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This application is based on Japanese Patent
Application No. 11-238547 filed August 25, 1999, the contents of
which are incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
Field of the Invention
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The present invention relates to a method of
forming a hollow head portion of a piston for a swash plate type
compressor, by welding a closing member to a hollow cylindrical
member which is open at at least one of opposite ends thereof, so
as to close an open end of the hollow cylindrical member.
Discussion of Related Art
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In a swash plate type compressor having a rotary
drive shaft which is rotated about its axis, a swash plate which is
rotatably supported by the drive shaft, and a plurality of pistons
each of which includes a head portion slidably fitted in a cylinder
bore formed in a cylinder block of the compressor and a neck
portion which slidably engages the swash plate, the pistons are
reciprocated by a rotary movement of the swash plate which is
rotated together with the drive shaft. In this case, it is desirable
that the pistons have a reduced weight especially when installed
in a swash plate type compressor of variable capacity type
wherein the angle of inclination of the swash plate with respect
to the direction perpendicular to the axis of the drive shaft is
variable, as well as when installed in a swash plate type
compressor of fixed capacity type wherein the angle of inclination
of the swash plate is fixed. In an attempt to reduce the weight of
the piston, it has been proposed to form the piston with a hollow
head portion. The hollow head portion of the piston is formed by
welding a dosing member to a hollow cylindrical member which
is open at at least one of opposite ends thereof, so as to close an
open end of the hollow cylindrical member. The closing member
is fixed to the hollow cylindrical member by a beam welding
method such as electron beam welding or laser beam welding.
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In welding the closing member to the hollow
cylindrical member so as to close its open end for forming the
hollow head portion of the piston, the welding beam is usually
incident on the two members in a direction parallel to an
interface between the inner and outer circumferential surfaces of
the two members (welding surfaces), which circumferential
surfaces are adjacent to or held in contact with each other, so
that the two members are bonded to each other at the
circumferential surfaces by the welding beam incident thereon.
The circumferential surfaces of the two members, which are
adjacent to or in close contact with each other, need to be formed
so as to extend in a specific direction depending upon the welding
condition, such that the welding beam is incident on the
circumferential surfaces in the direction parallel to the interface.
In other words, it is rather difficult to form the circumferential
surfaces so that the interface between these surfaces extends in a
direction that is desirable or suitable for the purpose of
improving the mechanical strength or durability of the piston
and reducing its cost of manufacture. In addition, the
above-described method may undesirably cause a variation of
weld strength at the interface.
SUMMARY OF THE INVENTION
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The present invention was made in the light of the
background art described above. It is an object of the present
invention to provide a method of forming a hollow head portion of
a piston for a swash plate type compressor, which method
assures a high degree of freedom in the direction of extension of
the circumferential surfaces of the hollow cylindrical member
and the dosing member, while avoiding a variation of the weld
strength at the interface.
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The object indicated above may be achieved
according to any one of the following forms or modes of the
present invention, each of which is numbered like the appended
claims and depend from the other form or forms, where
appropriate, to indicate and clarify possible combinations of
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 and
their combinations described below. It is also to be understood
that any technical feature described below in combination with
other technical features may be a subject matter of the present
invention, independently of those other technical features.
- (1) A method of forming a hollow head portion of a
piston for a swash plate type compressor, comprising the steps of
fixing a closing member to a hollow cylindrical member which is
open at at least one of opposite ends thereof, so as to close an
open end of the hollow cylindrical member, and applying a
welding beam to welding surfaces of the closing member and the
hollow cylindrical member, which welding surfaces are adjacent
to or in contact with each other, so that the closing member and
the hollow cylindrical member are bonded to each other at the
welding surfaces, wherein the welding beam is incident on the
welding surfaces of the closing member and the hollow
cylindrical member in a direction which intersects the welding
surfaces.
In the method according to the above form (1) of the
present invention, the hollow cylindrical member may be open at
one or both of its opposite ends. In an attempt to minimize weld
portions at which the hollow cylindrical member and the closing
member are bonded to each other by welding, it is preferable that
the hollow cylindrical member be open at only one of its opposite
ends. In this case, the hollow cylindrical member may be open on
the side corresponding to the end face of the piston to be obtained,
which end face partially defines a pressurizing chamber in the
compressor. Alternatively, the end face may be open on the other
side remote from the end face of the piston. When the piston
includes a head portion which is fitted in the corresponding
cylinder bore formed in the cylinder block of the compressor and
a neck portion which engages a radially outer portion of the
swash plate through a pair of shoes, the hollow cylindrical
member may be formed integrally with the neck portion, and
may be closed, by the closing member, at its open end which is
remote from the neck portion and which corresponds to the end
face of the piston which cooperates with the cylinder bore to
define the pressurizing chamber. Alternatively, the hollow
cylindrical member may be closed at its open end by the closing
member which is formed integrally with the neck portion.When the two members are fixed together by
welding at their welding surfaces which are located adjacent to or
in contact with each other, the laser beam is conventionally
incident upon the two members in a direction parallel to the
interface of the welding surfaces. As explained in the
"DETAILED DESCRIPTION OF THE PREFERRED
EMBODIMENTS" provided below, it may be difficult to irradiate
the two members with the laser beam in the above-indicated
direction parallel to the interface of the welding surfaces,
particularly because of a possible interference between a device
used to generate the welding beam and any other device located
near the beam generating device, such as a device for holding
and rotating an assembly of the hollow cylindrical member and
the closing member. Further, the bonding strength of the two
members at the welding surfaces may undesirably vary if the
position of the laser beam is offset in a radially inward or
outward direction from the radial position of the interface of the
welding surfaces. In contrast, the present method wherein the
laser beam is incident upon the welding surfaces in a direction
which intersects the welding surfaces eliminates the
above-described conventionally experienced problems.
