Screw compressor and screw rotor

Abstract

In the screw compressor of the present invention, the tooth profile of the female rotor (3) that rotates around the second rotation center (A2) varies axially in a cross-section perpendicular to the axial direction. One tooth of the tooth profile of the female rotor (3) includes: a first contour line (71s, 71d) that defines the advancing surface on the rotation direction side of the female rotor (3) with the tooth bottom (75s, 75d) as the boundary point; a second contour line (72d, 72d) that defines the retreating surface on the side opposite to the rotation direction; and a third contour line (73s, 73d) that defines the tooth top with both ends being the maximum radius. The angles formed by two line segments connecting the second rotation center (A2) to both ends of the first contour line (71s, 71d) with the second rotation center (A2) as the vertex, the angles formed by two line segments connecting the second rotation center (A2) to both ends of the second contour line (72d, 72d), and the angles formed by two line segments connecting the second rotation center (A2) to both ends of the third contour line (73s, 73d) are respectively defined as the first angle (φLs, φLd), the second angle (φTs, φTd), and the third angle (φSs, φSd). In the tooth profile of the female rotor (3), the third angle (φSs, φSd) is larger on the discharge side in the axial direction and the first angle (φLs, φLd) is smaller on the discharge side in the axial direction.

Description

Technical Field

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

[0002] Screw compressors are widely used as air compressors and compressors for refrigeration and air conditioning. In recent years, there has been a strong demand for energy conservation. Therefore, in screw compressors, it has become more important to achieve a higher energy conversion efficiency.

[0003] A screw compressor includes a male and a female screw rotor that rotate while meshing with each other, and a housing that houses the two screw rotors. The two screw rotors each have helical teeth (tooth grooves). In this compressor, the volume of a plurality of working chambers formed by the tooth grooves of the two screw rotors and the inner wall surface of the housing surrounding them increases and decreases as the two screw rotors rotate, thereby sucking and compressing gas.

[0004] In a screw compressor, a minute gap is provided between the rotating screw rotor and the housing so that they do not contact each other. 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 housing. Therefore, the compressed gas leaks from the working chamber with a relatively high pressure to the working chamber with a relatively low pressure through the outer diameter gap. When the compressed gas leaks, correspondingly, the consumed compression power is wasted, or power for re-compression is required, thus reducing the compressor efficiency.

[0005] In a liquid supply type screw compressor, by supplying a liquid such as oil or water to the working chamber, a sealing effect is produced on the outer diameter gap. Thereby, leakage of the compressed gas through the outer diameter gap between the working chambers is prevented, but further suppression of the leakage of the compressed gas is required to improve the compressor efficiency. In addition, in the case of a non-liquid supply type screw compressor, since no liquid is supplied to the working chamber, a sealing effect of the liquid on the outer diameter gap cannot be expected. Thus, in a non-liquid supply type screw compressor, a reduction in the compressor efficiency due to leakage of the compressed gas through the outer diameter gap between the working chambers is particularly a concern.

[0006] In addition, in single-stage screw compressors, in recent years, there have been many products with a compression ratio exceeding 8, and there is a tendency for the pressure difference between the working chambers on the discharge side in the axial direction of the screw rotor to increase. There is a concern that when the pressure difference between the working chambers increases, correspondingly, leakage of the compressed gas through the outer diameter gap between the working chambers may further reduce the compressor efficiency.

[0007] Accordingly, in order to improve the efficiency of the compressor, it is required to reduce the leakage of compressed gas through the outer diameter clearance between the working chambers in the axial discharge side region of the compressor. As a technique for reducing the leakage of compressed gas in the discharge side region, for example, the technique described in Patent Document 1 is known. In the screw compressor described in Patent Document 1, in order to reduce the ratio of the leakage air volume to the suction air volume and prevent seizure caused by contact between the two screw rotors, the tooth thickness of a plurality of teeth provided in the female rotor is formed such that the discharge port side is thicker than the suction port side. Herein, the "tooth thickness" refers to the thickness of the tooth in the tooth profile of the cross-section of the screw rotor perpendicular to the axial direction.

[0008] Prior Art Documents

[0009] Patent Documents

[0010] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2004-144035 Summary of the Invention

[0011] Problems to be Solved by the Invention

[0012] As in the screw compressor described in Patent Document 1, when the tooth thickness of the teeth of the female rotor is thicker on the discharge port side (the discharge side end in the axial direction of the female rotor), correspondingly, the width (distance) of the boundary between the working chambers on the discharge port side of the female rotor increases. Thus, the leakage of compressed gas through the outer diameter clearance between the working chambers on the discharge port side of the female rotor can be suppressed.

[0013] However, in a variable lead screw rotor in which the lead of the screw rotor decreases from the axial suction side to the discharge side, compared with a constant lead screw rotor, the tooth thickness of the tooth tip of the female rotor tends to be thinner. However, the "tooth thickness" herein refers to the thickness of the tooth tip in the tooth profile of the cross-section of the female rotor perpendicular to the extending direction of the tooth tip line. The lead represents the distance that the spiral of the screw rotor advances in the axial direction for one turn.

[0014] When the lead of the screw rotor decreases from the axial suction side to the discharge side, the spiral of the screw rotor becomes tighter as it goes from the suction side to the discharge side. Thus, under the condition that the tooth profile of the cross-section of the screw rotor perpendicular to the axial direction is the same, compared with a constant lead screw rotor, the tooth thickness of the tooth tip of the female rotor tends to become thinner on the discharge side.

[0015] Accordingly, in a variable lead screw rotor in which the lead decreases from the axial suction side to the discharge side, the tooth thickness of the tooth tip of the female rotor is thinner on the discharge side, and there is a concern that the leakage of compressed gas through the outer diameter clearance between the working chambers located on the discharge side will increase accordingly. Thus, a structure in which the tooth thickness of the tooth tip of the female rotor is thicker on the discharge side as in the screw compressor described in Patent Document 1 is considered.

[0016] However, in a screw compressor having a screw rotor with a constant or variable lead, as in the screw compressor described in Patent Document 1, when the tooth thickness of the tip of the female rotor is thicker on the discharge side in the axial direction than on the suction side, there is a case where a vibration phenomenon called flank separation vibration occurs in the screw rotor. In a screw compressor having a male rotor and a female rotor that mesh with each other, generally, the tooth surfaces of the two rotors are in direct contact with each other, or mesh with a synchronous gear provided on the same axis as the two rotors. Thus, the driving torque of the male rotor is transmitted to the female rotor to drive the female rotor. Depending on the pressure conditions acting on the tooth surfaces of the rotors, a phenomenon such as flank separation may occur, in which the transmitted torque from the male rotor to the female rotor temporarily changes to negative and the tooth surfaces transmitting the torque separate from each other. After that, when the transmitted torque from the male rotor to the female rotor returns to positive again, the once-separated tooth surfaces collide with each other. As a result, flank separation and flank collision occur repeatedly, generating large vibrations and noises. This is called flank separation vibration.

[0017] As described above, in order to prevent the working gas from leaking through the outer diameter gap between the working chambers located on the discharge side in the axial direction of the screw rotor, when the tooth thickness of the tip of the female rotor is thicker on the discharge side, there is a case where a vibration phenomenon called flank separation vibration occurs in the screw rotor. However, in Patent Document 1, no particular mention is made of a structure for suppressing flank separation vibration.

[0018] The present invention is made to eliminate the above problems, and an object thereof is to provide a screw compressor and a screw rotor capable of achieving both prevention of leakage of the working gas between the working chambers through the gap formed between the screw rotor and the housing and prevention of occurrence of flank separation vibration.

[0019] Technical means for solving the problem

[0020] The present application includes various technical solutions for solving the above problems. Taking one example, it includes: a male rotor having twisted male teeth that can rotate around a first rotation center; a female rotor having twisted female teeth that can mesh with the male rotor and rotate around a second rotation center parallel to the first rotation center; and a housing having a housing chamber that houses the male rotor and the female rotor in a rotatable state while they are meshed, and forming a plurality of working chambers together with the male rotor and the female rotor. The tooth profile representing the contour shape of a cross-section perpendicular to the axial direction of the female rotor is formed such that there is a change between an arbitrary first position in the axial direction and a second position on the discharge side in the axial direction compared to the first position. One tooth in the tooth profile of the female rotor includes: a first contour line that defines an interval of a forward face extending from the boundary point on the side of the rotation direction of the female rotor with the tooth bottom having the minimum radius and reaching a first end point with the maximum radius; a second contour line that defines an interval of a rearward face extending from the boundary point on the side opposite to the rotation direction of the female rotor and reaching a second end point with the maximum radius; and a third contour line that defines an interval of a tooth top portion with both end points having the maximum radius, and any one of the two end points is a connection point with the first end point of the first contour line or the second end point of the second contour line. Define the angle formed by two line segments connecting the second rotation center and both ends of the first contour line with the second rotation center as the vertex as the first angle, the 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 the vertex as the second angle, and the 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 the vertex as the third angle. The tooth profile of the female rotor is set such that the third angle at the second position is greater than the third angle at the first position, and the first angle at the second position is less than the first angle at the first position.

[0021] Advantages of the Invention

[0022] According to the present invention, by setting the third angle corresponding to the shape of the tooth top portion in the tooth profile of the female rotor to be larger on the discharge side in the axial direction than on the suction side, the thickness of the tooth top portion of the female rotor becomes thicker on the discharge side. Accordingly, it is possible to prevent the high-pressure working gas from leaking through the outer diameter gap between the working chambers located on the discharge side in the axial direction. At the same time, by setting the first angle corresponding to the shape of the forward face in the tooth profile of the female rotor to be smaller on the discharge side in the axial direction than on the suction side, tooth surface separation is prevented. Thus, it is possible to achieve both preventing the working gas between the working chambers from leaking through the gap provided between the female rotor and the housing and preventing the occurrence of tooth surface separation vibration.

[0023] Problems, configurations, and effects other than those described above will be described in the following embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a cross-sectional view of a screw compressor showing a first embodiment of the present invention.

[0025] Figure 2 It is a cross-sectional view seen from the II-II direction Figure 1 showing a cross-section of the screw compressor of the first embodiment of the present invention shown in the figure.

[0026] Figure 3 It is a cross-sectional view showing in a partially enlarged state the tooth profile of a pair of screw rotors constituting a part of the screw compressor of the first embodiment of the present invention, which is the contour shape of a cross-section perpendicular to the axial direction.

[0027] Figure 4 It is a cross-sectional view showing in an overlapping state the tooth profile of one tooth of the female rotor when observing the screw compressor of the first embodiment of the present invention from the S1-S1 direction and the D1-D1 direction. Figure 2 shown in the figure.

[0028] Figure 5 It is a diagram for explaining the cause of tooth surface separation vibration in the entire screw compressor.

