JP2000220640A - Motor and turbo-molecular pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high vacuum from the atmospheric pressure, by securing the clearance of a ceramic gas bearing to the heat in a high frequency rotation condition, even when the clearance of the ceramic gas bearing is set narrow by the reason of the high frequency rotation condition or the like, in a motor using a ceramic gas bearing. SOLUTION: In the rotary body 25 of a motor 10, its outer peripheral part is formed of an inner tube 28, and a dynamic pressure groove is formed on the outer peripheral surface of the inner tube. An outer tube 29 is provided at the outer peripheral side of the rotary body 25. An air bearing 30 (a ceramic dynamic pressure gas bearing) to support the load of the rotary body in the radial direction is composed of an inner tube and an outer tube. In a motor used to a turbo-molecular pump, the clearance is set at 3 to 6 μm, for example, by its exhaust gas speed, the using rotation frequency, and the like. The ceramic material of the inner tube is a silicon carbide, while the ceramic material of the outer tube consists of an alumina, and the thermal expansion coefficient is made smaller in the ceramic material of the inner tube, than in the ceramic material of the outer tube.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor and a turbo molecular pump using a ceramic gas bearing.

[0002]

2. Description of the Related Art For example, a turbo-molecular pump is used in a semiconductor-related apparatus such as a sputtering apparatus, a CVD apparatus, and an etching apparatus, an electron microscope, a surface analysis apparatus, an environmental test apparatus, and the like to obtain an ultra-high vacuum state. . The turbo-molecular pump generates ultra-high vacuum by rotating a rotating shaft having moving blades to create a molecular flow to exhaust gas. In order to obtain an ultra-high vacuum, it is necessary to rotate the rotating shaft of the motor at high speed, and to smoothly rotate at high speed, it is necessary to employ a bearing suitable for high-speed rotation in the motor.

Heretofore, ball bearings have generally been used as bearings for rotary shafts. However, with a pump that creates an ultra-high vacuum, such as a turbo-molecular pump, the lubricating oil injected into the bearings is vaporized due to the high degree of vacuum, and not only is it not possible to obtain an ultra-high vacuum, but also the lubricating oil A problem arises in that it flows into the vacuum chamber and causes contamination. For this reason, a turbo molecular pump using a non-contact type bearing such as an air bearing or a magnetic bearing has been proposed so as not to use a lubricating oil (Japanese Utility Model Laid-Open No. 63-14894, Japanese Unexamined Patent Publication No. -16389). Conventional turbomolecular pumps cannot be pulled from the atmosphere and require an auxiliary pump. By configuring the motor with a gas bearing, a turbo molecular pump that obtains a high vacuum from the atmosphere can be obtained.

[0004] For example, as a bearing structure for supporting a radial load of a rotating shaft, an air bearing in which a pressure gas film is formed on the outer peripheral surface of a rotating body (rotor) of a motor is formed. When the air bearing is, for example, a dynamic pressure air bearing, a predetermined clearance for forming a pressurized gas film is formed around the rotating body, a cylinder is arranged, and a dynamic pressure groove is formed on the outer peripheral surface of the rotating body. . In other words, the air bearing is composed of an outer cylinder (bearing fixed body) fixedly arranged outside with a clearance, and an inner cylinder (bearing rotating body) having a dynamic pressure groove formed on its surface and integrally rotating with the rotating body. It consists of. The inner cylinder and the outer cylinder slide until the rotating body starts to float by the pressure gas film. For this reason, relatively wear-resistant ceramics such as alumina and zirconia have been used as the material of the air bearing.

[0005] In designing a turbo-molecular pump, when the required pumping speed is determined, design values such as the number of blade stages and the number of revolutions are determined. For example, a small turbo-molecular pump needs to rotate at a high speed of 50,000 to 70,000 rpm. Therefore, it is necessary to set the clearance of the air bearing to about 5 μm or less based on the number of rotations.

[0006]

In a turbo-molecular pump, air is exhausted by the relative rotation of a moving blade and a stationary blade to create an ultra-high vacuum state. When the motor rotates at high speed, the air bearing becomes hot due to the viscous friction of the air. On this occasion,
The outer cylinder of the dynamic pressure gas bearing is in a state where heat can relatively easily escape from the outer peripheral surface, whereas the rotating body floating in the air has no escape place for heat, so the inner cylinder and the outer cylinder that constitute the dynamic pressure gas bearing And a temperature difference is generated. Conventional inner and outer cylinders are made of alumina or zirconia, and have a coefficient of thermal expansion of 7 to 8 × 10 ^-6 /
Because the temperature difference was relatively large, the value of clearance greatly changed due to the difference in thermal expansion between the inner cylinder and the outer cylinder caused by this temperature difference.In some cases, the inner cylinder contacted the outer cylinder, and high-speed rotation was obtained by the sliding friction. Was no longer possible.

