U.S. patent application number 10/151281 was filed with the patent office on 2002-11-21 for shoe for swash plate type compressor and method of producing the same.
Invention is credited to Hiramatsu, Osamu, Iida, Hidenori, Inoue, Yoshinori, Kurakake, Hirotaka, Narukawa, Kiyoshi, Ota, Masaki, Tarutani, Tomoji, Usui, Naoki, Wakita, Tomohiro.
Application Number | 20020170425 10/151281 |
Document ID | / |
Family ID | 26615385 |
Filed Date | 2002-11-21 |
United States Patent
Application |
20020170425 |
Kind Code |
A1 |
Tarutani, Tomoji ; et
al. |
November 21, 2002 |
Shoe for swash plate type compressor and method of producing the
same
Abstract
A method of producing a shoe for a swash plate type compressor,
said shoe being disposed between a swash plate and a piston of said
swash plate type compressor, the method comprising: a forming step
of forming a steel blank into a shoe product including an end
product shoe and a pre size-adjusted shoe; and a nitriding step of
effecting a nitriding treatment on said shoe product; and wherein a
quenching treatment is not effected after said forming step.
Inventors: |
Tarutani, Tomoji;
(Kariya-shi, JP) ; Wakita, Tomohiro; (Kariya-shi,
JP) ; Kurakake, Hirotaka; (Kariya-shi, JP) ;
Iida, Hidenori; (Kariya-shi, JP) ; Usui, Naoki;
(Kariya-shi, JP) ; Ota, Masaki; (Kariya-shi,
JP) ; Hiramatsu, Osamu; (Kariya-shi, JP) ;
Narukawa, Kiyoshi; (Kariya-shi, JP) ; Inoue,
Yoshinori; (Kariya-shi, JP) |
Correspondence
Address: |
MORGAN & FINNEGAN, L.L.P.
345 Park Avenue
New York
NY
10154
US
|
Family ID: |
26615385 |
Appl. No.: |
10/151281 |
Filed: |
May 20, 2002 |
Current U.S.
Class: |
92/70 |
Current CPC
Class: |
F05C 2253/24 20130101;
B23P 15/00 20130101; F05C 2253/12 20130101; F04B 27/086 20130101;
F04B 27/0886 20130101 |
Class at
Publication: |
92/70 |
International
Class: |
F01B 003/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 21, 2001 |
JP |
2001-150406 |
Nov 16, 2001 |
JP |
2001-351106 |
Claims
What is claimed is:
1. A method of producing a shoe for a swash plate type compressor,
said shoe being disposed between a swash plate and a piston of said
swash plate type compressor, the method comprising: a forming step
of forming a steel blank into a shoe product including an end
product shoe and a pre size-adjusted shoe; and a nitriding step of
effecting a nitriding treatment on said shoe product; and wherein a
quenching treatment is not effected after said forming step.
2. A method according to claim 1, wherein any heat-treatment other
than said nitriding treatment is not effected after said forming
step.
3. A method according to claim 1, wherein a size-adjustment
grinding operation is not effected after said nitriding step.
4. A method according to claim 3, wherein said end product shoe is
formed in said forming step and said size-adjustment grinding
operation is not effected after said forming step.
5. A method according to claim 1, wherein said shoe is a
part-spherical crown shoe having a flat portion to be held in
sliding contact with said swash plate and a part-spherical portion
to be held in sliding contact with said piston, said flat portion
being formed to have a slightly convex surface.
6. A method according to claim 1, wherein said steel blank consists
of a high carbon chrome bearing steel.
7. A method according to claim 1, wherein said nitriding treatment
consists of a gas soft nitriding treatment.
8. A shoe for a swash plate type compressor, said shoe being
disposed between a swash plate and a piston of said swash plate
type compressor and produced according to a method as defined in
claim 1.
Description
[0001] This application is based on Japanese Patent Application
Nos. 2001-150406 filed May 21, 2001, and 2001-351106 filed Nov. 16,
2001, the contents of which are incorporated hereinto by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates in general to a shoe which is
used for a swash plate type compressor and which is disposed
between a swash plate and a piston of the swash plate type
compressor. The invention is also concerned with a method of
producing the shoe.
[0004] 2. Discussion of the Related Art
[0005] A swash plate type compressor used as a refrigerant
compressor in an air conditioning system of an automotive vehicle
includes (a) a rotary drive shaft, (b) a swash plate supported by
the drive shaft such that the swash plate is inclined or tiltable
with respect to a plane perpendicular to an axis of rotation of the
drive shaft, (c) a housing which supports the drive shaft such that
the drive shaft is rotatable and axially immovable relative to the
housing, which has a plurality of cylinder bores which are located
at respective circumferential portions radially spaced from the
axis of the drive shaft and which extend in a direction parallel to
the drive shaft, and (d) a plurality of pistons, each of which
includes a head portion slidably engaging a corresponding one of
the cylinder bores and an engaging portion engaging a radially
outer portion of opposite surfaces of the swash plate, each piston
being reciprocated by the swash plate rotated with the rotary drive
shaft. Between the swash plate and each piston, a pair of shoes are
disposed. Each shoe functions as a sliding member to slide on both
of the swash plate and the piston. Since the swash plate is rotated
at a relatively high speed and the piston is reciprocated at a
relatively high speed, it is required that the shoe exhibits a good
sliding characteristic. In other words, the shoe needs to exhibit
various excellent characteristics such as high degrees of wear
resistance and seizure resistance.
