U.S. patent application number 10/116471 was filed with the patent office on 2002-10-17 for die-casting method and die-casting apparatus.
Invention is credited to Hiramatsu, Osamu, Ito, Masafumi, Kawaguchi, Masahiro, Ota, Masaki, Yoshida, Yoshiharu.
Application Number | 20020148591 10/116471 |
Document ID | / |
Family ID | 18963752 |
Filed Date | 2002-10-17 |
United States Patent
Application |
20020148591 |
Kind Code |
A1 |
Hiramatsu, Osamu ; et
al. |
October 17, 2002 |
Die-casting method and die-casting apparatus
Abstract
A method of die-casting a die-cast article having at least one
of an inner circumferential surface and an outer circumferential
surface, whose cross sectional shape is a circle, the die-casting
article being formed with a die-casting apparatus having a mold
cavity therein and a molding portion for forming one of the inner
and outer circumferential surfaces of the die-cast article, the
method comprising the steps of introducing a molten metal into the
mold cavity; and separating the die-cast article and the molding
portion from each other while the die-cast article and the molding
portion are rotated relative to each other, after the molten metal
has solidified into the die-cast article. A die-casting apparatus
for practicing the method is also disclosed.
Inventors: |
Hiramatsu, Osamu;
(Kariya-shi, JP) ; Kawaguchi, Masahiro;
(Kariya-shi, JP) ; Ota, Masaki; (Kariya-shi,
JP) ; Ito, Masafumi; (Kariya-shi, JP) ;
Yoshida, Yoshiharu; (Kariya-shi, JP) |
Correspondence
Address: |
MORGAN & FINNEGAN, L.L.P.
345 Park Avenue
New York
NY
10154
US
|
Family ID: |
18963752 |
Appl. No.: |
10/116471 |
Filed: |
April 4, 2002 |
Current U.S.
Class: |
164/113 ;
164/131; 164/312 |
Current CPC
Class: |
B22D 17/22 20130101;
B22D 17/24 20130101; B22D 17/20 20130101 |
Class at
Publication: |
164/113 ;
164/131; 164/312 |
International
Class: |
B22D 017/00; B22D
029/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 11, 2001 |
JP |
2001-112310 |
Claims
What is claimed is:
1. A method of die-casting a die-cast article having at least one
of an inner circumferential surface and an outer circumferential
surface, whose cross sectional shape is a circle, said die-casting
article being formed with a die-casting apparatus having a mold
cavity therein and a molding portion for forming one of said inner
and outer circumferential surfaces of said die-cast article, the
method comprising the steps of: introducing a molten metal into
said mold cavity; and separating said die-cast article and said
molding portion from each other while said die-cast article and
said molding portion are rotated relative to each other, after said
molten metal has solidified into said die-cast article.
2. A method according to claim 1, wherein said die-cast article has
a cylindrical hole, said molding portion consisting of a
cylindrical portion which forms said cylindrical hole, said
cylindrical portion being rotated relative to said die-cast article
when said die-cast article and said cylindrical portion are
separated from each other.
3. A method according to claim 2, wherein said die-casting
apparatus includes: a mold assembly as a main body; and a slide
core which has a circular shape in transverse cross section and
which is rotatable and axially movable relative to said mold
assembly, said slide core being rotated relative to said mold
assembly when said slide core is separated from said cylindrical
hole of said die-cast article, after said die-cast article has been
formed in said mold cavity.
4. A method according to claim 1, wherein said one of said inner
and outer circumferential surfaces of said die-cast article
includes a plurality of axial portions which have respective
different diameters and which are coaxial with one another.
5. A method according to claim 1, wherein said die-cast article is
a housing which is used for a compressor and which has a
cylindrical hole, said inner circumferential surface of said
die-cast article being an inner circumferential surface of said
cylindrical hole of said housing.
6. A method according to claim 1, wherein said die-cast article is
a cylinder block which is used for a compressor and which has a
plurality of cylinder bores, said inner circumferential surface of
said die-cast article being an inner circumferential surface of
each of said cylinder bores.
7. A die-casting apparatus for die-casting a die-cast article
having at least one of an inner circumferential surface and an
outer circumferential surface, whose cross sectional shape is a
circle, said apparatus comprising: a first molding member for
forming one of said inner and outer circumferential surfaces of
said die-cast article; a second molding member for forming at least
one surface of said die-cast article other than said one of said
inner and outer circumferential surfaces, said first molding member
being rotatable and axially movable relative to said second molding
member; and a drive device for moving said first and second molding
members relative to each other in an axial direction thereof while
rotating said first and second molding members relative to each
other.
8. An apparatus according to claim 7, wherein said drive device
includes: a drive source operable to effect one of a relative
rotation and a relative axial movement between said first and
second molding members; and a motion-generating device operable to
effect the other of said relative rotation and said relative axial
movement, based on said one of said relative rotation and said
relative axial movement.
9. An apparatus according to claim 7, wherein said first molding
member consists of a cylindrical portion for forming said inner
circumferential surface of said die-cast article.
10. An apparatus according to claim 7, wherein said first molding
member includes a slide core for forming said inner circumferential
surface of said die-cast article while said second molding member
includes a pair of molds which are opened and closed for forming at
least one surface of said die-cast article other than said inner
circumferential surface.
11. An apparatus according to claim 10, wherein said drive device
includes: an axial moving member which is axially movable relative
to said pair of molds; an actuator operable to axially move said
axial moving member relative to said pair of molds; a connecting
device disposed between said axial moving member and said slide
core and operable to connect said axial moving member and said
slide core such that said axial moving member and said slide core
are rotatable relative to each other and axially immovable relative
to each other; and a first engaging portion and a second engaging
portion which are provided on said pair of molds and said slide
core, respectively, said first and second engaging portions being
held in engagement with each other and operable to cause said pair
of molds and said slide core to be rotated relative to each other
on the basis of an axial movement of said pair of molds and said
slide core relative to each other.
12. An apparatus according to claim 11, wherein said pair of molds
and said slide core have respective two fitting surfaces which
engage each other, and wherein said first and second engaging
portions have one and the other of an engaging groove and an
engaging protrusion fitted in said engaging groove, said engaging
groove being formed in one of said two fitting surfaces and having
an inclined portion which extends in a direction inclined with
respect to an axial direction of said slide core, said engaging
protrusion being formed on the other of said two fitting surfaces.
Description
[0001] This application is based on Japanese Patent Application No.
2001-112310 filed Apr. 11, 2001, the contents of which are
incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates in general to a method of
producing a die-cast article having at least one of an inner and an
outer circumferential surface which has a cylindrical or
substantially cylindrical shape. The present invention is also
concerned with a die-casting apparatus suitable for practicing the
method.
