JP2000136786A - Vacuum pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vacuum pump with excellent suction characteristics and a great exhaust speed. SOLUTION: A pump housing 11 has grooves 11f, 11g defining enlarged suction passages 31, 32 radially outwardly of large lead suction port side screw portions 21c, 22c. The ends of the enlarged suction passages 31, 32 at their exhaust port sides are located near a junction A between large and small lead screw portions. When operating chambers 24, 25 communicated with a suction port 11a with the rotation of male and female screw rotors 21, 22 is increased in volume, these perform suction operation through the enlarged suction passages 31, 32 and when the operating chambers 24, 25 communicated with the suction port 11a is maximized in volume, these ends are partitioned with the engaged portions of both exhaust port side screw portions 21d, 22d.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw-type vacuum pump, and is particularly suitable for a low-to-medium vacuum region from atmospheric pressure to a level of ^10.sup.-4 , and is used for manufacturing semiconductors from 200 mm wafers to 300 mm wafers. The present invention relates to the improvement of the suction characteristics of a large-capacity positive-displacement vacuum pump required in connection with the transition to.

[0002]

2. Description of the Related Art 10 ^-4 which is frequently used in semiconductor manufacturing and the like.
In general, a screw pump for obtaining a low / medium vacuum region of about 10 ^-1 Torr has a pumping speed falling from about ¹ to 10 Torr, and a large-capacity pump is used in anticipation of this drop. A mechanical pump was provided between the vacuum chamber and the screw pump to obtain the required pumping speed.

[0003] There is known a screw pump in which suction is performed from a radial direction of a screw groove (working chamber) opened to an intake end.

[0004]

However, due to the structure using a screw rotor, the installation range of such a passage for performing suction in the radial direction (hereinafter referred to as an intake passage) is limited. The thread groove part of one section from the start of suction of one lead of the screw and the thread groove part (working chamber) of some section just before the end of suction cannot communicate with the intake passage, and the suction efficiency is greatly increased. No improvement could be expected.

The present invention has been made in view of such conventional problems, and provides a large capacity positive displacement vacuum pump having excellent suction characteristics.

[0006]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a pump housing having an intake port and an exhaust port, and male and female rotatably housed in the pump housing so as to rotate while meshing with each other. A plurality of working chambers, which are separated from each other by a meshing portion of the two screw rotors between the pump housing and the respective screw rotors and are transferred from the intake port side to the exhaust port side by rotation of the two screw rotors. In the vacuum pump formed, the male and female screw rotors each include an inlet-side screw portion having a larger helical tooth lead and an outlet-side screw portion having a helical tooth lead smaller than the inlet-side screw portion. And the pump housing communicates with the working chamber at a radially outer side of the inlet-side screw portion. And a groove forming an enlarged intake path, and an end on the exhaust port side of the enlarged intake path is located near a connection point between the intake port side screw section and the exhaust port side screw section, and the male and female screws are When the volume of the working chamber connected to the intake port increases with the rotation of the rotor, the working chamber performs the suction operation through the enlarged intake path, and when the volume of the working chamber connected to the intake port reaches a maximum. The distal end portion of the working chamber is partitioned by a meshing portion between the exhaust port side screw portions.

According to the present invention, the working chamber partitioned at one end by the screw rotor meshing portion at the other end and by the screw rotor meshing portion is partitioned by the meshing portion of the exhaust port side screw portion of the small lead when the suction operation is completed. By doing so, the conductance immediately before the completion of the intake operation is increased. Therefore, the intake efficiency is significantly improved. In addition, since the compression ratio is increased by using teeth having different leads in combination, the exhaust speed can be increased. If the expanded shape of the enlarged intake passage has a substantially triangular shape extending over a plurality of working chambers during the intake operation, the intake efficiency can be further increased.

