Patent Application
20230392598
The present invention relates to a screw compressor including a pair of screw rotors having helical lobes that mesh with each other, and the screw rotor included in the screw compressor.
Screw compressors have been used widely as air compressors or freezing air conditioning compressors, and there has been a strong demand for energy conservation of screw compressors in recent years. Accordingly, it has been becoming increasingly more important to achieve high energy efficiency with screw compressors.
A screw compressor includes a pair of female and male screw rotors that rotate meshing with each other, and a casing that houses both the screw rotors. Both the screw rotors have helical lobes (grooves). This compressor sucks in and compresses a gas by using an increase and decrease in the volumes of a plurality of working chambers formed by the grooves of both the screw rotors and the inner wall surface of the casing surrounding both the screw rotors, which increase and decrease accompany rotation of both the screw rotors.
In the screw compressor, a micro-clearance is provided between the rotating screw rotors and the casing such that they do not contact each other. For example, a clearance (hereinafter, called as an outer diameter clearance, in some cases) is provided between lobe tips of each screw rotor and the inner circumferential surface in the casing. Accordingly, via the outer diameter clearance, a compressed gas leaks from a working chamber having a relatively high pressure to a working chamber having a relatively low pressure, undesirably. When the compressed gas leaks, by a corresponding degree, spent compression power is wasted, re-compression power is required, and therefore the compressor efficiency deteriorates.
In a liquid-flooded-type screw compressor, supplying a liquid such as oil or water to working chambers results in an effect of sealing an outer diameter clearance. Thereby, leakage of a compressed gas via the outer diameter clearance between the working chambers is inhibited, but further inhibition of leakage of the compressed gas is required for enhancing the compressor efficiency. In addition, in a liquid-free-type screw compressor, a liquid is not supplied to working chambers, thus an effect of sealing an outer diameter clearance by a liquid cannot be expected. Accordingly, there is a particular concern that the compressor efficiency of the liquid-free-type screw compressor deteriorates due to leakage of a compressed gas via an outer diameter clearance between working chambers.
In addition, in recent years, there are a large number of products of single-stage screw compressors with the compression ratio which exceeds eight, where there is a tendency that the differential pressure between working chambers positioned on the delivery side in the axial direction of a screw rotor increases. If there is an increase in the differential pressure between working chambers, the concern over further deterioration of the compressor efficiency due to leakage of a compressed gas via an outer diameter clearance between the working chambers increases by a degree corresponding to the increase.
Accordingly, in order to realize enhancement of compressor efficiency, it is required to reduce leakage of a compressed gas via an outer diameter clearance between working chambers in a delivery-side area in the axial direction of a compressor. As a technology to reduce leakage of a compressed gas in a delivery-side area, a technology described in Patent Document 1 is known, for example. In a screw compressor described in Patent Document 1, in order to reduce the ratio of a leakage air volume to a suction air volume, and also to prevent scuffing due to contact between both screw rotors, a plurality of lobes provided to the female rotor are formed such that their lobe thicknesses are greater on the delivery-port side than on the suction-port side. Note that “lobe thicknesses” here mean the thicknesses of lobes in lobe profiles in cross-sections perpendicular to the axial direction of the screw rotors.
Patent Document 1: JP-2004-144035-A
If the lobe thicknesses of lobes of a female rotor are increased on the delivery-port side (at a delivery-side end portion in the axial direction of the female rotor) as in the screw compressor described in Patent Document 1, the width (distance) of the boundary between working chambers on the delivery-port side of the female rotor increases by a corresponding degree. Accordingly, leakage of a compressed gas via an outer diameter clearance between working chambers on the delivery-port side of the female rotor can be inhibited.
Meanwhile, in variable-lead screw rotors whose lead decreases from the suction side toward the delivery side in the axial direction, the lobe thicknesses of lobe tips of a female rotor tend to decrease as compared to invariable-lead screw rotors. It should be noted that “lobe thickness” here mean the thickness of a lobe tip in a lobe profile in cross-sections perpendicular to the extending direction of the lobe tip line of the female rotor. The lead represents the distances of advance in the axial direction per rotation of twists of the screw rotors.
In a case where the lead of a screw rotor decreases from the suction side toward the delivery side in the axial direction, the degree of twists of the screw rotor increases from the suction side toward the delivery side. Accordingly, under a condition that the lobe profiles of screw rotors in cross-sections perpendicular to the axial direction are the same, the lobe thicknesses of lobe tips of a female rotor tend to be smaller on the delivery side as compared to invariable-lead screw rotors.
Accordingly, there is a concern that, in variable-lead screw rotors whose lead decreases from the suction side toward the delivery side in the axial direction, leakage of a compressed gas via an outer diameter clearance between working chambers positioned on the delivery side increases by a degree corresponding to a reduction of the lobe thicknesses of lobe tips of a female rotor on the delivery side. In view of this, configuration in which the lobe thicknesses of lobe tips of a female rotor are increased on the delivery side as in the screw compressor described in Patent Document 1 can be conceived.
However, if the lobe thicknesses of lobe tips of a female rotor are made greater on the delivery side than on the suction side in the axial direction in a screw compressor including invariable-lead or variable-lead screw rotors as in the screw compressor described in Patent Document 1, a vibration phenomenon called as vibration of tooth flank separation occurs in the screw rotors in some cases. In a screw compressor including a male rotor and a female rotor that mesh with each other, typically, when flanks of both the rotors contact directly, or when timing gears provided coaxially with both the rotors mesh with each other, the drive torque of the male rotor is transmitted to the female rotor, and the female rotor is driven. Depending on a condition of a pressure that acts on the flanks of the rotors, a phenomenon called as tooth flank separation occurs in some cases. In the tooth flank separation, the transmission torque from the male rotor to the female rotor turns negative temporarily, and the flanks having been transmitting the torque are separated from each other. Thereafter, when the transmission torque transmitted from the male rotor to the female rotor turns positive again, the temporarily separated flanks collide with each other. As a result, tooth flank separation and tooth flank collision are repeated, and this generates significant vibration and noise. This is called as vibration of tooth flank separation.
As mentioned above, if the lobe thicknesses of lobe tips of a female rotor are increased on the delivery side in order to inhibit leakage of a working gas via an outer diameter clearance between working chambers positioned on the delivery side in the axial direction of screw rotors, the vibration phenomenon called as vibration of tooth flank separation occurs in the screw rotors in some cases. However, Patent Document 1 does not particularly mention a structure for inhibiting vibration of tooth flank separation.
