Screw compressor and screw rotor

Abstract

To provide a screw compressor which is made compatible in both the suppression of the leakage of a working gas in a working chamber via a clearance formed between a rotor and a casing, and the suppression of the generation of tooth-face separation vibration.SOLUTION: In a screw compressor, a tooth wave of a cross section vertical to an axial direction of a female rotor which rotates around a second rotation center is changed in the axial direction. One tooth having the tooth wave of the female rotor is constituted of a first contour line for regulating a forward traveling face of the female rotor at a rotation direction side, a second contour line for regulating a backward traveling face at a direction side opposite to the rotation direction, and a third contour line for regulating a tooth tip part at which both end points form a maximum radius with a tooth bottom as a boundary point. In the tooth wave of the female rotor, when a second rotation center is set as an apex, and an angle formed of two line components for connecting the second rotation center and both ends of the first contour line, an angle formed of two line components for connecting the second rotation center and both ends of the second contour line, and an angle formed of two line components for connecting the second rotation center and both ends of the third contour line are defined as a first angle, a second angle and a third angle, respectively, the third angle is large at a discharge side in the axial direction, and the first angle is small at the discharge side in the axial direction.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a screw compressor including a pair of screw rotors having meshing helical teeth, and to a screw rotor constituting the screw compressor. [Background technology]

[0002] Screw compressors are widely used as air compressors and compressors for refrigeration and air conditioning, and in recent years, there has been a strong demand for energy saving, so it is becoming increasingly important for screw compressors to achieve high energy efficiency.

[0003] A screw compressor is equipped with a pair of male and female screw rotors that rotate while meshing with each other, and a casing that houses both screw rotors. Both screw rotors have helical teeth (tooth grooves). This compressor draws in and compresses gas by increasing and decreasing the volume of multiple working chambers formed by the tooth grooves of both screw rotors and the inner wall surface of the casing that surrounds them as both screw rotors rotate.

[0004] In a screw compressor, a small gap is provided between the rotating screw rotor and the casing so that the rotor does not come into contact with the casing. For example, a gap (hereinafter sometimes referred to as an outer diameter gap) is provided between the tooth tip of each screw rotor and the inner peripheral surface of the casing. Therefore, compressed gas leaks from a working chamber with a relatively high pressure to a working chamber with a relatively low pressure through the outer diameter gap. When compressed gas leaks, the compression power consumed is wasted or power for recompression is required, thereby reducing the efficiency of the compressor.

[0005] In a liquid-feed screw compressor, a sealing effect is generated for the outer diameter gap by supplying a liquid such as oil or water to the working chamber. This suppresses leakage of compressed gas through the outer diameter gap between the working chambers, but further suppression of leakage of compressed gas is required to improve compressor efficiency. In addition, in the case of a liquid-free screw compressor, since no liquid is supplied to the working chambers, a sealing effect of liquid for the outer diameter gap cannot be expected. Therefore, in a liquid-free screw compressor, there is a particular concern that the compressor efficiency will decrease due to leakage of compressed gas through the outer diameter gap between the working chambers.

[0006] In addition, in recent years, there are many single-stage screw compressors with a compression ratio of more than 8, and the pressure difference between the working chambers located on the discharge side in the axial direction of the screw rotor tends to increase. If the pressure difference between the working chambers increases, there is a concern that the efficiency of the compressor will further decrease due to leakage of compressed gas through the outer diameter gap between the working chambers.

[0007] Therefore, in order to improve the compressor efficiency, it is required to reduce the leakage of compressed gas through the outer diameter gap between the working chambers in the axial discharge side region of the compressor. As a technology for reducing the leakage of compressed gas in the discharge side region, for example, the one described in Patent Document 1 is known. In the screw compressor described in Patent Document 1, in order to reduce the ratio of the amount of leakage air to the amount of intake air and to prevent galling due to contact between the two screw rotors, the tooth thickness of the multiple teeth provided on the female rotor is formed so that the tooth thickness is thicker on the discharge port side than on the suction port side. Note that the "tooth thickness" here refers to the thickness of the teeth in the tooth profile of a cross section perpendicular to the axial direction of the screw rotor. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2004-144035 A Summary of the Invention [Problem to be solved by the invention]

[0009] As in the screw compressor described in Patent Document 1, when the tooth thickness of the female rotor is increased on the discharge port side (the discharge side end in the axial direction of the female rotor), the width (distance) of the boundary between the working chambers on the discharge port side of the female rotor increases accordingly, and therefore leakage of compressed gas through the outer diameter gap between the working chambers on the discharge port side of the female rotor can be suppressed.

[0010] In unequal lead screw rotors, where the lead of the screw rotor decreases from the suction side to the discharge side in the axial direction, the tooth thickness of the female rotor teeth tends to be thinner than in equal lead screw rotors. However, the "tooth thickness" here refers to the thickness of the tooth tip in the tooth profile of the cross section perpendicular to the extension direction of the female rotor tooth tip line. The lead refers to the distance traveled in the axial direction with one twist of the screw rotor.

[0011] When the lead of the screw rotor becomes smaller from the suction side to the discharge side in the axial direction, the twist of the screw rotor becomes tighter from the suction side to the discharge side. Therefore, under the condition that the tooth profile of the cross section perpendicular to the axial direction of the screw rotor is the same, the tooth thickness of the female rotor tooth tip tends to be thinner on the discharge side compared to screw rotors with equal lead.

[0012] Therefore, in an unequal lead screw rotor in which the lead decreases from the suction side to the discharge side in the axial direction, the tooth thickness of the female rotor's tooth tips becomes thinner on the discharge side, which raises concerns about increased leakage of compressed gas through the outer diameter gap between the working chambers located on the discharge side. Therefore, a configuration in which the tooth thickness of the female rotor's tooth tips is made thicker on the discharge side, as in the screw compressor described in Patent Document 1, may be considered.

[0013] However, in a screw compressor with an equal or unequal lead screw rotor, if the tooth thickness of the female rotor's tooth tip is made thicker on the discharge side than on the suction side in the axial direction, as in the screw compressor described in Patent Document 1, a vibration phenomenon called tooth surface separation vibration may occur in the screw rotor. In a screw compressor with a male rotor and a female rotor that mesh with each other, the tooth surfaces of the two rotors generally come into direct contact with each other, or a synchronous gear provided coaxially with the two rotors meshes with each other, so that the driving torque of the male rotor is transmitted to the female rotor and the female rotor is driven. Depending on the pressure conditions acting on the rotor tooth surface, the torque transmitted from the male rotor to the female rotor may temporarily become negative, causing a phenomenon called tooth surface separation in which the tooth surfaces that transmitted the torque are separated from each other. After that, when the torque transmitted from the male rotor to the female rotor returns to positive again, the tooth surfaces that were once separated collide with each other. As a result, tooth surface separation and collision of the tooth surfaces are repeated, generating large vibrations and noise. This is called tooth surface separation vibration.

[0014] As described above, if the tooth thickness of the female rotor's tooth tip is increased on the discharge side in order to suppress leakage of working gas through the outer diameter gap between the working chambers located on the discharge side in the axial direction of the screw rotor, a vibration phenomenon called tooth surface separation vibration may occur in the screw rotor. However, Patent Document 1 does not particularly mention a structure for suppressing tooth surface separation vibration.

[0015] The present invention has been made to solve the above-mentioned problems, and its object is to provide a screw compressor and a screw rotor that can simultaneously suppress leakage of working gas between the working chambers via the gap formed between the screw rotor and the casing, and suppress the occurrence of tooth surface separation vibration. [Means for solving the problem]

[0016] The present application includes a plurality of means for solving the above-mentioned problems, and an example thereof is a rotor having twisted male teeth and rotating around a first center of rotation, a female rotor having twisted female teeth and meshing with the male rotor and rotating around a second center of rotation parallel to the first center of rotation, and a casing having an accommodation chamber for rotatably accommodating the male rotor and the female rotor in an meshed state, the casing forming a plurality of working chambers together with the male rotor and the female rotor, wherein a tooth profile representing a contour shape of a cross section perpendicular to the axial direction of the female rotor is formed so as to change between a certain first position in the axial direction and a second position on the discharge side of the axial direction from the first position, and one tooth of the tooth profile of the female rotor has a first contour line that defines a section of a forward surface extending from a tooth bottom having a minimum radius as a boundary point to a first end point having a maximum radius, and a second contour line that defines a section of a forward surface extending from the boundary point to a first end point having a maximum radius in the opposite direction to the rotation direction of the female rotor, the first contour line defining a section of a forward surface extending from the boundary point to a first end point having a maximum radius in the opposite direction to the rotation direction of the female rotor, the second ... and a third contour line defining a section of a tooth tip portion having a maximum radius, one of the two end points being a connection point between the first end point of the first contour line or the second end point of the second contour line. The tooth profile of the female rotor is configured such that, when an angle formed by two line segments connecting the second center of rotation and both ends of the first contour line with the second rotation center as a vertex is defined as a first angle, an angle formed by two line segments connecting the second center of rotation and both ends of the second contour line with the second rotation center as a vertex is defined as a second angle, and an angle formed by two line segments connecting the second center of rotation and both ends of the third contour line with the second rotation center as a vertex is defined as a third angle, the third angle at the second position is set to be larger than the third angle at the first position, and the first angle at the second position is set to be smaller than the first angle at the first position. Effect of the Invention

[0017] According to the present invention, by setting the third angle corresponding to the shape of the tooth tip of the female rotor's tooth profile to be larger on the axial discharge side than on the suction side, the thickness of the tooth tip of the female rotor becomes thicker on the discharge side, thereby suppressing leakage of high-pressure working gas through the outer diameter gap between the working chambers located on the axial discharge side. At the same time, by setting the second angle corresponding to the shape of the forward moving surface of the female rotor's tooth profile to be smaller on the axial discharge side than on the suction side, the occurrence of tooth flank separation is suppressed. Therefore, it is possible to suppress both leakage of working gas between the working chambers through the gap provided between the female rotor and the casing and the occurrence of tooth flank separation vibration. Problems, configurations and effects other than those described above will become apparent from the following description of the embodiments. [Brief description of the drawings]

