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Patent Abstract
A normally closed solenoid valve includes a fixed core, a valve
portion including a valve seat and a valve body, a movable core
disposed between the fixed core and the valve seat, a resilient
biasing member for biasing the movable core in a valve-closing direction
and a coil. When energized, the coil generates an attracting force
between the movable core and the fixed core against a biasing force
by the resilient biasing member to cause the movable core to retreat
from an initial position where the valve seat is in a closed state.
When a characteristic graph line of spacing distance/attracting
force that defines the attracting force in relation with a spacing
distance between the fixed core and the movable core provides an
inclination A (N/mm) at the initial position, the compression resiliency
coefficient of the resilient biasing member is set to A(N/mm).
Patent Claims
What is claimed is:
1. A normally closed solenoid valve, comprising: a fixed core;
a valve portion for opening and closing a flow path of a hydraulic
fluid, the valve portion including a valve seat and a valve body
disposed opposed to the valve seat to be seated therein; a movable
core disposed between the fixed core and the valve seat; which is
capable of advancing and retreating along with the valve body with
respect to the valve seat; a resilient biasing member for biasing
the movable core in a valve-closing direction along which the valve
body is seated in the valve seat for closing the valve; and a coil
for generating an attracting force between the movable core and
the fixed core when energized to cause the movable core to retreat
in a valve-opening direction from an initial position thereof where
the valve portion is in a closed state, the attracting force acted
against a biasing force exerted by the resilient biasing member;
wherein, when a characteristic graph line of spacing distance/attracting
force that defines the attracting force in relation with a spacing
distance between the fixed core and the movable core provides an
inclination A(N/mm) at the initial position, the compression resiliency
coefficient of the resilient biasing member is set to A(N/mm).
2. The normally closed solenoid valve according to claim wherein
the valve body is separately formed with the movable core and is
engaged and fixed to a tip ends of the movable core on a valve seat
side of the movable core.
3. The normally closed solenoid valve according to claim 1, wherein
the resilient biasing member is a spring member; and the compression
resiliency coefficient is a spring constant of the spring member.
4. A normally closed solenoid valve, comprising: a fixed core;
a valve portion for opening and closing a flow path of a hydraulic
fluid, the valve portion including a valve seat and a valve body
disposed opposed to the valve seat to be seated therein; a movable
core disposed between the fixed core and the valve seat, which is
capable of advancing and retreating along with the valve body with
respect to the valve seat; a resilient biasing member for biasing
the movable core in a valve-closing direction along which the valve
body is seated in the valve seat for closing the valve; and a coil
for generating an attracting force between the movable core and
the fixed core when energized to cause the movable core to retreat
in a valve-opening direction from an initial position thereof where
the valve portion is in a closed state, the attracting force acted
against a biasing force exerted by the resilient biasing member;
wherein, when an assembling allowance range of a spacing distance
between the fixed core and the movable core at the initial position
is established, a characteristic graph line of spacing distance/attracting
force is defined for expressing a relation between the attracting
force and the spacing distance, and the characteristic graph line
provides attracting forces at a minimum spacing distance and a maximum
spacing distance within the assembling allowance range, which are
connectable by a straight line having an inclination A(N/mm), the
compression resiliency coefficient of the resilient biasing member
in the assembling allowance range is set to A(N/mm).
5. The normally closed solenoid valve according to claim 4, wherein
the valve body is separately formed with the movable core and is
engaged and fixed to a tip ends of the movable core disposed on
a valve seat side of the movable core.
6. The normally closed solenoid valve according to claim 4, wherein
the resilient biasing member is a spring member; and the compression
resiliency coefficient is a spring constant of the spring member.
Patent Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a normally closed solenoid
valve provided with a valve body for opening and closing a flow
path of a hydraulic fluid.