- (2) A method according to the above form (1), the
closing member is fitted in the open end of the hollow cylindrical
member, so that an outer circumferential surface of the closing
member and an inner circumferential surface of the hollow
cylindrical member engage each other, as the welding surfaces.
- (3) A method according to the above form (1), the hollow
cylindrical member includes a large-diameter portion having an
inside diameter larger than that of the other portion thereof, the
large-diameter portion being located on the side of the open end
of the hollow cylindrical member, and the closing member
includes a large-diameter plate portion and a small-diameter
annular protruding portion, the dosing member being fitted in
the open end of the hollow cylindrical member such that an outer
circumferential surface of the large-diameter plate portion of the
closing member engages an inner circumferential surface of the
large-diameter portion of the hollow cylindrical member, and
such that an outer circumferential surface of the small-diameter
annular protruding portion of the closing member engages an
inner circumferential surface of the other portion of the hollow
cylindrical member, the inner circumferential surface of the
large-diameter portion of the hollow cylindrical member and the
outer circumferential surface of the large-diameter plate portion
of the closing member serving as the welding surfaces.
In the method according to the above form (3) of the
present invention, the inner circumferential surface of the
large-diameter portion of the hollow cylindrical member may be
tapered, or may be cylindrical as explained below with respect to
the following form (4). The outer circumferential surface of the
large-diameter plate portion of the closing member is shaped to
match the configuration of the inner circumferential surface of
the large-diameter portion of the hollow cylindrical member.
When the inner circumferential surface of the large-diameter
portion of the hollow cylindrical member and the outer
circumferential surface of the large-diameter plate portion of the
closing member are tapered, the closing member is fitted in the
open end of the hollow cylindrical member such that the tapered
inner and outer circumferential surfaces are held in abutting
contact with each other. When the hollow cylindrical member
includes a shoulder formed between the large-diameter portion
and the other portion thereof and the closing member includes a
shoulder formed between the large-diameter plate portion and
the small-diameter annular protruding portion, the closing
member is fitted in the open end of the hollow cylindrical
member such that the shoulders are held in abutting contact
with each other. Alternatively, the closing member is fitted in the
open end of the hollow cylindrical member such that the shoulder
of the closing member is held in abutting contact with an annular
end face of the hollow cylindrical member.
- (4) A method according to the above form (3), the inner
circumferential surface of the large-diameter portion of the
hollow cylindrical member and the outer circumferential surface
of the large-diameter plate portion of the closing member have
constant diameters.
- (5) A method according to the above form (4), the hollow
cylindrical member includes a shoulder formed between the
large-diameter portion and the other portion while the closing
member includes a shoulder formed between the large-diameter
plate portion and the small-diameter annular protruding portion,
the inner circumferential surface of the large-diameter portion of
the hollow cylindrical member and the outer circumferential
surface of the large-diameter plate portion of the closing member
are welded together by the welding beam while the closing
member is fitted in the open end of the hollow cylindrical
member such that the shoulder of the hollow cylindrical member
and the shoulder of the closing member are held in abutting
contact with each other.
In the above method, the closing member is fitted
into the open end of the hollow cylindrical member with high
accuracy by abutting contact between the shoulder of the hollow
cylindrical member and the shoulder of the closing member,
permitting easy axial positioning of the two members relative to
each other, so that the two members can be welded together with
high accuracy. When the closing member is fitted into the open
end of the hollow cylindrical member and one of opposite end
faces of the large-diameter plate portion of the closing member
remote from the small-diameter annular protruding portion
functions as the end face of the piston which partially defines the
pressurizing chamber, the pressure of a compressed gas which
acts on the end face of the piston during operation of the
compressor is received by the shoulders which are held in
abutting contact with each other, so as to improve the mechanical
strength at the end wall of the hollow head portion of the
obtained piston.
- (6) A method according to any one of the above forms
(4)-(5), the welding beam is incident on the welding surfaces in a
direction perpendicular to a centerline of the hollow cylindrical
member.
Though the welding beam may be incident on the
welding surfaces in a direction which intersects the centerline of
the hollow cylindrical member at an angle other than 90°, the
welding beam is preferably incident on the welding surfaces in a
direction which is perpendicular to the centerline of the hollow
cylindrical member. In this case, the dimension of the weld
nugget (the depth of fusion or the distance of penetration across
the interface between the welding surfaces) as measured in the
direction of the incidence of the electron beam, which is required
to assure a high degree of weld strength between the two
members, can be reduced. In this respect, it is noted that the
dimension of the weld nugget in the radial direction is important
from the standpoint of the weld strength.