[0004] 2. Discussion of the Related Art
[0005] A die-cast article to be produced by a die-casting method
using a die-casting apparatus may be required to have a cylindrical
or substantially cylindrical inner circumferential surface
depending upon its application. For instance, in producing a
housing used for a variable displacement swash plate type
compressor by die-casting of an aluminum alloy, it is necessary to
form a valve hole for accommodating a control valve which controls
the pressure in a crank chamber of the compressor. In producing a
cylinder block for the swash plate type compressor, a plurality of
cylinder bores need to be formed in the cylinder block. The inner
circumferential surfaces of the valve hole and the cylinder bore
need to have respective constant diameters. For forming a die-cast
article having a straight inner circumferential surface whose
diameter is constant over a suitable axial length thereof, a slide
core which forms the inner circumferential surface is provided with
a draft for easy removal of the slide core from the inner
circumferential surface of the die-cast article. If the slide core
which does not have the draft is forcibly removed from the die-cast
article, the die-cast article undesirably suffers from a defect
so-called "chipping" at a portion of its inner circumferential
surface formed by the draft-less slide core. In addition, a
relatively large force is required to remove the die-cast article
and the slide core away from each other, resulting in an increased
size and a lowered durability of the die-casting apparatus.
Accordingly, the slide core inevitably has the draft, and the
die-cast article whose inner circumferential surface has an
inclination corresponding to the draft of the slide core must be
subjected to a machining operation at its inner circumferential
surface after the die-casting process. In this case, the required
amount of stock removal by the machining operation conducted on the
inner circumferential surface of the die-cast article is inevitably
large due to the draft provided on the slide core.
[0006] EP 0642855 A (corresponding to JP-A-7-60399) proposes one
example of a method of minimizing an angle of inclination to be
provided on the inner circumferential surface of the die-cast
article. In the proposed method, the slide core is formed of a
material whose thermal expansion coefficient is equal to or higher
than that of a molten metal to be introduced into the mold cavity.
According to this arrangement, the slide core has been heated to a
temperature substantially equal to that of the molten metal before
the molten metal solidifies into a die-cast article. Thereafter,
the temperature of the slide core is lowered with a decrease of the
temperature of the die-cast article. Since the thermal expansion
coefficient of the slide core is equal to or higher than that of
the molten metal, the slide core is subjected to shrinkage whose
amount is equal to or larger than that of shrinkage of the molten
metal. Therefore, the slide core is easily removed from the
die-cast article. In the proposed method, however, the material of
the slide core is inevitably limited to that which is suitable for
a casting mold and which has a thermal expansion coefficient equal
to or higher than the molten metal for forming the die-cast
article. In addition, the proposed method is not available for
eliminating or reducing an angle of inclination to be provided on
an outer circumferential surface of the die-cast article.
SUMMARY OF THE INVENTION
[0007] It is therefore an object of the present invention to
provide a method of die-casting a die-cast article having at least
one of an inner and outer circumferential surfaces, whose cross
sectional shape is a circle, the method permitting reduction in the
angle of inclination provided on the inner or outer circumferential
surface. It is another object of the invention to provide a
die-casting apparatus suitably used for the method.
[0008] This object may be achieved according to any one of the
following modes of the present invention, each of which is numbered
like the appended claims and depends from the other mode or modes,
where appropriate, to indicate and clarify possible combinations of
elements or technical features of the present invention, for easier
understanding of the invention. It is to be understood that the
present invention is not limited to the technical features or any
combinations thereof which will be described for illustrative
purpose only. It is to be further understood that a plurality of
elements or features included in any one of the following modes of
the invention are not necessarily provided all together, and that
the invention may be embodied without some of the elements or
features described with respect to the same mode.
[0009] (1) A method of die-casting a die-cast having at least one
of an inner circumferential surface and an outer circumferential
surface, whose cross sectional shape is a circle, the die-casting
article being formed with a die-casting apparatus having a mold
cavity therein and a molding portion for forming one of the inner
and outer circumferential surfaces of the die-cast article, the
method comprising the steps of: introducing a molten metal into the
mold cavity; and separating the die-cast article and the molding
portion from each other while the die-cast article and the molding
portion are rotated relative to each other, after the molten metal
has solidified into the die-cast article.
[0010] If a die-cast article to be produced needs to have an inner
or an outer circumferential surface, a die-casting apparatus is
arranged to have a molding portion which partially defines a mold
cavity and which has an outer or an inner circumferential surface
for forming the corresponding inner or outer circumferential
surface of the die-cast article. The die-cast article may have one
of, or both of, the inner and outer circumferential surfaces whose
transverse cross sectional shape is a circle. Even if the die-cast
article has both of the inner and outer circumferential surfaces,
it is not essential that both of the inner and outer
circumferential surfaces are formed according to the principle of
the present invention. Similarly, where the die-cast article has a
plurality of inner or outer circumferential surfaces, all of the
plurality of the inner or outer circumferential surfaces need not
be formed according to the principle of the present invention, but
at least one of the plurality of the inner or outer circumferential
surfaces may be formed according to the present invention.
[0011] The molding portion of the die-casting apparatus which forms
one of the inner and outer circumferential surfaces of the die-cast
article is removed or separated from the corresponding one of the
outer and inner circumferential surfaces of the die-cast article,
after the molten metal has solidified into the die-cast article. In
this case, the die-cast article and the molding portion can be more
easily removed or separated from each other by a combination of a
relative axial movement between the molding portion and the
die-cast article, and a relative rotation therebetween, than an
arrangement wherein the die-cast article and the molding portion
are removed or separated from each other simply by only the
relative axial movement. Accordingly, even where the angle of
inclination of the inner or outer circumferential surface of the
die-cast article is made smaller than that in a conventional
arrangement, the die-cast article can be easily removed from the
molding portion. Depending upon various conditions such as a ratio
of the diameter of the inner or outer circumferential surface to
its axial length or a relationship between the thermal expansion
coefficients of the portion of the die-cast article having the
inner or outer circumferential surface, and the molding portion of
the die-cast apparatus, the draft to be provided on the molding
portion of the die-cast apparatus can be eliminated. In this
respect, the principle of the present invention does not
necessarily exclude the technique disclosed in the publication
described above, but permits the disclosed technique to be used in
combination, for thereby increasing a degree of freedom in
selecting the material for the molding portion of the die-casting
apparatus which forms the inner and outer circumferential surface
of the die-cast article.
[0012] In the present method wherein the angle of inclination of
the inner or outer circumferential surface of the die-cast article
can be minimized, it is possible to reduce the required amount of
stock removal by a cutting operation conducted on the inner or
outer circumferential surface of the die-cast article after the
die-casting process, for thereby improving the yield and reducing
the cost of the cutting operation. Alternatively, the inner or
outer circumferential surface of the die-cast article can be
finished only by a grinding operation without a cutting operation.
