Rotor casing of screw compressor, and screw compressor

Abstract

To reduce undesired contact between a screw rotor and the inner wall face of a rotor casing in a screw compressor.SOLUTION: The rotor casing of the screw compressor in at least one embodiment of this invention includes a first rotor casing communicated with a suction port and arranged on one side in the axial direction of the screw rotor, and a second rotor casing communicated with a discharge port and arranged on the other side in the axial direction, and different from the first rotor casing, the rotor casing having an inner wall face forming a closed space to compress compressed gas sucked from the suction port, the inner wall face having a flank which is defined by a curve in view from the axial direction, the flank being located radially outside of a virtual cylindrical face of which the radius is the curvature radius of the inner wall face at the end on the other side in the axial direction, out of the inner wall face.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a rotor casing for a screw compressor and a screw compressor. [Background technology]

[0002] A screw compressor includes a screw rotor including a pair of male and female rotors, and a rotor casing that houses the screw rotor (see, for example, Patent Document 1). Screw compressors have excellent advantages such as a simple structure and good durability, and are therefore widely used. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2018 / 100911 Summary of the Invention [Problem to be solved by the invention]

[0004] In a screw compressor, the pressures in the multiple trapped spaces created by the meshing of the teeth are different, so the entire shaft of the screw rotor is pushed in the direction of the lower pressure. However, because both ends of the screw rotor are supported by radial bearings, the area where the teeth are provided is displaced in an arcuate shape, which may result in undesired contact between the screw rotor and the inner wall surface of the rotor casing. Furthermore, the pressure in the confined spaces in the axial direction of the screw rotor is higher on the discharge side than on the suction side, and due to the twisted shape of the screw rotor, the pressure in each tooth groove (each confined space) differs even in a cross section with the same axial position. Due to the relationship between this difference in pressure in each tooth groove and the support position of the screw rotor, the position where the bow-shaped deformation in the region where the teeth of the screw rotor are provided is greatest is a position shifted toward the discharge side from the axial center position of the region where the teeth are provided.

[0005] In view of the above circumstances, at least one embodiment of the present disclosure aims to reduce undesired contact between a screw rotor and an inner wall surface of a rotor casing in a screw compressor. [Means for solving the problem]

[0006] (1) A rotor casing of a screw compressor according to at least one embodiment of the present disclosure includes: A rotor casing for a screw compressor that houses a screw rotor including a pair of male and female rotors, The rotor casing includes: a first rotor casing that is in communication with the suction port and is disposed on one side of the screw rotor in the axial direction; a second rotor casing different from the first rotor casing, the second rotor casing communicating with the discharge port and disposed on the other side in the axial direction; Including, The first rotor casing and the second rotor casing are joined together, a dividing position between the first rotor casing and the second rotor casing is shifted toward the discharge port from a center position of the rotor casing in the axial direction, the rotor casing has an inner wall surface that forms a confined space for compressing the gas to be compressed that is drawn in through the suction port, the inner wall surface has a relief surface defined by a curve when viewed in the axial direction, The relief surface is located radially outward of an imaginary cylindrical surface of the inner wall surface, the imaginary cylindrical surface having a radius equal to the radius of curvature of the inner wall surface at the other end in the axial direction.

[0007] (2) A screw compressor according to at least one embodiment of the present disclosure includes: a screw rotor including a pair of male and female rotors; A rotor casing of the screw compressor having the configuration (1) above; Equipped with. [Effects of the Invention]

