GB2572870A

GB2572870A - Multi-stage scroll compressor

Info

Publication number: GB2572870A
Application number: GB1905567.2A
Authority: GB
Inventors: Koyama Shuhei; Matsui Tomokazu; Yano Kenji
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2017-01-12
Filing date: 2017-01-12
Publication date: 2019-10-16
Anticipated expiration: 2037-01-12
Also published as: JPWO2018131111A1; GB201905567D0; WO2018131111A1; GB2572870B; JP6689414B2

Abstract

Provided is a multi-stage scroll compressor configured such that vibration and noise can be suppressed and the multi-stage scroll compressor is highly reliable. This multi-stage scroll compressor is provided with: a closed container; at least two compression mechanisms arranged within the closed container and compressing a refrigerant; and a drive mechanism for driving the compression mechanisms. The closed container has three internal spaces, which are a low-pressure space into which the refrigerant is sucked by one compression mechanism, an intermediate-pressure space into which the refrigerant sucked in from the low-pressure chamber and compressed by the one compression mechanism is discharged, and a high-pressure space into which the refrigerant sucked in from the intermediate-pressure space and compressed by the other compression mechanism is discharged. The compression mechanisms each have: a compression chamber formed by combining a stationary scroll and an orbiting scroll, which have spiral bodies protruding from base plates; and a discharge port located at the center of the spiral bodies and providing communication between the compression chamber and the internal spaces. At least one compression mechanism has a sub-port for providing communication between the compression chamber and the internal spaces, and the sub-port provides communication between the compression chamber and the internal spaces before the compression chamber is in communication with the discharge port.

Description

The present invention relates to a multi-stage scroll compressor usually installed in a refrigerating machine, an air-conditioning apparatus, or a hot water supply apparatus.

Background Art [0002]

In the past, a multi-stage compressor has been known which uses carbon dioxide as refrigerant and has a multi-stage compression mechanism including a rolling piston compression mechanism disposed at one end inside a sealed housing, a scroll compression mechanism disposed at the other end inside the sealed housing, and a motor (electric motor) disposed between the rolling piston compression mechanism and the scroll compression mechanism to drive the two compression mechanisms.

[0003]

According to the disclosure in Patent Literature 1, a multi-stage compressor includes a low-pressure-side compression mechanism and a high-pressure-side compressor, which are formed as a rolling piston compression mechanism and a scroll compression mechanism, respectively. The scroll compression mechanism as the high-pressure-side compression mechanism forms a compression chamber with a combination of a fixed scroll and a revolving scroll, and is configured to meet L > Worb, wherein Worb represents the thickness of an end plate of the revolving scroll, and L represents the height of a lap of the revolving scroll. This configuration makes it possible to suppress deformation of respective end plates of the fixed scroll and the revolving scroll, and increase the capacity of the compressor.

Citation List

Patent Literature [0004]

Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2008-232041 (Page 8 and Fig. 1)

Summary of Invention

Technical Problem [0005]

In the multi-stage compressor disclosed in Patent Literature 1, however, the rolling piston compression mechanism is disposed at one end inside the sealed housing. To prevent a low-stage-side rolling piston from being damaged by liquid flowing backward from a refrigerant circuit, therefore, the multi-stage compressor needs to be equipped with a suction muffler. If the suction muffler is attached to a side surface of the compressor, the balance of the compressor is disturbed, increasing vibration and noise. Particularly in the case of refrigerant that operates at high pressure, such as carbon dioxide, the suction muffler is increased in thickness and weight, thereby raising an issue of a further increase in vibration and noise. [0006]

The present invention has been made to address the above-described issue, and obtains a multi-stage scroll compressor including two or more scroll compression mechanisms in a sealed housing, suppressing an increase in vibration and noise, and, at the same time, maintaining performance.

Solution to Problem [0007]

A multi-stage scroll compressor according to an embodiment of the present invention includes a sealed container, at least two compression mechanism units disposed in the sealed container to compress refrigerant, and a drive mechanism unit that drives the at least two compression mechanism units. The sealed container includes three internal spaces: a low-pressure space from which the refrigerant is suctioned by one of the at least two compression mechanism units, an intermediatepressure space into which the refrigerant suctioned from the low-pressure space and compressed by the one of the at least two compression mechanism units is discharged, and a high-pressure space into which the refrigerant suctioned from the intermediate-pressure space and compressed by an other one of the at least two compression mechanism units is discharged. Each of the at least two compression mechanism units includes a compression chamber, which is formed by a combination of a fixed scroll and an orbiting scroll each including a baseplate and a scroll wrap projecting from the baseplate, and a discharge port, which is located at a central portion of the scroll wrap and allows communication between the compression chamber and one of the three internal spaces. At least one of the at least two compression mechanism units includes a sub-port that allows communication between the compression chamber and the one of the three internal spaces. In a compression process of the refrigerant, the sub-port allows communication between the compression chamber and the one of the three internal spaces before the compression chamber communicates with the discharge port.

Advantageous Effects of Invention [0008]

The multi-stage scroll compressor according to the embodiment of the present invention is configured as described above. Even if one of the at least two compression mechanism units compresses liquid refrigerant in the event of liquid backflow from a refrigerant circuit, therefore, the refrigerant is released from the subport, thereby making it possible to prevent an excessive increase in pressure. Accordingly, it is possible to ensure reliability without a suction muffler, and efficiently operate both of the at least two compression mechanism units without excessive compression of the refrigerant while suppressing the increase in vibration and noise occurring in the multi-stage scroll compressor. It is thereby possible to suppress deterioration in the performance of the multi-stage scroll compressor.

Brief Description of Drawings [0009] [Fig. 1] Fig. 1 is an explanatory diagram illustrating a section of a sealed twostage scroll compressor according to Embodiment 1 of the present invention.

[Fig. 2] Fig. 2 illustrates a gas-liquid separator-equipped refrigerant circuit to which the sealed two-stage scroll compressor according to Embodiment 1 of the present invention is applied.

[Fig. 3] Fig. 3 illustrates a COP calculation result of a gas-liquid separatorequipped refrigeration cycle to which the sealed two-stage scroll compressor according to Embodiment 1 of the present invention is applied.

[Fig. 4] Fig. 4 includes Mollier diagrams of the gas-liquid separator-equipped refrigeration cycle to which the sealed two-stage scroll compressor according to Embodiment 1 of the present invention is applied.

[Fig. 5] Fig. 5 includes diagrams illustrating a compression process in first compression chambers of the sealed two-stage scroll compressor according to Embodiment 1 of the present invention.

[Fig. 6] Fig. 6 illustrates a calculation result of a pressure increase curve of the pressure in the first compression chambers obtained when a first compression mechanism unit includes sub-ports and a calculation result of the pressure increase curve of the pressure in the first compression chambers obtained when the first compression mechanism unit does not include sub-ports.

