U.S. patent application number 10/382189 was filed with the patent office on 2003-11-13 for shoe for use in swash plate type compressor and method of forming the same.
Invention is credited to Tomita, Masanobu, Tsushima, Hironobu.
Application Number | 20030209137 10/382189 |
Document ID | / |
Family ID | 27751195 |
Filed Date | 2003-11-13 |
United States Patent
Application |
20030209137 |
Kind Code |
A1 |
Tsushima, Hironobu ; et
al. |
November 13, 2003 |
Shoe for use in swash plate type compressor and method of forming
the same
Abstract
A shoe in a swash plate type compressor has a spherical engaging
surface that engages with a piston, and a plane engaging surface
that is substantially a plane and engages with a swash plate. The
plane engaging surface includes a substantially planar sliding
surface, a substantially radially extending peripheral surface and
a connecting surface. The sliding surface is formed near a center
of the plane engaging surface and slides over the swash plate. The
peripheral surface is formed near a periphery of the plane engaging
surface, is formed at a distance from the sliding surface away from
the surface of the swash plate so as to form an inwardly-directed
step in the plane engaging surface, and is connected to the
spherical engaging surface at its outer periphery. The connecting
surface connects the sliding surface to the peripheral surface.
Inventors: |
Tsushima, Hironobu;
(Kariya-shi, JP) ; Tomita, Masanobu; (Kariya-shi,
JP) |
Correspondence
Address: |
WOODCOCK WASHBURN LLP
ONE LIBERTY PLACE, 46TH FLOOR
1650 MARKET STREET
PHILADELPHIA
PA
19103
US
|
Family ID: |
27751195 |
Appl. No.: |
10/382189 |
Filed: |
March 5, 2003 |
Current U.S.
Class: |
91/499 ; 417/269;
92/12.2 |
Current CPC
Class: |
F04B 27/0886
20130101 |
Class at
Publication: |
91/499 ; 417/269;
92/12.2 |
International
Class: |
F04B 001/12 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 7, 2002 |
JP |
2002-061513 |
Claims
What is claimed is:
1. A shoe in a swash plate type compressor including a swash plate
and a piston, the shoe being interposed between the swash plate and
the piston, the shoe comprising: a spherical engaging surface for
engaging with the piston; and a plane engaging surface being
substantially a plane, the plane engaging surface engaging with the
swash plate, the plane engaging surface comprising: a substantially
planar sliding surface formed near a center of the plane engaging
surface, the sliding surface sliding over a surface of the swash
plate; a substantially radially extending peripheral surface formed
near a periphery of the plane engaging surface, the peripheral
surface being formed at a distance from the extended sliding
surface away from the surface of the swash plate so as to form an
inwardly-directed step in the plane engaging surface, the
peripheral surface being connected to the spherical engaging
surface at its outer periphery; and a connecting surface connecting
the sliding surface to the peripheral surface.
2. The shoe according to claim 1, wherein a distance between the
peripheral surface and the extended sliding surface of the shoe
ranges from 0.02 mm to 0.5 mm.
3. The shoe according to claim 2, wherein the distance between the
peripheral surface and the extended sliding surface is 0.05 mm or
above.
4. The shoe according to claim 3, wherein the distance between the
peripheral surface and the extended sliding surface is 0.1 mm or
above.
5. The shoe according to claim 4, wherein the distance between the
peripheral surface and the extended sliding surface is 0.15 mm or
above.
6. The shoe according to claim 2, wherein the distance between the
peripheral surface and the extended sliding surface is 0.3 mm or
below.
7. The shoe according to claim 6, wherein the distance between the
peripheral surface and the extended sliding surface is 0.25 mm or
below.
8. The shoe according to claim 1, wherein the peripheral surface is
substantially parallel to the sliding surface.
9. The shoe according to claim 1, wherein the peripheral surface is
inclined with respect to the sliding surface, an angle between the
peripheral surface and the extended sliding surface is 10.degree.
or below.
10. The shoe according to claim 1, wherein the connecting surface
further comprises: a chamfered surface forming a side surface of a
truncated cone, a diameter of the chamfered surface near the
peripheral surface being larger than that of the chamfered surface
near the sliding surface; and a rounded corner connecting the
chamfered surface to the sliding surface.
11. The shoe according to claim 10, wherein the connecting surface
further comprising another rounded corner that connects the
chamfered surface to the peripheral surface.
12. The shoe according to claim 1, wherein the spherical engaging
surface further comprises a spherical sliding surface that is
substantially a part of sphere surface and slides over a surface of
the piston, and a peripheral rounded surface that connects the
spherical sliding surface to the peripheral surface.
13. The shoe according to claim 1 further comprising a base member
made of metal.
14. The shoe according to claim 13, wherein the metal is aluminum
series alloy.
15. The shoe according to claim 14, wherein the surface of the base
member is coated with metal plating layer.
16. The shoe according to claim 13, wherein the metal is iron
series alloy.
17. The shoe according to claim 16, wherein the iron series alloy
includes high carbon chromium bearing steel.
18. The shoe according to claim 13, wherein the metal includes
magnesium.
19. The shoe according to claim 1 further comprising a base member
made of resin.
20. A swash plate type compressor comprising: a housing; a drive
shaft rotatably supported by the housing; a swash plate operatively
connected to the drive shaft; a piston accommodated in the housing,
the piston being operatively connected to the swash plate; and a
pair of shoes interposed between the swash plate and the piston,
each of the shoes including: a spherical engaging surface for
engaging with the piston; and a plane engaging surface being a
substantially plane, the plane engaging surface engaging with the
swash plate, the plane engaging surface comprising: a substantially
planar sliding surface formed near a center of the plane engaging
surface, the sliding surface sliding over a surface of the swash
plate; a substantially radially extending peripheral surface formed
near a periphery of the plane engaging surface, the peripheral
surface being formed at a distance from the extended sliding
surface away from the surface of the swash plate so as to form an
inwardly-directed step in the plane engaging surface, the
peripheral surface being connected to the spherical engaging
surface at its outer periphery; and a connecting surface connecting
the sliding surface to the peripheral surface.
21. The swash plate type compressor according to claim 20, wherein
the connecting surface further comprises: a chamfered surface
forming a side surface of a truncated cone, a diameter of the
chamfered surface near the peripheral surface being larger than
that of the chamfered surface near the sliding surface; and a
rounded corner connecting the chamfered surface to the sliding
surface.
22. A method of forming a shoe that is interposed between a swash
plate and a piston in a swash plate type compressor, the shoe
including a spherical engaging surface and a plane engaging surface
that is substantially a plane, the plane engaging surface having a
substantially planar sliding surface that is formed near a center
of the plane engaging surface and has a predetermined outer
diameter, a substantially radially extending peripheral surface
that is formed near a periphery of the plane engaging surface and
is formed at a distance from the extended sliding surface so as to
form an inwardly-directed step in the plane engaging surface, and a
connecting surface that connects the sliding surface to the
peripheral surface, the method comprising the steps of: preparing a
blank piece having a predetermined outer diameter that is smaller
than that of the planar sliding surface; preparing a pair of dies
including a first die for molding the spherical engaging surface
and a second die for molding the plane engaging surface; setting
the blank piece in the pair of the dies; and closing the pair of
the dies for forging the shoe.
23. The method according to claim 22, wherein the first preparing
step further includes preparing the blank piece from a blank by
forging.
24. The method according to claim 22, wherein the first preparing
step further includes preparing the blank piece with a cylindrical
shape.
25. The method according to claim 22, wherein the first preparing
step further includes preparing the blank piece with a spherical
shape.
26. A shoe manufactured by a method according to claim 22.
27. A shoe in a swash plate type compressor including a swash plate
and a piston, the shoe being interposed between the swash plate and
the piston, the shoe comprising: a spherical engaging surface for
engaging with the piston; and a plane engaging surface being
substantially a plane, the plane engaging surface engaging with the
swash plate, the plane engaging surface comprising: a substantially
planar sliding surface formed near a center of the plane engaging
surface, the sliding surface sliding over a surface of the swash
plate; a peripheral surface formed near a periphery of the plane
engaging surface, the peripheral surface being formed at a distance
from the extended sliding surface away from the surface of the
swash plate so as to form an inwardly-directed step in the plane
engaging surface, the peripheral surface being substantially
parallel with the sliding surface such that the peripheral surface
is oriented at an angle, with respect to the extended sliding
surface of the shoe, of from about 0 degree to about 10 degrees;
and a connecting surface connecting the sliding surface to the
peripheral surface.
