Screw compressor and refrigeration system equipped with a screw compressor

Abstract

The present invention provides a screw compressor and a refrigeration system equipped with a screw compressor that can shorten the reverse rotation time and restart time of the compression mechanism when the system is stopped, and improve the reliability of the compression mechanism. [Solution] A screw compressor is a compressor that compresses a refrigerant containing refrigerant oil that is drawn in, in a compression chamber of a compression mechanism, and discharges it through at least one discharge port. The screw compressor includes an oil separator located downstream of at least one discharge port and separating the refrigerant discharged from at least one discharge port from the refrigerant oil; a first check valve located downstream of at least one discharge port and upstream of the oil separator to suppress backflow of the refrigerant; a communication passage located upstream of the compression chamber and connecting a low-pressure space where the refrigerant drawn into the compression chamber is located, and a high-pressure space located downstream of the first check valve and including the internal space of the oil separator; and an on / off valve for opening and closing the communication passage.

Description

Technical Field

[0001] The present disclosure relates to a screw compressor provided with an oil separator and a refrigeration device provided with the screw compressor.

Background Art

[0002] Conventionally, as one type of positive displacement compressor, a screw compressor is known. The screw compressor is used, for example, as a component of a refrigerant circuit incorporated in a refrigeration device or the like. The screw compressor has a compression mechanism and a motor for driving the compression mechanism. The compression mechanism includes one screw rotor having a spiral screw groove and one or two gate rotors having a plurality of gate rotor teeth that fit into the screw groove.

[0003] In a screw compressor, a plurality of compression chambers are formed by the screw groove and the gate rotor teeth meshing and engaging with each other. One end of the screw rotor in the axial direction of the rotation axis is the refrigerant suction side, and the other end is the discharge side. The inside of the casing in which the screw rotor and the gate rotor are housed is partitioned into a low-pressure space provided on the suction side of the compression chamber and a high-pressure space provided on the discharge side of the compression chamber.

[0004] In this type of screw compressor, when the screw compressor stops, the refrigerant flows backward from the high-pressure space through the compression chamber to the low-pressure space due to the pressure difference of the refrigerant. When the refrigerant flows backward from the high-pressure space through the compression chamber to the low-pressure space, reverse rotation of the compression mechanism occurs. Specifically, reverse rotation of the compression mechanism means that the screw rotor rotates reversely, and due to this reverse rotation, the gate rotor rotates reversely. In a screw compressor, when such reverse rotation of the compression mechanism occurs, there is a concern that damage may occur to the gate rotor.

[0005] Conventionally, one technique for suppressing the backflow of refrigerant when the compressor stops is the refrigeration system described in Patent Document 1. The refrigeration system in Patent Document 1 suppresses the backflow of refrigerant from external equipment such as the condenser into the inside of the compressor by placing a check valve on the discharge side of the compressor in a refrigerant circuit having a compressor, condenser, pressure reducing device and evaporator. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 6486217 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The refrigeration system described in Patent Document 1 is a technology that suppresses the backflow of refrigerant from outside the compressor to inside the compressor, but does not address the backflow of refrigerant inside the compressor.

[0008] As mentioned above, in screw compressors, reverse rotation of the compression mechanism occurs when the unit is stopped, and restarting during this reverse rotation places a load on the motor. Therefore, in screw compressors, measures such as restricting restart for a certain period of time after reverse rotation occurs are necessary. The restart time, which is the period during which restarting is restricted, is determined by considering factors such as the reverse rotation time, and there is a problem that the longer the reverse rotation time, the longer the restart time will be.

[0009] Furthermore, in a screw compressor, when the compressor is stopped, refrigerant flows from the high-pressure space to the low-pressure space, equalizing the pressure between the two spaces. In a screw compressor, oil inside the casing is supplied to the compression chamber and bearings via a differential pressure lubrication system through a flow path within the compressor, for purposes such as improving the sealing performance of the compression chamber and lubricating the bearings. Therefore, when the compressor is stopped, oil continues to be supplied from the high-pressure space to the compression chamber until the pressure between the high-pressure and low-pressure spaces equalizes. As the oil that continues to be supplied from the high-pressure space to the compression chamber flows from the compression chamber to the low-pressure space, if the time until equalization is long, a large amount of oil will flow into the low-pressure space. If the screw compressor is restarted in this state, the screw compressor will draw in a large amount of oil from the low-pressure space into the compression chamber, causing liquid compression, which may damage the gate rotor and reduce the reliability of the compression mechanism.

[0010] This disclosure has been made in view of the above-mentioned problems, and aims to provide a screw compressor and a refrigeration system equipped with a screw compressor that can shorten the reverse rotation time and restart time of the compression mechanism when the system is stopped, and improve the reliability of the compression mechanism. [Means for solving the problem]

[0011] The screw compressor of this disclosure is a screw compressor that compresses a refrigerant containing refrigerant oil that has been drawn in in a compression chamber of a compression mechanism and discharges it through at least one discharge port, and comprises: an oil separator located downstream of at least one discharge port and separating the refrigerant discharged from at least one discharge port from the refrigerant oil; a first check valve located downstream of at least one discharge port and upstream of the oil separator and suppressing backflow of the refrigerant; a communication passage located upstream of the compression chamber and connecting a low-pressure space where the refrigerant drawn into the compression chamber is located and a high-pressure space located downstream of the first check valve and including the internal space of the oil separator; and an on-off valve provided in the communication passage and opening and closing the communication passage.