[0008]

Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 and FIG. 2 are views showing a screw type vacuum pump according to an embodiment of the present invention. First, the configuration will be described. Reference numeral 11 denotes a pump housing having an intake port 11a and an exhaust port 11b. 21 and 22
Male and female screw rotors are rotatably housed in the pump housing 11 so as to rotate while meshing with each other. The female screw rotor 21 has spiral teeth 21 a and spiral grooves 21 b having female screw shapes, and a male screw rotor 22. Has a spiral tooth 22a and a spiral groove 22b, each of which has a female screw shape. In FIG. 1, the teeth 21a, 21 of the screw rotors 21, 22 are shown.
The portion corresponding to the thread 2a is shown by an oblique solid line in the upper half above the center line, and the lower half is shown by a cross-section without hatching.

Reference numeral 15 denotes drive means for driving the male and female screw rotors, which are fixed to the electric motor 16 (only a part is shown) connected to one end of the male screw rotor 22 and the male and female screw rotors. And synchronous gears 17a and 17b meshing with each other. The synchronous gears 17a and 17b have the function of rotating the male and female screw rotors 21 and 22 synchronously.

The male and female screw rotors 21 and 22 are formed by the inlet-side screw portions 21c and 22c in which the leads (screw leads) of the helical teeth 21a and 22a are large, and the spiral from the inlet-side screw portions 21c and 22c. Tooth 2
Exhaust port side screw part 2 with small leads 1a and 22a
1d and 22d are combined. The number of turns of the screw is at least 2 or more, preferably 4 to 5 as a whole, and the number of turns of the inlet-side screw portions 21c and 22c having a large lead is set to be slightly less than one turn. And
Helical teeth 21a, 22 defining the groove width of the spiral groove 22b
The pitch a (the distance between adjacent teeth in the rotor axial direction) is large in the inlet-side screw portions 21c and 22c and small in the exhaust-side screw portions 21d and 22d.

Further, the inlet side screw portions 21c, 22
c and the exhaust-port-side screw portions 21d, 2
The meshing gap between the meshing portions of the 2d and the clearance between the pump housing 11 and each of the scut rotors 21 and 22 are set to, for example, about 50 μm, respectively.
A plurality of working chambers 24 and 25 are formed between the working chambers 22 and 22 at a meshing portion between the screw portions 21 c and 21 d of the female screw rotor 21 and the screw portions 22 c and 22 d of the male screw rotor 22. 24, 25
Is the intake port 1 by the rotation of both screw rotors 21 and 22.
The air is transferred from the side 1a to the exhaust port 11b.

Here, the exhaust port side screw portions 21d and 22d of the small lead may themselves be constituted by larger and smaller lead portions. In other words, a multi-stage screw structure in which the leads become smaller toward the exhaust port may be used.

The intake port 11a is connected to the pump housing 1
1 and an intake chamber 23 formed between the entire end surfaces of the screw rotors 21 and 22 on the intake port side.
Are communicated with all of the working chambers 24 and 25 that open to the outside. When the rotors 21 and 22 rotate,
Each of the working chambers 24 and 25 increases its volume in a transfer section on the suction side communicating with the suction port 11a while increasing its volume.
After the action of sucking gas from the outside through the inlet port 11a, the screw rotors 21 and 22 are finally shut off at the discharge side transfer sections of the small lead screw portions 21d and 22d which are shut off from the intake port 11a and communicate with the exhaust port 11b. The volume of the gas is reduced to reach the discharge-side end surface of the gas discharge port, and the gas is discharged.

2, the male and female screw rotors 21 and 22 rotate in the directions of arrows R1 and R2 in FIG.
Numeral 4 increases the volume of the screw rotors 21 and 22 in accordance with the rotation of the screw rotors 21 and 22 to perform the suction operation. On the other hand, similarly, the working chamber 25 also performs the suction operation while increasing its volume with the rotation of the screw rotors 21 and 22. When the volume of each of the working chambers 24 and 25 communicating with the intake port 11a reaches the maximum, the distal ends of the large-volume working chambers 24 and 25 are connected to the exhaust port side screw portions 21d and 22 of the small lead.
d are partitioned by a meshing portion Pm (see FIG. 2).

Further, the working chambers 24 and 25 when the intake is completed,
The volume ratio between the discharge-side working chambers 24 and 25 that are closed and transferred at both ends between the exhaust-port-side screw portions 21d and 22d and the pump housing 11 is set to at least 4 to 1, and preferably 10 to 10. : The volume ratio is set to about 1 or larger.

