JP2000130378A - Vacuum pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the influence of conductance and increase the exhausting speed by providing an intake port with an intake part communicated to a working chamber, wire a length not more than one lead of crossed helical gears formed on a male rotor and a female rotor. SOLUTION: One axial end of a casing 4 covering the end surfaces of the male and female rotors 1, 2 is opened as an gas intake port 4a, and an end plate 5 on the opposite side is provided with a discharge port. The casing 3 covers the male and female rotors 1, 2 with fine clearance, and a V-shaped working chamber is formed with the rotors 1, 2 and the casing 3. The intake ports 3a, 3b communicated to the working chamber and having a length approximately one lead, are formed along respective tooth traces of the crossed helical gears 1a, 2a formed on the male rotor 1 and the female rotor 2. By applying this structure, the influence of conductance when the gas is taken in the working chamber can be reduced, and the high exhausting speed can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a vacuum pump,
In particular, the present invention relates to a vacuum pump having a large conductance and a high pumping speed.

[0002]

2. Description of the Related Art Conventionally, various types of vacuum pumps such as an oil rotary pump, a root pump and a diffusion pump have been used in a low / medium vacuum region. For example, in the semiconductor manufacturing field, a predetermined process is performed by storing a wafer in a container in a vacuum state. In this process, a vacuum pump is used while supplying an inert gas such as N ₂ gas into the container. Inhalation and removal of impurities (O ₂ , CO _2, etc.) in the container, and several Torr to 1
And a vacuum of 0 ^over 4 Torr level.

As a vacuum pump used in such a semiconductor manufacturing process, an oil rotary pump, a roots type mechanical booster pump, or the like is used. But,
In the case of oil rotary pumps, the pressure range for normal operation is narrow, so several types of pumps must be switched and used until the predetermined pressure is reached. Pumps are being used.

FIG. 6 shows this screw vacuum pump.
Referring to FIG. 7, the male rotor 31 and the female rotor 3
2 are housed in a main casing 33 and a suction casing 34, bearings 36 and 37 of an end plate 35, and a sub-casing 38.
Are rotatably supported by the bearings 39 and 40.

[0005] The male rotor 31 and the female rotor 32 are formed with screw gears 31a and 32a, respectively. In the screw gears 31a and 32a, the helical helix angle is always constant, and the pitch in the rotation axis direction and the pitch in the plane perpendicular to the axis are also constant. The suction casing 34 is provided with a suction port 34a, and a discharge port 35a is provided at the rear end side of the male rotor 31 and the female rotor 32. Except for the suction port 34a and the discharge port 35a, the casing 3 covers the male and female rotors 31, 32 with a small gap, and the V-shaped operation is performed by the rotors 31, 32 (the tooth grooves of the screw gears 31a, 32a) and the casing 33. A chamber is formed. When the male rotor 31 and the female rotor 32 rotate, the screw gears 31a and 32a
It is configured to inhale, transfer, compress, and exhaust gas.

Timing gears 41 and 42 are attached to the shaft ends of the rotors 31 and 32, respectively, so that the male and female rotors 31 and 32 do not contact each other.
32 is adjusted.

In the vacuum pump constructed as described above, when the male and female rotors 31 and 32 rotate, the gas in the tank flows through the suction port 34a through the end faces of the screw gears formed on the male and female rotors 31 and 32 (see FIG. 1). From the suction port side end face) to the screw gear 31
a and 32a are sucked into the V-shaped working chamber formed by the case 32 and the casing 32. Then, as the male and female rotors 31, 32 rotate, the working chamber moves toward the discharge port. At this time, the gas in the working chamber is moved and compressed, and is discharged to the outside through the discharge port 35a.

[0008]

As described above, the screw vacuum pump is composed of the male and female rotors 31, 32.
The gas is sucked in from the end faces (end faces on the suction port side) of the screw gears 31a and 32a formed in the above. Therefore, there is a technical problem that an exhaust speed higher than a certain exhaust speed cannot be obtained due to the influence of the conductance due to the tooth groove shape of the screw gear (the cross-sectional shape perpendicular to the axis of the rotor).

That is, the pumping speed of the pump is represented by G ₀ (unit: l).
/ S (liter / second)) and the pressure inside the pump (inside the working chamber) is P ₀ (unit: Pa (Pascal)), the amount of gas flowing into the pump is Q (Pa · l / s) is Q = G ₀ P ₀ (unit: Pa · l / s). But,
In practice, the gas flowing into the working chamber is affected by the conductance due to the tooth groove shape of the screw gear (the cross-sectional shape perpendicular to the axis of the rotor). This conductance is C (unit: l)
/ S (l / sec)), and the pressure of the gas just before flowing into the working chamber when the _{P 1 P 1 -P 0 = Q} / C ( unit:
Pa).

