Screw-type compressor

Abstract

To provide a screw-type compressor that can suppress deformation around the opening. [Solution] The compressor 1 comprises a pair of male and female rotors 2, a rotor chamber 7 that houses the pair of rotors 2 and is divided in the circumferential direction into an intake side and a discharge side, and a casing 6 having a bore wall 8 that defines the rotor chamber 7, an opening 20 provided in the bore wall 8 that opens the intake side of the rotor chamber 7 radially, a discharge port 14 that discharges compressed fluid from the discharge side of the rotor chamber 7, and a projection 40 provided on the periphery of the opening 20 and projecting outward from the bore wall 8.

Description

Technical Field

[0005] , , , ,

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

Background Art

[0002] Patent Document 1 discloses a screw compressor having a bore wall that defines a rotor chamber for accommodating a pair of rotors. The bore wall includes a partial cylindrical male bore wall for accommodating a male rotor and a partial cylindrical female bore wall for accommodating a female rotor. The male bore wall and the female bore wall have a certain thickness. In an axial cross-section, an arc indicating the inner peripheral surface of the male bore wall and an arc indicating the inner peripheral surface of the female bore wall form a cusp at two points. An arc indicating the outer peripheral surface of the male bore wall and an arc indicating the outer peripheral surface of the female bore wall also form a cusp at two points.

[0003] Patent Document 2 discloses a screw compressor provided with an opening for communicating the rotor chamber to the outside and a discharge port in the bore wall. The opening opens the rotor chamber in the radial direction and is also referred to as a radial port. The opening is used for assembly or maintenance work and also sucks fluid into the rotor chamber. The discharge port discharges the compressed fluid from the rotor chamber. The opening is separated from the discharge port in both the axial direction and the circumferential direction.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] When the compressor starts, the area around the discharge port rapidly heats up due to the compressed fluid, while the area around the opening remains cool because relatively cold fluid flows through it before compression. Due to this temperature difference, the bore wall does not expand uniformly during the heating process, but rather expands unevenly in the axial and circumferential directions. At this time, the bore wall deforms unevenly, partly due to the low rigidity around the opening, and it has been found that deformation such as inward displacement around the opening may occur before the area around the opening has sufficiently heated up.

[0006] The present invention aims to provide a screw-type compressor capable of suppressing deformation around the opening. [Means for solving the problem]

[0007] One aspect of the present invention provides a screw-type compressor comprising: a pair of male and female rotors; a rotor chamber that houses the pair of rotors and is divided in the circumferential direction into a suction side and a discharge side; a casing having a bore wall defining the rotor chamber; an opening provided in the bore wall that radially opens the suction side of the rotor chamber; a discharge port for discharging compressed fluid from the discharge side of the rotor chamber; and a projection provided on the periphery of the opening and projecting outward from the bore wall.

[0008] According to the above configuration, the rigidity around the opening is improved by providing the protrusion. Even when the bore wall attempts to deform due to a temperature difference between the discharge side and the suction side (circumferential temperature difference) or a temperature difference between the discharge end face side and the suction end face side in the rotor chamber (axial temperature difference), inward displacement deformation around the opening can be suppressed. Furthermore, since the protrusion extends outward from the bore wall, it does not affect the inner circumferential surface, and an appropriate clearance can be secured between the bore wall and the rotor.

[0009] The bore wall includes a male bore wall defining a male rotor chamber for housing the male rotor of the pair of rotors, and a female bore wall defining a female rotor chamber for housing the female rotor of the pair of rotors, and in a cross section perpendicular to the axis, the outer circumferential surface on the suction side of the bore wall, excluding the protruding portion, at the connection portion between the male bore wall and the female bore wall, may extend along the common tangent between the inner circumferential surface of the male bore wall on the suction side and the inner circumferential surface of the female bore wall on the suction side.

[0010] According to the above configuration, the thickness of the bore wall increases on the suction side where the opening is located. As a result, the rigidity of the bore wall is improved on the suction side including the opening, and deformation around the opening can be further suppressed. In addition, the outer surface of the bore wall becomes flat along the common tangent, eliminating the cusp. Therefore, stress concentration caused by deformation around the opening can be mitigated.