The present invention has been made in order to solve the problems described above, and an object of the present invention is to provide a screw compressor and a screw rotor that make it possible to realize both inhibition of leakage of a working gas between working chambers via a clearance formed between a screw rotor and a casing, and inhibition of occurrence of vibration of tooth flank separation.
The present application includes a plurality of means for solving the problems described above. An example thereof is a screw compressor including: a male rotor that has twisted male lobes, and rotates about a first rotation center; a female rotor that has twisted female lobes, meshes with the male rotor, and rotates about a second rotation center parallel to the first rotation center; and a casing that has a housing chamber rotatably housing the male rotor and the female rotor in a meshing state, and forms a plurality of working chambers together with the male rotor and the female rotor. A lobe profile of the female rotor representing contour shapes of the female rotor in cross-sections perpendicular to an axial direction of the female rotor is formed such that the lobe profile changes between a certain first position in the axial direction and a second position on a delivery side in the axial direction relative to the first position. One lobe in the lobe profile of the female rotor includes: a first contour line defining a zone of a leading flank extending in a rotation direction of the female rotor from a lobe bottom, as a boundary point, at which the female rotor has a minimum radius to a first endpoint at which the female rotor has a maximum radius; a second contour line defining a zone of a trailing flank extending in a direction opposite to the rotation direction of the female rotor from the boundary point to a second endpoint at which the female rotor has the maximum radius; and a third contour line defining a zone of a lobe tip having both endpoints at which the female rotor has the maximum radius, either one of both the endpoints being a point of connection with the first endpoint of the first contour line or the second endpoint of the second contour line. In the lobe profile of the female rotor, when a first angle is defined as an angle formed by two line segments linking the second rotation center as a vertex and both ends of the first contour line, a second angle is defined as an angle formed by two line segments linking the second rotation center as a vertex and both ends of the second contour line, and a third angle is defined as an angle formed by two line segments linking the second rotation center as a vertex and both ends of the third contour line, the third angle at the second position is set greater than the third angle at the first position, and the first angle at the second position is set smaller than the first angle at the first position.
According to the present invention, setting the third angle, which corresponds to the shape of the lobe tip in the lobe profile of the female rotor, greater on the delivery side than on the suction side in the axial direction results in the thickness of the lobe tip of the female rotor being thicker on the delivery side, and therefore, by a corresponding degree, leakage of a high-pressure working gas via an outer diameter clearance between working chambers positioned on the delivery side in the axial direction can be inhibited. Simultaneously, setting the second angle, which corresponds to the shape of the leading flank in the lobe profile of the female rotor, smaller on the delivery side than on the suction side in the axial direction results in inhibition of occurrence of tooth flank separation. Accordingly, it is possible to realize both inhibition of leakage of a working gas between working chambers via a clearance provided between the female rotor and the casing, and inhibition of occurrence of vibration of tooth flank separation.
Problems, configuration, and advantages other than those described above are made clear by the following explanation of embodiments.
Screw compressors according to embodiments of the present invention are explained below by illustrating examples by using the figures.
The configuration of a screw compressor according to a first embodiment is explained by using
In
In
The male rotor 2 includes: a rotor lobe section 21 on which a plurality of helical male lobes (lobes) 21a are formed; and a suction-side shaft section 22 and a delivery-side shaft section 23 provided to end portions of the rotor lobe section 21 on both sides in the axial direction. The rotor lobe section 21 has a suction-side end surface 21b and a delivery-side end surface 21c that are perpendicular to the axial direction (the rotation center A1) on one end (the left end in
The female rotor 3 includes: a rotor lobe section 31 on which a plurality helical female lobes 31a (see
The body casing 4 includes a main casing 41, and a delivery-side casing 42 attached to the delivery side (the right side in
A bore 45 is formed inside the body casing 4 as a housing chamber that houses the rotor lobe section 21 of the male rotor 2 and the rotor lobe section 31 of the female rotor 3 in a mutually meshing state. The bore 45 is formed by covering, with the delivery-side casing 42, an opening on one side (the right side in
The suction-side bearing 5 for the male rotor 2 and the suction-side bearing 7 for the female rotor 3 are disposed in a suction-side end portion of the main casing 41. The delivery-side bearings 6a and 6b for the male rotor 2 and the delivery-side bearings 8a and 8b for the female rotor 3 are disposed in the delivery-side casing 42. A delivery-side cover 43 is attached to the delivery-side casing 42 so as to cover the delivery-side bearings 6a and 6b and the delivery-side bearings 8a and 8b.
As depicted in
In addition, the delivery-side casing 42 of the body casing 4 is provided with a delivery flow channel 52 for delivering a compressed gas from the working chambers C to the outside of the body casing 4. The delivery flow channel 52 establishes communication between the bore 45 (the working chambers C) and the outside of the body casing 4. The delivery flow channel 52 has a delivery port 52a formed at the delivery-side inner wall surface 49 of the body casing 4. The delivery port 52a can be formed so as to open in the axial direction and/or the radial direction of the male and female rotors 2 and 3.
The main casing 41 of the body casing 4 is provided with a liquid supply path 53 that supplies, to the working chambers C, a liquid supplied from the outside of the compressor body 1. For example, the liquid supply path 53 has an opening at the inner wall surface of the bore 45 and in an area where the working chambers C are at a compression process.
For example, as depicted in
Note that whereas an electric motor is used as the drive section 80 in the example depicted in the present embodiment, this does not particularly limit the rotation-drive source. In addition, in other possible configuration, the drive section 80 may rotation-drive not the male rotor 2, but the female rotor 3 or both the male and female rotors 2 and 3. In addition, in other possible configuration, the shaft sections of the drive section 80 and the compressor body 1 may not be coaxial.
Next, the basic configuration of lobe profiles of both the male and female rotors in the screw compressor according to the first embodiment is explained by using
In
Whether or not the clearance at the meshing portion of both the rotors 2 and 3 is set is not directly related to the essence of the present invention. In view of this, in the following explanation, it is supposed that the lobe profiles 60 and 70 of the rotor lobe sections 21 and 31 of the male rotor 2 and the female rotor 3 have shapes according to the geometric design in which the clearance is zero, although the presence of a clearance at the meshing portion of both the rotors 2 and 3 is examined. Accordingly, even if there is the expression that the male rotor 2 and the female rotor 3 “contact” in the following explanation, there is a micro-clearance at actual meshing portion of the lobe profiles 60 and 70 of the male rotor 2 and female rotor 3 in some cases.