From the above two equations, P ₁ = (1 / C + 1)
/ G ₀ ) Q (unit: Pa). Here, the tooth groove shape of screw gear (B - motor axis perpendicular to the cross-sectional shape of) the screw in consideration of the influence of conductance by - the pumping speed of the vacuum pump obtaining the G ₁ when _{1 / G 1 = 1 / C} + 1 / G ₀ .

[0011] As is apparent from this equation, the tooth groove shape of the screw gear - when the conductance C by (b and the axis perpendicular to the cross-sectional shape of the data) is small, the screw - pumping speed G ₁ of the vacuum pump decreases. That is, the screw - G ₁ pumping speed of the vacuum pump, tooth shape of the screw gear - is limited by the value of conductance C by (ii another axis perpendicular cross-section).

This problem can be solved by forming the tooth groove shape of the screw gear (cross section perpendicular to the axis of the rotor) larger. However, forming a larger tooth groove shape (cross-sectional shape perpendicular to the axis of the rotor) of the screw gear leads to an increase in the size of the pump. Not preferred.

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned problem. By increasing the conductance when gas is sucked into the working chamber, the influence of the conductance is reduced as much as possible. It is an object of the present invention to provide a vacuum pump capable of obtaining a large pumping speed.

[0014]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and comprises a male gear and a female rotor which are formed with a screw gear and mesh with each other, and at least both rotors are housed. A working chamber formed by the male and female rotors and the casing; a gas inlet provided in the casing and communicating with the working chamber; and a working chamber provided in the casing. And a gas discharge port communicating with the working chamber, wherein the suction port communicates with the working chamber with a length of one lead or less of a screw gear formed on the male rotor and the female rotor. It is characterized by having a suction part.

As described above, the gas suction port is provided with a suction portion which is shorter than one lead of the screw gear formed on the male rotor and the female rotor and communicates with the working chamber. Therefore, compared to the conventional screw vacuum pump in which gas is sucked only from the end face of the working chamber (the end face of the screw gear), the conductance when gas is sucked into the working chamber can be increased. As a result, the influence of the conductance when the gas is sucked into the working chamber can be minimized, so that a higher exhaust speed can be obtained.

When the suction portion is formed to have a length exceeding one lead of the screw gear formed on the male rotor and the female rotor,
The engagement between the lead and the next lead is exceeded, and the compression ratio cannot be increased. Therefore, it is preferable that the length of the suction part is one lead or less.

Here, the suction portion of the suction port is (1-1)
/ The number of teeth of the screw gear). In order to achieve higher conductance and higher pumping speed,
It is better that the length of the suction portion, that is, the size of the suction portion communicating with the working chamber is larger. However, since it is necessary to avoid the meshing area of the screw gear, it is preferable that the lead gear is formed with a lead length represented by (1-1 / number of teeth of the screw gear). In particular,
For example, if the number of teeth of the screw gear is 5, 4/5
(0.8) The lead is preferably formed to be shorter than the length.

[0018] The suction portion of the suction port is provided on the inner peripheral surface of the casing for accommodating the male rotor and the female rotor along one tooth of the screw gear. It is desirable to be formed with a length of not more than- Further, it is desirable that the suction portion of the suction port is formed so as to gradually expand toward the suction port.

As described above, the suction portion is provided with the male rotor and the female rotor.
Is formed on the inner peripheral surface of the casing for accommodating the screw gear along the tooth trace of the screw gear with a length of one lead or less of the screw gear, so that the suction resistance can be further reduced, and the conductance is reduced. Can be increased, so that a higher pumping speed can be obtained.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a vacuum pump according to the present invention will be described with reference to FIGS. In addition, FIG.
FIG. 2 shows a schematic configuration of the vacuum pump. FIG. 3 is a front view showing a state where the male rotor 1 and the female rotor 2 are housed in the main casing, and FIG. 4 is a perspective view of the main casing.