- (7) A method according to the above form (1), the closing
member includes a large-diameter plate portion, a
small-diameter annular protruding portion, and a shoulder
formed therebetween, and the closing member is fitted in the
open end of the hollow cylindrical member such that the shoulder
of the closing member is held in abutting contact with an end
face of the hollow cylindrical member on the side of the open end,
the shoulder of the closing member and the end face of the hollow
cylindrical member serving as the welding surfaces.
When one of the opposite end faces of the
large-diameter plate portion of the dosing member remote from
the small-diameter annular protruding portion functions as the
end face of the piston partially defining the pressurizing chamber,
the pressure of the compressed gas which acts on the end face of
the piston during operation of the compressor is received by the
shoulder of the closing member and the annular end face of the
hollow cylindrical member which are held in abutting contact
with each other, resulting in an improved mechanical strength of
the hollow head portion of the piston at its end wall partially
defining the pressurizing chamber.
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BRIEF DESCRIPTION OF THE DRAWINGS
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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:
- Fig. 1 is a front elevational view in cross section of a
swash plate type compressor equipped with a piston having a
hollow head portion produced by a method of the present
invention;
- Fig. 2 is a front elevational view in cross section of
the piston shown in Fig. 1;
- Fig. 3 is a front elevational view partly in cross
section showing a blank used for manufacturing the piston of Fig.
2, before closing members are fixed to a body member of the
blank;
- Fig. 4 is a front elevational view in cross section
showing engagement of a hollow head section of the body
member with the closing member to provide the hollow head
portion of the piston;
- Fig. 5 is a fragmentary front elevational view in
cross section showing a method of forming the hollow head
portion of the piston by welding according to one embodiment of
the present invention;
- Fig. 6 is a fragmentary front elevational view in
cross section showing a conventional method of forming the
hollow head portion of the piston by welding;
- Fig. 7 is a fragmentary front elevational view in
cross section showing a method of forming the hollow head
portion of the piston by welding according to another
embodiment of the invention;
- Fig. 8 is a fragmentary front elevational view in
cross section showing a method of forming the hollow head
portion of the piston by welding according to still another
embodiment of the invention;
- Fig. 9 is a fragmentary front elevational view in
cross section showing a method of forming the hollow head
portion of the piston by welding according to yet another
embodiment of the invention;
- Fig. 10 is a fragmentary front elevational view in
cross section showing a method of forming the hollow head
portion of the piston by welding according to a further
embodiment of the invention; and
- Fig. 11 is a view showing a yet another embodiment.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
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Referring first to Figs. 1 and 2, there will be
described a piston for a swash plate type compressor, which is
constructed according to one embodiment of the present
invention. Fig. 1 shows the swash plate type compressor
incorporating a plurality of single-headed pistons (hereinafter
referred to simply as "pistons").
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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. The piston generally indicated at 14 is
reciprocably received in each of the 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 body 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 26 and an
outlet 28, respectively. The valve plate 20 has suction ports 32,
suction valves 34, discharge ports 36 and discharge valves 38.
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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, for
supporting the drive shaft 50 at its rear end portion. The front
end portion of the drive shaft 50 extends through a central
portion of the front housing 16, such that the front end of the
drive shaft 50 is located outside the front housing 16, so that the
drive shalt 50 is connected to a drive power source (not shown).
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 is mounted on the drive shaft
50 such that the drive shaft 50 passes through a central
mounting hole 61 formed in the central portion of the swash plate
60. The diameter of the central mounting hole 61 of the swash
plate 60 gradually increases in the axially opposite directions
from its axially intermediate portion towards the axially opposite
ends. To the drive shaft 50, there is fixed a rotary member 62
which is held in engagement with the front housing 16 through a
thrust bearing 66. The swash plate 60 is rotated with the drive
shaft 50 by a hinge mechanism 64 during rotation of the drive
shaft 50. The hinge mechanism 64 guides the swash plate 60 for
its axial and tilting motions. The hinge mechanism 64 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
mounting hole 61 of the swash plate 60, and the outer
circumferential surface of the drive shaft 50.
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The piston 14 indicated above includes a neck
portion 70 engaging the swash plate 60, and a head portion 72
formed integrally with the neck portion 70 and fitted in the
corresponding cylinder bore 12. The neck portion 70 has a groove
74 formed therein, and the swash plate 60 is held in engagement
with the groove 74 through a pair of hemi-spherical shoes 76. The
hemi-spherical shoes 76 are held in the groove 74 such that the
shoes 76 slidably engage the neck portion 70 at their
hemi-spherical surfaces and such that the shoes 76 slidably
engage the radially outer portions of the opposite surfaces of the
swash plate 60 at their flat surfaces. The configuration of the
piston 14 will be described in detail.
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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 79 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 79 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 is discharged into the discharge chamber 24
through the discharge port 36 and the discharge valve 38. A
reaction force acts on the piston 14 in the axial direction as a
result of compression of the refrigerant gas in the pressurizing
chamber 79. This compression reaction force is received by the
front housing 16 through the piston 14, swash plate 60, rotary
member 62 and thrust bearing 66.
