U.S. patent application number 10/151446 was filed with the patent office on 2003-01-09 for swash plate type compressor.
Invention is credited to Hiramatsu, Osamu, Inoue, Yoshinori, Kurakake, Hirotaka, Narukawa, Kiyoshi, Ota, Masaki, Tarutani, Tomoji.
Application Number | 20030005821 10/151446 |
Document ID | / |
Family ID | 26615386 |
Filed Date | 2003-01-09 |
United States Patent
Application |
20030005821 |
Kind Code |
A1 |
Ota, Masaki ; et
al. |
January 9, 2003 |
Swash plate type compressor
Abstract
A swash plate type compressor including; a rotary drive shaft
having an axis of rotation; a swash plate supported by the drive
shaft such that the swash plate is inclined or tiltable with
respect to a plane perpendicular to the axis of rotation of the
shaft; 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 rotation of the drive shaft and which extend in a direction
parallel to the drive shaft; a plurality of pistons each including
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 drive shaft; and a
plurality of shoes each of which is disposed between one of the
opposite surfaces of the swash plate and the engaging portion of
each piston for sliding on both of the swash plate and each piston;
and wherein the swash plate is formed of a ferrous material and has
lubricating films formed on sliding surfaces thereof which slide on
the shoes; and wherein each of at least one of the plurality of
shoes is a nitrided shoe which is formed of a ferrous material and
which has been subjected to a soft nitriding treatment on at least
a sliding surface thereof which slides on the swash plate.
Inventors: |
Ota, Masaki; (Kariya-shi,
JP) ; Tarutani, Tomoji; (Kariya-shi, JP) ;
Kurakake, Hirotaka; (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: |
26615386 |
Appl. No.: |
10/151446 |
Filed: |
May 20, 2002 |
Current U.S.
Class: |
92/70 |
Current CPC
Class: |
B23P 15/00 20130101;
F04B 27/086 20130101; F04B 27/1054 20130101; F05C 2203/086
20130101; F05C 2203/083 20130101; F05C 2253/12 20130101; F04B
27/0886 20130101; F05C 2253/24 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 |
2001-351107 |
Claims
What is claimed is:
1. A swash plate type compressor including; a rotary drive shaft
having an axis of rotation; a swash plate supported by said rotary
drive shaft such that said swash plate is inclined or tiltable with
respect to a plane perpendicular to said axis of rotation of said
rotary drive shaft; a housing which supports said rotary drive
shaft such that said rotary drive shaft is rotatable and axially
immovable relative to said housing, which has a plurality of
cylinder bores which are located at respective circumferential
portions radially spaced from said axis of rotation of said rotary
drive shaft and which extend in a direction parallel to said rotary
drive shaft; a plurality of pistons each including a head portion
slidably engaging a corresponding one of said cylinder bores, and
an engaging portion engaging a radially outer portion of opposite
surfaces of said swash plate, each piston being reciprocated by
said swash plate rotated with said rotary drive shaft; and a
plurality of shoes each of which is disposed between one of said
opposite surfaces of said swash plate and said engaging portion of
said each piston for sliding on both of said swash plate and said
each piston; and wherein said swash plate is formed of a ferrous
material and has lubricating films formed on sliding surfaces
thereof which slide on said plurality of shoes; and wherein each of
at least one of said plurality of shoes is a nitrided shoe which is
formed of a ferrous material and which has been subjected to a soft
nitriding treatment on at least a sliding surface thereof which
slides on said swash plate.
2. A swash plate type compressor according to claim 1, wherein all
of said plurality of shoes are the nitrided shoes.
3. A swash plate type compressor according to claim 1, wherein each
of said plurality of pistons is a single-headed piston, and said
plurality of shoes engaging said engaging portion of said
single-headed piston consist of a pair of shoes which are
respectively disposed between said opposite surfaces of said swash
plate and said engaging portion of said single-headed piston, and
wherein at least the shoe which slides on one of said opposite
surfaces of said swash plate on the side of said head portion of
said single-headed piston is said nitrided shoe.
4. A swash plate type compressor according to claim 1, wherein said
nitrided shoe is formed of a medium-carbon steel or a high-carbon
steel.
5. A swash plate type compressor according to claim 1, wherein said
nitrided shoe is formed of a high-carbon chrome bearing steel.
6. A swash plate type compressor according to claim 1, wherein said
nitrided shoe is formed of a stainless steel.
7. A swash plate type compressor according to claim 1, wherein said
soft nitriding treatment is effected according to a salt bath
method.
8. A swash plate type compressor according to claim 1, wherein said
nitrided shoe has a compound layer formed on a surface thereof by
said soft nitriding treatment and having a thickness value in a
range of not smaller than 5 .mu.m and not larger than 20 .mu.m.
9. A swash plate type compressor according to claim 1, wherein said
nitrided shoe is formed by a forging operation, said soft nitriding
treatment being effected after said forging operation.
10. A swash plate type compressor according to claim 1, wherein
said swash plate is formed of a spheroidal graphite cast iron.
11. A swash plate type compressor according to claim 1, wherein
said lubricating films comprise a solid lubricant and a synthetic
resin as a binder.
12. A swash plate type compressor according to claim 11, wherein
said solid lubricant includes at least one of molybdenum disulfide
(MoS.sub.2), boron nitride (BN), tungsten disulfide (WS.sub.2),
grahite, and polytetrafluoroethylene (PTFE).
13. A swash plate type compressor according to claim 11, wherein
said synthetic resin includes at least one of polyamidimide, epoxy
resin, polyether ketone, and phenol resin.
14. A swash plate type compressor according to claim 1, wherein
said swash plate includes, on at least said sliding surfaces
thereof which slides on said shoes, metal sprayed films formed of a
material selected from the group consisting of aluminum, copper, an
aluminum alloy, and a copper alloy, each of said lubricating films
being formed on each of said metal sprayed films.
15. A swash plate type compressor according to claim 1, wherein
said swash plate is subjected to a quenching treatment on at least
said sliding surfaces thereof which slide on said shoes.
16. A swash plate type compressor according to claim 1, further
including a swash plate inclination angle changing device for
changing an inclination angle of said swash plate.
Description
[0001] This application is based on Japanese Patent Application
Nos. 2001-150406 filed May 21, 2001, and 2001-351107 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 swash plate
type compressor. In particular, the present invention is concerned
with an improvement of a sliding characteristic of a swash plate
and pistons in the compressor.
[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, (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, and (e) a plurality of shoes each of which is disposed
between one of the opposite surfaces of the swash plate and the
engaging portion of each piston, for sliding on both of the swash
plate and the piston. Since the swash plate is rotated at a
relatively high speed, the compressor is required to exhibit a good
sliding characteristic of the shoes and the swash plate. In other
words, the compressor needs to exhibit various excellent
characteristics such as a high degree of lubrication characteristic
for smooth sliding contact of the shoes and the swash plate, high
degrees of resistance to wear and resistance to seizure of the
shoes and the swash plate.