[0006] The shoe is preferably formed of a steel material since the
shoe can be produced at a relatively low cost by using the steel
and the shoe formed of the steel (hereinafter referred to as "steel
shoe") exhibits a high degree of strength. To permit the steel shoe
to exhibit high degrees of wear resistance and seizure resistance
described above, the steel shoe is subjected to a thermal refining
treatment such as quenching and tempering, and a surface treatment
such as a nitriding treatment. The thermal refining treatment and
the nitriding treatment, however, require an energy source for
heating the shoe and a relatively long period of time to effect the
treatments on the shoe, undesirably pushing up a cost of
manufacture of the shoe.
SUMMARY OF THE INVENTION
[0007] It is therefore an object of the present invention to
provide a steel shoe which exhibits a good sliding characteristic
and which is economical to manufacture, with a minimum or limited
heat treatment performed on the shoe. It is an optional object of
the invention to provide a method of producing a steel shoe in a
simplified and economical manner. The objects may be achieved
according to any one of the following modes of the present
invention, each of which is numbered like the appended claims and
depends from the other mode or modes, where appropriate, to
indicate and clarify possible combinations of elements or technical
features of the present invention, for easier understanding of the
invention. It is to be understood that the present invention is not
limited to the technical features or any combinations thereof which
will be described for illustrative purpose only. It is to be
further understood that a plurality of elements or features
included in any one of the following modes of the invention are not
necessarily provided all together, and that the invention may be
embodied without some of the elements or features described with
respect to the same mode.
[0008] (1) A method of producing a shoe for a swash plate type
compressor, the shoe being disposed between a swash plate and a
piston of the swash plate type compressor, the method
comprising:
[0009] a forming step of forming a steel blank into a shoe product
including an end product shoe and a pre size-adjusted shoe; and
[0010] a nitriding step of effecting a nitriding treatment on the
shoe product;
[0011] and wherein a quenching treatment is not effected after the
forming step.
[0012] The wear of the shoe influences the durability of the swash
plate type compressor. The nitriding treatment permits the shoe to
have a high degree of hardness in its surface portion, so that the
steel shoe subjected to the nitriding treatment exhibits a good
wear resistance as well as a good corrosion resistance.
Accordingly, the swash plate type compressor equipped with the
steel shoe which has been subjected to the nitriding treatment has
a high degree of durability.
[0013] The wear resistance of the shoe is largely dependent upon
the hardness of its surface portion (hereinafter referred to as
"surface hardness"). Accordingly, the shoe exhibits a sufficiently
high degree of wear resistance when the shoe has a high degree of
surface hardness. The conventionally effected quenching treatment
permits the shoe to exhibit a high degree of hardness in not only
the surface portion but also its inner portion. The hardness of the
shoe in its inner portion, however, does not give a large influence
on the wear resistance of the shoe. Accordingly, even if the
quenching treatment is not performed on the shoe, the shoe exhibits
a good sliding characteristic without suffering from a considerable
decrease in its wear resistance. The quenching treatment causes
transformation of the material of the shoe, so that the shoe
suffers from a large residual stress. The residual stress is
removed from the shoe when the shoe is heated in the subsequent
nitriding treatment. Accordingly, when the nitriding treatment is
performed on the shoe which has been subjected to the quenching
treatment, the shoe undesirably suffers from a strain. Since the
configuration of the shoe influences the sliding characteristic of
the shoe, the shoe needs to be subjected to an additional working
operation such as a grinding operation, for adjusting its size,
when the configuration of the shoe is changed due to the strain. In
this case, the process steps for producing the shoe are inevitably
complicated, and the cost of manufacture of the shoe is undesirably
increased.
[0014] The present method of producing a shoe according to the
above mode (1) permits economical and simple production of the shoe
by eliminating the quenching treatment while permitting the shoe to
exhibit a good sliding characteristic by effecting the nitriding
treatment on the shoe.
[0015] The forming step in the present method according to the
above mode (1) may be effected according to any known method which
will be described in the DETAILED DESCRIPTION OF PREFERRED
EMBODIMENTS. The term "end product shoe" refers to a shoe which can
be installed on the compressor without effecting a grinding
operation to adjust its size while the term "pre size-adjusted
shoe" refers to a shoe which needs to be subjected to the grinding
operation to adjust its size before the shoe is installed on the
compressor. The nitriding treatment will be described.
[0016] (2) A method according to the above mode (1), wherein any
heat-treatment other than the nitriding treatment is not effected
after the forming step.
[0017] In producing the steel shoe, the shoe is conventionally
subjected, after the forming step, to another heat treatment in
addition to the quenching treatment. For instance, the shoe is
subjected to a tempering treatment effected following the quenching
treatment, or a tempering treatment effected following the
nitriding treatment to adjust its hardness. In the present method
according to the above mode (2) wherein the quenching treatment is
not effected after the forming step, it is not necessary to effect
the tempering treatment which is usually effected following the
quenching treatment. Further, the surface hardness of the shoe
which is usually adjusted by the quenching and tempering treatments
can be adjusted by the nitriding treatment if effected under
suitable and optimum conditions. Therefore, the present method
according to the mode (2) wherein the heat treatment is minimized
permits economical and simple production of the steel shoe. In
general, the heat treatment causes a residual stress in the shoe or
a change of the configuration of the shoe, depending upon the
heating conditions such as the heating temperature. In view of
this, the shoe produced by the method according to the mode (2)
wherein the heat treatment effected on the shoe is minimized or
limited assures an improvement in its quality without suffering
from the disadvantages of the heat treatment.
[0018] (3) A method according to the above mode (1) or (2), wherein
a size-adjustment grinding operation is not effected after the
nitriding step.