[0003] 2. Background Art
[0004] Conventionally, there are two types of solenoid valves for
opening and closing a flow path of a hydraulic fluid, one of which
is a normally closed solenoid valve that is normally closed and
is opened by excitation of a fixed core and a movable core when
a current is rendered to flow into a coil, and the other of which
is a normally open valve that is normally opened and is closed by
excitation of a fixed core and a movable core when a current is
rendered to flow into a coil. Such a normally closed solenoid valve
is provided with a valve seat for opening and forming a flow path
of a hydraulic fluid and a valve body formed at the tip end of a
movable core capable of being brought into contact with the valve
seat and moving away therefrom. In a demagnetized state, the movable
core is seated on the valve body by a spring force of a spring member
secured between the movable core and fixed core and is pressed into
the direction of closing the valve. In a magnetized state where
a current is rendered to flow into a coil, an attracting force works
between the fixed core and movable core, and when the attracting
force exceeds the spring force of the spring member, the valve body
is separated from the valve seat, wherein the flow path of a hydraulic
fluid can be opened. Herein, a force in which the attracting force
and the spring force working in the direction opposite the attracting
force are synthesized or composed is called a "thrust force"
working on the movable core.
[0005] Such a normally closed solenoid valve is used for a fluid
pressure control unit such as, for example, an anti-lock brake unit,
etc-, in a vehicle. In such a fluid pressure control unit, in order
to use a normally closed solenoid valve in a high fluid pressure
range, it was necessary to select a spring member having an intensive
spring force in order to maintain a valve closed state against a
high fluid pressure in a demagnetized state. Accordingly, if a spring
member having an intensive spring force is selected, it was necessary
to secure a great attracting force in order to secure a thrust force
of the movable core against the spring force.
[0006] Therefore, the inventor, et al. commenced development of
a normally closed solenoid valve that is able to set the attracting
force to a greater level by increasing the area of the plane of
the movable core opposed to the fixed core. Where a characteristic
line S of spacing distance/attracting force is obtained in association
with the attracting force thus obtained and the spacing distance
between the fixed core and movable core, such a characteristic line
as shown in FIG. 3 was obtained. The characteristic lines S1 and
S2 of spacing distance/attracting force are based on the normally
closed solenoid valve in which the attracting force is set to a
greater level, and the characteristic line S3 of spacing distance/attracting
force is based on a prior art normally closed solenoid valve. As
has been made clear from the characteristic lines shown in the same
drawing, in the assembling allowance range from L1 to L2, the characteristic
line S3 of spacing distance/attracting force produces almost the
same attracting force, and the normally closed solenoid valve in
the assembling allowance range produces almost the same initial
performance. However, the characteristic lines S1 and S2 of spacing
distance/attracting force produce steep slopes, and even in the
assembling allowance range, there is a comparatively large difference
in the initial performance. That is, a difference will be brought
about in the initial thrust force of the normally closed solenoid
valve in an assembled state. (See JP-A-11-141723.)
SUMMARY OF THE INVENTION
[0007] It is therefore an object of the present invention to provide
a normally closed solenoid valve in which the thrust force of a
movable core working against a resilient biasing member in the initial
position or assembling allowance range is fixed.
[0008] To achieve the object, the invention provides a normally
closed solenoid valve, includes: a fixed core; a valve portion for
opening and closing a flow path of a hydraulic fluid, the valve
portion including a valve seat and a valve body disposed opposed
to the valve seat to be seated therein; a movable core disposed
between the fixed core and the valve seat, which is capable of advancing
and retreating along with the valve body with respect to the valve
seat; a resilient biasing member for biasing the movable core in
a valve-closing direction along which the valve body is seated in
the valve seat for closing the valve; and a coil for generating
an attracting force between the movable core and the fixed core
when energized to cause the movable core to retreat in a valve-opening
direction from an initial position thereof where the valve portion
is in a closed state, the attracting force acted against an biasing
force exerted by the resilient biasing member. When a characteristic
graph line of spacing distance/attracting force that defines the
attracting force in relation with a spacing distance between the
fixed core and the movable core provides an inclination A(N/mm)
at the initial position, the compression resiliency coefficient
of the resilient biasing member is set to A(N/mm).
[0009] According to this aspect of the invention, even if there
are more or less differences in the initial positions of respective
products, the initial thrust force of the movable core can be made
constant only by setting the compression resiliency coefficient
of a resilient biasing member when the attracting force of the movable
core is increased by widening the areas of respective opposed planes
of the fixed core and movable core. Therefore, even in a case where
the current value to be supplied to the coil by current controlling
means is made variable, it is possible to obtain a planned initial
thrust force of the movable core, wherein respective products are
freed from any unevenness. Further, since the compression resiliency
coefficient, to be established, of a resilient biasing member can
be obtained by securing the characteristic line of spacing distance
between a fixed core and a movable core and the attracting force
thereof in advance, the compression resiliency coefficient can be
securely established.