[0011] The casing is formed of casting, and in the cross-section perpendicular to the axis, the end face of the protrusion may extend along the common tangent between the inner surface of the male bore wall on the suction side and the inner surface of the female bore wall on the suction side.

[0012] According to the above configuration, the thickness of the protruding portion can be made uniform, making it less likely to cause casting defects such as shape defects or distortion of the protruding portion when forming the casing by casting.

[0013] The opening may be a through hole, and the entire circumference of the opening may be surrounded by the protruding portion.

[0014] With the above configuration, the area around the opening is less prone to deformation compared to the case where the opening is formed by cutting a notch in the bore wall.

[0015] The screw-type compressor in question may also be an oil-free machine.

[0016] According to the above configuration, by not adopting an oil injection structure, the axial temperature difference of the bore wall becomes large. Providing a protruding portion in a screw compressor of such a form is beneficial because it can effectively suppress deformation around the opening.

Effect of the Invention

[0017] According to the present invention, it is possible to provide a screw compressor capable of suppressing deformation around the opening.

Brief Description of the Drawings

[0018] [Figure 1] Cross-sectional view of the screw compressor according to the first embodiment. [Figure 2] Perspective view of the bore wall and rotor of FIG. 1. [Figure 3] View taken along the arrow III-III of FIG. 1. [Figure 4] Plan view of the bore wall and rotor of FIG. 2. [Figure 5] Partial cross-sectional view of the screw compressor shown along the line V-V of FIG. 4. [Figure 6] Partial cross-sectional view of the screw compressor shown along the line VI-VI of FIG. 4. [Figure 7] Plan view of the bore wall and rotor of the screw compressor according to the second embodiment. [Figure 8] Perspective view of the bore wall of the screw compressor according to the conventional example.

Modes for Carrying Out the Invention

[0019] Hereinafter, embodiments will be described with reference to the drawings. In addition, the same or corresponding elements are denoted by the same reference numerals throughout the drawings, and redundant detailed descriptions are omitted.

[0020] Figure 1 is a cross-sectional view of the compressor 1 according to the first embodiment, Figure 2 is a perspective view showing only the pair of rotors 2 and the bore wall 8 extracted from the compressor 1 in Figure 1, and Figure 3 is a view taken along the line III-III in Figure 1, that is, a view of the casing 6 in Figure 1 seen axially from the suction end face 8b side, with the rotor 2 omitted from the illustration to clearly show the rotor chamber 7. In the following description, "axial direction," "radial direction," and "circumferential direction" are based on the axis of the rotor 2. "Up" and "down" correspond to the up and down directions on the paper in Figures 1 and 3, but are merely examples of the radial direction or the circumferential direction, and can be appropriately changed depending on the orientation of the compressor 1. "Up" corresponds to the suction side of the rotor chamber 7 in the circumferential direction, and "down" corresponds to the discharge side of the rotor chamber 7 in the circumferential direction.

[0021] The compressor 1 according to this embodiment is a screw-type compressor and is oil-free. The compressor 1 comprises a pair of male rotors 2m and female rotors 2f (sometimes collectively referred to as rotor 2), a casing 6, and a cover 18.

[0022] Referring to Figures 1 and 2, the female rotor 2f has a rotor shaft 3f, a plurality of helical teeth 4f provided on the outer circumference of the rotor shaft 3f, and helical tooth grooves 5f defined between adjacent teeth 4f. The rotor shaft 3f is rotatably supported by the casing 6 and cover 18 via bearings 19, so as to be about the axis Af of the female rotor 2f.

[0023] Referring to Figure 2, the male rotor 2m also has a rotor shaft (not shown), teeth 4m, and tooth grooves 5m, similar to the above, and is supported so as to be rotatable around its own axis Am. The rotor 2 is housed in the casing 6 with its two axes Am and Af extending parallel to each other, and with the teeth 4m of the male rotor 2m engaged with the tooth grooves 5f of the female rotor 2f in a meshed state. The male rotor 2m is mechanically connected to a drive mechanism (not shown) including a motor, and is rotationally driven by the drive mechanism. The female rotor 2f may be rotationally driven by the drive mechanism instead of or in addition to the male rotor 2m.