[0012] The refrigeration system of this disclosure comprises the above-mentioned screw compressor, a condenser, a pressure reducing device, an evaporator, and a control device that opens an on / off valve when the screw compressor is stopped. [Effects of the Invention]

[0013] According to this disclosure, it is possible to shorten the reverse rotation time and restart time of the compression mechanism when the system is stopped, and to improve the reliability of the compression mechanism. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic cross-sectional view of a screw compressor according to Embodiment 1. [Figure 2] This is a schematic side view of the compressor body of the screw compressor 1 according to Embodiment 1, as seen from the first connection surface side. [Figure 3] Figure 2 is a schematic diagram of the AA section. [Figure 4] This is a schematic plan view showing the closed state of the first check valve of the screw compressor according to Embodiment 1. [Figure 5] This is a cross-sectional view AA in Figure 4. [Figure 6] Figure 4 is a schematic plan view showing the open state of the first check valve. [Figure 7] This is a cross-sectional view of BB in Figure 6. [Figure 8] This is a schematic plan view showing the closed state of the first check valve in another example of the screw compressor according to Embodiment 1. [Figure 9] This is a cross-sectional view AA in Figure 8. [Figure 10] Figure 8 is a schematic plan view showing the open state of the first check valve. [Figure 11] Figure 10 is a cross-sectional view of BB. [Figure 12] This is a conceptual diagram illustrating the compression principle of a screw compressor according to Embodiment 1. [Figure 13] This is an explanatory diagram of the operation of a screw compressor according to Embodiment 1. [Figure 14] This is an explanatory diagram of the operation of a screw compressor according to Embodiment 1 when it is stopped. [Figure 15] It is a schematic cross-sectional view of the screw compressor according to Embodiment 2. [Figure 16] It is a schematic side view of the compressor main body of the screw compressor according to Embodiment 2 as viewed from the first connection surface side. [Figure 17] It is a plan view of the flow path forming plate of the screw compressor according to Embodiment 2. [Figure 18] It is a circuit diagram showing an example of the configuration of the refrigeration device according to Embodiment 3. [Figure 19] It is a diagram for explaining the opening and closing timing of the on-off valve in the screw compressor according to Embodiment 3. [Figure 20] It is a diagram for explaining another opening and closing timing of the on-off valve in the screw compressor according to Embodiment 3.

Mode for Carrying Out the Invention

[0015] Hereinafter, the screw compressor according to Embodiment 1 will be described. In the following drawings, those with the same reference numerals are the same or corresponding ones, and this is common throughout the entire specification. And the forms of the components shown throughout the specification are merely examples and are not limited to the forms described in the specification. In particular, the combinations of components are not limited to only the combinations in each embodiment, and the components described in other embodiments can be applied to other embodiments. Also, regarding the high and low of pressure, etc., it is not determined particularly in relation to absolute values, but is determined relatively in the state or operation, etc. in the system and device, etc. Furthermore, in the drawings, the relationship of the sizes of each component member may be different from the actual one.

[0016] Embodiment 1. Figure 1 is a schematic cross-sectional view of a screw compressor 1 according to Embodiment 1. Figure 2 is a schematic side view of the compressor body 10 of the screw compressor 1 according to Embodiment 1, viewed from the first connection surface 10a side. Figure 3 is a schematic cross-sectional view of AA of Figure 2. The screw compressor 1 according to Embodiment 1 has a compressor body 10 and an oil separator 40. The screw compressor 1 is constructed by fastening the first connection surface 10a of the compressor body 10 and the second connection surface 40a of the oil separator 40 together with bolts (not shown) in contact with each other. The first connection surface 10a is the end face of the first casing 11 that constitutes the outer shell of the compressor body 10. The second connection surface 40a is the end face of the second casing 41 that constitutes the outer shell of the oil separator 40.

[0017] (Compressor body 10) The compressor body 10 comprises a cylindrical first casing 11, a motor 12 housed within the first casing 11, a screw shaft 13 rotationally driven by the motor 12, and a compression mechanism 20 for compressing the refrigerant. The compression mechanism 20 is connected to the motor 12 via the screw shaft 13. The compression mechanism 20 is the part that compresses the refrigerant by the driving force transmitted from the motor 12 via the screw shaft 13, and comprises one screw rotor 14 and two gate rotors 15 (see Figure 12 below). Figure 1 shows a single-screw type compression mechanism 20 in which two gate rotors 15 are engaged with one screw rotor 14, but the compression mechanism 20 is not limited to a single-screw type and may be a twin-screw type.

[0018] The motor 12 comprises a stator 12a fixed in contact with the inner circumferential surface of the first casing 11, and a motor rotor 12b positioned inside the stator 12a. The motor rotor 12b is fixed to the screw shaft 13 and is positioned on the same line as the screw rotor 14. The end of the screw shaft 13 not fixed to the motor 12 is rotatably supported by a bearing 17. The motor 12's rotational speed can be changed by inverter drive, and the compressor body 10 is driven by the inverter. The motor 12 may also be a constant-speed motor that rotates at a constant rotational speed.

[0019] The screw rotor 14 is cylindrical, and multiple screw grooves 14a extending spirally from one end to the other are formed on its outer surface. One end of the screw rotor 14 (right side in Figure 1) is the refrigerant gas intake side, and the screw grooves 14a communicate with the intake pressure side. The other end of the screw rotor 14 (left side in Figure 1) is the refrigerant gas discharge side, and the screw grooves 14a communicate with the discharge pressure side. The first casing 11 is divided by a partition wall 18 into an intake pressure side (right side in Figure 1) filled with low-pressure refrigerant gas and a discharge pressure side (left side in Figure 1) filled with high-pressure refrigerant gas.

[0020] Two gate rotors 15 are positioned on the side of the screw rotor 14, arranged axially symmetrically with respect to the screw shaft 13. The gate rotors 15 are disc-shaped, and multiple teeth 15a are provided on their outer circumferential surface. The teeth 15a of the gate rotors 15 are arranged to mesh with the screw grooves 14a of the screw rotor 14. The space enclosed by the screw grooves 14a, the teeth 15a of the gate rotors 15, the inner circumferential surface of the first casing 11, and the slide valve 16 (described later) is formed as a compression chamber 19, which compresses low-pressure refrigerant gas into high-pressure refrigerant gas.

[0021] A slide groove 21 is formed on the inner surface of the first casing 11, extending in the axial direction of the screw shaft 13 of the screw rotor 14. A slide valve 16 is positioned within the slide groove 21. The slide valve 16 is slidable within the slide groove 21 along the outer surface of the screw rotor 14 in the axial direction of the screw shaft 13. The slide valve 16 may be used for mechanical volume control or for variable internal volume control to change the discharge timing. The slide valve 16 has an opening 16a in the axial center of the screw shaft 13. The refrigerant compressed in the compression chamber 19 is discharged from the discharge port 1a (see Figure 12, described later) formed from the opening 16a of the slide valve 16 and the first casing 11.

