JPS61123793A - Roots vacuum pump - Google Patents

Abstract

PURPOSE:To improve sealing capability between working chambers and bearing chambers in sidewalls of a roots vacuum pump by forming openings communicating with the bearing chambers in positions never exposed to the working chambers. CONSTITUTION:Openings formed in parts of side wall members 8, 8a of a roots vacuum pump which are never exposed to working chambers are communicated with bearing chambers through communicating routes 14, 14a. Therefore, pressure within the bearing chamber 7 always becomes equal to pressure on the side of a pump room 1 in seal parts 13b, 13c of a rotor shaft 5, with the result that the pressure difference near the seal parts becomes close to 0. As a result, leakage of lubricating oil in the bearing chambers to the working chambers through the seal parts can be prevented, and unnecessary air flows do not occur, so that air-exhausting capability for creating vacuum can be improved.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is a Roots vacuum pump that is mainly used in combination with an auxiliary pump such as an oil rotary pump and is suitable for vacuum evacuation from medium and low vacuum regions to high vacuum regions. In particular, the present invention relates to a Roots vacuum pump with measures against oil leakage.

(Prior Art) As is well known, this type of Roots vacuum pump has a pump chamber 1e in which two cocoon-shaped rotors 6e are housed and where suction and exhaust operations are performed, as shown in FIG. 5, and a partition plate between the pump chamber 1e and the pump chamber 1e. 8
It consists of an intermediate chamber 7e which is partitioned by 1.e and is for supporting and driving the rotor shaft 5e to which the rotor 6e is attached.The intermediate chamber 7e is filled with oil 11 for lubricating bearings, gears, etc. The stored oil 11 is stirred and scattered in the intermediate chamber 7e during pump operation. Therefore, as shown in FIG. 2A, a non-contact sealing means 2 such as a labyrinth seal is installed in the gap 20 between the rotor shaft 5e and the partition plate 8e.
If 3 is simply provided, for example, the seal part will not develop its sealing function at all during initial exhaust by the auxiliary pump when the pump is stopped, and even during continued operation, the exhaust pressure will drop rapidly. If this occurs, the evaporation seal effect will not be exhibited, making it impossible to prevent oil from flowing from the intermediate chamber 7e to the pump chamber 1e. When a contact type seal is used, a large pressure difference close to one atmosphere occurs between the intermediate chamber 7e and the pump chamber 1e, resulting in a disadvantage that the life of the seal member 21 is significantly shortened.

Therefore, in order to solve the above-mentioned drawbacks, in the conventional art, as shown in FIGS. 6 and 7, the intermediate chamber 7e and the suction side of the pump chamber 1e, or the intermediate chamber 7e and the discharge side of the pump chamber 1e are connected. A system has been developed in which the pressure difference between the intermediate chamber 7e and the pump chamber 1e is reduced by communicating them through connecting pipes 22 and 22, respectively. (America
n Vacuum 5ociety published “J, Vac.

Sci, Technol,, Vol, IEL N
o, 3+April 1981 J) (Problems to be Solved by the Invention) However, in the prior art, for example, Fig. 6 (a)
As shown in the figure, when a non-contact seal 23 is applied to the rotor shaft 5e and the suction port 2e side of the pump chamber 1e is communicated with the intermediate chamber 7e, the pressure difference between the suction side pressure P1 and the discharge side pressure P2 increases. Accordingly, air flows from the intermediate chamber 7e to the suction port 2e side of the pump chamber 1e, from inside the pump chamber le to the intermediate chamber 7e via the seal portion 23, and as shown in FIG. Even when the 3e side and the intermediate chamber 7e are communicated with each other, air flows from the outlet 3e side of the pump chamber 1e to the intermediate chamber 7e- and from the acid intermediate chamber 7e into the pump chamber le through the seal portion 23. As a result, the air entrains the oil in the intermediate chamber 7e, causing a situation in which the inside of the pump chamber le is contaminated with oil, and also enters into the seal $23 during the air circulation and forms a film. This poses a serious problem in that the oil that has been used for this purpose drips into the pump chamber le when the pump stops operating. In addition, in the conventional pump, it can be predicted that as the pressure difference between PI and P2 increases, the air flow increases and the pump's exhaust performance deteriorates.

