JP2020094761A - Multi-stage compression system - Google Patents

Abstract

To solve such the problem that each of the compressors in a refrigeration device using a plurality of multi-stage compressors needs to keep a proper amount of refrigeration oil.SOLUTION: A multi-stage compression system 20 includes a low-stage compressor 21, a high-stage compressor 23, refrigerant piping 151-156, 16, pressure lowering elements 26, 15b and an oil discharge pipe 32. The refrigerant piping 151-156, 16 introduces refrigerant compressed and discharged by the low-stage compressor 21 into a suction part of the high-stage compressor 23. The pressure lowering elements 26, 15b are arranged in the middle of intermediate pressure refrigerant piping 151-156, 16. The oil discharge pipe 32 discharges oil from the low-stage compressor 21. The oil discharge pipe 32 connects the low-stage compressor 21 to refrigerant piping located downstream relative to the pressure lowering elements 26, 15b.SELECTED DRAWING: Figure 1

Description

A multi-stage compression system that uses refrigerant and oil.

In a refrigeration system, a multistage compression mechanism using a plurality of compressors is recommended and used depending on the working refrigerant. In a multi-stage compression mechanism using a plurality of compressors, it is important to control the refrigerating machine oil in an appropriate amount in the plurality of compressors. In other words, it is necessary to control so that oil is not excessively unevenly distributed in one compressor.

In Patent Document 1 (Japanese Patent Laid-Open No. 2008-261227), in order to keep the height of the oil level of the low-stage and high-stage compressors at a constant level, the low-stage compressor has a low stage. The side oil drain passage is provided with an oil return passage for returning the oil discharged on the high stage side to the suction pipe of the low stage compressor.

In Patent Document 1, the low-stage side oil drain passage is connected to the suction side of the high-stage side compressor downstream of the high-stage side accumulator. Further, no particular consideration is given to the refrigerant confluence point of the intercooler or the intermediate injection. However, in the refrigerant pipe from the low-stage side refrigerant discharge part to the high-stage side refrigerant suction part, if a pressure reduction element such as a refrigerant confluence point of an intercooler or an intermediate injection is provided, the pressure in the refrigerant pipe is reduced. Occurs. Therefore, the refrigerant and the amount of oil passing through the oil drain passage vary depending on the connection position of the oil drain passage, and the amount of oil in the low-stage compressor also varies. Therefore, when the pressure reducing element is provided, the connection position of the oil drain passage to the refrigerant pipe needs to be appropriately selected according to the amount of oil in the low-stage compressor.

The multistage compression system of the first aspect uses a refrigerant and oil. The multi-stage compression system has a low stage compressor, a high stage compressor, a refrigerant pipe, a pressure reducing element, and an oil discharge pipe. The low-stage compressor compresses the refrigerant. The high-stage compressor further compresses the refrigerant compressed by the low-stage compressor. The refrigerant pipe introduces the refrigerant compressed by the low-stage compressor and discharged to the suction part of the high-stage compressor. The pressure reducing element is arranged in the middle of the refrigerant pipe. The oil discharge pipe discharges oil from the low-stage compressor. The oil discharge pipe connects the low-stage compressor and the refrigerant pipe downstream of the pressure reducing element.

In the multistage compression system according to the first aspect, since the oil discharge pipe is connected to the low-stage compressor and the refrigerant pipe downstream of the pressure reducing element, the amount of oil discharged from the oil discharge pipe increases, It is possible to control that the amount of oil in the low-stage compressor becomes too large.

The multistage compression system according to the second aspect is the system according to the first aspect, and the low stage compressor includes a compression unit, a motor, and a container. The compression unit is a rotary type. A compression chamber is formed in the compression section. The refrigerant is compressed in the compression chamber. The motor drives the compression unit. The motor is arranged above the compression section. The container houses the compression unit and the motor. The oil drain pipe is connected to the container below the motor and above the compression chamber. When the low-stage compressor has two or more compression chambers having different heights, the compression chamber referred to here means the lowermost compression chamber.

In the multistage compression system according to the second aspect, since the oil discharge pipe is connected to a position above the compression chamber of the container and below the motor, the low stage compressor does not have an excess or deficiency of excess oil in the low stage compressor. Can be discharged from.

The multistage compression system of the third aspect is the system of the first aspect or the second aspect, and the pressure reducing element is an intercooler. The intercooler cools the refrigerant discharged from the low-stage compressor before being sucked into the high-stage compressor.

In the multi-stage compression system according to the third aspect, the oil discharge pipe is connected to the low-stage compressor and the refrigerant pipe on the downstream side of the intercooler, so the amount of oil discharged from the oil discharge pipe increases. The amount of oil in the low-stage compressor can be controlled appropriately.

