Screw compressor

Abstract

In a screw compressor according to at least one embodiment of the present disclosure, a slide valve comprises: a pair of facing surfaces that are continuous with an inner wall surface forming a rotor chamber in a rotor casing and face a pair constituted of a male rotor and a female rotor; a non-facing surface that, among surfaces of the slide valve, is on the side opposite the pair of facing surfaces when viewing the slide valve from the rotor axial direction; and a groove section that is formed in the non-facing surface and communicates with a discharge space into which compressed gas is discharged. The length of the groove section in the rotor axial direction is 5% or more of the length of the slide valve in the rotor axial direction. Given 0% as the position of the end of the slide valve on the discharge port side and 100% as the position of the end of the slide valve on the suction port side, the position of the end of the groove section on the suction port side is at 30% or less.

Description

Screw Compressor

[0001] The present disclosure relates to screw compressors.

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

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

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

[0005] The pressure of the compressed gas inside the rotor casing presses the slide valve radially outward from the rotor casing, generating friction between the slide valve and the rotor casing. Therefore, in conventional screw compressors, a relatively large driving force is required to move the slide valve along the rotor axial direction of the screw rotor. To generate this driving force, it is necessary to increase the pressurizing capacity of the hydraulic pump or increase the diameter of the hydraulic piston driven by the pressurized oil from the hydraulic pump, which requires an increase in the size of the screw compressor casing and the hydraulic pump.

[0006] In view of the above circumstances, at least one embodiment of the present disclosure has an object to reduce the driving force for moving a slide valve in a screw compressor.

[0007] a rotor casing that houses the screw rotor and communicates with an intake port for sucking in a gas to be compressed and a discharge port for discharging the compressed gas; and a capacity-controlling slide valve that is provided movably along the rotor axial direction of the screw rotor, wherein the slide valve has: a pair of opposing surfaces that are continuous with an inner wall surface that forms a rotor chamber in the rotor casing and that face the pair of male rotors and the female rotor; a non-opposing surface on a surface of the slide valve that is opposite to the pair of opposing surfaces when the slide valve is viewed from the rotor axial direction; and a groove that is formed on the non-opposing surface and communicates with a discharge space from which the compressed gas is discharged, the length of the groove in the rotor axial direction being 5% or more of the length of the slide valve in the rotor axial direction, and wherein, with respect to the rotor axial position of the slide valve, when the position of an end of the slide valve on the discharge port side is set to 0% and the position of an end of the slide valve on the suction port side is set to 100%, The position of the end of the groove portion on the suction port side is a position where the position in the rotor axial direction of the slide valve is 30% or less, and at least a part of the groove portion exists on the non-opposing surface within a range of up to 45 degrees in the circumferential direction to each of one side and the other side of the slide valve in the circumferential direction of the slide valve, on the non-opposing surface, across a second line segment that is perpendicular to a first line segment connecting a pair of connection points between the pair of opposing surfaces and the non-opposing surface and passes through the central axis of the slide valve, when the slide valve is viewed from the rotor axial direction.

[0008] According to at least one embodiment of the present disclosure, the driving force for moving the slide valve in a screw compressor can be reduced.

[0009] 1 is a schematic cross-sectional view of a screw compressor according to an embodiment, showing a state in which the slide valve is completely accommodated in the slide valve accommodating chamber; FIG. 2 is a schematic cross-sectional view of a screw compressor according to an embodiment, showing a state in which the slide valve protrudes to the discharge space to the maximum extent; FIG. 3 is a perspective view of a slide valve according to some embodiments; FIG. 4 is a view of the slide valve as viewed from the discharge side toward the suction side in the axial direction of the screw rotor, showing a case in which the diameter of the male rotor and the diameter of the female rotor are the same in a screw compressor; FIG. 5 is a view of the slide valve as viewed from the discharge side toward the suction side in the axial direction of the screw rotor, showing a case in which the diameter of the male rotor and the diameter of the female rotor are different in a screw compressor; FIG. 6 is a development view of the slide valve in the vicinity of the groove shown in FIGS. 2 and 3 , seen from the radially outer side about the central axis of the slide valve; FIG. 7 is a development view of the slide valve in the vicinity of the groove according to another embodiment, seen from the radially outer side about the central axis of the slide valve; FIG. 8 is a view showing a modified example of a slide valve having a groove according to another embodiment; FIG. 9 is a view for explaining a radial force of a casing acting on a slide valve not provided with a groove; FIG. 10 is a view for explaining a radial force of a casing acting on a slide valve not provided with a groove; FIG. 1 is a diagram for explaining radial forces of a casing acting on a slide valve not provided with a groove portion. FIG. 2 is a diagram for explaining radial forces of a casing acting on a slide valve according to some embodiments. FIG. 3 is a diagram for explaining radial forces of a casing acting on a slide valve according to some embodiments. FIG. 4 is a diagram for explaining radial forces of a casing acting on a slide valve according to some embodiments. FIG. 5 is a diagram for explaining radial forces of a casing acting on a slide valve in which the length of a groove in the axial direction of the slide valve is unnecessarily long. FIG. 6 is a diagram for explaining radial forces of a casing acting on a slide valve in which the length of a groove in the axial direction of the slide valve is unnecessarily long. FIG. 7 is a diagram for explaining radial forces of a casing acting on a slide valve in which the length of a groove in the axial direction of the slide valve is unnecessarily long.

[0010] Several embodiments of the present disclosure will be described below 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 not intended to limit the scope of the present disclosure and are merely illustrative examples. For example, expressions expressing relative or absolute arrangements, such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial," not only strictly express such arrangements, but also express relative displacements with a tolerance or angle or distance to the extent that the same function is achieved. For example, expressions expressing the equality of things, such as "same," "equal," and "homogeneous," not only express strict equality, but also express tolerance or differences to the extent that the same function is achieved. For example, expressions expressing shapes such as a square or cylindrical shape not only express shapes such as a square or cylindrical shape in the strict geometric sense, but also express shapes including concave and convex portions, chamfered portions, etc., to the extent that the same effect is achieved. 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] 1A is a schematic cross-sectional view of a screw compressor according to one embodiment, showing a state in which a slide valve is fully accommodated in a slide valve accommodating chamber, and FIG. 1B is a schematic cross-sectional view of a screw compressor according to one embodiment, showing a state in which the slide valve is maximally protruded into a discharge space.

[0012] In some embodiments, as shown in FIGS. 1A and 1B , the screw compressor 1 includes a screw rotor 10 and a casing 20 that covers at least the screw rotor 10. In the following description, the direction in which the central axis AXr of the screw rotor 10 extends, i.e., the axial direction of the screw rotor 10, is also referred to as the rotor axial direction. In the rotor axial direction, the side where the suction space is located is referred to as the suction side, and the side where the discharge space is located is referred to as the discharge side. For convenience of explanation, the up-down direction of the screw compressor 1 is defined as shown in each figure. For example, in FIGS. 1A and 1B , the top of the screw compressor 1 is referred to as the upper side in the figure, and the bottom of the screw compressor 1 is referred to as the lower side in the figure. In the following description, the top side of the screw compressor 1 or the top side of the screw compressor 1 in the up-down direction will be simply referred to as the upper side or the top, and the bottom side of the screw compressor 1 or the bottom side of the screw compressor 1 in the up-down direction will be simply referred to as the lower side or the bottom.