The lobe profiles 60 and 70 of both the male and female rotors 2 and 3 are configured such that points on the lobe profile 60 of the male rotor 2 and points on the lobe profile 70 of the female rotor 3 form pairs in a one-to-one relation, and a meshing condition, “the common normal line of both flanks when the male and female rotors 2 and 3 mesh with each other at an invariable speed ratio passes through a pitch point,” is satisfied. In other words, this can be expressed as “when a point on a flank is at a position satisfying the meshing condition, the flank contacts its paired flank.” Since a pair of screw rotors that mesh with each other needs to satisfy this condition, this means that if the lobe profile of either of the male rotor 2 and the female rotor 3 is decided, the lobe profile of the other is determined uniquely. In the following explanation, the lobe profile of the male rotor 2 is called as a male lobe profile, and the lobe profile of the female rotor 3 is called as a female lobe profile, in some cases. Note that a point at which a line segment linking the rotation center A1 of the male rotor 2 and the rotation center A2 of the female rotor 3 is internally divided at the ratio between the number of lobes of the male rotor 2 and the number of lobes of the female rotor 3 is a pitch point P, which is a position important in terms of the geometric design of the lobe profiles.
In
One lobe in the male lobe profile 60 of the male rotor 2 includes a first contour line 61 defining a zone of a leading flank, a second contour line 62 defining a zone of a trailing flank, and a third contour line 63 defining a zone of a lobe bottom portion. In this explanation, the leading flank of the male rotor 2 is defined as a flank on a side located in the rotation direction of the male rotor 2 from the lobe tip, as the boundary, at which the male rotor 2 has the maximum radius, and the trailing flank of the male rotor 2 is defined as a flank on a side located in the direction opposite to the rotation direction. Specifically, the first contour line 61 defines a zone extending in the rotation direction of the male rotor 2 from the lobe tip 65, as the boundary point, to a first endpoint 66 at which the male rotor 2 has the minimum radius. The second contour line 62 defines a zone extending in the direction opposite to the rotation direction of the male rotor 2 from the lobe tip 65, as the boundary point, to a second endpoint 67 at which the male rotor 2 has the minimum radius. The third contour line 63 defines a zone having both endpoints at which the male rotor 2 has the minimum radius, and, for example, one endpoint of the endpoints is a point of connection with the first endpoint 66 of the first contour line 61, and also the other endpoint is a point of connection with the second endpoint 67 of the second contour line 62 of an adjacent one lobe. Note that one endpoint of the endpoints of the third contour line 63 may be a point of connection with the first endpoint 66 of the first contour line 61 of an adjacent one lobe, and also the other endpoint may be a point of connection with the second endpoint 67 of the second contour line 62.
One lobe in the female lobe profile 70 of the female rotor 3 includes a first contour line 71 defining a zone of a leading flank, a second contour line 72 defining a zone of a trailing flank, and a third contour line 73 defining a zone of a lobe tip. In this explanation, the leading flank of the female rotor 3 is defined as a flank on a side located in the rotation direction of the female rotor 3 from the lobe bottom, as the boundary, at which the female rotor 3 has the minimum radius, and the trailing flank of the female rotor 3 is defined as a flank on a side located in the direction opposite to the rotation direction. Specifically, the first contour line 71 defines a zone extending in the rotation direction of the female rotor 3 from the lobe bottom 75, as the boundary point, to a first endpoint 76 at which the female rotor 3 has the maximum radius. The second contour line 72 defines a zone extending in the direction opposite to the rotation direction of the female rotor 3 from the lobe bottom 75, as the boundary point, to a second endpoint 77 at which the female rotor 3 has the maximum radius. The third contour line 73 defines a zone having both endpoints at which the female rotor 3 has the maximum radius, and, for example, one endpoint of the endpoints is a point of connection with the first endpoint 76 of the first contour line 71, and also the other endpoint is a point of connection with the second endpoint 77 of the second contour line 72 of an adjacent one lobe. Note that one endpoint of the endpoints of the third contour line 73 may be a point of connection with the first endpoint 76 of the first contour line 71 of an adjacent one lobe, and also the other endpoint may be a point of connection with the second endpoint 77 of the second contour line 72.
The first contour line 61 defining the leading flank and the second contour line 62 defining the trailing flank in the lobe profile 60 of the male rotor 2 include a plurality of lobe profile elements. Similarly, the first contour line 71 defining the leading flank and the second contour line 72 defining the trailing flank in the lobe profile 70 of the female rotor 3 include a plurality of lobe profile elements.
An example of the lobe profiles 60 and 70 of the male rotor 2 and the female rotor 3 is depicted in
Specifically, for example, the second contour lines 62 and 72 defining the trailing flanks on the lobe profiles 60 and 70 of both the male and female rotors 2 and 3 are created on the basis of: one first arc, as a convex surface, starting from the lobe tip 65 (one endpoint of the second contour line 62) in the second contour line 62 of the male rotor 2; and one second arc, as a convex surface, ending at the second endpoint 77 (the other endpoint of the second contour line 72) in the second contour line 72 of the female rotor 3. The first arc of the second contour line 62 of the male rotor 2 is a curve having a certain radius R1, and a point 62a as its endpoint. The second arc of the second contour line 72 of the female rotor 3 is a curve having a certain radius R2, and a point 72a as its start point. In the second contour line 62 of the male rotor 2, the remaining part from the endpoint 62a of the first arc to the second endpoint 67 of the second contour line 62 is created so as to satisfy the meshing condition described above according to the shape of the second contour line 72 of the female rotor 3 including the second arc. In addition, in the second contour line 72 of the female rotor 3, the remaining part from the lobe bottom 75 (one endpoint of the second contour line 72) to the start point 72a of the second arc is created so as to satisfy the meshing condition described above according to the shape of the second contour line 62 of the male rotor 2 including the first arc.
In addition, for example, the first contour line 71 in the lobe profile 70 of the female rotor 3 is created on the basis of one parabola forming a concave surface and one third arc forming a convex surface. The parabola has its focal point F positioned on a line segment linking 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 from the lobe bottom 75 (one endpoint of the first contour line 71) to a point 71a as its endpoint. The third arc of the first contour line 71 of the female rotor 3 is a curve having a certain radius R3, and extending from the endpoint 71a of the parabola, as its start point, to the first endpoint 76 of the first contour line 71. The first contour line 61 of the male rotor 2 is created so as to satisfy the meshing condition described above according to the shapes of the parabola and third arc as lobe profile elements of the first contour line 71 of the female rotor 3.
