BACKGROUND OF THE INVENTION
[0001] The present invention relates to a compressor having a valve port plate made of a
steel.
[0002] In a piston type compressor, a piston is received in a cylinder bore which is formed
in a cylinder block and a housing is connected to the end surface of the cylinder
block through a valve port plate and has formed therein a suction chamber and a discharge
chamber. The valve port plate has formed therethrough a suction port and a discharge
port. The rotation of a rotary shaft of the compressor is converted through a drive
mechanism into the reciprocation of the piston. The reciprocation of the piston causes
refrigerant gas in the suction chamber to be introduced through the suction port into
a compression chamber in the cylinder bore for compression therein, and the compressed
refrigerant gas is discharged through the discharge port into the discharge chamber.
[0003] The discharge chamber in the housing is heated to a high temperature by the compressed
refrigerant gas (discharged gas). Therefore, a low-temperature refrigerant gas flowing
from external refrigerant circuit into the suction chamber is heated by heat transmitted
through the wall surfaces of the housing and the valve port plate which cooperate
to define the discharge chamber and the suction chamber. The refrigerant gas in the
suction chamber is heated to expand before it is introduced into the compression chamber
of the cylinder bore. This results in a decrease in the amount of refrigerant gas
that substantially flows into the compression chamber and hence causes a decrease
in volumetric efficiency of the compressor. If the suction refrigerant gas is thus
heated, the temperature of the gas compressed in the compression chamber also increases,
accordingly. Thus, there has been a problem that a seal member for the compressor
or the refrigerant circuit tends to be degraded by the heat.
[0004] A solution for the above problem is disclosed by Unexamined Japanese Patent Publication
No. 5-164042, according to which thermal insulation means is provided in a partition
wall between suction chamber and discharge chamber of a piston type compressor. As
shown in FIG. 8 of the above-cited Publication, the compressor has a housing 53 having
formed therein a suction chamber 51 and a discharge chamber 52 and connected through
a valve port plate 57 to the end surface of a cylinder block 54 of the compressor.
The valve plate assembly 57 has formed therethrough a suction port 55 and a discharge
port 56. The suction chamber 51 and the discharge chamber 52 are partitioned by a
partition wall 58 which has formed therein a thermal insulation groove 58a as a thermal
insulation means.
[0005] A compressor disclosed in Unexamined Japanese Utility Model Publication No. 2-31382
is provided with a cylinder head which has formed therein a suction chamber and a
discharge chamber on one end of a cylinder and is made of a material having a higher
heat radiation, and the suction chamber in the cylinder head is formed by a thermal
insulation material.
[0006] A rotary fluid compressor disclosed in Unexamined Japanese Patent Publication No.
5-33119 is provided with a vane-shaped steel material which has formed on the surface
thereof an ion-nitriding layer for enhancing abrasion resistance of a vane used for
the compressor.
[0007] The compressor in the above-cited Publication No. 5-164042 is disadvantageous in
that the housing 53 is different in structure from a housing of conventional compressor
because the thermal insulation groove 58a is formed in the partition wall 68, with
the result that an existing housing is not usable in a compressor. Furthermore, the
compressor disclosed in the above-cited Publication No. 2-31382, whose suction chamber
is formed by a thermal insulation material, requires the structure of suction chamber
to be changed accordingly if a conventional housing is to be used for the compressor.
[0008] Also, the compressor (vane compressor) disclosed in the above-cited Publication No.
5-33119, whose vane surface is ion-nitrided, is directed to enhance abrasion resistance
of steel material, which is a conventional usage of the ion nitriding. Additionally,
the above-cited Publication No. 5-33119 does not disclose or teach anything about
nitriding for decreasing a thermal conductivity of steel material.
[0009] The present invention is directed to provide a compressor which prevents an increase
in temperature of suction refrigerant gas while improving the compression efficiency
thereof by providing an appropriate treatment to the low-cost ferrous material valve
port plate without structural change to any part of the compressor.
SUMMARY OF THE INVENTION
[0010] In accordance with the present invention, a compressor has a valve port plate made
of a steel. The valve port plate is nitrided or nitrocarburized.