28. A set of dies for molding a shoe that is interposed between a
swash plate and a piston in a swash plate type compressor, the shoe
including a spherical engaging surface for engaging with the piston
and a plane engaging surface for engaging with the swash plate, the
plane engaging surface having a substantially planar sliding
surface that is formed near a center of the plane engaging surface,
a substantially radially extending peripheral surface that is
formed near a periphery of the plane engaging surface and is formed
at a distance from the extended sliding surface so as to form an
inwardly-directed step in the plane engaging surface and a
connecting surface that connects the sliding surface to the
peripheral surface, the set of dies comprising: a first die having
a spherical molding surface for molding the spherical engaging
surface; and a second die having a plane molding surface for
molding the plane engaging surface, the plane molding surface
including: a first molding surface formed near a center of the
plane molding surface for molding the sliding surface; a second
molding surface formed near a periphery of the plane molding
surface for molding the peripheral surface; and a third molding
surface connecting the first molding surface to the second molding
surface for molding the connecting surface.
Description
BACKGROUND OF INVENTION
[0001] The present invention relates to a shoe for use in a swash
plate type compressor and a method of forming the shoe.
[0002] A swash plate type compressor compresses gas by converting
rotation of a swash plate to reciprocation of a piston. A pair of
shoes, or sliding members, is interposed between the swash plate,
which rotates at a high speed, and the piston, which reciprocates
at a high speed, to ensure smooth operations of the swash plate and
the piston. Since the swash plate rotates at a high speed, sliding
performance between the swash plate and the piston is required to
be relatively high. The shoe is generally hemispherical
crown-shaped. Namely, the shoe includes a substantially plane
engaging surface engaging with the swash plate, and a substantially
hemispherical engaging surface engaging with the piston. In the
hemispherical crown shoe, sliding performance between a plane
sliding surface and a sliding surface of the swash plate is desired
to be relatively high. Lubricant oil is thus generally required to
be involved in between the sliding surfaces. On the other hand,
existing foreign substances are required not to be involved in
between the sliding surfaces so that the foreign substances do not
flaw the sliding surfaces.
[0003] In order to fulfill the above two contradicting
requirements, as shown in Japanese Unexamined Patent Publication
No. 2002-332959, a shoe, in which a side surface connects a
hemispherical engaging surface to a plane engaging surface, is
disclosed. For example, the side surface is formed such that the
side surface is inclined with respect to the surface of the swash
plate at an angle of 45.degree.. The shoe has relatively high
sliding performance.
[0004] The above mentioned shoe is preferably formed by forging
similarly to a common shoe. In forging the above mentioned shoe, a
pair of dies that includes a first die for forming the
hemispherical engaging surface and a second die for forming the
plane engaging surface and the side surface is utilized. A blank
piece is set in the middle of the pair of dies, and the pair of
dies is closed so as to form the shoe. The blank piece plastically
flows to an outer periphery of a cavity of the pair of dies in the
cavity and reaches a surface corresponding to a side surface of the
pair of dies. Then, the blank piece plastically flows along the
surface, and finally the shoe is formed by strongly pressing the
blank piece against the entire surface of the pair of dies.
[0005] Dimensional accuracy in a shoe is required to be relatively
high. Especially, the dimensional accuracy in the height of the
shoe, or the dimensional accuracy in a distance between the plane
engaging surface and the hemispherical engaging surface, is
required to be relatively high since tolerance for clearance is
small due to a mechanism of a swash plate type compressor. On the
other hand, variation in quantities of blank pieces may be
permitted to some extent.
[0006] Although the periphery of the cavity in the pair of dies
molds a surface that connects the side surface to the hemispherical
engaging surface, the periphery of the cavity functions as a space
for absorbing the above variation in the quantities of the blank
pieces. However, as mentioned above, since the side surface is
inclined with respect to the surface of the swash plate at a
relatively large angle, a part of a surface of the pair of dies for
molding the side surface causes resistance to plastic flow of the
blank piece. As a result, for example, when the quantity of the
blank piece is larger than a predetermined normal quantity, rate of
increase in reactive force from the blank piece to the pair of dies
and in amount of spring back becomes large. Namely, when a shoe is
manufactured through forging, in which relatively large resistance
to the plastic flow of the blank piece is generated, the shoe is
not accurately forged due to the variation in the quantities of the
blank pieces.
SUMMARY OF THE INVENTION
[0007] The present invention provides a shoe that has relatively
high sliding performance and dimensional accuracy.
[0008] According to one preferred embodiment, a shoe for use in a
swash plate type compressor, interposed between a swash plate and a
piston, has a spherical engaging surface and a plane engaging
surface. The spherical engaging surface engages with the piston.
The plane engaging surface being substantially a plane engages with
the swash plate. The plane engaging surface includes a
substantially planar sliding surface, a substantially radially
extending peripheral surface and a connecting surface. The sliding
surface is formed near a center of the plane engaging surface and
slides over a surface of the swash plate. The peripheral surface is
formed near a periphery of the plane engaging surface. The
peripheral surface is formed at a distance from the sliding surface
away from the surface of the swash plate so as to form an
inwardly-directed step in the plane engaging surface. The
peripheral surface is connected to the spherical engaging surface
at its outer periphery. The connecting surface connects the sliding
surface to the peripheral surface.
[0009] According to one method embodiment, the present invention
also provides a method of forming a shoe that is interposed between
a swash plate engaging surface and a plane engaging surface. The
plane engaging surface is substantially a plane and has a
substantially planar sliding surface, a substantially radially
extending peripheral surface and a connecting surface. The sliding
surface is formed near a center of the plane engaging surface and
has a predetermined outer diameter. The peripheral surface is
formed near a periphery of the plane engaging surface and is formed
at a distance from the sliding surface so as to form an
inwardly-directed step in the engaging surface. The connecting
surface connects the sliding surface to the peripheral surface. The
method embodiment includes the steps of preparing a blank piece
having a predetermined outer diameter that is smaller than that of
the sliding surface, preparing a pair of dies including a first die
for molding the spherical engaging surface and a second die for
molding the plane engaging surface, setting the blank piece in the
pair of the dies and closing the pair of the dies for forging the
shoe.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The features of the present invention that are believed to
be novel are set forth with particularity in the appended claims.
The invention together with objects and advantages thereof, may
best be understood by reference to the following description of the
presently preferred embodiments together with the accompanying
drawings in which:
[0011] FIG. 1 is a longitudinal cross-sectional view of a swash
plate type compressor provided with a pair of shoes in an
embodiment according to the present invention;
[0012] FIG. 2 is an enlarged cross-sectional view of one of the
pair of shoes in FIG. 1;
[0013] FIG. 3 is a partially enlarged cross-sectional view of one
of the pair of shoes in FIG. 2 sliding over the swash plate
according to the embodiment;
[0014] FIG. 4 is a partially enlarged cross-sectional view of one
of pair of shoes in another embodiment according to the present
invention;
[0015] FIG. 5 is a perspective view of a blank piece from which the
shoe is forged;
[0016] FIG. 6 is a schematic view of a preparing process for
preparing a blank piece;
[0017] FIG. 7 is a schematic view of a forging process for forging
a shoe;
[0018] FIG. 8 shows plastic flow of a part of the blank piece
corresponding to the periphery of the shoe upon forging the
shoe;
[0019] FIG. 9 is a cross-sectional view of a comparative shoe;
[0020] FIG. 10 is a schematic view of a forging process for forging
a comparative shoe;
[0021] FIG. 11 shows plastic flow of a part of a blank of the
comparative shoe corresponding to the periphery of the comparative
shoe upon forging the comparative shoe;
[0022] FIG. 12 is a graph of the change of the reactive force with
respect to the molding time upon forging the shoe in the embodiment
and the comparative shoe; and
[0023] FIG. 13 is a graph of the change of the maximal reactive
force with respect to the change of the quantity of the blank piece
upon forging the shoe in the embodiment and the comparative
shoe.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0024] An embodiment of the present invention will now be described
by referring to FIGS. 1 to 13. A pair of shoes in a swash plate
type compressor for use in an air conditioner of a vehicle will be
described, for example. The front side and the rear side
respectively correspond to the left side and the right side in FIG.
1.
[0025] As shown in FIG. 1, a reference numeral 10 denotes a
cylinder block, and a plurality of cylinder bores 12 is formed in
the cylinder block 10 on an identical circumference relative to the
central axis of the cylinder block 10. The cylinder bores 12 extend
in the direction of the central axis of the cylinder block 10. A
single-headed piston 14 is accommodated in each of the cylinder
bores 12 so as to reciprocate. A front housing 16 is fixed to the
front end surface of the cylinder block 10, and a rear housing 18
is fixed to the rear end of the cylinder block 10 through a valve
plate assembly 20. The front housing 16, the rear housing 18 and
the cylinder block 10 constitute a housing of the swash plate type
compressor. A suction chamber 22 and a discharge chamber 24 are
defined between the rear housing 18 and the valve plate assembly 20
and are connected to an external refrigerant circuit, which is not
shown, through an inlet 26 and an outlet 28, respectively. A
suction port 32, a suction valve 34, a discharge port 36 and a
discharge valve 38 are formed in the valve plate assembly 20.