[0010] The invention provides a normally closed solenoid valve,
including: a fixed core; a valve portion for opening and closing
a flow path of a hydraulic fluid, the valve portion including a
valve seat and a valve body disposed opposed to the valve seat to
be seated therein; a movable core disposed between the fixed core
and the valve seat, which is capable of advancing and retreating
along with the valve body with respect to the valve seat; a resilient
biasing member for biasing the movable core in a valve-closing direction
along which the valve body is seated in the valve seat for closing
the valve; and a coil for generating an attracting force between
the movable core and the fixed core when energized to cause the
movable core to retreat in a valve-opening direction from an initial
position thereof where the valve portion is in a closed state, the
attracting force acted against a biasing force exerted by the resilient
biasing member. When an assembling allowance range of a spacing
distance between the fixed core and the movable core at the initial
position is established, a characteristic graph line of spacing
distance/attracting force is defined for expressing a relation between
the attracting force and the spacing distance, and the characteristic
graph line provides attracting forces at a minimum spacing distance
and a maximum spacing distance within the assembling allowance range,
which are connectable by a straight line having an inclination A(N/mm),
the compression resiliency coefficient of the resilient biasing
member in the assembling allowance range is set to A(N/mm).
[0011] With the structure as described above, it is possible to
obtain a rough inclination even if the characteristic line of the
spacing distance and attracting force in the assembling allowance
range is not straight, and it is possible to make constant the thrust
force of the movable core, which works against the biasing force
of a resilient biasing member, in the assembling allowance range.
Therefore, in the normally closed solenoid valve assembled in the
assembling allowance range, it is possible to make roughly constant
the initial thrust force of at least the movable core, wherein respective
products will be almost freed from any unevenness. In addition,
even in a case where the current value supplied to the coil is made
variable by current controlling means, it is possible to secure
a planned initial thrust force of the movable core, wherein the
respective products will be free from any unevenness.
[0012] Preferably, the valve body is separately formed with the
movable core and is engaged and fixed to a tip ends of the movable
core disposed on a valve seat side of the movable core.
[0013] With the structure as described above, the valve body for
which precise machining is required and a movable core which is
long-sized and is comparatively easily machined may be produced
in separate processes, whereby an efficiency can be achieved in
the machining processes.
[0014] Preferably, the resilient biasing member is a spring member;
and the compression resiliency coefficient is a spring constant
of the spring member.
[0015] By this, even when the thrust force of a movable core is
increased by widening the area of a surface opposed to the movable
core, it is possible to make constant the initial thrust force in
the initial position of the movable core by selecting or producing
a spring member having a spring constant fitted to the characteristic
line of spacing distance and thrust force.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The present invention may be more readily described with
reference to the accompanying drawings, in which:
[0017] FIG. 1 is a longitudinal sectional view of a normally closed
solenoid valve according to one preferred embodiment of the invention;
[0018] FIG. 2 is a partially enlarged longitudinal sectional view
of the movable core and fixed core;
[0019] FIG. 3 is a graph showing the characteristic lines of spacing
distance/attracting force of the normally closed solenoid valve
and the characteristic line of spacing distance/spring force thereof;
and
[0020] FIG. 4 is a graph showing the characteristic line of spacing
distance/thrust force of the normally closed solenoid valve according
to one embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] Hereinafter, a detailed description is given of embodiments
of the invention with reference to the drawings.
[0022] FIG. 1 is a longitudinal sectional view of a normally closed
solenoid valve according to one embodiment of the invention, FIG.
2 is a partially enlarged longitudinal section view of a movable
core and a fixed core, FIG. 3 is a graph showing the characteristic
lines of spacing distance and thrust force of the normally closed
solenoid valve and characteristic lines of spacing distance and
spring force thereof, and FIG. 4 is a graph showing the characteristic
line of spacing distance and thrust force of a normally closed solenoid
valve according to one embodiment of the invention.
[0023] (Structure of a Normally Closed Solenoid Valve)
[0024] As shown in FIG. 1, a solenoid valve according to one embodiment
of the invention is a normally closed solenoid valve 10 for opening
and closing a flow path of a hydraulic fluid of, for example, an
anti-lock brake system (ABS) for a vehicle.
