Screw Compressor

Abstract

To provide a screw compressor that can reduce internal leakage of compressed gas via an axial communication passage.SOLUTION: A casing 4 of a screw compressor 1 comprises a discharge side inner wall surface 49 opposed to discharge side end surfaces 21c and 31c of a male rotor 2 and a female rotor 3. The discharge side inner wall surface 49 of the casing 4 comprises a shield region 49a for shielding at least a portion of a trajectory of an axial communication passage G2 that periodically appears in the discharge side end surfaces 21c and 31c in accordance with a change of engagement caused by rotation of the male rotor 2 and the female rotor 3, and is a gap sandwiched between backward surfaces 21e and 31e of the male rotor 2 and the female rotor 3. A groove 60 having a longitudinal direction is provided in the shield region 49a of the casing 4. The groove 60 is constituted in such a manner that normal lines Ng1 and Ng2 at respective positions 61, 62, and 66 in the longitudinal direction coincide with tangent lines in a circumferential direction of the female rotor 3 at the positions (in a direction orthogonal to a radial direction R2 of the female rotor 3).SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a screw compressor, and more particularly to a screw compressor having a pair of intermeshing screw rotors. [Background technology]

[0002] A typical factor that reduces the performance of a screw compressor is internal leakage of compressed gas. Internal leakage of compressed gas refers to the phenomenon in which compressed gas flows back from a high-pressure space where the pressure has increased as compression progresses to a relatively low-pressure space where compression has not yet started or is not progressing. This internal leakage requires energy to return the compressed gas to a low-pressure state, resulting in energy loss.

[0003] One example of a means for suppressing internal leakage of compressed gas is the technology described in Patent Document 1. In the oil-cooled screw compressor disclosed in Patent Document 1, a plurality of labyrinth grooves are provided in the discharge-side end wall of the rotor chamber between the rotor shafts of a pair of screw rotors, with the length direction being the direction between the rotor shafts. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-226160 Summary of the Invention [Problem to be solved by the invention]

[0005] The technology described in Patent Document 1 seals a portion of the gap formed between the discharge end face of the screw rotor and the discharge end wall of the rotor chamber (hereinafter sometimes referred to as the discharge end face gap), which is located between the highest-pressure compression action space 31H during the discharge stroke and the low-pressure compression action space 31L adjacent to the high-pressure compression action space before or immediately after intake air is trapped. However, there are multiple internal gaps that serve as paths for internal leakage of compressed gas in addition to the above-mentioned portion of the discharge end face gap. The technology described in Patent Document 1 does not consider suppressing internal leakage of compressed gas through internal gaps other than the above-mentioned portion of the discharge end face gap, and there is room for improvement in reducing internal leakage.

[0006] One example of an internal gap is a gap called an axial communication passage. The axial communication passage is a gap that periodically appears on the discharge end face in response to changes in meshing between the male and female rotors due to rotation. It is a flat, crescent-shaped opening sandwiched between the reversing surfaces of the rotors and open only in the axial direction. The axial communication passage connects the working chamber during the suction stroke, which is a relatively low-pressure space, with the discharge passage (discharge space), which is a relatively high-pressure space, through the axial communication passage, which can cause backflow of compressed gas. Among the multiple internal leakage paths present on the discharge end face, the axial communication passage tends to have a large leakage rate because of the particularly large pressure difference between the high-pressure space from which the leakage originates and the low-pressure space to which the leakage destination originates. Internal leakage through the axial communication passage is a common issue in both liquid-feed screw compressors, in which a liquid such as oil is supplied to the working chamber as described in Patent Document 1, and liquid-free screw compressors, which operate without supplying liquid to the working chamber.

[0007] The present invention has been made to solve the above problems, and one of its objects is to provide a screw compressor that can reduce internal leakage of compressed gas through the axial communicating passage. [Means for solving the problem]

[0008] The present application includes multiple means for solving the above problems, and one example is characterized in that it comprises a male rotor having a first discharge side end face on one axial side, a female rotor having a second discharge side end face on one axial side, and a casing having a housing chamber that rotatably houses the male rotor and the female rotor in an intermeshed state, the casing having a discharge side inner wall surface that faces the first discharge side end face of the male rotor and the second discharge side end face of the female rotor, the discharge side inner wall surface of the casing having a shielding region that periodically appears at the first discharge side end face and the second discharge side end face in response to changes in the intermeshing of the male rotor and the female rotor due to rotation of the male rotor and the female rotor, and that shields at least a part of the locus of an axial communicating passage, which is a gap between the reverse surfaces of the male rotor and the female rotor, and a longitudinal groove is provided within the shielding region of the casing, and the normal of the groove at each position in the longitudinal direction coincides with a circumferential tangent of the female rotor at that position. [Effects of the Invention]

[0009] According to one embodiment of the present invention, a liquid or gas in a groove provided on the inner wall surface of the discharge side of the casing (fluid) The shear force caused by the rotation of the female rotor causes the oil to flow in the width direction of the groove over the entire length of the groove and is blocked by the side of the groove, causing the static pressure to rise. fluid Therefore, the internal leakage of compressed gas through the axial communication passage can be reduced. Problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a longitudinal sectional view showing a screw compressor according to a first embodiment of the present invention and a system diagram showing an external oil supply path for the screw compressor. [Figure 2] 2 is a cross-sectional view of the screw compressor according to the first embodiment of the present invention, taken along the line II-II in FIG. 1. [Figure 3] 3 is an enlarged view of the portion indicated by the reference symbol L1 in FIG. 2, illustrating the axial communication passage. FIG. [Figure 4] 4 is a cross-sectional view of the screw compressor according to the first embodiment of the present invention, taken along the line IV-IV in FIG. 1. [Figure 5] 5 is an enlarged view of a portion indicated by reference symbol L2 in FIG. 4, showing the groove structure of the casing in the screw compressor according to the first embodiment of the present invention. FIG. [Figure 6] 6 is a cross-sectional view of the groove structure of the casing in the screw compressor according to the first embodiment of the present invention, taken along the arrows VI-VI in FIG. 5. FIG. [Figure 7] 3A to 3C are diagrams illustrating the operation of the groove structure of the casing in the screw compressor according to the first embodiment of the present invention. [Figure 8] 6 is an enlarged view similar to FIG. 5, showing a groove structure of a casing in a screw compressor according to a second embodiment of the present invention. [Figure 9] FIG. 9 is a diagram illustrating the relationship between the groove shape and the shear force and centrifugal force acting on the liquid in one of the groove structures of the casing shown in FIG. 8 as a representative. [Figure 10] 6A and 6B are diagrams illustrating the function of the groove structure of the casing in the screw compressor according to the second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A screw compressor according to an embodiment of the present invention will now be described with reference to the accompanying drawings. In this embodiment, the present invention is applied to an oil-injected screw compressor that compresses air.