[Fig. 7] Fig. 7 is a graph illustrating the relationship between a low-stage-side built-in volume ratio p1, a high-stage displacement, and a low-stage displacement of the sealed two-stage scroll compressor according to Embodiment 1 of the present invention.

[Fig. 8] Fig. 8 is a sectional view of a sealed two-stage scroll compressor according to Embodiment 2 of the present invention.

[Fig. 9] Fig. 9 includes explanatory diagrams each illustrating a horizontal section of a second eccentric part formed on an upper end portion of a crank shaft in Fig. 8.

Description of Embodiments [0010]

Embodiments 1 and 2 of the present invention will be described below based on the drawings. In the drawings, devices or parts assigned with identical reference signs are identical or equivalent to each other, which applies to the entire text of the specification. Further, the forms of component elements appearing throughout the text of the specification are basically illustrative, and the present invention is not exclusively limited to the description in the specification. In particular, combinations of component elements are not exclusively limited to the combinations in Embodiments 1 and 2, and a component element described in one of Embodiments 1 and 2 may be applied to the other one of Embodiments 1 and 2. Further, when there is no particular need to distinguish or identify a plurality of devices or parts of the same type distinguished by suffixes, such devices or parts may be described without the suffixes. Further, in the drawings, the dimensional relationships between component members may be different from actual ones.

[0011] Embodiment 1

Fig. 1 is an explanatory diagram illustrating a section of a sealed two-stage scroll compressor 100 according to Embodiment 1 of the present invention. The sealed two-stage scroll compressor 100 suctions fluid such as refrigerant, and compresses and discharges the fluid in a high-temperature, high-pressure state. The sealed two-stage scroll compressor 100 includes a sealed container 11, which is a sealed container forming an exterior of the sealed two-stage scroll compressor 100. The sealed container 11 houses therein a first compression mechanism unit 35, a second compression mechanism unit 36, a drive mechanism unit 37, and other component parts. In the sealed container 11, the first compression mechanism unit 35 is disposed below the drive mechanism unit 37, and the second compression mechanism unit 36 is disposed above the drive mechanism unit 37, as illustrated in Fig. 1. A lower part of the sealed container 11 includes an oil sump 21.

[0012]

The first compression mechanism unit 35 compresses refrigerant suctioned from a suction pipe 8 communicating with a pipe outside the sealed container 11, and discharges the compressed refrigerant into an intermediate-pressure space 23 in the sealed container 11. Further, the second compression mechanism unit 36 compresses fluid suctioned from the intermediate-pressure space 23, and discharges the compressed fluid into a high-pressure space 24 formed in an upper part inside the sealed container 11. High-temperature, high-pressure refrigerant discharged into the high-pressure space 24 is discharged from a discharge pipe 9 into a pipe outside the first compression mechanism unit 35. To compress fluid, the drive mechanism unit 37 drives a first orbiting scroll 2 forming the first compression mechanism unit 35 and a second orbiting scroll 5 forming the second compression mechanism unit 36. That is, the drive mechanism unit 37 drives the first orbiting scroll 2 and the second orbiting scroll 5 via a crank shaft 7, to thereby compress the refrigerant with the first compression mechanism unit 35 and the second compression mechanism unit 36. [0013]

The first compression mechanism unit 35 includes a first fixed scroll 1 and the first orbiting scroll 2. As illustrated in Fig. 1, the first orbiting scroll 2 is disposed on the upper side, and the first fixed scroll 1 is disposed on the lower side. Another method may be employed which disposes the first orbiting scroll 2 on the lower side and disposes the first fixed scroll 1 on the upper side. According to this method, however, it is necessary to fix the first fixed scroll to a first frame 3 fixed to the inside of the sealed container 11, and thereafter combine the first orbiting scroll 2 with the first fixed scroll and add a housing that holds the first orbiting scroll 2 from below. Therefore, the sealed two-stage scroll compressor 100 of Embodiment 1 is more advantageous in reducing the number of parts and suppressing an increase in cost. [0014]

The first fixed scroll 1 includes a first fixed baseplate 1 c and a first fixed scroll wrap 1 b that is a scroll wrap standing on one surface of the first fixed baseplate 1 c. The first orbiting scroll 2 includes a first orbiting baseplate 2c and a first orbiting scroll wrap 2b that is a scroll wrap standing on one surface of the first orbiting baseplate 2c. The first fixed scroll 1 and the first orbiting scroll 2 are disposed in the sealed container 11 with the first fixed scroll wrap 1b and the first orbiting scroll wrap 2b meshing with each other. Further, between the first fixed scroll wrap 1 b and the first orbiting scroll wrap 2b, first compression chambers 12 are formed which are reduced in capacity when moving toward the inside in the radial direction. In other words, the space between the scroll wraps of the first fixed scroll wrap 1 b and the first orbiting scroll wrap 2b forms a refrigerant passage in a process of compressing the refrigerant. The refrigerant passage is divided into spaces of predetermined capacities by the first fixed scroll wrap 1 b and the first orbiting scroll wrap 2b meshing with each other, thereby forming the first compression chambers 12. When the first orbiting scroll 2 rotates, the first compression chambers 12 move from the outer circumferences of the first fixed scroll 1 and the first orbiting scroll 2 toward the centers of the first fixed scroll 1 and the first orbiting scroll 2 while being reduced in capacity, and thereby compress the refrigerant in the first compression chambers 12. [0015]

The first fixed scroll 1 is fixed to the first frame 3. The first frame 3 is fixed to the sealed container 11. A central portion of the first fixed scroll 1 includes a first discharge port 1a to discharge fluid compressed to an intermediate pressure. An outlet opening of the first discharge port 1a is equipped with a first valve 15 formed by a leaf spring that covers the outlet opening to prevent backflow of fluid. When the refrigerant is compressed to the intermediate pressure in a central part inside the first compression chambers 12, the first valve 15 is lifted against elastic force thereof, allowing the compressed refrigerant to be discharged into the intermediate-pressure space 23 from the first discharge port 1 a. Further, the first valve 15 is equipped with a first valve holder 14 that limits the amount of lift of the first valve 15. The first valve holder 14 covers, from below, the first valve 15 covering the outlet opening, and thereby limits the movement of the first valve 15 lifted by the refrigerant discharged from the first discharge port to a predetermined amount.

[0016]

As well as the first discharge port 1a, sub-ports 1d that communicate with the intermediate-pressure space 23 are formed in the first fixed scroll 1. Each of the sub-ports 1d is formed on the refrigerant passage formed by the first fixed scroll wrap 1 b of the first fixed scroll 1 at a middle between the outer circumference and a central part. Further, the sub-port 1d is a hole that allows communication between the intermediate-pressure space 23 and the first compression chambers 12 formed as the divided spaces of the refrigerant passage. An outlet opening of the sub-port 1 d is equipped with a sub-port valve 29 formed by a leaf spring that covers the outlet opening to prevent backflow of the refrigerant. One end of the sub-port valve 29 is equipped with a sub-port valve holder 28 that limits the amount of lift of the sub-port valve 29. That is, when the refrigerant being compressed in the first compression chambers 12 is compressed to reach or exceed the intermediate pressure, the subport valve 29 is lifted against elastic force thereof, allowing the compressed refrigerant to be discharged into the intermediate-pressure space 23 from the subport 1d.