[0013] In the embodiment shown in Figures 1A and 1B, the screw rotor 10 is a pair of screw rotors consisting of a male rotor 10A and a female rotor 10B (see Figures 4 and 5 described below). The male rotor 10A and the female rotor 10B are arranged side by side in the depth direction of the paper on Figures 1A and 1B. In this case, the male rotor 10A and the female rotor 10B have intermeshing spiral-shaped teeth. Multiple tooth groove spaces are formed by the tooth grooves of the male rotor 10A and the female rotor 10B and the inner wall surface of the casing 20 (the inner wall surface 21W of the rotor chamber 21 described below). The rotating shaft 11 of the male rotor 10A is connected to the output shaft of a drive source (not shown) and is rotated by the drive source. The female rotor 10B rotates following the rotation of the male rotor 10A. The female rotor 10B rotates in the direction opposite to the rotation direction of the male rotor 10A. When the male rotor 10A and the female rotor 10B rotate in an engaged state, the tooth groove space of the screw rotor 10 moves in the rotor axial direction from the suction side to the discharge side.

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

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

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

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

[0018] The slide valve 40 is provided so as to form a part of the inner wall surface 21W of the rotor chamber 21. Specifically, the surface of the outer surface 43 of the slide valve 40 facing the rotor chamber 21 is continuous with the inner wall surface of the casing 20C and, together with the inner wall surface of the casing 20C, forms the inner wall surface 21W of the rotor chamber 21. That is, the slide valve 40 has a pair of opposing surfaces 43A, 43B facing the pair of male rotors 10A and female rotors 10B, which are continuous with the inner wall surface 21W that forms the rotor chamber 21 in the casing 20C, and a non-opposing surface 43C opposite the pair of opposing surfaces 43A, 43B when the slide valve 40 is viewed from the rotor axial direction. Of the pair of opposing surfaces 43A, 43B, the opposing surface 43A faces the male rotor 10A, and the opposing surface 43B faces the female rotor 10B.

[0019] The non-opposing surface 43C of the slide valve 40 has a circular cross section in the radial direction centered on the central axis AXs that is parallel to the central axis AXr of the screw rotor 10. As described above, the slide valve 40 is movable in the axial direction of the screw rotor 10, and adjusts the opening area of ​​the inlet 33 (see FIG. 1B ) of the bypass passage 30 according to the axial position of the screw rotor 10, thereby controlling the capacity of the screw compressor 1.

[0020] In the following description, the direction in which the center axis AXs of the slide valve 40 extends, i.e., the axial direction of the slide valve 40, will also be referred to as the slide valve axial direction. As in the rotor axial direction described above, the side of the slide valve axial direction where the suction space is located will be referred to as the suction side, and the side where the discharge space is located will be referred to as the discharge side.

[0021] When the slide valve 40 is in the position shown in Fig. 1A, the outer surface 43 of the slide valve 40 is continuous with the inner wall surface of the casing 20C over the entire area facing the rotor chamber 21, and forms the inner wall surface 21W of the rotor chamber 21 together with the inner wall surface of the casing 20C. At this time, the slide valve 40 is completely accommodated in the slide valve accommodating chamber 24, and the inlet 33 of the bypass passage 30 (see Fig. 1B) is closed by the slide valve 40. Thus, in the state shown in Fig. 1A where the slide valve 40 is completely accommodated in the slide valve accommodating chamber 24, the opening area of ​​the inlet 33 of the bypass passage 30 is zero. Hereinafter, the position of the slide valve 40 in this state in the x-coordinate system along the axial direction of the screw rotor 10 is defined as x = 1, and is referred to as the fully closed position.

[0022] In contrast, when the slide valve 40 moves to the discharge side, as shown in Fig. 1B, the end of the slide valve 40 protrudes into the discharge space 23, and the inlet 33 of the bypass passage 30 opens to the inner wall surface 21W of the rotor chamber 21. When the slide valve 40 protrudes to the maximum extent into the discharge space 23 (see Fig. 1B), the opening area of ​​the inlet 33 of the bypass passage 30 becomes maximum. In this state, the position of the slide valve 40 in the x-coordinate system along the axial direction of the screw rotor 10 is defined as the origin x = 0, and is referred to as the fully open position.

[0023] The bypass passage 30 connects the rotor chamber 21 and the suction space 22 and guides a portion of the low-pressure gas G1 in the tooth gap space (return low-pressure gas G3) to the suction space 22. The return low-pressure gas G3 flows into the bypass passage 30 via the inlet 33 and is guided to the suction space 22, where it merges with the uncompressed low-pressure gas G0. The return low-pressure gas G3 then passes through the suction port 12 and enters the tooth gap space again. The greater the flow rate of the return low-pressure gas G3, the smaller the flow rate of the low-pressure gas G0 drawn in from outside the screw compressor 1. As shown in FIG. 1A, when the slide valve 40 is in the fully closed position, the inlet 33 is closed by the slide valve 40, and the flow rate of the return low-pressure gas G3 is zero. In contrast, as shown in FIG. 1B, when the slide valve 40 is in the fully open position, the flow rate of the return low-pressure gas G3 is maximized. In this way, the slide valve 40 can move in the rotor axial direction within the range of 0≦x≦1, and the flow rate of the low-pressure gas G0 sucked in from outside the screw compressor 1 is adjusted by changing the opening area of ​​the inlet 33 of the bypass passage 30 depending on the position of the slide valve 40.

[0024] Fig. 2 is a perspective view of a slide valve 40 according to some embodiments. Fig. 3 is a view of the slide valve 40 as viewed from the discharge side toward the suction side in the axial direction of the screw rotor 10, showing a case in which the diameter of the male rotor 10A and the diameter of the female rotor 10B are the same in the screw compressor 1. Fig. 4 is a view of the slide valve 40 as viewed from the discharge side toward the suction side in the axial direction of the screw rotor 10, showing a case in which the diameter of the male rotor 10A and the diameter of the female rotor 10B are different in the screw compressor 1.

[0025] 1A and 1B , the slide valve 40 includes an intake end portion 45 disposed on the intake side and an exhaust end portion 46 disposed on the exhaust side. The outer surface 43 of the slide valve 40 includes an intake end face 45P and an exhaust end face 46P. Furthermore, the slide valve 40 includes, as part of the outer surface 43 of the slide valve 40, a sliding surface 44 that faces a guide surface 51 of a slide valve guide 50 (described later). In the portion of the slide valve 40 accommodated in the slide valve accommodating chamber 24, the sliding surface 44 faces an inner wall surface 25 of the slide valve accommodating chamber 24.

[0026] A recess 28 extending along the rotor axial direction is formed in the inner wall surface 25 of the slide valve accommodating chamber 24. The recess 28 communicates with the bypass passage 30. That is, the recess 28 communicates with the suction space 22 and the suction port 12 via the bypass passage 30. An end 28P (see Figures 8A to 10C described later) of the recess 28 on the discharge side in the rotor axial direction is positioned between the suction side end 45 and the discharge side end 46 of the slide valve 40 when the slide valve 40 is in the fully closed position.

[0027] 1B, when the slide valve 40 moves to the discharge side, the suction side end surface 45P of the slide valve 40 forms part of the contour of the inlet 33 of the bypass passage 30 that opens to the inner wall surface 21W of the rotor chamber 21. In the embodiment shown in FIGS. 1A and 1B, a notch 47 is formed in the discharge side end 46 to define the discharge position of the high-pressure gas G2 that is discharged from the tooth groove space to the discharge space 23.