[0008] According to at least one embodiment of the present disclosure, undesired contact between the screw rotor and the inner wall surface of the rotor casing in a screw compressor can be reduced. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional plan view of a screw compressor according to some embodiments. FIG. [Figure 2] FIG. 2 is a perspective view showing a schematic cross section of a rotor casing of a screw compressor according to some embodiments. [Figure 3] FIG. 4 is a schematic perspective view of a second rotor casing. [Figure 4] FIG. [Figure 5] FIG. 2 is a longitudinal cross-sectional view of a rotor casing. [Figure 6] FIG. 10 is a vertical cross-sectional view of another rotor casing. [Figure 7] FIG. 10 is a vertical cross-sectional view of another rotor casing. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, several embodiments of the present disclosure will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of components described as embodiments or shown in the drawings are merely illustrative examples and are not intended to limit the scope of the present disclosure. For example, expressions expressing relative or absolute arrangement such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial" not only express such an arrangement exactly, 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 such as "identical," "equal," and "homogeneous" that indicate that something is in an equal state not only indicate a state of strict equality, but also indicate a state in which there is a tolerance or a difference to the extent that the same function is obtained. For example, expressions representing shapes such as a square shape or a cylindrical shape not only represent shapes such as a square shape or a cylindrical shape in the strict geometric sense, but also represent shapes including uneven portions, chamfered portions, etc., to the extent that the same effect can be obtained. On the other hand, the expressions "comprise," "include," "have," "includes," or "have" of one element are not exclusive expressions that exclude the presence of other elements.

[0011] (Screw compressor configuration) Fig. 1 is a schematic cross-sectional plan view of a screw compressor according to some embodiments. As shown in Fig. 1, the screw compressor 2 includes a pair of screw rotors (a male rotor 15 and a female rotor 17) including a pair of rotor shafts 14, 16, and a rotor casing 12 that houses the pair of screw rotors.

[0012] In the screw compressor 2 according to some embodiments, the rotor casing 12 includes a first rotor casing 121 disposed on one axial side (suction side) of the screw rotor, and a second rotor casing 122 disposed on the other axial side (discharge side) and different from the first rotor casing 121. In the screw compressor 2 according to some embodiments, the rotor casing 12 is formed by joining the first rotor casing 121 and the second rotor casing 122 together. In some embodiments of the screw compressor 2, the dividing position P between the first rotor casing 121 and the second rotor casing 122 is shifted toward the discharge side from the axial center position Cr of the rotor casing 12 (i.e., the axial center position of the portion where the spiral-shaped teeth are formed on the male rotor 15 and the female rotor 17).

[0013] The pair of rotor shafts 14, 16 are supported by a radial bearing 18 and a thrust bearing 20 so as to be rotatable about central axes AX1, AX2 of the rotor shafts 14, 16, respectively. In the following description, the direction along the central axes AX1, AX2 will be referred to as the axial direction of the screw rotor, or simply as the axial direction; the radial direction centered on the central axes AX1, AX2 will also be referred to as the radial direction of the male rotor 15, the radial direction of the female rotor 17, or simply as the radial direction; and the circumferential direction centered on the central axes AX1, AX2 will also be referred to as the circumferential direction of the male rotor 15, the circumferential direction of the female rotor 17, or simply as the circumferential direction.

[0014] In the screw compressor 2 according to some embodiments, the suction-side radial bearing 18 among the radial bearings 18 is held in a suction-side bearing housing 21. In the screw compressor 2 according to some embodiments, the suction-side bearing housing 21 is separate from the first rotor casing 121 and is coupled to the suction-side end of the first rotor casing 121. In the screw compressor 2 according to some embodiments, the radial bearing 18 on the discharge side of the radial bearings 18 and the thrust bearing 20 are held in a discharge-side bearing housing 22. In the screw compressor 2 according to some embodiments, the discharge-side bearing housing 22 is formed integrally with the second rotor casing 122. The discharge side bearing housing 22 may be separate from the second rotor casing 122 and may be connected to the end of the second rotor casing 122 on the discharge side. Moreover, the radial bearing 18 may be, for example, a sliding bearing or a rolling bearing.

[0015] In the screw compressor 2 according to some embodiments, the axial end of the discharge-side bearing housing 22 on the discharge side is covered with a cover 23. The axial end 14a of the rotor shaft 14 of the male rotor 15 protrudes from the cover 23 to the outside.

[0016] The male rotor 15 and the female rotor 17 have helical teeth that mesh with each other. A plurality of tooth groove spaces are formed along the axial direction of the rotor shafts 14, 16 by the meshing of the teeth of the male rotor 15 and the female rotor 17 and the inner wall surface 12W of the rotor casing 12.

