JPH0819906B2 - Vacuum pump and vacuum pump - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to a cylindrical cylinder,
The present invention relates to a vacuum pump including a reciprocating piston and a vacuum exhaust device including the vacuum pump.

[0002]

2. Description of the Related Art Conventionally, various types of vacuum pumps are known. The oil rotary pump is the most common pump that can exhaust air from atmospheric pressure, and is widely used in various fields. However, since the oil in the pump is inevitable that the oil in the pump diffuses back to the vacuum container side, in the field where a clean vacuum is required such as semiconductor device manufacturing equipment and food manufacturing equipment, the oil rotary pump Measures have been taken to prevent pollution, and recently, roots-type and screw-type vacuum pumps with less oil pollution have been developed.

In the above-mentioned roots type pump, a pair of rotors are arranged side by side with parallel rotating shafts at a fine interval.
In addition, the rotor and the cylindrical casing are assembled with a small gap maintained. The operation is such that each rotor is rotated at a high speed in the opposite directions, and gas is confined between the rotors and transferred by volume to the exhaust side, which is usually composed of 5 to 6 stages. Further, the screw type pump is designed to rotate at a high speed in a state where a pair of screw teeth are intermeshed with each other. It is a structure that mechanically exhausts.

[0004]

The roots-type and screw-type vacuum pumps have achieved the effect of obtaining an oil-free clean vacuum, but still have the following problems. That is, in the case of a roots type vacuum pump, in order to be able to exhaust from atmospheric pressure to 10 ^-1 Pa, a single stage pump having a fine gap between rotors and between the rotor and the case has 5 to 6 stages. In the case of a screw type vacuum pump, it is necessary to maintain a non-contact fine gap between the teeth of one set of screws.
All vacuum pumps require high part accuracy and assembly accuracy, resulting in high cost because they are difficult to manufacture. Also, in order to obtain the required ultimate pressure, it is necessary to increase the number of stages, which makes the pump large. There was a problem that became.

Further, the roots type and screw type vacuum pumps such as the oil rotary pump described above have a fixed mounting posture, and there is a problem in that a free mounting posture cannot be selected. There was an inconvenience that you had to handle it while keeping the installation posture.

[0006]

The present invention has been made in view of the above problems, and a vacuum pump and a vacuum exhaust device which can obtain a clean vacuum, can be easily manufactured, and can be miniaturized. Is intended to provide. Another object is to provide a vacuum pump that allows the posture of the pump to be freely set when mounting or transporting.

In the vacuum pump of the present invention which achieves the above object, the piston portion is housed in a multistage piston constituted by a reciprocating shaft rotatably supported by a bearing provided with piston portions having different diameters. A cylinder in which a piston chamber is formed is mounted, and a fluid space can be formed between each piston end surface and an inner end surface of the piston chamber by reciprocating movement of a multistage piston, and a passage for communicating the fluid spaces with each other. Is provided inside the multistage piston, and the communication passage / cutoff valve of the passage is constituted by the opening formed in the side wall of the piston portion of the passage and the inner wall of the piston chamber.

Further, another vacuum pump according to the present invention is a multi-stage piston having a reciprocating shaft slidably supported by bearings, and piston parts having different diameters provided on the reciprocating shaft. It is composed of two members that come in and out of contact with each other,
A cylinder having a piston chamber in which the piston portion is accommodated is attached to the multistage piston, and a fluid space can be formed between each piston end face and an inner end face of the piston chamber by reciprocating movement of the multistage piston. A passage for communicating the fluid spaces with each other is provided inside the multistage piston, and a communication / shutoff valve of the passage is connected / disconnected to the two.
It is characterized in that it is formed in the facing portion of the member.

On the other hand, the vacuum exhaust apparatus of the present invention is characterized by comprising a plurality of vacuum pumps as described above and a switching path for connecting the respective vacuum pumps in series or in parallel.

[0010]

According to the vacuum pump of the present invention, when the multi-stage piston is repeatedly reciprocated in the cylinder through the reciprocating shaft, the passage provided inside the multi-stage piston connects and disconnects via the communication / cutoff valve. Repeatedly, the fluid (gas) in the fluid space formed on both sides in the reciprocating direction of each piston
Can be compressed or can be sequentially transferred to another adjacent fluid space via the piston portion without being compressed.