When an attempt is made to cool the dynamic pressure gas bearing with an air cooling fan in order to remove the heat generated in the dynamic pressure gas bearing, the temperature difference between the inner cylinder and the outer cylinder is reduced because the outer cylinder is forcibly air cooled. It tends to be even larger, making it more difficult to maintain the clearance between the inner cylinder and the outer cylinder. In particular, since the clearance is a value determined to some extent from the design, it is not possible to take measures to greatly change the value, and it is necessary to reduce the clearance in response to recent demands for further downsizing and higher rotation speed of turbo molecular pumps. As a result, the effect of heat generated by the hydrodynamic gas bearing on the clearance cannot be ignored.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a motor using a ceramic gas bearing, even if the clearance of the ceramic gas bearing is set to be narrow for reasons such as high rotation speed. It is another object of the present invention to provide a motor and a turbo-molecular pump which can ensure the clearance of the ceramic gas bearing even with heat during high-speed rotation.

[0009]

In order to achieve the above object, according to the first aspect of the present invention, there is provided a rotating body for rotating a rotating shaft, and an armature disposed on an outer peripheral side of the rotating body. A ceramic gas bearing that supports a radial load of the rotating body, and a non-contact bearing that supports a thrust load of the rotating body, wherein the ceramic gas bearing forms an outer peripheral surface of the rotating body. A bearing rotating body, and a bearing fixed body provided with clearance on the outer peripheral side of the bearing rotating body, wherein the ceramic material of the bearing rotating body has a higher coefficient of thermal expansion than the ceramic material of the bearing fixed body. The point is to be small.

[0010] According to the second aspect of the present invention, a rotating body for rotating a rotating shaft, an armature disposed on an outer peripheral side of the rotating body, and a ceramic gas supporting a radial load of the rotating body. A bearing and a non-contact type bearing that supports a load in the thrust direction of the rotating body, wherein the ceramic gas bearing is provided on a bearing rotating body forming an outer peripheral surface of the rotating body, and on an outer peripheral side of the bearing rotating body. At least the bearing rotor is made of a low thermal expansion ceramic material having a coefficient of thermal expansion of 5 × 10 ⁻⁶ / ° C. or less.

According to a third aspect of the present invention, in the first aspect of the present invention, the ceramic material of the bearing rotating body has a coefficient of thermal expansion of 5 × 10 ⁻⁶ / ° C. or less. According to a fourth aspect of the present invention, in the third aspect, the ceramic material of the bearing fixing body is an oxide.

[0012] In the fifth aspect of the present invention, the second aspect is provided.
In the invention according to any one of the first to fourth aspects, the ceramic material of the bearing rotating body is carbide or nitride. According to a sixth aspect of the present invention, in any one of the first to fifth aspects, an air cooling hole is formed in the motor casing in order to forcibly air-cool an outer peripheral surface of the bearing fixed body of the ceramic gas bearing. did.

According to a seventh aspect of the present invention, there is provided a turbo molecular pump comprising: the motor according to any one of the first to sixth aspects; and a rotor blade provided on the rotating shaft of the motor. And a stationary blade necessary for producing a molecular flow by rotating the moving blade.

According to an eighth aspect of the present invention, in the invention of the seventh aspect, an air cooling means for forcibly air cooling an outer peripheral surface of the bearing fixed body of the ceramic gas bearing is provided. (Operation) According to the first aspect of the invention, the rotating shaft is rotated by the rotating body being rotated by the armature. At this time, the radial load of the rotating body is supported by the ceramic gas bearing, and the thrust load of the rotating body is supported by the non-contact bearing. During high-speed rotation, the bearing rotating body and the bearing fixed body constituting the ceramic gas bearing become hot due to rotational friction heat. Since the bearing rotating body is confined in a non-contact state, the bearing rotating body has a high temperature without a heat escape area.
On the other hand, heat is released from the outer peripheral surface side of the bearing fixed body,
A temperature difference occurs between the bearing rotating body and the bearing fixed body. Here, since the ceramic material of the bearing rotating body on the high temperature side is a material having a smaller coefficient of thermal expansion than the ceramic material of the bearing fixed body on the low temperature side, even if such a temperature difference occurs, a clearance between the two is ensured. easy.

According to the second aspect of the present invention, the rotating shaft is rotated by the rotating body being rotated by the armature. At this time, the radial load of the rotating body is supported by the ceramic gas bearing, and the thrust load of the rotating body is supported by the non-contact bearing. During high-speed rotation, the bearing rotating body and the bearing fixed body constituting the ceramic gas bearing become hot due to rotational friction heat. Since the bearing rotating body is confined in a non-contact state, the bearing rotating body has a high temperature without a heat escape area. On the other hand, since the heat escapes from the outer peripheral surface side of the bearing fixed body, a temperature difference occurs between the bearing rotating body and the bearing fixed body.
Here, at least the bearing rotating body on the high temperature side has a coefficient of thermal expansion of 5 ×
Because it is a low thermal expansion ceramic material of 10 ^-6 / ° C or less,
Even if such a temperature difference occurs, a clearance between the two can be easily secured.

According to the third aspect of the present invention, the first aspect is provided.
In addition to the effect of the invention, the thermal expansion coefficient of the ceramic material of the bearing rotating body is 5 × 10 ⁻⁶ / ° C. or less, so that a clearance between the two can be easily secured.

According to the invention described in claim 4, according to claim 3,
In addition to the effect of the invention of the present invention, since the ceramic material of the bearing fixed body is an oxide, it is easy to set the bearing fixed body to a larger coefficient of thermal expansion than the bearing rotating body, and it is easy to manufacture and process the bearing fixed body. Cheaply.