[0017]

With a first Oldham ring 25, the first orbiting scroll 2 performs eccentric revolving motion with respect to the first fixed scroll 1, without rotating around the axis of the first orbiting scroll 2. Further, a central portion of the first orbiting scroll 2 includes a first orbiting bearing portion 2d to receive drive force. A later-described first eccentric part 7a on the crank shaft 7 is fitted in the first orbiting bearing portion 2d of the first orbiting scroll 2 with a slight gap formed between the first eccentric part 7a and the first orbiting bearing portion 2d.

[0018]

The second compression mechanism unit 36 includes a second fixed scroll 4 and the second orbiting scroll 5. As illustrated in Fig. 1, the second orbiting scroll 5 is disposed on the lower side, and the second fixed scroll 4 is disposed on the upper side. The second fixed scroll 4 includes a second fixed baseplate 4c and a second fixed scroll wrap 4b that is a scroll wrap standing on one surface of the second fixed baseplate 4c. The second orbiting scroll 5 includes a second orbiting baseplate 5c and a second orbiting scroll wrap 5b that is a scroll wrap standing on one surface of the second orbiting baseplate 5c. The second fixed scroll 4 and the second orbiting scroll 5 are disposed in the sealed container 11 with the second fixed scroll wrap 4b and the second orbiting scroll wrap 5b meshing with each other. Further, between the second fixed scroll wrap 4b and the second orbiting scroll wrap 5b, second compression chambers 13 are formed which are reduced in capacity when moving toward the inside in the radial direction. In other words, the space between the scroll wraps of the second fixed scroll wrap 4b and the second orbiting scroll wrap 5b forms a refrigerant passage in a process of compressing the refrigerant. The refrigerant passage is divided into spaces of predetermined capacities by the second fixed scroll wrap 4b and the second orbiting scroll wrap 5b meshing with each other, thereby forming the second compression chambers 13. When the second orbiting scroll 5 rotates, the second compression chambers 13 move from the outer circumferences of the second fixed scroll 4 and the second orbiting scroll 5 toward the centers of the second fixed scroll 4 and the second orbiting scroll 5 while being reduced in capacity, and thereby compress the refrigerant in the second compression chambers 13. [0019]

The second fixed scroll 4 is fixed to a second frame 6. The second frame 6 is fixed to the sealed container 11. A central portion of the second fixed scroll 4 includes a second discharge port 4a to discharge the refrigerant compressed to a high pressure. An outlet opening of the second discharge port 4a is equipped with a second valve 17 formed by a leaf spring that covers the outlet opening to prevent backflow of the refrigerant. One end of the second valve 17 is equipped with a second valve holder 16 that limits the amount of lift of the second valve 17. When the fluid is compressed to a predetermined pressure in the second compression chambers 13, the second valve 17 is lifted against elastic force thereof, allowing the compressed refrigerant to be discharged into the high-pressure space 24 from the second discharge port 4a and then discharged to the outside of the sealed two-stage scroll compressor 100 through the discharge pipe 9.

[0020]

With a second Oldham ring 26, the second orbiting scroll 5 performs eccentric revolving motion with respect to the second fixed scroll 4, without rotating around the axis of the second orbiting scroll 5. Further, a central portion of the second orbiting scroll 5 includes a second orbiting bearing portion 5d to receive drive force. A laterdescribed second eccentric part 7b on the crank shaft 7 is fitted in the second orbiting bearing portion 5d of the second orbiting scroll 5 with a slight gap formed between the second eccentric part 7b and the second orbiting bearing portion 5d. A surface of the second orbiting scroll 5 opposite to a surface of the second orbiting scroll 5 having the second orbiting scroll wrap 5b is supported in the axial direction by a thrust bearing portion 6b included in the second frame 6.

[0021]

The drive mechanism unit 37 includes a stator 20 fixedly held inside the sealed container 11, a rotor 19 fixed to the crank shaft 7 and rotatably disposed inside the inner circumferential surface of the stator 20, and the crank shaft 7 housed in the sealed container 11 with the longitudinal direction of the crank shaft 7 oriented vertically and serving as a rotary shaft that rotates integrally with the rotor 19. With power supplied to the stator 20, the stator 20 functions to drive the rotor 19 to rotate. Further, the stator 20 is fixedly supported by the sealed container 11, with the outer circumferential surface of the stator 20 being shrink-fitted in the sealed container 11, for example. The rotor 19 is driven to rotate by the stator 20 supplied with power, and thereby rotates the crank shaft 7. The rotor 19, which includes therein a permanent magnet, is fixed around the outer circumference of the crank shaft 7, and is held with a slight gap formed between the rotor 19 and the stator 20.

[0022]

With the rotation of the rotor 19, the crank shaft 7 rotates to drive the first orbiting scroll 2 and the second orbiting scroll 5 to rotate. In an upper part inside the sealed container 11, the crank shaft 7 is rotatably supported by a bearing portion 6a formed in a central portion of the second frame 6. Further, in a lower part inside the sealed container 11, the crank shaft 7 is rotatably supported by a bearing portion 3a formed in a central portion of the first frame 3 fixedly disposed in the sealed container 11. A lower end portion of the crank shaft 7 is formed with the first eccentric part 7a, which is fitted in the first orbiting bearing portion 2d to allow the first orbiting scroll 2 to eccentrically rotate. An upper end portion of the crank shaft 7 is formed with the second eccentric part 7b, which is fitted in the second orbiting bearing portion 5d to allow the second orbiting scroll 5 to eccentrically rotate. The outer circumferential surface of the second frame 6 may be fixed to the inner circumferential surface of the sealed container 11 by shrink-fitting or welding, for example.

[0023]

The sealed container 11 is connected to the suction pipe 8 for suctioning the refrigerant into the sealed container 11, the discharge pipe 9 for discharging the refrigerant to the outside of the sealed container 11, and an injection pipe 10 that guides the refrigerant for cooling the intermediate-pressure space 23.

[0024]

The first frame 3 is fixed to the inside of the sealed container 11 below the drive mechanism unit 37, and the second frame 6 is fixed to the inside of the sealed container 11 above the drive mechanism unit 37. The first frame 3 is fixed to the inner circumferential surface of the sealed container 11, and a central portion of the first frame 3 includes a through-hole to pivotally support the crank shaft 7. With the bearing portion 3a, the first frame 3 rotatably supports the crank shaft 7. The bearing portion 3a is formed as a rolling bearing, for example. Further, the second frame 6 is firmly fixed to the inner circumferential surface of the sealed container 11, and a central portion of the second frame 6 includes a through-hole to pivotally support the crank shaft 7. The second frame 6 supports the second orbiting scroll 5, and rotatably supports the crank shaft 7 with the bearing portion 6a.

