Screw fluid machine

Abstract

To provide a screw fluid machine in which a power loss is suppressed by preventing generation of a remaining volume at a discharge side end face while thinning a tooth tip of a male rotor.SOLUTION: In a screw fluid machine in which a fluid is compressed and conveyed by rotation of a male rotor (21) having a plurality of teeth and a female rotor corresponding to the male rotor (21), a cross-sectional tooth-profile 21d portion of a first section near a discharge-side end portion of the male rotor (21) when viewed in an axial direction is formed to be thick so as to be located outside a pitch-point 21s circle (CP) on a tip and an advancing surface side of the tip, and a cross-sectional tooth-profile center portion of a second section near a suction-side end portion is formed to be thin so as to be located inside the pitch-point center circle (CP). The cross-sectional tooth profile of the male rotor 21 between the first section and the second section in the axial direction is continuously changed from the second cross-sectional shape to the first cross-sectional shape.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a screw fluid machine having a male rotor and a female rotor that rotate while meshing with each other on parallel rotation axes. [Background technology]

[0002] A screw fluid machine comprises a pair of male and female screw rotors that rotate while meshing with each other, and a casing that houses both rotors (male rotor, female rotor). The male and female rotors each have spiral teeth and tooth grooves. A screw fluid machine draws in and compresses gas by increasing or decreasing the volume of multiple working chambers formed by the two screw rotor tooth grooves and the inner wall surface of the casing that surrounds them as the two screw rotors rotate. The space between the screw rotor tooth tips and the casing is designed to have a very small gap (external diameter gap), preventing leakage of the working fluid.

[0003] FIG. 9 shows an example of a conventional screw fluid machine. The compressor 100 includes a motor 201 that supplies rotational power and a screw fluid machine 101 that generates compressed air using the rotational force of the motor 201. The motor 201 is an interior permanent magnet synchronous motor (IMSM), which houses a rotor 205 and a stator 210 in a motor housing 202. The motor housing 202 is composed of a cylindrical body 202a with openings on the front and rear sides, a front end bracket 202b attached to the front opening of the body 202a, and a rear end bracket 202c attached to the rear opening of the body 202a. A through hole is formed in the rear end bracket 202c, and one end of a shaft 204, to which the rotor 205 is fixed, protrudes from the interior of the motor housing 202 toward the exterior on the rear side. The stator 210 includes a stator core 211 and a coil 220.

[0004] The screw fluid machine 101 has a male rotor 120 and a female rotor 140. The male rotor 120 is connected to a shaft 204 of a motor 201 by connecting means (e.g., spline, coupling, gear, etc.), and supplies rotational power of the motor 201 to a first shaft 105 of the screw fluid machine 101. In this example, the shaft 204 and the first shaft 105 are directly connected, and their rotation axis is A1. A first bevel gear 110 is provided at the tip of the first shaft 105, and the first bevel gear 110 is meshed with an adjacent second bevel gear 130, thereby rotating the second bevel gear 130 at the same speed as the first bevel gear 110 but in the opposite direction. Since the second bevel gear 130 is provided at the tip of the second shaft 135, the female rotor 140 fixed to the second shaft 135 by the rotation of the second bevel gear 130 rotates at the same speed but in the opposite direction to the male rotor 120 fixed to the first shaft 105. Note that screw fluid machines that do not use bevel gears 110, 130, but rotate the female rotor 140 by meshing the male rotor 120 and female rotor 140, are also widely used.

[0005] As the motor 201 rotates, the male rotor 120 and the female rotor 140 rotate, and air is sucked in through the suction port (not shown in the figure) of the male rotor 120. As the male rotor 120 and the female rotor 140 further rotate, the teeth of each rotor disengage, and air is sucked into the tooth space. As the male rotor 120 and the female rotor 140 further rotate, the air is blocked by the wall of the casing 102, completing the suction process. The air trapped between the tooth space and the casing is compressed by the meshing of the rotors 120 and 140. As the rotors 120 and 140 rotate, the air moves axially and is further compressed between the tooth space 145 and the casing 102, reaching the discharge port (not shown in the figure) and reaching a predetermined pressure. The compressed air is discharged from the discharge port on the discharge side opened in the casing 102.

[0006] In this screw fluid machine 101, the high-speed rotation of the male and female rotors creates a large speed difference between them and the casing through a small gap. This causes a large shear force on the fluid present in the gap, resulting in friction loss and reducing the energy-saving performance of the screw fluid machine. To reduce the friction loss due to the shear force, it is desirable to shorten the gap length along the tangential direction of the screw rotor's rotation. This can be achieved by thinning the internal tooth profile near the tip of the screw rotor in the axial cross section (hereinafter referred to as the "cross-sectional tooth profile" or simply the "tooth profile"). However, if the tooth profile near the tip and on the forward side is made too thin, a closed space called a "residual volume" is created, where the volume of the working chamber becomes zero and the flow path for discharge from the working chamber is lost before the discharge from the working chamber is completed. This is known to cause excessive compression of the fluid in the residual volume, resulting in power loss and vibration.

[0007] Patent Document 1 discloses a technology for a screw fluid machine in which the tooth profile curve on the forward moving surface of a female rotor, from the innermost radial root point to the outermost radial outer periphery point in a cross section perpendicular to the axis, is formed as an elliptical arc for the most part so that it is located outside the pitch point center arc passing through the root point. Patent Document 1 states that forming the female rotor's tooth profile curve so that it is located outside the pitch point arc prevents the generation of residual volume. Patent Document 2 also discloses a screw rotor formed so that the cross-sectional tooth profile varies depending on the axial position. In particular, by making the tooth thickness of the female rotor in a cross section perpendicular to the axis thicker near the discharge side while satisfying specific conditions, tooth flank separation is suppressed and leakage loss near the discharge port, where high pressure occurs, is reduced. Note that "tooth thickness" in this specification refers to the tooth thickness of the tooth profile in a cross section perpendicular to the rotational axis of the screw rotor. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-133763 [Patent Document 2] Japanese Patent Publication No. 2022-69105 Summary of the Invention [Problem to be solved by the invention]

[0009] In the screw fluid machine described in Patent Document 1, the tooth profile of the female rotor is positioned outside the pitch point center arc to prevent the generation of residual volume at the discharge end face, but imposing this restriction means that the tooth profile near the tip of the male rotor tooth cannot be made thinner than a certain range, making it difficult to further increase the effect of reducing friction loss of the fluid in the minute gaps at the tip of the rotor tooth. Patent Document 1 does not specifically mention any measures to address this issue.

