Screw compressor

Abstract

This screw compressor includes a screw rotor, a rotor chamber, a suction space, a discharge space, a slide valve, and a slide valve guide provided in the discharge space. The slide valve is configured to open an inlet of a bypass passage, which communicates the rotor chamber with the suction space, on an inner wall surface of the rotor chamber when the slide valve moves to the discharge space side. The slide valve guide has a guide surface and a first groove that is provided on the guide surface and communicates with the discharge space. The slide valve has a sliding surface facing the guide surface, and a second groove provided on the sliding surface. When the inlet of the bypass passage is opened and the first groove and the second groove are positioned opposite each other, a communication passage including the first groove and the second groove communicates the bypass passage with the discharge space.

Description

Screw Compressor

[0001] The present disclosure relates to a screw compressor.

[0002] Some screw compressors allow the capacity to be controlled by a slide valve.

[0003] For example, Patent Document 1 describes a compressor that uses a slide valve to control capacity. In the screw compressor described in Patent Document 1, the slide valve is moved to return a portion of the gas sucked into the tooth groove space of the screw rotor (the portion where the male rotor and female rotor mesh) to the suction space (the suction port side), thereby reducing the capacity of the screw compressor.

[0004] Japanese Patent Application Laid-Open No. 2018-178815

[0005] However, if an attempt is made to ensure the capacity control range of the screw compressor by simply adjusting the flow rate of gas returning from the tooth groove space to the suction space, as in Patent Document 1, the movable range of the slide valve must be made sufficiently large, which results in a problem of an increase in the size of the compressor.

[0006] In view of the above circumstances, at least some embodiments of the present invention have an object to provide a screw compressor that can achieve both an expanded capacity control range and compactness.

[0007] A screw compressor according to at least some embodiments of the present invention comprises: a screw rotor; a casing that includes a rotor chamber that houses the screw rotor, a suction space, and a discharge space; a slide valve that is movable in the axial direction of the screw rotor and is provided so as to form part of an inner wall surface of the rotor chamber; and a slide valve guide that is provided in the discharge space and supports an end of the slide valve that protrudes into the discharge space, wherein the slide valve is configured to open an inlet of a bypass passage that communicates the rotor chamber and the suction space to the inner wall surface of the rotor chamber when it moves toward the discharge space, the slide valve guide has a guide surface that slidably guides the slide valve, and a first groove that is provided on the guide surface and communicates with the discharge space, and the slide valve has a sliding surface that faces the guide surface of the slide valve guide on the outer surface of the slide valve, and a second groove that is provided on the sliding surface, When the inlet of the bypass passage is open and the first groove and the second groove are positioned opposite each other, a communication passage including the first groove and the second groove is configured to communicate the bypass passage with the discharge space.

[0008] According to at least some embodiments of the present invention, when the inlet of the bypass passage is opened, not only the low-pressure gas before compression in the rotor chamber but also the high-pressure gas after compression in the discharge space is returned to the bypass passage via the communication passage including the first groove and the second groove, thereby further reducing the actual gas intake amount of the compressor. Thus, a screw compressor is provided that can achieve both an expanded capacity control range and a compact design.

[0009] FIG. 1 is a schematic cross-sectional view of a screw compressor according to one embodiment, showing a state in which the slide valve is completely accommodated in the slide valve accommodating chamber. FIG. 1 is a schematic cross-sectional view of a screw compressor according to one embodiment, showing a state in which the slide valve protrudes to the discharge space to the maximum extent. FIG. 2 is a partial cross-sectional view showing the internal structure of a screw compressor according to one embodiment. FIG. 3 is a perspective view showing a part of a casing and a slide valve guide according to one embodiment. FIG. 4 is a plan view of a slide valve guide according to one embodiment. FIG. 5 is a plan view of a slide valve guide according to another embodiment. FIG. 6 is a view of a slide valve guide and a slide valve according to one embodiment, as viewed from the discharge space side. FIG. 7 is a perspective view of a slide valve according to one embodiment. FIG. 8 is a schematic view of a slide valve according to another embodiment. FIG. 9 is a partial cross-sectional perspective view showing the internal structure of a screw compressor according to one embodiment. FIG. 10 is a plan view of a slide valve and a slide valve guide according to one embodiment, showing a state in which the slide valve is in a fully closed position. FIG. 11 is a plan view of a slide valve and a slide valve guide according to one embodiment, showing a state in which the slide valve is positioned between the fully closed position and a position where the first groove and the second groove start to oppose each other. FIG. 12 is a plan view of a slide valve and a slide valve guide according to one embodiment, showing a state immediately after the first groove and the second groove start to oppose each other. FIG. 1 is a plan view of a slide valve and a slide valve guide according to one embodiment, showing a state in which the slide valve is in a fully open position; FIG. 2 is a schematic diagram showing a change in the communication area S between the first groove and the second groove as the slide valve moves in one embodiment; FIG. 3 is a graph of the derivative of the communication area S between the first groove and the second groove according to one embodiment; FIG. 4 is a graph of the second derivative of the communication area S between the first groove and the second groove according to one embodiment; FIG. 5 is a plan view of a slide valve and a slide valve guide according to one embodiment; FIG. 6 is a plan view of a slide valve and a slide valve guide according to another embodiment; FIG. 7 is a plan view of a slide valve and a slide valve guide according to yet another embodiment; FIG. 8 is a graph showing the relationship between the position of the slide valve and the gas intake amount of the screw compressor in some embodiments.

[0010] An embodiment of the present invention will be described below with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described as an embodiment or shown in the drawings are merely illustrative examples and are not intended to limit the scope of the present invention. In this specification, unless otherwise specified, the "axial direction" refers to the axial direction of the screw rotor, and the side in the axial direction where the suction space is located is referred to as the suction side, and the side where the discharge space is located is referred to as the discharge side.