[0012] [First embodiment] The basic configuration of a screw compressor according to a first embodiment will be described with reference to Figs. 1 and 2. Fig. 1 is a longitudinal cross-sectional view showing a screw compressor according to a first embodiment of the present invention and a system diagram showing an external oil supply path for the screw compressor. Fig. 2 is a cross-sectional view of the screw compressor according to the first embodiment of the present invention as seen from the arrows II-II in Fig. 1. In Fig. 1, the left side is the axial suction side of the screw compressor, and the right side is the axial discharge side. In Fig. 2, the thick arrow indicates the rotation direction of the screw rotor, and the two-dot chain lines indicate the discharge ports of the casing projected onto the discharge end faces of both the male and female rotors. Note that the outer peripheral surface of the casing is omitted in Fig. 2.

[0013] 1, in an oil-lubricated screw compressor 1 (hereinafter referred to as a screw compressor), oil (liquid) is supplied from the outside to the inside of the compressor. Therefore, an external oil supply system 100 that supplies oil is connected to the screw compressor 1. The external oil supply system 100 is made up of, for example, devices such as an oil separator 101, an oil cooler 102, and an oil filter 103, and a pipe 104 that connects them.

[0014] 1 and 2, the screw compressor 1 includes a male rotor 2 (male screw rotor) and a female rotor 3 (female screw rotor) that rotate while meshing with each other, and a casing 4 that houses the male and female rotors 2, 3 rotatably in an intermeshed state. The male rotor 2 and the female rotor 3 are arranged so that their central axes A1, A2 are parallel to each other. The male rotor 2 is rotatably supported on both sides in its axial direction (left-right direction in FIG. 1) by a suction-side bearing 6 and a discharge-side bearing 7, 8, respectively, and is connected to a motor 90, which serves as a rotary drive source. The female rotor 3 is rotatably supported on both sides in its axial direction by a suction-side bearing and a discharge-side bearing (neither of which are shown), respectively.

[0015] The male rotor 2 is composed of a rotor tooth portion 21 having a plurality of twisted male teeth (lobes) 21a (four in FIG. 2), and a suction-side (left side in FIG. 1) shaft portion 22 and a discharge-side (right side in FIG. 1) shaft portion 23 provided at both axial ends of the rotor tooth portion 21. The rotor tooth portion 21 has a suction-side end face 21b and a discharge-side end face 21c at one axial end (left end in FIG. 1) and the other axial end (right end in FIG. 1), respectively. The suction-side shaft portion 22 extends outside the casing 4 and is integral with, for example, the shaft portion of the motor 90. A shaft sealing member 9, such as an oil seal or a mechanical seal, is attached to the suction-side shaft portion 22 closer to the tip than the suction-side bearing 6.

[0016] The female rotor 3 is composed of a rotor tooth portion 31 having a plurality (six in FIG. 2) of twisted female teeth (lobes) 31a, and a suction-side shaft portion (not shown) and a discharge-side shaft portion 33 provided at both axial ends (direction perpendicular to the plane of FIG. 2) of the rotor tooth portion 31. The rotor tooth portion 31 has a suction-side end face (not shown) and a discharge-side end face 31c at one axial end and the other axial end, respectively.

[0017] The casing 4 includes a main casing 41 and a discharge-side casing 42 attached to the axial discharge side (right side in FIG. 1) of the main casing 41.

[0018] A housing chamber (bore) 45 is formed inside the casing 4 to house the rotor teeth 21 of the male rotor 2 and the rotor teeth 31 of the female rotor 3 in a meshed state. The housing chamber 45 is formed by closing the opening on one side (the right side in FIG. 1 ) of two partially overlapping cylindrical spaces formed in the main casing 41 with the discharge-side casing 42. The wall surfaces that form the housing chamber 45 are composed of a substantially cylindrical male-side inner circumferential surface 46 that covers the radial outside of the rotor teeth 21 of the male rotor 2, a substantially cylindrical female-side inner circumferential surface 47 that covers the radial outside of the rotor teeth 31 of the female rotor 3, a suction-side inner wall surface 48 that faces the suction-side end faces 21 b of the rotor teeth 21, 31 of both the male and female rotors 2, 3, and a discharge-side inner wall surface 49 that faces the discharge-side end faces 21 c, 31 c of the rotor teeth 21, 31 of both the male and female rotors 2, 3. The rotor teeth 21, 31 of the male and female rotors 2, 3 are arranged with gaps of several tens to several hundreds of μm between the male inner peripheral surface 46 and the female inner peripheral surface 47 of the casing 4. Furthermore, the discharge side end faces 21c, 31c of the male and female rotors 2, 3 face the discharge side inner wall surface 49 of the casing 4 with gaps of several tens to several hundreds of μm (hereinafter referred to as discharge side end face gap G1). A plurality of working chambers C with different pressures are formed by the rotor teeth 21, 31 of the male and female rotors 2, 3 and the inner wall surfaces of the accommodation chamber 45 of the casing 4 that surround them (the male inner peripheral surface 46, the female inner peripheral surface 47, the suction side inner wall surface 48, and the discharge side inner wall surface 49).

[0019] 1, a suction-side bearing 6 on the male rotor 2 and female rotor 3 side is disposed at the end of the main casing 41 on the motor 90 side, and a suction-side cover 43 is attached to cover the suction-side bearing 6. Discharge-side bearings 7 and 8 on the male rotor 2 and female rotor 3 side are disposed in the discharge-side casing 42.

[0020] The casing 4 is provided with an intake passage 51 for drawing air into the working chamber C (accommodation chamber 45). The casing 4 is also provided with a discharge passage 52 for discharging compressed air from the working chamber C to the outside. The discharge passage 52 connects the accommodation chamber 45 (working chamber C) to the outside of the casing 4, and is connected to an external oil supply system 100. The discharge passage 52 has a discharge port 52a (the portion indicated by the two-dot chain line in FIG. 2 ) formed in the discharge-side inner wall surface 49 of the casing 4. The casing 4 is also provided with an oil supply passage 53 for supplying oil from the external oil supply system 100 to the working chamber C (accommodation chamber 45). The oil supply passage 53 opens, for example, to a region of the accommodation chamber 45 where the working chamber C undergoes a compression stroke.

[0021] In the screw compressor 1 having the above-described configuration, the motor 90 shown in FIG. 1 drives the male rotor 2, which in turn drives the female rotor 3 shown in FIG. 2 to rotate. As a result, the working chamber C moves in the axial direction as both the male and female rotors 2, 3 rotate. At this time, the working chamber C increases its volume to draw in air from the outside through the suction passage 51 shown in FIG. 1, and compresses the air to a predetermined pressure by reducing its volume. When the working chamber C communicates with the discharge port 52a, the compressed air in the working chamber C passes through the discharge passage 52 via the discharge port 52a and is discharged to the oil separator 101 of the external oil supply system 100.

[0022] In the screw compressor 1, oil is supplied to the working chamber C, so oil is mixed into the discharged compressed air. The oil contained in this compressed air is separated by the oil separator 101. The compressed air from which the oil has been removed by the oil separator 101 is supplied to an external device as required.