[0019] When the shoe is subjected to the grinding operation after
the nitriding treatment, the nitrided layer formed on the surface
of the shoe by the nitriding treatment is inevitably removed
therefrom. In view of this, it is necessary to form, on the surface
of the shoe, the nitrided layer having a relatively large thickness
by increasing the time period during which the nitriding treatment
is effected, for instance. The shoe produced according to the
present method wherein the quenching treatment is eliminated is
free from deformation which is experienced in the conventional shoe
due to the nitriding treatment effected following the quenching
treatment. Accordingly, the shoe maintains the desired
configuration after the nitriding treatment. Therefore, the present
method according to the above mode (3) wherein the grinding
operation is not effected on the shoe after the nitriding step is
effective to reduce the required time for the nitriding treatment
and produce the shoe at a relatively low cost.
[0020] (4) A method according to the above mode (3), wherein the
end product shoe is formed in the forming step and the
size-adjustment grinding operation is not effected after the
forming step.
[0021] As described above, the present method wherein the quenching
treatment is eliminated is effective to prevent the deformation of
the shoe. By using a suitable die assembly in a press forging, the
steel blank can be formed into the end product shoe in the forming
step. In this case, it is not necessary to effect the
size-adjustment grinding operation on the shoe after the forming
step. In general, it takes a relatively long period of time to
effect the grinding operation. Accordingly, the present method
according to the above mode (4) wherein the grinding operation is
not effected after the forming step permits economical and simple
production of the steel shoe.
[0022] (5) A method according to any one of the above modes
(1)-(4), wherein the shoe is a part-spherical crown shoe having a
flat portion to be held in sliding contact with the swash plate and
a part-spherical portion to be held in sliding contact with the
piston, the flat portion being formed to have a slightly convex
surface.
[0023] In general, the shoe has a part-spherical crown shape and
slides on the swash plate at its flat portion. Since the swash
plate is rotated at a relatively high speed, the sliding
characteristic of the shoe with respect to the swash plate is
particularly important in the swash plate type compressor. The flat
portion of the shoe is lubricated by a lubricant included in the
refrigerant. The shoe exhibits a sufficiently high degree of
sliding characteristic if the lubricant is effectively introduced
into the central part of the flat portion. To this end, the flat
portion of the shoe desirably has a convex shape in which the
central part is slightly higher than the radially outer portion. As
is clear from the results of the experiment described below, it is
confirmed by the inventors of the present invention that the convex
flat portion was deformed into a concave shape due to the nitriding
treatment effected following the quenching treatment. As described
above, it is desirable that the flat portion of the shoe is formed
to be convex for assuring a sufficiently high sliding
characteristic. Accordingly, the flat portion which has been
deformed into the concave shape needs to be subjected to a grinding
operation in which the radially outer portion of the concave flat
portion is ground to provide the convex flat portion. In this case,
the amount of the stock removal of the radially outer portion of
the concave flat potion by the grinding operation is inevitably
large, resulting in an excessive removal of the nitrided layer
formed on the surface of the shoe. Further, the time period during
which the grinding operation is effected is undesirably increased.
Therefore, the present method according to the mode (5) directed to
the shoe having the convex flat portion effectively enjoys the
advantages of minimizing the heat treatment.
[0024] (6) A method according to any one of the above modes
(1)-(5), wherein the steel blank consists of a high-carbon chrome
bearing steel.
[0025] The material of the steel shoe to which the principle of the
present invention is applied is not particularly limited, but may
be suitably selected from among those having a sufficiently high
degree of strength and permitting the formation of a suitable
nitrided layer on the surface of the shoe by the nitriding
treatment. Since the shoe formed of the high-carbon chrome bearing
steel (SUJ according to the Japanese Industry Standad G 4805)
described in the mode (6) has a high degree of surface hardness
exceeding Hv 500 by a soft nitriding treatment which will be
described, the shoe formed of the high-carbon chrome bearing steel
exhibits an excellent wear resistance. It is desirable that the
high-carbon chrome bearing steel SUJ2 (according to the JIS G 4805)
is employed for forming the shoe, in view of the fact that the shoe
is a relatively small component.
[0026] If the soft nitriding treatment is employed in the nitriding
step, the material of the shoe is selected from among various kinds
of materials. For instance, the shoe can be formed of alloy steels
such as a soft steel, a low-carbon steel, a medium-carbon steel, a
high-carbon steel, a low alloy steel, and a stainless steel, or
ferrous materials such as cast iron. The surface hardness of the
shoe given by the soft nitriding treatment is increased with an
increase in the amount of carbon included in the steel, so that the
shoe to be obtained exhibits an excellent wear resistance. When the
base body of the shoe is formed of the medium carbon steel or the
high carbon steel such as S45C, S50C, S55C according to the JIS G
4051, or the low-carbon and low alloy steel such as SCM 415
according to the JIS G 4105, the shoe has the surface hardness of
not lower than Hv 400 in Vickers hardness, for thereby exhibiting
an excellent wear resistance. Since the medium-carbon steel,
high-carbon steel and low-carbon and low-alloy steel do not include
a large amount of expensive alloy elements and are relatively
inexpensive, the shoe whose base body is formed of those steels is
relatively inexpensive. By changing the kind and the amount of the
alloy elements to be added, individual stainless steels to be
obtained exhibit respective different characteristics (such as a
good heat resistance and a good corrosion resistance). Accordingly,
where the stainless steel is used as the material of the base body
of the shoe, the shoe has the desired characteristics corresponding
to those of the stainless steel.
[0027] (7) A method according to any one of the above modes
(1)-(6), wherein the nitriding treatment consists of a gas soft
nitriding treatment.