A multistage compression system of a fourth aspect is the system of the first aspect or the second aspect, and the pressure reducing element is a confluent portion of the intermediate injection passage. The merging portion of the intermediate injection passage cools the refrigerant discharged from the low-stage compressor before being sucked into the high-stage compressor.

In the multistage compression system according to the fourth aspect, since the oil discharge pipe is connected to the low-stage compressor and the refrigerant pipe downstream of the confluent portion of the intermediate injection passage, the amount of oil discharged from the oil discharge pipe is increased. The amount of oil in the low-stage compressor can be controlled to an appropriate amount.

A multistage compression system according to a fifth aspect is the system according to the first aspect or the second aspect, in which the pressure reducing element is an intercooler and a confluent portion of the intermediate injection passage. The intercooler cools the refrigerant discharged from the low-stage compressor before being sucked into the high-stage compressor. The merging portion of the intermediate injection passage cools the refrigerant discharged from the low-stage compressor before being sucked into the high-stage compressor.

In the multi-stage compression system according to the fifth aspect, the oil discharge pipe is connected to the low-stage compressor, the intercooler, and the refrigerant pipe downstream of the confluent portion of the intermediate injection passage. The amount of oil discharged by is increased, and the amount of oil in the low-stage compressor can be controlled to an appropriate amount.

A multistage compression system according to a sixth aspect is the system according to any one of the first to fifth aspects, in which the refrigerant is a refrigerant mainly containing carbon dioxide, and the oil is an oil incompatible with carbon dioxide. is there.

In the multistage compression system according to the sixth aspect, since the refrigerant and the oil are incompatible with each other, the refrigerant and the oil are easily separated from each other in the oil pool of the low-stage compressor, and the surplus refrigerant is mainly discharged from the oil discharge pipe. It's easy to do.

The refrigerant circuit diagram of the refrigerating device 1 of 1st Embodiment. The longitudinal cross-sectional view of the low-stage compressor 21 of 1st Embodiment. AA sectional view of the low-stage compressor 21 of the first embodiment BB sectional drawing of the low-stage compressor 21 of 1st Embodiment. CC sectional drawing of the low-stage compressor 21 of 1st Embodiment. A refrigerant circuit diagram of refrigeration equipment 1 of modification 1C.

<First Embodiment>
(1) Refrigerant circuit of refrigeration apparatus 1 (1-1) Entire refrigerant circuit of refrigeration apparatus 1 The refrigerant circuit configuration of the refrigeration apparatus 1 of the first embodiment is shown in FIG. The refrigeration system 1 of the present embodiment is a device that performs a two-stage compression refrigeration cycle using carbon dioxide, which is a refrigerant that operates in the supercritical range. The refrigerating apparatus 1 of this embodiment can be used for an air conditioning apparatus that performs cooling and heating, an air conditioning apparatus dedicated to cooling, a hot and cold water dispenser, a refrigerating apparatus, a freezing storage apparatus, and the like.

The refrigerant circuit of the refrigeration system 1 of the present embodiment includes a multi-stage compression system 20, a four-way switching valve 5, a heat source side heat exchanger 2, a bridge circuit 3, expansion mechanisms 8 and 9, and a use side heat exchanger 4. And an economizer heat exchanger 7.

The multi-stage compression system 20 compresses the refrigerant. The gas refrigerant is introduced into the first accumulator 22 at the inlet of the low-stage compressor 21 via the four-way switching valve 5 and the refrigerant pipe 13. The refrigerant is compressed by the low-stage compressor 21 and the high-stage compressor 23, and reaches the four-way switching valve 5 via the pipe 18.

The four-way switching valve 5 switches between the heat source side heat exchanger 2 and the use side heat exchanger 4 in which direction the refrigerant from the multi-stage compression system 20 flows. For example, when the refrigeration system 1 is an air conditioner and the cooling operation is performed, the refrigerant flows from the four-way switching valve 5 to the heat source side heat exchanger 2 (condenser). The refrigerant flowing through the heat source side heat exchanger 2 (condenser) reaches the receiver 6 via the check valve 3a of the bridge circuit 3, the pipe 11, and the check valve 11e. The liquid refrigerant from the receiver 6 continues to flow through the pipe 11, is decompressed by the expansion mechanism 9, and goes to the use side heat exchanger 4 (evaporator) via the check valve 3c of the bridge circuit 3. The refrigerant heated by the utilization side heat exchanger 4 (evaporator) is compressed again by the multi-stage compression system 20 via the four-way switching valve 5. On the other hand, during the heating operation, the refrigerant flows from the four-way switching valve 5 to the use side heat exchanger 4 (condenser), the check valve 3b of the bridge circuit 3, the pipe 11, the receiver 6, the expansion mechanism 9, and the reverse of the bridge circuit 3. The stop valve 3d, the use side heat exchanger 4 (evaporator), and the four-way switching valve 5 flow in this order.