[0011] 1A is a schematic cross-sectional view of a screw compressor according to one embodiment, showing a state in which a slide valve is completely accommodated in a slide valve accommodating chamber, and FIG. 1B is a schematic cross-sectional view of a screw compressor according to one embodiment, showing a state in which the slide valve is maximally protruded into a discharge space.

[0012] In some embodiments, the screw compressor 1 includes a screw rotor 10 and a casing 20 that covers at least the screw rotor 10, as shown in FIGS. 1A and 1B.

[0013] In the embodiment shown in Figures 1A and 1B, the screw rotor 10 is a pair of screw rotors consisting of a male rotor and a female rotor. The male rotor and female rotor are arranged side by side in the depth direction of the paper in Figures 1A and 1B. In this case, the male rotor and female rotor have helical teeth that mesh with each other. The tooth grooves of the male rotor and female rotor and the inner wall surface of the casing 20 (the inner wall surface 21W of the rotor chamber 21 described below) form multiple tooth groove spaces. The rotating shaft 11 of the male rotor is connected to the output shaft of a drive source (not shown) and is rotated by the drive source. The female rotor rotates following the rotation of the male rotor. The female rotor rotates in the direction opposite to the rotation of the male rotor. When the male rotor and female rotor rotate in an intermeshed state, the tooth groove spaces of the screw rotor 10 move axially from the suction side to the discharge side.

[0014] The casing 20 includes at least a rotor chamber 21 that accommodates the screw rotor 10, a suction space 22, and a discharge space 23. In addition to the rotor chamber 21, the suction space 22, and the discharge space 23, the casing 20 may also include a bearing chamber 27 that accommodates a bearing that rotatably supports the rotary shaft 11. In the embodiment shown in FIGS. 1A and 1B , the casing 20 is composed of multiple casing components 20A to 20D that respectively define the bearing chamber 27, the discharge space 23, the rotor chamber 21, and the suction space 22. Specifically, the casing 20 is composed of a casing 20A that defines the bearing chamber 27, a casing 20B that defines the discharge space 23, a casing 20C that defines the rotor chamber 21, and a casing 20D that defines the suction space 22. The casings 20A to 20D are separably connected in series with each other by fastening members such as bolts. A portion of the inner wall surface of the casing 20C forms the inner wall surface 21W of the rotor chamber 21. As described above, the inner wall surface 21W of the rotor chamber 21 forms a plurality of tooth groove spaces together with the tooth grooves of the screw rotor 10 (male rotor and female rotor). In addition to the rotor chamber 21, the casing 20C also includes a slide valve accommodating chamber 24 for accommodating a slide valve 40 (described later). The slide valve accommodating chamber 24 is a portion of the internal space of the casing 20C that communicates with the rotor chamber 21 and the discharge space 23, respectively.

[0015] Uncompressed low-pressure gas G0 flows into the suction space 22 from outside the screw compressor 1. The low-pressure gas G0 is sucked from the suction space 22 into the tooth groove space via the suction port 12. When the suction port 12 is closed during the process of movement of the tooth groove space accompanying the rotation of the screw rotor 10 (male rotor and female rotor), the volume of the sealed tooth groove space decreases and the gas G1 in the tooth groove space is compressed. When the tooth groove space reaches the discharge port 13 and the tooth groove space and the discharge space 23 communicate with each other, compressed high-pressure gas G2 is discharged into the discharge space 23 via the discharge port 13.

[0016] A discharge port (not shown) opens in the discharge space 23 at a position different from the discharge port 13. The high-pressure gas G2 in the discharge space 23 is discharged from the discharge port to the outside of the screw compressor 1. Lubricating oil also flows into the discharge space 23. The lubricating oil that has lubricated the screw rotor 10 mixes with the gas G1 in the tooth groove space, is compressed, and is discharged from the discharge space 23 together with the compressed high-pressure gas G2 to the outside of the screw compressor 1. A portion of the lubricating oil is stored in the discharge space 23, and the oil level may vary depending on the operating state of the screw compressor 1.

[0017] As shown in FIGS. 1A and 1B , in some embodiments, the screw compressor 1 includes a slide valve 40 that is movable in the axial direction of the screw rotor 10 and a slide valve guide 50 that supports an end of the slide valve 40, in order to achieve a capacity control function.

[0018] The slide valve 40 is provided so as to form a part of the inner wall surface 21W of the rotor chamber 21. Specifically, the surface of the outer surface 43 of the slide valve 40 that faces the rotor chamber 21 is continuous with the inner wall surface of the casing 20C and forms the inner wall surface 21W of the rotor chamber 21 together with the inner wall surface of the casing 20C.

[0019] As described above, the slide valve 40 is movable in the axial direction of the screw rotor 10 and adjusts the opening area of ​​the inlet 33 of the bypass passage 30 according to its axial position, thereby controlling the capacity of the screw compressor 1.

[0020] When the slide valve 40 is in the position shown in Fig. 1A, the outer surface 43 of the slide valve 40 is continuous with the inner wall surface of the casing 20C over the entire area facing the rotor chamber 21, and forms the inner wall surface 21W of the rotor chamber 21 together with the inner wall surface of the casing 20C. At this time, the slide valve 40 is completely accommodated in the slide valve accommodating chamber 24, and the inlet 33 of the bypass passage 30 (see Fig. 1B) is closed by the slide valve 40. Thus, in the state shown in Fig. 1A where the slide valve 40 is completely accommodated in the slide valve accommodating chamber 24, the opening area of ​​the inlet 33 of the bypass passage 30 is zero. Hereinafter, the position of the slide valve 40 in this state in the x-coordinate system along the axial direction of the screw rotor 10 is defined as x = 1, and is referred to as the fully closed position.