[0017] The rotor shaft 14 that constitutes the male rotor 15 is connected to the output shaft of a motor (not shown) and is configured to be rotated by the motor. The female rotor 17 that meshes with the male rotor 15 is rotated in the direction indicated by arrow a in Figure 1 and Figure 4, which will be described later, by the rotation of the male rotor 15. The female rotor 17 rotates in the opposite direction to the rotation of the male rotor 15, as indicated by arrow b in Figures 1 and 4. When the male rotor 15 and female rotor 17 rotate in their meshed state, the tooth groove spaces move axially from the suction side to the discharge side.

[0018] The tooth groove space described above receives compressed gas from an intake space 50 formed in the rotor casing 12 via an intake port 52. When the male rotor 15 and the female rotor 17 rotate, the tooth groove space moves axially from the intake side to the discharge side in accordance with the rotation of these screw rotors. During this process, the intake port 52 is closed, and the tooth groove space becomes a sealed confined space. The volume of the confined space decreases as the screw rotor rotates, compressing the compressed gas in the confined space. When the confined space reaches the discharge port 54 and is connected to a discharge space (not shown) formed in the rotor casing 12, the compressed gas in the confined space is discharged into the discharge space. The discharge port 54 is formed by an opening (not shown) provided at the discharge end of the rotor casing 12.

[0019] An expanded diameter portion 12a is provided on the suction side inner wall surface 12W of the rotor casing 12. The expanded diameter portion 12a is in communication with the suction port 52 and connects adjacent tooth groove spaces in the axial direction. The expanded diameter portion 12a has an inner diameter larger than that of the compression section inner wall surface 12Wp, which is the inner wall surface 12W that forms the confinement space. As the screw rotor rotates, the tooth groove spaces move axially from the suction side to the discharge side, and the compressed gas flows into tooth groove spaces that were not able to sufficiently suck in the compressed gas via the expanded diameter portion 12a. As described above, the inner diameter of the enlarged diameter portion 12a is set to a degree that allows the compressed gas to flow between adjacent tooth groove spaces via the enlarged diameter portion 12a. On the other hand, the inner diameter of the compression portion inner wall surface 12Wp is set to minimize leakage of the compressed gas from the tooth groove spaces. The enclosed space is isolated from the enlarged diameter portion 12a.

[0020] 2 is a perspective view showing a schematic cross section of a rotor casing of a screw compressor according to some embodiments, in which the discharge-side bearing housing 22 is omitted. 3 is a schematic perspective view of the second rotor casing, in which the discharge side bearing housing 22 is omitted. FIG. 4 is a view of the flank as seen from the axial direction. FIG. 5 is a vertical cross-sectional view of the rotor casing. FIG. 6 is a vertical cross-sectional view of another rotor casing. FIG. 7 is a vertical cross-sectional view of another rotor casing.

[0021] (Regarding flank 30) In general, in a screw compressor, the screw rotor is deformed into a bow shape due to the pressure of the gas being compressed, which may cause undesired contact between the screw rotor and the inner wall surface of the rotor casing. Therefore, in the screw compressor 2 according to some embodiments, the compression section inner wall surface 12Wp, which is the inner wall surface 12W that forms the confined space, is formed to have an escape surface 30 that is defined by a curve when viewed from the axial direction. The flank surface 30 is, for example, a curve that is convex radially outward when viewed from the axial direction, and is, for example, a curve having an arc shape. The relief surface 30 is located radially outward of an imaginary cylindrical surface 25 (see Figure 4) whose radius is the radius of curvature of the compression section inner wall surface 12Wp at the end 12e (see Figure 1) on the other axial side (discharge side) of the compression section inner wall surface 12Wp. The above-mentioned virtual cylindrical surface 25 corresponds to the trajectory of a virtual circle having a radius equal to the radius of curvature of the compression section inner wall surface 12Wp at the end 12e on the other axial side (discharge side) of the compression section inner wall surface 12Wp, and centered on the central axes AX1 and AX2, when the circle is moved axially toward the intake side. The difference in the radius of curvature between the flank 30 and the compression section inner wall surface 12Wp is slight, and it is not intended to actively allow compressed gas to leak from the tooth groove space through the flank 30. In the screw compressor 2 according to some embodiments, the provision of the relief surfaces 30 can reduce undesired contact between the male rotor 15 and the female rotor 17 and the inner wall surface 12W of the rotor casing 12. Furthermore, according to the screw compressor 2 of some embodiments, the rotor casing 12 is composed of the first rotor casing 121 and the second rotor casing 122, which makes it easier to machine the relief surface 30 compared to when the rotor casing 12 is formed as a single piece.