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The cylinder block 10 has an intake passage 80
formed therethrough for communication between the discharge
chamber 24 and a crank chamber 86 which is defined between
the front housing 16 and the cylinder block 10. The intake
passage 80 is connected to a solenoid-operated control valve 90
provided to control the pressure in the crank chamber 86. The
solenoid-operated control valve 90 includes a solenoid coil 92, and
a shut-off valve 94 which is selectively closed and opened by
energization and de-energization of the solenoid coil 92. Namely,
the shut-off valve 94 is placed in its closed state when the
solenoid coil 92 is energized, and is placed in its open state when
the coil 92 is de-energized.
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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 to the crank chamber 86 at the other end. The central
bearing hole 56 communicates at its bottom with the suction
chamber 22 through a communication port 104.
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By controlling the solenoid-operated control valve 90
as described above, the crank chamber 86 is selectively connected
and disconnected to and from the discharge chamber 24, so as to
control the pressure in the crank chamber 86 for adjusting the
angle of inclination of the swash plate 60 with respect to the
direction perpendicular to the axis of rotation of the rotary drive
shaft 50, whereby the discharge capacity of the compressor is
controlled. Thus, the swash plate type compressor of the present
invention is a variable capacity type. Described more specifically,
when the solenoid coil 92 of the solenoid-operated control valve
90 is energized, the intake passage 80 is closed, so that the
pressurized refrigerant gas in the discharge chamber is not
delivered into the crank chamber 86. In this condition, the
refrigerant gas in the crank chamber 86 flows into the suction
chamber 22 through the bleeding passage 100 and the
communication port 104, so that the pressure in the crank
chamber 86 is lowered, to thereby increase the angle of
inclination of the swash plate 60. The reciprocating stroke of the
piston 14 which is reciprocated by rotation of the swash plate 60
increases with an increase of the angle of inclination of the swash
plate 60, so as to increase an amount of change of the volume of
the pressurizing chamber 79, whereby the discharge capacity of
the compressor is increased. When the solenoid coil 92 is
de-energized, the intake passage 80 is opened, permitting the
pressurized refrigerant gas to be delivered from the discharge
chamber 24 into the crank chamber 86, resulting in an increase
in the pressure in the crank chamber 86, and the angle of
inclination of the swash plate 60 is reduced, so that the discharge
capacity of the compressor is accordingly reduced. The solenoid
coil 92 of the solenoid-operated control valve 90 is controlled by a
control device not shown depending upon a load acting on the air
conditioning system including the present compressor. The
control device is principally constituted by a computer.
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The cylinder block 10 and each piston 14 are formed
of an aluminum alloy. The piston 14 is coated at its outer
circumferential surface with a fluoro resin film which prevents a
direct contact of the aluminum alloy of the piston 14 with the
aluminum alloy of the cylinder block 10 so as to prevent seizure
therebetween, and makes it possible to minimize the amount of
clearance between the piston 14 and the cylinder bore 12. The
cylinder block 10 and the piston 14 may also be formed of a
hyper-eutectic aluminum silicon alloy. Other materials may be
used for the cylinder block 10, the piston 14, and the coating film.
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There will next be described the configuration of the
piston 14.
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The end portion of the neck portion 70 of the piston
14, which is remote from the head portion 72, has a U-shape in
cross section, as shown in Fig. 2. The two opposed lateral walls of
the U-shape of that end portion has respective recesses 110
which are opposed to each other. Each of these recesses 110 is
defined by a part-spherical inner surface of the lateral wall. The
pair of shoes 76 indicated above are held in contact with the
opposite surfaces of the swash plate 60 at its radially outer
portion and are received in the respective part-spherical recesses
110. Thus, the neck portion 70 slidably engages the swash plate
60 through the shoes 76. In the present embodiment, the neck
portion 70 constitutes an engaging portion which engages the
drive member in the form of the swash plate 60.
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The head portion 72 of the piston 14 is formed
integrally with the neck portion 70, and includes a cylindrical
body portion 114 and a closure member 116 fixed to the body
portion 114. The cylindrical body portion 114 is open at one of its
opposite ends which is remote from the neck portion 70, and is
closed at the other end. The closure member 116 closes the open
end of the body portion 114. The hollow cylindrical section of the
body portion 114 has an inner circumferential surface 120 which
is divided into two portions, i.e., a large-diameter portion 122 on
the side of the open end of the body portion 114 and a
small-diameter portion 124 remote from the open end, which two
portions cooperate with each other to define a shoulder 126
formed therebetween.
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The closure member 116 is a generally disc-shaped
member which consists of a circular plate portion 130, and an
annular protruding portion 132 which extends from one of the
opposite end faces of the plate portion 130 and which has a
diameter smaller than that of the plate portion 130. The circular
plate portion 130 may be referred to as a large-diameter portion
while the annular protruding portion 132 may be referred to as a
small-diameter portion. A shoulder 134 is formed between the
circular plate portion 130 and the annular protruding portion 132.
The annular protruding portion 132 of the closure member 116
has a circular recess 136 open in the end face of the closure
member 116 remote from the circular plate portion 130, as shown
in Fig. 2, so that the weight of the closure member 116 is reduced.