For example, the third contour line 73 defining the lobe tip of the female rotor 3 can be configured as an arc having its center at the rotation center A2 of the female rotor 3, and having the maximum radius of the female rotor 3. The third contour line 63 defining the lobe bottom portion of the male rotor 2 is created so as to satisfy the meshing condition described above according to the shape of the third contour line 73 of the female rotor 3. For example, the third contour line 63 can be configured as an arc having its center at the rotation center A1 of the male rotor 2, and having the minimum diameter of the male rotor 2.
In the female lobe profile 70 of the female rotor 3, the first contour line 71 defining the leading flank, the second contour line 72 defining the trailing flank, and the third contour line 73 defining the lobe tip can be represented by using angles expressed with the rotation center A2 of the female rotor 3 as the vertex in the following manner. An angle formed by two line segments linking the rotation center A2 of the female rotor 3 as the vertex, and the lobe bottom 75 and first endpoint 76 which are both ends of the first contour line 71 is defined as a leading flank angle φL. An angle formed by two line segments linking the rotation center A2 of the female rotor 3 as the vertex, and the lobe bottom 75 and second endpoint 77 which are both ends of the second contour line 72 is defined as a trailing flank angle φT. An angle formed by two line segments linking the rotation center A2 of the female rotor 3 as the vertex, and the first endpoint 76 of the first contour line 71 and the second endpoint 77 of the second contour line 72 which are both ends of the third contour line 73 is defined as a lobe tip angle φS.
Next, features of the lobe profiles of both the male and female rotors in the screw compressor according to the first embodiment are explained by using
In
Specifically, the lobe profile 70 (see
In
By appending a reference character s representing the suction side, and also appending a reference character d representing the delivery side to the first contour line 71, second contour line 72, and third contour line 73 in the female lobe profile 70, distinctions are made between the suction-side first lobe profile 70s and the delivery-side second lobe profile 70d.
Similarly, by appending the reference character s representing the suction side, and also appending the reference character d representing the delivery side to the lobe bottom 75, which is the start point of the first contour line 71 and the second contour line 72 of the female lobe profile 70, distinctions are made between the suction-side first lobe profile 70s and the delivery-side second lobe profile 70d. By appending the reference character s representing the suction side, and also appending the reference character d represent the delivery side to both the ends 76 and 77 of the third contour line 73 of the female lobe profile 70, distinctions are made between the suction-side first lobe profile 70s and the delivery-side second lobe profile 70d. Note that, as mentioned above, one endpoint of the third contour line 73 is the first endpoint 76 of the first contour line 71, and the other endpoint of the third contour line 73 is a point that matches the second endpoint 77 of the second contour line 72.
In addition, by appending the reference character s representing the suction side, and also appending the reference character d representing the delivery side to the lobe tip angle φS, the leading flank angle φL, and the trailing flank angle φT in the female lobe profile 70, distinctions are made between the suction-side first lobe profile 70s and the delivery-side second lobe profile 70d.
In the present embodiment, as depicted in
In addition, a leading flank angle φLd of the delivery-side second lobe profile 70d of the female rotor 3 is set smaller than a leading flank angle φLs of the suction-side first lobe profile 70s. Note that, in the present embodiment, a second contour line 72s of the suction-side first lobe profile 70s and a second contour line 72d of the delivery-side second lobe profile 70d of the female rotor 3 have the same shape. That is, a delivery-side trailing flank angle φTd and a suction-side trailing flank angle φTs of the female lobe profile 70 are set to the same angle.
Note that the suction-side first lobe profile 70s of the female rotor 3 needs to satisfy the following Formula (1). In addition, the delivery-side second lobe profile 70d needs to satisfy the following Formula (2). Note that angles in Formula (1) and Formula (2) are expressed in units of degree.
φSs+φLs+φTs=360/(the number of lobes of female rotor) Formula (1)
μSd+μLd+μTd=360/(the number of lobes of female rotor) Formula (2)
By organizing Formula (1) and Formula (2) described above, the following Formula (3) holds true.
(φLs−φLd)+(φTs−φTd)=φSd−φSs Formula (3)
According to a condition that a lobe tip defined by a third contour line 73d of the delivery-side second lobe profile 70d of the female rotor 3 is made thicker than a lobe tip defined by a third contour line 73s of the suction-side first lobe profile 70s, the following is true of Formula (3) described above.
(φLs−φLd)+(φTs−φTd)=φSd−φSs>0
Accordingly, the relation between the leading flank angle φL and the trailing flank angle φT needs to satisfy the following Formula (4).
φLs−φLd>φTd−φTs Formula (4)
Next, a factor of occurrence of vibration of tooth flank separation of screw compressors in general is explained by using
Typically, in a liquid-flooded-type screw compressor, flanks of the male rotor 2 and the female rotor 3 directly contact, and thereby drive torque of the male rotor 2 is transmitted to the female rotor 3 to drive the female rotor 3. Depending on a condition of a pressure that acts on the flanks of both the male and female rotors 2 and 3, a phenomenon called as tooth flank separation in which the transmission torque from the male rotor 2 to the female rotor 3 turns negative temporarily, and flanks having been transmitting the torque are separated from each other occurs, in some cases. Thereafter, when the transmission torque from the male rotor 2 to the female rotor 3 turns positive again, the temporarily separated flanks collide with each other. As a result, tooth flank separation and tooth flank collision are repeated, and this generates significant vibration and noise. This is called as vibration of tooth flank separation, and there is a concern that this causes damage to the flanks.
When both the male and female rotors 2 and 3 are at rotation angles depicted in
Here, a rotation radius of the female rotor 3 from the rotation center A2 to the first contact point S1 is called as a first female radius RL, and a rotation radius of the female rotor 3 from the rotation center A2 to the second contact point S2 is called as a second female radius RT. The remaining length obtained by subtracting a lobe bottom diameter RB of the female rotor 3 from the first female radius RL is defined as L, and the remaining length obtained by subtracting the lobe bottom diameter RB from the second female radius RL is defined as T.