[0018] [Figure 1] 1 is a cross-sectional view showing a screw compressor according to a first embodiment of the present invention. [Diagram 2] 2 is a cross-sectional view of the screw compressor according to the first embodiment of the present invention shown in FIG. 1, taken along the line II-II of the arrows. [Diagram 3] 1 is a cross-sectional view showing, in an enlarged state, a tooth profile that represents the contour shape of a cross section perpendicular to the axial direction in a pair of screw rotors that constitute a part of a screw compressor according to a first embodiment of the present invention. FIG. [Figure 4] 3 is a cross-sectional view showing the screw compressor according to the first embodiment of the present invention shown in FIG. 2 in a state where a tooth profile of one tooth of a female rotor is superimposed when viewed from the S1-S1 arrow and D1-D1 arrow views. [Diagram 5] FIG. 2 is a diagram for explaining causes of tooth surface separation vibration in general screw compressors. [Figure 6] 1 is a table comparing the likelihood of tooth flank separation occurring when the tooth profile elements of the forward and reverse surfaces are changed while the shape of the tooth tip portion (tooth tip angle) of the tooth profile of a female rotor that constitutes a screw compressor is fixed. [Figure 7]FIG. 7 is a table comparing the likelihood of tooth surface separation occurring when the tooth profile elements of the forward and reverse surfaces are changed when the shape of the tooth tip portion (tooth tip angle) of the tooth profile of a female rotor that constitutes a screw compressor is fixed in a state where it is larger than the shape of the tooth tip portion (tooth tip angle) shown in FIG. [Figure 8] FIG. 1 is an explanatory diagram showing a blowhole as an internal gap in a general screw compressor. [Figure 9] 3 is a cross-sectional view showing a screw compressor according to a second embodiment of the present invention, showing a state in which a tooth profile of one tooth of a female rotor is superimposed when viewed from the same arrow direction as the S1-S1 arrow direction and the D1-D1 arrow direction shown in FIG. [Figure 10] FIG. 11 is a characteristic diagram showing a change in tooth flank separation tolerance torque with respect to the rotation angle of a male rotor in a screw compressor according to a second embodiment of the present invention. [Figure 11] FIG. 11 is a cross-sectional view showing a screw compressor according to a third embodiment of the present invention. [Figure 12] 12 is a cross-sectional view showing the screw compressor according to the third embodiment of the present invention shown in FIG. 11 in a state where a tooth profile of one tooth of a female rotor is superimposed when viewed from the S3-S3 arrow direction and the D3-D3 arrow direction. [Figure 13] FIG. 11 is a cross-sectional view showing an unequal lead screw compressor as a comparative example for the screw compressor according to the third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a screw compressor according to the present invention will be described with reference to the drawings.

[0020] [First embodiment] The configuration of a screw compressor according to a first embodiment will be described with reference to Fig. 1 and Fig. 2. Fig. 1 is a cross-sectional view showing the screw compressor according to the first embodiment of the present invention. Fig. 2 is a cross-sectional view of the screw compressor according to the first embodiment of the present invention shown in Fig. 1, as viewed from the arrows II-II. In Figs. 1 and 2, the left side is the suction side of the screw compressor, and the right side is the discharge side.

[0021] 1, the screw compressor is composed of a compressor body 1 that compresses gas, and a drive unit 80 that drives the compressor body 1. The screw compressor is, for example, of a liquid supply type in which liquid is supplied from the outside to the inside of the compressor body 1.

[0022] 1 and 2, the compressor body 1 includes a male rotor 2 and a female rotor 3 as a pair of screw rotors that rotate while meshing with each other, and a main casing 4 that houses the male rotor 2 and the female rotor 3 inside so that they can rotate while meshing with each other. The male rotor 2 and the female rotor 3 are arranged so that their rotation centers A1 and A2 are parallel to each other. The male rotor 2 is rotatably supported at both ends in the axial direction (left and right direction in Figs. 1 and 2) by a suction side bearing 5 and a discharge side bearing 6a and 6b, respectively. The female rotor 3 is rotatably supported at both ends in the axial direction by a suction side bearing 7 and a discharge side bearing 8a and 8b, respectively.

[0023] The male rotor 2 is composed of a rotor tooth portion 21 having a plurality of helical male teeth (lobes) 21a formed thereon, and a suction-side shaft portion 22 and a discharge-side shaft portion 23 provided on 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 perpendicular to the axial direction (center of rotation A1) at one axial end (left end in Figs. 1 and 2) and the other axial end (right end in Figs. 1 and 2), respectively. Tooth grooves are formed between the plurality of male teeth 21a of the rotor tooth portion 21. The suction-side shaft portion 22 extends, for example, to the outside of the main casing 4, and is configured to be common to the shaft portion of the drive unit 80.

[0024] The female rotor 3 is composed of a rotor tooth portion 31 having a plurality of spiral female teeth 31a (see FIG. 3 described later) formed thereon, and a suction-side shaft portion 32 and a discharge-side shaft portion 33 provided on both axial end portions of the rotor tooth portion 31. The rotor tooth portion 31 has a suction-side end face 31b and a discharge-side end face 31c perpendicular to the axial direction (center of rotation A2) at one axial end (left end in FIGS. 1 and 2) and the other axial end (right end in FIGS. 1 and 2), respectively. Tooth grooves are formed between the plurality of female teeth 31a of the rotor tooth portion 31.

[0025] The main casing 4 includes a main casing 41 and a discharge side casing 42 attached to the discharge side of the main casing 41 (the right side in Figs. 1 and 2).

[0026] A bore 45 is formed inside the main casing 4 as an accommodation chamber for accommodating the rotor teeth 21 of the male rotor 2 and the rotor teeth 31 of the female rotor 3 in a mutually meshed state. The bore 45 is formed by closing an opening on one axial side (the right side in Figs. 1 and 2) of two partially overlapping cylindrical spaces formed in the main casing 41 with the discharge side casing 42. The inner wall surface forming the bore 45 is composed of a substantially cylindrical first inner circumferential surface 46 covering the radial outside of the rotor teeth 21 of the male rotor 2, a substantially cylindrical second inner circumferential surface 47 covering the radial outside of the rotor teeth 31 of the female rotor 3, a suction side inner wall surface 48 on one axial side (left side in Figs. 1 and 2) facing the suction side end faces 21b, 31b of the rotor teeth 21, 31 of both the male and female rotors 2, 3, and a discharge side inner wall surface 49 on the other axial side (right side in Figs. 1 and 2) facing the discharge side end faces 21c, 31c of the rotor teeth 21, 31 of both the male and female rotors 2, 3. The first circumferential surface 46 and the second circumferential surface 47 form a pair of intersection lines, which are called cusp lines 45a (see Fig. 3). The cusp lines 45a extend in the axial direction and are formed on the expansion side and compression side of the rotor meshing portion (only the expansion side is shown in FIG. 3). A plurality of working chambers C are formed by the rotor teeth 21, 31 of the male and female rotors 2, 3 and the inner wall surface of the main casing 4 surrounding them (the first inner circumferential surface 46, the second inner circumferential surface 47, the suction side inner wall surface 48, and the discharge side inner wall surface 49 of the bore 45).

[0027] A suction side bearing 5 on the male rotor 2 side and a suction side bearing 7 on the female rotor 3 side are disposed at the suction side end of the main casing 41. Discharge side bearings 6a, 6b on the male rotor 2 side and discharge side bearings 8a, 8b on the female rotor 3 side are disposed in the discharge side casing 42. A discharge side cover 43 is attached to the discharge side casing 42 so as to cover the discharge side bearings 6a, 6b and the discharge side bearings 8a, 8b.

[0028] 1, the main casing 41 of the body casing 4 is provided with an intake passage 51 for drawing gas into the working chamber C. The intake passage 51 connects the outside of the body casing 4 with the bore 45 (working chamber C). The intake passage 51 has, for example, an intake port 51a that opens into the inner wall surface of the body casing 4. The intake port 51a can be formed so as to open in the axial direction or radial direction of the male and female rotors 2, 3, or in both directions.

[0029] Further, the discharge side casing 42 of the main casing 4 is provided with a discharge flow passage 52 for discharging compressed gas from the working chamber C to the outside of the main casing 4. The discharge flow passage 52 connects the bore 45 (working chamber C) with the outside of the main casing 4. The discharge flow passage 52 has a discharge port 52a formed in the discharge side inner wall surface 49 of the main casing 4. The discharge port 52a can be formed so as to open in the axial direction or radial direction of the male and female rotors 2, 3, or in both directions.

[0030] The main casing 41 of the body casing 4 is provided with a liquid supply passage 53 that supplies liquid supplied from outside the compressor body 1 to the working chamber C. The liquid supply passage 53 opens, for example, to a region on the inner wall surface of the bore 45 where the working chamber C undergoes a compression process.

[0031] 1, the drive unit 80 is an electric motor, and is configured integrally with the compressor body 1. The drive unit 80 includes a motor 83 consisting of a rotor 81 and a stator 82, a motor casing 85 that houses the motor 83 therein, and a motor cover 86 that closes the opening of the motor casing 85. The rotor 81 is connected to the male rotor 2 of the compressor body 1. A motor-side bearing 87 that rotatably supports the rotor 81, and a shaft seal member 88 that prevents leakage of liquid from the compressor body 1 to the drive unit 80 are disposed in the motor casing 85.

[0032] In this embodiment, an example has been shown in which an electric motor is used for the drive unit 80, but the rotational drive source is not particularly limited. Also, a configuration is possible in which the drive unit 80 rotates the female rotor 3, or both the male and female rotors 2, 3, instead of the male rotor 2. Also, a configuration is possible in which the drive unit 80 and the compressor body 1 do not share a shaft portion.

[0033] Next, the basic configuration of the tooth profiles of the male and female rotors in the screw compressor according to the first embodiment will be described with reference to Fig. 3. Fig. 3 is a cross-sectional view showing, in a partially enlarged state, the tooth profiles that represent the contour shapes of cross sections perpendicular to the axial direction in a pair of screw rotors that constitute a part of the screw compressor according to the first embodiment of the present invention. In Fig. 3, the thick arrows indicate the rotation directions of the male rotor and the female rotor. That is, in Fig. 3, the male rotor rotates clockwise and the female rotor rotates counterclockwise.

[0034] 3, tooth profiles 60, 70 representing the contour shapes of cross sections perpendicular to the axial direction (centers of rotation A1, A2) of rotor tooth portions 21, 31 of the male rotor 2 and female rotor 3 are geometrically designed so that the gap between the meshing portions of the male and female rotors 2, 3 is theoretically zero. However, in reality, the tooth profiles are designed with an appropriate gap set to allow for thermal deformation, gas pressure deformation, vibration, and processing errors in the meshing portions of the two rotors 2, 3, and are manufactured with a reduced thickness corresponding to the geometrically designed shape.

[0035] The essence of the present invention is not directly related to the presence or absence of a gap in the meshing portion of both rotors 2, 3. Therefore, although the tooth profiles 60, 70 of the rotor tooth portions 21, 31 of the male rotor 2 and female rotor 3 will be considered regarding the presence of a gap in the meshing portion of both rotors 2, 3, the tooth profiles 60, 70 will be described as having a geometric design shape in which the gap is zero. Therefore, even if the following description expresses "contact," there may actually be a minute gap in the meshing portion of the tooth profiles 60, 70 of the male rotor 2 and female rotor 3.

[0036] The tooth profiles 60, 70 of the male and female rotors 2, 3 are configured so that each point on the tooth profile 60 of the male rotor 2 and each point on the tooth profile 70 of the female rotor 3 are paired one-to-one, and are configured to satisfy the meshing condition "the common normal of both tooth surfaces when meshed at a constant speed ratio passes through the pitch point". In other words, it can be expressed as "when a point on a tooth surface is in a position that satisfies the meshing condition, it comes into contact with the mating tooth surface". Since a pair of screw rotors that mesh with each other must satisfy this condition, when the tooth profile of either the male rotor 2 or the female rotor 3 is determined, the tooth profile of the other is uniquely determined. In the following explanation, the tooth profile of the male rotor 2 may be referred to as the male tooth profile, and the tooth profile of the female rotor 3 may be referred to as the female tooth profile. Note that the point obtained by internally dividing the line segment connecting the rotation center A1 of the male rotor 2 and the rotation center A2 of the female rotor 3 by the ratio of the number of teeth of the male rotor 2 to the number of teeth of the female rotor 3 is the pitch point P, which is an important position in the geometric design of the tooth profile.

