JP2003254268A - Screw rotor and screw machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a screw machine in which performance is improved by reducing a mesh clearance between screw rotors, and seizure between the rotors is also effectively prevented even in a long time and high speed continuous operation. <P>SOLUTION: The screw rotors have screw threads with a helical crest portion and a root portion forming a helical groove between crest portions, around a rotation axis, are used in a male-female pair in a reverse thread relation, and have pitch circumference portions forming an arc of a constant radius and in a given angle range on an arbitrary cross section perpendicular to the rotation axis, between the crest portion and root portion of the screw threads. Both rotors have two or more threads of thread parts, and a plurality of pitch circumference portions. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw rotor applied to a screw machine, and a screw machine such as a dry vacuum pump using the same.

[0002]

2. Description of the Related Art Conventionally, a positive displacement screw machine having a pair of screw rotors in a housing is known as a pump or a compressor capable of continuous operation at high speed for a long time.

In this type of screw machine, for example, a screw machine used as a dry type vacuum pump, male and female screw rotors having mutually opposite threads are arranged in parallel, and both rotors are meshed with each other with a minute clearance. A working chamber is formed between the rotor and a housing that surrounds these rotors, and is partitioned by the meshing portions of both rotors. Further, by rotating the male and female screw rotors synchronously, the volume of the working chamber is increased on the intake side while the male and female screw rotors are in a substantially non-contact state,
It is designed to be reduced on the exhaust side.

Further, in vacuum pumps, generally, two important performances, that is, ultimate pressure and evacuation speed, are highly required. In a screw machine such as a dry type vacuum pump, male and female screw rotors arranged in parallel are provided. And the clearance between both rotors and the housing have a great influence on any performance. Therefore, in such a screw machine, the performance is improved by minimizing the clearance between the male and female screw rotors and the clearance with the housing.

The screw machine includes a Rishorum type screwdriver, a square screw type screwdriver (having a Quinnby type (square type) tooth profile), and a spiral type screw (spiraxial screw (sp) which is composed of epitrochoid and Archimedes spiral.
iraxial screw) has a tooth profile).

[0006]

However, in the above-mentioned conventional screw machine, since the number of male and female screw rotors is one to seal the exhaust chamber,
Since the center of gravity of the rotor is not on the shaft in the axial cross section and the balance against rotation is poor, if the clearance between the male and female screw rotors or the clearance with the housing is very small, vibration will occur when both screw rotors are rotated at high speed with a large load. As a result, the rotors or the rotor and the casing frequently come into contact with each other. Therefore, seizure occurred between the rotors and between the rotor and the housing. In order to avoid this, there has been a problem that the clearance between the male and female screw rotors and the clearance with the housing must be increased more than necessary, and the number of rotations must be significantly limited.

In order to avoid this, in a cross section orthogonal to the rotation axis, a large hole is formed in the end surface of the screw rotor in order to balance the couple so that the center of gravity of the cross section does not largely deviate from the center of rotation. There is also a problem that it is necessary to form a cavity, which complicates the manufacturing process.

Therefore, the present invention aims to improve the performance by reducing the meshing gap between the screw rotors, and in addition to this, it is possible to effectively prevent the seizure between the rotors even during a high-speed continuous operation for a long time. It is intended to provide.

[0009]

In order to solve the above-mentioned problems, the present invention provides a tooth top surface portion which forms a spiral tooth top surface portion and a spiral groove between the tooth top surface portions around a rotation axis. Provided with a screw tooth having a pair of male and female having a reverse screw relationship with each other, between the tooth tip surface portion and the tooth root surface portion of the screw tooth, a constant radius on an arbitrary cross section orthogonal to the rotation axis. In the screw rotor provided with the pitch circumferential portion that is an arc having a predetermined angle range, each of the screw portions of both rotors has two or more threads.

With this structure, the center of gravity does not deviate significantly from the center of rotation on the cross section orthogonal to the rotation axis, and the center of gravity rotates over the entire length of the rotor in any cross section perpendicular to the axis. Since it is near the central axis, it is possible to obtain a very good rotational balance. Therefore, it is not necessary to form a complicated cavity by casting or the like, and it is possible to reduce the manufacturing cost, and since it rotates in a well-balanced manner around the rotating shaft, the clearance between the male and female screw rotors and the clearance with the housing can be reduced. The vacuum pump can be made extremely narrow, the degree of sealing in the pump can be improved, the backflow of the outside air from the exhaust side can be suppressed, and a more efficient vacuum pump can be formed.

Further, by making the gap between the pitch circumferential portions of the meshing gap of the male and female screw teeth smaller than the gaps of other portions, when the screw rotor thermally expands, the pitch of the same radius is obtained. Seizure is less likely to occur as compared with a conventional machine in which the circumferential portions first come into contact with each other and make rolling contact with each other, and the tooth portions of both rotors make sliding contact.