Even the grinding operation can be eliminated. Further, it is
possible to totally eliminate any machining operation. Where the
machining operation is totally eliminated, the cost of manufacture
of the die-cast article can be effectively minimized, and the
die-cast article exhibits improved durability and wear resistance
owing to the hard surface layer so-called "chilled layer" which
remains uncut on the superficial portion (i.e. the inner and outer
circumferential surface) of the die-cast article. As is apparent
from the description given above, the present method is applicable
to an arrangement wherein the inner or outer circumferential
surface of the die-cast article to be produced needs to be a
straight cylindrical surface having a constant diameter over a
suitable axial length. The present method is also applicable to an
arrangement wherein the inner or outer circumferential surface has
an angle of inclination. In the latter arrangement, too, the
reduction or elimination of the angle of inclination on the inner
or outer circumferential surface of the die-cast article is
effective to reduce a weight of a final product obtained from the
die-cast article and improve the yield in the die-casting
process.
[0013] (2) A method according to the above mode (1), wherein the
die-cast article has a cylindrical hole, the molding portion
consisting of a cylindrical portion which forms the cylindrical
hole, the cylindrical portion being rotated relative to the
die-cast article when the die-cast article and the cylindrical
portion are separated from each other.
[0014] While the present method can reduce or eliminate the angle
of inclination on both of the inner and outer circumferential
surfaces of the die-cast article, the present method advantageously
reduces or eliminates the angle of inclination on the inner
circumferential surface since it is rather easy to arrange a slide
core to be not only axially movable but also rotatable, which slide
core is generally used for forming the inner circumferential
surface and which is described in the following mode (3).
[0015] (3) A method according to the above mode (2), wherein the
die-casting apparatus includes: a mold assembly as a main body; and
a slide core which has a circular shape in transverse cross section
and which is rotatable and axially movable relative to the mold
assembly, the slide core being rotated relative to the mold
assembly when the slide core is separated from the cylindrical hole
of the die-cast article, after the die-cast article has been formed
in the mold cavity.
[0016] (4) A method according to any one of the above modes
(1)-(3), wherein the one of the inner and outer circumferential
surfaces of the die-cast article includes a plurality of axial
portions which have respective different diameters and which are
coaxial with one another.
[0017] For instance, the above-described valve hole formed in the
housing of the compressor for accommodating the control valve
therein, in general, consists of a plurality of axial portions
which have respective different diameters. In this case, the
die-cast article having such a cylindrical hole which have
different diameters can be more easily removed from the die-casting
apparatus than the die-cast article having a simple cylindrical
hole which has a constant diameter over its axial length, where
those cylindrical holes have the same axial length. The present
mode is one of particularly advantageous arrangements according to
the present invention.
[0018] (5) A method according to any one of the above modes
(1)-(4), wherein the die-cast article is a housing which is used
for a compressor and which has a cylindrical hole, the inner
circumferential surface of the die-cast article being an inner
circumferential surface of the cylindrical hole of the housing.
[0019] The cylindrical hole includes the above-described valve
hole, and a recess of the housing which partially defines the crank
chamber of the compressor and whose inner circumferential surface
is provided for sliding contact with a rotation preventive part
provided on the piston for preventing a rotary motion of the piston
about its centerline.
[0020] (6) A method according to any one of the above modes
(1)-(4), wherein the die-cast article is a cylinder block which is
used for a compressor and which has a plurality of cylinder bores,
the inner circumferential surface of the die-cast article being an
inner circumferential surface of each of the cylinder bores.
[0021] (7) A die-casting apparatus for die-casting a die-cast
article having at least one of an inner circumferential surface and
an outer circumferential surface, whose cross sectional shape is a
circle, the apparatus comprising: a first molding member for
forming one of the inner and outer circumferential surfaces of the
die-cast article; a second molding member for forming at least one
surface of the die-cast article other than the one of the inner and
outer circumferential surfaces, the first molding member being
rotatable and axially movable relative to the second molding
member; and a drive device for moving the first and second molding
members relative to each other in an axial direction thereof while
rotating the first and second molding members relative to each
other.
[0022] The present die-casting apparatus is suitably used for
practicing the die-casting method according to the above mode (1).
As described in the following DETAILED DESCRIPTION OF THE PREFERRED
EMBODIMENTS, a substantial part of the die-cast article is
generally formed by a pair of molds such that at least one of the
inner and outer circumferential surfaces having a circular
transverse cross sectional shape is formed in a portion of the
die-cast article. In this case, the above-indicated first molding
member for forming one of the inner and outer circumferential
surfaces of the die-cast article is usually made rotatable and
axially movable relative to the pair of molds. Depending upon the
configuration of the die-cast article, the first molding member for
forming one of the inner and outer circumferential surfaces of the
die-cast article is provided on a first mold which is one of the
pair of molds, as an integral part of the first mold. The first
molding member as the integral part of the first mold may be
rotated relative to a second mold which is the other of the pair of
molds, by opening and closing the first and second molds while
being rotated relative to each other. In this case, the die-cast
article is arranged to be held by the second mold when the two
molds are separated from each other.
[0023] (8) An apparatus according to the above mode (7), wherein
the drive device includes: a drive source operable to effect one of
a relative rotation and a relative axial movement between the first
and second molding members; and a motion-generating device operable
to effect the other of the relative rotation and the relative axial
movement, based on the above-indicated one of the relative rotation
and the relative axial movement.
[0024] If one of the relative rotation and relative axial movement
between the first and second molding members is caused by the drive
source while the other of the relative rotation and axial movement
is caused by the motion-generating device based on the
above-indicated one of the relative rotation and relative axial
movement, both of the relative rotation and axial movement can be
caused by utilizing the single drive source. Accordingly, the
present arrangement permits a simplified structure of the
die-casting apparatus.
[0025] (9) An apparatus according to the above mode (7) or (8),
wherein the first molding member consists of a cylindrical portion
for forming the inner circumferential surface of the die-cast
article.
[0026] (10) An apparatus according to any one of the above modes
(7)-(9), wherein the first molding member includes a slide core for
forming the inner circumferential surface of the die-cast article
while the second molding member includes a pair of molds which are
opened and closed for forming at least one surface of the die-cast
article other than the inner circumferential surface.
[0027] (11) An apparatus according to the above mode (10), wherein
the drive device includes:
[0028] an axial moving member which is axially movable relative to
the pair of molds;
[0029] an actuator operable to axially move the axial moving member
relative to the pair of molds;
[0030] a connecting device disposed between the axial moving member
and the slide core and operable to connect the axial moving member
and the slide core such that the axial moving member and the slide
core are rotatable relative to each other and axially immovable
relative to each other; and
[0031] a first engaging portion and a second engaging portion which
are provided on the pair of molds and the slide core, respectively,
the first and second engaging portions being held in engagement
with each other and operable to cause the pair of molds and the
slide core to be rotated relative to each other on the basis of an
axial movement of the pair of molds and the slide core relative to
each other.
