JPH10281089A - Vacuum pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the reliability of a bearing part which is the main part for supporting its rotation in a vacuum pump used in a semiconductor manufacturing equipment. SOLUTION: Pipes 19 and 20 for performing the sucking action of cooling oil by a centrifugal force are installed inside rotating shafts 1 and 2, and nozzles 15 and 16 at the top ends of them are dipped in cooling fluid 18 for cooling and bearing lubrication filled n a cooling fluid tank 17. Also the cooling fluid 18 falls inside the spaces 21 and 22 between the inner walls of the holes inside the rotating shafts 1 and 2 and the outer walls of the pipes 19 and 20 after it has been sucked to a height of bearings 4 and 5, and returns to the cooling fluid tank 17. By this, the rotating shafts 1 and 2 and the inner rings of the bearings 4 and 5 are cooled, the amount of thermal expansion of the inner rings relative to the outer rings of the bearings 4 and 5 is suppressed from increasing excessively, and a contact pressure between the balls inside the bearings and the inner and outer rings is prevented from increasing excessively. Thus the high reliability of the bearing part can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a vacuum pump used for semiconductor manufacturing equipment and the like.

[0002]

2. Description of the Related Art As shown in FIG. 5, a pump body portion for performing a gas suction / discharge operation of a conventional positive displacement dry vacuum pump has rotating shafts 103 and 104 having a housing 100 and a pair of rotors 101 and 102 and these rotary shafts. Gears 105 and 106 and the rotating shaft 10 for synchronously rotating the
The motor 107 as a power source is installed separately from the pump body, and the power is transmitted by a plurality of gears 108 and 109. In the positive displacement dry vacuum pump having two rotors having such a configuration, the rotation speed cannot be increased due to the contact-type synchronous rotation using the timing gear, and the suction / discharge volume per rotation and the rotation speed are reduced. In order to increase the pumping capacity determined by the product, the size of the rotor that performs the pumping operation increases, and many gears are required for power transmission and synchronous rotation. Since all the gears transmit power by contact, lubricating oil must be supplied to the contacting parts of the gears to prevent wear and seizure, and this lubricating oil does not leak to the vacuum exhaust path. In addition, there are problems such as the necessity of oil seal parts and the mechanical contact of a plurality of gears causing vibration and noise.

In order to solve the above-mentioned problems (1) to (4), the inventors of the present application have arranged a built-in type motor on each rotating shaft on which a rotor of a positive displacement vacuum pump composed of a combination of two rotors is installed. In addition, by operating these two shafts synchronously by electronic control, there is no gear wheel for power transmission and synchronization, and a high-speed small-sized rotor with a simple structure and a small size is provided. This is proposed by Japanese Patent Application Laid-Open No. 4-175541.

[0004]

The above-described vacuum pump for synchronously operating two shafts by electronic control has a built-in structure in which motors are directly connected to respective rotating shafts. Therefore, the rotor can be easily rotated at a high speed, and as a result, the size of the entire apparatus can be reduced.

On the other hand, however, the following heat-generating element parts are arranged in a condensed configuration in a small space. That is, the heat generated by the compression of the transport gas in the rotor of the pump, the heat generated by sliding in the bearing, and the heat generated by the eddy current loss in the motor rotor. . As a result, there has been a problem that the temperature of the member has a major effect on the reliability and life of the bearing.

If the housing holding the stator of the motor is cooled by circulating cooling water or the like, the temperature rise of the entire pump can be suppressed. However, the temperature difference between the fixed side, which is easy to cool, and the rotating shaft, which is in a thermally isolated state, is insignificant. As a result of analyzing the temperature distribution of each part in detail, the inventors of the present application have revealed that the temperature of the inner ring of the ball bearing is considerably higher than that of the outer ring, particularly in the bearing part. Therefore, the inner ring is thermally expanded excessively with respect to the outer ring, the clearance inside the bearing is reduced, and the pressure of contact between the ball of the bearing and the inner ring and between the ball and the outer ring becomes abnormally large. The problem was that the length was significantly reduced or the bearing was seized.

An object of the present invention is to improve the bearing reliability of a positive displacement dry vacuum pump that operates synchronously by such electronic control.