As shown in the figure, a male rotor 1 and a female rotor 2
Are housed in the main casing 3 and the suction casing 4 and have bearings 6 and 7 of the end plate 5 and bearings 9 and 10 of the auxiliary casing 8.
It is rotatably supported by. The male rotor 1 and the female rotor 2 are formed with screw gears 1a and 2a, respectively, and mesh with each other. In the screw gears 1a and 2a, the helical helix angle is always constant, and the pitch in the rotation axis direction and the pitch in the plane perpendicular to the axis are also constant.

As shown in FIG.
The casing 4 which covers the end face of the casing has one end in the axial direction largely open as a gas intake port 4a, and the end plate 5 on the opposite side.
Is provided with a discharge port 5a. Except for the suction port 4a, the discharge port 5a, and suction sections 3a and 3b described later, the casing 3 covers the male and female rotors 1 and 2 with a small gap.
A V-shaped working chamber is formed by the rotors 1 and 2 (the tooth grooves of the screw gears 1a and 2a) and the casing 3.

On the inner peripheral surface of the casing 3 on the side of the suction port 4a, substantially one tooth is formed along the respective tooth traces of the screw gears 1a, 2a formed on the male rotor 1 and the female rotor 2. Suction parts 3a and 3b communicating with the working chamber are formed with the length of the lead. That is, as shown by a dotted line in FIG. 2, the suction portion 3b (3a) formed on the inner peripheral surface of the casing 3 is a casing 3 on which the end face of the screw gear 1a (2a) is located.
It is formed as a recess extending gradually from the end face into the inside of the casing 3 according to the rotation of the male rotor 1 and the female rotor 2 along the respective tooth traces of the respective screw gears 1a (2a). . The length L of the suction portions 3a, 3b in the direction inside the casing 3 is short immediately after the mesh gears 1a, 2a are disengaged. The portion immediately before the meshing of the screw gears 1a and 2a is long, and has a length corresponding to approximately one lead of the screw gears 1a and 2a.

However, since the screw gears 1a and 2a are engaged with each other, the length L of the suction portions 3a and 3b in the inner direction is shorter than one lead. Further, the suction portions 3a, 3b
The length S of the concave portion in the radial direction (the gap between the rotors 1 and 2 and the casing 3 in the suction portions 3a and 3b) is set as appropriate, but the length S is set to increase the conductance. Is preferably larger.

As described above, the suction section 3 communicating with the working chamber 3
a and 3b communicate with the working chamber along the tooth traces of the screw gears formed on the male rotor 1 and the female rotor 2 with a length of approximately one lead. The gas sucked in from 4a is the end face of the tooth groove of the screw gear and the suction portions 3a, 3b.
The gas can be sucked into the working chamber from the. As a result, the conductance can be increased and the gas can be sucked into the working chamber as compared with a conventional screw vacuum pump that sucks gas into the working chamber from the end face of the working chamber (the end face of the toothed groove of the screw gear). In this case, the influence of the conductance can be minimized, so that a higher pumping speed can be obtained.

Here, the length L of the suction portions 3a, 3b
Are (1-) of the screw gears formed on the male rotor and the female rotor.
1 / number of teeth of the screw gear). In order to increase the conductance and obtain a higher evacuation speed, it is preferable that the length of the suction portions 3a and 3b, that is, the size communicating with the working chamber is larger. However, the screw gears 1a, 2
Since it is necessary to avoid the meshing area a, it is desirable that the lead length is formed by (1-1 / number of teeth of the screw gear).

Specifically, since the screw gear 1a shown in FIG. 3 has five teeth, the suction portion 3b on the gear 1a side is 4/5.
(0.8) The lead is preferably formed to be shorter than the length. Since the number of teeth of the suction portion 3a on the side of the gear 2a is 6, it is preferable that the suction portion 3a is formed to have a length of 5/6 (0.83) lead or less.

Timing gears 11 and 12 are attached to the shaft ends of the rotors 1 and 2, respectively.
Are adjusted so that the rotors do not contact each other. The bearings 6, 7, 9 and 10 are lubricated by splash lubrication, and lubricating oil (not shown) accumulated in the sub-casing 8 is splashed by timing gears 11 and 12. Shaft seals 13, 14, 15 are formed in the vicinity of the bearings 6, 7, 9 as parts to which the inert gas is supplied. An inert gas is supplied to the shaft seal portions 13, 14, and 15 from an inert gas supply unit (not shown) to prevent lubricating oil or outside air from entering the working chamber.

Since the temperature rises due to gas compression outside the main casing 3, a cooling jacket 16 is provided, through which cooling water is passed.
And compressed gas is cooled.