[0006] In general, the swash plate and the shoes used for the swash
plate type compressor are formed of respective suitable ferrous
materials since the swash plate and the shoes can be economically
produced by using the ferrous materials and the swash plate and the
shoes formed of the ferrous materials exhibit relatively high
degrees of strength, hardness, and wear resistance. For assuring a
sufficiently high degree of lubrication characteristic between the
swash plate and the shoes formed of the ferrous materials
(hereinafter respectively referred to as "ferrous swash plate" and
"ferrous shoes"), various techniques are proposed. For instance,
the sliding surfaces of the ferrous swash plate, on which the shoes
slide, are coated with lubricating films. The lubricating films
formed on the sliding surfaces of the ferrous swash plate, however,
have a strength lower than those of the ferrous materials which
provide respective base bodies of the swash plate and the shoes.
Accordingly, local portions of the lubricating films may be
separated or removed from the sliding surfaces of the swash plate
due to wear, for instance, which is caused by the sliding contact
with the shoes over a long period of time. If the local portions of
the lubricating films are separated from the sliding surfaces of
the swash plate, the ferrous materials of the swash plate and the
shoes directly contact with each other, causing seizure
therebetween, for instance. The sliding characteristic between the
swash plate and the shoes in the compressor is undesirably
deteriorated by the seizure.
SUMMARY OF THE INVENTION
[0007] It is therefore an object of the present invention to
provide a swash plate type compressor which exhibits a good sliding
characteristic of its swash plate and shoes by improving the
seizure resistance of the swash plate and the shoes, for instance.
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 swash plate type compressor including;
[0009] a rotary drive shaft having an axis of rotation;
[0010] a swash plate supported by the rotary drive shaft such that
the swash plate is inclined or tiltable with respect to a plane
perpendicular to the axis of rotation of the rotary drive
shaft;
[0011] a housing which supports the rotary drive shaft such that
the rotary 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 rotation of the rotary drive shaft and which extend in
a direction parallel to the rotary drive shaft;
[0012] a plurality of pistons each including 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; and
[0013] a plurality of shoes each of which is disposed between one
of the opposite surfaces of the swash plate and the engaging
portion of each piston,;
[0014] and wherein the swash plate is formed of a ferrous material
and has lubricating films formed on sliding surfaces thereof which
slide on the plurality of shoes;
[0015] and wherein each of at least one of the plurality of shoes
is a nitrided shoe which is formed of a ferrous material and which
has been subjected to a soft nitriding treatment on at least a
sliding surface thereof which slides on the swash plate.
[0016] The nitriding treatment permits a hard layer to be formed on
the surface of the above-indicated at least one of the plurality of
shoes. The hard layer formed by the nitriding treatment exhibits
high degrees of wear resistance and corrosion resistance. The
nitriding treatment is classified into a gas nitriding treatment in
which the nitrogen (N) is diffused in the atmosphere of the
NH.sub.3 gas so as to form a nitride, and a soft nitriding
treatment including a salt-bath nitriding method which will be
described. The gas nitriding treatment is effected mainly on steels
for nitriding for a relatively long period of time, whereas the
soft nitriding treatment can be effected on various ferrous
materials in a relatively short period of time. Accordingly, the
soft nitriding treatment is advantageous as the surface treatment
of the ferrous shoe. By the soft nitriding treatment, the shoe
having high degrees of wear resistance and corrosion resistance can
be economically obtained. The soft nitriding treatment permits the
desired article to have a relatively high degree of hardness
without effecting a quenching treatment. Accordingly, the shoe
which has been subjected to the soft nitriding treatment without
the quenching treatment does not suffer from a change of its
configuration, assuring a high degree of dimensional accuracy.
[0017] In the swash plate type compressor according to the mode
(1), the swash plate is formed of a ferrous material. The ferrous
swash plate is relatively inexpensive. In addition, the ferrous
swash plate can be rotated with high stability. In the swash plate
type compressor of a variable capacity type which will be
described, for instance, the displacement capacity of the
compressor is adjusted or changed by changing an angle of the swash
plate with respect to a plane perpendicular to the rotation axis of
the rotary drive shaft, namely by changing an angle of inclination
of the swash plate with respect to the above-indicated plane. (The
angle is hereinafter referred to as an "inclination angle" of the
swash plate.) While the compressor is operated so as to maintain a
predetermined constant displacement capacity, the swash plate is
desirably rotated while being kept at a predetermined inclination
angle. If the swash plate has a relatively large mass, the inertial
force permits the swash plate to be rotated with high stability
while being kept at the predetermined inclination angle.
Accordingly, the swash plate type compressor equipped with the
ferrous swash plate exhibits a high degree of operating stability
since the ferrous swash plate can be rotated with high
stability.
[0018] The lubricating films formed on the sliding surfaces of the
swash plate assure good lubrication between the swash plate and the
shoes, so that the compressor exhibits a good sliding
characteristic. As described above, the strength of the lubricating
films is lower than those of the ferrous materials which provide
the respective base bodies of the swash plate and the shoes.
Accordingly, the lubricating films may be worn in a long time
operation of the compressor. Further, the lubricating films may be
damaged due to various foreign matters such as those adhering to
the components of the compressor in the manufacturing process,
those generated by the sliding contact of the components during the
operation of the compressor, and those introduced into the
compressor from the refrigerant piping. The foreign matters may
enter between the sliding surfaces of the swash plate and the
shoes, so that the lubricating films may be damaged due to the
foreign matters, and accordingly removed from the sliding surfaces
of the swash plate. If the lubricating films are locally removed
from the sliding surfaces of the swash plate due to the wear and
damage described above, the base body of the swash plate directly
contacts the base bodies of the shoes at local portions of the
swash plate from which the lubricating films have been removed.
When both of the shoes and the swash plate are formed of suitable
ferrous materials, the seizure may be caused between the swash
plate and the shoes. Each of at least one of the plurality of shoes
which has been subjected to the soft nitriding treatment, i.e., the
nitrided shoe, has a compound layer formed on its surface and
principally constituted by the iron nitride, which compound layer
exhibits an excellent seizure resistance. In the present swash
plate type compressor according to the above mode (1) wherein the
swash plate and the nitrided shoe slide on each other, the seizure
between the swash plate and the nitrided shoe is not likely to
occur even when the lubricating films formed on the sliding
surfaces of the swash plate are locally removed therefrom.
Accordingly, the present swash plate type compressor exhibits a
high degree of resistance to seizure. In other words, the present
swash plate type compressor has a good sliding characteristic, and
exhibits a good sliding characteristic for a long time service.