The economizer heat exchanger 7 is arranged in the middle of the refrigerant pipe 11 between the receiver 6 and the expansion mechanism 9. A part of the refrigerant is branched at a branch 11a of the pipe 11 and is reduced to an intermediate pressure by the expansion mechanism 8. The intermediate-pressure refrigerant is heated by the high-pressure refrigerant flowing through the pipe 11 in the economizer heat exchanger 7, and is injected into the intermediate-pressure merging portion 15b of the multistage compression system 20 via the intermediate injection pipe 12. Further, the gas component of the refrigerant from the receiver 6 merges with the intermediate injection pipe 12 via the pipe 19.

(1-2) Flow of Refrigerant and Oil in Multi-Stage Compression System 20 As shown in FIG. 1, the multi-stage compression system 20 of the present embodiment includes a first accumulator 22, a low-stage compressor 21, an intercooler 26, The second accumulator 24, the high-stage compressor 23, the oil separator 25, the oil cooler 27, and the pressure reducer 31a are provided.

In the present embodiment, the refrigerant compressed by the low-stage compressor 21 is further compressed by the high-stage compressor 23. The compressors 21 and 23 include accumulators 22 and 24, respectively. The accumulators 22 and 24 play a role of temporarily storing the refrigerant before entering the compressor and preventing the liquid refrigerant from being sucked into the compressor.

Next, the flow of refrigerant and oil in the multi-stage compression system 20 of the present embodiment will be described with reference to FIG.

In the present embodiment, the low-pressure gas refrigerant heated by the evaporator (use-side heat exchanger 4 or heat-source-side heat exchanger 2) flows into the first accumulator 22 via the refrigerant pipe 13. The gas refrigerant in the first accumulator 22 flows to the low-stage compressor 21 via the suction pipe 14. The refrigerant compressed by the low-stage compressor 21 is discharged from the discharge pipe 15a, flows through the intermediate-pressure refrigerant pipes 151 to 153, and reaches the second accumulator 24.

The intercooler 26 is arranged in the middle of the intermediate pressure refrigerant pipes 151 and 152. The intercooler 26 is a heat exchanger that cools the intermediate-pressure refrigerant with, for example, outdoor air. The intercooler 26 may be disposed adjacent to the heat source side heat exchanger 2 and may exchange heat with air by a common fan. The intercooler 26 enhances the efficiency of the refrigeration system 1 by cooling the intermediate pressure refrigerant.

Further, the intermediate pressure refrigerant is injected into the merging portion 15b of the intermediate pressure refrigerant pipe from the intermediate injection pipe 12. In the present embodiment, the joining portion 15b of the intermediate injection pipe 12 to the pipe 152 is arranged on the downstream side of the intercooler 26. The temperature of the refrigerant injected by the intermediate injection is lower than that of the refrigerant flowing through the pipe 152. Therefore, the intermediate injection reduces the temperature of the refrigerant flowing through the pipe 152 and improves the efficiency of the refrigeration system 1.

The multi-stage compression system 20 of the present embodiment further includes an oil discharge pipe 32 that discharges excess oil of the low-stage compressor. The oil discharge pipe 32 connects the low-stage compressor 21 and the intermediate pressure pipe 153. The oil discharge pipe 32 discharges not only the excess oil accumulated in the oil sump of the low-stage compressor but also the excess refrigerant accumulated in the oil sump. The connection portion of the oil discharge pipe 32 with the intermediate pressure refrigerant pipe 153 is downstream of the confluence portion 15b of the intermediate injection passage and upstream of the suction portion of the second accumulator 24.

The refrigerant sent to the second accumulator 24 through the pipe 153 is introduced into the high-stage compressor 23 through the suction pipe 16. The refrigerant is compressed in the high-stage compressor 23, becomes a high pressure, and is discharged to the discharge pipe 17.

The refrigerant discharged to the discharge pipe 17 flows to the oil separator 25. The oil separator 25 separates the refrigerant and the oil. The separated oil is returned to the low-stage compressor 21 via the oil return pipe 31.