[0011] Other aspects and advantages of the invention will become apparent from the following
description, taken in conjunction with the accompanying drawings, illustrating by
way of example the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The features of the present invention that are believed to be novel are set forth
with particularity in the appended claims. The invention together with objects and
advantages thereof, may best be understood by reference to the following description
of the presently preferred embodiments together with the accompanying drawings in
which:
FIG. 1 is a longitudinal cross-sectional view of a variable displacement piston type
compressor according to a preferred embodiment of the present invention;
FIG. 2 is a partially enlarged longitudinal cross-sectional view around a valve plate
assembly of FIG. 1;
FIG. 3 is a cross-sectional view that is taken along the line I-I in FIG. 1;
FIG. 4 is a partially enlarged schematic cross-sectional view of a nitrided valve
port plate according to the preferred embodiment of the present invention;
FIG. 5 is a graph showing the relation between a thickness of nitride layer and a
thermal conductivity according to the preferred embodiment of the present invention;
FIG. 6 is a partially enlarged longitudinal cross-sectional view around a valve plate
assembly of a compressor according to an alternative embodiment;
FIG. 7 is a partially enlarged longitudinal cross-sectional view around a valve plate
assembly of a compressor according to an alternative embodiment;
FIG. 8 is a partially longitudinal cross-sectional view of a compressor according
to an alternative embodiment; and
FIG. 9 is a partially longitudinal cross-sectional view of a compressor according
to a prior art.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0013] The following will describe a preferred embodiment of a variable displacement piston
type compressor 10 according to the present invention which is used for a refrigerant
circuit in a vehicle air conditioner with reference to FIGS. 1 through 5.
[0014] Referring to FIG. 1 showing a longitudinal cross-sectional view of the variable displacement
compressor 10, in which the left side and the right side of the drawing correspond
to the front side and the rear side of the compressor 10, respectively, the compressor
10 has a housing, which includes a cylinder block 11, a front housing 12 and a rear
housing 14. The front housing 12 is fixedly connected to the front end of the cylinder
block 11. The rear housing 14 is fixedly connected through a valve plate assembly
13 to the rear end of the cylinder block 11.
[0015] The housing has formed therein a crank chamber 15 between the cylinder block 11 and
the front housing 12. Between the cylinder block 11 and the front housing 12 is rotatably
supported a drive shaft 16 for extension through the crank chamber 15. The drive shaft
16 is operatively connected to a vehicle engine (not shown) for rotation thereby in
arrow direction R.
[0016] In the crank chamber 15, a substantially disc-shaped lug plate 17 is secured to the
drive shaft 16 for integral rotation therewith. In the crank chamber 15, a swash plate
or a cam plate 18 is accommodated. The swash plate 18 has formed at the center therethrough
a through hole 18a, through which the drive shaft 16 is inserted. Between the lug
plate 17 and the swash plate 18 is interposed a hinge mechanism 19. The swash plate
18 is connected to the lug plate 17 through the hinge mechanism 19 and supported by
the drive shaft 16 through the through hole 18a. This permits the swash plate 18 to
rotate integrally with the lug plate 17 and the drive shaft 16 and incline with respect
to the drive shaft 16 while sliding in the direction of the axis T of the drive shaft
16.
[0017] The cylinder block 11 has formed therein a plurality of cylinder bores 20 (only one
of them being shown in FIG. 1) around the drive shaft 16 at equiangular spaced intervals,
extending in the direction of the axis T. Each cylinder bore 20 receives therein a
single-headed piston 21 for reciprocation. The front and rear openings of the cylinder
bore 20 are closed by the piston 21 and the valve plate assembly 13, respectively.
In each cylinder bore 20, a compression chamber 22 is defined, the volume of which
varies in accordance with the reciprocation of the piston 21.
[0018] The piston 21 engages with the outer periphery of the swash plate 18 through a pair
of shoes 23. The housing has formed therein a suction chamber 24 and a discharge chamber
25 between the valve plate assembly 13 and the rear housing 14.