Furthermore, when a contact type seal such as an oil seal 21 is used for the rotor shaft 5e as shown in FIG. Connect to either the intake or exhaust side of the
Even in the case of communication, the pressure P4 in the intermediate chamber 7e
are equivalent to the suction side pressure P1 or the discharge side pressure 'P2 which are communicated, respectively, and as the pressure difference between Pl and 22 becomes larger, the pressure difference acting on both sides of the seal member such as the oil seal 21 also becomes larger, and the pressure difference Since it is practically impossible to remove the pressure difference, the disadvantage that the service life of the sealing member 21 is shortened by the pressure difference has not yet been solved, and the complicated parts of the sealing member have to be replaced repeatedly. This had a big problem in that it had to be done frequently. Furthermore, selecting a sealing member such as the oil seal is extremely difficult as it requires consideration of both the pressure difference and the circumferential rotational speed of the rotor shaft. It also had problems that forced its use.

As described above, in order to eliminate the pressure difference between the intermediate chamber and the pump chamber, there has conventionally been a means for communicating the suction or discharge side of the pump chamber with the intermediate chamber. In reality, it is impossible to balance the pressures acting on the seal portion of the rotor shaft between the pump chamber side and the intermediate chamber side, and even if either non-contact or contact type sealing means is used for the rotor shaft seal, the above-mentioned problems will occur. It had various problems.

The present invention was invented to solve the above-mentioned problems, and its purpose is to balance the pressures on the pump chamber side and the intermediate chamber side that act on the seal portion of the rotor shaft. By using the seal part under good operating conditions, it has a sufficient sealing function, and when a non-contact sealing means is provided on the rotor shaft, it is possible to maintain the seal between the pump chamber and the intermediate chamber as in the conventional case. It is possible to prevent the oil in the intermediate chamber from flowing into the pump chamber without causing an undue air flow, and to improve the vacuum pumping performance of the pump. There is no need to use any expensive or special sealing member, the service life is long, and the troublesome work of replacing the sealing member is also eliminated.

(Means for Solving the Problems) The present invention eliminates the need to communicate the intermediate chamber with either the suction side or the discharge side of the pump chamber as in the past. It was constructed to solve the above problems by communicating with a specific position of the pump chamber, and the gist of the construction is that the rotor 6
．． Two circles B, B or each rotor 6 whose diameter is the minimum external dimension centered on each rotor axis 5.5 of 6.
The pump chamber 1 and the intermediate chamber 7 are located on the inner surface of the partition plate 8 on the pump chamber 1 side, facing the intersection A of the respective circular arc trajectories of the outer end tips 6a and 6a of 6a. A communication hole 14 is provided for communication.

(Function) Therefore, in the Roots vacuum pump characterized by the above configuration, the communication hole 14 is located at an intermediate position between the suction side and the discharge side of the pump chamber 1, and at a position near the rotor shaft 5. Because the pressure in the intermediate chamber 7 is equal to the pressure on the pump chamber 1 side of the sealed portion of the rotor shaft 5. The pump chamber 1 is uniform or approximately uniform and is not subject to pressure pulsations due to pump operation, and the pump chamber 1 acts on both sides of the seal portion.
The side pressure and the pressure inside the intermediate chamber 7 are not affected by the suction pressure and discharge pressure of the pump, and are always in a balanced state.

(Example) Hereinafter, embodiments of the present invention will be described according to an example shown in the drawings.

That is, in Figure 1 (a), (b), and (c), 1
2 shows a pump chamber provided in a casing 4 with an inlet 2 and an outlet 3 facing each other, and inside the pump chamber 1 are cocoon-shaped rotors 6 . 6 is provided.