[0024] Referring to Figure 1, the casing 6 has a bore wall 8, an end wall 8a, and an outer case 9 surrounding the bore wall 8. The inner surfaces of the bore wall 8 and the end wall 8a define a rotor chamber 7 that houses the rotor 2. The rotor chamber 7 is divided in the circumferential direction into an intake side and a discharge side by housing the rotor 2. The casing 6 is a metal casting having a double structure of a bore wall 8 and an outer case 9 as a single unit, and the bore wall 8 can be connected to the outer case 9 via a connection part 10. The outer case 9 is generally elliptical and defines an internal space 11 in which the bore wall 8 is housed, and is open at one end in the axial direction (right side of the plane of Figure 1). The cover 18 is fastened to one end of the outer case 9 and closes the outer case 9.

[0025] Referring to Figures 2 and 3, the rotor chamber 7 includes a male rotor chamber 7m that houses the male rotor 2m and a female rotor chamber 7f that houses the female rotor 2f, and is open at one axial end (suction end face 8b side). The bore wall 8 includes a male bore wall 8m that defines the male rotor chamber 7m and a female bore wall 8f that defines the female rotor chamber 7f. The other axial end of the rotor chamber 7 (discharge end face side) is closed by an end wall 8a.

[0026] The male bore wall 8m and the female bore wall 8f are partially cylindrical in a C-shape when viewed in the axial direction. The centerline of the male bore wall 8m substantially coincides with the axis Am of the male rotor 2m, and the centerline of the female bore wall 8f substantially coincides with the axis Af of the female rotor 2f, and the two centerlines extend parallel to each other. The male bore wall 8m and the female bore wall 8f are continuous at two points, upper and lower. As a result, the bore wall 8 as a whole is roughly cocoon-shaped or gourd-shaped when viewed in the axial direction, and the male rotor chamber 7m and the female rotor chamber 7f are spatially connected to each other and can accommodate the male rotor 2m and the female rotor 2f in a meshed state.

[0027] Referring to Figures 1 and 3, the internal space 11 of the casing 6 includes a suction passage 12 that guides fluid drawn into the compressor 1 from outside the compressor 1. The suction passage 12 communicates with a suction port 13 formed in the cover 18. The suction port 13 is connected to an opening at one axial end of the bore wall 8.

[0028] The casing 6 is provided with a discharge port 14. The discharge port 14 is provided, for example, at the other end of the bore wall 8 in the axial direction, and is recessed or penetrates the end wall 8a. The discharge port 14 is provided on the lower side of the bore wall 8 in the circumferential direction.

[0029] Referring to Figures 1 to 3, an opening 20 is provided in the bore wall 8. The opening 20 is also called a radial port. The opening 20 radially opens the intake side of the rotor chamber 7 and connects the intake passage 12 to the rotor chamber 7 via a separate route from the intake port 13. The opening 20 is provided axially towards the intake end face 8b side of the bore wall 8. The opening 20 is provided at the top of the bore wall 8 in the circumferential direction. The opening 20 makes it possible to see inside the rotor chamber 7 from the outer circumference of the bore wall 8. Workers can perform assembly or maintenance work on the compressor 1 while visually checking the meshing state of the rotor 2 housed in the rotor chamber 7 through the opening 20.

[0030] The opening 20 and the discharge port 14 are positioned on opposite sides of each other with respect to the straight line connecting the axis Am of the male rotor 2m and the axis Af of the female rotor 2f, when viewed in the axial direction or in a cross-sectional area perpendicular to the axis (see Figure 3 or Figure 5). In the illustrated example, the straight line connecting the axes Am and Af extends horizontally, with the opening 20 positioned on the upper side and the discharge port 14 positioned on the lower side. In this invention, with respect to the plane containing the axes Am and Af, the side where the opening 20 is located is considered the suction side, and the side where the discharge port 14 is located is considered the discharge side.