[0022] The first casing 11 has a discharge channel 22 connected to the discharge port 1a. The discharge channel 22 is partitioned within the first casing 11. The discharge channel 22 has an inlet 22a and an outlet 22b. The inlet 22a communicates with the discharge port 1a via a slide groove 21, and the outlet 22b opens to the first connection surface 10a of the first casing 11. The refrigerant, including high-pressure refrigerant oil, discharged from the discharge port 1a flows into the discharge channel 22 from the inlet 22a and out from the outlet 22b, flowing into the oil separator 40.

[0023] Furthermore, within the first casing 11, there is an oil storage section 23 that communicates with the oil storage section 41a of the oil separator 40 (described later), and an oil passage 24 that guides the refrigeration oil stored in the oil storage section 23 to the compression chamber 19. The oil passage 24 is composed of a hole that connects the oil storage section 23 and the compression chamber 19. The refrigeration oil stored in the oil storage section 23 is supplied to the compression chamber 19 through the oil passage 24 due to the pressure difference, lubricating the bearing 17 and sealing the compression chamber 19.

[0024] A first check valve 25 is installed in the discharge channel 22 to suppress the backflow of refrigerant. The first check valve 25 is installed downstream of the discharge port 1a and upstream of the oil separator 40 to suppress the backflow of refrigerant. The first check valve 25 allows the flow of refrigerant from the inlet 22a to the outlet 22b of the discharge channel 22, while preventing reverse flow. The structure of the first check valve 25 is not particularly limited, but a structure that can secure a flow area when the valve is open and has low pressure loss is desirable. An example of the structure of the first check valve 25 will be explained with reference to the following Figures 4 to 11.

[0025] Figure 4 is a schematic plan view showing the closed state of the first check valve 25 of the screw compressor 1 according to Embodiment 1. Figure 5 is a cross-sectional view AA of Figure 4. Figure 6 is a schematic plan view showing the open state of the first check valve 25 of Figure 4. Figure 7 is a cross-sectional view BB of Figure 6. Figure 8 is a schematic plan view showing the closed state of the first check valve 25 in another example of the screw compressor 1 according to Embodiment 1. Figure 9 is a cross-sectional view AA of Figure 8. Figure 10 is a schematic plan view showing the open state of the first check valve 25 of Figure 8. Figure 11 is a cross-sectional view BB of Figure 10.

[0026] As shown in Figures 4 to 7, the first check valve 25 has a cylindrical base 26 with a circular flow path 26a in its center, and a valve portion 27 positioned in the flow path 26a of the base 26 to open and close the flow path 26a. A valve seat 26a1, which is made up of steps, is formed in the middle of the flow path 26a of the base 26. The valve portion 27 has a shaft portion 27a that extends radially through the center of the base 26 when viewed in the axial direction of the base 26, and a pair of semicircular plate portions 27b arranged on both sides of the shaft portion 27a. The shaft portion 27a is fixed at both ends to the base 26, and the pair of plate portions 27b are rotatably connected to the shaft portion 27a.

[0027] In the closed state shown in Figures 4 and 5, the first check valve 25 closes the passage 26a by having a pair of plate portions 27b contact the valve seat 26a1. In the open state shown in Figures 6 and 7, the first check valve 25 opens the passage 26a by having the pair of plate portions 27b rotate relative to the shaft portion 27a in a direction away from the valve seat 26a1.

[0028] In the configuration described above, the first check valve 25 is positioned in the discharge passage 22 such that, in the flow of refrigerant in the discharge passage 22, the pair of plate portions 27b are located downstream of the valve seat 26a1. The first check valve 25 is fixed to the first casing 11 by bolts (not shown) passing through bolt holes 26b formed in the base portion 26. By fixing the first check valve 25 to the first casing 11 in the above position, the first check valve 25 allows the flow of refrigerant from the inlet 22a to the outlet 22b in the discharge passage 22 and prevents reverse flow.

[0029] The first check valve 25 is not limited to the configuration shown in Figures 4 to 7, but may also have the configuration shown in Figures 8 to 11. The first check valve 25 shown in Figures 8 to 11 differs from the valve portion 27 shown in Figures 4 to 7 in the configuration of the valve portion 27A. The valve portion 27A has a shaft portion 27c that extends in a chordal manner from the end of the flow path 26a when viewed in the axial direction of the base portion 26, and a disc-shaped plate portion 27d. Both ends of the shaft portion 27c are fixed to the base portion 26, and the plate portion 27d is rotatably connected to the shaft portion 27c.

[0030] In the closed state shown in Figures 8 and 9, the first check valve 25 closes the passage 26a by the plate portion 27d contacting the valve seat 26a1. In the open state shown in Figures 10 and 11, the first check valve 25 opens the passage 26a by the plate portion 27d rotating relative to the shaft portion 27c in a direction away from the valve seat 26a1.

[0031] The first check valve 25 in the above configuration is positioned in the discharge passage 22 such that the plate portion 27d is located downstream of the valve seat 26a1 in the flow of refrigerant in the discharge passage 22. The first check valve 25 is fixed to the first casing 11 by a bolt (not shown) passed through a bolt hole 26b formed in the base portion 26. By fixing the first check valve 25 to the first casing 11 in the above configuration, the first check valve 25 allows the flow of refrigerant from the inlet 22a to the outlet 22b in the discharge passage 22 and prevents the flow in the reverse direction.

[0032] In the first embodiment, the screw compressor 1 has a configuration with two gate rotors 15, and therefore there are two compression chambers 19 and two slide valves 16, corresponding to the two gate rotors 15, and there are also two discharge ports 1a. As shown in Figures 2 and 3, the screw compressor 1 has two sets of discharge passages 22 and first check valves 25, and the refrigerant flows out from the outlets 22b of each of the two discharge passages 22 toward the oil separator 40. The screw compressor 1 is not limited to a twin-gate rotor configuration with two gate rotors 15, but may also be a mono-gate rotor configuration with one gate rotor 15. The screw compressor 1 has at least one compression chamber and is configured to discharge refrigerant through at least one discharge port 1a.

[0033] Now, let's return to the explanation of Figure 1.

[0034] (Oil separator 40) The oil separator 40 is a cyclone-type oil separator that separates oil and refrigerant gas by centrifugal force using the density difference between gas and liquid. The oil separator 40 is located downstream of the discharge port 1a and separates the refrigerant and refrigeration oil discharged from the discharge port 1a. The oil separator 40 has a second casing 41, an oil separation section 42, a partition plate 43, and a second check valve 44. The second casing 41 has a communication port 41a1 that opens to the second connection surface 40a. The communication port 41a1 communicates with the outlet 22b that opens to the first connection surface 10a of the first casing 11, and the refrigerant containing refrigeration oil that flows out from the outlet 22b flows into the oil separator 40 through the communication port 41a1. The bottom of the second casing 41 is an oil storage section 41a that stores refrigeration oil.