Further, by providing a plurality of the pitch circumferential portions in the axial cross section, the contact points in the axial direction can be increased when the two rotors come into contact with each other, and the seizure of the rotor caused at the time of contact is dispersed throughout the rotor. It is possible to prevent expansion contact of the rotor due to temperature rise only at a specific place, and it is possible to extremely narrow the gap between the male and female screw rotors and the clearance with the housing.

If the pitch circumferential portion is formed in a band shape at a radial position substantially in the middle between the tooth crest surface portion and the tooth root surface portion, the tooth profile of each rotor can be made common to facilitate machining. In addition, the required pitch sealing performance can be achieved at the meshing portion of the screw rotor due to the pitch circumferential portion having a constant width.

It is characterized in that the screw tooth profile is a trocoloid tooth profile or an epitrocolloid tooth profile. With such a configuration, the airtightness of the transfer chamber can be increased and the exhaust capacity can be improved.

In the screw machine according to the present invention, the screw rotors are male and female rotors that mesh with each other, and both rotors are housed in parallel in a housing having an intake port and an exhaust port so as to mesh with each other in a non-contact meshing state. A plurality of working chambers that are transferred in the axial direction of the rotation shaft by the rotation of the screw rotor are formed between the housing and both rotors.

According to the present invention, when the screw rotor is thermally expanded, the pitch circumferential portions having a constant radius first come into contact with each other to make rolling contact, so that seizure hardly occurs. Moreover, since the meshing gap itself between the rotors can be narrowed between the pitch circumferential portions, the efficiency can be improved.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. 1 to 6 are views showing a screw rotor and a screw machine according to an embodiment of the present invention.

The screw machine of this embodiment is one in which the present invention is applied to a dry vacuum pump. FIG. 1 is a front sectional view of a main part of a dry type vacuum pump embodying the present invention. A housing 11 having an intake port 11a and an exhaust port 11b formed therein, and a male and female screw rotor 21 housed in the housing 11 in parallel so as to mesh with each other in a non-contact meshing state with a predetermined clearance (a minute gap),
22, bearings 23a and 23b interposed between the housing 11 and the screw rotors 21 and 22, seal members 24a and 24b for sealing shaft holes, and both rotors 2
Synchronous gears 25a, 2 mounted integrally on the screw rotors 21, 22 so as to synchronously rotate 1, 2 in opposite directions.
5b and a drive means 27 having a motor 26 connected to one end of the rotor 22.

The female-side screw rotor 21 and the male-side screw rotor 22 have a predetermined clearance with respect to the inner wall surface 11i of the housing 11, for example, an outer diameter dimension and an axial length that separate a gap of 50 microns. Between the housing 11 and both screw rotors 21 and 22,
A plurality of spiral-shaped working chambers are formed which are partitioned from each other by the meshing portions of the screw rotors 21 and 22 and are transferred in the axial direction of the rotation shaft by the rotation of the screw rotors 21 and 22.

As shown in FIG. 2, the screw rotor 21 has helical screw teeth 21 around the rotation axis C1.
1 is provided, and the screw tooth 211 has a tooth top surface portion 2 a that forms a spiral belt-shaped tooth top surface portion 211 a and a spiral groove 211 b having a predetermined groove width between the tooth top surface portions 211 a.
11c. Further, between the tooth top surface portion 211a and the tooth root surface portion 211c of the screw tooth 211, a pitch circumferential portion 211p, a tooth tip side inclined surface 211d closer to the tooth tip surface portion 211a than the pitch circumferential portion 211p, and a pitch circle. Root-side inclined surface 21 on the root surface 211c side of the peripheral portion 211p
1e are provided.

On the other hand, the screw rotor 22 is provided with spiral screw teeth 221 around its rotation axis C2 so as to have a reverse screw relationship with the screw rotor 21, and the screw teeth 221 are , A tooth top surface portion 221c that forms a spiral belt-shaped tooth top surface portion 221a and a spiral groove 221b having a predetermined groove width between the tooth top surface portion 221a.
And have. In addition, between the tooth crest 221a and the tooth crest 221c of the screw tooth 221, a pitch circumferential portion 221p, and the tooth crest 2 from the pitch circumferential portion 221p.
21a side tooth tip side inclined surface 221d and pitch circumferential portion 22
Root-side inclined surface 221e on the root-face portion 221c side from 1p
And are provided.