[0023] On the other hand, the oil separated from the compressed air in the oil separator 101 is cooled by an oil cooler 102 of the external oil supply system 100, and then injected into the working chamber C via the oil supply passage 53 of the screw compressor 1. Oil can be supplied to the screw compressor 1 using the pressure of the compressed air flowing into the oil separator 101 as a driving source, without using a power source such as a pump.

[0024] Next, the axial communication passage, which is one of the internal gaps of the screw compressor, will be described with reference to Figures 2 and 3. Figure 3 is an enlarged view of the portion designated by the symbol L1 in Figure 2, and is a view illustrating the axial communication passage. In Figure 3, the thick arrows indicate the rotational directions of the male and female rotors, and the two-dot chain lines indicate the discharge ports projected onto the discharge end faces of the male and female rotors.

[0025] 3, the tooth flank on the rotational direction side, defined as the tooth tip of the male rotor 2, is defined as the forward moving surface 21d of the male rotor 2, and the tooth flank on the opposite side to the rotational direction is defined as the reverse moving surface 21e of the male rotor 2. Also, the tooth bottom of the female rotor 3 is defined as the tooth flank on the rotational direction side, defined as the forward moving surface 31d of the female rotor 3, and the tooth flank on the opposite side to the rotational direction is defined as the reverse moving surface 31e of the female rotor 3.

[0026] 2 and 3 show the meshing state at a certain rotation angle of the male and female rotors 2, 3. Theoretically, as shown in Fig. 3, the male rotor 2 and female rotor 3 are in a meshing state at three points on the discharge-side end faces 21c, 31c: a first contact point P1 where the reversing surface 21e of the male rotor 2 comes into contact with the reversing surface 31e of the female rotor 3; a second contact point P2 where the portion of the reversing surface 21e of the male rotor 2 closer to the tooth tip than the first contact point P1 comes into contact with the portion of the reversing surface 31e of the female rotor 3 closer to the tooth bottom; and a third contact point P3 where the advancing surface 21d of the male rotor 2 comes into contact with the advancing surface 31d of the female rotor 3.

[0027] Of these, the area surrounded by the first contact point P1, the second contact point P2, and the tooth contours of the male and female rotors 2, 3 is an internal gap called the axial communication passage G2. The axial communication passage G2 is sandwiched between the reversing surfaces 21e, 31e of the male and female rotors 2, 3, and is a crescent-shaped opening that is open only in the axial direction at the discharge end faces 21c, 31c. The axial communication passage G2 appears periodically at the discharge end faces 21c, 31c as the meshing between the male and female rotors 2, 3 changes due to rotation.

[0028] Specifically, the axial communication passage G2 is generated near the intersection point P0 on the discharge port 52a side of the intersection points between the outer diameter line D1 of the male rotor 2 (dashed line in Fig. 3) and the pitch circle D2 of the female rotor 3 (dashed line in Fig. 3), and moves toward the center axis lines A1, A2 of the male and female rotors 2, 3 (upper side in Fig. 2) while expanding its opening area (size) as the male and female rotors 2, 3 rotate, and finally disappears when the meshing state in which they contact at three points is released. The range of existence of the first contact point P1 is inside the pitch circle D2 of the female rotor 3, and the range of existence of the second contact point P2 is inside the outer diameter line D1 of the male rotor 2.

[0029] The pitch circle D2 of the female rotor 3 has a center coincident with the central axis A2 of the female rotor 3, and its diameter dpf is calculated by the following formula (1).

[0030]

number

[0031] Here, a, Zm, and Zf are the distance between the central axis A1 of the male rotor 2 and the central axis A2 of the female rotor 3, the number of teeth of the male rotor 2, and the number of teeth of the female rotor 3, respectively.

[0032] The axial communication passage G2 is connected to the working chamber C for the suction stroke, which is a relatively low-pressure space, but is located close to the working chamber Cd for the discharge stroke, which is connected to the discharge passage 52 (see FIG. 1) and the discharge port 52a, which are relatively high-pressure spaces, as shown in Figures 2 and 3. Therefore, the axial communication passage G2 causes compressed air to flow back from the discharge passage 52 and the working chamber Cd for the discharge stroke to the working chamber C for the suction stroke.

[0033] Therefore, in order to prevent internal leakage of compressed air via the axial communicating passage G2, the discharge-side inner wall surface 49 of the casing 4 has a shielding region 49a (see FIG. 4 ) described below that shields at least a portion, preferably most, of the path of the axial communicating passage G2. However, during the discharge stroke, some of the compressed air in the working chamber Cd and the discharge flow path 52 passes through the discharge-side end face gap G1 (see FIG. 1 ) between the discharge-side end faces 21c, 31c of the male and female rotors 2, 3 and the shielding region 49a of the discharge-side inner wall surface 49 of the casing 4, reaches the axial communicating passage G2, and flows back into the low-pressure space. This is one of the factors that reduces the compression performance and energy-saving performance of the compressor.

[0034] In the case of an oil-lubricated screw compressor, the oil supplied into the working chamber C forms an oil film in part of the discharge-side end face gap G1, which is expected to have the effect of reducing internal leakage of compressed air via the discharge-side end face gap G1. However, with regard to internal leakage via the axial communicating passage G2, the pressure difference between the high-pressure space from which the leakage originates (the working chamber Cd or the discharge flow path 52 during the discharge stroke) and the low-pressure space to which the leakage originates (the working chamber C during the suction stroke) is greater than in the case of other internal leakage, making it difficult to maintain the oil film formed in the discharge-side end face gap G1 near the axial communicating passage G2, and the effect of the oil film in reducing internal leakage tends to be small.

[0035] Therefore, this embodiment is characterized by the inclusion of a groove structure for pressurizing the oil film formed in the discharge end face gap G1 near the axial communicating passage G2. This groove structure is particularly intended to form a high-pressure oil film along the longitudinal direction of the flattened crescent-shaped axial communicating passage G2. By forming a high-pressure oil film in the discharge end face gap G1 along the longitudinal direction of the axial communicating passage G2, it is possible to maintain the oil film even in the event of an internal leakage where there is a large pressure difference between the space where the leakage originates and the space where the leakage destination occurs.

[0036] Next, details of the groove structure of the screw compressor according to the first embodiment will be described with reference to FIGS. 4 and 5. FIG. 4 is a cross-sectional view of the screw compressor according to the first embodiment of the present invention, as seen from the arrows IV-IV in FIG. 1. FIG. 5 is an enlarged view of the portion indicated by reference symbol L2 in FIG. 4, showing the groove structure of the casing in the screw compressor according to the first embodiment of the present invention. In FIG. 4, the two-dot chain line indicates the shape of the discharge-side end faces of the male and female rotors projected axially onto the discharge-side inner wall surface of the casing at a certain rotation angle (when the axial communicating passage is formed), and the thick arrow indicates the rotation direction of the two rotors. In FIG. 5, the thick arrow indicates the rotation direction of the female rotor. Note that the outer peripheral surface of the casing is omitted from FIG. 4.

