GB2240666A

GB2240666A - Using unidirectional magnets for careless torsional magnetic coupling

Info

Publication number: GB2240666A
Application number: GB9102239A
Authority: GB
Inventors: Mark Alan Preston
Original assignee: United Technologies Corp
Current assignee: RTX Corp
Priority date: 1990-02-01
Filing date: 1991-02-01
Publication date: 1991-08-07
Also published as: GB9102239D0; FR2660497A1

Abstract

A coreless magnetic coupling is comprised of a driven member (40) having a plurality of tangentially polarized magnets (54-59) interposed between radially polarized magnets (48-53) and a driving member (42) having a plurality of tangentially polarized magnets (66-71) interposed between radially polarized magnets (60-65). Rotating the driving member (42) causes a tangential force to be generated on the driven member (40) which rotates the driven member (40). A non magnetic separator 44 allows the drive to be communicated to a sealed chamber. <IMAGE>

Description

Description Using Unidirectional Magnets for Coreless Torsional Magnetic Coupling Technical Field This invention relates to magnetic coupling and more particularly to torsional magnetic coupling.

Background Art The principle of torsional magnetic coupling is employed in a variety of applications where isolation between a torsional driving member and a corresponding driven member is important. For example, an apparatus for circulating corrosive liquids within a sealed container includes a pump within the container and a motor external to the container for driving the pump. Rotation of the driving member of the motor is translated to rotation of the driven member of the pump by torsional magnetic coupling of the driving member to the driven member. No part of the motor comes in contact with any part of the pump. The torsional magnetic coupling eliminates the need for dynamic seals (i.e. seals which come in contact with moving parts), thereby eliminating a common source of system leaks.

Referring to FIG. 1, a prior art torsional magnetic coupling 8 is comprised of a driven member 10 and a driving member 12. Both the driven member 10 and the driving member 12 rotate about a common central axis 14, which is perpendicular to the cross sectional view of FIG. 1. A plurality of unidirectionally polarized magnets 16-21 is disposed about the outer circumference of the driven member 10. Similarly, a plurality of unidirectionally polarized magnets 22-27 is disposed about the inner circumference of the driving member 12. Arrows on the magnets 16-27 indicate the polarity of the magnets 16-27 wherein the arrows point from the south to the north poles of each of the magnets 16-27. Each of the magnets 16-27 is radially polarized (i.e. the polarity gradients of the magnets 16-27 are parallel to radii which extend from the axis of rotation 14 to intersect the magnets 16-27).The polarities of the magnets 16-21 alternate about the circumference of the driven member 10. Likewise, the polarities of the magnets 22-27 alternate about the circumference of the driving member 10 (i.e. a magnet having a north pole facing inward is flanked on each side by magnets having a north pole facing outward and vice versa).

The driven member 10 has a ferromagnetic core 30 which is radially inward of the magnets 16-21.

The core 30 aids the flow of magnetic flux between the circumferentially adjacent magnets 16-21 of the driven member 10 . For example, magnetic flux flows from the magnet 16 to the magnet 21 via the core 30. Similarly, the driving member 12 has a ferromagnetic core 32, which is radially outward of the magnets 22-27. The core 32 aids the flow of magnetic flux between circumferentially adjacent magnets 22-27 of the driving member 12 . For example, magnetic flux flows from the magnet 27 to the magnet 22 via the core 32. The amount of tangential magnetic force experienced by the driven member 10 in response to rotation of the driving member 12 is dependant upon the amount of magnetic flux which flows between circumferentially adjacent magnets of both the driven member 10 and the driving member 12.

Therefore, the cores 30, 32, which increase the flow of magnetic flux between circumferentially adjacent magnets, increase the torsional force experienced by the driven member 10. However, the cores 30,32 increase the weight and the number of parts of the torsional magnetic coupling 8.

Increasing the weight of the driven member 10 increases the inertia of the driven member 10 thereby decreasing the effectiveness of any torsional force acting on the driven member 10.

Other types of torsional magnetic couplings exist which do not employ cores. The magnets and the core of the driven member are replaced by a multidirectionally polarized magnetic ring and the magnets and the core of the driving member are replaced by another multidirectionally polarized magnetic ring. However, the rings, which are multidirectionally polarized in order to approximate the alternating radial polarity of a plurality of unidirectionally polarized magnets, cannot be manufactured from anisotropic magnetic materials, which are otherwise desirable for some applications.

Disclosure of Invention Objects of the invention include employing unidirectionally polarized magnets to provide coreless torsional magnetic coupling.

According to the present invention, one or both members of a torsional magnetic coupling have radially polarized magnets disposed about the circumference of said member or members which are interposed by tangentially polarized magnets.