[0025] The normally closed solenoid valve 10 includes a thin cylindrical
body 20 which is inserted into the attachment hole 3 of the base
material 1 and is fixed by a fastener 4 so as not to come off, a
fixed core 22 fixed at one end of the body 20, a coil 24 for exciting
or magnetizing the fixed core 22 by feeding a current, a valve body
30 disposed opposite a valve seat 42 so as to be seated thereon
and working together with the valve seat 42 as a valve portion for
opening and closing a flow path of a hydraulic fluid, a movable
core 32 disposed between the fixed core 22 and the valve seat so
as to advance and retreat along with the valve body 30 with respect
to the valve seat, and a spring member 34, which is disposed between
the fixed core 22 and the movable core .sup.32, functioning as a
resilient biasing member for biasing the movable core 32 in the
closing direction with the valve body 30 seated in the valve seat
42. The coil 24 is electrically connected via a terminal 25 to current
controlling means (not illustrated) which controls the current value
to be supplied to the coil 24. The coil 24 generates an attracting
force between the movable core 32 and the fixed core 22 by being
energized, and causes the movable core 32 to retreat in the valve-opening
direction against the spring force working as the biasing force
of the spring member 34 from the initial position of a closed state
thereof.
[0026] (Body)
[0027] The body 20 is thin and cylindrical, and has the fixed core
22 provided at one end thereof and the valve seat body 40 fixed
inside the other end thereof. The movable core 32 is disposed so
as to advance and retreat between the fixed core 22 and the valve
seat body 40, and the other end thereof on which the valve seat
body 40 is fixed is inserted into amounting hole 3 of the base material
1. The outer circumferential surface at the other end side of the
body 20 is sealed in a fluid-tight state with respect to a hydraulic
fluid by a plurality of annular sealing members between the base
material 1 and the mounting hole 3. The body 20 has an inlet port
6 and an outlet port 8, which are open to the hydraulic fluid flow
path 2 formed in the base material 1. A filtering member 5 and the
cylindrical valve seat body 40 are mounted in the inlet port 6.
A coil 24 wound on a resin-made bobbin 26 and a coil case 28 to
cover up the outside of the coil 24 are attached to the outside
of the body 20 protruding from the base material 1 to the exterior.
[0028] (Fixed Core)
[0029] The fixed core 22 is made of a magnetic material and is
roughly cylindrical. Almost the half part of the outer circumferential
plane is inserted into the interior of the body 20 and is welded
to and fixed at the body 20. A projection 221 with which one end
of the spring member 34 is brought into contact is formed at the
center of the tip end at the body 20 side of the fixed core 22.
[0030] (Movable Core)
[0031] The movable core 32 is made of a magnetic material and is
roughly cylindrical. A recess portion 321 having a circular cross-section
is formed to open at one end part opposed to the fixed core 22.
The valve body 30 is pressure-fitted to the other tapered end opposed
to the valve seat body 40. The spring member 34 is brought into
contact with the bottom part of the recess portion 321 and is disposed
in the recess portion 321. Therefore, the spring member 34 has one
end thereof brought into contact with the inside of the recess portion
321 of the movable core 32 and has the other end thereof brought
into contact with the projection 221 of the fixed core 22. The open
end of the recess portion 321 of the movable core 32 is formed to
be larger than the outer diameter of the projection 221 of the fixed
core 22, and accommodates the projection 221 when the movable core
32 and the fixed core 22 are adsorbed to each other.
[0032] (Valve Body)
[0033] The valve body 30 has a tapered and roughly conical shape,
the tip end of which is spherical, and is brought into contact with
the funnel-shaped valve seat 42 formed at a small-diameter opening
part of the valve seat body 40 to close the valve. In a demagnetized
state where the coil 24 is not excited, the spring force of the
spring member 34 is set to a spring force level, at which the valve
body 30 can be seated on the valve seat 42, against the fluid pressure
of a hydraulic fluid applied to the sealing area of the closed valve
body 30. That is, the fixed core 22 and the movable core 32 are
assembled together with the spring member 34 placed therebetween
and with a prescribed spring force generated.
[0034] In an assembling work step in the production process of
the normally closed solenoid valve 10, the fixed core 22 and the
movable core 32 are assembled after the spacing distance X between
the fixed core 22 and the movable core 32 is adjusted so as to enter
an assembling allowance range determined in advance.
[0035] (Operation of the Normally Closed Solenoid Valve)
[0036] Hereinafter, a description is given of operations of the
normally closed solenoid valve 10 according to the embodiments.