[0025]

An oil pump 40 is disposed on the lower side of the crank shaft 7. The first fixed scroll 1 includes a through-hole to transmit rotational force of the crank shaft 7 to the oil pump 40. The oil pump 40 is a displacement pump. With the rotation of the crank shaft 7, the oil pump 40 supplies refrigerating machine oil stored in the oil sump 21 to the first orbiting bearing portion 2d, the bearing portion 3a, the second orbiting bearing portion 5d, the bearing portion 6a, and the thrust bearing portion 6b via an oil circuit 27 formed inside the crank shaft 7.

[0026]

The sealed container 11 includes therein the first Oldham ring 25 for preventing rotational motion of the first orbiting scroll 2 during the eccentric revolving motion of the first orbiting scroll 2 and the second Oldham ring 26 for preventing rotational motion of the second orbiting scroll 5 during the eccentric revolving motion of the second orbiting scroll 5. The first Oldham ring 25 is disposed between the first orbiting scroll 2 and the first frame 3, and functions to prevent the rotational motion of the first orbiting scroll 2 and allow orbital motion of the first orbiting scroll 2. Further, the second Oldham ring 26 is disposed between the second orbiting scroll 5 and the second frame 6, and functions to prevent the rotational motion of the second orbiting scroll 5 and allow orbital motion of the second orbiting scroll 5.

[0027]

An operation of the sealed two-stage scroll compressor 100 will now be described. With power supplied to a not-illustrated power supply terminal formed on the sealed container 11, torque is generated in the stator 20 and the rotor 19, thereby rotating the crank shaft 7. The first orbiting scroll 2 is rotatably fitted around the first eccentric part 7a on the crank shaft 7, and the second orbiting scroll 5 is rotatably fitted around the second eccentric part 7b on the crank shaft 7. The first orbiting scroll 2 and the first fixed scroll 1, which include the scroll wraps each formed to follow an involute curve (the first orbiting scroll wrap 2b and the first fixed scroll wrap 1 b), mesh with each other to form the plural first compression chambers 12. The second orbiting scroll 5 and the second fixed scroll 4, which include the scroll wraps each formed to follow an involute curve (the second orbiting scroll wrap 5b and the second fixed scroll wrap 4b), mesh with each other to form the plural second compression chambers 13.

[0028]

Then, with the eccentric revolving motion of the first orbiting scroll 2, the first compression chambers 12 with gas suctioned therein from the suction pipe 8 reduce the respective capacities thereof while moving toward the center from an outer circumferential area, and thereby compress the refrigerant. The refrigerant gas compressed in the first compression chambers 12 is discharged, against the first valve 15, into the intermediate-pressure space 23 from the first discharge port 1a formed in the first fixed scroll 1. The refrigerant compressed in the first compression chambers 12 mixes with refrigerant flowing from the injection pipe 10 that allows communication between the intermediate-pressure space 23 and a pipe outside the sealed container 11.

[0029]

Then, with the eccentric revolving motion of the second orbiting scroll 5, the second compression chambers 13 with the refrigerant suctioned therein from the intermediate-pressure space 23 reduce the respective capacities thereof while moving toward the center from an outer circumferential area, and thereby compress the refrigerant. The refrigerant gas compressed in the second compression chambers 13 is discharged, against the second valve 17, from the second discharge port 4a formed in the second fixed scroll 4, and then is exhausted to the outside of the sealed container 11 from the discharge pipe 9. The first valve holder 14 and the second valve holder 16 regulate deformation of the first valve 15 and deformation of the second valve 17, respectively, such that the first valve 15 and the second valve 17 are not unnecessarily deformed, thereby preventing damage of the first valve 15 and the second valve 17.

[0030]

Fig. 2 illustrates a gas-liquid separator-equipped refrigerant circuit to which the sealed two-stage scroll compressor 100 according to Embodiment 1 of the present invention is applied. The high-temperature, high-pressure refrigerant discharged from the compressor 100 is cooled by a gas cooler 51. The refrigerant cooled by the gas cooler 51 is expanded to the intermediate pressure by a first expansion valve 52. Thereafter, the refrigerant flows into a gas-liquid separator 54. Liquid refrigerant accumulating in a bottom part of the gas-liquid separator 54 is expanded to the low pressure by a second expansion valve 53. Thereafter, the liquid refrigerant turns into gas refrigerant in an evaporator 55, and is suctioned into the sealed two-stage scroll compressor 100 from the suction pipe 8 thereof. Thus configured to perform the expansion at two stages with two expansion valves, the refrigerant circuit is more improved in refrigeration capacity than when configured to perform the expansion at one stage. Meanwhile, gas refrigerant separated from the liquid refrigerant in the gas-liquid separator 54 and accumulated in an upper part of the gas-liquid separator 54 flows into the intermediate-pressure space 23 from the injection pipe 10 of the sealed two-stage scroll compressor 100, and is suctioned into the second compression chambers 13 to be compressed therein.

[0031]

Fig. 3 illustrates a COP calculation result of a gas-liquid separator-equipped refrigeration cycle to which the sealed two-stage scroll compressor 100 according to Embodiment 1 of the present invention is applied. Fig. 3 illustrates a COP calculation result obtained when carbon dioxide (R744) is used as the refrigerant and the high pressure and the low pressure are set to 10 MPa and 1 MPa, respectively, with the intermediate pressure being illustrated as a parameter on the horizontal axis. According to the calculation result, the lower the intermediate pressure is set, the higher the COP is.

[0032]

Fig. 4 includes Mollier diagrams of the gas-liquid separator-equipped refrigeration cycle to which the sealed two-stage scroll compressor 100 according to Embodiment 1 of the present invention is applied. Fig. 4 illustrates Mollier diagrams obtained when carbon dioxide (R744) is used as the refrigerant and the high pressure and the low pressure are set to 10 MPa and 1 MPa, respectively. In Fig. 4, (a) illustrates the result of the refrigeration cycle with the intermediate pressure set to 2 MPa, and (b) illustrates the result of the refrigeration cycle with the intermediate pressure set to 3 MPa. As illustrated in (a) of Fig. 4, a reduction in the intermediate pressure increases the enthalpy difference, and improves the refrigeration capacity and the COP. That is, it is desirable to set the compression ratio of the first compression chambers 12 on the low-stage side to be smaller than the compression ratio of the second compression chambers 13 on the high-stage side. If the refrigeration cycle is configured to use carbon dioxide, the high pressure corresponds to a supercritical pressure owing to characteristics of the refrigerant. Therefore, the refrigeration cycle has lower refrigeration capacity than the refrigeration capacity obtained with HFC refrigerant such as R410A, and thus the COP is also reduced.

Accordingly, the advantage of improving the refrigeration capacity with the gas-liquid separator-equipped two-stage expansion cycle is increased.