The closure member 116 is fitted into the inner circumferential
surface 120 of the hollow cylindrical section of the body portion
114 such that the shoulder 134 of the closure member 116 is held
in abutting contact with the shoulder 126 of the hollow
cylindrical section of the body portion 114. In this state, the outer
circumferential surface of the circular plate portion 130 of the
closure member 116 engages the large-diameter portion 122 of
the inner circumferential surface 120 of the body portion 114
while the outer circumferential surface of the annular protruding
portion 132 of the closure member 116 engages the
small-diameter portion 124 of the inner circumferential surface
120 of the body portion 114. The closure member 116 is fixed to
the body portion 114 by welding. The compression reaction force
which acts on the end face of the piston 14 as a result of
compression of the refrigerant gas in the pressurizing chamber
79 during the compression stroke of the piston 14 is received by
the shoulders 126 and 134 which are held in abutting contact
with each other as well as the contacting circumferential surfaces
of the body portion 114 and the closure member 116, which
surfaces are bonded by welding.
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Two pieces of the piston 14 constructed as described
above are produced from a single blank 150 shown in Fig. 3. The
blank 150 used for producing the two pistons 14 has a body
member 152 and two closing members 154. The body member
152 consists of a twin neck section 156 and two cylindrical hollow
head sections 158 formed integrally with the twin neck section
156 such that the two hollow head sections 158 extend from the
opposite ends of the twin neck section 156 in the opposite
directions. The twin-neck section 156 consists of mutually
integrally formed two portions which correspond to the neck
portions 70 of the two single-headed pistons 14. Each of the two
hollow head sections 158 is closed at one of its opposite ends
which is on the side of the twin neck section 156, and has a
hollow cylindrical section which is open at the other end and
which corresponds to the hollow cylindrical body portion 114 of
the head portion 72.
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As shown in Fig. 3, the hollow head section 158 has
an inner circumferential surface which is divided into two
sections, i.e., a large-diameter portion 162 located on the side of
the open end of the hollow head section 158, and a
small-diameter portion 164 located on the side of the twin neck
section 156. A shoulder 166 is formed between the large-diameter
portion 162 and the small-diameter portion 164. This shoulder
166 function as the shoulder 126 of the piston 14. The body
member 152 is formed by die-casting of a metallic material in the
form of an aluminum alloy. This formation of the body member
152 by die-casting is a step of preparing the body member 152.
Reference numeral 168 in Fig. 3 denotes two bridge portions each
provided for increasing the rigidity of the body member 152 and
functions as a reinforcing portion by which the body portion 152
is protected from being deformed due to heat.
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The two closing members 154 are identical in
construction with each other. Like the closure member 116, each
of these closing members 154 includes a circular plate portion
174 and an annular protruding portion 176 which extends from
one of the opposite end faces of the circular plate portion 174. A
shoulder 177 is formed between the circular plate portion 174
and the annular protruding portion 176. The circular plate
portion 174 of the closing member 154 has a circular recess 178.
The shoulder 177 and the recess 178 of the closing member 154
function as the shoulder 134 and the recess 136 of the closure
member 116.
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The circular plate portion 174 of each closing
member 154 has a holding portion 182 formed on one of its
opposite end faces remote from the annular protruding portion
176. The holding portion 182 has a circular shape in cross section,
and has a center hole 182. In the present embodiment, the
closing member 154 is formed by die-casting of a metallic
material in the form of an aluminum alloy. This formation of the
closing members 154 by die-casting is a step of preparing the
closing members 154. The circular plate portion 174 and the
annular protruding portion 176 of the closing member 154 have
the same dimensional relationship as the circular plate portion
130 and the annular protruding portion 132 of the closure
member 116, and a detailed description of which is dispensed
with.
-
As shown in Fig. 4, the closing member 154 is fitted
into the open end of the hollow head section 158 such that the
circular plate portion 174 of the closing member 154 engages the
large-diameter portion 162 of the hollow head section 158 and
such that the annular protruding portion 176 of the closing
member 154 engages the small-diameter portion 164 of the
hollow head section 158. The closing member 154 is inserted into
the hollow head section 158 until the shoulder 177 is brought
into abutting contact with the shoulder 166. With each closing
member 154 fitted in the body member 152, the inner
circumferential surface of the large-diameter portion 162 of the
hollow head section 158 and the outer circumferential surface of
the circular plate portion 174 of the closing member 154 are held
close to or in abutting contact with each other, so that these inner
and outer circumferential surfaces are bonded to each other by
means of an electron beam welding. This welding process will be
described in greater detail. In the present embodiment, since the
body member 152 and each closing member 154 are both formed
by die-casting and have a high dimensional accuracy, the closing
member 154 is fitted in the body member 152 without
mechanical working operations such as machining and grinding
operations, resulting in a reduced cost of manufacture of the
blank 150 for the single-headed pistons 14.
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After the two closing members 154 are fixedly fitted
in the respective open end portions of the body member 152 as
described above, a machining operation is performed on the outer
circumferential surfaces of the hollow head sections 158 of the
body member 152 and the exposed outer circumferential surfaces
(Fig. 9) of the closing members 154. This machining operation is
effected on a lathe or turning machine such that the blank 150 is
held by chucks at the holding portions 180 of the closing
members 154, with the blank 150 being centered with two
centers engaging the center holes 182, and such that the blank
150 is rotated by a suitable drive device. Since the closing
members 154 are fixed to the body member 152 by welding, the
closing members 154 and the body member 152 are prevented
from rotating relative to each other, so that the blank 150 can be
turned as a whole for efficient machining on its outer
circumferential surface.