[0031] When rotor 2 is driven to rotate, the male rotor 2m and female rotor 2f rotate synchronously in a meshed state. Fluid also flows from outside the casing 6 into the suction passage 12. A portion of the fluid is drawn axially into the rotor chamber 7 through the suction port 13. Another portion of the fluid may be drawn radially from the suction passage 12 through the opening 20 to the suction side of the rotor chamber 7. The drawn-in fluid flows into the tooth grooves 5m and 5f, where it is compressed and heated while being transported axially. The compressed fluid is discharged from the discharge side of the rotor chamber 7 to the outside of the casing 6 through the discharge port 14.

[0032] Hereafter, unless otherwise specified, the fluid compressed by compressor 1 will be referred to as air. Before compressor 1 is started, the casing temperature throughout the casing 6 is equivalent to the ambient temperature (e.g., ambient temperature), i.e., room temperature. When compressor 1 is started, the discharge side of casing 6 rises in temperature due to exposure to the high temperature of the compressed air, while the suction side of casing 6 does not change significantly from room temperature because the incoming air is ambient temperature. As compressor 1 continues to operate, the heat from the discharge side is transferred to the entire casing 6. The casing temperature throughout the casing 6 becomes higher than the ambient temperature.

[0033] During the transient period from the start-up of compressor 1 until the casing temperature stabilizes at a high temperature, a large temperature difference occurs between the suction side and the discharge side, or between the suction end face and the discharge end face, especially immediately after startup. Thermal deformation of casing 6 begins on the discharge side, and thermal deformation on the suction side occurs with a delay. In this process, distortion may occur on the suction side of casing 6. If the distortion is large, the suction side of casing 6 may come into contact with rotor 2.

[0034] In particular, in this embodiment, since the discharge port 14 and the opening 20 are separated not only axially but also circumferentially, the temperature difference is difficult to eliminate (transient conditions tend to be prolonged), and distortion is likely to occur on the suction side. In this embodiment, since the compressor 1 is an oil-free machine, the temperature difference between the suction side and the discharge side, or between the suction end face side and the discharge end face side, tends to be larger compared to the case where the compressor 1 is an oil-injection machine, and distortion is likely to occur on the suction side. Furthermore, in this embodiment, an opening 20 that can be used for various operations is provided on the suction side of the bore wall 8, separate from the suction port 13. Therefore, the rigidity of the suction side is relatively low, and distortion is likely to occur on the suction side. In the compressor 1 according to this embodiment, the following configuration effectively suppresses distortion on the suction side under transient conditions.

[0035] Figure 8 is a perspective view of a bore wall 8 according to a conventional example. Referring together to Figures 2 and 8, the male bore wall 8m has a male inner surface 31m that defines the male rotor chamber 7m and a male outer surface 32m opposite to the rotor chamber 7. The female bore wall 8f has a female inner surface 31f that defines the female rotor chamber 7f and a female outer surface 32f opposite to the rotor chamber 7.

[0036] In the following explanation, the diameter of the male inner surface 31m will be referred to as "male inner diameter rm," the diameter of the female inner surface 31f as "female inner diameter rf," the diameter of the male outer surface 32m as "male outer diameter Rm," and the diameter of the female outer surface 32f as "female outer diameter Rf." Furthermore, in a cross section perpendicular to the axes, the straight-line distance between the two axes Am and Af will be referred to as "center-to-center distance D" (see Figure 5).

[0037] The male inner surface 31m and the female inner surface 31f are arcs when viewed in the axial direction. The male inner diameter rm and the female inner diameter rf are constant in the axial direction. The male inner diameter rm is slightly larger than the diameter of the tip circle of the male rotor 2m. The female inner diameter rf is slightly larger than the diameter of the tip circle of the female rotor 2f and smaller than the male inner diameter rm. The center-to-center distance D is greater than the difference between the male inner diameter rm and the female inner diameter rf, and less than the sum of the male inner diameter rm and the female inner diameter rf. Therefore, when viewed in the axial direction or in a cross-section perpendicular to the axis, the arc of the male inner surface 31m and the arc of the female inner surface 31f intersect at two points on opposite sides of the straight line connecting the axes Af and Am, i.e., on the suction side and the discharge side. In the following description, the lower of the two intersections will be called the "first inner cusp 33a" and the upper one will be called the "second inner cusp 33b". The first internal cusp 33a and the second internal cusp 33b extend linearly along the axial direction.