[0021] In contrast, when the slide valve 40 moves to the discharge side, as shown in Fig. 1B, the end of the slide valve 40 protrudes into the discharge space 23, and the inlet 33 of the bypass passage 30 opens to the inner wall surface 21W of the rotor chamber 21. When the slide valve 40 protrudes to the maximum extent into the discharge space 23 (see Fig. 1B), the opening area of ​​the inlet 33 of the bypass passage 30 becomes maximum. In this state, the position of the slide valve 40 in the x-coordinate system along the axial direction of the screw rotor 10 is defined as the origin x = 0, and is referred to as the fully open position.

[0022] The bypass passage 30 connects the rotor chamber 21 and the suction space 22 and guides a portion of the low-pressure gas G1 (return low-pressure gas G3) in the tooth gap space to the suction space 22. The return low-pressure gas G3 flows into the bypass passage 30 through the inlet 33 and is guided to the suction space 22, where it merges with the uncompressed low-pressure gas G0. The return low-pressure gas G3 then passes through the suction port 12 and enters the tooth gap space again. The greater the flow rate of the return low-pressure gas G3, the smaller the flow rate of the low-pressure gas G0 drawn in from outside the screw compressor 1. As shown in FIG. 1A, when the slide valve 40 is in the fully closed position, the inlet 33 is closed by the slide valve 40, and the flow rate of the return low-pressure gas G3 is zero. In contrast, as shown in FIG. 1B, when the slide valve 40 is in the fully open position, the flow rate of the return low-pressure gas G3 is maximized. In this way, the slide valve 40 can move axially within the range of 0≦x≦1, and the flow rate of the low-pressure gas G0 sucked in from outside the screw compressor 1 is adjusted by changing the opening area of ​​the inlet 33 of the bypass passage 30 depending on the position of the slide valve 40.

[0023] 1A and 1B, the slide valve 40 includes a suction-side end portion 45 disposed on the suction side and a discharge-side end portion 46 disposed on the discharge side. The outer surface 43 of the slide valve 40 includes a suction-side end face 45P and a discharge-side end face 46P. Furthermore, the slide valve 40 includes, as part of the outer surface 43 of the slide valve 40, a sliding surface 44 that faces a guide surface 51 of a slide valve guide 50 (described later). In the portion of the slide valve 40 accommodated in the slide valve accommodation chamber 24, the sliding surface 44 faces the inner wall surface 25 of the slide valve accommodation chamber 24. When the slide valve 40 moves to the discharge side, the suction-side end face 45P of the slide valve 40 forms part of the contour of the inlet 33 of the bypass passage 30 that opens to the inner wall surface 21W of the rotor chamber 21, as shown in FIG. 1B. In the embodiment shown in FIGS. 1A and 1B, a notch 47 is formed in the discharge end portion 46 to define the discharge position of the high-pressure gas G2 discharged from the tooth groove space to the discharge space 23.

[0024] The slide valve 40 may, together with other components, constitute the capacity control device 2 of the screw compressor 1. In addition to the slide valve 40, the capacity control device 2 includes a piston rod 41 connected to the suction side end face 45P of the slide valve 40, and a piston 42 connected to the piston rod 41 on the side opposite to the slide valve 40. The piston 42 is housed in a cylinder chamber 26 formed in the casing 20D. The capacity control device 2 may be hydraulically driven, and the slide valve 40 may move axially by the pressure of oil supplied into the cylinder chamber 26.

[0025] The slide valve guide 50 is provided in the discharge space 23 and supports the discharge side end 46 of the slide valve 40 that protrudes into the discharge space 23. In the embodiment shown in Figures 1A and 1B, the slide valve guide 50 is provided below the movement path of the slide valve 40 within the discharge space 23 so as to support the discharge side end 46 of the slide valve 40 from below.

[0026] The slide valve guide 50 includes a guide surface 51 that slidably guides the slide valve 40. The guide surface 51 of the slide valve guide 50 faces the sliding surface 44 of the slide valve 40 when the slide valve 40 moves toward the discharge side. In addition to the guide surface 51, the slide valve guide 50 also includes an intake side end 54 located on the intake side, an exhaust side end 55 located on the discharge side, an intake side end face 54P, and an exhaust side end face 55P. The slide valve guide 50 is disposed so that the intake side end 54 is adjacent to the casing 20C.

[0027] As described above, the slide valve 40 and the slide valve guide 50 can change the opening area of ​​the inlet 33 of the bypass passage 30 depending on the position of the slide valve 40, thereby enabling capacity control of the screw compressor 1. In some embodiments, in addition to the capacity control based on the change in the opening area of ​​the inlet 33 of the bypass passage 30 described above, capacity control utilizing communication between the discharge space 23 and the bypass passage 30 is also performed.

[0028] A configuration for additional capacity control by communication between the discharge space 23 and the bypass passage 30 will be described below with reference to FIGS. 2 to 8 . FIG. 2 is a partial cross-sectional view showing the internal structure of a screw compressor according to one embodiment. FIG. 3 is a perspective view showing a slide valve guide and a portion of a casing according to one embodiment. FIG. 4A is a plan view of a slide valve guide according to one embodiment. FIG. 4B is a plan view of a slide valve guide according to another embodiment. FIG. 5 is a view of the slide valve guide and slide valve according to one embodiment, viewed from the discharge space side. FIG. 6 is a perspective view of a slide valve according to one embodiment. FIG. 7A is a schematic diagram of a slide valve according to one embodiment. FIG. 7B is a schematic diagram of a slide valve according to another embodiment. FIG. 8 is a partial cross-sectional perspective view showing the internal structure of a screw compressor according to one embodiment. Note that the screw rotor 10 is omitted in FIG. 8 . The slide valve 40 is shown as one half of a vertically divided section along an axial plane.

[0029] In the exemplary embodiment shown in Fig. 3, the sliding valve guide 50 has a half-pipe shape, and the guide surface 51 is the inner peripheral surface of the half-pipe-shaped sliding valve guide 50. In this case, the portion of the sliding valve 40 that forms the sliding surface 44 has a semi-cylindrical shape that is complementary to the half-pipe-shaped sliding valve guide 50, and the sliding surface 44 is the outer peripheral surface of the semi-cylindrical sliding valve 40, as shown in Figs.