[0010] The inventors of the present application have noticed that the residual volume becomes an issue at the discharge end face of the rotor, and have devised a means of solving the above problem by changing the cross-sectional tooth profile perpendicular to the rotation axis depending on the axial position of the rotor, thereby allowing the tooth profile to be located inside the pitch point center arc upstream of the discharge end face, while at the discharge end face, as in Patent Document 1, the tooth profile is located outside (or on) the pitch point center arc.

[0011] Furthermore, a screw rotor with a cross-sectional tooth profile that changes in the axial direction is proposed in Patent Document 2, but it does not consider how to avoid the generation of residual volume or the positional relationship between the pitch point center arc and the tooth profile, which is the condition for its generation. The inventors focused particularly on how to avoid the generation of residual volume in a screw fluid machine and studied the positional relationship between the pitch point center arc and the tooth profile, which is the condition for its generation. As a result, the inventors discovered that, depending on the conditions for changing the cross-sectional tooth profile in the axial direction, a residual volume that is a closed space can also occur upstream of the discharge end face, as will be described later, and that there are certain conditions for avoiding this.

[0012] The object of the present invention is to provide a highly efficient and reliable screw fluid machine that reduces fluid friction loss in the gap between the screw rotor tooth tips and the casing while avoiding power loss and vibration caused by compressing the fluid in the residual volume. [Means for solving the problem]

[0013] In order to solve the above problems, for example, the configurations described in the claims are adopted. According to one aspect of the present invention, in a screw fluid machine comprising a male rotor having twisted male teeth and rotating around a first center of rotation, a female rotor having twisted female teeth and rotating around a second center of rotation parallel to the first center of rotation, and a casing having a housing chamber for rotatably housing the male and female rotors in meshed state, and which conveys fluid at a changed pressure between a suction port and a discharge port by rotating the male and female rotors, the male rotor is formed as follows: At the discharge-side end face of the male rotor and its vicinity, a cross-sectional shape at a predetermined position between the suction end and the discharge end of the male rotor is defined. That is, the cross section perpendicular to the first center of rotation is formed to have a first cross-sectional shape in which the cross-sectional tooth profile near the tooth tips is thickened so that the length from an arbitrary point in the rotor forward direction from the tooth tips to the pitch point of each tooth is equal to or longer than the length from the tooth tips to the pitch point of the tooth. In addition, a cross section perpendicular to the first center of rotation at a predetermined position between the suction side end face and the discharge side end face when viewed in the axial direction is formed into a second cross-sectional shape in which the cross-sectional tooth profile near the tooth tip is thinned so that the length from a predetermined point in the rotor forward direction of the tooth tip to the pitch point of the tooth is shorter than the length from the tooth tip to the pitch point of the tooth.

[0014] According to another feature of the present invention, the male rotor has a transition section between the section of the first cross-sectional shape and the section of the second cross-sectional shape of the male rotor, as viewed in the axial direction, where the cross section of the male rotor continuously changes from the second cross-sectional shape to the first cross-sectional shape. The section of the male rotor from the suction end face to the transition section as viewed in the axial direction is formed with the same cross-sectional shape as the second cross-sectional shape, while the section of the male rotor from the transition section to the discharge end face as viewed in the axial direction is formed with the same cross-sectional shape as the first cross-sectional shape. Furthermore, the tooth profile around the tooth tip of the male rotor, particularly on the forward moving face side, has a relationship such that the product of the angle formed by connecting the point where a normal drawn from a point on the forward moving face intersects with the pitch circle, the rotor center, and the tooth tip, in that order, and the lead does not exceed the axial length of the transition section. [Effects of the Invention]

[0015] According to the present invention, at the discharge end face of the male rotor and its vicinity, the cross-sectional tooth profile near the tooth tips of the screw rotor is thickened to form a shape that does not generate residual volume, while the cross-sectional tooth profile near the tooth tips in other parts is thinned, thereby reducing the friction loss of fluid in the gap between the screw rotor tooth tips and the casing. Furthermore, by changing the tooth profile so as to eliminate residual volume at the discharge end face of the male rotor, a highly efficient and reliable screw fluid machine has been realized. Problems, configurations and effects other than those described above will become apparent from the following description of the embodiments. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a horizontal cross-sectional view showing a screw compressor 1 according to an embodiment of the present invention. [Figure 2] 2 is a cross-sectional view of the screw compressor 1 of FIG. 1 taken along B1-B1. [Figure 3] 2 is a cross-sectional view taken along the line AA of the screw compressor 1 in FIG. 1. [Figure 4] FIG. 3 is an enlarged view of one tooth of the male rotor 2 of the screw compressor 1 of FIG. 2. [Figure 5]2 is a view of the male rotor and seal line of the screw compressor 1 shown in FIG. 1, viewed from the bottom to the top of FIG. [Figure 6] 4 is a partially enlarged view of the male rotor of the screw compressor 1 shown in FIG. 3, showing the relationship between the cross-sectional tooth profile and the residual volume width. FIG. [Figure 7] FIG. 10 is a diagram showing a seal line of a screw compressor in a second embodiment of the present invention when the transition section It is short. [Figure 8] FIG. 10 is a diagram showing a seal line of a screw compressor according to a third embodiment of the present invention. [Figure 9] FIG. 1 is a cross-sectional perspective view showing a conventional screw fluid machine 101. DETAILED DESCRIPTION OF THE INVENTION

