JP2680156B2 - Vacuum pump - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a vacuum pump having an exhaust port at atmospheric pressure, and more particularly to a vacuum pump suitable for producing a clean vacuum in a semiconductor manufacturing apparatus or the like. [Prior Art] As a conventional vacuum pump, the one described in JP-A-51-38113 is known. The structure of this vacuum pump will be described with reference to FIG. In the figure, since this vacuum pump is vertically symmetrical with respect to the X-X line,
The upper half side will be described. 1 is an intake port 1A and an exhaust port
A housing 1B has a rotary shaft 2 which is rotatably supported in the housing 1 through a bearing 7. In the housing 1, an axial turbo molecular pump stage 3, an additional molecular pump stage 4 and a centrifugal compression pump are provided. Stage 5 and vortex compression pump stage 6
Are sequentially arranged from the intake port 1A side to the exhaust port 1B side. The axial flow turbo molecular pump stage 3 includes a fixed plate 3B attached to the inner wall of the housing 1 and a rotary disc attached to the rotary shaft 2.
3A and 3A are alternately combined. The additional molecular pump stage 4 includes a fixing plate 4B attached to the inner wall of the housing 1,
It is configured by alternately combining disc-shaped impellers 4A attached to the rotary shaft 2. The centrifugal compression pump stage 5 includes a diffuser fixing plate 5B attached to the inner wall of the housing 1 and a rotary shaft 2
It is configured by alternately combining with the impeller 5A attached to.
The vortex compression pump stage 6 is configured by alternately combining a fixed plate 6B attached to the inner wall of the housing 1 and a rotary disc 6A attached to the rotary shaft 2. On the other hand, the rotary shaft 2 is driven via the drive turbine 8,
The drive turbine 8 is connected to an air inlet 9A and an air outlet 9B provided on the side wall of the housing 1. [Problems to be Solved by the Invention] In the vacuum pump having the above-described structure, when the steady state is reached, each pump stage performs a sufficient compression action, and the pressure at the suction port, that is, the ultimate vacuum pressure becomes a sufficiently low pressure. Can be reached However, in the initial so-called transient state of pump operation, it is not possible to obtain a high pumping speed. Since the pressure inside the pump is high in such a transient state, the gas flow is originally a molecular flow, and the axial flow turbo molecular pump stage 3 and the additional molecular pump stage 4 are effective in the intermediate flow.
Has almost no compression action, and in particular, since the additional molecular pump stage has a narrow channel cross-sectional area, on the contrary, the fluid resistance is large and a compression loss is generated for a large flow rate. It is an object of the present invention to obtain a vacuum pump that can obtain a large pumping speed in a transient state at the initial stage of pump operation and that exerts sufficient pressure action even on a molecular flow in a steady state. [Means for Solving the Problems] In order to achieve the above object, the present invention has an intake port, an exhaust port, and a pump stage that performs a pumping action, and in a steady state, a dilute gas in a molecular flow pressure region is used as the intake port. In a vacuum pump that is sucked in from and compressed from the exhaust port, and is discharged from the exhaust port, the pump stage has at least a centrifugal compression pump stage, and the centrifugal compression pump stage is attached to a rotating shaft and has a plurality of retracting blades. It is characterized by comprising a shaped impeller and a fixed disc arranged so as to face the front surface of the impeller. Another feature of the present invention is to have an intake port, an exhaust port, and a pump stage that performs a pumping action, and in a steady state, a lean gas in a molecular flow pressure region is sucked in from the intake port, compressed, and discharged from the exhaust port. In such a vacuum pump, the pump stage has at least a centrifugal compression pump stage, and the centrifugal compression pump stage has an open type impeller having a plurality of retracting blades attached to a rotating shaft, and a front face of the impeller. A fixed disc disposed so as to oppose to each other, a fixed disc disposed so as to oppose the back face of the open type impeller, and a fixed disc disposed on the back face side of the fixed disc in the rotational direction of the impeller. It has a blade provided in the direction. [Operation] The centrifugal compression pump stage functions as a centrifugal compressor in a transient state at the initial stage of pump operation, as a result, a large pumping speed can be obtained, and as a Ziegburn molecular pump for a molecular flow in a steady state. Therefore, a sufficient compression action can be obtained for the molecular flow. That is, the viscous flow is centrifugally compressed by the open type impeller having a plurality of retracting vanes with respect to the viscous flow in the initial stage of the pump movement.
