Rotor assembly having split large capacity magnets

Abstract

To provide a rotor assembly for an electric motor having a divided high-capacity magnet.SOLUTION: The rotor assembly for an electric motor includes a rotor core and a plurality of magnets. The rotor core defines a rotary shaft. Each magnet includes a magnet stem portion and a magnet arm portion. The magnet stem portion extends radially with respect to the rotary shaft and presents a radially outermost stem end portion. The magnet arm portion is located at least partially radially outwardly from the stem end portion. Additionally, the magnet arm portion extends circumferentially in the opposite direction to the magnet stem portion.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE Embodiments described herein relate generally to spoked rotor assemblies for electric motors. More particularly, embodiments of the invention relate to rotor assemblies having segmented high mass magnets. [Background technology]

[0002] At least some known spoked rotor motors utilize flat rectangular magnet slabs arranged radially like the blades of a pedal boat wheel, but with a pie-shaped sector of laminated steel between each "blade". Spoked rotor motors typically concentrate the magnetic flux generated by two adjacent magnetic poles onto the curved surface of a single steel sector, thereby producing a higher magnetic flux density than a single magnet could produce if mounted on the surface of the rotor. As such, the flux-concentrating properties of spoked rotor motors typically facilitate the use of less expensive magnet materials to produce motor performance equivalent to surface-mounted rotor motors that contain stronger but more expensive rare earth materials.

[0003] However, cheaper materials usually produce a much weaker magnetic field per unit volume. Therefore, a larger magnet volume is needed to provide sufficient overall magnetic flux when focused on the poles. One of the most important magnet dimensions is the thickness of the magnet slab. Generally, the larger the thickness dimension, the better the motor performance. However, thicker magnets interfere with each other near the center of the rotor. Reducing the radial height of the magnets provides additional space near the center of the rotor, but reduces the overall available magnetic flux.

[0004] The use of tapered magnets can alleviate magnet crowding at the center of the rotor. However, tapered magnets are susceptible to serious manufacturing problems caused by large variations in the thickness of the ferrite material. Tapered ferrite magnets crack in most grades of ferrite material. Therefore, simply tapering the magnets to account for crowding at the center of the rotor would result in prohibitive costs and manufacturing problems. Summary of the Invention [Problem to be solved by the invention]

[0005] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Other aspects and advantages of the present disclosure will become apparent from the following Detailed Description of the embodiments and the accompanying drawings. [Means for solving the problem]

[0006] In one aspect, a rotor assembly for an electric motor is provided. The rotor assembly includes a rotor core that defines an axis of rotation and a plurality of magnets spaced in an arc about the rotor core. Each magnet includes a magnet stem portion and a magnet arm portion. The magnet stem portion extends radially relative to the axis of rotation and presents a radially outermost stem end. The magnet arm portion is located at least partially radially outward from the stem end and extends in an opposite circumferential direction relative to the magnet stem portion.

[0007] Advantages of these and other embodiments will become more apparent to those skilled in the art from the following description of exemplary embodiments shown and described by way of example. As will be realized, the present embodiments described herein may be capable of other different embodiments and their details may be modified in various respects. Accordingly, the drawings and description should be regarded as illustrative in nature and not restrictive.

[0008] The figures described below depict various aspects of the systems and methods disclosed therein. It is to be understood that each figure depicts an embodiment of a particular aspect of the disclosed systems and methods, and each figure corresponds to a possible embodiment thereof. Moreover, wherever possible, the following description will refer to reference numerals contained in the following figures, and features depicted in multiple figures will be designated with consistent reference numerals. [Brief description of the drawings]