[0029] Figure 6 It is a table for comparing the susceptibility to tooth surface separation in the case of changing the tooth profile elements of the leading face and the trailing face while fixing the shape (tooth tip angle) of the tooth tip in the tooth profile of the female rotor constituting the screw compressor.

[0030] Figure 7 It is for the case of fixing the shape (tooth tip angle) of the tooth tip in the tooth profile of the female rotor constituting the screw compressor in a state larger than the Figure 6 shown shape (tooth tip angle) of the tooth tip and comparing the susceptibility to tooth surface separation in the case of changing the tooth profile elements of the leading face and the trailing face.

[0031] Figure 8 It is an explanatory diagram showing the air holes as internal clearances in various screw compressors.

[0032] Figure 9 It is for the case of Figure 2 overlapping and showing the tooth profile of one tooth of the female rotor when observing the screw compressor of the second embodiment of the present invention in the same viewing direction as the S1-S1 direction and the D1-D1 direction shown in the figure.

[0033] Figure 10It is a characteristic diagram showing the change in the tooth surface separation margin torque corresponding to the rotation angle of the male rotor in the screw compressor according to the second embodiment of the present invention.

[0034] Figure 11 It is a cross-sectional view of the screw compressor according to the third embodiment of the present invention.

[0035] Figure 12 It is a cross-sectional view showing the tooth profile of one tooth of the female rotor in an overlapping state when observing the screw compressor according to the third embodiment of the present invention as viewed from S3 - S3 and D3 - D3. Figure 11 It is a cross-sectional view showing the tooth profile of one tooth of the female rotor in an overlapping state when observing the screw compressor according to the third embodiment of the present invention as shown.

[0036] Figure 13 It is a cross-sectional view of a variable lead screw compressor as a comparative example relative to the screw compressor according to the third embodiment of the present invention. Detailed Embodiment

[0037] Hereinafter, embodiments of the screw compressor of the present invention will be described with reference to the drawings by way of example.

[0038] [First Embodiment]

[0039] Use Figure 1 And Figure 2 To illustrate the structure of the screw compressor according to the first embodiment. Figure 1 It is a cross-sectional view of the screw compressor according to the first embodiment of the present invention. Figure 2 It is a cross-sectional view of the screw compressor according to the first embodiment of the present invention as viewed from II - II. Figure 1 As shown. Figure 1 And Figure 2 In, the left side is the suction side of the screw compressor, and the right side is the discharge side.

[0040] Figure 1 In, the screw compressor is composed of a compressor main body 1 for compressing gas and a drive unit 80 for driving the compressor main body 1. The screw compressor is, for example, a liquid supply type compressor that supplies liquid from the outside to the inside of the compressor main body 1.

[0041] Figure 1 And Figure 2 In, the compressor main body 1 has a male rotor 2 and a female rotor 3 as a pair of screw rotors that rotate in mesh with each other, and a main body housing 4 that rotatably houses the male rotor 2 and the female rotor 3 in a meshed state. The male rotor 2 and the female rotor 3 are arranged such that their rotational centers A1, A2 are parallel to each other. In the male rotor 2, its axial direction ( Figure 1 And Figure 2On both sides in the left - right direction (in the figure), the suction - side bearing 5 and the discharge - side bearings 6a and 6b rotatably support the male rotor 2. In the female rotor 3, on both axial sides thereof, the suction - side bearing 7 and the discharge - side bearings 8a and 8b rotatably support it.

[0042] The male rotor 2 is composed of a rotor tooth part 21 having a plurality of helical male teeth (lobes) 21a, and a suction - side shaft part 22 and a discharge - side shaft part 23 respectively provided at both axial - end portions of the rotor tooth part 21. The rotor tooth part 21 has, at one axial end ( Figure 1 and Figure 2 the left - end in the figure) and the other end ( Figure 1 and Figure 2 the right - end in the figure), a suction - side end face 21b and a discharge - side end face 21c perpendicular to the axial direction (rotation center A1) respectively. Tooth grooves are formed between the plurality of male teeth 21a of the rotor tooth part 21. The suction - side shaft part 22, for example, extends outward from the main body housing 4 and is configured to share the shaft part with the drive part 80.

[0043] The female rotor 3 is composed of a rotor tooth part 31 having a plurality of helical female teeth 31a (refer to the following Figure 3 ), and a suction - side shaft part 32 and a discharge - side shaft part 33 respectively provided at both axial - end portions of the rotor tooth part 31. The rotor tooth part 31 has, at one axial end ( Figure 1 and Figure 2 the left - end in the figure) and the other end ( Figure 1 and Figure 2 the right - end in the figure), a suction - side end face 31b and a discharge - side end face 31c perpendicular to the axial direction (rotation center A2) respectively. Tooth grooves are formed between the plurality of female teeth 31a of the rotor tooth part 31.

[0044] The main body housing 4 has a main housing 41 and a discharge - side housing 42 installed on the discharge side ( Figure 1 and Figure 2 the right side in the figure) of the main housing 41.

[0045] Inside the main body housing 4, a hole 45 serving as a storage chamber is formed to store the rotor tooth part 21 of the male rotor 2 and the rotor tooth part 31 of the female rotor 3 in a meshed state with each other. The hole 45 is formed by closing the axial - side ( Figure 1 and Figure 2 the right side in the figure) opening of two overlapping cylindrical spaces formed in the main housing 41 with the discharge - side housing 42. The inner wall surface forming the hole 45 includes: a substantially cylindrical first inner peripheral surface 46 covering the radially outer side of the rotor tooth part 21 of the male rotor 2; a substantially cylindrical second inner peripheral surface 47 covering the radially outer side of the rotor tooth part 31 of the female rotor 3; and an axial - side ( Figure 1and Figure 2 the inner wall surface 48 on the suction side (on the left side in [[ ]]); on the other axial side opposite to the discharge side end surfaces 21c, 31c of the rotor teeth 21, 31 of the male and female rotors 2, 3 Figure 1 and Figure 2 the inner wall surface 49 on the discharge side (on the right side in [[ ]]). A pair of intersection lines is formed by the first peripheral surface 46 and the second peripheral surface 47, and this pair of intersection lines is called the cusp line 45a (refer to Figure 3 ). The cusp line 45a extends axially and is formed on the expansion side and the compression side of the rotor engagement part ( Figure 3 only the expansion side is illustrated in [[ ]]). 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 surfaces of the main body housing 4 surrounding them (the first inner peripheral surface 46, the second inner peripheral surface 47, the suction side inner wall surface 48, the discharge side inner wall surface 49 of the hole 45).

[0046] On the suction side end of the main housing 41, a suction side bearing 5 on the side of the male rotor 2 and a suction side bearing 7 on the side of the female rotor 3 are provided. In the discharge side housing 42, discharge side bearings 6a, 6b on the side of the male rotor 2 and discharge side bearings 8a, 8b on the side of the female rotor 3 are provided. A discharge side cover 43 is mounted on the discharge side housing 42 so as to cover the discharge side bearings 6a, 6b and the discharge side bearings 8a, 8b.

[0047] In the main housing 41 of the main body housing 4, as Figure 1 shown, a suction flow path 51 for sucking gas into the working chamber C is provided. The suction flow path 51 connects the outside of the main body housing 4 with the hole 45 (working chamber C). The suction flow path 51 has, for example, a suction port 51a that opens on the inner wall surface of the main body housing 4. The suction port 51a can be formed so as to open axially, radially, or both axially and radially of the male and female rotors 2, 3.

[0048] In addition, in the discharge side housing 42 of the main body housing 4, a discharge flow path 52 for discharging compressed gas from the working chamber C to the outside of the main body housing 4 is provided. The discharge flow path 52 connects the hole 45 (working chamber C) with the outside of the main body housing 4. The discharge flow path 52 has a discharge port 52a formed on the discharge side inner wall surface 49 of the main body housing 4. The discharge port 52a can be formed so as to open axially, radially, or both axially and radially of the male and female rotors 2, 3.

[0049] In the main housing 41 of the main body housing 4, a liquid supply passage 53 for supplying the liquid supplied from the outside of the compressor main body 1 to the working chamber C is provided. The liquid supply passage 53 opens, for example, in the region of the inner wall surface of the hole 45 where the working chamber C is in the compression stroke.

[0050] The drive unit 80 is, for example, as Figure 1Shown is a motor, which is integrally formed with the compressor main body 1. The drive unit 80 includes a motor 83 composed of a rotor 81 and a stator 82, a motor housing 85 that houses the motor 83 therein, and a motor cover 86 that closes the opening of the motor housing 85. The rotor 81 is connected to the male rotor 2 of the compressor main body 1. In the motor housing 85, a motor-side bearing portion 87 that rotatably supports the rotor 81 and a shaft seal member 88 that prevents liquid from leaking from the compressor main body 1 to the drive unit 80 are provided.

[0051] In addition, in the present embodiment, an example in which a motor is used as the drive unit 80 is shown, but the rotational drive source is not particularly limited. In addition, a structure in which the drive unit 80 rotates and drives not the male rotor 2 but the female rotor 3 or both the male and female rotors 2 and 3 can also be adopted. In addition, a structure in which the drive unit 80 does not share the shaft portion of the compressor main body 1 can also be adopted.

[0052] Next, the basic structure of the tooth profiles of the male and female rotors in the screw compressor of the first embodiment is described using Figure 3 for illustration. Figure 3 is a cross-sectional view showing in a partially enlarged state the tooth profiles of the pair of screw rotors that form a part of the screw compressor of the first embodiment of the present invention and that are the contour shapes of the cross-sections perpendicular to the axial direction. Figure 3 In, the thick arrows indicate the rotational directions of the male rotor and the female rotor. That is, Figure 3 in, the male rotor rotates clockwise and the female rotor rotates counterclockwise.

[0053] Figure 3 In, the tooth profiles 60 and 70 that are the contour shapes of the cross-sections perpendicular to the axial direction (the rotational centers A1 and A2) of the rotor tooth portions 21 and 31 of the male rotor 2 and the female rotor 3 are geometrically designed such that the clearance at the meshing portion of the male and female rotors 2 and 3 theoretically becomes 0. However, the actual tooth profiles are manufactured by reducing the corresponding amount relative to the geometrically designed shape by setting an appropriate clearance at the meshing portion of the two rotors 2 and 3 in order to allow for thermal deformation, pneumatic deformation, vibration, and machining errors.

[0054] Whether to set the clearance at the meshing portion of the two rotors 2 and 3 has no direct relation to the essence of the present invention. Thus, regarding the tooth profiles 60 and 70 of the rotor tooth portions 21 and 31 of the male rotor 2 and the female rotor 3, although the existence of the clearance at the meshing portion of the two rotors 2 and 3 is studied, the description is made according to the geometrically designed shape in which the clearance is 0. Therefore, even if it is expressed as "contact" in the following description, there is a case where a minute clearance exists at the meshing portion of the actual tooth profiles 60 and 70 of the male rotor 2 and the female rotor 3.