[0038] Referring to Figure 8, in the conventional example, the thickness of the bore wall 8 is constant throughout both the circumferential and axial directions. It is common practice to set the thickness in this way during casting because it allows for uniform cooling rates and makes it easier to obtain the desired shape.

[0039] The male outer diameter Rm is larger than the male inner diameter rm by the thickness of the bore wall 8, and the female outer diameter Rf is larger than the female inner diameter rf by the thickness of the bore wall 8. When viewed in the axial direction or in a cross section perpendicular to the axis, the arc of the male outer surface 32m and the arc of the female outer surface 32f intersect at two points, upper and lower. In the following description, the lower of the two intersections will be called the "first outer cusp 34a" and the upper one will be called the "second outer cusp 34b". The first outer cusp 34a and the second outer cusp 34b extend linearly along the axial direction.

[0040] In the conventional example, the opening 20 is provided on one axial end side (suction end face 8b side) and on the upper side of the bore wall 8. The opening 20 is formed to span both the male bore wall 8m and the female bore wall 8f. The second inner cusp 33b and the second outer cusp 34b are divided into one axial side and the other side by the opening 20.

[0041] Referring to Figure 2, in this embodiment, the compressor 1 is provided on the periphery of the opening 20 and has a projection 40 that protrudes radially to the outer circumference opposite to the rotor chamber 7. The bore wall 8 is locally thickened at the periphery of the opening 20.

[0042] Furthermore, referring to Figures 2 and 5, in this embodiment, in a cross-section perpendicular to the axis or viewed in the axial direction, the outer circumferential surface of the bore wall 8 extends along the common tangent TLa between the male inner circumferential surface 31m and the female inner circumferential surface 31f on the suction side, which is the side closer to the opening 20. Note that two common tangents between two intersecting circles can be drawn on the suction side and the discharge side with respect to the straight line connecting their centers.

[0043] The outer surface of the bore wall 8 includes not only the male outer surface 32m and the female outer surface 32f that intersect at the first outer cusp 34a, but also a connecting surface 32a that connects the male outer surface 32m and the female outer surface 32f on the opposite side of the first outer cusp 34a (towards the suction end surface 8b) with respect to the straight line connecting the axes Am and Af. The male outer surface 32m and the female outer surface 32f are partially cylindrical surfaces, and the connecting surface 32a is a flat surface. In a cross section perpendicular to the axis, the male outer surface 32m and the female outer surface 32f form arcs, and the connecting surface 32a forms the common tangent TLb on the suction side between the arc of the male outer surface 32m and the arc of the female outer surface 32f.

[0044] Referring to Figures 4 and 5, since the outer surface of the bore wall 8 extends along the common tangents TLa and TLB, the second outer cusp 34b present in the conventional example (see Figure 8) is eliminated. The bore wall 8 becomes locally thicker in the circumferential direction on the side closer to the opening 20, filling in the space where the second outer cusp 34b was located. The thickness of the bore wall 8 is maximized at the location where the second inner cusp 33b is provided.

[0045] Referring to Figure 4, the opening 20 is home plate shaped in plan view. The home plate is a right-angled pentagon with two adjacent right angles and is a convex pentagon with line symmetry. The opening 20 has five vertices: two right-angled vertices 21a, two obtuse-angled vertices 21b, and a central vertex 21c on the axis of symmetry C20. Each vertex may be rounded and does not necessarily have to be sharp. The opening 20 also has five edges: a horizontal edge 22a connecting the right-angled vertices 21a, a pair of vertical edges 22b connecting the right-angled vertices 21a to the obtuse-angled vertices 21b, and a pair of obtuse-angled vertices 22c connecting the obtuse-angled vertices 21b to the central vertex 21c.