[0009] [Figure 1] 1 is a perspective view of an exemplary electric motor according to one aspect of the present invention. [Diagram 2] FIG. 2 is an exploded perspective view of at least a portion of the electric motor shown in FIG. 1; [Diagram 3] 2 is a perspective view of a rotor assembly of the electric motor shown in FIG. 1 showing the insertion of permanent magnets into axially extending magnet-receiving slots in the rotor core. [Figure 4] FIG. 4 is a front plan view of the rotor assembly shown in FIG. 3. [Diagram 5] FIG. 4 is a perspective view of a stack of laminations used to define a rotor core of the rotor assembly shown in FIG. [Figure 6] FIG. 6 is a front plan view of one of the stacks shown in FIG. 5. [Figure 7] FIG. 7 is a partial enlarged front plan view of an outer portion of the stack shown in FIG. [Figure 8] 7 is another partial enlarged front plan view of the outer portion of the stack shown in FIG. 6. FIG. [Figure 9] FIG. 7 is a partial enlarged front plan view of a central portion of the stack shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Unless otherwise indicated, the drawings provided herein are intended to illustrate features of embodiments of the present disclosure. These features are believed to be applicable to a wide variety of systems that include one or more embodiments of the present disclosure. Thus, the drawings are not intended to include all conventional features known by those skilled in the art that are required to practice the embodiments disclosed herein. Although the drawings do not necessarily provide precise dimensions or tolerances of the components or structures illustrated, the drawings are to scale with respect to the relationships between the components of the structures depicted in the drawings.

[0011] The following detailed description of the embodiments of the present disclosure refers to the accompanying drawings. The embodiments describe aspects of the present disclosure in sufficient detail to enable those skilled in the art to practice the disclosure. The embodiments of the present disclosure are presented by way of example and not by way of limitation. Other embodiments may be utilized, and changes may be made without departing from the scope of the claims. Therefore, the following description is not limiting. The scope of the present disclosure is defined solely by the appended claims, along with the full scope of equivalents to which such claims are entitled.

[0012] Reference herein to "an embodiment," "an embodiment," or "embodiments" means that one or more features being referenced are included in at least one embodiment of the technology. Separate references herein to "an embodiment," "an embodiment," or "embodiments" do not necessarily refer to the same embodiment, nor are they mutually exclusive, unless so stated and / or apparent to one of ordinary skill in the art from the description. For example, features, structures, operations, etc. described in one embodiment may, but are not necessarily, included in other embodiments. Thus, the technology can include various combinations and / or integrations of the embodiments described herein.

[0013] In the following specification and claims, reference will be made to a number of terms which shall be defined to have the following meanings: The singular forms include plural references unless the context clearly dictates otherwise. "Optional" or "optionally" means that the subsequently described event or circumstance may or may not occur, and that the description includes instances in which the event occurs as well as instances in which the event does not occur.

[0014] Approximate language used herein throughout the specification and claims may be applied to modify any quantitative expression that may vary permissibly without resulting in a change in the basic function to which it relates. Thus, values ​​modified by one or more terms such as "about," "approximately," and "substantially" should not be limited to the exact value specified. In at least some instances, the approximate language may correspond to the precision of an instrument for measuring the value. Here, and throughout the specification and claims, range limitations may be combined and / or substituted. Such ranges are identified and include all subranges contained therein unless the context or language dictates otherwise.

[0015] The terms "axial" and "axially" as used herein refer to directions and orientations that extend substantially parallel to the longitudinal or rotational axis of the motor assembly. The terms "radial" and "radially" refer to directions and orientations that extend substantially perpendicular to the axis of rotation. The terms "tangential" and "tangential" refer to directions and orientations that extend substantially perpendicular to the radial direction of the motor assembly. In addition, the terms "circumferential" and "circumferentially" as used herein refer to directions and orientations that extend in an all-around direction about the axis of rotation of the motor assembly (such references are not limited to a purely circular extension or to the periphery or circumference of an object unless the context clearly indicates otherwise). Moreover, directional references such as "upper", "lower", "front", "rear", "side", and similar terms are used herein merely for convenience and should be understood only in relation to one another. For example, components may in fact be oriented such that the faces referred to herein as "upper" and "lower" are in fact sideways, angled, inverted, etc., relative to a selected frame of reference.