[0037] 3, the center of rotation A1 of the male rotor 2, the center of rotation A2 of the female rotor 3, the tooth tip 65 which is the maximum radius of the male rotor 2, and the tooth bottom 75 which is the minimum radius of the female rotor 3 are located on the same line, and the tooth tip 65 of the male rotor 2 and the tooth bottom 75 of the female rotor 3 are in contact. The rotation angle of both the male and female rotors 2 and 3 at this time is defined as the reference angle (0°).

[0038] One tooth of the male tooth profile 60 of the male rotor 2 is composed of a first contour line 61 that defines the section of the forward surface, a second contour line 62 that defines the section of the reverse surface, and a third contour line 63 that defines the section of the tooth bottom. In this description, the tooth tip, which is the maximum radius of the male rotor 2, is defined as the boundary, and the tooth surface on the rotation direction side of the male rotor 2 is defined as the forward surface of the male rotor 2, and the tooth surface on the opposite side to the rotation direction is defined as the reverse surface of the male rotor 2. Specifically, the first contour line 61 defines a section that extends from the tooth tip 65 as the boundary point to the rotation direction of the male rotor 2 to a first end point 66 that is the minimum radius. The second contour line 62 defines a section that extends from the tooth tip 65 as the boundary point to the opposite side to the rotation direction of the male rotor 2 to a second end point 67 that is the minimum radius. The third contour line 63 defines a section whose both end points form the minimum radius, and for example, one of the both end points is a connection point with a first end point 66 of the first contour line 61 and the other end point is a connection point with a second end point 67 of the second contour line 62 of an adjacent tooth. Note that the third contour line 63 may have one of the both end points be a connection point with the first end point 66 of the first contour line 61 of an adjacent tooth and the other end point be a connection point with the second end point 67 of the second contour line 62.

[0039] One tooth of the female tooth profile 70 of the female rotor 3 is composed of a first contour line 71 that defines a section of the forward surface, a second contour line 72 that defines a section of the reverse surface, and a third contour line 73 that defines a section of the tooth tip. In this description, the tooth surface on the rotation direction side of the female rotor 3 is defined as the forward surface of the female rotor 3, and the tooth surface on the opposite side to the rotation direction is defined as the reverse surface of the female rotor 3, with the tooth bottom 75 as the boundary point. Specifically, the first contour line 71 defines a section that extends from the boundary point, which is the tooth bottom 75, to the rotation direction side of the female rotor 3 to reach a first end point 76 that is the maximum radius. The second contour line 72 defines a section that extends from the boundary point, which is the tooth bottom 75, to the opposite side to the rotation direction of the female rotor 3 to reach a second end point 77 that is the maximum radius. The third contour line 73 defines a section whose both end points form the maximum radius, and for example, one of the both end points is a connection point with a first end point 76 of the first contour line 71 and the other end point is a connection point with a second end point 77 of the second contour line 72 of an adjacent tooth. Note that the third contour line 73 may have one of the both end points be a connection point with a first end point 76 of the first contour line 71 of an adjacent tooth and the other end point be a connection point with a second end point 77 of the second contour line 72.

[0040] A first contour line 61 that defines the forward surface and a second contour line 62 that defines the reverse surface of the tooth profile 60 of the male rotor 2 are made up of a plurality of tooth profile elements. Similarly, a first contour line 71 that defines the forward surface and a second contour line 72 that defines the reverse surface of the tooth profile 70 of the female rotor 3 are made up of a plurality of tooth profile elements.

[0041] An example of the tooth profiles 60, 70 of the male rotor 2 and the female rotor 3 is shown in Figure 3. The tooth profiles 60, 70 are obtained by forming a first contour line 61, 71 that defines the forward movement surface with tooth profile elements of one parabola and one circular arc, and forming a second contour line 62, 72 that defines the reverse movement surface with tooth profile elements of two circular arcs.

[0042] Specifically, the second contour lines 62, 72 that define the reversing surfaces of the tooth profiles 60, 70 of the male and female rotors 2, 3 are generated based on, for example, one first arc as a convex curved surface starting from a tooth tip 65 (one end point of the second contour line 62) of the second contour line 62 of the male rotor 2, and one second arc as a convex curved surface ending from a second end point 77 (the other end point of the second contour line 72) of the second contour line 72 of the female rotor 3. The first arc of the second contour line 62 of the male rotor 2 has a certain radius R1 and is a curved line ending at a point 62a. The second arc of the second contour line 72 of the female rotor 3 has a certain radius R2 and is a curved line starting from a point 72a. Of the second contour line 62 of the male rotor 2, the remaining section from the end point 62a of the first arc to the second end point 67 of the second contour line 62 is generated so as to satisfy the above-mentioned meshing conditions according to the shape of the second contour line 72 including the second arc of the female rotor 3. Moreover, of the second contour line 72 of the female rotor 3, the remaining section from the tooth bottom 75 (one end point of the second contour line 72) to the start point 72a of the second arc is generated so as to satisfy the above-mentioned meshing conditions according to the shape of the second contour line 62 including the first arc of the male rotor 2.

[0043] The first contour line 71 of the tooth profile 70 of the female rotor 3 is generated based on, for example, one parabola constituting a concave curved surface and one third arc constituting a convex curved surface. The parabola has a focal point F located on a line segment connecting the rotation center A1 of the male rotor 2 and the rotation center A2 of the female rotor 3, and has a certain focal length Lf. The parabola of the first contour line 71 of the female rotor 3 is a curved line extending from the tooth bottom 75 (one end point of the first contour line 71) to a point 71a as an end point. The third arc of the first contour line 71 of the female rotor 3 has a certain radius R3 and is a curved line extending from the end point 71a of the parabola as a start point to a first end point 76 of the first contour line 71. The first contour line 61 of the male rotor 2 is generated so as to satisfy the above meshing conditions according to the shapes of the parabola and the third arc, which are the tooth profile elements of the first contour line 71 of the female rotor 3.

[0044] The third contour line 73 that defines the tooth tip of the female rotor 3 can be configured, for example, as a circular arc centered on the rotation center A2 of the female rotor 3 and having the maximum radius of the female rotor 3. The third contour line 63 that defines the tooth bottom of the male rotor 2 is generated so as to satisfy the above meshing conditions according to the shape of the third contour line 73 of the female rotor 3. The third contour line 63 can be configured, for example, as a circular arc centered on the rotation center A1 of the male rotor 2 and having the minimum radius of the male rotor 2.

[0045] In the female tooth profile 70 of the female rotor 3, the first contour line 71 that defines the forward surface, the second contour line 72 that defines the reverse surface, and the third contour line 73 that defines the tooth tip can be expressed using angles with the center of rotation A2 of the female rotor 3 as a vertex, as follows. The forward surface angle φL is defined as the angle formed by two line segments that connect the center of rotation A2 of the female rotor 3 with the tooth bottom 75 and the first end point 76, which are both ends of the first contour line 71, and the center of rotation A2 of the female rotor 3 is defined as the vertex. The reverse surface angle φT is defined as the angle formed by two line segments that connect the center of rotation A2 of the female rotor 3 with the tooth bottom 75 and the second end point 77, which are both ends of the second contour line 72, and the The tooth tip angle φS is defined as the angle formed by two line segments connecting the rotation center A2 of the female rotor 3 as its vertex and the first end point 76 of the first contour line 71 and the second end point 77 of the second contour line 72, which are both ends of the third contour line 73.

[0046] Next, the characteristics of the tooth profiles of the male and female rotors in the screw compressor according to the first embodiment will be described with reference to Fig. 2 and Fig. 4. Fig. 4 is a cross-sectional view showing the tooth profile of one tooth of the female rotor superimposed when the screw compressor according to the first embodiment of the present invention shown in Fig. 2 is viewed from the S1-S1 arrow and the D1-D1 arrow. In Fig. 4, the solid line indicates the tooth profile of one tooth on the discharge side (D1-D1 cross section) of the female rotor 3, and the dashed line indicates the tooth profile of one tooth on the suction side (S1-S1 cross section) of the female rotor 3. In Fig. 4, like Fig. 3, the rotation angle of the female rotor is set to the reference angle (0°).

[0047] In Fig. 2, the male rotor 2 and the female rotor 3 are configured as screw rotors with equal lead over the entire axial region from the suction side end (left end in Fig. 2) to the discharge side end (right end in Fig. 2) of the rotor tooth portions 21, 31. In addition, the male rotor 2 and the female rotor 3 are formed so that the tooth profile in a cross section perpendicular to the axial direction (rotation centers A1, A2) changes along the axial direction.

[0048] Specifically, the tooth profile 70 of the female rotor 3 (see FIG. 4) has the same shape along the axial direction in a region from the suction side end face 31b of the rotor tooth portion 31 to a certain first position closer to the axial discharge side, for example, a substantially middle position in the axial direction (S1-S1 position). On the other hand, in a region from the first position to the discharge side end face 31c (D1-D1 position) of the female rotor 3, the female tooth profile 70 is formed so as to gradually change from the first tooth profile 70s (the tooth profile at the S1-S1 position shown in FIG. 2) on the suction side shown by the dashed line in FIG. 4 to the second tooth profile 70d (the tooth profile at the D1-D1 position shown in FIG. 2) on the discharge side shown by the solid line. The tooth tip angle φS, the forward surface angle φL, and the reverse surface angle φT (see FIG. 3) of the female tooth profile 70 are set to change monotonically with respect to the axial length or the rotation angle from the first position (S1-S1 position) to the discharge side end face 31c (D1-D1 position).

[0049] In FIG. 4, the first tooth profile 70s on the suction side (S1-S1 position) in the axial direction of the female rotor 3 is indicated by a dashed line, and the second tooth profile 70d on the discharge side (D1-D1 position) is indicated by a solid line.

[0050] The first tooth profile 70s on the suction side and the second tooth profile 70d on the discharge side are distinguished from each other by adding the symbol s indicating the suction side and the symbol d indicating the discharge side to the first contour line 71, the second contour line 72, and the third contour line 73 of the female tooth profile 70.

[0051] Similarly, the first tooth profile 70s on the suction side and the second tooth profile 70d on the discharge side are distinguished by adding the symbol s indicating the suction side and the symbol d indicating the discharge side to the tooth bottom 75, which is the starting point of the first contour line 71 and the second contour line 72 of the female tooth profile 70. The first tooth profile 70s on the suction side and the second tooth profile 70d on the discharge side are distinguished by adding the symbol s indicating the suction side and the symbol d indicating the discharge side to both ends 76, 77 of the third contour line 73 of the female tooth profile 70. As described above, one end point of the third contour line 73 is the first end point 76 of the first contour line 71, and the other end point of the third contour line 73 is a point that coincides with the second end point 77 of the second contour line 72.