[0046] A pair of vertical edges 22b extend along the axial direction. The right-angle vertex 21a is located on one side in the axial direction (the suction end face 8b side), and the central vertex 21c is located on the other side in the axial direction (the discharge end face side). The axis of symmetry C20 of the opening 20 extends axially at a position offset toward the male bore wall 8m side with respect to the second internal cusp 33b. The pair of vertical edges 22b extend along the ridge line 32b between the male outer peripheral surface 32m and the connecting surface 32a, and along the ridge line 32c between the female outer peripheral surface 32f and the connecting surface 32a. All or most of the horizontal edge 22a and the pair of oblique edges 22c are provided on the connecting surface 32a.

[0047] In this embodiment, the opening 20 is a through hole, and its entire circumference is surrounded by a bore wall 8. In other words, all five edges of the opening 20 are defined by the bore wall 8. The lateral edge 22a extends parallel to the periphery of one end of the bore wall 8 (suction end face 8b) in a plan view. The bore wall 8 has a bridge portion 25 that extends parallel to the periphery and the lateral edge 22a between this periphery and the lateral edge 22a, defining the opening 20.

[0048] The projection 40 surrounds the opening 20 all around. In this embodiment, the projection 40 includes a lateral projection 41 provided on the bridge portion 25 along the lateral edge 22a, a pair of vertical projections 42 provided along a pair of vertical edges 22b, and a pair of inclined projections 43 provided along a pair of slanted edges 22c. The lateral projection 41 forms the periphery at one end of the bore wall 8.

[0049] The projection 40 has a closed loop-shaped end face 40a that surrounds the opening 20. The end face 40a is located radially on the outer circumference side with respect to the connecting surface 32a and is generally parallel to the connecting surface 32a. The end face 40a is connected to the outer circumference surface of the bore wall 8 (connecting surface 32a, male outer circumference surface 32m, or female outer circumference surface 32f) via an inclined surface 40b (see Figures 5 and 6).

[0050] As described above, the compressor 1 according to this embodiment includes an opening 20 provided in the bore wall 8 that radially opens the suction side of the rotor chamber 7, a discharge port 14 that discharges compressed fluid from the discharge side of the rotor chamber 7, and a protrusion 40 provided on the periphery of the opening 20 and projecting outward from the bore wall 8.

[0051] The provision of the protrusion 40 improves rigidity around the opening 20. Even when the bore wall 8 is about to deform due to a temperature difference between the discharge side and the suction side (circumferential temperature difference) or a temperature difference between the discharge end face side and the suction end face side in the rotor chamber 7 (axial temperature difference), deformation that would cause inward displacement around the opening 20 can be suppressed. Furthermore, since the protrusion 40 protrudes outward from the bore wall 8, the protrusion 40 does not affect the inner circumferential surface side of the bore wall 8, and the clearance between the bore wall 8 and the rotor 2 can be appropriately secured.

[0052] The bore wall 8 includes a male bore wall 8m that defines a male rotor chamber 7m for housing a male rotor 2m, and a female bore wall 8f that defines a female rotor chamber 7f for housing a female rotor 2f. In a cross-section perpendicular to the axis, the outer circumferential surface on the suction side of the bore wall 8, excluding the protruding portion 40, at the connection between the male bore wall 8m and the female bore wall 8f, extends along the common tangent TLa between the inner circumferential surface of the male bore wall 8m on the suction side and the inner circumferential surface of the female bore wall 8f on the suction side. As a result, the thickness of the bore wall 8 increases on the suction side where the opening 20 is located. Therefore, the rigidity of the bore wall 8 is improved on the suction side including the opening 20, and deformation around the opening 20 can be further suppressed. In addition, the outer circumferential surface of the bore wall 8 becomes flat along the common tangent TLa, eliminating the second outer cusp. Therefore, stress concentration caused by deformation around the opening 20 can be mitigated.

[0053] The casing 6 is formed from casting. In a cross-section perpendicular to the axis, the end face 40a of the projection 40 extends along the common tangent TLa between the male inner circumferential surface 31m and the female inner circumferential surface 31f on the suction side. This allows the thickness of the projection 40 to be uniform. Therefore, when forming the casing 6 from casting, casting defects such as shape defects and distortion of the projection 40 are less likely to occur.