[0026] A drive shaft 50 is supported by the housing so as to rotate
with respect to the central axis of the cylinder block 10. The
drive shaft 50 is rotatably supported by the front housing 16 and
the cylinder block 10 through bearings. A support hole 56 is formed
in the center of the cylinder block 10 along the central axis of
the cylinder block 10 and supports the rear end of the drive shaft
50 through one of the bearings. The front end of the drive shaft 50
is connected to a vehicle engine, as a driving source, which is not
shown, through a clutch mechanism such as an electromagnetic
clutch. Therefore, when the drive shaft 50 is connected to the
vehicle engine by the clutch mechanism upon an operation of the
vehicle engine, the drive shaft 50 rotates around its axis.
[0027] A swash plate 60 is operatively connected to the drive shaft
50 so as to move along and to tilt with respect to the axis of the
drive shaft 50. A through hole 61 is formed in the swash plate 60
along the central axis of the swash plate 60, and the drive shaft
50 is interposed through the through hole 61. The through hole 61
gradually increases in diameter toward both opening ends of the
through hole 61, and the cross section of the opening ends are
oblong holes. A lug plate 62 is secured to the drive shaft 50 and
is supported by the front housing 16 through a thrust bearing 64. A
hinge mechanism 66 allows the swash plate 60 to integrally rotate
with the drive shaft 50 and to tilt with respect to the axis of the
drive shaft 50. The hinge mechanism 66 includes a pair of support
arms 67 fixed to the lug plate 62, a pair of guide pins 69 slidably
fitted into a pair of guide holes 68 of the support arms 67, the
through hole 61 of the swash plate 60, and the outer
circumferential surface of the drive shaft 50.
[0028] The piston 14 includes an engaging portion 70 and a head 72.
The engaging portion 70 overpasses the periphery of the swash plate
60. The head 72 is integral with the engaging portion 70 and is
fitted into the cylinder bore 12. The head 72 in the present
embodiment is a hollow head to be light in weight. The head 72, the
cylinder bore 12 and the valve plate assembly 20 cooperatively
define a compression chamber. The engaging portion 70 engages with
the periphery of the swash plate 60 through a pair of shoes 76,
which is substantially hemispherical. The shoes 76 will be
described later.
[0029] Rotation of the swash plate 60 is converted into
reciprocation of the piston 14 through the pair of shoes 76. As the
piston 14 moves from a top dead center toward a bottom dead center,
refrigerant gas in the suction chamber 22 is sucked into the
compression chamber in the cylinder bore 12 through the suction
port 32 and the suction valve 34. As the piston moves from the dead
center toward the top center, the refrigerant gas in the
compression chamber in the cylinder bore 12 is compressed and
discharged into the discharge chamber 24 through the discharge port
36 and the discharge valve 38. Compression reactive force is
applied to the piston 14 in a direction of the axis of the drive
shaft 50 in accordance with compressing the refrigerant gas. The
front housing 16 receives the compression reactive force through
the piston 14, the swash plate 60, the lug plate 62 and the thrust
bearing 64.
[0030] A supply passage 80 is formed in the cylinder block 10 so as
to extend through the cylinder block 10. The supply passage 80
interconnects the discharge chamber 24 and a crank chamber 86 that
is defined between the front housing 16 and the cylinder block 10.
A control valve 90 is disposed on the supply passage 80. The value
of an electric current supplied to a solenoid 92 of the control
valve 90 is controlled by a controller mainly constituted of a
computer, which is not shown, based on information such as cooling
load.
[0031] A bleed passage 100 is formed inside the drive shaft 50. The
bleed passage 100 opens its one end to the support hole 56, and
opens its other end to the crank chamber 86. The support hole 56
interconnects to the suction chamber 22 through a bleed port
104.
[0032] The swash plate type compressor in the present embodiment is
a variable displacement type. The pressure in the crank chamber 86
is controlled by utilizing pressure differential between the
discharge chamber 24 as a relatively high pressure region and the
suction chamber 22 as a relatively low pressure region. Thereby,
pressure differential between the pressure in the compression
chambers in the cylinder bores 12 applied to the pistons 14 and the
pressure in the crank chamber 86 is adjusted, and strokes of the
pistons 14 are varied by varying the inclination angle of the swash
plate 60, thus adjusting the displacement of the compressor.
Additionally, the crank chamber 86 disconnects from the discharge
chamber 24 and interconnects with the discharge chamber 24 by
opening and closing the control valve 90. Thereby, the pressure in
the crank chamber 86 is controlled.
[0033] The cylinder block 10 and the pistons 14 are preferably made
of aluminum alloy. The outer circumferential surfaces of the
pistons 14 are preferably coated with fluororesin. With the pistons
14 coated with fluororesin, seizure is inhibited by avoiding
directly contacting with a metal of the same kind, and clearances
between the cylinder block 12 and the pistons 14 are reduced. The
material of the cylinder block 10, the pistons 14 and the coating
layers are not limited as described above, but may be changed into
other materials.
[0034] The engaging portions 70 of the pistons 14 are substantially
U-shaped. The engaging portions 70 each provide a pair of arms
120,122 and a connecting portion 124. The pair of arms 120,122
extends in parallel with each other in a direction perpendicular to
the central axis of the head 72. The connecting portion 124
interconnects the bases of the arms 120, 122. Spherical concave
surfaces 128 are formed on the facing surfaces of the arms 120, 122
for supporting the shoes 76 and sliding over the shoes 76,
respectively. The spherical concave surfaces 128 cooperatively form
a part of an identical hypothetical spherical sliding surface.
[0035] A base member of the swash plate 60, which slides over the
shoes 76, is made of ductile iron. Aluminum layers are formed on
the sliding surfaces 132,134 of the base member of the swash plate
60 by metal spraying, and lubricant layers are further formed on
the aluminum layers. The lubricant layers are made of synthetic
resin dispersedly containing molybdenum disulfide and graphite as a
solid lubricant. The aluminum layers sufficiently reduce friction
generated between the sliding surfaces, and ensure relatively high
sliding performance between the shoes 76 and the swash plate 60.
Even if the lubricant layers abrade or peel off due to some causes,
the aluminum layers maintain a smooth slide. The structure of the
swash plate 60, such as material of the base member of the swash
plate 60, the material and the thickness of the lubricant layer,
with or without the lubricant layer, the thickness of the aluminum
spraying layers, and with or without the aluminum spraying layer,
can be varied.
[0036] As shown in FIG. 2, the shoe 76 includes a spherical
engaging surface 150 and a plane engaging surface 152. The
spherical engaging surface 150 is substantially a part of a sphere
surface in shape and engages with the piston 14. The plane engaging
surface 152 is substantially a plane in shape and engages with the
swash plate 60. The plane engaging surface 152 includes a plane
sliding surface 154, a peripheral surface 156 and an annular
connecting surface 158. The plane sliding surface 154 is formed
near the center of the plane engaging surface 152 and slides over
the sliding surfaces 132 or 134 of the swash plate 60. The
peripheral surface 156 is formed adjacent to the periphery of the
plane engaging surface 152. The peripheral surface 156 extends in a
substantially radial direction, such that the peripheral surface
156 is oriented in a range from substantially parallel to the plane
sliding surface 154 to slightly inclined with respect to the plane
siding surface 154. The peripheral surface 156 and the plane
sliding surface 154 form an inwardly-directed step therebetween.
Namely, the peripheral surface 156 is formed at a distance from an
extended plane surface of the plane sliding surface 154 away from
the sliding surface 132 or 134 facing the plane sliding surface
154. The peripheral surface 156 is connected to the spherical
engaging surface 150. The connecting surface 158 connects the plane
sliding surface 154 to the peripheral surface 156. In FIG. 2, the
step between the peripheral surface 156 and the plane sliding
surface 154 is exaggeratingly shown for easy understanding.