[0008]

SUMMARY OF THE INVENTION In view of the above-mentioned object, a first aspect of the present invention is characterized in that a cooling means for cooling a rotating shaft and an inner ring of a bearing with a cooling fluid circulated in the rotating shaft is provided. A vacuum pump.

According to a second aspect of the present invention, in the first aspect, the cooling liquid is circulated using rotation of the pipeline.

According to a third aspect of the present invention, in the first aspect, the coolant is circulated by a forced oil supply pump for circulating the coolant, which is provided separately from the housing.

According to a fourth aspect of the present invention, in the first, second, and third aspects, a part of the coolant is supplied as lubricating oil for a bearing that supports the rotating shaft.

A fifth aspect of the present invention is directed to the first, second, and third aspects.
In the invention, the cooling effect is provided only to the bearing portion without cooling the rotor.

According to a sixth aspect of the present invention, in the fifth aspect, the flow path of the cooling liquid is formed from the end of the rotating shaft to the vicinity of the position where the bearing is arranged.

According to the present invention, a vacuum pump having high bearing reliability can be obtained.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the first aspect of the present invention, a plurality of rotors housed in a housing, a bearing for supporting a rotating shaft of these rotors, and a plurality of rotors are independently provided. A displacement type vacuum pump comprising a plurality of motors, each of which is provided with cooling means for cooling an inner ring of a rotating shaft and a bearing by a cooling liquid circulated in the rotating shaft, wherein heat of the inner ring with respect to an outer ring is provided. By suppressing the expansion, the contact pressure between the ball of the bearing and the inner and outer rings is prevented from becoming excessive, and seizure of the bearing is prevented.

According to a second aspect of the present invention, as the cooling means of the first aspect, the cooling liquid is sucked up to near the upper end of the shaft in a pipe inserted into the axis of the rotating shaft by utilizing the centrifugal force of rotation. Further, a passage is provided for returning the sucked cooling oil to the coolant tank provided at the bottom of the pump through the inside of the rotating shaft and the housing, and while the coolant circulates in the rotating shaft, the passage of the rotating shaft and the bearing inner ring is provided. Has the effect of removing heat.

According to a third aspect of the present invention, as the cooling means of the first aspect, a fixed conduit for circulating a cooling liquid which is disposed at the axis of the rotating shaft and does not contact the rotating shaft is separately provided,
This fixed conduit is connected to a forced oil supply pump for circulating the coolant, which is driven by a drive source different from the drive motor for the rotary shaft, and a space formed by the inner wall of the rotary shaft and the outer wall of the fixed conduit. Is formed as a return passage for the coolant and a heat absorbing wall of the rotating shaft and the bearing inner ring, thereby suppressing the temperature rise of the rotating shaft.

According to a fourth aspect of the present invention, the rotary shaft is provided with a small-diameter hole through which the coolant can flow radially from the axis of the rotary shaft. Has the effect of being supplied as lubricating oil for bearings that support.

The invention according to claim 5 and claim 6 is as follows.
A cooling fluid flow passage is formed so that a main cooling effect can be obtained only in the vicinity of the bearing of the rotating shaft and the rotor, and the vacuum pump of the present invention is used in a process of generating a reactive product. When applied, the rotor and the gas exhaust path so that the reactive product is prevented from solidifying due to temperature drop and pressure increase at the discharge side of the pump and discharged to the downstream side of the vacuum pump in a gaseous state. Is maintained at a high temperature.

FIG. 1 shows an embodiment of the present invention.
This will be described with reference to FIG. (Embodiment 1) FIG. 1 is a front sectional view of a vacuum pump according to a first embodiment of the present invention. 1st rotation axis 1, 2nd
The rotating shaft 2 is supported by bearings 4 and 5 housed in a housing 3. First rotating shaft 1 and second rotating shaft 2
The cylindrical rotors 6 and 7 are fitted to. Each rotor 6,
Rectangular screw grooves 8 and 9 are formed on the outer peripheral surface of 7 so as to mesh with each other. The sealed space formed by being surrounded by the concave portions of the meshing portions of the two screw grooves 8 and 9 and the convex portions of the screw grooves of the casing 10 and the opposed rotors 6 and 7 is such that the two rotating shafts 1 and 2 are in opposite directions. The volume changes periodically due to the rotation in synchronism with the rotation, and the suction / discharge operation is repeated by the volume change.
Rotor portions 11 and 12 of a built-in type servo motor for applying a driving force to the rotary shafts are provided below the first rotary shaft 1 and the second rotary shaft 2.
4 are provided. In this embodiment, both rotating shafts 1, 2
A resolver utilizing an electromagnetic induction action is used to detect the rotation angle and the rotation speed of the motor. A resolver is a type of rotary transformer that detects a rotation angle by a voltage change induced when an alternating current is applied to the primary side.