[0028] The slide valve 40 may, together with other components, constitute the capacity control device 2 of the screw compressor 1. In addition to the slide valve 40, the capacity control device 2 includes a piston rod 41 connected to the suction side end face 45P of the slide valve 40, and a piston 42 connected to the piston rod 41 on the side opposite to the slide valve 40. The piston 42 is housed in a cylinder chamber 26 formed in the casing 20D. The capacity control device 2 may be hydraulically driven, and the slide valve 40 may move in the rotor axial direction by the pressure of oil supplied into the cylinder chamber 26.

[0029] The slide valve guide 50 is provided in the discharge space 23 and supports the discharge side end 46 of the slide valve 40 that protrudes into the discharge space 23. In the embodiment shown in Figures 1A and 1B, the slide valve guide 50 is provided below the movement path of the slide valve 40 within the discharge space 23 so as to support the discharge side end 46 of the slide valve 40 from below.

[0030] The slide valve guide 50 includes a guide surface 51 that slidably guides the slide valve 40. The guide surface 51 of the slide valve guide 50 faces the sliding surface 44 of the slide valve 40 when the slide valve 40 moves toward the discharge side. In addition to the guide surface 51, the slide valve guide 50 also includes an intake side end portion 54 disposed on the intake side, a discharge side end portion 55 disposed on the discharge side, an intake side end surface 54P, a discharge side end surface 55P, and a pair of end surfaces (circumferential end surfaces 56P) in the circumferential direction centered on the central axis AXs of the slide valve 40 (described later). The slide valve guide 50 is disposed so that the intake side end portion 54 is adjacent to the casing 20C. The slide valve guide 50 has a partially annular shape when viewed along the central axis AXs. The range in which the slide valve guide 50 extends in the circumferential direction about the central axis AXs, that is, the circumferential angular range from one of the pair of circumferential end faces 56P to the other, is, for example, 180 degrees.

[0031] As described above, the capacity of the screw compressor 1 can be controlled by changing the opening area of ​​the inlet 33 of the bypass passage 30 according to the position of the slide valve 40 using the slide valve 40 and the slide valve guide 50.

[0032] In the following description, the direction radially away from the central axis AXr of the male rotor 10A and the female rotor 10B around the central axis AXr is referred to as the radially outer side of the casing 20C, and the direction radially toward the central axis AXr of the male rotor 10A and the female rotor 10B around the central axis AXr is referred to as the radially inner side of the casing 20C. Furthermore, when there is no particular restriction on whether the direction is radially away from or toward the central axis AXr of the male rotor 10A and the female rotor 10B around the central axis AXr, it will be referred to as the radial direction of the casing 20C. Note that when referring to the slide valve 40, the radially outer side of the casing 20C is the lower side in the up-down direction, and the radially inner side of the casing 20C is the upper side in the up-down direction.

[0033] In conventional screw compressors, the pressure of the gas to be compressed in the tooth groove space presses the slide valve radially outward from the casing, generating friction between the slide valve and a support surface that slidably supports the slide valve (e.g., the guide surface 51 of the slide valve guide 50 or the inner wall surface 25 of the slide valve accommodating chamber 24 in the screw compressor 1 according to some embodiments). Therefore, in conventional screw compressors, a relatively large driving force is required to move the slide valve along the rotor axial direction of the screw rotor. This requires increasing the pressurizing capacity of the hydraulic pump to generate this driving force or increasing the diameter of the hydraulic piston driven by the pressurized oil from the hydraulic pump, which in turn requires increasing the size of the screw compressor casing and the hydraulic pump. The force pressing the slide valve radially outward from the casing (the normal force, described below) is greatest when the slide valve is in the fully closed position, as described below.

[0034] Therefore, in the screw compressor 1 according to some embodiments, a groove 48 communicating with the discharge space 23 from which the compressed gas is discharged is formed on the non-opposing surface 43C of the outer surface 43 of the slide valve 40 near the discharge-side end 46. As a result, as shown in Fig. 1A , a bottom surface 48a of the groove 48, i.e., the outer surface 43 of the slide valve 40 at the groove 48, is separated from the inner wall surface 25 of the slide valve accommodating chamber 24, so that the pressure of the high-pressure gas G2 discharged into the discharge space 23 acts on the groove 48. Because the groove 48 is formed on the non-opposing surface 43C opposite to the pair of opposing surfaces 43A, 43B, a pressing force (a push-up force Fu, described later) acts on the groove 48, pressing the groove 48 radially inward of the casing 20C due to the pressure of the high-pressure gas G2 acting on the groove 48. Therefore, the pressing force (normal force Fn, described later) that presses the slide valve 40 radially outward from the casing 20C can be reduced, the driving force for moving the slide valve 40 along the rotor axial direction can be reduced, and the size of the casing 20 of the screw compressor 1 and the size of the hydraulic pump can be made relatively small.

[0035] Here, the vertical force acting on the slide valve 40 due to the pressure of the gas surrounding the slide valve 40 will be described. A pressing force due to the pressure of the gas contacting the outer surface 43 acts on the slide valve 40. The direction of this pressing force is normal to the outer surface 43, from the outside to the inside of the slide valve 40. Of the pressing forces due to the pressure of the gas contacting the outer surface 43, a pressing force acting in a direction that moves the slide valve 40 away from the screw rotor 10 (radially outward of the casing 20C, vertically downward) is referred to as a downward force Fd. Of the pressing forces due to the pressure of the gas contacting the outer surface 43, a pressing force acting in a direction that moves the slide valve 40 closer to the screw rotor 10 (radially inward of the casing 20C, vertically upward) is referred to as an upward force Fu. The difference between the downward force Fd and the upward force Fu (Fd - Fu) is referred to as the normal force Fn acting on the slide valve 40. Strictly speaking, by definition, the "normal force" is the "reaction" of the pressing force that presses the slide valve 40 against the casing 20C. That is, by definition, the "reaction" of the difference (Fd - Fu) between the downward force Fd and the upward force Fu is the "normal force." Therefore, the pressing force that presses the slide valve 40 against the casing 20C and the "normal force" that is the reaction of the pressing force have the same absolute value, but the vector directions are opposite. In the following explanation, for convenience of explanation, the pressing force, i.e., the difference (Fd - Fu) between the downward force Fd and the upward force Fu will be explained as the "normal force Fn." Therefore, when the downward force Fd is greater than the upward force Fu (Fu<Fd), the normal force Fn will be positive (0<Fd-Fu), and when the downward force Fd is smaller than the upward force Fu (Fd<Fu), the normal force Fn will be negative (Fd-Fu<0). The frictional force generated between the sliding surface 44 of the slide valve 40 and the guide surface 51 of the slide valve guide 50 or the inner wall surface 25 of the slide valve accommodating chamber 24 is proportional to the magnitude of the normal force Fn. The groove 48 will be further described below.

[0036] Fig. 5 is a development view of the slide valve 40 in the vicinity of the groove portion 48 shown in Figs. 2 and 3 as seen from the radially outer side about the central axis AXs of the slide valve 40. Fig. 6 is a development view of the slide valve 40 in the vicinity of the groove portion 48 according to another embodiment as seen from the radially outer side about the central axis AXs of the slide valve 40. Fig. 7 is a view showing a modified example of the slide valve 40 including the groove portion 48 according to another embodiment.