The seal portion of the fluid space for containing the fluid to be transferred is composed of the side wall of the piston portion of the multistage piston and the inner wall of the cylinder, and the side wall of the reciprocating shaft and the inner wall of the cylinder. There is.

As described above, the gap of the seal portion formed by the axially long planar gap is determined by the supporting structure portion of the reciprocating shaft slidably supported by the bearing. Therefore, the piston and the cylinder can be configured in a non-contact manner, oil for lubrication is not necessary, and heat generation due to friction can be reduced, so that a clean vacuum without oil contamination can be obtained.

A high precision is required for the piston and the cylinder in order to secure a very small gap in the seal portion having a long axial gap in the axial direction. In both the piston and the cylinder, the seal portion is a cylindrical surface. Therefore, as compared with the above-mentioned conventional roots type or screw type, the work is significantly easier. Further, since the pump mechanism can be configured in multiple stages with one set of piston and cylinder, a small vacuum pump can be provided.

Furthermore, since it is possible to eliminate the use of oil, it is possible to freely set the posture during mounting and transportation.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Some embodiments of the present invention will be described below with reference to the drawings.

1 and 2 show a vacuum pump according to a first embodiment of the present invention, in which 1 is an integrated multi-stage piston, 2
Is a multi-stage cylinder. Multistage piston 1
As shown in FIG. 2, the reciprocating shaft 3 is integrally provided with a small-diameter piston portion 4 and a cylindrical large-diameter piston portion 5 at an intermediate portion thereof. The upper surface of the piston portion 4 forms the piston end surface 6 and the lower surface forms the piston end surface 7, and the upper surface of the piston 5 forms the piston end surface 8 and the lower surface forms the piston end surface 9. Although the piston portions 4 and 5 are integrally formed with the reciprocating shaft 3, the piston portions 4 and 5 may be fixed to the reciprocating shaft 3 so as to be integrated with each other.

On the other hand, the multi-stage cylinder 2 has a first piston chamber 10 for accommodating the small-diameter piston portion 4 and a second piston chamber 11 for accommodating the large-diameter piston portion 5, which are vertically formed inside. An insertion hole 12 for the reciprocating shaft 3 is formed at the center, and bearings 13a and 13b for slidably supporting the reciprocating shaft 3 are installed at the ends of the insertion hole 12.

The first piston chamber 10 and the second piston chamber 11 are formed over a distance in which the piston portions 4 and 5 can reciprocate (up and down in the figure), and the piston portions 4 and 5 reciprocate. According to the movement, the piston end surface 6 and the cylinder inner end surface 14 of the first piston chamber 10 face each other, and the annular fluid space 15 and the piston end surface 7 and the cylinder inner end surface 16 of the first piston chamber 10 face each other. Fluid space 17, and the piston end surface 8 and the second piston chamber 1
An annular fluid space 19 in which the first cylinder inner end surface 18 faces and an annular fluid space 21 in which the piston end surface 9 faces the inner cylinder end surface 20 of the second piston chamber 11.
However, each can be formed.

Inside the piston portion 4, passages 22,
22 is formed. The passage 22 opens at the piston end surface 6 of the piston portion 4 at the opening 23, and at the outer wall 24 of the piston portion 4 at the opening 25. In addition, inside the piston portion 5, two types of passages 26, 2 are provided.
6, 27, 27 are formed. Out of these passages
The passage 26 opens at the inner wall 28 of the piston portion 5 at the opening 29 and at the piston end surface 9 at the opening 30. On the other hand, the passage 27 opens at the piston end surface 8 of the piston portion 5 at the opening 31 and also at the opening 33.
It opens at the outer wall 32 of the piston portion 5.

On the other hand, a recess 35 is formed in the inwardly directed inner wall 34 of the first piston chamber 10 formed in the cylinder 2. The recessed portion 35 is provided so that when the piston portion 4 is most raised, the passage 2
The second opening 25 is formed at a position facing each other over an angle that faces the opening 25, and has a width that allows the passage 22 and the fluid space 17 to communicate with each other. Also, cylinder 2
The recess 3 is formed in the inward inner wall 36 of the second piston chamber 11 formed in
7 is formed. The concave portion 37 is formed at a position where the opening portion 33 of the passage 27 faces the piston portion 5 when the piston portion 5 is most raised, and is formed at an angle facing the opening portion 33.
In addition, the passage 27 and the fluid space 21 are formed to have a width that allows them to communicate with each other.