Further, the tooth crests 211a and 221a of the screw rotors 21 and 22 and the pitch circumferential portions 211p and 2p are formed.
The connection portion between 21p is a connection curve that is smoothly connected on the cross section of each rotor 21, 22 and has, for example, an arc shape,
Pitch circumferential portion 211 of each screw rotor 21, 22
The connection between p, 221p and the root surface portions 211c, 221c is a creation curve obtained by the connection curve so as to be smoothly connected on the cross section of each rotor 21, 22,
Tooth crests 211a, 2 of each screw rotor 21, 22
21a and the tooth root surface portions 211c and 221c are connected by
On the cross-section of each rotor 21, 22, each connection shape is set so as to form a trochoidal curve drawn by the addendum (one side end portion of the addendum surface portion 221a, 211a) of the counterpart screw rotor 22, 21. There is.

FIG. 3 is a curve diagram of a right-angled tooth profile showing an embodiment of the screw rotor according to the present invention. In FIG. 3, reference numerals 301 and 302 designate two rotors that mesh with each other. Both rotors are rotor chambers having an 8-shaped cross section formed by rotating cylinders of the tips of the rotors shown by the outermost dotted lines in the figure. It is housed in a casing that has. The space 305 formed by the cutouts 303 and 304 is transferred from the intake side to the exhaust side by the rotation of the rotor, so that vacuum exhaust is performed. 306, 307, 308, 309, 3
10 and 311 are pitch circles. In the case of two threads as shown in FIG. 9, the balance can be improved by arranging the pitch circles on the diagonal sides 306 and 309 with respect to the respective rotation axes of the cutouts 303 and 304. Further, by providing a pitch circle portion at a diagonal position with respect to a pair of rotating shafts like 308 and 307 and 310 and 311, the center of gravity can be brought closer to the center of rotation, and the points where both screw rotors come into contact are determined. It can be increased and the force due to contact is dispersed.

As shown in FIG. 4, the screw rotor 2
When the male and female screw rotors 1 and 22 mesh with each other, the gap g between the pitch circumferential portions 211p and 221p among the meshing gaps of the male and female screw teeth 211 and 221.
1 (gap between facing surfaces, eg, 20 μm) is the gap g2, g3, g4 of other meshing parts (gap between facing surfaces, eg, 50 μm)
m) etc., the pitch circumferential portion 211p, 2
A radius of 21p and a screw tooth profile (screw tooth profile in each rotor vertical section) are set.

In the screw machine of the present embodiment constructed as described above, the male and female screw rotors 21 and 22 mesh with each other in a non-contact meshing state with a small clearance at the time of normal operation start or operation. At this time, the gap g1 between the pitch circumferential portions 211p and 221p of the meshing gaps between the male and female screw teeth 211 and 221 is smaller than the gaps g2, g3, g4, etc. of the other meshing portions. , 22 is the pitch gap 211p,
Although it becomes narrower between 221p, when the screw rotors 21 and 22 thermally expand due to high-speed / long-time continuous operation or the like, pitch circumferential portions 211p and 221 having a constant radius are formed.
As a result, seizure is less likely to occur as compared with a conventional machine in which the teeth p of the rotors 21 and 22 come into sliding contact with each other because the teeth of the rotors 21 and 22 come into rolling contact with each other. Further, even in the case of contact, it is possible to disperse the heat generated by the contact of the rotor by increasing the number of pitch circles on the cross section perpendicular to the axis, and thus suppress the partial thermal expansion of the rotor. Therefore, the clearance between the male and female screw rotors and the clearance with the housing can be extremely narrowed. Therefore, unlike the conventional case, the clearance is unnecessarily enlarged to prevent the seizure, and the pump performance and the compressor performance are not sacrificed. Therefore, a high-performance screw machine can be provided.

Further, the screw rotors 21 and 22 are 2
With the above configuration, the offset from the center of rotation C1 and C2 at the center of gravity becomes extremely small.
Combined with positioning the center of gravity on the center axis of rotation by setting the number of leads to an integer, it is not necessary to form a complicated cavity by casting or the like to balance the couple, and a simple shallow recess is formed. The number of processing steps can be reduced to the extent that

Further, the pitch circumferential portions 211p, 221p
Of the tooth crests 211a, 221a and the tooth crests 211c,
Since it is formed in a strip shape at a radial position approximately in the middle of 221c, the tooth shapes of the rotors 21 and 22 can be made common to facilitate the processing, and the pitch circumferential portions 211p and 221p having a constant width can be used. Screw rotor 2
The required sealing performance is achieved at the meshing portions 1 and 22 (between the adjacent work chambers).

In the above embodiments, the screw rotors have been described as having the same screw lead from the intake side to the exhaust side. However, the leads on the compression side are different from each other so that the leads on the compression side are smaller than the intake side. A plurality of screw parts may be provided, or the pitch between the screw teeth may be gradually reduced steplessly as the screw side is closer to the exhaust side. That is, a screw rotor having unequal leads can be used.