The multi-stage compression system 20 of the present embodiment further includes an oil discharge pipe 33 that discharges excess oil of the high-stage compressor. The oil discharge pipe 33 connects the high-stage compressor 23 and the discharge pipe 17 of the high-stage compressor 23.

A pressure reducer 31 a is arranged in the middle of the oil return pipe 31. The decompressor 31a is for decompressing the high-pressure oil discharged from the oil separator 25. As the decompressor 31a, specifically, for example, a capillary tube is used.

An oil cooler 27 is arranged in the middle of the oil return pipe 31. The oil cooler 27 is a heat exchanger that cools the oil flowing through the oil return pipe 31 with, for example, outdoor air. The oil cooler 27 is for cooling the high temperature oil discharged from the oil separator 25. The oil cooler 27 may be arranged, for example, in the vicinity of the heat source side heat exchanger 2 and exchange heat with air by a common fan.

Incidentally, the oil of the present embodiment (the refrigerating machine oil), if the refrigerating machine oil used in the CO ₂ refrigerant is not particularly limited, CO ₂ refrigerant and incompatible oils are particularly suitable. Examples of refrigerating machine oil include PAG (polyalkylene glycols) and POE (polyol esters).

The refrigeration system 1 of this embodiment performs two-stage compression with two compressors. Two or more stages of compression may be performed using three or more compressors. Moreover, you may perform compression of three steps or more.

In the present embodiment, the oil return pipe 31 returns the oil from the oil separator 25 to the low stage compressor 21. The oil return pipe 31 may directly return the oil discharged from the high-stage compressor 23 to the low-stage compressor 21.

(2) Configuration of compressor, piping connected to the compressor, and device The low-stage compressor 21 and the high-stage compressor 23 of the present embodiment are both 2-cylinder type and swing type rotary compressors. is there. Since the compressors 21 and 23 have almost the same configuration, the low-stage compressor 21 will be used for the detailed description.

2 is a vertical sectional view of the low-stage compressor 21, and FIGS. 3 to 5 are horizontal sectional views at positions AA to CC in FIG. 2, respectively. However, the components of the motor 40 are not shown in the BB sectional view of FIG.

The low-stage compressor 21 includes a container 30, a compression unit 50, a motor 40, a crankshaft 60, and a terminal 35.

(2-1) Container 30
The container 30 has a substantially cylindrical shape with the rotation axis RA of the motor 40 as a central axis. The inside of the container is kept airtight, and the intermediate pressure is maintained in the low-stage compressor 21 and the high pressure is maintained in the high-stage compressor 23 during operation. The lower part inside the container 30 is an oil reservoir (not shown) for storing oil (lubricating oil).

The container 30 accommodates the motor 40, the crankshaft 60, and the compression unit 50 inside. A terminal 35 is arranged on the top of the container 30. Further, the container 30 is connected with refrigerant suction pipes 14 a and 14 b and a discharge pipe 15 a, an oil return pipe 31, and an oil discharge pipe 32.

(2-2) Motor 40
The motor 40 is a brushless DC motor. The motor 40 generates power for rotating the crankshaft 60 around the rotation axis RA. The motor 40 is arranged in the space inside the container 30, below the upper space, and above the compression section 50. The motor 40 has a stator 41 and a rotor 42. The stator 41 is fixed to the inner wall of the container 30. The rotor 42 rotates by magnetically interacting with the stator 41.

The stator 41 has a stator core 46 and an insulator 47. The stator core 46 is made of steel. The insulator 47 is made of resin. The insulator 47 is arranged above and below the stator core 46, and has a winding wound around it.

(2-3) Crankshaft 60
The crankshaft 60 transmits the power of the motor 40 to the compression unit 50. The crankshaft 60 has a main shaft portion 61, a first eccentric portion 62a, and a second eccentric portion 62b.

The main shaft portion 61 is a portion that is concentric with the rotation axis RA. The main shaft portion 61 is fixed to the rotor 42.

The first eccentric portion 62a and the second eccentric portion 62b are eccentric with respect to the rotation axis RA. The shape of the first eccentric portion 62a and the shape of the second eccentric portion 62b are symmetric with respect to the rotation axis RA.

An oil tube 69 is provided at the lower end of the crankshaft 60. The oil tube 69 pumps oil (lubricating oil) from the oil reservoir. The pumped lubricating oil rises in the oil passage inside the crankshaft 60 and is supplied to the sliding portion of the compression unit 50.

(2-4) Compressor 50
The compression unit 50 is a two-cylinder type compression mechanism. The compression unit 50 has a first cylinder 51, a first piston 56, a second cylinder 52, a second piston 66, a front head 53, a middle plate 54, a rear head 55, and front mufflers 58a and 58b.