[0019] The present swash plate type compressor according to the
above mode (1) aims at improving the sliding characteristic of the
swash plate and the shoes relative to each other. In view of this,
the soft nitriding treatment may be effected only on the sliding
surface of the shoe, which sliding surface slides on the swash
plate. (The sliding surface of the shoe which slides on the swash
plate is hereinafter referred to as a "swash-plate side sliding
surface" of the shoe.) Where it is desired to improve the sliding
characteristic of the shoe with respect to the corresponding
piston, the soft nitriding treatment may also be effected on the
sliding surface of the shoe, which sliding surface slides on the
piston. (The sliding surface of the shoe which slides on the piston
is hereinafter referred to as a "piston-side sliding surface".)
Where the soft nitriding treatment is effected only on a part of
the surface of the shoe, the other part which need not be subjected
to the soft nitriding treatment must be covered, for instance,
undesirably making the soft nitriding treatment troublesome.
Accordingly, if it is desired to effect the soft nitriding
treatment on the shoe in a simplified manner, the soft nitriding
treatment may be effected on the entire surface of the shoe.
Further, a part of the surface of the shoe, e.g., the
swash-plate-side sliding surface of the shoe, may be subjected to a
relatively large degree of the soft nitriding treatment so that the
hard layer to be formed has a relatively large thickness while the
other part may be subjected to a relatively small degree of the
soft nitriding treatment so that the hard layer to be formed has a
relatively small thickness. In other words, the thickness values of
the hard layer including the compound layer formed by the soft
nitriding treatment may be changed at different portions of the
surface of the shoe. In the present specification, the term
"nitrided shoe" refers to a ferrous shoe which has been subjected
to the soft nitriding treatment at least on its swash-plate-side
sliding surface which slides on the swash plate.
[0020] (2) A swash plate type compressor according to the above
mode (1), wherein all of the plurality of shoes are the nitrided
shoes.
[0021] (3) A swash plate type compressor according to the above
mode (1), wherein each of said plurality of pistons is a
single-headed piston, and the plurality of shoes engaging the
engaging portion of the single-headed piston consist of a pair of
shoes which are respectively disposed between the opposite surfaces
of the swash plate and the engaging portion of the single-headed
piston, and wherein at least the shoe which slides on one of the
opposite surfaces of the swash plate on the side of the head
portion of the single-headed piston is the nitrided shoe.
[0022] In the swash plate type compressor equipped with a plurality
of pistons, in general, a pair of shoes are respectively disposed
between the opposite surfaces of the swash plate and the engaging
portion of each piston. The swash plate type compressor is
classified into: a swash plate, type compressor equipped with
double-headed pistons each of which includes two head portions at
its opposite ends; and a swash plate type compressor equipped with
single-headed pistons each of which includes a single head portion
at one of its opposite ends. The head portion of the piston
receives a compression reaction force of the refrigerant gas in the
axial direction of the piston from cylinder bore toward the head
portion of the piston. In the swash plate type compressor equipped
with the single-headed pistons, therefore, the pair of shoes
respectively receive different magnitudes of the pressing force of
the swash plate. Described in detail, one of the pair of shoes,
which engages one of the opposite surfaces of the swash plate
nearer to the head portion of the piston, receives a larger
pressing force from the swash plate than the other shoe which
engages the other of the opposite surfaces of the swash plate
remote from the head portion of the piston. Accordingly, the
above-indicated one shoe which engages the surface of the swash
plate nearer to the head portion of the piston slides on the swash
plate under a heavier load condition than the other of the pair of
shoes which engages the other surface of the swash plate remote
from the head portion of the piston. In the swash plate type
compressor equipped with the single headed pistons, therefore, the
compressor exhibits a considerably improved sliding characteristic
if one of the pair of shoes, which engages one of the opposite
surfaces of the swash plate nearer to the head portion of the
piston, is the nitrided shoe, namely if all of the shoes which
engage the above-indicated one surface of the swash plate nearer to
the head portion of each piston are the nitrided shoes.
[0023] In the swash plate type compressor equipped with the
double-headed pistons having two head portions at the opposite ends
thereof, the compression reaction force of the refrigerant gas acts
on opposite ends of each double-headed piston. Accordingly, the
pair of shoes respectively disposed between the opposite surfaces
of the swash plate and the engaging portion of each piston is
subjected to the pressing force of the swash plate under
substantially the same condition. In view of this, if all of the
shoes which are installed on the compressor equipped with the
double-headed pistons are the nitrided shoes, the compressor
exhibits improved sliding characteristic. It is further noted that
the sliding characteristic of the compressor equipped with the
single-headed pistons is improved if all of the shoes are the
nitrided shoes.
[0024] Where each of the at least one of the plurality of shoes is
the nitrided shoe, the other shoes are non-nitrided shoes which are
not subjected to the soft nitriding treatment. The kind of the
material of the shoe, the kind of the surface treatment effected on
the shoe, etc., are not particularly limited. For instance, the
non-nitrided shoes may be ferrous shoes which are subjected to any
suitable surface treatment other than the soft nitriding treatment.
Further, the non-nitrided shoes may be formed of any other suitable
metallic material such as an aluminum alloy.
[0025] (4) A swash plate type compressor according to any one of
the above modes (1)-(3), wherein the nitrided shoe is formed of a
medium-carbon steel or a high-carbon steel.
[0026] (5) A swash plate type compressor according to any one of
the above modes (1)-(3), wherein the nitrided shoe is formed of a
high-carbon chrome bearing steel.
[0027] (6) A swash plate type compressor according to any one of
the above modes (1)-(3), wherein the nitrided shoe is formed of a
stainless steel.
[0028] The ferrous material which constitutes the base body of the
nitrided shoe is not particularly limited. The soft nitriding
treatment is advantageous in that the soft nitriding treatment can
be effected on various kinds of materials for the base body of the
shoe. Accordingly, various ferrous materials such as alloy steels
including a soft steel, a low-carbon steel, a medium-carbon steel,
a high-carbon steel, a stainless steel, etc., and a cast iron can
be used as the material for the base body of the shoe.
[0029] The hardness of the surface of the shoe (hereinafter
referred to as "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
produced 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 Japanese Industry
Standard (JIS) G 4051, 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 and the
high-carbon steel do not include a large amount of expensive alloy
elements and relatively inexpensive, the shoe whose base body is
formed of those steels is relatively inexpensive.
[0030] Since the shoe formed of the high-carbon chrome bearing
steel has a high degree of surface hardness exceeding Hv 500 by the
soft nitriding treatment, the shoe formed of the high-carbon chrome
bearing steel exhibits an excellent wear resistance. Where the shoe
is formed of the high-carbon chrome bearing steel, it is desirable
that the high-carbon chrome bearing steel SUJ2 according to JIS G
4805 is employed in view of the fact that the shoe is a relatively
small component.
[0031] The base body of the nitrided shoe may be formed of the
stainless steel. 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
nitrided shoe, the nitrided shoe has the desired characteristics
corresponding to those of the stainless steel.