The foregoing and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of exemplary embodiments thereof, as illustrated in the accompanying drawings.

Brief Description of Drawings FIG. 1 is a schematic cross sectional view of a prior art torsional magnetic coupling.

FIG. 2 is a schematic cross sectional view of a torsional magnetic coupling according to the invention in an equilibrium state.

FIG. 3 is a schematic cross sectional view of a torsional magnetic coupling according to the invention in an equilibrium state which illustrates the path of magnetic flux through the coupling.

FIG. 4 is a schematic cross sectional view of a torsional magnetic coupling according to the invention in a nonequilibrium state.

Best Mode for Carrying Out the Invention Referring to the FIG. 2, a torsional magnetic coupling 36 of the invention is comprised of a driven member 40 and a driving member 42 which are separated by a nonmagnetic material 44. The driven member 40 is part of a sealed system (not shown) wherein at least part of the system is sealed by the nonmagnetic material 44. The driven member 40 and the driving member 42 are coaxial and hence rotate about a common axis 46 which is located at the radial center of both members 40, 42. The common axis 46 is perpendicular to the cross sectional view of FIG. 2.

The driven member 40 is comprised of six radially polarized unidirectional sector shaped magnets 48-53 and six tangentially polarized unidirectional inverse sector shaped magnets 54-59 disposed in an alternating sequence about the circumference of the driven member 40. The direction of polarization of the radially polarized magnets 48-53 is parallel to radial lines extending from the axis of rotation 46. The direction of polarity of the tangentially polarized magnets 54-59 is perpendicular to radial lines extending from the axis of rotation 46 The arrows on each of the magnets 48-59 indicate the direction of polarity of the magnets 48-59, wherein the arrows point from the south to the north pole of each of the magnets 48-59.

The driving member 42 is comprised of six radially polarized unidirectional inverse sector shaped magnets 60-65 and six tangentially polarized unidirectional sector shaped magnets 66-71 disposed in an alternating sequence about the circumference of the driving member 42. The direction of polarization of the magnets 60-71 is shown by arrows on the magnets 60-71 using the same convention as described above.

Referring to FIG. 3, flux paths within the magnetic coupling 36 are illustrated by a plurality of flux lines 72-77. Magnetic flux travels through the magnets 48-71 from the south pole to the north pole. Therefore, the arrows of the magnets 48-71, which indicate the polarity of each of the magnets 48-71, also indicate the direction of the flow of flux through each of the magnets 48-71. Note that magnetic flux flows between the magnets 48-71 by flowing from the north pole of one of the magnets 48-71 to the south pole of another one of the magnets 48-71.

The flux lines 72-77 illustrate that magnetic flux flows from the driving member 42 into the driven member 40 via the radially polarized magnets 49,51,53 which have the south pole facing radially outward (hereinafter referred to as "south facing" magnets) and that magnetic flux flows out of the driven member 40 via the radially polarized magnets 48,50,52 which have the north pole facing radially outward (hereinafter referred to as "north facing" magnets). The polarities of the radially polarized magnets 48-53 alternate about the circumference of the driven member 40 between south facing and north facing. Magnetic flux which flows into the driven member 40 via the south facing magnets 49,51,53 flows out of the driven member 40 via one or the other of the north facing magnets 48,50,52 which is circumferentially adjacent to a corresponding one of the south facing magnets 49,51,53.For example, the flux lines 72,73 illustrate that magnetic flux which flows into the driven member 40 via the magnet 49 flows out of the driven member 40 either via the magnet 48 (in the case of the flux line 72) or via the magnet 50 (in the case of the flux line 73).

Note that both of the north facing magnets 48,50 are circumferentially adjacent to the south facing magnet 49.

The radially polarized magnets 48-53 of the driven member 40 are interposed by tangentially polarized magnets 54-59. The north pole of each of the tangentially polarized magnets 54-59 abuts the north facing radially polarized magnets 48,50,52 while the south pole of the tangentially polarized magnets 5459 abuts the south facing radially polarized magnets 49,51,53. This arrangement aids the flow of magnetic flux between the south facing magnets 49,51,53 and the north facing magnets 48,50,52 within the driven member 40.