[0037] As shown in Fig. 4, a discharge port 52a, which is the inlet of the discharge flow path 52 (see Fig. 1), is formed in the discharge-side inner wall surface 49 of the casing 4. In order to reduce internal leakage of compressed air via the above-mentioned axial communicating passage G2, the discharge port 52a is formed so as not to overlap, for example, with the area obtained by projecting the path of the axial communicating passage G2 onto the discharge-side inner wall surface 49 in the rotor axial direction.

[0038] In other words, the discharge-side inner wall surface 49 has a shielding region 49a for suppressing internal leakage via the axial communicating passage G2. The shielding region 49a shields at least a portion, preferably most of, the path of the axial communicating passage G2 and is set to overlap at least a portion, preferably most of, the area obtained by projecting the path onto the discharge-side inner wall surface 49 in the rotor axial direction. As a specific example, the shielding region 49a is the region on the discharge port 52a side of the line connecting the central axis A1 of the male rotor 2 and the central axis A2 of the female rotor 3, within the area obtained by projecting the area surrounded by both the outer diameter line D1 of the male rotor 2 and the pitch circle D2 of the female rotor 3 onto the discharge-side inner wall surface 49 in the rotor axial direction. The outer edge of the shielding region 49a forms part of the contour of the discharge port 52a and has, for example, a tongue-like protrusion shape that protrudes toward the center of the discharge port 52a. The shielding area 49a of the discharge-side inner wall surface 49 minimizes the direct communication area (opposing area) between the axial communication passage G2 and the discharge port 52a.

[0039] As shown in FIGS. 4 and 5 , the shielded region 49a of the discharge-side inner wall surface 49 is provided with a groove group consisting of multiple grooves 60 into which a portion of the oil (liquid) supplied into the working chamber C can flow. The multiple grooves 60 are arranged side by side in the circumferential direction about the central axis A2 of the female rotor 3. Each groove 60 is formed as an elongated groove having a longitudinal direction, and the multiple grooves 60 are arranged so that their longitudinally extending sides are adjacent to each other. The multiple grooves 60 in the groove group are configured so that the longitudinal lengths of the grooves located on the forward side in the rotational direction of the female rotor 3 are relatively longer than the grooves located on the rearward side in the rotational direction of the female rotor 3. In other words, the longitudinal lengths of the multiple grooves 60 in the groove group are relatively longer as they progress in the rotational direction of the female rotor 3. This is intended to set the longitudinal length of each groove 60 in the groove group to correspond to the axial communicating passage G2, which becomes longer in the longitudinal direction as the rotation of the female rotor 3 progresses.

[0040] As shown in FIG. 5 , one longitudinal end 61 of each groove 60 is located closer to the outer periphery of the female rotor 3 than the other longitudinal end 62. For example, the groove 60 extends linearly from the other longitudinal end 62 to the one longitudinal end 61 along the radial direction R2 of the female rotor 3. That is, the groove 60 is configured such that normals Ng1, Ng2, and Ng3 (normals to the first and second longitudinal sides 63 and 64) at each position from the other longitudinal end 62 through position 66 to the one longitudinal end 61 coincide with tangents to the circumferential direction of the female rotor 3 at the positions 62, 61, and 66 (directions perpendicular to the radial direction R2). The normals Ng1, Ng2, and Ng3 at the positions 62, 61, and 66 of each groove 60 face in the same direction. The first longitudinal end 63 is a side located on the front side in the rotational direction of the female rotor 3. On the other hand, the second longitudinal end 64 is a side located on the rear side in the rotational direction of the female rotor 3. The groove 60 is limited to a position inside the pitch circle D2 of the female rotor 3 and not reaching the contour line of the shielding region 49a (the opening edge of the discharge port 52a). In other words, the groove 60 is configured to extend from the vicinity of the contour line of the shielding region 49a on the female rotor 3 side (the opening edge of the discharge port 52a) to the vicinity of the contour line of the shielding region 49a on the male rotor 2 side (the opening edge of the discharge port 52a), along the longitudinal direction of the flattened crescent-shaped axial communicating passage G2 (see FIG. 4).

[0041] The grooves 60 have a substantially constant depth. The grooves 60 are intended as a type of dynamic pressure groove, as will be described in detail later. The depth of the grooves 60 as dynamic pressure grooves has an appropriate value depending on the magnitude of the shear force, described below, that acts on the oil that has flowed therein. For example, when the discharge side end face gap G1 is approximately several tens to 200 μm, the preferred depth of the grooves 60 is in the range of 1 μm to 1 mm.

[0042] Next, the operation and effect of the groove structure of the casing in the screw compressor according to the first embodiment will be explained with reference to Figures 6 and 7. Figure 6 is a cross-sectional view of the groove structure of the casing in the screw compressor according to the first embodiment of the present invention, taken along the arrows VI-VI in Figure 5. Figure 7 is a diagram explaining the operation of the groove structure of the casing in the screw compressor according to the first embodiment of the present invention. Figure 6 shows the female rotor facing the shielded area of ​​the casing. In Figure 6, the outline arrow indicates the rotation direction of the female rotor, and the thick arrow indicates the flow of oil. In Figure 7, the two-dot chain line indicates the shape of the discharge-side end faces of the male and female rotors projected in the rotor axial direction onto the discharge-side inner wall surface of the casing.

[0043] In the screw compressor 1 of this embodiment, as shown in FIG. 7, a shear force Sf acts on the oil that has flowed into each groove 60 formed in the shielding region 49a of the discharge-side inner wall surface 49 of the casing 4 by the discharge-side end surface 31c of the rotating female rotor 3 in a tangential direction (a direction perpendicular to the radial direction R2 of the female rotor 3) to the rotational direction (circumferential direction) of the female rotor 3, that is, in the same direction as the rotational direction.

[0044] In this embodiment, each groove 60 extends linearly from the other end 62 to the one end 61 along the radial direction R2 of the female rotor 3. That is, the direction of the normals Ng1, Ng2, Ng3 at each position 62, 61, 66 in the longitudinal direction of the groove 60 coincides with the tangential direction of the circumferential direction of the female rotor 3 at that position (a direction perpendicular to the radial direction R2), and therefore coincides with the direction in which the shear force Sf acts. As a result, the shear force Sf caused by the rotation of the female rotor 3 causes the oil in each groove 60 to flow in the width direction of the groove 60, which is the same direction as the rotational direction of the female rotor 3. 6 and 7, the oil flowing in the groove 60 is blocked by the first side surface 63, which is the side surface located forward in the width direction of the groove 60 in the rotation direction of the female rotor 3, thereby converting kinetic energy (dynamic pressure) and increasing static pressure, and finally flows out to the discharge-side end face gap G1 (toward the female rotor 3) over the entire longitudinal area of ​​the first side surface 63 of the groove 60. As a result, the pressure of the oil in the discharge-side end face gap G1 becomes relatively high in the vicinity of the entire longitudinal area of ​​the first side surface 63 of the groove 60. In other words, the formation of a high-pressure oil film W along the longitudinal direction of the first side surface 63 of the groove 60 is promoted in the discharge-side end face gap G1.