[0019] The valve plate assembly 13 includes a valve port plate 26, a suction valve plate
27 provided on one side of the valve port plate 26 adjacent to the cylinder block
11, and a discharge valve plate 28 provided on the other side of the valve port plate
26 adjacent to the rear housing 14. As shown in FIGS. 1 and 3, the valve port plate
26 has formed therethrough suction ports 29 and discharge ports 30. The suction ports
29 are located in radially outward positions of the valve port plate 26 in correspondence
with the respective cylinder bores 20. The discharge ports 30 are located radially
inward of the suction port 29 in correspondence with the respective cylinder bores
20. The suction valve plate 27 has formed therein suction valves 31 in correspondence
with the respective suction ports 29. The discharge valve plate 28 has formed therein
discharge valves 32 in correspondence with the respective discharge ports 30. The
degree of opening of the discharge valves 32 is regulated by a retainer 33 which is
fixed to the valve port plate 26.
[0020] The compressor 10 has a bleed passage 34, a supply passage 35 and a control valve
36 in the housing. The bleed passage 34 connects the crank chamber to the suction
chamber 24. The supply passage 35 connects the discharge chamber 25 to the crank chamber
15. The control valve 36 which is a known electromagnetic valve is located in the
supply passage 35.
[0021] The valve port plate 26 will now be described more in detail. The valve port plate
26 is made of steel (electromagnetic soft steel in the preferred embodiment) and nitrocarburized
to have a thermal conductivity of 60W/mK or less. The valve port plate 26 has nitride
layers 26a formed on both front and rear surfaces thereof, as shown in FIG. 2. When
the valve port plate 26 is nitrided, a base material 37 of the valve port plate 26
has formed on the surface thereof a nitride layer 26a and also has formed at a deeper
portion than the nitride layer 26a a diffusion layer 37a, as shown in FIG. 4. The
diffusion layer 37a is not illustrated in FIGS. 1 and 2 for the sake of convenience
of illustration.
[0022] A thermal conductivity of the valve port plate 26 which has formed therein the nitride
layers 26a depends on a method for forming the nitride layer 26a and a thickness of
the nitride layer 26a, which will be described later. For example, the nitride layers
26a are formed by salt-bath nitriding to have a thickness of 20
µm or more. The valve port plate 26 is, for example, formed to have a thickness of
2 to 3 mm. An increase in temperature of suction refrigerant gas can be prevented
more effectively by increasing the nitride layer thickness and, therefore, forming
the thicker nitride layers 26a is preferable in terms of the prevention of an increase
in temperature of suction refrigerant gas. However, the thicker nitride layers 26a
require a longer time for nitrocarburizing and hence more treatment cost than the
thinner one. The thickness of the nitride layers 26a in the preferred embodiment has
been determined by the trade-off between the effectiveness to prevent temperature
rise of the nitride layers and the treatment cost thereof.
[0023] The following will describe the relation between a thickness of the nitride layer
formed by salt-bath nitriding and a thermal conductivity of a material for nitriding.
The salt-bath nitriding was performed by a known method. The salt-bath mainly contains
cyanate. Using sodium cyanate (or NaCNO) or potassium cyanate (or KCNO) as cyanate,
a material for nitriding was nitrided at a temperature of 580 to 600 degrees C. The
nitriding was performed using unpolished electromagnetic soft iron plate having a
thickness of 1 mm as the material for nitriding. The results are shown in FIG. 5.
[0024] FIG. 5 shows the results, as measured when gas nitrocarburizing was performed as
nitriding. Electromagnetic soft iron was used as the material for nitriding. The gas
nitrocarburizing was performed at a temperature of about 580 degrees C. The results
are also shown in FIG. 5. In FIG. 5, triangular dots (or "Δ") indicate the results
in salt-bath nitriding, and quadrangular dots (or "□") indicate the results in gas
nitrocarburizing.
[0025] FIG. 5 confirms that an increase in thickness of the nitride layer (compound layer)
results in a decrease in thermal conductivity of a valve port plate as a whole. FIG.
5 also confirms that a thermal conductivity depends on which nitriding is performed
for forming a nitride layer having substantially the same thickness. If a nitride
layer is formed with salt-bath nitriding, the results show a larger percentage of
decrease in thermal conductivity relative to an increase in thickness of the nitride
layer in comparison to a nitride layer formed by gas nitrocarburizing. A required
thickness of the nitride layer should be 20
µm or more in salt-bath nitriding to gain a thermal conductivity of 60 W/mK or less.
In contrast, the nitride layer formed by gas nitrocarburizing requires twice as thick
as the nitride layer formed by salt-bath nitriding.