[0016] Broadly, the present disclosure relates to a spoked rotor electric machine that includes a geometry in each of the laminated rotor core magnet slots that facilitates an increase in the capacity of the permanent magnets housed therein. Each magnet slot is generally defined or defined as a "T" shape, and the corresponding magnets include two commonly available flat rectangular slab-shaped magnets. Simple slab-shaped magnets are commonly available and are produced with highly optimized manufacturing processes. The magnet arm portions (i.e., the horizontal portions of the "T" shape) are magnetized to maintain a near circumferential orientation of the magnetic poles. The magnet stem portions (i.e., the vertical portions of the "T" shape) are positioned in a conventional spoked rotor orientation and have a thinner circumferential profile than the circumferential profile of the arm portions, facilitating placement and mating within a crowded region near the center of the rotor core. Additionally, the present disclosure provides a geometry that positions the magnet arm portions relative to the nominal circumferential surface of the rotor core to facilitate a reduction in the demagnetizing field strength potentially generated by the windings of the electric machine.

[0017] The advantage of this spoked rotor design is that it eliminates the need for tapered magnets, which are prohibitively expensive to manufacture and susceptible to cracking. Therefore, the use of simple slab-shaped magnets as provided by the present invention leads to significant cost savings and productivity gains. An additional advantage is the ability to increase the magnetic flux focused at each pole of the rotor by increasing the volume of magnetic material in each pole. Increasing the magnetic flux facilitates improved motor performance.

[0018] Exemplary Electric Motor FIGURE 1 is a perspective view of an exemplary electric motor 10 in accordance with one aspect of the present invention. FIGURE 2 is an exploded perspective view of at least a portion of electric motor 10. In the exemplary embodiment, electric motor 10 is shown as an internal rotor motor. As described, an internal rotor motor has magnets disposed radially inward relative to the windings that function as a stator. However, in accordance with some aspects of the present invention, electric motor 10 may alternatively be an external rotor motor or a dual rotor motor.

[0019] As shown in Figure 2, the illustrated electric motor 10 generally includes a stator assembly 12 and a rotor assembly 14 substantially enclosed within a shell 16. The rotor assembly 14 is supported for rotation relative to the stator assembly 12 about an axis of rotation "A." The shell 16 is generally cylindrical in shape and includes a cavity 18 for receiving at least a portion of the stator assembly 12 and the rotor assembly 14.

[0020] The stator assembly 12 is generally toroidal in shape and defines a stator axis that is coaxial with the axis of rotation "A". However, in accordance with some aspects of the present invention, it is permitted that the axis be non-coaxial. The stator assembly 12 preferably includes a stator core 20 and a plurality of coils 22 wound about the stator core 20. Additionally, in some embodiments, the stator assembly 12 includes a plurality of electrically insulating coatings 26 disposed between the stator core 20 and the coils.

[0021] The stator core 20 is preferably fabricated from steel and may be of either solid or laminated construction. Alternatively or additionally, the stator core 20 may be of segmented configuration. However, according to certain aspects of the present invention, the stator core 20 may be fabricated from any one or more of a variety of suitable materials and / or construction methods.

[0022] The stator core 20 preferably includes an annular yoke (not shown) and a plurality of arcuately spaced apart teeth (not shown) extending at least generally radially inward from the yoke. It is contemplated that the stator core 20 may have any number of teeth that enables the electric motor 10 to function as described herein. A plurality of coils 22 are formed by conductive wiring wound around each tooth. The wiring surrounds each tooth to form a coil 22, each of the coils 22 corresponding to one of the teeth. The wiring is preferably copper, although aluminum or any one or more of a variety of conductive materials may be used without departing from the scope of the present invention.

[0023] In the exemplary embodiment, rotor assembly 14 is depicted as a brushless permanent magnet rotor assembly and includes rotor core 24, rotor shaft 28, and shaft coupler 40. Rotor shaft 28 defines an axis of rotation for rotor assembly 14. Rotor assembly 14 also includes a plurality of magnets 48, each including a magnet stem portion 48a and a magnet arm portion 48b, as described in more detail below. The axis of rotation for rotor assembly 14 is coaxial with axis of rotation "A". It should be noted that in accordance with certain aspects of the invention, rotor core 24 may be constructed for use in a generator or other electric machine that includes stator assembly 12.

[0024] Rotor core 24 is generally cylindrical in shape and is preferably fabricated from steel. Rotor core 24 may be either a solid or laminated structure. Alternatively or additionally, rotor core 24 may be segmented in shape. However, according to certain aspects of the present invention, rotor core 24 may be fabricated from any one or more of a variety of suitable materials and / or construction methods.