Preferably, the plane sliding surface 154 forms a convex surface,
the radius of the curvature of which is very large. In the present
embodiment, where a first hypothetical plane includes the periphery
of the plane engaging surface 152, and where a second hypothetical
plane that is parallel with the first hypothetical plane contacts
the plane engaging surface 152, a distance between the first and
second hypothetical planes is 5 .mu.m along a straight line
perpendicular to the first and second hypothetical planes. A first
shoe recess 160 is formed at the center of the plane engaging
surface 152 so as to store lubricant oil therein. Thereby, high
sliding performance is ensured. Consequently, the plane engaging
surface 152 is annular in shape. Meanwhile, the spherical engaging
surface 150 includes a spherical sliding surface 162 and a
peripheral rounded surface 164. The spherical sliding surface 162
is substantially a part of a sphere surface and slides over the
spherical concave surface 128 of the piston 14. A second shoe
recess 163 is formed at the center of the spherical sliding surface
162 so as to be pressed by a dowel pin upon forging. The peripheral
rounded surface 164 connects the spherical sliding surface 162 to
the peripheral surface 156 of the plane engaging surface 152. The
shoe 76 is generally called a hemispherical crown shoe.
Practically, a spherical engaging surface and a plane engaging
surface of the hemispherical crown shoe are respectively modified
from a strict spherical engaging surface and a strict plane
engaging surface so as to improve sliding performance. For example,
a plane sliding surface forms a convex surface such that the center
of the plane sliding surface protrudes by 5 to 10 .mu.m from the
periphery of the plane sliding surface. The hemispherical crown
shoe in the present embodiment includes the modified plane engaging
surface.
[0037] Although the shoe in the present embodiment can be used in
variable and fixed displacement type compressors, generally, a shoe
for use in a variable displacement type compressor is smaller than
a hemisphere, and a shoe for use in a fixed displacement type
compressor is larger than a hemisphere. In the variable
displacement type compressor, both spherical engaging surfaces of
the pair of shoes on each side of the swash plate needs to
cooperatively form a part of identical hypothetical spherical
surface. Each of the shoes is substantially a part of sphere and is
smaller in thickness by substantially a half of the thickness of
the swash plate than a hemisphere. On the other hand, in the fixed
displacement type compressor, no such limitations as that of the
variable displacement type compressor is required. Therefore,
thickness of each of the shoes is more than a hemisphere in order
to inhibit the area of the sliding surface of the shoe from
reducing even if the plane engaging surface abrades.
[0038] Referring to FIGS. 1 and 2, the pair of shoes 76 is slidably
held by the spherical concave surface 128 of the piston engaging
portion 70. The plane sliding surfaces 154 of the pair of shoes 76
are in contact with the sliding surfaces 132 and 134, which are
both surfaces of the periphery of the swash plate 60, and the swash
plate 60 is interposed between the pair of shoes 76. In other
words, the plane sliding surfaces 154 of the pair of shoes 76 slide
over the swash plate 60, and the spherical sliding surfaces 162 of
the pair of shoes 76 slide over the piston 14. The spherical
sliding surfaces 162 of the pair of shoes 76 cooperatively form a
part of an identical hypothetical spherical sliding surface.
Namely, the shoe 76 is substantially a part of a sphere, the
thickness of which is substantially smaller than a hemisphere by a
half of the thickness of the swash plate 60.
[0039] The shoe 76 includes a base member and a metal plating layer
that coats the surface of the base member of the shoe 76. The base
member is made of Al--Si series alloy such as A4032, the base of
which is aluminum and contains silicone such that the composition
ratio is closer to that of eutectic. The metal plating layer is
formed by electroless plating with nickel. The hardness and the
strength of the metal plating layer is relatively high. Thereby,
the shoe is inhibited from abrading and being flawed. The average
thickness of the electroless nickel plating layer is 50 .mu.m and
is omitted in FIG. 2. The structure of the shoe 76, such as the
material of the base member of the shoe 76, and the material and
the thickness of the metal plating layer, are not limited to that
in the present embodiment. The shoe, the base member of which is
made of aluminum series alloy, is relatively right in weight.
Therefore, the shoe is appropriate for use in a swash plate type
compressor installed in an air conditioner of a vehicle. A kind of
aluminum series alloy is not limited. Aluminum series alloy, which
is generally used in various fields, or which is well known, may be
applied. For example, Al--Si having eutectic composition of
approximately A4032 (JIS H 4000) may be applied. Al--Si series
alloy has relatively small coefficient of thermal expansion and
relatively high abrasion resistance. Therefore, the shoe, the base
member of which is made of Al--Si series alloy, slides smoothly.
Also, for example, Al--Cu--Mg series alloy such as A2017 and A2024
(JIS H 4000) may be applied. Since the strength of the Al--Cu--Mg
series alloy is relatively high, the shoe, the base member of which
is made of Al--Cu--Mg series alloy, performs relatively high
strength and high durability. It is preferable that the surface of
the base member made of aluminum series alloy is coated with metal
plating layer. The metal plating layer is preferably electroless
nickel plating layer such as Ni--P and Ni--B. Electroless nickel
plating layer is uniform. When solidified, electroless nickel
plating layer has a hardness of more than Hv500 (Vickers hardness).
Thereby, electroless nickel plating layer performs relatively high
abrasion and high anti-corrosion. Furthermore, the shoe made of
aluminum series alloy is usually forged from a cylindrical blank
piece. Quantities of the cylindrical blank pieces vary in a wide
range. However, since the shoe in the present invention is
accurately forged as mentioned later, the shoe made of aluminum
series alloy is advantageous to the present invention. The base
member of the shoe in the present invention may also be made of
iron series alloy. Iron series alloy is relatively low cost and
relatively high in strength and hardness. Therefore, the shoe, the
base member of which is made of iron series alloy, is relatively
low cost, and provides relatively high abrasion resistance and high
durability. A kind of iron series alloy is not limited. High carbon
chromium bearing steel SUJ2 (JIS G 4805) is preferably employed.
The shoe made of high carbon chromium bearing steel is manufactured
by thermal refining such as quenching or tempering, and nitriding.
A relatively large load is required upon forging the shoe made of
high carbon chromium bearing steel compared to the shoe made of
aluminum series alloy. In the shoe in the present invention, since
the blank piece plastically flows easily upon forging even when the
quantities of the blank pieces vary in a wide range, cost of a die
is reduced. Therefore, the shoe made of high carbon chromium
bearing steel is advantageous to the present invention.
Furthermore, metallic material such as magnesium, and resin may be
employed as material of the base member of the shoe.
[0040] As shown in FIG. 3, the connecting surface 158 is located in
the step between the plane sliding surface 154 and the peripheral
surface 156. The connecting surface 158 includes a chamfered
surface 180, a first rounded corner 182 and a second rounded corner
184. The chamfered surface 180 is a side surface of a circular
truncated cone. The diameter of the chamfered surface 180 near the
peripheral surface 156 is larger than that of the chamfered surface
180 near the plane sliding surface 154. The first rounded corner
182 connects the chamfered surface 180 to the plane sliding surface
154. The second rounded corner 184 connects the chamfered surface
180 to the peripheral surface 156. Each boundary is indicated by a
circle in FIG. 3 for the sake of convenience. A distance D of the
step between the plane sliding surface 154 and the peripheral
surface 156 is a predetermined distance. The distance D of the step
corresponds to a distance between an extended plane sliding surface
186, which is substantially perpendicular to the central axis of
the shoe 76 and contacts the plane sliding surface 154, and a
periphery of the peripheral surface 156 connecting to the second
rounded corner 184. When the plane sliding surface 154 is a plane
in shape and parallel to the peripheral surface 156, the distance D
is a distance between the plane sliding surface 154 and the
peripheral surface 156. In the present embodiment, the distance D
is 0.2 mm. A chamfered surface angle .alpha. between the chamfered
surface 180 and the extended plane sliding surface 186, the radius
r of curvature of the first rounded corner 182 and the radius r' of
the second rounded corner 184 are respectively determined. In the
shoe 76 in the present embodiment, the chamfered angle is
preferably 45.degree., and the radii r and r' of curvature are
preferably 0.2 mm.
[0041] In FIG. 3, the shoe 76 is in contact with the swash plate 60
such that a central axis of the shoe 76 is perpendicular to the
sliding surface 132 of swash plate 60. The plane sliding surface
154 of the shoe 76 is slightly convex in shape as mentioned above.
Therefore, a small clearance 190 that gradually increases in a
direction of the periphery of the shoe 76 is maintained between the
plane sliding surface 154 and the sliding surface 132. The
clearance 190 is exaggeratingly shown in FIG. 3 for easy
understanding. A layer of lubricant oil is formed in between the
sliding surfaces. Thereby, sliding performance improves. The
extended plane sliding surface 186 as a standard for the distance D
and chamfered surface angle .alpha. is a plane that is
perpendicular to the central axis of the shoe 76 and contacts the
plane sliding surface 154 as mentioned above. In FIG. 3, since the
plane sliding surface 154 of the shoe 76 is slightly convex in
shape, the extended plane sliding surface 186 corresponds to the
sliding surface 132 of the swash plate 60. The distance D
corresponds to a distance between the sliding surface 132 of the
swash plate 60 and the peripheral surface 156, and the chamfered
surface angle .alpha. corresponds to an angle between the chamfered
surface 180 and the sliding surface 132 of the swash plate 60.