In the figure, 38 is an intake port and 39 is an exhaust port. The intake port 38 communicates with a passage 40 formed in the cylinder 2, and an opening 41 of the passage 40 has an opening 41.
1 inwardly facing inner wall 36. The opening portion 41 has a height such that it opens into the fluid space 19 when the piston portion 5 descends most. The exhaust port 39 communicates with a passage 42 formed in the cylinder 2, and an opening 43 of the passage 42 opens to the inner wall of the insertion hole 12. The opening 43 is located at a position where the fluid space 17 and the passage 42 communicate with each other via the groove 44 formed in the side wall of the reciprocating drive shaft 3 when the piston portion 4 descends most.

The cylinder inner end surfaces 14, 16, 18, 20 forming the fluid spaces 15, 17, 19, 21 are
The pressure receiving side of the release valve 45 faces, and the passage 42 that communicates with each release valve 45 and the exhaust port 39 is communicated with the bypass passage 46.
When the pressure in 7, 19 and 21 becomes higher than atmospheric pressure or a predetermined pressure, the release valve 45 is opened so that the fluid space can directly communicate with the exhaust port 39.

The vacuum pump of the above embodiment has a reciprocating drive shaft 3
Is reciprocated by a reciprocating drive mechanism (not shown) as indicated by an arrow A to move the gas on the intake port 38 side to the fluid space 19,
A vacuum container (not shown) which is sequentially transferred to 21, 15, 17 and discharged to the exhaust port 39 side and connected to the intake port 38.
Can be evacuated.

FIG. 3 shows the piston parts 4 and 5 in the most lowered state (a) and the most raised state (b), respectively. Arrows show the manner of gas transfer caused by the reciprocating movement of the piston portions 4 and 5. The arrows shown in (a) are from the state shown in (b) of the pistons 4 and 5 in (a).
It is the state of the process of transitioning to the state shown in Fig. 4, and the arrow shown in (b) is the state of the reverse process.

The gas sucked into the fluid space 19 through the intake port 38 is passed through the passage 2 when the piston portion 5 is most raised.
7 and the fluid space 21 communicate with each other in the recess 37, and as a result, they are transferred to the fluid space 21 side (see FIG. (B)).

The gas transferred to the fluid space 21 is transferred to the fluid space 15 as a result of the passage 26 and the fluid space 15 communicating with each other when the piston portion 5 descends most (see FIG. (A)).

The gas transferred to the fluid space 15 is transferred to the fluid space 17 side as a result of the passage 22 and the fluid space 17 communicating with each other at the recess 35 when the piston portion 4 rises most (see FIG. 2 (b)). ).

Next, the gas transferred to the fluid space 17 is
When the piston portion 4 descends most, the fluid space 17 and the passage 42 communicate with each other through the groove 44, and as a result, the fluid space 17 is discharged through the exhaust port 39 (see FIG. (A)).

When the piston portions 4 and 5 are moved up and down, the gas in the fluid space is temporarily compressed. As a result of being compressed, when the pressure in the fluid space exceeds a predetermined pressure (for example, atmospheric pressure), the release valve 45 is opened and the gas in the fluid space is discharged through the bypass passage 46 to the exhaust port 39. Part is discharged directly. However, since the pressure in the fluid space becomes high due to the compression for a short time immediately after the vacuum container starts exhausting from the atmospheric pressure state, the release valve 45 is always opened and closed during the operation of the pump. It does not repeat. Therefore, the bypass passage 46 provided with the release valve 45 is not necessarily used for all the fluid spaces 15, 17,
It is not necessary to provide it for 19 and 21, and it is possible to make changes such as providing only for the fluid space 19.