[0055] Among the tooth profiles 60 and 70 of the male and female rotors 2 and 3, each point on the tooth profile 60 of the male rotor 2 pairs one-to-one with each point on the tooth profile 70 of the female rotor 3, constituting the satisfaction of the meshing condition that "the common normal of the two tooth surfaces at a constant speed ratio meshing passes through the pitch point". In other words, it can be expressed as "when a point on a certain tooth surface is at a position satisfying the meshing condition, it contacts the other tooth surface". A pair of screw rotors that mesh with each other need to satisfy this condition. Therefore, when the tooth profile of either the male rotor 2 or the female rotor 3 is determined, the tooth profile of the other is also uniquely determined. In the following description, the tooth profile of the male rotor 2 is sometimes referred to as the male tooth profile, and the tooth profile of the female rotor 3 is sometimes referred to as the female tooth profile. In addition, 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 according to 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.

[0056] Figure 3 Among them, the rotation center A1 of the male rotor 2, the rotation center A2 of the female rotor 3, the tooth tip 65 with the largest radius of the male rotor 2, and the tooth root 75 with the smallest radius of the female rotor 3 are located on the same straight line, and the tooth tip 65 of the male rotor 2 contacts the tooth root 75 of the female rotor 3. The rotation angles of the male and female rotors 2 and 3 at this time are taken as the reference angle (0°).

[0057] One tooth in the male tooth profile 60 of the male rotor 2 includes a first contour line 61 that defines an interval of the specified forward face, a second contour line 62 that defines an interval of the specified backward face, and a third contour line 63 that defines an interval of the specified tooth bottom. In this description, with the tooth tip with the largest radius of the male rotor 2 as the boundary, the tooth surface on the rotation direction side of the male rotor is defined as the forward face of the male rotor 2, and the tooth surface on the side opposite to the rotation direction is defined as the backward face of the male rotor 2. Specifically, the first contour line 61 takes the tooth tip 65 as the boundary point and defines an interval that extends from the boundary point to the rotation direction side of the male rotor 2 and reaches the first end point 66 with the smallest radius. The second contour line 62 takes the tooth tip 65 as the boundary point and defines an interval that extends from the boundary point to the side opposite to the rotation direction of the male rotor 2 and reaches the second end point 67 with the smallest radius. The third contour line 63 defines an interval where both end points are the minimum radius. For example, one of the two end points is the connection point with the first end point 66 of the first contour line 61, and the other end point is the connection point with the second end point 67 of the second contour line 62 of an adjacent tooth. In addition, in the third contour line 63, it is also possible that one of the two end points is the connection point with the first end point 66 of the first contour line 61 of an adjacent tooth, and the other end point is the connection point with the second end point 67 of the second contour line 62.

[0058] One tooth in the female tooth profile 70 of the female rotor 3 includes a first contour line 71 that defines an interval of a specified advancing surface, a second contour line 72 that defines an interval of a specified retreating surface, and a third contour line 73 that defines an interval of a tooth top. In this description, with the bottom of the tooth having the smallest radius of the female rotor 3 as a boundary, the tooth surface on the rotation direction side of the female rotor 3 is defined as the advancing surface of the female rotor 3, and the tooth surface on the side opposite to the rotation direction is defined as the retreating surface of the female rotor 3. Specifically, the first contour line 71 has the tooth bottom 75 as a boundary point and defines an interval that extends from the boundary point to the rotation direction side of the female rotor 3 and reaches the first end point 76 with the largest radius. The second contour line 72 has the tooth bottom 75 as a boundary point and defines an interval that extends from the boundary point to the side opposite to the rotation direction of the female rotor 3 and reaches the second end point 77 with the largest radius. The third contour line 73 defines an interval where both end points are the maximum radius. For example, one of the two end points is a connection point with the first end point 76 of the first contour line 71 and the other end point is a connection point with the second end point 77 of the second contour line 72 of an adjacent tooth. Additionally, in the third contour line 73, it is also possible that one of the two end points is a connection point with the first end point 76 of the first contour line 71 of an adjacent tooth and the other end point is a connection point with the second end point 77 of the second contour line 72.

[0059] The first contour line 61 that defines the advancing surface and the second contour line 62 that defines the retreating surface in the tooth profile 60 of the male rotor 2 are composed of a plurality of tooth profile elements. Similarly, the first contour line 71 that defines the advancing surface and the second contour line 72 that defines the retreating surface in the tooth profile 70 of the female rotor 3 are composed of a plurality of tooth profile elements.

[0060] In Figure 3 An example of the tooth profiles 60 and 70 of the male rotor 2 and the female rotor 3 is shown. The tooth profiles 60 and 70 are obtained by forming the first contour lines 61 and 71 that define the advancing surface with tooth profile elements of one parabola and one arc, and forming the second contour lines 62 and 72 that define the retreating surface with tooth profile elements of two arcs.

[0061] Specifically, the second contour lines 62 and 72 of the specified trailing faces of the tooth profiles 60 and 70 of the male and female rotors 2 and 3, respectively, are generated, for example, based on one first circular arc as a convex surface starting from the 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 circular arc as a convex surface ending at the 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 circular arc of the second contour line 62 of the male rotor 2 has a certain radius R1 and is a curve ending at point 62a. The second circular arc of the second contour line 72 of the female rotor 3 has a certain radius R2 and is a curve starting at point 72a. In the second contour line 62 of the male rotor 2, the remaining section from the end point 62a of the first circular arc to the second end point 67 of the second contour line 62 is generated in a manner that satisfies the above meshing condition corresponding to the shape of the second contour line 72 of the female rotor 3 including the second circular arc. Additionally, in the second contour line 72 of the female rotor 3, the remaining section from the tooth root 75 (one end point of the second contour line 72) to the start point 72a of the second circular arc is generated in a manner that satisfies the above meshing condition corresponding to the shape of the second contour line 62 of the male rotor 2 including the first circular arc.

[0062] In addition, the first contour line 71 in the tooth profile 70 of the female rotor 3 is generated, for example, based on one parabola forming a concave surface and one third circular arc forming a convex surface. In the parabola, the focus F is located on the 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 curve starting from the tooth root 75 (one end point of the first contour line 71) and ending at point 71a. The third circular arc of the first contour line 71 of the female rotor 3 has a certain radius R3 and is a curve starting from the end point 71a of the parabola and extending to the first end point 76 of the first contour line 71. The first contour line 61 of the male rotor 2 is generated in a manner that satisfies the above meshing condition corresponding to the shapes of the parabola and the third circular arc, which are the tooth profile elements of the first contour line 71 of the female rotor 3.

[0063] The third contour line 73 specifying the tooth top 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 specifying the tooth bottom of the male rotor 2 is generated in a manner that satisfies the above meshing condition corresponding 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.

[0064] In the female tooth profile 70 of the female rotor 3, the first contour line 71 defining the specified advance surface, the second contour line 72 defining the specified retreat surface, and the third contour line 73 defining the tooth top can be represented by angles with the rotation center A2 of the female rotor 3 as the vertex as follows. The angle formed by two line segments connecting the rotation center A2 of the female rotor 3 as the vertex to both ends of the first contour line 71, namely the tooth bottom 75 and the first end point 76, is defined as the advance surface angle φL. The angle formed by two line segments connecting the rotation center A2 of the female rotor 3 as the vertex to both ends of the second contour line 72, namely the tooth bottom 75 and the second end point 77, is defined as the retreat surface angle φT. The angle formed by two line segments connecting the rotation center A2 of the female rotor 3 as the vertex to both ends of the third contour line 73, namely the first end point 76 of the first contour line 71 and the second end point 77 of the second contour line 72, is defined as the tooth top angle φS.

[0065] Next, the characteristics of the tooth profiles of the male and female rotors in the screw compressor of the first embodiment will be described using Figure 2 and Figure 4 for illustration. Figure 4 is a cross-sectional view showing the tooth profile of one tooth of the female rotor when observing the screw compressor of the first embodiment of the present invention as shown in the S1-S1 end view and the D1-D1 end view in an overlapping state. Figure 2 In this figure, the solid line represents the tooth profile of one tooth on the discharge side (D1-D1 section) of the female rotor 3, and the dashed line represents the tooth profile of one tooth on the suction side (S1-S1 section) of the female rotor 3. Figure 4 Similarly, the rotation angle of the female rotor is the reference angle (0°). Figure 4 And Figure 3 In this figure, the male rotor 2 and the female rotor 3 are configured as screw rotors having the same lead in the entire axial region from one end on the axial suction side (

[0066] Figure 2 the left end in Figure 2 ) of the rotor tooth portions 21 and 31 to one end on the discharge side ( Figure 2 the right end in

[0067] Specifically, the tooth profile 70 of the female rotor 3 (refer to Figure 4 ) is of the same shape along the axis in the region from the suction side end face 31b of the rotor tooth portion 31 to a certain first position near the discharge side in the axis, for example, the substantially middle position (S1-S1 position) in the axis. On the other hand, in the region from the first position to the discharge side end face 31c (D1-D1 position) of the female rotor 3, the first tooth profile 70s on the suction side represented by the dashed line in Figure 4 Figure 2The tooth profile at the S1-S1 position shown) gradually changes to the second tooth profile 70d on the discharge side represented by a solid line ( Figure 2 The tooth profile at the D1-D1 position shown) to form the female tooth profile 70. The tooth tip angle φS, the leading face angle φL, and the trailing face angle φT in the female tooth profile 70 (refer to Figure 3 ) are set in such a way that they monotonically change 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).

[0068] Figure 4 In, the first tooth profile 70s on the axial suction side (S1-S1 position) in the female rotor 3 is represented by a dashed line, and the second tooth profile 70d on the discharge side (D1-D1 position) is represented by a solid line.

[0069] By adding the reference numeral s indicating the suction side and the reference numeral d indicating the discharge side to the first contour line 71, the second contour line 72, and the third contour line 73 in 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.

[0070] Similarly, by adding the reference numeral s indicating the suction side and the reference numeral 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 reference numeral s indicating the suction side and the reference numeral d indicating the discharge side to both ends 76 and 77 of the third contour line 73 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. In addition, 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 coincides with the second end point 77 of the second contour line 72.

[0071] In addition, by adding the reference numeral s indicating the suction side and the reference numeral d indicating the discharge side to the tooth tip angle φS, the leading face angle φL, and the trailing face angle φT in 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.

[0072] In the present embodiment, as Figure 4As shown, the tip angle φSd of the second tooth profile 70d on the axial discharge side in the female rotor 3 is set to be greater than the tip angle φSs of the first tooth profile 70s on the axial suction side compared to the second tooth profile 70d. That is, the female tooth profile 70 is configured such that the thickness of the tip portion of the second tooth profile 70d on the discharge side is thicker than the thickness of the tip portion of the first tooth profile 70s on the suction side. In this way, the tip portion of the female rotor 3 is thicker on the axial discharge side, and accordingly, it is possible to prevent the compressed gas between the working chambers on the axial discharge side from leaking through the outer diameter gap.