[0042] When the shoe 76 slides over the swash plate 60, that is,
the shoe 76 relatively moves toward a direction indicated by an
arrow in FIG. 3, lubricant oil on the surface of the swash plate
60, which is omitted in the drawings, is led from a space 192
between the connecting surface 158 of the shoe 76 and the sliding
surface 132 of the swash plate 60 into the clearance 190. The cross
section of the space 192 is wedge-shaped. When foreign substances
194 are involved in the space 192, since the chamfered surface
angle .alpha. and the radius r of curvature of the first corner 182
are appropriately designed, relatively large foreign substances
194, which may affect sliding performance, is retarded from being
involved in the clearance 190. Namely, when the connecting surface
158 is appropriately formed at the periphery of the plane sliding
surface 154 as shown in FIG. 3, the foreign substances 194 can be
excluded while the lubricant oil is included between the sliding
surfaces. Therefore, when the shoe includes the connecting surface
158, the shape of which is appropriate, high sliding performance is
ensured. As mentioned above, unless lubricant oil is included
between the sliding surfaces and harmful foreign substances are not
included between the sliding surfaces, relatively high sliding
performance between the sliding surfaces cannot be obtained.
Including the lubricant oil and excluding the foreign substances
will be described by referring to a swash plate type compressor
constituting an air conditioner. The lubricant oil is included in
the refrigerant gas, and the lubricant oil forms oil film such that
relatively high sliding performance between the sliding surfaces is
maintained. Therefore, when the lubricant oil is not included
between the sliding surfaces, sliding performance deteriorates.
Also, there may be various foreign substances in the swash plate
type compressor, such as, for example, tailing generated due to
friction in various places, remaining microscopic burrs from
manufacturing, and dusts introduced from a refrigerant conduit
connected to the compressor. These foreign substances should be
sufficiently managed.
[0043] However, it is hard to completely remove these foreign
substances. Therefore, these foreign substances exist in between
the sliding surfaces, and then remain. When the foreign substances
remain between the sliding surfaces, the sliding surfaces are
flawed, and sliding performance between the sliding surfaces
deteriorates. To sufficiently include the lubricant oil and to
sufficiently exclude the is foreign substances, the geometry of the
shoe 76, which slides over the swash plate 60, is important. In the
shoe in the present invention, these requirements can be satisfied
by adjusting the shape of the connecting surface 158 adjacent to
the periphery of the plane sliding surface 154. The structure in
the present embodiment is one of the examples. Characteristics for
excluding foreign substances and characteristics for including
lubricant oil are regulated by adjusting the shapes of the
chamfered surface 180 and the first rounded corner 182. Therefore,
a shoe having relatively high sliding performance is obtained.
Meanwhile, since the chamfered surface is formed in the step, which
is relatively small, the length of the chamfered surface 180, which
is a distance of the chamfered surface 180 in the height of the
shoe, is relatively short. For example, when the step is relatively
small and the first and second rounded corners 182 and 184 are
relatively large, the length of the chamfered surface 180 is
extremely short. In an ultimate case, the length of the chamfered
surface 180 is zero. In this case, a boundary between the first
rounded corner 182 and the second rounded corner 184 can be
regarded as the chamfered surface 180. In the present embodiment,
the chamfered surface 180 includes the above configurations.
[0044] In FIG. 3, a representative foreign substance 194 is
substantially a sphere in shape, the diameter of which is about 100
.mu.m. Since the foreign substance 194, which is relatively large,
contacts the chamfered surface 180, characteristics for excluding
foreign substance is determined based on the chamfered angle
.alpha.. When the foreign substances are relatively small, the
foreign substances contact the first rounded corner 182, not the
chamfered surface 180. Therefore, characteristics for excluding
foreign substances are determined based on the radius r of
curvature of the first rounded corner 182. More particularly, when
the foreign substances contact the first rounded corner 182,
characteristics for excluding foreign substances is determined
based on a tangent plane angle between the extended plane sliding
surface 186 and a tangent plane to the first sliding rounded corner
182 at a point of contact, where the foreign substances contact the
first rounded corner 182. When the tangent plane angle is
relatively large, the foreign substance is easily excluded. When
the tangent plane angle is relatively small, the foreign substances
are easily included between the sliding surfaces. When the diameter
of the foreign substance is unchanged, as the radius r of curvature
of the first rounded corner 182 is small, characteristics for
excluding foreign substances become excellent. On the other hand,
as the radius r of curvature of the first rounded corner 182 is
large, the lubricant oil is easily included between the sliding
surfaces. When the radius r of curvature of the first rounded
corner 182 is extremely small and the first rounded corner 182
contacts the sliding surface 132 of the swash plate 60, the first
rounded corner 182 may peel off the lubricant layer containing a
solid lubricant because of the relatively low strength and hardness
of the lubricant layer. Also, when the radius r of curvature of the
first rounded corner 182 is extremely small, the rounded corner 182
excludes not only the foreign substances but also the lubricant
oil. Furthermore, the surfaces of the shoes 76 are usually smoothed
by barrel polishing, and the shoes 76 abut against each other upon
barrel polishing. Therefore, when the radius r of curvature of the
first rounded corner 182 is extremely small, the shoes 76 may be
flawed from the first rounded corner 182. Accordingly, the
chamfered surface angle a and the radius r of curvature of the
first rounded corner 182 can be appropriately determined in
accordance with the purpose of the shoe 76 in view of
characteristics for excluding foreign substances and
characteristics for including lubricant oil. When the chamfered
surface angle .alpha. is an appropriate angle, which is relatively
small, the lubricant oil is sufficiently included between the
sliding surfaces. However, when the chamfered surface angle .alpha.
is too small, characteristics for excluding foreign substances
deteriorates. In other words, the foreign substances are easily
caught in between the chamfered surface 180 and the sliding surface
132 of the swash plate 60, when the shoe 76 moves in this state,
the foreign substances are included between the plane sliding
surface 154 of the shoe 76 and the sliding surface 132 of the swash
plate 60. On the other hand, when the chamfered surface angle
.alpha. is increased to an angle of 90.degree., the chamfered
surface 180 pushes the foreign substances aside. Namely, as the
chamfered surface angle .alpha. is large, characteristics for
excluding foreign substances improves. Even when the chamfered
surface angle .alpha. is relatively large, the chamfered surface
180 substantially does not restrict the plastic flow of the blank
piece upon forging due to the relatively small distance D.
Therefore, the chamfered surface 180 hardly becomes one of causes
that reduce the dimensional accuracy in the shoe 76. To obtain
relatively high characteristics for excluding foreign substances,
it is preferable that the chamfered surface angle .alpha. is
35.degree. or above. The chamfered surface angle .alpha. is more
preferably 40.degree. or above. On the other hand, it is preferable
that the chamfered surface angle a is 90.degree. or below. In view
of characteristics for involving lubricant oil and for restricting
the plastic flow of the blank piece upon forging, the smooth
plastic flow requires the smaller chamfered surface angle .alpha.,
the chamfered surface angle .alpha. is preferably 75.degree. or
below, more preferably 60.degree. or below, and much more
preferably 50.degree. or below. When the length of the chamfered
surface 180 is substantially zero, the chamfered surface angle
.alpha. is defined as an angle between the first and second rounded
corner. That is, where the cross-section of the shoe is taken along
a hypothetical plane including a central axis of the shoe and
perpendicular to the plane sliding surface 154, the chamfered
surface angle .alpha. is defined as an angle between the extended
plane sliding surface 186 and a hypothetical tangent line of both
the first and second rounded corners 182 and 184. In view of
characteristics for involving the lubricant oil in between the
sliding surfaces, for inhibiting the shoe from being flawed upon
barrel polishing, and for avoiding the metal plating layer from
abrading, the radius r of curvature of the first rounded corner 182
is preferably 0.05 mm or above. The radius r of curvature of the
first rounded corner 182 is more preferably 0.1 mm or above, and is
much more preferably 0.15 mm or above. When the radius r of
curvature of the first rounded corner 182 is relatively large,
relatively small foreign substances contact the first rounded
corner 182, not the chamfered surface 180. In such a state,
characteristics for excluding foreign substances depends on an
angle between a tangent plane at a point of contact with foreign
substance and the extended plane sliding surface, that is, a
tangent plane angle. When the shoe contacts foreign substances at
its chamfered surface, characteristics for excluding foreign
substances improves as the tangent plane angle increases. In
addition, when a foreign substance of the same diameter contacts
the first rounded corner 182, the tangent plane angle increases as
the radius r of curvature of the first rounded corner 182
decreases. Namely, as the radius r of curvature of the first
rounded corner 182 reduces, characteristics for excluding foreign
substances improves. Accordingly, when focusing on characteristics
for excluding foreign substances, the radius r of curvature of the
first rounded corner 182 is 0.5 mm or below, is preferably 0.4 mm
or below, and is more preferably 0.3 mm or below. Furthermore,
Japanese Unexamined Patent No. 2002-332959 can be referred to about
a relationship between the diameter of the foreign substance and
the radius r of curvature for a help of understanding.