According to the invention described in claim 5, according to claim 2,
In addition to the same operation as the invention of any one of claims 4 to 4,
Since the ceramic material of the bearing rotating body is carbide or nitride, it generally has better thermal conductivity and higher heat dissipation effect than oxides, and easily obtains high wear resistance.

According to the invention described in claim 6, according to claim 1,
In addition to the effect of the invention according to any one of claims to 5, the outer peripheral surface of the bearing fixed body of the ceramic gas bearing is forcibly air-cooled by the air cooling hole formed in the motor casing. High temperature rise of the ceramic gas bearing can be suppressed.

According to the seventh aspect of the present invention, the motor according to any one of the first to sixth aspects is used in the turbo-molecular pump to rotate the rotor blade. A high degree of vacuum can be achieved by high-speed rotation of the blades.

According to the invention of claim 8, according to claim 7,
In addition to the operation of the invention, the outer peripheral surface of the bearing fixed body of the ceramic gas bearing is forcibly air-cooled by the air-cooling means, so that the rotor blades can rotate at high speed.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] A first embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows a turbo-molecular pump. The housing 2 of the turbo-molecular pump 1 includes an upper housing 3 and
It comprises a lower housing 4 and an annular support block 5 sandwiched between the housings 3 and 4. The housings 3 and 4 are joined by a plurality of bolts 6 while holding the support block 5 therebetween.

At the tip of the upper housing 3, an air inlet 3 serving as a suction port for air exhausted from a vacuum chamber (not shown) is provided.
a is formed. A plurality of stationary blades 7 are attached to the inner peripheral surface of the upper housing 3 using a support member 8 so as to extend inward. An annular support block 9 is fixed to the lower surface of the support block 5.

A brushless motor (hereinafter simply referred to as a motor) 10 is fitted and fixed to the inner peripheral surfaces of the support blocks 5 and 9 via rubber seal members (O-rings) 11 and 12. The motor 10 is arranged in a state where the protruding end of the rotating shaft 13 is located on the side of the intake port 3a. The rotor 14 is attached by fastening a nut 15 to the tip of the rotating shaft 13. The rotor 14 has a substantially cylindrical shape with a bottom, and a plurality of moving blades 16 extending from the outer peripheral surface thereof are arranged in a state of being inserted into the gap between the respective stationary blades 7.

The rotor 14 rotates relative to the motor casing 17 with a very small clearance from the outer peripheral surface thereof. The space on the upper surface side of the support block 5 is an air intake chamber 18, and the space on the lower surface side of the support block 5 is an exhaust chamber 19. A spiral groove 17 a is formed on the upper outer peripheral surface of the motor casing 17 at a position facing the inner peripheral surface of the rotor 14. The motor casing 17 has a plurality of slit holes 17b as air cooling holes formed in a lower portion protruding into the exhaust chamber 19.

When the motor 10 is driven to rotate the rotor 14, the intake port 3 a is provided between the moving blade 16 and the stationary blade 7.
A suction force for drawing air is generated. The drawn air passes through a spiral groove 17 a between the rotor 14 and the motor casing 17, is drawn into the inside of the motor casing 17 from a gap around the rotation shaft 13, and a plurality of air formed at a lower portion of the motor casing 17. Slit hole 17
The gas is exhausted from b into the exhaust chamber 19. The air exhausted to the exhaust chamber 19 is exhausted to the outside through an exhaust port 4 a formed in the lower housing 4. Here, the spiral groove 17a functions as a kind of gas seal, and the spiral groove 17a
A pressure difference is generated in the process of passing through the suction port 3a, which plays a role in increasing the degree of vacuum of the suction port 3a.

An air cooling fan unit 20 as air cooling means is attached to a side of the lower housing 4. The air-cooling fan unit 20 includes a motor 21 and an air-cooling fan 22, and the rotation of the air-cooling fan 22 directs air to a slit hole 17 b formed below the motor 10.

Next, the structure of the brushless motor 10 will be described. As shown in FIGS. 1 and 2, both ends of the motor casing 17 are closed by annular closing members 23 and 24. The rotating shaft 13 is rotatably supported in a state where the rotating shaft 13 is inserted through insertion holes 23a and 24a formed in the axial centers of the closing members 23 and 24.

As shown in FIG. 2, a rotating body 25 is provided on the rotating shaft 13 so as to be integrally rotatable. The rotating body 25 has a built-in field magnet 26. The field magnet 26 is composed of four permanent magnet pieces, and the permanent magnet pieces are arranged in the circumferential direction around the rotating shaft 13 such that magnetic poles adjacent to each other have different polarities. An inner cylinder 28 is fixed to a pair of bushes 27, 27 holding the field magnet 26 from both sides in the axial direction in a state of being externally fitted. The bush 27 has a function of adjusting the balance of the rotating body 25.

Outer cylinder 29 which houses and arranges inner cylinder 28 inside
Is fixed to the motor casing 17 side so as to be coaxial with the motor 10. The inner cylinder 28 and the outer cylinder 29 constitute an air bearing (ceramic dynamic pressure gas bearing) 30 as a ceramic gas bearing. On the outer peripheral surface of the outer cylinder 29, three armature coils 31 as armatures are arranged at equal intervals in the circumferential direction. The mechanical angle in the circumferential direction of each armature coil 31 is set in a range of approximately 90 ° to 120 °. Further, a cylindrical yoke 32 is provided on the inner peripheral surface of the motor casing 17 so as to be located outside the armature coil 31. The bearing rotating body is constituted by the inner cylinder 28, and the bearing fixed body is constituted by the outer cylinder 29.