[0022] In the examples shown in Figures 2, 3, 5, and 6, the dividing position P between the first rotor casing 121 and the second rotor casing 122 coincides with the boundary position between the area 31 where the clearance surface 30 is formed and the area 32 where the clearance surface 30 is not formed. This makes it easier to machine the flank 30 compared to when the dividing position P does not coincide with the position of the boundary.

[0023] In the example shown in FIGS. 2, 3, and 5, the relief surface 30 is formed on the inner wall surface 12W of the second rotor casing 122. In the example shown in FIG. 6, the flank 30 is formed on the inner wall surface 12W of the first rotor casing 121.

[0024] 7, the dividing position P between the first rotor casing 121 and the second rotor casing 122 is a position that overlaps with the region 31 where the flank 30 is formed. That is, in the example shown in FIG. 7, the flank 30 is formed on the inner wall surface 12W of the first rotor casing 121 and the second rotor casing 122. This makes it easier to machine the flank 30 compared to when the dividing position P is formed in the region 32 where the flank 30 is not formed. 7, the flank 30 is distributed between the first rotor casing 121 and the second rotor casing 122, so that the axial machining range of the first rotor casing 121 and the second rotor casing 122 when machining the flank 30 can be narrowed compared to when the flank 30 is provided on only one of the first rotor casing 121 and the second rotor casing 122. This reduces deflection of the machining tool, making it easier to ensure machining accuracy of the flank 30 even when the axial dimension of the flank 30 is relatively large.

[0025] As described above, the second rotor casing 122 is formed integrally with the discharge side bearing housing 22 . This makes it easier to ensure the accuracy of the gaps between the inner wall surface 12W of the second rotor casing 122 and the teeth of the male rotor 15 and the female rotor 17. If the flanks 30 are formed on the inner wall surface 12W of the second rotor casing 122 as in the examples shown in Figures 2, 3, 5, and 7, it becomes easier to ensure the accuracy of the gaps between the flanks 30 and the teeth of the male rotor 15 and the female rotor 17.

[0026] (Regarding the axial position of the flank 30) As a result of careful investigation by the inventors, it was found that the position at which the amount of radially outward deformation when the male rotor 15 and the female rotor 17 are deformed into a bow shape is greatest is a position shifted toward the discharge side from the axial center position Cr of the rotor casing 12. That is, the pressure in the confined spaces at the axial position of the screw rotor is higher on the discharge side than on the suction side, and the twisted shape of the screw rotor causes the pressure in each tooth groove (each confined space) to differ even in a cross section at the same axial position. Due to the relationship between this difference in pressure between the tooth grooves and the support position of the screw rotor, the position where the bow-shaped deformation in the region where the screw rotor teeth are provided is greatest is a position shifted toward the discharge side from the axial center position of the region where the teeth are provided.

[0027] Therefore, in the screw compressor 2 according to some embodiments, as shown in Figures 2, 5, 6, and 7, the relief surface 30 is formed at a position shifted toward the discharge side from the axial center position Cr of the rotor casing 12. According to the screw compressor 2 according to some embodiments, a flank 30 can be provided in an area where there is a high possibility of contact with the male rotor 15 and the female rotor 17. In some embodiments of the screw compressor 2, the relief surface 30 does not extend in the axial direction to the end 12e (see Figure 1) on the other axial side (discharge side) of the compression section inner wall surface 12Wp, nor to the axial center position Cr of the rotor casing 12.

