44
mounted on the lower surface of the upper coil
41
, a third phase stator portion
45
mounted on the upper surface of the lower coil
42
, and a fourth phase stator portion
46
mounted on the lower surface of the lower coil
42
. The shape of each of the phase stator portions
43
,
44
,
45
,
46
is annular, and each has claw portions
43
a
,
44
a
,
45
a
,
46
a
formed on its inner edge and bent towards coils
41
and
42
, respectively. The claw portions
43
a
of the first phase stator portion
43
are arranged so as to interlock with the claw portions
44
a
of the second phase stator portion
44
, and the claw portions
45
a
of the third phase stator portion
45
are arranged so as to interlock with the claw portions
46
a
of the fourth phase stator portion
46
.
In the above EGR valve, when a current is passed through the upper coil
41
and the lower coil
42
, magnetic poles is formed in each phase of the stator portions
43
,
44
,
45
,
46
and like magnetic poles is formed in the corresponding claw portions
43
a
,
44
a
,
45
a
,
46
a.
The direction of the current in the upper coil
41
can be reversed, and similarly the direction of the current in the lower coil
42
can also be reversed, so that there are four possible patterns of current direction and the magnetic poles which arise in each of the phase stator portions
43
,
44
,
45
,
46
change with each pattern. Then, within the magnetic field generated by the claw portions
43
a
,
44
a
,
45
a
,
46
a
, the magnet portion
30
and the female thread portion
26
rotate to and are maintained in a position where the magnetic forces acting on between the claw portions
43
a
,
44
a
,
45
a
,
46
a
and the magnet portion
30
are in equilibrium.
Also, if the order of the above changes in current pattern (steps) is reversed, the magnetic portion
30
and the female thread portion
26
will rotate in the opposite direction.
With the rotation of the magnetic portion
30
and the female thread portion
26
, the male thread portion
25
, whose thread matches that of the female thread portion
26
, also rotates and motor shaft
23
moves along the direction of the shaft axis.
In the aforementioned EGR valve, when the motor shaft
23
is moved downwards by the action of the aforementioned stepper motor, the motor shaft
23
starts to act midway in opposition to the elasticity of the compressed coil spring
11
, pushing the head of the valve shaft
8
and moving the valve shaft
8
downwards and thus separating the valve
7
from the valve seat
6
, whereby the exhaust gas inflow passage
3
connects with the exhaust gas outflow passage
4
and exhaust gas flows from the exhaust gas inflow passage
3
into the exhaust gas outflow passage
4
.
By reversing the direction of rotation of the magnetic portion
30
and the female thread portion
26
, the motor shaft
23
will move upwards along the direction of the shaft axis and the valve shaft
8
will also be moved upwards by the elasticity of the compressed coil spring
11
, its head in contact with the shaft portion
24
. Then, the valve
7
will come into contact with the valve seat
6
, closing the valve main body
1
, whereby the exhaust gas inflow passage
3
is cut off from the exhaust gas outflow passage
4
and exhaust gas cannot flow. If the magnetic portion
30
and the female thread portion
26
are rotated further in this direction, the motor shaft
23
will move further upwards and the shaft portion
24
will separate from the valve shaft
8
.
FIG. 17
shows the relationship between the number of steps (number of changes in current pattern) in the stepper motor
2
and the amount of flow through the EGR valve. It can be seen from the graph that the amount of flow is proportional to the number of steps.
Now, in order to operate the stepper motor
2
exactly as instructed by the control unit (not shown), it is necessary to initialize the position of the motor shaft
23
of the stepper motor
2
beforehand.
To perform this initialization reliably, the stepper motor
2
is given a greater number of steps than is needed to place the motor shaft
23
of the stepper motor
2
at the end of the motor. In this way, the shaft portion
24
of the motor shaft
23
is separated to an appointed distance from the head of the valve shaft
8
, and once the motor shaft
23
reaches the motor end position, even if current is passed through the upper
Kato Yasuhiko
Miyake Toshihiko
Miyoshi Sotsuo
Okada Hidetoshi
Bonderer D. A.
Mitsubishi Denki & Kabushiki Kaisha
Shaver Kevin
Sughrue Mion Zinn Macpeak & Seas, PLLC
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