Title of Invention	PERMANENT MAGNET ASSEMBLY
Abstract	The invention relates to a permanent magnet assembly comprising an arc- shaped flux return section formed of magnetically permeable material and extending along a portion of an arc and having an upper portion with a first end and a second end, a lower portion with a first end and a second end, and a middle portion with a first end and a second end, wherein the first end of the upper portion is operatively coupled to the first end of the middle portion and the first end of the lower portion is operatively coupled to the second end of the middle portion; an upper arc-shaped permanent magnet section having a north end and a south end, wherein the north end of the upper arc-shaped permanent magnet section is operatively coupled to the second end of the upper portion of the arc-shaped flux return section; and a lower arc-shaped permanent magnet section having a north end and a south end, wherein the south end of the lower arc-shaped permanent magnet section is operatively coupled to the second end of the lower portion of arc-shaped flux return section; wherein an arc-shaped gap is formed between the south end of the upper arc-shaped permanent magnet section and the north end of the lower arc-shaped permanent magnet section.

Title of Invention

PERMANENT MAGNET ASSEMBLY

Abstract

The invention relates to a permanent magnet assembly comprising an arc- shaped flux return section formed of magnetically permeable material and extending along a portion of an arc and having an upper portion with a first end and a second end, a lower portion with a first end and a second end, and a middle portion with a first end and a second end, wherein the first end of the upper portion is operatively coupled to the first end of the middle portion and the first end of the lower portion is operatively coupled to the second end of the middle portion; an upper arc-shaped permanent magnet section having a north end and a south end, wherein the north end of the upper arc-shaped permanent magnet section is operatively coupled to the second end of the upper portion of the arc-shaped flux return section; and a lower arc-shaped permanent magnet section having a north end and a south end, wherein the south end of the lower arc-shaped permanent magnet section is operatively coupled to the second end of the lower portion of arc-shaped flux return section; wherein an arc-shaped gap is formed between the south end of the upper arc-shaped permanent magnet section and the north end of the lower arc-shaped permanent magnet section.