A first compression chamber 71 and a second compression chamber 72 are formed in the compression section 50. The first and second compression chambers are spaces in which the refrigerant is supplied and compressed.

In the multi-stage compression system 20 of the first embodiment, the compressors 21 and 23 are both 2-cylinder type compressors. Both or one compressor may be a one cylinder type compressor.

(2-4-1) First Compression Chamber 71 and Flow of Refrigerant Compressed in First Compression Chamber 71 The first compression chamber 71 includes a first cylinder 51 and a first cylinder 51, as shown in FIG. It is a space surrounded by the piston 56, the front head 53, and the middle plate 54.

As shown in FIG. 5, the first cylinder 51 is provided with a suction hole 14e, a discharge recess 59, a bush accommodating hole 57a, and a blade moving hole 57b. The first cylinder 51 accommodates the main shaft 61 of the crankshaft 60, the first eccentric portion 62 a, and the first piston 56. The suction hole 14e connects the first compression chamber 71 and the inside of the suction pipe 14a. A pair of bushes 56c are housed in the bush housing holes 57a.

The first piston 56 has an annular portion 56a and a blade 56b. The first eccentric portion 62a of the crankshaft 60 is fitted into the annular portion 56a. The blade 56b is sandwiched by a pair of bushes 56c. The first piston 56 divides the first compression chamber 71 into two. One is a low pressure chamber 71a communicating with the suction hole 14e. The other is a high-pressure chamber 71b communicating with the discharge recess 59. In FIG. 5, the annular portion 56a revolves clockwise, the volume of the high pressure chamber 71b becomes small, and the refrigerant in the high pressure chamber 71b is compressed. When the annular portion 56a revolves, the tip of the blade 56b reciprocates between the blade moving hole 57b side and the bush accommodating hole 57a side.

As shown in FIG. 2, the front head 53 is fixed inside the container 30 by an annular member 53a.

Front mufflers 58a and 58b are fixed to the front head 53. The front muffler reduces noise when the refrigerant is discharged.

The refrigerant compressed in the first compression chamber 71 is discharged to the first front muffler space 58e between the front muffler 58a and the front head 53 via the discharge recess 59. After the refrigerant further moves to the second front muffler space 58f between the two front mufflers 58a and 58b, the refrigerant is discharged below the motor 40 from the discharge holes 58c and 58d (see FIG. 4) provided in the front muffler 58b. Is blown out into the space.

The refrigerant that has been compressed and blown from the discharge holes 58c and 58d of the front muffler 58a moves to the upper space of the container 30 through the gap of the motor 40, is blown from the discharge pipe 15a, and goes to the high-stage compressor 23.

(2-4-2) Second Compression Chamber 72 and Flow of Refrigerant Compressed in Second Compression Chamber 72 The second compression chamber 72 includes the second cylinder 52, the second piston 66, the rear head 55, and the middle. It is a space surrounded by the plate 54.

Since the flow of the refrigerant compressed in the second compression chamber 72 is almost the same as the flow of the refrigerant compressed in the first compression chamber 71, detailed description will be omitted. However, in the case of the refrigerant compressed in the second compression chamber 72, it is first sent to the rear muffler space 55a provided in the rear head 55 and then sent to the front muffler spaces 58e and 58f by the front mufflers 58a and 58b. However, it is different.

In the multistage compression system 20 of the first embodiment, the rotary compression unit of the compressor 21 uses the first piston 56 in which the annular portion 56a and the blade 56b are integrated. For the rotary compression unit, a vane may be used instead of the blade, and a vane and a piston may be used separately.

(2-5) Compressor and Connection Position of Oil Return Pipe 31 and Oil Discharge Pipe 32 The oil return pipe 31 is located below the motor 40 in the space above the compression unit 50, as shown in FIG. It is connected to the container 30 so that the internal flow paths communicate with each other. The oil blown from the oil return pipe 31 into the container 30 collides with the insulator 47 of the motor 40, and then falls onto the front muffler 58b and the annular member 53a for fixing the front head 53, and further, the container 30 Joins the oil sump in the lower part of the inside.

The oil return pipe 31 is preferably connected to the space above the second compression chamber 72. If the oil return pipe 31 is connected to the space below the second compression chamber 72, there is a high possibility that the oil return pipe 31 will be below the oil level in the oil sump, and this will cause foaming, which is not preferable.

The oil return pipe 31 may be connected to the upper portion of the container 30. For example, it may be connected to the core cut portion of the stator 41 of the motor 40. However, it is preferable to connect to a low portion that is as close as possible to the oil sump, because oil is supplied to the sliding portions (in the vicinity of the compression chambers 71 and 72) sooner.