[0037] In the screw compressor 1 according to some embodiments, as shown in FIGS. 2 to 5 , the discharge-side end 48b of the groove 48 in the slide valve axial direction and the discharge-side end face 46P of the slide valve 40 may be located at the same position in the slide valve axial direction. That is, the groove 48 may have an opening 48c that opens to the discharge-side end face 46P of the slide valve 40. That is, the groove 48 shown in FIGS. 2 to 5 extends from the discharge-side end face 46P of the slide valve 40 toward the suction side in the slide valve axial direction. The opening 48c extends from one end 48d of the groove 48 to the other end 48d in the circumferential direction around the central axis AXs of the slide valve 40. This allows the groove 48 to communicate with the discharge space 23 with a relatively simple configuration.

[0038] In the screw compressor 1 according to some embodiments, as shown in FIGS. 6 and 7 , the end 48b of the groove 48 on the discharge side in the axial direction of the slide valve may be located at a position farther toward the suction side in the axial direction of the slide valve than the discharge side end face 46P of the slide valve 40.

[0039] In this case, in order to guide the high-pressure gas G2 in the discharge space 23 to the groove portion 48, for example, as shown in Figure 6, a communication groove 49G extending from the discharge-side end portion 48b of the groove portion 48 to the discharge-side end face 46P of the slide valve 40 may be formed in the outer surface 43 of the non-opposing surface 43C of the slide valve 40. As a result, the groove portion 48 and the discharge space 23 communicate with each other via the communication groove 49G, so that the high-pressure gas G2 in the discharge space 23 is guided to the groove portion 48.

[0040] 7, a communication hole 49H that connects from the discharge side end surface 46P of the slide valve 40 to the groove portion 48 may be formed inside the slide valve 40. This allows the groove portion 48 to communicate with the discharge space 23 via the communication hole 49H, so that the high-pressure gas G2 in the discharge space 23 can be guided to the groove portion 48 with a relatively simple configuration.

[0041] In the screw compressor 1 according to some embodiments, the longer the length Lg of the groove 48 in the slide valve axial direction, the larger the area of ​​the groove 48 on which the pressure of the high-pressure gas G2 acts, and the larger the push-up force Fu, thereby further reducing the normal force Fn. Therefore, in the screw compressor 1 according to some embodiments, the length Lg of the groove 48 in the slide valve axial direction, i.e., the distance from the discharge-side end 48b of the groove 48 in the slide valve axial direction to the suction-side end 48e, is set to 5% or more of the length Ls of the slide valve 40 in the slide valve axial direction.

[0042] (Regarding the Downward Force Fd and the Upward Force Fu Acting on the Slide Valve 40) The radial force of the casing 20C acting on the slide valve 40, i.e., the downward force Fd and the upward force Fu, will be described in more detail. FIG. 8A is a diagram for explaining the radial force of the casing 20C acting on a slide valve 40X not provided with a groove 48, showing the case where the slide valve 40X is located in the fully closed position. FIG. 8B is a diagram for explaining the radial force of the casing 20C acting on a slide valve 40X not provided with a groove 48, showing the case where the slide valve 40X is located in a position where 0 < x < 1 in the x-coordinate system. FIG. 8C is a diagram for explaining the radial force of the casing 20C acting on a slide valve 40X not provided with a groove 48, showing the case where the slide valve 40X is located in the fully open position.

[0043] 8A to 8C and later-described Figures 9A to 10C, graph 70 is a graph for explaining the radial force of the casing 20C acting on the slide valves 40, 40X, 40Y. Note that the slide valve 40Y is the slide valve described later in Figures 10A to 10C, and details will be described later. In graph 70 in Figures 8A to 8C and later-described Figures 9A to 10C, the vertical axis represents the pressure of the gas around the slide valves 40, 40X, 40Y, and the horizontal axis represents the position of the slide valves 40, 40X, 40Y in the slide valve axial direction. In the graphs 70 in Figures 8A to 8C and in the graphs in Figures 9A to 10C described later, the pressure P1 shown by the solid graph line represents the pressure of the gas G1 in the tooth groove space acting to press the slide valves 40, 40X, 40Y radially outward of the casing 20C, or the pressure of the gas G2 in the discharge space 23, i.e., the pressure acting to generate the downward force Fd. In the graphs 70 in Figures 8A to 8C and in the graphs in Figures 9A to 10C described later, the pressure P2 shown by the dashed graph line represents the pressure of the gas acting to press the slide valves 40, 40X, 40Y radially inward of the casing 20C, i.e., the pressure acting to generate the upward force Fu. In the following description, the magnitude of the pressure of the gas G2 in the discharge space 23 is assumed to be pressure Pd, and the magnitude of the pressure of the gas G0 in the suction space 22 is assumed to be pressure Ps.

[0044] 8A , when the slide valve 40X is in the fully closed position, the magnitude of the pressure P1 is pressure Pd from the discharge-side end face 46P of the slide valve 40X to the suction-side end 47e in the axial direction of the slide valve of the notch 47. From the suction-side end 47e in the axial direction of the slide valve of the notch 47 to the suction-side end face 45P, the magnitude of the pressure P1 gradually decreases from pressure Pd to pressure Ps toward the suction side in the axial direction of the slide valve.

[0045] 8A, when the slide valve 40X is in the fully closed position, the magnitude of the pressure P2 gradually decreases from the pressure Pd at the position of the discharge-side end face 46P of the slide valve 40X to the pressure Ps at the position of the discharge-side end 28P of the recess 28 toward the suction side in the axial direction of the slide valve. The magnitude of the pressure P2 is the pressure Ps on the suction side in the axial direction of the slide valve relative to the end 28P.

[0046] In graphs 70 in Figures 8A to 8C, the size of the dashed downward arrow 81 represents the magnitude of the downward force Fd due to the pressure P1 per unit distance in the axial direction of the slide valve. In graphs 70 in Figures 8A to 8C, the size of the dashed upward arrow 82 represents the magnitude of the upward force Fu due to the pressure P2 per unit distance in the axial direction of the slide valve. Note that in graphs 70 from Figure 8B onwards, the arrows 81 and 82 are omitted. In graphs 70 in Figures 8A to 8C, the direction and size of the solid arrow 83 indicating the difference between pressures P1 and P2 (P1 - P2), i.e., the difference between pressures P1 and P2 in graph 70, represent the direction and size of the normal force Fn acting on the slide valves 40, 40X, and 40Y per unit distance in the axial direction of the slide valve.

[0047] In the region where pressure P1 is greater than pressure P2 (P2<P1), the value of P1-P2 is a positive value. In the region where the value of P1-P2 is a positive value, a normal force Fn directed toward the radially outward direction of the casing 20C acts on the slide valves 40, 40X, 40Y. In this case, the direction of arrow 83 is downward. In the region where pressure P1 is smaller than pressure P2 (P1<P2), the value of P1-P2 is a negative value. In the region where the value of P1-P2 is a negative value, a normal force Fn directed toward the radially inward direction of the casing 20C acts on the slide valves 40, 40X, 40Y. In this case, the direction of arrow 83 is upward.