[0032] As described above, the surface hardness of the shoe can be
sufficiently increased by the soft nitriding treatment, so that the
nitrided shoe need not be subjected to a quenching treatment. Where
the shoe is not subjected to the quenching treatment, the shoe has
a high degree of dimensional accuracy without suffering from a
change of its configuration. The shoe may be subjected to the
quenching treatment. Where the shoe is subjected to the quenching
treatment, the shoe exhibits high degrees of hardness and wear
resistance.
[0033] (7) A swash plate type compressor according to any one of
the above modes (1)-(6), wherein the soft nitriding treatment is
effected according to a salt bath method.
[0034] The soft nitriding treatment is not particularly limited,
but can be effected according to various known methods such as a
salt-bath nitriding method, a gas soft nitriding method, and an ion
nitriding method.
[0035] Preferably, the salt-bath nitriding method is employed for
effecting the soft nitriding treatment on the shoe. The salt-bath
nitriding method is generally called as "a tufftride mathod,
wherein a substance which is constituted principally by cyanate
(such as KCNO, NaCNO) is melted, and an article to be treated is
immersed in the molten substance. The soft nitriding treatment can
be effected in a relatively short period of time according to the
salt-bath nitriding method, permitting economical manufacture of
the shoe.
[0036] The hard layer formed on the surface of the shoe by the
nitriding treatment includes a compound layer functioning as a
superficial or outermost layer, and a diffusion layer wherein the
nitrogen and the carbon are diffused such that the concentrations
of the nitrogen and the carbon decrease in a direction away from
the compound layer toward the inner portion of the shoe. The
compound layer formed by the salt-bath nitriding method is
substantially constituted by Fe.sub.4N which has a considerably
high degree of seizure resistance. Further, the compound layer
formed by the salt-bath nitriding method has a porous structure.
The refrigerant used in the swash plate type compressor contains a
lubricating oil for lubricating the components of the compressor.
The lubricating oil is present between the swash plate and the
shoes. In the nitrided shoe which has been subjected to the soft
nitriding treatment according to the salt-bath nitriding method,
the porous structure of the compound layer of the nitrided shoe is
soaked with the lubricating oil, so that the sliding
surface/surfaces of the nitrided shoe has/have a good lubrication
characterisitic.
[0037] In view of the above advantages, the salt-bath nitriding
method is preferably employed for effecting the soft nitriding
treatment on the shoe of the present swash plate type
compressor.
[0038] The salt-bath nitriding method is effected according to a
known manner. For instance, the salt-bath method is effected such
that the shoe to be treated is immersed in the molten substance
principally constituted by the cyanate and accommodated in a vessel
while an air is blown into the vessel to keep the concentration of
the cyanate at a predetermined constant value. In this case, the
shoe is immersed in the molten substance kept at a temperature of
560-570.degree. C. for about 0.2-4 hours, for instance.
[0039] (8) A swash plate type compressor according to any one of
the above modes (1)-(7), wherein the nitrided shoe has a compound
layer formed on a surface thereof by the soft nitriding treatment
and having a thickness value in a range of not smaller than 5 .mu.m
and not larger than 20 .mu.m.
[0040] For obtaining substantial effects of the soft nitriding
treatment such as an improvement of the seizure resistance, the
compound layer formed by the soft nitriding treatment desirably has
a thickness value of not smaller than 5 .mu.m. If the compound
layer has an excessively large thickness, the adhesion of the
compound layer with respect to the base body (in a strict sense,
with respect to the diffusion layer) is deteriorated, resulting in
a removal of local portions of the compound layer. In addition, if
the thickness of the compound layer is excessively large, the
surface of the shoe tends to be rough, resulting in an increase of
a time required for a polishing operation for surface finishing.
Moreover, the formation of the compound layer having an excessively
large thickness requires a long time for the nitriding treatment.
In view of the above, it is desirable that the thickness of the
compound layer is not larger than 20 .mu.m.
[0041] (9) A swash plate type compressor according to any one of
the above modes (1)-(8), wherein the nitrided shoe is formed by a
forging operation, the soft nitriding treatment being effected
after the forging operation.
[0042] The shoe is preferably formed by a forging operation which
permits a quick formation of the shoe. For permitting the shoe to
have high degrees of dimensional accuracy and surface smoothness,
the cold forging is preferably employed.
[0043] The soft nitriding treatment may be effected before or after
the forging operation. If the forging operation is effected after
the soft nitriding treatment, the compound layer formed on the
surface of the shoe by the soft nitriding treatment may be removed
therefrom, in particular where the thickness of the compound layer
is excessively large or the forging ratio is relatively high. To
avoid this, the soft nitriding treatment is preferably effected
after the forging operation. The shoe which is subjected to the
soft nitriding treatment after it has been forged has a uniform
surface condition.
[0044] (10) A swash plate type compressor according to any one of
the above modes (1)-(9), wherein the swash plate is formed of a
spheroidal graphite cast iron.
[0045] The ferrous material which provides the base body of the
swash plate is not particularly limited. Various ferrous materials
such as a soft steel, a high-tensile-strength steel, a stainless
steel, and a cast iron. Where the configuration of the swash plate
is complicated, the swash plate is preferably formed by casting. In
view of this, the cast iron is preferably used as the ferrous
material which provides the base body of the swash plate. Where the
base body of the swash plate is formed of the cast iron, the carbon
precipitated in the matrix of iron is present on the surface of the
swash plate, so that the carbon functions as the lubricant when the
swash plate slides on the shoes. Among various cast irons, it is
preferable to use the spheroidal graphite cast iron according to
the above mode (10), in which the precipitated carbon is
spheroidized by inoculation. The spheroidal graphite cast iron is
generally called as "ductile cast iron" and exhibits high degrees
of strength and durability. In particular, the ductile cast iron
FCD 700 according to the JIS G 5502 having a considerably high
degree of strength is preferably employed.
[0046] (11) A swash plate type compressor according to any one of
the above modes (1)-(11), wherein the lubricating films comprise a
solid lubricant and a synthetic resin as a binder.
[0047] In the lubricating films according to the mode (11), the
particles of the solid lubricant are dispersed in a matrix of the
synthetic resin, for instance. The lubricating films according to
the mode (11) can be uniformly and simply formed on the sliding
surfaces of the swash plate by a coating method such as spraying or
roll coating, resulting in a reduced cost of manufacture of the
swash plate. The thickness of the lubricating films is preferably
held in a range of not smaller than 3 .mu.m and not larger than 30
.mu.m. The lubricating films effective to reduce the friction
between the sliding surfaces of the swash plate and the shoes may
be referred to as "friction-reducing films".
[0048] (12) A swash plate type compressor according to the above
mode (11), wherein the solid lubricant includes at least one of
molybdenum disulfide (MoS.sub.2), boron nitride (BN), tungsten
disulfide (WS.sub.2), grahite, and polytetrafluoroethylene
(PTFE).
[0049] The solid lubricants described in the above mode (12) have
excellent lubricating properties. The swash plate whose sliding
surfaces are covered with the lubricating films including at least
one of those solid lubricants has excellent lubricating properties
with respect to the shoes. Preferably, the solid lubricant includes
at least MoS.sub.2. More preferably, the solid lubricant includes
graphite in addition to MoS.sub.2.