[0017] A screw fluid machine according to an embodiment of the present invention will be described with reference to the drawings. In the following embodiment, a twin-rotor screw compressor will be used as an example of a screw fluid machine. In the following drawings, the same parts will be given the same reference numerals, and repeated explanations will be omitted. In addition, in FIG. 1, the left side will be the suction side of the screw compressor 1, and the right side will be the discharge side. Here, the "suction side" refers to the side in the axial direction of the screw compressor 1 that sucks in gas, and the "discharge side" refers to the side in the axial direction of the screw compressor 1 that discharges gas. [Example]

[0018] 1 is a longitudinal cross-sectional view showing a screw compressor 1 according to this embodiment. The screw compressor 1 includes a male rotor 2 and a female rotor 3 as a pair of screw rotors that rotate in mesh with each other, and a casing 4 (41, 42, 43) that houses the male rotor 2 and the female rotor 3. The male rotor 2 is fixed to a shaft 22 and is rotatable in one direction about a rotation axis A1, and the female rotor 3 is fixed to a shaft 32 and is rotatable in the other direction about a rotation axis A2. The teeth of the male rotor 2 and the female rotor 3 are in mesh with each other, so that when the male rotor 2 rotates, the female rotor 3 rotates accordingly.

[0019] The casing 4 comprises a main casing 41, a discharge-side casing 42, and a suction-side casing 43, which are joined together along a dividing plane perpendicular to both the rotation axis A1 of the male rotor 2 and the rotation axis A2 of the female rotor 3. The main casing 41 has a discharge-side joining surface 41a perpendicular to the rotation axes A1, A2 of both the male and female rotors 2, 3, and is joined to the discharge side (right side in Figure 1) with the discharge-side casing 42.

[0020] The casing 4 has a housing chamber 45 that houses the male rotor 2 and the female rotor 3. The rotor teeth 21 of the male rotor 2 and the rotor teeth 31 of the female rotor 3 are arranged in the housing chamber 45 so that they can rotate while meshing with each other. The housing chamber 45 is formed by closing an opening on one axial side (the protruding side on the right side in Figure 1) of a space surrounded by two partially overlapping cylindrical surfaces (inner peripheral surfaces of the bore) formed in the main casing 41 with the discharge-side casing 42. The discharge-side casing 42 is provided with a discharge-side bearing chamber 54 in which the discharge-side bearing 6 on the male rotor 2 side is arranged, and a discharge-side bearing chamber 55 in which the discharge-side bearing 8 on the female rotor 3 side is arranged.

[0021] The shaft 22 penetrating the male rotor 2 and the shaft 32 penetrating the female rotor 3 are arranged so that their rotation axes A1, A2 are parallel. The suction side 22a of the shaft 22 is supported on the casing 4 (41) by one suction-side bearing 5 on the suction side in the axial direction, and is rotatably supported on the casing 4 (42) by two discharge-side bearings 6 on the discharge side in the axial direction. Similarly, the discharge side 22b of the shaft 22 is supported on the casing 4 (41) by one suction-side bearing 7 on the suction side in the axial direction, and is rotatably supported on the casing 4 (42) by two discharge-side bearings 8 on the discharge side in the axial direction. The bearings 5 ​​and 7 are ball bearings, and the bearings 6 and 8 are a combination of a roller bearing and a ball bearing. The types and number of bearings used for the bearings 5 ​​to 8 are not limited to those shown in FIG. 1.

[0022] The male rotor 2 has a rotor tooth portion 21 with a plurality of spiral male teeth (lobes) 21a, and a suction side 22a and a discharge side 22b of a shaft 22 extend outward from both axial ends of the rotor tooth portion 21. The rotor tooth portion 21 has a suction side end face 21b and a discharge side end face 21c at one axial end (left end in FIG. 1) and the other axial end (right end in FIG. 1), respectively, which are perpendicular to the axial direction (rotation axis A1). Tooth grooves are formed between the male teeth 21a of the rotor tooth portion 21. The suction side 22a of the shaft 22 is configured to extend outward, for example, penetrating the suction side casing 43, and is connected to the output shaft of a rotary drive source such as a motor (not shown). A shaft seal member 9 is disposed between the shaft 22 of the male rotor 2 and the casing 4 to seal the gap therebetween. The shaft seal member 9 may be a known member such as an oil seal or a mechanical seal.

[0023] The female rotor 3 has a rotor tooth portion 31 with a plurality of spiral female teeth (lobes) 31a, and a suction side 32a of a shaft 32 extends from both axial end portions of the rotor tooth portion 31 outside the main casing 41, and a discharge side 32b of the shaft 32 extends from the opposite end. The rotor tooth portion 31 has a suction side end face 31b and a discharge side end face 31c at one axial end (left end in FIG. 1) and the other axial end (right end in FIG. 1), respectively, which are perpendicular to the axial direction (rotation axis A2). Tooth spaces are formed between the female teeth 31a of the rotor tooth portion 31.

[0024] A suction side casing 43 is attached to the suction side end of the main casing 41, and the main casing 41 forms a suction side bearing chamber 51 in which the suction side bearing 5 on the male rotor 2 side is arranged, and a suction side bearing chamber 52 in which the suction side bearing 7 on the female rotor 3 side is arranged, and these spaces are isolated from the external space by the suction side casing 43.