[0028] (Regarding the circumferential position of the flank 30) The circumferential position of the flank 30 will be described with reference to Figure 4. For ease of explanation, on the inner wall surface 12W facing the teeth of the male rotor 15, the line segment connecting the central axis AX1 of the male rotor 15 and the central axis AX2 of the female rotor 17 is referred to as a first line segment S1. As a result of careful investigation by the inventors, it was found that when the rotor casing 12 is viewed from the axial direction, the position at which the amount of radially outward deformation when the male rotor 15 is deformed into a bow shape is greatest exists within a range Rm1 of up to 90 degrees from the first line segment S1 in the direction opposite to the rotational direction of the male rotor 15, as indicated by arrow a. Furthermore, when the rotor casing 12 is viewed from the axial direction, it was found that the position at which the amount of radially outward deformation when the female rotor 17 is deformed into a bow shape is greatest exists within a range Rf1 of up to 90 degrees from the first line segment S1 in the direction opposite to the rotational direction of the female rotor 17, as indicated by arrow b.

[0029] Therefore, in the screw compressor 2 according to some embodiments, the clearance 30 on the inner wall surface 12W that faces the teeth of the male rotor 15 is provided within the above-mentioned range Rm1. In the screw compressor 2 according to some embodiments, the flank 30 on the inner wall surface 12W that faces the teeth of the female rotor 17 is provided within the above-mentioned range Rf1. 4, the flank 30 on the inner wall surface 12W facing the teeth of the male rotor 15 includes the entire range Rm1 and is provided beyond the range Rm1, while the flank 30 on the inner wall surface 12W facing the teeth of the female rotor 17 includes the entire range Rf1 and is provided beyond the range Rf1. However, the flank 30 on the inner wall surface 12W facing the teeth of the male rotor 15 may be provided only in a part of the range Rm1. Similarly, the flank 30 on the inner wall surface 12W facing the teeth of the female rotor 17 may be provided only in a part of the range Rf1. According to the screw compressor 2 according to some embodiments, a flank 30 can be provided in an area where there is a high possibility of contact with the male rotor 15 and the female rotor 17.

[0030] Furthermore, as a result of careful investigation by the inventors, it was found that when the rotor casing 12 is viewed from the axial direction, the circumferential position at which the amount of radially outward deformation when the male rotor 15 is deformed into a bow shape is greatest is the direction in which the radial load Fm acting on the male rotor 15 acts. Furthermore, when the rotor casing 12 is viewed from the axial direction, it was found that the circumferential position at which the amount of radially outward deformation of the female rotor 17 when it is deformed in a bow shape is greatest is the direction in which the radial load Ff acting on the female rotor 17 acts.

[0031] The magnitude and direction of the radial loads Fm and Ff generated in the radial bearing 18 are determined by the pressure distribution around the male rotor 15 and the female rotor 17. As shown in FIG. 4, four regions are roughly defined at different circumferential positions on each of the male rotor 15 and the female rotor 17, and the pressure in the enclosed space for each of these four regions will be described. The four regions at different circumferential positions on the male rotor 15 are designated as region cm1, region cm2, region cm3, and region cm4, in that order along the rotation direction of the male rotor 15 indicated by arrow a, starting from the region closest to the upper cusp 124. Similarly, the four regions with different circumferential positions on the female rotor 17 are designated as region cf1, region cf2, region cf3, and region cf4, in that order along the rotation direction of the female rotor 17 indicated by arrow b, starting from the region closest to the upper cusp 124.

[0032] As the male rotor 15 rotates, the pressure in the confined space in the male rotor 15 increases in the order of area cm1 → area cm2 → area cm3 → area cm4. Similarly, as the female rotor 17 rotates, the pressure in the confined space in the female rotor 17 increases in the order of area cf1 → area cf2 → area cf3 → area cf4. That is, the pressure in the confined space is highest around the lower cusp 125 around the discharge port 54, and the pressure in the confined space is lowest around the upper cusp 124. Due to this pressure difference, the radial load Fm acting on the male rotor 15 is in the diagonally upper right direction as shown in FIG. 4, and the radial load Ff acting on the female rotor 17 is in the diagonally upper left direction as shown in FIG.