[0028] By the nitriding treatment, the nitrided layer as the hard
layer is formed on the surface of the base body of the shoe. The
nitrided layer exhibits excellent wear resistance and corrosion
resistance. The nitriding treatment is generally classified into a
gas nitriding treatment in which the nitrided layer to be formed is
relatively hard and a soft nitriding treatment in which the
nitrided layer to be formed is relatively soft. In the following
description, the gas nitriding treatment is referred to as "a hard
nitriding treatment". In the hard nitriding treatment, the nitrogen
(N) is diffused in an atmosphere of the NH.sub.3 gas to form the
nitride. The soft nitriding treatment includes a gas soft nitriding
method, a salt-bath nitriding method (generally called as a
tufftride method) and an ion nitriding method, for instance. Any of
those nitriding treatments can be employed. Other nitriding
treatments such as carbonitriding and nitrosulphurizing can also be
employed. The nitriding treatment is effected according to a known
manner and under appropriate conditions determined depending upon
the desired characteristics of the shoe to be obtained.
[0029] As described above, the soft nitriding treatment is
advantageous in that the soft nitriding treatment can be effected
on various kinds of materials for forming the shoe in a relatively
short period of time. On the other hand, the hard nitriding
treatment requires an additional step of removing the superficial
or outermost portion of the nitrided layer or heating and softening
that portion since the superficial or outermost portion of the
nitrided layer formed by the hard nitriding treatment has
excessively high hardness. In the light of the above, the soft
nitriding treatment is desirably employed in the present
method.
[0030] As described in the above mode (5), the gas soft nitriding
treatment is preferably employed as the soft nitriding treatment.
In the gas soft nitriding treatment, the nitrogen (N) and the
carbon (C) are diffused in the steel in an atmosphere of a mixed
gas consisting of the RX gas and the NH.sub.3 gas. By effecting the
gas soft nitriding treatment, the shoe exhibits a high degree of
surface hardness of not lower than Hv 500. The gas soft nitriding
treatment does not cause a serious pollution problem, permitting an
improvement in the working environment. Further, the gas soft
nitriding treatment can be effectively performed for
mass-production of the shoes, and is advantageous for the surface
treatment of the shoes.
[0031] (8) A shoe for a swash plate type compressor, the shoe being
disposed between a swash plate and a piston of the swash plate type
compressor and produced according to a method as defined in any one
of the above modes (1)-(7).
[0032] The shoe produced by the method according to any one of the
above modes (1)-(7) is relatively inexpensive while exhibiting high
degrees of seizure resistance and wear resistance as well as an
excellent sliding characteristic.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] 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:
[0034] FIG. 1 is a front elevational view in cross section of a
swash plate type compressor equipped with the shoe to which the
principle of the present invention is applied;
[0035] FIG. 2 is a front elevational view in cross section of the
shoe of FIG. 1;
[0036] FIG. 3 is an elevational view schematically showing a flat
portion of the shoe, wherein the amount of convexity of the flat
portion is exaggerated;
[0037] FIG. 4 is a flow chart showing process steps for producing
the shoe according to one embodiment of the invention;
[0038] FIG. 5 is a flow chart showing details of a forming step S1
in the flow chart of FIG. 3;
[0039] FIG. 6 is a flow chart showing details of a nitriding step
S4 in the flow chart of FIG. 3;
[0040] FIG. 7A shows a principal part of a flow chart of process
steps for producing the shoe according to another embodiment of the
invention;
[0041] FIG. 7B shows a principal part of a flow chart of process
steps for producing the shoe according to still another embodiment;
and
[0042] FIG. 8 is an elevational view schematically showing a
deformed flat portion of a shoe which has been subjected to the
nitriding treatment after the quenching treatment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0043] Referring to the accompanying drawings, there will be
described presently preferred embodiments of this invention as
applied to a shoe installed on a swash plate type compressor used
for an air conditioning system of an automotive vehicle. In the
following description, the structure of the swash plate type
compressor, the configuration and structure of the shoe, and the
method of producing the shoe are explained in this order.
[0044] Referring first to FIG. 1, there is shown a compressor of
swash plate type on which the shoe produced according to the
present invention is installed. In FIG. 1, reference numeral 10
denotes a cylinder block having a plurality of cylinder bores 12
formed so as to extend in its axial direction such that the
cylinder bores 12 are arranged along a circle whose center lies on
a centerline of the cylinder block 10. Single-headed pistons
generally indicated at 14 (hereinafter simply referred to as
"piston 14") are reciprocably received in the respective cylinder
bores 12. To one of the axially opposite end faces of the cylinder
block 10, (the left end face as seen in FIG. 1, which will be
referred to as "front end face"), there is attached a front housing
16. To the other end face (the right end face as seen in FIG. 1,
which will be referred to as "rear end face"), there is attached a
rear housing 18 through a valve plate 20. The front housing 16,
rear housing 18 and cylinder block 10 cooperate to constitute a
housing assembly of the swash plate type compressor. The rear
housing 18 and the valve plate 20 cooperate to define a suction
chamber 22 and a discharge chamber 24, which are connected to a
refrigerating circuit (not shown) through an inlet 26 and an outlet
28, respectively. The valve plate 20 has suction ports 32, suction
valves 34, discharge ports 36 and discharge valves 38.
[0045] A rotary drive shaft 50 is disposed in the cylinder block 10
and the front housing 16 such that the axis of rotation of the
drive shaft 50 is aligned with the centerline of the cylinder block
10. The drive shaft 50 is supported at its opposite end portions by
the front housing 16 and the cylinder block 10, respectively, via
respective bearings. The cylinder block 10 has a central bearing
hole 56 formed in a central portion thereof, and the bearing is
disposed in this central bearing hole 56, for supporting the drive
shaft 50 at its rear end portion. The front end portion of the
drive shaft 50 is connected, through a clutch mechanism such as an
electromagnetic clutch, to an external drive source (not shown) in
the form of an engine of an automotive vehicle. In operation of the
compressor, the drive shaft 50 is connected through the clutch
mechanism to the vehicle engine in operation so that the drive
shaft 50 is rotated about its axis.
