US20070286749A1

US20070286749A1 - Drive for vacuum pump

Info

Publication number: US20070286749A1
Application number: US11/800,092
Authority: US
Inventors: Juergen Wagner
Original assignee: Pfeiffer Vacuum GmbH
Current assignee: Pfeiffer Vacuum GmbH
Priority date: 2006-05-16
Filing date: 2007-05-02
Publication date: 2007-12-13
Also published as: EP1857681A3; EP1857681A2; DE102006022772A1; JP5303117B2; EP1857681B1; JP2007309314A

Abstract

A drive arrangement for a vacuum pump includes a separation member arranged between the motor stator and the motor rotor, and at least two, coaxial with each other and axially spaced from each other, guide surfaces, the separation member being formed as a separation sleeve which is supported and centered between the at least two guide surfaces, with the guide surfaces contacting an outer surface of the separation sleeve.

Description

A. BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a drive arrangement for a vacuum pump and including a motor stator, a motor rotor, and a separation member arranged between the motor stator and the motor rotor.
2. Description of the Prior Art
Vacuum pumps have rotating shafts the bearing of which are often lubricated by operating means such as, e.g., oil. In many vacuum pumps, this operating means is simultaneously used for sealing the working chamber, e.g., in so-called vane rotary vacuum pumps. Vacuum pumps have one or more shafts at least one of which is driven and held.
Often, as a motor, an asynchronous motor is used. It is generally forbidden to locate a motor in a space filled with operating means. This requires a bulky, hermetical separation which is realized, according to the state of the art, primarily by using so-called split pot elements. The split pot element is arranged either directly in the motor gap or in a magnetic coupling and is formed of a material in which an alternating magnetic field generates no or very small eddy currents. An example of use of a split pot element in a vacuum pump is disclosed in German Publication DE-OS 10 2004 024 554. The use of a split pot element leads to increase of the motor gap which reduces the efficiency of the motor and increases power consumption.
The negative influence of the split pot element on the width of the motor gap is based on a sum of separate effects. On one hand, the walls, because of manufacturing conditions, are parallel to each other only at a small degree, therefore, the wall thickness increases from the pot bottom to the attachment flange. On the other hand, a one-sided attachment by the attachment flange causes tilting of the pot element. The pot element height acts as an elongate lever, and tilting at the pot element bottom is the greatest. Therefore, the motor gap must be correspondingly large. Generally, attachment with the flange can lead in many non-magnetic materials to a danger of distortion due to stresses caused by a non-uniform application of force over the flange connection.
An object of the invention is to provide a drive arrangement with a hermetically sealed separation between the rotor and stator components of an electric motor and with as small as possible motor gap.