[0054] The opening 20 is a through hole. The entire circumference of the opening 20 is surrounded by the protrusion 40. This makes the area around the opening 20 less prone to deformation compared to the case where the opening 20 is formed by cutting out the bore wall 8. In this embodiment, the presence of the bridge portion 25 of the bore wall 8, which is stiffened by the lateral protrusion 41, effectively suppresses deformation around the opening 20.

[0055] The opening 20 and the discharge port 14 are positioned on opposite sides of the straight line connecting the axis Am of the male rotor 2m and the axis Af of the female rotor 2f in a cross-sectional area perpendicular to the axis, i.e., on the suction side and the discharge side. When the opening 20 and the discharge port 14 are separated in the circumferential direction in this way, heat transfer from the discharge side to the suction side takes time, and there is a risk that the temperature difference between the discharge side and the suction side will not be easily eliminated. Providing a protrusion 40 in a compressor 1 of this configuration is beneficial because it can effectively suppress deformation around the opening 20.

[0056] The compressor 1 is an oil-free machine. By not employing an oil injection structure, the axial temperature difference of the bore wall 8 becomes large. Providing a protrusion 40 to a compressor 1 of this type is beneficial because it can effectively suppress deformation around the opening 20.

[0057] Next, with reference to Figure 7, a screw-type compressor 1 according to the second embodiment will be described, focusing on the differences from the above embodiment.

[0058] In this embodiment, the opening 20 is a notch. A pair of vertical edges and a pair of oblique edges of the opening 20 are defined by the bore wall 8, while the opening 20 is open to one end of the bore wall 8. The projection 40 has a pair of vertical projections 42 and a pair of inclined projections. In this embodiment, the bore wall 8 does not have a bridge portion 25 (see Figure 4), and the projection 40 does not include a lateral projection 41 (see Figure 4).

[0059] However, in this embodiment as well, rigidity is improved around the opening 20. Therefore, as in the first embodiment, deformation around the opening 20 can be suppressed.

[0060] The configuration of the above embodiment is merely an example and can be modified as appropriate within the scope of the present invention.

[0061] In the above embodiment, the projection 40 surrounds the entire circumference of the opening 20. The projection 40 may also be provided along a portion of the periphery of the opening 20.

[0062] In the above embodiment, the connecting surface 32a extends over the entire axial length of the bore wall 8, and the second outer cusp 34b is completely eliminated. The connecting surface 32a may be partially provided in the axial length of the bore wall 8.

[0063] In the above embodiment, both the connecting surface 32a and the end surface 40a are flat surfaces that extend along the common tangent TLa between the male inner surface 31m and the female inner surface 31f when viewed in the axial direction or in a cross section perpendicular to the axis, and form the common tangent TLb between the male outer surface 32m and the female outer surface 32f. The connecting surface 32a may be a curved surface that follows a curve that is above the second inner cusp 33b and below the common tangent TLb, or it may be a curved surface that follows a curve that is above the common tangent TLb. The end surface 40a is not limited to extending along the common tangent TLa, but may also be a surface parallel to a virtual plane that includes the axis Am of the male rotor 2m and the axis Af of the female rotor 2f.

[0064] In the above embodiment, the opening 20 is home plate shaped (i.e., a symmetrical and convex right-angled pentagon). The shape of the opening 20 is not particularly limited as long as it can perform the functions required of the opening 20 (e.g., improved workability and fluid suction), and can be appropriately changed to other shapes such as a circle or a rectangle.

[0065] In the above embodiment, the compressor 1 is an oil-free machine. The protruding portion 40 and the connecting surface 32a are also applicable to screw-type compressors, which are oil-injection machines. Furthermore, the connecting surface may be provided to connect not only the suction side, but also the male outer peripheral surface 32m and the female outer peripheral surface 32f on the discharge side.