[0032] The drive device according to the mode (11) is one
embodiment of the drive device described in the above mode (8). The
axial moving member in the above mode (11) may be axially movable
relative to at least one of the pair of molds. The actuator in the
above mode (11) may be operable to axially move the axial moving
member relative to at least one of the pair of molds. The first and
second engaging portions in the above mode (11) may be operable to
cause at least one of the pair of molds and the slide core to be
rotated relative to each other on the basis of an axial movement of
at least one of the pair of molds and the slide core relative to
each other. The axial moving member is preferably arranged not to
be rotatable relative to the pair of molds. In the drive device
according to the above mode (11), if a movable sleeve which forms
an outer circumferential surface of a cylindrical protrusion of a
die-cast article is used in place of the slide core which forms the
inner circumferential surface of the cylindrical hole of the
die-cast article, the movable sleeve and the cylindrical protrusion
of the die-cast article can be easily separated from each
other.
[0033] (12) An apparatus according to the above mode (11), wherein
the pair of molds and the slide core have respective two fitting
surfaces which engage each other, and wherein the first and second
engaging portions have one and the other of an engaging groove and
an engaging protrusion fitted in the engaging groove, the engaging
groove being formed in one of the two fitting surfaces and having
an inclined portion which extends in a direction inclined with
respect to an axial direction of the slide core, the engaging
protrusion being formed on the other of the two fitting
surfaces.
[0034] According to the mode (12), the first and second engaging
portions in the above mode (11) can be easily provided. In
particular, an arrangement wherein the engaging groove is formed in
the fitting surface (outer circumferential surface) of the slide
core and the engaging protrusion is formed on the fitting surface
(inner circumferential surface) of the pair of molds permits more
easier formation of the engaging groove by a machining operation
than an arrangement wherein the engaging groove is formed in the
fitting surface of the pair of molds and the engaging protrusion is
formed on the fitting surface of the slide core.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] The above and optional objects, features, advantages and
technical and industrial significance of the present invention will
be better understood and appreciated by reading the following
detailed description of presently preferred embodiments of the
invention, when considered in connection with the accompanying
drawings, in which:
[0036] FIG. 1 is a front elevational view in cross section of a
swash plate type compressor including a component which is produced
according to one embodiment of a die-casting method and apparatus
of the present invention;
[0037] FIG. 2 is an enlarged front elevational view in cross
section showing a part of the compressor of FIG. 1;
[0038] FIG. 3 is a front elevational view schematically showing the
die-casting apparatus;
[0039] FIG. 4 is a front elevational view showing a part of the
die-casting apparatus;
[0040] FIG. 5 is a front elevational view showing a molding member
for forming the inner circumferential surface of the die-cast
article, and the inner circumferential surface of the die-cast
article formed by the molding member; and
[0041] FIG. 6 is a front elevational view in cross section
schematically showing a principal part of a die-casting apparatus
constructed according to another embodiment of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0042] Referring to the accompanying drawings, there will be
described presently preferred embodiments of a die-casting method
and apparatus according to the present invention as applied to the
production of a swash plate type compressor.
[0043] Referring first to FIG. 1, there is shown a compressor of
swash plate type used for an air conditioning system of an
automotive vehicle. In FIG. 1, reference numeral 10 denotes a
cylinder block having a plurality of cylinder bores 12 formed so as
to extend in its axial direction such that the cylinder bores 12
are arranged along a circle whose center lies on a centerline of
the cylinder block 10. Single-headed pistons generally indicated at
14 (hereinafter simply referred to as "piston 14") are reciprocably
received in the respective cylinder bores 12. To one of the axially
opposite end faces of the cylinder block 10, (the left end face as
seen in FIG. 1, which will be referred to as "front end face"),
there is attached a front housing 16. To the other end face (the
right end face as seen in FIG. 1, which will be referred to as
"rear end face"), there is attached a rear housing 18 through a
valve plate 20. The front housing 16, rear housing 18 and cylinder
block 10 cooperate to constitute a housing assembly of the swash
plate type compressor. The rear housing 18 and the valve plate 20
cooperate to define a suction chamber 22 and a discharge chamber
24, which are connected to a refrigerating circuit (not shown)
through an inlet and an outlet (not shown), respectively. The valve
plate 20 has suction ports 32, suction valves 34, discharge ports
36 and discharge valves 38.
[0044] A rotary drive shaft 50 is disposed in the cylinder block 10
and the front housing 16 such that the axis of rotation of the
drive shaft 50 is aligned with the centerline of the cylinder block
10. The drive shaft 50 is supported at its opposite end portions by
the front housing 16 and the cylinder block 10, respectively, via
respective bearings. The cylinder block 10 has a central bearing
hole 56 formed in a central portion thereof, and the bearing is
disposed in this central bearing hole 56, for supporting the drive
shaft 50 at its rear end portion. The front end portion of the
drive shaft 50 is connected, through a clutch mechanism such as an
electromagnetic clutch, to an external drive source (not shown) in
the form of an engine of an automotive vehicle. In operation of the
compressor, the drive shaft 50 is connected through the clutch
mechanism to the vehicle engine in operation so that the drive
shaft 50 is rotated about its axis.
[0045] The rotary drive shaft 50 carries a swash plate 60 such that
the swash plate 60 is axially movable and tiltable relative to the
drive shaft 50. The swash plate 60 has a central hole 61 through
which the drive shaft 50 extends. The inner dimension of the
central hole 61 as measured in a vertical direction of FIG. 1
gradually increases in a direction from the axially intermediate
portion toward each of the axially opposite ends, and the
transverse cross sectional shape of the central hole 61 at each of
the axially opposite ends is elongated. To the drive shaft 50,
there is fixed a rotary member 62 as a torque transmitting member,
which is held in engagement with the front housing 16 through a
thrust bearing 64. The swash plate 60 is rotated with the drive
shaft 50 by a hinge mechanism 66 during rotation of the drive shaft
50. The hinge mechanism 66 guides the swash plate 60 for its axial
and tilting motions. The hinge mechanism 66 includes a pair of
support arms 67 fixed to the rotary member 62, guide pins 69 which
are formed on the swash plate 60 and which slidably engage guide
holes 68 formed in the support arms 67, the central hole 61 of the
swash plate 60, and the outer circumferential surface of the drive
shaft 50.
[0046] The piston 14 indicated above includes an engaging portion
70 engaging the radially outer portion of the opposite surfaces of
the swash plate 60, and a head portion 72 formed integrally with
the engaging portion 70 and fitted in the corresponding cylinder
bore 12. The head portion 72 in the present embodiment is made
hollow, for thereby reducing the weight of the piston 14. The head
portion 72, cylinder bore 12, and valve plate 20 cooperate with one
another to define a pressurizing chamber 74. The engaging portion
70 engages the radially outer portion of the opposite surfaces of
the swash plate 60 through a pair of hemispherical shoes 76. The
engaging portion 70 of the piston 14 has an integrally formed
rotation preventive part (not shown), which is arranged to be held
in sliding contact with the inner circumferential surface of the
front housing 16, for thereby preventing a rotary motion of the
piston 14 about its centerline.