Next, the operation of the vacuum pump according to the present invention will be described. When the male and female rotors 1 and 2 rotate, gas in a tank (not shown) is sucked into the working chamber from the suction port 4a. At this time, gas flows into the casing 3 from the suction port 4a, and the tooth groove end faces of the screw gears 1a and 2a and the suction section 3
a and 3b flow into the working chamber. The suction portions 3a, 3
b is formed so as to gradually extend into the casing as the screw gears 1a, 2a rotate immediately after the mesh gears 1a, 2a are disengaged, so that gas flows into the working chamber without receiving resistance. I do. And screw gear 1
When a and 2a mesh with each other, the working chamber is closed, and the gas in the working chamber moves toward the discharge port and is compressed. Finally, the gas is exhausted from the discharge port 5a.

The same screw vacuum pump having the same shape and the same dimensions as the screw vacuum pump configured as in the above embodiment is used except that the suction portions 3a and 3b are not formed. The verification was performed under the following operating conditions. As a result, the atmospheric pressure (760Torr) 10 ^{- 4} Torr
In the operating range, a larger pumping speed could be obtained as compared with the conventional screw vacuum pump.

Next, another embodiment will be described with reference to FIG. In this embodiment, the suction units 3a, 3b
However, it is characterized in that it is formed so as to gradually expand toward the suction port. That is, the suction portion 3a, and not the radial direction of the length S of 3b is formed always constant, as in the first embodiment, the largest radial length S ₀ of the inlet-side Are formed such that the length S in the radial direction gradually decreases toward the inside of the casing. With this configuration, the gas sucked into the working chamber can be sucked into the working chamber without receiving resistance, and the influence of the conductance of the suction port can be reduced as much as possible. Can be obtained.

In the above-described embodiment, the screw gears 1a and 2a are formed such that the helical helix angle is always constant, and the pitch in the rotation axis direction and the pitch in the plane perpendicular to the axis are also constant. Although the case has been described, the present invention is not particularly limited thereto, and may be applied to, for example, a vacuum pump in which the pitch in the rotation axis direction is unequal. Further, the present invention can also be applied to a vacuum pump in which the screw gears 1a and 2a are screw gears having two kinds of helical helix angles.

[0034]

As is apparent from the above description, according to the vacuum pump of the present invention, the conductance of the suction port can be further increased by providing the suction portion while having a simple pump structure. . As a result, the influence of the conductance of the suction port can be minimized, and a higher exhaust speed can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view taken along line II-II of FIG. 2, showing an embodiment of a vacuum pump according to the present invention.

FIG. 2 is a sectional view taken along the line II of FIG. 1, showing an embodiment of the vacuum pump according to the present invention.

FIG. 3 is a side view of a casing used in the vacuum pump according to the present invention.

FIG. 4 is a perspective view of a casing used for the vacuum pump according to the present invention.

FIG. 5 is a view showing another embodiment of the vacuum pump according to the present invention, and is a cross-sectional view corresponding to FIG. 1;

FIG. 6 shows an embodiment of a conventional vacuum pump;
It is II-II sectional drawing of FIG.

FIG. 7 shows an embodiment of a conventional vacuum pump;
It is II sectional drawing of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Male rotor 1a Screw gear 2 Female rotor 2a Screw gear 3 Main casing 3a Suction part 3b Suction part 4 Suction casing 4a Suction port 5 End plate 5a Discharge port 8 Sub-casing

Claims (4)

[Claims] An intermeshing male and female rotor having a screw gear formed thereon, a casing for accommodating at least both rotors, and the male and female rotor and the casing. Working chamber, provided in the casing,
In a vacuum pump having a gas inlet communicating with the working chamber and a gas outlet provided in the casing and communicating with the working chamber, the suction port is a male rotor and a female rotor. A vacuum pump having a suction portion communicating with the working chamber with a length of not more than one lead of the screw gear formed in the vacuum pump. 2. A suction portion of the screw gear is provided on an inner peripheral surface of a casing for accommodating a male rotor and a female rotor along a tooth trace of the screw gear. 2. The vacuum pump according to claim 1, wherein the vacuum pump is formed to have a length equal to or less than a length of the negative electrode. 3. The suction portion of the suction port is formed with a length equal to or less than a lead length represented by (1-1 / number of teeth of a screw gear). Claim 2
Vacuum pump described in 1. 4. The vacuum pump according to claim 1, wherein a suction portion of the suction port is formed so as to gradually expand toward the suction port.