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Patent Abstract
A method of manufacturing a movable core having a valve shaft, of
a solenoid valve with which the movable core and the valve shaft
can be easily and accurately aligned with each other. The valve
shaft and the movable core are manufactured by sintering as follows.
First, with a lower punch inserted in a cavity of a first mold,
SUS powder having an average particle diameter of 150 micrometer
is put in the cavity. The powder is compacted into a powder compact
in the shape of a valve shaft by lowering an upper punch into the
cavity. The first mold is slightly lowered so that the powder compact
slightly protrudes from the cavity. Fe powder having an average
particle diameter of 150 micrometers is put in a cavity of a second
mold so as to be deposited on the powder compact in the cavity of
the first mold. The upper punch is lowered to compact the powder
in the second mold into a powder compact in the shape of the core.
After releasing the powder compacts, they are joined together by
sintering.
Patent Claims
What is claimed is:
1. A method of manufacturing a movable core member for use in a
solenoid valve, said movable core member comprising a core and a
valve shaft, said solenoid valve being structured to be opened and
closed by moving said valve shaft together with said core, said
method comprising: preparing a mold; putting a first powder selected
from a non-magnetizable powder and a mixture of a non-magnetizable
powder and another powder into said mold; compacting said first
powder to form a first powder compact in the shape of said valve
shaft; putting a second powder selected from a magnetizable powder
and a mixture of a magnetizable powder and another powder into said
mold so as to be deposited on said first powder compact; compacting
said second powder to form a second powder compact in the shape
of said core; and sintering said first and second powder compacts
to join said first and second powder compacts together, thereby
forming said valve shaft from said first powder compact and said
core from said second powder compact as a one-piece article.
2. The movable core member manufactured by the method of claim
1.
3. A method of manufacturing a movable core member for use in a
solenoid valve, said movable core member comprising a core and a
valve shaft, said solenoid valve being structured to be opened and
closed by moving said valve shaft together with said core, said
method comprising: preparing a mold; putting a first powder selected
from a magnetizable powder and a mixture of a magnetizable powder
and another powder into said mold; compacting said first powder
to form a first powder compact in the shape of said core; putting
a second powder selected from a non-magnetizable powder and a mixture
of a non-magnetizable powder and another powder into said mold so
as to be deposited on said first powder compact; compacting said
second powder to form a second powder compact in the shape of said
valve shaft; and sintering said first and second powder compacts
to join said first and second powder compacts together, thereby
forming said valve shaft from said second powder compact and said
core from said first powder compact as a one-piece article.
4. The movable core member manufactured by the method of claim
3.
Patent Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to a movable core carrying a valve
shaft, of a solenoid valve for use in an actuator for controlling
vehicle brake hydraulic pressure, and a method of manufacturing
the same.
[0002] FIG. 2 shows a typical actuator for controlling vehicle
brake hydraulic pressure, which comprises a hydraulic pressure control
unit 1, a motor unit 2 coupled to one side of the control unit 1,
and an electronic control unit (ECU) 3 coupled to the opposite side
of the control unit 1. This type of actuator is disclosed in JP
patent publication 2001-260846.
[0003] The control unit 1 includes a housing 10, typically made
of an aluminum alloy, in which are mounted a reservoir 12, a pump
13 and a pair of pressure control valves 30 and 20 for increasing
and reducing pressure, respectively. The housing 10 is formed with
a first passage 16 extending from a master cylinder port 14 to the
pressure increase valve 30 and then to a wheel cylinder port 15,
a second passage 17 extending from the wheel cylinder port 15 to
the reservoir 12 through the pressure reduction valve 20, and a
third passage 18 extending from the reservoir 12 through the pump
13 and the pressure increase valve 30 to the wheel cylinder port
15.
[0004] The control valves 20 and 30 are typically solenoid valves.