[0046] The rotary drive shaft 50 carries a swash plate 60 such that
the swash plate 60 is axially movable and tiltable relative to the
drive shaft 50. The swash plate 60 has a central hole 61 through
which the drive shaft 50 extends. The inner dimension of the
central hole 61 as measured in a vertical direction of FIG. 1
gradually increases in a direction from the axially intermediate
portion toward each of the axially opposite ends, and the
transverse cross sectional shape of the central hole 61 at each of
the axially opposite ends is elongated. To the drive shaft 50,
there is fixed a rotary member 62 as a torque transmitting member,
which is held in engagement with the front housing 16 through a
thrust bearing 64. The swash plate 60 is rotated with the drive
shaft 50 by a hinge mechanism 66 during rotation of the drive shaft
50. The hinge mechanism 66 guides the swash plate 60 for its axial
and tilting motions. The hinge mechanism 66 includes a pair of
support arms 67 fixed to the rotary member 62, guide pins 69 which
are formed on the swash plate 60 and which slidably engage guide
holes 68 formed in the support arms 67, the central hole 61 of the
swash plate 60, and the outer circumferential surface of the drive
shaft 50.
[0047] The piston 14 indicated above includes an engaging portion
70 engaging the radially outer portion of the opposite surfaces of
the swash plate 60, and a head portion 72 formed integrally with
the engaging portion 70 and fitted in the corresponding cylinder
bore 12. The head portion 72 in the present embodiment is made
hollow, for thereby reducing the weight of the piston 14. The head
portion 72, cylinder bore 12, and valve plate 20 cooperate with one
another to define a pressurizing chamber. The engaging portion 70
engages the radially outer portion of the opposite surfaces of the
swash plate 60 through a pair of part-spherical-crown shoes 76. The
shoes 76 will be described in greater detail.
[0048] 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 of the cylinder bore 12 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 is pressurized by the piston 14 when the
piston 14 is moved from its lower dead point to its upper dead
point, that is, when the piston 14 is in the compression stroke.
The pressurized refrigerant gas in the pressurizing chamber 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. This compression
reaction force is received by the front housing 16 through the
piston 14, swash plate 60, rotary member 62 and thrust bearing
64.
[0049] 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. The amount of electric current applied
to the solenoid coil 92 is controlled depending upon the air
conditioner load by a control device not shown constituted
principally by a computer.
[0050] The rotary drive shaft 50 has a bleeding passage 100 formed
therethrough. The bleeding passage 100 is open at one of its
opposite ends to the central bearing hole 56, and is open at the
other end to the crank chamber 86. The central bearing hole 56
communicates at its bottom with the suction chamber 22 through a
communication port 104.
[0051] The present swash plate type compressor is of variable
capacity type. By controlling the pressure in the crank chamber 86
by utilizing a difference between the pressure in the discharge
chamber 24 as a high-pressure source and the pressure in the
suction chamber 22 as a low pressure source, a difference between
the pressure in the pressurizing chamber and the pressure in the
crank chamber 86 is regulated to change the angle of inclination of
the swash plate 60 with respect to a plane perpendicular to the
axis of rotation of the drive shaft 50, for thereby changing the
reciprocating stroke (suction and compression strokes) of the
piston 14, whereby the displacement capacity of the compressor can
be adjusted. Described in detail, by energization and
de-energization of the solenoid coil 92 of the solenoid-operated
control valve 90, the crank chamber 86 is selectively connected to
and disconnected from the discharge chamber 24, so that the
pressure in the crank chamber 86 is controlled.
[0052] 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. Other
materials may be used for the cylinder block 10, the piston 14, and
the coating film.
[0053] The end portion of the engaging portion 70 of the piston 14,
which is remote from the head portion 72, has a U-shape in cross
section. Described in detail, the engaging portion 70 has a base
section 124 which defines the bottom of the U-shape, and a pair of
substantially parallel arm sections 120, 122 which extend from the
base section 124 in a direction perpendicular to the axis of the
piston 14. The two opposed lateral walls of the U-shape of the
engaging portion 70 have respective recesses 128 which are opposed
to each other. Each of these recesses 128 is defined by a
part-spherical inner surface of the lateral wall. The
part-spherical inner surfaces of the recesses 128 are located on
the same spherical surface.
[0054] The base body of the swash plate 60 which engages the shoes
76 is formed of spheroidal graphite cast iron, generally called as
ductile cast iron such as FCD 700 or FCD 600 according to the JIS G
5502. The swash plate 60 includes sliding surfaces 132, 134 which
are to be held in sliding contact with the shoes 76. At each
portion of the base body of the swash plate 60 providing each of
the sliding surfaces 132, 134, an aluminum sprayed film and a
lubricating film are formed in this order. The lubricating film is
formed of a synthetic resin in which MoS.sub.2 and graphite are
dispersed. The lubricating film is effective to improve the sliding
characteristic of the swash plate 60 and the shoe 76 by reducing
the friction between the sliding surfaces of the swash plate 60 and
the shoe 76. The aluminum sprayed film is effective to maintain a
good sliding characteristic while preventing a direct contact of
the base body of the swash plate 60 with the shoe 76 even when the
lubricating film is removed or separated due to wear, for
instance.
