JP4382689B2 - Touchdown bearing for turbomolecular pump and turbomolecular pump - Google Patents

Description

  The present invention relates to a touchdown bearing for protecting a rotating body supported by a magnetic bearing in a turbomolecular pump when rotation is stopped or when control is abnormal, and a turbomolecular pump including the touchdown bearing.

  In the turbo molecular pump, a configuration in which a rotating body including an exhaust blade is supported by a magnetic bearing in a non-contact manner is often used. An example is shown in a sectional view in FIG. In this example, a fixed blade 11 is disposed on the inner periphery of the case 10, and a rotating shaft 13 having a rotating blade 12 fixed on the outer periphery is rotatably disposed in the case 10. The rotary shaft 13 is rotated by an electric motor 14, and in the rotated state, the rotary shaft 13 is integrally formed with the two radial magnetic bearings 15 and 16 disposed close to the outer peripheral surface of the rotary shaft 13 and the rotary shaft 13. A pair of axial magnetic bearings 17 arranged above and below the flange portion 13a is supported in a non-contact state in a magnetically levitated state. In the figure, 8 is an intake port and 9 is an exhaust port.

  In the case 10, one full ball type deep groove ball bearing 21 and a pair of angular ball bearings 22 in which oblique contact directions are combined in opposite directions are arranged as a touchdown bearing. These touchdown bearings 21 and 22 are rolling bearings for protecting the rotating shaft 13 from being damaged by contact with the radial magnetic bearings 15 and 16 and the axial magnetic bearing 17 when the rotating shaft 13 is stopped or abnormally controlled. The clearance between the outer peripheral surface of the rotating shaft 13 and the inner peripheral surface of the inner ring of each touchdown bearing 21, 22 is slightly smaller than the clearance between the rotating shaft 13 and each of the magnetic bearings 15, 16, and 17. Is intervening. Thereby, in the state where the rotating shaft 13 is rotatably supported by the magnetic bearings 15, 16 and 17 in a magnetically levitated state, the rotating shaft 13 maintains a non-contact state with respect to the touchdown bearings 21 and 22, When the shaft 13 is stopped or when the control is abnormal due to the action of an external force or the like, the rotating shaft 13 contacts the inner rings of the touch-down bearings 21 and 22 and is rotatably supported before contacting the magnetic bearings 15, 16 and 17.

  Although the example in which the inner ring is a rotating ring has been described above, a structure in which a touch-down bearing is arranged inside the cylindrical rotating body using a cylindrical rotating body having rotating blades is also known. It has been. In this structure, the outer ring of the touch-down bearing is arranged on the inner peripheral surface of the cylindrical rotating body through a predetermined gap, and the inner peripheral surface of the rotating body is the touch-down bearing when the rotating body is stopped or when the control is abnormal. The rotating body is rotated and supported in contact with the outer circumferential surface of the outer ring.

  By the way, the touchdown bearings 21 and 22 in such a vacuum pump conventionally have been made of ceramics as the material of the rolling elements (balls) for the purpose of improving the durability, and mainly used for the inner and outer rings. Martensitic stainless steel such as SUS440C is used.

  Since each of the touchdown bearings 21 and 22 made of such a material is provided with magnetic bearings 15, 16 and 17 adjacent to each other, the inner and outer rings made of a ferromagnetic material such as martensitic stainless steel are included. The rotating wheel (inner ring in the example of FIG. 4) is idled with respect to the fixed wheel (outer ring in the example of FIG. 4) even though it is not in contact with the rotating shaft 13 due to the magnetic field of the magnetic bearing. However, there is a problem that idling noise of the touch-down bearing is generated as an abnormal noise during normal rotation of the pump.

In order to eliminate such a phenomenon, conventionally, a technology for suppressing the rotation of the rotating wheel by forming the rotating wheel and the rolling element of the touch-down bearing with a material having a relative permeability of 1.4 or less is known. (For example, refer to Patent Document 1).
JP 2002-221226 A

  In the technique described in Patent Document 1 described above, the rotating wheel needs to be formed of a limited material such as austenitic stainless steel or cemented carbide, and it is impossible to select an optimum material for the bearing ring of the rolling bearing. There is a problem that expensive materials must be used.