Full Text	PERMANENT MAGNET ASSEMBLY FIELD OF THE INVENTION This invention relates generally to magnets, and more particularly to permanent magnet assemblies adapted to provide a time-varying magnetic field to an annular region. BACKGROUND OF THE INVENTION Permanent magnets have been used for many years and for many purposes. However, new applications of permanent magnets are driving the development of increasingly sophisticated permanent magnet assemblies. A permanent magnet assembly that can produce a high amplitude magnetic field intensity across a gap is of particular interest, especially in applications of magnetocaloric materials. Magnetocaloric materials near a transition from a ferromagnetic state to a paramagnetic state will warm when magnetized and cool when demagnetized. An apparatus that applies a time-varying magnetic field to magnetocaloric materials can be used to provide heating or cooling, for example in a magnetic refrigerator. A magnet assembly that produces a magnetic field intensity across a gap can be used to apply a time-varying magnetic field to magnetocaloric materials by moving the magnetocaloric materials in and out of the gap. This can be accomplished, for example, by moving the magnetocaloric materials relative to a stationary magnetic assembly, or by moving a magnet assembly relative to stationary magnetocaloric materials. Movement of magnetocaloric material relative to a magnet assembly can be accomplished through rotational or translational motion. One approach is to arrange magnetocaloric material in a stationary annular (ring- shaped) structure, and then to rotate a permanent magnet assembly around the ring. Another approach is to arrange magnetocaloric material in an annular structure partially surrounded by a stationary permanent magnet assembly, and then to rotate the annular structure containing the magnetocaloric material. Thus, a permanent magnet assembly specially adapted to provide a time-varying magnetic field to an annular region is of interest, for applications including, but not limited to, magnetic refrigeration. SUMMARY OF THE INVENTION A permanent magnet assembly according to the present invention utilizes one or more permanent magnet blocks and one or more flux return sections to form a permanent magnet assembly specially adapted to provide a time-varying magnetic field to an annular region. The permanent magnet assembly can include one or more pole pieces, although this is not required. The annular region can have a rectangular cross-section, although this is not required. A permanent magnet assembly according to the invention can be used, for example, in a rotating bed or rotating magnet magnetic refrigerator apparatus A preferred embodiment of a permanent magnet assembly according to the present invention includes an arc-shaped flux return section formed of magnetically permeable material having a C-shaped cross-section with two ends forming an opening, and upper and lower arc-shaped permanent magnet sections operatively coupled to the ends of the C of the flux return section, wherein an arc-shaped gap is formed between the south end of the upper arc-shaped permanent magnet section and the north end of the lower arc-shaped permanent magnet section. The flux return section of a permanent magnet assembly according to the invention can be positioned in the interior of the assembly in which case the opening of the flux return section faces outwardly from the central axis of the assembly. Alternatively, the flux return section can be positioned on the exterior of the assembly, at a radius from the central axis of the assembly, in which case the opening of the flux return section faces inwardly toward the central axis of the assembly. An alternative permanent magnet assembly according to the invention includes an upper flux return section formed of magnetically permeable material with a first arc-shaped upper permanent magnet section at one end and a second arc-shaped upper permanent magnet section at the other end, and a lower flux return section formed of magnetically permeable material with a first arc-shaped lower permanent magnet section at one end and a second arc-shaped lower permanent magnet section at the other end, wherein two arc-shaped gaps are formed between the permanent magnet sections at the ends of the upper and lower flux return sections. Another permanent magnet assembly according to the invention includes a central permanent magnet section and upper and lower pole pieces formed of magnetically permeable material that include arc-shaped side pole piece portions having pole faces that surround two arc-shaped gaps on the sides of the central permanent magnet section. A different embodiment of a permanent magnet assembly according to the invention includes an upper flux return section formed of magnetically permeable material with a first arc-shaped upper permanent magnet section at one end and a second arc-shaped upper permanent magnet section at the other end, and a lower flux return section formed of magnetically permeable material with a first arc-shaped lower permanent magnet section at one end and a second arc-shaped lower permanent magnet section at the other end, with a central flux return section between the upper and lower flux return sections, wherein two arc-shaped gaps are formed between the permanent magnet sections at the ends of the upper and lower flux return sections. A variety of structures can be used in an apparatus according to the invention. For example, the permanent magnet sections shown in the illustrative embodiments herein may be comprised of a single permanent magnet, or these permanent magnet sections may be comprised of one or more multiple permanent magnets and one or more sections of magnetically permeable material to form a magnetic array structure. Although the illustrative embodiments may show pole pieces or flux return sections formed as unitary structures, these structure may be comprised of individual sections which are operatively coupled together. Similarly, the relative dimensions, shapes, and positions of the permanent magnet sections, pole pieces, or flux return sections can be optimized for a particular application. A magnet assembly according to the invention can provide a time- varying magnetic field to an annular region. The particular shape and structure of such an annular region can be especially well suited for a rotating bed or rotating magnet magnetic refrigerator. Such a magnet assembly can allow constant access to the annular region that is subject to the time-varying magnetic field intensity, and this can enable components of a magnetic refrigerator such as magnetocaloric material and heat transfer fluid plumbing to be stationary and positioned within the annular region. Alternatively, the magnet assembly can be stationary, and components of a magnetic refrigerator such as magnetocaloric material and heat transfer fluid can rotate within the annular region. A magnet assembly according to the invention can have relatively low operating costs, for example by minimizing space requirements and by minimizing the mass of any moving parts. Such a magnet assembly can also have relatively low manufacturing costs, for example by reducing the need for precisely machined permanent magnets. Each of the permanent magnet portions of such a magnet assembly can be arc-shaped with a rectangular cross section or generally rectangular in shape, in either case with an orthogonal magnetization vector to minimize production costs. This geometry can be especially well suited to the manufacture of sintered NdFeB magnets by current pressing methods, and the relatively low number of magnet mating surfaces can reduce the number of precision grinding operations that might otherwise be required. Precisely machined structures used in a magnet assembly according to the invention, for example pole pieces that surround a gap at high magnetic field, may have surfaces that benefit from close tolerances to allow these surfaces to nest closely together with other components of a magnetic refrigerator, such as containers of magnetocaloric materials. By forming any structures requiring precise machining, such as pole pieces, of magnetically permeable material, and operatively coupling those precisely machined structures to rectangular permanent magnet portions, any precision machining of permanent magnet material can be reduced or avoided. A permanent magnet assembly according to the present invention can be used to generate a time-varying field over an annular region while minimizing the volume, mass, and fabrication cost of such an assembly. The magnetic field in the annular region can be used wherever a stationary or rotating wheel mechanism needs to be magnetized along part of its circumference. The particular design of this structure can allow unimpeded access to the annular region from one side, either from the exterior or from the interior, for example for plumbing carrying heat transfer fluid into and out of beds containing magnetocaloric materials located in the annular region. A permanent magnet assembly according to the invention can be of particular interest for use in a magnetic refrigeration device. Exemplary magnetic refrigeration devices that use rotational motion are shown in U.S. Pat. No. 6,526,759 and U.S. Pat. App. Pub. No. US 2003/0106323 A1, the disclosures of which are incorporated by reference. Further objects, features, and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: FIG. 1 is a perspective view of a permanent magnet assembly according to the invention with an exterior flux return path; FIG. 2 is a perspective view of the permanent magnet assembly of Fig. 1, showing the axis of rotation and the annular region swept by the rotation of the permanent magnet assembly; FIG. 3 is a perspective view of a permanent magnet assembly according to the invention with an interior flux return path; FIG. 4 is a perspective view of another permanent magnet assembly according to the invention with upper and lower interior flux return paths; FIG. 5 is a perspective view of an alternative permanent magnet assembly according to the invention with a central magnet and upper and lower pole pieces; FIG. 6 is a cross-sectional view of the permanent magnet assembly of Fig. 5 taken along the line 6-6 thereof; and FIG. 7 is a perspective view of an alternative permanent magnet assembly according to the invention with an upper interior flux return path and a lower interior flux return path connected by a central flux return path. DETAILED DESCRIPTION OF THE INVENTION Referring to the drawings, Fig. 1 is a perspective view of a permanent magnet assembly according to the invention, indicated generally at 20. The permanent magnet assembly 20 surrounds an arc-shaped gap at high magnetic field 21 having a rectangular cross section 22 over an arc length of approximately 120 degrees, although the gap cross-section may have a different shape and the arc length may be greater than or less than 120 degrees. As perhaps best shown in Fig. 2, the permanent magnet assembly 20 is adapted to rotate about an axis of rotation 23, thereby sweeping an annular region 24. The permanent magnet assembly 20 includes an exterior flux return portion, indicated generally at 30, to provide a return path for the lines of magnetic flux and thereby complete the magnetic circuit. The flux return portion 30 is preferably of sufficient dimension to avoid saturation with magnetic flux, and is preferably shaped and exteriorly positioned at a sufficient distance from the gap at high magnetic field 21 to prevent shunting of the gap flux into the flux return portion 30. The flux return portion 30 can be formed of any suitable magnetically permeable material, for example a structural alloy such as low-carbon steel that has the ability to carry flux, or a specifically permeable material intended for use in magnetics such as the material sold by High Temp Metals of California, USA under the trademark Permendur 2V, or a combination of these materials, with or without additional non-permeable materials used, for example, to provide structural support. The flux return portion 30 can include one or more chamfered corners 31, for example along the outer corners, or filled-in corners 32, for example along interior corners, to optimize flux return performance while minimizing stray flux and assembly weight. The permanent magnet assembly 20 includes an upper permanent magnet portion, indicated generally at 33, having a North pole 34 (marked "N") and a South pole 35 (marked "S"), and a lower permanent magnet portion, indicated generally at 36, having a North pole 37 and a South pole 38. The upper permanent magnet portion 33 and lower permanent magnet portion 36 can be formed of any suitable permanent magnet material, for example of the type sold by Sumitomo Special Metals of Japan under the trademark Neomax 50. As shown in Figs. 1 and 2, the South pole 35 of the upper permanent magnet portion 33 and the North pole 37 of the lower permanent magnet portion 36 face the gap at high magnetic field 21. Fig. 3 is a perspective view of a permanent magnet assembly according to the invention, indicated generally at 45, having an interior flux return path. The permanent magnet assembly 45 may be especially useful in rotating magnet applications where the rotational moment of inertia is of concern. The permanent magnet assembly 45 surrounds an arc-shaped gap at high magnetic field 56 having a rectangular cross section over a given arc length, although this is not required and the cross-section may have different shapes and the arc length may be greater than or less than the arc length of the permanent magnet assembly 45. The permanent magnet assembly 45 includes an interior flux return portion, indicated generally at 46, to provide a return path for the lines of magnetic flux and thereby complete the magnetic circuit. The permanent magnet assembly 45 can be adapted to rotate about an axis of rotation 47, thereby sweeping an annular region. The flux return portion 46 of the permanent magnet assembly 45 is preferably of sufficient dimension to avoid saturation with magnetic flux and to avoid flux leakage elsewhere in the wheel. The flux return portion 46 is preferably shaped and interiorly positioned at a sufficient distance from the gap at high magnetic field 56 to prevent shunting of the gap flux into the flux return portion 46. The flux return portion 46 can be formed of any suitable magnetically permeable material, for example of the types discussed above. Although the interior flux return portion 46 may come to an abrupt corner at the central axis of the assembly, other shapes may be used depending on flux density, mounting considerations, and counter-weighting among other factors. The flux return portion 46 can include one or more chamfered corners 48, for example along the outer corners, or filled-in corners 49, for example along interior corners, to optimize flux return while minimizing stray flux, assembly weight, and rotational moment of inertia. The permanent magnet assembly 45 includes an upper permanent magnet portion, indicated generally at 50, having a North pole 51 (marked "N") and a South pole 52 (marked "S"), and a lower permanent magnet portion, indicated generally at 53, having a North pole 54 and a South pole 55. The upper permanent magnet portion 50 and lower permanent magnet portion 53 can be formed of any suitable permanent magnet material, for example of the types discussed above. As shown in Fig. 3, the South pole 52 of the upper permanent magnet portion 50 and the North pole 54 of the lower permanent magnet portion 53 surround the gap at high magnetic field 56. Fig. 4 is a perspective view of another permanent magnet assembly according to the invention, indicated generally at 60, having upper and lower interior flux return paths and providing two gaps at high magnetic field. Compared to the permanent magnet assemblies