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Then, the outer circumferential surfaces of the
hollow head sections 158 of the body member 152 and the closing
members 154 are coated with a suitable material, such as a film
of polytetrafluoroethylene. The blank 150 is then subjected to a
machining operation to cut off the holding portions 180 from the
closing members 154, and a centerless grinding operation on the
coated outer circumferential surfaces of the hollow head sections
158 and the closing members 154, so that the two portions which
provide the head portions 72 of the two pistons 14 are formed. In
the next step, a cutting operation is performed near the two
bridge portions 168 of the twin-neck portion 156, to form the
recesses 110 in which the shoes 76 of the pistons 14 are received.
Thus, the two portions which provide the neck portions 70 of the
two pistons 14 are formed at the twin neck portion 156. Finally,
the twin neck portion 156 is subjected at its axially central
portion to a cutting operation to cut the blank 150 into two pieces
which provide the respective two pistons 14.
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The process of welding each closing member 154 to
the body member 152 will be described.
-
The closing member 154 and the body member 152
which engage each other as described above are irradiated with
an electron beam emitted from an electron beam emitting device
of an electron beam welding apparatus, so that the
large-diameter portion 162 of the inner circumferential surface of
the hollow head section 158 and the outer circumferential surface
of the circular plate portion 174 of the closing member 154 are
bonded to each other by welding, so that these bonded surfaces
provide an interface. The inner and outer circumferential
surfaces of the hollow head section 158 and the circular plate
portion 174 at which the two members 152, 154 are welded
together will be hereinafter referred to as "welding surfaces".
Described in detail referring to Fig. 4, the body member 152 and
the two closing members 154 fitted in the body member 152 are
held and sandwiched by and between a pair of jigs 186 such that
each closing member 154 is pressed onto the body member 152 by
each jig with the holding portion 180 of the closing member 154
being fitted in a hole formed in the jig 186. In this state, a torque
is applied to each closing member 154 through the jig 180 by a
suitable drive device, so that the body member 152 and the
closing members 154 are rotated together. In this state, the
electron beam is incident upon the body member 152 and the
closing members 154, so that these members are welded together
at the welding surfaces described above. The closing members
154 are prevented from being moved away from the body member
152 by the jigs 180 which press the closing members 154 onto the
body member 152, permitting an efficient welding of the these
members. The welding in the present embodiment is effected
under vacuum or at a reduced pressure, so as to avoid air
expansion due to heat and to eliminate a need of breathing the
interior of the body member 152 air-tightly dosed by the closing
members 154, and a need of providing the piston with an air vent
or breather.
-
The drive device for rotating the body member 152
and the closing members 154 and the electron beam emitting
device are known in the art, and a detailed explanation of which
is dispensed with. In the present embodiment, the rotation of the
blank 150 in which the closing members 154 are fitted permits
the spot of the electron beam to be moved in the circumferential
direction of the blank 150. Alternatively, the electron beam
emitting device or the spot of the electron beam may be rotated
while the blank 150 is kept stationary.
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As shown in Fig. 5, the electron beam emitted from
the electron beam emitting device is incident upon the blank 150
along a straight line which is inclined with respect to a centerline
of the body member 152 indicated by a one-dot chain line such
that a distance between the above-indicated straight line and the
centerline of the body member 152 in the radial direction of the
hollow head section 158 decreases as the straight line approaches
the shoulder surface 166 in the direction parallel to the
centerline of the body member 152 and in the direction from the
large-diameter portion 162 toward the small-diameter portion
164. That is, the line of incidence of the electron beam upon the
interface of the welding surfaces intersects the welding surfaces
such that the line of incidence approaches the interface in the
radially inward direction of the hollow head section 158 as the
line of incidence approaches the interface in the axial direction of
the hollow head section 158 from the large-diameter portion 162
toward the small-diameter portion 164. In other words, the
electron beam is incident upon the blank 150 along obliquely
extending arrow-headed straight lines indicated in Fig. 5.
-
If the electron beam is incident upon the blank 150
in a direction parallel to the interface of the contacting
circumferential surfaces as in the prior art shown in Fig. 6, the
amounts of fusion of the materials of the body member 152 and
the closing members 154 can be made uniform for the two
members 152, 154 as long as the electron beam is accurately
aligned with the interface (162) in the radial direction of the
hollow head section 158. However, if the spot of the electron
beam is offset from the interface in a radially inward or outward
direction of the hollow head section 158, the amounts of fusion of
the materials of the body member 152 and the closing members
154 cannot be made uniform for these members 152, 154,
reducing a weld area, namely, an area in which those members
152, 154 are welded together, resulting in a decrease of the weld
strength between the body member 152 and the closing members
154. If the spot of the welding beam is slightly offset from the
interface in the radially outward direction of the hollow head
section 158 as indicated by an upper arrow-headed line in Fig. 6,
for instance, the amount of fusion of the material of the body
member 152 is larger than that of the closing members 154, so
that the weld area in which these members are welded together
is reduced. Thus, in the prior art welding method, the weld
strength between the body member 152 and the closing members
154 undesirably varies depending upon individual blanks. In the
present embodiment of Fig. 5, in contrast, the weld area does not
largely varies even if the spot of the electron beam is offset from
the interface in the radially outward direction of the hollow head
section 158 as in Fig. 6, so that a variation of the weld strength
in the individual blanks 150 can be prevented according to the
method of Fig. 5.