For example, in JP patent publication 4-287840, a solenoid valve
similar to the one shown in FIG. 1 is used as the pressure increase
valve 30. It is to be understood that FIG. 1 itself shows one embodiment
of the present invention. This valve comprises a tubular yoke 31,
a tubular bobbin 32 mounted in the yoke 31, a current-excited coil
33 wound on the bobbin 32, a movable core (plunger) 34 axially movably
inserted in a guide member 37 fitted in the bobbin 32, and a valve
shaft 35 fixed to the core 34 and having at its front end a valve
body 38 adapted to contact a valve seat 39. By selectively activating
and deactivating the coil, the valve shaft 35 is moved axially together
with the core 34 so that its valve body 38 is brought into and out
of contact with the valve seat 39.
[0005] In order to move the core 34 in its axial direction under
the magnetic force produced by the coil 33, the core 34 has to be
formed of a magnetizable material. On the other hand, the valve
shaft 35 is desirably not influenced by the magnetic force from
the coil. It is thus formed of a non-magnetizable material. In other
words, the core 34 and the valve shaft 35 are formed of different
materials. Conventional such cores and valve shafts were therefore
manufactured separately and joined together.
[0006] JP patent publication 2000-087117 proposes to compact ferromagnetic
powder or a mixture of such ferromagnetic powder and other powders
into the shape of the core 34, fitting this compacted green article
onto the valve shaft 35 and sintering it. By sintering, the core
is joined to the valve shaft 35. That is, when the core is formed,
it is simultaneously joined to the valve shaft.
[0007] But with this arrangement too, the valve shaft 35 still
has to be separately formed by e.g. cutting. Moreover, the step
of fitting the compacted green article onto the valve shaft 35 makes
it more troublesome to manufacture and assemble the core and the
valve shaft. Furthermore, it is difficult to fit the core onto the
valve shaft such that they are accurately aligned with each other.
If they are even slightly misaligned with each other, the valve
body 38 may not be properly seated on the valve seat 39, thus making
it difficult to reliably open and close the valve. It will be particularly
difficult to completely seal the valve when so desired.
[0008] An object of this invention is to provide a method of manufacturing
a movable core having a valve shaft, of a solenoid valve with which
the movable core and the valve shaft can be easily and accurately
aligned with each other.
SUMMARY OF THE INVENTION
[0009] To accomplish this object, the movable core and the valve
shaft are formed by simultaneous sintering.
[0010] Specifically, the present invention provides the following
two methods:
[0011] 1) A method of manufacturing a movable core member for use
in a solenoid valve, said movable core member comprising a core
and a valve shaft, said solenoid valve being adapted to be opened
and closed by moving said valve shaft together with said core, said
method comprising the steps of preparing a mold; putting a first
powder selected from a non-magnetizable powder and a mixture of
a non-magnetizable powder and another powder into said mold; compacting
said first powder to form a first powder compact in the shape of
said valve shaft; putting a second powder selected from a magnetizable
powder and a mixture of a magnetizable powder and another powder
into said mold so as to be deposited on said first powder compact;
compacting said second powder to form a second powder compact in
the shape of said core; and sintering said first and second powder
compacts to join said first and second powder compacts together,
thereby forming said valve shaft from said first powder compact
and said core from said second powder compact as a one-piece article.
[0012] 2) A method of manufacturing the movable core member as
described above, said method comprising the steps of preparing a
mold; putting a first powder selected from a magnetizable powder
and a mixture of a magnetizable powder and another powder into said
mold; compacting said first powder to form a first powder compact
in the shape of said core; putting a second powder selected from
a non-magnetizable powder and a mixture of a non-magnetizable powder
and another powder into said mold so as to be deposited on said
first powder compact; compacting said second powder to form a second
powder compact in the shape of said valve shaft; and sintering said
first and second powder compacts to join said first and second powder
compacts together, thereby forming said valve shaft from said second
powder compact and said core from said first powder compact as a
one-piece article.
[0013] With either of the above methods, the core and the valve
shaft are rigidly joined together as a practical one-piece article.
The core and the valve shaft can be formed exactly following the
contour of the mold cavity with their axes accurately aligned with
each other.