[0073] In addition, the leading face angle φLd of the second tooth profile 70d on the discharge side of the female rotor 3 is set to be smaller than the leading face angle φLs of the first tooth profile 70s on the suction side. In addition, in the present 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 are the same shape. That is, the trailing face angle φTd of the female tooth profile 70 on the discharge side is set to the same angle as the trailing face angle φTs on the suction side.

[0074] In addition, the first tooth profile 70s on the suction side of the female rotor 3 needs to satisfy the following formula (1). In addition, the second tooth profile 70d on the discharge side needs to satisfy the following formula (2). In addition, in formulas (1) and (2), the unit of the angle is degrees.

[0075] φSs + φLs + φTs = 360 / number of teeth of the female rotor... Formula (1)

[0076] φSd + φLd + φTd = 360 / number of teeth of the female rotor... Formula (2)

[0077] By arranging the above formulas (1) and (2), the following formula (3) holds.

[0078] (φLs - φLd) + (φTs - φTd) = φSd - φSs... Formula (3)

[0079] The above formula (3) becomes as follows according to the condition that the tip portion 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 tip portion defined by the third contour line 73s of the first tooth profile 70s on the suction side:

[0080] (φLs - φLd) + (φTs - φTd) = φSd - φSs > 0

[0081] Accordingly, the relationship between the leading face angle φL and the trailing face angle φT needs to satisfy the following formula (4).

[0082] φLs - φLd > φTd - φTs... Formula (4)

[0083] Next, the causes of tooth surface separation vibration in various screw compressors are described using Figure 5 as follows. Figure 5 It is a diagram showing the causes of tooth surface separation vibration in the entire screw compressor. Figure 5 In the figure, the thick arrows respectively indicate the rotation directions of the male rotor and the female rotor.

[0084] In a liquid supply type screw compressor, generally, the tooth surfaces of the male rotor 2 and the female rotor 3 are in direct contact with each other, and thus the driving 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 the two rotors 2 and 3, sometimes a phenomenon of tooth surface separation occurs where the transmitted torque from the male rotor 2 to the female rotor 3 temporarily changes to negative and the tooth surfaces transmitting the torque are separated from each other. After that, when the transmitted torque from the male rotor 2 to the female rotor 3 returns to positive again, the once-separated tooth surfaces collide with each other. As a result, tooth surface separation and tooth surface collision occur repeatedly, generating large vibrations and noises. This is called tooth surface separation vibration, and there is a concern of causing tooth surface damage.

[0085] Figure 5 At the rotation angles of the male and female rotors 2 and 3 shown, three contact points S1, S2, and S3 are generated due to the meshing of the two rotors 2 and 3, and thus two crescent-shaped working chambers C1 and C2 that are only open axially are formed in this cross-section. The first working chamber C1 is formed between the first contact point S1 where the forward surface (first contour line 61) of the male rotor 2 contacts the forward surface (first contour line 71) of the female rotor 3, and the second contact point S2 where the rearward surface (second contour line 62) of the male rotor 2 contacts the rearward surface (second contour line 72) of the female rotor 3. The first working chamber C1 has a reduced volume as the male and female rotors 2 and 3 rotate, and is a working chamber in the compression stroke or the discharge stroke. The second working chamber C2 is formed between the second contact point S2 and the third contact point S3 where the part on the bottom side of the rearward surface (second contour line 62) of the male rotor 2 compared to the second contact point S2 contacts the part on the top side of the rearward surface (second contour line 72) of the female rotor 3. The second working chamber C2 has an expanding volume as the male and female rotors 2 and 3 rotate, and is a working chamber in the suction stroke.

[0086] Here, the rotation radius from the rotation center A2 of the female rotor 3 to the first contact point S1 is called the first female radius RL, and the rotation radius from the rotation center A2 to the second contact point S2 is called the second female radius RT. Let the remaining length obtained by subtracting the root radius RB of the female rotor 3 from the first female radius RL be L, and let the remaining length obtained by subtracting the root radius RB from the second female radius RL be T.

[0087] Figure 5At the rotation angles of the male and female rotors 2 and 3 shown, according to the positional relationship between the first contact point S1 and the second contact point S2, the first female radius RL > the second female radius RT. That is, L > T. In this case, in the tooth surface on the cross-section of the female rotor 3, due to the difference in the compressed area, the torque of the compressed gas (gas torque) in the first working chamber C1 acts in the rotation direction. That is, the torque acts in the direction in which the tooth surfaces of the male and female rotors 2 and 3 separate. The gas torque is the torque exerted by the gas around the two rotors 2 and 3 on the tooth surfaces, and the direction that hinders the rotation of the female rotor 3, that is, the direction opposite to the rotation direction of the female rotor 3, is defined as positive. Thus, the torque that causes tooth surface separation (tooth surface separation torque) between the two rotors 2 and 3 represents a negative torque.

[0088] However, in each working chamber C of the screw compressor, there are various pressure levels in the axial direction and they are formed into different shapes corresponding to the rotation angle. Therefore, the calculation of the tooth surface separation torque needs to be integrated from the suction side to the discharge side in the axial direction of the working chamber. Even if Figure 5 the tooth surface separation torque is generated on the specific cross-section shown, the calculated value when integrating the gas torque in the axial direction is not necessarily a negative torque. However, when suction throttling control is performed, when the suction pressure becomes very low and the discharge pressure increases, there is a tendency to easily generate the tooth surface separation torque. When the tooth surface separation torque is generated on a part of the tooth surfaces of the male and female rotors 2 and 3, tooth surface collisions will occur repeatedly and tooth surface separation vibration will occur.

[0089] Next, the effects of the screw compressor of the first embodiment are described using Figures 5 to 8 for illustration. Figure 6 It is a table comparing the susceptibility to tooth surface separation when changing the tooth profile elements of the leading face and the trailing face while fixing the shape (tooth tip angle) of the tooth tip in the tooth profile of the female rotor constituting the screw compressor. Figure 7 It is a table comparing the susceptibility to tooth surface separation when changing the tooth profile elements of the leading face and the trailing face while fixing the shape (tooth tip angle) of the tooth tip in a state larger than the Figure 6 shown shape (tooth tip angle) of the tooth tip. Figure 8 It is an explanatory diagram showing the air holes as internal clearances in various screw compressors.

[0090] Figure 6 and Figure 7 The tooth profiles (the first contour line defining the leading face, the second contour line defining the trailing face, the third contour line defining the tooth tip) of the female rotor shown are generated based on the same tooth profile elements as the Figure 3 tooth profile of the female rotor 3 shown. That is, the second contour line is based on Figure 3Generated by two tooth profile elements: an arc with a radius R1 starting from the tip 65 of the male rotor 2 and an arc with a 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 based on Figure 3 Generated by two tooth profile elements: a parabola with a focal length Lf starting from the root 75 of the female rotor 3 and an arc with a radius R3 ending at the first end point 76 of the first contour line 71 of the female rotor 3. Figure 6 and Figure 7 In [relevant figure], for one tooth of the tooth profile of the female rotor, the dimensions of each tooth profile element and the leading face angle φL, trailing face angle φT, and tip angle φS corresponding to the tooth profile dimensions are shown. In addition, the % corresponding to the leading face angle, trailing face angle, and tip angle represents the ratio of each angle when the angle of one tooth of the tooth profile is 100%.

[0091] The dimensions of each tooth profile element need to satisfy the meshing conditions, and the range in which each tooth profile element can exist in an interrelated manner is limited. The range in which each tooth profile element can exist is shown for each number (No.). However, for the radius R2 of the second contour line, it is set to a fixed value in order to easily understand the occurrence tendency of tooth surface separation. The occurrence tendency of tooth surface separation corresponding to the tooth profile of each number is shown in the tooth surface separation column. In addition, the occurrence tendency of tooth surface separation is represented by a tooth surface separation torque obtained based on a numerical calculation of integrating the gas torque acting on the tooth surface in the axial direction.

[0092] Figure 6 and Figure 7 The tooth profile of the female rotor shown in [relevant figure] is different from the tooth profile of the female rotor 3 of the present embodiment, but has the same shape along the axial direction. Figure 6 The angle ratio of the tip angle φS shown in [relevant figure] is fixed at 1%, Figure 7 The angle ratio of the tip angle φS shown in [relevant figure] is fixed at 3.5%.

[0093] According to Figure 6 it can be seen that when the angle ratio of the tip angle φS is fixed, tooth surface separation is less likely to occur when the angle ratio of the leading face angle φL is smaller. That is, when the angle ratio of the trailing face angle φT is larger, tooth surface separation is less likely to occur. The reason is based on the principle of generation of the tooth surface separation torque explained by Figure 5 This is because when the angle ratio of the tip angle φS is fixed, the smaller the angle ratio of the leading face angle φL and the larger the angle ratio of the trailing face angle φT, then Figure 5 the length L shown in [relevant figure] decreases more, while on the other hand, the length T increases.

[0094] In addition, the larger the focal length Lf of the parabola constituting the first contour line, then Figure 5The more the first contact point S1 shown moves toward the root side of the teeth of the male rotor 3, the correspondingly shorter the length L becomes. As a result, there is a tendency for the relationship L>T to be less likely to hold, and tooth surface separation is less likely to occur.

[0095] However, even when the angular ratio of the leading face angle φL is small, there are combinations (dimensions) of tooth profile elements in which tooth surface separation is likely to occur. This is the case where even when the angular ratio of the leading face angle φL is decreased, Figure 5 the relationship L>T described also holds depending on the combination (dimensions) of tooth profile elements. For example, Figure 6 in the tooth profile shown in No.7, the focal length Lf of the parabola is set relatively small.

[0096] In this way, in the case of the tooth profile shown where the angular ratio of the tip angle φS is relatively small, Figure 6 there is a tendency for tooth surface separation to be less likely to occur when the angular ratio of the leading face angle φL is small. Furthermore, by adjusting the focal length Lf of the parabola, which is one of the tooth profile elements, the occurrence of tooth surface separation can be avoided. For example, in the case of the tooth profile shown where the angular ratio of the tip angle φS is relatively small, Figure 6 by adjusting it so that the focal length Lf of the parabola is relatively large (adjusted to the dimensions shown in No.3, No.6, No.8, No.9), tooth surface separation is less likely to occur.