On the other hand, in a steady state of high vacuum, the molecular flow is compressed in a certain direction by the action of the retracting impeller of the open type impeller and the fixed disc arranged so as to face the front surface of the open type impeller. can do. Further, in the case where a fixed disc facing the receiving surface of the open type impeller and a vane provided inward in the rotation direction of the impeller on the back face side of the impeller of the fixed disc are used, In addition to obtaining the action, the back side of the impeller can also act as a Ziegburn pump in the steady state, so that the compression action in the steady state can be further improved. [Embodiment] An embodiment of the present invention will be described below with reference to FIGS. 1 to 7. FIG. 1 shows the overall structure of a vacuum pump according to the present invention. In FIG. 1, this vacuum pump has a housing 11 having an intake port 11A and an exhaust port 11B.
And a rotary shaft 12 rotatably supported in the housing 11 via bearings 21, and a centrifugal compression pump stage 13 sequentially arranged in the housing 11 between the intake port 11A side and the exhaust port 11B side. And a circumferential flow compression pump stage 14. The rotating shaft 12 is driven by a motor 15 connected thereto. As shown in FIG. 2 and FIG. 3, the centrifugal compression pump stage 13 has an open impeller 13A, which has a plurality of blades 16 inwardly facing the rotation direction on the back surface and is attached to the rotation shaft 12.
As shown in FIGS. 2 and 4, a blade attached to the inner wall of the housing 11 and facing the back surface of the impeller 13A (the surface on which the blade 16 is not provided) faces inward with respect to the rotation direction.
A fixed disk 13B provided with a plurality of 17 is alternately arranged in parallel. The diameter of the rotating body of the centrifugal compression pump stage 13 is larger than the diameter of the rotating body of the circumferential flow compression pump stage 14 described later. As shown in FIGS. 5 and 6, the circumferential flow compression pump stage 14 includes an impeller 14A attached to the rotary shaft 12 and having a plurality of blades 18 radially provided on the outer peripheral surface thereof. As shown in FIGS. 7 and 7, a fixed disk 14B attached to the inner wall of the housing 11 and having a U-shaped groove 19 on the surface facing the surface of the impeller 14A (the surface on which the blade 18 is provided). 5 and 7 are alternately arranged in parallel, and as shown in FIGS. 5 and 7, a hole 19A is formed at the terminal end of the groove 19 to form an air passage 20. The diameter of the circumferential flow compression pump stage 14 on the outlet side of the rotor is smaller than the diameter on the inlet side thereof.
As a result, the rotational power of this portion can be reduced. Next, the operation of the present embodiment will be described. In the transient state at the initial stage of pump operation, the inside of the pump is entirely under a high pressure close to the atmospheric pressure, and a viscous flow of gas is generated, so that the centrifugal compression pump stage 13 functions as a centrifugal compressor. That is, the centrifugal compression pump stage impeller 13A functions as a compressor impeller, and the flow path formed between the impeller 13A and the fixed disk 13B between the impellers 13A and 13B forms a flow from the outer diameter side to the inner diameter side. Work as a return channel to guide you to. Since the impeller 13A has a compression function, the centrifugal compression pump stage 1
As 3, it can act as a compressor to flow a large amount of flow rather than as a pressure loss portion. In a steady state in which the compression ratio of the circumferential flow compression pump stage 14 is increased and the inlet pressure of the circumferential flow compression pump stage is sufficiently low, that is, in the steady state where this pressure is several Torr or less, centrifugal force is applied. The gas flow near the inlet of the compression pump stage 13, that is, near the suction port 11A of the vacuum pump becomes an intermediate flow or a molecular flow, and the centrifugal compression pump stage 13 acts as a Ziegburn molecular pump. That is, the impeller 13A having the blades 16 acts as a rotating disc having a spiral groove,
In combination with the back surface of the fixed disk 13B (the surface on which the blades 17 are not provided), it functions as a Ziegburn molecular pump that compresses from the inner diameter side toward the outer diameter side. Further, the fixed disk 13B provided with a plurality of blades 17 acts as a fixed disk having a spiral groove processed, and in combination with the back surface of the impeller 13A (the surface where the blades 16 are not provided), from the outer diameter side. It works as a Ziegburn molecular pump that compresses toward the inner diameter side. Similarly, in the steady state, the gas flowing into the circumferential compression pump stage 14 is sufficiently compressed in the centrifugal compression pump stage 13, so that the volume flow rate is almost zero. That is, the circumferential flow compression pump stage 14 is operated in a state close to the dead state, but since the circumferential flow compression pump stage has a characteristic that a high compression ratio can be obtained in the dead state, the number of stages is small. A sufficiently low ultimate pressure can be reached. Number of centrifugal compression pump stages 13, circumferential flow compression pump stages 14,
The pump rotation speed is the number of Torr at which the pressure at the boundary between the two stages switches between viscous flow and intermediate flow in steady operation.