[0033]

The COP is improved by setting the compression ratio of the first compression chambers 12 on the low-stage side to be smaller than the compression ratio of the second compression chambers 13 on the high-stage side. In the case of a scroll compression mechanism, however, the pressure of the suctioned refrigerant may be increased to exceed a discharge-side pressure (over-compressed) in the compression chambers, depending on the built-in volume ratio of the compression mechanism. Compressing the refrigerant to a pressure higher than the dischargeside pressure is unnecessary work, which leads to deterioration in the performance of the sealed two-stage scroll compressor 100. In the sealed two-stage scroll compressor 100 according to Embodiment 1, therefore, a built-in volume ratio p2 of the second compression chambers 13 on the high-stage side is set to be greater than a built-in volume ratio p1 of the first compression chambers 12 on the low-stage side. It is thereby possible to reduce the unnecessary work in the low-stage-side compression mechanism, and improve the performance.

[0034]

Herein, for example, the built-in volume ratio p1 of the first compression chambers is the ratio between a compression chamber volume V_si immediately after the completion of confinement in Fig. 5 described later (displacement = 2 x Vsi) and a compression chamber volume Vei immediately before communication with an innermost chamber of the first compression chambers, and is expressed as p1 = Vsi/Vei. Further, the built-in volume ratio p2 of the second compression chambers is similarly expressed as p2 = V_S2/Ve2, wherein V_S2 represents a compression chamber volume immediately after the completion of confinement and Ve2 represents a compression chamber volume immediately before communication with an innermost chamber of the second compression chambers. Since it is impossible to compress the refrigerant when the built-in volume ratio is 1 or less, the built-in volume ratios are set as 1 < p1 < p2.

[0035]

Fig. 5 includes diagrams illustrating a compression process in the first compression chambers 12 of the sealed two-stage scroll compressor according to Embodiment 1 of the present invention. In Fig. 5, (a) to (f) illustrate the compression process in the first compression chambers 12 at intervals of 60 degrees. With the revolving motion of the first orbiting scroll 2, the first compression chambers 12 move toward the center while reducing the respective capacities thereof, and thereby compress the refrigerant. The sub-ports 1d are formed in first compression chambers 12 located symmetrically to each other with respect to the center of the first fixed scroll 1 such that each of the symmetrically located first compression chambers 12 has one sub-port 1d to equalize the pressure between the symmetrically located first compression chambers 12.

[0036]

In Fig. 5, (a) illustrates a state in which the suction of the refrigerant into one of the first compression chambers 12 formed by the first fixed scroll 1 and the first orbiting scroll 2 has been completed (a confinement completion angle of 0 degrees). The sub-ports 1d are formed at respective positions at which the sub-ports 1d do not communicate with the low-pressure space 22.

In Fig. 5, (b) and (c) illustrate a state in which the first orbiting scroll 2 has rotated from the state in (a) of Fig. 5. With the rotation of the first orbiting scroll, the first compression chamber 12 gradually moves toward the inside of the scroll wraps, gradually reducing the capacity thereof.

In (d) of Fig. 5, with progress of the revolving motion of the first orbiting scroll 2, the first fixed scroll wrap 1 b and the first orbiting scroll wrap 2b have moved to respective positions above the sub-ports 1d.

In (e) of Fig. 5, with further progress of the revolving motion of the first orbiting scroll 2, the first compression chamber 12 having suctioned the refrigerant in (a) described above has moved toward a central portion, and communicates with one of the sub-ports 1d. If the pressure in the first compression chamber 12 exceeds the pressure in the intermediate-pressure space 23, the refrigerant starts to be discharged from the sub-port 1d.

In (f) of Fig. 5, with further progress of the revolving motion of the first orbiting scroll 2, the first compression chamber 12 and the sub-port 1d continue to communicate with each other. If the pressure in the first compression chamber 12 is higher than the pressure in the intermediate-pressure space 23, therefore, the refrigerant continues to be discharged from the sub-port 1 d. If the pressure in the first compression chamber 12 is reduced to be equal to the pressure in the intermediate-pressure space 23, the sub-port valve 29 is closed, and the discharge is completed.

Returning back to the state in (a) of Fig. 5, with further progress of the revolving motion of the first orbiting scroll 2, the sub-ports 1d are closed by the first orbiting scroll.

Further, in (b) of Fig. 5, the revolving motion of the first orbiting scroll 2 has further progressed to a state immediately before communication between the innermost chamber with the first discharge port 1a and the first compression chamber 12 next to the innermost chamber. If the revolving motion of the first orbiting scroll 2 further progresses from this state, the innermost chamber and the first compression chamber 12 next thereto communicate with each other. If the pressure in the innermost chamber exceeds the pressure in the intermediate-pressure space 23, the refrigerant is discharged from the first discharge port 1a.

[0037]

Fig. 6 illustrates a calculation result of a pressure increase curve of the pressure in the first compression chambers 12 obtained when the first compression mechanism unit 35 includes the sub-ports 1d and a calculation result of the pressure increase curve of the pressure in the first compression chambers 12 obtained when the first compression mechanism unit 35 does not include the sub-ports 1d. The overshoot of the pressure increase curve and the loss are smaller in the calculation result of the first compression mechanism unit 35 with the sub-ports 1d than in the calculation result of the first compression mechanism unit 35 without the sub-ports 1d.

Accordingly, it is possible to suppress the deterioration in the performance of the twostage scroll compressor 100 by forming the sub-ports 1d in the first compression mechanism unit 35.

[0038]

If the refrigerant flowing back from the suction pipe 8 is in the liquid state, the first compression chambers 12 compress the liquid, causing an abnormal increase in the pressure of the first compression chambers 12. With the sub-ports 1 d, however, the liquid refrigerant is released, making it possible to suppress the abnormal increase in pressure and prevent damage of the first compression chambers 12. Accordingly, the sealed two-stage scroll compressor 100 is capable of ensuring reliability thereof without installation of a suction muffler upstream of the suction pipe 8. With no need to install a suction muffler, the sealed two-stage scroll compressor 100 according to Embodiment 1 is capable of reducing costs. Further, whereas a suction muffler attached to a side surface of a compressor disturbs the balance of the compressor and thus increases vibration and noise, the sealed two-stage scroll compressor 100 according to Embodiment 1 is capable of suppressing vibration and noise.

[0039]

In Embodiment 1, a description has been given of the configuration in which the sub-ports 1d are formed in the first fixed scroll 1 of the first compression mechanism unit to allow communication between the first compression chambers 12 and the intermediate-pressure space 23. However, the second fixed scroll 4 of the second compression mechanism unit 36 may include sub-ports. In this configuration, the sub-ports allow communication between the second compression chambers 13 and the high-pressure space 24.

