EP0864751A2

EP0864751A2 - Compressor for use in a transcritical refrigeration cycle system

Info

Publication number: EP0864751A2
Application number: EP98301867A
Authority: EP
Inventors: Hiroshi C/O Zexel Corporation Kanai; Shunichi c/o Zexel Corporation Furuya
Original assignee: Zexel Corp
Current assignee: Valeo Thermal Systems Japan Corp
Priority date: 1997-03-12
Filing date: 1998-03-12
Publication date: 1998-09-16
Also published as: JPH10253177A; EP0864751A3

Abstract

A compressor (101) for use in a transcritical refrigeration cycle system, comprises a housing (4), a drive shaft (5) supported rotatably by a bearing (24) within the housing (4), a shaft seal (30, 31) interposed between the housing (4) and the drive shaft (5) so as to prevent a high-pressure fluid consisting essentially of a refrigerant and a lubricating oil from leaking from the compressor (101), and a space (40) in which are received the bearing (24) and the shaft seal (30, 31). Pressure within the space (40) is lower than the discharge pressure of the high-pressure fluid. The housing (4) is formed with a lubricating oil return passage (50) for returning lubricating oil separated from the high-pressure fluid discharged from a discharge port (3a) of the compressor (101, to the space (40).

Description

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to a compressor for use in a transcritical refrigeration cycle system, and more particularly to a compressor of this kind having a construction which is capable of promoting lubrication of sliding contact members within the compressor so as to prevent seizure or wear of the components.

Description of the Prior Art

FIG. 1 shows a refrigeration cycle system using a chlorofluorocarbon as a refrigerant, and FIG. 2 is a Mollier chart of the chlorofluorocarbon. Reference numerals (1) to (4) in FIG. 1 correspond to reference numerals (1) to (4) in FIG. 2, respectively.

In the typical refrigeration cycle system using chlorofluorocarbon as a refrigerant, the refrigerant in a gaseous state is compressed within a compressor 201 into high-pressure and high-temperature refrigerant gas ((1) to (2) in FIG. 2), which is discharged from the compressor 201 via a discharge port of the same and flows into a condenser 202. Then, the high-pressure and high-temperature refrigerant gas is cooled in the condenser 202 due to a difference in temperature between the refrigerant gas and the air outside the condenser 202, to be transformed from a gaseous state to a liquid state ((2) to (3) in FIG. 2). The liquefied refrigerant flows to an expansion valve 203 via a liquid tank 206. In the expansion valve 203, the liquefied high-pressure refrigerant gas is drastically expanded and changed into atomized low-pressure and low-temperature refrigerant ((3) to (4) in FIG. 2). The atomized low-pressure and low-temperature refrigerant gas flows into an evaporator 204 and absorbs heat from air surrounding the evaporator 204 to completely vaporize, followed by returning into the compressor 201 in a gaseous state ((4) to (1) in FIG. 2).

Lubricating oil contained in the refrigerant gas flows out of the compressor 201 via the discharge port of the same together with the refrigerant gas, and dissolves into the liquefied refrigerant within the condenser 202. The liquid mixture of the lubricating oil and the liquefied refrigerant gas is far less viscous than the lubricating oil itself, and the lubricating oil and the liquefied refrigerant are uniformly blended with each other in the mixture, which inhibits the lubricating oil from affecting a flow of the refrigerant within the expansion valve 203. Further, since the lubricating oil and the refrigerant flow into the expansion valve 203 in a state of liquid mixture, it is easy to set a degree of throttling or restriction of the expansion valve 203.

Differently from the above typical refrigeration cycle system using the chlorofluorocarbon as a refrigerant, a transcritical refrigeration cycle system in which e.g. carbon dioxide is used as a refrigerant has a high-pressure line between the discharge port of a compressor and the inlet port of an expansion valve as a transcritical zone in which refrigerant gas is not condensed (see FIG. 6 Mollier chart). This means that there is no liquefied refrigerant flowing through the high-pressure line, so that refrigerant gas and lubricating oil, which are two fluids quite different from each other in viscosity, enter the expansion valve in a state separated from each other. The lubricating oil having a high viscosity increases resistance to the flow of the refrigerant gas, whereby pressure within the high-pressure line between the discharge port of the compressor and the inlet port of the expansion valve is increased. As a result, discharge pressure/temperature within the compressor is increased, and at the same time, the amount of lubricating oil returned to the compressor becomes insufficient, which causes seizure or wear of sliding contact members within the compressor.