[0030] 2 and 8 , the slide valve guide 50 has a first groove 61 provided in the guide surface 51, and the slide valve 40 has a second groove 62 provided in the sliding surface 44. The first groove 61 communicates with the discharge space 23. The second groove 62 communicates with the bypass passage 30.

[0031] 2 and 8 , when the inlet 33 of the bypass passage 30 is open, the first groove 61 and the second groove 62 face each other. That is, when the slide valve 40 is in at least a portion of the positional range of 0≦x<1, the first groove 61 and the second groove 62 face each other. When the inlet 33 of the bypass passage 30 is open and the first groove 61 and the second groove 62 face each other, the bypass passage 30 and the discharge space 23 are connected to each other via the communication passage 60, which includes the first groove 61 and the second groove 62. Therefore, a portion of the high-pressure gas G2 in the discharge space 23 (high-pressure return gas G4) is guided through the communication passage 60 to the bypass passage 30, which is filled with the low-pressure return gas G3 from the tooth gap space. The high-pressure return gas G4 merges with the low-pressure return gas G3 and is guided from the bypass passage 30 to the suction space 22, where it passes through the suction port 12 again and enters the tooth gap space.

[0032] The first groove 61 has a suction side end region 63R including the suction side end 63 and a discharge side end region 64R including the discharge side end 64. In some embodiments, as shown in Figures 3 to 4B, the first groove 61 is formed along the circumferential direction of the guide surface 51 of the sliding valve guide 50.

[0033] 3 and 4A, the first groove 61 is in communication with the discharge space 23 by opening to the discharge space 23 at the vertical upper end 52 of the guide surface 51 of the slide valve guide 50. In the exemplary embodiment shown in FIGS. 3 and 4A, the suction side end 63 of the first groove 61 coincides with the suction side end 54 of the guide surface 51, and the discharge side end 64 of the first groove 61 is arranged parallel to the suction side end 63.

[0034] 4B , the first groove 61 does not open directly to the discharge space 23, but communicates with the discharge space 23 via an internal flow path 56 of the sliding valve guide 50. In the exemplary embodiment shown in FIG. 4B , the suction side end 63 of the first groove 61 is located closer to the discharge side than the suction side end 54 of the guide surface 51 of the sliding valve guide 50.

[0035] In some embodiments, as shown in FIG. 5, the first groove 61 communicates with the discharge space 23 above the center position of the guide surface 51 of the slide valve guide 50 in the vertical direction.

[0036] As shown in Figure 5, if a vertical z-coordinate system is defined, and the position of the lower end 53 of the guide surface 51 is z = Z1 and the position of the upper end 52 of the guide surface 51 is z = Z2 (where Z2 > Z1), the center position of the guide surface 51 is expressed as z = (Z1 + Z2) / 2. The first groove 61 communicates with the discharge space 23 at position z, where z > (Z1 + Z2) / 2. In the embodiment shown in Figure 5, the first groove 61 communicates with the discharge space 23 via an internal flow path 56 of the sliding valve guide 50. The internal flow path 56 of the sliding valve guide 50 opens to the outer surface of the sliding valve guide 50 at position z, where z > (Z1 + Z2) / 2, and communicates with the discharge space 23.

[0037] The second groove 62 has a suction-side end region 65R including the suction-side end 65 and a discharge-side end region 66R including the discharge-side end 66. In some embodiments, as shown in Figures 6 to 7B, the second groove 62 is provided on the sliding surface 44 of the slide valve 40 along the axial direction.

[0038] 6 , 7A, and 8 , the slide valve 40 includes, as part of the communication passage 60, an internal flow passage 67 that extends from one end 67I that opens into the second groove 62 to the other end 67O that opens into the suction side end face 45P of the slide valve 40. In this case, the second groove 62 communicates with the bypass passage 30 via the internal flow passage 67 of the slide valve 40.

[0039] 6, 7A, and 8, one end 67I of the internal flow passage 67 of the slide valve 40 opens to the suction side end region 65R of the second groove 62. The internal flow passage 67 extends vertically upward from the one end 67I, then turns axially and extends linearly to the other end 67O. The other end 67O of the internal flow passage 67 opens to the suction side end face 45P vertically below the position where the piston rod 41 is connected to the suction side end face 45P of the slide valve 40. In this way, when the slide valve 40 has the internal flow passage 67, a portion of the high-pressure gas G2 in the discharge space 23 (high-pressure return gas G4) flows into the first groove 61 and is guided to the bypass passage 30 via the second groove 62 and the internal flow passage 67.

[0040] In the embodiment shown in FIG. 8 , the bypass passage 30 includes a bypass hole 31 forming an inlet 33 and a side passage 32 communicating with the bypass hole 31. The bypass hole 31 is a space defined by the suction-side end surface 45P of the slide valve 40, the inner wall surface 25 of the slide valve accommodating chamber 24, and the screw rotor 10 when the slide valve 40 moves toward the discharge side. The side passage 32 is a space formed in the casing 20C and communicates with the bypass hole 31 on the upstream side. The downstream end of the side passage 32 communicates with the suction space 22. When the inlet 33 of the bypass passage 30 is open, the low-pressure return gas G3 from the tooth groove space and the high-pressure return gas G4 from the discharge space 23 are guided from the bypass hole 31 through the side passage 32 to the suction space 22.