B. SUMMARY OF THE NEW INVENTION

This and other objects of the present invention, which will become apparent hereinafter, are achieved by a drive arrangement which includes at least two, coaxial with each other and axially spaced from each other, guide surfaces, and in which the separation member is formed as a separation sleeve which is supported and centered between the at least two guide surfaces, with the guide surfaces contacting the outer surface of the separation sleeve.
By forming the separation member as a separation sleeve which is supported and centered between at least two guide surfaces, with the guide surfaces contacting an outer surface of the separation sleeve, it is possible to form the separation member very precisely. Sleeves can be produced with high precision by grinding, turning, or drawing process which provides for a uniform wall thickness over the sleeve length. Arrangement of the sleeve within coaxial surfaces insures a precise alignment of the separation sleeve, resulting in a small motor gap. In order to prevent problems which might be caused by a thermal effect, the guide surfaces are so arranged that they contact the sleeve outer surface. This is advantageous with separation sleeves formed of a weak magnetic material, because generally the sleeve may be heated by eddy currents and, as a result, would expand greater than the components with guide surfaces. Thereby, leakage can be produced.
Vice versa, even with non-magnetic materials, this arrangement is advantageous as such separation sleeve does not become heated and, therefore, does not expand. When the components with the guide surfaces slightly expands, the tension which is produced in the separation sleeve, can cause distortion.
According to an advantageous embodiment of the invention, there are provided at least two components which define, together with the separation member, a chamber in which the motor stator is located. The at least two guide surfaces are provided, respectively, on the at least two components. The at least two components are aligned relative to each other by respective connection surfaces provided on the at least two components and arranged coaxially with the guide surfaces. With two components carrying the guide surfaces, a guide surface is provided at each axial end of the coils. Therefore, the separation sleeve can be held at its ends and be precisely positioned.
Advantageously, the separation sleeve is formed as a glass tube. Glass has a very small heat expansion coefficient, is non-magnetic, so that no eddy current is generated, and the glass tube can be produced with precise dimensions. In addition, a type of glass having a high chemical resistance can be used.
According to a further advantageous embodiment of the invention, elastomeric ring means is arranged on the outer side of the glass tube for sealing a space inside the glass tube from outside. The elastomeric ring means bears against the outer surface of the separation sleeve. Thus, even when the separation sleeve expands, sealing of the arrangement is insured.
According to a still further advantageous embodiment of the invention, the at least two components form stationary, axially spaced from each other, stops for the glass tube, with an axial distance between the stops being greater than a length of the glass tube. This insures that the separation sleeve is not stressed, but rather is floatingly supported in the axial direction.
With the motor rotor including permanent magnets and the motor stator including electrical coils, there is formed a motor with a high efficiency and a narrow motor gap.
A vacuum pump according to the present invention includes pumping components, a shaft for supporting the pumping components, and a drive arrangement for driving the shaft. The drive arrangement includes, as discussed above, motor stator and rotor, a separation member arranged between the motor stator and the motor rotor, and at least two, coaxial with each other and axially spaced from each other, guide surfaces. The separation member is formed as a separation sleeve which is supported and centered between the at least two guide surfaces, with the guide surfaces contacting an outer surface of the separation sleeve. With such a vacuum pump, the motor rotor can be formed integrally with the shaft, so that the bearings in the motor region can be dispensed with. This reduces costs of production and sources of failure.
The use of the inventive drive arrangement in vacuum pumps formed as vane rotary pumps or Roots pumps enhances the advantages the inventive drive arrangement provides.
The novel features of the present invention, which are considered characteristics for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments when read with reference to the accompanying drawings.

C. BRIEF DESCRIPTION OF THE DRAWINGS

The drawings show:

FIG. 1 shows a cross-sectional view of a vane rotary vacuum pump; and

FIG. 2 shows a cross-sectional view of a further embodiment of a vacuum pump drive arrangement according to the present invention.

D. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shoes a vane rotary vacuum pump 1, further just a vacuum pump, sealed and lubricated with oil 16. The main component of the vacuum pump is a support 2 to which components of the pump system, on one hand, and the drive arrangement, on the other hand, are secured. A shaft 3 is rotatably supported in a slide bearing 4 and eccentrically extends through a cylindrical hollow chamber of the vacuum pump 1. The hollow chamber is formed by a body having a cylindrical opening and cover plates at its opposite axial ends. The shaft 3 supports one or more vanes 5 which contact the walls of the hollow chamber, thereby forming a compression chamber 6. The rotation of the shaft 3 and the resulting movement of the vanes produce the per se known pumping effect.
For simplicity sake, vanes which are well known in the state of the art are not shown. The shaft 3 carries permanent magnets 7 which cooperate with electrical coils 8 for rotating the shaft 3. Between the permanent magnets 7 and the electrical coils 8, there is provided a motor gap, shown at an increased, overproportional scale. In the motor gap, a separation member 9, which is formed as a glass tube, is arranged. The glass tube 9 is supported against a cylindrical guide surface 10 provided on the support 2 and against a likewise cylindrical guide surface 11 provided on a cover 12. The guide surfaces 10 and 11 are coaxial and are axially spaced apart from each other. With the glass tube having a constant outer diameter, the guide surfaces 10,11 would have the same radices. In order to prevent stresses, which can be produced by a non-uniform heat expansion of the glass tube and support and/or cover, the guide surfaces 10,11 contact the outer surface of the glass tube 9. A spacer 14 connects the cover 12 and the support 23. Together with a separation sleeve, these components form a chamber in which the electric coils 8 are arranged. Connection surfaces 17 insure coaxiality of the guide surfaces 10,11. The connection surfaces 17 are provided on the inner side of the spacer 14, on the support 2 and on the cover 12. In the right low portion of FIG. 1, this arrangement is shown in exploded view, the connection surfaces, which are provided on the support 2 and the cover 12, are designated with a reference numeral 17 a, and the connection surfaces on the spacer 14 are designated with a reference numeral 17 b. The connection surfaces 17 b of the spacer 14 can be produced in a common operational step, e.g., by turning. Likewise, the guide surface 10 and the connection surface 17 a on the support 2 and the guide surface 11 and the connection surface 17 a on the cover 12 can be produced in one operational step. The alignment of the cover 12 and the support 2 and, thereby, of the guide surfaces 10 and 17 a is, as a result, very precise and produces a small motor gap.
The support 2 and the cover 12 provide stops in both axial directions. The distance between the stops is greater than the axial length of the glass tube so that the glass tube has a certain axial play. It is advantageous when the guide surfaces do not have narrow tolerances as no preload is produced. In this case, the glass tube is displaceable within certain limits. Elastomeric rings 13 support the glass tube 9 floatingly for axial and radial displacement, with the guide surfaces 10,11 guiding the glass tube 9.
FIG. 2 shows an improved embodiment of the inventive drive. In this embodiment, the support 2 is formed that it simultaneously functions as a spacer. The support 2, the separation tube 9, and the cover 12, form a chamber in which the electrical coils 8 are arranged. The embodiment of FIG. 2 is more compact than that of FIG. 1.
Another advantage of the embodiment of FIG. 2 consists in that the number of coaxial with each other surfaces is reduced. Only one connection interface between the cover 2 and support 2 is needed, so that the guide surfaces 17 are provided only in this region. The guide surfaces on the support can be formed in one operational step.
In a second operational step, the guide surface 11 and the connection surface on the cover can be formed. As a result, the coaxiality of the guide surfaces with respective connection surfaces and of the guide surfaces with each other is very precise. All of this insures a very high precision of the entire arrangement, and a clearance between the permanent magnets 7, which are supported on the shaft 3, and the electrical coils 8 can be retained optimally small. The power parameters of the motor are correspondingly improved or a necessary motor power consumption is reduced as losses, which are associated with the motor gap, are significantly reduced.
Though the present invention was shown and described with references to the preferred embodiments, such are merely illustrative of the present invention and are not to be construed as a limitation thereof and various modifications of the present invention will be apparent to those skilled in the art. It is, therefore, not intended that the present invention be limited to the disclosed embodiments or details thereof, and the present invention includes all variations and/or alternative embodiments within the spirit and scope of the present invention as defined by the appended claims.

Claims

1. A drive arrangement for a vacuum pump, comprising a motor stator; a motor rotor; a separation member arranged between the motor stator and the motor rotor; and at least two, coaxial with each other and axially spaced from each other, guide surfaces, the separation member having a separation sleeve which is supported and centered between the at least two guide surfaces, with the guide surfaces contacting an outer surface of the separation sleeve.

2. A drive arrangement as set forth in claim 1, comprising at least two components which define, together with the separation member, a chamber in which the motor stator is located, and wherein the at least two guide surfaces are provided, respectively on the at least two components, and the at least two components are aligned relative to each other by respective surfaces provided on the at least two components and arranged coaxially with the guide surfaces.

3. A drive arrangement as set forth in claim 1, wherein the separation sleeve is formed as a glass tube.

4. A drive arrangement as set forth in claim 3, further comprising elastomeric ring means arranged on the outer side of the glass tube for sealing a space inside the glass tube from outside.

5. A drive arrangement as set forth in claim 2, wherein the at least two components form stationary, axially spaced from each other, stops for the glass tube, with an axial distance between the stops being greater than a length of the glass tube.

6. A drive arrangement as set forth in claim 1, wherein the motor stator comprises electrical coils, and the motor rotor comprises permanent magnets.

7. A vacuum pump, comprising pumping component;, a shaft for supporting the pumping components; and a drive arrangement for driving the shaft; the drive arrangement including motor stator and rotor, a separation member arranged between the motor stator and the motor rotor and at least two, coaxial with each other and axially spaced from each other, guide surfaces, the separation member having a separation sleeve which is supported and centered between the at least two guide surfaces, with the guide surfaces contacting an outer surface of the separation sleeve.

8. A vacuum pump as set forth in claim 7, further comprising oil-lubricated bearing means for supporting the shaft.

9. A vacuum pump as set forth in claim 7, wherein the vacuum pump is formed as a vane rotary pump.

10. A vacuum pump as set forth in claim 7, wherein the vacuum pump is formed as a Roots pumps.