of Figs. 1 and 3 which use a single flux return path, the lines of flux travel a comparatively shorter distance from one magnetic pole to the next in the permanent magnet assembly 60, such that the two flux return paths in the permanent magnet assembly 60 can be individually less massive that the single flux return paths of Figs. 1 and 3. This property can make the permanent magnet assembly 60 especially useful in rotating magnet applications that require at least some central free space along the axis of rotation where the rotational moment of inertia is also of concern. As shown in Fig. 4, the permanent magnet assembly 60 surrounds two arc-shaped gaps at high magnetic field 74 having a rectangular cross section over an arc length, where each arc-shaped gap extends approximately 60 degrees, although this is not required and the gap cross-sections may have a different shape and the arc lengths may be greater than or less than 60 degrees. The permanent magnet assembly 60 includes two interior flux return portions, an upper flux return portion, indicated generally at 62, and a lower flux return portion, indicated generally at 63, to provide a return path for the lines of magnetic flux and thereby complete the magnetic circuit. The permanent magnet assembly 60 can be adapted to rotate about an axis of rotation 61, thereby sweeping an annular region. The upper flux return portion 62 and lower flux return portion 63 each include a central portion 64 extending outward from the axis of rotation. The upper flux return portion 62 and lower flux return portion 63 each preferably also include horizontally tapered portions 65 that concentrate the lines of flux in the central portion 64. A non-permeable axial link along the axis of rotation 61 that connects the upper flux return portion 62 and the lower flux return portion 63 through the center of the assembly can be used to provide structural support. The upper flux return portion 62 and lower flux return portion 63 of the permanent magnet assembly 60 are preferably of sufficient dimension to avoid saturation with magnetic flux and to avoid flux leakage elsewhere in the wheel. The upper flux return portion 62 and lower flux return portion 63 are preferably shaped and positioned at a sufficient distance from the gaps at high magnetic field 74 to prevent shunting of the gap flux into those flux return portions. The upper flux return portion 62 and lower flux return portion 63 can be formed of any suitable magnetically permeable material, for example of the types discussed above. The upper flux return portion 62 has a first end operatively coupled to a first upper permanent magnet portion 66 and a second end operatively coupled to a second upper permanent magnet portion 67, with each of the upper permanent magnet portions 66 and 67 having a North pole 68 (marked "N") and a South pole 69 (marked "S"). Similarly, the lower flux return portion 63 has a first end operatively coupled to a first lower permanent magnet portion 70 and a second end operatively coupled to a second lower permanent magnet portion 71, with each of the lower permanent magnet portions 70 and 71 having a North pole 68 (marked "N") and a South pole 69 (marked "S"). As shown in Fig. 4, the polar orientations of the upper and lower permanent magnet portions 66, 67, 70, and 71 are aligned to produce a circular flux around the magnetic circuit formed by the permanent magnet portions and the flux return portions. Relative to the first lower permanent magnet portion 70 and the first upper permanent magnet portion 66 which are aligned together in one direction, the second upper permanent magnet portion 67 and the second lower permanent magnet portion 71 are aligned together in the opposite direction, thereby forming a circular flux loop. The upper permanent magnet portions 66 and 67 and the lower permanent magnet portions 70 and 71 can be formed of any suitable permanent magnet material, for example of the types discussed above. As shown in Fig. 4, the South pole 73 of the first lower permanent magnet portion 70 and the North pole 68 of the first upper permanent magnet portion 66 surround one gap at high magnetic field 74, and the South pole 69 of the second upper permanent magnet portion 67 and the North pole 72 of the second lower permanent magnet portion 71 surround a second gap at high magnetic field 74. Although in Fig. 4 the upper flux return portion 62 and the lower flux return portion 63 have a uniform thickness in the vertical direction, and although these flux return portions join the upper and lower permanent magnet portions 66, 67, 70, and 71 at abrupt corners, other shapes may be used depending on flux density, mounting considerations, and counter- weighting among other factors. The flux return portions can include one or more chamfered or rounded corners, for example along the outer corners or edges of the flux return portions, or filled-in corners, for example along the junction between the flux return portions and the permanent magnet portions, to optimize flux return while minimizing stray flux and assembly weight. Fig. 5 is a perspective view of an alternative permanent magnet assembly according to the invention indicated generally at 80, with a central magnet and upper and lower pole pieces and providing two gaps at high magnetic field. In the permanent magnet assembly 80, the majority of the assembly sits within the outer diameter of the wheel, thereby minimizing the rotational moment of inertia of the assembly. As shown in Fig. 5, the permanent magnet assembly 80 includes a central permanent magnet portion 81 with an upper pole piece 85 and a lower pole piece 86 which direct the magnetic flux from the central permanent magnet portion 81 through two arc-shaped gaps at high magnetic field 94 over a given arc length. Each gap typically extends 60 degrees, but this is not required and greater or lesser arc lengths can be used. The permanent magnet assembly 80 can be adapted to rotate about an axis of rotation 82, thereby sweeping an annular region. The central permanent magnet portion 81 of permanent magnet assembly 80 has a North pole 83 (marked "N") and a South pole 84 (marked "S"), with the magnetic vector of the central permanent magnet portion 81 aligned with the axis of rotation 82. The central permanent magnet portion 81 can be formed of any suitable permanent magnet material, for example of the types discussed above. The permanent magnet assembly 80 includes an upper pole piece, indicated generally at 85, and a lower pole piece, indicated generally at 86. The upper and lower pole pieces 85 and 86 are of similar construction, each having a central pole piece portion 87 with two ends, where each end of each central pole piece bears a side pole piece portion 88. The upper pole piece 85 and lower pole piece 86 can be formed of any suitable magnetically permeable material, for example of the types discussed above. Each side pole piece portion 88 can include one or more chamfered corners 89. Fig. 6 is a cross-sectional view of the permanent magnet assembly of Fig. 5 taken along the line 6-6 thereof. As shown in Figs. 5 and 6, each end of the upper pole piece 85 terminates in an upper pole face 92. Each end of the lower pole piece 86 terminates in a lower pole face 93. The upper pole faces 92 and the lower pole faces 93 surround the two gaps at high magnetic field 94. As perhaps best shown in Fig. 6, the side pole piece portions 88 preferably include vertically tapered portions 90, and as perhaps best shown in Fig. 5, the side pole piece portions 88 preferably also include horizontally tapered portions 91. The vertically tapered portions 90 and horizontally tapered portions 91 can be used, for example, to concentrate the magnetic flux into the two gaps at high magnetic field 94. As lines of flux leave the permanent magnet portion 81, the lines of flux converge along the vertically tapered portions 90 and horizontally tapered portions 91, whereby the flux lines crossing the gaps 94 can be at a higher density than the flux lines within the permanent magnet portion 81, providing a magnetic flux density in the gaps 94 that can be greater than the saturation flux density of the magnetic material comprising the permanent magnet portion 81 without the need for a multi-pole magnet array. The upper pole piece 85 and the lower pole piece 86 of the permanent magnet assembly 80 are preferably of sufficient dimension to avoid saturation with magnetic flux and to avoid flux leakage elsewhere in the wheel. The vertically tapered portions 90, the horizontally tapered portions 91, and the pole faces 92 and 93 are preferably shaped and positioned to place the gaps at high magnetic field 94 at a sufficient distance from the permanent magnet portion 81 to prevent shunting of the gap flux back into the permanent magnet portion 81. Although the central portions 87 of the upper and lower pole pieces 85 and 86 have a uniform thickness in the vertical direction, other shapes may be used depending on flux density, mounting considerations, and counter- weighting among other factors. The upper and lower pole pieces 85 and 86 may include additional tapering in one or more directions, for example between the central pole piece portion 87 and the upper and lower pole faces 92 and 93, to further concentrate the lines of flux into the gaps 94. The upper and lower pole pieces 85 and 86 may include additional chamfered or rounded corners, for example along the outer corners or edges of the flux return portions, or filled-in corners, for example along the junction between the flux return portions and the permanent magnet portions, to optimize flux density through the gaps 94 while minimizing stray flux and assembly weight. As perhaps best shown in Fig. 6, the cross-section of the gaps at high magnetic field 94 can be trapezoidal, with an angle theta 95 between the horizontal and the lower pole face 93. There can also be a complementary angle between the horizontal and the upper pole face 92, although this is not required. The angle theta 95 is positive in the permanent magnet assembly 80 of Figs. 5 and 6, such that the interior dimension of the cross-section of the gaps at high magnetic field 94 is less than the exterior dimension of that cross- section, although this is not required. The angle theta 95 can also be zero, in which case the interior dimension of the cross-section of the gaps at high magnetic field would be equal to the exterior dimension of that cross-section. The angle theta 95 can also be negative, in which case the interior dimension of the cross-section of the gaps at high magnetic field would be greater than the exterior dimension of that cross-section. Although the upper pole faces 92 and the lower pole face 93 are shown as essentially planar, this is not required and other shapes may be used. For example, in some applications of a permanent magnet assembly according to the invention the pole faces could be concave or convex. Thus, the cross- section of the gaps at high magnetic field 94 can include, but not be limited to, a rectangle (including but not limited to a square), a parallelogram, a trapezoid, a circle, an oval, or nearly any other shape or combination of shapes. Fig. 7 is a perspective view of an alternative permanent magnet assembly according to the invention, indicated generally at 100, with an upper interior flux return path and a lower interior flux return path connected by a central flux return path. The permanent magnet assembly 100 of Fig. 7 is similar to the permanent magnet assembly 60 of Fig. 4, except that the permanent magnet assembly 100 includes a central flux return path and the permanent magnet sections have different polarities. By including the central flux return path in the permanent magnet assembly 100, and by aligning the polarities of the permanent magnet sections as shown in Fig. 7, the two arc-shaped gaps in the permanent magnet assembly 100 experience a magnetic field having the same polarity. In contrast, the two arc-shaped gaps at each end of in the permanent magnet assembly 60 shown in Fig. 4 experience a magnetic field having opposite polarities. Compared to the permanent magnet assembly 60 of Fig. 4, a structure positioned within the annular volume swept by the permanent magnet assembly 100 will experience less magnetic hysteresis, since the magnetic field does not reverse direction at the two ends of the permanent magnet assembly 100. This property can make the permanent magnet assembly 100 especially useful for applications in which it is desirable to minimize magnetic hysteresis. As shown in Fig. 7, the permanent magnet assembly 100 surrounds two arc-shaped gaps at high magnetic field 115 having a rectangular cross section over a given arc length, although this is not required and the cross- section may have a different shape. Each arc-shaped gap typically extends 60 degrees, although this is not required and greater or lesser arc lengths can be used. The permanent magnet assembly 100 includes an upper flux return portion 102, a lower flux return portion 103, and a central flux portion 104, to provide a return path for the lines of magnetic flux and thereby complete the magnetic circuit. The permanent magnet assembly 100 can be adapted to rotate about an axis of rotation 101, thereby sweeping an annular region. The upper flux return portion 102 and lower flux return portion 103 each include a central portion 105 extending outward from the axis of rotation 101. The central flux return portion 104 operatively couples the central portion 105 of the upper flux return portion 102 and the central portion 105 of the lower flux return portion 103. The upper flux return portion 102 and lower flux return portion 103 each preferably also include horizontally tapered portions 106 that concentrate the lines of flux in the central portion 105 of the upper flux return portion 102, the central portion 105 of the lower flux return portion 103, and the central flux return portion 104. In addition to the central flux return portion 104, the permanent magnet assembly 100 may also include one or more non-permeable members between the upper flux return portion 102 and the lower flux return portion 103 to provide additional structural support, although this is not required. The upper flux return portion 102, lower flux return portion 103, and central flux return portion 104 of the permanent magnet assembly 100 are preferably of sufficient dimension to avoid saturation with magnetic flux and to avoid flux leakage elsewhere in the wheel. The upper flux return portion 102, lower flux return portion 103, and central flux return portion 104 are preferably shaped and positioned at a sufficient distance from the gap at high magnetic field 115 to prevent shunting of the gap flux into those flux return portions. The upper flux return portion 102, lower flux return portion 103, and central flux return portion 104 can be formed of any suitable magnetically permeable material, for example of the types discussed above. The upper flux return portion 102 has a first end operatively coupled to a first upper permanent magnet portion 107 and a second end operatively coupled to a second upper permanent magnet portion 108, with each of the upper permanent magnet portions 107 and 108 having a North pole 109 (marked "N") and a South pole 110 (marked "S"). Similarly, the lower flux return portion 103 has a first end operatively coupled to a first lower permanent magnet portion 111 and a second end operatively coupled to a second lower permanent magnet portion 112, with each of the lower permanent magnet portions 111 and 112 having a North pole 113 (marked "N") and a South pole 114 (marked "S"). As shown in Fig. 7, the polar orientations of the upper and lower permanent magnet portions 107, 108, 111, and 112 are all aligned in the same direction. This alignment produces two circular flux loops around the magnetic circuits formed by the permanent magnet portions