The inner diameter of the oil return pipe 31 is, for example, 10 mm or more and 12 mm or less.

As shown in FIG. 2, the oil discharge pipe 32 is connected to the container 30 under the motor 40 so that the internal flow path communicates with the space above the compression unit 50.

If the connection position of the oil discharge pipe 32 to the container 30 is lower than the compression chamber 72, the oil may be excessively lost from the oil reservoir. Further, at a position higher than the motor 40, the difference between the discharge pipe 15a and the discharge pipe 15a becomes small, and the significance of separately providing the oil discharge pipe 32 is lost.

Further, in the present embodiment, as shown in FIG. 2, the mounting height position of the oil discharge pipe 32 to the container 30 is the same as the mounting height position of the oil return pipe 31 to the container 30. This facilitates the height adjustment of the oil surface of the oil sump.

Further, as shown in FIG. 4, the oil discharge pipe 32 is attached to the flat container 30 at a position opposite to the rotation axis RA of the motor 40 from the discharge holes 58c and 58d of the front muffler 58b. .. Here, the opposite position means a range of 180° other than a total of 180°, which is 90° to the left and right with respect to the rotation axis RA from the connection position of the oil discharge pipe 32. In addition, in FIG. 4, the discharge holes 58c are not partly opposite to each other, but here it is meant that more than half of the area of the discharge holes 58c and 58d is on the opposite side.

In this embodiment, since the connection position of the oil discharge pipe 32 to the container 30 is separated from the positions of the discharge holes 58c and 58d of the front muffler 58b, the refrigerant discharged from the discharge holes 58c and 58d of the front muffler 58b is The direct oil discharge pipe 32 can reduce discharge from the low-stage compressor 21.

The inner diameter of the oil discharge pipe 32 is equal to the inner diameter of the oil return pipe 31. A pipe having a diameter smaller than the inner diameter of the discharge pipe 15a is used. More specifically, the inner diameter of the oil discharge pipe 32 is, for example, 10 mm or more and 12 mm or less.

Further, as shown in FIG. 5, when the planar positional relationship between the oil discharge pipe 32 and the oil return pipe 31 is seen, the connection position of the oil discharge pipe 32 to the container 30 is the position of the oil return pipe 31 to the container 30. It is a position away from the connection position by 90° or more in the rotation direction of the motor 40 (direction of arrow in FIG. 5). Preferably, the position is 180° or more. In the present embodiment, this angle is represented by θ. Theta is 270° or more. Further, θ should be 330° or less.

In the present embodiment, since the positions of the oil discharge pipe 32 and the oil return pipe 31 are sufficiently separated, the oil introduced into the container 30 of the low-stage compressor 21 by the oil return pipe 31 is directly transferred to the oil discharge pipe 32. It is possible to reduce discharge to the outside of the container 30 and easily realize oil equalization of the low-stage compressor 21.

In the multi-stage compression system 20 of the first embodiment, the height of the connection position of the oil return pipe 31 to the container 30 was equal to the height of the connection position of the oil discharge pipe 32 to the container 30. The height of the connection position of the oil return pipe 31 to the container 30 may be higher than the height of the connection position of the oil discharge pipe 32 to the container 30.

(2-6) Accumulator 22
In the multistage compression system 20 of the present embodiment, the first accumulator 22 is arranged upstream of the low stage compressor 21, and the second accumulator 24 is arranged upstream of the high stage compressor 23. The accumulators 22 and 24 temporarily store the flowing refrigerant, prevent the liquid refrigerant from flowing into the compressor, and prevent the liquid compression of the compressor. Since the first accumulator 22 and the second accumulator 24 have almost the same configuration, the first accumulator 22 will be described with reference to FIG.

The low-pressure gas refrigerant heated by the evaporator flows through the refrigerant pipe 13 via the four-way switching valve 5 and is introduced into the accumulator 22. The gas refrigerant is introduced into the first and second compression chambers 71 and 72 from the suction pipes 14a and 14b of the compressor 21. Liquid refrigerant and oil are accumulated below the inside of the accumulator. Small holes 14c and 14d are formed in the suction pipes 14a and 14b below the inside of the accumulator. The diameter of the holes 14c and 14d is, for example, 1 mm to 2 mm. The oil, together with the liquid refrigerant, joins the gas refrigerant through the holes 14c and 14d little by little, and is sent to the compression chamber.