  The present invention has been made in view of such circumstances, and the rotating wheel in the touchdown bearing is made of martensitic stainless steel which has been conventionally optimized from a comprehensive viewpoint such as cost and performance. A touch-down bearing for a turbo molecular pump in which the rotating wheel is not rotated by the magnetic field generated by the magnetic bearing without generating a noise without sacrificing the basic performance as a bearing or significantly increasing the cost, and its The challenge is to provide a turbomolecular pump with a touchdown bearing.

  In order to solve the above-mentioned problems, a touchdown bearing for a turbo molecular pump according to the present invention is used in a turbo molecular pump having a rotating body supported by a magnetic bearing, and only when the rotating body is stopped or abnormally controlled. A touch-down bearing that supports the rotating body with respect to the fixed ring that is the other of the outer ring or the inner ring that is fixed to the fixed member by contact with the rotating ring that is one of the inner ring or the outer ring, and Among the inner ring and the outer ring, in a touch-down bearing in which at least a rotating ring that contacts the rotating body is made of a ferromagnetic material, and a plurality of ceramic rolling elements are disposed between the inner ring and the outer ring, the inner ring and the outer ring It is characterized in that at least one magnetized member is provided between the rolling element rows in between (claim 1).

  Here, in this invention, the structure (Claim 2) which made the said magnetized member the same shape as the said rolling element can be employ | adopted suitably.

  In the present invention, each of the rolling element and the magnetized member is a ball, and the diameter of the magnetized member in the use state of the touchdown bearing is smaller than the diameter of the rolling element (claim). It is preferable to adopt 3).

  Furthermore, in the invention which concerns on Claim 2 or 3, the structure (Claim 4) which is arrange | positioned in the said rolling element row | line | column in the state with which the said 2 magnetized member continued was also employable.

  In addition, the turbo molecular pump of the present invention has a rotating body supported by a magnetic bearing and a rotating wheel that is one of an inner ring or an outer ring is in contact with the rotating body only when the rotating body is stopped or abnormally controlled. In a turbo molecular pump including a touchdown bearing that supports the rotating body with respect to a fixed ring that is the other of an outer ring or an inner ring fixed to a fixing member, at least rotation of the inner ring and the outer ring of the touchdown bearing is performed. The rotating wheel in contact with the body is made of a ferromagnetic material, and a plurality of ceramic rolling elements are arranged between the inner ring and the outer ring, and mixed with the rolling element row between the inner ring and the outer ring, It is characterized by the provision of at least one magnetized member (claim 5).

  Here, also in the turbo molecular pump of the present invention, the magnetized member has the same shape as the rolling element (Claim 6), and the rolling element and the magnetized member are balls. In addition, in the use state of the touchdown bearing, a configuration (Claim 7) in which the diameter of the magnetized member is smaller than the diameter of the rolling element can be adopted. It is also possible to adopt a configuration (claim 8) arranged in the rolling element row in a continuous state.

  The present invention relates to a touchdown bearing using a rotating wheel made of a ferromagnetic material and a ceramic rolling element, and by mixing at least one magnetized member in the rolling element row, Attempts to prevent rotation of the rotating wheel due to the magnetic field of the magnetic bearing by magnetically attracting the rotating wheel made of a ferromagnetic material or by magnetically attracting the rotating wheel to the fixed ring by a magnetized member Is.

  That is, in order for the rotating wheel to rotate with respect to the fixed wheel, the rolling element needs to revolve. However, if a magnetized member is arranged in the rolling element row, the magnetized member is removed from the ferromagnetic material. When the rotating wheel is magnetically attracted to the rotating wheel and the rotating wheel tries to rotate with the magnetic field of the magnetic bearing, the rolling element is prevented from revolving by the magnetized member adsorbed to the rotating wheel. It is possible to prevent revolving. This effect is further enhanced by using a ferromagnetic material on the fixed ring side, whereby the rotating ring and the fixed ring are attracted to each other via the magnetized member. Since a large torque acts when the rotating wheel rotates during touchdown, the attracting force of the magnetized member is almost negligible, and the rotation is not impaired.