[0045] In this embodiment, as shown in Fig. 7, multiple grooves 60 are arranged side by side so that their longitudinally extending sides are adjacent to each other. As a result, pressurized oil flows out of each first side surface 63 of the multiple grooves 60 (the side surface located forward in the direction of rotation of the female rotor 3, out of both longitudinally extending side surfaces of the groove) into the discharge-side end face gap G1. As a result, multiple high-pressure oil films W are formed so as to be aligned in the circumferential direction (direction of rotation) of the female rotor 3. Note that the closer one end 61 of the groove 60 is positioned to the outer periphery of the female rotor 3, the greater the shear force acting due to the rotation of the female rotor 3, and accordingly, the greater the effect of suppressing internal leakage due to the pressurization of the oil film W.

[0046] In this way, not only does the oil in the groove 60 seal the discharge-side end face gap G1, but the oil flowing out of the first side surface 63 of the groove 60 forms an oil film W at a higher pressure than the surrounding area, extending from near the contour of the female rotor 3 side (on the outer diameter line D1 side) in the shielded region 49a of the casing 4 to near the contour of the male rotor 2 side (on the pitch circle D2 side). This high-pressure oil film W prevents compressed air in high-pressure spaces such as the discharge flow path 52 (see FIG. 1) and the working chamber Cd (see FIG. 3) in the discharge stroke from leaking from the tip end side of the shielded region 49a (projection) through the axial communicating passage G2 to the working chamber (low-pressure space) in the suction stroke when the axial communicating passage G2 overlaps with the shielded region 49a via the discharge-side end face gap G1. As a result, the compression performance and energy-saving performance of the screw compressor 1 can be improved.

[0047] The groove structure (plurality of grooves 60) of this embodiment can be said to be a type of dynamic pressure groove, which blocks oil flowing due to shear force Sf at the first side surface 63 in the groove width direction, converting dynamic pressure into static pressure and forming a high-pressure oil film W. By setting the depth of each groove 60 to an appropriate value (for example, in the range of 1 μm to 1 mm) that maximizes the pressure of the oil film W depending on the magnitude of the shear force Sf acting on the oil and the size of the discharge-side end face gap G1, it is possible to further suppress internal leakage via the axial communicating passage G2.

[0048] In this embodiment, each groove 60 is disposed inside the pitch circle D2 of the female rotor 3 and is formed so as not to communicate with the discharge port 52a, thereby preventing the plurality of grooves 60 from simultaneously communicating with the working chamber Cd during the discharge stroke and the axial communicating passage G2 and becoming a route for internal leakage.

[0049] In this embodiment, a plurality of grooves 60 are provided in the casing 4, which is a part of the stationary body. Therefore, the plurality of grooves 60 do not move together with the screw rotor, and are located in fixed positions relative to the trajectories of the discharge port 52a of the casing 4 and the axial communicating passage G2, so a stable suppression effect against internal leakage via the axial communicating passage G2 can be expected.

[0050] The screw compressor 1 according to the first embodiment described above includes a male rotor 2 having a first discharge side end face 21c on one axial side, a female rotor 3 having a second discharge side end face 31c on one axial side, and a casing 4 having an accommodation chamber 45 for rotatably accommodating the male rotor 2 and the female rotor 3 in an intermeshed state. The casing 4 has a discharge side inner wall surface 49 that faces the first discharge side end face 21c of the male rotor 2 and the second discharge side end face 31c of the female rotor 3, and the discharge side inner wall surface 49 of the casing 4 appears periodically at the first discharge side end face 21c and the second discharge side end face 31c in accordance with changes in the intermeshing due to the rotation of the male rotor 2 and the female rotor 3, and appears as a reverse rotation surface of the male rotor 2 and the female rotor 3. 21e, 31e The casing 4 has a shielding region 49a that shields at least a portion of the path of the axial communicating passage G2, which is a gap sandwiched between the female rotor 3 and the male rotor 4. A longitudinal groove 60 is provided within the shielding region 49a of the casing 4. The groove 60 is configured so that normals Ng1, Ng2, Ng3 at respective positions 62, 61, 66 in the longitudinal direction coincide with circumferential tangents of the female rotor 3 at those positions (direction perpendicular to the radial direction R2 of the female rotor 3).

[0051] According to this configuration, the oil (liquid) in the groove 60 provided in the discharge-side inner wall surface 49 of the casing 4 flows in the groove width direction over the entire longitudinal direction of the groove due to the shear force Sf caused by the rotation of the female rotor 3 and is blocked by the first side surface 63 of the groove 60, thereby increasing the static pressure, and a high-pressure oil film W (liquid film) can be formed in the longitudinal direction of the flattened crescent-shaped axial communicating passage G2 in the discharge-side end face gap G1. Therefore, internal leakage of compressed gas via the axial communicating passage G2 can be reduced.

[0052] In this embodiment, the groove 60 is configured to extend linearly along the radial direction of the female rotor 3. With this configuration, the groove 60 can be easily formed in the casing 4.

[0053] In this embodiment, a groove group having a plurality of grooves 60 is provided in the shielded region 49a of the casing 4, and the grooves 60 of the groove group are arranged side by side in the circumferential direction of the female rotor 3 so that the sides extending in the longitudinal direction of the grooves 60 are adjacent to each other. With this configuration, a high-pressure oil film W( fluid Therefore, it is possible to further reduce internal leakage of compressed gas via the axial communicating passage G2.

[0054] Furthermore, the grooves 60 of the groove group in this embodiment are configured so that the grooves located on the front side in the rotation direction of the female rotor 3 are longer in the longitudinal direction than the grooves located on the rear side in the rotation direction of the female rotor 3. With this configuration, the longitudinal length of each groove 60 of the groove group can be adjusted to match the axial communicating passage G2, which becomes longer in the longitudinal direction as the rotation of the female rotor 3 progresses.

[0055] [Second embodiment] Next, a screw compressor according to a second embodiment will be illustrated with reference to FIGS. 8 to 10. In FIGS. 8 to 10, the same reference numerals as those in FIGS. 1 to 7 denote similar parts, and detailed descriptions thereof will be omitted. FIG. 8 is an enlarged view similar to FIG. 5, showing the groove structure of the casing in a screw compressor according to a second embodiment of the present invention. FIG. 9 is a diagram illustrating the relationship between the groove shape and the shear force and centrifugal force acting on the liquid in one of the groove structures of the casing shown in FIG. 8, using the groove as a representative. In FIGS. 8 and 9, the thick arrow indicates the rotation direction of the female rotor. In FIG. 9, the two-dot chain line shows the shapes of the discharge-side end faces of the male and female rotors projected in the rotor axial direction onto the discharge-side inner wall surface of the casing.