and the upper, lower, and central flux return portions. The upper permanent magnet portions 107 and 108 and the lower permanent magnet portions 111 and 112 can be formed of any suitable permanent magnet material, for example of the types discussed above. As shown in Fig. 7, the South pole 110 of the first upper permanent magnet portion 107 and the North pole 113 of the first lower permanent magnet portion 111 surround one gap at high magnetic field 115, and the South pole 110 of the second upper permanent magnet portion 108 and the North pole 113 of the second lower permanent magnet portion 112 surround a second gap at high magnetic field 115. Although in Fig. 7 the upper flux return portion 102 and the lower flux return portion 103 have a uniform thickness in one direction and the central flux return portion 104 has a uniform thickness in two directions, and although these flux return portions can be joined together and to the upper and lower permanent magnet portions 107, 108, 111, and 112 at abrupt corners, other shapes may be used depending on flux density, mounting considerations, and counter-weighting among other factors. The flux return portions can include one or more chamfered or rounded corners, for example along the outer corners or edges of the flux return portions. The flux return portions can also have filled-in corners, for example along the junctions between the flux return portions or the junctions between the flux return portions and the permanent magnet portions. In a particular application, the specific shapes can be chosen, for example, to maximize flux return while minimizing stray flux and assembly weight. There are various possibilities with regard to alternative embodiments and applications of a magnet assembly according to the invention. Although the exemplary embodiments of the present invention refer to specific materials, other materials known to those skilled in the art as having suitable properties can be appropriately substituted. Although particular structures and portions of the embodiments described herein are referred to using the terms "upper," "lower," "vertical," and "horizontal," and the like, it is understood that those terms are used in reference to the exemplary orientations shown in the drawings herein. It is understood that a permanent magnet assembly according to the invention can be used in any orientation, and the use of a particular term such as "vertical" or "horizontal" is used to describe the relationship between particular structures and portions of the embodiments described herein and not to limit those structures or portions of the embodiments to any particular orientation or frame of reference. Although the exemplary embodiments of the present invention show particular shapes and relative dimensions, other shapes and dimensions can be used. For example, although the total arc length at high magnetic field will usually range between 90 and 180 degrees, with 120 degrees being typical, other arc lengths may be used in an appropriate case and the exact arc length is not important to the invention. Further, the total arc length at high magnetic field may be comprised of a single arc-shaped gap at high magnetic field, or the total arc length at high magnetic field may be divided among a plurality of arc-shaped gaps at high magnetic field. Although the exemplary embodiments of the present invention herein may show individual portions and sections having unitary construction, other constructions can be used. For example, a flux return section or portion can have a unitary construction, or such a flux return section or portion can be comprised of a plurality of pieces which are attached together. Similarly, a permanent magnet section or portion can have a unitary construction, or such a permanent magnet section or portion can be comprised of a plurality of permanent magnet pieces, possibly including magnetically permeable pieces or magnetically impermeable pieces, which are attached together. For example, a rectangular permanent magnet section may be operatively coupled to an arc-shaped pole piece to obtain a structure which is the equivalent of an arc-shaped permanent magnet section. Although the exemplary embodiments of the present invention herein may show individual portions and sections having square or rectangular cross-sections, other constructions can be used. For example, a flux return section could have a continuously curved shape, a trapezoidal shape, or any combination of shapes. Although the exemplary embodiments of the present invention here may show permanent magnet sections or portions positioned adjacent to an arc-shaped gap without any intermediate components, this is not required. For example, one or more pole faces formed of magnetically permeable material may be positioned between the permanent magnet sections or portions and the arc-shaped gap in order to direct or concentrate the magnetic flux through the arc-shaped gap. The exemplary embodiments herein are described as being adapted to rotate about an axis whereby the permanent magnet assembly provides a gap at high magnetic field that sweeps an annular region, to thereby apply a time- varying magnetic field to the annular region. By rotating the permanent magnet assembly, a time-varying magnetic field can be applied to a structure located within the annular region, such as a ring of beds containing magnetocaloric materials. In this fashion, a rotating permanent magnet assembly according to the invention can be combined with stationary magnetocaloric materials for use in a rotating magnet magnetic refrigerator. However, it should be understood that a permanent magnet according to the invention can also be used in a stationary configuration, wherein an annular structure, such as a ring of beds containing magnetocaloric materials, is adapted to rotate relative to the permanent magnet assembly. In this fashion, a stationary permanent magnet assembly according to the invention can be combined with rotating magnetocaloric materials for use in a rotating bed magnetic refrigerator. Of course, a permanent magnet assembly according to the invention can also be used in a configuration in which both the permanent magnet assembly and the magnetocaloric materials rotate, in opposite directions or in the same direction at different angular velocities. Similarly, a permanent magnet assembly according to the invention can be used in a configuration in which either or both of the permanent magnet assembly or the magnetocaloric materials oscillate back and forth or otherwise move relative to each other. It is understood that the invention is not limited to the particular embodiments described herein, but embraces all such modified forms thereof as come within the scope of the following claims. WE CLAIM 1. A permanent magnet assembly comprising: an arc-shaped flux return section formed of magnetically permeable material and extending along a portion of an arc and having an upper portion with a first end and a second end, a lower portion with a first end and a second end, and a middle portion with a first end and a second end, wherein the first end of the upper portion is operatively coupled to the first end of the middle portion and the first end of the lower portion is operatively coupled to the second end of the middle portion; an upper arc-shaped permanent magnet section having a north end and a south end, wherein the north end of the upper arc-shaped permanent magnet section is operatively coupled to the second end of the upper portion of the arc-shaped flux return section; and a lower arc-shaped permanent magnet section having a north end and a south end, wherein the south end of the lower arc-shaped permanent magnet section is operatively coupled to the second end of the lower portion of arc-shaped flux return section; wherein an arc-shaped gap is formed between the south end of the upper arc-shaped permanent magnet section and the north end of the lower arc- shaped permanent magnet section. 2. The permanent magnet assembly as claimsed in claim 1 wherein the arc-shaped flux return section has a unitary construction. 3. The permanent magnet assembly as claimed in claim 1 wherein the arc-shaped flux return section is formed of at least two pieces which are operatively connected to carry magnetic flux. 4. The permanent magnet assembly as claim wherein the upper arc- shaped permanent magnet section has a unitary construction and the lower arc-shaped permanent magnet section has a unitary construction. 5. The permanent magnet assembly as claimed in claim 1 wherein at least one of the upper arc-shaped permanent magnet section and the lower arc-shaped permanent magnet section comprises at least two permanent magnet portions. 6. The permanent magnet assembly ef claim 1 wherein the arc-shaped gap has a rectangular cross-section. 7. The permanent magnet assembly as claimed in claim 1 wherein the arc-shaped gap has a trapezoidal cross-section. 8. The permanent magnet assembly ef claim 1 comprising at least one pole piece operatively coupled to the south end of the upper arc-shaped permanent magnet section. 9. The permanent magnet assembly as claimed in claim 1 comprising at least one pole piece operatively coupled to the north end of the lower arc-shaped permanent magnet section. 10.The permanent magnet assembly of claim 1 comprising at least one pole piece operatively coupled to the south end of the upper arc-shaped permanent magnet section and at least one pole piece operatively coupled to the north end of the lower arc-shaped permanent magnet section. 11. A permanent magnet assembly comprising: a central flux return section formed of magnetically permeable material and having an upper portion with a first end and a second end, a lower portion with a first end and a second end, and a central portion with a first end and a second end wherein the first end of the upper portion is operatively coupled to the first end of the central portion and the first end of the lower portion is operatively coupled to the second end of the central portion; an upper arc-shaped permanent magnet section having a north end and a south end, wherein the north end of the upper arc-shaped permanent magnet section is operatively coupled to the second end of the upper portion of the central flux return section; and a lower arc-shaped permanent magnet section having a north end and a south end, wherein the south end of the lower arc-shaped permanent magnet section is operatively coupled to the second end of the lower portion of the central flux return section; wherein an arc-shaped gap is formed between the south end of the upper arc-shaped permanent magnet section and the north end of the lower arc- shaped permanent magnet section. 12.A permanent magnet assembly comprising: an upper flux return section formed of magnetically permeable material and having a middle section, a first end, and a second end; a first arc-shaped upper permanent magnet section having a south end, and a north end operatively coupled to the first end of the upper flux return section; a second arc-shaped upper permanent magnet section having a north end, and a south end operatively coupled to the second end of the upper flux return section; a lower flux return section formed of magnetically permeable material and having a middle section, a first end, and a second end; a first arc-shaped lower permanent magnet section having a north end, and a south end operatively coupled to the first end of the lower flux return section; and a second arc-shaped lower permanent magnet section having a south end, and a north end operatively coupled to the second end of the lower flux return section; wherein a first arc-shaped gap is formed between the south end of the first arc-shaped upper permanent magnet section and the north end of the first arc-shaped lower permanent magnet section and wherein a second arc-shaped gap is formed between the north end of the second arc-shaped upper permanent magnet section and the south end of the second arc-shaped lower permanent magnet section. 13. A permanent magnet assembly comprising: a central permanent magnet section having a north end and a south end; an upper pole piece formed of magnetically permeable material and having a first end bearing an arc-shaped side pole piece portion having a pole face, and a second end bearing an arc-shaped side pole piece portion having a pole face; and a lower pole piece formed of magnetically permeable material and having a first end bearing an arc-shaped side pole piece portion having a pole face, and a second end bearing an arc-shaped side pole piece portion having a pole face; wherein a first arc-shaped gap is formed between the pole face of the arc- shaped side pole piece portion of the first end of the upper pole piece and the pole face of the arc-shaped side pole piece portion of the first end of the lower pole piece and a second arc-shaped gap is formed between the pole face of the arc-shaped side pole piece portion of the second end of the upper pole piece and the pole face of the arc-shaped side pole piece portion of the second end of the lower pole piece. 14.A permanent magnet assembly comprising: an upper flux return section formed of magnetically permeable material and having a middle portion, a first end, and a second end; a first arc-shaped upper permanent magnet section having a south end, and a north end operatively coupled to the first end of the upper flux return section; a second arc-shaped upper permanent magnet section having a south end, and a north end operatively coupled to the second end of the upper flux return section; a lower flux return section formed of magnetically permeable material and having a middle portion, a first end, and a second end; a first arc-shaped lower permanent magnet section having a north end, and a south end operatively coupled to the first end of the lower flux return section; a second arc-shaped lower permanent magnet section having a north end, and a south end operatively coupled to the second end of the lower flux return section; and a central flux return section formed of magnetically permeable material and having a middle section, a first end operatively coupled to the middle portion of the upper flux return section, and a second end operatively coupled to the middle portion of the lower flux return section; wherein a first arc-shaped gap is formed between the south end of the first arc-shaped upper permanent magnet section and the north end of the firs arc-shaped lower permanent magnet section and wherein a second arc-shaped gap is formed between the south end of the second arc-shaped upper permanent magnet section and the north end of the second arc-shaped lower permanent magnet section. The invention relates to a permanent magnet assembly comprising an arc- shaped flux return section formed of magnetically permeable material and extending along a portion of an arc and having an upper portion with a first end and a second end, a lower portion with a first end and a second end, and a middle portion with a first end and a second end, wherein the first end of the upper portion is operatively coupled to the first end of the middle portion and the first end of the lower portion is operatively coupled to the second end of the middle portion; an upper arc-shaped permanent magnet section having a north end and a south end, wherein the north end of the upper arc-shaped permanent magnet section is operatively coupled to the second end of the upper portion of the arc-shaped flux return section; and a lower arc-shaped permanent magnet section having a north end and a south end, wherein the south end of the lower arc-shaped permanent magnet section is operatively coupled to the second end of the lower portion of arc-shaped flux return section; wherein an arc-shaped gap is formed between the south end of the upper arc-shaped permanent magnet section and the north end of the lower arc-shaped permanent magnet section.