[0041] In the exemplary embodiment shown in FIGS. 6 and 7A , the second groove 62 has a rounded rectangular shape with semicircular ends. The second groove 62 is provided at the lowest vertical position on the sliding surface 44 of the slide valve 40. The suction side end 65 of the second groove 62 is located closer to the discharge side than the suction side end 45 of the slide valve 40. The discharge side end 66 of the second groove 62 is located closer to the suction side than the discharge side end 46 of the slide valve 40. In contrast, in another embodiment shown in FIG. 7B , the second groove 62 has a rounded rectangular shape extended toward the suction side along the axial direction. The suction side end 65 of the second groove 62 extends to the suction side end 45 of the slide valve 40, opens to the suction side end face 45P of the slide valve 40, and communicates with the bypass passage 30.

[0042] Next, with reference to FIGS. 9A to 9D , a process in which the first groove 61 and the second groove 62 oppose each other due to movement of the slide valve 40 will be described. FIG. 9A is a schematic plan view of a slide valve and a slide valve guide according to one embodiment, viewed from above in the vertical direction, showing a state in which the slide valve is in a fully closed position. FIG. 9B is a schematic plan view of a slide valve and a slide valve guide according to one embodiment, viewed from above in the vertical direction, showing a state in which the slide valve is positioned between the fully closed position and a position in which the first groove and the second groove begin to oppose each other. FIG. 9C is a schematic plan view of a slide valve and a slide valve guide according to one embodiment, viewed from above in the vertical direction, showing a state immediately after the first groove and the second groove begin to oppose each other. FIG. 9D is a schematic plan view of a slide valve and a slide valve guide according to one embodiment, viewed from above in the vertical direction, showing a state in which the slide valve is in a fully open position.

[0043] As the slide valve 40 begins to move from the fully closed position ( FIG. 9A ) toward the discharge side, the discharge end 46 of the slide valve 40 passes through the first groove 61 ( FIG. 9B ). As the slide valve 40 moves further toward the discharge side, the axial positions of the suction end 63 of the first groove 61 and the discharge end 66 of the second groove 62 coincide, and the first groove 61 and the second groove 62 begin to face each other. The position of the slide valve 40 at this time is referred to as the communication start position X*. From the communication start position X*, communication between the bypass passage 30 and the discharge space 23 through the communication passage 60 begins ( FIG. 9C ). The communication area between the first groove 61 and the second groove 62 is defined as S. As the slide valve 40 moves toward the discharge side from the communication start position X*, the communication area S increases. The communication area S reaches its maximum between the slide valve 40 and the fully open position ( FIG. 9D ).

[0044] In some embodiments, in order to achieve both stable operation of the compressor and ensuring a highly efficient operating range of the compressor, the first groove 61 and the second groove 62 are provided so that the axial positions of the suction side end 63 of the first groove 61 and the discharge side end 66 of the second groove 62 coincide when the slide valve 40 is in a position of 0.3≦x≦0.5. In other words, the communication start position X* may be 0.3≦X*≦0.5.

[0045] 10 to 12, the effect of a change in the communication area S relative to the position x of the slide valve 40 on the capacity control characteristics will be considered. FIG. 10 is a schematic diagram showing a change in the communication area S between the first groove and the second groove as the slide valve 40 moves in one embodiment. FIG. 11 is a graph of the derivative of the communication area S between the first groove and the second groove in one embodiment. FIG. 12 is a graph of the second derivative of the communication area S between the first groove and the second groove in one embodiment.

[0046] As shown in Figure 10, consider the case where the slide valve 40 moves from position X1 to position X1 + dx on the suction side from a state in which the first groove 61 and the second groove 62 are opposed to each other. At this time, the communication area S decreases by w x dx, and the following equation holds for the change dS in the communication area S between the first groove 61 and the second groove 62. dS = -w dx (1) Equation (2) can be derived from equation (1). dS / dx = -w (2) Furthermore, from equation (2), the second derivative of the communication area S is given by the following equation. d ２ S / dx ２ =-dw / dx (3) When the second groove 62 is rectangular as shown in FIG. 10, in equation (2), the reduction rate (dS / dx) of the communication area S is constant (see graph A1 in FIG. 11), and the second derivative (d ２ S / dx ２ ) becomes 0 (see graph A2 in FIG. 12).

[0047] In contrast, in some embodiments, the dimensions, positions, and shapes of the first groove 61 and the second groove 62 are such that when the slide valve 40 is in a position range represented by X1≦x≦X* (where X1≧0), the second derivative value of the communication area S is d ２ S / dx ２ > 0 (see graph B1 in FIG. 11 and graph B2 in FIG. 12). In this case, when the slide valve 40 moves to the discharge side, the communication area S between the first groove 61 and the second groove 62 gradually increases from the communication start position X*, so that a sudden increase in the flow rate of the high-pressure return gas G4 flowing from the discharge space 23 into the communication passage 60 can be suppressed.

[0048] In the exemplary embodiment shown in graph B1 of FIG. 11 and graph B2 of FIG. 12, for X1≦x≦X*, dS / dx increases linearly with position x from negative values ​​toward zero, and d ２ S / dx ２ is a positive constant. In another embodiment, for X1≦x≦X*, the first derivative of the communication area S is defined by a curve that monotonically increases with increasing position x from negative values ​​to zero, and the second derivative of the communication area S is a function of x that takes positive values.

[0049] 13A to 13C and 14, the second derivative value of the communication area S is d ２ S / dx ２ > 0 will be described. FIG. 13A is a plan view of a slide valve and a slide valve guide according to one embodiment. FIG. 13B is a plan view of a slide valve and a slide valve guide according to another embodiment. FIG. 13C is a plan view of a slide valve and a slide valve guide according to yet another embodiment. In the embodiment shown in FIGS. 13A to 13C, the first groove 61 is formed along the circumferential direction of the guide surface 51 of the slide valve guide 50 and opens into the discharge space 23 at the vertical upper end 52 of the guide surface 51. FIG. 14 is a graph showing the relationship between the position of the slide valve and the gas intake volume of the screw compressor in several embodiments. In FIG. 14, the horizontal axis represents the position x of the slide valve in a coordinate system along the axial direction, and the vertical axis represents the gas intake volume V when the upper limit value Vmax of the gas intake volume of the screw compressor is set to 100%. Graph N in FIG. 14 shows a conventional capacity control characteristic that only regulates the flow rate of gas returned from the tooth groove space to the suction space 22.