[0055] As shown in FIG. 2, each of the pair of shoes 76 has a
part-spherical crown shape, and includes a part-spherical portion
136 having a generally convex part-spherical surface and a flat
portion 138 having a generally flat surface. Strictly speaking, the
flat portion 138 is slightly convex and has a recess 140 formed at
its central portion for accommodating a lubricant oil as the
lubricant to assure a good sliding characteristic of the shoe 76
with respect to the swash plate 60. Accordingly, the flat portion
138 provides an annular sliding surface which is to be held in
sliding contact with the swash plate 60. Between the part-spherical
portion 136 and the flat portion 138, there is formed a rounded
edge 142 having a relatively small radius of curvature. The convex
flat portion 138 and the rounded edge 142 are effective to
introduce the lubricant oil between the sliding surfaces 132, 134
of the swash plate 60 and the flat portion 138 of each of the pair
of shoes 76 while preventing foreign matters from entering between
the sliding surfaces 132, 134 of the swash plate 60 and the flat
portion 138 of each of the pair of shoes 76, when the shoes 76
slidably engage the swash plate 60. The pair of shoes 76 slidably
engage the part-spherical inner surfaces of the recesses 128 of the
piston 14 at their part-spherical portions 136 and slidably engage
the radially outer portion of the opposite surfaces of the swash
plate 60, i.e., the sliding surfaces 132, 134, at their flat
portions 138. In other words, the pair of shoes 76 slide on the
swash plate 60 and the piston 14 at their flat portions 138 and
part-spherical portions 136, respectively. The pair of shoes 76 are
designed such that the convex part-spherical surfaces of the
part-spherical portions 136 are located on the same spherical
surface. In other words, each shoe 76 has a part-spherical crown
shape whose size is smaller than a hemi-sphere by an amount
corresponding to a half of the thickness of the swash plate 60. The
shape of the shoe is not limited to that described above. For
instance, the shoe used for a compressor of fixed capacity type has
a size slightly larger than the hemi-sphere for preventing a
reduction in the sliding surface area even when the flat portion of
the shoe is worn.
[0056] As described above, the amount of convexity (hereinafter
referred to as "convexity amount") of the flat portion 138 and the
presence of the rounded edge 142 influence the sliding
characteristic of the shoe 76. FIG. 3 schematically shows the flat
portion 138 of the shoe 76, wherein the convexity amount "h" of the
flat portion 138 is exaggerated. The convexity amount "h" of the
flat portion 138 is preferably held in a range of not smaller than
1 .mu.m and not larger than 10 .mu.m. If the convexity amount of
the flat portion 138 is held within the specified range, the
lubricant oil can be effectively introduced between the sliding
surfaces of the swash plate 60 and the shoe 76 while preventing the
foreign matters entering therebetween, so that the shoe 76 exhibits
a good sliding characteristic. The convex flat portion 138 is
deformed into a concave shape when the nitriding treatment is
effected following the quenching treatment, as described in the
following Experiment. Where the radius of curvature of the rounded
edge 142 is smaller than needed, the shoes may be dented due to
collision of the shoes with one another during the barrel polishing
operation, for instance. In view of this, the radius of curvature
of the rounded edge 142 is suitably determined.
[0057] The shoe 76 is a steel shoe which has been subjected to the
nitriding treatment. In the present embodiment, the base body 146
of the shoe 76 is formed of a high-carbon chrome bearing steel
(SUJ2 according to the JIS G 4805), and the entire surface of the
shoe 76 (the entire surface of the base body 146) is covered with a
nitrided layer 152 as a hard layer, which nitrided layer 152 is
formed by the soft nitriding treatment, i.e., gas soft nitriding
treatment. In FIG. 2, the thickness of the nitrided layer 152 is
exaggerated for easier understanding. Described in detail, the
nitrided layer 152 includes a compound layer having a high degree
of hardness and functioning as a superficial or outermost layer,
and a diffusion layer wherein the nitrogen is diffused such that
the concentration of the nitrogen decreases in a direction away
from the compound layer toward the inner portion of the shoe.
Although the boundary between the compound layer and the diffusion
layer is not clear, the compound layer preferably has a thickness
of about 5-20 .mu.m. The material of the base body 146 of the shoe
76 is not limited to the above-described SUJ2. Further, the
nitriding treatment and the thickness of the compound layer are not
limited to those described above, but may be modified as described
in the
SUMMARY OF THE INVENTION
[0058] There will be next explained a method of producing the shoe
76 according to a first embodiment of the present invention by
referring to the flow chart of FIG. 4. The method according to the
first embodiment comprises: a forming step of forming a shoe; a
grinding step of grinding the formed shoe; a buff polishing step of
effecting a buff polishing operation on the shoe; a nitriding step
of effecting a nitriding treatment; a barrel polishing step of
effecting a barrel polishing operation on the shoe so as to polish
the surface of the shoe which has been subjected to the nitriding
step; and a surface cleaning step of cleaning the surface of the
shoe. In the present method, any heat treatment (e.g., quenching
treatment) other than the nitriding treatment is not effected on
the shoe.