In the transcritical refrigeration cycle system, the pressure level of the refrigerant gas is approximately ten times higher than that of the chlorofluorocarbon used in the typical refrigeration cycle system, so that high pressure acts on surfaces of the sliding contact members within the compressor, and a PV value (quantity of gas) is also increased. The is requires the housing of the compressor and the sliding contact members within the same to have high rigidity and strength. A further problem is that mechanical seals, which are provided as a shaft seal between the housing and a drive shaft so as to prevent leakage of refrigerant gas into the atmosphere, easily wear out if the supply of lubricating oil to the mechanical seals is insufficient.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a compressor for use in a transcritical refrigeration cycle system, which is constructed to be capable of promoting lubrication of sliding contact members within the compressor to thereby prevent seizure or wear of the components, as well as a transcritical refrigeration cycle system incorporating the compressor.

To attain the above object, according to a first aspect of the present invention, there is provided a compressor for use in a transcritical refrigeration cycle system, including a housing, a drive shaft, a bearing arranged within the housing, for rotatably supporting the drive shaft, a shaft seal interposed between the housing and the drive shaft so as to prevent a high-pressure fluid essentially consisting of a refrigerant and a lubricating oil from leaking out of the compressor, a space in which are received the bearing and the shaft seal, and a discharge port via which the high-pressure fluid in discharged from the compressor, wherein pressure within the space is lower than discharge pressure.

The compressor according to the first aspect of the invention is characterized by comprising a lubricating oil return passage formed through the housing, for returning the lubricating oil separated from the high-pressure fluid discharged from the discharge of the compressor port to the space within the compressor.

According to the compressor of the invention, since lubricating oil is constantly supplied to the bearing and the shaft seal, lubrication of these sliding contact members can be promoted.

Preferably, the transcritical refrigeration cycle system includes an oil separator for separating out the lubricating oil from the high-pressure fluid, the oil separator having an oil outlet port, and a lubricating oil return line extends from the oil outlet of the oil separator, and the lubricating oil return passage has an inlet port thereof connected to the lubricating oil return line.

According to the preferred embodiment, since the lubricating oil separated from the refrigerant gas within the oil separator can flow to the lubricating oil return passage via the lubricating oil return line by differential pressure between the discharge port of the compressor and the space, a lubricating oil-feeding device, such as a lubricating oil pump, can be dispensed with. Therefore, the transcritical refrigeration cycle system including the compressor is not required to have a complicated construction, which makes it possible to prevent manufacturing costs thereof from being increased.

Preferably, the lubricating oil return passage is formed through an upper wall of the housing, for communicating with the space.

According to the preferred embodiment, since lubricating oil returned via the lubricating oil return passage is sprayed directly onto the bearing and the shaft seal within the space, the compressor is not required to have a device for drawing up lubricating oil collected in a lower portion within the compressor, so that complication of the construction of the compressor can be avoided.

To attain the above object, according to a second aspect of the invention, there is provided a transcritical refrigeration system comprising:

a compressor for compressing a fluid essentially consisting of a refrigerant and a lubricating oil into a high-pressure fluid and discharging the high-pressure fluid therefrom, the compressor having a housing and a lubricating oil return passage formed through the housing;

an oil separator connected to the compressor for separating the lubricating oil from the high-pressure fluid discharged from the compressor, the oil separator having an oil outlet port;

an lubricating oil return line connecting between the oil outlet port of the oil separator and the lubricating oil return passage;

a cooler;

an expansion valve; and

an evaporator.

According to this transcritical refrigeration cycle system, since the lubricating oil is returned to the compressor via the lubricating oil return line, gaseous refrigerant alone flows into the expansion valve. Therefore, an abnormal rise in pressure within the high-pressure line can be avoided, which makes it possible to prevent an increase in discharge pressure within the compressor and a decrease in efficiency of the compressor resulting therefrom. Further, since layers of lubricating oil deposited on inner wall surfaces of the cooler and the evaporator become much thinner, heat exchange efficiency can be enhanced. Moreover, the degree of throttling or restriction of the expansion valve can be set easily.

More specifically, the compressor includes a drive shaft, a bearing arranged within the housing, for rotatably supporting the drive shaft, a shaft seal interposed between the housing and the drive shaft so as to prevent the high-pressure fluid from leaking out of the compressor, and a space in which are received the bearing and the shaft seal, and the lubricating oil return passage communicates with the space.