[0025] FIG. 2 is a B1-B1 cross-sectional view of the screw compressor 1 of FIG. 1. When the cross-section B1-B1 of FIG. 2 (a vertical cross-section perpendicular to the rotation axes A1 and A2) is viewed from the discharge side to the suction side, the male rotor 2 has four convex male teeth 21a in the circumferential direction, and the female rotor 3 has six female teeth (lobes) 31a in the circumferential direction. When the B1-B1 cross-section of FIG. 1 is viewed from the suction side to the discharge side, the direction of rotation of the shafts 22 and 32 is indicated by the arrows in the figure. The tooth profile (cross-sectional tooth profile) shown by the outline of the male rotor 2 in a cross-section perpendicular to the rotation axis A1 changes shape at different axial positions, for example, at the B3-B3 cross-section, B2-B2 cross-section, and B1-B1 cross-section of FIG. 1, as will be described later, and the shape of the corresponding tooth spaces also changes.

[0026] 3 is a longitudinal sectional view of the screw compressor 1 according to the embodiment shown in FIG. 1 along the line AA. As can be seen from FIGS. 1 to 3, the wall surface of the main casing 41 forming the accommodation chamber 45 is composed of a substantially cylindrical male bore inner peripheral surface 46 (see FIG. 1) located radially outward from the rotor tooth portion 21 of the male rotor 2, a substantially cylindrical female bore inner peripheral surface 47 located radially outward from the rotor tooth portion 31 of the female rotor 3, a suction-side inner wall surface 48 on one axial side facing the suction-side end faces 21b (see FIG. 1), 31b of the rotor tooth portions 21, 31 of both the male and female rotors 2, 3, and a discharge-side inner wall surface 49 on the other axial side facing the discharge-side end faces 21c (see FIG. 1), 31c of the rotor tooth portions 21, 31 of both the male and female rotors 2, 3. That is, the suction-side end of the accommodation chamber 45 in the axial direction is the suction-side inner wall surface 48, and the discharge-side end in the axial direction is the discharge-side inner wall surface 49. The casing 4 is configured such that the main casing 41 and the discharge-side casing 42 are separated at the position of the discharge-side inner wall surface 49 of the accommodation chamber 45 and joined to each other.

[0027] Multiple working chambers C are formed by the rotor teeth 21, 31 of the male and female rotors 2, 3 and the surrounding inner wall surface (accommodation chamber 45) of the casing 4, which includes the male bore inner peripheral surface 46 (see FIG. 1), the female bore inner peripheral surface 47, the suction-side inner wall surface 48, and the discharge-side inner wall surface 49. As the screw rotor rotates, the volume of each working chamber C increases, drawing in gas from outside the casing 4 (suction stroke), and as the screw rotor rotates, the volume decreases, compressing the gas (compression stroke). If the screw compressor 1 is a liquid-feed type, a liquid such as oil or water is supplied to the working chambers C during the suction stroke or compression stroke. The purpose of supplying the liquid to the working chambers C is to cool the compressed gas within the working chambers C, lubricate the male rotor 2 and female rotor 3, and seal gaps between the male and female rotors 2, 3 and the wall surface of the accommodation chamber 45 (the inner wall surface of the casing 4) and between the male rotor 2 and female rotor 3.

[0028] The casing 4 is provided with an intake passage 61 and an intake space 62 for drawing external gas into the working chamber C. The intake passage 61 is, for example, a passage having one side that opens to the outer wall surface of the main casing 41 and the other side (downstream side) that is connected to the intake space 62. The intake space 62 is formed in a position facing the intake side end faces 21b, 31b of the rotor tooth portions 21, 31 of the male and female rotors 2, 3 in the main casing 41. The casing 4 is provided with a discharge passage 64 for discharging compressed gas from the working chamber C to the outside of the casing 4. The discharge passage 64 connects the accommodation chamber 45 (working chamber C) with the outside of the casing 4, and is formed in the discharge-side casing 42. The discharge port 65, which serves as the entrance from the working chamber C to the discharge flow path 64, is open only below the horizontal plane passing through the rotation axes A1 and A2, and is closed above, so as to prevent the working fluid in the working chamber C from communicating with the discharge flow path 64 before it is compressed to a predetermined pressure.

[0029] In the screw compressor 1 configured as described above, when the male rotor 2 is driven by a drive source (not shown), such as a motor, the female rotor 3 meshing with the male rotor 2 also rotates. As a result, the working chamber C moves axially as both the male and female rotors 2 and 3 rotate. During this process, the working chamber C gradually increases in volume from zero, entering a suction stroke in which gas is drawn in from the suction passage 61 of the casing 4 via the suction space 62 shown in FIG. 2. Thereafter, when the volume of the working chamber C approaches its maximum value, communication with the suction space 62 is blocked, and the volume gradually decreases as both the male and female rotors 2 and 3 rotate, entering a compression stroke in which air is compressed. When the working chamber C communicates with the discharge passage 64, the compressed gas in the working chamber C is discharged via the discharge passage 64 to an external system (not shown).

[0030] As described above, the cross-sectional tooth profile of the male rotor 2 changes depending on the axial position along the rotation axis A1. Figure 4 is an enlarged partial cross-sectional view of one tooth portion of the male rotor 2 of the screw compressor shown in Figure 2. In Figure 4, the tooth profiles of the male rotor 2 in different axial cross sections are shown overlapping with solid and dashed lines. The cross-sectional tooth profile 21s shown by the solid line is the cross-sectional tooth profile on the upstream side (suction side) of the cross-sectional tooth profile 21d on the discharge side end face 21c, for example, at B2-B2 in Figure 1. The cross-sectional tooth profile 21d shown by the dashed line is the cross-sectional tooth profile on the downstream side (discharge side) of the cross-sectional tooth profile 21s, for example, at B1-B1 in Figure 1. The tooth tip 21t is the point on the cross-sectional tooth profile that is farthest from the rotation axis A1 (rotor center) of the male rotor 2. FIG. 4 is a diagram showing the cross-sectional tooth profile 21s and the cross-sectional tooth profile 21d rotated so that the positions of their tooth tips are aligned on a reference line L located on a plane connecting the rotation axes A1 and A2. cp is the pitch point, and the circle CP is the pitch point O cpThe pitch point center circle has its center at and passes over the tooth tip 21t. The difference between the shapes of the cross-sectional tooth profiles 21d and 21s is greatest near the position shifted in the forward direction by a predetermined angle θ1 from the reference line L. In this embodiment, the angle θ1 from the tooth tip 21t to the maximum deviation point of the cross-sectional tooth profile on the forward side is approximately 30 degrees. However, if there are four teeth in the circumferential direction, the position of the maximum deviation point can be set in the range of, for example, approximately 20 to 40 degrees. Furthermore, near the position shifted in the forward direction by a predetermined angle θ2 from the tooth tip 21t, the shapes of the cross-sectional tooth profiles 21d and 21s again coincide. In this embodiment, the angle θ2 of this coincidence point is approximately 75 degrees.