Each armature coil 3 is provided on the outer peripheral surface of the outer cylinder 29.
Three magnetic sensors (Hall elements) 3 at positions corresponding to 1
3 are provided. The three armature coils 31 and the respective magnetic sensors 33 are connected to a plurality of connector pins 34 (only one is shown in FIG. 2) inserted into the closing member 24. The connector pins 34 are electrically connected to an external control circuit (not shown). Then, the rotation speed detection signal obtained by the magnetic sensor 33 detecting the magnetic pole of the permanent magnet piece constituting the field magnet 26 is:
The feedback of the current flowing through each armature coil 31 is fed back to control the rotating shaft 13 at a constant speed.

Near the front and rear ends in the axial direction of the rotating body 25,
A pair of magnetic bearings 37 and 38 as non-contact type bearings are provided. The rotating shaft 1 includes a pair of magnetic bearings 37 and 38.
3 is supported in the thrust direction. The pair of magnetic bearings 37 and 38 include permanent magnets 39 and 40 fixed to both ends of the rotating body 25 and permanent magnets 41 and 42 fixed to the closing members 23 and 24, respectively. A pair of permanent magnets 39 and 41 forming the magnetic bearing 37 and a pair of permanent magnets 40 and 42 forming the magnetic bearing 38 are arranged such that opposing surfaces of the pair have the same polarity. A repulsive force acts between the two. Permanent magnet 39-4
The material 2 is a neodymium magnet or a samarium magnet.

On the other hand, the inner cylinder 28 and the outer cylinder 29 constituting the air bearing 30 are both made of a sintered ceramic material. The inner cylinder 28 and the outer cylinder 29 are arranged such that their axes coincide with each other, and a predetermined bearing clearance C1 is set between the two. The initial bearing clearance C1 is determined from design values such as the exhaust speed and the number of revolutions of the turbo-molecular pump 1, and is set to, for example, C1 = 3 to 6 μm in the present embodiment used at the number of revolutions of 50,000 to 70,000 rpm. .

The inner cylinder 28 is made of silicon carbide, and the outer cylinder 28 is made of alumina. The coefficient of thermal expansion of silicon carbide is 3 to 4 × 10 ⁻⁶ / ° C., and the coefficient of thermal expansion of alumina is 7 to 8 × 10 ⁻⁶ / ° C. That is, the ceramic material of the outer cylinder 29 has a larger coefficient of thermal expansion than the ceramic material of the inner cylinder 28. In this embodiment, a low thermal expansion ceramic material having a relatively low coefficient of thermal expansion (5 × 10 ⁻⁶ / ° C. or less) is used as the ceramic material of the inner cylinder 28.

As shown in FIG. 3, two air bearing bands 43 and one gas seal band 44 are formed on the outer peripheral surface of the inner cylinder 28. In the air bearing band 43, a plurality of herringbone-shaped dynamic pressure grooves 45 are formed at equal intervals in the circumferential direction. The gas seal band 44 is adjacent to the two air bearing bands 43 on the rotor 14 side, and has a spiral gas seal groove 46 formed on the surface thereof. Further, two circumferential grooves 47 are formed on the outer peripheral surface of the inner cylinder 28 at the boundary between the two air bearing bands 43 and the gas seal band 44. In this example, the groove depth of each of the grooves 45 to 47 is individually adapted. The dynamic pressure groove 45 has a shallower groove depth than the gas seal groove 46, and the circumferential groove 47 has the deepest groove depth.

As shown in FIGS. 2 and 3, an air supply hole 48 is formed in the outer cylinder 29 at a position facing each circumferential groove 47. When the motor 10 is driven, air is introduced into the clearance between the inner peripheral surface of the outer cylinder 29 and the outer peripheral surface of the inner cylinder 28 through the air supply holes 48 by the dynamic pressure grooves 45. When the rotating body 25 rotates in a predetermined direction, the introduction of air into the clearance between the inner cylinder 28 and the outer cylinder 29 is promoted by the action of the dynamic pressure groove 45, and a pressure gas film is formed.
Is supported in the radial direction. Note that the inner peripheral surface of the outer cylinder 28 is polished so as to have a peripheral surface having excellent contact slidability.

Next, the operation of the thus configured device will be described. When the drive of the motor 10 is started and the rotor 14 rotates, air is drawn in from the intake port 3 a by the relative rotation of the moving blade 16 and the stationary blade 7. The drawn air passes through the spiral groove 17a in the gap between the motor casing 17 and the rotor 14, and further reaches the clearance through the gas seal groove 46. The air that has reached the clearance exits into the chamber 36 through the air supply hole 48. And room 3
6 through the slit hole 17b and the motor casing 17
Of the housing 2 through the exhaust port 4a.
It is exhausted to outside. At this time, since the pressure reduction effect is enhanced by the differential pressure generated when air passes through the spiral groove 17a and the gas seal groove 46, a high degree of vacuum is obtained at the intake port 3a by adding the pressure reduction effect at these locations.