[0097] On the other hand, compared with the tooth profile shown in Figure 6 in the tooth profile shown where the angular ratio of the tip angle φS is large, Figure 7 the range in which tooth surface separation is likely to occur expands. Figure 7 In the tooth profile shown in, the only tooth profile in which tooth surface separation is less likely to occur is the tooth profile shown in No.9. That is, it can be seen that in the case of a tooth profile in which the angular ratio of the tip angle φS is relatively large, even if the setting of the focal length Lf of the parabola, which is a tooth profile element of the first contour line, is adjusted, an effect of making tooth surface separation less likely to occur cannot be obtained. Therefore, in order to make tooth surface separation less likely to occur, it is necessary to decrease the angular ratio of the leading face angle φL.

[0098] Here, based on Figure 6 and Figure 7 the tendency of the occurrence of tooth surface separation corresponding to the tooth profile shown, the combination of the first tooth profile 70s on the suction side and the second tooth profile 70d on the discharge side of the male rotor 3 is considered.

[0099] As the second tooth profile 70d on the discharge side, in order to prevent the high-pressure gas on the axial discharge side from leaking through the outer diameter gap and to prevent tooth surface separation from occurring, among the tooth profiles shown where the angular ratio of the tip angle φS is relatively large, Figure 7 the tooth profile shown in No.9, in which tooth surface separation is less likely to occur, is selected.

[0100] On the other hand, as the first tooth profile 70s on the suction side, in the tooth profile where the angular ratio of the tooth tip angle φS is relatively small Figure 6 In the tooth profiles shown, one of the tooth profiles No.3, No.6, No.8, and No.9 that are less likely to cause tooth surface separation can be considered. However, the purpose of the present embodiment is to suppress tooth surface separation vibration and suppress the reduction in energy conversion efficiency due to compressed gas leakage. However, Figure 6 In the tooth profiles shown by No.8 and No.9 of Figure 6 compared with the tooth profiles shown by No.3 and No.6 of Figure 6 In the tooth profiles shown by No.8 and No.9 of Figure 7 In the tooth profile shown by No.9 of

[0101] The air hole H refers to a leakage flow path that connects adjacent working chambers C and is formed along the cusp line 45a of the main body housing 4 as shown in Figure 8 and is generally triangular. The vertex Sa of the air hole H is the starting contact point at the moment when the tooth profiles of the male and female rotors 2 and 3 mesh and start to contact due to rotation. The bottom side of the air hole H is formed by the cusp line 45a. One end point Bm of the bottom side of the air hole H is the intersection position of the tooth tip line 21d of the male rotor 2 and the cusp line 45a. In addition, since there is a slight 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 bottom side of the air hole 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 slight 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.

[0102] Regarding the area of the air hole H, the higher the starting contact point (vertex) Sa is located, the higher the height of the approximate triangular shape and the longer the length of the bottom side, so the area increases. Therefore, in order to reduce the leakage of compressed gas through the air hole H, the starting contact point Sa is set below. In the tooth profile 70 of the female rotor 3, when the angular ratio of the leading face angle φL is fixed and the angular ratio of the trailing face angle φT is increased, the starting contact point Sa moves upward, so there is a tendency for the leakage of compressed fluid through the air hole H to increase.

[0103] Thus, in the case where the angular ratio of the trailing face angle φT is relatively large Figure 6Although the tooth profiles shown in No.8 and No.9 are shapes that are not prone to tooth surface separation, they are not suitable for the purpose of suppressing a decrease in energy conversion efficiency caused by leakage of compressed gas. Thus, in the first tooth profile 70s on the suction side of the female rotor 3, in order to achieve both prevention of a decrease in energy conversion efficiency due to leakage of compressed gas and suppression of tooth surface separation vibration, it is necessary to increase the angular ratio of the leading face angle φL with respect to the second tooth profile 70d on the discharge side. In addition, for the angular ratio of the trailing face angle φT, a structure can be adopted that is the same as or smaller than that of the second tooth profile on the discharge side. That is, either of the tooth profiles shown in No.3 and No.6 of Figure 6 can be used.

[0104] In the present embodiment, as shown in Figure 4 , it is set such that the tip angle φSd on the axial discharge side of the female tooth profile 70 is larger than the tip angle φSs on the axial suction side, and the leading face angle φLd on the discharge side is smaller than the leading face angle φLs on the suction side. In addition, the trailing face angle φTd on the discharge side of the female tooth profile 70 is set to the same angle as the trailing face angle φTs on the suction side. That is, when the rotor tooth portion 31 of the female rotor 3 in the present embodiment uses the structure of the tooth profiles shown in Figure 6 and Figure 7 , the tooth profile shown in No.9 of Figure 7 is used as the second tooth profile 70d on the discharge side, and the tooth profile shown in No.6 shown in Figure 6 is used as the first tooth profile 70s on the suction side.

[0105] Thus, the thickness of the tooth top portion defined by the third contour line 73 of the female tooth profile 70 is increased on the axial discharge side, whereby it is possible to prevent compressed gas from leaking through the outer diameter gap relative to an increase in the pressure difference with the working chamber located on the axial discharge side, and it is possible to prevent tooth surface separation from occurring. Thus, it is possible to achieve both prevention of a decrease in energy conversion efficiency due to leakage of the working gas and prevention of tooth surface separation vibration.

[0106] As described above, in the screw compressor of the first embodiment, there is provided a male rotor 2 capable of rotating about a first rotation center A1 and having twisted male teeth 21a; a female rotor 3 capable of meshing with the male rotor 2 and rotating about a second rotation center A2 parallel to the first rotation center A1 and having twisted female teeth 31a; a housing chamber 45 for housing the male rotor 2 and the female rotor 3 in a rotatable state in a meshed state, and a main housing 4 (housing) 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 vary between an S1-S1 position (a certain first position) in the axial direction and a D1-D1 position (a second position) on the discharge side in the axial direction compared to the first position. One tooth in the tooth profile 70 of the female rotor 3 includes: a first contour line 71 defining an interval of a forward face that extends from a boundary point, which is the tooth root 75 with the minimum radius, in the rotation direction of the female rotor 3 and reaches a first end point 76 with the maximum radius; a second contour line 72 defining an interval of a backward face that extends from the boundary point in a direction opposite to the rotation direction of the female rotor 3 and reaches a second end point 77 with the maximum radius; and a third contour line 73 defining an interval of a tooth top portion where both end points have the maximum radius and either one of the two end points is a 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. An angle formed by two line segments connecting the second rotation center A2 to both ends 65, 76 of the first contour line 71 with the second rotation center A2 as the vertex is defined as the forward face angle φL (first angle), an angle formed by two line segments connecting the second rotation center A2 to both ends 65, 77 of the second contour line 72 with the second rotation center A2 as the vertex is defined as the backward face angle φT (second angle), and an angle formed by two line segments connecting the second rotation center A2 to both ends 76, 77 of the third contour line 73 with the second rotation center A2 as the vertex is defined as the tooth top angle φS (third angle). The tooth profile 70 of the female rotor 3 is set such that the tooth top angle φSd (third angle) at the D1-D1 position (second position) is greater than the tooth top angle φSs (third angle) at the S1-S1 position (first position), and the forward face angle φLd (first angle) at the D1-D1 position (second position) is less than the forward face angle φLs (first angle) at the S1-S1 position (first position).

[0107] According to this structure, by setting the tip angle φS (the 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 discharge side in the axial direction than on the suction side, the thickness of the tooth tip of the female rotor 3 becomes thicker on the discharge side. Accordingly, it is possible to prevent the high-pressure working gas from leaking through the outer diameter gap between the working chambers located on the discharge side in the axial direction. At the same time, by setting the leading face angle φL (the first angle) corresponding to the shape of the leading face in the tooth profile 70 of the female rotor 3 to be smaller on the discharge side in the axial direction than on the suction side, tooth surface separation is prevented. Thus, it is possible to achieve both prevention of leakage of the working gas between the working chambers C through the gap provided between the female rotor 3 and the main body housing (housing) 4 and prevention of tooth surface separation vibration.

[0108] In addition, in the tooth profile 70 of the female rotor 3 in the present embodiment, the trailing face angle φTd (the second angle) at the D1-D1 position (the second position) is set to be the same as the trailing face angle φTs (the second angle) at the S1-S1 position (the first position).

[0109] According to this structure, the trailing face (the 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. Accordingly, the machining of the tooth profile becomes easy.

[0110] In addition, in the female rotor 3 in the present embodiment, in the entire axial direction, the tooth profile 70 changes in the region biased toward the discharge side in the axial direction, while the tooth profile 70 has the same shape in the remaining suction side region in the axial direction.

[0111] According to this structure, it changes in such a way as to thicken the tooth tip of the female rotor 3 only in the region on the discharge side where the pressure difference between the working chambers is relatively large, thereby preventing leakage of the compressed gas between the working chambers. On the other hand, in the region on the suction side in the axial direction where the pressure difference between the working chambers is relatively small, the thickness of the tooth tip of the female rotor 3 is not changed. Thus, compared with the case where the thickness of the tooth tip is thickened, a reduction in the volume of the working chamber is avoided. Thus, it is possible to ensure the suction capacity without increasing the size of the compressor main body 1. In addition, in the case of an oil-fed screw compressor, when the thickness of the tooth tip of the female rotor 3 thickens from the suction side end in the axial direction to the discharge side, accordingly, in the working chamber located on the discharge side, the internal pressure rises due to the volume reduction, so the oil supply pressure difference (the difference between the pressure of the pressure source and the pressure in the working chamber) decreases. In contrast, if only the tooth profile 70 of the female rotor 3 is changed in the region biased toward the discharge side in the axial direction, in the working chamber on the discharge side near the start position where the tooth profile 70 of the female rotor 3 changes, an increase in the internal pressure due to the change in the tooth profile 70 can be prevented, and thus the pressure difference for oil supply can be ensured.

[0112] [Second Embodiment]

[0113] Next, the screw compressor of the second embodiment will be used as an example. Figure 9 For example. Figure 9 This is a cross-sectional view showing the tooth profile of one tooth of the female rotor when observing the screw compressor of the second embodiment of the present invention in the viewing direction that is the same as the S1-S1 view and the D1-D1 view shown in Figure 2 . In addition, Figure 9 in Figures 1 to 8 , the parts with the same reference numerals as those shown in

[0114] Figure 9 are the same parts, so their detailed descriptions are omitted. Figure 4 The differences between the screw compressor of the second embodiment shown in and the screw compressor of the first embodiment (refer to Figure 4 ) are as follows. The shape of the first tooth profile 70s on the axial suction side (S1-S1 position) of the female rotor 3 in the first embodiment is a shape in which the angle ratio of the leading face angle φL is relatively large and the angle ratio of the trailing face angle φT is the same with respect to the second tooth profile 70d on the axial discharge side (D1-D1 position). On the other hand, the shape of the first tooth profile 70As on the axial suction side (S1-S1 position) of the female rotor 3A in the second embodiment is a shape in which the angle ratio of the leading face angle φLA is relatively large and the angle ratio of the trailing face angle φTA is relatively small with respect to the second tooth profile 70Ad on the axial discharge side (D1-D1 position).