Magnetic flux flows from the driven member 40 into the driving member 42 via the radially polarized magnets 60,62,64 which have the south pole facing radially inward (hereinafter referred to as "south facing" magnets). Magnetic flux flows out of the driving member 42 via the radially polarized magnets 61,63,65 which have the north pole facing radially inward (hereinafter referred to as "north facing" magnets). The polarities of the radially polarized magnets 60-65 alternate about the circumference of the driving member 42 between south facing and north facing. Magnetic flux which flows into the driving member 42 via the south facing magnets 60,62,64 flows out of the driving member 42 via one or the other of the north facing magnets 61,63,65 which is circumferentially adjacent to a corresponding one of the south facing magnets 60,62,64.For example, the flux lines 73,74 illustrate that magnetic flux which flows into the driving member 42 via the magnet 62 flows out of the driving member 42 either via the magnet 61 (in the case of the flux line 73) or via the magnet 63 (in the case of the flux line 74). Note that both of the north facing magnets 61,63 are circumferentially adjacent to the south facing magnet 62.

The radially polarized magnets 60-65 of the driving member 42 are interposed by the tangentially polarized magnets 66-71. The north pole of each of the tangentially polarized magnets 66-71 abuts the north facing radially polarized magnets 61,63,65 while the south pole of the tangentially polarized magnets 66-71 abuts the south facing radially polarized magnets 60,62,64.

This arrangement aids the flow of magnetic flux between the south facing magnets 60,62,64 and the north facing magnets 61,63,65 within the driving member 42.

FIG. 2 and FIG. 3 illustrate the torsional magnetic coupling 36 at an equilibrium position wherein the north facing magnets 48,50,52 of the driven member 40 are aligned with the south facing magnets 60,62,64 of the driving member 42 and the south facing magnets 49,51,53 of the driven member 40 are aligned with the north facing magnets 61,63,65 of the driving member 42. At the equilibrium position, the tangential components of the magnetic flux acting on the driven member 40 equal zero, as indicated by the flux lines 72-73.

Tangential magnetic force acting on the driven member 40 is proportional to the product of the tangential flux and the radial flux. Since there is no tangential flux acting on the driven member 40 at the equilibrium position, there is no tangential force acting on the driven member 40 at the equilibrium position and therefore the driven member 40 is at rest. Note that although FIG. 2 and FIG. 3 show the magnet 48 aligned with the magnet 60, a similar equilibrium position exists when the magnet 48 aligns with the magnet 62 or when the magnet 48 aligns with the magnet 64.

Referring to FIG. 4, the driving member 42 is physically attached to and rotated in a clockwise direction by external means such as a motor (not shown). The relative angular positions of the driven member 40 and the driving member 42 in FIG.

4 (i.e. the angular displacement) cause both tangential and radial components of magnetic flux to exist at the driven member 40, as indicated by the flux lines 72-77. A tangential force 78, which acts on the driven member 40, is proportional to the product of the tangential component of the magnetic flux which acts on the driven member 40 and the radial component of the magnetic flux which acts on the driven member 40. The tangential force 78 causes the driven member 40 to rotate in a clockwise direction (i.e. the same direction as the driving member 42).The force 78 will act on the driven member 40 until the driven member 40 has rotated to an equilibrium position wherein the south facing magnets 49,51,53 of the driven member 40 align with the north facing magnets 61,63,65 of the driving member 42 and the north facing magnets 48,50,52 of the driven member 40 align with the south facing magnets 60,62,64 of the driving member 42 (i.e. the position shown in FIG. 2 and FIG. 3). Note that as the driven member 40 rotates closer to the equilibrium position, the magnitude of the force 78 decreases because the tangential component of the magnetic flux which acts on the driven member 40 decreases.

A pseudo equilibrium position exists wherein the south facing magnets 49,51,53 of the driven member 40 align with the south facing magnets 60,62,64 of the driving member 42 and the north facing magnets 48,50,52 of the driven member 40 align with the north facing magnets 61,63,65 of the driving member 42. This position is deemed the pseudo equilibrium position because even though the resultant tangential component of the magnetic flux which acts on the driven member 40 becomes zero, any angular displacement from this position causes a tangential magnetic force which acts in the same tangential direction as the displacement thereby tending to increase the amount of the displacement. For the equilibrium position, on the other hand, the tangential force 78 acts in the opposite direction of the displacement, thereby tending to decrease the displacement and hence return the driven member 40 to the equilibrium position.

When the driving member 42 is moved from the equilibrium position (e.g. by a motor which rotates the driving member 42), inertial effects cause the driven member 40 to lag behind the driving member 42. If the driving member 42 is rotated at a constant rate, the coupling 36 will eventually reach a steady state wherein the driven member 40 rotates at the same speed as the driving member 42, providing that the load on the driven member 40 is not excessive. Even at steady state, however, the driven member 40 will lag behind the driving member 42. The amount of lag is an angular displacement which is sufficient to generate a tangential force equal to the load on the driven member 40. If the displacement required to generate the load force causes the driven member 40 to rotate beyond the pseudo equilibrium position, the load is too great to be driven by the magnetic coupling 36.