[0050] (13) A swash plate type compressor according to the above
mode (11) or (12), wherein the synthetic resin includes at least
one of polyamidimide, epoxy resin, polyether ketone, and phenol
resin.
[0051] On the at least sliding surfaces of the swash plate, metal
coating films such as metal sprayed films described in the
following mode (14) may be formed. The lubricating films described
above are formed on the metal coating films. If at least one of the
synthetic resins described in the above mode (13) is used for
forming the lubricating films, the lubricating films to be formed
on the metal coating films have good adhesion properties with
respect to the metal coating films, and exhibit good heat
resistance. Accordingly, the lubricating films which comprise the
solid lubricant and at least one synthetic resin selected from
among those described above maintain good lubricating properties
for a relatively long period of time and exhibit a high degree of
durability.
[0052] (14) A swash plate type compressor according to any one of
the above modes (1)-(13), wherein the swash plate includes, on at
least the sliding surfaces thereof which slide on the shoes, metal
sprayed films formed of a material selected from the group
consisting of aluminum, copper, an aluminum alloy, and a copper
alloy, the lubricating films being formed on the metal sprayed
films.
[0053] As described above, the strength of the lubricating films is
lower than those of the ferrous materials which provides the
respective base bodies of the swash plate and the shoes. If the
lubricating films are locally removed from the swash plate due to
the wear, for instance, the base body of the swash plate slides
directly on the base bodies of the shoes at local portions of the
swash plate from which the lubricating films have been removed. In
this case, the sliding characteristic of the swash plate with
respect to the shoes is deteriorated at the local portions of the
swash plate from which the lubricating films have been removed. The
swash plate in which the metal sprayed films are formed between its
base body and the lubricating films maintains a good sliding
characteristic owing to the metal sprayed films, even when the
lubricating films are removed from the swash plate. Since the swash
plate and the shoes are formed of the ferrous materials, the
seizure may be caused between the swash plate and the shoes if the
lubricating films are removed from the swash plate. The metal
sprayed films are effective to prevent or minimize the seizure
between the swash plate and the shoes, so that the swash plate type
compressor according to the above mode (14) exhibits a high degree
of seizure resistance owing to the seizure-preventing effect given
by not only the nitrided shoe but also the metal sprayed films. The
metal sprayed films are preferably aluminum sprayed films since the
aluminum sprayed films are relatively inexpensive. The metal
sprayed films desirably have a film thickness of 10-200 .mu.m.
[0054] (15) A swash plate type compressor according to any one of
the above modes (1)-(14), wherein the swash plate is subjected to a
quenching treatment on at least the sliding surfaces thereof which
slide on said shoes.
[0055] If the surface strength of the base body of the swash plate
is increased, the wear of the sliding surfaces of the swash plate
on which the shoes slide can be reduced, for thereby improving the
durability of the swash plate. The swash plate type compressor
according to the mode (15) having the ferrous swash plate which is
subjected to the quenching treatment on at least its sliding
surface exhibits a high degree of durability. While the quenching
treatment can be effected according to any known method, it is
desirable to employ an induction hardening, which permits uniform
hardening of the sliding surfaces. It is preferable that the swash
plate which has been subjected to the quenching treatment has a
surface hardness of not lower than H.sub.RC 40 in Rockwell
hardness.
[0056] The swash plate may be arranged such that the metal sprayed
films are formed on the sliding surfaces which have been subjected
to the quenching treatment. Although the thus arranged swash plate
assures considerably high degrees of sliding characteristic and
durability, the manufacturing cost of the swash plate is inevitably
increased. In the present swash plate type compressor, the sliding
surfaces of the swash plate on which each of the nitrided shoes
slides are protected from seizing on the base body of the shoe even
when the lubricating films are removed therefrom, owing to the hard
layer formed by the nitriding treatment on the swash-plate-side
sliding surface of the nitrided shoe. In view of this, the
compressor having the swash plate in which the lubricating films
are directly formed on the quenched sliding surfaces without
including the metal sprayed films therebetween can exhibit an
excellent sliding characteristic. Accordingly, the swash plate type
compressor having the thus formed swash plate can be produced at a
relatively low cost and is suitable for a practical use.
[0057] (16) A swash plate type compressor according to any one of
the above modes (1)-(15), further including a swash plate
inclination angle changing device for changing an inclination angle
of the swash plate.
[0058] In the swash plate type compressor of a variable capacity
type, the displacement capacity of the compressor is generally
adjusted by changing the inclination angle of the swash plate with
respect to the plane perpendicular to the rotation axis of the
drive shaft, for thereby changing the reciprocating stroke of the
pistons. In the thus arranged swash plate type compressor of
variable capacity type, when the swash plate is inclined with
respect to the above-indicated plane, the shoes have an elliptical
path on the swash plate. With an increase in the inclination angle
of the swash plate, the major axis of an ellipse of the path is
increased. Since the swash plate type compressor needs to be
compact, the size, i.e., the diameter of the swash plate is made
small to such an extent that the swash plate does not interfere
with the pistons when the swash plate is not inclined. In other
words, the diameter of the swash plate is determined so as to
permit the shoes to engage the swash plate such that the end of the
shoe on the radially outer side of the swash plate is flush with
the outer circumferential surface of the swash plate, in other
words, to prevent the shoe from radially outwardly protruding from
the radially outer portion of the swash plate, when the swash plate
is not inclined. In the compressor having the thus designed swash
plate, when the swash plate is inclined at a relatively large
angle, the shoes engaging the pistons which are located near the
opposite ends of the major axis of the elliptical path of the
shoes, namely, the shoes engaging the pistons located near the
compression stroke end and the suction stroke end, respectively,
slide on the swash plate such that portions of the shoes radially
outwardly protrude from the radially outer portion of the swash
plate, depending upon the structure of the compressor. In this
case, the area of contact or engagement of the swash plate and the
shoes is undesirably reduced, so that a relatively large pressing
force of the shoes acts on the swash plate at its small surface
area contacting the shoes. The shoes may slide on the swash plate
while the shoes are inclined. In this case, the pressing force of
the shoes acts on portions of the swash plate in the vicinity of
its circumferential edges having an extremely small surface
area.