In the exhaust operation as described above, the passage that connects the fluid spaces 19 and 21 is constituted by the passage 27, and the flow / shutoff valve of the passage 27 has the opening 33 and the inwardly directed inner wall 36 of the second piston chamber 11. And a concave portion 37 formed in the inward inner wall 36. The passage that connects the fluid spaces 21 and 15 is constituted by the passage 26, and the passage / flow of the passage 26
The shutoff valve is constituted by the opening 29 and the outward inner wall 47 of the second piston chamber 11. Further, the passage that connects the fluid passages 15 and 17 is constituted by the passage 22, and the passage / flow of the passage /
The shutoff valve is composed of an opening 25 and an inwardly directed inner wall 34 of the first piston chamber 10 and a recess 35 formed in the inwardly directed inner wall 34.

When these flow / shut-off valves are closed, the seal portion of each fluid space is such that the outer wall 24 of the piston portion 4 and the inward inner wall 34 of the first piston chamber 10 face each other, and the reciprocating shaft. 3 and the inner wall of the insertion hole 12 face-to-face, the inner wall 28 of the piston part 5 and the outward facing inner wall 47 of the second piston chamber 11 and the outer wall 32 of the piston part 5.
And an inwardly facing inner wall 36 of the second piston chamber 11 in a planar shape.

That is, each of the seal portions can be formed as a plane-shaped gap that is long in the axial direction, and can exert its sealing function without interposing sealing oil or the like. The opposing parts of each are
It suffices that the distance is sufficiently short (50 to 100 μm) with respect to the mean free path of the exhausted gas, and the assembly of the multistage piston 1 and the cylinder 2 does not require an assembling jig, and a normal assembly is required. It can be done during assembly. As a result, manufacturing is easy.

The facing portion forming the seal portion can be brought into contact with each other. For example, the diameter of the piston portion 4 is manufactured with a plus side tolerance, and the diameter of the first piston chamber 10 of the cylinder 2 is manufactured with a minus side tolerance. After the assembly, the multistage piston 1 is reciprocated to move the outer wall 24 of the piston portion 4.
And the inwardly facing inner wall 34 of the first piston chamber 10 wear against each other,
It is possible to obtain a seal portion in which the facing gap is substantially zero.
In this case, it is desirable that the hardness of the outer side wall 24 of the piston portion 4 be smaller than the hardness of the inwardly facing inner wall 34 of the first piston chamber 10, and the material and surface treatment may be considered.

The outer walls 24, 3 of the piston parts 4, 5 are
It is also possible to form annular recessed grooves in the outwardly facing inner wall 47 of the cylinder 2 and the cylinder 2 to mount wear resistant rings, and to interpose a sealing material in each seal portion. Only by mounting the wear resistant ring, it is possible to easily improve the sealing performance of the axially long planar gap.

In the above embodiment, four fluid spaces 1
The maximum volumes of 5, 17, 19 and 21 are made equal to each other. For example, the diameter of the piston part 4 is 80m
m, the diameter of the inner wall 28 of the piston part 5 is 80 mm, the diameter of the outer wall 32 is 110 mm, and the stroke of reciprocating movement is 2
2.5mm, the maximum volume of each fluid space is about 11
0cc and minimum volume can be about 3.5cc. Therefore, with this size, the compression ratio is about 30, the theoretical ultimate pressure is 1 × 10 ⁻¹ Pa, the reciprocating speed is 1800 rpm, and the theoretical pumping speed is about 200 l / min. it can.

FIG. 4 shows the measurement results of the pumping speed of the prototype in which the sizes of the pistons 4 and 5 are as described above.
A pumping speed of about 200 l / min was observed in the range of ⁵ Pa to 10 Pa. At low pressures from around 10 Pa, a reduction in pumping speed was observed.

FIG. 5 shows the pressure measured at the intake port 38 of the prototype, which is 8 × 10 ^-2 Pa. The exhaust port 39 is at atmospheric pressure (about 10 ⁵ Pa), and the fluid space 19 corresponds to the stage 4, the fluid space 21 corresponds to the stage 3, the fluid space 15 corresponds to the stage 2, and the fluid space 17 corresponds to the stage 1. .

Next, FIG. 6 is a graph showing the results of measuring exhaust characteristics by connecting vacuum containers of different volumes to the air supply port 38. The vacuum container up to about 50 l could be exhausted to the ultimate pressure of 10 ^-1 Pa in about 30 minutes.

Next, FIG. 7 shows a vacuum pump according to a second embodiment of the present invention. The structure is almost the same as that of the first embodiment. The piston part has three stages of 48, 49, 50. Correspondingly, six fluid chambers 51, 52, 53, 54, 55, 56 can be formed on both sides in the reciprocating direction of the piston part. It has become.