[0056] 8 and 9 differs from the first embodiment in that the shape (groove structure) of the plurality of grooves 60A provided in the discharge-side inner wall surface 49 of the casing 4A for forming a high-pressure oil film W in the longitudinal direction of the axial communicating passage G2 is different. The groove structure of this embodiment was determined by taking into consideration centrifugal force Cf in addition to shear force Sf caused by rotation of the female rotor 3 as forces acting on the oil (liquid) in the grooves 60A.

[0057] Specifically, as shown in FIG. 8, a groove group consisting of multiple grooves 60A is formed in the shielded region 49a of the discharge-side inner wall surface 49, into which a portion of the oil (liquid) supplied into the working chamber C can flow. The multiple grooves 60A are arranged side by side in the circumferential direction with respect to the central axis A2 of the female rotor 3. Each groove 60A is formed as an elongated groove having a longitudinal direction extending from the inner periphery side toward the outer periphery side of the female rotor 3. One longitudinal end 61 of each groove 60A is located closer to the outer periphery of the female rotor 3 than the other longitudinal end 62. The multiple grooves 60A are arranged so that their longitudinally extending sides are adjacent to each other. The multiple grooves 60A are configured so that the grooves located on the front side in the rotational direction of the female rotor 3 are longer in the longitudinal direction than the grooves located on the rear side in the rotational direction of the female rotor 3.

[0058] Each groove 60A is configured so that its longitudinal direction from the other end 62 to the one end 61 (from the inner periphery to the outer periphery of the female rotor 3) is inclined in the opposite direction to the rotational direction of the female rotor 3, relative to the radial direction R2 of the female rotor 3. In addition, the groove 60A is formed in a convex curve in the rotational direction of the female rotor 3. As shown in FIG. 9, this structure is designed taking into consideration the centrifugal force Cf caused by the rotation of the female rotor 3 as well as the shear force Sf caused by the rotation of the female rotor 3, as forces acting on the oil (liquid) in the groove 60A. When the radius of the female rotor 3 is large or the rotational speed (angular velocity) of the female rotor 3 is high, the magnitude of the centrifugal force Cf acting on the liquid that is dragged by the discharge end face 31c of the female rotor 3 and flows in the circumferential direction of the female rotor 3 due to the rotation of the female rotor 3 may not be negligible compared to the shear force Sf caused by the rotation of the female rotor 3.

[0059] Similar to the first embodiment, the multiple grooves 60A in this embodiment are intended to form a high-pressure oil film along the longitudinal direction of the flattened, crescent-shaped axial communicating passage G2. Therefore, each groove 60A is configured so that the normals Ng1, Ng2, Ng3 at each longitudinal position coincide with the direction of resultant forces F1, F2, F3 of shear forces Sf1, Sf2, Sf3 caused by the rotation of the female rotor 3 and centrifugal forces Cf1, Cf2, Cf3 caused by the rotation of the female rotor 3. The directions of resultant forces F1, F2, F3 at each longitudinal position of the groove 60A are inclined toward the direction in which the centrifugal forces Cf1, Cf2, Cf3 act, relative to the direction of the shear forces Sf1, Sf2, Sf3 (the direction perpendicular to the radial direction R2 of the female rotor 3). Therefore, when attempting to align the normals Ng1, Ng2, and Ng3 at each position in the longitudinal direction of the groove 60A with the directions of the resultant forces F1, F2, and F3, as shown in Figure 8, the longitudinal direction of the groove 60A from the other end 62 to the one end 61 with respect to the radial direction R2 of the female rotor 3 is inclined in the opposite direction to the rotational direction of the female rotor 3, and the groove 60A becomes curved and convex in the rotational direction of the female rotor 3.

[0060] The direction of the normal N at each position in the longitudinal direction of the groove 60A, i.e., the direction of the normal to the first side surface 63A and the second side surface 64A of the groove 60A, can be set, for example, as follows: Consider the other end 62, the one end 61, and an arbitrary position 66 between the other end 62 and the one end 61 as positions in the longitudinal direction of the groove 60A. The distances from the center axis A2 of the female rotor 3 to the other end 62, the one end 61, and the position 66 of the groove 60A are defined as r1, r2, and r3, respectively. In this case, the resultant forces F1, F2, and F3 at the other end 62, the one end 61, and the position 66 of the groove 60A can be calculated based on the following equations (2) to (4): Shear forces Sf1, Sf2, and Sf3 can be calculated based on the following equations (5) to (7): Cf1, Cf2, and Cf3 can be calculated based on the following equations (8) to (10):

[0061]

number

[0062]

number

[0063]

number

[0064] Here, in equations (5) to (7), μ is the viscosity coefficient of the oil (liquid), ΔA is the area of ​​each of the positions 61, 62, and 66, h is the sum of the size of the discharge-side end face gap G1 and the depth of the groove 60A, and ω is the angular velocity of the female rotor 3. Also, in equations (8) to (10), Δm is the mass of the oil (liquid) at each of the positions 61, 62, and 66, and ω is the angular velocity of the female rotor 3.

[0065] Here, as the directions of the resultant forces F1, F2, F3 at each position in the longitudinal direction of the groove 60A, consider the angle θ (inclination) of the directions of the resultant forces F1, F2, F3 with respect to the direction perpendicular to the radial direction R2 of the female rotor 3 at each position in the longitudinal direction of the groove 60A, as shown in Fig. 9. Specifically, the angles θ1, θ2, θ3 of the resultant forces F1, F2, F3 at the other end 62, one end 61, and position 66 of the groove 60A can be calculated based on the following equations (11) to (13).

[0066]

number

[0067] It can be seen from equations (11) to (13) that the angle θ1 of the resultant force F1, the angle θ2 of the resultant force F2, and the angle θ3 of the resultant force F3 are all the same. That is, the angle θ (direction) of the resultant forces F1, F2, and F3 at each longitudinal position of the groove 60A relative to the direction perpendicular to the radial direction R2 of the female rotor 3 is a constant angle. Each groove 60A in this embodiment is configured so that the normals Ng1, Ng2, and Ng3 at each longitudinal position 61, 62, and 66 coincide with the directions of the resultant forces F1, F2, and F3 of the shear forces Sf1, Sf2, and Sf3 and the centrifugal forces Cf1, Cf2, and Cf3 at the corresponding positions 61, 62, and 66. That is, each groove 60A is configured so that the normals Ng1, Ng2, Ng3 at each longitudinal position 61, 62, 66 have a certain inclination with respect to the circumferential tangent of the female rotor 3 at that position 61, 62, 66 (a direction perpendicular to the radial direction R2 of the female rotor 3).

[0068] Next, the operation and effect of the groove structure of the casing in the screw compressor according to the second embodiment will be described with reference to Figures 8 to 10. Figure 10 is a diagram for explaining the operation of the groove structure of the casing in the screw compressor according to the second embodiment of the present invention.