At the lower ends of the rotary shafts 1 and 2, nozzles 15 and 16 are provided for sucking up a cooling liquid, and are immersed in a cooling liquid 18 filled for cooling and bearing lubrication. I have. The nozzles 15 and 16 are provided on the rotating shafts 1 and 2 for sucking the coolant 18 by centrifugal force.
When the coolant 18 rises to the upper part of the rotating shafts 1 and 2, the flow changes in the radial direction by centrifugal force. The space 21, 22 between the inner wall of the hole and the outer wall of the conduit 19, 20 falls by its own weight and returns to the oil tank 17. When the coolant 18 falls along the inner walls of the holes of the rotating shafts 1 and 2, the difference in thermal expansion between the inner and outer rings of the bearings 4 and 5 is suppressed by removing the heat of the rotating shaft and the inner rings of the bearings 4 and 5. The contact pressure between the ball in the bearing and the inner and outer rings is prevented from abnormally increasing. FIG. 2 shows the relationship between the temperature difference between the inner and outer races of the ball bearing and the fatigue life of the bearing, limited to the bearing configuration such as the bearings 4 and 5 in FIG. Referring to FIG. 2, when the temperature difference between the inner and outer rings is 50 degrees, the life is expected to be about 1/30 of that when the temperature difference is 10 degrees, and the possibility of seizure occurring in a very short time is high. I understand.

The coolant 18 is provided above the rotating shafts 1 and 2.
Small-diameter hole 2 communicating from the circulation paths 21 and 22
In some cases, bearings 4 and 5 are provided through the holes 23 and 24 by centrifugal force acting on the coolant 18.
The coolant 18 flowing to the side performs lubrication and heat absorption on the bearings 4 and 5, flows through coolant return passages 25 and 26 provided in the casing 10, and returns to the coolant tank 17.

FIG. 1 shows a method of using a centrifugal force to suck up a coolant to a bearing position. However, if a predetermined pressure and flow rate required for cooling can be obtained, a viscous shaft having a screw-shaped shaft end may be used. Pumps and positive displacement pumps such as trochoids,
The same effect can be obtained even if a cooling liquid circulation mechanism is constituted by various self-contained pumps utilizing the rotation of a shaft.

(Embodiment 2) FIG. 3 shows a second embodiment of the present invention. The basic structure is the same as that of the first embodiment, except that there is no nozzle at the lower end of the rotating shafts 1 and 2, and the tube 29 inserted in the shafts is completely separated from the rotating shafts 1 and 2 and cooled. It is fixed to the bottom of the liquid tank 17. This pipe 29 for sending the coolant 18 to the vicinity of the upper end of the shaft penetrates the bottom plate of the coolant tank, and a circulation liquid pump 30 separately installed outside the pump via a pipe 27 arranged outside the pump.
Is connected to The coolant 18 is temporarily stored in the coolant tank 17.
From the forced oil pump 30 through the pipe 28, and from the forced oil pump 30 through the pipe 29 to the rotating shaft 1,
It is sent to the top of the second hole. As in the first embodiment, the heat absorption is performed while passing through the spaces 21 and 22 between the inner walls of the holes of the rotating shafts 1 and 2 and the outer wall of the tube. The route in which the coolant 18 returns to the coolant tank 17 when a part of the coolant 18 is used for lubricating the bearings 4 and 5 may be considered to be the same as in the first embodiment.