[0115] Figure 9 In , the first tooth profile 70As on the axial suction side of the female rotor 3A is represented by a dashed line, and the second tooth profile 70Ad on the axial discharge side is represented by a solid line. By adding the suffix s indicating the suction side and the suffix d indicating the discharge side to the first contour line 71A of the specified leading face, the second contour line 72A of the specified trailing face, and the third contour line 73A of the specified tooth top in the tooth profile 70A of the female rotor 3A, the first tooth profile 70As on the suction side and the second tooth profile 70Ad on the discharge side are distinguished. Similarly, by adding the suffix s indicating the suction side and the suffix d indicating the discharge side to the two end points 76A and 77A of the third contour line 73A of the female tooth profile 70A, the first tooth profile 70As on the suction side and the second tooth profile 70Ad on the discharge side are distinguished. In addition, by adding the suffix s indicating the suction side and the suffix d indicating the discharge side to the tooth top angle φSA, the leading face angle φLA, and the trailing face angle φTA in the female tooth profile 70A, the first tooth profile 70As on the suction side and the second tooth profile 70Ad on the discharge side are distinguished.

[0116] In the tooth profile 70A of the female rotor 3A of the present embodiment, specifically, as shown in Figure 9As shown, the tip angle φSAd of the second tooth profile 70Ad set to the axial discharge side is larger than the tip angle φSAs of the first tooth profile 70As on the axial suction side, and the leading face angle φLAd of the second tooth profile 70Ad on the discharge side is set to be smaller than the leading face angle φLAs of the first tooth profile 70As on the suction side. In addition, for the trailing face angle φTAd of the second tooth profile 70Ad on the discharge side, it is set to be larger than the trailing face angle φTAs of the first tooth profile 70As on the suction side. That is, in the rotor tooth portion 31A of the female rotor 3A of the present embodiment, when using the tooth profile structure shown in Figure 6 and Figure 7 in the case of the tooth profile structure shown, use the tooth profile shown as No. 9 in Figure 7 as the second tooth profile 70Ad on the discharge side and use the tooth profile shown as No. 3 in Figure 6 as the first tooth profile 70As on the suction side.

[0117] That is, in the present embodiment, similarly to the first embodiment, it is configured such that the tooth top portion defined by the third contour line 73Ad in the second tooth profile 70Ad on the discharge side of the female rotor 3A is thicker than the tooth top portion defined by the third contour line 73As in the first tooth profile 70As on the suction side. In this way, the tooth top portion of the tooth profile 70A of the female rotor 3A is thicker on the axial discharge side, and accordingly, it is possible to prevent the compressed gas from leaking through the outer diameter gap between the working chambers located on the axial discharge side.

[0118] Furthermore, in the present embodiment, the leading face angle φLAd on the discharge side of the female rotor 3A is set to be smaller than the leading face angle φLAs on the suction side, while the trailing face angle φTAd on the discharge side of the female rotor 3A is set to be larger than the trailing face angle φTAs on the suction side. In the case of this structure, for the following reasons, compared with the tooth profile 70 of the female rotor 3 in the first embodiment, tooth surface separation can be suppressed.

[0119] Next, the effects of the screw compressor of the second embodiment are described using Figure 10 as follows. Figure 10 is a characteristic diagram showing the change in the tooth surface separation margin torque corresponding to the rotation angle of the male rotor in the screw compressor of the second embodiment of the present invention. Figure 10 In this figure, the horizontal axis is the rotation angle of the meshing of one tooth of the male rotor, and the maximum value is relatively represented as 1 P.U. The vertical axis is the tooth surface separation margin torque obtained by numerical calculation based on the set tooth profile, and the maximum value of this torque when it is the tooth profile of the female rotor in the first embodiment is relatively represented as 1 P.U. The tooth surface separation margin torque is the tooth surface transmission torque received by the female rotor from the male rotor, and represents the margin torque when resisting the tooth surface separation torque without tooth surface separation. That is, the larger the value of the tooth surface separation margin torque, the less likely tooth surface separation occurs.

[0120] In the case of the tooth profile 70A of the female rotor 3A in the second embodiment, as Figure 10 shown, compared with the case of the tooth profile 70 of the female rotor 3 in the first embodiment, the tooth surface separation margin torque increases. Thus, the tooth profile 70A of the female rotor 3A in the present embodiment can prevent tooth surface separation from occurring compared with the case of the tooth profile 70 of the female rotor 3 in the first embodiment.

[0121] In addition, the trailing face angle φTAd on the discharge side of the female rotor 3A is different from that in the first embodiment and is set to be larger than the trailing face angle φTAs on the suction side. In the case of this structure, as described above, compared with the case of the tooth profile 70 of the female rotor 3 in the first embodiment, there is a tendency for the vertex of the air hole H (refer to Figure 8 ) i.e., the starting contact point Sa to move downward. Thus, there is a tendency for the area of the air hole H to decrease, and therefore leakage of the compressed gas through the air hole H can be prevented.

[0122] In addition, in the second embodiment as well as in the first embodiment, in the tooth profile 70A of the female rotor 3A, with respect to the leading face angle φLA, the trailing face angle φTA, and the tip angle φSA, the following formulas (5) and (6) need to be satisfied.

[0123] φSAd - φSAs > 0 … Formula (5)

[0124] φLAs - φLAd > φTAd - φTAs … Formula (6)

[0125] According to the above second embodiment, as in the first embodiment, by setting the tip angle φSA (the third angle) corresponding to the shape of the tip portion in the tooth profile 70A of the female rotor 3A to be larger on the discharge side in the axial direction than on the suction side, the thickness of the tip portion of the female rotor 3A becomes thicker on the discharge side. Accordingly, leakage of the 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 prevented. At the same time, by setting the leading face angle φLA (the first angle) corresponding to the shape of the leading face in the tooth profile 70A of the female rotor 3A to be smaller on the discharge side in the axial direction than on the suction side, tooth surface separation can be prevented. Thus, it is possible to achieve both prevention of leakage of the working gas between the working chambers C through the gap provided between the female rotor 3A and the main body housing (housing) 4 and prevention of tooth surface separation vibration.

[0126] In addition, in the tooth profile 70A of the female rotor 3A in the present embodiment, it is set that the trailing face angle φTd (the second angle) at the D1 - D1 position (the second position) is larger than the trailing face angle φTs (the second angle) at the S1 - S1 position (the first position).

[0127] According to this structure, there is an air hole H (refer to Figure 8) tends to have a reduced area, so it can prevent the compressed gas from leaking through the air holes H. Furthermore, the tooth surface separation margin torque is increased compared to the first embodiment, so it can further prevent tooth surface separation from occurring.

[0128] [Third Embodiment]

[0129] Next, the structure of the screw compressor according to the third embodiment will be described using Figure 11 and Figure 12 as an example. Figure 11 is a cross-sectional view of the screw compressor according to the third embodiment of the present invention, Figure 12 is a cross-sectional view showing the tooth profile of one tooth of the female rotor when observing the screw compressor according to the third embodiment of the present invention shown in Figure 11 in a superimposed state in the S3-S3 direction view and the D3-D3 direction view. Additionally, Figure 11 and Figure 12 In, parts with the same reference numerals as those shown in Figures 1 to 10 are the same parts, so detailed descriptions thereof are omitted.

[0130] Figure 11 The screw compressor according to the third embodiment shown in is different from the first embodiment (refer to Figure 2 and Figure 4 ) as follows. In the compressor body 1 of the first embodiment, the male and female rotors 2 and 3 are composed of screw rotors with a constant lead, and the outer diameters of the rotor tooth portions 21 and 31 of the two rotors 2 and 3 are the same from the suction side end faces 21b and 31b to the discharge side end faces 21c and 31c. On the other hand, in the compressor body 1B of the third embodiment, the male and female rotors 2B and 3B are composed of screw rotors with a variable lead whose lead decreases from the suction side in the axial direction to the discharge side, and it is set that the outer diameter of the rotor tooth portion 21B of the male rotor 2B gradually decreases from a certain first position in the axial direction to the discharge side end face 21c. That is, the male rotor 2B is composed of a conical and variable-lead screw rotor that tapers from the first position in the axial direction to the front end of the discharge side end face 21c. The female rotor 3B is composed of a variable-lead screw rotor with the same outer diameter from the suction side end face 31b to the discharge side end face 31c in the axial direction.

[0131] Specifically, Figure 11 In, among the rotor tooth portions 21B and 31B of the male rotor 2B and the female rotor 3B, the lead is formed to change in the part that is biased toward the discharge side in the axial direction (from the S3-S3 position to the D3-D3) in the overall axial direction, while the lead is the same in the remaining suction side part in the axial direction (from the suction side end faces 21b and 31b to the S3-S3 position). Additionally, the leads of the male rotor 2B and the female rotor 3B can also be configured to change in the entire axial region.

[0132] The tooth profile 70B of the cross-section perpendicular to the axial direction (rotation center A2) in the female rotor 3B (refer to Figure 12 ) is of the same shape along the axial direction in the region from the suction-side end face 31b of the rotor tooth portion 31B to the first position close to the discharge side in the axial direction, for example, the substantially middle position (S3-S3 position) in the axial direction. On the other hand, in the region from the first position in the axial direction to the discharge-side end face 31c (D3-D3 position) of the female rotor 3B, the first tooth profile 70Bs on the suction side ( Figure 12 represented by the dashed line) of Figure 11 the tooth profile at the S3-S3 position shown) gradually changes to the second tooth profile 70Bd on the discharge side ( Figure 11 represented by the solid line) shown at the D3-D3 position) to form the female tooth profile 70B. That is, the tip angle φSB, the leading face angle φLB, and the trailing face angle φTB in the female tooth profile 70B are set in such a way that they monotonically change with respect to the length or rotation angle in the axial direction from the first position (S3-S3 position) to the discharge-side end face 31c (D3-D3 position).

[0133] The second tooth profile 70Bd on the axial discharge side (D3-D3 position) of the female rotor 3B in the present embodiment is a shape in which the angle ratio of the tip angle φSB is relatively large and the angle ratio of the leading face angle φLB is relatively small with respect 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 a shape in which the angle ratio of the trailing face angle φTB is relatively small and the region including the tooth bottom 75B is relatively shallow with respect to the first tooth profile 70Bs. In addition, Figure 11 the rotor tooth portion 21B of the male rotor 2B shown generates a tooth profile in a manner meshing with the rotor tooth portion 31B of the female rotor 3B.

[0134] Figure 12 In Figure 4 , the first tooth profile 70Bs on the axial suction side in the rotor tooth portion 31B of the female rotor 3B is represented by a dashed line, and the second tooth profile 70Bd on the axial discharge side is represented by a solid line. In addition, similar to Figure 4 , the rotation angle of the female rotor 3B is the reference angle (0°).