When the motor 10 is driven, a high-pressure air reservoir is formed at the center of the air bearing zone 3 by the air introduced from each air supply hole 48 by the action of the dynamic pressure groove 45, and this forms a pressure gas film and Become. Due to the pressure gas film, the rotating body 25 floats with respect to the inner peripheral surface of the outer cylinder 29 when the rotation speed exceeds about 5,000 rpm. Rotating shaft 13
Is supported by an air bearing 30 which forms a pressurized gas film in a clearance between the inner cylinder 28 and the outer cylinder 29.

When a certain period of time has elapsed after the motor 10 has been rotated at a steady high speed, the inner cylinder 28 and the outer cylinder 29 generate heat due to viscous friction of air. At this time, the air cooling fan unit 2
The air from 0 directly hits the outer peripheral surface of the outer cylinder 29 through the slit hole 17b, and the outer cylinder 29 is forcibly air-cooled. Outer cylinder 2
Heat 9 escapes from the outer peripheral surface due to forced air cooling. On the other hand, the inner cylinder 28 floats while being covered with the air film, and there is almost no escape for the heat. Therefore, in the use range, for example, 80 to 1 between the inner cylinder 28 and the outer cylinder 29.
A temperature difference of about 00 ° C. will occur.

However, since the inner cylinder 28 made of silicon carbide has a relatively small coefficient of thermal expansion of 3 to 4 × 10 ⁻⁶ / ° C.,
The rate of increase of the outer diameter is small for the high temperature reached in the range of use. The outer cylinder 29 has a ceramic material made of alumina and has a higher coefficient of thermal expansion than silicon carbide, which is a ceramic material of the inner cylinder 28. Although the increase is smaller than that of the inner cylinder 28, the increase rate of the inner diameter of the outer cylinder 29 increases. Therefore, the clearance between the inner cylinder 28 and the outer cylinder 29 is less likely to be smaller than the temperature difference between the two.

FIG. 4 shows the inner cylinder 28 and the outer cylinder 2 of the air bearing 30.
Temperature difference ΔT (° C) from 9 and bearing clearance (μm)
Is shown in a graph. This is a comparison between a practical product in which the combination of the materials of the inner cylinder 28 and the outer cylinder 29 is “silicon carbide-alumina” and a comparative product in which the combination is “alumina-alumina”.

The initial bearing clearance C1 is a design value required for the small turbo-molecular pump 1 based on its pumping speed, rotation speed, and the like, and is, for example, 3 to 6 μm. The number of rotations used is 50,000 to 70,000 rpm. In the graph, ΔTma
x is the maximum temperature difference within the use range of the inner cylinder 28 and the outer cylinder 29, and when used at a rotation speed of 50,000 to 70,000 rpm, Δ
Tmax is about 80 to 120 ° C.

In this graph, the rate of decrease (clearance gradient) of the clearance with respect to the temperature difference between the inner cylinder and the outer cylinder is represented by the inner cylinder 2
8 is smaller, and as the difference between the thermal expansion coefficients of the outer cylinder 29 and the inner cylinder 28 is larger than the thermal expansion coefficient of the inner cylinder 28, the thermal expansion coefficient is smaller.

In the comparative product, the thermal expansion coefficients of the inner cylinder and the outer cylinder are both 7 to 8 × 10 ⁻⁶ / ° C., the thermal expansion coefficient of the inner cylinder 28 is relatively large, and the thermal expansion coefficient difference is “0”. ". Therefore, in the comparative product, the clearance becomes “0” just before the maximum temperature difference ΔTmax is reached. That is, it cannot be used in the usage range.

On the other hand, in the embodiment, the thermal expansion coefficient of the inner cylinder 28 is 3-4 × 10 ⁻⁶ / ° C., while the thermal expansion coefficient of the outer cylinder 29 is 7-8 × 10 ⁻⁶ / ° C. ° C. For this reason, the inner cylinder 2
8 has a relatively small coefficient of thermal expansion and a difference in coefficient of thermal expansion of about 4
Since it is × 10 ⁻⁶ / ° C., the gradient of decrease in the clearance with respect to the temperature difference becomes gentler than that of the comparative product. For this reason, even if the maximum temperature difference ΔTmax in the use range is reached, the clearance between the inner cylinder 28 and the outer cylinder 29 does not become “0”. As a result, even if the initial value C1 of the bearing clearance is as small as 3 to 6 μm, high-speed rotation is maintained,
It is possible to further increase the rotation speed. If the inner cylinder 28 has a low thermal expansion coefficient of 5 × 10 ⁻⁶ / ° C. or less, a certain effect can be obtained, and if the thermal expansion coefficient is 4 × 10 ⁻⁶ / ° C. or less, a great effect can be expected. it can. The thermal expansion coefficient difference between the inner cylinder and the outer cylinder is, 1 × 10 ^-6 / ℃ is prima facie effect if more obtained, is expected to provide more effective if particularly 2 × 10 ^-6 / ℃ above.