[0037] (Demagnetized State)
[0038] In a demagnetized state where no current is supplied to
the coil 24, the fixed core 22 is not excited, wherein the movable
core 32 is located at the initial position as shown in FIG. 1, and
is pressed in the valve-closing direction by a spring force of the
spring member 34. The valve body 30 is brought into contact with
the valve seat 42 and is seated and disposed therein, wherein a
closed state of the valve is maintained. Therefore, a hydraulic
fluid does not flow in the demagnetized state because the inlet
port 6 does not communicate with the outlet port S.
[0039] (Magnetized State)
[0040] If a current is fed from current controlling means (not
illustrated) to the coil 24, and the fixed core 22 is excited, an
attracting force is generated between the fixed core 22 and the
movable core 32, and the movable core 32 is caused to retreat to
the fixed core 22 side against the spring force of the spring member
34, wherein the valve body 30 is separated from the valve seat 42
and disposed apart therefrom. Therefore, in a state where a current
is fed to the coil 24, a hydraulic fluid flows from the inlet port
6 into the outlet port 8.
[0041] (Pressure-Regulated State)
[0042] It is possible to control the fluid pressure of a hydraulic
fluid at the outlet port 8 side of the normally closed solenoid
valve 10 by controlling the amperage of the current fed to the coil
24. The current controlling means (not illustrated) controls the
amperage of the current fed to the coil 24 in compliance with signals
coming from a pressure sensor (not illustrated) which is disposed
at, for example, the outlet port 8 side. By controlling the current
amperage to the coil 24, the intensity of the attracting force working
on the movable core 32 can be controlled. The thrust force of the
movable core 32 is determined by the attracting force and spring
force, wherein it is possible to balance the thrust force and the
fluid pressure of the hydraulic fluid. Therefore, by controlling
the intensity of the attracting force, the spacing distance between
the fixed core 22 and the movable core 32, that is, the valve-opening
amount can be adjusted, thereby controlling the fluid pressure of
the hydraulic fluid flown to the outlet port 8 side.
[0043] (Force Working on the Fixed Core)
[0044] As shown in FIG. 2, an attracting force F brought about
by excitation, spring force T brought about by the spring member
34, and fluid pressure P of a hydraulic fluid applied onto the valve
body 30 work on the movable core 32. As described above, in a demagnetized
state, no attracting force F is generated between the fixed core
22 and the movable core 32, an unequal Fluid pressure P<Spring
force T is obtained, wherein a valve closed state is maintained.
And, if a current is fed to the coil 24 by the current controlling
means (not illustrated), the attracting force F works in the direction
along which the fixed core 22 absorbs the movable core 32, wherein
an unequal Attracting force F+Fluid pressure P>Spring force T
is brought about, and the spring member 34 is compressed to open
the valve body 30.
[0045] In the present embodiment, the spring force is set to 15(N)
when the valve is closed in a demagnetized state, in compliance
with the use requirement of the normally closed solenoid valve in
which the fluid pressure is set to, for example, 11(N) or more which
is higher than in prior arts. And, if the area of the plane 320
opposed to the movable core 32 which is opposed to the fixed core
22 is increased in response thereto, it becomes possible to generate
a higher attracting force F. Also, the attracting force F can be
varied by the current amperage (A) fed from the current controlling
means (not illustrated) to the coil 24. In addition, the attracting
force F working on the movable core 32 is varied in accordance with
the spacing distance X between the fixed core 22 and the movable
core 32, in further detail, in accordance with the spacing distance
X between the respective planes 220 and 320 opposed to each other
of the fixed core 22 and the movable core 32.
[0046] (Characteristics of Spacing Distance-Attracting Force)
[0047] Next, using FIG. 3, a description is given of the characteristic
line of spacing distance between the fixed core 22 and movable core
32 and attracting force in a normally closed solenoid valve 10 according
to the present invention.
[0048] FIG. 3 is a view showing the characteristic lines of spacing
distance and attracting force of the normally closed solenoid valve
10, wherein an axis x indicates the spacing distances X between
the plane 220 of the fixed core and the plane 320 of the movable
core 32, and an axis y indicates attracting forces F working on
the plane 320 of the movable core 32 by feeding a current to the
coil 24. The spacing distance X of axis x varies from the initial
position L0 of the reference to the retreated position 0 in line
with retraction of the movable core 32 to the fixed core 22 side
by a current fed to the coil 24. The initial position L0 of the
spacing distance X means the spacing distance between the fixed
core 22 and the movable core 32 when the valve body 30 is brought
into contact with the valve seat body 42 and the valve is opened.