When the male and female rotors 2 and 3 are at the rotation angles depicted in
It should be noted that since working chambers C of the screw compressor are at various pressure levels in the axial direction, and also are formed in different shapes depending on the rotation angle, a computation of tooth flank separating torque requires integration from the suction side to the delivery side in the axial direction in the working chambers. Even if tooth flank separating torque is generated in the particular cross-section depicted in
Next, advantages of the screw compressor according to the first embodiment are explained by using
Lobe profiles (the first contour line defining the leading flank, the second contour line defining the trailing flank, and the third contour line defining the lobe tip) of a female rotor depicted in
The dimensions of lobe profile elements need to satisfy the meshing condition, and the lobe profile elements affect each other to limit a range within which they can be present. A range within which each lobe profile element can be present is depicted for each number (No.). It should be noted that the radius R2 of the second contour line is fixed to a value in order to make it easy to grasp the tendency of occurrence of tooth flank separation. Fields of tooth flank separation depict the tendency of occurrence of tooth flank separation of a lobe profile of each number. Note that the tendency of occurrence of tooth flank separation is depicted on the basis of tooth flank separating torque obtained on the basis of numerical calculations of integrating, in the axial direction, gas torque acting on flanks.
Lobe profiles of the female rotor depicted in
It can be known from
In addition, with an increase in the focal length Lf of the parabola forming the first contour line, the first contact point S1 depicted in
It should be noted that there are combinations (dimensions) of lobe profile elements that make occurrence of tooth flank separation likely even if the angular ratio of the leading flank angle φL is small. Such cases include a case where even if the angular ratio of the leading flank angle φL is reduced, the relation of L>T is satisfied as explained in
In this manner, in a case of lobe profiles depicted in
On the other hand, lobe profiles depicted in
Here, taking into consideration the tendency of occurrence of tooth flank separation of the lobe profiles depicted in
As the delivery-side second lobe profile 70d, the lobe profile denoted as No. 9 that makes occurrence of tooth flank separation unlikely is selected from the lobe profiles depicted in
On the other hand, as the suction-side first lobe profile 70s, lobe profiles of No. 3, No. 6, No. 8, and No. 9 that make occurrence of tooth flank separation unlikely in the lobe profiles depicted in
As depicted in
As the position of the contact start point (vertex) Sa becomes higher, the height of a triangle which is an approximate shape of the blow hole H becomes taller, also the length of the base increases, and accordingly the area size of the blow hole H increases. Accordingly, in order to reduce leakage of a compressed gas via the blow hole H, the contact start point Sa needs to be set lower. Since the contact start point Sa moves upward if the angular ratio of the leading flank angle φL is fixed, and the angular ratio of the trailing flank angle φT is increased in the lobe profile 70 of the female rotor 3, this leads to a tendency that leakage of a compressed fluid via the blow hole H increases.
Accordingly, the lobe profiles denoted as No. 8 and No. 9 in
In the present embodiment, as depicted in
Accordingly, by increasing, on the delivery side in the axial direction, the thickness of the lobe tip defined by the third contour line 73 of the female lobe profile 70, it is possible to inhibit leakage of a compressed gas via an outer diameter clearance against an increase in the differential pressure between working chambers positioned on the delivery side in the axial direction, and additionally it is possible to inhibit occurrence of tooth flank separation. Accordingly, it is possible to realize both inhibition of deterioration of the energy efficiency due to leakage of a working gas, and inhibition of occurrence of vibration of tooth flank separation.
As mentioned above, the screw compressor according to the first embodiment includes: the male rotor 2 that has the twisted male lobes 21a, and rotates about the first rotation center A1; the female rotor 3 that has the twisted female lobes 31a, meshes with the male rotor 2, and rotates about the second rotation center A2 parallel to the first rotation center A1; and the body casing 4 (casing) that has the housing chamber 45 rotatably housing the male rotor 2 and the female rotor 3 in a meshing state, and forms the plurality of working chambers C together with the male rotor 2 and the female rotor 3. The lobe profile 70 representing the contour shapes of the female rotor 3 in cross-sections perpendicular to the axial direction of the female rotor 3 is formed such that the lobe profile 70 changes between the position S1-S1 (a certain first position) in the axial direction and the position D1-D1 (a second position) on the delivery side in the axial direction relative to the first position. One lobe in the lobe profile of the female rotor 3 includes: the first contour line 71 defining the zone of the leading flank extending in the rotation direction of the female rotor 3 from the lobe bottom as a boundary point, at which the female rotor 3 has the minimum radius to the first endpoint 76 at which the female rotor 3 has the maximum radius; the second contour line 72 defining the zone of the trailing flank extending in the direction opposite to the rotation direction of the female rotor 3 from the boundary point to the second endpoint 77 at which the female rotor 3 has the maximum radius; and the third contour line 73 defining the zone of the lobe tip having both endpoints at which the female rotor 3 has the maximum radius, either one endpoint of the endpoints being a point of connection with the first endpoint 76 of the first contour line 71 or the second endpoint 77 of the second contour line 72. When the leading flank angle φL (the first angle) is defined as an angle formed by two line segments linking the second rotation center A2, as the vertex, and both the ends 65 and 76 of the first contour line 71, the trailing flank angle φT (the second angle) is defined as an angle formed by two line segments linking the second rotation center A2, as the vertex, and both the ends 65 and 77 of the second contour line 72, and the lobe tip angle φS (the third angle) is defined as an angle formed by two line segments linking the second rotation center A2, as the vertex, and both the ends 76 and 77 of the third contour line 73, the lobe profile 70 of the female rotor 3 is set such that the lobe tip angle φSd (the third angle) at the position D1-D1 (the second position) is greater than the lobe tip angle φSs (the third angle) at the position S1-S1 (the first position), and also is set such that the leading flank angle φLd (the first angle) at the position D1-D1 (the second position) is smaller than the leading flank angle φLs (the first angle) at the position S1-S1 (the first position).
According to this configuration, setting the lobe tip angle φS (the third angle), which corresponds to the shape of the lobe tip in the lobe profile 70 of the female rotor 3, greater on the delivery side than on the suction side in the axial direction results in the thickness of the lobe tip of the female rotor 3 being thicker on the delivery side, and thus, by a corresponding degree, leakage of a high-pressure working gas via an outer diameter clearance between working chambers positioned on the delivery side in the axial direction can be inhibited. Simultaneously, setting the leading flank angle φL (the first angle), which corresponds to the shape of the leading flank in the lobe profile 70 of the female rotor 3, smaller on the delivery side than on the suction side in the axial direction results in inhibition of occurrence of tooth flank separation. Accordingly, it is possible to realize both inhibition of leakage of a working gas between working chambers C via a clearance provided between the female rotor 3 and the body casing (casing) 4, and inhibition of occurrence of vibration of tooth flank separation.
In addition, in the lobe profile 70 of the female rotor 3 in the present embodiment, the trailing flank angle φTd (the second angle) at the position D1-D1 (the second position) is set to a value which is the same as the trailing flank angle φTs (the second angle) at the position S1-S1 (the first position).