Further, even when zirconia is used as the ceramic material of the outer cylinder 29, the same effect can be obtained because the coefficient of thermal expansion of zirconia is 7 to 8 × 10 ⁻⁶ / ° C., which is close to that of alumina. . Further, even when silicon nitride is used as the ceramic material of the inner cylinder 28, the same effect can be obtained because the thermal expansion coefficient of silicon nitride is 3 to 4 × 10 ⁻⁶ / ° C., which is close to that of silicon carbide. . If silicon carbide or silicon nitride is used as the material of the inner cylinder 28, the thermal conductivity is relatively high, and from this point, the heat dissipation effect of the inner cylinder 28 is enhanced.

As described in detail above, according to the present embodiment,
The following effects can be obtained. (1) Since the inner cylinder 28 constituting the air bearing (ceramic dynamic pressure gas bearing) 30 is made of a low thermal expansion coefficient ceramic material having a smaller thermal expansion coefficient than the outer cylinder 29, a temperature difference occurs between the two in the usage range. Can also ensure clearance. Therefore,
Even when the clearance is designed to be as small as several μm, a high rotational speed can be realized by optimizing the thermal expansion coefficients of the inner cylinder 28 and the outer cylinder 29. Therefore, in the turbo-molecular pump 1 including the motor 10, the degree of vacuum can be further increased.

(2) Since the outer cylinder 29 is made of an oxide ceramic made of alumina or zirconia, its manufacture and processing are relatively easy, which leads to a reduction in the cost of the air bearing 30.

(3) Since the inner cylinder 28 is made of silicon carbide or silicon nitride, the inner cylinder 28 can be configured to have a low thermal expansion, and is a material having a high thermal conductivity and easy to release heat. 28 can be kept small and the clearance can be hardly narrowed. Therefore, it is possible to further increase the rotation speed of the motor 10.

(4) The ceramic material of the inner cylinder 28 is silicon carbide or silicon nitride, and the ceramic material of the outer cylinder 28 is alumina or zirconia.
Since the combination is set to × 10 ⁻⁶ / ° C. or higher, it is easy to secure the clearance of the air bearing 30 in the usage range of the turbo molecular pump 1. The difference between the two coefficients of thermal expansion was 1 × 10
A combination of ^-6 / ° C. or higher has a certain effect.

(5) An air cooling slit hole 17b is formed in the motor casing 17, and the air cooling fan unit 20 is mounted on the turbo molecular pump 1 so that the slit hole 17b is directed to the air blower. The air bearing 30 can be forcibly air-cooled by the use of the motor 20, so that the rotation speed of the motor 10 can be further increased.

[Second Embodiment] Next, a second embodiment will be described with reference to FIG. This embodiment differs from the first embodiment in the combination of the ceramic material of the inner cylinder and the outer cylinder. The description of the same configuration as that of the first embodiment will be omitted, and only different points will be described.

Air bearing (ceramic dynamic pressure gas bearing) 30
The ceramic material of the inner cylinder 28 is made of silicon carbide, and the ceramic material of the outer cylinder 29 is made of silicon nitride. Inner cylinder 28 and outer cylinder 2
The thermal expansion coefficients of No. 9 are almost the same as 3 to 4 × 10 ⁻⁶ / ° C.

Even in such a configuration where there is almost no difference in the thermal expansion coefficient between the inner cylinder 28 and the outer cylinder 29, the thermal expansion coefficient of the inner cylinder 28 is 3 to
Relatively small at 4 × 10 ⁻⁶ / ° C. Therefore, as shown in FIG. 5, in the embodiment in which the inner cylinder 28 and the outer cylinder 29 are a combination of “silicon carbide-silicon nitride”, the inner cylinder 28 and the outer cylinder 29 are a combination of “alumina-alumina”. Since the rate of decrease of the clearance with respect to the temperature difference is gentler than that of the product, the clearance does not become "0" even when the maximum temperature difference .DELTA.Tmax in the operating range is reached.

Further, the combination of the materials of the inner cylinder 28 and the outer cylinder 29 may be "silicon carbide-silicon carbide" or "silicon nitride-silicon nitride", and conversely, "silicon nitride-silicon carbide". it can. In these cases as well, the relationship between the coefficients of thermal expansion is the same as above, and for the same reason, the clearance between the inner cylinder 28 and the outer cylinder 29 is ensured within the usage range, and the turbo molecular pump 1
It becomes possible to use as. The inner cylinder 28 and the outer cylinder 29
Even if the thermal expansion coefficients of the inner cylinder 28 are substantially the same, a certain effect can be obtained as long as the thermal expansion coefficient of the inner cylinder 28 is 5 × 10 ⁻⁶ / ° C. or less, and 4 × 10 ⁻⁶ / ° C. or less. If so, a great effect can be expected. In addition, since the ceramic material of both the inner cylinder 28 and the outer cylinder 29 is a carbide or a nitride, they generally have a higher thermal conductivity and a higher heat dissipation effect than oxides, and also have high wear resistance.

The embodiment is not limited to the above, but can be carried out in the following modes. The combination of the ceramic material of the inner cylinder 28 and the outer cylinder 29 is not limited to the above embodiment. As long as the ceramic material of the inner cylinder 28 has a smaller coefficient of thermal expansion than the ceramic material of the outer cylinder 29, any combination of materials can be used. In this case, the ceramic material of inner cylinder 28 is not limited to carbide or nitride such as silicon carbide or silicon nitride. For example, a combination of ceramic oxides in which the inner cylinder 28 is made of alumina and the outer cylinder 29 is made of zirconia and the coefficient of thermal expansion of the ceramic material of the inner cylinder 28 is smaller than that of the ceramic material of the outer cylinder 29 is also possible. Further, as a material of the inner cylinder 28 and the outer cylinder 29, for example, boron nitride, aluminum nitride, or the like can be used.