[0052] In addition, the tooth tip angle φS, forward surface angle φL, and reverse surface angle φT of the female tooth profile 70 are marked with the symbol s indicating the suction side and the symbol d indicating the discharge side to distinguish between the first tooth profile 70s on the suction side and the second tooth profile 70d on the discharge side.

[0053] In this embodiment, as shown in Fig. 4, the tooth tip angle φSd of the second tooth profile 70d on the axial discharge side of the female rotor 3 is set to be larger than the tooth tip angle φSs of the first tooth profile 70s located on the axial suction side of the second tooth profile 70d. That is, the female tooth profile 70 is configured so that the thickness of the tooth tip of the second tooth profile 70d on the discharge side is thicker than the thickness of the tooth tip of the first tooth profile 70s on the suction side. In this way, the tooth tip of the female rotor 3 is made thicker on the axial discharge side, thereby making it possible to suppress leakage of compressed gas through the outer diameter gap between the working chambers located on the axial discharge side.

[0054] The forward advance surface angle φLd of the second tooth profile 70d on the discharge side of the female rotor 3 is set to be smaller than the forward advance surface angle φLs of the first tooth profile 70s on the suction side. In this embodiment, the second contour line 72s of the first tooth profile 70s on the suction side of the female rotor 3 and the second contour line 72d of the second tooth profile 70d on the discharge side have the same shape. In other words, the rearward advance surface angle φTd on the discharge side of the female tooth profile 70 is set to be the same angle as the rearward advance surface angle φTs on the suction side.

[0055] The first tooth profile 70s on the suction side of the female rotor 3 must satisfy the following formula (1). The second tooth profile on the discharge side must satisfy the following formula (2). In formulas (1) and (2), the angle is expressed in degrees. φSs+φLs+φTs=360 / number of teeth of female rotor … Equation (1) φSd+φLd+φTd=360 / number of teeth of female rotor … Equation (2)

[0056] By rearranging the above equations (1) and (2), the following equation (3) is obtained. (φLs-φLd)+(φTs-φTd)=φSd-φSs … Formula (3)

[0057] The above formula (3) is derived from the condition that the tooth tip defined by the third contour line 73d of the second tooth profile 70d on the discharge side of the female rotor 3 is thicker than the tooth tip defined by the third contour line 73s of the first tooth profile 70s on the suction side, as follows: (φLs-φLd)+(φTs-φTd)=φSd-φSs>0

[0058] Therefore, the relationship between the advancing surface angle φL and the reversing surface angle φT must satisfy the following formula (4). φLs-φLd>φTd-φTs … Formula (4)

[0059] Next, the cause of tooth flank separation vibration in general screw compressors will be described with reference to Fig. 5. Fig. 5 is a diagram for explaining the cause of tooth flank separation vibration in general screw compressors. In Fig. 5, the thick arrows indicate the rotation directions of the male rotor and the female rotor, respectively.

[0060] In a liquid-feed screw compressor, the tooth surfaces of the male rotor 2 and the female rotor 3 generally come into direct contact with each other, and the drive torque of the male rotor 2 is transmitted to the female rotor 3 to drive the female rotor 3. Depending on the pressure conditions acting on the tooth surfaces of both the male and female rotors 2 and 3, the torque transmitted from the male rotor 2 to the female rotor 3 may temporarily turn negative, causing a phenomenon called tooth surface separation in which the tooth surfaces transmitting the torque separate from each other. When the torque transmitted from the male rotor 2 to the female rotor 3 then turns positive again, the tooth surfaces that were once separated collide with each other. As a result, tooth surface separation and tooth surface collision are repeated, generating large vibrations and noise. This is called tooth surface separation vibration, and there is a concern that it may cause damage to the tooth surfaces.

[0061] At the rotation angle of the male and female rotors 2, 3 shown in Fig. 5, three contact points S1, S2, and S3 are generated by the meshing of the rotors 2, 3, and two crescent-shaped working chambers C1, C2 that are open only in the axial direction in the cross section are formed. The first working chamber C1 is formed between the first contact point S1 where the forward moving surface (first contour line 61) of the male rotor 2 and the forward moving surface (first contour line 71) of the female rotor 3 contact, and the second contact point S2 where the reverse moving surface (second contour line 62) of the male rotor 2 and the reverse moving surface (second contour line 72) of the female rotor 3 contact. The first working chamber C1 is a working chamber whose volume decreases with the rotation of the male and female rotors 2, 3 and is in the compression process or the discharge process. The second working chamber C2 is formed between the above-mentioned second contact point S2 and a third contact point S3 where a portion of the rearward moving surface (second contour line 62) of the male rotor 2 closer to the tooth bottom side than the second contact point S2 comes into contact with a portion of the rearward moving surface (second contour line 72) of the female rotor 3. The second working chamber C2 expands in volume as both the male and female rotors 2 and 3 rotate, and is a working chamber in the suction process.

[0062] Here, the radius of rotation from the center of rotation A2 to the first contact point S1 in the female rotor 3 is called the first female radius RL, and the radius of rotation from the center of rotation A2 to the second contact point S2 is called the second female radius RT. The length remaining after subtracting the tooth bottom diameter RB of the female rotor 3 from the first female radius RL is called L, and the length remaining after subtracting the tooth bottom diameter RB from the second female radius RL is called T.

[0063] At the rotation angle of the male and female rotors 2, 3 shown in FIG. 5, the first female radius RL>the second female radius RT from the positional relationship between the first contact point S1 and the second contact point S2. That is, L>T. In this case, the torque of the compressed gas in the first working chamber C1 (gas torque) acts in the rotation direction on the tooth surface of the female rotor 3 in the cross section due to the difference in the pressure-receiving area. That is, the torque acts in the direction in which the tooth surfaces of the male and female rotors 2, 3 are separated. The gas torque is the torque that the gas around both rotors 2, 3 acts on the tooth surfaces, and the direction that prevents the rotation of the female rotor 3, that is, the opposite direction to the rotation direction of the female rotor 3, is positive. Therefore, the torque that causes tooth surface separation between both rotors 2, 3 (tooth surface separation torque) means a negative torque.

[0064] However, since each working chamber C of the screw compressor has various pressure levels in the axial direction and is formed in a different shape depending on the rotation angle, the calculation of the tooth surface separation torque requires integration from the suction side to the discharge side in the axial direction of the working chamber. Even if the tooth surface separation torque occurs in a specific cross section shown in Figure 5, the calculated value when the gas torque is integrated in the axial direction does not necessarily become a negative torque. However, when suction throttling control is performed, if the suction pressure is very low and the discharge pressure is high, the tooth surface separation torque tends to occur easily. If the tooth surface separation torque occurs on a part of the tooth surfaces of both the male and female rotors 2 and 3, tooth surface collision will occur repeatedly, and tooth surface separation vibration will occur.

[0065] Next, the effects of the screw compressor according to the first embodiment will be described with reference to Figs. 5 to 8. Fig. 6 is a table comparing the likelihood of tooth flank separation occurring when the tooth profile elements of the forward and reverse surfaces are changed when the shape of the tooth tip portion (tooth tip angle) of the tooth profile of the female rotor constituting the screw compressor is fixed. Fig. 7 is a table comparing the likelihood of tooth flank separation occurring when the tooth profile elements of the forward and reverse surfaces are changed when the shape of the tooth tip portion (tooth tip angle) of the tooth profile of the female rotor constituting the screw compressor is fixed in a state where it is larger than the shape of the tooth tip portion (tooth tip angle) shown in Fig. 6. Fig. 8 is an explanatory diagram showing a blowhole as an internal gap in a general screw compressor.

[0066] The tooth profile of the female rotor shown in Figures 6 and 7 (the first contour line defining the forward movement surface, the second contour line defining the reverse movement surface, and the third contour line defining the tooth tip) is generated based on the same tooth profile elements as the tooth profile of the female rotor 3 shown in Figure 3. That is, the second contour line is generated based on two tooth profile elements, a circular arc of radius R1 starting from the tooth tip 65 of the male rotor 2 shown in Figure 3 and a circular arc of radius R2 ending at the second end point 77 of the second contour line 72 of the female rotor 3. The first contour line is generated based on two tooth profile elements, a parabola with a focal length Lf starting from the tooth bottom 75 of the female rotor 3 shown in Figure 3 and a circular arc of radius R3 ending at the first end point 76 of the first contour line 71 of the female rotor 3. 6 and 7 show the dimensions of each tooth profile element for one tooth of the female rotor tooth profile, and the forward advance surface angle φL, reverse advance surface angle φT, and tooth tip angle φS corresponding to the tooth profile dimensions. Also, the % for the forward advance surface angle, reverse advance surface angle, and tooth tip angle indicates the ratio of each angle when the angle of one tooth of the tooth profile is taken as 100%.

[0067] The dimensions of each tooth profile element must satisfy the meshing conditions, and the range in which each tooth profile element can exist in relation to each other is limited. The range in which each tooth profile element can exist is indicated by a number. However, the radius R2 of the second contour line is set to a fixed value to make it easier to grasp the tendency for tooth surface separation to occur. The column for tooth surface separation shows the tendency for tooth surface separation to occur for each number of tooth profiles. The tendency for tooth surface separation to occur is shown based on the tooth surface separation torque obtained from a numerical calculation that integrates the gas torque acting on the tooth surface in the axial direction.

[0068] The tooth profile of the female rotor shown in Figures 6 and 7 is different from the tooth profile of the female rotor 3 of this embodiment and has the same shape along the axial direction. The angle ratio of the tooth tip angle φS shown in Figure 6 is constant at 1%, and the angle ratio of the tooth tip angle φS shown in Figure 7 is constant at 3.5%.

[0069] From Fig. 6, it can be seen that when the angle ratio of the tooth tip angle φS is constant, the smaller the angle ratio of the forward advance surface angle φL, the less likely tooth flank separation will occur. In other words, the larger the angle ratio of the reverse advance surface angle φT, the less likely tooth flank separation will occur. The reason for this is due to the principle of tooth flank separation torque generation explained in Fig. 5. When the angle ratio of the tooth tip angle φS is constant, the smaller the angle ratio of the forward advance surface angle φL and the larger the angle ratio of the reverse advance surface angle φT, the smaller the length L shown in Fig. 5 becomes, while the longer the length T becomes.

[0070] In addition, as the focal length Lf of the parabola constituting the first contour line increases, the first contact point S1 shown in Fig. 5 moves toward the tooth bottom side of the female rotor 3, and the length L decreases accordingly. As a result, it becomes difficult to establish the relationship L>T, and tooth surface separation becomes less likely to occur.

[0071] However, there are combinations (dimensions) of tooth profile elements that are prone to tooth surface separation even if the angle ratio of the forward movement surface angle φL is small. This is the case where the relationship L>T as explained in Figure 5 is established depending on the combination (dimensions) of tooth profile elements even if the angle ratio of the forward movement surface angle φL is small. For example, there is the tooth profile shown in No. 7 in Figure 6, where the focal length Lf of the parabola is set relatively small.