[0014] The magnetizable powder may be Fe--P powder, Fe--Si powder,
Fe--Si--P powder, permalloy powder, permendur alloy powder, or an
electromagnetic stainless powder such as SUS 401. The non-magnetizable
powder may be a non-magnetizable stainless steel such as SUS 304.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Other features and objects of the present invention will
become apparent from the following description with reference to
the accompanying drawings, in which:
[0016] FIG. 1 is a sectional side view of a movable core member
embodying the present invention as used in a solenoid valve;
[0017] FIG. 2 is a schematic side view of a hydraulic pressure
controlling actuator including solenoid valves each having the movable
core member shown in FIG. 1;
[0018] FIGS. 3A-3D show a first method for manufacturing the movable
core member according to the present invention;
[0019] FIGS. 4A-4D show a second method for manufacturing the movable
core member according to the present invention;
[0020] FIG. 5 shows a third method for manufacturing the movable
core member according to the present invention; and
[0021] FIG. 6 shows a different movable core member embodying the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0022] FIG. 1 shows the pressure increase control valve 30 embodying
the present invention, which is mounted in the hydraulic pressure
control unit 1 shown in FIG. 2 instead of the conventional pressure
increase valve 30. This particular control unit 1 is mounted in
an actuator of an antilock brake system (ABS) for controlling the
vehicle brake hydraulic pressure in a known manner. The pressure
increase control valve 30 is liquid-tightly mounted to the housing
10 of the control unit 1 by means of a metal seal that is fitted
in the housing 10 so as to extend across the passage 17, which extends
from the wheel cylinder port 15. The pump 13 is driven by a motor
M.
[0023] The tubular yoke 31 of the pressure increase control valve
30 has its inner end open. The tubular bobbin 32 is coaxial with
the yoke 31. The coil 33 is wound around the bobbin 32, as described
above. The space between the coil 33 and the yoke 31 is filled with
an epoxy resin 36. The core (plunger) 34 carrying the valve shaft
35 is received in the bobbin 32 so as to be movable in its axial
direction, as described earlier. Its axial stroke is limited to
t which is the gap between the guide 37 and the end of the core
34. By selectively activating and deactivating the coil, the valve
body 38 at the tip of the valve shaft 35 is adapted to be moved
into and out of contact with the valve seat 39. The valve thus selectively
opens and closes. Electric power is supplied to the coil through
terminals 4. When the coil is deactivated, the valve shaft 35 is
pushed by a return spring 38a until the valve body 38 separates
from the valve seat 39.
[0024] The valve shaft 35 and the movable core 34 of the solenoid
valve 30 according to the invention are formed by sintering, using
one of the three methods shown in FIGS. 3A-D, FIGS. 4A-D and FIG.
5, respectively.
[0025] The method of FIGS. 3A-3D comprises the following steps:
[0026] 1) inserting a die or mold 41 for forming the valve shaft
35 into a die or mold 45 for forming the core 34;
[0027] 2) inserting a lower punch 43 into a cavity 42 of the die
41 from below the die;
[0028] 3) putting a non-magnetizable powder, typically SUS powder
a having an average particle diameter of 150 micrometers into the
cavity 42 (FIG. 3A);
[0029] 4) lowering an upper punch 44 into the cavity 42 to compact
the powder a into the shape of the valve shaft 35 (FIG. 3B);
[0030] 5) raising the upper punch 44 and then raising the lower
punch 43 or lowering the die 41 until the compact a slightly protrudes
from the top of the die 41;
[0031] 6) putting a magnetizable powder, typically Fe powder b
having an average particle diameter of 150 micrometers into a cavity
46 of the core-forming die 45 (FIG. 3C);
[0032] 7) lowering the upper punch 47 into the cavity 46 to compact
the powder b into the shape of the core 34 (FIG. 3D);
[0033] 8) releasing the compacts a and b from the die; and
[0034] 9) sintering the compacts a and b at 1150.degree. C. for
30 minutes to form a one-piece core member comprising the core 34
and the valve shaft 35.