Since, according to this configuration, the trailing flank (the second contour line 72) of the lobe profile 70 of the female rotor 3 has a shape that does not change from the suction side to the delivery side in the axial direction, the processing of the lobe profile becomes easier by a corresponding degree.
In addition, in the female rotor 3 in the present embodiment, the lobe profile 70 changes in an area, of the entire range in the axial direction, closer to the delivery side in the axial direction, but the lobe profile 70 is kept the same shape in the remaining area on the suction side in the axial direction.
According to this configuration, by setting the thicknesses of the lobe tip of the female rotor 3 so as to change to be greater only in an area on the delivery side where the differential pressures between working chambers are relatively large, leakage of a compressed gas between the working chambers is inhibited; on the other hand, by setting the thicknesses of the lobe tip of the female rotor 3 so as not to change in an area on the suction side in the axial direction where the differential pressures between working chambers are relatively low, a decrease in the volumes of the working chambers is avoided as compared with a case where the thicknesses of the lobe tip are made greater. Accordingly, it is possible to make sure that sufficient suction capacity is attained without a size increase of the compressor body 1. In addition, in a case of an oil-flooded type screw compressor, if the thicknesses of the lobe tip of the female rotor 3 are increased from the suction-side end portion toward the delivery side in the axial direction, an internal pressure increase due to a volume decrease occurs at working chambers positioned on the delivery side by a degree corresponding to the increase in the thicknesses, and therefore differential pressures for oil supply (the difference between a pressure of a pressure source, and pressures in working chambers) decrease undesirably. In contrast, by changing the lobe profile 70 of the female rotor 3 only in an area closer to the delivery side in the axial direction, an internal pressure increase due to changes in the lobe profile 70 can be inhibited in working chambers on the delivery side near the start position of the changes in the lobe profile 70 of the female rotor 3, and thus it is possible to attain a sufficient differential pressure for oil supply.
Next, a screw compressor according to a second embodiment is explained by illustrating examples by using
The screw compressor according to the second embodiment depicted in
In
In the lobe profile 70A of the female rotor 3A according to the present embodiment, as depicted in
That is, similarly to the first embodiment, in the present embodiment, a lobe tip defined by a third contour line 73Rd in the delivery-side second lobe profile 70Ad of the female rotor 3A is formed thicker than a lobe tip defined by a third contour line 73As of the suction-side first lobe profile In this manner, by a degree corresponding to the increase in the thickness of the lobe tip of the lobe profile of the female rotor 3A on the delivery side in the axial direction, it is possible to inhibit leakage of a compressed gas via an outer diameter clearance between working chambers positioned on the delivery side in the axial direction.
Furthermore, in the present embodiment, the delivery-side leading flank angle φLAd of the female rotor 3A is set smaller than the suction-side leading flank angle φLAs, but the delivery-side trailing flank angle φTAd of the female rotor 3A is set greater than the suction-side trailing flank angle φTAs. In a case of this configuration, tooth flank separation can be inhibited more than in the case of the lobe profile 70 of the female rotor 3 of the first embodiment for the following reason.
Next, advantages of the screw compressor according to the second embodiment are explained by using
In a case of the lobe profile 70A of the female rotor 3A according to the second embodiment, as depicted in
In addition, the delivery-side trailing flank angle φTAd of the female rotor 3A is set greater than the suction-side trailing flank angle φTAs, unlike the first embodiment. In a case of this configuration, as mentioned before, there is a tendency that the contact start point Sa, which is the vertex of the blow hole H (see
Note that, similarly to the first embodiment, in the second embodiment also, the lobe profile 70A of the female rotor 3A needs to satisfy the following Formula (5) and Formula (6) about the leading flank angle φLA, the trailing flank angle φTA, and the lobe tip angle φSA.
φSad−φSAs>0 Formula (5)
φLas−φLAd>φTad−φTAs Formula (6)
Similarly to the first embodiment, according to the second embodiment mentioned above, by setting the lobe tip angle φSA (the third angle) corresponding to the shape of the lobe tip in the lobe profile 70A of the female rotor 3A such that it is greater on the delivery side than on the suction side in the axial direction, the thickness of the lobe tip of the female rotor 3A becomes thicker on the delivery side, and thus, by a corresponding degree, leakage of a high-pressure working gas via an outer diameter clearance between working chambers C positioned on the delivery side in the axial direction can be inhibited. Simultaneously, by setting the leading flank angle φLA (the first angle) corresponding to the shape of the leading flank in the lobe profile 70A of the female rotor 3A such that it is smaller on the delivery side than on the suction side in the axial direction, occurrence of tooth flank separation is likely to be inhibited. Accordingly, it is possible to realize both inhibition of leakage of a working gas between working chambers C via a clearance provided between the female rotor 3A and the body casing (casing) 4, and inhibition of occurrence of vibration of tooth flank separation.
In addition, in the lobe profile 70A of the female rotor 3A in the present embodiment, the trailing flank angle φTd (the second angle) at the position D1-D1 (the second position) is set greater than the trailing flank angle φTs (the second angle) at the position S1-S1 (the first position).
Since, according to this configuration, there is a tendency that the area size of the blow hole H (see
Next, a configuration of a screw compressor according to a third embodiment is explained by illustrating examples by using
The screw compressor according to the third embodiment depicted in
Specifically, in
A lobe profile 70B (see
The second lobe profile 70Bd on the delivery side (at position D3-D3) in the axial direction of the female rotor 3B in the present embodiment has a shape in which the angular ratio of the lobe tip angle φSB is relatively high, but the angular ratio of the leading flank angle φLB is relatively low relative to the first lobe profile 70Bs on the suction side (at position S3-S3) in the axial direction. Furthermore, the second lobe profile 70Bd of the female rotor 3B has a shape in which the angular ratio of the trailing flank angle φTB is relatively low, and also an area including a lobe bottom 75B is relatively shallow relative to the first lobe profile 70Bs. Note that the rotor lobe section 21B of the male rotor 2B depicted in
In
By appending the reference character s representing the suction side, and also appending the reference character d representing the delivery side to a first contour line 71B defining the leading flank, a second contour line 72B defining the trailing flank and a third contour line 73B defining the lobe tip in the lobe profile 70B of the female rotor 3B, distinctions are made between the suction-side first lobe profile 70Bs and the delivery-side second lobe profile 70Bd.