[0026] A coefficient of thermal expansion of a nitrided product was measured, and it showed
a substantially equivalent value to a non-nitrided product. This is because the thickness
of the nitride layers is thin enough.
[0027] Surface hardness of the nitride layers was measured. The nitride layer having a thickness
of 19
µ m has a surface hardness of about 675 in salt-bath nitriding, while the nitride layer
having a thickness of 20
µ m has a surface hardness of about 580 in gas nitrocarburizing.
[0028] The following will describe the operation of the compressor.
[0029] As the drive shaft 16 is rotated, the swash plate 18 rotates therewith, and the rotation
of the swash plate 18 is converted through a pair of the shoes 23 into the reciprocation
of each piston 21 in its associated cylinder bore for a stroke length corresponding
to the inclination angle of the swash plate 18 (which the swash plate 18 makes with
a plane perpendicular to the axis T of the drive shaft 16). Thus, refrigerant gas
is drawn from the suction chamber 24 into the compression chamber 22 for compression
therein, and the compressed refrigerant gas is discharged into the discharge chamber
25, repeatedly. As the piston 21 moves from the top dead center toward the bottom
dead center, the refrigerant gas in the suction chamber 24 (carbon dioxide in the
preferred embodiment) flows into the compression chamber 22 through the suction port
29 while pushing open the suction valve 31. As the piston 21 moves from the bottom
dead center toward the top dead center, on the other hand, the refrigerant gas introduced
into the compression chamber 22 is compressed to a predetermined pressure and discharged
into the discharge chamber 25 through the discharge port 30 while pushing open the
discharge valve 32. The refrigerant gas discharged into the discharge chamber 25 is
sent to the external refrigerant circuit through a discharge hole (not shown).
[0030] The control valve 36 is operable to control the opening degree thereof for adjustment
of the balance between the amount of high-pressure discharged gas through the supply
passage 35 into the crank chamber 15 and the amount of gas from the crank chamber
15 through the bleed passage 34, thus determining the pressure in the crank chamber
15. As the pressure in the crank chamber 15 is varied, the pressure difference between
the crank chamber 15 and the compression chambers 22 across the pistons 21 is varied,
accordingly, so that the inclination angle of the swash plate 18 is altered, thereby
changing the stroke of the piston 21 and hence the displacement of the compressor
10.
[0031] For example, a decrease in the pressure in the crank chamber 15 increases the inclination
angle of the swash plate 18, thereby increasing the stroke of the piston 21, resulting
in an increase in the displacement of the compressor 10. On the other hand, an increase
in the pressure in the crank chamber 15 reduces the inclination angle of the swash
plate 18, thereby reducing the stroke of the piston 21, resulting in a reduction in
displacement of the compressor 10.
[0032] In operation of the compressor 10, compressed refrigerant gas is temporarily reserved
in the discharge chamber 25 under high pressure and temperature. If the valve port
plate 26 is made of non-nitrided or non-nitrocarburized cold-rolled steel plate or
made of non-nitrided or non-nitrocarburized electromagnetic soft iron having a thermal
conductivity of about 80 W/mK, the heat of the refrigerant gas in the discharge chamber
25 is easily transmitted through the valve port plate 26. Accordingly, the refrigerant
gas in the suction chamber 24 or passing through the suction port 29 is heated, resulting
in a decrease in the amount of refrigerant gas substantially introduced into the compression
chamber 22, thus reducing a volumetric efficiency of the compressor.
[0033] However, the valve port plate 26 of the preferred embodiment is so nitrided to have
formed thereon the nitride layers 26a that the valve port plate 26 has a thermal conductivity
of 60 W/mK or less as a whole, with the result that transmission of the heat of the
refrigerant gas in the discharge chamber 25 through the valve port plate 26 to the
refrigerant gas in the suction chamber 24 is prevented. Additionally, the suction
refrigerant gas passing through the suction port 29 is prevented from being heated,
so that the amount of the refrigerant gas substantially introduced into the compression
chamber 22 is increased and the volumetric efficiency and compression efficiency of
the compressor are improved, accordingly.