[0069] In the screw compressor 1 of this embodiment, as shown in Fig. 9, oil that has flowed into each groove 60A formed in the shielded region 49a of the discharge-side inner wall surface 49 of the casing 4A is subjected to shear forces Sf1, Sf2, and Sf3 by the discharge-side end face 31c of the rotating female rotor 3 at positions 61, 62, and 66 in the longitudinal direction of the groove 60A. These shear forces are tangential to the rotational direction of the female rotor 3 (a direction perpendicular to the radial direction R2 of the female rotor 3) and directed in the same direction as the rotational direction. In addition, centrifugal forces Cf1, Cf2, and Cf3 are generated in the oil in the discharge-side end face gap G1 as it flows in the rotational direction of the female rotor 3 due to the discharge-side end face 31c of the female rotor 3. The centrifugal forces Cf1, Cf2, and Cf3 act radially outward in the radial direction R2 of the female rotor 3.

[0070] As shown in FIG. 9, each groove 60A in this embodiment is formed at each position 6 in the longitudinal direction. 2 , 6 1, 66 (normal lines at the first side surface 63 and the second side surface 64 extending in the longitudinal direction) 2 , 6 1 , 66 coincide with the direction of the resultant forces F1, F2, F3 of the shear forces Sf1, Sf2, Sf3 and the centrifugal forces Cf1, Cf2, Cf3 in the grooves 60A. As a result, as shown in FIG. 10, the oil in each groove 60A flows in the width direction of the groove 60A, in the same direction as the rotation direction of the female rotor 3, due to the shear force Sf and centrifugal force Cf caused by the rotation of the female rotor 3. The oil flowing in the groove 60A is blocked by the first side surface 63A in the width direction of the groove 60A, whereby its kinetic energy (dynamic pressure) is converted and its static pressure increases, and finally, the oil flows out to the discharge-side end face gap G1 (toward the female rotor 3) over the entire longitudinal area of ​​the first side surface 63A of the groove 60A. As a result, the pressure of the oil in the discharge-side end face gap G1 becomes relatively high in the vicinity of the entire longitudinal area of ​​the first side surface 63A of the groove 60A. That is, in the discharge-side end face gap G1, the formation of a high-pressure oil film W along the longitudinal direction of the first side surface 63A of the groove 60A is promoted.

[0071] In this embodiment, as shown in Fig. 10, the plurality of grooves 60A are arranged side by side with their longitudinally extending sides adjacent to each other. Therefore, pressurized oil flows from each of the first side surfaces 63A of the plurality of grooves 60A into the discharge-side end face gap G1. This forms a plurality of high-pressure oil films W aligned in the circumferential direction (rotational direction) of the female rotor 3.

[0072] In this way, not only does the oil in the groove 60A seal the discharge-side end face gap G1, but the oil flowing out of the first side surface 63A of the groove 60A forms an oil film W at a higher pressure than the surrounding area, extending from near the contour of the female rotor 3 side (the outer diameter line D1 side) in the shielded region 49a of the casing 4A to near the contour of the male rotor 2 side (the pitch circle D2 side). This high-pressure oil film W prevents compressed air in the discharge passage 52 (see FIG. 1) or the high-pressure space of the working chamber Cd (see FIG. 3) in the discharge stroke from leaking from the tip of the shielded region 49a (protrusion) through the axial communicating passage G2 to the working chamber (low-pressure space) in the suction stroke when the axial communicating passage G2 overlaps with the shielded region 49a via the discharge-side end face gap G1. As a result, the compression performance and energy-saving performance of the screw compressor 1 can be improved.

[0073] The groove structure (plurality of grooves 60A) of this embodiment can be said to be a type of dynamic pressure groove, which blocks oil flowing due to shear force Sf and centrifugal force Cf at the first side surface 63A in the groove width direction, converting dynamic pressure into static pressure and forming a high-pressure oil film W. By setting the depth of each groove 60A to an appropriate value (for example, in the range of 1 μm to 1 mm) that maximizes the pressure of the oil film W, depending on the magnitude of the shear force Sf and centrifugal force Cf acting on the oil and the size of the discharge-side end face gap G1, it is possible to further suppress internal leakage via the axial communicating passage G2.

[0074] The screw compressor 1 according to the second embodiment described above includes a male rotor 2 having a first discharge side end face 21c on one axial side, a female rotor 3 having a second discharge side end face 31c on one axial side, and a casing 4 having an accommodation chamber 45 for rotatably accommodating the male rotor 2 and the female rotor 3 in an intermeshed state. The casing 4 has a discharge side inner wall surface 49 that faces the first discharge side end face 21c of the male rotor 2 and the second discharge side end face 31c of the female rotor 3, and the discharge side inner wall surface 49 of the casing 4 appears periodically at the first discharge side end face 21c and the second discharge side end face 31c in accordance with changes in the intermeshing due to the rotation of the male rotor 2 and the female rotor 3, and appears as a reverse rotation surface of the male rotor 2 and the female rotor 3. 21e, 31eThe casing 4 has a shielding area 49a that shields at least a part of the path of the axial communication passage G2, which is a gap sandwiched between the female rotor 3 and the female rotor 3. A groove 60A having a longitudinal direction extending from the inner periphery side to the outer periphery side of the female rotor 3 is provided within the shielding area 49a of the casing 4. The groove 60A is configured so that the longitudinal direction from the inner periphery side to the outer periphery side of the female rotor 3 is inclined in the opposite direction to the rotation direction of the female rotor 3 with respect to the radial direction R2 of the female rotor 3, and is formed in a curved shape that is convex in the rotation direction of the female rotor 3. Furthermore, the groove 60A has a longitudinal direction 6 2 , 6 1 , 66, the normals Ng1, Ng2, and Ng3 at the position 6 2 , 6 1 , 66 have a certain inclination with respect to a tangent in the circumferential direction of the female rotor 3 (a direction perpendicular to the radial direction R2 of the female rotor 3).

[0075] According to this configuration, the oil (liquid) in the groove 60A provided in the discharge side inner wall surface 49 of the casing 4A flows in the groove width direction over the entire longitudinal direction of the groove due to the shear force Sf and centrifugal force Cf caused by the rotation of the female rotor 3, and is blocked by the first side surface 63A of the groove 60A, thereby increasing the static pressure. Therefore, a high-pressure oil film W( fluid Therefore, it is possible to reduce internal leakage of compressed gas via the axial communicating passage G2.

[0076] In this embodiment, a groove group having a plurality of grooves 60A is provided in the shielded region 49a of the casing 4A, and the grooves 60A of the groove group are arranged side by side in the circumferential direction of the female rotor 3 so that the sides extending in the longitudinal direction of the grooves 60A are adjacent to each other. With this configuration, a high-pressure oil film W( fluid Therefore, it is possible to further reduce internal leakage of compressed gas through the axial communicating passage G2. Therefore, it is possible to further reduce internal leakage of compressed gas through the axial communicating passage G2.