[0048] 8A to 8C and the graphs in FIGS. 9A to 10C described later, a region 75 where a normal force Fn acting radially outward of the casing 20C acts is represented by hatching, and a region 76 where a normal force Fn acting radially inward of the casing 20C acts is represented by cross-hatching. The area of ​​the hatched or cross-hatched region 75, 76 corresponds to the value obtained by multiplying the magnitude of the radial normal force Fn of the casing 20C acting per unit distance in the axial direction of the slide valves 40, 40X, 40Y by the distance in the axial direction of the slide valves 40, 40X, 40Y. Therefore, the value obtained by subtracting the cross-hatched region 76 from the area of ​​the hatched region 75 shown in the graph 70 corresponds to the magnitude of the normal force Fn acting radially outward of the casing 20C for the entire slide valves 40, 40X, 40Y.

[0049] (When the position of the slide valve 40X is 0<x<1) Figure 8B shows a case where the position of the slide valve 40X in the x-coordinate system is 0<x<1, and the suction-side end 47e of the notch 47 in the slide valve axial direction is located closer to the discharge side in the rotor axial direction than the discharge-side end 10P of the screw rotor 10. As shown in Figure 8B, the magnitude of the pressure P1 from the discharge-side end face 46P of the slide valve 40X to the discharge-side end 10P of the screw rotor 10 is pressure Pd. Note that, when the suction-side end 47e of the notch 47 is located closer to the discharge side in the rotor axial direction than the discharge-side end 10P of the screw rotor 10, the discharge-side end 10P of the screw rotor 10 determines the discharge position of the high-pressure gas G2 discharged from the tooth groove space to the discharge space 23. From the discharge-side end 10P of the screw rotor 10 to the suction-side end face 45P, the magnitude of the pressure P1 gradually decreases from pressure Pd to pressure Ps as it moves toward the suction side in the slide valve axial direction.

[0050] 8B, the magnitude of pressure P2 is pressure Pd from the position of the discharge side end face 46P of the slide valve 40X to the position of the discharge side end face 55P of the slide valve guide 50. The magnitude of pressure P2 gradually decreases toward the suction side in the slide valve axial direction, from pressure Pd at the position of the discharge side end face 55P of the slide valve guide 50 to pressure Ps at the position of the discharge side end 28P of the recess 28. The magnitude of pressure P2 is pressure Ps on the suction side in the slide valve axial direction of the end 28P.

[0051] 8C , when the slide valve 40X is in the fully open position, the magnitude of the pressure P1 is pressure Pd from the discharge side end face 46P of the slide valve 40X to the discharge side end 10P of the screw rotor 10. From the discharge side end 10P of the screw rotor 10 to the suction side end face 45P, the magnitude of the pressure P1 gradually decreases from pressure Pd to pressure Ps toward the suction side in the axial direction of the slide valve.

[0052] 8C, the magnitude of pressure P2 is pressure Pd from the position of the discharge side end face 46P of the slide valve 40X to the position of the discharge side end face 55P of the slide valve guide 50. The magnitude of pressure P2 gradually decreases toward the suction side in the slide valve axial direction, from pressure Pd at the position of the discharge side end face 55P of the slide valve guide 50 to pressure Ps at the position of the discharge side end 28P of the recess 28. The magnitude of pressure P2 is pressure Ps on the suction side in the slide valve axial direction of the end 28P.

[0053] As shown in Figures 8A to 8C, as is clear from the size of the area of ​​the hatched region 75 in the graph 70, the magnitude of the normal force Fn on the slide valve 40X is greatest when the slide valve 40X is positioned in the fully closed position, and decreases as the slide valve 40X moves toward the fully open position.

[0054] (In the case of a slide valve 40 provided with a groove 48) Figure 9A is a diagram for explaining the radial force of the casing 20C acting on the slide valve 40 according to some embodiments, showing the slide valve 40 in the fully closed position. Figure 9B is a diagram for explaining the radial force of the casing 20C acting on the slide valve 40 according to some embodiments, showing the slide valve 40 in the x-coordinate system in the case where the position of the slide valve 40 is 0 < x < 1. Figure 9C is a diagram for explaining the radial force of the casing 20C acting on the slide valve 40 according to some embodiments, showing the slide valve 40 in the fully open position. Note that in the examples shown in Figures 9A to 9C, the groove 48 is the groove 48 shown in Figures 2, 3, and 5.

[0055] 9A , when the slide valve 40 according to some embodiments is in the fully closed position, the magnitude of the pressure P1 is pressure Pd from the discharge-side end face 46P of the slide valve 40 to the suction-side end 47e of the notch 47. From the suction-side end 47e of the notch 47 to the suction-side end face 45P, the magnitude of the pressure P1 gradually decreases from pressure Pd to pressure Ps toward the suction side in the axial direction of the slide valve.

[0056] 9A , when the slide valve 40 is in the fully closed position, the magnitude of the pressure P2 is pressure Pd from the discharge-side end face 46P of the slide valve 40 to the suction-side end 48e of the groove 48. The magnitude of the pressure P2 gradually decreases toward the suction side in the axial direction of the slide valve, from pressure Pd at the suction-side end 48e of the groove 48 to pressure Ps at the discharge-side end 28P of the recess 28. The magnitude of the pressure P2 is pressure Ps on the suction side in the axial direction of the slide valve relative to end 28P.

[0057] (When the position of the slide valve 40 is 0<x<1) Figure 9B shows a case where, among the cases where the position of the slide valve 40 in the x-coordinate system is 0<x<1, the rotor axial position of the suction-side end 48e of the groove 48 coincides with the rotor axial position of the discharge-side end face 55P of the slide valve guide 50. As shown in Figure 9B, the magnitude of the pressure P1 from the discharge-side end face 46P of the slide valve 40 to the discharge-side end 10P of the screw rotor 10 is pressure Pd. From the discharge-side end 10P of the screw rotor 10 to the suction-side end face 45P, the magnitude of the pressure P1 gradually decreases from pressure Pd to pressure Ps as it moves toward the suction side in the slide valve axial direction.

[0058] 9B, the magnitude of pressure P2 is pressure Pd from the position of the discharge side end face 46P of the slide valve 40 to the position of the discharge side end face 55P of the slide valve guide 50, i.e., the position of the suction side end 48e of the groove portion 48. The magnitude of pressure P2 gradually decreases toward the suction side in the slide valve axial direction, from pressure Pd at the position of the discharge side end face 55P of the slide valve guide 50 to pressure Ps at the position of the discharge side end 28P of the recess 28. The magnitude of pressure P2 is pressure Ps on the suction side in the slide valve axial direction of the slide valve relative to end 28P.

[0059] 9C , when the slide valve 40 is in the fully open position, the magnitude of the pressure P1 is pressure Pd from the discharge side end face 46P of the slide valve 40 to the discharge side end 10P of the screw rotor 10. From the discharge side end 10P of the screw rotor 10 to the suction side end face 45P, the magnitude of the pressure P1 gradually decreases from pressure Pd to pressure Ps toward the suction side in the axial direction of the slide valve.

[0060] 9C, the magnitude of pressure P2 is pressure Pd from the position of the discharge side end face 46P of the slide valve 40 to the position of the discharge side end face 55P of the slide valve guide 50. The magnitude of pressure P2 gradually decreases toward the suction side in the slide valve axial direction, from pressure Pd at the position of the discharge side end face 55P of the slide valve guide 50 to pressure Ps at the position of the discharge side end 28P of the recess 28. The magnitude of pressure P2 is pressure Ps on the suction side in the slide valve axial direction of the end 28P.