[0047] A rotary motion of the swash plate 60 is converted into a
reciprocating linear motion of the piston 14 through the shoes 76.
A refrigerant gas in the suction chamber 22 is sucked into the
pressurizing chamber 74 through the suction port 32 and the suction
valve 34, when the piston 14 is moved from its upper dead point to
its lower dead point, that is, when the piston 14 is in the suction
stroke. The refrigerant gas in the pressurizing chamber 74 is
pressurized by the piston 14 when the piston 14 is moved from its
lower dead point to its upper dead point, that is, when the piston
14 is in the compression stroke. The pressurized refrigerant gas in
the pressurizing chamber 74 is discharged into the discharge
chamber 24 through the discharge port 36 and the discharge valve
38.
[0048] The present swash plate type compressor is of variable
capacity type. By controlling the pressure in the crank chamber 86
by utilizing a difference between the pressure in the discharge
chamber 24 as a high-pressure source and the pressure in the
suction chamber 22 as a low pressure source, a difference between
the pressure in the pressurizing chamber 74 and the pressure in the
crank chamber 86 is regulated to change the angle of inclination of
the swash plate 60 with respect to a plane perpendicular to the
axis of rotation of the drive shaft 50, for thereby changing the
reciprocating stroke (suction and compression strokes) of the
piston 14, whereby the discharge capacity of the compressor can be
adjusted. Described in detail, the pressure in the crank chamber 86
is controlled by a pressure control device 90 disposed for
communication with the suction chamber 22, discharge chamber 24,
and crank chamber 86, such that the crank chamber 86 is selectively
connected and disconnected to and from the discharge chamber 24,
for thereby controlling the pressure in the crank chamber 86. The
pressure control device 90 will be described.
[0049] A supply passage 80 is formed through the cylinder block 10
and the rear housing 18 for communication between the discharge
chamber 24 and the crank chamber 86. The pressure control device 90
is disposed on the supply passage 90. The rotary drive shaft 50 has
a bleeding passage 100 formed therethrough. The bleeding passage
100 is open at one of its opposite ends to the central bearing hole
56, and is open at the other end to a space defined by the front
housing 16. The bleeding passage 100 is held in communication with
the crank chamber 86 via the space. The central bearing hole 56
communicates at its bottom with the suction chamber 22 through a
communication port 104.
[0050] There will be described the pressure control device 90. The
rear housing 18 is formed with a valve hole 110 which extends in a
direction perpendicular to the centerline of the housing. As shown
in FIG. 2, the valve hole 110 is a cylindrical hole having a
circular transverse cross sectional shape, and has a plurality of
axial portions which have respective different diameters and which
are coaxial with one another. Described more specifically, the
valve hole 110 has different inner diameters which decrease in
steps in its axial direction from its open end which is distant
from the centerline of the housing of the compressor, toward its
closed end which is nearer to the centerline of the housing. The
valve hole 110 includes a plurality of straight inner
circumferential surfaces 130, 132, 134 which have respective
different constant diameters over respective axial lengths and
which are spaced from each other in the axial direction of the
valve hole 110. The straight inner circumferential surface 134 is
located on the side of the closed end of the valve hole 110 which
is nearer to the centerline of the housing. The diameter of the
straight inner circumferential surface 130 located on the side of
the open end of the valve hole 110 which is more distant from the
centerline of the housing is larger than those of the other two
straight inner circumferential surfaces 132, 134. Between the
adjacent two straight inner circumferential surfaces 130, 132, 134,
tapered inner circumferential surfaces 136, 137, 138, 139, 140 are
formed such that the tapered inner circumferential surfaces 136,
137, 138 are interposed between the two straight inner
circumferential surfaces 130, 132, such that the tapered inner
circumferential surface 139 is interposed between the two straight
inner circumferential surfaces 132, 134, and such that the tapered
inner circumferential surface 140 is located adjacent to the
straight inner circumferential surface 134. The diameter of each of
the tapered inner circumferential surfaces gradually increases in
the axial direction of the valve hole 110 from the closed end which
is nearer to the centerline of the housing toward the open end
which is distant from the centerline of the housing.
[0051] A sleeve 144 as one component of the pressure control device
90 is fitted in the valve hole 110 formed as described above. The
sleeve 144 is a generally hollow cylindrical member including a
plurality of axial portions having respective different diameters.
In a strict sense, the sleeve 144 consists of a plurality of
members which are assembled together. The sleeve 144 has a
plurality of straight outer circumferential surfaces 150, 152, 154
which have respective different constant diameters over respective
axial lengths and which are spaced apart from each other in the
axial direction of the sleeve 144. These straight outer
circumferential surfaces 150, 152, 154 engage the straight inner
circumferential surfaces 130, 132, 134 of the valve hole 110,
respectively. Annular grooves are formed in the respective straight
outer circumferential surfaces 150, 152, 154 of the sleeve 144 so
as to extend in the circumferential direction. Sealing members in
the form of 0-rings 160, 162, 164 are fitted in the respective
circumferential annular grooves of the straight outer
circumferential surfaces 150, 152, 154 of the sleeve 144, so as to
define, within the valve hole 110, three fluid-tightly sealed
spaces (first through third spaces) which are arranged in the axial
direction of the valve hole 110. Described more specifically, the
first space, which is the nearest to the centerline of the housing,
is held in communication with a discharge pressure chamber 170
formed in the sleeve 144 while communicating with the discharge
chamber 24 via a high-pressure passage 180 formed in the rear
housing 18. The second space, which is intermediate between the
first and third spaces, is held in communication with an annular
chamber 174 formed in the sleeve 144 while communicating with the
crank chamber 86 via a control pressure passage 176 (FIG. 1) formed
through the rear housing 18 and the cylinder block 10. The third
space, which is the most distant from the centerline of the
housing, is held in communication with a suction pressure chamber
178 formed in the sleeve 144 while communicating with the suction
chamber 22 via a low-pressure passage 172 (FIG. 1). The
high-pressure passage 180 and the control pressure passage 176
cooperate to constitute the supply passage 80.
[0052] A valve element 190 is disposed within the discharge
pressure chamber 170, and is biased by biasing means in the form of
a compression coil spring 192 in a direction that causes the valve
element 190 to be seated on a valve seat 196. A valve rod 200 is
fitted in an engaging hole of the sleeve 144 such that the valve
rod 200 is slidably moved in the axial direction. The valve element
190 is attached to the distal end of the valve rod 200 such that
the valve element 190 is movable together with the valve rod
200.