[0077] Furthermore, the grooves 60A of the groove group in this embodiment are configured so that the grooves located on the front side in the rotation direction of the female rotor 3 are longer in the longitudinal direction than the grooves located on the rear side in the rotation direction of the female rotor 3. With this configuration, the longitudinal length of each groove 60A of the groove group can be adjusted to match the axial communicating passage G2, which becomes longer in the longitudinal direction as the rotation of the female rotor 3 progresses.

[0078] [Other embodiments] In the above-described embodiment, the screw compressor 1 that compresses air has been described as an example, but the present invention can be applied to screw compressors that compress various gases, such as ammonia and CO2 refrigerants. Furthermore, while the oil-lubricated screw compressor 1 has been described as an example, the present invention can also be applied to screw compressors that are supplied with liquids other than oil. While oil is preferred from the standpoint of sealing performance and ease of liquid film formation, it can be substituted with various liquids that have sufficient properties to form a liquid film, such as water.

[0079] The groove structures of the respective embodiments can also be applied to a liquid-free screw compressor in which no liquid such as oil is supplied to the inside of the working chamber. In the case of a liquid-free screw compressor, compressed air is present in place of oil in the grooves on the discharge end face of the rotor or the discharge inner wall surface of the casing.

[0080] An example will be described using Figures 6 and 7. If oil is replaced with air, a shear force Sf acts on the air present in the groove 60 due to friction with the opposing discharge-side end face 31c of the female rotor 3, which has a relative speed. The shear force Sf causes the air in the groove 60 to flow in the width direction over the entire longitudinal direction of the groove 60. The air flowing in the groove width direction is blocked by the first side surface 63 of the groove 60, and as a result, flows out into the discharge-side end face gap G1. Therefore, in the discharge-side end face gap G1, a region W where the air pressure is relatively higher than the surrounding area is generated near the entire longitudinal region of the first side surface 63 of the groove 60.

[0081] The amount of internal air leakage through the end face gap increases as the pressure difference between the upstream high-pressure working chamber and the downstream end face gap increases. As described above, when groove 60 is provided, the pressure in the vicinity of the entire longitudinal area of ​​first side surface 63 of groove 60 in discharge-side end face gap G1 increases, so the pressure difference between working chamber Cd and discharge-side end face gap G1 during the discharge stroke decreases compared to when groove 60 is not provided. Therefore, providing groove 60 makes it possible to suppress internal air leakage.

[0082] Furthermore, the present invention is not limited to the above-described embodiments, but includes various modifications. The above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. In other words, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

[0083] In the above-described embodiments, the casing with grooves or the male and female rotors can be manufactured using, for example, molding or cutting. However, the casing with grooves, the rotor, or both, can also be manufactured using a three-dimensional modeling machine. The data used in the three-dimensional modeling machine is generated by processing 3D data generated using CAD or CG software or a 3D scanner into NC data using CAM. This data is input into the three-dimensional modeling machine using any method to perform modeling. Note that NC data can also be generated directly from the 3D data using CAD / CAM software. [Explanation of symbols]

[0084] DESCRIPTION OF SYMBOLS 1...Screw compressor, 2...Male rotor, 3...Female rotor, 4, 4A...Casing, 21c...Discharge side end face (first discharge side end face), 21e...Reverse surface, 31c...Discharge side end face (second discharge side end face), 31e...Reverse surface, 45...Accommodation chamber, 49...Discharge side inner wall surface, 49a...Shielding area, 60, 60A...Groove, 61, 62, 66...Longitudinal position, Ng1, Ng2, Ng3...Normal line, G2...Axial communicating passage

Claims

1. a male rotor having a first discharge end surface on one axial side; a female rotor having a second discharge end surface on one axial side; a casing having an accommodation chamber that accommodates the male rotor and the female rotor in a rotatable state while they are meshed together, the casing has a discharge side inner wall surface facing the first discharge side end surface of the male rotor and the second discharge side end surface of the female rotor, the discharge-side inner wall surface of the casing has a shielding region that periodically appears at the first discharge-side end surface and the second discharge-side end surface in response to changes in the meshing state due to rotation of the male rotor and the female rotor, and that shields at least a portion of the locus of an axial communicating passage that is a gap sandwiched between the reverse surfaces of the male rotor and the female rotor, a groove having a longitudinal direction is provided in the shielding region of the casing; The groove is configured so that a normal at each position in the longitudinal direction coincides with a tangent in the circumferential direction of the female rotor at that position. A screw compressor characterized by:

2. 2. The screw compressor according to claim 1, The groove is configured to extend linearly along the radial direction of the female rotor. A screw compressor characterized by:

3. 2. The screw compressor according to claim 1, a groove group having a plurality of the grooves is provided in the shielding region of the casing; The grooves of the groove group are arranged side by side in the circumferential direction of the female rotor so that their sides extending in the longitudinal direction are adjacent to each other. A screw compressor characterized by:

4. 4. The screw compressor according to claim 3, The grooves of the groove group are configured so that the grooves located on the front side in the rotation direction of the female rotor have a longer length in the longitudinal direction than the grooves located on the rear side in the rotation direction of the female rotor. A screw compressor characterized by:

5. a male rotor having a first discharge end surface on one axial side; a female rotor having a second discharge end surface on one axial side; a casing having an accommodation chamber that accommodates the male rotor and the female rotor in a rotatable state while they are meshed together, the casing has a discharge side inner wall surface facing the first discharge side end surface of the male rotor and the second discharge side end surface of the female rotor, the discharge-side inner wall surface of the casing has a shielding region that periodically appears at the first discharge-side end surface and the second discharge-side end surface in response to changes in the meshing state due to rotation of the male rotor and the female rotor, and that shields at least a portion of the locus of an axial communicating passage that is a gap sandwiched between the reverse surfaces of the male rotor and the female rotor, a groove having a longitudinal direction extending from an inner circumferential side to an outer circumferential side of the female rotor is provided in the shielding region of the casing, the groove is configured so that its longitudinal direction from the inner circumferential side to the outer circumferential side of the female rotor is inclined in the opposite direction to the rotational direction of the female rotor with respect to the radial direction of the female rotor, and is formed in a curved shape that is convex in the rotational direction of the female rotor, The groove is configured so that a normal line at each position in the longitudinal direction has a constant inclination with respect to a tangent line in the circumferential direction of the female rotor at that position. A screw compressor characterized by:

6. 6. The screw compressor according to claim 5, a groove group having a plurality of the grooves is provided in the shielding region of the casing; The grooves of the groove group are arranged side by side in the circumferential direction of the female rotor so that their sides extending in the longitudinal direction are adjacent to each other. A screw compressor characterized by:

7. 7. The screw compressor according to claim 6, The grooves of the groove group are configured so that the grooves located on the front side in the rotation direction of the female rotor have a longer length in the longitudinal direction than the grooves located on the rear side in the rotation direction of the female rotor. A screw compressor characterized by:

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