[0031] One of the features of the present invention is the relationship between the cross-sectional tooth profile and the pitch point center circle CP. Cross-sectional tooth profile 21s is located inside the pitch point center circle CP near tooth tip 21t and on the advancing surface side (above reference line L in Figure 4), while cross-sectional tooth profile 21d, which is further on the discharge side, coincides with or is located outside the pitch point center circle CP near tooth tip 21t and on the advancing surface side. Note that although a description of the shape of the female rotor 3 is omitted here, the cross-sectional shape of the male rotor 2 determines the corresponding end face shape of the female rotor 3.

[0032] 5 shows the state of the seal line formed on the male rotor 2 of this embodiment, and is a view of the male rotor and seal line of the screw compressor 1 shown in FIG. 1, viewed from above to below in FIG. 1. That is, the left side of FIG. 5 is the suction side, and the right side is the discharge side, and the male rotor 2 is viewed from the female rotor 3 side. In FIG. 5, the male rotor 2 is shown in the axial direction as I2 and I t, I1. Of these, section I2 indicates the portion where the cross-sectional tooth profile near the tooth tip 21t and on the advancing surface side, i.e., the tooth profile in the range indicated by θ1 in FIG. 4, is located inside the pitch point center circle CP. Section I1 indicates the portion where the cross-sectional tooth profile near the tooth tip 21t and on the advancing surface side is located on the pitch point center circle CP or is located outside it. Section I2 has the longest axial length, accounting for more than half of the length of the male rotor 2 in the axial direction. Note that in this example, the tooth profile cross section does not change in section I2 except for the twist (rotation) of the tooth profile cross section, which changes depending on the axial position. Therefore, section B2-B2, which is a cross section on section I2, corresponds to the shape of cross-sectional tooth profile 21s shown in FIG. 4, and section B1-B1, which is a cross section on section I1, corresponds to the shape of cross-sectional tooth profile 21d shown in FIG. 4.

[0033] Section I t The boundary between the suction section I1 and the section I2 is similar to section I2, in that the cross-sectional tooth profile near the tooth tip 21t and on the advancing surface side is located inside the pitch point center circle CP. t The tooth profile cross section changes continuously from the shape of the connection point with section I2 within section I, and the cross-sectional tooth profile changes so that it becomes thicker from the inside to the outside of the pitch point center circle CP. t At the discharge end of the tooth profile, the cross section changes to coincide with or be positioned outside the pitch point center circle CP. This shape is continuously transitioned in Section I. t Hereafter, we will refer to this as "transition section I t The end of the section I1 on the discharge side opens into the discharge port 65. As will be described later, the transition section I in FIG. t One of the features of the present invention is that the width (length in the axial direction) of the slit is set to a predetermined size or more.

[0034] Seal lines S1, S2, and S3 are overlapping views of the same seal line at three different moments as it moves from the suction side to the discharge side due to the rotation of the male rotor 2. As the seal line created by the male rotor 2 moves from S1 to S2 to S3, the working chamber moves from the inlet side to the discharge side (to the right in Figure 3) in the direction of the rotation axis A1 in accordance with the rotation of the male rotor 2 and female rotor 3, reducing its volume and compressing the fluid. The compressed fluid is then discharged from the discharge port 65 facing the discharge end face 21c of the casing 4.

[0035] First, when we look at the seal line S1, in the region above the reference line L (see also Figure 4), there is a part (shown by hatching) that protrudes further toward the suction side from the intersection of the reference line L and the seal line S1 on the suction side (left side). In this specification, the space surrounded by this part is referred to as V res This space V res If the seal line S1 keeps its shape (corresponding to the case where the tooth profile cross section does not change in the axial direction) and moves to the discharge side, the space V res reaches the end face of the discharge-side casing 42. Here, the opposing surface of the discharge-side end face 21c is closed above the reference line L, so the space V res becomes a closed space, and the rotation of the male rotor 2 further closes the closed space V res The fluid trapped in this reduced space rises to an extremely high pressure, causing abnormal vibration of the rotor and power loss.

[0036] In this way, the remaining volume can be V res The condition for this to occur is that the cross-sectional tooth profile near the tooth tip and on the forward moving surface side of the male rotor 2 is located inside the pitch point center circle CP. This point will be explained further using Figure 6. Figure 6 shows the cross-sectional tooth profile of the male rotor 2 in a certain cross section, and only the male rotor 2 is shown. Pitch point O cp is the position determined by dividing the rotation axes A1 and A2 internally by the ratio of the number of teeth of the male rotor 2 to the number of teeth of the female rotor, and the pitch circle C shown by the dashed line pchis the pitch point O around the rotation center O (rotation axis A1). cp is an imaginary circle passing through

[0037] Figure 6 shows the relationship between the cross-sectional tooth profile of the male rotor 2 and the residual volume width. Here, attention is focused on a point (point P) indicated by a black circle near the forward moving surface side of the tip of one tooth on the left side of Figure 6. The normal line extending from point P on the tooth profile in the direction approaching the male rotor center O is defined as L1, and the relationship between L1 and the pitch circle C is pch The intersection point between these two lines is designated as Q. Furthermore, the line connecting the intersection point Q and the rotor center O is designated as L2. In this case, in the portion (including point P) of the cross-sectional tooth profile near the tooth tip 21t and on the advancing face side (above the tooth tip 21t in Fig. 6), if the cross-sectional tooth profile is located inside the pitch point center circle CP shown in Fig. 4, the radius of curvature near the tooth tip 21t will be smaller than the pitch point center circle CP, and the normal line L1 drawn from point P will be located on the pitch circle C as shown in Fig. 6. pch is point O cp The pitch point O is the point Q below the pitch point O. cp If the angle formed by connecting the rotor center O and point Q in order is θ, then in this tooth profile, if the male rotor 2 is rotated in the rotor rotation direction by θ from the moment in Figure 6, point Q will reach pitch point O. cp matches.