The combination of the ceramic materials of the inner cylinder 28 and the outer cylinder 29 is not limited to a combination having a difference in thermal expansion coefficient equal to or more than a predetermined value. If the thermal expansion coefficient of the inner cylinder 28 is a low thermal expansion ceramic material of 5 × 10 ⁻⁶ / ° C. or less, the clearance of the air bearing can be secured at a temperature difference within the range of use even with a combination of materials having a small thermal expansion coefficient difference. .

The ceramic material of the outer cylinder 29 is not limited to alumina or zirconia. Any oxide ceramic, such as mullite or zircon, which is generally said to have wear resistance can be used.

The low thermal expansion ceramic material is not limited to carbides and nitrides. For example, cordierite which is an oxide having a low coefficient of thermal expansion can be used. The air bearing (ceramic dynamic pressure gas bearing) 30 may have a configuration in which the dynamic pressure groove is formed on the inner peripheral surface of the outer cylinder 29.

The ceramic gas bearing is not limited to the ceramic dynamic pressure gas bearing. For example, it may be constituted by a ceramic static pressure gas bearing. ○ The number of rotations of the motor is not limited to 50,000 to 70,000 rpm. For even higher rotational speeds, for example, 80,000 to 90,000 r
It can be carried out by a motor or a turbo molecular pump having pm as the maximum operating speed. In this case, the inner cylinder 28 and the outer cylinder 2
The ceramic material of No. 9 is not limited to the combination of the coefficients of thermal expansion of the above-described embodiments, but can be optimized so that the clearance can be secured in the usage range. For example, as the ceramic material of the inner cylinder 28, a ceramic material having a lower coefficient of thermal expansion than silicon carbide or silicon nitride is selected, or in order to widen the difference in the coefficient of thermal expansion between the inner cylinder 28 and the outer cylinder 29, the outer cylinder 2 is used.
As the ceramic material of No. 9, a material having a higher coefficient of thermal expansion than alumina or zirconia can also be selected.

The non-contact type bearing that supports the load in the thrust direction of the rotating shaft is not limited to the magnetic bearing. An air bearing may be used. ○ The motor is not limited to the turbo molecular pump. For example, the motor 10 may be used for a compressor.

The technical ideas other than the claims grasped from the above embodiments and other examples are described below. (1) In any one of the first, third, and fourth aspects, the difference between the coefficients of thermal expansion of the ceramic materials of the bearing fixed body and the bearing rotating body is 1 × 10 ⁻⁶ / ° C. or more. In this case, since there is a difference in the coefficient of thermal expansion, the clearance of the air bearing can be secured even if a temperature difference occurs between the two in the usage range.

(2) In any one of the first, third, and fourth aspects, the difference between the coefficients of thermal expansion of the ceramic materials of the bearing fixed body and the bearing rotating body is 2 × 10 ⁻⁶ / ° C. or more. in this case,
Since there is a difference in the coefficient of thermal expansion, a sufficient clearance for the air bearing can be secured even if a temperature difference occurs between the two in the usage range.

(3) In any one of claims 2 to 8,
The value of the coefficient of thermal expansion of the ceramic material is 5 × 10 ⁻⁶ / ° C. or less, and the coefficient of thermal expansion is 4 × 10 ⁻⁶ / ° C. or less. in this case,
Even if a temperature difference occurs between the two in the use range, the clearance of the air bearing can be sufficiently ensured.

(4) In claim 5, the ceramic material of the bearing rotating body is silicon carbide or silicon nitride. (5) In claim 4, the oxide is alumina or zirconia.

(6) In claim 2, both the bearing rotating body and the bearing fixed body are made of a ceramic material having a low thermal expansion coefficient of 5 × 10 ⁻⁶ / ° C. or less. (7) In any one of claims 1 to 8 and (1) to (6), the ceramic gas bearing is a ceramic dynamic pressure gas bearing.

[0068]

As described in detail above, according to the first to third aspects of the present invention, the bearing rotating body and the bearing fixed body constituting the ceramic gas bearing for supporting the radial load of the rotating body. Since the rotating body of the bearing has a smaller thermal expansion coefficient than that of the fixed bearing body, the ceramic material is used. Thus, the clearance of the ceramic gas bearing can be secured.

According to the second to sixth aspects of the present invention, the bearing rotating body constituting the ceramic gas bearing is provided with a thermal expansion coefficient of 5 × 1.
Since it is made of a low thermal expansion ceramic material of 0 ^-6 / ° C or less, the clearance of the ceramic gas bearing can be ensured by the temperature difference in the use range even if the clearance setting has to be reduced due to a high rotation speed or the like.

According to the third aspect of the present invention, the first aspect is provided.
In addition to the effects of the invention, since the thermal expansion coefficient of the ceramic material of the bearing rotating body is 5 × 10 ⁻⁶ / ° C. or less, the clearance of the ceramic gas bearing can be secured at a temperature difference in the use range.