[0034] When the valve port plate 26 is nitrided (nitrocarburized), the valve port plate
26, that is, the base material 37, has formed on the surface thereof the nitride layer
26a, while having formed therein the diffusion layer 37a of nitrogen contiguously
to the nitride layer 26a, as shown in FIG. 4. The nitride layer 26a and the diffusion
layer 37a cooperate to contribute to a decrease in thermal conductivity of the valve
port plate 26 and an increase in surface hardness thereof.
[0035] In the preferred embodiment, electromagnetic soft iron is used as a material for
nitriding in both salt-bath nitriding and gas nitrocarburizing but low-carbon steel
plate such as SPCC (or steel plate cold commercial), SPCD (or steel plate cold deep
drawn), and SPCE (or steel plate cold deep drawn extra) may also be used.
[0036] According to the preferred embodiment, the following advantageous effects are achieved.
(1) The valve port plate 26 of the compressor 10 has formed thereon the nitride layers
26a to have a thermal conductivity of 60W/mK or less. Accordingly, the valve port
plate 26 made of an inexpensive ferrous material may also have a thermal conductivity
of 60 W/mK or less, so that transmission of the heat of the refrigerant gas in the
discharge chamber 25 through the valve port plate 26 to the refrigerant gas in the
suction chamber 24 is inhibited, thus preventing an increase in temperature of the
suction refrigerant gas and improving the compression efficiency of the compressor.
The valve port plate 26 by the nitriding (nitrocarburizing) is made harder and, therefore,
may be made thinner in comparison with a non-nitrided valve port plate.
(2) Since the valve port plate 26 is salt-bath nitrided, a thickness of nitride layer
26a required for a target thermal conductivity or less of the valve port plate 26
can be formed more quickly in comparison to gas nitrocarburizing. In contrast to gas
nitriding, nitrogen and carbon are synchronously diffused in the valve port plate
26 in the salt-bath nitriding, so that diffusion of nitrogen is facilitated in comparison
to the gas nitriding in which only nitrogen is diffused. For gas nitriding, it is
difficult to nitride steel material which is not suitable for nitriding (that is,
steel other than nitriding steel). However, for the salt-bath nitriding, it is easy
to nitride (nitrocarburize) steel material (ferrous material) other than nitriding
steel. Additionally, it is possible to nitride (nitrocarburize) steel material other
than nitriding steel by gas nitrocarburizing.
(3) The valve port plate 26 is made of cold-rolled steel plate or electromagnetic
soft iron plate which is easy to machine in comparison to nitriding steel.
(4) The compressor 10 is of a piston type, having the cylinder block 11 and the piston
21 received in the cylinder bore 20 that is formed in the cylinder block 11, in which
refrigerant gas is introduced into the cylinder bore 20 for compression therein and
discharge therefrom in conjunction with the reciprocation of the piston 21 in the
cylinder bore 20. In such piston type compressor, the discharge chamber 25 is located
relatively close to the suction chamber 24 in comparison to other types of compressor,
and the heat in the discharge chamber 25 is easily transmitted through the valve port
plate 26 to the suction refrigerant gas in the suction chamber 24. However, by using
a nitriding (nitrocarburizing) process which is low in cost and easy to perform, an
increase in temperature of suction refrigerant gas due to the heat conduction is prevented.
(5) The valve port plate 26 is located between the cylinder block 11 and the rear
housing 14 which has formed therein the suction chamber 24 and the discharge chamber
25, and the nitride layers 26a are formed on the opposite front and rear surfaces
of the valve port plate 26. With the valve port plate 26 having on opposite surfaces
thereof the nitride layers 26a of substantially the same thickness, an increase in
temperature of the suction refrigerant gas is prevented more effectively than with
a valve port plate having a nitride layer only on one surface thereof. To put in other
words, the suction valve plate 27 is disposed on the surface of the valve port plate
26 on the side which is adjacent to the cylinder bore 20, and the valve port plate
26 is exposed directly to the refrigerant gas in the compression chamber 22 in the
region of the valve port plate 26 adjacent to the suction valve 31. Therefore, the
valve port plate 26 is exposed to the high-temperature refrigerant gas which is compressed
to a discharge pressure in the compression stroke, so that the heat of the refrigerant
gas is transmitted to the suction port 29 through the contact portion and then to
the suction refrigerant gas. In the above-described preferred embodiment of the present
invention, however, the valve port plate 26 having the nitride layers 26a on both
front and rear surfaces thereof can prevent the heat transmission through the above
path to the suction refrigerant gas.