Reference numerals 7.7a indicate intermediate chambers separated from the pump chamber 1 by partition plates 8 and 8a, and the intermediate chambers 7 and 7a have bearings 9 and 7 that support both ends of the rotor shaft 5.5. It has a gear 10 and the like, and lubricating oil 11 is stored at the bottom thereof. Reference numeral 12 denotes an electric motor connected to one end of one of the rotor shafts 5 and driven to rotate the rotors 6.degree. 6 in opposite directions. Reference numerals 13.13a and 13.13a each indicate a sealing portion at the position of the partition plate 8.8a of the rotor shaft 5.5. /Loom This is a so-called labyrinth seal with a large diameter hole. 14.14a
is the partition plate so as to be located at the exact center of the intersection A of the circular loci drawn by the outer end tips 6a, 6a of the two rotors 6.6, that is, at the exact center between the two rotor shafts 5, 5. The communication holes 14.14a formed on the inner surfaces 24.24a of the pump chamber 1 side of 8 and 8a are shown, respectively.
It extends to the intermediate chambers 7, 7a, and communicates the intermediate chambers 7, 7a with the pump chamber 1.

The present embodiment has the above-mentioned configuration. Next, we will explain its usage and operation. First, this type of Roots vacuum pump is used in conjunction with an auxiliary pump such as an oil rotary pump, and the Roots vacuum pump is installed in advance. When the pump is stopped, only the auxiliary pump is operated to perform evacuation work in the low and medium vacuum range, but when the auxiliary pump is used for evacuation, the gap is considerably larger than the minute gap in the seal part 13.13a. Diameter communication hole 14. , I4a, the intermediate chambers 7, 7a are smoothly evacuated, and no undue flow of air entraining oil occurs. Further, since the intermediate chambers 7, 7a are evacuated through the communication hole 14.14a, no air flow accompanied by oil occurs in the seal portion 13.13a. Furthermore, if the oil 11 stored in the intermediate chamber 7.7a is new oil containing a large amount of air, the intermediate chamber 7.
, 7a becomes a vacuum state, a bubbling phenomenon occurs, but even in this case, the communication hole 14.1
Since the intermediate chambers 7, 7a are quickly evacuated through the intermediate chambers 7, 7a, the bubbling oil does not fill the intermediate chambers 7, 7a, and the oil does not leak into the pump chamber 1. It is prevented. Next, when the pump exhaust atmosphere reaches a predetermined vacuum range, the Roots vacuum pump according to this embodiment is operated, and as a result of the pump operation, the suction port 2 side and the discharge port 3 side of the pump chamber 1 are respectively connected to P1. and P2
This causes a pressure difference. Therefore, the seal portions 13, 13 that perform the sealing function by the rotation of the rotor shafts 5, 5.
Since a is located between the suction and discharge ports 2.3 of the pump chamber 1, the pressure value P3 acting on the reseal portion 13.13a from the pump chamber 1 satisfies Pi<P3<P2. On the other hand, the two rotors 6.6 are almost always present in the communication hole 14.14a, and the width between the end surface 25.25 of the rotor 6.6 and the partition plates 8, 8a is extremely narrow (usually 0.25 mm). Since the opening of the communication hole 14.14a is provided at a position where a gap from 1 to several O0 is formed, the opening of the communication hole 14.14a is easily closed by the rotor 6.6 and becomes a quasi-sealed state. The communication hole 14.14a is not affected by the pressure pulsation of the pump operation, and the communication hole 14.14a is located between the suction and discharge ports 2.3 in the same manner as the seal portion 13.13a.
Since the communication hole 14 is provided at a position near the
The pressure P4 in the intermediate chamber 7.7a communicated through 14a is naturally the pressure P4 on the pump chamber 1 side of the seal portion 13.13a.
3, and the pressure P3 on the pump chamber 1 side of the seal portion 13.13a and the pressure P4 in the intermediate chamber 7.7a are in a balanced state. Therefore, by pump operation, the suction and discharge ports 2.3 of the pump chamber l
Even if a large pressure difference occurs between the side pressures PL and P2, the P3. P4 always maintains a mutually equal pressure state, and the intermediate chamber 7
．． The air in 7a flows through the seal portion 13° 13a or the communication hole 1.
4.14a into the pump chamber 1, which not only prevents the oil 11 from flowing out due to the air flow, but also prevents the oil 11 from flowing out due to the air flow. There is no reduction in exhaust efficiency, and furthermore, the oil in the intermediate chambers 7 and 7a is completely removed from the seal portions 13 and 13.
a and the communication hole 14.14a, the seal portion 13 is closed when the pump is stopped.
There is no possibility that the oil 11 will drip into the pump chamber 1 from the opening 13a and the communication hole 14.14a.