Full Text

PERMANENT MAGNET ASSEMBLY
FIELD OF THE INVENTION
This invention relates generally to magnets, and more particularly to
permanent magnet assemblies adapted to provide a time-varying magnetic
field to an annular region.
BACKGROUND OF THE INVENTION
Permanent magnets have been used for many years and for many
purposes. However, new applications of permanent magnets are driving the
development of increasingly sophisticated permanent magnet assemblies. A
permanent magnet assembly that can produce a high amplitude magnetic
field intensity across a gap is of particular interest, especially in applications of
magnetocaloric materials. Magnetocaloric materials near a transition from a
ferromagnetic state to a paramagnetic state will warm when magnetized and
cool when demagnetized. An apparatus that applies a time-varying magnetic
field to magnetocaloric materials can be used to provide heating or cooling,
for example in a magnetic refrigerator.
A magnet assembly that produces a magnetic field intensity across a
gap can be used to apply a time-varying magnetic field to magnetocaloric
materials by moving the magnetocaloric materials in and out of the gap. This
can be accomplished, for example, by moving the magnetocaloric materials
relative to a stationary magnetic assembly, or by moving a magnet assembly
relative to stationary magnetocaloric materials.
Movement of magnetocaloric material relative to a magnet assembly
can be accomplished through rotational or translational motion. One
approach is to arrange magnetocaloric material in a stationary annular (ring-
shaped) structure, and then to rotate a permanent magnet assembly around
the ring. Another approach is to arrange magnetocaloric material in an
annular structure partially surrounded by a stationary permanent magnet
assembly, and then to rotate the annular structure containing the
magnetocaloric material. Thus, a permanent magnet assembly specially
adapted to provide a time-varying magnetic field to an annular region is of
interest, for applications including, but not limited to, magnetic refrigeration.
SUMMARY OF THE INVENTION
A permanent magnet assembly according to the present invention
utilizes one or more permanent magnet blocks and one or more flux return
sections to form a permanent magnet assembly specially adapted to provide a
time-varying magnetic field to an annular region. The permanent magnet
assembly can include one or more pole pieces, although this is not required.
The annular region can have a rectangular cross-section, although this is not
required. A permanent magnet assembly according to the invention can be
used, for example, in a rotating bed or rotating magnet magnetic refrigerator
apparatus
A preferred embodiment of a permanent magnet assembly according
to the present invention includes an arc-shaped flux return section formed of
magnetically permeable material having a C-shaped cross-section with two
ends forming an opening, and upper and lower arc-shaped permanent
magnet sections operatively coupled to the ends of the C of the flux return
section, wherein an arc-shaped gap is formed between the south end of the
upper arc-shaped permanent magnet section and the north end of the lower
arc-shaped permanent magnet section.
The flux return section of a permanent magnet assembly according to
the invention can be positioned in the interior of the assembly in which case
the opening of the flux return section faces outwardly from the central axis of
the assembly. Alternatively, the flux return section can be positioned on the
exterior of the assembly, at a radius from the central axis of the assembly, in
which case the opening of the flux return section faces inwardly toward the
central axis of the assembly.
An alternative permanent magnet assembly according to the invention
includes an upper flux return section formed of magnetically permeable
material with a first arc-shaped upper permanent magnet section at one end
and a second arc-shaped upper permanent magnet section at the other end,
and a lower flux return section formed of magnetically permeable material with
a first arc-shaped lower permanent magnet section at one end and a second
arc-shaped lower permanent magnet section at the other end, wherein two
arc-shaped gaps are formed between the permanent magnet sections at the
ends of the upper and lower flux return sections.
Another permanent magnet assembly according to the invention
includes a central permanent magnet section and upper and lower pole
pieces formed of magnetically permeable material that include arc-shaped
side pole piece portions having pole faces that surround two arc-shaped gaps
on the sides of the central permanent magnet section.
A different embodiment of a permanent magnet assembly according to
the invention includes an upper flux return section formed of magnetically
permeable material with a first arc-shaped upper permanent magnet section
at one end and a second arc-shaped upper permanent magnet section at the
other end, and a lower flux return section formed of magnetically permeable
material with a first arc-shaped lower permanent magnet section at one end
and a second arc-shaped lower permanent magnet section at the other end,
with a central flux return section between the upper and lower flux return
sections, wherein two arc-shaped gaps are formed between the permanent
magnet sections at the ends of the upper and lower flux return sections.
A variety of structures can be used in an apparatus according to the
invention. For example, the permanent magnet sections shown in the
illustrative embodiments herein may be comprised of a single permanent
magnet, or these permanent magnet sections may be comprised of one or
more multiple permanent magnets and one or more sections of magnetically
permeable material to form a magnetic array structure.
Although the illustrative embodiments may show pole pieces or flux
return sections formed as unitary structures, these structure may be
comprised of individual sections which are operatively coupled together.
Similarly, the relative dimensions, shapes, and positions of the permanent
magnet sections, pole pieces, or flux return sections can be optimized for a
particular application.
A magnet assembly according to the invention can provide a time-
varying magnetic field to an annular region. The particular shape and
structure of such an annular region can be especially well suited for a rotating
bed or rotating magnet magnetic refrigerator. Such a magnet assembly can
allow constant access to the annular region that is subject to the time-varying
magnetic field intensity, and this can enable components of a magnetic
refrigerator such as magnetocaloric material and heat transfer fluid plumbing
to be stationary and positioned within the annular region. Alternatively, the
magnet assembly can be stationary, and components of a magnetic
refrigerator such as magnetocaloric material and heat transfer fluid can rotate
within the annular region. A magnet assembly according to the invention can
have relatively low operating costs, for example by minimizing space
requirements and by minimizing the mass of any moving parts.
Such a magnet assembly can also have relatively low manufacturing
costs, for example by reducing the need for precisely machined permanent
magnets. Each of the permanent magnet portions of such a magnet
assembly can be arc-shaped with a rectangular cross section or generally
rectangular in shape, in either case with an orthogonal magnetization vector
to minimize production costs. This geometry can be especially well suited to
the manufacture of sintered NdFeB magnets by current pressing methods,
and the relatively low number of magnet mating surfaces can reduce the
number of precision grinding operations that might otherwise be required.
Precisely machined structures used in a magnet assembly according to
the invention, for example pole pieces that surround a gap at high magnetic
field, may have surfaces that benefit from close tolerances to allow these
surfaces to nest closely together with other components of a magnetic
refrigerator, such as containers of magnetocaloric materials. By forming any
structures requiring precise machining, such as pole pieces, of magnetically
permeable material, and operatively coupling those precisely machined
structures to rectangular permanent magnet portions, any precision machining
of permanent magnet material can be reduced or avoided.
A permanent magnet assembly according to the present invention can
be used to generate a time-varying field over an annular region while
minimizing the volume, mass, and fabrication cost of such an assembly. The
magnetic field in the annular region can be used wherever a stationary or
rotating wheel mechanism needs to be magnetized along part of its
circumference. The particular design of this structure can allow unimpeded
access to the annular region from one side, either from the exterior or from
the interior, for example for plumbing carrying heat transfer fluid into and out
of beds containing magnetocaloric materials located in the annular region.
A permanent magnet assembly according to the invention can be of
particular interest for use in a magnetic refrigeration device. Exemplary
magnetic refrigeration devices that use rotational motion are shown in U.S.
Pat. No. 6,526,759 and U.S. Pat. App. Pub. No. US 2003/0106323 A1, the
disclosures of which are incorporated by reference.
Further objects, features, and advantages of the invention will be
apparent from the following detailed description when taken in conjunction
with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 is a perspective view of a permanent magnet assembly
according to the invention with an exterior flux return path;
FIG. 2 is a perspective view of the permanent magnet assembly of Fig.
1, showing the axis of rotation and the annular region swept by the rotation of
the permanent magnet assembly;
FIG. 3 is a perspective view of a permanent magnet assembly
according to the invention with an interior flux return path;
FIG. 4 is a perspective view of another permanent magnet assembly
according to the invention with upper and lower interior flux return paths;
FIG. 5 is a perspective view of an alternative permanent magnet
assembly according to the invention with a central magnet and upper and
lower pole pieces;
FIG. 6 is a cross-sectional view of the permanent magnet assembly of
Fig. 5 taken along the line 6-6 thereof; and
FIG. 7 is a perspective view of an alternative permanent magnet
assembly according to the invention with an upper interior flux return path and
a lower interior flux return path connected by a central flux return path.
DETAILED DESCRIPTION OF THE INVENTION
Referring to the drawings, Fig. 1 is a perspective view of a permanent
magnet assembly according to the invention, indicated generally at 20. The
permanent magnet assembly 20 surrounds an arc-shaped gap at high
magnetic field 21 having a rectangular cross section 22 over an arc length of
approximately 120 degrees, although the gap cross-section may have a
different shape and the arc length may be greater than or less than 120
degrees. As perhaps best shown in Fig. 2, the permanent magnet assembly
20 is adapted to rotate about an axis of rotation 23, thereby sweeping an
annular region 24.
The permanent magnet assembly 20 includes an exterior flux return
portion, indicated generally at 30, to provide a return path for the lines of
magnetic flux and thereby complete the magnetic circuit. The flux return
portion 30 is preferably of sufficient dimension to avoid saturation with
magnetic flux, and is preferably shaped and exteriorly positioned at a
sufficient distance from the gap at high magnetic field 21 to prevent shunting
of the gap flux into the flux return portion 30.
The flux return portion 30 can be formed of any suitable magnetically
permeable material, for example a structural alloy such as low-carbon steel
that has the ability to carry flux, or a specifically permeable material intended
for use in magnetics such as the material sold by High Temp Metals of
California, USA under the trademark Permendur 2V, or a combination of
these materials, with or without additional non-permeable materials used, for
example, to provide structural support. The flux return portion 30 can
include one or more chamfered corners 31, for example along the outer
corners, or filled-in corners 32, for example along interior corners, to optimize
flux return performance while minimizing stray flux and assembly weight.
The permanent magnet assembly 20 includes an upper permanent
magnet portion, indicated generally at 33, having a North pole 34 (marked
"N") and a South pole 35 (marked "S"), and a lower permanent magnet
portion, indicated generally at 36, having a North pole 37 and a South pole 38.
The upper permanent magnet portion 33 and lower permanent magnet
portion 36 can be formed of any suitable permanent magnet material, for
example of the type sold by Sumitomo Special Metals of Japan under the
trademark Neomax 50. As shown in Figs. 1 and 2, the South pole 35 of the
upper permanent magnet portion 33 and the North pole 37 of the lower
permanent magnet portion 36 face the gap at high magnetic field 21.
Fig. 3 is a perspective view of a permanent magnet assembly
according to the invention, indicated generally at 45, having an interior flux
return path. The permanent magnet assembly 45 may be especially useful in
rotating magnet applications where the rotational moment of inertia is of
concern.
The permanent magnet assembly 45 surrounds an arc-shaped gap at
high magnetic field 56 having a rectangular cross section over a given arc
length, although this is not required and the cross-section may have different
shapes and the arc length may be greater than or less than the arc length of
the permanent magnet assembly 45. The permanent magnet assembly 45
includes an interior flux return portion, indicated generally at 46, to provide a
return path for the lines of magnetic flux and thereby complete the magnetic
circuit. The permanent magnet assembly 45 can be adapted to rotate about
an axis of rotation 47, thereby sweeping an annular region.
The flux return portion 46 of the permanent magnet assembly 45 is
preferably of sufficient dimension to avoid saturation with magnetic flux and to
avoid flux leakage elsewhere in the wheel. The flux return portion 46 is
preferably shaped and interiorly positioned at a sufficient distance from the
gap at high magnetic field 56 to prevent shunting of the gap flux into the flux
return portion 46. The flux return portion 46 can be formed of any suitable
magnetically permeable material, for example of the types discussed above.
Although the interior flux return portion 46 may come to an abrupt
corner at the central axis of the assembly, other shapes may be used
depending on flux density, mounting considerations, and counter-weighting
among other factors. The flux return portion 46 can include one or more
chamfered corners 48, for example along the outer corners, or filled-in corners
49, for example along interior corners, to optimize flux return while minimizing
stray flux, assembly weight, and rotational moment of inertia.
The permanent magnet assembly 45 includes an upper permanent
magnet portion, indicated generally at 50, having a North pole 51 (marked
"N") and a South pole 52 (marked "S"), and a lower permanent magnet
portion, indicated generally at 53, having a North pole 54 and a South pole 55.
The upper permanent magnet portion 50 and lower permanent magnet portion
53 can be formed of any suitable permanent magnet material, for example of
the types discussed above. As shown in Fig. 3, the South pole 52 of the
upper permanent magnet portion 50 and the North pole 54 of the lower
permanent magnet portion 53 surround the gap at high magnetic field 56.
Fig. 4 is a perspective view of another permanent magnet assembly
according to the invention, indicated generally at 60, having upper and lower
interior flux return paths and providing two gaps at high magnetic field.
Compared to the permanent magnet assemblies of Figs. 1 and 3 which use a
single flux return path, the lines of flux travel a comparatively shorter distance
from one magnetic pole to the next in the permanent magnet assembly 60,
such that the two flux return paths in the permanent magnet assembly 60 can
be individually less massive that the single flux return paths of Figs. 1 and 3.
This property can make the permanent magnet assembly 60 especially useful
in rotating magnet applications that require at least some central free space
along the axis of rotation where the rotational moment of inertia is also of
concern.
As shown in Fig. 4, the permanent magnet assembly 60 surrounds two
arc-shaped gaps at high magnetic field 74 having a rectangular cross section
over an arc length, where each arc-shaped gap extends approximately 60
degrees, although this is not required and the gap cross-sections may have a
different shape and the arc lengths may be greater than or less than 60
degrees. The permanent magnet assembly 60 includes two interior flux return
portions, an upper flux return portion, indicated generally at 62, and a lower
flux return portion, indicated generally at 63, to provide a return path for the
lines of magnetic flux and thereby complete the magnetic circuit. The
permanent magnet assembly 60 can be adapted to rotate about an axis of
rotation 61, thereby sweeping an annular region.
The upper flux return portion 62 and lower flux return portion 63 each
include a central portion 64 extending outward from the axis of rotation. The
upper flux return portion 62 and lower flux return portion 63 each preferably
also include horizontally tapered portions 65 that concentrate the lines of flux
in the central portion 64. A non-permeable axial link along the axis of rotation
61 that connects the upper flux return portion 62 and the lower flux return
portion 63 through the center of the assembly can be used to provide
structural support.
The upper flux return portion 62 and lower flux return portion 63 of the
permanent magnet assembly 60 are preferably of sufficient dimension to
avoid saturation with magnetic flux and to avoid flux leakage elsewhere in the
wheel. The upper flux return portion 62 and lower flux return portion 63 are
preferably shaped and positioned at a sufficient distance from the gaps at
high magnetic field 74 to prevent shunting of the gap flux into those flux return
portions. The upper flux return portion 62 and lower flux return portion 63 can
be formed of any suitable magnetically permeable material, for example of the
types discussed above.
The upper flux return portion 62 has a first end operatively coupled to a
first upper permanent magnet portion 66 and a second end operatively
coupled to a second upper permanent magnet portion 67, with each of the
upper permanent magnet portions 66 and 67 having a North pole 68 (marked
"N") and a South pole 69 (marked "S"). Similarly, the lower flux return portion
63 has a first end operatively coupled to a first lower permanent magnet
portion 70 and a second end operatively coupled to a second lower
permanent magnet portion 71, with each of the lower permanent magnet
portions 70 and 71 having a North pole 68 (marked "N") and a South pole 69
(marked "S").
As shown in Fig. 4, the polar orientations of the upper and lower
permanent magnet portions 66, 67, 70, and 71 are aligned to produce a
circular flux around the magnetic circuit formed by the permanent magnet
portions and the flux return portions. Relative to the first lower permanent
magnet portion 70 and the first upper permanent magnet portion 66 which are
aligned together in one direction, the second upper permanent magnet portion
67 and the second lower permanent magnet portion 71 are aligned together in
the opposite direction, thereby forming a circular flux loop.
The upper permanent magnet portions 66 and 67 and the lower
permanent magnet portions 70 and 71 can be formed of any suitable
permanent magnet material, for example of the types discussed above. As
shown in Fig. 4, the South pole 73 of the first lower permanent magnet portion
70 and the North pole 68 of the first upper permanent magnet portion 66
surround one gap at high magnetic field 74, and the South pole 69 of the
second upper permanent magnet portion 67 and the North pole 72 of the
second lower permanent magnet portion 71 surround a second gap at high
magnetic field 74.
Although in Fig. 4 the upper flux return portion 62 and the lower flux
return portion 63 have a uniform thickness in the vertical direction, and