[0045] The distance D of the step between the peripheral surface
156 and the plane sliding surface 154 affects characteristics of
the shoe 76. In the present embodiment, since the distance D of the
step between the peripheral surface 156 and the plane sliding
surface 154 is preferably about 0.2 mm, the foreign substance, the
diameter of which is smaller than 200 .mu.m, is not caught in
between the sliding surface 132 of the swash plate 60 and the
peripheral surface 156. The distance D can be set in accordance
with largeness of expected foreign substances, the shape of the
connecting surface 158 and easiness of plastic flow of a blank
piece upon forging as will be mentioned later. When the distance D
is too small, it is hard to include the lubricant oil between the
sliding surface 132 of the swash plate 60 and the plane sliding
surface 154 of the shoe 76. When considering the above description,
it is preferable that the distance D is 0.02 mm or above. As the
distance D is small, it is easy to include relatively small foreign
substances in between the peripheral surface 156 and the sliding
surface 132 of the swash plate 60. When the distance D is much
smaller, the shape of the connecting surface 158 is limited, and
the connecting surface 158 may not be appropriately formed such
that the lubricant oil is sufficiently included between the sliding
surface 132 of the swash plate 60 and the plane sliding surface 154
of the shoe 76 and the foreign substances are sufficiently
excluded. When considering the above descriptions, it is preferable
that the distance D is 0.05 mm or above. When focusing on excluding
larger foreign substances, the distance D is preferably 0.1 mm or
above, and is more preferably 0.15 mm or above. On the other hand,
when the distance D is relatively large, the resistance to the
plastic flow of the blank piece upon forging becomes large. When
considering the above description, it is preferable that the
distance D is 0.5 mm or below. When focusing on that the resistance
is reduced more, the distance is preferably 0.3 mm or below, and is
more preferably 0.25 mm or below. Furthermore, in the above
mentioned embodiment, the peripheral surface 156 is substantially
parallel to the plane sliding surface 154. When considering that
the resistance to the plastic flow of the blank piece upon forging
is reduced, the structure is preferable. However, as shown in FIG.
4, the peripheral surface 156 can be inclined with respect to the
plane sliding surface 154. In this case, it is desired that the
peripheral surface 156 is formed such that an angle .beta. between
the peripheral surface 156 and the extended plane sliding surface
186 is less than 10.degree.. In the above range of the angle
.beta., the resistance to the plastic flow of the blank piece does
not increase upon forging as will be mentioned in detail later. In
addition, the width of the peripheral surface 156, that is, a
distance between the outer and the inner edges of the peripheral
surface 156, can be determined by considering variation in
quantities of blank pieces and the easiness of plastic flow of the
blank upon forging. As the area of the plane sliding surface 154 is
large, sliding becomes stable. It is desired that the width of the
peripheral surface 156 is determined such that the sufficient area
of the plane sliding surface 154 is ensured. Since the peripheral
rounded surface 164, which is an outer periphery of the shoe 76, is
a part for absorbing variation in quantities of blank pieces, the
shape of the peripheral rounded surface 164 is different in each
shoe.
[0046] One of the manufacturing processes of the shoe 76 in the
present embodiment will be described. The shoe is manufactured by
the steps of a preparing process for preparing a blank piece, a
forging process, a thermal refining process, a grinding and
polishing process, a plating process and a finishing process. A
method of forming a shoe according to an embodiment of the present
invention includes the preparing process and the forging
process.
[0047] The blank is the aluminum series alloy as mentioned above. A
blank piece 200 formed from the blank is cylindrical as shown in
FIG. 5. Particularly, the cylindrical blank 200 has an outer
diameter that is smaller than that of the plane sliding surface 154
of the shoe 76, and a height that is larger than that of the shoe
76. A first recess 202 corresponding to the first shoe recess 160
on the plane engaging surface 152 of the shoe 76 is formed on one
end surface and a second recess 203 corresponding to the second
shoe recess 163 on the plane engaging surface 152 of the shoe 76 is
formed on the other end surface. The blank piece 200 is made by
forming the first and second recesses 202 and 203 in a cylindrical
blank base. The blank base is preferably made by the steps of
molding a billet made of aluminum series alloy with predetermined
composition, forming a cylindrical rod with a predetermined
diameter by extruding and drawing the billet, annealing the
cylindrical rod, cutting the cylindrical rod into pieces with a
predetermined length by a sawing machine or a shear, and smoothing
a surface of the cut blank by barrel polishing.
[0048] As shown in FIG. 6, the first and second recesses 202 and
203 are formed by upset forging. A pair of dies 206 for forming a
recess includes a drag is 212 supported by a base 210 through a
spring damper 208, and a cope 213 opposite to the drag 212. The
drag 212 has a setting recess 214 where a blank base 204 is set.
The setting recess 214 is formed such that the inner diameter of
the setting recess 214 is slightly larger than the outer diameter
of the blank base 204 and the depth of the setting recess 214 is
smaller than the height of the blank piece 200. The drag 212 has a
circular through hole 215 that connects the center of the bottom of
the setting recess 214. A cylindrical pin 216 is formed on the base
210. One end of the cylindrical pin 216 is fixed to the base 210,
and the other end of the cylindrical pin 216 is interposed in the
circular through hole 215. The cope 213 has a contacting recess 218
such that the bottom of the contacting recess 218 contacts one end
of the blank base 204 when the pair of dies 206 is closed. The
inner diameter of the contacting recess 218 is slightly larger than
the outer diameter of the blank base 204. A protrusion 219 is
formed on the center of the bottom of the contacting recess 218. In
a state when the blank base 204 is set in the setting recess 214 of
the drag 212, when the cope 213 is operated downward, the cope 213
and the drag 212 are closed, and then the drag 212 is lowered with
respect to the base 210. Therefore, the one end of the cylindrical
pin 216 lo protrudes into the setting recess 214 from the circular
through hole 215, and the one end of the cylindrical pin 216 and
the protrusion 219 of the cope 213 are pressed against each of the
end surfaces of the blank base 204. Accordingly, the first and
second recesses 202 and 203 are formed on each of the surfaces of
the blank base 204, and the blank piece 200 is completed.
[0049] The preparing process finishes as mentioned above. The
preparing process is not limited to the above mentioned embodiment.
For example, when a shoe is formed from a spherical blank piece,
the spherical blank piece is made in the preparing process. In this
case, the preparing process includes the steps of cutting a
cylindrical blank into pieces, pressing, flushing, grinding and
polishing. When a shoe is formed from a blank piece that does not
have a recess, a recess does not need to be formed in the blank
piece in the preparing process. When a predetermined blank piece is
purchased, the preparing process is not necessarily performed. A
shoe may be formed from the purchased predetermined blank
piece.
[0050] The blank piece 200 is applied to the forging process. A
forging process is schematically shown in FIG. 7. A forging
apparatus with a pair of dies 224 including a cope 220 and a drag
222 is used for cold forging. In a state when the cope 220 and the
drag 222 are closed, a cavity, which has substantially the same
shape as the shoe 76, is formed. The cavity has substantially the
same shape as the base member of the shoe 76. The cavity is smaller
than the shoe 76 substantially by a portion corresponding to the
thickness of the electroless nickel plating layer formed on the
surface of the base member of the shoe 76. The drag 222 has a
protrusion 226, the shape of which is substantially the same shape
as the first recess 202. The blank piece 200 is positioned on the
drag 222 by fitting the protrusion 226 into the first recess 202.
The cope 220 has a movable dowel pin 227. The top end of the dowel
pin 227 is fitted into the second recess 203 formed in the blank
piece 200. In this manner, since the first and second recesses 202
and 203 are previously formed before a forging process, the blank
piece 200 is positioned appropriately in the pair of dies 224 by
means of the first and second recesses 202 and 203, the protrusion
226 and the dowel pin 227. Thereby, the blank piece 200 plastically
flows isotropically. The shapes and the dimensions of the forged
base members of the shoes 76 vary in a narrow range, and the shoes
76 ensure high quality. After putting the blank piece 200 on the
drag 222, the base member of the shoe 76 is forged by operating the
cope 220 downward and fitting the cope 220 onto the drag 222.