[0040]

Fig. 7 is a graph illustrating the relationship between the low-stage-side built-in volume ratio p1, a high-stage displacement, and a low-stage displacement of the sealed two-stage scroll compressor 100 according to Embodiment 1 of the present invention. Dots plotted in the graph of Fig. 7 represent lower limits of values at which over-compression does not occur in the first compression chambers 12 on the low-stage side, and denote that the deterioration in the performance of the two-stage scroll compressor 100 is suppressed in the range above a curve connecting the dots. The relationship between a displacement (low-stage displacement) V1 of the first compression mechanism and a displacement (high-stage displacement) V2 of the second compression mechanism is set as V2/V1 < 1 such that the second compression chambers 13 do not suction the refrigerant by an amount exceeding the amount of refrigerant suctioned from the suction pipe 8. The condition preventing over-compression in the first compression chambers 12 corresponds to the hatched area in Fig. 7. With an increase in the low-stage-side built-in volume ratio p1, the range of possible values of V2/V1 is increased. The condition of the relationship between p1 and V2/V1 preventing over-compression in the first compression chambers 12 is expressed as V2/V1 > 1/p1. Further, the upper limit of the built-in volume ratio p1 is determined by the respective shapes of the first fixed scroll 1 and the first orbiting scroll 2 storable in the sealed container 11. The upper limit of the built-in volume ratio p1 is 4.0 in Fig. 7, but is not limited thereto.

[0041]

Further, in Embodiment 1, the sealed two-stage scroll compressor 100 including the first compression mechanism unit 35 and the second compression mechanism unit 36 has been described as an example. However, a compressor may include more stages of compression mechanism units. The sealed two-stage scroll compressor 100 corresponds to a multi-stage scroll compressor of the present invention.

[0042] (Effects of Embodiment 1) (1) The sealed two-stage scroll compressor 100 according to Embodiment 1 includes the sealed container 11, at least two compression mechanism units including the first compression mechanism unit 35 and the second compression mechanism unit 36 and disposed in the sealed container 11 to compress refrigerant, and the drive mechanism unit 37 that drives the first compression mechanism unit 35 and the second compression mechanism unit 36. The sealed container 11 includes three internal spaces: the low-pressure space 22 from which the refrigerant is suctioned by the first compression mechanism unit 35 as one of the at least two compression mechanism units, the intermediate-pressure space 23 into which the refrigerant suctioned from the low-pressure space 22 and compressed by the first compression mechanism unit 35 as one of the at least two compression mechanism units is discharged, and the high-pressure space 24 into which the refrigerant suctioned from the intermediate-pressure space 23 and compressed by the second compression mechanism unit 36 as the other one of the at least two compression mechanism units is discharged. The first compression mechanism unit 35 includes the first compression chambers 12 and the first discharge port 1a, and the second compression mechanism unit 36 includes the second compression chambers 13 and the second discharge port 4a. The first compression chambers 12 are formed by a combination of the first fixed scroll 1 and the first orbiting scroll 2. The first fixed scroll 1 includes the first fixed baseplate 1 c and the first fixed scroll wrap 1 b projecting therefrom, and the first orbiting scroll 2 includes the first orbiting baseplate 2c and the first orbiting scroll wrap 2b projecting therefrom. The second compression chambers 13 are formed by a combination of the second fixed scroll 4 and the second orbiting scroll 5. The second fixed scroll 4 includes the second fixed baseplate 4c and the second fixed scroll wrap 4b projecting therefrom, and the second orbiting scroll 5 includes the second orbiting baseplate 5c and the second orbiting scroll wrap 5b projecting therefrom. The first discharge port 1a is located at respective central portions of the first fixed scroll wrap 1 b and the first orbiting scroll wrap 2b, and allows communication between the first compression chambers 12 and one of the three internal spaces. The second discharge port 4a is located at respective central portions of the second fixed scroll wrap 4b and the second orbiting scroll wrap 5b, and allows communication between the second compression chambers 13 and one of the three internal spaces. The first compression mechanism unit 35 as at least one of the at least two compression mechanism units includes the sub-ports 1d to allow communication between the first compression chambers 12 and one of the three internal spaces. In the compression process of the refrigerant, the sub-ports 1d allow communication between the first compression chambers 12 and the one of the three internal spaces before the first compression chambers 12 communicate with the first discharge port 1a. The first compression mechanism unit 35 corresponds to one of the at least two compression mechanism units of the present invention, and the second compression mechanism unit 36 corresponds to an other one of the at least two compression mechanism units of the present invention. Further, each of the first fixed scroll wrap 1 b, the first orbiting scroll wrap 2b, the second fixed scroll wrap 4b, and the second orbiting scroll wrap 5b corresponds to a scroll wrap of the present invention, and each of the first fixed baseplate 1c, the first orbiting baseplate 2c, the second fixed baseplate 4c, and the second orbiting baseplate 5c corresponds to a baseplate of the present invention. Further, each of the first compression chambers 12 and the second compression chambers 13 corresponds to compression a chamber of the present invention.

(2) In the sealed two-stage scroll compressor 100 according to Embodiment 1, each of the sub-ports is formed at a middle on the refrigerant passage extending from the outer circumference of the first fixed scroll wrap 1 b of the first fixed scroll 1 to the first discharge port 1a.

With this configuration, even if liquid refrigerant is suctioned from the suction pipe 8 and thus the pressure in the first compression chambers 12 is increased, for example, the refrigerant is released from the sub-ports 1 d, thereby enhancing the reliability of the sealed two-stage scroll compressor 100 according to Embodiment 1. Further, there is no need to install a muffler upstream of the position at which the refrigerant is suctioned into the first compression mechanism unit 35. It is therefore possible to prevent vibration and noise occurring in the sealed two-stage scroll compressor 100, and suppress an increase in cost. Further, if the second compression mechanism unit 36 also includes sub-ports, the pressure in the second compression chambers 13 is not increased to exceed the discharge-side pressure. Consequently, the sealed two-stage scroll compressor 100 is saved from unnecessary work, and thus is improved in efficiency.

[0043] (3) In the sealed two-stage scroll compressor 100 according to Embodiment 1, the outlet opening of each of the sub-ports 1d is equipped with the sub-port valve 29 that prevents the refrigerant from flowing backward into the compression chambers from one of the three internal spaces.

With this configuration, the refrigerant discharged into the intermediatepressure space 23 from the first compression chambers 12 does not flow backward into the first compression chambers 12, for example, thereby enhancing the reliability of the sealed two-stage scroll compressor 100.

[0044] (4) In the sealed two-stage scroll compressor 100 according to Embodiment 1, the at least two compression mechanism units include the first compression mechanism unit 35, which compresses the refrigerant suctioned from the lowpressure space 22 and discharges the compressed refrigerant into the intermediatepressure space 23, and the second compression mechanism unit 36, which compresses the refrigerant suctioned from the intermediate-pressure space 23 and discharges the compressed refrigerant into the high-pressure space 24. The built-in volume ratio p1 of the first compression mechanism unit 35 is smaller than the built-in volume ratio p2 of the second compression mechanism unit 36.