On the other hand, on the inner wall of the pump housing 11,
Grooves 11f, 11g are formed on the intake port 11a side from the connection point A (position in the axial direction) between the intake port side screw sections 21c, 22c and the exhaust port side screw sections 21d, 22d.

As shown in FIGS. 3 and 4, these grooves 11f and 11g are provided on the inlet side screw portions 21c and 22c.
The enlarged intake passages 31 and 32 which are located radially outward of c and communicate with the working chambers 24 and 25 respectively are formed. Then, with the rotation of the male and female screw rotors 21 and 22, the intake port 1
When the volumes of the working chambers 24 and 25 communicating with 1a increase, the working chambers 24 and 25 perform the suction operation not only through the suction chamber 23 but also through the enlarged suction passages 31 and 32.

These enlarged intake passages 31 and 32 correspond to the screw development diagrams of the screw rotors 21 and 22 shown in FIG.
It is formed to open to the hatched triangular portion. That is, the working chamber 2 communicating with the intake port 11a
When the volume of 4,25 reaches a maximum, the working chambers 24,25
Of the small lead is partitioned by a meshing portion Pm between the small-lead exhaust-port-side screw portions.
At the exhaust port side ends of the first and second connection points A (the screw-shaped teeth 21a, 22), the large lead intake port side screw portions 21c, 22c and the small lead exhaust port side screw portions 21d, 22d are joined.
(a bending position of a).

In FIG. 1, 26a and 26b are bearings interposed between the female screw rotor 21 and the pump housing 11, and 27a and 27b are interposed between the male screw rotor 22 and the pump housing 11. Bearing, 2
Reference numerals 8a and 28b denote seal members provided between the shafts at both ends of the female screw rotor 21 and the pump housing 11 inside the bearings 26a and 26b, and reference numerals 29a and 29b denote bearings 27.
a sealing member interposed between the shafts at both ends of the male screw rotor 22 and the pump housing 11 inwardly of a and 27b.

In the vacuum pump of the present embodiment having the above-described structure, when the rotors 21 and 22 rotate, the working-side chambers 24 and 25 increase their suction-side opening area while communicating with the suction port 11a. The conductance of the working chambers 24 and 25 reaches a maximum.

FIG. 5A shows this state in one spiral groove 21.
The wide part on the left end side in the drawing is a large lead and large pitch transfer section in the inlet side screw parts 21c and 22c, and the narrow part on the right end side is the exhaust side. Small leads, small-pitch transfer sections in the screw portions 21d, 22d, hatched portions 53a, 53
b is a meshing portion of the screw rotors 21 and 22, and numerals (1) to (3) in parentheses in the figure are the same spiral groove 21 before and after.
b, 22b show three working chambers 24 or 25 being transferred.

The two working chambers 24 and 25 (the working chamber (1) in FIG. 5) which have reached the maximum volume after the suction has been completed through the suction port side end face of the screw and the enlarged suction paths 31 and 32 are shown in FIG.
As shown in (b), at the end on the suction side, it is cut off from the inlet 11a by the meshing portion 53a of the screw portions 21c, 22c between the inlet ports, and at the same time, the enlarged suction passages 31, 32 are also cut off. The working chamber 2 is separated from the preceding working chamber 2 by an engagement portion 53b between the exhaust port side screw portions 21d and 22d at the end on the side.

Next, the working chambers 24 and 25 (working chamber (1) in FIG. 5) gradually enter the inlet side screw portions 21d and 22d from the tip side, and when the volumes of the working chambers 24 and 25 decrease. (The state of the working chambers (2) and (3) in FIG. 5), and the internal pressure is the volume ratio of the working chambers 24 and 25 on the intake side and the discharge side (for example, at least about 4: 1, preferably about 10: 1). Higher ratio). Thereafter, the working chambers 24 and 25 are further transferred to the exhaust port 11b side. When the working chambers 24 and 25 communicate with the exhaust port 11b near the meshing center C, the working chambers 24 and 25 (FIG. 5)
The working chamber (3) of (c) performs an exhausting action while reducing the volume as the rotors 21 and 22 rotate, and the teeth 21a and 22
When the end of “a” reaches the exhaust port 11b near the meshing portion, the exhaust is completed.