In this embodiment, it is difficult to make the maximum volumes of the respective fluid spaces equal to each other, and the maximum volumes gradually decrease in the transfer direction from the air supply port 57 to the exhaust port 58. 56 and the exhaust ports 58
Between them, a bypass passage 60 having a release valve 59 interposed is formed in the cylinder 61.

The vacuum pump of this embodiment also has a reciprocating shaft 6.
By reciprocally driving the pistons 48, 49, 50 via the gas passage 2, the gas on the intake port 57 side is moved to the fluid space 55,
It can be sequentially transferred to 56, 53, 54, 51, 52 and discharged to the exhaust port 58.

Next, a vacuum pump according to a third embodiment of the present invention will be described with reference to FIG. Since this embodiment has substantially the same configuration as that of the first embodiment, the same members are designated by the same reference numerals and detailed description thereof will be omitted.

The part different from the first embodiment is the reciprocating shaft 3.
Are bearings 13c and 13d installed on both sides of the cylinder 2.
The vertical recesses 63, 64, 65, 66 are provided in place of the recesses 35, 37 provided for connecting / disconnecting the slidingly and rotatably pivotally supported parts and the passages of the respective parts. It is the part that is.

That is, the vertical recesses 63 and 64 are provided in the lower portion of the inward inner wall 34 of the first piston chamber 10 and the lower portion of the inward inner wall 36 of the second piston chamber 11 of the cylinder 2 (Fig. (C), ( d)). Further, vertical recesses 65 and 66 are provided in the lower part of the outward inner wall 47 of the second piston chamber 11 of the cylinder 2 and the upper part of the outer wall 32 of the piston part 5 (see FIGS. (A) and (b)).

The vertical recesses 63, 64 and the vertical recesses 65,
66 are provided in the same angle direction as viewed from the reciprocating shaft 3, respectively, whereas the vertical recesses 63 and 65 or the vertical recess 6 are provided.
4 and 66 are provided at different angles. That is, when the piston portions 4 and 5 are reciprocally moved through the reciprocating shaft 3, the piston portions 4 and 5 are rotated so that the vertical concave portion 63 and the opening portion 25 and the vertical concave portion 64 and the opening portion 33 face each other. It is changed between the non-opposition and the passages 22 and 27 are connected / disconnected. Similarly, the vertical recessed portion 65, the opening 29 formed in the inner wall 28 of the piston portion 5, the vertical recessed portion 66, and the opening 41 of the passage 40 communicating with the intake port 38 change between facing and non-facing. 26 and 40 are connected / disconnected. On the other hand, on the side wall of the reciprocating shaft 3 below the piston 4, a vertical recess 69
Is formed in the same direction as the direction of one of the openings 28, 29, 33 (right side in the drawing).

With the above construction, when the multistage piston 1 is reciprocated as shown in (a), (b), (c) and (d) of the figure, in the lowering process of (a) and (b), , Passages 40, 26,
42 can be in a communicating state and the passages 27 and 22 can be in a blocking state, whereas in the ascending steps of (c) and (d), the passages 27 and 22 are in a communicating state and the passages 40, 26 and 42 are in a blocking state You can The multi-stage piston is rotated when moving up and down, but the drawing shows the cylinder 2 relatively rotated.

The vacuum pump of this embodiment also has a piston portion 4,
By repeating the rotation of 5 and the reciprocating movement as shown in (a), (b), (c), and (d) of FIG.
The gas can be transferred sequentially to the fluid spaces 19, 21, 15, 17 towards 9. The gas flow in each step is represented by an arrow.

In the case of this embodiment, since the compression operation of the gas in the fluid space due to the reciprocating movement of the piston portions 4 and 5 can be eliminated, the bypass passage provided with the release valve can be omitted and the gas can be eliminated. Since there is no compression, it is possible to make the required power of the drive source for reciprocating the piston parts 4, 5 extremely small.

When exhausting a condensable gas such as water vapor, it is possible to avoid condensation of the gas in the exhaust.