[0038] According to the gear meshing theory, when point P contacts the female rotor 3, the normal L1 is cp Therefore, the state where the male rotor 2 is advanced by an angle θ from the state in Figure 6 becomes the "point of contact at point P," that is, it coincides with a point on the seal line on this cross section. Conversely, at the point in Figure 6, the rotor rotation angle is θ before point P comes into contact.

[0039] On the other hand, the normal line drawn from the tooth tip 21t is at pitch point O in the state shown in Figure 6. cp Since the tooth tip 21t passes through the seal line S1 in FIG. 5, the tooth tip 21t becomes the contact point at this moment. This contact point is located on the reference line L, so the space V resOn the other hand, point P comes into contact on the cross section where point U exists when it has moved forward by the angle θ, and therefore at the timing of seal line S1, it corresponds to the contact point (a point on the seal line) on the cross section that has moved toward the suction side from the cross section where point U exists by the distance corresponding to the angle θ.

[0040] Therefore, the seal line corresponding to point P is the space V in Figure 5. res The space V shown in Fig. 5 is located behind the bottom point U (suction side). res Similarly, when the cross-sectional tooth profile near tooth tip 21t and on the advancing surface side of tooth tip 21t coincides with or is located outside pitch point center circle CP, the seal line does not protrude toward the suction side behind (left side of) seal line S1 and above reference line L in Figure 5, so no space that could become residual volume is created.

[0041] Furthermore, when the female rotor 3 rotates and advances by an angle θ, the distance the seal line moves in the axial direction is the product of the lead Ld of the male rotor 2 and θ. Therefore, if point P is taken as the point where θ (positive in the rotor rotation direction) is minimum (maximum in the negative direction) when moved along the tooth profile, then the space V shown in Figure 5 res The axial width Lv of the rotor is expressed as Lv = Ld × θ using θ at that time. Here, the lead Ld indicates the distance traveled in the axial direction by one rotation of the male rotor. Therefore, the above-mentioned transition section I t is the space V res The condition that the width of the transition section I is larger than the width of t This can be rephrased as being greater than Ld×θ.

[0042] Based on the above, returning to Figure 5, we will explain the changes in the seal lines S1, S2, and S3. In the seal line S1 located in section I2, the cross-sectional tooth profile near the tooth tip of the male rotor 2 and on the forward moving surface side is located inside the pitch point center circle CP, and as mentioned above, the space V that can become the residual volume is resOn the other hand, in the section I1 adjacent to the discharge side end face 21c (see FIG. 1), the cross-sectional tooth profile near the tooth tip of the male rotor 2 and on the forward moving surface side is not located inside the pitch point center circle CP, so there is a space V at the seal line S3. res There is no transition section I between them. t By forming the cross-sectional tooth profile so as to be continuously interpolated, the space V is created as shown by the seal line S2. res The magnitude of the pressure decreases as it approaches the discharge side.

[0043] As mentioned above, in sections I2 and I t So, the remaining volume is V res The tooth thickness near the tooth tip of the male rotor 2 is thinned to allow for the presence of the tooth tip, thereby reducing friction loss due to the shear force of the fluid between the tooth tip and the casing. Furthermore, in the section I1 including the discharge side end face, the space V res By designing the tooth profile to eliminate this, it was possible to eliminate vibrations and power loss caused by abnormal compression of the fluid within the remaining volume, which was a problem in conventional fluid equipment. [Example]

[0044] Next, a second embodiment of the present invention will be described with reference to FIG. 7. In the study of the present invention, the inventors have t Depending on how the setting is made, the space V may be located at places other than the discharge end surface. res It was discovered that this could result in a residual volume that is a closed space, and a means for avoiding this was devised. Fig. 7 shows, for comparison, the seal line in the case where the first embodiment of the present invention is not satisfied (where the transition section It is smaller than Ld × θ) in the same configuration as Fig. 5. The common point with the seal line shown in Fig. 5 is that the end face (discharge side end face 21c) that contacts the discharge end of the male rotor 2 has a tooth profile with the shape of section I1, and the side that contacts the suction side end face has a tooth profile with the shape of section I2. The difference is that in Fig. 7, the transition section I t space V in the interval I1 res The point is that the width of the transition section I is shorter than the width Lv of the transition section I. tThe shape of the seal line S3 immediately after passing through is shown by a broken line, and the seal line S3' when the seal line S1 reaches the same position as the seal line S3 while maintaining that shape is shown by a solid line.

[0045] Since the seal line S3 is a seal line in the section I1, the seal line is actually formed in this shape, and the working chamber C3 is divided. t Since the cross-sectional tooth profile on section I1 is different from that of seal line S1, seal line S3' is not actually formed. However, in the part of seal line S3' that overlaps section I1, the cross-sectional tooth profile is the same shape as seal line S1, so seal line S3' is actually formed.

[0046] As a result, the working chamber C3', which is separated by the seal line S3 and is located on the discharge side (right side of Figure 7) from the working chamber C3, and is surrounded by the seal line S3' located on the section I1, is separated from the working chamber C3 by the seal line S3. t Since the tooth profile changes continuously in the transition section I1, the seal line connecting to the seal line S3' on the transition section I2 also changes in the transition section I3. t C3' is a closed space with a shrinking volume, causing the same problem as the residual volume that occurs at the discharge end face.