[0035] The oil separation unit 42 has an outer cylinder portion 42a, an inner cylinder portion 42b, and a lid portion 42c. The outer cylinder portion 42a and the inner cylinder portion 42b are arranged coaxially, and the oil separation unit 42 is formed in a double cylindrical shape.

[0036] The outer cylinder portion 42a is composed of a part of the second casing 41. The outer cylinder portion 42a receives the refrigerant containing refrigerant oil (hereinafter simply referred to as refrigerant) discharged from the compressor body portion 10 and swirls it between the outer cylinder portion 42a and the inner cylinder portion 42b, separating the refrigerant gas and refrigerant oil by centrifugal force. The separated refrigerant oil flows out from the oil outlet 42a1 formed at the lower end of the outer cylinder portion 42a and falls into the oil reservoir portion 41a.

[0037] The inner cylinder portion 42b is located inside the outer cylinder portion 42a. The inner cylinder portion 42b guides the refrigerant gas, which is separated by the outer cylinder portion 42a and folded back by the partition plate 43, upward.

[0038] The lid portion 42c is provided on the upper part of the outer cylinder portion 42a and the inner cylinder portion 42b, and covers the openings at the top of the outer cylinder portion 42a and the inner cylinder portion 42b. The lid portion 42c is, for example, disc-shaped, and an outlet portion 42c1 is formed in the center. The outlet portion 42c1 is the part that discharges the refrigerant gas, after the refrigerant oil has been separated in the oil separator 40, from the screw compressor 1 to the outside. The outlet portion 42c1 is formed as a through hole with an inner diameter smaller than the inner diameter of the inner cylinder portion 42b.

[0039] The partition plate 43 extends from the inner circumferential wall of the outer cylinder portion 42a and separates the oil separation portion 42 from the oil storage portion 41a. The partition plate 43 may be provided, for example, parallel to the opening surface at the lower end of the inner cylinder portion 42b. The partition plate 43 is formed integrally with the outer cylinder portion 42a by casting or the like.

[0040] The oil storage section 41a is located within the second casing 41, below the oil separation section 42, and stores refrigerant oil separated from the refrigerant gas. In plan view, the oil storage section 41a extends further toward the compressor body 10 than the oil separation section 42 and communicates with the oil storage section 23 within the first casing 11.

[0041] The second check valve 44 prevents the backflow of refrigerant from the condenser to the screw compressor 1 in a refrigeration system equipped with a screw compressor 1. The second check valve 44 is also located downstream of the oil separation section 42 to suppress the backflow of refrigerant separated in the oil separation section 42. The second check valve 44 is located downstream of the outlet section 42c1 of the cover section 42c. In the illustrated example, the second check valve 44 is shown to be located outside the oil separator 40, but the second check valve 44 may also be located inside the oil separator 40. The refrigerant gas separated in the oil separation section 42 passes through the second check valve 44 and is then discharged outside the screw compressor 1.

[0042] Here, the internal space of the screw compressor 1 includes a low-pressure space 50 and a high-pressure space 60. In Figure 1, the areas indicated by light dots represent the low-pressure space 50, and the areas indicated by dark dots represent the high-pressure space 60. In the screw compressor 1, the low-pressure space 50 and the high-pressure space 60 are separated by a partition wall 18, which is part of the first casing 11. The low-pressure space 50 is located upstream of the compression chamber 19 and is the space where the refrigerant drawn into the compression chamber 19 is located. The high-pressure space 60 is the space where the refrigerant compressed in the compression chamber 19 is located and includes the space 22A in the discharge passage 22 and the internal space 60A of the oil separator 40. The internal space 60A of the oil separator 40 is the internal space of the second casing 41.

[0043] The screw compressor 1 has a communication passage 30 that connects the low-pressure space 50 and the high-pressure space 61 downstream of the first check valve 25 within the high-pressure space 60, and bypasses the refrigerant in the high-pressure space 61 to the low-pressure space 50. The communication passage 30 is provided with an on-off valve 31 that opens and closes the communication passage 30. The on-off valve 31 is, for example, a solenoid valve. The on-off valve 31 is controlled by a control device (not shown). The communication passage 30 may be formed outside the screw compressor 1 by copper piping or steel pipes, or it may be formed inside the first casing 11 and the second casing 41, and the means of forming the communication passage 30 are not limited.

[0044] The high-pressure space 61 is the space where the refrigerant compressed in the compression chamber 19 is located, and is located downstream of the first check valve 25, and includes the internal space 60A of the oil separator 40. The high-pressure space 61 consists of the space 22A within the discharge flow path 22 downstream of the first check valve 25 and the internal space 60A of the oil separator 40.

[0045] Furthermore, although the illustrated example shows that the end 30a of the communication channel 30 on the high-pressure space 60 side is connected to the second casing 41 and opens to the internal space 60A, it may also be configured to be connected to the first casing 11 and open to the discharge channel 22. In the case where the end 30a of the communication channel 30 on the high-pressure space 60 side opens to the discharge channel 22, the end 30a of the communication channel 30 on the high-pressure space 60 side opens to the portion of the space 22A within the discharge channel 22 downstream of the first check valve 25.

[0046] [Operation of Screw Compressor 1] Next, the operation of the screw compressor 1 according to Embodiment 1 will be described. Figure 12 is a conceptual diagram showing the compression principle of the screw compressor 1 according to Embodiment 1. In Figure 12, the "suction stroke," "compression stroke," and "discharge stroke" are shown in order from left to right on the page.

[0047] When the motor 12 is started, the screw rotor 14 rotates in the direction of the solid arrow as the screw shaft 13 (see Figure 1) rotates. At this time, the teeth 15a of the gate rotor 15 are engaged with the screw groove 14a of the screw rotor 14. Therefore, as the screw rotor 14 rotates, the teeth 15a of the gate rotor 15 move relatively within the screw groove 14a, and the gate rotor 15 rotates in the direction of the thin white arrow. As a result, the intake stroke, compression stroke, and discharge stroke constitute one cycle within the compression chamber 19, and this cycle is repeated. Here, we will explain each stroke focusing on the compression chamber 19, which is shown with dot hatching in Figure 12.