[0051] More particularly, a molding surface of the cope 220 as a
first die molds the spherical engaging surface 150 of the shoe 76.
A molding surface of the drag 222 as a second die molds the plane
engaging surface 152 of the shoe 76. In a state when the cope 220
and the drag 222 are closed, a space between a part of the surface
of the drag 222 that molds the plane sliding surface 154 and the
surface of the cope 220 determines the dimension of the height of
the base member of the shoe 76. The cope 220 and the drag 222 are
closed so that the periphery of the cope 220 contacts the periphery
of the drag 222. Therefore, the pair of the dies 224 contributes to
improve dimensional accuracy in the height of the base member of
the shoe 76. However, since the contact between the pair of dies
224 has an influence on a durability of the dies, it is desired to
determine whether the cope 220 contacts the drag 222 or not, and
which parts of the cope 220 and the drag 222 contact each other by
considering the influence.
[0052] The cavity of the pair of dies 224 is formed such that a
surplus space 228 that is not filled with the blank piece in the
periphery of the cavity is left. The surplus space 228 absorbs the
variation in the quantities of the blank pieces 200. In other
words, the surface of the drag 222 that molds the peripheral
surface 156 extends toward the periphery of drag 222, and the
surface of the cope 220 that molds the spherical sliding surface
162 extends. The surplus space 228 is defined by the extended
surfaces of the drag 222 and the cope 220. On the contrary, the
quantity of the blank piece 200 is determined such that the surplus
space 228 is left unfilled. The peripheries of the base materials
of the shoes 76, which are formed in the surplus space 228, are
slightly different from each other due to the variation in the
quantities of the blank pieces 200. However, in a state when the
shoe 76 is put in a swash plate type compressor, since the
peripheral rounded surface 164 corresponding to the surface of the
periphery of the base material of the shoe 76 dose not slide over a
piston and a swash plate, the above mentioned variation does not
affect performance of the swash plate type compressor.
[0053] After the blank piece 200 is set in the pair of dies 224,
once the pair of is dies 224 begins to close, the blank piece 200
is pressed by the pair of dies 224 in a vertical direction.
Thereby, the blank piece 200 deforms such that the blank piece 200
spreads toward the outer periphery of the cavity. Namely, the blank
piece 200 plastically flows toward the outer periphery of the
cavity. As the cope 220 is lowered, the side surface of the blank
piece 200 moves toward the outer periphery of the cavity. When the
pair of dies 224 has finished closing, the cope 220 and the drag
222 tightly press the blank piece 200, and the cavity is filled
with the blank piece 200 except the above mentioned surplus space
228. At the time, the forging process has finished. Besides, in a
case that the forged shoe 76 is taken from the pair of dies 224,
the dowel pin 227 is pushed down as the cope 220 is operated
upward. Thereby, the forged shoe 76 is separated from the cope 220
and is easily taken from the pair of dies 224.
[0054] Plastic flow of a part of the blank piece 200 corresponding
to the periphery of the shoe 76 is shown in FIG. 8. In the forging
process for the shoe 76 in the present embodiment, the blank piece
200 spreads toward the outer periphery of the cavity. A step part
230 of the surface of the drag 222 for forming the connecting
surface 158 can cause resistance to the plastic flow of the blank
piece 200. However, since the distance D of the step between the
peripheral surface 156 and the plane sliding surface 154 is
relatively short, the blank piece 200 plastically flows over the
step part 230. Therefore, the resistance to the plastic flow of the
blank piece 200 is relatively small. As a result, relatively large
is load is not required upon forging, and the amount of spring back
is relatively small after forging. Besides, when the blank piece
200, the quantity of which is larger than a predetermined normal
quantity, is forged with the pair of dies 224, increase in the
resistance to the plastic flow of the blank piece 200 is relatively
small. Accordingly, the variation in the dimensions of the forged
shoes 76 by the variation in the quantities of the blank pieces 200
becomes relatively small due to the shape of the shoe 76.
[0055] For comparison, a comparative shoe that has a side surface
connecting a spherical engaging surface to a plane engaging
surface, and forging the comparative shoe will be described. A
cross-sectional view of a comparative shoe 250 is shown in FIG. 9.
The comparative shoe 250 includes a spherical engaging surface 252
for engaging with a piston, a plane engaging surface 254 for
engaging with a swash plate and a peripheral surface 256 on its
outer surface. The peripheral surface 256 connects the spherical
engaging surface 252 to the plane engaging surface 254. The
peripheral surface 256 includes a chamfered surface 260 and a
rounded surface 264. The chamfered surface 260 is inclined with
respect to a plane sliding surface 258 of the plane engaging
surface 254 at an angle of 45.degree.. The rounded surface 264
connects the chamfered surface 260 to a spherical sliding surface
262 of the spherical engaging surface 252. Similarly to the shoe 76
in the present embodiment, the chamfered surface 260 is adjacent to
the plane sliding surface 258 through a small rounded corner, and
the rounded surface 264 corresponds to a part for absorbing
variation in quantities of blank pieces upon forging. Furthermore,
the plane engaging surface 254 and the spherical engaging surface
252 respectively include a first shoe recess 266 and a second shoe
recess 268.
[0056] A forging process for forging the comparative shoe 250 is
schematically shown in FIG. 10. With respect to a pair of dies, the
same reference numerals denote the same identical elements as those
in FIG. 7. Upon forging the comparative shoe 250, the same pair of
dies 224 is utilized, and the same forging process is performed as
the shoe 76 of the present embodiment. What is different with
respect to the pair of dies 224 is that a drag 222 includes a
surface that can mold the chamfered surface 260 of the peripheral
surface 256. Similarly, the cavity in the pair of dies 224 is
formed such that a surplus space 228 that is not filled with the
blank piece 200 in the periphery of the cavity is left for
absorbing the variation in the quantities of the blank pieces
200.
[0057] Plastic flow of a part of the blank corresponding to the
periphery of the lo shoe 250 is shown in FIG. 11. Upon forging the
comparative shoe 250, the blank piece 200 similarly spreads toward
the outer periphery of the cavity. What is different from forging
the shoe 76 in the present embodiment is that the drag 222 includes
a molding surface 270, toward which the side surface of the blank
piece 200 moves. After the side surface of the blank piece 200
contacts the molding surface 270 at a point of A in FIG. 11, the
molding surface 270 causes relatively large resistance to the
plastic flow of the blank piece 200. More particularly, a force for
pressing the blank piece 200 toward a corner part B in FIG. 11, and
a force for moving the blank piece 200 toward the surplus space 228
along the molding surface 270 while pressing the blank piece 200
against the molding surface 270, that is, a force indicated by an
arrow a and a force indicated by an arrow b, are required.
Therefore, a relatively large load has to be applied to the blank
piece 200. When the blank piece 200, the quantity of which is
larger than a predetermined normal quantity, is forged with the
pair of dies 224, a much larger load is required for forging. Since
the blank piece 200 receives a much larger load, the amount of
spring back becomes large after forging. As a result, in the
comparative shoe 250, the resistance to the plastic flow of the
blank 200 is generated due to the shape of the comparative shoe
250, and the comparative shoe 250 may vary in shape when the
quantities of the blank pieces 200 vary. Since a relatively large
load is applied upon forging, the pair of dies 224 receives a
relatively large load. When a shoe is forged from a blank piece
made of material having relatively high strength such as high
carbon chromium bearing steel, the strength of the pair of dies 224
has to be enhanced. Thereby, cost for manufacturing a shoe
increases.
[0058] With respect to reactive force that the pair of dies 224
receives upon forging, the case of forging the shoe 76 in the
present embodiment is compared with that of forging the comparative
shoe 250. When the reactive force is large, the load upon forging
has to be relatively large, and the blank piece 200 receives a
relatively large load. The comparison is analyzed by CAE
(computer-aided experiment). For the analysis, blank pieces are
aluminum alloy, and a normal quantity of the blank piece is
estimated to be 3 g. Cases of forging from blank pieces having the
normal quantity and a quantity of 3.04 g, which is heavier than the
normal quantity by 0.04 g, are evaluated. In FIG. 12, the change of
the reactive force with respect to the molding time upon forging
the shoe in the embodiment and the comparative shoe is shown. In
FIG. 13, the change of the maximal reactive force with respect to
the change of the quantities of the blank pieces upon forging the
shoe of embodiment and the comparative shoe is shown.
[0059] According to FIG. 12, reactive forces gradually increase
after the forging starts in both shoes. As the blanks approach a
part corresponding to the periphery of the shoe, gradients of the
reactive forces become large. Each reactive force becomes its
maximum just before the forging has finished. In the case of
forging from the blank piece having the normal quantity, when the
shoe in the present embodiment is compared with the comparative
shoe, the reactive force for the comparative shoe is larger than
that for the shoe in the present embodiment as mentioned above. The
maximum reactive force for the shoe in the present embodiment is
about 9 t while the maximum reactive force for the comparative shoe
is about 15 t. In the case of forging from the blank piece having
the quantity of 3.04 g, the reactive force increase upon forging
both the shoe in the present embodiment and the comparative shoe.