[0059] Since the strength of the lubricating films formed on the
sliding surfaces of the swash plate is relatively small, the
lubricating films are likely to be worn when the shoes slide on a
small surface area of the swash plate as described above. In the
swash plate type compressor wherein the inclination angle of the
swash plate is changed, the shoes and the swash plate slide on each
other under a very severe or heavy load conditions, so that the
lubricating films tend to be easily worn. In the present swash
plate type compressor wherein at least one of the plurality of
shoes is the nitrided shoe, the sliding surfaces of the swash plate
and the shoes are protected from the seizure even when the
lubricating films formed on the sliding surfaces of the swash plate
are worn. Therefore, the present swash plate type compressor
maintains a good sliding characteristic. Thus, the principle of the
present invention is particularly advantageously applicable to the
swash plate type compressor of variable capacity type in which the
inclination angle of the swash plate is changed to change the
displacement capacity of the compressor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0060] 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 a presently preferred embodiment of the
invention, when considered in connection with the accompanying
drawings, in which:
[0061] FIG. 1 is a front elevational view in cross section of a
swash plate type compressor of variable capacity type equipped with
single-headed pistons; and
[0062] FIG. 2 is an enlarged front elevational view in cross
section showing a shoe and a portion of the swash plate, which
engage each other.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0063] Referring to the accompanying drawings, there will be
described a presently preferred embodiment of this invention as
applied to a swash plate type compressor used for an air
conditioning system of an automotive vehicle, in particular, a
swash plate type compressor of variable capacity type equipped with
single-headed pistons.
[0064] Referring first to FIG. 1, there is shown a compressor of
swash plate type. 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. [0053 ] 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, such that the
drive shaft 50 is rotatable and axially immovable relative to the
front housing 16 and the cylinder block 10. 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. The
drive shaft 50 and the cylinder bores 12 are positioned relative to
each other such that the cylinder bores 12 are located at
respective circumferential portions of the housing which are
radially spaced from the axis of rotation of the drive shaft 50,
and such that the cylinder bores 12 extend in a direction parallel
to the drive shaft 50.
[0065] 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.
[0066] 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 slidably fitted in the corresponding
cylinder bore 12. The head portion 72 of the piston 14 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, 78. The shoes 76, 78 will be
described in greater detail. The piston 14 in the present
embodiment has a single head portion 72 at one of its opposite
ends, and is referred to as the single-headed piston.
[0067] The piston 14 is reciprocated by rotation of the swash plate
60. Described in detail, a rotary motion of the swash plate 60 is
converted into a reciprocating linear motion of the piston 14
through the shoes 76. (Where it is not necessary to distinguish the
pair of shoes 76, 78 from each other, the shoe is referred to
simply as "the shoe 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 of the cylinder bore 12
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.
[0068] 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.
[0069] 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.
[0070] 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 of the cylinder bore 12
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. The swash plate inclination angle changing device for
changing the inclination angle of the swash plate in the present
embodiment is constituted by the hinge mechanism 66, cylinder bores
12, pistons 14, suction chamber 22, discharge chamber 24, central
bearing hole 56, crank chamber 86, bleeding passage 100,
communication port 104, control device not shown, etc.
[0071] 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.
[0072] 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.
[0073] As shown in FIG. 2, each of the pair of shoes 76 has a
substantially part-spherical crown shape, and includes a generally
convex part-spherical sliding surface 132 which slides on the
piston 14 (hereinafter referred to as "piston-side sliding surface
132"), and a generally flat sliding surface 138 which slides on the
swash plate 60 (hereinafter referred to as "swash-plate-side
sliding surface 138"). Strictly speaking, the swash-plate-side
sliding surface 138 is a slightly convex curved surface (e.g., a
convex part-spherical surface having a considerably large radius of
curvature), and includes a tapered portion formed at a radially
outer portion thereof. The piston-side sliding surface 132 has a
cylindrical portion formed adjacent to the swash-plate-side sliding
surface 138. The boundary between the convex curved surface and the
tapered portion, the boundary between the tapered portion and the
cylindrical portion, and the boundary between the cylindrical
portion and the part-spherical convex surface, are rounded so as to
have respective different small radii of curvature. The pair of
shoes 76 slidably engage the part-spherical inner surfaces of the
recesses 128 of the piston 14 at their piston-side sliding surface
138 and slidably engage the radially outer portion of the opposite
surfaces of the swash plate 60, i.e., the sliding surfaces 140, 142
of the swash plate 60, at their swash-plate-side sliding surface
138. (Where it is not necessary to distinguish one of the sliding
surfaces 140, 142 from each other, the sliding surface is referred
to simply as "sliding surface 140".) The pair of shoes 76 are
designed such that their convex part-spherical surfaces of the
piston-side sliding surfaces 132 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
desirably 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.
[0074] The shoe 76 is a nitrided shoe which has been subjected to
the soft nitriding treatment. In the present embodiment, the base
body 146 of the shoe 76 is formed of a ferrous material, e.g., a
high-carbon chrome bearing steel (SUJ 2 according to the JIS G
4805), and the entire surface of the shoe 76 including the
swash-plate-side sliding surface 138 is covered with a hard layer
formed by the soft nitriding treatment according to the salt-bath
nitriding method. Namely, the superficial surface portion of the
base body 146 of the shoe 76 is changed into the hard layer by the
soft nitriding treatment. As described above, the hard layer formed
by the soft nitriding treatment includes the compound layer and the
diffusion layer. In FIG. 2, only the compound layer (indicated at
152) is shown, and the base body 146 of the shoe 76 does not
include the hard layer. The thickness of the compound layer 152 in
FIG. 2 is exaggerated for easier understanding. In general, the
compound layer 152 has a thickness of 3-30 .mu.m. The material of
the base body 146 of the shoe 76 is not limited to the
above-described SUJ 2. Further, the soft nitriding treatment and
the thickness of the compound layer are not limited to those
described above.
[0075] There will be next explained a method of producing the shoe
76. The base body 146 of the shoe 76 is produced by a closed-die
forging operation in a cold condition effected on a cylindrical or
spherical blank cut from a wire rod. The thus obtained base body
146 is then subjected to surface polishing and barrel polishing for
adjusting the size of the base body 146 and smoothing the surface
of the base body 146. Thereafter, the base body 146 is subjected to
the soft nitriding treatment according to the salt-bath nitriding
method under predetermined conditions, for thereby providing the
shoe 76. The obtained shoe 76 is subjected to a surface finishing
operation including the surface polishing, barrel polishing, and
buff polishing. The method of producing the shoe 76 is not limited
to that described above.
[0076] The base body 160 of the swash plate 60 is formed of a
ferrous material, e.g., a spheroidal graphite cast iron, generally
called as ductile cast iron such as FCD 700 according to the JIS G
5502. On the sliding surfaces 140 located at a radially outer
portion of the opposite surfaces of the swash plate 60, there are
formed lubricating films 166. Each lubricating film 166 comprises
MoS.sub.2 and graphite as the solid lubricant, and a synthetic
resin in the form of polyamidimide, as a binder. In FIG. 2, the
thickness of the lubricating film 166 is exaggerated for easier
understanding. In general, the lubricating film 166 has a thickness
value of 3-30 .mu.m. The base body 160 of the swash plate 60 is
subjected to a quenching treatment at its portions corresponding to
the sliding surfaces 140. The base body 160 has the surface
hardness of not smaller than H.sub.RC 40 by the quenching
treatment. The structure of the swash plate type compressor is not
limited to that as described above. For instance, the kind of the
ferrous material of the base body 160 of the swash plate 60 and the
thickness value of the lubricating film 166 are not limited to
those described above. The quenching treatment may or may not be
effected on the portions of the base body 160 corresponding to the
sliding surfaces 140. While the metal sprayed films are not
provided in the present embodiment, each of the metal sprayed films
may be provided between the base body 160 of the swash plate 60 and
each lubricating film 166.