The retreated position 0 means the spacing distance between the
fixed core 22 and the movable core 32 in a state where the valve
body 30 is separated from the valve seat body 42 and the valve is
opened, and where the movable core 32 is adsorbed to the fixed core
22. In an actual normally closed solenoid valve 10, the initial
position is produced so as to be placed within a scope of the assembling
allowance range (L1to L2) with respect to the reference initial
position L0, which is determined in advance. Accordingly, the initial
position may change more or less in the assembling allowance range
in respective normally closed solenoid valves 10 that are actually
produced.
[0049] As shown in FIG. 3, in the characteristic line S3 of spacing
distance/attracting force of a prior art normally closed solenoid
valve, the initial attracting force has almost fixed attracting
force in the assembling allowance range L1 to L2 including the reference
initial position L0. Therefore, it was possible to easily establish
the initial thrust force of the normally closed solenoid valve.
[0050] FIG. 3 shows the characteristic lines S1 and S2 of spacing
distance/attracting force when currents 2.0 (A) and 3.0 (A) are
flown to the coil 24 of the normally closed solenoid valve 10 according
to the present embodiment. The characteristic lines S1 and S2 of
spacing distance/attracting force have comparatively large inclinations
in the assembling allowance range L1 to L2.
[0051] The characteristic line S1 of spacing distance/attracting
force shows that, when the spacing distance X between the fixed
core 22 and the movable core 32 is L0 (mm) in the assembled state
of the so-called initial state, the initial attracting force F is
F3(N) when a current flows to the coil. For example, in the present
embodiment, L0 is 0.37 (mm) and F3 is 13 (N). However, the assembling
allowance is .+-.(L0-L1) or .+-.(L2-L0), for example, 0.07 (mm)
with respect to L0 when the normally closed solenoid valve 10 is
assembled, and in the assembling allowance range, the initial attracting
force F has a difference of (F1-F2), for example, 2 (N). That is,
even if a normally closed solenoid valve 10 is satisfactory, the
allowance of which is in the assembling allowance range, the initial
attracting force may change in each product when a current is caused
to flow to the coil 24.
[0052] The characteristic line S1 of spacing distance/attracting
force is a straight line in which the inclination in the assembling
allowance range is almost fixed, and the inclination of the straight
line can be expressed by A=(F2-F1)/(L2-L1). Therefore, in the present
embodiment, for example, it is possible to obtain an inclination
of A=-2/0.14=-14.29(N/mm).
[0053] Therefore, in the embodiment according to the invention,
the compression resiliency coefficient of the spring member 34,
the so-called spring constant is set to an inclination A, for example,
-14.29 (N/mm). As shown in FIG. 2, the spring force T of the spring
member 34 works in the direction of separating the fixed core 22
from the movable core 32, that is, in the direction opposed to the
attracting force F. Also, with respect to the spring force T of
the spring member 34, the spring member 34 is compressed in line
with a decrease in the spacing distance X, wherein a greater force
is generated. The spring force of the spring member, for which an
inclination of the spring constant is set to A(N/mm), has a characteristic
shown as the characteristic line T1 of spacing distance/spring force
shown in FIG. 3. As has been expressed by the characteristic line
T1 of spacing distance/spring force, the spring force T of the spring
member 34 is increased in a negative direction (that is, in a reverse
direction of the attracting force of the movable core) in line with
a decrease in the spacing distance X.
[0054] Also, where the characteristic line S of spacing distance/attracting
force in the assembling allowance range is not straight, a straight
line connecting the attracting force F1 at the minimum value L1
to the attracting force F2 of the maximum value L2 in the assembling
allowance range is obtained, and the inclination of the straight
line is made into A, whereby it is possible to establish the spring
constant. In addition, it may be calculated by acquiring an equation
of the characteristic line S1 of spacing distance/attracting force
and differentiating the inclination at the reference initial position
L0 of the movable core 32.
[0055] Further, as shown in FIG. 3, it is found that the characteristic
line S2 of spacing distance/attracting force when current amperage
of 3.0(A) is fed to the coil 24 has an inclination A as in the characteristic
line S.