[0050] In some embodiments, as shown in FIGS. 13A to 13C , the second groove 62 has a shape in which the groove width increases toward the suction side at least in the discharge-side end region 66R. In the embodiment shown in FIG. 13A , the second groove 62 has an isosceles triangular shape in the discharge-side end region 66R, with the discharge-side end 66 as the apex and the groove width increasing toward the suction side. In other embodiments, as shown in FIG. 13B , the second groove 62 may have a trumpet-shaped shape in the discharge-side end region 66R, with the discharge-side end 66 as the apex. In yet another embodiment, as shown in FIG. 13C , the second groove 62 may have a bell-shaped shape in the discharge-side end region 66R, with the discharge-side end 66 as the apex. By combining the second groove 62 shaped as shown in FIGS. 13A to 13C with the first groove 61 formed along the circumferential direction of the guide surface 51 of the slide valve guide 50, the second differential value of the communication area S can be calculated as follows: ２ S / dx ２ >0 can be established.

[0051] In some other embodiments, the first groove 61 has a shape in which the groove width narrows toward the suction side at least in the suction side end region 63R. In this case, the first groove 61 may have an isosceles triangular shape in the suction side end region 63R, with the suction side end 63 as its apex and the groove width narrowing toward the suction side. In other embodiments, the first groove 61 may have a trumpet-shaped shape in the suction side end region 63R, with the suction side end 63 as its apex. In still another embodiment, the first groove 61 may have a bell-shaped shape in the suction side end region 63R, with the suction side end 63 as its apex. In this way, when the first groove 61 has a shape in which the groove width narrows toward the suction side at least in the suction side end region 63R, by combining it with the second groove 62 formed along the circumferential direction of the sliding surface 44 of the slide valve 40, ２ S / dx ２ >0 can be satisfied.

[0052] Graph A in FIG. 14 represents the displacement control characteristics when the first groove 61 and the second groove 62 have the shapes shown in FIG. 13A. When the slide valve 40 moves further toward the discharge side than the communication start position X*, the gas intake amount becomes smaller than that shown in graph N. As the communication area S between the first groove 61 and the second groove 62 gradually increases (as x decreases), the decrease in gas intake amount compared to the conventional displacement control characteristics gradually increases. Graph B in FIG. 14 represents the displacement control characteristics when the first groove 61 and the second groove 62 have the shapes shown in FIG. 13B. Graph C in FIG. 14 represents the displacement control characteristics when the first groove 61 and the second groove 62 have the shapes shown in FIG. 13C. Graph D in FIG. 14 represents the displacement control characteristics when the second groove 62 has a rectangular shape as shown in FIG. 10. Because the rate of increase in the communication area S between the first groove 61 and the second groove 62 is constant from x = X* to x = 0, the gas intake amount compared to the conventional displacement control characteristics decreases linearly.

[0053] The characteristic configurations of the screw compressors according to the above-described embodiments can be summarized as follows.

[0054] [1] A screw compressor (1) according to at least some embodiments of the present invention comprises: a screw rotor (10); a casing (20) including a rotor chamber (21) accommodating the screw rotor (10), a suction space (22), and a discharge space (23); a slide valve (40) movable in the axial direction of the screw rotor (10) and provided so as to form a part of an inner wall surface (21W) of the rotor chamber (21); and a slide valve guide (50) provided in the discharge space (23) for supporting an end portion (46) of the slide valve (40) projecting into the discharge space (23), wherein the slide valve (40) is configured to open an inlet (33) of a bypass passage (30) communicating between the rotor chamber (21) and the suction space (22) to the inner wall surface (21W) of the rotor chamber (21) when moving toward the discharge space (23), The slide valve guide (50) has a guide surface (51) that slidably guides the slide valve (40), and a first groove (61) that is provided on the guide surface (51) and communicates with the discharge space (23). The slide valve (40) has a sliding surface (44) that faces the guide surface (51) of the slide valve guide (50) on the outer surface (43) of the slide valve (40), and a second groove (62) that is provided on the sliding surface (44). When the inlet (33) of the bypass passage (30) is open and the first groove (61) and the second groove (62) are in opposing positions, a communication passage (60) including the first groove (61) and the second groove (62) communicates the bypass passage (30) with the discharge space (23).

[0055] If, as in the conventional art, an attempt is made to ensure the capacity control range of the screw compressor (1) solely by adjusting the flow rate of gas returned from the tooth groove space to the suction space (22) via the bypass passage (30), the movable range of the slide valve (40) must be sufficiently large, making it difficult to simultaneously expand the capacity control range of the screw compressor (1) and make the screw compressor (1) more compact. According to the configuration [1] above, when the inlet (33) of the bypass passage (30) is open and the first groove (61) and the second groove (62) are positioned opposite each other, the bypass passage (30) and the discharge space (23) are communicated by the communication passage (60) including the first groove (61) and the second groove (62), and the gas in the discharge space (23) is returned to the suction space (22), thereby further suppressing the amount of gas suction into the screw compressor (1). That is, not only a portion of the low-pressure gas before compression from the tooth groove space (return low-pressure gas G3) but also a portion of the high-pressure gas after compression in the discharge space (23) communicating with the bypass passage (30) via the communication passage (60) (return high-pressure gas G4) is returned to the suction space (22) via the bypass passage (30), thereby further reducing the substantial amount of gas suctioned by the screw compressor (1). Thus, it is possible to achieve both an expansion of the capacity control range of the screw compressor (1) and a compact size of the screw compressor (1).