[0053] Within the suction pressure chamber 178, there is
accommodated a bellows member 206 which is extensible and
contractible. The bellows member 206 divides the inner space of the
sleeve 144 into two annular sections, i.e., a radially outer
section which functions as the above-described suction pressure
chamber 178 and a radially inner section which functions as an
atmospheric pressure chamber 208. The bellows member 206 is biased
by biasing means in the form of a compression coil spring 210 in a
direction of extension of the bellows member 206, in other words,
toward the discharge pressure chamber 170. A holding member 212
which holds the distal end of the bellows member 206, and the valve
rod 200 are connected to each other, so that a shut-off valve
including the valve element 190 and the valve seat 196 is
selectively opened and closed by advancing and the retracting
movements of the valve rod 200 in response to extending and
contracting movements of the bellows member 206. Described more
specifically, the bellows member 206 extends and contracts
depending upon a suction pressure Ps introduced into the suction
pressure chamber 178. The bellows member 206 contracts with an
increase in the suction pressure Ps within the suction pressure
chamber 178 while the bellows member 206 extends with a decrease in
the suction pressure Ps. The bellows member 206 moves the valve rod
200 toward the discharge pressure chamber 170 when the suction
pressure Ps in the suction pressure chamber 178 is lower than a
predetermined value. Accordingly, the valve element 190 is moved
away from the valve seat 196 against the biasing force of the
compression coil spring 192, whereby the shut-off valve is opened
to establish a fluid communication between the discharge chamber 24
and the crank chamber 86 via the high-pressure passage 180,
discharge pressure chamber 170, annular chamber 174, and control
pressure passage 176.
[0054] There will be next explained the operation of the pressure
control device 90. The pressure control device 90 of the present
embodiment is arranged to control the pressure Pc in the crank
chamber 86 depending upon the change of the suction pressure Ps in
the suction pressure chamber 178. Described in detail, where a
cooling load required for air-conditioning the vehicle compartment
is large, the suction pressure Ps is accordingly high, and exceeds
the predetermined reference value. Accordingly, the bellows member
206 in the suction chamber 178 which is held in communication with
the suction chamber 22 via the low-pressure passage 172 is
contracted, whereby the valve element 190 is seated on the valve
seat 196 so as to close the shut-off valve for inhibiting the fluid
communication between the discharge pressure chamber 170 and the
annular chamber 174. In the meantime, since the crank chamber 86 is
held in communication with the suction chamber 22 via the bleeding
passage 100 and the communication port 104, the pressure Pc in the
crank chamber 86 is lowered, so that the swash plate 60 is placed
in its maximum inclined position owing to the difference between
the pressure in the crank chamber 86 and the pressure in the
pressurizing chamber 74, for thereby maximizing the discharge
capacity of the compressor.
[0055] The suction pressure Ps is lowered with a decrease of the
cooling load. When the suction pressure Ps is lower than the
predetermined reference value, the bellows member 206 is extended
so as to advance the valve rod 200 toward the discharge pressure
chamber 170, whereby the valve element 190 is moved away from the
valve seat 196. Accordingly, the discharge pressure chamber 170 and
the annular chamber 174 are brought into communication with each
other, so that the refrigerant gas in the discharge chamber 24 is
introduced into the crank chamber 86 via the high-pressure passage
180, discharge pressure chamber 170, annular chamber 174, and
control pressure passage 176. Therefore, the pressure in the crank
chamber 86 is increased to decrease the inclination angle of the
swash plate 60, for thereby decreasing the displacement capacity of
the compressor. With a further decrease in the suction pressure Ps,
the swash plate 60 is placed in its minimum inclination position,
whereby the displacement capacity of the compressor is
minimized.
[0056] There will be next described a method of producing, by
die-casting, a portion of the rear housing 18, according to a first
embodiment of the present invention. The above-indicated portion
(hereinafter referred to as "die-cast article 220") has the valve
hole 110 for accommodating the pressure control device 90
constructed as described above. FIG. 3 schematically shows a
die-casting apparatus used in the present die-casting method. In
the actual die-casting process, the above-indicated portion having
the valve hole 110 is produced integrally with the other portions
of the rear housing 18. Accordingly, the structure of the
die-casting apparatus of FIG. 3 is different from that of the
actual die-casting apparatus. For producing the rear housing 18
having a complicated configuration, the actual die-casting
apparatus has a complicated structure including a stationary and a
movable mold which are opened and closed, a plurality of moving
members, and other components. For easier understanding of the
present invention, only portions of the die-casting apparatus
relating to the formation of the valve hole 110 are schematically
shown in FIG. 3 while other portions not relating to the formation
of the valve hole 110 are dispensed with.
[0057] The die-casting apparatus illustrated in a simplified manner
in FIG. 3 includes a stationary mold 224 and a movable mold 226
which are moved toward and away from each other, so that the
stationary and movable molds 224, 226 are opened and closed. The
following explanation is made on the assumption that the
die-casting apparatus illustrated in FIG. 3 is used in an ordinary
casting system which includes a pair of stationary platens, and a
movable platen which is disposed between the pair of stationary
platens and which is moved toward and away from one of the
stationary platens by actuation of a mold-opening-and-closing
device such as a cylinder. The stationary mold 224 is attached to
one of the opposite major surfaces of the above-indicated one
stationary platen while the movable mold 226 is attached to one of
the opposite major surfaces of the movable platen such that the
stationary mold 224 and the movable mold 226 are opposed to each
other with a high degree of positioning accuracy. Each of the
stationary and movable molds 224, 226 consists of a plurality of
plate members which are superposed on one another.
[0058] The stationary and movable molds 224, 226 are opened and
closed at respective contact surfaces 230, 232. The movable mold
226 is moved toward the stationary mold 224 by a drive force of a
cylinder functioning as the mold-opening-and-closing-device, so
that the two molds 224, 226 are closed with the contact surfaces
230, 232 being held in close contact with each other, for thereby
defining a mold cavity 236 having a profile which follows that of
the valve hole 110 of the die-cast article 220. The stationary mold
224 and the movable mold 226 have respective molding surfaces 242,
240 which cooperate with each other to provide an outer
circumferential surface of the valve hole 110 of the die-cast
article 220.