(6) Carbon dioxide which is often used as refrigerant for vehicle air conditioner
has a higher refrigerating performance per unit volume in comparison to fluorocarbon
refrigerant, and the cylinder bores of a compressor using such carbon dioxide refrigerant
are made smaller than those of a fluorocarbon refrigerant compressor, accordingly.
Therefore, when the refrigerant gas in the suction chamber 24 expands by heating to
reduce the amount of refrigerant gas substantially introduced into the compression
chambers 22, a decrease in volumetric efficiency is large in percentage. Accordingly,
in the compressor 10 using carbon dioxide refrigerant, the improvement in volumetric
efficiency by preventing the expansion of refrigerant gas due to heating of the suction
refrigerant gas is larger than that of a fluorocarbon refrigerant compressor. Thus,
the present invention is particularly suitable for the compressor 10 which is designed
for compressing carbon dioxide refrigerant.
(7) When the valve port plate 26 is nitrided (nitrocarburized), the base material
37 has formed on the surface thereof the thin and hard nitride layer 26a, while having
formed therein the diffusion layer 37a of nitrogen contiguously to the nitride layer
26a. Thus, the valve port plate 26 will have higher abrasion resistance and better
bedding-in pattern.
[0037] The present invention is not limited to the embodiments described above but may be
modified into the following alternative embodiments.
[0038] In an alternative embodiment, the valve port plate 26 is nitrided or nitrocarburized
to have a thermal conductivity of 60 W/mK or less. For example, as shown in FIG. 6,
the nitride layer 26a is formed only on the rear surface of the valve port plate 26
adjacent to the rear housing 14. FIG. 7 shows another alternative embodiment wherein
the nitride layer 26a is formed only on the front surface of the valve port plate
26 adjacent to the cylinder block 11. If the nitride layer 26 is formed only on one
surface of the valve port plate 26, the nitride layer 26a is preferably formed on
the rear surface of the valve port plate 26 adjacent to the rear housing 14 because
the rear surface of the valve port plate 26 has a larger area exposed to discharged
gas.
[0039] The present invention is not limited to the valve port plate 26 which is nitrided
or nitrocarburized to have a thermal conductivity of about 60 W/mK or less, for which,
for example, the valve port plate 26 needs to be salt-bath nitrided to have the nitride
layer 26a having a thickness of about 20
µ m or more. Alternatively, for example, the valve port plate 26 needs to be gas nitrocarburized
to have the nitride layer 26a having a thickness of about 50
µ m or more according to the results shown in FIG. 5. In an alternative embodiment,
the valve port plate 26 is salt-bath nitrided or gas nitrocarburized to have the nitride
layer 26a having a thickness of about 10
µ m or more, which shows a decrease in thermal conductivity of the valve port plate
26 according to the results shown in FIG. 5.
[0040] In an alternative embodiment, the suction chamber 24 is formed in radially outer
region of the rear housing 13, while the discharge chamber 25 is formed in radially
inner region, as shown in FIG. 8.
[0041] The nitriding or nitrocarburizing is not limited to the salt-bath nitriding or gas
nitrocarburizing. In an alternative embodiment, other nitriding processes are usable.
Other nitriding processes include gas nitriding and ion nitriding (plasma nitriding).
The relation between a thickness of the nitride layer 26a and a thermal conductivity
of the valve port plate 26 depends on which nitriding or nitrocarburizing is performed
for forming the nitride layer 26a. Therefore, a thickness of nitride layer 26a required
for gaining a target thermal conductivity of the valve port plate 26 is determined
adequately depending on which nitriding or nitrocarburizing is performed.
[0042] The material for the valve port plate 26 is not limited to cold-rolled steel plate
and electromagnetic soft iron plate, but any ferrous material is usable. For example,
hot-rolled mild steel plate or nitriding steel is usable. Additionally, the nitriding
steel may be nitrided (nitrocarburized) easier than other ferrous material.
[0043] The present invention is not limited to the above-described swash plate type variable
displacement compressor, but it is also applicable to a swash plate type compressor
with a double-headed piston or a fixed displacement. Additionally, the compressor
of the present invention may be of a wobble type in which the swash plate wobbles
with the rotation of the drive shaft without making integral rotation with the drive
shaft.