  Further, as in the invention according to claim 2 or claim 6, the magnetized member has a shape equivalent to that of the rolling element, and further, these are balls as in the member according to claim 3 or claim 7. This facilitates the manufacture and assembly of the touchdown bearing and is advantageous in terms of cost. In this case, the magnetized member is made smaller in diameter by the diameter of the magnetized member than the diameter of the rolling element. Functions as a rolling element, that is, no load is applied during rotation, and the durability as a rolling bearing is not affected.

  The invention according to claim 4 or claim 8 improves the revolution preventing function of the rolling element by the magnetized member. With this configuration, even if the fixed ring is not a ferromagnetic body, the rolling element It is possible to prevent the rotation of the rotating wheel by reliably preventing the revolution of the rotating wheel.

  According to the present invention, as the material of the rotating wheel, an optimum material that has been widely used as a bearing ring of a touchdown bearing, such as SUS440C, is used, and a non-magnetic material such as ceramics is used as a rolling element. While using this, it is possible to prevent the accompanying rotation caused by the magnetic field produced by the magnetic bearing and to prevent the generation of abnormal noise.

  Further, as in the inventions according to claims 2 and 3 or claims 6 and 7, the magnetized member provided in the rolling element row has the same shape as the rolling element, in particular, a ball, and is magnetized in its use state. By making the diameter of the member smaller than the diameter of the rolling element, the manufacturing cost and the assembly cost are kept low, and the durability of the bearing is not deteriorated due to the presence of the magnetized member.

  Furthermore, if two magnetized members are continuously arranged in the rolling element row as in the invention according to claim 4 or claim 8, the ability of the rolling element to prevent revolution, and consequently, the rotation of the rotating wheel is prevented. Ability can be made more certain.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a front view of an embodiment in which the present invention is applied to a touchdown bearing composed of a full ball type deep groove ball bearing in FIG. 4, and FIG. 2 is an axial parallel sectional view thereof.

  The inner ring 1 and the outer ring 2 are each made of SUS440C, which is martensitic stainless steel, and a plurality of ceramic balls 3 are arranged between them so as to roll freely. In the row of ceramic balls 3, three balls 4 made of SUS440C are arranged at a position where the rows are equally arranged, and these balls 4 made of SUS440C are magnetized. In addition, the diameter of the ball 4 made of SUS440C is smaller than the diameter of each ceramic ball 3 when the touch-down bearing is used. Therefore, when the inner ring 1 which is a rotating wheel rotates, only the ceramic balls 3 are loaded as rolling elements, and the balls 4 made of SUS440C are not loaded and do not function as rolling elements.

  Then, each ball 4 made of magnetized SUS440C has an inner ring (rotating wheel) 1 and outer ring 2 made of ferromagnetic SUS440C as illustrated in FIG. 2 in a state where the touchdown bearing is not rotating. Both are magnetically attracted. This state is the same even when the rotating shaft 13 in FIG. 4 is rotated in a magnetically levitated state by the magnetic bearings 15, 16, and 17, and is therefore stronger by the magnetic field generated by the magnetic bearings 15, 16, and 17. Even if the inner ring 1 made of a magnetic material tries to rotate, the balls 3 made of magnetized SUS440C cannot revolve the ceramic balls 3, so that the inner ring 1 is not rotated by the magnetic field.

  On the other hand, when the rotating shaft 13 stops or when the magnetic bearings 15, 16, and 17 are abnormally controlled, a large torque acts on the inner ring 1 when the rotating shaft 13 comes into contact with the inner peripheral surface of the inner ring 1, that is, during touchdown. Therefore, since each ceramic ball 3 revolves against the magnetic attraction force of the ball 4 made of magnetized SUS440C, no problem occurs. Further, since the diameter of the magnetized balls 4 in use is smaller than the diameter of the ceramic balls 3, no load is applied to the magnetized balls 4 when rotating by touchdown. The durability of the bearing does not deteriorate due to peeling or the like.