[0033] Therefore, in the screw compressor 2 according to some embodiments, the relief surface 30 on the inner wall surface 12W that faces the teeth of the male rotor 15 may be provided so as to include a range Rm2 of up to 35 degrees in both the rotational direction of the male rotor 15 indicated by the arrow a and the direction opposite to the rotational direction, with the direction of action of the radial load Fm acting on the male rotor 15 as the center, when viewed from the axial direction. In the screw compressor 2 according to some embodiments, the relief surface 30 on the inner wall surface 12W that faces the teeth of the female rotor 17 may be provided, when viewed from the axial direction, so as to include a range Rf2 of up to 35 degrees in both the rotational direction of the female rotor 17 indicated by the arrow b and the direction opposite to the rotational direction, with the direction of action of the radial load Ff acting on the female rotor 17 as the center. This allows the relief surfaces 30 to be provided in areas that are likely to come into contact with the male rotor 15 and the female rotor 17 .

[0034] The present disclosure is not limited to the above-described embodiments, but also includes modifications to the above-described embodiments and appropriate combinations of these modifications.

[0035] The contents described in each of the above embodiments can be understood, for example, as follows. (1) A rotor casing 12 of a screw compressor 2 according to at least one embodiment of the present disclosure is a rotor casing 12 of a screw compressor 2 that houses a screw rotor (male rotor 15 and female rotor 17) including a pair of a male rotor 15 and a female rotor 17. The rotor casing 12 includes a first rotor casing 121 that communicates with a suction port 52 and is disposed on one axial side (suction side) of the screw rotor (male rotor 15 and female rotor 17). The rotor casing 12 includes a second rotor casing 122 that is different from the first rotor casing 121 and that communicates with a discharge port 54 and is disposed on the other axial side (discharge side). The rotor casing 12 is formed by joining the first rotor casing 121 and the second rotor casing 122. A dividing position P between the first rotor casing 121 and the second rotor casing 122 is shifted toward the discharge port 54 (discharge side) from a center position Cr of the rotor casing 12 in the axial direction. The rotor casing 12 has an inner wall surface 12W (compressor section inner wall surface 12Wp) that forms a confined space for compressing the gas to be compressed that has been drawn in through the suction port 52. The inner wall surface 12W has a relief surface 30 that is defined by a curve when viewed in the axial direction. The relief surface 30 is located radially outward of an imaginary cylindrical surface 25 whose radius is the radius of curvature of the inner wall surface 12W (compressor section inner wall surface 12Wp) at the end 12e on the other axial side (discharge side) of the inner wall surface 12W.

[0036] According to the above configuration (1), by providing the relief surface 30, undesired contact between the screw rotors (male rotor 15 and female rotor 17) and the inner wall surface 12W of the rotor casing 12 can be reduced. Furthermore, according to the configuration (1) above, the rotor casing 12 is composed of the first rotor casing 121 and the second rotor casing 122, so that it is easier to machine the relief surface 30 compared to when the rotor casing 12 is formed as a single piece. When the rotor casing 12 is formed as a single piece, it is difficult to machine the flank 30, making it difficult to form the flank 30 into the desired shape. However, the configuration of (1) above is expected to improve machining accuracy (i.e., control of the gap between the flank 30 and the teeth of the screw rotor).

[0037] (2) In some embodiments, in the configuration of (1) above, the dividing position P may coincide with the boundary between the region 31 where the flank 30 is formed and the region 32 where the flank 30 is not formed. The flank 30 may be formed on the inner wall surface 12W of the second rotor casing 122.

[0038] According to the above configuration (2), the flank 30 can be machined more easily.

[0039] (3) In some embodiments, in the configuration of (1) above, the dividing position P may coincide with the boundary between the region 31 where the flank 30 is formed and the region 32 where the flank 30 is not formed. The flank 30 may be formed on the inner wall surface 12W of the first rotor casing 121.

[0040] According to the above configuration (3), the flank 30 can be machined more easily.