[0047] The cause of this problem is the space V in section I1. res The width Lv of the transition section I t Since the width is larger than the width of the seal line S3, the space V res Therefore, in the example shown in FIG. 7, the effect of the present invention cannot be maximized, but depending on the shape and number of teeth of the male rotor 2, it is possible to t Although the residual volume occurs in the vicinity of the male rotor 2, the influence is small enough to be tolerable, and it is possible to provide a male rotor 2 having a seal line as in the second embodiment. tBy adding the requirement that the axial length of the nozzle be greater than the width Lv as one of the conditions, the problem of residual volume occurring at areas other than the discharge end surface, as shown in the first embodiment, can be effectively solved.

[0048] According to Example 2, sections I1 and I t So, the remaining volume is V res By allowing the presence of the tooth thickness near the tooth tip of the male rotor 2 to be thin, the friction loss due to the shear force of the fluid between the tooth tip and the casing can be reduced, and in the section I1 including the discharge side end face, the space V res Furthermore, the generation of residual volume that can occur due to changes in the tooth profile cross section in the axial direction can also be avoided, eliminating vibrations and power loss caused by abnormal compression of the fluid within the residual volume, resulting in a highly efficient and reliable screw compressor. [Example]

[0049] In the above-mentioned first and second embodiments, the male rotor 2 is divided into three sections in the axial direction, and the first section I2, viewed from the suction side, has a thin tooth thickness near the tooth tip, and section I1 has a thick tooth thickness near the tooth tip. However, the number of sections I into which the rotor is divided may be increased. For example, the tooth thickness near the tooth tip of the male rotor 2 near the suction end face may be thickened. Figure 8 shows the rotor and seal line in this case, and here we will add new sections I3 and I4. t2 is provided upstream (suction) of I1. Here, for example, the tooth profile of section I3 is the same as that of section I1, and the transition section I t2 is the transition section I t1 In other words, as can be seen from the seal lines S4 and S3, in the sections I3 and I1, there is a space V that can be the remaining volume. res On the other hand, in section I2, there is a space V that can be the remaining volume. res This section I t2In this case, the tooth thickness near the tooth tip is changed so as to continuously connect section I3 and section I2. In this way, it is preferable to form the tooth profile of the male rotor 2 so that the tooth thickness near the tooth tip is thin in some areas in the rotational axis direction, particularly in the vicinity of the suction end face and the middle area excluding the vicinity of the discharge end face. This effect is particularly noticeable in liquid feed type screw compressors. In liquid feed type screw compressors, the amount of liquid fed immediately after the suction side end face 21b may not be sufficient, so it may be better not to make the tooth thickness near the tooth tip too thin. Therefore, high efficiency can be achieved in such compressors.

[0050] While the present invention has been described above based on the embodiments, it is not limited to the above-described embodiments and various modifications are possible without departing from the spirit of the present invention. For example, in the above-described embodiments, the male rotor 2 is divided into three or five sections in the axial direction, but it may be divided into more than this number. Furthermore, the present invention can be applied not only to oil-lubricated screw compressors that use oil, but also to oil-free screw compressors. [Explanation of symbols]

[0051] 1 screw compressor 2 male rotor 3 female rotor 4 Casing 5, 7 (Suction side) Bearings 6, 8 (Discharge side) Bearings 9 Shaft seal member 21 Rotor tooth portion 21a Male tooth 21b Suction side end face 21c Discharge side end face 21d (Discharge side) cross-sectional tooth profile 21s (intake side) cross-sectional tooth profile 21t tooth tip 22 shaft 22a (suction side of shaft) 22b (discharge side of shaft) 31 rotor tooth portion 31a female tooth 31b suction side end surface 31c Discharge side end surface 32 Shaft 32a (suction side of shaft) 32b (discharge side of shaft) 41 main casing (first casing segment) 41a joint surface 42 Discharge side casing (second casing segment) 43 Suction side casing (third casing segment) 44 Bolt hole 45 Receiving chamber 46 Inner surface of male bore 47 female side bore inner peripheral surface 48 suction side inner wall surface 49 discharge side inner wall surface 51 suction side bearing chamber 52 suction side bearing chamber 54 discharge side bearing chamber 55 Discharge side bearing chamber 61 Suction passage 62 Suction space 64 Discharge passage 65 Discharge port 101 screw fluid machine 102 casing 105 first shaft 120 male rotor 135 second shaft 140 female rotor 145 Tooth space 201 Motor 204 Shaft 205 Rotor C Working chamber CP Pitch point center circle C pch Pitch circle A1, A2 rotation axis

Claims

1. a male rotor having twisted male teeth and rotating about a first center of rotation; a female rotor having twisted female teeth and rotating about a second center of rotation parallel to the first center of rotation; a casing having an accommodation chamber that accommodates the male rotor and the female rotor in a rotatable state while they are meshed together; A screw fluid machine that conveys fluid between a suction port and a discharge port while changing the pressure of the fluid by rotating the male rotor and the female rotor, The male rotor is a cross section at the discharge side end surface that is perpendicular to the first center of rotation is formed in a first cross-sectional shape in which a length from an arbitrary point in the rotor forward direction from the tooth tip to the pitch point is equal to or longer than a length from the tooth tip to the pitch point of the tooth, a screw fluid machine characterized in that a cross section perpendicular to the first center of rotation at a predetermined position between the suction side end face and the discharge side end face as viewed in the axial direction has a section having a second cross section shape in which the length from a predetermined point in the rotor forward direction of the tooth tip to the pitch point of the tooth is shorter than the length from the tooth tip to the pitch point of the tooth.