The maximum reactive force for the shoe in the present embodiment
is about 12 t and increases by 3 t. The degree of the increase is
relatively small. On the other hand, the maximum reactive force for
the comparative shoe is about 26 t and increases by lit. The degree
of the increase is relatively large. FIG. 13 indicates that the
degree of the increase for the shoe in the present embodiment is
smaller than that for the comparative shoe when the quantity of the
blank increases. As a result, the required load upon forging is
smaller in the shoe in the present embodiment than in the
comparative shoe. Even when the quantities of the blank pieces
vary, since the difference between the reactive forces that the
blank pieces receive is relatively small, the shoe in the present
embodiment is accurately forged. Roughly speaking, the shoe in the
present embodiment includes a periphery surface that is offset with
respect to the middle part of a plane engaging surface, so as to
form a step on its part corresponding to a periphery of a plane
engaging surface in a common shoe. It is desired that the periphery
of the plane engaging surface includes lubricant oil between a
plane sliding surface and a sliding surface of a swash plate and
inhibits relatively large foreign substances from being allowed
between the sliding surfaces. Therefore, the above mentioned
connecting surface, which is located in the step corresponding to
the periphery of the plane engaging surface, is important. Although
the shape of the connecting surface is not limited, the connecting
surface can include lubricant oil and exclude foreign substances
due to its above mentioned structure. In a shoe shown in Japan
Unexamined Patent Publication No. 2002-332959, a side surface
formed as a chamfered surface can include lubricant oil and exclude
foreign substances. However, relatively large resistance can be
generated upon forging due to the side surface. On the other hand,
since the shoe in the present embodiment does not have such a side
surface that can be cause of relatively large resistance upon
forging, the shoe in the present embodiment is accurately forged.
Therefore, relatively high sliding performance is ensured and
dimensional accuracy is obtained. When a shoe is forged with
relatively low dimensional accuracy, for example, it takes
relatively long time to adjust the dimension of the shoe by
grinding after forging, and cost for manufacturing a shoe
increases. In this point, the shoe in the present embodiment is
manufactured at a relatively low cost.
[0060] Dimensional accuracy will be described in detail. In the
forging process, the blank piece is set in the pair of dies, and
the blank piece plastically flows toward the periphery of the
cavity. As mentioned above, when resistance to the plastic flow of
the blank piece is relatively large upon forging, the load is
required to be relatively large upon forging. Therefore, the
reactive force becomes relatively large from the blank piece to the
pair of dies. When a relatively large force is applied to the blank
piece and the pair of dies, elastic deformation is generated in the
blank piece and the pair of dies. For example, when relatively
large elastic deformation is generated in the pair of dies, the
shape of the cavity changes. When relatively large elastic
deformation is generated in the blank piece, the amount of spring
back becomes relatively large after forging. It is assumed that
variation in quantities of blank pieces is permitted to some extent
and resistance to the plastic flow of the blank piece is generated
upon forging. In this case, even though a space for absorbing
variation in quantities of blank pieces is unfilled, variation in
dimension becomes relatively large due to the variation in the
quantities of the blank pieces. In the shoe in the present
embodiment, since the blank piece plastically flows over the above
mentioned step upon forging, a relatively large resistance is not
generated. Therefore, the shoe can be forged with a relatively
small load. As a result, dimensional accuracy in the height of the
shoe is obtained. In short, the periphery of the shoe between the
peripheral surface and the spherical engaging surface can function
as a part for effectively absorbing variation in quantities of
blank pieces. In conclusion, sliding performance is compatible with
relatively high dimensional accuracy in the shoe in the present
embodiment due to the shape of the shoe. Incidentally, when
dimensional accuracy in the height of a shoe is relatively low, for
example, a distance between a plane engaging surface and a
spherical engaging surface is too large, foreign substances are
easily allowed between the sliding surfaces. On the other hand,
when a distance between a plane engaging surface and a spherical
engaging surface is too small, friction between the sliding
surfaces becomes relatively large. Therefore, sliding performance
deteriorates in both cases.
[0061] As mentioned above, the blank piece plastically flows easily
upon forging due to the shape of the shoe in the present invention.
Therefore, the present invention is effective to a shoe
manufactured through forging. The cylindrical blank piece is
utilized in the above mentioned forging process. Although the
cylindrical blank piece is made by cutting a cylindrical rod at a
relatively low cost, quantities of the cylindrical blanks vary.
Especially, when the cylindrical blank piece is made by means of a
shear, although the cost is cheaper, quantities of the cylindrical
blank pieces vary in a wide range. However, since the shoe in the
present invention is accurately forged even though quantities of
the blank pieces vary, the present invention is effective to a shoe
forged from the cylindrical blank piece. When the relatively cheap
cylindrical blank piece is utilized, a relatively cheap shoe can be
obtained. Also, a spherical blank piece can be utilized. In this
case, similarly to manufacturing bearing ball, the spherical blank
piece is made through processes such as flushing and grinding, and
quantities of the spherical blank pieces vary in a narrow range.
The shape of the blank is not limited to cylinder and sphere, and
blanks having various shapes can be utilized. Regardless of the
shape of the blank piece, since the required load is relatively
small upon forging the shoe in the present invention and the degree
of the increase in the reactive force in accordance with the
increase in the quantity of the blank piece is relatively small,
the shoe of the present invention is accurately forged.
[0062] The above mentioned forging process includes one process.
However, a multi-process, which includes a plurality of sub-forging
processes, may be employed. For example, a precursor of the shoe
76, which does not have a part corresponding to the periphery of
the shoe 76, can be forged first, and then the part corresponding
to the periphery of the shoe 76 can be forged. In this case, the
first forging corresponds to the forging process in the
manufacturing process in the present invention, and the precursor
of the shoe 76 corresponds to the blank piece. Also, another
precursor having substantially a final shape of the shoe 76 is
forged first, and then a finishing process can be conducted for
adjusting dimension of the precursor. In this case, the forging
corresponds to the forging process in the manufacturing process of
the present invention. When a multi-forging process is conducted,
annealing can be conducted after any processes.
[0063] The shoe 76 formed in the forging process is preferably
treated by thermal refining including T6 treatment and T7 treatment
(JIS H0001) in the thermal refining process. The shoe 76 treated by
thermal refining is ground and polished for grinding its surface in
the grinding and polishing process. The grinding and polishing
process includes a surface grinding process and a barrel polishing
process. The plane sliding surface 154 of the shoe 76 is ground in
the surface grinding process. Several pieces of shoes 76 are
aligned, and then ground by a surface grinding apparatus by means
of free abrasive grains. The plane sliding surface 154 can form the
convex surface in the surface grinding process. The entire surface
of the shoe 76 is polished in the barrel polishing process. The
shoe 76 together with free abrasive grains is put in a barrel
polishing apparatus, and then started. Either of the surface
grinding process and the barrel polishing process can be conducted
first. Then, a plating process is preferably conducted. For
example, the surface of the shoe 76 can be coated with electroless
nickel plating layer in the plating process. Finally, the finishing
process is conducted. The shoe 76 is ground by barrel polishing in
the finishing process. When necessary, the shoe 76 is treated by
surface grinding. The shoe 76 can be polished by buffing. The above
mentioned shoe 76 is completed through the above mentioned
processes. Manufacturing processes are not limited to the above
mentioned processes. The shoe in the present invention may be
manufactured by various kinds of processes in accordance with
specifications of target shoes.
[0064] The manufacturing processes for the shoe made of aluminum
alloy is described above. In a case of manufacturing processes for
a shoe made of metal alloy, such as high carbon chromium bearing
steel, for example, after the above mentioned forging process, a
thermal refining process including quenching is conducted when
necessary, and the shoe is completed through a grinding and
polishing process, a nitriding process and a finishing process. The
shoe may be is distorted by heat in the thermal refining process.
In this case, dimension of the shoe can be determined in the
forging process by foreseeing the deformation. Since the shoe in
the present invention is accurately forged, the above mentioned
manufacturing processes can be conducted. Namely, since the shoe in
the present invention is accurately forged, that facilitates
adjusting dimension of the shoe after forging. Therefore, cost for
manufacturing a shoe reduces.
[0065] Therefore, the present examples and embodiments are to be
considered as illustrative and not restrictive, and the invention
is not to be limited to the details given herein but may be
modified within the scope of the appended claims.
* * * * *