[0041] (4) In some embodiments, in the configuration of (1) above, the dividing position P may be a position overlapping with the region 31 where the flank 30 is formed. The flank 30 may be formed on the inner wall surface 12W of the first rotor casing 121 and the second rotor casing 122.

[0042] According to the above configuration (4), the flank 30 can be machined more easily. Furthermore, according to the configuration (4) above, the flank 30 is distributed between the first rotor casing 121 and the second rotor casing 122, and therefore, compared to when the flank 30 is provided on only one of the first rotor casing 121 and the second rotor casing 122, it is possible to narrow the axial machining range of the first rotor casing 121 and the second rotor casing 122 when machining the flank 30. This reduces deflection of the machining tool, making it easy to ensure machining accuracy of the flank 30 even when the axial dimension of the flank 30 is relatively large.

[0043] (5) In some embodiments, in any of the configurations (1) to (4) above, the relief surface 30 may be formed at a position shifted toward the discharge port 54 (discharge side) from the axial center position Cr of the rotor casing 12.

[0044] According to the above configuration (5), the relief surface 30 can be provided in an area that is likely to come into contact with the screw rotors (the male rotor 15 and the female rotor 17).

[0045] (6) In some embodiments, in any of the configurations (1) to (5) above, when the rotor casing 12 is viewed axially, if a line segment connecting the imaginary central axis (central axis AX1) of the male rotor 15 and the imaginary central axis (central axis AX2) of the female rotor 17 is defined as a first line segment S1, the flank 30 on the inner wall surface 12W facing the teeth of the male rotor 15 may be located within a range Rm1 of up to 90 degrees from the first line segment S1 in the direction opposite to the rotational direction of the male rotor 15. The flank 30 on the inner wall surface 12W facing the teeth of the female rotor 17 may be located within a range Rf1 of up to 90 degrees from the first line segment S1 in the direction opposite to the rotational direction of the female rotor 17 in the axial direction.

[0046] According to the above configuration (6), the relief surface 30 can be provided in an area that is likely to come into contact with the screw rotors (the male rotor 15 and the female rotor 17).

[0047] (7) In some embodiments, in any of the configurations (1) to (5) above, the flank 30 on the inner wall surface 12W facing the teeth of the male rotor 15 may be provided, when viewed from the axial direction, to include a range Rm2 of up to 35 degrees in both the rotational direction of the male rotor 15 and the direction opposite to said rotational direction, with the direction of action of the radial load Fm acting on the male rotor 15 as its center. The flank 30 on the inner wall surface 12W facing the teeth of the female rotor 17 may be provided, when viewed from the axial direction, to include a range Rf2 of up to 35 degrees in both the rotational direction of the female rotor 17 and the direction opposite to said rotational direction, with the direction of action of the radial load Ff acting on the female rotor 17 as its center.

[0048] According to the above configuration (7), the relief surface 30 can be provided in an area that is likely to come into contact with the screw rotors (the male rotor 15 and the female rotor 17).

[0049] (8) In some embodiments, in any of the configurations (1) to (7) above, the second rotor casing 122 may be formed integrally with the housing (discharge side bearing housing 22) of the bearings (radial bearing 18, thrust bearing 20) for supporting the screw rotors (male rotor 15 and female rotor 17).

[0050] According to the configuration (8) above, the second rotor casing 122 and the housing (discharge side bearing housing 22) of the bearings (radial bearing 18, thrust bearing 20) can be integrally formed, making it easier to ensure the accuracy of the gap between the inner wall surface 12W of the second rotor casing 122 and the teeth of the screw rotors (male rotor 15 and female rotor 17).

[0051] (9) A screw compressor 2 according to at least one embodiment of the present disclosure includes a screw rotor (male rotor 15 and female rotor 17) including a pair of a male rotor 15 and a female rotor 17, and a rotor casing 12 of the screw compressor 2 having any of the configurations described above in (1) to (8).