[0061] As shown in Figures 9A to 9C, as is clear from the size of the hatched region 75 in graph 70, the magnitude of the normal force Fn on the slide valve 40 in some embodiments is greatest when the slide valve 40 is in the fully closed position, and decreases as the slide valve 40 moves toward the fully open position.

[0062] 8A, when the graph line of pressure P2 is traced from the discharge side to the suction side in the rotor axial direction, the position in the rotor axial direction of point 71 where pressure P2 starts to decrease from pressure Pd is the position of the discharge-side end face 46P of the slide valve 40X. In contrast, in graph 70 in FIG. 9A, when the graph line of pressure P2 is traced from the discharge side to the suction side in the rotor axial direction, the position in the rotor axial direction of point 71 described above is the position of the suction-side end 48e of the groove portion 48.

[0063] In this way, by providing the groove 48 in the slide valve 40, the point 71 where the pressure P2 starts to decrease from the pressure Pd moves toward the suction side in the rotor axial direction, and therefore the area of ​​the hatched region 75, which is the region where the normal force Fn acting radially outward of the casing 20C acts in the graph 70 in Figures 8A and 9A, becomes smaller. In other words, by providing the groove 48 in the slide valve 40, the magnitude of the normal force Fn acting on the slide valve 40 toward the radially outward of the casing 20C becomes smaller.

[0064] (Regarding the Position of the Intake-Side End 48e of the Groove 48) By moving the position of the inlet-side end 48e of the groove 48 closer to the inlet side in the axial direction of the slide valve, the length Lg of the groove 48 in the axial direction of the slide valve can be increased, thereby increasing the area of ​​the groove 48, thereby increasing the upward force Fu acting on the groove 48. Furthermore, by increasing the upward force Fu acting on the groove 48, the normal force Fn can be further reduced. However, if the normal force Fn is excessively small, there is a risk that the slide valve 40 may rise and come into contact with the screw rotor 10 due to, for example, fluctuations (pulsations) in the gas pressure in the tooth groove space. Therefore, it is desirable that the normal force Fn pressing the slide valve 40 radially outward from the casing 20C be at least a certain magnitude.

[0065] Fig. 10A is a diagram for explaining the radial force of the casing 20C acting on the slide valve 40Y in which the length Lg of the groove 48 in the slide valve axial direction is unnecessarily large, showing the case where the slide valve 40Y is located in the fully closed position. Fig. 10B is a diagram for explaining the radial force of the casing 20C acting on the slide valve 40Y in which the length Lg of the groove 48 in the slide valve axial direction is unnecessarily large, showing the case where the position of the slide valve 40Y in the x-coordinate system is at a position where 0 < x < 1. Fig. 10C is a diagram for explaining the radial force of the casing 20C acting on the slide valve 40Y in which the length Lg of the groove 48 in the slide valve axial direction is unnecessarily large, showing the case where the slide valve 40Y is located in the fully open position.

[0066] 10A , when the slide valve 40Y is in the fully closed position, the magnitude of the pressure P1 is pressure Pd from the discharge side end face 46P of the slide valve 40Y to the suction side end 47e of the notch 47. From the suction side end 47e of the notch 47 to the suction side end face 45P, the magnitude of the pressure P1 gradually decreases from pressure Pd to pressure Ps toward the suction side in the axial direction of the slide valve.

[0067] 10A , when the slide valve 40Y is in the fully closed position, the magnitude of the pressure P2 is pressure Pd from the discharge-side end face 46P of the slide valve 40Y to the suction-side end 48e of the groove 48. The magnitude of the pressure P2 gradually decreases toward the suction side in the axial direction of the slide valve, from pressure Pd at the suction-side end 48e of the groove 48 to pressure Ps at the discharge-side end 28P of the recess 28. The magnitude of the pressure P2 is pressure Ps on the suction side in the axial direction of the slide valve relative to end 28P.

[0068] 10A , when the slide valve 40Y is positioned at the fully closed position, a region 76 appears in the region relatively closer to the discharge side in the axial direction of the slide valve in the graph 70, where a normal force Fn acting radially inward of the casing 20C acts. In the example shown in FIG. 10A , the area of ​​the region 76 is approximately equal to the area of ​​the region 75 where the normal force Fn acting radially outward of the casing 20C acts. Therefore, for the entire slide valve 40Y, the normal force Fn pressing the slide valve 40Y radially outward of the casing 20C becomes excessively small, or a normal force Fn pressing the slide valve 40Y radially inward of the casing 20C is generated. Therefore, there is a risk that the slide valve 40Y may float up and come into contact with the screw rotor 10 due to, for example, fluctuations (pulsations) in the pressure of the gas in the tooth groove space.

[0069] (When the position of the slide valve 40Y is 0<x<1) Figure 10B shows a case where the position of the slide valve 40Y in the x-coordinate system is 0<x<1, and the rotor axial direction position of the suction-side end 48e of the groove 48 is between the position of the discharge-side end 10P of the screw rotor 10 and the rotor axial direction position of the discharge-side end face 55P of the slide valve guide 50. Note that the arrow 83 is omitted in Figure 10B. As shown in Figure 10B, from the discharge-side end face 46P of the slide valve 40Y to the discharge-side end 10P of the screw rotor 10, the magnitude of the pressure P1 is pressure Pd. From the discharge-side end 10P of the screw rotor 10 to the suction-side end face 45P, the magnitude of the pressure P1 gradually decreases from pressure Pd to pressure Ps as it moves toward the suction side in the slide valve axial direction.

[0070] 10B, the magnitude of pressure P2 is pressure Pd from the position of discharge side end face 46P of slide valve 40Y to the position of suction side end 48e of groove 48. The magnitude of pressure P2 gradually decreases from pressure Pd at the position of suction side end 48e of groove 48 to pressure Ps at the position of suction side end face 45P toward the suction side in the slide valve axial direction.

[0071] 10B , a region 76 appears in a region relatively closer to the suction side in the axial direction of the slide valve in the graph 70, where a normal force Fn acting radially inward of the casing 20C is applied. In the example shown in FIG. 10B , the area of ​​the region 76 is approximately equal to the area of ​​the region 75 in which a normal force Fn acting radially outward of the casing 20C is applied. Therefore, for the entire slide valve 40Y, the normal force Fn pressing the slide valve 40Y radially outward of the casing 20C becomes excessively small, or a normal force Fn pressing the slide valve 40Y radially inward of the casing 20C is generated. Therefore, there is a risk that the slide valve 40Y may be lifted up and come into contact with the screw rotor 10 due to, for example, fluctuations (pulsations) in the pressure of the gas in the tooth groove space.

[0072] 10C , when the slide valve 40Y is in the fully open position, the magnitude of the pressure P1 is pressure Pd from the discharge side end face 46P of the slide valve 40Y to the discharge side end 10P of the screw rotor 10. From the discharge side end 10P of the screw rotor 10 to the suction side end face 45P, the magnitude of the pressure P1 gradually decreases from pressure Pd to pressure Ps toward the suction side in the axial direction of the slide valve.

[0073] 10C, the magnitude of pressure P2 is pressure Pd from the position of discharge side end face 46P of slide valve 40Y to the position of suction side end 48e of groove 48. The magnitude of pressure P2 gradually decreases from pressure Pd at the position of suction side end 48e of groove 48 to pressure Ps at the position of suction side end face 45P toward the suction side in the slide valve axial direction.