[0059] In the forming step S1, a steel blank, i.e., a wire rod of
SUJ2 (JIS G 4805) in the present embodiment, is formed into a pre
size-adjusted shoe. The forming step S1 includes a plurality of
sub-steps as indicated in the flow chart of FIG. 5, namely, a
cutting step S11, a blank forging step S12, a flushing step S13, a
steel ball grinding step S14, an annealing step S15, a first
forging step S16, and a second forging step S17. Described in
detail, in the cutting step S11, a bar-shaped steel blank of SUJ2
is cut into a plurality of pieces, each of which has a
predetermined length. The length of the cut piece of the steel
blank is determined such that the volume of the cut piece is
slightly larger than that of a steel ball blank which will be
forged into the shoe product in the first and second forging steps
S16 and S17 described below. The bar-shaped blank is cut by a
sawing machine or a shearing machine. The cutting step S11 is
followed by the blank forging step S12 wherein the cut piece is
subjected to close-die forging in a cold condition, so that the cut
piece has a steel ball shape. The die assembly used in the blank
forging step S12 is designed such that an excess material forms
burrs or flashes, so that the steel ball to be obtained has a
substantially constant volume. In the next flushing step S13, the
burrs or flashes are removed from the steel ball, so as to provide
the steel ball having the substantially constant volume. The
flushing step S13 is effected, for instance, first by sandwiching
the steel ball with the burrs or flashes, between two grooved cast
iron discs, and then rotating the two discs relative to each other
under the pressure. The flushing step S13 is followed by the steel
ball grinding step S14 wherein the steel ball from which the burrs
or flashes have been removed is subjected to a grinding operation.
The grinding operation is performed on the steel ball for improving
the dimensional accuracy and the surface roughness of the steel
ball by using cast iron discs or a grinding stone, for instance. In
the next annealing step S15, the steel ball is subjected to an
annealing operation for the purpose of facilitating the forging
operations subsequently performed on the steel ball. The steel ball
is annealed to lower its hardness, in a vacuum furnace under
appropriate annealing conditions including the heating temperature
and the cooling rate.
[0060] The steel ball which has been subjected to the annealing
step S15 is forged into the shoe product in the first and second
forging steps S16 and S17. In the first forging step S16, the steel
ball blank is forged into an intermediate shoe, and the
intermediate shoe is forged into a pre size-adjusted shoe in the
second forging step S17. Each of the forging operations in these
steps S16 and S17 is a cold press forging using a die assembly. In
the present embodiment, the steel ball blank is subjected to the
two forging steps. Where the forging ratio is relatively low, the
steel ball blank may be subjected to a single forging step. On the
other hand, the steel ball blank may be subjected to three or more
forging steps where the forging ratio is relatively high or the
steel ball blank needs to be forged with a considerably high degree
of accuracy. Between successive two forging steps, an annealing
treatment may be effected.
[0061] The forming step S1 is followed by the surface grinding step
S2 wherein the pre size-adjusted shoe obtained in the forming step
S1 is subjected at its flat portion to a grinding operation. Since
the height of the shoe gives a great influence on its sliding
characteristic, the shoe is required to have the intended height
with high accuracy. The surface grinding operation in the surface
grinding step S2 is performed mainly for adjusting the height of
the shoe. In the present embodiment, the surface grinding operation
in the surface grinding step S2 corresponds to a size-adjustment
grinding operation. The surface grinding operation performed by a
surface grinding machine using free abrasive grains, for instance.
The pre-size adjusted shoe is formed into an end product shoe by
the surface grinding operation. In the next buff polishing step S3
as a finishing step, the flat portion of the shoe is polished, the
convexity amount of the flat portion and the radius of curvature of
the rounded edge are adjusted to respective intended values. The
buff polishing operation is performed by a buff polishing machine
using the free abrasive grains, for instance.
[0062] The buff polishing step S3 is followed by the nitriding step
S4 wherein the buff-polished shoe is subjected to the nitriding
treatment. In the present embodiment, the nitriding treatment is
effected according to the gas soft nitriding method. The nitriding
step S4 includes a plurality of sub-steps as indicated in the flow
chart of FIG. 6, namely, a degreasing step S41, a preliminary
oxidizing step S42, a nitriding treatment step S43 as a main
sub-step of the nitriding step S4, and a post-cleaning step S44.
Described in detail, in the degreasing step S41, the oil component
which have adhered to the shoe is removed. In the next preliminary
oxidizing step S42, the aqueous component included in the shoe is
removed. In this regard, the preliminary oxidizing step may be
referred to as a dehydrating step. Owing to those two preliminary
treatments, the substances such as a coolant and an inhibitor
adhering to the surface of the shoe are removed, so that the
flatness of the surface of the nitrided layer is improved. The
preliminary oxidizing step S42 is followed by the nitriding
treatment step S43 wherein the shoe is subjected to the gas soft
nitriding treatment. The conditions under which the gas soft
nitriding treatment is effected are suitably determined depending
upon the kind of the material of the base body of the shoe, the
thickness of the nitrided layer to be formed, etc. In the present
embodiment, the shoe is subjected to the gas soft nitriding
treatment at about 560-580.degree. C. for a time period ranging
from one hour to three hours. By the gas soft nitriding treatment,
the nitrided layer, strictly speaking, the compound layer, having
the thickness of about 10-20 .mu.m is formed on the surface of the
shoe. The thus formed nitrided layer has a hardness of about Hv
600-1000. In the next post-cleaning step S44, the oil component on
the surface of the shoe is removed.
[0063] The shoe which has been subjected to the nitriding step S4
described above is subsequently subjected to a barrel polishing
operation in the barrel polishing step S5. The barrel polishing
operation is performed for smoothing the surface of the shoe. In
the next surface cleaning step S6, the surface of the shoe is
cleaned, for thereby providing the shoe to be installed on the
compressor.
[0064] In the method described above, any heat treatment (e.g., the
quenching treatment) other than the nitriding treatment is not
effected after the forming step. The present method permits speedy
and simplified manufacture of the shoe. In the present method
wherein the quenching treatment is not effected, the shoe is free
from the deformation which is conventionally experienced due to the
nitriding treatment effected following the quenching treatment, so
that the size-adjustment grinding operation is not necessarily
effected after the nitriding treatment. Accordingly, the nitrided
layer formed by the nitriding treatment and having a sufficient
thickness can be left without being removed by the grinding
operation.