(3) Features (3-1)
The multi-stage compression system 20 of the present embodiment is a system including a low-stage compressor 21, a high-stage compressor 23, intermediate pressure refrigerant pipes 151 to 153 and 16, a pressure reducing element, and an oil discharge pipe 32. .. The intermediate-pressure refrigerant pipes 151 to 153, 16 introduce the refrigerant compressed and discharged by the low-stage compressor 21 into the suction portion of the high-stage compressor 23. The pressure reducing element is arranged in the middle of the refrigerant pipes 151 to 153. The pressure reducing element reduces the pressure of the refrigerant flowing through the intermediate pressure refrigerant pipe. The oil discharge pipe 32 discharges excess oil or liquid refrigerant of the low-stage compressor 21. The oil discharge pipe 32 connects the low-stage compressor 21 and the intermediate pressure refrigerant pipe 153 on the downstream side of the pressure reducing element.

In the present embodiment, the pressure reducing element is the intercooler 26, the merging portion 15b of the intermediate injection passage, or both. The intercooler 26 reduces the temperature and pressure of the refrigerant itself. At the merging portion 15b of the intermediate injection passage, the relatively low temperature and low pressure refrigerant flowing through the intermediate injection pipe 12 merges with the refrigerant flowing through the intermediate pressure refrigerant pipe 152, so that the pressure of the refrigerant flowing through the intermediate pressure refrigerant pipe 152 decreases. To do.

In the multi-stage compression system 20 of the present embodiment, the oil discharge pipe 32 is connected to a portion of the intermediate pressure refrigerant pipe, which is downstream of the pressure reducing element. Since the pressure in the intermediate-pressure refrigerant pipe 153 is lowered by the pressure reducing element, the pressure difference between the inside of the low-stage compressor becomes large, and a large amount of refrigerant or oil is quickly discharged from the oil discharge pipe 32. Thereby, the oil amount of the low-stage compressor can be controlled appropriately.

(3-2)
In the multi-stage compression system 20 of the present embodiment, the oil discharge pipe 32 is connected to the container 30 above the compression chamber 72 and below the motor 40. In addition, in the present embodiment, the low-stage compressor 21 is a two-cylinder type compressor, and there are two compression chambers, a first compression chamber 71 and a second compression chamber 72. In such a case, the term "compression chamber" refers to the second compression chamber 72.

In the multi-stage compression system 20 of the present embodiment, the oil discharge pipe 32 is connected to a position above the compression chamber 72 of the container 30 and below the motor 40, so excess oil in the low-stage compressor 21 is excessive or insufficient. Instead, it can be discharged from the low-stage compressor. Therefore, the oil amount of the low-stage compressor can be controlled more quickly.

(3-3)
In the multi-stage compression system 20 of the present embodiment, the refrigerant is a refrigerant mainly containing carbon dioxide, and the oil is an oil incompatible with carbon dioxide. Examples of oils that are incompatible with carbon dioxide are PAG (polyalkylene glycols) and POE (polyol esters).

With such a mixed liquid of incompatible oil and a carbon dioxide refrigerant, when the refrigeration system 1 is operated under normal temperature conditions (-20°C or higher), the oil is below and the refrigerant is below due to the specific gravity. Be on top.

Then, in the oil sump of the low-stage compressor 21, the liquid refrigerant is likely to collect upward, and the excess liquid refrigerant can be easily discharged from the oil discharge pipe 32.

(3-4)
The multistage compression system 20 of the present embodiment further includes an oil return pipe 31. The oil return pipe 31 returns the oil discharged from the high-stage compressor 23 to the low-stage compressor 21.

Since the multi-stage compression system 20 of the present embodiment has both the oil discharge pipe 32 and the oil return pipe 31, it is possible to smoothly control the amount of oil in the low-stage compressor 21.

(4) Modified Example (4-1) Modified Example 1A
The multi-stage compression system 20 of the first embodiment includes an intercooler 26 on the upstream side of the intermediate pressure refrigerant pipes 151 to 153 connected to the discharge pipe 15a of the low-stage compressor 21, and a confluent portion 15b of the intermediate injection passage on the downstream side. It was In the multistage compression system 20 of Modification 1A, only the intercooler 26 is provided in the intermediate pressure refrigerant pipe, and the merging portion 15b of the intermediate injection passage is not provided. The modified example 1A does not include the economizer heat exchanger 7. Other configurations are similar to those of the first embodiment. The oil discharge pipe 32 is connected downstream of the intercooler 26 between the intermediate pressure refrigerant pipes, as in the first embodiment.

Further, contrary to Modification Example 1A, the present disclosure is effective even when the multi-stage compression system 20 includes only the joining portion 15b of the intermediate injection passage in the intermediate pressure refrigerant pipe and does not include the intercooler 26. ..