In the above embodiment, the rotor shafts 5, 5 are sealed with a non-contact type labyrinth seal, but the present invention is not limited to this, and other non-contact type seals such as screw pump type seals are used. In addition to a type sealing means, contact type sealing means such as an oil seal may also be used.

That is, FIG. 2 shows an embodiment in which an oil seal is used in place of the seal portion 13.13a of the labyrinth seal in the embodiment described above, and in which the position of the communication hole 14.14a and the like are all the same as in the embodiment described above. To explain this, the pressure P3 on the pump chamber 1 side acting on the oil seals 13b and 13c provided at the positions of the partition plates 8 and 8a of the rotor shafts 5 and 5 and the communication holes 14 and 14a act on the pump. Since the pressure P4 in the intermediate chambers 7, 7a communicating with the chamber 1 is the same pressure or approximately the same pressure, the oil seals 13b, 1
3c will not be subjected to any unbalanced pressure difference on both sides, and its operating conditions will be favorable and its operating life will be extended. Further, when the oil seals 13b and 13c are used for a long time, a slight gap is formed with the rotor shaft 5.5 due to contact wear with the rotor shaft 5.5. Since the pressure P3 on the side of the pump chamber 1 and the pressure P4 in the intermediate chambers 7 and 7a are balanced, the gap is the same as when a non-contact type sealing means similar to the above embodiment is provided. Having a sealing function, it is possible to prevent undue air flow from the intermediate chamber 7.7a into the pump chamber 1 and prevent oil from flowing in the same manner as in the embodiment described above, without replacing any parts of the oil seals L3b and 13c. This makes it possible to prevent air leakage and a decrease in exhaust efficiency.

Further, in each of the above embodiments, the communication hole is bored at the exact midpoint between the two rotor shafts, but the present invention is not limited to this, and the point is that each rotor 6.6
Two circles B, B whose diameter is the intersection A of the respective arcuate trajectories of the outer end tips 6a, 6a, or the minimum outer diameter dimension centered on each rotor axis 5.5 of each rotor 6.6.
It is sufficient that a communication hole 14 is bored in the side surface of the partition plate 8 on the pump chamber 1 side corresponding to the position inside. Kedashi, the above A,
B.

In any position B, the opening of the communication hole 14 is always or almost always semi-sealed at the end face of the rotor 6.6, so that it is not subjected to pressure pulsations and is sealed against the rotor shaft 5.5. This is because the pressure on the pump chamber side of the seal portion and the pressure in the intermediate chamber can be equalized by being located near the seal portion.

In addition, the present invention provides means for expanding the diameter of the labyrinth seal portion of the rotor shaft, or providing continuous notch holes in the labyrinth seal portion, etc., when drilling the communication hole at the B position, for example. However, the present invention resides in a means for forming a separate communication hole in the partition plate, which is independent of the hole in the seal portion, in order to communicate the intermediate chamber and the pump chamber.

Furthermore, the specific number of communication holes according to the present invention is not limited to one, but may be provided in a plurality, and although a diameter of several millimeters is usually sufficient, the specific dimensions can also be changed as desired. In addition, as a means to particularly prevent the oil 11 in the intermediate chamber 7 from entering the communication hole 14 formed in the partition plate 8 as shown in FIG. It is also possible to change the design such that the pipe 15 is connected to the communication hole 14 or the pipe 15 is connected to the communication hole 14.

In addition, the present invention relates to a pump chamber, an intermediate chamber, and a rotor.

The specific structure of the rotor shaft and other parts can be changed within the scope of the present invention.

(Effects of the Invention) As described above, the present invention equalizes the pressure on the pump chamber side of the seal portion of the rotor shaft and the pressure in the intermediate chamber by providing communication holes at specific positions of the partition plate. Therefore, the seal portion can have a suitable sealing function without any uneven pressure difference acting on both sides of the seal portion.