FIG. 9 shows a vacuum pump according to the fourth embodiment of the present invention. Instead of forming the piston parts 4 and 5 of the first embodiment as one body, the piston parts 4 and 5 are composed of two members, a first member 68 and a second member 69, and a second member 69. Slides along the reciprocating shaft 3,
The first member 68 can be separated from and contacted with the first member 68.

The first member 68 constituting the piston parts 4 and 5
And in the second member 69, the passages 70, 71, 72, 7
3, 74, 75, 76, 77, 78 are formed as shown, and the communication / blocking of these passages is accomplished by the first member 68.
And the second member 69 is separated and contacted. 79 is a pin, and 80 is a relief for the pin 79. The same reference numerals as those in the first embodiment are the same components.

FIG. 10 is a diagram for explaining the operation of this embodiment. In the figure, (a) shows a case where the piston portions 4 and 5 are moved in the direction of arrow A and in the direction of arrow B through the reciprocating shaft 3, respectively. In the step of moving in the direction of arrow A, the first member 68 and the second member 69 are separated,
While the passages 73 and 74 are formed between both members, in the step of moving in the direction of the arrow B, the first and second members 68 and 6 are formed.
9 are adjacent to each other, and these passages 73 and 74 are not formed.

The flow of gas in each step is represented by an arrow. Also in the case of this embodiment, the compression operation can be eliminated when the gas in the fluid space is transferred. Therefore, the bypass passage with the release valve interposed can be eliminated, and the required power of the drive source can be reduced. During exhaust,
The third point is that the condensable gas can be prevented from condensing.
It is similar to the embodiment.

FIG. 11 is a schematic view of the fifth embodiment in which the shape of the piston portion is changed. The piston portion 90 has a shape without a recessed portion so as to facilitate processing and improve working accuracy. Although illustration of the fluid passage formed between the piston portion 90 and the cylinder portion 91 is omitted, it goes without saying that the fluid passage is provided in the same way as the first to fourth embodiments.

Next, FIG. 12 is a diagram of a vacuum exhaust device constructed by using the vacuum pump of the above embodiment. The vacuum pumps are designated by P ₁ and P ₂ , and are the same as the first to fifth embodiments.
Any of the vacuum pumps of the embodiments may be used. Between the intake port 38 and the exhaust port 39 of each vacuum pump, a pipe line 81 as shown
Is installed, valves V ₁ , V ₂ and V ₃ are provided in the conduit 81, and a pressure gauge G is provided near the connecting portion 83 with the vacuum container 82.

According to the vacuum exhaust apparatus having the above-described structure, the vacuum pumps P ₁ and P ₂ are switched between the parallel connection state and the series connection state by controlling the opening and closing of the valves V ₁ , V ₂ and V _3. It is possible to switch. That is, the valves V ₁ and V
_{When 3} is opened and valve V ₂ is closed, vacuum pumps P ₁ , P
₂ becomes a parallel connection state, and it is possible to provide a vacuum exhaust device having an exhaust speed twice as high as the exhaust speed of one vacuum pump.
On the other hand, when the valves ₁ and V ₃ are closed and the valve V ₂ is opened, the vacuum pumps P ₁ and P ₂ are connected in series, and a vacuum exhaust device having a low ultimate pressure can be obtained. Valve ₁ , V ₂ , V ₃
It is also possible to perform the opening / closing control by a control device (not shown) according to the output of the pressure gauge G.

Various modes can be considered for the drive mechanism of the reciprocating shaft of each pump. Arrange the reciprocating shafts in series,
It is also possible to install a drive source (not shown) in the middle and drive the vacuum pumps P ₁ and P ₂ with one drive source.
In this case, it may be possible to reduce vibration due to driving by setting the reciprocating movements of the pumps in opposite phases.

In the case of parallel connection, the vacuum pump P ₁
The phase of the communication of the intake port 38 of the vacuum pump P ₂ with the fluid space 19 and the phase of the communication of the intake port 38 of the vacuum pump P ₂ with the fluid space 19 are shifted by 180 degrees to reduce the pulsation of the exhaust gas to the vacuum container 82. be able to.

[0059]

As described above, according to the present invention, it is possible to provide a vacuum pump and a vacuum exhaust device that can obtain a clean vacuum, can be easily manufactured, and can be miniaturized.

[Brief description of drawings]

FIG. 1 is a sectional view of a first embodiment of the present invention.