With this configuration, the built-in volume ratio p2 of the second compression chambers 13 on the high-stage side is set to be greater than the built-in volume ratio p1 of the first compression chambers 12 on the low-stage side in the sealed twostage scroll compressor 100 according to Embodiment 1. It is thereby possible to reduce unnecessary work in the first compression mechanism unit 35 on the lowstage side, and improve the performance.

[0045] (5) In the sealed two-stage scroll compressor 100 according to Embodiment 1, the sub-ports 1d formed in the first compression mechanism unit 35 allow communication between the first compression chambers 12 formed in the first compression mechanism unit 35 and the intermediate-pressure space 23.

(6) Further, in the sealed two-stage scroll compressor 100 according to Embodiment 1, the sub-ports formed in the second compression mechanism unit 36 allow communication between the second compression chambers 13 formed in the second compression mechanism unit 36 and the high-pressure space 24.

With this configuration, the sealed two-stage scroll compressor 100 according to Embodiment 1 obtains the effects described above in (1) and (2).

[0046] (7) In the sealed two-stage scroll compressor 100 according to Embodiment 1, the first compression mechanism unit 35 is disposed below the drive mechanism unit 37, and the second compression mechanism unit 36 is disposed above the drive mechanism unit 37.

With this configuration, the sealed two-stage scroll compressor 100 is capable of efficiently driving the first compression mechanism unit 35 on the low-stage side and the second compression mechanism unit 36 on the high-stage side.

[0047] (8) In the sealed two-stage scroll compressor 100 according to Embodiment 1, the first orbiting scroll 2 included in the first compression mechanism unit 35 is disposed above the first fixed scroll 1 included in the first compression mechanism unit 35, and the first fixed scroll 1 is fixed to the inside of the sealed container.

With this configuration, the sealed two-stage scroll compressor 100 is capable of suppressing an increase in the number of parts and thus suppressing an increase in cost.

[0048] (9) In the sealed two-stage scroll compressor 100 according to Embodiment 1, when V1 represents the displacement of the first compression mechanism unit 35 and V2 represents the displacement of the second compression mechanism unit 36, the displacements V1 and V2 and the built-in volume ratio p1 are set to meet the relationship: V2/V1 < 1/p1.

With this configuration, the second compression chambers 13 do not suction the refrigerant from the intermediate-pressure space 23 by an amount exceeding the amount of refrigerant suctioned from the suction pipe 8 in the sealed two-stage scroll compressor 100. Consequently, over-compression does not occur in the first compression chambers 12 on the low-stage side.

[0049]

Embodiment 2

As for the sealed two-stage scroll compressor 100 according to Embodiment 1, a fixed crank mechanism having the second orbiting scroll 5 directly and rotatably attached around the crank shaft 7 has been described as an example. As to a sealed two-stage scroll compressor 200 according to Embodiment 2, a description will be given of a configuration employing a driven crank mechanism that pushes the second orbiting scroll 5 against the second fixed scroll 4 with centrifugal force and a structure that applies back pressure to the back surface of the first orbiting scroll 2, to thereby improve the airtightness of the first compression mechanism unit 35 and the second compression mechanism unit 36.

[0050]

Fig. 8 is a sectional view of the sealed two-stage scroll compressor 200 according to Embodiment 2 of the present invention. Fig. 9 includes explanatory diagrams each illustrating a horizontal section of the second eccentric part 7b formed on the upper end portion of the crank shaft 7 in Fig. 8. In Fig. 9, (a) illustrates a compressor stopped state, in which the crank shaft 7 is not rotating, and thus the center of a bush 18 is aligned with the center of the second eccentric part 7b. In Fig. 9, (b) illustrates a compressor operating state, in which the crank shaft 7 is rotating, and thereby the center of the bush 18 is deviated from the center of the second eccentric part 7b. The inner circumferential surface of the bush 18 disposed on the upper end portion of the crank shaft 7 includes flat surface portions 7ba that are in contact with the outer circumferential surface of the second eccentric part 7b. When the crank shaft 7 rotates, the bush 18 moves in the radial direction along the flat surface portions, thereby pushing a side surface of the second orbiting scroll wrap 5b of the second orbiting scroll 5 against a side surface of the second fixed scroll wrap 4b of the second fixed scroll 4. With this configuration, a driven crank mechanism that improves the airtightness of the second compression chambers 13 is formed in the second compression mechanism unit 36. As to a gap in the axial direction between the second fixed scroll 4 and the second orbiting scroll 5, a tip seal made of resin, for example, is attached to each of a distal end of the second orbiting scroll wrap 5b and a distal end of the second fixed scroll wrap 4b, to thereby improve the airtightness. With this improvement in airtightness, the refrigerant gas is efficiently compressed, and the sealed two-stage scroll compressor 200 is improved in performance.

[0051]

Further, with a back pressure chamber 30 formed near the back surface of the first orbiting scroll wrap 2b of the first orbiting scroll 2, it is possible to push the first orbiting scroll 2 against the first fixed scroll 1 during the operation and thereby improve the airtightness. The back pressure chamber 30 communicates with the intermediate-pressure space 23, for example, to generate force for pushing the first orbiting scroll 2 toward the first fixed scroll 1.

[0052]

As for the sealed two-stage scroll compressor 200 according to Embodiment 2, a description has been given of the configuration in which the first compression mechanism unit 35 employs a structure that pushes the first orbiting scroll 2 in the axial direction, and the second orbiting scroll 5 of the second compression mechanism unit 36 employs a driven crank mechanism. However, only one of these structures may be employed.

[0053] (Effects of Embodiment 2) (10) During the operation of the sealed two-stage scroll compressor 200 according to Embodiment 2, the first orbiting scroll 2 included in the first compression mechanism unit 35 is pushed against the first fixed scroll 1 by the pressure of the refrigerant in the intermediate-pressure space 23.

With this configuration, the sealed two-stage scroll compressor 200 is capable of pushing the first orbiting scroll 2 against the first fixed scroll 1 in the first compression mechanism unit 35 on the low-stage side with the pressure of the intermediate-pressure space 23. Consequently, the airtightness of the first compression chambers 12 is improved, thereby improving the efficiency of the compressor.

[0054] (11) The sealed two-stage scroll compressor 200 according to Embodiment 2 includes the crank shaft 7 that transmits the rotation of the drive mechanism unit 37 to the first compression mechanism unit 35 and the second compression mechanism unit 36. The second orbiting scroll 5 included in the second compression mechanism unit 36 is driven by the driven crank mechanism disposed between the crank shaft 7 and the second compression mechanism unit 36.

With this configuration, the sealed two-stage scroll compressor 200 is capable of pushing the side surface of the second orbiting scroll wrap 5b against the side surface of the second fixed scroll wrap 4b in the second compression mechanism unit 36 on the high-stage side. Consequently, the airtightness of the second compression chambers 13 is improved, thereby improving the efficiency of the compressor.