-
In the conventional welding method shown in Fig. 6
wherein the electron beam is incident on the welding surfaces in
the direction parallel to their interface, the welding surfaces need
to be irradiated by the electron beam on the side of the end face
of each closing member 154 on which the holding portion 180 is
formed, such that the direction of incidence of the electron beam
is parallel to the centerline of the body member 152 (indicated by
the one-dot chain line in Fig. 6). In this arrangement, since the
electron beam emitting device is inevitably positioned close to the
jig 186, there may arise an interference between the electron
beam emitting device and the jig 186. In contrast, according to
the present arrangement wherein the electron beam is incident
on the welding surfaces along the straight line which is inclined
with respect to the rotation axis of the jig 186 shown in Fig. 5,
the interference between the jig 186 and the electron beam
emitting device can be advantageously avoided.
-
In the present embodiment, each of the hollow head
sections 158 of the body member 152 corresponds to a hollow
cylindrical member which cooperates with the closing member
154 to provide the head portion 72 of the piston 14, which is a
hollow head portion. The large-diameter portion 162 serves as a
large-diameter portion of each hollow head section 158. The
circular plate portion 174 serves as a large-diameter portion of
each closing member 154, while the annular protruding portion
176 serves as a small-diameter portion of each closing member
154.
-
The electron beam is incident upon the welding
surfaces in any directions which intersect the welding surfaces.
For instance, the electron beam may be incident on the welding
surfaces along a straight line which is inclined with respect to
the centerline of the body member 152 (indicated by the one-dot
chain line), as shown in Fig. 7, such that a distance between the
above-indicated straight line and the centerline of the body
member 152 in the radial direction of the hollow head section 158
decreases as the straight line approaches the end face of the
circular plate portion 174 in the direction parallel to the
centerline of the body member 152 and in the direction from the
small-diameter portion 164 toward the large-diameter portion
162. That is, the line of incidence of the electron beam upon the
interface of the welding surfaces intersects the welding surfaces
such that the line of incidence approaches the interface in the
radially inward direction of the hollow head section 158 as the
line of incidence approaches the interface in the axial direction of
the hollow head section 158 from the small-diameter portion 164
toward the large-diameter portion 162. In other words, the
electron beam is incident upon the blank 150 along an obliquely
extending arrow-headed straight line indicated in Fig. 7. This
arrangement is also effective to prevent the interference between
the electron beam emitting device and the jig 186.
-
Alternatively, the electron beam may be incident on
the welding surfaces in a direction perpendicular to the welding
surfaces, as shown in Fig. 8. This arrangement is particularly
effective to avoid the interference between the electron beam
emitting device and the jig 186. In this embodiment, the
dimension of the weld nugget (the depth of fusion or the distance
of penetration across the interface between the welding surfaces)
as measured in the direction of the incidence of the electron beam,
which is required for obtaining a desired weld strength between
the body member 152 and the dosing members 154, can be made
smaller than that in the embodiments of Figs. 5 and 7
wherein the electron beam is incident on the welding surfaces in
the directions inclined with respect to the centerline. In this
respect, it is noted that the dimension of the weld nugget in the
radial direction is important from the standpoint of the weld
strength.
-
In the embodiments of Figs, 5 and 7-8, the welding
surfaces are parallel to the centerline of the body member 152.
The welding surfaces need not be parallel to the centerline of the
body member 152, but may extend in the other directions, as
shown in Figs. 9 and 10, wherein the same reference numbers as
used in Figs 5 and 7-8 are used to identify the corresponding
components, and a detailed explanation of which is dispensed
with.
-
Referring to Fig. 9, a hollow head section 200 of the
body member 152 is dosed at one of its opposite ends and open at
the other end. The closing member 154 is fitted in a bore 202 of
the body member 152 such that the shoulder 177 is held in
abutting contact with an annular end face 204 of the body
member 152, so that the annular protruding portion 176 of the
closing member 154 is fitted at its outer circumferential surface
in the corresponding portion of the inner circumferential surface
of the hollow head section 200 of the body member 152. The head
section 200 of the body member 152 of the present arrangement
is simple in configuration with a constant small wall thickness.
In the present embodiment, the annular end face 204 of the head
section 200 and the shoulder 177 of the closing member 154 are
bonded together by welding. Further, the axial end portion of the
inner circumferential surface 202 of the head section 200 and the
corresponding axial end portion of the outer circumferential
surface of the annular protruding portion 176 of the closing
member 154 are also bonded together by welding. As indicated by
an arrow-headed line in Fig. 9, the electron beam is incident on
the welding surfaces along a straight line which is inclined with
respect to the centerline of the body member 152 such that a
distance between the above-indicated straight line and the
centerline of the body member 152 in the radial direction of the
hollow head section 200 decreases as the straight line approaches
the end face 204 or the shoulder surface 177 in the direction
parallel to the centerline and in the direction from the hollow
head section 200 toward the closing member 154. That is, the line
of incidence of the electron beam upon the interface of the
welding surfaces 177, 204 intersects the welding surfaces such
that the line of incidence approaches the interface in the radially
inward direction of the hollow head section 200 as the line of
incidence approaches the interface in the axial direction from the
hollow head section 200 toward the closing member 154.