[0056] (Characteristic Line of Spacing Distance/Attracting Force)
[0057] FIG. 4 shows characteristic lines W1 and W2 of spacing distance/thrust
force, which are obtained by synthesizing the characteristic lines
S1 and S2 of spacing distance/attracting force shown in FIG. 3 and
the characteristic line T1 of spacing distance/spring force. The
characteristic line W1 of spacing distance/attracting force is obtained
by synthesizing the characteristic line S1 of spacing distance/attracting
force and the characteristic line T1 of spacing distance/spring
force, and the characteristic line W2 of spacing distance/attracting
force is obtained by synthesizing the characteristic line S2 of
spacing distance/attracting force and the characteristic line T1
of spacing distance/spring force. Thus, by synthesizing the characteristic
lines of the attracting force F of the movable core 32 and the spring
force T of the spring member 34, the characteristic lines W1 and
W2 of spacing distance/thrust force of the normally closed solenoid
valve 10 in which a spring member 34 is actually incorporated can
be obtained. These characteristic lines W1 and W2 are almost straight
in at least the assembling allowance range, wherein it is understood
that attracting forces G1 and G2 can be obtained, respectively.
Therefore, in normally closed solenoid valves produced in the assembling
allowance range (L1 to L2), the initial thrust forces G1 and G2,
which are generated at the initial position of the movable core
32 when a current is fed to the coil 24, will become almost constant.
[0058] Also, where the amperage of a current fed from the current
controlling means to the coil 24 is variably controlled, it is possible
to obtain a prescribed thrust force G of the movable core 32 corresponding
to the prescribed amperage. Therefore, reliable control can be carried
out. For example, a normally closed solenoid valve 10 that has been
assembled at the initial position L1 where a current whose amperage
is 3.0 (A) is supplied to the coil 24 generates an initial thrust
force G1, wherein the movable core 32 is adsorbed to the fixed core
22 side and the valve body 30 is closed. And, the current controlling
means controls the amperage to 2.0 (A) on the basis of a signal
from a pressure sensor secured at the hydraulic fluid path 2 at
the outlet port 8 side, the thrust force of the movable core 32
is controlled to G2 if the spacing distance X is in a regulating
range shown in FIG. 4. As the thrust force of the movable core 32
becomes G2, the valve body 30 equivalently moves in the valve closing
direction against the fluid pressure P to throttle the valve opening
degree, wherein it is possible to lower the fluid pressure P in
the hydraulic fluid path 2 at the outlet port side. As shown in
FIG. 4, with respect to the pressure regulating range of the spacing
distance X, it is possible to set a prescribed fluid pressure at
the outlet port 8 side by controlling the current amperage if the
characteristic lines W1 and W2 of spacing distance/thrust force
are almost in a straight range and the spacing distance X is in
a pressure-regulating range.
[0059] Thus, in the normally closed solenoid valve 10 according
to the present embodiment of the invention, the assembling allowance
range of the spacing distance X between the fixed core 22 and the
movable core 32 when no current is fed to the coil 24 is first established,
and the characteristic line S of spacing distance/attracting force
of the fixed core 22 and movable core 32 is obtained without taking
the spring force of the spring member 34 in to consideration. Next,
the inclination A(N/mm) of the characteristic line S of spacing
distance/attracting force in the assembling allowance range is obtained,
a spring member 34 in which the inclination of the characteristic
line T of spacing distance/spring force in the assembling allowance
range when no current is fed, the so-called spring constant, is
set to A(N/mm) is produced or selected, and the normally closed
solenoid valve 10 is assembled. The normally closed solenoid valve
10 thus produced shows a constant thrust force at least when the
characteristic line W of spacing distance/thrust force is in the
assembling allowance range. Accordingly, in the normally closed
solenoid valve 10 assembled with the reference initial position
L0 in the assembling allowance range, the initial thrust force becomes
constant.
[0060] In addition, the present invention is not limited to the
present embodiment. It maybe subject to modification in various
embodiments within the scope of the invention.
[0061] For example, as for the spring member 34, it is possible
to choose a resilient body having a constant resiliency coefficient
other than a spring. At this time, it is possible to select the
resiliency coefficient as in selecting the spring constant.
[0062] Also, an integral type valve body in which the tip end of
the movable core 32 is tapered may be formed instead of the valve
body 30 separately formed from the movable core 32. |