(Embodiment 3) FIG. 4 shows the case where the vacuum pump of the present invention is applied to the case of exhausting a gas that generates a reactive product among the processes such as CVD and etching. FIG. 14 shows a vacuum pump according to a third embodiment in which a coolant flow passage is formed so as to obtain a main cooling effect only in the vicinity of a bearing. Ammonium chloride, aluminum chloride, T
In a process in which a reactive product such as EOS is generated, the casing 31 and the rotor portions 32 and 33 are compressed by heat so that the gas is maintained without being solidified on the discharge side of the pump where the gas partial pressure is increased. Rotor parts 32 and 3 of the rotating parts that perform a pumping operation so as to maintain the high temperature state.
Reference numeral 3 denotes an example in which a cooling liquid circulation path is provided so that only the bearing portion has a cooling effect without cooling as much as possible.
This is different from the vacuum pump, which aims to increase the reliability of the bearings only for the purpose of cooling, and suppresses the thermal expansion of the rotor by cooling the entire pump rotor to maintain a small gap with the casing. Means

[0026]

As described above, according to the present invention, in a small-sized vacuum pump using the proposed high-speed synchronous operation system by electronic control, the height of the bearing portion, which is necessary to support its rotation even in the high-speed rotation region, is improved. An advantageous effect that reliability can be secured is obtained.

[Brief description of the drawings]

FIG. 1 is a front sectional view showing one embodiment of a vacuum pump of the present invention.

FIG. 2 is a diagram showing the relationship between the temperature difference between the inner and outer rings of the bearing of the vacuum pump shown in FIG. 1 and the expected life;

FIG. 3 is a front sectional view showing a second embodiment of the vacuum pump of the present invention.

FIG. 4 is a front sectional view showing a third embodiment of the vacuum pump of the present invention.

FIG. 5 is a front sectional view showing the structure of a conventional vacuum pump.

[Explanation of symbols]

 1, 2 Rotary shaft 3 Housing 4, 5 Bearing 6, 7 Rotor 10 Casing 11, 12 Rotor part of servo motor 13, 14 Rotary position sensor 15, 16 Nozzle 17 Coolant tank 18 Coolant 19, 20 Pipeline 25, 26 Coolant return passage 29 Pipe 30 Forced lubrication pump 31 Housing 32, 33 Rotor part

Claims (6)

[Claims] A plurality of rotors housed in a housing; a bearing for supporting a rotating shaft of the rotors;
A gas suction port and a discharge port formed in the housing, a plurality of motors for independently rotating the plurality of rotors, and detection means for detecting the rotation angle and the number of rotations of the motor, A positive displacement type in which gas is taken in and exhausted by utilizing a change in volume of a closed space formed by the plurality of rotors and the housing by synchronously rotating the rotors using a signal from the detection means. A vacuum pump, comprising: cooling means for cooling the rotating shaft and the bearing by circulating a cooling liquid in the rotating shaft. 2. A cooling liquid circulation means provided as a cooling means has a pipe line for cooling liquid circulation inserted at the axis of a rotary shaft, and rotates the rotary shaft and the inserted pipe line. The pump is configured as a self-contained pump that pumps the coolant from a coolant tank provided at the bottom of the housing, and a return passage for returning the sucked coolant to the coolant tank is provided in the rotary shaft. 2. The vacuum pump according to claim 1, wherein the vacuum pump is provided in the housing. 3. As a cooling liquid circulation means provided as a cooling means, a fixed conduit for cooling liquid circulation not in contact with the rotation shaft is provided at the axis of the rotation shaft. It is driven by a drive source different from the motor for rotating the rotor and is connected to a forced oil pump for cooling liquid circulation installed separately from the housing, and is connected to the inner wall of the rotating shaft and the outer wall of the fixed conduit. 2. The vacuum pump according to claim 1, wherein the formed space is configured as a return passage for the coolant and a heat absorbing wall of the rotating shaft and the bearing inner ring. 4. The cooling means includes a small-diameter hole radially extending from the shaft center near the fitting of the rotating shaft with the bearing, and a part of the coolant is supplied as lubricating oil for the bearing supporting the rotating shaft. 4. The vacuum pump according to claim 1, wherein the vacuum pump is used. 5. The rotating shaft according to claim 1, wherein a cooling fluid flow passage is formed in a part of the rotating shaft so that a main cooling effect is obtained only in the vicinity of the bearing. The described vacuum pump. 6. The passage according to claim 5, wherein the flow passage is formed from the end of the rotating shaft to a position near the position where the bearing is disposed, the rotor side is a sealed end, and not formed near the position where the rotor is disposed. Vacuum pump.