[0025] As discussed above, the electric motor 10 includes an outer shell 16. The outer shell 16 is generally cylindrical in shape and extends generally circumferentially around the stator assembly 12. Alternatively, according to certain aspects of the invention, the outer shell 16 may extend around the stator assembly 12 to provide one or more flat sides or alternatively be shaped. In an exemplary embodiment, the outer shell 16 presents axially opposed first and second shell ends 32, 34, respectively, and extends substantially continuously around the stator assembly 12 and the rotor assembly 14 to at least partially surround the stator assembly 12 and the rotor assembly 14. According to certain aspects of the invention, the outer shell 16 includes openings or slots therethrough. For example, in certain embodiments, one or more openings or slots may be provided to facilitate ventilation and / or access.

[0026] The shell 16 forms a portion of a motor case 46 of the electric motor 10. The motor case 46 includes the shell 16 and a first end shield 36 and a second end shield 38, respectively. The shell 16 and the first end shield 36 and the second end shield 38 cooperatively define a motor chamber 30 that at least substantially receives the stator assembly 12 and the rotor assembly 14. More specifically, the first end shield 36 is disposed adjacent to and coupled to the first shell end 32. Additionally, the second end shield 38 is disposed adjacent to and coupled to the second shell end 34. Specifically, the outer shell 16 extends between the first end shield 36 and the second end shield 38 and is coupled and held in place between the first end shield 36 and the second end shield 38 by a number of fasteners (not shown) coupled to the first end shield 36 and the second end shield 38. It is contemplated that in certain aspects of the invention, one or more of the first end shield 36 and the second end shield 38 may be positioned inboard or spaced outboard from the respective shell ends 32 and 34.

[0027] The electric motor 10 includes a first bearing assembly 42 and a second bearing assembly 44 that cooperate to rotatably support the rotor shaft 28 of the rotor assembly 14. The first end shield 36 is configured to support the first bearing assembly 42 and the second end shield 38 is configured to support the second bearing assembly 44. Alternative or additional bearing assembly supports may be provided without departing from the scope of the present invention.

[0028] Rotor Assembly FIG. 3 is a perspective view of rotor assembly 14 of electric motor 10 illustrating insertion of pairs of permanent magnet stem portions 48a and magnet arm portions 48b into axially extending magnet receiving slots 50 of rotor core 24. FIG. 4 is a front plan view of rotor assembly 14. In an exemplary embodiment, rotor shaft 28 extends axially through rotor core 24 to define an axis of rotation "A". Rotor shaft 28 is fixedly coupled to and concentrically disposed relative to rotor core 24. Rotor shaft 28 includes a first end 52 extending forwardly from rotor core 24 and a shorter second end 53 extending rearwardly from rotor core 24. Rotor shaft 28 includes keyhole slots 54 defined therein for locking laminations of rotor core 24 as described herein. Second end 53 includes slots 55, although in some aspects of the invention, slots 55 may be omitted.

[0029] The rotor assembly 14 includes a plurality of magnet receiving slots 50 arranged in an arc about the axis of rotation "A" or rotor shaft 28. Preferably, the magnet receiving slots are equally spaced apart. However, in accordance with some aspects of the invention, it is permitted that a non-uniform or variable spacing arrangement may be used. The rotor assembly 14 also includes a plurality of permanent magnet stem portions 48a and magnet arm portions 48b, with each magnet receiving slot 50 including one of the magnet stem portions 48a and one of the magnet arm portions 48b inserted therein. In the exemplary embodiment, the rotor core 24 and the magnet stem portions 48a and magnet arm portions 48b are rigidly coupled to one another and configured to rotate with the rotor shaft 28.