To be set. Normally, 1 to 3 centrifugal compression pump stages
By combining 6 to 10 stages and circumferential flow compression pump stages, the pressure at the intake port 11A of the pump can reach 10 ^-3 to 10 ^-4 Torr. EFFECTS OF THE INVENTION According to the present invention, the centrifugal compression pump stage functions as a centrifugal compressor in a transient state at the initial stage of pump operation, and a large exhaust speed can be obtained. It also acts as a Ziegburn molecular pump for steady state molecular flow,
There is an effect that a sufficient compression action can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view showing the entire structure of a vacuum pump according to the present invention, FIG. 2 is a sectional view showing details of a centrifugal compression pump stage of the vacuum pump shown in FIG. 1, and FIG. 2 is a view taken along the line III-III in FIG. 2, FIG. 4 is a view taken along the line IV-IV in FIG. 2, and FIG. 5 shows the details of the circumferential flow compression pump stage of the vacuum pump shown in FIG. A sectional view, FIG. 6 is a view taken along the line VI-VI in FIG. 5, FIG. 7 is a view taken along the line VII-VII in FIG. 5, and FIG. 8 is a longitudinal sectional view of a conventional vacuum pump. 11 …… Housing, 11A …… Intake port, 11B …… Exhaust port, 12
...... Rotary shaft, 13 …… Centrifugal compression pump stage, 13A …… Open type impeller, 13B …… Fixed disc, 14 …… Circumferential flow compression pump stage, 14A …… Impeller, 14B …… Fixed disc , 16, 17, 18 ...
... feathers.

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Minoru Taniyama               502 Kandate-cho, Tsuchiura-shi, Ibaraki Pref.               Hitachi Machinery Laboratory (72) Inventor Shin Terashima               502 Kandate-cho, Tsuchiura-shi, Ibaraki Pref.               Hitachi Machinery Laboratory                (56) References JP-A-51-38113 (JP, A)

Claims (1)

(57) [Claims] In a vacuum pump that has an intake port, an exhaust port, and a pump stage that acts as a pump, and in a steady state, a lean gas in a molecular flow pressure region is sucked in from the intake port, compressed, and discharged from the exhaust port, the pump stage is An open type impeller having at least a centrifugal compression pump stage, the centrifugal compression pump stage being attached to a rotating shaft and having a plurality of backward impellers, and a fixed disc arranged so as to face the front face of the impeller. And a vacuum pump. 2. In a vacuum pump that has an intake port, an exhaust port, and a pump stage that acts as a pump, and in a steady state, a lean gas in a molecular flow pressure region is sucked in from the intake port, compressed, and discharged from the exhaust port, the pump stage is An open type impeller having at least a centrifugal compression pump stage, the centrifugal compression pump stage being attached to a rotating shaft and having a plurality of backward impellers, and a fixed disc arranged so as to face the front face of the impeller. And a fixed disc disposed so as to face the back surface of the open type impeller, and a blade provided on the back surface side of the fixed disc inward of the impeller inward in the rotational direction of the impeller. A vacuum pump characterized by that. 3. The vacuum pump according to claim 2, wherein a plurality of blades are attached to a fixed disc facing the back surface side of the open type impeller. 4. The vacuum pump according to claim 2 or 3, wherein the centrifugal compression pump stages are provided in multiple stages.