[0072] Thus, in the case of the tooth profile shown in Figure 6, where the angle ratio of the tooth tip angle φS is relatively small, tooth flank separation tends to be less likely to occur if the angle ratio of the forward movement angle φL is small. Furthermore, it is possible to avoid tooth flank separation by adjusting the focal length Lf of the parabola, which is one of the tooth profile elements. For example, in the case of the tooth profile shown in Figure 6, where the angle ratio of the tooth tip angle φS is relatively small, tooth flank separation becomes less likely to occur by adjusting the focal length Lf of the parabola so that it is relatively large (to the dimensions shown in No. 3, No. 6, No. 8, and No. 9).

[0073] On the other hand, in the tooth profile shown in Fig. 7, in which the angle ratio of the tooth tip angle φS is larger than that of the tooth profile shown in Fig. 6, the range in which tooth surface separation is likely to occur is wider. Of the tooth profiles shown in Fig. 7, only one tooth profile, shown in No. 9, is less likely to cause tooth surface separation. In other words, in the case of a tooth profile in which the angle ratio of the tooth tip angle φS is relatively large, it is found that the effect of making tooth surface separation less likely to occur cannot be obtained even if the focal length Lf of the parabola, which is the tooth profile element of the first contour line, is adjusted. Therefore, in order to make tooth surface separation less likely to occur, it is essential to reduce the angle ratio of the forward movement angle φL.

[0074] Here, taking into consideration the tendency of tooth surface separation to occur for the tooth profiles shown in Figs. 6 and 7, a combination of the first tooth profile 70s on the suction side and the second tooth profile 70d on the discharge side of the female rotor 3 will be considered.

[0075] As the second tooth profile 70d on the discharge side, in order to suppress the occurrence of tooth surface separation while suppressing leakage of high-pressure gas on the axial discharge side through the outer diameter gap, the tooth profile shown in No. 9, which is less likely to cause tooth surface separation, is selected from the tooth profiles shown in FIG. 7 in which the angle ratio of the tooth tip angle φS is relatively large.

[0076] On the other hand, as the first tooth profile 70s on the suction side, any of tooth profiles No. 3, No. 6, No. 8, and No. 9, which are less likely to cause tooth surface separation, among the tooth profiles shown in FIG. 6 in which the angle ratio of the tooth tip angle φS is relatively small, can be considered. However, the object of this embodiment is to suppress the decrease in energy efficiency due to leakage of compressed gas in addition to suppressing the tooth surface separation vibration. However, the tooth profiles shown in No. 8 and No. 9 in FIG. 6 have a larger area of ​​the blow hole, which is the cause of leakage of compressed gas, compared to the tooth profiles shown in No. 3 and No. 6 in FIG. 6, so it is difficult to reduce the leakage loss of compressed gas. The tooth profiles shown in No. 8 and No. 9 in FIG. 6 are designed to increase the angle ratio of the reverse surface angle φT without changing the angle ratio of the forward advance surface angle φL, compared to the tooth profile shown in No. 9 in FIG. 7.

[0077] As shown in FIG. 8, the blowhole H is a leakage flow passage formed along the cusp line 45a of the main casing 4 to communicate the adjacent working chambers C, and has an approximately triangular shape. The apex Sa of the blowhole H is the contact start point at the moment when the teeth of the male and female rotors 2, 3 start to mesh with each other due to rotation. The base of the blowhole H is formed by the cusp line 45a. One end point Bm of the base of the blowhole H is the intersection position of the tooth tip line 21d of the male rotor 2 and the cusp line 45a. Since there is a small gap between the tooth tip line 21d of the male rotor 2 and the cusp line 45a, the closest position is regarded as the intersection position. The other end point Bf of the base of the blowhole H is the intersection position of the tooth tip line (not shown) of the female rotor 3 and the cusp line 45a. Similarly, since there is a small gap between the tooth tip line of the female rotor 3 and the cusp line 45a, the closest position is regarded as the intersection position.

[0078] The area of ​​the blowhole H increases as the contact start point (apex) Sa is positioned higher, because the height of the triangle that is its approximate shape increases and the length of the base also increases. Therefore, in order to reduce leakage of compressed gas through the blowhole H, the contact start point Sa should be set lower. In the tooth profile 70 of the female rotor 3, if the angle rate of the forward moving surface angle φL is fixed and the angle rate of the reverse moving surface angle φT is increased, the contact start point Sa moves upward, and leakage of compressed fluid through the blowhole H tends to increase.

[0079] Therefore, the tooth profiles shown in No. 8 and No. 9 in FIG. 6, in which the angle ratio of the backward flank angle φT is relatively large, are resistant to tooth flank separation, but do not meet the objective of suppressing the decrease in energy efficiency due to leakage of compressed gas. Therefore, in the first tooth profile 70s on the suction side of the female rotor 3, in order to simultaneously suppress the decrease in energy efficiency due to leakage of compressed gas and the tooth flank separation vibration, it is necessary to make the angle ratio of the forward flank angle φL larger than that of the second tooth profile 70d on the discharge side. Note that the angle ratio of the backward flank angle φT may be configured to be unchanged or to be smaller than that of the second tooth profile on the discharge side. In other words, either of the tooth profiles shown in No. 3 and No. 6 in FIG. 6 may be used.

[0080] In this embodiment, as shown in Fig. 4, the tooth tip angle φSd on the axial discharge side of the female tooth profile 70 is set to be larger than the tooth tip angle φSs on the axial suction side, and the forward advance surface angle φLd on the discharge side is set to be smaller than the forward advance surface angle φLs on the suction side. Also, the rearward advance surface angle φTd on the discharge side of the female tooth profile 70 is set to be the same angle as the rearward advance surface angle φTs on the suction side. That is, in the case where the rotor tooth portion 31 of the female rotor 3 in this embodiment is configured to use the tooth profile shown in No. 9 of Fig. 7 as the second tooth profile 70d on the discharge side, and the tooth profile shown in No. 6 of Fig. 6 is used as the first tooth profile 70s on the suction side, in the case where the tooth profile shown in Fig. 6 and Fig. 7 is used.

[0081] Therefore, by increasing the thickness of the tooth tip portion defined by the third contour line 73 of the female tooth profile 70 on the axial discharge side, it is possible to suppress leakage of compressed gas through the outer diameter gap in response to an increase in the pressure difference between the working chambers located on the axial discharge side, and also to suppress the occurrence of tooth surface separation. Therefore, it is possible to simultaneously suppress the decrease in energy efficiency due to leakage of working gas and the occurrence of tooth surface separation vibration.

[0082] As described above, the screw compressor according to the first embodiment includes the male rotor 2 having twisted male teeth 21a and rotating around the first center of rotation A1, the female rotor 3 having twisted female teeth 31a and meshing with the male rotor 2 and rotating around the second center of rotation A2 parallel to the first center of rotation A1, and a main casing 4 (casing) having an accommodation chamber 45 for rotatably accommodating the male rotor 2 and the female rotor 3 in an intermeshed state and forming a plurality of working chambers C together with the male rotor 2 and the female rotor 3. The tooth profile 70 representing the contour shape of a cross section perpendicular to the axial direction of the female rotor 3 is formed to change between an S1-S1 position (a certain first position) in the axial direction and a D1-D1 position (a second position) on the axial discharge side of the first position. One of the teeth of the tooth profile 70 of the female rotor 3 is composed of a first contour line 71 that defines a section of the forward surface extending from the boundary point, which is the tooth bottom 75 at the minimum radius, in the direction of rotation of the female rotor 3 to a first end point 76 at the maximum radius, a second contour line 72 that defines a section of the reverse surface extending from the boundary point in the opposite direction to the direction of rotation of the female rotor 3 to a second end point 77 at the maximum radius, and a third contour line 73 that defines a section of the tooth tip at the maximum radius, and one of the two end points is the connection point with the first end point 76 of the first contour line 71 or the second end point 77 of the second contour line 72. The tooth profile 70 of the female rotor 3 has an angle between the second rotation center A2 and both ends 65, 76 of the first contour line 71, the angle between the second rotation center A2 and both ends 65, 77 of the second contour line 72, the angle between the second rotation center A2 and both ends 76, 77 of the third contour line 73 ...65, 77 of the second contour line 72, the angle between the second rotation center A2 and both ends 76, 77 of the third contour line 73, the angle between the second rotation center A2 and both ends 76, 77 of the third contour line 73, the angle between the second rotation center A2 and both ends 76, 77 of the third contour line 73, the angle between the second rotation center A2 and both ends 76, 77 of the third contour line 73, the angle between the second rotation center A2 and both ends 77 of the third contour line 7 When the angle between the line segments is defined as the tooth tip angle φS (third angle), the tooth tip angle φSd (third angle) at the D1-D1 position (second position) is set to be larger than the tooth tip angle φSs (third angle) at the S1-S1 position (first position), and the forward movement angle φLd (first angle) at the D1-D1 position (second position) is set to be smaller than the forward movement angle φLs (first angle) at the S1-S1 position (first position).

[0083] According to this configuration, by setting the tooth tip angle φS (third angle) corresponding to the shape of the tooth tip in the tooth profile 70 of the female rotor 3 to be larger on the axial discharge side than on the suction side, the thickness of the tooth tip of the female rotor 3 becomes thicker on the discharge side, so that leakage of high-pressure working gas through the outer diameter gap between the working chambers located on the axial discharge side can be suppressed accordingly. At the same time, by setting the forward movement surface angle φL (first angle) corresponding to the shape of the forward movement surface in the tooth profile 70 of the female rotor 3 to be smaller on the axial discharge side than on the suction side, the occurrence of tooth surface separation is suppressed. Therefore, it is possible to simultaneously suppress leakage of working gas between the working chambers C through the gap provided between the female rotor 3 and the main casing (casing) 4 and suppress the occurrence of tooth surface separation vibration.

[0084] In addition, the tooth profile 70 of the female rotor 3 in this embodiment is set so that the rearward surface angle φTd (second angle) at the D1-D1 position (second position) is the same as the rearward surface angle φTs (second angle) at the S1-S1 position (first position).

[0085] According to this configuration, the rearward surface (second contour line 72) of the tooth profile 70 of the female rotor 3 has the same shape from the suction side to the discharge side in the axial direction, which makes machining of the tooth profile easier.

[0086] In addition, in the female rotor 3 in this embodiment, the tooth profile 70 changes in an area biased toward the axial discharge side of the entire axial direction, while the tooth profile 70 has the same shape in the remaining axial area on the suction side.

[0087] According to this configuration, the tooth tips of the female rotor 3 are changed to be thicker only in the discharge side region where the pressure difference between the working chambers is relatively large, thereby suppressing leakage of compressed gas between the working chambers, while the thickness of the tooth tips of the female rotor 3 is not changed in the axial suction side region where the pressure difference between the working chambers is relatively small, thereby avoiding a reduction in the volume of the working chamber compared to the case where the thickness of the tooth tips is made thicker. Therefore, the suction capacity can be secured without increasing the size of the compressor body 1. Also, in the case of an oil-lubricated screw compressor, if the thickness of the tooth tips of the female rotor 3 is increased from the axial suction side end toward the discharge side, the working chamber located on the discharge side will have an internal pressure increase due to a reduction in volume, so the oil supply differential (the difference between the pressure of the pressure source and the pressure in the working chamber) will be reduced. On the other hand, if the tooth profile 70 of the female rotor 3 is changed only in the region biased toward the discharge side in the axial direction, the internal pressure increase due to the change in the tooth profile 70 can be suppressed in the discharge side working chamber near the start position of the change in the tooth profile 70 of the female rotor 3, so that the pressure difference for oil supply can be secured.