2. The screw fluid machine according to claim 1, The male rotor is A screw fluid machine characterized in that, as viewed in the axial direction, there is a transition section between a section of the male rotor having the first cross-sectional shape and a section of the male rotor having the second cross-sectional shape, in which the cross-section of the male rotor continuously changes from the second cross-sectional shape to the first cross-sectional shape.

3. The screw fluid machine according to claim 2, A screw fluid machine, characterized in that a cross section of the male rotor at the suction side end surface is formed in the second cross section shape.

4. The screw fluid machine according to claim 3, the male rotor in a section from the suction side end face to the transition section as viewed in the axial direction is formed to have the same cross-sectional shape as the second cross-sectional shape, a second cross-sectional shape of the male rotor extending from the transition section to the discharge end surface as viewed in the axial direction, the second cross-sectional shape being the same as the first cross-sectional shape;

5. The screw fluid machine according to claim 4, a tooth profile on the advancing surface side of the tooth tip in the second cross-sectional shape of the male rotor is formed so that the product of the angle formed by connecting the point where a normal drawn from a point on the advancing surface intersects with the pitch circle, the center of the male rotor, and the tooth tip with straight lines in this order, and the lead does not exceed the axial length of the transition section.

6. The screw fluid machine according to claim 3, a section of a third cross-sectional shape, the length from an arbitrary point in the rotor forward direction from the tooth tip to the pitch point of the tooth being equal to or longer than the length from the tooth tip to the pitch point of the tooth, and a second transition section, the third cross-sectional shape being continuously changed from the third cross-sectional shape to the second cross-sectional shape, as viewed in the axial direction.

7. The screw fluid machine according to claim 6, A screw fluid machine, wherein the first cross-sectional shape and the third cross-sectional shape are the same shape.

8. The screw fluid machine according to claim 1, a shape of the male rotor from the tooth tip to the front side thereof in the section of the first cross-sectional shape such that the tooth tip coincides with or is located outside a pitch point center circle that has the pitch point as its center and passes through the tooth tip, and a contour of the tooth tip in the section of the second cross-sectional shape such that the contour of the tooth tip is located inside the pitch point center circle; A screw fluid machine characterized in that the cross-sectional shape of the female rotor taken perpendicular to the direction of the rotation axis corresponds to the cross-sectional shape of the male rotor.

9. The screw fluid machine according to claim 1, A screw fluid machine, characterized in that a lubricating liquid is supplied into the accommodating chamber that compresses the fluid.

10. a male rotor having twisted male teeth and rotating about a first center of rotation; a female rotor having twisted female teeth and rotating about a second center of rotation parallel to the first center of rotation; a casing having an accommodation chamber that accommodates the male rotor and the female rotor in a rotatable state while they are meshed together; A screw fluid machine that conveys fluid between a suction port and a discharge port while changing the pressure of the fluid by rotating the male rotor and the female rotor, The male rotor is a cross-sectional shape perpendicular to the rotation axis is formed in the order of a second cross-sectional shape, a continuously changing transition shape, and a first cross-sectional shape from the suction side end face to the discharge side end face as viewed in the axial direction of the rotation axis, the cross-sectional tooth profile of the section of the first cross-sectional shape is a cross-sectional shape that coincides with the pitch point center circle or is located outside the pitch point center circle at the tooth tip and the advancing surface side of the tooth tip, the cross-sectional tooth profile of the section of the second cross-sectional shape has a cross-sectional shape that is located inside the pitch point center circle at the tooth tip and at the advancing surface side of the tooth tip, In the transitional shape section, the cross-sectional tooth profile of the male rotor is made to have a shape that changes continuously from the second cross-sectional shape to the first cross-sectional shape.

11. The screw fluid machine according to claim 10, The axial length of the transitional shape section is shorter than the sections of the first and second cross-sectional shapes, and the remaining volume is a space V ｒｅｓ The screw fluid machine is characterized in that the maximum axial width Lv of the screw is larger than the maximum axial width Lv of the screw.

12. The screw fluid machine according to claim 11, the section of the second cross-sectional shape occupies half or more of the length of the male rotor in the direction of the rotation axis, The screw fluid machine, wherein the transitional shape section is disposed in a rear region near the discharge side of the male rotor.

13. The screw fluid machine according to claim 12, A screw fluid machine, characterized in that the length of the section of the first cross-sectional shape in the direction of the rotation axis is shorter than the length of the section of the transition shape in the direction of the rotation axis.

14. a male rotor having twisted male teeth and rotating about a first center of rotation; a female rotor having twisted female teeth and rotating about a second center of rotation parallel to the first center of rotation; a casing having an accommodation chamber that accommodates the male rotor and the female rotor in a rotatable state while they are meshed together; A screw fluid machine that conveys fluid between a suction port and a discharge port while changing the pressure of the fluid by rotating the male rotor and the female rotor, The male rotor is a cross section perpendicular to the rotation axis is formed in the order of a first cross-sectional shape, a continuously changing second transition shape, a second cross-sectional shape, a continuously changing first transition shape, and a first cross-sectional shape, from a suction side end face of the rotation axis to a discharge side end face thereof; the cross-sectional tooth profile of the section of the first cross-sectional shape is a cross-sectional shape that coincides with the pitch point center circle or is located outside the pitch point center circle at the tooth tip and the advancing surface side of the tooth tip, the cross-sectional tooth profile of the section of the second cross-sectional shape has a cross-sectional shape that is located inside the pitch point center circle at the tooth tip and at the advancing surface side of the tooth tip, In the second transitional shape section, the cross section continuously changes from the first cross-sectional shape to the second cross-sectional shape, A screw fluid machine, characterized in that in a section of the first transitional shape, the cross section continuously changes from the second cross-sectional shape to the first cross-sectional shape.

15. The screw fluid machine according to claim 14, A screw fluid machine, characterized in that a total length of the sections of the first cross-sectional shape in the direction of the rotation axis is shorter than a total length of the sections of the first cross-sectional shape in the direction of the rotation axis.

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