Similarly, by appending the reference character s representing the suction side, and also appending the reference character d representing the delivery side to the lobe bottom 75B, which is the boundary point of the first contour line 71B and the second contour line 72B of the female lobe profile 70B, distinctions are made between the suction-side first lobe profile 70Bs and the delivery-side second lobe profile 70Bd. In addition, by appending the reference character s representing the suction side, and also appending the reference character d represent the delivery side to the endpoints 76B and 77B of the third contour line 73B of the female lobe profile 70B, distinctions are made between the suction-side first lobe profile 70Bs and the delivery-side second lobe profile 70Bd.
In addition, by appending the reference character s representing the suction side, and also appending the reference character d representing the delivery side to the lobe tip angle φSB, the leading flank angle φLB and the trailing flank angle φTB in the female lobe profile 70B, distinctions are made between the suction-side first lobe profile 70Bs and the delivery-side second lobe profile 70Bd.
As depicted in
In addition, similarly to the first embodiment, a leading flank angle φLBd of the delivery-side second lobe profile 70Bd is set smaller than a leading flank angle φLBs of the suction-side first lobe profile 70Bs. Note that, unlike the first embodiment, a trailing flank angle φTBd of the delivery-side second lobe profile 70Bd is set smaller than a trailing flank angle φTBs of the suction-side first lobe profile 70Bs.
Furthermore, a lobe bottom 75Bd of the second lobe profile 70Bd on the delivery side in the axial direction is set shallower than a lobe bottom 75Bs of the first lobe profile 70Bs on the suction-side. Note that, in the first embodiment, the lobe bottom 75s of the suction-side first lobe profile 70s, and the lobe bottom 75d of the delivery-side second lobe profile 70d of the female rotor 3 are at the same radial position.
In a case of this configuration, the male rotor 2B is formed such that the outer diameter of a lobe tip (a portion of contact with the lobe bottom 75B of the female rotor 3B) of the male rotor 2B gradually decreases from the certain first position (the position S3-S3) on the suction side in the axial direction toward the delivery-side end surface 21c (the position D3-D3), according to the lobe profile 70B of the female rotor 3B. That is, the male rotor 2B is formed to have a tapered shape that dwindles from the suction-side first position toward the delivery side in the axial direction.
In a case of this configuration, in a body casing 4B depicted in
A delivery-side bearing 6 for the male rotor 2B and a delivery-side bearing 8 for the female rotor 3B are disposed in a delivery-side end portion of the main casing 41B. A body cover 43B is attached to the body casing 4B such that the body cover 43B covers the delivery-side bearing 6 and the delivery-side bearing 8. Suction-side bearings 5a and 5b for the male rotor 2B and suction-side bearings 7a and 7b for the female rotor 3B are disposed in the suction-side casing 42B. The suction-side bearing 5b for the male rotor 2B and the suction-side bearing 7b for the female rotor 3B include angular contact ball bearings that are capable of positioning, for example.
In a case of this configuration, adjustment of clearances (called as end surface clearances, in some cases) provided between the suction-side inner wall surface 48 of the suction-side casing 42B and the suction-side end surfaces 21b and 31b of both the male and female rotors 2B and 3B can be performed by means of the angular contact ball bearings 5b and 7b arranged on the suction-side casing 42B. Since, in this configuration, the adjustment of the end surface clearances is possible while checking the positional relation between the suction-side casing 42B and both the male and female rotors 2B and 3B before both the male and female rotors 2B and 3B are housed in the bore 45B of the body casing 4B, the clearance adjustment is easy.
Next, advantages of the screw compressor according to the third embodiment are explained by using
A compressor body 100 according to the comparative example depicted in
The compressor body 1B according to the present embodiment is configured as a variable-lead screw rotor including the rotor lobe sections 21B and 31B of both the male and female rotors 2B and 3B whose lead decreases from the suction side toward the delivery side in the axial direction in an area closer to the delivery side in the axial direction. In view of this, as depicted in
Furthermore, in the present embodiment, the lobe bottom of the delivery-side second lobe profile 70Bd in the female rotor 3B is configured to be shallower than the lobe bottom 75Bs of the suction-side first lobe profile 70Bs. In such a changing area of the lobe bottom 75B of the lobe profile 70B, the rate of reduction of the volumes of working chambers C relative to the rotation angle of the female rotor 3B increases as compared with the case of the first embodiment (the case where the radial positions of the lobe bottom 75 of the female lobe profile 70 and the lobe tip 65 of the male lobe profile 60 do not change along the axial direction). Accordingly, in this female lobe profile 70B, the design volume ratio of the compressor body 1B can be increased, and it is possible to realize enhancement of the efficiency due to operation at a high pressure ratio. In addition, in a case of operation at a normal pressure ratio, it becomes possible for a working gas in each working chamber C to reach a delivery pressure earlier than in the case of the first embodiment, by a degree corresponding to the decrease in the depth of the delivery-side lobe bottom 75Bd of the female rotor 3B as compared to the suction-side lobe bottom 75Bs. Accordingly, it becomes possible to make earlier the timing of the start of delivery of the compressed gas in the working chamber C. Since, in this case, it becomes possible to increase the opening area of the delivery port 52a (see
Note that, similarly to the first embodiment, in the third embodiment also, the lobe profile 70B of the female rotor 3B needs to satisfy the following Formula (7) and Formula (8) about the leading flank angle φLB, the trailing flank angle φTB and the lobe tip angle φSB.
φSBd−φSBs>0 Formula (7)
φLBs−φLBd >φTBd−φTBs Formula (8)
In this manner, in the present embodiment, even if the male and female rotors 2B and 3B are variable-lead screw rotors whose lead decreases from the suction side toward the delivery side in the axial direction, setting the lobe tip angle φSB (the third angle) corresponding to the shape of the lobe tip in the lobe profile 70B of the female rotor 3B such that it is greater on the delivery side than on the suction side in the axial direction leads to a tendency that the thickness of the lobe tip of the female rotor 3B becomes thicker on the delivery side, and thus, by a corresponding degree, leakage of a high-pressure working gas via an outer diameter clearance between working chambers C positioned on the delivery side in the axial direction can be inhibited. Simultaneously, by setting the leading flank angle φLB (the first angle) corresponding to the shape of the leading flank in the female lobe profile 70B such that it is smaller on the delivery side than on the suction side in the axial direction, occurrence of tooth flank separation is likely to be inhibited. Accordingly, it is possible to realize both inhibition of leakage of a working gas between working chambers C via a clearance provided between the female rotor 3B and the body casing (casing) 4B, and inhibition of occurrence of vibration of tooth flank separation.