[0077] The swash plate 60 is produced in a following manner.
Initially, the base body 160 is formed by casting. The base body
160 is subjected to a machining operation on predetermined portions
thereof including the radially outer portion of its opposite
surfaces corresponding to the sliding surfaces 140. Subsequently,
the sliding surfaces 140 are subjected to the induction hardening.
The base body 160 is then subjected to the surface polishing for
adjusting the size of the sliding surfaces 140 and smoothing the
surface of the base body 160. Thereafter, a mixture of the solid
lubricant and the synthetic resin is coated on the sliding surfaces
140 by a spraying method or a roll coating method. The mixture in
the form of paste is cured so as to provide the lubricating films
166. Thus, the swash plate 60 is produced. The method of producing
the swash plate 60 is not limited to that described above.
[0078] As described above, the strength of the lubricating films
166 formed on the sliding surfaces 140 of the swash plate 60 is
lower than those of the base body 146 of the shoes 76 and the base
body 160 of the swash plate 60. Accordingly, the lubricating films
166 may be worn due to the sliding contact with the shoes 76 after
a long time operation of the compressor. If the foreign matters
enter between the sliding surfaces 140 of the swash plate 60 and
the swash-plate-side sliding surfaces 138 of the shoes 76, the
foreign matters may damage the lubricating films 166, resulting in
the wear of the lubricating films 166. In the present swash plate
type compressor wherein the swash-plate-side sliding surfaces 138
of the shoes 76 have been subjected to the soft nitriding
treatment, the shoes 76 and the swash plate 60 are prevented from
seizing on each other even when the lubricating films 166 are
locally worn. Accordingly, the swash plate type compressor
according to the present embodiment has a good sliding
characteristic, and exhibits a good sliding characteristic for a
long period of service.
[0079] The present swash plate type compressor is equipped with a
plurality of single-headed pistons 14. The head portion 72 of each
single-headed piston 14 receives a compression reaction force of
the refrigerant gas in the axial direction of the piston from the
cylinder bore 12 toward the head portion 72. Therefore, one of the
pair of shoes (i.e., the shoe 78 in FIG. 1), which engages one of
the opposite surfaces of the swash plate 60 nearer to the head
portion 72 of the piston 14, receives a larger pressing force from
the swash plate 60 than the other shoe (i.e., the shoe 76 in FIG.
1) which engages the other of the opposite surfaces of the swash
plate 60 remote from the head portion 72 of the piston 14.
Accordingly, the sliding surface 142 of the swash plate 60 on which
the shoe 78 slides is placed under severer sliding conditions
during operation of the compressor than the sliding surface 140 on
which the shoe 76 slides. The severe sliding conditions undesirably
increase the wear of the lubricating films 166. In the present
swash plate type compressor, therefore, the lubricating film 166
formed on the sliding surface 142 of the swash plate 60 nearer to
the head portion 72 of the piston 14 suffers from a high rate of
wearing than that formed on the sliding surface 140 remote from the
head potion 72 of the piston 14. In the present swash plate type
compressor, both of the shoes 76, 78 are the nitrided shoes which
have been subjected to the soft nitriding treatment. Only the shoe
78 may be the nitrided shoe, which shoe 78 slides on the sliding
surface 142 of the swash plate 60 having the lubricating film 166
which suffers from a high rate of wearing. Namely, in the swash
plate type compressor equipped with the single-headed pistons, only
the shoes which engage one of the opposite surfaces of the swash
plate nearer to the head portion of each piston are the nitrided
shoes. This arrangement reduces the cost of manufacture of the
compressor.
[0080] The present swash plate type compressor is of variable
capacity type, and includes the swash plate angle changing device
for changing the inclination angle of the swash plate 60. When the
swash plate 60 is inclined with respect to the plane perpendicular
to the rotation axis of the drive shaft 50, the shoes have an
elliptical path on the swash plate. With an increase in the
inclination angle of the swash plate 60, the major axis of an
ellipse of the path is increased. Since the swash plate type
compressor needs to be compact, the diameter of the swash plate 60
is made small to such an extent that the swash plate does not
interfere with the engaging portions 70 of the pistons 14 when the
swash plate 60 is not inclined. Accordingly, when the swash plate
60 is inclined at a relatively large angle, the shoes 76 engaging
the pistons which are located near the compression stroke end and
the suction stroke end, respectively, slide on the swash plate 60
such that portions of the shoes 76 radially outwardly protrude from
the radially outer portion of the swash plate 60. For instance, the
piston 14 shown in FIG. 1 is at its compression stroke end, and the
shoes 76, 78 engaging that piston 14 partly protrude from the
radially outer portion of the swash plate 60. (FIG. 2 shows the
shoe which does not protrude from the radially outer portion of the
swash plate.) When the shoes partly protrude from the radially
outer portion of the swash plate 60 shown in FIG. 1, the area of
contact or engagement of the swash plate and the shoes is
undesirably reduced, so that a relatively large pressing force of
the shoes acts on the swash plate at its small surface area
contacting the shoes. The shoes may slide on the swash plate while
the shoes are inclined. In this case, the pressing force of the
shoes acts on portions of the swash plate in the vicinity of its
circumferential edges having an extremely small surface area. Thus,
the swash plate type compressor of variable capacity type wherein
the inclination angle of the swash plate is changed is operated
under a heavy load condition than the swash plate type compressor
of fixed capacity type. In the swash plate type compressor of
variable capacity type, therefore, the lubricating films formed on
the sliding surfaces of the swash plate tends to be easily worn, so
that the seizure of the shoes and the swash plate is likely to
occur. In view of this, the swash plate type compressor according
to the present invention equipped with the nitrided shoes is
suitable as the swash plate type compressor of variable capacity
type wherein the inclination angle of the swash plate is
changed.
[0081] While the presently preferred embodiment of this invention
has 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 embodiment. For example, the principle
of the invention is applicable to a swash plate type compressor
equipped with double-headed pistons each having head portions on
the opposite sides of the engaging portion, or 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.
EXPERIMENTS FOR CONFIRMING THE PROPERTIES OF THE SWASH PLATE TYPE
COMPRESSOR
[0082] The following experiments were conducted for examining the
properties such as the seizure resistance of the swash plate type
compressor described in the DETAILED DESCRIPTION OF THE PREFERRED
EMBODIMENT. In the compressor used in the experiments, a portion of
the lubricating film formed on the sliding surface of the swash
plate nearer to the head portion of the piston was removed by
positive wearing. In this state, the compressor was operated under
various conditions described below. The surface area of the portion
of the sliding surface from which the lubricating film was removed
is about one-fifth of the area of the swash-plate-side sliding
surface of the shoe.