The invention may be practiced by having more than one tangentially polarized magnet between every pair of radially polarized magnets.

Similarly, even though the invention is shon having one radially polarized magnet between every pair of tangentially polarized magnets, the invention may be practiced by having more than one radially polarized magnet between every pair of tangentially polarized magnets.

The invention may be practiced on the driven member 40 alone wherein the driving member 42 employs the old art, or the invention may be practiced on the driving member 42 alone wherein the driven member 40 employs the old art. The number of radially polarized magnets and tangentially polarized magnets used for the driving member 42 or for the driven member 40 may be changed without departing from the spirit and scope of the invention. The polarities of the radial magnets 48-53 of the driven member 40 and the radial magnets 60-65 of the driving member 42 may be arranged differently than alternating north facing and south facing as shown so long as provision is made for altering polarities of corresponding tangentially polarized magnets 54-59 of the driven member 40 and corresponding tangentially polarized magnets 66-71 of the driving member 42. Even though the driven member 40 and the driving member 42 are shown to be coaxial, it should be understood that the term "coaxial" encompasses the case wherein the axis of rotation of the driven member 40 and the axis of rotation of driving member 42 are located substantially near to one another. The invention may be practiced with magnets having different shapes than the exact shapes of the magnets 48-71 shown in FIG. 2, FIG. 3, or FIG. 4.

Although the invention has been shown and described with respect to exemplary embodiments thereof, it should be understood by those skilled in the art that various changes, omissions and additions may be made therein and thereto, without departing from the spirit and the scope of the invention.

Claims

Claims

I claim: 1. A magnetic coupling comprising: a driven member; and a driving member, coaxial with and radially outward of said driven member, having radially polarized magnets disposed about the circumference of said driving member which are interposed with tangentially polarized magnets.
2. A magnetic coupling, as set forth in claim 1, wherein said radially polarized magnets are alternatively south facing and north facing.
3. A magnetic coupling, as set forth in claim 2, wherein the north poles of said tangentially polarized magnets abut said north facing radially polarized magnets and wherein the south poles of said tangentially polarized magnets abut said south facing radially polarized magnets.
4. A magnetic coupling, as set forth in claim 3, wherein the number of radially polarized magnets equals six.
5. A magnetic coupling, as set forth in claim 4, wherein said tangentially polarized magnets are sector shaped.
6. A magnetic coupling, as set forth in claim 5, wherein said radially polarized magnets are inverse sector shaped.
7. A magnetic coupling comprising: a driving member; and a driven member, coaxial with and radially inward of said driving member, having radially polarized magnets disposed about the circumference of said driven member which are interposed with tangentially polarized magnets.
8. A magnetic coupling, as set forth in claim 7, wherein said radially polarized magnets are alternatively south facing and north facing.
9. A magnetic coupling, as set forth in claim 8, wherein the north poles of said tangentially polarized magnets abut said north facing radially polarized magnets and wherein the south poles of said tangentially polarized magnets abut said south facing radially polarized magnets.
10. A magnetic coupling, as set forth in claim 9, wherein the number of radially polarized magnets equals six.
11. A magnetic coupling, as set forth in claim 10, wherein said tangentially polarized magnets are inverse sector shaped.
12. A magnetic coupling, as set forth in claim 11, wherein said radially polarized magnets are sector shaped.
13. A magnetic coupling comprising: a driving member, having radially polarized magnets disposed about the circumference of said driving member which are interposed with tangentially polarized magnets; and a driven member, coaxial with and radially inward of said driving member, having radially polarized magnets disposed about the circumference of said driven member which are interposed with tangentially polarized magnets.
14. A magnetic coupling, as set forth in claim 13, wherein said radially polarized magnets are alternatively south facing and north facing.
15. A magnetic coupling, as set forth in claim 14, wherein the north poles of said tangentially polarized magnets abut said north facing radially polarized magnets and wherein the south poles of said tangentially polarized magnets abut said south facing radially polarized magnets.
16. A magnetic coupling, as set forth in claim 15, wherein the number of radially polarized magnets of said driving member equals six.
17. A magnetic coupling, as set forth in claim 16, wherein the number of radially polarized magnets of said driven member equals six.
18. A magnetic coupling, as set forth in claim 17, wherein said tangentially polarized magnets of said driven member are inverse sector shaped.
19. A magnetic coupling, as set forth in claim 18, wherein said radially polarized magnets of said driven member are sector shaped.
20. A magnetic coupling, as set forth in claim 19, wherein said tangentially polarized magnets of said driving member are sector shaped.
21. A magnetic coupling, as set forth in claim 20, wherein said radially polarized magnets of said driving member are inverse sector shaped.