although these flux return portions join the upper and lower permanent
magnet portions 66, 67, 70, and 71 at abrupt corners, other shapes may be
used depending on flux density, mounting considerations, and counter-
weighting among other factors. The flux return portions can include one or
more chamfered or rounded corners, for example along the outer corners or
edges of the flux return portions, or filled-in corners, for example along the
junction between the flux return portions and the permanent magnet portions,
to optimize flux return while minimizing stray flux and assembly weight.
Fig. 5 is a perspective view of an alternative permanent magnet
assembly according to the invention indicated generally at 80, with a central
magnet and upper and lower pole pieces and providing two gaps at high
magnetic field. In the permanent magnet assembly 80, the majority of the
assembly sits within the outer diameter of the wheel, thereby minimizing the
rotational moment of inertia of the assembly.
As shown in Fig. 5, the permanent magnet assembly 80 includes a
central permanent magnet portion 81 with an upper pole piece 85 and a lower
pole piece 86 which direct the magnetic flux from the central permanent
magnet portion 81 through two arc-shaped gaps at high magnetic field 94
over a given arc length. Each gap typically extends 60 degrees, but this is not
required and greater or lesser arc lengths can be used. The permanent
magnet assembly 80 can be adapted to rotate about an axis of rotation 82,
thereby sweeping an annular region.
The central permanent magnet portion 81 of permanent magnet
assembly 80 has a North pole 83 (marked "N") and a South pole 84 (marked
"S"), with the magnetic vector of the central permanent magnet portion 81
aligned with the axis of rotation 82. The central permanent magnet portion 81
can be formed of any suitable permanent magnet material, for example of the
types discussed above.
The permanent magnet assembly 80 includes an upper pole piece,
indicated generally at 85, and a lower pole piece, indicated generally at 86.
The upper and lower pole pieces 85 and 86 are of similar construction, each
having a central pole piece portion 87 with two ends, where each end of each
central pole piece bears a side pole piece portion 88. The upper pole piece
85 and lower pole piece 86 can be formed of any suitable magnetically
permeable material, for example of the types discussed above. Each side
pole piece portion 88 can include one or more chamfered corners 89.
Fig. 6 is a cross-sectional view of the permanent magnet assembly of
Fig. 5 taken along the line 6-6 thereof. As shown in Figs. 5 and 6, each end
of the upper pole piece 85 terminates in an upper pole face 92. Each end of
the lower pole piece 86 terminates in a lower pole face 93. The upper pole
faces 92 and the lower pole faces 93 surround the two gaps at high magnetic
field 94.
As perhaps best shown in Fig. 6, the side pole piece portions 88
preferably include vertically tapered portions 90, and as perhaps best shown
in Fig. 5, the side pole piece portions 88 preferably also include horizontally
tapered portions 91. The vertically tapered portions 90 and horizontally
tapered portions 91 can be used, for example, to concentrate the magnetic
flux into the two gaps at high magnetic field 94. As lines of flux leave the
permanent magnet portion 81, the lines of flux converge along the vertically
tapered portions 90 and horizontally tapered portions 91, whereby the flux
lines crossing the gaps 94 can be at a higher density than the flux lines within
the permanent magnet portion 81, providing a magnetic flux density in the
gaps 94 that can be greater than the saturation flux density of the magnetic
material comprising the permanent magnet portion 81 without the need for a
multi-pole magnet array.
The upper pole piece 85 and the lower pole piece 86 of the permanent
magnet assembly 80 are preferably of sufficient dimension to avoid saturation
with magnetic flux and to avoid flux leakage elsewhere in the wheel. The
vertically tapered portions 90, the horizontally tapered portions 91, and the
pole faces 92 and 93 are preferably shaped and positioned to place the gaps
at high magnetic field 94 at a sufficient distance from the permanent magnet
portion 81 to prevent shunting of the gap flux back into the permanent magnet
portion 81.
Although the central portions 87 of the upper and lower pole pieces 85
and 86 have a uniform thickness in the vertical direction, other shapes may be
used depending on flux density, mounting considerations, and counter-
weighting among other factors. The upper and lower pole pieces 85 and 86
may include additional tapering in one or more directions, for example
between the central pole piece portion 87 and the upper and lower pole faces
92 and 93, to further concentrate the lines of flux into the gaps 94. The upper
and lower pole pieces 85 and 86 may include additional chamfered or
rounded corners, for example along the outer corners or edges of the flux
return portions, or filled-in corners, for example along the junction between the
flux return portions and the permanent magnet portions, to optimize flux
density through the gaps 94 while minimizing stray flux and assembly weight.
As perhaps best shown in Fig. 6, the cross-section of the gaps at high
magnetic field 94 can be trapezoidal, with an angle theta 95 between the
horizontal and the lower pole face 93. There can also be a complementary
angle between the horizontal and the upper pole face 92, although this is not
required.
The angle theta 95 is positive in the permanent magnet assembly 80 of
Figs. 5 and 6, such that the interior dimension of the cross-section of the gaps
at high magnetic field 94 is less than the exterior dimension of that cross-
section, although this is not required. The angle theta 95 can also be zero, in
which case the interior dimension of the cross-section of the gaps at high
magnetic field would be equal to the exterior dimension of that cross-section.
The angle theta 95 can also be negative, in which case the interior dimension
of the cross-section of the gaps at high magnetic field would be greater than
the exterior dimension of that cross-section.
Although the upper pole faces 92 and the lower pole face 93 are shown
as essentially planar, this is not required and other shapes may be used. For
example, in some applications of a permanent magnet assembly according to
the invention the pole faces could be concave or convex. Thus, the cross-
section of the gaps at high magnetic field 94 can include, but not be limited to,
a rectangle (including but not limited to a square), a parallelogram, a
trapezoid, a circle, an oval, or nearly any other shape or combination of
shapes.
Fig. 7 is a perspective view of an alternative permanent magnet
assembly according to the invention, indicated generally at 100, with an upper
interior flux return path and a lower interior flux return path connected by a
central flux return path. The permanent magnet assembly 100 of Fig. 7 is
similar to the permanent magnet assembly 60 of Fig. 4, except that the
permanent magnet assembly 100 includes a central flux return path and the
permanent magnet sections have different polarities.
By including the central flux return path in the permanent magnet
assembly 100, and by aligning the polarities of the permanent magnet
sections as shown in Fig. 7, the two arc-shaped gaps in the permanent
magnet assembly 100 experience a magnetic field having the same polarity.
In contrast, the two arc-shaped gaps at each end of in the permanent magnet
assembly 60 shown in Fig. 4 experience a magnetic field having opposite
polarities.
Compared to the permanent magnet assembly 60 of Fig. 4, a structure
positioned within the annular volume swept by the permanent magnet
assembly 100 will experience less magnetic hysteresis, since the magnetic
field does not reverse direction at the two ends of the permanent magnet
assembly 100. This property can make the permanent magnet assembly 100
especially useful for applications in which it is desirable to minimize magnetic
hysteresis.
As shown in Fig. 7, the permanent magnet assembly 100 surrounds
two arc-shaped gaps at high magnetic field 115 having a rectangular cross
section over a given arc length, although this is not required and the cross-
section may have a different shape. Each arc-shaped gap typically extends
60 degrees, although this is not required and greater or lesser arc lengths can
be used. The permanent magnet assembly 100 includes an upper flux return
portion 102, a lower flux return portion 103, and a central flux portion 104, to
provide a return path for the lines of magnetic flux and thereby complete the
magnetic circuit. The permanent magnet assembly 100 can be adapted to
rotate about an axis of rotation 101, thereby sweeping an annular region.
The upper flux return portion 102 and lower flux return portion 103
each include a central portion 105 extending outward from the axis of rotation
101. The central flux return portion 104 operatively couples the central
portion 105 of the upper flux return portion 102 and the central portion 105 of
the lower flux return portion 103. The upper flux return portion 102 and lower
flux return portion 103 each preferably also include horizontally tapered
portions 106 that concentrate the lines of flux in the central portion 105 of the
upper flux return portion 102, the central portion 105 of the lower flux return
portion 103, and the central flux return portion 104.
In addition to the central flux return portion 104, the permanent magnet
assembly 100 may also include one or more non-permeable members
between the upper flux return portion 102 and the lower flux return portion 103
to provide additional structural support, although this is not required.
The upper flux return portion 102, lower flux return portion 103, and
central flux return portion 104 of the permanent magnet assembly 100 are
preferably of sufficient dimension to avoid saturation with magnetic flux and to
avoid flux leakage elsewhere in the wheel. The upper flux return portion 102,
lower flux return portion 103, and central flux return portion 104 are preferably
shaped and positioned at a sufficient distance from the gap at high magnetic
field 115 to prevent shunting of the gap flux into those flux return portions.
The upper flux return portion 102, lower flux return portion 103, and central
flux return portion 104 can be formed of any suitable magnetically permeable
material, for example of the types discussed above.
The upper flux return portion 102 has a first end operatively coupled to
a first upper permanent magnet portion 107 and a second end operatively
coupled to a second upper permanent magnet portion 108, with each of the
upper permanent magnet portions 107 and 108 having a North pole 109
(marked "N") and a South pole 110 (marked "S"). Similarly, the lower flux
return portion 103 has a first end operatively coupled to a first lower
permanent magnet portion 111 and a second end operatively coupled to a
second lower permanent magnet portion 112, with each of the lower
permanent magnet portions 111 and 112 having a North pole 113 (marked
"N") and a South pole 114 (marked "S").
As shown in Fig. 7, the polar orientations of the upper and lower
permanent magnet portions 107, 108, 111, and 112 are all aligned in the
same direction. This alignment produces two circular flux loops around the
magnetic circuits formed by the permanent magnet portions and the upper,
lower, and central flux return portions.
The upper permanent magnet portions 107 and 108 and the lower
permanent magnet portions 111 and 112 can be formed of any suitable
permanent magnet material, for example of the types discussed above. As
shown in Fig. 7, the South pole 110 of the first upper permanent magnet
portion 107 and the North pole 113 of the first lower permanent magnet
portion 111 surround one gap at high magnetic field 115, and the South pole
110 of the second upper permanent magnet portion 108 and the North pole
113 of the second lower permanent magnet portion 112 surround a second
gap at high magnetic field 115.
Although in Fig. 7 the upper flux return portion 102 and the lower flux
return portion 103 have a uniform thickness in one direction and the central
flux return portion 104 has a uniform thickness in two directions, and although
these flux return portions can be joined together and to the upper and lower
permanent magnet portions 107, 108, 111, and 112 at abrupt corners, other
shapes may be used depending on flux density, mounting considerations, and
counter-weighting among other factors. The flux return portions can include
one or more chamfered or rounded corners, for example along the outer
corners or edges of the flux return portions. The flux return portions can also
have filled-in corners, for example along the junctions between the flux return
portions or the junctions between the flux return portions and the permanent
magnet portions. In a particular application, the specific shapes can be
chosen, for example, to maximize flux return while minimizing stray flux and
assembly weight.
There are various possibilities with regard to alternative embodiments
and applications of a magnet assembly according to the invention. Although
the exemplary embodiments of the present invention refer to specific
materials, other materials known to those skilled in the art as having suitable
properties can be appropriately substituted.
Although particular structures and portions of the embodiments
described herein are referred to using the terms "upper," "lower," "vertical,"
and "horizontal," and the like, it is understood that those terms are used in
reference to the exemplary orientations shown in the drawings herein. It is
understood that a permanent magnet assembly according to the invention can
be used in any orientation, and the use of a particular term such as "vertical"
or "horizontal" is used to describe the relationship between particular
structures and portions of the embodiments described herein and not to limit
those structures or portions of the embodiments to any particular orientation
or frame of reference.
Although the exemplary embodiments of the present invention show
particular shapes and relative dimensions, other shapes and dimensions can
be used. For example, although the total arc length at high magnetic field will
usually range between 90 and 180 degrees, with 120 degrees being typical,
other arc lengths may be used in an appropriate case and the exact arc length
is not important to the invention. Further, the total arc length at high magnetic
field may be comprised of a single arc-shaped gap at high magnetic field, or
the total arc length at high magnetic field may be divided among a plurality of
arc-shaped gaps at high magnetic field.
Although the exemplary embodiments of the present invention herein
may show individual portions and sections having unitary construction, other
constructions can be used. For example, a flux return section or portion can
have a unitary construction, or such a flux return section or portion can be
comprised of a plurality of pieces which are attached together.
Similarly, a permanent magnet section or portion can have a unitary
construction, or such a permanent magnet section or portion can be
comprised of a plurality of permanent magnet pieces, possibly including
magnetically permeable pieces or magnetically impermeable pieces, which
are attached together. For example, a rectangular permanent magnet section
may be operatively coupled to an arc-shaped pole piece to obtain a structure
which is the equivalent of an arc-shaped permanent magnet section.
Although the exemplary embodiments of the present invention herein
may show individual portions and sections having square or rectangular
cross-sections, other constructions can be used. For example, a flux return
section could have a continuously curved shape, a trapezoidal shape, or any
combination of shapes.
Although the exemplary embodiments of the present invention here
may show permanent magnet sections or portions positioned adjacent to an
arc-shaped gap without any intermediate components, this is not required.
For example, one or more pole faces formed of magnetically permeable
material may be positioned between the permanent magnet sections or
portions and the arc-shaped gap in order to direct or concentrate the magnetic
flux through the arc-shaped gap.
The exemplary embodiments herein are described as being adapted to
rotate about an axis whereby the permanent magnet assembly provides a gap
at high magnetic field that sweeps an annular region, to thereby apply a time-
varying magnetic field to the annular region. By rotating the permanent
magnet assembly, a time-varying magnetic field can be applied to a structure
located within the annular region, such as a ring of beds containing
magnetocaloric materials. In this fashion, a rotating permanent magnet
assembly according to the invention can be combined with stationary
magnetocaloric materials for use in a rotating magnet magnetic refrigerator.
However, it should be understood that a permanent magnet according
to the invention can also be used in a stationary configuration, wherein an
annular structure, such as a ring of beds containing magnetocaloric materials,
is adapted to rotate relative to the permanent magnet assembly. In this
fashion, a stationary permanent magnet assembly according to the invention
can be combined with rotating magnetocaloric materials for use in a rotating
bed magnetic refrigerator.
Of course, a permanent magnet assembly according to the invention
can also be used in a configuration in which both the permanent magnet
assembly and the magnetocaloric materials rotate, in opposite directions or in
the same direction at different angular velocities. Similarly, a permanent
magnet assembly according to the invention can be used in a configuration in
which either or both of the permanent magnet assembly or the magnetocaloric
materials oscillate back and forth or otherwise move relative to each other.
It is understood that the invention is not limited to the particular
embodiments described herein, but embraces all such modified forms thereof
as come within the scope of the following claims.
WE CLAIM
1. A permanent magnet assembly comprising:
an arc-shaped flux return section formed of magnetically permeable
material and extending along a portion of an arc and having an upper
portion with a first end and a second end, a lower portion with a first end
and a second end, and a middle portion with a first end and a second end,
wherein the first end of the upper portion is operatively coupled to the
first end of the middle portion and the first end of the lower portion is
operatively coupled to the second end of the middle portion;
an upper arc-shaped permanent magnet section having a north end and a
south end, wherein the north end of the upper arc-shaped permanent
magnet section is operatively coupled to the second end of the upper
portion of the arc-shaped flux return section; and
a lower arc-shaped permanent magnet section having a north end and a
south end, wherein the south end of the lower arc-shaped permanent
magnet section is operatively coupled to the second end of the lower
portion of arc-shaped flux return section;
wherein an arc-shaped gap is formed between the south end of the upper
arc-shaped permanent magnet section and the north end of the lower arc-
shaped permanent magnet section.
2. The permanent magnet assembly as claimsed in claim 1 wherein the arc-shaped flux
return section has a unitary construction.
3. The permanent magnet assembly as claimed in claim 1 wherein the arc-shaped flux
return section is formed of at least two pieces which are operatively
connected to carry magnetic flux.
4. The permanent magnet assembly as claim wherein the upper arc-
shaped permanent magnet section has a unitary construction and the
lower arc-shaped permanent magnet section has a unitary construction.
5. The permanent magnet assembly as claimed in claim 1 wherein at least one of the
upper arc-shaped permanent magnet section and the lower arc-shaped
permanent magnet section comprises at least two permanent magnet
portions.
6. The permanent magnet assembly ef claim 1 wherein the arc-shaped gap
has a rectangular cross-section.
7. The permanent magnet assembly as claimed in claim 1 wherein the arc-shaped gap
has a trapezoidal cross-section.
8. The permanent magnet assembly ef claim 1 comprising at least one pole
piece operatively coupled to the south end of the upper arc-shaped
permanent magnet section.