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view schematically showing a typical refrigeration cycle system using a chlorofluorocarbon as a refrigerant;

FIG. 2 is a Mollier chart of the chlorofluorocarbon;

FIG. 3 is a longitudinal cross-sectional view showing the whole arrangement of a compressor for use in a transcritical refrigeration cycle system, according to an embodiment of the invention;

FIG. 4 is an enlarged sectional view showing essential parts of the FIG. 3 compressor;

FIG. 5 is a view schematically showing the transcritical refrigeration cycle system including the FIG. 3 compressor; and

FIG. 6 is a Mollier chart of carbon dioxide (CO₂).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention will now be described in detail with reference to drawings showing a preferred embodiment thereof.

FIG. 5 shows a transcritical refrigeration cycle system including a compressor according to an embodiment of the invention, and FIG. 6 shows a Mollier chart of carbon dioxide. Reference numerals (1) to (4) in FIG. 5 correspond to reference numerals (1) to (4) in FIG. 6.

The transcritical refrigeration cycle system in which e.g. carbon dioxide (CO₂) is used as refrigerant gas includes the compressor 101, an oil separator 106, a cooler 102, an expansion valve 103, an evaporator 104, and a liquid tank (accumulator) 105. The oil separator 106 is arranged between the compressor 101 and the cooler 102.

Refrigerant gas is compressed within the compressor 101 into high-pressure and high-temperature refrigerant gas ((1) to (2) in FIG. 6), and discharged from the compressor 101 as a high-pressure fluid containing lubricating oil via a discharge port 3a of the same to flow into to the oil separator 106. Within the oil separator 106, lubricating oil is separated from the refrigerant gas. The separated lubricating oil is returned to the compressor 101 via a lubricating oil return line C (communicating between an outlet port of the oil separator 106 and an inlet port 50a of a lubricating oil return passage 50 formed in the compressor 101), while the refrigerant gas is delivered to the cooler 102 along a high-pressure line A (extending between the discharge port 3a of the compressor 101 and an inlet port of the expansion valve 103). Within the cooler 102, the refrigerant gas is cooled due to the difference in temperature between the refrigerant gas and air outside the cooler. However, since the refrigerant gas is in a transcritical zone, it is not condensed ((2) to (3) in FIG. 2). Accordingly, the refrigerant gas flows from the cooler 102 to the expansion valve 103 in a state in which it is not liquefied (i.e. in a state of high-density gas). In the expansion valve 103, the high-pressure refrigerant gas is drastically expanded and changed into low-pressure and low-temperature refrigerant gas. At this time point, the refrigerant gas becomes saturated and is liquefied for the first time ((3) to (4) in FIG. 6). The low-pressure and low-temperature refrigerant gas flows from the expansion valve 103 to the evaporator 104 along a low-pressure line B (extending between the outlet port of the expansion valve 103 and a suction port of the compressor 101) and absorbs heat from air surrounding the evaporator 104 to completely vaporize ((4) to (1) in FIG. 6). The evaporator 104 has an outlet port thereof connected to the liquid tank 105. The refrigerant gas is separated into gaseous refrigerant and liquid refrigerant in the liquid tank 105, followed by the gaseous refrigerant being drawn into the compressor 101 via the suction port of the same.

FIG. 3 shows the whole arrangement of the compressor according to the embodiment of the invention. FIG. 4 shows essential parts of the FIG. 3 compressor on an enlarged scale. In the figures, the internal construction of the compressor is schematically shown, and hence component parts such as a swash plate are not illustrated in detail.

The compressor 101 for use within the transcritical refrigeration cycle system has a cylinder block 1 having one end thereof secured to a rear head 3 via a valve plate 2 and the other end thereof secured to a front head (housing) 4. The cylinder block 1, the rear head 3, and the front head 4 are tightened in a longitudinal direction by through

bolts

80, 81. The cylinder block 1 has a plurality of cylinder bores 6 axially extending therethrough at predetermined circumferential intervals about a drive shaft 5. Each cylinder bore 6 has a piston 7 slidably received therein.

The front head 4 defines a crankcase 8 in which a swash plate 10 is received. The swash plate 10 is fixedly fitted on the drive shaft 5. The swash plate 10 has an inclined surface 10a which is inclined at a predetermined angle with respect to an imaginary plane orthogonal to the drive shaft 5. The length of stroke of each piston 7 is determined according to the predetermined inclination angle of the inclined surface 10a of the swash plate 10. Further, the swash plate 10 has a vertical surface 10b orthogonal to the drive shaft 10. The vertical surface 10b of the swash plate 10 is rotatably supported on an inner wall surface of the front head 4 by a thrust bearing 33. Each connecting rod 11 has one end thereof secured to a corresponding one of the pistons 7 and the other end 11a, spherical in shape, connected to the inclined surface 10a of the swash plate 10 such that it slides on the inclined surface 10a to the swash plate 10.