[0052] According to the above configuration (9), undesired contact between the screw rotors (the male rotor 15 and the female rotor 17) and the inner wall surface 12W of the rotor casing 12 can be reduced. Furthermore, according to the configuration (9) above, the rotor casing 12 is composed of the first rotor casing 121 and the second rotor casing 122, so that it is easier to machine the relief surface 30 compared to when the rotor casing 12 is formed as a single piece. [Explanation of symbols]

[0053] 2. Screw compressor 12 rotor casing 12a Expanded diameter part 12e end 12W inner wall 12Wp Compression section inner wall 15 Male Rotor 17 Female rotor 18 Radial bearing 20 Thrust bearing 21 Suction side bearing housing 22 Discharge side bearing housing 25 Cylindrical Surfaces 30 Flank 31 areas 32 areas 50 Suction space 52 Intake port 54 Discharge port 121 First rotor casing 122 Second rotor casing

Claims

1. A rotor casing for a screw compressor that houses a screw rotor including a pair of male and female rotors, The rotor casing includes: a first rotor casing that is in communication with the suction port and is disposed on one side of the screw rotor in the axial direction; a second rotor casing different from the first rotor casing, the second rotor casing communicating with the discharge port and disposed on the other side in the axial direction; Including, The first rotor casing and the second rotor casing are joined together, a dividing position between the first rotor casing and the second rotor casing is shifted toward the discharge port from a center position of the rotor casing in the axial direction, the rotor casing has an inner wall surface that forms a confined space for compressing the gas to be compressed that is drawn in through the suction port, the inner wall surface has a relief surface defined by a curve when viewed in the axial direction, the relief surface is located radially outward of an imaginary cylindrical surface of the inner wall surface, the imaginary cylindrical surface having a radius equal to the radius of curvature of the inner wall surface at the end portion on the other side in the axial direction. Rotor casing of a screw compressor.

2. the dividing position coincides with a boundary position between a region where the flank is formed and a region where the flank is not formed, the relief surface is formed on the inner wall surface of the second rotor casing.

2. A rotor casing for a screw compressor according to claim 1.

3. the dividing position coincides with a boundary position between a region where the flank is formed and a region where the flank is not formed, the relief surface is formed on the inner wall surface of the first rotor casing, 2. A rotor casing for a screw compressor according to claim 1.

4. the dividing position is a position overlapping with a region where the flank surface is formed, the relief surfaces are formed on the inner wall surfaces of the first rotor casing and the second rotor casing; 2. A rotor casing for a screw compressor according to claim 1.

5. the relief surface is formed at a position shifted toward the discharge port from the center position in the axial direction of the rotor casing. A rotor casing for a screw compressor according to any one of claims 1 to 4.

6. When the rotor casing is viewed from the axial direction, if a line segment connecting an imaginary central axis of the male rotor and an imaginary central axis of the female rotor is defined as a first line segment, the relief surface on the inner wall surface facing the teeth of the male rotor is located within a range of up to 90 degrees from the first line segment as a starting point in a direction opposite to the rotation direction of the male rotor when viewed from the axial direction, the relief surface on the inner wall surface facing the teeth of the female rotor is provided within a range of up to 90 degrees from the first line segment as a starting point in a direction opposite to a rotation direction of the female rotor when viewed from the axial direction. A rotor casing for a screw compressor according to any one of claims 1 to 4.

7. the relief surface on the inner wall surface facing the teeth of the male rotor is provided, when viewed from the axial direction, to include a range of up to 35 degrees in both the rotational direction of the male rotor and the direction opposite to the rotational direction, with the direction of action of a radial load acting on the male rotor as the center; the relief surface on the inner wall surface facing the teeth of the female rotor is provided so as to include a range of up to 35 degrees in both the rotational direction of the female rotor and the direction opposite to the rotational direction, with the direction of action of a radial load acting on the female rotor as the center, when viewed from the axial direction. A rotor casing for a screw compressor according to any one of claims 1 to 4.

8. the second rotor casing is integrally formed with a housing of a bearing for supporting the screw rotor; A rotor casing for a screw compressor according to any one of claims 1 to 4.

9. a screw rotor including a pair of male and female rotors; A rotor casing for a screw compressor according to any one of claims 1 to 4; A screw compressor comprising:

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