[0059] The die-casting apparatus of the present embodiment includes
a slide core 250 which forms an inner circumferential surface of
the valve hole 110. With the slide core 250 being located within
the mold cavity 236, a molten metal (e.g., a molten aluminum alloy
whose major component is aluminum) is injected into the mold cavity
236 via a runner not shown, whereby the die-cast article 220 is
formed in the mold cavity 236. The slide core 250 is held by the
stationary mold 224 via a guide bushing 252 such that the slide
core 250 is rotatable and axially movable relative to the
stationary mold 224. The inner circumferential surface of the valve
hole 110 is formed by the outer circumferential surface of the
distal end portion of the slide core 250. As shown in FIG. 5, the
slide core 250 has a circular shape in transverse cross section and
a plurality of axial portions which have respective different
diameters and which are coaxial with one another. The slide core
250 includes straight outer circumferential surfaces 254, 256, 258
whose diameters are constant in the axial direction and which
correspond to the straight inner circumferential surfaces 130, 132,
134 of the valve hole 110, respectively. The diameter of the outer
circumferential surface of the slide core 250 decreases in the
axial direction from its proximal end portion toward its distal end
portion which forms the inner circumferential surface of the valve
hole 110. Between the adjacent two straight outer circumferential
surfaces 254, 256, 258, a plurality of tapered outer
circumferential surfaces 260, 261, 262, 263, 264 are formed such
that the tapered outer circumferential surfaces 260, 261, 262 are
interposed between the two straight outer circumferential surfaces
254, 256, such that the tapered outer circumferential surface 263
is interposed between the two straight outer circumferential
surfaces 256, 258, and such that the tapered outer circumferential
surface 264 is located adjacent to the straight outer
circumferential surface 258. The tapered outer circumferential
surfaces 260, 261, 262, 263, 264 have respective different angles
of draft .theta..sub.1, .theta..sub.2, .theta..sub.3,
.theta..sub.4, .theta..sub.5. These tapered outer circumferential
surfaces 260, 262, 262, 263, 264 form the tapered inner
circumferential surfaces 136, 137, 138, 139, 140 of the valve hole
110, respectively.
[0060] The slide core 250 is axially moved by a drive device 270
relative to the stationary mold 224 while being rotated relative to
the stationary mold 224. The drive device 270 includes an axial
moving member 272 and a hydraulic cylinder 274. The axial moving
member 272 is held by the stationary mold 224 such that the member
272 is axially movable relative to the stationary mold 224. The
hydraulic cylinder 274 functions as an actuator for moving the
axial moving member 272 in the axial direction. In the present
embodiment, the axial moving member 272 is formed integrally with a
piston rod of the hydraulic cylinder 274. The axial moving member
272 and the slide, core 250 are connected to each other by a
connecting device 280 such that the member 272 and the slide core
250 are rotatable relative to each other and axially immovable
relative to each other. The connecting device 280 of the present
embodiment includes a coupling member 282 having a cylindrical
shape. The coupling member 282 has a first engaging recess 284 and
a second engaging recess 290, each of which has a T shape in
vertical cross section. An engaging protrusion 286 which is formed
integrally with the slide core 250 and which has a T shape in
vertical cross section engages the first engaging recess 284 such
that the engaging protrusion 286 is rotatable and axially immovable
relative to the first engaging recess 284. An engaging protrusion
292 which is formed integrally with the axial moving member 272 and
which has a T shape in vertical cross section engages the second
engaging recess 290 such that the engaging protrusion 292 is
rotatable and axially immovable relative to the second engaging
recess 290. For reducing the friction caused between the first and
second engaging recesses 284, 290 and the engaging protrusions 286,
292, it is desirable to provide a rolling bearing between the
coupling member 282 and the engaging protrusions 286, 292.
[0061] A fitting sleeve 310 is fitted on the outer circumferential
surface of the slide core 250 at an axially intermediate portion
thereof. The fitting sleeve 310 is a cylindrical member. The
fitting sleeve 310 is fixed to the stationary mold 224 by bolts 314
such that the fitting sleeve 310 is positioned with high accuracy
relative to the stationary mold 224 by a positioning pin 312,
preferably a plurality of positioning pins 312, and such that the
fitting sleeve 310 is strictly prevented from rotating relative to
the stationary mold 224. The fitting sleeve 310 fixed to the
stationary mold 224 functions as a part of the stationary mold 224.
The slide core 250 is provided with an engaging protrusion 300
which is located at its axial position corresponding to the fitting
sleeve 310 and which radially outwardly extends from its outer
circumferential surface. The fitting sleeve 310 is formed with an
engaging groove 320 (FIG. 4) which is formed through the
cylindrical wall and which engages the engaging protrusion 300 of
the slide core 250. The engaging groove 320 includes an inclined
portion 322 which extends in a direction inclined with respect to
the axial direction of the slide core 250, and an axially extending
portion 324 which is adjacent to the inclined portion 322 and which
extends in a direction parallel to the axial direction of the slide
core 250. While the slide core 250 is placed in its advanced
position for forming the die-cast article 220, the engaging
protrusion 300 of the slide core 250 is positioned at one of the
opposite ends of the inclined portion 322 of the engaging groove
320, which end is remote from the axially extending portion 324. As
the slide core 250 is retracted from the mold cavity 236, the
engaging protrusion 300 is moved relative to the fitting sleeve 310
along the inclined portion 322 of the engaging groove 320, whereby
the slide core 250 is rotated while it is axially moved from its
advanced position toward its retracted position. In the present
embodiment, the hydraulic cylinder 274 constitutes the drive source
operable to cause a relative axial movement of the slide core 250.
The fitting sleeve 310 having the engaging groove 320, and the
engaging protrusion 300 of the slide core 250 cooperate to
constitute the motion-generating device operable to effect a
relative rotation of the slide core 250 based on the relative axial
movement described above. The engaging groove 320 constitutes the
first engaging portion while the engaging protrusion 300
constitutes the second engaging portion. The engaging groove 320
having the inclined portion 322 may be formed in the slide core 250
while the engaging protrusion 300 may be formed on the fitting
sleeve 310 (i.e., on the side of the stationary mold 224).
[0062] There will be next explained a die-casting method using the
die-casting apparatus constructed as described above. Initially,
the mold-opening-and-closing cylinder is actuated to move the
movable mold 226 toward the stationary mold 224, so that the two
molds 224, 226 are closed together with the contact surfaces 230,
232 being held in close contact with each other. The distal end
portion of the slide core 250 is positioned in the mold cavity 236
which is defined by the two molds 224, 226 when they are closed
together. In this state, the molten metal is introduced into the
mold cavity 236.
[0063] The molten metal solidifies into the die-cast article 220 a
predetermined time after the molten metal has been introduced into
the mold cavity 236. The valve hole 110 of the die-cast article 220
is formed by the outer circumferential surface of the slide core
250. After the molten metal has solidified, the hydraulic cylinder
274 is actuated, so that the slide core 250 is rotated relative to
the die-cast article 220 and retracted in the axial direction (as
indicated by an arrow A in FIG. 3), by the engagement of the
engaging protrusion 300 with the engaging groove 320 of the fitting
sleeve 310. According to the present arrangement, the slide core
250 can be easily removed from the die-cast article 220. If the
slide core 250 is forcibly removed from the die-cast article 220
without the rotating movement, the die-cast article 220 may suffer
from defects called "chipping" at a portion of the inner
circumferential surface which contacts the slide core 250. The
die-cast article 220 produced by the present die-casting apparatus
is free from such defects.