The drive shaft 5 has a rear end thereof rotatably supported by a radial bearing 26 within the cylinder block 1, and an intermediate portion thereof rotatably supported by a radial bearing (bearing) 24 within the front head 4. Mechanical seals (shaft seal) 30, 31 are interposed between an inner peripheral wall of the front head 4 and a front-end portion of the drive shaft 5. A space 40 in which are received the radial bearing 24 and the

mechanical seals

30, 31 is communicated with the crankcase 8. The mechanical seal 30 is fixed to the front head 4, using dowels 90 for properly positioning the mechanical seal 30, while the mechanical seal 31 is rigidly fitted on the drive shaft 5. A rear end face of the mechanical seal 30 and a front end face of the mechanical seal 31 are in intimate contact with each other in an axial direction.

The front head 4 has an upper wall portion 4a formed therethrough with the lubricating oil return passage 50 which communicates with the space 40. The lubricating oil return line C is connected to the inlet port 50a of the passage 50.

Within the rear head 3, there are formed a discharge chamber 12 and a suction chamber 13 surrounding the discharge chamber 12.

The valve plate 2 is formed with refrigerant outlet ports 16 for each communicating between a compression chamber within a corresponding one of the cylinder bores 6 and the discharge chamber 12, and refrigerant inlet ports 15 for each communicating between a compression chamber within a corresponding one of the cylinder bores 6 and the suction chamber 13. The refrigerant outlet ports 16 and the refrigerant inlet ports 15 are arranged at predetermined circumferential intervals about the drive shaft 5. Each refrigerant outlet port 16 is opened and closed by a discharge valve 17. The discharge valve 17 is fixed to a rear head-side end face of the valve plate 2 by a bolt 19 and a nut 20 together with a valve stopper 18.

On the other hand, each refrigerant inlet port 15 is opened and closed by a suction valve 21 arranged between the valve plate 2 and the cylinder block 1. A communication passage 60 is formed through the cylinder block 1 to connect between the suction chamber 13 and the crankcase 8.

Next, the operation of the compressor constructed as above will be described.

Torque of an engine, not shown, installed on an automotive vehicle, not shown, is transmitted to the drive shaft 5 to rotate the same. As the drive shaft 5 rotates, the swash plate 10 rotates in unison with the drive shaft 5.

The rotation of the swash plate 10 causes the spherical end 11a of each of the connecting rods 11 to slide on the inclined surface 10a of the swash plate 10, whereby the torque transmitted from the swash plate 10 is converted into the reciprocating motion of the piston 7. As the piston 7 reciprocates within the cylinder bore 6, the volume of the compression chamber within the cylinder bore 6 changes. As a result, suction, compression and delivery of refrigerant gas are sequentially carried out in the compression chamber. During the suction stroke of the piston 7, the suction valve 21 opens to draw low-pressure refrigerant gas from the suction chamber 13 into the compression chamber within the cylinder bore 6, while during the discharge stroke of the same, the discharge valve 17 opens to deliver high-pressure refrigerant gas from the compression chamber to the discharge chamber 12.

The refrigerant gas delivered to the discharge chamber 12 is discharged from the compressor 101 via the discharge port 3a together with lubricating oil contained therein (i.e. as the high-pressure fluid essentially consisting of refrigerant and lubricating oil), and then flows into the oil separator 106, in which the refrigerant gas and the lubricating oil are separated from each other. After having undergone the oil separation, the refrigerant gas flows to the cooler 102 along the high-pressure line A.

Pressure (discharge pressure) within the discharge port 3a is higher than pressure within the space 40, so that the lubricating oil separated from the refrigerant gas within the oil separator 106 is returned to the compressor 101 via the lubricating oil return line C.

The lubricating oil returned to the compressor 101 is supplied to the space 40 via the lubricating oil return passage 50 to lubricate the radial bearing 24 and the

mechanical seals

30, 31.

Since the lubricating oil is returned to the compressor 101 via the lubricating oil return line C as described above, gaseous refrigerant alone flows into the expansion valve 103. Therefore, an abnormal rise in pressure within the high-pressure line A can be avoided, which makes it possible to prevent an increase in discharge pressure within the compressor 101 and a decrease in efficiency of the compressor 101 resulting therefrom.