Alternatively, the electron beam may be incident on the welding
surfaces along a straight line which extends in the lower
left-hand direction as in the embodiment of Fig. 5. It is noted
that only the end face 204 of the head section 200 and the
shoulder 177 of the closing member 154 may be welded together.
In this case, the welding surfaces are perpendicular to the
centerline of the body member 152.
-
The embodiment shown in Fig. 9 is particularly
effective to avoid the interference between the electron beam
emitting device and the jig 186, and permits effective bonding
between the end face 204 of the head section 200 and the
shoulder 177 of the dosing member 154, which extend in the
direction perpendicular to the centerline of the body member 152.
In the present embodiment, the circular plate portion 174 serves
as a large-diameter portion of the closing member 154 while the
annular protruding portion 176 serves as a small-diameter
portion of the closing member 154.
-
Referring to Fig. 10, the body member 152 has a
hollow head section 300 whose annular end face 304 is tapered
with its inside diameter continuously decreasing in the axially
inward direction in which a closing member 310 is fitted into a
bore 302 of the head section 300. The closing member 310 has the
circular plate portion 174 whose outer circumferential surface
312 is tapered with its outside diameter continuously decreasing
in the axially inward direction described above. The tapered
surface 304 of the bead section 300 and the tapered surface 312
of the plate portion 174 of the closing member 310 are bonded
together by welding. In the present embodiment, the direction of
incidence of the electron beam upon the welding surfaces 304,
312 is perpendicular to the centerline of the body member 152,
and intersects these tapered welding surfaces 304 and 312. If the
direction of incidence of the electron beam is parallel to the
interface of the tapered welding surfaces as in the conventional
method, the piston to be obtained is undesirably fused by the
electron beam at the periphery of its end face which partially
defines the pressurizing chamber 79. In this case, the minimum
volume of the pressurizing chamber 79 when the piston is located
at the end of the compression stroke undesirably is increased due
to deformation by the fusion, resulting in a reduced operating
efficiency of the compressor. The present embodiment shown in
Fig. 10 wherein the direction of incidence of the electron beam
intersects the tapered welding surfaces 304, 312 effectively
avoids the above-indicated problem. In this arrangement, the
welding surfaces are irradiated with the electron beam without
suffering from the interference between the electron beam
emitting device and the jig 186. As described above, the electron
beam may be incident on the welding surfaces 304, 312 in any
directions that intersect the welding surfaces. Accordingly, the
welding can be easily effected even when the welding surfaces
are inclined with respect to the centerline of the body member
152 as in the embodiment of Fig. 10. The tapered surface 304 of
the head section 300 serves as an inner circumferential surface of
the large-diameter portion of a hollow cylindrical member which
cooperates with a closing member to provide the piston.
-
For enjoying the advantages of the present
invention, it is desired that the angle of inclination of the welding
beam with respect to the welding surfaces be larger than 10
degrees, preferably larger than 20 degrees, and more preferably
larger than 30 degrees.
-
In the illustrated embodiments of Figs. 4, 5, 7, 8, 9,
10, the closing member 154, 310 is fixed to the hollow cylindrical
section 158, 200, 300 such that the closing member is fitted in the
open end of the hollow head section. The closing member may be
fitted on the hollow cylindrical section, as shown in Fig. 11. In
the embodiment of Fig. 11, a hollow head section 400 has an
annular protruding end portion 402 which is formed at its open
end. The annular protruding end portion 402 has an outside
diameter which is smaller than that of the other portion thereof,
so that a shoulder 404 is formed between the annular protruding
end portion 402 and the other portion. The closing member 154 is
fitted on the outer circumferential surface of the annular
protruding end portion 402 of the hollow head section 400 such
that an annular end face 352 of an annular protruding portion
350 is held in abutting contact with the shoulder 404 of the
hollow head section 400. In this embodiment, the annular end
face 852 of the annular protruding portion 350 of the closing
member 154 and the shoulder 404 of the hollow head section 400
are bonded together by welding.
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In the blank 150 shown in Fig. 3, each of the two
cylindrical hollow head sections 158 is formed integrally with the
twin neck section 156, and is open at one of its opposite ends
remote from the twin neck section 156 while the opening of each
hollow head section 158 is closed by the separately formed closing
member 154. The blank 150 may be otherwise constructed. For
instance, two closing members are formed integrally with a twin
neck member by die-casting, and each closing member is bonded
by welding to a corresponding one of two separately die-cast
hollow cylindrical members, so as to close an open end of the
hollow cylindrical member.
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The closing members and the hollow cylindrical
members may be formed by forging.
-
The pistons in the illustrated embodiments may be
used in a swash plate type compressor of fixed capacity type as
well as a swash plate type compressor of variable capacity type.
Further, the pistons may be double-headed.
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While some 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.