[0055] (12) Further, during the operation of the sealed two-stage scroll compressor

200 according to Embodiment 2, the distal end of the first orbiting scroll wrap 2b of the first orbiting scroll 2 and the first fixed baseplate 1c of the first fixed scroll 1 come into contact with each other. The distal end of the first fixed scroll wrap 1 b of the first fixed scroll 1 and the first orbiting baseplate 2c of the first orbiting scroll 2 come into contact with each other. The side surface of the second orbiting scroll wrap 5b of the second orbiting scroll 5 included in the second compression mechanism unit 36 and the side surface of the second fixed scroll wrap 4b of the second fixed scroll 4 included in the second compression mechanism unit 36 come into contact with each other.

With this configuration, the sealed two-stage scroll compressor 200 is improved in the airtightness of the first compression mechanism unit 35 and the second compression mechanism unit 36. Accordingly, it is possible to improve the efficiency of the compressor.

Reference Signs List [0056] first fixed scroll 1a first discharge port 1b first fixed scroll wrap 1c first fixed baseplate 1d sub-port 2 first orbiting scroll 2b first orbiting scroll wrap 2c first orbiting baseplate 2d first orbiting bearing portion 3 first frame 3a bearing portion 4 second fixed scroll 4a second discharge port 4b second fixed scroll wrap 4c second fixed baseplate 5 second orbiting scroll 5b second orbiting scroll wrap 5c second orbiting baseplate 5d second orbiting bearing portion 6 second frame 6a bearing portion 6b thrust bearing portion 7 crank shaft 7a first eccentric part 7b second eccentric part 8 suction pipe 9 discharge pipe 10 injection pipe 11 sealed container 12 first compression chamber 13 second compression chamber 14 first valve holder 15 first valve 16 second valve holder 17 second valve 18 bush 19 rotor 20 stator 21 oil sump 22 low-pressure space 23 intermediatepressure space 24 high-pressure space 25 first Oldham ring 26 second

Oldham ring 27 oil circuit 28 sub-port valve holder 29 sub-port valve 30 back pressure chamber 35 first compression mechanism unit 36 second compression mechanism unit 37 drive mechanism unit 40 oil pump 51 gas cooler 52 first expansion valve 53 second expansion valve 54 gas-liquid separator 55 evaporator 100 sealed two-stage scroll compressor 200 sealed two-stage scroll compressor compression chamber volume V_si compression chamber volume p1

Vei compression chamber volume Ve2 compression chamber volume V_S2 built-in volume ratio p2 built-in volume ratio

Claims

CLAIMS [Claim 1]

A multi-stage scroll compressor comprising:

a sealed container;

at least two compression mechanism units disposed in the sealed container to compress refrigerant; and a drive mechanism unit configured to drive the at least two compression mechanism units, the sealed container including three internal spaces including a low-pressure space from which the refrigerant is suctioned by one of the at least two compression mechanism units, an intermediate-pressure space into which the refrigerant suctioned from the low-pressure space and compressed by the one of the at least two compression mechanism units is discharged, and a high-pressure space into which the refrigerant suctioned from the intermediate-pressure space and compressed by an other one of the at least two compression mechanism units is discharged, each of the at least two compression mechanism units including a compression chamber formed by a combination of a fixed scroll and an orbiting scroll, the fixed scroll and the orbiting scroll each including a baseplate and a scroll wrap projecting from the baseplate, and a discharge port located at a central portion of the scroll wrap to allow communication between the compression chamber and one of the three internal spaces, at least one of the at least two compression mechanism units including a subport configured to allow communication between the compression chamber and the one of the three internal spaces, and in a compression process of the refrigerant, the sub-port allowing communication between the compression chamber and the one of the three internal spaces before the compression chamber communicates with the discharge port.
[Claim 2]

The multi-stage scroll compressor of claim 1, wherein the sub-port is formed at a middle on a refrigerant passage extending from an outer circumference of the scroll wrap of the fixed scroll to the discharge port.
[Claim 3]

The multi-stage scroll compressor of claim 1 or 2, wherein an outlet opening of the sub-port is equipped with a sub-port valve that prevents the refrigerant from flowing backward into the compression chamber from the one of the three internal spaces.
[Claim 4]

The multi-stage scroll compressor of any one of claims 1 to 3, wherein the at least two compression mechanism units include a first compression mechanism unit configured to compress the refrigerant suctioned from the low-pressure space and discharge the refrigerant into the intermediate-pressure space, and a second compression mechanism unit configured to compress the refrigerant suctioned from the intermediate-pressure space and discharge the refrigerant into the high-pressure space, and wherein a built-in volume ratio p1 of the first compression mechanism unit is smaller than a built-in volume ratio p2 of the second compression mechanism unit. [Claim 5]

The multi-stage scroll compressor of claim 4, wherein the sub-port formed in the first compression mechanism unit allows communication between a first compression chamber formed in the first compression mechanism unit and the intermediate-pressure space.

[Claim 6]

The multi-stage scroll compressor of claim 4 or 5, wherein the sub-port formed in the second compression mechanism unit allows communication between a second compression chamber formed in the second compression mechanism unit and the high-pressure space.

[Claim 7]

The multi-stage scroll compressor of any one of claims 4 to 6, wherein the first compression mechanism unit is disposed below the drive mechanism unit, and the second compression mechanism unit is disposed above the drive mechanism unit. [Claim 8]

The multi-stage scroll compressor of any one of claims 4 to 7, wherein a first orbiting scroll included in the first compression mechanism unit is disposed above a first fixed scroll included in the first compression mechanism unit, and wherein the first fixed scroll is fixed to an inside of the sealed container. [Claim 9]

The multi-stage scroll compressor of claim 8, wherein, during an operation of the multi-stage scroll compressor, the first orbiting scroll included in the first compression mechanism unit is pushed against the first fixed scroll by pressure of the refrigerant in the intermediate-pressure space.

[Claim 10]

The multi-stage scroll compressor of claim 8 or 9, comprising a crank shaft configured to transmit rotation of the drive mechanism unit to the first compression mechanism unit and the second compression mechanism unit, wherein a second orbiting scroll included in the second compression mechanism unit is driven by a driven crank mechanism disposed between the crank shaft and the second compression mechanism unit.

[Claim 11]

The multi-stage scroll compressor of any one of claims 8 to 10, wherein, during an operation of the multi-stage scroll compressor, a distal end of the scroll wrap of the first orbiting scroll and the baseplate of the first fixed scroll come into contact with each other, a distal end of the scroll wrap of the first fixed scroll and the baseplate of the first orbiting scroll come into contact with each other, and a side surface of the scroll wrap of the second orbiting scroll included in the second compression mechanism unit and a side surface of the scroll wrap of the second fixed scroll included in the second compression mechanism unit come into contact with each other.

[Claim 12]

The multi-stage scroll compressor of any one of claims 4 to 11, wherein when

5 V1 represents a displacement of the first compression mechanism unit and V2 represents a displacement of the second compression mechanism unit, the displacement V1, the displacement V2, and the built-in volume ratio p1 are set to meet a relationship: V2/V1 < 1/p1.