EP1582741A2

EP1582741A2 - Compressor valve plate coating

Info

Publication number: EP1582741A2
Application number: EP05005187A
Authority: EP
Inventors: Fuminobu Enokijima; Tetsuhiko Fukanuma; Masaki Ota; Kyoichi Kinoshita; Katsufumi Tanaka; Motoharu Tanizawa
Original assignee: Toyota Industries Corp
Current assignee: Toyota Industries Corp
Priority date: 2004-03-31
Filing date: 2005-03-09
Publication date: 2005-10-05
Also published as: US20050220632A1; JP2005291008A

Abstract

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.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a compressor having a valve port plate made of a steel.
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.
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.
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.
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.
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.
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.
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.
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

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.
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

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

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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
The following will describe the operation of the compressor.
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).
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.
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.
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.
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.
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.
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.
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.
The present invention is not limited to the embodiments described above but may be modified into the following alternative embodiments.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.

Claims

A compressor having a valve port plate made of a steel, characterized in that:

the valve port plate is nitrided or nitrocarburized.
The compressor according to claim 1, wherein the valve port plate has a thermal conductivity of about 60 W/mK or less.
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.
The compressor according to any one of claims 1 through 3, wherein the valve port plate is made of nitriding steel.
The compressor according to any one of claims 1 through 3, wherein the valve port plate is made of electromagnetic soft iron.
The compressor according to any one of claims 1 through 3, wherein the valve port plate is made of cold-rolled steel plate.
The compressor according to any one of claims 1 through 3, wherein the valve port plate is made of hot-rolled mild steel plate.
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.
The compressor according to claim 8, wherein the gas is refrigerant gas.
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.
The compressor according to claim 10, wherein the nitride layer is formed on the surface of the valve port plate adjacent to the housing.
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.
The compressor according to claim 10, wherein the nitride layer is formed on opposite surfaces of the valve port plate.
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.
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.
The compressor according to claim 15, wherein the nitride layer has a thickness of about 20 µ m or more.
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.
The compressor according to any one of claims 1 through 17, wherein carbon dioxide is used as refrigerant for the compressor.