[0135] By adding the drawing reference s indicating the suction side and the drawing reference d indicating the discharge side to the first contour line 71B of the specified leading face, the second contour line 72B of the specified trailing face, and the third contour line 73B of the specified tooth top in the tooth profile 70B of the female rotor 3B, the first tooth profile 70Bs on the suction side and the second tooth profile 70Bd on the discharge side are distinguished.

[0136] Similarly, by adding the reference numeral s indicating the suction side and the reference numeral d indicating the discharge side to the boundary points, i.e., the tooth bottom 75B, of the first contour line 71B and the second contour line 72B of the female tooth profile 70B, the first tooth profile 70Bs on the suction side and the second tooth profile 70Bd on the discharge side are distinguished. Further, by adding the reference numeral s indicating the suction side and the reference numeral d indicating the discharge side to the two end points 76B, 77B of the third contour line 73B of the female tooth profile 70B, the first tooth profile 70Bs on the suction side and the second tooth profile 70Bd on the discharge side are distinguished.

[0137] Further, by adding the reference numeral s indicating the suction side and the reference numeral d indicating the discharge side to the tip angle φSB, the leading face angle φLB, and the trailing face angle φTB in the female tooth profile 70B, the first tooth profile 70Bs on the suction side and the second tooth profile 70Bd on the discharge side are distinguished.

[0138] In the tooth profile 70B of the female rotor 3B of the present embodiment, as Figure 12 shown, the tip angle φSBd of the second tooth profile 70Bd on the axial discharge side is set to be larger than the tip angle φSBs of the first tooth profile 70Bs on the axial suction side, similarly to the first embodiment. That is, similarly to the first embodiment, the tooth tip portion defined by the third contour line 73Bd in the second tooth profile 70Bd on the discharge side of the female rotor 3B is formed to be thicker than the tooth tip portion defined by the third contour line 73Bs in the first tooth profile 70Bs on the suction side.

[0139] Further, for the leading face angle φLBd of the second tooth profile 70Bd on the discharge side, it is set to be smaller than the leading face angle φLBs of the first tooth profile 70Bs on the suction side, similarly to the first embodiment. Further, for the trailing face angle φTBd of the second tooth profile 70Bd on the discharge side, it is set to be smaller than the trailing face angle φTBs of the first tooth profile 70Bs on the suction side, which is different from the first embodiment.

[0140] 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 bottoms 75s of the first tooth profile 70s on the suction side of the male rotor 3 and the tooth bottoms 75d of the second tooth profile 70d on the discharge side are located at the same radial position.

[0141] In this structure, corresponding to the tooth profile 70B of the male rotor 2B and the female rotor 3B, the outer diameter of the tooth tip (the portion in contact 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 axial suction side to the discharge side end face 21c (D3 - D3 position) on the discharge side. That is, the male rotor 2B is formed in a tapered shape that tapers from the first position on the axial suction side to the front end on the discharge side.

[0142] In the case of this structure, Figure 11 in the main body housing 4B shown, the first inner peripheral surface 46B of the hole 45B also needs to be formed in a conical shape corresponding to the conical shape of the male rotor 2B. Thus, in terms of the assembly relationship, the main body housing 4B has a main housing 41B and a suction side housing 42B mounted on the suction side ( Figure 11 the left side in the figure) of the main housing 41B. The main housing 41B is open at the suction side in the axial direction and has an internal space capable of accommodating the male rotor 2B and the female rotor 3B in a meshed state. The suction side housing 42B closes the opening of the main housing 41B and forms, together with the main housing 41B, the hole 45B as a storage chamber.

[0143] On the discharge side end of the main housing 41B, a discharge side bearing 6 on the male rotor 2B side and a discharge side bearing 8 on the female rotor 3B side are provided. On the main body housing 4B, a main body cover 43B is mounted so as to cover the discharge side bearing 6 and the discharge side bearing 8. In the suction side housing 42B, suction side bearings 5a, 5b on the male rotor 2B side and suction side bearings 7a, 7b on the female rotor 3B side are provided. The suction side bearing 5b on the male rotor 2B side and the suction side bearing 7b on the female rotor 3B side are constituted by angular contact ball bearings capable of positioning, for example.

[0144] In the case of this structure, the angular contact ball bearings 5b, 7b arranged in the suction side housing 42B can be used to adjust the clearance (sometimes referred to as the end face clearance) provided between the suction side inner wall surface 48 of the suction side housing 42B and the suction side end faces 21b, 31b of the male and female rotors 2B, 3B. In this structure, the end face clearance can be adjusted while confirming the positional relationship between the suction side housing 42B and the male and female rotors 2B, 3B before accommodating the male and female rotors 2B, 3B in the hole 45B of the main body housing 4B, so this clearance adjustment is easy.

[0145] Next, the effects of the screw compressor of the third embodiment will be described while comparing with a variable lead screw compressor of a comparative example using Figures 11 to 13 for explanation. Figure 13 is a cross-sectional view showing a variable lead screw compressor of a comparative example relative to the screw compressor of the third embodiment of the present invention. In addition, Figure 13 in, for the parts with the same reference numerals as those shown in Figures 1 to 12 are the same parts, so the detailed description thereof is omitted.

[0146] Figure 13 The compressor main body 100 of the comparative example shown includes the rotor tooth portions 210, 310 of the male and female rotors 200, 300 from the axial suction side end faces 21b, 31b ( Figure 12toward the discharge side end faces 21c and 31c (left end in the middle) Figure 12

[0147] A screw rotor with a variable lead whose lead decreases from the suction side in the axial direction to the discharge side (right end in the middle) in the compressor body 1B of the present embodiment. In this case, the spiral lines of the male teeth 210a and female teeth 310a of the rotor tooth parts 210 and 310 become closer as they go from the suction side in the axial direction to the discharge side. Therefore, generally, the tooth thickness t of the tooth tip of the female teeth 310a of the female rotor 300 (the thickness of the cross-section of the female rotor 300 orthogonal to the extending direction of the tooth tip line) tends to be thinner than that of a screw rotor with a constant lead. When the tooth thickness t of the tooth tip of the female teeth 310a of the female rotor 300 becomes thinner, correspondingly, at the position on the axial discharge side where the pressure difference between the working chambers C increases, the leakage of the compressed gas between the working chambers C through the outer diameter gap increases. Figure 12 The compressor body 1B of the present embodiment is composed of a screw rotor with a variable lead whose lead decreases from the suction side in the axial direction to the discharge side in a region biased toward the discharge side in the axial direction by the rotor tooth parts 21B and 31B of the male and female rotors 2B and 3B. Thus, in the present embodiment, as shown, it is set that the tooth tip angle φSBd of the second tooth profile 70Bd on the axial discharge side of the female rotor 3B is larger than the tooth tip angle φSBs of the first tooth profile 70Bs on the axial suction side. Thus, similarly to the first embodiment, the tooth tip part on the discharge side defined by the tooth tip angle φSBd in the second tooth profile 70Bd of the female rotor 3B is thicker than the tooth tip part on the suction side defined by the tooth tip angle φSBs of the first tooth profile 70Bs. Accordingly, even if the male and female rotors 2B and 3B are composed of screw rotors with a variable lead, it is possible to prevent the compressed gas from leaking through the outer diameter gap against the increase in the pressure difference between the working chambers C located on the axial discharge side.

[0148] Figure 1 Furthermore, in the present embodiment, it is configured such that the tooth bottom 75Bd of the second tooth profile 70Bd on the discharge side in the female rotor 3B is shallower than the tooth bottom 75Bs of the first tooth profile 70Bs on the suction side. In such a changing range of the tooth bottom 75B of the tooth profile 70B, compared with the case of the first embodiment (the case 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), the reduction rate of the volume of the working chamber C corresponding to the rotation angle of the female rotor 3B increases. Accordingly, in this female tooth profile 70B, it is possible to increase the design volume ratio of the compressor body 1B, and it is possible to improve the efficiency by operating at a high pressure ratio. In addition, when operating at a normal pressure ratio, the tooth bottom 75Bd on the discharge side of the female rotor 3B is shallower than the tooth bottom 75Bs on the suction side. Correspondingly, compared with the case of the first embodiment, the working gas in each working chamber C reaches the discharge pressure earlier. Thus, it is possible to advance the start time of 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 (refer to )), and therefore it is possible to reduce the pressure loss when the compressed gas passes through the discharge port 52a.

[0149] In addition, in the third embodiment, similar to the first embodiment, in the tooth profile 70B of the female rotor 3B, with respect to the leading face angle φLB, the trailing face angle φTB, and the tip angle φSB, the following formulas (7) and (8) need to be satisfied.

[0150] φSBd - φSBs > 0 … Formula (7)

[0151] φLBs - φLBd > φTBd - φTBs … Formula (8)

[0152] Thus, in the present embodiment, even for the variable lead screw rotors where the lead of the male and female rotors 2B and 3B decreases from the axial suction side to the discharge side, since the tip angle φSB (the third angle) corresponding to the shape of the tip portion in the tooth profile 70B of the female rotor 3B is set to be larger on the axial discharge side than on the suction side, there is a tendency for the thickness of the tip portion of the female rotor 3B to be thicker on the discharge side. Accordingly, it is possible to prevent the high-pressure working gas from leaking through the outer diameter gap between the working chambers C located on the axial discharge side. At the same time, by setting the leading face angle φLB (the first angle) corresponding to the shape of the leading face in the female tooth profile 70B to be smaller on the axial discharge side than on the suction side, tooth surface separation is prevented. Thus, it is possible to achieve both preventing the working gas between the working chambers C from leaking through the gap provided between the female rotor 3B and the main body housing (housing) 4B and preventing tooth surface separation vibration.

[0153] In addition, in the female rotor 3B of the present embodiment, the lead changes in the axially biased discharge side portion in the overall axial direction, while the lead is the same in the remaining suction side portion in the axial direction.

[0154] According to this structure, the leads of the axially suction side portions of the male rotor 2B and the female rotor 3B are maintained relatively large, so the moving distance per revolution of the working chambers located on the suction side is relatively large. Thus, the suction volume of the compressor main body 1B can be ensured.

[0155] Furthermore, in the tooth profile 70B of the female rotor 3B of the present embodiment, the tooth bottom 75Bd at the second position (D3 - D3 position) is set shallower than the tooth bottom 75Bs at the first position (S3 - S3 position). Furthermore, correspondingly to the tooth profile 70B of the male rotor 2B and the female rotor 3B, the outer diameter at the second position (D3 - D3 position) is configured to be smaller than the outer diameter at the first position (S3 - S3 position).