FIG. 5 is a sectional view perpendicular to the shaft when the screw tooth profile of the present invention has three threads. In FIG. 5, 401 and 402 are three rotors meshed with each other, and both rotors are 8-shaped rotor chambers formed by rotating cylinders of the tips of both rotors shown by the outermost dotted lines in the figure. It is housed in a casing having. The space 405 formed by the cutouts 403 and 404 is transferred from the intake side to the exhaust side by the rotation of the rotor, so that vacuum exhaust is performed. 406, 407, 408, 409.410 and 41
1 is a pitch circle part. Notch 40 even in the case of 3 articles
A good balance can be achieved by arranging pitch circles at 406, 407 and 409, 410 on each side for each of 3 and 404. Further, by providing another pair of pitch circles 408 and 411, the center of gravity can be brought closer to the center of rotation, the points where both screw rotors make contact can be increased, and the force due to contact can be dispersed. Therefore, it is possible to disperse the heat generated by the contact of the rotors, thus suppressing the partial thermal expansion of the rotors, and it is possible to make the gap between the male and female screw rotors and the clearance with the housing extremely narrow.

Further, by making the tooth profile of this embodiment a trochoroidal tooth profile or an epitrocolloidal tooth profile, the airtightness of the exhaust phase space formed by the both screw rotors and the housing can be improved.

[0031]

EFFECTS OF THE INVENTION According to the present invention, the number of screws is two or more so that the balance of the screw rotor is improved during continuous and high-speed operation, and when the thermal expansion is performed, the pitch circumferential portions having a constant radius are joined to each other. It is possible to prevent seizure due to the tooth portions of both rotors making sliding contact with each other by first bringing them into contact with each other for rolling contact. Further, by providing a plurality of pitch circumferential portions, it is possible to prevent further seizure, and even if the exhaust performance is sacrificed, the meshing gap of the screw rotor must be set large in order to prevent seizure. It is possible to solve the conventional problem of not becoming. In addition, the airtightness of the phase space formed by both screws can be improved by making the tooth profile a trocolloid tooth profile or an epitrocolloid tooth profile.

[Brief description of drawings]

FIG. 1 is a front cross-sectional view of an essential part showing a schematic internal structure of a screw machine according to an embodiment of the present invention.

FIG. 2 is a front view showing a meshed state of the male and female screw rotors according to the embodiment of the present invention.

3 is a cross-sectional view taken along the line AA of FIG.

FIG. 4 is a schematic cross-sectional view showing a setting state of the meshing gap of the male and female screw rotors according to the embodiment of the present invention.

FIG. 5 is a front view showing a meshed state of male and female screw rotors according to another embodiment of the present invention.

[Explanation of symbols]

11 housing 11a intake port 11b exhaust port 21 Female screw rotor 22 Male side screw rotor 25a, 25b Synchronous gear 26 motor 121, 122 screw rotor 121h1, 121h2, 122h1, 122h2 recesses 211,221 screw teeth 211a, 221a Tip surface part 211c, 221c Tooth root surface portion 211d, 221d Tooth tip side inclined surface 211e, 221e Tooth root side inclined surface 211p, 221p pitch circumference

Claims (6)

[Claims] 1. A screw tooth having a spiral tooth top surface portion and a tooth root surface portion forming a spiral groove between the tooth top surface portions is provided around a rotation shaft, and the male and female members are in a reverse screw relationship with each other. A pair of pitch circumferential portions, which are used in a pair, are provided between the addendum surface portion and the tooth root surface portion of the screw tooth and have an arc of a predetermined angle range having a constant radius on an arbitrary cross section orthogonal to the rotation axis. In the screw rotor, each screw portion of both rotors has two or more threads. 2. The screw rotor according to claim 1, wherein a gap between pitch circumferential portions of a meshing gap of the male and female screw teeth is set to be equal to or smaller than a gap of other portions. 3. The screw rotor according to claim 1, 2 or 3, wherein a plurality of the pitch circumferential portions are provided on the cross section. 4. The screw rotor according to claim 1, wherein the pitch circumferential portion is formed in a band shape at a radial position substantially in the middle between the tooth crest surface portion and the tooth root surface portion. 5. The screw rotor according to claim 1, 2, 3 or 4, wherein the screw tooth profile is a trocoloid tooth profile or an epitrocolloid tooth profile. 6. The screw rotor according to claim 1, 2, 3, 4 or 5, wherein both rotors are parallel to each other in a non-contact meshing state in a housing having an intake port and an exhaust port formed therein. After storing, between the housing and both rotors,
A screw machine comprising a plurality of exhaust chambers that are transferred in the axial direction of the rotating shaft by the rotation of the screw rotor.