In particular, non-contact sealing means can prevent improper air flow between the intermediate chamber and the pump chamber through the seal, and can also prevent oil from entering the seal and the communication hole. In order to prevent oil leakage into the pump chamber when the pump is operating and oil dripping flow when the pump is stopped, which conventionally occurred due to air flow and oil intrusion into seal parts, etc., the inside of the pump chamber can be completely prevented. The special effect of being able to keep it in a clean state at all times was obtained.

Moreover, since the non-contact type seal eliminates undue air flow between the intermediate chamber and the pump chamber as described above, it is also possible to prevent phenomena that reduce the vacuum pumping efficiency of the pump. It's arrived.

In addition, since an unreasonable pressure difference does not occur on both sides of the sealing member in the contact type sealing means, the usage conditions of the sealing member are improved and its service life is significantly extended compared to the conventional one. In addition, there is no need to use an expensive and special sealing member, so the cost can be reduced, and furthermore, the selection of the sealing member can be made easier, which has great practical benefits.

Furthermore, an important effect of the present invention is that even if the sealing member in the contact type sealing means is worn out and a gap is created between the sealing member and the rotor shaft 1, the pump chamber side pressure of the sealing portion and the intermediate chamber side pressure can be maintained. This was previously considered essential for this type of contact seal because the pressure is maintained in an equal pressure state and no air movement occurs in the seal part where the gap is created, preventing oil from flowing out from the gap. This has the great advantage of eliminating the need for complicated replacement work of the sealing member, facilitating maintenance and management, and further reducing the cost of such parts.

As described above, the present invention has the above-mentioned various special effects in order to solve the various problems that could not be solved conventionally by simply drilling communication holes at specific positions of the partition plate, and also has the above-mentioned various special effects. The presence of the communication hole promotes exhaustion of the intermediate chamber, and has the advantage of being able to suitably deal with the foaming phenomenon especially when new oil is used, and its practical value is great.

[Brief explanation of the drawing]

Fig. 1 shows this embodiment of the Roots vacuum pump according to the present invention, in which (a) is a plan sectional view, and (b) is a sectional view of the same figure (a).
A cross-sectional view taken along the line X-X of FIG. FIG. 2 is a plan sectional view showing another embodiment. FIG. 3 is an explanatory diagram showing the drilling position of the communication hole according to the present invention. FIGS. 4(A) and 4(B) are sectional views of main parts showing other embodiments. Figure 5 (a), (b), Figure 6 (a), (b) 7
Figures (A) and (B) are schematic explanatory diagrams showing conventional examples.

Claims (1)

[Claims] 1. A rotor shaft 5 having a pair of cocoon-shaped rotors 6, 6 provided in the pump chamber 1, and having the rotors 6, 6 attached thereto;
5 is divided into the pump chamber 1 and an intermediate chamber 7 by a partition plate 8.
In the Roots vacuum pump, the pump chamber 1 of the partition plate 8 is configured to have the partition plate 8 and sealing means therein and to be pivotally supported to rotate the rotors 6, 6 in mutually opposite directions. Inside two circular parts B, B whose diameter is the minimum external dimension centered on each rotor axis 5, 5 of the rotors 6, 6 on the inner surface 24 of the side, or the outer end tip of each of the rotors 6, 6. At the position within the intersection part A of each of the arc trajectories of 6a and 6a,
A Roots vacuum pump characterized in that a communication hole 14 is bored for communicating the pump chamber 1 and the intermediate chamber 7. 2. The Roots vacuum pump according to claim 1, wherein the sealing means between the rotors 6, 6 and the partition plate 8 is a non-contact type sealing means such as a labyrinth seal. 3. The Roots vacuum pump according to claim 1, wherein the sealing means between the rotors 6, 6 and the partition plate 8 is a contact type sealing means using an oil seal or the like. 4. The Roots vacuum pump according to claim 1, wherein the communication hole 14 is formed to have a diameter of about several millimeters.