In addition, in the female rotor 3B of the present embodiment, the lead changes in a portion, of the entire range in the axial direction, closer to the delivery side in the axial direction, but the lead is kept equal in the remaining portion on the suction side in the axial direction.
Since, according to this configuration, the lead of the male rotor 2B and the female rotor 3B in the suction-side portions is kept relatively large, the moving distances per rotation of working chambers positioned on the suction side become relatively long. Accordingly, it is possible to attain sufficient suction amount of the compressor body 1B.
Furthermore, in the lobe profile 70B of the female rotor 3B in the present embodiment, the lobe bottom 75Bd at the second position (the position D3-D3) is set shallower than the lobe bottom 75Bs at the first position (the position S3-S3). Furthermore, the male rotor 2B is configured such that the outer diameter at the second position (the position D3-D3) is smaller than the outer diameter at the first position (the position S3-S3) according to the lobe profile 70B of the female rotor 3B.
Since, according to this configuration, a rate of reduction of the volumes of working chambers C relative to the rotation angle of the female rotor 3B increases by a degree corresponding to the reduction of the depth of the lobe bottom on the delivery side of the female rotor 3B as compared to the lobe bottom 75Bs on the suction side, it is possible to increase the design volume ratio of the compressor body 1B than in the case of the first embodiment that the radial position of the lobe bottom 75 does not change in the axial direction.
Furthermore, in the female rotor 3B in the present embodiment, the radial position of the lobe bottom 75B of the lobe profile 70B changes in an area, of the entire range in the axial direction, closer to the delivery side in the axial direction, but the radial position of the lobe bottom 75B of the lobe profile 70B is kept equal in the remaining area on the suction side in the axial direction.
Since, according to this configuration, a rate of reduction of the volumes of working chambers C of the female rotor 3B increases in a delivery-side area in the axial direction toward the delivery side, it is possible to make a working gas in the working chambers C reach a delivery pressure earlier. Furthermore, in a suction-side area in the axial direction where the radial position of the lobe bottom 75B of the female rotor 3B does not change, a decrease in the volumes of the working chambers C is avoided, and thereby a decrease in suction volumes can be avoided.
Furthermore, the compressor body 1B in the present embodiment includes: the suction-side bearings 7a and 7b for the female rotor 3B (female-side bearings) that rotatably support the female rotor 3B on the suction side in the axial direction; and the suction-side bearings 5a and 5b for the male rotor 2B (male-side bearings) that rotatably support the male rotor 2B on the suction side in the axial direction. Furthermore, the body casing (casing) 4B has: the main casing 41B having an inner space that has an opening toward the suction side in the axial direction, and is capable of housing the male rotor 2B and the female rotor 3B in a meshing state; and the suction-side casing 42B that is attached to the main casing 41B such that the opening of the main casing 41B is covered, and forms the housing chamber 45 together with the main casing 41B. The suction-side bearings 7a and 7b for the female rotor 3B (the female-side bearings) and the suction-side bearings 5a and 5b for the male rotor 2B (the male-side bearings) are disposed in the suction-side casing 42B.
According to this configuration, it is possible to house the male rotor 2B having a tapered shape that dwindles toward the delivery side in the body casing (casing) 4B, and also it becomes possible to adjust end surface clearances provided between the suction-side end surfaces 21b and 31b of the male rotor 2B and the female rotor 3B and the suction-side inner wall surface 48 of the body casing (casing) 4B by means of the suction-side bearings 7a and 7b for the female rotor 3B (the female-side bearings) and the suction-side bearings 5a and 5b for the male rotor 2B (the male-side bearings). Accordingly, since the end surface clearances can be adjusted by positioning of the male rotor 2B and the female rotor 3B relative to the suction-side casing 42B before both the male and female rotors 2B and 3B are housed, the clearance adjustment becomes easier.
Note that the present invention is not limited to the embodiments mentioned above, but includes various modification examples. The embodiments described above are explained in detail for explaining the present invention in an easy-to-understand manner, and the present invention is not necessarily limited to those including all constituent elements explained. That is, it is possible to replace some of constituent elements of an embodiment with constituent elements of another embodiment, and it is also possible to add constituent elements of an embodiment to the constituent elements of another embodiment. In addition, some of constituent elements of each embodiment can also have other constituent elements additionally, be deleted, or be replaced.
For example, in the examples of configuration depicted in the first to third embodiments mentioned above, the first position in the axial direction, which is the start position of changes in the lobe profiles 70, 70A, and 70B of cross-sections perpendicular to the axial direction in the rotor lobe sections 31, 31A ,and 31B of the female rotors 3, 3A, and 3B, is the position S1-S1 or the position S3-S3, which is an approximately middle position in the axial direction, and also the second position, which is the end position of changes in the lobe profiles 70, 70A, and 70B, is the position D1-D1 or the position D3-D3, which is the delivery-side end surface 31c. However, the first position and second position in the axial direction, which are the start position and end position, respectively, of changes in the lobe profiles of the female rotors, can be change to any positions according to operation pressure conditions and the like. For example, in a case where the delivery pressure is high, the first position can be moved to the suction side in order to further increase the lobe thicknesses of lobe tips of a female rotor. On the other hand, in a case where the delivery pressure is low, the first position can be moved to the delivery side.
In addition, the start position (the first position) of changes in the lobe profiles 70, 70A, and 70B of the female rotors 3, 3A, and 3B can also be set to the suction-side end surface 31b of the rotor lobe sections 31, 31A, and 31B. That is, a female rotor can be configured such that a lobe profile changes over an entire range in an axial direction. In a case of this configuration, processing of the lobe profile is relatively easy as compared with a case where the lobe profiles of the female rotors change from intermediate positions.
In addition, in the example of configuration depicted in the third embodiment, the delivery-side lobe bottom 75Bd of the lobe profile 70B of the female rotor 3B changes such that it becomes shallower than the suction-side lobe bottom 75Bs. However, similarly to the cases of the first and second embodiments, delivery-side lobe bottoms and suction-side lobe bottoms of the female rotor may be at the same radial position, and the lobe bottoms of the female rotor may not change in the axial direction, in other possible configuration. On the other hand, regarding the first and second embodiments, in a case where both the male and female rotors are formed as invariable-lead screw rotors, delivery-side lobe bottoms in lobe profiles of the female rotor may change such that they become shallower than suction-side lobe bottoms, in other possible configuration. In a case of this configuration, the delivery-side outer diameter of the male rotor is formed smaller than the suction-side outer diameter according to the lobe profile of the female rotor.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-178084 | Oct 2020 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/038447 | 10/18/2021 | WO |
