Exhaust gas recirculation valve device

Internal-combustion engines – Charge forming device – Exhaust gas used with the combustible mixture

Reexamination Certificate

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Details

C251S129120

Reexamination Certificate

active

06453891

ABSTRACT:

BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to an exhaust gas recirculation valve device disposed in an exhaust gas recirculation passage of an internal combustion engine for example of an automobile.
Prior Art 1.
FIG. 1
is a cross sectional figure showing the internal structure of a conventional exhaust gas recirculation valve device. In the figure, the valve housing
1
has an input port
2
communicating with an exhaust system (not shown) of an engine which is an internal combustion engine, an output port
3
communicating with an air intake system (not shown) of the engine and a passage
4
interposed between the output port
3
and the input port
2
. A valve seat
5
is press fitted into the passage
4
.
6
is a valve rod passing through a bush
7
. A valve
8
is mounted on the lower end of the valve rod
6
to abut or separate with the valve seat
5
.
9
is a spring holder pushed upwardly by a coil spring
10
. A through hole
11
is formed in the central section of the spring holder
9
. A tip
6
a of the valve rod
6
is fixed by caulking through the through hole
11
. The valve rod
6
and the spring holder
9
are integrated by such a caulking and the valve
8
mounted on the lower end of the valve rod
6
is normally pushed in a closed positioning with respect to the valve seat
5
by the coil spring
10
.
12
is a cooling water passage cooling the valve body and the motor to be described below.
20
is a stepping motor main body, and is mounted on the top section of the valve housing
1
so that the axial centers are aligned by a mounting screw
21
.
22
is a motor housing,
23
is a motor holder disposed concentrically between the motor housing
22
and the valve housing
1
.
24
are bobbins which are wound coils
25
.
26
and
27
are yokes. A magnetic path is formed through the outer periphery of the yokes
26
and
27
.
28
is a terminal which is electrically connected to the coils
25
. The terminal
28
and the motor housing
22
form a connector.
29
is a plate which shields the two coil sections magnetically.
30
is a magnet.
31
is a rotor retaining the magnet
30
. The rotor
31
has a threaded section
31
a
threadably attached to a threaded section
32
a
of the motor shaft
32
.
33
is a bushing mounted on the upper end of the rotor
31
.
34
is a ball supported by the bushing
33
.
35
is an adjustment plate, and
36
is a ball bearing mounted at the lower end of the rotor
31
.
In the case that the valve housing
1
and the motor housing
22
above are assembled so that the axial centers are aligned by the mounting screw
21
, an upper face of the tip
6
a
of the valve rod
6
near the valve housing
1
is set to oppose a lower face of the motor shaft
32
near the motor housing
22
at a required distance from the tip
6
a.
The operation of the invention will be described below.
Firstly, when the engine is started and the valve is completely closed, the rotor
31
which contains a magnet
30
rotates in a stepwise manner in a direction of valve opening due to a pulsed voltage sent from the control unit (not shown) to the terminal
28
during the valve opening operation. The stepwise rotation is converted into linear motion by the threaded section
31
a
of the rotor
31
and the threaded section
32
a
of the motor shaft
32
and the motor shaft
32
displaces in a direction of valve opening (downwardly). As the displacement continues, at the moment when the upper face of the tip
6
a
of the valve rod
6
near the valve housing
1
touches to the lower face of the motor shaft
32
near the motor housing
22
, the valve rod
6
is depressed by the drive force of the motor shaft
32
against the pushing upward force of the spring
10
. Also the valve
8
which is mounted on the lower section of the valve rod
6
is lowered and opens with respect to the valve seat
5
and the input port
2
and the output port
3
are connected by the passage
4
.
During the valve closure operation, the rotor
31
which contains a magnet
30
rotates in a stepwise manner in a direction of valve closure due to a pulsed voltage sent from the control unit (not shown) to the terminal
28
in an operation which is the opposite of the above. The motor shaft
32
displaces in a direction of valve closure (upwardly) due to the rotation. In addition to the rotation, the valve rod
6
is raised by the upward pushing force of the spring
10
and the valve
8
shuts the passage between the valve
8
and the valve seat
5
.
It is noted that in the above exhaust gas recirculation valve device which uses a stepping motor, when a valve opening step varies, the rate of exhaust gas flow also varies. Therefore, in order to pass a target flow rate of the exhaust gas, the valve opening step must be constant. The valve opening step is determined by a distance L between the tip
6
a
of the valve rod
6
and the lower face of the motor shaft
22
. However, the distance L depends on the accuracy of dimension of parts such as bushing
33
and the ball
34
, which are disposed on the upper section of the motor shaft
32
. Therefore, the distance L, which is defined between the tip
6
a
of the valve rod
6
and the lower face of the motor shaft
22
, must be adjusted when the valve housing
1
and the motor housing
22
do assembly about every exhaust gas recirculation valve device.
According to the conventional adjustment method, firstly a distance L
1
between the upper face of the tip
6
a
of the valve rod
6
and the upper face of the valve housing
1
and a distance L
2
between the lower face of the motor shaft
32
and the lower face of the motor housing
22
are measured. In order to determine an appropriate distance L, a stroke of the motor shaft
32
is then considered to calculate an adjustment thickness L
3
. The adjustment plate
35
having a thickness corresponding to the adjustment thickness L
3
is interposed between the both abutting sections of the valve housing
1
and the motor housing
22
to adjust the distance L so as to be constant. In other words, with the conventional adjustment method, since the distance L satisfies an equation of L=(L
1
-L
2
)+L
3
and the distances L
1
and L
2
vary in all products, the distance L is adjusted by varying the adjustment thickness L
3
.
However, since the conventional exhaust gas recirculation valve device is constituted as described above, when one kind of metallic plate functioning as the adjustment plate
35
having a thickness of 0.1 mm, for example, is prepared, there are occasions when many metallic plates must be interposed therebetween. This raises the manufacturing costs. Therefore, in order to reduce the number of metallic plates interposed therebetween, various kinds of metallic plates which function as an adjustment plate
35
are prepared with a thickness varying from 0. 1 mm to 0.5 mm in increments of 0.1 mm. Therefore, the use of the plates differs as a result of this processing. As a result, there are problems in time and effort with respect to the stock-control.
Prior Art 2.
JP-A-1997/256916 discloses an exhaust gas recirculation valve including a seat valve for opening/closing an exhaust gas circulation passage, and a valve actuator moving a valve body of the seat valve in a forward or backward direction to open/close the passage above. With the exhaust gas recirculation valve, seat parts with a variety of thicknesses are disposed between a valve shaft of the seat valve and a central piston of the valve actuator. Thus, the axial variations in component dimensions are absorbed in order to control a stroke of the valve on opening.
However, with the exhaust gas recirculation valve, the seat parts for adjustment of thicknesses are also used, and the axial variations in component dimensions of the valve shaft and so on, are absorbed in a like manner of the prior art 1. Since the seat parts prepared have a variety of thicknesses, there are problems with respect to increase in manufacturing costs and in the time and effort expended in stock control.
The pre

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