In such an operation state, one end communicates with the intake port 11a and the other end communicates with the screw rotors 21 and 22.
The working chambers 24 and 25 partitioned by the meshing portions of
When the intake is completed, the small lead exhaust side screw section 21
Since the partitioning is made by the meshing portion Pm of d and 22d (the meshing portion 53b at the left end in FIG. 5A), the opening area for gas flow into the working chambers 24 and 25 immediately before the completion of the intake becomes large. In addition, the intake and exhaust volumes (conductance) of the working chambers 24 and 25 increase.

Further, by using the teeth 21a and 22a having different leads in combination, a compression action can be performed during the transfer by the screw rotors 21 and 22, and the exhaust speed can be increased.

Further, the shapes of the enlarged intake passages 31, 32 are as follows:
The developed shape may be an arbitrary shape such as a trapezoid or a triangle having the bottom side at the end face of the rotor on the intake side, and the open end thereof has a plurality of working chambers 24, 2 during the intake operation, particularly as shown in FIG.
By having approximately five triangular shapes, the intake efficiency can be sufficiently increased.

[0028]

According to the present invention, the working chamber between the teeth of the large reed is partitioned by the meshing portion of the screw portion on the exhaust port side of the small reed when the intake is completed. The expanded intake passage communicating with the working chamber until just before the completion of the intake of the working chamber is provided, so it has excellent suction characteristics, and the compression ratio is increased by using large and small reeds, so that the required ultimate vacuum degree can be obtained at a high exhaust speed. The vacuum pump which can be provided can be provided.

[Brief description of the drawings]

FIG. 1 is a front sectional view showing a vacuum pump according to an embodiment of the present invention.

FIG. 2 is a development view showing spiral teeth and spiral grooves of the screw rotor.

FIG. 3 is a perspective view of a main part showing a shape of the enlarged intake passage.

FIG. 4 is an explanatory view of the intake, transfer and exhaust operations.

FIG. 5 is a development view of tooth traces of the screw rotor in one embodiment.

[Explanation of symbols]

 11 Pump Housing 11a Inlet 11b Exhaust 11f, 11g Groove 21 Female Screw Rotor 21a, 22a Helical Teeth 21ao, 22ao Teeth at Specific Rotation Position 21b, 22b Helical Grooves 21c, 22c Inlet Screws 21d, 22d Exhaust Side screw part 22 Male screw rotor 23 Intake chamber 24,25 Working chamber 24f, 25f Subsequent working chamber 31,32 Enlarged intake path 51 Wide part 52 Narrow part 53a, 53b Meshing part A Joining point P1 Intake start position P2 Intake completion Position Pm Meshing part

Claims (2)

[Claims] A pump housing having an intake port and an exhaust port; and male and female screw rotors rotatably housed in the pump housing so as to rotate while meshing with each other. In a vacuum pump that forms a plurality of working chambers that are separated from each other by a meshing portion of the two screw rotors and that are transferred from the intake port side to the exhaust port side by rotation of the two screw rotors, the male and female screw rotors are Each of the pump housing is formed by coupling an inlet-side screw portion having a larger helical tooth lead and an outlet-side screw portion having a helical tooth lead smaller than the inlet-side screw portion. Having a groove forming an enlarged intake passage communicating with the working chamber outside of the screw portion; An end on the exhaust port side of the enlarged intake path is located near a connection point between the intake port side screw portion and the exhaust port side screw portion, and communicates with the intake port with rotation of the male and female screw rotors. When the volume of the working chamber increases, the working chamber performs a suction operation through the enlarged intake path, and when the volume of the working chamber connected to the intake port reaches a maximum, the tip of the working chamber is connected to the exhaust port. A vacuum pump characterized in that it is partitioned by a meshing portion between side screw portions. 2. The expanded shape of the enlarged intake passage has a substantially triangular shape extending over a plurality of working chambers during the intake operation.
The vacuum pump according to 1.