[0088] [Second embodiment] Next, a screw compressor according to a second embodiment will be illustrated with reference to Fig. 9. Fig. 9 is a cross-sectional view showing a screw compressor according to a second embodiment of the present invention, in which a tooth profile for one tooth of a female rotor is superimposed when viewed from the same arrow directions as the S1-S1 and D1-D1 arrow directions shown in Fig. 2. In Fig. 9, the same reference numerals as those shown in Figs. 1 to 8 denote similar parts, and therefore detailed description thereof will be omitted.

[0089] The screw compressor according to the second embodiment shown in Fig. 9 differs from the screw compressor according to the first embodiment (see Fig. 4) in the following points. The first tooth profile 70s on the axial suction side (S1-S1 position) of the female rotor 3 in the first embodiment is shaped such that the angle ratio of the forward advance surface angle φL is relatively large and the angle ratio of the reverse advance surface angle φT is the same as that of the second tooth profile 70d on the axial discharge side (D1-D1 position). On the other hand, the first tooth profile 70As on the axial suction side (S1-S1 position) of the female rotor 3A in the second embodiment is shaped such that the angle ratio of the forward advance surface angle φLA is relatively large and the angle ratio of the reverse advance surface angle φTA is relatively small as compared to the second tooth profile 70Ad on the axial discharge side (D1-D1 position).

[0090] In Fig. 9, the first tooth profile 70As on the suction side in the axial direction of the female rotor 3A is shown by a broken line, and the second tooth profile 70Ad on the discharge side in the axial direction is shown by a solid line. The first tooth profile 70As on the suction side and the second tooth profile 70Ad on the discharge side are distinguished by adding the symbol s indicating the suction side and the symbol d indicating the discharge side to the first contour line 71A that defines the forward movement surface, the second contour line 72A that defines the reverse movement surface, and the third contour line 73A that defines the tooth tip portion of the tooth profile 70A of the female rotor 3A. Similarly, the first tooth profile 70As on the suction side and the second tooth profile 70Ad on the discharge side are distinguished by adding the symbol s indicating the suction side and the symbol d indicating the discharge side to both end points 76A and 77A of the third contour line 73A of the female tooth profile 70A. In addition, the tooth tip angle φSA, the forward advance surface angle φLA, and the reverse advance surface angle φTA of the female tooth profile 70A are marked with the symbol s indicating the suction side and the symbol d indicating the discharge side to distinguish between the first tooth profile 70As on the suction side and the second tooth profile 70Ad on the discharge side.

[0091] In the tooth profile 70A of the female rotor 3A according to this embodiment, as shown in Fig. 9, the tooth tip angle φSAd of the second tooth profile 70Ad on the axial discharge side is set to be larger than the tooth tip angle φSAs of the first tooth profile 70As on the axial suction side, and the forward advance angle φLAd of the second tooth profile 70Ad on the discharge side is set to be smaller than the forward advance angle φLAs of the first tooth profile 70As on the suction side. Also, the rearward advance angle φTAd of the second tooth profile 70Ad on the discharge side is set to be larger than the rearward advance angle φTAs of the first tooth profile 70As on the suction side. That is, in the case of the configuration using the tooth profiles shown in Figs. 6 and 7, the rotor tooth portion 31A of the female rotor 3A according to this embodiment uses the tooth profile shown in No. 9 of Fig. 7 as the second tooth profile 70Ad on the discharge side, and uses the tooth profile shown in No. 3 of Fig. 6 as the first tooth profile 70As on the suction side.

[0092] That is, in this embodiment, as in the first embodiment, the tooth tip portion defined by the third contour line 73Ad of the second tooth profile 70Ad on the discharge side of the female rotor 3A is configured to be thicker than the tooth tip portion defined by the third contour line 73As of the first tooth profile 70As on the suction side. In this way, by making the tooth tip portion of the tooth profile 70A of the female rotor 3A thicker on the axial discharge side, leakage of compressed gas through the outer diameter gap between the working chambers located on the axial discharge side can be suppressed.

[0093] Furthermore, in this embodiment, the advancing surface angle φLAd on the discharge side of the female rotor 3A is set to be smaller than the advancing surface angle φLAs on the suction side, while the reversing surface angle φTAd on the discharge side of the female rotor 3A is set to be larger than the reversing surface angle φTAs on the suction side. With this configuration, tooth flank separation can be suppressed more effectively than in the case of the tooth profile 70 of the female rotor 3 in the first embodiment, for the following reasons.

[0094] Next, the effect of the screw compressor according to the second embodiment will be described with reference to FIG. 10. FIG. 10 is a characteristic diagram showing the change in tooth flank separation tolerance torque with respect to the rotation angle of the male rotor in the screw compressor according to the second embodiment of the present invention. In FIG. 10, the horizontal axis is the rotation angle of one tooth of the male rotor meshing, and the maximum value is relatively displayed as 1 P.U. The vertical axis is the tooth flank separation tolerance torque calculated by numerical calculation based on the set tooth profile, and the maximum value of the torque in the tooth profile of the female rotor in the first embodiment is relatively displayed as 1 P.U. The tooth flank separation tolerance torque is the tooth surface transmission torque that the female rotor receives from the male rotor, and indicates the margin torque when tooth flank separation does not occur against the tooth flank separation torque. In other words, the tooth flank separation tolerance torque indicates that the larger the value, the less likely tooth flank separation is to occur.

[0095] In the tooth profile 70A of the female rotor 3A according to the second embodiment, the tooth surface separation tolerance torque is greater than in the case of the tooth profile 70 of the female rotor 3 according to the first embodiment, as shown in Fig. 10. Therefore, the tooth profile 70A of the female rotor 3A according to the present embodiment can suppress the occurrence of tooth surface separation more than the tooth profile 70 of the female rotor 3 according to the first embodiment.

[0096] Also, unlike the first embodiment, the rearward surface angle φTAd on the discharge side of the female rotor 3A is set to be larger than the rearward surface angle φTAs on the suction side. In this configuration, as described above, the contact start point Sa, which is the apex of the blowhole H (see FIG. 8), tends to move downward more than in the case of the tooth profile 70 of the female rotor 3 in the first embodiment. Therefore, the area of ​​the blowhole H tends to become smaller, making it possible to suppress leakage of compressed gas through the blowhole H.

[0097] In the second embodiment, as in the first embodiment, the tooth profile 70A of the female rotor 3A must also satisfy the following equations (5) and (6) for the forward advance surface angle φLA, the reverse advance surface angle φTA, and the tooth tip angle φSA. φSAd-φSAs>0 … Equation (5) φLAs-φLAd>φTAd-φTAs … Formula (6)

[0098] According to the second embodiment described above, as in the first embodiment, by setting the tooth tip angle φSA (third angle) corresponding to the shape of the tooth tip in the tooth profile 70A of the female rotor 3A to be larger on the axial discharge side than on the suction side, the thickness of the tooth tip of the female rotor 3A becomes thicker on the discharge side, so that leakage of high-pressure working gas through the outer diameter gap between the working chambers C located on the axial discharge side can be suppressed accordingly. At the same time, by setting the forward movement surface angle φLA (first angle) corresponding to the shape of the forward movement surface in the tooth profile 70A of the female rotor 3A to be smaller on the axial discharge side than on the suction side, the occurrence of tooth surface separation can be suppressed. Therefore, it is possible to simultaneously suppress leakage of working gas between the working chambers C through the gap provided between the female rotor 3A and the main casing (casing) 4 and suppress the occurrence of tooth surface separation vibration.

[0099] In addition, the tooth profile 70A of the female rotor 3A in this embodiment is set so that the rearward surface angle φTd (second angle) at the D1-D1 position (second position) is larger than the rearward surface angle φTs (second angle) at the S1-S1 position (first position).

[0100] According to this configuration, the area of ​​the blowhole H (see FIG. 8) tends to be smaller, so it is possible to suppress leakage of compressed gas through the blowhole H. Furthermore, since the tooth flank separation tolerance torque is larger than that of the first embodiment, the occurrence of tooth flank separation can be further suppressed.

[0101] [Third embodiment] Next, the configuration of a screw compressor according to a third embodiment will be illustrated with reference to Figs. 11 and 12. Fig. 11 is a cross-sectional view showing a screw compressor according to a third embodiment of the present invention. Fig. 12 is a cross-sectional view showing the screw compressor according to the third embodiment of the present invention shown in Fig. 11 in a state in which the tooth profile of one tooth of the female rotor is superimposed when viewed from the S3-S3 arrow and D3-D3 arrow views. In Figs. 11 and 12, the same reference numerals as those shown in Figs. 1 to 10 denote similar parts, and detailed description thereof will be omitted.

[0102] The screw compressor according to the third embodiment shown in FIG. 11 differs from the first embodiment (see FIG. 2 and FIG. 4) in the following points. In the compressor body 1 of the first embodiment, both the male and female rotors 2, 3 are configured as screw rotors with equal leads, and the outer diameters of the rotor teeth 21, 31 of both rotors 2, 3 are the same from the suction side end faces 21b, 31b to the discharge side end faces 21c, 31c. On the other hand, in the compressor body 1B of the third embodiment, both the male and female rotors 2B, 3B are configured as screw rotors with unequal leads in which the lead decreases from the suction side toward the discharge side in the axial direction, and the outer diameter of the rotor teeth 21B of the male rotor 2B is set to gradually decrease from a certain first position in the axial direction toward the discharge side end face 21c. That is, the male rotor 2B is configured as a tapered screw rotor with unequal leads that tapers from the first position in the axial direction toward the discharge side end face 21c. The female rotor 3B is configured as an unequal lead screw rotor whose outer diameter is the same from the suction side end face 31b to the discharge side end face 31c in the axial direction.

[0103] 11, the rotor teeth 21B, 31B of the male rotor 2B and the female rotor 3B are formed so that the lead varies in the axial portion biased toward the discharge side (from S3-S3 position to D3-D3) while the lead is the same in the remaining axial portion on the suction side (from suction side end faces 21b, 31b to S3-S3 position). Note that the lead of the male rotor 2B and the lead of the female rotor 3B can also be configured to vary over the entire axial region.

[0104] The tooth profile 70B (see FIG. 12) in a cross section perpendicular to the axial direction (center of rotation A2) of the female rotor 3B has the same shape along the axial direction in a region from the suction side end face 31b of the rotor teeth portion 31B to a certain first position closer to the axial discharge side, for example, a substantially middle position in the axial direction (position S3-S3). On the other hand, in a region from the first axial position to the discharge side end face 31c (position D3-D3) of the female rotor 3B, the female tooth profile 70B is formed so as to gradually change from the first tooth profile 70Bs on the suction side shown by the dashed line in FIG. 12 (the tooth profile at position S3-S3 shown in FIG. 11) to the second tooth profile 70Bd on the discharge side shown by the solid line (the tooth profile at position D3-D3 shown in FIG. 11). That is, the tooth tip angle φSB, forward surface angle φLB, and reverse surface angle φTB of the female tooth profile 70B are set to change monotonically with respect to the axial length or rotation angle from the first position (S3-S3 position) to the discharge side end face 31c (D3-D3 position).