[0044] In an alternative embodiment, the housing of the compressor 10 is not limited to
the structure that the front housing 12 and the rear housing 14 hold the cylinder
block 11 therebetween. For example, the housing of the compressor includes a front
housing and a rear housing, and either one of the front and rear housings has formed
therein a crank chamber, while the other receives therein a cylinder that has formed
therein a cylinder bore.
[0045] Alternatively, the present invention is applicable to a compressor having a piston
which is operated by means other than the swash plate. Additionally, the present invention
is not limited to a piston type compressor but is usable for a scroll type compressor.
[0046] The present invention is not limited to a compressor that uses carbon dioxide as
refrigerant for vehicle air conditioner but is usable for a compressor that uses fluorocarbon
refrigerant.
[0047] The present invention is not limited to a compressor whose drive shaft is rotated
by the power of the engine, but the drive shaft of the compressor may be driven by
a motor.
[0048] In an alternative embodiment, the compressor is not limited to be used for a vehicle
air conditioner but may be a motor compressor that is used for a domestic air conditioner.
[0049] The present invention is not limited to a compressor used for air conditioning, but
it is applicable to a compressor for other refrigerant circuits, such as a compressor
used for a refrigerant circuit of a refrigerator or a freezer.
[0050] Therefore, the present examples and embodiments are to be considered as illustrative
and not restrictive, and the invention is not to be limited to the details given herein
but may be modified within the scope of the appended claims.
[0051] A compressor has a valve port plate made of a steel, through which heat of compressed
gas having a relatively higher temperature is transmitted to suction gas having a
relatively lower temperature. The valve port plate is nitrided or nitrocarburized
for reducing heat transmission from the compressed gas to the suction gas.
1. A compressor having a valve port plate made of a steel,
characterized in that:
the valve port plate is nitrided or nitrocarburized.
2. The compressor according to claim 1, wherein the valve port plate has a thermal conductivity
of about 60 W/mK or less.
3. The compressor according to any one of claims 1 and 2, wherein the nitriding or nitrocarburizing
is selected from a group comprising salt-bath nitriding, gas nitrocarburizing, gas
nitriding and ion nitriding.
4. The compressor according to any one of claims 1 through 3, wherein the valve port
plate is made of nitriding steel.
5. The compressor according to any one of claims 1 through 3, wherein the valve port
plate is made of electromagnetic soft iron.
6. The compressor according to any one of claims 1 through 3, wherein the valve port
plate is made of cold-rolled steel plate.
7. The compressor according to any one of claims 1 through 3, wherein the valve port
plate is made of hot-rolled mild steel plate.
8. The compressor according to any one of claims 1 through 7, wherein the compressor
is of a piston type,
characterized in that:
a cylinder block has formed therethrough a cylinder bore; and
a piston is received in the cylinder bore for reciprocation therein, whereby gas is
introduced, compressed and discharged.
9. The compressor according to claim 8, wherein the gas is refrigerant gas.
10. The compressor according to any one of claims 8 and 9,
characterized in that:
a housing has formed therein a suction chamber and a discharge chamber, in that the valve port plate is located between the housing and the cylinder block, and in that a nitride layer is formed on at least one surface of the valve port plate.
11. The compressor according to claim 10, wherein the nitride layer is formed on the surface
of the valve port plate adjacent to the housing.
12. The compressor according to claim 10, wherein the nitride layer is formed on the surface
of the valve port plate adjacent to the cylinder block.
13. The compressor according to claim 10, wherein the nitride layer is formed on opposite
surfaces of the valve port plate.
14. The compressor according to any one of claims 10 through 13, wherein the valve port
plate has formed therein a diffusion layer of nitrogen contiguously to the nitride
layer.
15. The compressor according to claim 1, wherein the valve port plate is salt-bath nitrided
or gas nitrocarburized to have a nitride layer having a thickness of about 10 µ m or more.
16. The compressor according to claim 15, wherein the nitride layer has a thickness of
about 20 µ m or more.
17. The compressor according to claim 15, wherein the valve port plate is gas nitrocarburized
to have a nitride layer having a thickness of about 50 µ m or more.
18. The compressor according to any one of claims 1 through 17, wherein carbon dioxide
is used as refrigerant for the compressor.