[0156] According to this structure, the bottom of the tooth 75Bd on the discharge side of the female rotor 3B is shallower than the bottom of the tooth 75Bs on the suction side. Correspondingly, the reduction rate of the volume of the working chamber C corresponding to the rotation angle of the female rotor 3B increases. Therefore, compared with the case of the first embodiment where the radial position of the bottom of the tooth 75 is axially unchanged, the design volume ratio of the compressor main body 1B can be increased.

[0157] Furthermore, in the female rotor 3B of the present embodiment, in the entire axial direction, the radial position of the bottom of the tooth 75B of the tooth profile 70B changes in the region biased towards the discharge side in the axial direction, while the radial position of the bottom of the tooth 75B of the tooth profile 70B is the same in the remaining suction side region in the axial direction.

[0158] According to this structure, in the region on the axial discharge side, the reduction rate of the volume of the working chamber C of the female rotor 3B increases towards the discharge side, whereby the working gas in the working chamber C can reach the discharge pressure earlier. Furthermore, in the axial suction side region where the radial position of the bottom of the tooth 75B of the female rotor 3B is unchanged, a reduction in the volume of the working chamber C is avoided, whereby a reduction in the suction volume can be avoided.

[0159] Furthermore, the compressor main body 1B in the present embodiment includes suction side bearings 7a, 7b (female side bearings) on the side of the female rotor 3B that rotatably support the axial suction side of the female rotor 3B, and suction side bearings 5a, 5b (male side bearings) on the side of the male rotor 2B that rotatably support the axial suction side of the male rotor 2B. Furthermore, the main body housing (housing) 4B includes a main housing 41B that is open on the axial suction side and has an internal space capable of accommodating the male rotor 2B and the female rotor 3B in a meshed state; and a suction side housing 42B that is installed on the main housing 41B so as to close the opening of the main housing 41B and forms a storage chamber 45 together with the main housing 41B. The suction side bearings 7a, 7b (female side bearings) on the side of the female rotor 3B and the suction side bearings 5a, 5b (male side bearings) on the side of the male rotor 2B are arranged in the suction side housing 42B.

[0160] According to this structure, the tapered male rotor 2B that tapers towards the discharge side front end can be accommodated in the main body housing (housing) 4B, and the end face clearance between the suction side end faces 21b, 31b of the male rotor 2B and the female rotor 3B and the suction side inner wall surface 48 of the main body housing (housing) 4B is adjusted by the suction side bearings 7a, 7b (female side bearings) on the side of the female rotor 3B and the suction side bearings 5a, 5b (male side bearings) on the side of the male rotor 2B. Thus, the end face clearance can be adjusted by positioning the male rotor 2B and the female rotor 3B relative to the suction side housing 42B before accommodating the two rotors 2B, 3B of the male and female, and therefore the clearance adjustment becomes easy.

[0161] [Other Embodiments]

[0162] In addition, the present invention is not limited to the above-described embodiments, and includes various modified examples. The above-described embodiments have been described in detail for easy understanding of the present invention, and are not limited to having all the structures described. That is, a part of the structure of a certain embodiment can be replaced with the structure of another embodiment, and the structure of another embodiment can also be added to the structure of a certain embodiment. In addition, for a part of the structure of each embodiment, other structures can be added, deleted, or replaced.

[0163] For example, in the above-described first to third embodiments, the start position in the axial direction of the change in the tooth profiles 70, 70A, 70B of the rotor tooth portions 31, 31A, 31B of the female rotors 3, 3A, 3B, which is the cross-sectional tooth profile perpendicular to the axial direction, i.e., the first position in the axial direction, is the S1-S1 position or the S3-S3 position, which is the substantially middle position in the axial direction, and the end position of the change in the tooth profiles 70, 70A, 70B, i.e., the second position, is the D1-D1 position or the D3-D3 position of the discharge-side end face 31c, is shown as an example of the structure. However, the start position in the axial direction, i.e., the first position, and the end position in the axial direction, i.e., the second position, of the change in the tooth profile of the female rotor can be changed to any position according to the operating pressure conditions and the like. For example, when the discharge pressure is high, in order to make the tooth thickness of the tooth tip of the female rotor thicker, the first position can be moved toward the suction side. On the other hand, when the discharge pressure is low, the first position can be moved toward the discharge side.

[0164] In addition, the start position (first position) of the change in the tooth profiles 70, 70A, 70B of the female rotors 3, 3A, 3B can also be set on the suction-side end face 31b of the rotor tooth portions 31, 31A, 31B. That is, the female rotor can be configured such that the tooth profile changes in the entire axial region. In this case, compared with the case where the tooth profile of the female rotor changes from an intermediate position, the machining of the tooth profile is easier.

[0165] In addition, in the third embodiment, an example of the structure in which the tooth bottom 75Bd on the discharge side of the tooth profile 70B of the female rotor 3B is shallower than the tooth bottom 75Bs on the suction side is shown. However, similarly to the cases of the first and second embodiments, a structure in which the tooth bottom on the discharge side of the female rotor is in the same radial position as the tooth bottom on the suction side and the tooth bottom of the female rotor does not change in the axial direction can also be adopted. Conversely, in the first and second embodiments, when the male and female rotors are configured as constant-lead screw rotors, a structure in which the tooth bottom on the discharge side of the tooth profile of the female rotor is shallower than the tooth bottom on the suction side can also be adopted. In this case, it is configured such that the outer diameter on the discharge side of the male rotor is smaller than the outer diameter on the suction side corresponding to the tooth profile of the female rotor.

[0166] Description of Reference Numerals

[0167] 1, 1B... Compressor body, 2, 2B... Male rotor, 3, 3A, 3B... Female rotor, 4, 4B... Main housing (housing), 5a, 5b... Suction side bearing (male side bearing), 7a, 7b... Suction side bearing (male side bearing), 21a... Male tooth, 31a... Female tooth, 41B... Main housing, 42B... Suction side housing, 45... Hole (accommodation 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), 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)... Advance face angle (first angle) (suction side, discharge side), φT(s, d), φTA(s, d), φTB(s, d)... Retard face 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 screw compressor, characterized in that, comprising: a male rotor having twisted male teeth, which is capable of rotating about a first rotation center; a female rotor having twisted female teeth, which is capable of meshing with the male rotor and rotating about a second rotation center parallel to the first rotation center; and a housing having a receiving chamber for receiving the male rotor and the female rotor in a rotatable state while being engaged, and forming a plurality of working chambers together with the male rotor and the female rotor, a tooth profile of the female rotor representing a contour shape of a cross section perpendicular to the axial direction is formed such that there is a change between an arbitrary first position in the axial direction and a second position on the discharge side in the axial direction compared with the first position, one tooth in the tooth profile of the female rotor includes: a first contour line, which is bounded by a tooth bottom with the smallest radius, and defines an interval of a forward face extending from the boundary point on the rotation direction side of the female rotor and reaching a first end point with the largest radius; a second contour line, which defines an interval of a rearward face extending from the boundary point on the side opposite to the rotation direction of the female rotor and reaching a second end point with the largest radius; and a third contour line, which defines an interval of a tooth top with two end points having the largest radius, and any one of the two end points is a connection point with the first end point of the first contour line or the second end point of the second contour line, defining an angle formed by two line segments connecting the second rotation center and both ends of the first contour line with the second rotation center as the vertex as a first angle, defining 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 the vertex as a second angle, defining 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 the vertex as a third angle, the tooth profile of the female rotor is set such that the third angle at the second position is greater than the third angle at the first position, and the first angle at the second position is less than the first angle at the first position, the tooth profile of the female rotor is set such that the second angle at the second position is greater than or equal to the second angle at the first position.

2. The screw compressor according to claim 1, characterized in that: in the female rotor, in the entire axial direction, the tooth profile changes in a region biased toward the discharge side of the axial direction, while the tooth profile is of the same shape in the remaining suction side region of the axial direction.

3. The screw compressor according to claim 1, characterized in that: in the female rotor, the tooth profile changes in the entire axial region.

4. The screw compressor according to claim 1, characterized in that: the male rotor and the female rotor are configured such that the lead is smaller on the discharge side in the axial direction than on the suction side, where the lead represents the distance advanced in the axial direction per revolution due to the twist of the male teeth and the female teeth.

5. The screw compressor according to claim 4, characterized in that: In the male rotor and the female rotor, the lead varies in a portion biased toward the discharge side in the axial direction throughout the entire axial direction, while the lead is the same in the remaining suction side portion in the axial direction.

6. The screw compressor according to claim 1 or 4, wherein: the tooth bottom of the female rotor at the second position is shallower than the tooth bottom at the first position; the outer diameters of the male rotor and the female rotor at the second position are configured to be smaller than the outer diameters at the first position accordingly.

7. The screw compressor according to claim 6, wherein: in the female rotor, the radial position of the tooth bottom of the tooth profile varies in a region biased toward the discharge side in the axial direction throughout the entire axial direction, while the radial position of the tooth bottom of the tooth profile is the same in the remaining suction side region in the axial direction.

8. The screw compressor according to claim 6, characterized in that it includes: a female side bearing rotatably supporting the axial suction side of the female rotor; and a male side bearing rotatably supporting the axial suction side of the male rotor, the housing includes: a main housing that is open at the axial suction side and has an internal space capable of accommodating the male rotor and the female rotor in a meshed state; and a suction side housing that is mounted on the main housing so as to close the opening of the main housing and forms the accommodation chamber together with the main housing, the female side bearing and the male side bearing are disposed in the suction side housing.

9. A screw rotor that meshes with a male rotor having twisted male teeth and capable of rotating about a first rotation center, and is capable of rotating about a second rotation center parallel to the first rotation center, wherein: the tooth profile representing the contour shape of a cross section perpendicular to the axial direction of the screw rotor is formed to vary between an arbitrary first position in the axial direction and a second position located on the discharge side in the axial direction compared to the first position; one tooth in the tooth profile of the screw rotor includes: a first contour line that takes the tooth bottom with the smallest radius as a boundary point and defines an interval of the forward face extending from the boundary point to a first end point with the largest radius on the rotation direction side of the screw rotor; a second contour line that defines an interval of the backward face extending from the boundary point to a second end point with the largest radius on the side opposite to the rotation direction of the screw rotor; and a third contour line that defines an interval of the tooth top with two end points having the largest radius, and any one of the two end points is a connection point with the first end point of the first contour line or the second end point of the second contour line, defining the angle formed by two line segments connecting the second rotation center with both ends of the first contour line with the second rotation center as the vertex as a first angle, defining the angle formed by two line segments connecting the second rotation center with both ends of the second contour line with the second rotation center as the vertex as a second angle, Define the third angle as the angle formed by two line segments with the second rotation center as the vertex and connecting the second rotation center to both ends of the third contour line. The tooth profile of the screw rotor is set such that the third angle at the second position is greater than the third angle at the first position, and the first angle at the second position is less than the first angle at the first position. The tooth profile of the screw rotor is set such that the second angle at the second position is greater than or equal to the second angle at the first position.

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