[0105] In this embodiment, the second tooth profile 70Bd on the axial discharge side (D3-D3 position) of the female rotor 3B is shaped such that the angle ratio of the tooth tip angle φSB is relatively large, while the angle ratio of the forward moving surface angle φLB is relatively small, compared to the first tooth profile 70Bs on the axial suction side (S3-S3 position). Furthermore, the second tooth profile 70Bd of the female rotor 3B is shaped such that the angle ratio of the reverse moving surface angle φTB is relatively small, and the region including the tooth bottom 75B is relatively shallow, compared to the first tooth profile 70Bs. The rotor tooth portion 21B of the male rotor 2B shown in FIG. 11 is formed to mesh with the rotor tooth portion 31B of the female rotor 3B.

[0106] In Fig. 12, the first tooth profile 70Bs on the axial suction side of the rotor teeth portion 31B of the female rotor 3B is indicated by a dashed line, and the second tooth profile 70Bd on the axial discharge side is indicated by a solid line. Similarly to Fig. 4, the rotation angle of the female rotor 3B is the reference angle (0°).

[0107] The first contour line 71B that defines the forward surface of the tooth profile 70B of the female rotor 3B, the second contour line 72B that defines the reverse surface, and the third contour line 73B that defines the tooth tip are marked with the symbol s indicating the suction side and the symbol d indicating the discharge side to distinguish between the first tooth profile 70Bs on the suction side and the second tooth profile 70Bd on the discharge side.

[0108] Similarly, the first tooth profile 70Bs on the suction side and the second tooth profile 70Bd on the discharge side are distinguished by adding the symbol s indicating the suction side and the symbol d indicating the discharge side to the tooth bottom 75B, which is the boundary point between the first contour line 71B and the second contour line 72B of the female tooth profile 70B. Also, the first tooth profile 70Bs on the suction side and the second tooth profile 70Bd on the discharge side are distinguished by adding the symbol s indicating the suction side and the symbol d indicating the discharge side to both end points 76B, 77B of the third contour line 73B of the female tooth profile 70B.

[0109] In addition, the tooth tip angle φSB, forward surface angle φLB, and reverse surface angle φTB of the female tooth profile 70B are marked with the symbol s indicating the suction side and the symbol d indicating the discharge side to distinguish between the first tooth profile 70Bs on the suction side and the second tooth profile 70Bd on the discharge side.

[0110] In the tooth profile 70B of the female rotor 3B according to this embodiment, as shown in Fig. 12, the tooth tip angle φSBd of the second tooth profile 70Bd on the axial discharge side is set to be larger than the tooth tip angle φSBs of the first tooth profile 70Bs on the axial suction side, similar to the first embodiment. That is, similar to the first embodiment, the tooth tip portion defined by the third contour line 73Bd of the second tooth profile 70Bd on the discharge side of the female rotor 3B is configured to be thicker than the tooth tip portion defined by the third contour line 73Bs of the first tooth profile 70Bs on the suction side.

[0111] Similarly to the first embodiment, the forward advance surface angle φLBd of the second tooth profile 70Bd on the discharge side is set to be smaller than the forward advance surface angle φLBs of the first tooth profile 70Bs on the suction side. Unlike the first embodiment, the rearward advance surface angle φTBd of the second tooth profile 70Bd on the discharge side is set to be smaller than the rearward advance surface angle φTBs of the first tooth profile 70Bs on the suction side.

[0112] Furthermore, the tooth bottom 75Bd of the second tooth profile 70Bd on the axial discharge side is set to be shallower than the tooth bottom 75Bs of the first tooth profile 70Bs on the suction side. In the first embodiment, the tooth bottom 75s of the first tooth profile 70s on the suction side of the female rotor 3 and the tooth bottom 75d of the second tooth profile 70d on the discharge side are at the same radial position.

[0113] In this configuration, the male rotor 2B is formed so that the outer diameter of the tooth tip (contact portion with the tooth bottom 75B of the female rotor 3B) of the male rotor 2B gradually decreases from a certain first position (S3-S3 position) on the suction side in the axial direction to the discharge side end face 21c (D3-D3 position) on the discharge side according to the tooth profile 70B of the female rotor 3B. In other words, the male rotor 2B is formed in a tapered shape that tapers from the first position on the suction side in the axial direction to the discharge side.

[0114] In this configuration, the main casing 4B shown in Fig. 11 must have a first inner peripheral surface 46B of the bore 45B tapered in accordance with the tapered shape of the male rotor 2B. For assembly purposes, the main casing 4B includes a main casing 41B and a suction-side casing 42B attached to the suction side (left side in Fig. 11) of the main casing 41B. The main casing 41B has an internal space that opens to the suction side in the axial direction and can accommodate the male rotor 2B and the female rotor 3B in an interlocked state. The suction-side casing 42B closes the opening of the main casing 41B and forms a bore 45B as an accommodation chamber together with the main casing 41B.

[0115] Discharge side bearing 6 on the male rotor 2B side and discharge side bearing 8 on the female rotor 3B side are disposed at the discharge side end of main casing 41B. A body cover 43B is attached to body casing 4B so as to cover discharge side bearing 6 and discharge side bearing 8. Suction side bearings 5a, 5b on the male rotor 2B side and suction side bearings 7a, 7b on the female rotor 3B side are disposed in suction side casing 42B. Suction side bearing 5b on the male rotor 2B side and suction side bearing 7b on the female rotor 3B side are configured, for example, by positionable angular contact ball bearings.

[0116] In this configuration, the gap (sometimes called the end face gap) between the suction side inner wall surface 48 of the suction side casing 42B and the suction side end faces 21b, 31b of the male and female rotors 2B, 3B can be adjusted by the angular ball bearings 5b, 7b arranged in the suction side casing 42B. In this configuration, the end face gap can be adjusted while checking the positional relationship between the suction side casing 42B and the male and female rotors 2B, 3B before housing the male and female rotors 2B, 3B in the bore 45B of the main body casing 4B, so that the gap adjustment is easy.

[0117] Next, the effects of the screw compressor according to the third embodiment will be described with reference to Figs. 11 to 13 in comparison with a comparative example of an unequal lead screw compressor. Fig. 13 is a cross-sectional view showing a comparative example of an unequal lead screw compressor compared to the screw compressor according to the third embodiment of the present invention. In Fig. 13, the same reference numerals as those in Figs. 1 to 12 denote similar parts, and therefore detailed description thereof will be omitted.

[0118] The compressor body 100 of the comparative example shown in Fig. 13 is configured as an unequal lead screw rotor in which the rotor tooth portions 210, 310 of the male and female rotors 200, 300 have smaller leads from the suction side end faces 21b, 31b (left end in Fig. 12) toward the discharge side end faces 21c, 31c (right end in Fig. 12). In this case, the male teeth 210a and female teeth 310a of the rotor tooth portions 210, 310 become tighter as they move from the suction side toward the discharge side in the axial direction. For this reason, the tooth thickness t of the tooth tip of the female tooth 310a of the female rotor 300 (thickness in a cross section perpendicular to the extension direction of the tooth tip line of the female rotor 300) generally tends to be thinner than that of an equal lead screw rotor. When the tooth thickness t of the tooth tips of the female teeth 310a of the female rotor 300 becomes thinner, the leakage of compressed gas between the working chambers C through the outer diameter gap increases at the axial discharge side position where the differential pressure between the working chambers C increases.

[0119] The compressor body 1B of this embodiment is configured as an unequal lead screw rotor in which the rotor teeth 21B, 31B of the male and female rotors 2B, 3B have a smaller lead from the suction side in the axial direction toward the discharge side in the region biased toward the discharge side in the axial direction. Therefore, in this embodiment, as shown in FIG. 12, the tooth tip angle φSBd of the second tooth profile 70Bd on the axial discharge side of the female rotor 3B is set to be larger than the tooth tip angle φSBs of the first tooth profile 70Bs on the axial suction side. As a result, as in the first embodiment, the tooth tip on the discharge side defined by the tooth tip angle φSBd of the second tooth profile 70Bd of the female rotor 3B is thicker than the tooth tip on the suction side defined by the tooth tip angle φSBs of the first tooth profile 70Bs. Therefore, even if the male and female rotors 2B, 3B are configured as unequal lead screw rotors, leakage of compressed gas through the outer diameter gap can be suppressed in response to an increase in the pressure difference between the working chambers C located on the axial discharge side.

[0120] Furthermore, in this embodiment, the tooth bottom 75Bd of the second tooth profile 70Bd on the discharge side of the female rotor 3B is shallower than the tooth bottom 75Bs of the first tooth profile 70Bs on the suction side. In such a section where the tooth bottom 75B of the tooth profile 70B changes, the reduction rate of the volume of the working chamber C with respect to the rotation angle of the female rotor 3B is larger than in the first embodiment (where the radial positions of the tooth bottom 75 of the female tooth profile 70 and the tooth tip 65 of the male tooth profile 60 do not change along the axial direction). Therefore, with this female tooth profile 70B, it is possible to increase the design volume ratio of the compressor body 1B, and high efficiency can be achieved by operating at a high pressure ratio. In addition, when operating at a normal pressure ratio, the working gas in each working chamber C reaches the discharge pressure earlier than in the first embodiment because the tooth bottom 75Bd on the discharge side of the female rotor 3B is shallower than the tooth bottom 75Bs on the suction side. Therefore, it is possible to advance the timing of starting the discharge of the compressed gas in the working chamber C. In this case, it is possible to increase the opening area of ​​the discharge port 52a (see FIG. 1), thereby reducing the pressure loss when the compressed gas passes through the discharge port 52a.

[0121] In the third embodiment, as in the first embodiment, the tooth profile 70B of the female rotor 3B must satisfy the following equations (7) and (8) for the forward moving surface angle φLB, the reverse moving surface angle φTB, and the tooth tip angle φSB. φSBd-φSBs>0 … Formula (7) φLBs-φLBd>φTBd-φTBs … Formula (8)

[0122] Thus, in this embodiment, even if the male and female rotors 2B, 3B are screw rotors with unequal leads in which the lead decreases from the suction side to the discharge side in the axial direction, by setting the tooth tip angle φSB (third angle) corresponding to the shape of the tooth tip of the tooth profile 70B of the female rotor 3B to be larger on the discharge side in the axial direction than on the suction side, the thickness of the tooth tip of the female rotor 3B tends to be thicker on the discharge side, so that leakage of high-pressure working gas through the outer diameter gap between the working chambers C located on the discharge side in the axial direction can be suppressed. At the same time, by setting the forward movement surface angle φLB (first angle) corresponding to the shape of the forward movement surface of the female tooth profile 70B to be smaller on the discharge side in the axial direction than on the suction side, the occurrence of tooth surface separation is suppressed. Therefore, it is possible to simultaneously suppress leakage of working gas between the working chambers C through the gap provided between the female rotor 3B and the main casing (casing) 4B and suppress the occurrence of tooth surface separation vibration.