[0056] [2] In some embodiments, in the configuration of the above [1], the first groove (61) communicates with the discharge space (23) above the center position of the guide surface (51) in the vertical direction.

[0057] In a screw compressor (1), lubricating oil stored in a casing (20) may be supplied to the screw rotor (10) and bearings via an oil supply system in order to lubricate the screw rotor (10) and bearings. The oil level of the lubricating oil stored in the casing (20) may vary depending on the operating state of the screw compressor (1). Therefore, when lubricating oil is stored in the discharge space (23) of the casing (20), depending on the operating state of the screw compressor (1), a portion of the guide surface (51) of the slide valve guide (50) below the center position in the vertical direction may be immersed in the lubricating oil level. According to the configuration [2] above, the flow of the high-pressure gas (G4) returning from the discharge space (23) to the suction space (22) via the communication passage (60) including the first groove (61) and the bypass passage (30) is less susceptible to the rise in the oil level of the lubricating oil, and the effect of expanding the capacity control range of the screw compressor (1) described in [1] above can be stably enjoyed regardless of fluctuations in the oil level height.

[0058] [3] In some embodiments, in the configuration of [1] or [2] above, the first groove (61) is formed along the circumferential direction of the guide surface (51) of the slide valve guide (50), and opens into the discharge space (23) at the vertical upper end (52) of the guide surface (51).

[0059] According to the configuration [3] above, the effect of expanding the capacity control range of the screw compressor (1) described in [1] above can be enjoyed more stably, regardless of fluctuations in the oil level of the lubricating oil.

[0060] [4] In some embodiments, in any of the configurations [1] to [3] above, the slide valve (40) includes, as a part of the communication passage (60), an internal flow path (67) extending from one end (67I) opening into the second groove (62) to the other end (67O) opening into an end face (45P) of the slide valve (40) opposite to the discharge space (23).

[0061] If the second groove (62) were to be connected directly to the bypass passage (30) without passing through the internal flow path (67) of the slide valve (40), the second groove (62) would need to reach the suction-side end face (45P) of the slide valve (40), which would reduce the area of ​​the sliding surface (44) of the slide valve (40) by the amount of the second groove (62), and this could hinder smooth guiding of the slide valve (40) by the slide valve guide (50). According to the configuration [4] above, the second groove (62) can be connected to the bypass passage (30) by the internal flow path (67) of the slide valve (40), which is part of the communication passage (60), so that the second groove (62) can be shortened and the reduction in the area of ​​the sliding surface (44) due to the second groove (62) can be suppressed. Therefore, smoother guidance of the slide valve (40) by the slide valve guide (50) can be achieved compared to when the second groove (62) is directly connected to the bypass passage (30) without going through the internal flow path (67) of the slide valve (40).

[0062] [5] In some embodiments, in any of the configurations [1] to [4] above, in a coordinate system along the axial direction of the screw rotor (10), the origin x=0 is the fully open position of the slide valve (40) where the opening area of ​​the inlet (33) of the bypass passage (30) is maximum, and x=1 is the fully closed position of the slide valve (40) where the opening area of ​​the inlet (33) of the bypass passage (30) is zero, and X* is the position of the slide valve (40) where the axial positions of the end (63) of the first groove (61) opposite to the discharge space (23) and the end (66) of the second groove (62) on the discharge space (23) side coincide, and S is the communication area between the first groove (61) and the second groove (62), when the slide valve (40) is within a position range expressed by X1≦x≦X* (where X1≧0), the second differential value of the communication area (S) is d ２ S / dx ２ >0.

[0063] If the increase in the communication area (S) between the first groove (61) and the second groove (62) relative to the amount of movement of the slide valve (40) when the slide valve (40) moves toward the discharge side is excessively large, the flow rate of the high-pressure gas (G4) flowing from the discharge space (23) into the communication passage (60) and returning to the suction space (22) increases rapidly, which may cause unstable operation of the screw compressor (1). According to the configuration [5] above, the communication area (S) between the first groove (61) and the second groove (62) gradually increases when the slide valve (40) moves toward the discharge side, thereby preventing a sudden increase in the flow rate of the high-pressure gas (G4) flowing from the discharge space (23) into the communication passage (60). Therefore, it is possible to achieve both stable operation of the screw compressor (1) and the expansion of the capacity control range of the screw compressor (1) described in [1] above.

[0064] [6] In some embodiments, in the configuration of the above [5], the second groove (62) has a shape in which the groove width increases toward the opposite side to the discharge space (23) at least in the end region (66R) on the discharge space (23) side.

[0065] According to the configuration [6] above, the communication area (S) between the first groove (61) and the second groove (62) gradually increases when the slide valve (40) moves toward the discharge side, thereby suppressing a sudden increase in the flow rate of the high-pressure gas (G4) flowing from the discharge space (23) into the communication passage (60). Therefore, it is possible to achieve both stable operation of the screw compressor (1) and the expansion of the capacity control range of the screw compressor (1) described in [1] above.

[0066] [7] In some embodiments, in the configuration of the above [5], the first groove (61) has a shape in which the groove width narrows toward the side opposite to the discharge space (23), at least in the end region (63R) opposite to the discharge space (23).

[0067] According to the configuration [7] above, the communication area (S) between the first groove (61) and the second groove (62) gradually increases when the slide valve (40) moves toward the discharge side, thereby suppressing a sudden increase in the flow rate of the high-pressure gas (G4) flowing from the discharge space (23) into the communication passage (60). Therefore, it is possible to achieve both stable operation of the screw compressor (1) and the expansion of the capacity control range of the screw compressor (1) described in [1] above.