[0064] After the slide core 250 has been removed from the die-cast
article 220, the movable mold 226 is moved away from the stationary
mold 224, whereby the two molds 224, 226 are opened. When the two
molds 224, 226 are separated from each other, the die-cast article
220 is moved together with the movable mold 226 while being held by
the movable mold 226. At the terminal stage or at the end of the
movement of the movable mold 226 away from the stationary mold 224,
an ejecting device (not shown) provided in the movable mold 226 is
actuated, for thereby pushing the die-cast article 220 in a
direction away from the movable mold 226.
[0065] The present arrangement wherein the slide core 250 can be
easily removed from the die-cast article 220 permits formation of
the inner circumferential surface of the die-cast article 220 by
the slide core having a reduced angle of draft or no draft. The
straight inner circumferential surfaces 130, 132, 134 of the valve
hole 110 functioning as sealing surfaces which are held in sealing
contact with the sealing members 160, 162, 164 of the sleeve 144 of
the pressure control device 90 need to be formed as highly
cylindrical surfaces without any taper while portions of the inner
circumferential surface of the valve hole 110 other than those
straight inner circumferential surfaces 130, 132, 134 need not to
have a high degree of cylindricity. Accordingly, the slide core 250
does not have any draft on the straight outer circumferential
surfaces 254, 256, 258 which respectively forms the straight inner
circumferential surfaces 130, 132, 134 of the valve hole 110 that
are required to have a high degree of cylindricity. On the other
hand, the slide core 250 has respective different angles of draft
provided on the respective portions of its outer circumferential
surface other than the straight outer circumferential surfaces 254,
256, 258. Namely, the slide core 250 has the tapered outer
circumferential surfaces 260, 262, 262, 263, 264, for easy removal
of the slide core 250 from the die-cast article 220. In the present
embodiment wherein the straight inner circumferential surfaces 130,
132, 134 of the valve hole 110 can be accurately formed as highly
cylindrical surfaces without any taper, the straight inner
circumferential surfaces 130, 132, 134 need not be subjected to a
machining operation after the die-casting process. The present
embodiment at least reduces portions of the die-cast article which
are subjected to the machining operation. Accordingly, the present
embodiment is effective to reduce the time and cost required for
the machining operation. Although the valve hole 110 has the
tapered inner circumferential surfaces 136 through 140 in the
present embodiment, the present arrangement is more effective to
improve the yield, shorten the time required for the machining
operation, and reduce the cost of manufacture of the die-cast
article 220, than a conventional arrangement wherein the outer
circumferential surface of the slide core for forming the inner
circumferential surface of the valve hole is provided with a draft
over the entire axial length so that the entire inner
circumferential surface of the valve hole is required to be
subjected to a machining operation to provide the tapered and
straight inner circumferential surfaces. Further, since the
straight inner circumferential surfaces 130, 132, 134 of the valve
hole 110 formed according to the present embodiment remain uncut
after the die-casting process, i.e., remain as-cast, there exists
the chilled layer at the superficial portion of the inner
circumferential surfaces, which chilled layer has high degrees of
hardness and strength. Therefore, the die-cast article 220 exhibits
high degrees of strength and wear resistance.
[0066] The die-casting method and die-casting apparatus according
to the present invention used for producing the die-cast article
having the cylindrical hole can be employed for forming the inner
circumferential surface of each of the cylinder bores 12 of the
cylinder block 10 shown in FIG. 1 and the inner circumferential
surface of the front housing 16. Since the head portion 72 of the
piston 14 slidably moves on the inner circumferential surface of
the cylinder bore 12 and the rotation preventive part formed
integrally with the engaging portion 70 of the piston 14 is held in
sliding contact with the inner circumferential surface of the front
housing 16, those inner circumferential surfaces need to have a
high degree of cylindricity. If the slide core is provided with a
small angle of draft or no draft, the machining operation on those
inner circumferential surfaces can be reduced or eliminated. The
present die-casting method and die-casting apparatus permit the
formation of the inner circumferential surface of the axial
through-hole such as the inner circumferential surface of the
cylinder bore 12, and the inner circumferential surface of the
recess having a closed end such as the inner circumferential
surface of the front housing 16.
[0067] In the present embodiment, the slide core 250 is a molding
portion. The stationary mold 224 and the movable mold 226 cooperate
to constitute a mold assembly as a main body of the die-casting
apparatus. The slide core 250 functions as a first molding member
while the stationary and movable molds 224, 226 cooperate to
function as a second molding member. The slide core 250 and the
stationary mold 224 (the fitting sleeve 310) have respective two
fitting surfaces which engage each other. The engaging groove 320
is formed in the fitting surface of the fitting sleeve 310 while
the engaging protrusion 300 is formed on the fitting surface of the
slide core 250.
[0068] The die-casting apparatus according to the present invention
may be arranged to have a member for forming an outer
circumferential surface of a die-cast article. Referring next to
FIG. 6, there is explained a die-casting apparatus constructed
according to a second embodiment of the present invention, for
producing a die-cast article 426. The die-casting device of the
second embodiment includes a stationary mold 402 and a movable mold
404 which are similar to the stationary mold 224 and the movable
mold 226 of the above-described first embodiment. A movable sleeve
410 is held by the movable mold 404 such that the movable sleeve
410 is rotatable and axially movable relative to the movable mold
404. A drive device having a structure similar to that of the drive
device 270 used in the first embodiment is connected to the movable
sleeve 410. The movable sleeve 410 is fixed to a distal end of a
rod 412. The rod 412 is axially moved while being rotated by the
drive device. A detailed explanation of the drive device is
dispensed with. The movable sleeve 410 has an inner circumferential
surface 414 which is provided with a small angle of draft or no
draft. The inner circumferential surface 414 of the movable sleeve
410 forms an outer circumferential surface 428 of a cylindrical
protrusion 427 of the die-cast article 426. The stationary and
movable molds 402, 404 have respective molding surfaces 420, 422
which cooperate with the inner circumferential surface 414 of the
movable sleeve 410 to define a mold cavity 430 having a
configuration which follows that of the die-cast article 426 to be
produced. In the present embodiment, the movable sleeve 410 can be
easily removed from the die-cast article 426 while the movable
sleeve 410 is rotated as indicated by an arrow A in FIG. 6.
Accordingly, the outer circumferential surface 428 of the
cylindrical protrusion 427 of the die-cast article 426 has no taper
or a small taper angle.
[0069] In the present embodiment, the movable sleeve 410 is the
molding portion. The movable sleeve 410 also functions as the first
molding member while the stationary mold 402 and the movable mold
404 cooperate to function as the second molding member.
[0070] While the presently preferred embodiments of this invention
have been described above, for illustrative purpose only, it is to
be understood that the present invention may be embodied with
various changes and improvements such as those described in the
SUMMARY OF THE INVENTION, which may occur to those skilled in the
art.
* * * * *