Further, since layers of lubricating oil deposited on inner wall surfaces of the cooler 102 and the evaporator 104 become much thinner, heat exchange efficiency can be enhanced.

Moreover, the degree of throttling or restriction of the expansion valve 103 can be set easily.

According to the compressor of the embodiment, since lubricating oil is constantly supplied to the radial bearing 24 and the

mechanical seals

30, 31, lubrication of sliding contact members within the compressor is promoted, which makes it possible to prevent seizure or wear of the components.

Further, since lubricating oil is fed to the space 40, in which the radial bearing 24 and the

mechanical seals

30, 31 are received, by the use of differential pressure between the discharge port 3a formed through a wall of the rear head 3 and the space 40, a lubricating oil-feeding device such as a lubricating oil pump (e.g. a trochoid pump) can be dispensed with. Therefore, the transcritical refrigeration cycle system including the compressor is not required to have a complicated construction, which makes it possible to prevent manufacturing costs thereof from being increased.

Still further, since the lubricating oil return passage 50 is formed through the upper wall portion 4a of the front head 4 so as to spray lubricating oil directly on the radial bearing 24 and the

mechanical seals

30, 31, it is not necessary to provide the compressor with a device for drawing up lubricating oil collected in a portion within the compressor. This advantageously makes it possible to avoid complication of the construction of the compressor to thereby prevent manufacturing costs of the compressor from being increased.

Although in the above embodiment, description is made of a case in which the invention is applied to a fixed capacity swash plate compressor, this is not limitative, but the invention may be applied to other kinds of compressors for use within the transcritical refrigeration cycle system, such as a variable capacity swash plate compressor.

It is further understood by those skilled in the art that the foregoing is the preferred embodiment and variations of the invention, and that various changes and modifications may be made without departing from the spirit and scope thereof.

Claims

A compressor (101) for use in a transcritical refrigeration cycle system, comprising a housing (4), a drive shaft (5), a bearing (24) arranged within the housing (4) and rotatably supporting the drive shaft (5), a shaft seal (30, 31) interposed between the housing (4) and the drive shaft (5) so as to prevent a high-pressure fluid consisting essentially of a refrigerant and a lubricating oil from leaking from the compressor (101), a space (40) in which are received the bearing (24) and the shaft seal (30, 31), and a discharge port (3a) via which the high-pressure fluid is dischargable from the compressor (101), wherein the pressure within the space (40) is lower than the discharge pressure of the high-pressure fluid,
characterised in that a lubricating oil return passage (50) is formed through the housing (4), for returning lubricating oil separated from the high-pressure fluid discharged from the compressor discharge port (3a) to the space (40) within the compressor (101).
A compressor (101) according to claim 1, wherein the lubricating oil return passage (50) is formed through an upper wall (4a) of the housing (4) for communicating with the space (40).
A transcritical refrigeration cycle system comprising a compressor (101) according to claim 1 or 2 and an oil separator (106) which is arranged to separate lubricating oil from the high-pressure fluid discharged from the compressor (101) and which has an oil outlet port, and a lubricating oil return line (C) which extends from the oil outlet of the oil separator (106) and which is connected to an inlet port (50a) of the lubricating oil return passage (50) of the compressor (101).
A transcritical refrigeration cycle system comprising:

a compressor (101) for compressing a fluid consisting essentially of a refrigerant and a lubricating oil into a high-pressure fluid and discharging the high-pressure fluid therefrom, the compressor (101) having a housing (4) and a lubricating oil return passage (50) formed through the housing (4);

an oil separator (106) which is connected to the compressor (101) for separating lubricating oil from the high-pressure fluid discharged from the compressor (101) and which has an oil outlet port;

a lubricating oil return line (C) connected between the oil outlet port of the oil separator (106) and the lubricating oil return passage (50);

a cooler (102;

an expansion valve (103); and

an evaporator (104).
A transcritical refrigeration cycle system according to claim 4, wherein the compressor (101) comprises a drive shaft (5), a bearing (24) arranged within the housing (4) and rotatably supporting the drive shaft (5), a shaft seal (30, 31) interposed between the housing (4) and the drive shaft (5) so as to prevent the high-pressure fluid from leaking from the compressor (101), and a space (40) in which are received the bearing (24) and shaft seal (30, 31), and wherein the lubricating oil return passage (50) communicates with the space (40).