[0074] In the example shown in Figure 10C, there is no area 76 where a normal force Fn acting radially inward of the casing 20C acts, and the area of ​​the area 75 where a normal force Fn acting radially outward of the casing 20C acts is secured to a certain extent, so there is a relatively small possibility that the slide valve 40Y will float up and come into contact with the screw rotor 10.

[0075] As described above, if the length Lg of the groove 48 in the slide valve axial direction is unnecessarily large, there is a risk that the slide valve 40 will float up and come into contact with the screw rotor 10. As a result of extensive study by the inventors, it has been found that the length Lg of the groove 48 in the slide valve axial direction is preferably 30% or less of the length Ls of the slide valve 40 in the slide valve axial direction. Therefore, in the screw compressor 1 according to some embodiments, with regard to the position of the slide valve 40 in the rotor axial direction, when the position of the discharge-side end face 46P of the slide valve 40 is 0% and the position of the suction-side end face 45P of the slide valve 40 is 100%, as shown in FIG. 2 , the position of the suction-side end 48e of the groove 48 in the slide valve axial direction is set to a position where the position of the slide valve 40 in the rotor axial direction is 30% or less. This makes it possible to reduce the driving force for moving the slide valve 40 along the rotor axial direction and reduce the possibility of the slide valve 40 coming into contact with the screw rotor 10.

[0076] (Regarding the position of the groove 48 in the circumferential direction about the central axis AXs) The discharge pressure of the high-pressure gas G2 acts perpendicularly on the bottom surface 48a of the groove 48. Therefore, to effectively generate the upward force Fu, at least a portion of the groove 48 may be located within the following range. That is, as shown in FIGS. 3 and 4 , when the slide valve 40 is viewed from the rotor axial direction (the slide valve axial direction), at least a portion of the groove 48 may be located within a range of up to 45 degrees circumferentially on one side and the other side of the slide valve 40 on the non-opposing surface 43C, across a second line segment L2 that is perpendicular to a first line segment L1 connecting a pair of connection points 43d between the pair of opposing surfaces 43A, 43B and the non-opposing surface 43C and passes through the central axis AXs of the slide valve 40. This allows the upward force Fu to be effectively generated, and the normal force Fn that presses the slide valve 40 radially outward from the casing 20C to be effectively reduced.

[0077] In the screw compressor 1 according to some embodiments, the circumferential angle range of the groove 48 from one end 48 d to the other end 48 d in the circumferential direction about the central axis AXs may be 180 degrees or less. The discharge pressure of the high-pressure gas G2 acts perpendicularly to the bottom surface 48 a of the groove 48. Therefore, if the circumferential angle range of the groove 48 from one end 48 d to the other end 48 d in the circumferential direction exceeds 180 degrees, not only will an upward force Fu pressing the slide valve 40 radially inward of the casing 20C be generated, but also a downward force Fd pressing the slide valve 40 radially outward of the casing 20C will be generated, thereby reducing the effect of the upward force Fu pressing the slide valve 40 radially inward of the casing 20C. By setting the circumferential angle range of the groove 48 from one end 48d on one side in the circumferential direction about the central axis AXs to the other end 48d to be 180 degrees or less, it is possible to reduce the possibility of undesirably reducing the effect of the pushing-up force Fu that presses the slide valve 40 radially inward of the casing 20C. Furthermore, by setting the circumferential angle range of the groove 48 from one end 48d on one side in the circumferential direction about the central axis AXs to the other end 48d to be 180 degrees or less, the area of ​​the groove 48 does not become unnecessarily large, thereby reducing the processing cost for providing the groove 48.

[0078] (Regarding the recess 28) In the screw compressor 1 according to some embodiments, the casing 20C may have an inner wall surface 25 that faces the non-opposing surface 43C of the slide valve 40 and serves as a support surface that supports the slide valve 40 movably along the rotor axial direction. The inner wall surface 25 has a recess 28 formed therein that extends along the rotor axial direction. The recess 28 is in communication with the suction port 12.

[0079] If the recess 28 is not provided in the casing 20C, for example, the position of the discharge-side end 28P of the recess 28 in FIG. 9A would be the same as being located closer to the suction side than the suction-side end face 45P of the slide valve 40. In this case, in the graph 70 in FIG. 9A, the point 72 where the pressure P2 gradually decreases from the pressure Pd to reach the pressure Ps would move from the position of the discharge-side end 28P of the recess 28 in FIG. 9A to the position of the suction-side end face 45P of the slide valve 40, and the pressure P2 would change as shown by the dashed-dotted graph line 73. As a result, at least a portion of the dashed-dotted graph line 73 representing the pressure P2 would change above the graph line representing the pressure P1. Therefore, the area of ​​the hatched region 75 would be excessively small, and there is a risk that the slide valve 40 would lift up and come into contact with the screw rotor 10 due to, for example, fluctuations (pulsations) in the gas pressure in the tooth groove space.

[0080] In the screw compressor 1 according to some embodiments, the area of ​​the hatched region 75 is secured to a certain extent, so that the magnitude of the normal force Fn acting radially outward of the casing 20C can be set to the level necessary to prevent the slide valve 40 from floating up, thereby reducing the possibility of the slide valve 40 floating up and coming into contact with the screw rotor 10.

[0081] In the screw compressor 1 according to some embodiments, the suction-side end 48e of the groove 48 is located closer to the discharge side in the rotor axial direction than the recess 28 when the slide valve 40 is located at the suction-most position, i.e., at the fully closed position. This separates the groove 48 and the recess 28 in the rotor axial direction, making it difficult for the high-pressure gas G2 in the discharge space 23 introduced into the groove 48 to leak into the bypass passage 30.

[0082] The present disclosure is not limited to the above-described embodiments and includes modifications of the above-described embodiments and appropriate combinations of these embodiments. For example, in the screw compressor 1 according to some of the above-described embodiments, two or more grooves 48 may be provided at intervals in the circumferential direction centered on the central axis AXs of the slide valve 40. In this case, the circumferential angle range from the end 48 d on one circumferential side of the groove 48 located on the one circumferential side of the plurality of grooves 48 provided at intervals in the circumferential direction to the end 48 d on the other circumferential side of the groove 48 located on the other circumferential side may be 180 degrees or less.

[0083] The contents of the above-described embodiments can be understood, for example, as follows: (1) A screw compressor 1 according to at least one embodiment of the present disclosure includes a screw rotor 10 including a pair of a male rotor 10A and a female rotor 10B, a rotor casing (casing 20C) that houses the screw rotor 10 and communicates with an intake port 12 for sucking in a gas to be compressed and a discharge port 13 for discharging the compressed gas, and a capacity-control slide valve 40 that is provided movably along the rotor axial direction of the screw rotor 10. The slide valve 40 has a pair of opposing surfaces 43A, 43B that are continuous with the inner wall surface 21W that forms the rotor chamber 21 in the rotor casing (casing 20C) and that face the pair of male rotors 10A and female rotor 10B, a non-opposing surface 43C on the surface (outer surface 43) of the slide valve 40 that is opposite the pair of opposing surfaces 43A, 43B when the slide valve 40 is viewed from the rotor axial direction, and a groove 48 that is formed in the non-opposing surface 43C and communicates with the discharge space 23 from which the compressed gas is discharged. The length Lg of the groove 48 in the rotor axial direction is 5% or more of the length Ls of the slide valve 40 in the rotor axial direction. With respect to the position of the slide valve 40 in the rotor axial direction, when the position of the end (discharge-side end face 46P) on the discharge port side (discharge side) of the slide valve 40 is defined as 0% and the position of the end (suction-side end face 45P) on the suction port side (suction side) of the slide valve 40 is defined as 100%, the position of the end (suction-side end face 45P) on the suction port side (suction side) of the groove 48 is a position where the position in the rotor axial direction of the slide valve 40 is 30% or less. When the slide valve 40 is viewed from the rotor axial direction, at least a part of the groove 48 exists within a range of up to 45 degrees in the circumferential direction to each of one side and the other side of the slide valve 40 on the non-opposing surface 43C, across a second line segment L2 that is perpendicular to a first line segment L1 connecting a pair of connection points 43d between the pair of opposing surfaces 43A, 43B and the non-opposing surface 43C and passes through the central axis AXs of the slide valve 40.