[0048] The left-hand diagram in Figure 12 shows the state of the compression chamber 19 during the intake stroke. When the screw rotor 14 is driven by the motor 12 and rotates in the direction of the solid arrow, the teeth 15a of the gate rotor 15 rotate sequentially toward the discharge port in conjunction with this rotation. As a result, the volume of the compression chamber 19 is reduced, and the refrigerant gas inside the compression chamber 19 is compressed, as shown in the center diagram of Figure 12.

[0049] As the screw rotor 14 continues to rotate, the compression chamber 19 communicates with the discharge port 1a, as shown in the right-hand diagram of Figure 12. As a result, the high-pressure refrigerant gas compressed in the compression chamber 19 is discharged from the discharge port 1a. Then, the same compression is performed again on the back of the screw rotor 14. The refrigerant discharged into the discharge channel 22 flows toward the oil separator 40.

[0050] Here, as shown in Figure 1, a first check valve 25 is installed in the discharge channel 22. Therefore, the refrigerant discharged from the outlet 1a and flowing into the inlet 22a of the discharge channel 22 flows through the discharge channel 22, and its own pressure opens the first check valve 25, causing it to flow out from the outlet 22b. The refrigerant flowing out from the outlet 22b flows into the oil separator 40 via the communication port 41a1.

[0051] The refrigerant flowing into the oil separator 40 flows into the interior of the outer cylinder 42a through an inlet (not shown) formed on the upper side of the outer cylinder 42a. The refrigerant flowing into the interior of the outer cylinder 42a descends while swirling through the gap between the outer cylinder 42a and the inner cylinder 42b. Of the refrigerant swirling downwards, the refrigerant oil, which has a higher density than the refrigerant gas, is thrown towards the inner circumferential surface of the outer cylinder 42a by centrifugal force and separated from the refrigerant. The separated refrigerant oil then flows downward along the inner circumferential surface of the outer cylinder 42a by gravity and falls into the oil storage section 41a through the oil outlet 42a1. The oil stored in the oil storage section 41a and the oil storage section 23 is supplied to the compression chamber 19 or the bearing 17 through the oil passage 24 provided in the first casing 11.

[0052] Meanwhile, the refrigerant separated from the refrigerant oil descends while swirling in the gap between the outer cylinder 42a and the inner cylinder 42b, folds back at the partition plate 43, and flows into the interior of the inner cylinder 42b as an upward flow while continuing to swirl. The refrigerant that has flowed into the interior of the inner cylinder 42b rises inside the inner cylinder 42b and flows out from the outlet 42c1. Then, when the pressure of the refrigerant flowing out from the outlet 42c1 opens the second check valve 44, the refrigerant gas is discharged into the refrigerant circuit.

[0053] [Operation of screw compressor 1 when it is shut down] Next, the operation of the screw compressor 1 according to Embodiment 1 when it is stopped will be described.

[0054] Figure 13 is an explanatory diagram of the operation of the screw compressor 1 according to Embodiment 1 during operation. Figure 14 is an explanatory diagram of the operation of the screw compressor 1 according to Embodiment 1 when it is stopped. In Figures 13 and 14, the arrows indicate the flow of refrigerant.

[0055] During operation, the on-off valve 31 is closed as shown in Figure 13. The refrigerant gas compressed in the compression chamber 19 is discharged from the compression chamber 19 to the discharge channel 22, as shown by the arrow in Figure 13, passes through the first check valve 25, and flows into the oil separator 40.

[0056] When the system is stopped, the on-off valve 31 is opened as shown in Figure 14. As a result, the refrigerant in the high-pressure space 60 downstream of the first check valve 25 flows into the low-pressure space 50 through the communication channel 30.

[0057] Here, if the screw compressor 1 does not have a connecting passage 30, the flow of refrigerant from the high-pressure space 61 to the low-pressure space 50 will be through the small gaps between the components inside the screw compressor 1, so the time it takes for the high-pressure space 61 and the low-pressure space 50 to equalize will be longer. If the time it takes for the high-pressure space 61 and the low-pressure space 50 to equalize is longer, as described above, a large amount of refrigerant oil will flow into the low-pressure space 50. If the screw compressor 1 is restarted in this state, a large amount of refrigerant oil in the low-pressure space 50 will be drawn into the compression chamber 19, and there is a concern that the compression mechanism 20 will undergo liquid compression and the gate rotor 15 will be damaged.

[0058] In contrast, the screw compressor 1 has a communication passage 30, and when the unit is stopped, the refrigerant in the high-pressure space 61 is bypassed to the low-pressure space 50 via the communication passage 30, thus shortening the time it takes for the high-pressure space 61 and the low-pressure space 50 to equalize pressure. By shortening the time it takes for the high-pressure space 61 and the low-pressure space 50 to equalize pressure, the screw compressor 1 can reduce the amount of refrigerant oil flowing into the low-pressure space 50, and as a result, damage to the gate rotor 15 can be suppressed. Therefore, the screw compressor 1 can improve the reliability of the compression mechanism 20.

[0059] Furthermore, if the screw compressor 1 is not equipped with a first check valve 25 in the discharge passage 22, when the unit is stopped, the refrigerant in the high-pressure space 60 will flow back into the low-pressure space 50 through the compression chamber 19, causing the compression mechanism 20 to rotate in reverse.

[0060] In contrast, the screw compressor 1 is equipped with a first check valve 25 in the discharge passage 22, and when operation stops, the flow of refrigerant from the compression chamber 19 to the discharge passage 22 stops, causing the first check valve 25 to close as shown in Figure 14. By closing the first check valve 25, the screw compressor 1 can prevent backflow of refrigerant from the high-pressure space 61 downstream of the first check valve 25 in the high-pressure space 60 (hereinafter referred to as downstream refrigerant).