Experiment 1
[0083] The swash plate type compressor was operated at a discharge
pressure value in the vicinity of a maximum value expected when
installed on an automotive vehicle. The compressor was inspected
for the wear of the lubricating films and the seizure of the
swash-plate-side sliding surfaces of the shoes and the sliding
surfaces of the swash plate. The experiment was conducted under the
following three different operating conditions (#11, #12, and #13)
of the compressor. In the operating condition #11, the discharge
pressure Pd was 3 MPa and the rotating speed Nc of the swash plate
was 700 rpm. In the operating condition #12, the discharge pressure
Pd was 2 MPa and the rotating speed Nc of the swash plate was 4000
rpm. In the operating condition #13, the discharge pressure Pd was
2.5 MPa and the rotating speed Nc of the swash plate was 4000 rpm.
The compressor was operated for two hours under any of these three
operating conditions. The following TABLE 1 shows the results
together with the operating conditions.
1TABLE 1 Nc Pd operating time No. (rpm) (MPa) (Hr) results #11 700
3 2 no increase of wear of lubricating films .cndot. no seizure #12
4000 2 2 no increase of wear of lubricating films .cndot. no
seizure #13 4000 2.5 2 no increase of wear of lubricating films
.cndot. no seizure
[0084] As is apparent from the results indicated in the TABLE 1, no
increase in the amount of wear of the lubricating films and no
seizure between the shoes and the swash plate were observed under
any of those three different operating conditions of the
compressor. It was therefore confirmed that the present compressor
exhibits a high degree of seizure resistance and a good sliding
characteristic while it is operated at the maximum discharge
pressure value where the shoes and the swash plate are held in
sliding contact with each other with a relatively large pressing
force acting therebetween.
Experiment 2
[0085] The swash plate type compressor was operated with the swash
plate being rotated at relatively high speeds described below. The
compressor was inspected for the wear of the lubricating films and
the seizure between the swash-plate-side sliding surfaces of the
shoes and the sliding surfaces of the swash plate. The experiment
was conducted under the following four different operating
conditions (#21, #22, #23, and #24) of the compressor. In the
operating condition #21 through #24, the discharge pressure Pd was
1.5 MPa, and the swash plate was rotated at respective different
speeds Nc, namely, 5000 rpm, 6500 rpm, 7000 rpm, and 8000 rpm. In
the operating conditions #21 and #23, the compressor was operated
for 2 hours, while the compressor was operated for 24 hours in the
operating conditions #22 and #24. The following TABLE 2 shows the
results together with the operating conditions.
2TABLE 2 Nc Pd operating time No. (rpm) (MPa) (Hr) results #21 5000
1.5 2 no increase of wear of lubricating films .cndot. no seizure
#22 6500 1.5 24 no increase of wear of lubricating films .cndot. no
seizure #23 7000 1.5 2 no increase of wear of lubricating films
.cndot. no seizure #24 8000 1.5 24 no increase of wear of
lubricating films .cndot. no seizure
[0086] As is apparent from the results indicated in the TABLE 2, no
increase in the amount of wear of the lubricating films and no
seizure between the shoes and the swash plate were observed under
any of those four different operating conditions of the compressor.
It was therefore confirmed that the present compressor exhibits a
high degree of seizure resistance and a good sliding characteristic
even when it is operated with the swash plate being rotated at
relatively high speeds.
Experiment 3
[0087] When the swash plate type compressor is turned off, the
temperature of the compressor is lowered, and the refrigerant gas
is liquefied and stored in the cylinder bores. When the compressor
is subsequently re-started, the refrigerant in the liquid form is
compressed in the cylinder bores. This operating condition of the
compressor is referred to as "liquid compression state". In this
liquid compression state of the compressor, a considerably large
compression reaction force of the liquid-form refrigerant is
caused, so that the shoes and the swash plate are subjected to a
relatively large pressing force acting on each other. In the
refrigerant gas, the lubricating oil is included in the form of
mist. Under the normal operation of the compressor, the mist-form
lubricating oil is present between the swash plate and the shoes
for assuring good lubrication therebetween. When the compressor is
turned off, a mist of the refrigerant gas changes into dew drops in
the crank chamber, and the lubricating oil present between the
swash pate and the shoes is washed away by the dew drops. If the
compressor is re-started in this state, the swash plate and the
shoes slide on each other without the lubricating oil being present
therebetween for a while after the re-start of the compressor.
Accordingly, the swash plate and the shoes are subjected to
extremely severe sliding conditions while the compressor is
operated in the above-described liquid compression state which is
caused upon re-starting of the compressor after the interruption
(intermission) of the compressor.
[0088] In the following experiment, the swash plate type compressor
was alternately and intermittently turned on and off. Each time the
compressor was re-started, the compressor was in the
liquid-compression state. The experiment was conducted under the
following three different operating conditions (#31, #32, and #33)
in which the swash plate was rotated at respective different speeds
Nc. In the operating conditions #31 through #33, the rotating
speeds Nc of the swash plate were 4500 rpm, 5500 rpm, and 6500 rpm,
respectively. In the operating condition #31, the compressor was
operated such that the compressor was subjected to the liquid
compression state twenty-five times. In the operating conditions
#32, and #33, the compressor was operated such that the compressor
was subjected to the liquid compression state five times. The
following TABLE 3 shows the results of the experiment together with
the operating conditions.
3TABLE 3 liquid compression No. Nc (rpm) state (times) results #31
4500 25 no increase of wear of lubricating films .cndot. no seizure
#32 5500 5 no increase of wear of lubricating films .cndot. no
seizure #33 6500 5 no increase of wear of lubricating films .cndot.
no seizure
[0089] As is apparent from the results of the TABLE 3, no increase
in the amount of wear of the lubricating films and no seizure
between the swash plate and the shoes were observed under any of
those three different operating conditions of the compressor. It
was therefore confirmed that the present swash plate type
compressor exhibits a high degree of seizure resistance and a good
sliding characteristic even when the compressor is operated under
the extremely severe condition, i.e., in the liquid compression
state.
Experiment 4
[0090] A durability test was conducted in the following manner
under predetermined conditions to inspect an influence of the
nitrided shoes on the lubricating films of the swash plate. A
clearance between each shoe and the swash plate was measured before
and after the test. A difference between the clearance values
before and after the test was obtained as an amount of wear of the
lubricating films., The amount of wear of the lubricating films in
the swash plate type compressor equipped with the nitrided shoes
was substantially equal to that in the compressor equipped with the
non-nitrided shoes. It was therefore confirmed that the lubricating
films are not considerably worn due to the sliding contact with the
nitrided shoes. It was also confirmed in the durability test that
the nitrided shoes have a sufficiently high degree of durability
without suffering from removal of the compound layers formed on the
surfaces thereof by the nitriding treatment.
* * * * *