9. The permanent magnet assembly as claimed in claim 1 comprising at least one pole
piece operatively coupled to the north end of the lower arc-shaped
permanent magnet section.
10.The permanent magnet assembly of claim 1 comprising at least one pole
piece operatively coupled to the south end of the upper arc-shaped
permanent magnet section and at least one pole piece operatively coupled
to the north end of the lower arc-shaped permanent magnet section.
11. A permanent magnet assembly comprising:
a central flux return section formed of magnetically permeable material
and having an upper portion with a first end and a second end, a lower
portion with a first end and a second end, and a central portion with a
first end and a second end wherein the first end of the upper portion is
operatively coupled to the first end of the central portion and the first end
of the lower portion is operatively coupled to the second end of the
central portion;
an upper arc-shaped permanent magnet section having a north end and a
south end, wherein the north end of the upper arc-shaped permanent
magnet section is operatively coupled to the second end of the upper
portion of the central flux return section; and
a lower arc-shaped permanent magnet section having a north end and a
south end, wherein the south end of the lower arc-shaped permanent
magnet section is operatively coupled to the second end of the lower
portion of the central flux return section;
wherein an arc-shaped gap is formed between the south end of the upper
arc-shaped permanent magnet section and the north end of the lower arc-
shaped permanent magnet section.
12.A permanent magnet assembly comprising:
an upper flux return section formed of magnetically permeable material
and having a middle section, a first end, and a second end;
a first arc-shaped upper permanent magnet section having a south end,
and a north end operatively coupled to the first end of the upper flux
return section;
a second arc-shaped upper permanent magnet section having a north
end, and a south end operatively coupled to the second end of the upper
flux return section;
a lower flux return section formed of magnetically permeable material and
having a middle section, a first end, and a second end;
a first arc-shaped lower permanent magnet section having a north end,
and a south end operatively coupled to the first end of the lower flux
return section; and
a second arc-shaped lower permanent magnet section having a south
end, and a north end operatively coupled to the second end of the lower
flux return section;
wherein a first arc-shaped gap is formed between the south end of the
first arc-shaped upper permanent magnet section and the north end of
the first arc-shaped lower permanent magnet section and wherein a
second arc-shaped gap is formed between the north end of the second
arc-shaped upper permanent magnet section and the south end of the
second arc-shaped lower permanent magnet section.
13. A permanent magnet assembly comprising:
a central permanent magnet section having a north end and a south end;
an upper pole piece formed of magnetically permeable material and
having a first end bearing an arc-shaped side pole piece portion having a
pole face, and a second end bearing an arc-shaped side pole piece portion
having a pole face; and
a lower pole piece formed of magnetically permeable material and having
a first end bearing an arc-shaped side pole piece portion having a pole
face, and a second end bearing an arc-shaped side pole piece portion
having a pole face;
wherein a first arc-shaped gap is formed between the pole face of the arc-
shaped side pole piece portion of the first end of the upper pole piece and
the pole face of the arc-shaped side pole piece portion of the first end of
the lower pole piece and a second arc-shaped gap is formed between the
pole face of the arc-shaped side pole piece portion of the second end of
the upper pole piece and the pole face of the arc-shaped side pole piece
portion of the second end of the lower pole piece.
14.A permanent magnet assembly comprising:
an upper flux return section formed of magnetically permeable material
and having a middle portion, a first end, and a second end;
a first arc-shaped upper permanent magnet section having a south end,
and a north end operatively coupled to the first end of the upper flux
return section;
a second arc-shaped upper permanent magnet section having a south
end, and a north end operatively coupled to the second end of the upper
flux return section;
a lower flux return section formed of magnetically permeable material and
having a middle portion, a first end, and a second end;
a first arc-shaped lower permanent magnet section having a north end,
and a south end operatively coupled to the first end of the lower flux
return section;
a second arc-shaped lower permanent magnet section having a north end,
and a south end operatively coupled to the second end of the lower flux
return section; and
a central flux return section formed of magnetically permeable material
and having a middle section, a first end operatively coupled to the middle
portion of the upper flux return section, and a second end operatively
coupled to the middle portion of the lower flux return section;
wherein a first arc-shaped gap is formed between the south end of the
first arc-shaped upper permanent magnet section and the north end of
the firs arc-shaped lower permanent magnet section and wherein a
second arc-shaped gap is formed between the south end of the second
arc-shaped upper permanent magnet section and the north end of the
second arc-shaped lower permanent magnet section.