[0066] This disclosure may include the following aspects: (Aspect 1) A pair of male and female rotors, A casing having a rotor chamber that houses the pair of rotors and is divided in the circumferential direction into an intake side and a discharge side, and a bore wall that defines the rotor chamber, An opening is provided in the bore wall, which radially opens the suction side of the rotor chamber, A discharge port for discharging compressed fluid from the discharge side of the rotor chamber, A projection is provided on the periphery of the opening and protrudes outward from the bore wall, A screw-type compressor equipped with [a specific feature]. (Aspect 2) The bore wall includes a male bore wall defining a male rotor chamber for housing the male rotor of the pair of rotors, and a female bore wall defining a female rotor chamber for housing the female rotor of the pair of rotors. In a cross-section perpendicular to the axis, the outer circumferential surface on the suction side of the bore wall, excluding the protruding portion, at the connection between the male bore wall and the z-root female bore wall, extends along the common tangent between the inner circumferential surface of the male bore wall on the suction side and the inner circumferential surface of the female bore wall on the suction side. A screw-type compressor as described in Embodiment 1. (Aspect 3) The casing is formed from casting, In the cross-section perpendicular to the axis, the end face of the protrusion extends along the common tangent between the inner circumferential surface of the male bore wall on the suction side and the inner circumferential surface of the female bore wall on the suction side. Screw-type compressor as described in aspect 2, (Aspect 4) The opening is a through hole, and the entire circumference of the opening is surrounded by the protrusion. A screw-type compressor according to any one of embodiments 1 to 3. (Aspect 5) The screw-type compressor in question is an oil-free machine. A screw-type compressor according to any one of embodiments 1 to 4. [Explanation of symbols]

[0067] 1. Compressor 2 rotors 2f Female Rotor 2m Male Rotor 3f rotor shaft 4f,4m Teeth 5f,5m tooth groove 6. Casing 7. Rotor chamber 7F Female Rotor Chamber 7m Male rotor chamber 8 Bore Wall 8a End wall 8b Suction end face 8f Female bore wall 8m Male Bore Wall 9 Outer case 10 Connection part 11 Interior space 12 Suction passage 13 Intake port 14 Discharge Ports 18 Cover 19 battalions 20 openings 21a Right-angled vertex 21b Obtuse vertex 21c Central vertex 22a Transverse edge 22b Vertical edge 22c Hypothesis 25 Hashibe 31f Female inner surface 31m male inner circumference 32a Connection surface 32b, 32c Ridge 32f Female outer circumference 32m male outer circumference 33a First internal cusp 33b Second internal cusp 34a First outer cusp 34b Second outer cusp 40 Protrusion 40a end face 40b Slope 41 Lateral protrusion 42 Vertical protrusion 43 Inclined protrusion Af,Am axis C20 axis of symmetry D. Center-to-center distance Rf Female outer diameter Rm Male outer diameter rf female inner diameter rm male inner diameter TLa, TLb common wiring

Claims

1. A pair of male and female rotors, A casing having a rotor chamber that houses the pair of rotors and is divided in the circumferential direction into an intake side and a discharge side, and a bore wall that defines the rotor chamber, An opening is provided in the bore wall, which radially opens the suction side of the rotor chamber, A discharge port for discharging compressed fluid from the discharge side of the rotor chamber, A projection is provided on the periphery of the opening and protrudes outward from the bore wall, A screw-type compressor equipped with [a specific feature].

2. The bore wall includes a male bore wall defining a male rotor chamber for housing the male rotor of the pair of rotors, and a female bore wall defining a female rotor chamber for housing the female rotor of the pair of rotors. In a cross-section perpendicular to the axis, the outer circumferential surface on the suction side of the bore wall, excluding the protruding portion, at the connection portion between the male bore wall and the female bore wall, extends along the common tangent between the inner circumferential surface of the male bore wall on the suction side and the inner circumferential surface of the female bore wall on the suction side. The screw-type compressor according to claim 1.

3. The casing is formed from casting, In the cross-section perpendicular to the axis, the end face of the protrusion extends along the common tangent between the inner circumferential surface of the male bore wall on the suction side and the inner circumferential surface of the female bore wall on the suction side. The screw-type compressor according to claim 2.

4. The opening is a through hole, and the entire circumference of the opening is surrounded by the protrusion. The screw-type compressor according to claim 1.

5. The screw-type compressor in question is an oil-free machine. A screw-type compressor according to any one of claims 1 to 4.

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