JPH02136595A - Vacuum pump - Google Patents

Abstract

PURPOSE:To achieve the high vacuum degree in an early time without using an auxiliary pump by arranging a centrifugal compression pump in an exhaust passage and using a impeller and the shaft of the rotor of a vacuum pump in common, in the vacuum pump consisting of the molecular drag pump. CONSTITUTION:A molecular drag pump 10 is constituted of a housing 1, roller 12, and a stator 13, and each screw groove is formed on the inside surface of the housing 11 and the outside surface of the stator 13. Inside of the stator of such a vacuum pump, centrifugal compression pumps consisting of impellers 25 and 27 and diffusers 26 and 28 are built in two stages, and the impellers 25 and 27 are fixed onto a common shaft 19, together with the rotor 12 of the pump 10 and the rotor of a motor 32. In the initial stage of the pump operation, exhaust action is carried out mainly by the centrifugal type compression pump, and the gas sucked from a suction port E is introduced into the suction port H of the centrifugal type compression pump 20 through the gaps F and G.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a vacuum pump whose exhaust port pressure is atmospheric pressure, and which is suitable for creating a clean vacuum required in semiconductor manufacturing equipment and the like.

(Prior Art) A conventional vacuum pump of this type is a molecular drag pump.

The structure of this vacuum pump is shown in FIG. 4 (front sectional view).

This housing 1 has a threaded groove formed on its inner surface (surface A).

The shaft 2 is supported by an upper ball bearing 3 and a lower ball bearing 4, and a rotor 5 and a rotor 6 of a motor 9 are attached thereto.

An impeller 7 is attached to the outer periphery of the upper surface of the rotor 5 .

The stator 8 is fixed to the housing 1, and has thread grooves formed on its outer surface (8 surfaces).

The motor 9 is incorporated inside this pump as shown in the figure.

This vacuum pump operates as follows. When the rotor 5 is driven by the motor 9 and rotates at high speed, the impeller 7 attached to the rotor 5 acts as an axial flow compressor and sucks gas from the intake port B. Due to its viscosity, the inhaled gas is given rotational energy by the outer surface (plane 0) of the cylindrical portion of the rotor 5, where it obtains centrifugal force and moves along the thread groove (plane A) on the inner surface of the housing 1 as shown by the arrow. 101, it descends while being compressed.

The gas that has reached the bottom of the housing (lower part of the figure) is indicated by arrow 10.
After passing around the lower end of the cylindrical portion of the rotor 5 and entering the inside of the cylindrical portion of the rotor 5 as shown in 2, centrifugal force is further applied by the inner surface (D surface) of the cylindrical portion of the rotor 5.

Here again, the gas that has gained centrifugal force rises while being compressed along the thread grooves (8 faces) on the outer surface of the stator 8.

The gas that has reached the second end enters the internal ventilation path F of the stator 8 as shown by arrow 103, passes through this path, and reaches the exhaust port G.

The exhaust port G is connected to an auxiliary pump such as an oil rotary pump, and the gas is compressed by the auxiliary pump, raised to near atmospheric pressure, and then discharged into the atmosphere.

(Problems to be Solved by the Invention) However, the above conventional molecular drug pump has the following drawbacks.

Due to its characteristics, the molecular drag pump can achieve maximum efficiency when the gas flow is in the intermediate flow region and molecular flow region, and the maximum pressure near the inlet E is I
X 10-'torr is reached. However, when the gas flow is in the viscous flow region at the beginning of pump operation, the pumping effect is so small that the molecular drag pump alone cannot be activated. Therefore, an auxiliary pump such as an oil rotary pump is connected to the exhaust port G of the molecular drag pump, and the pressure at the exhaust port G is several tens of torr, which is the maximum continuous exhaust pressure of the molecular drag pump.
I had to evacuate until it was below.

In addition, the auxiliary oil rotary pump lubricates the inside,
In addition, oil is used to maintain airtightness, but as a result, oil vapor flows back into the exhaust system passageway, degrading the quality of the vacuum in the exhaust system.

(Objective of the Invention) The present invention does not require an auxiliary pump, and can maintain the maximum continuous exhaust pressure near atmospheric pressure for a long period of time.
The purpose of the present invention is to provide a vacuum pump that can provide a clean vacuum free of oil vapor.

(Means for solving the problem) In order to achieve the above purpose, a vacuum pump is configured with a molecular drag pump and a centrifugal compression pump that are driven by a common shaft, and the centrifugal compression pump is a molecular drag pump that is driven by a common shaft.・Connected to the exhaust route of the drag pump.

As the centrifugal compression pump, one consisting of one to several sets of impellers and a differential user is used.

[For production]

When the pump starts operating, the inside of the pump is under high pressure close to atmospheric pressure, and the gas flow is a viscous flow. During this transition period, the centrifugal compression pump primarily acts.

The gas that passes through the internal flow path of the molecular drag pump and reaches the intake port of the centrifugal compression pump is compressed by the internal impeller and diffuser to near atmospheric pressure.
After being pressurized, it is discharged into the atmosphere from the exhaust port. In the viscous flow region, an efficient impeller with the optimal shape to send out a large amount of gas works as a compressor with a diffuser that rectifies the gas, achieving a high compression ratio and pumping out a large amount of gas. of gas can be efficiently discharged and a large exhaust speed can be obtained.

As the pumping process progresses and the pressure at the pump's inlet port decreases and the gas flow enters the intermediate flow region, the molecular drag pump takes over from the centrifugal compression pump.