[0065] Referring next to FIGS. 7A and 7B, there will be explained
modifications of the method of producing a shoe according to a
second and a third embodiment, respectively. In the methods
according to the second and third embodiments, the surface grinding
step S2 is eliminated, and the end product shoe is obtained in the
forming step S1. Namely, the shoe having the intended height with
high accuracy is formed in the forming step S1, and the surface
grinding step S2 performed mainly to adjust the height of the shoe
is eliminated. In the method according to the flow chart of FIG. 7A
of the second embodiment, the die assembly used in the second
forging step S17 is designed such that the shoe to be obtained has
the intended height and such that the rounded edge 142 has the
intended radius of curvature, so that the end product shoe is
formed in the forming step S1. The end product shoe obtained in the
forming step S1 is subsequently subjected to the buff polishing
step S3 without effecting the surface grinding step S2, so that the
convexity amount of the flat portion of the shoe is adjusted by the
buff polishing operation. The method according to the flow chart of
FIG. 7A of the second embodiment permits simple and speedy
manufacture of the shoe. Referring next to the flow chart of FIG.
7B, there is shown a method of producing a shoe according to the
third embodiment of the present invention. In the method according
to the flow chart of FIG. 7B, the forming step S1 includes an
additional forging step, i.e., a finish forging step S18 effected
following the second forging step S17. In the finishing forging
step S18, the pre size-adjusted shoe obtained in the second forging
step S17 is formed into the end product shoe. The end product shoe
obtained in the finish forging step S18 is then subjected to the
buff polishing step S3 without effecting the surface grinding step
S2. The method of producing a shoe is not limited to the details of
the illustrated embodiments, but may be modified depending upon the
configuration of the shoe to be obtained.
[0066] While the presently preferred embodiments of this invention
have been described above, for illustrative purpose only, it is to
be understood that the present invention is not limited to the
details of the illustrated embodiments. For example, the principle
of the invention is applicable to a shoe used for a swash plate
type compressor equipped with a double-headed piston having head
portions on the opposite sides of the engaging portion, or a shoe
used for a swash plate type compressor of fixed capacity type. 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.
[0067] <Experiment for Confirming the Effect of Eliminating the
Quenching Treatment>
[0068] Between the buff polishing step and the nitriding step in
the method according to the present invention, a vacuum hardening
or quenching treatment was performed on five specimen shoes as
comparative examples, so that the shoes were inspected for
deformation of their flat portions. Another five specimens shoes
were subjected to the nitriding treatment without effecting the
quenching treatment, as in the above-described embodiments of the
present invention. The shoes were also inspected for deformation of
their flat portions. As described below, it is confirmed that the
method without effecting the quenching treatment is superior to the
method wherein the quenching treatment is effected prior to the
nitriding treatment.
[0069] Each of the shoes is formed of the above-indicated SUJ2. The
vacuum hardening treatment was effected such that each of the five
specimen shoes as the comparative examples was kept at
500-750.degree. C. for 45-60 minutes, and subsequently at
800-840.degree. C. for 60-90 minutes, and then rapidly cooled. The
five specimen shoes which have been subjected to the vacuum
hardening treatment described above were then subjected to the buff
polishing operation, so that the convexity amount h of the flat
portions of the shoes was held in a range of 1-2 .mu.m. The gas
soft nitriding treatment was performed on those shoes. After the
gas soft nitriding treatment, the average convexity amount of the
five comparative shoes was about -21 .mu.m, that is, the average
amount of concavity was about 2 .mu.m. In other words, the central
part of the flat portion of each shoe was recessed by an average
amount of about 4 .mu.m, that is, the flat portion became concave,
as shown in FIG. 8, after the gas soft nitriding treatment.
[0070] Another five specimen shoes whose convexity amount of the
flat portions had been adjusted by the buff polishing operation in
a range of 1-2 .mu.m were subjected to the nitriding treatment
without effecting the quenching treatment. The flat portion of each
shoe maintained the convex shape. The average convexity amount of
the five shoes was about 1.6 .mu.m. In other words, the flat
portion of each shoe was raised at the central part by an average
amount of about 0.2 .mu.m. Accordingly, in the shoes which have
been subjected to the nitriding treatment without the quenching
treatment, the flat portions were raised at the central parts, or
the flat portions maintained the convexity amount prior to the
nitriding treatment.
[0071] It is confirmed from the results described above that the
shoe is not deformed if it is not subjected to the quenching
treatment prior to the nitriding treatment. When the flat portion
which has deformed into the concave shape due to the nitriding
treatment effected following the quenching treatment is formed into
the convex shape, the grinding or polishing operation needs to be
performed on the radially outer portion of the flat portion of the
shoe wherein the required amount of stock removal by the grinding
or polishing operation is inevitably large. Further, it takes a
relatively long period of time to effect the grinding or polishing
operation on the shoe. The grinding or polishing operation on the
radially outer portion of the flat portion of the shoe inevitably
removes a considerably large amount of the nitrided layer formed at
that portion, resulting in a deterioration of the properties of the
shoe such as the wear resistance. To avoid this, it is necessary to
form the nitrided layer having a considerably large thickness by
increasing the time during which the nitriding treatment is
effected. In this case, the total time required for producing the
shoe (including the grinding or polishing operation and the
nitriding treatment) is undesirably increased, deteriorating the
production efficiency of the shoe. In contrast, the present method
wherein the quenching treatment is not effected prior to the
nitriding treatment permits simple and speedy manufacture of the
shoe having a good sliding characteristic.
* * * * *