[0061] On the other hand, the refrigerant in the high-pressure space 60 upstream of the first check valve 25, in other words, the refrigerant in the discharge passage 22 upstream of the first check valve 25 (hereinafter referred to as the upstream refrigerant), flows backward through the discharge passage 22 into the compression chamber 19. Therefore, although the compression mechanism 20 does rotate backward, the amount of upstream refrigerant is significantly less than the amount of downstream refrigerant. As a result, the screw compressor 1 can shorten the reverse rotation time of the compression mechanism 20. By shortening the reverse rotation time of the compression mechanism 20, the screw compressor 1 can shorten the waiting time until restart, i.e., the restart time. In other words, by providing the first check valve 25, the screw compressor 1 can reduce the flow rate of refrigerant that flows backward compared to a configuration without the first check valve 25, thereby shortening the reverse rotation time and restart time of the compression mechanism 20.

[0062] As described above, the screw compressor 1 of Embodiment 1 is a compressor that compresses a refrigerant containing refrigerant oil that has been drawn in, in the compression chamber 19 of the compression mechanism 20, and discharges it through at least one discharge port 1a. The screw compressor 1 is equipped with an oil separator 40 located downstream of at least one discharge port 1a, which separates the refrigerant discharged from the discharge port 1a from the refrigerant oil. The screw compressor 1 is equipped with a first check valve 25 located downstream of at least one discharge port 1a and upstream of the oil separator 40, which suppresses the backflow of refrigerant. The screw compressor 1 is equipped with a communication passage 30 that connects a low-pressure space 50 and a high-pressure space 61. The low-pressure space 50 is located upstream of the compression chamber 19 and is the space where the refrigerant drawn into the compression chamber 19 is located. The high-pressure space 61 is the space where the refrigerant compressed in the compression chamber 19 is located, is located downstream of the first check valve 25, and is the space which includes the internal space 60A of the oil separator 40. The screw compressor 1 is provided in the communication passage 30 and includes an on-off valve 31 that opens and closes the communication passage 30.

[0063] With the above configuration, the screw compressor 1, by being equipped with a first check valve 25, can reduce the flow rate of refrigerant flowing back compared to a configuration without the first check valve 25, thereby shortening the reverse rotation time and restart time of the compression mechanism 20. Furthermore, since the screw compressor 1 is equipped with an on-off valve 31 in the communication passage 30 that connects the low-pressure space 50 and the high-pressure space 61, when the on-off valve 31 is opened when the operation is stopped, the refrigerant in the high-pressure space 61 can be bypassed to the low-pressure space 50, reducing the amount of refrigerant oil flowing into the compression chamber 19 and the low-pressure space 50, and suppressing liquid compression during startup, thereby suppressing damage to the gate rotor 15. Thus, the screw compressor 1 can improve the reliability of the compression mechanism 20. In other words, the screw compressor 1 can shorten the reverse rotation time and restart time of the compression mechanism when the operation is stopped, and improve the reliability of the compression mechanism.

[0064] Embodiment 2. Embodiment 2 differs from Embodiment 1 in the installation position and number of the first check valves 25. The following description will focus on the configurations in Embodiment 2 that differ from Embodiment 1, while configurations not described in Embodiment 2 are the same as in Embodiment 1.

[0065] Figure 15 is a schematic cross-sectional view of the screw compressor 1 according to Embodiment 2. Figure 16 is a schematic side view of the compressor body 10 of the screw compressor 1 according to Embodiment 2, viewed from the first connection surface 10a side. Figure 16 shows the flow path forming plate 72 superimposed in front of the first connection surface 10a to explain the arrangement position of the flow path forming plate 72. Figure 17 is a plan view of the flow path forming plate 72 of the screw compressor 1 according to Embodiment 2.

[0066] The screw compressor 1 of Embodiment 2 has a confluence passage 70 that combines the refrigerants flowing out from the two discharge passages 22. The confluence passage 70 is formed at the contact surfaces of the first connection surface 10a and the second connection surface 40a. In Figure 16, the confluence passage 70 is indicated by dots. Specifically, the confluence passage 70 is composed of an arc-shaped recess 71 that is recessed on the first connection surface 10a of the first casing 11 on the side opposite to the second connection surface 40a, and an arc-shaped flow path forming plate 72 that covers the opening surface of the arc-shaped recess 71. The flow path forming plate 72 is fixed to the first connection surface 10a with bolts or the like. When the first casing 11 and the second casing 41 are fixed together, the flow path forming plate 72 is housed in a recess 80 for fitting the flow path forming plate 72 provided on the second connection surface 40a. The flow channel forming plate 72 is fixed to the first connection surface 10a and covers the opening surface of the arc-shaped recess 71, thereby forming a confluence flow channel 70 between it and the arc-shaped recess 71.

[0067] The flow channel forming plate 72 has an outlet 72a that penetrates in the thickness direction of the plate. The outlet 72a is a hole that allows the refrigerant from the confluence flow channel 70 to flow out of the confluence flow channel 70.

[0068] In the first embodiment, the screw compressor 1 had a first check valve 25 installed in each of the two discharge passages 22. In contrast, the second embodiment has a single first check valve 25 installed downstream of the outlet 72a of the flow path forming plate 72. The flow path that merges the refrigerant flowing out from each of the two discharge passages 22 is not limited to the above configuration and may be partitioned and formed within the second casing 41 of the oil separator 40. In short, the second embodiment of the screw compressor 1 only needs to have a configuration in which a single first check valve 25 is installed at the position after the refrigerant flowing out from each of the two discharge passages 22 has merged.

[0069] The operation of the above configuration will now be explained. The refrigerant flowing out from each of the two discharge channels 22 merges in the confluence channel 70 and flows out from the outlet 72a. The refrigerant flowing out from the outlet 72a opens the first check valve 25 and flows into the internal space 60A of the oil separator 40. The flow of refrigerant thereafter is the same as described above.

[0070] In the screw compressor 1 of Embodiment 2, a first check valve 25 is installed at the point where the refrigerant flowing out from each of the two discharge passages 22 merges. Therefore, the screw compressor 1 can reduce the number of first check valves 25.

[0071] Furthermore, the first check valve 25 is installed in the second casing 41 in a position where it is exposed when viewed from the second connection surface 40a side. Therefore, the screw compressor 1 has the effect of facilitating the installation of the first check valve 25.

[0072] In the illustrated example, the first check valve 25 is shown installed inside the second casing 41. However, the first check valve 25 may also be installed inside the first casing 11 together with the flow path forming plate 72. In this configuration, the first check valve 25 is installed in a position where it is exposed when viewed from the first connection surface 10a, making it easier to install the first check valve 25.