The invention relates to a permanent magnet assembly comprising an arc-
shaped flux return section formed of magnetically permeable material and
extending along a portion of an arc and having an upper portion with a first end
and a second end, a lower portion with a first end and a second end, and a
middle portion with a first end and a second end, wherein the first end of the
upper portion is operatively coupled to the first end of the middle portion and the
first end of the lower portion is operatively coupled to the second end of the
middle portion; an upper arc-shaped permanent magnet section having a north
end and a south end, wherein the north end of the upper arc-shaped permanent
magnet section is operatively coupled to the second end of the upper portion of
the arc-shaped flux return section; and a lower arc-shaped permanent magnet
section having a north end and a south end, wherein the south end of the lower
arc-shaped permanent magnet section is operatively coupled to the second end
of the lower portion of arc-shaped flux return section; wherein an arc-shaped
gap is formed between the south end of the upper arc-shaped permanent
magnet section and the north end of the lower arc-shaped permanent magnet
section.

Documents:

418-KOLNP-2006-(05-01-2012)-FORM-27.pdf

418-KOLNP-2006-FORM 27.pdf

418-kolnp-2006-granted-abstract.pdf

418-kolnp-2006-granted-assignment.pdf

418-kolnp-2006-granted-claims.pdf

418-kolnp-2006-granted-correspondence.pdf

418-kolnp-2006-granted-description (complete).pdf

418-kolnp-2006-granted-drawings.pdf

418-kolnp-2006-granted-examination report.pdf

418-kolnp-2006-granted-form 1.pdf

418-kolnp-2006-granted-form 18.pdf

418-kolnp-2006-granted-form 2.pdf

418-kolnp-2006-granted-form 26.pdf

418-kolnp-2006-granted-form 3.pdf

418-kolnp-2006-granted-form 5.pdf

418-kolnp-2006-granted-reply to examination report.pdf

418-kolnp-2006-granted-specification.pdf

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Patent Number

233798

Indian Patent Application Number

418/KOLNP/2006

PG Journal Number

15/2099

Publication Date

10-Apr-2009

Grant Date

08-Apr-2009

Date of Filing

23-Feb-2006

Name of Patentee

ASTRONAUTICS CORPORATION OF AMERICA

Applicant Address

4115 N. TEUTONIA AVENUE, MILWAUKEE WI

Inventors:

#	Inventor's Name	Inventor's Address
1	CHELL, JEREMY	1243 WILLIAMSON STREET NO. 2, MADISON, WI 53703

PCT International Classification Number

H01F 3/00, 3/14

PCT International Application Number

PCT/US2004/027748

PCT International Filing date

2004-08-26

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	60/499,134	2003-08-29	U.S.A.