FIG. 2 is a perspective view of the multistage piston of the first embodiment.

3 (a) and 3 (b) are diagrams for explaining the operation of the first embodiment.

FIG. 4 is a graph showing the relationship between pressure and exhaust speed in the first embodiment.

FIG. 5 is a graph showing pressure distributions at the intake port and the exhaust port of the first embodiment.

FIG. 6 is a graph showing the relationship between exhaust time and pressure in the first embodiment.

FIG. 7 is a sectional view of a second embodiment of the present invention.

8 (a), (b), (c) and (d) are cross-sectional views of a third embodiment of the present invention, respectively, for explaining the operation in accordance with the reciprocating process of the piston portion. .

FIG. 9 is a sectional view of a fourth embodiment of the present invention.

10 (a) and 10 (b) are diagrams for explaining the operation of the fourth embodiment.

FIG. 11 is a schematic sectional view of a fifth embodiment of the present invention.

FIG. 12 is a system diagram showing an embodiment of the vacuum exhaust device of the present invention.

[Explanation of symbols]

1 Multistage Piston 2, 61 Cylinder 3, 62 Reciprocating Shaft 4, 5, 48, 49, 50 Piston Part 6, 7, 8, 9 Piston End Face 10 First Piston Chamber 11 Second Piston Chamber 13a, 13b Bearing 15, 17 , 19, 21, 51, 52, ... 56 Fluid space 14, 16, 18, 20 Inner end face 22, 26, 27, 40, 42, 70, 71, ... 78
Passages 23, 25, 29, 30, 31, 33, 41, 43 Openings 35, 37 Recesses 38, 57 Intake ports 39, 58 Exhaust ports 45, 59 Release valves 46, 60 Bypass passages 63, 64, ... 66 Vertical recesses 68 1st member 69 2nd member 81 Pipe line 82 Vacuum container

Claims (9)

[Claims] 1. A multistage piston comprising a reciprocating shaft rotatably supported by bearings and piston parts having different diameters provided on a reciprocating shaft, and a cylinder having a piston chamber for accommodating the piston part is attached to the multistage piston. By the reciprocating movement of the piston, a fluid space can be formed between each piston end surface and the inner end surface of the piston chamber, and a passage for communicating the fluid space is provided inside the multistage piston.
A vacuum pump, characterized in that an opening formed in a side wall of a piston portion of the passage and an inner wall of the piston chamber constitute a communication / cutoff valve for the passage. 2. The vacuum pump according to claim 1, wherein the fluid spaces formed between the piston end face and the inner end face of the piston chamber of each piston portion of the multistage piston have the same maximum volume. 3. The vacuum pump according to claim 1, wherein the fluid space formed between the piston end surface and the inner end surface of the piston chamber of each piston portion of the multistage piston has a maximum volume that is different for each piston portion. 4. A bypass in which a release valve is provided between at least one of the fluid spaces formed between the piston end surface and the inner end surface of the piston chamber of each piston portion of the multistage piston, and a discharge port. The vacuum pump according to claim 1, wherein a passage is provided. 5. The vacuum pump according to claim 1, wherein the multistage piston is rotatable about a reciprocating shaft. 6. A multi-stage piston comprising a reciprocating shaft slidably supported by a bearing, and piston parts having different diameters provided on the reciprocating shaft. The piston part is composed of two members which separate from and contact each other in the reciprocating shaft direction. A cylinder having a piston chamber in which the piston portion is housed is attached to the multistage piston, and a fluid space can be formed between each piston end face and the inner end face of the piston chamber by reciprocating movement of the multistage piston. A vacuum pump, wherein a passage for communicating the fluid spaces with each other is provided inside the multistage piston, and a communication / cutoff valve of the passage is formed at an opposed portion of the two members that are in contact with each other. 7. The vacuum pump according to claim 6, wherein the fluid spaces formed between the piston end surface and the inner end surface of the piston chamber of each piston portion of the multistage piston have the same maximum volume. 8. A plurality of vacuum pumps according to claim 1,
A vacuum exhaust device comprising a switching path for connecting each vacuum pump in series or in parallel. 9. A plurality of vacuum pumps according to claim 6,
A vacuum exhaust device comprising a switching path for connecting each vacuum pump in series or in parallel.