[0084] According to the configuration (1) above, the groove 48 provided in the above-mentioned range communicates with the discharge space 23 from which the compressed gas is discharged, so that the discharge pressure of the compressed gas acts on this groove 48. As a result, a pressing force (push-up force Fu) that presses the slide valve 40 inward in the radial direction of the rotor casing (radially inward of the casing 20C) is generated, so that the pressing force (normal force Fn) that presses the slide valve 40 outward in the radial direction of the rotor casing (casing 20C) can be reduced, and the driving force for moving the slide valve 40 along the rotor axial direction of the screw rotor 10 can be reduced. Therefore, the size of the casing 20 of the screw compressor 1 and the size of the hydraulic pump can be made relatively small.

[0085] (2) In some embodiments, in the configuration of (1) above, the circumferential angle range from one circumferential end (end 48d) of the groove portion 48 to the other circumferential end (end 48d) may be 180 degrees or less.

[0086] The discharge pressure of the compressed gas acts perpendicularly on the surface (bottom surface 48a) of the groove 48. Therefore, when the circumferential angular range from one circumferential end (end 48d) to the other circumferential end (end 48d) of the groove 48 exceeds 180 degrees, not only a pressing force (push-up force Fu) pressing the slide valve 40 radially inward of the rotor casing (casing 20C) but also a pressing force (push-down force Fd) pressing the slide valve 40 radially outward of the rotor casing (casing 20C) is generated, thereby reducing the effect of the pressing force (push-up force Fu) pressing the slide valve radially inward of the rotor casing. The configuration (2) above reduces the possibility of undesirably reducing the effect of the pressing force (push-up force Fu) pressing the slide valve 40 radially inward of the rotor casing (casing 20C). Furthermore, according to the above configuration (2), the area of ​​the groove 48 is not unnecessarily large, so the cost of processing for providing the groove 48 can be reduced.

[0087] (3) In some embodiments, in the configuration of (1) or (2) above, the groove portion 48 may have an opening 48c that opens to the end (discharge side end surface 46P) on the discharge port side (discharge side) of the slide valve 40.

[0088] According to the above configuration (3), the groove portion 48 can be connected to the discharge space 23 with a relatively simple configuration.

[0089] (4) In some embodiments, in the configuration of (1) or (2) above, the slide valve 40 may have a communication hole 49H that connects the discharge space 23 and the groove portion 48.

[0090] According to the above configuration (4), the groove portion 48 can be connected to the discharge space 23 with a relatively simple configuration.

[0091] (5) In some embodiments, in any of the configurations (1) to (4) above, the rotor casing (casing 20C) may have a support surface (inner wall surface 25) that faces the non-opposing surface 43C of the slide valve 40 and supports the slide valve 40 movably along the rotor axial direction. The support surface (inner wall surface 25) may have a recess 28 formed therein that extends along the rotor axial direction. The recess 28 may be in communication with the suction port 12.

[0092] According to the configuration (5) above, the magnitude of the force (normal force Fn) directed radially outward from the casing 20C can be set to the level necessary to prevent the slide valve 40 from floating up, thereby reducing the possibility of the slide valve 40 floating up and coming into contact with the screw rotor 10.

[0093] (6) In some embodiments, in the configuration of (5) above, the end 48e of the groove portion 48 on the suction port side (suction side) may be positioned closer to the discharge port side (discharge side) in the rotor axial direction than the recess 28 when the slide valve 40 is positioned closest to the suction port side (suction side).

[0094] According to the configuration (6) above, the groove 48 and the recess 28 are separated in the rotor axial direction, so that gas introduced into the groove 48 is less likely to leak to the intake port side (intake side).

[0095] REFERENCE SIGNS LIST 1 Screw compressor 10 Screw rotor 10A Male rotor 10B Female rotor 12 Suction port 13 Discharge port 20 Casing 20C Casing (casing part) 21 Rotor chamber 21W Inner wall surface 22 Suction space 23 Discharge space 25 Inner wall surface 28 Recessed portion 28P End portion 30 Bypass passage 40 Slide valve 43 Outer surface 43A, 43B Opposing surface 43C Non-opposing surface 43d Connection point 44 Sliding surface 45 Suction side end 45P Suction side end face 46 Discharge side end 46P Discharge side end face 47 Notch 48 Groove portion 48a Bottom surface 48b End portion 48c Opening 48d End portion 48e End portion 49G Communication groove 49H Communication hole 50 Slide valve guide 51 Guide surface

Claims

1. A device comprising: a screw rotor including a pair of male and female rotors; a rotor casing that houses the screw rotor and communicates with an intake port for sucking in compressed gas and a discharge port for discharging the compressed gas; and a capacity-control slide valve that is provided movably along the rotor axial direction of the screw rotor, wherein the slide valve has: a pair of opposing surfaces that face the pair of male and female rotors and are continuous with an inner wall surface that forms a rotor chamber in the rotor casing; a non-opposing surface on the surface of the slide valve that is opposite the pair of opposing surfaces when the slide valve is viewed from the rotor axial direction; and a groove that is formed on the non-opposing surface and communicates with a discharge space from which the compressed gas is discharged, the length of the groove in the rotor axial direction being 5% or more of the length of the slide valve in the rotor axial direction; and when the position of the end of the slide valve on the discharge port side is set to 0% and the position of the end of the slide valve on the suction port side is set to 100%, a screw compressor in which an end of the groove on the suction port side is positioned at a position where its position in the rotor axial direction of the slide valve is 30% or less, and at least a part of the groove is present on the non-opposing surfaces within a range of up to 45 degrees in the circumferential direction to one side and the other side of the slide valve in the circumferential direction, across a second line segment that is perpendicular to a first line segment connecting a pair of connection points between the pair of opposing surfaces and the non-opposing surfaces and passes through a central axis of the slide valve, when the slide valve is viewed in the rotor axial direction.

2. A screw compressor according to claim 1, wherein the angular range in the circumferential direction from one end to the other end of the groove is 180 degrees or less.

3. The screw compressor according to claim 1 or 2, wherein the groove has an opening that opens to an end of the slide valve on the discharge port side.

4. The screw compressor according to claim 1 or 2, wherein the slide valve has a communication hole that connects the discharge space with the groove.

5. A screw compressor according to claim 1 or 2, wherein the rotor casing has a support surface that faces the non-opposing surface of the slide valve and supports the slide valve movably along the rotor axial direction, the support surface having a recess formed therein that extends along the rotor axial direction, and the recess communicates with the suction port.

6. The screw compressor according to claim 5, wherein the end of the groove on the suction port side is located closer to the discharge port in the rotor axial direction than the recess when the slide valve is located closest to the suction port.

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