(4-2) Modification 1B
In the multistage compression system 20 of the first embodiment, the receiver 6 and the economizer heat exchanger 7 are arranged in the upstream portion of the intermediate injection pipe. In the multi-stage compression system 20 of Modification 1B, only the receiver 6 is provided in the upstream portion of the intermediate injection pipe 12, and the economizer heat exchanger 7 is not provided. Other configurations are similar to those of the first embodiment.

The multi-stage compression system 20 of Modification 1B also has the same features (3-1) to (3-4) as the multi-stage compression system 20 of the first embodiment.

Further, contrary to Modification Example 1B, the present disclosure is effective even when the multi-stage compression system 20 includes only the economizer heat exchanger 7 in the upstream portion of the intermediate injection pipe 12 and does not include the receiver 6. is there.

(4-3) Modification 1C
The multi-stage compression system 20 of the first embodiment includes an intercooler 26 on the upstream side of the intermediate pressure refrigerant pipes 151 to 153 connected to the discharge pipe 15a of the low-stage compressor 21, and a confluent portion 15b of the intermediate injection passage on the downstream side. It was As shown in FIG. 6, the multistage compression system 20 of Modification 1E includes a confluent portion 15b of the intermediate injection passage on the upstream side of the intermediate pressure refrigerant pipes 154 to 156 and an intercooler 26 on the downstream side. The oil discharge pipe 32 is connected to the downstream side of the merging portion 15b of the intermediate injection passage on the intermediate pressure refrigerant pipe 156. Other configurations are the same as those in the first embodiment.

The multistage compression system 20 of Modification 1C also has the same features (3-1) to (3-4) as the multistage compression system 20 of the first embodiment.

While the embodiments of the present disclosure have been described above, it will be understood that various changes in form and details can be made without departing from the spirit and scope of the present disclosure described in the claims. ..

1 Refrigerator 2 Heat source side heat exchanger 3 Bridge circuit 4 Utilization side heat exchanger 5 Four-way switching valve 6 Receiver 7 Economizer heat exchanger 8, 9 Expansion mechanism 12 Intermediate injection pipes 151-156, 16 Intermediate pressure refrigerant pipe 15b Intermediate injection Confluent portion of passage 20 Multi-stage compression system 21 Low-stage compressor 22 First accumulator 23 High-stage compressor 24 Second accumulator 25 Oil separator 26 Intercooler 30 Container 31 Oil return pipe 31a Pressure reducer 32 Oil discharge pipe 40 Motor 50 Compression Portion 71 First compression chamber 72 Second compression chamber 58a, 58b Muffler 58c, 58d Discharge hole

Japanese Patent Laid-Open No. 2008-261227

Claims (6)

A multi-stage compression system (20) utilizing refrigerant and oil,
A low-stage compressor (21) for compressing the refrigerant,
A high-stage compressor (23) for further compressing the refrigerant compressed by the low-stage compressor,
A refrigerant pipe (151 to 156, 16) for introducing the refrigerant compressed by the low-stage compressor and discharged to the suction part of the high-stage compressor;
A pressure reduction element (26, 15b) arranged in the middle of the refrigerant pipe,
An oil discharge pipe (32) for discharging the oil of the low-stage compressor, the oil discharge pipe (32) connecting the low-stage compressor and the refrigerant pipe downstream of the pressure reducing element;
With
Multi-stage compression system. The low-stage compressor is
A rotary compression unit (50) for compressing the refrigerant,
A motor (40) for driving the compression unit, the motor (40) arranged above the compression unit;
A container (30) containing the compression unit and the motor,
Have
The oil discharge pipe is connected below the motor of the container and above the compressor.
The multi-stage compression system according to claim 1. The pressure reducing element is
An intercooler (26) that cools the refrigerant discharged from the low-stage compressor before being sucked into the high-stage compressor.
The multi-stage compression system according to claim 1. The pressure reducing element is
A confluent portion (15b) of an intermediate injection passage for injecting the refrigerant at an intermediate pressure into the refrigerant pipe,
The multi-stage compression system according to claim 1. The pressure reducing element is
An intercooler that cools the refrigerant discharged from the low-stage compressor before being sucked into the high-stage compressor,
It is a merging portion of an intermediate injection passage for injecting the refrigerant at an intermediate pressure into the refrigerant pipe,
The multi-stage compression system according to claim 1. The refrigerant is a refrigerant containing carbon dioxide as a main component,
The oil is a refrigerant that is incompatible with carbon dioxide,
The multi-stage compression system according to claim 1.

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