[0035] The valve shaft 35 of this core member penetrates into the
core 34. In contrast, the method shown in FIGS. 4A-4D forms a core
member comprising a core 34 and a valve shaft 35 which does not
penetrate into the core 34. In this method, a one-piece die comprising
the core-forming die 41 and the valve shaft-forming die 45 is used.
In this method, after compacting the powder a, the lower punch 43
is raised or the die (41, 45) is lowered until the top of the powder
a is substantially flush with the shoulder between the dies 41 and
45. Thus, when the powder b is compacted subsequently, the compacts
a and b are temporarily joined together along a horizontal plane
as shown in FIG. 4D. The thus joined compacts a and b are released
from the die (41, 45) and rigidly joined together by sintering.
In an alternative method of FIGS. 4A-4D, the die (41, 45) is positioned
upside down, and the powder b is first put in the cavity of the
die 45 and compacted, and then the powder a is put in the cavity
of the die 41 and compacted.
[0036] In the method of FIG. 5, a mold assembly 48 comprising molds
48a, 48b, 48c and 48d is used. A mixture a' comprising 50 wt % of
SUS powder having an average particle size of 150 micrometers and
50 wt % of a resin is injection-molded into a cavity 49 of the mold
48a from below the mold 48a, and a mixture b' comprising 50 wt %
of Fe powder having an average particle size of 150 micrometers
and 50 wt % of a resin is injection-molded into a cavity 49 from
above the mold 48a. After metal injection molding, the resin is
partially vaporized until its weight is 10-50% of the original weight,
and the compacts a' and b' are released from the mold 48a and then
sintered at 1150 degrees Celsius for 30 minutes. By sintering, the
resin completely vaporizes.
[0037] A steel ball as the valve body 38 is pressed into a recess
35a formed in the tip of the valve shaft 35 (FIG. 3D). If the steel
ball cannot be sufficiently rigidly fixed to the valve shaft 35
by press-fitting, any other joint means may be used such as bonding
for more rigid joining. Also, in order to more rigidly fix the steel
ball to the valve shaft, the powder a or a' may be compacted with
the steel ball placed on the lower punch 43 or the mold 48c to temporarily
join the steel ball to the compact a or a'. Then, when the compact
a or a' is sintered, the steel ball is rigidly joined to the valve
shaft. Also, the steel ball may be formed as an integral part of
the valve shaft by putting powder in a recess 43a (FIG. 3A) formed
in the top surface of the lower punch 43 or the mold 48c, and compacting
and sintering the powder together with the powder a or a'. The valve
body of a needle valve shaft as shown in FIG. 6 is actually a pointed
tip of the valve shaft. Such a valve body is formed when the powder
a or a' is compacted and sintered.
[0038] The core 34 and the valve shaft 35 of the present invention,
which are formed by simultaneous sintering, are rigidly joined together.
Since the core and the valve shaft are shaped exactly following
the shape of the cavity of the mold, they can be formed so as to
be accurately aligned with each other. The valve can thus be accurately
opened and closed. Particularly with the needle valve shaft shown
in FIG. 6, the taper angle of the tapered surface of the pointed
tip, which serves as the valve body 38, can be determined with high
accuracy. The degree of opening of the valve can thus be controlled
with high accuracy.
[0039] While the core of the embodiment has been described as being
a part of a pressure increase valve (such as the valve 30) to be
mounted in a hydraulic pressure control unit (such as the control
unit 1), it can also be used as a part of the pressure reduction
valve 20 or any other solenoid valve to be mounted not only in a
vehicle brake hydraulic pressure controlling actuator but in any
other device.
[0040] Since the movable core and the valve shaft are formed as
an integral, one-piece member by sintering powders, both the core
and the valve shaft can be formed with high dimensional accuracy
with their axes accurately aligned with each other. Also, they can
be formed easily at a low cost. The valve containing this movable
core can be opened and closed with high accuracy. |