The gas sucked in from the pump's intake port is given a large amount of centrifugal force energy by the outer and inner surfaces of the rotor, which is rotating at high speed, creating a spiral rotational motion that causes the inner surface of the housing and the outer surface of the stator to generate a spiral rotational motion. It is compressed while being fed under pressure along a spiral thread groove formed on the side surface. The gas discharged from the exhaust port of the molecular drag pump reaches the inlet port of the centrifugal compression pump, where it is further compressed by the internal impeller and diffuser, increasing the pressure to near atmospheric pressure, and then entering the atmosphere from the pump exhaust port. is discharged.

That is, in this steady state, the centrifugal compression pump acts as an auxiliary pump for the molecular drug pump.

Molecular drug pump reaches its maximum pressure I
Compression is performed from X 10-' torr to several IQ torr, followed by a centrifugal compression pump to several Qt.
Compress from orr to atmospheric pressure.

The number of sets of centrifugal compression pumps incorporated into one pump and the rotation speed of the pumps are several tens to
In order to be able to increase the pressure from rr to near atmospheric pressure, and the molecular drug pump
The settings are made in such a way that it can be compressed from orr to several IQ torr.

[Example] Examples of vacuum pumps according to the invention will be described below.

FIG. 1 shows a front sectional view of the schematic structure of this embodiment.

The molecular drag pump 10 is composed of a housing 11, a rotor 12, and a stator 13.
A thread groove is machined on the inner surface (side A).

An impeller 14 is attached to the outer periphery of the upper surface of the rotor 12.

The stator 13 is fixed to the housing 11, and thread grooves are machined on its outer surface (eight surfaces). .

The centrifugal compression pump 20 is composed of an impeller and a differential user, and in this embodiment, it incorporates two stages of centrifugal compression pumps NO, 1, and Nα2 connected in series.

The Nα1 centrifugal compression pump is composed of an impeller 25 and a differential user 26, and the N022 centrifugal compression pump is composed of an impeller 27 and two differential users. impeller 2
5 and 27 and differential users 26 and 28 have the same shape.

The shaft 19 is supported by an upper ball bearing 30 and a lower pole bearing 31. The shaft 19 includes a rotor 12, an impeller 25 of a No. 1 centrifugal compression pump, an impeller 27 of a No. 2 centrifugal compression pump,
A rotor (not shown) of a motor 32 is also attached.

The schematic structure of the impeller 25.27 is shown in Figure 2a (plan view).
b (front sectional view).

The schematic structure of the differential user 26, 28 is shown in FIGS. 3a (top view) and 3b (front sectional view).

Now, in the vacuum pump of this embodiment, since the gas is in a viscous flow region in a transient state at the beginning of pump operation, the centrifugal compression pump mainly performs the evacuation action. Due to the axial compression action of the impeller 14 attached to the rotor 12, the gas taken in from the intake port E is transferred between the rotor 12 and the housing 1.
1 and the stator 13 to reach the suction port H of the centrifugal compression pump 20.

Next, the gas is given a large centrifugal force by the impeller 25 of the Nα1 centrifugal compression pump which is rotating at high speed, flows from the center of the impeller 25 to the outer periphery, and then goes around the lower part of the impeller 25. The gas flow is disturbed and becomes turbulent.

A diffuser 26 installed opposite the lower surface of the impeller 25 rectifies this turbulent gas flow.

The rectified gas is sucked into the Nα2 centrifugal compression pump,
A large centrifugal force is again applied by the impeller 27 to reach the lower surface from the center to the outer periphery of the impeller 27, and after being rectified by the diffuser 28, it is discharged into the atmosphere from the exhaust port (2). The impeller of the centrifugal compression pump 20 has a shape suitable for discharging a large amount of gas in a viscous flow region, and can achieve a high pumping speed. After this evacuation progresses and the gas flow near the suction port E of the vacuum pump reaches an intermediate flow region, the molecular drag pump 10 mainly acts.

A high compression ratio is obtained by the threaded pump action of the housing 11, rotor 12, and stator 3, and the ultimate pressure near the intake port E reaches I x 10-'' torr.In the subsequent steady state, the centrifugal compression pump 20 acts as an auxiliary pump for the molecular drug pump 10 and serves to discharge gas directly into the atmosphere.

In the above embodiment, the centrifugal compression pump 20 is built inside the molecular drag pump 10, but as another method of configuring the device, a centrifugal compression pump 20 may be installed in the lower part (in the drawing) of the molecular drag pump 10. There is also a method of configuring the pump 20 and arranging the motor 32 inside the molecular drag pump 10, and the same effect can be obtained.

(Effects of the Invention) According to the device of the present invention, from atmospheric pressure to
．． It can be evacuated to X 10-'torr.

Furthermore, since no oil is used in the exhaust path, a clean vacuum can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a front sectional view of an embodiment of the vacuum pump of the present invention. 2a (top view) and b (front sectional view) are schematic views of the impeller of FIG. 1. FIG. 3a (plan view) and b (front sectional view) are schematic diagrams of the differential user shown in FIG. 1. FIG. 4 is a front sectional view of a conventional vacuum pump. 10...Molecular drug pump, 19...
Shaft, 20...Centrifugal compression pump, 32...Motor Patent applicant: Nichiden Anelpa Co., Ltd. Agent: Kenji Murakami, patent attorney. a Tomoe 5P threeyo A-A A

Claims (1)

[Claims] A housing having an intake port and an exhaust port, a shaft supported by a bearing inside the housing and capable of freely rotating, a rotor attached to the shaft, and a cavity inside the rotor. The stator is fixed to the housing, and the housing, rotor, and stator are combined to produce molecular drag.
A vacuum pump that constitutes a pump and discharges gas sucked in from the intake port from the exhaust port via an exhaust path, wherein a centrifugal compression pump is disposed in the exhaust path, and the rotor and the centrifugal compression pump A vacuum pump characterized by having its impeller share a shaft.