[0123] Moreover, in the female rotor 3B in this embodiment, the lead changes in a portion biased toward the axial discharge side of the entire axial direction, while the lead is the same in the remaining portion on the axial suction side.

[0124] According to this configuration, the lead of the male rotor 2B and the female rotor 3B on the axial suction side is maintained relatively large, so that the moving distance per rotation of the working chamber located on the suction side is relatively large, and therefore the suction amount of the compressor body 1B can be secured.

[0125] Furthermore, the tooth profile 70B of the female rotor 3B in this embodiment is set so that the tooth bottom 75Bd at the second position (D3-D3 position) is shallower than the tooth bottom 75Bs at the first position (S3-S3 position). Furthermore, the male rotor 2B is configured so that the outer diameter at the second position (D3-D3 position) is smaller than the outer diameter at the first position (S3-S3 position) according to the tooth profile 70B of the female rotor 3B.

[0126] With this configuration, the tooth bottom 75Bd on the discharge side of the female rotor 3B is shallower than the tooth bottom 75Bs on the suction side, and therefore the rate of decrease in the volume of the working chamber C with respect to the rotation angle of the female rotor 3B is greater. Therefore, it is possible to increase the design volume ratio of the compressor body 1B compared to the first embodiment in which the radial position of the tooth bottom 75 does not change in the axial direction.

[0127] Furthermore, in the female rotor 3B in this embodiment, the radial position of the bottom 75B of the tooth profile 70B changes in the entire axial region biased toward the discharge side in the axial direction, while the radial position of the bottom 75B of the tooth profile 70B remains the same in the remaining axial region on the suction side.

[0128] According to this configuration, in the axial suction side region, the rate of reduction in the volume of the working chamber C of the female rotor 3B becomes larger toward the discharge side, allowing the working gas in the working chamber C to quickly reach the discharge pressure. Furthermore, in the axial suction side region where the radial position of the tooth bottom 75B of the female rotor 3B does not change, a reduction in the volume of the working chamber C is avoided, thereby avoiding a reduction in the suction volume.

[0129] Furthermore, the compressor body 1B in this embodiment includes suction side bearings 7a, 7b (female side bearings) on the female rotor 3B side that rotatably support the suction side in the axial direction of the female rotor 3B, and suction side bearings 5a, 5b (male side bearings) on the male rotor 2B side that rotatably support the suction side in the axial direction of the male rotor 2B. Furthermore, the main body casing (casing) 4B includes a main casing 41B that has an internal space that opens to the suction side in the axial direction and can accommodate the male rotor 2B and the female rotor 3B in a meshed state, and a suction side casing 42B that is attached to the main casing 41B so as to close the opening of the main casing 41B and forms an accommodation chamber 45 together with the main casing 41B. The suction side bearings 7a, 7b (female side bearings) on the female rotor 3B side and the suction side bearings 5a, 5b (male side bearings) on the male rotor 2B side are disposed in the suction side casing 42B.

[0130] According to this configuration, the tapered male rotor 2B tapered toward the discharge side can be housed in the main casing (casing) 4B, and the end face gap provided between the suction side end faces 21b, 31b of the male rotor 2B and female rotor 3B and the suction side inner wall surface 48 of the main casing (casing) 4B can be adjusted by the suction side bearings 7a, 7b (female side bearings) on the female rotor 3B side and the suction side bearings 5a, 5b (male side bearings) on the male rotor 2B side. Therefore, the end face gap can be adjusted by positioning the male rotor 2B and female rotor 3B relative to the suction side casing 42B before housing both the male and female rotors 2B, 3B, making the gap adjustment easy.

[0131] [Other embodiments] The present invention is not limited to the above-described embodiment, but includes various modified examples. The above-described embodiment has been described in detail to easily explain the present invention, and is not necessarily limited to those having all of the configurations described. That is, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. It is also possible to add, delete, or replace a part of the configuration of each embodiment with another configuration.

[0132] For example, in the above-mentioned first to third embodiments, an example of a configuration was shown in which the first axial position, which is the start position of the change in the tooth profile 70, 70A, 70B in the cross section perpendicular to the axial direction in the rotor tooth portion 31, 31A, 31B of the female rotor 3, 3A, 3B, is the S1-S1 position or S3-S3 position, which is a substantially intermediate position in the axial direction, and the second position, which is the end position of the change in the tooth profile 70, 70A, 70B, is the D1-D1 position or D3-D3 position, which is the discharge side end surface 31c. However, the first axial position, which is the start position of the change in the tooth profile of the female rotor, and the second position, which is the end position, can be changed to any position depending on the operating pressure conditions, etc. For example, when the discharge pressure is high, it is possible to move the first position to the suction side in order to make the tooth thickness of the tooth tip of the female rotor thicker. On the other hand, when the discharge pressure is low, it is possible to move the first position to the discharge side.

[0133] It is also possible to set the start position (first position) of the change in the tooth profile 70, 70A, 70B of the female rotor 3, 3A, 3B on the suction side end surface 31b of the rotor tooth portion 31, 31A, 31B. In other words, the female rotor can be configured so that the tooth profile changes over the entire axial area. In this configuration, machining of the tooth profile is relatively easy compared to when the female rotor tooth profile changes from an intermediate position.

[0134] In the third embodiment, an example of a configuration has been shown in which the tooth bottom 75Bd on the discharge side of the tooth profile 70B of the female rotor 3B is changed to be shallower than the tooth bottom 75Bs on the suction side. However, as in the first and second embodiments, a configuration is also possible in which the tooth bottom on the discharge side and the tooth bottom on the suction side of the female rotor are located at the same radial position, and the tooth bottom of the female rotor does not change in the axial direction. [Explanation of symbols]

[0135] 1, 1B... compressor body, 2, 2B... male rotor, 3, 3A, 3B... female rotor, 4, 4B... body casing (casing), 5a, 5b... suction side bearing (male bearing), 7a, 7b... suction side bearing (male bearing), 21a... male teeth, 31a... female teeth, 41B... main casing, 42B... suction side casing, 45... bore (accommodating chamber), 60... tooth profile, 65... tooth tip, 70 (s, d), 70A (s, d), 70B (s, d)... tooth profile (suction side, discharge side), 71 (s, d), 71A (s, d), 71B (s, d)... first contour line (suction side, discharge side), 72(s,d), 72A(s,d), 72B(s,d)...Second contour line (suction side, discharge side), 73(s,d), 73A(s,d), 73B(s,d)...Third contour line (suction side, discharge side), 75(s,d), 75A(s,d), 75B(s,d)...Tooth bottom (suction side, discharge side), 76(s,d), 76A(s,d), 76B(s,d)(s,d)...First end point (suction side, discharge side), 77(s,d), 77A(s,d), 77B(s,d)...Second end point (suction side, discharge side), φL(s,d), φLA(s,d), φLB(s,d)...Advancing face angle (first angle) (suction side, discharge side), φT(s,d), φT(s,d), φTB(s,d)...Rearward surface angle (second angle) (suction side, discharge side), φS(s,d), φSA(s,d), φSB(s,d)...Tooth tip angle (third angle) (suction side, discharge side), A1...Rotation center (first rotation center), A2...Rotation center (first rotation center), C...Working chamber

Claims

1. a male rotor having twisted male teeth and rotating about a first center of rotation; a female rotor having twisted female teeth, meshing with the male rotor and rotating about a second center of rotation parallel to the first center of rotation; a casing having an accommodation chamber for rotatably accommodating the male rotor and the female rotor in a meshed state, the casing forming a plurality of working chambers together with the male rotor and the female rotor, a tooth profile representing a profile shape of a cross section perpendicular to the axial direction of the female rotor is formed to change between a first position in the axial direction and a second position on the discharge side in the axial direction of the female rotor, One of the teeth of the female rotor is a first contour line that defines a section of an advancement surface extending from a boundary point, which is a tooth bottom having a minimum radius, to a first end point, which is a maximum radius, in a rotational direction of the female rotor; a second contour line that defines a section of the reverse surface extending from the boundary point to a second end point having a maximum radius in a direction opposite to the rotational direction of the female rotor; a third contour line that defines a section of a tooth tip portion having a maximum radius, and one of the two end points is a connection point between the first end point of the first contour line or the second end point of the second contour line, The tooth profile of the female rotor is: a first angle is an angle formed by two line segments that connect the second rotation center and both ends of the first contour line with the second rotation center as a vertex; a second angle is an angle formed by two line segments connecting the second rotation center and both ends of the second contour line with the second rotation center as a vertex; When an angle formed by two line segments connecting the second rotation center and both ends of the third contour line with the second rotation center as a vertex is defined as a third angle, The third angle in the second position is set to be larger than the third angle in the first position, the first angle in the second position is set to be smaller than the first angle in the first position, The tooth profile of the female rotor is set so that the second angle at the second position is the same as the second angle at the first position, or so that the second angle at the second position is greater than the second angle at the first position. A screw compressor characterized by:

2. 2. The screw compressor according to claim 1, The female rotor has a tooth profile that changes in an area biased toward the discharge side in the axial direction, while the tooth profile is the same in the remaining area on the suction side in the axial direction. A screw compressor characterized by:

3. 2. The screw compressor according to claim 1, The female rotor has a tooth profile that changes over the entire area in the axial direction. A screw compressor characterized by:

4. A screw rotor having twisted male teeth and meshing with a male rotor rotating about a first rotation center and rotating about a second rotation center parallel to the first rotation center, a tooth profile representing a contour shape of a cross section perpendicular to an axial direction of the screw rotor is formed to change between a first position in the axial direction and a second position on a discharge side in the axial direction of the screw rotor, One tooth of the tooth profile of the screw rotor is a first contour line that defines a section of an advancement surface extending from a boundary point, which is a tooth bottom having a minimum radius, to a first end point, which is a maximum radius, in a rotational direction of the screw rotor; A second contour line that defines a section of the backward surface extending from the boundary point to a second end point having a maximum radius in a direction opposite to the rotation direction of the screw rotor; a third contour line that defines a section of a tooth tip portion having a maximum radius, and one of the two end points is a connection point between the first end point of the first contour line or the second end point of the second contour line, The tooth profile of the screw rotor is a first angle is an angle formed by two line segments that connect the second rotation center and both ends of the first contour line with the second rotation center as a vertex; a second angle is an angle formed by two line segments connecting the second rotation center and both ends of the second contour line with the second rotation center as a vertex; When an angle formed by two line segments connecting the second rotation center and both ends of the third contour line with the second rotation center as a vertex is defined as a third angle, The third angle in the second position is set to be larger than the third angle in the first position, the first angle in the second position is set to be smaller than the first angle in the first position, The tooth profile of the screw rotor is set so that the second angle at the second position is the same as the second angle at the first position, or so that the second angle at the second position is larger than the second angle at the first position. A screw rotor characterized by:

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