  The number of magnetized balls 4 is not particularly limited to three, and may be any number that can prevent idling of the inner ring 1 depending on the specifications of the turbo molecular pump to be incorporated. In addition, if two magnetized balls 4 are continuously arranged in a row of ceramic balls 3, the magnetized balls 4 also attract each other and contribute to the prevention of revolution of the rolling elements. As shown in a front view of another embodiment of the present invention, FIG. 3 shows a front view of another embodiment of the present invention. By arranging in the row, it is possible to prevent the inner ring 1 from slipping even if the outer ring 2 which is a fixed ring is not a ferromagnetic body.

  In the above embodiment, the magnetized member for suppressing the idling of the rotating wheel is a ball having the same shape as the rolling element. However, the present invention is not limited to this and is not limited to this. Any shape can be used as long as it does not hinder the revolution of the rolling element.

  Furthermore, in the above embodiment, the present invention is applied to a full-groove type deep groove ball bearing among touchdown bearings, but a pair of angular contact ball bearings used in combination is also applied to the above by applying the present invention. Similarly, it is possible to prevent the accompaniment.

  Furthermore, in the above embodiment, the example in which the present invention is applied to the touchdown bearing used for the turbo molecular pump having the inner ring 1 as the rotating ring has been shown. However, the touchdown bearing having the outer ring as the rotating ring has been described. Of course, the present invention is equally applicable.

It is a front view of an embodiment of the invention. It is an axial parallel sectional view of an embodiment of the invention. It is a front view of other embodiment of this invention. It is sectional drawing which shows the structural example of the turbo-molecular pump provided with the touchdown bearing.

Explanation of symbols

1 Inner ring (rotating wheel)
2 outer ring 3 ball made of ceramic 4 ball made of magnetized SUS440C 13 rotating shaft 15, 16, 17 magnetic bearing 21, 22 touchdown bearing

Claims (8)

Used for turbo-molecular pumps that have a rotating body supported by a magnetic bearing, and the rotating body that is one of the inner ring or the outer ring comes into contact with the rotating body only when the rotating body stops or is abnormally controlled, and is fixed to the fixed member. A touch-down bearing that supports the rotating body with respect to a fixed ring that is the other of the outer ring or the inner ring, and at least the rotating ring that contacts the rotating body is made of a ferromagnetic material among the inner ring and the outer ring. Yes, in a touchdown bearing in which a plurality of ceramic rolling elements are arranged between an inner ring and an outer ring,
A touchdown bearing for a turbo molecular pump, wherein at least one magnetized member is provided between the inner ring and the outer ring so as to be mixed with the rolling element row.   The touchdown bearing for a turbo molecular pump according to claim 1, wherein the magnetized member has the same shape as the rolling element.   The rolling element and the magnetized member are each a ball, and the diameter of the magnetized member is smaller than the diameter of the rolling element when the touchdown bearing is in use. Touchdown bearings for turbomolecules.   The turbo-molecular touchdown bearing according to claim 2 or 3, wherein two magnetized members are arranged in the rolling element row in a continuous state. A rotating body supported by a magnetic bearing, and an outer ring or an inner ring fixed to a fixing member by contact of the rotating body, which is one of an inner ring or an outer ring, with the rotating body only when the rotating body is stopped or abnormally controlled. In the turbo molecular pump provided with a touchdown bearing that supports the rotating body with respect to the stationary ring which is the other of
Of the inner ring and outer ring of the touchdown bearing, at least the rotating ring that contacts the rotating body is made of a ferromagnetic material, and a plurality of ceramic rolling elements are disposed between the inner ring and the outer ring, A turbo-molecular pump characterized in that at least one magnetized member is provided so as to be mixed with a rolling element row between an inner ring and an outer ring.   The turbo molecular pump according to claim 5, wherein the magnetized member has the same shape as the rolling element.   The rolling element and the magnetized member are each a ball, and the diameter of the magnetized member is smaller than the diameter of the rolling element when the touchdown bearing is in use. Turbo molecular pump.   The turbo-molecular pump according to claim 6 or 7, wherein two magnetized members are arranged in the rolling element row in a continuous state.

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