[0073] As described above, the screw compressor 1 of Embodiment 2 provides the same effects as Embodiment 1, while also offering the advantage of reducing the number of first check valves 25.

[0074] Embodiment 3. Figure 18 is a circuit diagram showing an example of the configuration of a refrigeration system 100 according to Embodiment 3. In Figure 18, solid lines indicate the flow of refrigerant, and dotted lines indicate the flow of refrigerant oil. As shown in Figure 18, the refrigeration system 100 includes a screw compressor 1, a condenser 2, a pressure reducing device 3, an evaporator 4, and a control device 5, all of which are described in Embodiments 1 to 2 above. In the refrigeration system 100, the screw compressor 1, condenser 2, pressure reducing device 3, and evaporator 4 are sequentially connected by refrigerant piping, thereby forming a refrigerant circuit through which the refrigerant circulates.

[0075] The refrigerant circulating in the refrigerant circuit is not particularly limited and can be applied regardless of the magnitude of the operating pressure, for example, fluorocarbon refrigerants such as HFCs (hydrofluorocarbons) and HFOs (hydrofluoroolefins), hydrocarbon refrigerants such as HC (hydrocarbons), or natural refrigerants such as CO2 (carbon dioxide) and ammonia.

[0076] The condenser 2 performs heat exchange between the air supplied by a blower (not shown) and the refrigerant. The condenser 2 releases heat from the refrigerant into the air and condenses the refrigerant gas discharged from the screw compressor 1. The condenser 2 is composed of a fin-and-tube heat exchanger or a plate heat exchanger, etc. The pressure reducing device 3 depressurizes and expands the refrigerant liquid that has flowed out of the condenser 2. The pressure reducing device 3 is composed of a valve whose opening degree can be controlled, such as an electronic expansion valve. In this case, the opening degree of the pressure reducing device 3 is controlled by the control device 5. Note that the pressure reducing device 3 is not limited to one whose opening degree can be controlled, and may be, for example, a capillary tube, etc. The evaporator 4 performs heat exchange between the air supplied by a blower (not shown) and the refrigerant. The evaporator 4 evaporates the refrigerant that has flowed out of the pressure reducing device 3. The evaporator 4 is composed of a fin-and-tube heat exchanger or a plate heat exchanger, etc.

[0077] The control device 5 controls the entire refrigeration system 100, including the screw compressor 1, the pressure reducing device 3, and the on / off valve 31. The control device 5 is composed of a microprocessor unit or the like. The control device 5 may also be composed of updatable components such as firmware.

[0078] The refrigerant gas discharged from the screw compressor 1 flows into the condenser 2, where it exchanges heat with the air or water passing through the condenser 2 and flows out as high-pressure liquid refrigerant. The high-pressure liquid refrigerant that has flowed out of the condenser 2 is depressurized by the depressurization device 3 to become low-pressure gas-liquid two-phase refrigerant and flows into the evaporator 4. The low-pressure gas-liquid two-phase refrigerant that has flowed into the evaporator 4 exchanges heat with the air, water, or brine passing through the evaporator 4 to become low-pressure gaseous refrigerant, which is then drawn back into the screw compressor 1.

[0079] The refrigeration system 100 of Embodiment 3 is equipped with a screw compressor 1 of any of Embodiments 1 to 2, and when the screw compressor 1 is stopped, the control device 5 opens the on-off valve 31. As a result, the refrigeration system 100 can shorten the reverse rotation time and restart time of the compression mechanism 20 when the screw compressor 1 is stopped, and can also improve the reliability of the compression mechanism 20.

[0080] The following describes the opening and closing timing of the on / off valve 31 by the control device 5.

[0081] Figure 19 is a diagram illustrating the opening and closing timing of the on-off valve 31 in the screw compressor 1 according to Embodiment 3. Figure 20 is a diagram illustrating other opening and closing timings of the on-off valve 31 in the screw compressor 1 according to Embodiment 3.

[0082] At time T0, the screw compressor 1 is operating. Time T1 is the time when the control device 5 receives a stop command from an external source to stop the screw compressor 1. Upon receiving the stop command, the control device 5 sends a stop signal to the motor 12 via the inverter to stop the motor 12. Time T2 is the time when the on-off valve 31 is opened. Time T3 is the time when the first check valve 25 is closed. Time T4 is the time after a preset equalization time has passed since the on-off valve 31 was opened, and is the time when the on-off valve 31 is closed.

[0083] As shown in Figure 19, after receiving a stop command, the control device 5 opens the on-off valve 31 at time T2, which is before time T3 when the first check valve 25 is closed. In Figure 19, the time T2 when the on-off valve 31 is opened is set to be between time T1 and time T3, but it may also be simultaneous with the time T1 when the stop command is received. In other words, the control device 5 may open the on-off valve 31 at the same time as the time T1 when the stop command is received. Alternatively, the opening timing of the on-off valve 31 may be simultaneous with the time T3 when the first check valve 25 is closed, as shown in Figure 20.

[0084] Thus, when the control device 5 opens the on-off valve 31 when the screw compressor 1 stops operating, the opening timing of the on-off valve 31 may be set to be before the closing timing of the first check valve 25, or it may be set to be simultaneous with the closing timing of the first check valve 25. Since the closing timing of the first check valve 25 is automatically determined by the refrigerant backflow time, the control device 5 can determine the opening and closing timing of the on-off valve 31 by pre-storing the time from when it sends a stop signal to the motor 12 via the inverter until the first check valve 25 closes.

[0085] The various aspects of this disclosure are summarized below as an appendix.