According to the invention set forth in claim 4, according to claim 3,
In addition to the effects of the invention of the present invention, since the ceramic material of the bearing fixed body is an oxide, it is easy to set the bearing fixed body to a larger coefficient of thermal expansion than the bearing rotating body, and it is easy to manufacture and process the bearing fixed body. Cheaply.

According to the fifth aspect of the present invention, since the ceramic material of the bearing rotating body is a carbide or a nitride, a low coefficient of thermal expansion is easily ensured, and the thermal conductivity is generally higher than that of the oxide, and the heat radiation is high. The effect is high, and high wear resistance is easily obtained.

According to the invention described in claim 6, according to claim 1,
In addition to the effects of the present invention, the outer peripheral surface of the bearing fixed body of the ceramic gas bearing can be forcibly air-cooled by the air cooling hole formed in the motor casing, and the cooling effect of the ceramic gas bearing can be enhanced. it can.

According to the invention of claim 7, according to claim 1,
By using the motor according to any one of (1) to (6), it is possible to achieve a higher rotation speed of the turbo-molecular pump and obtain a higher degree of vacuum.

According to the invention described in claim 8, according to claim 7,
In addition to the effects of the invention described above, since the ceramic gas bearing is forcibly air-cooled by the air-cooling means, it is possible to contribute to a higher rotational speed of the turbo molecular pump.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing a turbo-molecular pump according to a first embodiment.

FIG. 2 is a side sectional view showing a brushless motor.

FIG. 3 is a side view showing an air bearing.

FIG. 4 is a graph showing a relationship between a temperature difference between an inner cylinder and an outer cylinder of an air bearing and a bearing clearance.

FIG. 5 is a graph showing a relationship between a temperature difference between an inner cylinder and an outer cylinder of an air bearing and a bearing clearance in the second embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Turbo molecular pump, 7 ... Stator blade, 10 ... Brushless motor as a motor, 17 ... Motor casing, 17b
... Slit hole as air cooling hole, 13 ... Rotary shaft, 16 ...
Rotor blades, 20 ... fan unit for air cooling as air cooling means,
22: air cooling fan, 25: rotating body, 28: inner cylinder as bearing rotating body, 29: outer cylinder as bearing fixed body, 30 ...
Air bearing as ceramic gas bearing (ceramic dynamic pressure gas bearing), 31 ... armature coil as armature, 3
7, 38: magnetic bearings as non-contact bearings; 43, air bearing bands; 45, dynamic pressure grooves.

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) F16C 32/00 F16C 32/00 C 5H607 37/00 37/00 A H02K 7/08 H02K 7/08 A 7/14 7 / 14 B F term (for reference) 3H022 AA01 AA03 BA06 CA11 CA15 CA53 DA02 DA08 DA13 DA19 3H031 DA01 DA02 DA07 EA00 EA01 EA02 EA06 EA08 FA14 FA15 FA16 FA34 FA35 FA36 FA40 3J011 AA08 AA09 BA02 CA02 DA01 SD01 003 BA03 BA19 CA03 CA18 FA06 GA06 GA13 5H607 AA02 BB01 BB09 BB14 CC01 DD03 FF06 FF08 GG12 JJ05 KK00 KK10

Claims (8)

[Claims] A rotating body for rotating a rotating shaft; an armature disposed on an outer peripheral side of the rotating body; a ceramic gas bearing for supporting a radial load of the rotating body; A non-contact type bearing that supports a load in a thrust direction, wherein the ceramic gas bearing is disposed with a bearing rotating body forming an outer peripheral surface of the rotating body and a clearance provided on an outer peripheral side of the bearing rotating body. A motor comprising a bearing fixed body, wherein a ceramic material of the bearing rotating body has a smaller coefficient of thermal expansion than a ceramic material of the bearing fixed body. 2. A rotating body for rotating a rotating shaft, an armature disposed on an outer peripheral side of the rotating body, a ceramic gas bearing for supporting a radial load of the rotating body, A non-contact type bearing that supports a load in a thrust direction, wherein the ceramic gas bearing is disposed with a bearing rotating body forming an outer peripheral surface of the rotating body and a clearance provided on an outer peripheral side of the bearing rotating body. And a bearing fixed body, wherein at least the bearing rotating body is made of a low thermal expansion ceramic material having a coefficient of thermal expansion of 5 × 10 ⁻⁶ / ° C. or less. 3. The motor according to claim 1, wherein the coefficient of thermal expansion of the ceramic material of the bearing rotating body is 5 × 10 ⁻⁶ / ° C. or less. 4. The motor according to claim 3, wherein the ceramic material of the bearing fixing body is an oxide. 5. The motor according to claim 2, wherein the ceramic material of the bearing rotating body is carbide or nitride. 6. A motor casing according to claim 1, wherein an air cooling hole is formed in the motor casing for forcibly air cooling an outer peripheral surface of the bearing fixed body of the ceramic gas bearing. And the motor. 7. The motor according to any one of claims 1 to 6, a moving blade provided on the rotating shaft of the motor, and necessary for generating a molecular flow by rotating the moving blade. Turbo molecular pump with a simple stationary blade. 8. The turbo-molecular pump according to claim 7, further comprising air cooling means for forcibly air-cooling an outer peripheral surface of said bearing fixed body of said ceramic gas bearing.