[0068] [8] In some embodiments, in any of the configurations [1] to [7] above, in a coordinate system along the axial direction of the screw rotor (10), when the fully open position of the slide valve (40) where the opening area of ​​the inlet (33) of the bypass passage (30) is maximum is defined as the origin x=0, and the fully closed position of the slide valve (40) where the opening area of ​​the inlet (33) of the bypass passage (30) is zero is defined as x=1, the first groove (61) and the second groove (62) are provided so that the axial positions of the end (63) of the first groove (61) opposite to the discharge space (23) and the end (66) of the second groove (62) on the discharge space (23) side coincide with each other when the slide valve (40) is at a position of 0.3≦x≦0.5.

[0069] If the communication start position X* is too close to the fully open position, the increase in the communication area (S) between the first groove (61) and the second groove (62) relative to the amount of movement of the slide valve (40) becomes excessively large, causing a rapid increase in the flow rate of the high-pressure gas (G4) flowing from the discharge space (23) into the communication passage (60), resulting in unstable operation of the screw compressor (1). On the other hand, if the communication start position X* is too close to the fully closed position, the operating range in which a portion of the high-pressure gas (return high-pressure gas G4) in the discharge space (23) is returned to the suction space (22) via the communication passage (60) widens, thereby suppressing the gas intake amount of the screw compressor (1). According to the configuration [8] above, by starting communication between the first groove (61) and the second groove (62) at an appropriate position within the movable range of the slide valve (40), stable operation of the screw compressor (1) and a highly efficient operating range of the screw compressor (1) can both be achieved.

[0070] In this specification, expressions expressing relative or absolute arrangement, such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial," not only strictly express such arrangement, but also express a state in which there is a relative displacement with a tolerance or an angle or distance to the extent that the same function is obtained. For example, expressions expressing that things are in an equal state, such as "identical," "equal," and "homogeneous," not only express a state in which they are strictly equal, but also express a state in which there is a tolerance or a difference to the extent that the same function is obtained. Furthermore, in this specification, expressions expressing shapes such as a rectangular shape or a cylindrical shape not only refer to shapes such as a rectangular shape or a cylindrical shape in the strict geometric sense, but also refer to shapes including uneven portions, chamfered portions, etc., to the extent that the same effect is obtained. Furthermore, in this specification, the expressions "comprise," "include," "have," "includes," or "have" of one component are not exclusive expressions that exclude the presence of other components.

[0071] DESCRIPTION OF SYMBOLS 1: Screw compressor 10: Screw rotor 20 (20A-20D): Casing 21: Rotor chamber 21W: Inner wall surface 22: Suction space 23: Discharge space 30: Bypass passage 33: Inlet 40 (40A, 40B): Slide valve 43: Outer surface 44: Sliding surface 45P: Suction side end surface 46: Discharge side end portion 50 (50A, 50B): Slide valve guide 51: Guide surface 52: Upper end portion 60: Communication passage 61: First groove 63R: Suction side end region 63: Suction side end portion 62: Second groove 66R: Discharge side end region 66: Discharge side end portion 67: Internal flow path 67I: One end 67O: Other end S : communication area between the first groove and the second groove

Claims

1. A device comprising: a screw rotor; a casing that houses the screw rotor and includes a rotor chamber, a suction space, and a discharge space; a slide valve that is movable in the axial direction of the screw rotor and that is provided so as to form part of the inner wall surface of the rotor chamber; and a slide valve guide that is provided in the discharge space and that supports an end of the slide valve that protrudes into the discharge space, wherein the slide valve is configured to open an inlet of a bypass passage that communicates the rotor chamber and the suction space to the inner wall surface of the rotor chamber when it moves toward the discharge space; the slide valve guide has a guide surface that slidably guides the slide valve, and a first groove that is provided on the guide surface and communicates with the discharge space; and the slide valve has a sliding surface that faces the guide surface of the slide valve guide on the outer surface of the slide valve, and a second groove that is provided on the sliding surface, a communication passage including the first groove and the second groove communicating with each other when the inlet of the bypass passage is open and the first groove and the second groove are positioned to face each other.

2. The screw compressor according to claim 1, wherein the first groove communicates with the discharge space above the center of the guide surface in the vertical direction.

3. A screw compressor according to claim 1 or 2, wherein the first groove is formed along the circumferential direction of the guide surface of the slide valve guide and opens into the discharge space at the vertical upper end of the guide surface.

4. A screw compressor according to claim 1 or 2, wherein the slide valve includes, as part of the communication passage, an internal flow passage extending from one end opening into the second groove to the other end opening into the end face of the slide valve opposite the discharge space.

5. In a coordinate system along the axial direction of the screw rotor, the fully open position of the slide valve where the opening area of ​​the inlet of the bypass passage is maximum is defined as the origin x=0, the fully closed position of the slide valve where the opening area of ​​the inlet of the bypass passage is zero is defined as x=1, the position of the slide valve where the axial position of the end of the first groove opposite to the discharge space and the end of the second groove on the discharge space side coincides is defined as X*, and the communication area between the first groove and the second groove is defined as S, when the slide valve is within a position range expressed by X1≦x≦X* (where X1≧0), the second derivative value of the communication area is d ２ S / dx ２ The screw compressor according to claim 1 or 2, wherein the ratio of the saturation pressure to the saturation pressure satisfies > 0.

6. A screw compressor according to claim 5, wherein the second groove has a shape in which the groove width increases toward the opposite side from the discharge space at least in the end region on the discharge space side.

7. The screw compressor according to claim 5, wherein the first groove has a shape in which the groove width narrows toward the side opposite the discharge space, at least in an end region opposite the discharge space.

8. The screw compressor according to claim 1 or 2, wherein, in a coordinate system along the axial direction of the screw rotor, the fully open position of the slide valve where the opening area of ​​the inlet of the bypass passage is maximum is defined as the origin x=0, and the fully closed position of the slide valve where the opening area of ​​the inlet of the bypass passage is zero is defined as x=1, the first groove and the second groove are provided so that the axial positions of the end of the first groove opposite to the discharge space and the end of the second groove on the discharge space side coincide when the slide valve is at a position of 0.3≦x≦0.5.

Images