[0086] (Note 1) A screw compressor that compresses a refrigerant containing refrigerant oil that has been drawn in, in a compression chamber of a compression mechanism, and discharges it through at least one discharge port, An oil separator is provided, which is located downstream of the at least one discharge port and separates the refrigerant discharged from the at least one discharge port from the refrigerating oil. A first check valve is installed downstream of at least one discharge port and upstream of the oil separator to suppress the backflow of the refrigerant, A communication channel connecting a low-pressure space located upstream of the compression chamber, where the refrigerant drawn into the compression chamber is located, and a high-pressure space located downstream of the first check valve, which includes the internal space of the oil separator, A screw compressor comprising an on-off valve provided in the aforementioned communication channel for opening and closing the aforementioned communication channel. (Note 2) It has a first casing that houses the compression mechanism inside, The screw compressor according to Appendix 1, wherein the first check valve is partitioned within the first casing and installed in at least one discharge channel connecting the at least one discharge port and the oil separator. (Note 3) The aforementioned at least one discharge port includes two discharge ports, The screw compressor according to Appendix 2, wherein the at least one discharge channel includes two discharge channels. (Note 4) The screw compressor described in Appendix 3, wherein the first check valve is installed at the position after the refrigerant flowing out from each of the two discharge channels has merged. (Note 5) The system has a confluence channel that combines the refrigerant discharged from each of the two discharge channels, The aforementioned confluence channel is configured to include a channel forming plate, The flow path forming plate has an outlet that penetrates in the thickness direction and allows the refrigerant from the confluence flow path to flow out. The screw compressor described in Appendix 4, wherein the first check valve is installed downstream of the outlet. (Note 6) A casing for housing the compression mechanism, comprising the first casing having a first connecting surface that contacts the oil separator, The oil separator comprises a second casing having a second connecting surface that contacts the first connecting surface of the first casing, The screw compressor described in Appendix 5, wherein the first check valve is installed in a position that is exposed when the first casing is viewed from the first connection surface side or when the second casing is viewed from the second connection surface side. (Note 7) The aforementioned oil separator is An oil separation unit for separating the refrigerant and the refrigeration oil, A second check valve is provided, which is located downstream of the oil separation section and suppresses the backflow of the refrigerant separated in the oil separation section. A screw compressor equipped with any one of the features described in Appendix 1 to Appendix 6. (Note 8) A refrigeration system comprising a screw compressor as described in any one of the appendices 1 to 7, a condenser, a pressure reducing device, an evaporator, and a control device that opens the on / off valve when the screw compressor is stopped. (Note 9) The refrigeration apparatus according to Appendix 8, wherein the control device sets the opening timing of the on / off valve to be earlier than the closing timing of the first check valve. (Note 10) The refrigeration apparatus according to Appendix 8, wherein the control device sets the opening timing of the on / off valve to coincide with the closing timing of the first check valve. [Explanation of Symbols]

[0087] 1 Screw compressor, 1a Discharge port, 2 Condenser, 3 Pressure reducing device, 4 Evaporator, 5 Control device, 10 Compressor body, 10a First connection surface, 11 First casing, 11b First casing end opening, 12 Motor, 12a Stator, 12b Motor rotor, 13 Screw shaft, 14 Screw rotor, 14a Screw groove, 15 Gate rotor, 15a Teeth, 16 Slide valve, 16a Opening, 17 Bearing, 18 Partition, 19 Compression chamber, 20 Compression mechanism, 21 Slide groove, 22 Discharge passage, 22A Space, 22a Inlet, 22b Outlet, 23 Oil reservoir, 24 Oil passage, 25 First check valve, 26 Base, 26a Passage, 26a1 Valve seat, 26b Bolt hole, 27 Valve section, 27A Valve section, 27a Shaft section, 27b Plate section, 27c Shaft section, 27d Plate section, 30 Communication channel, 30a End section, 31 On / off valve, 40 Oil separator, 40a Second connection surface, 41 Second casing, 41a Oil storage section, 41a1 Communication port, 41b Second casing end opening, 42 Oil separation section, 42a Outer cylinder section, 42a1 Oil outlet, 42b Inner cylinder section, 42c Cover section, 42c1 Outlet section, 43 Partition plate, 44 Second check valve, 50 Low-pressure space, 60 High-pressure space, 60A Internal space, 61 High-pressure space, 70 Confluence channel, 71 Arc-shaped recess, 72 Channel forming plate, 72a Outlet, 80 Recess, 100 Refrigeration device.

Claims

1. A screw compressor that compresses a refrigerant containing refrigerant oil that has been drawn in, in a compression chamber of a compression mechanism, and discharges it through at least one discharge port, An oil separator is provided, which is located downstream of the at least one discharge port and separates the refrigerant discharged from the at least one discharge port from the refrigerating oil. A first check valve is installed downstream of at least one discharge port and upstream of the oil separator to suppress the backflow of the refrigerant, A communication channel connecting a low-pressure space located upstream of the compression chamber, where the refrigerant drawn into the compression chamber is located, and a high-pressure space located downstream of the first check valve, which includes the internal space of the oil separator, A screw compressor comprising an on-off valve provided in the aforementioned communication channel for opening and closing the aforementioned communication channel.

2. It has a first casing that houses the compression mechanism inside, The screw compressor according to claim 1, wherein the first check valve is partitioned within the first casing and installed in at least one discharge channel connecting the at least one discharge port and the oil separator.

3. The aforementioned at least one discharge port includes two discharge ports, The screw compressor according to claim 2, wherein the at least one discharge channel includes two discharge channels.

4. The screw compressor according to claim 3, wherein the first check valve is installed at the position after the refrigerant flowing out from each of the two discharge channels has merged.

5. The system has a confluence channel that combines the refrigerant discharged from each of the two discharge channels, The aforementioned confluence channel is configured to include a channel forming plate, The flow path forming plate has an outlet that penetrates in the thickness direction and allows the refrigerant from the confluence flow path to flow out. The screw compressor according to claim 4, wherein the first check valve is installed downstream of the outlet.

6. A casing for housing the compression mechanism, comprising the first casing having a first connecting surface that contacts the oil separator, The oil separator comprises a second casing having a second connecting surface that contacts the first connecting surface of the first casing, The screw compressor according to claim 5, wherein the first check valve is installed in a position that is exposed when the first casing is viewed from the first connection surface side or in a position that is exposed when the second casing is viewed from the second connection surface side.

7. The oil separator is, An oil separation unit for separating the refrigerant and the refrigeration oil, A second check valve is positioned downstream of the oil separation section and suppresses the backflow of the refrigerant separated in the oil separation section, A screw compressor according to claim 1 or claim 2, comprising:

8. A refrigeration system comprising a screw compressor according to claim 1 or claim 2, a condenser, a pressure reducing device, an evaporator, and a control device that opens the on / off valve when the screw compressor is stopped.

9. The refrigeration apparatus according to claim 8, wherein the control device sets the opening timing of the on / off valve to be earlier than the closing timing of the first check valve.

10. The refrigeration apparatus according to claim 8, wherein the control device sets the opening timing of the on / off valve to coincide with the closing timing of the first check valve.

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