[0030] In an exemplary embodiment, rotor core 24 is fabricated from a plurality of lamination stacks 56, each of which may be rotated or arcuately offset at various angles about axis of rotation "A". Lamination stacks 56 are in the form of plates or laminations 156 (see FIG. 6) stacked or arranged in face-to-face contact and one on top of the other such that rotor core 24 extends axially a predetermined length along axis of rotation "A". Each lamination stack 56 presents opposing axial faces 110 and 112 (see FIG. 5), with one of faces 110 or 112 facing a first axial direction and the other facing an opposite axial direction. The plurality of laminations 156 defining each stack are preferably interlocked (e.g., bonded to one another), although certain aspects of the invention contemplate the use of loose laminations. In an exemplary embodiment, each of laminations 156 is fabricated (e.g., machined, stamped, punched, etc.) from a suitable material, including, for example, but not limited to, a magnetically permeable material such as iron, steel, or a steel alloy. It should be noted that in various aspects of the present invention, the stack may include stacks having different morphologies or stacks having substantially the same morphology.

[0031] As discussed above, the rotor core 24 includes a plurality of generally radially extending magnet receiving slots 50. Each magnet receiving slot 50 is disposed within a pole sector 58 of the rotor assembly 14. The illustrated embodiment includes ten magnet receiving slots 50, thus defining ten rotor pole sectors 58. It is noted that in other aspects of the invention, the rotor core 24 may include more or fewer pole sectors 58, depending on design requirements. It is also noted that the magnet stem portion 48a and magnet arm portion 48b are shown somewhat diagrammatically for purposes of illustration, but are generally sized to fit closely within the magnet receiving slots 50 to facilitate a secure and immovable fit with the rotor core 24. The illustrated embodiment depicts a single pair of magnet stem portion 48a and magnet arm portion 48b extending substantially the entire axial length of the corresponding magnet receiving slot 50 of each lamination stack 56. However, aspects of the present invention contemplate multiple magnet stem portions 48 a and magnet arm portions 48 b axially disposed within respective magnet receiving slots 50 .

[0032] With reference to FIG. 3, in an exemplary embodiment, the rotor assembly 14 includes four lamination stacks 56 that define the rotor core 24. As described herein, the exemplary rotor core 24 is a ten pole rotor core. Each lamination stack 56 shown in FIGS. 3 and 4 is substantially identical. However, to define the skew of the rotor core 24, axially adjacent lamination stacks 56 are rotated about the axis of rotation "A" by a predetermined amount relative to each adjacent lamination. In a preferred embodiment, each lamination stack 56 is rotated in the same direction relative to adjacent laminations by an amount equal to approximately four degrees (4°). For example, each lamination stack 56 may be rotated by an amount within a range between approximately three degrees (3°) and approximately five degrees (5°), inclusive. In other aspects of the invention, the lamination stacks 56 may be rotated about the axis of rotation "A" by any alternative amount that enables the rotor core 24 to function as described herein.

[0033] Exemplary Stacking FIG. 5 is a perspective view of a lamination stack 56 according to one embodiment of the present invention. FIG. 6 is a front plan view of one of the laminations 156 of the lamination stack 56 shown in FIG. 5. FIGS. 7 and 8 are enlarged partial front plan views of an outer portion of the lamination 156 shown in FIG. 6, particularly illustrating its geometric features. FIG. 9 is an enlarged partial front plan view of a central portion of the lamination 156 shown in FIG. 6, particularly illustrating its geometric features. With reference to FIG. 6, as discussed above, the laminations 156 define ten pole sectors 58. Each of the magnet receiving slots 50 is disposed radially outward from the axis of rotation "A" of the rotor core 24, which is shown as the center of the laminations 156.

[0034] The laminations 156 include a plurality of central slot axes 72. A plurality of radial pole pitch lines 74 extend through the center of the laminations 156 (e.g., axis of rotation "A"), with each radial pole pitch line 74 being angularly centered between a pair of adjacent magnet receiving slots 50 such that each adjacent pair of magnet receiving slots 50 is symmetrically disposed about the respective radial pole pitch line 74. Each radial pole pitch line 74 defines a boundary between two adjacent pole sectors 58, with adjacent radial pole pitch lines 74 defining a pole sector 58 therebetween. Each central slot axis 72 passes through the center of rotation of the laminations 156 and bisects a respective pole sector 58 (i.e., is angularly centered between adjacent radial pole pitch lines 74). In FIG. 6, only four of the slot axes 72 are shown for clarity.

[0035] The laminations 156 preferably include a plurality of substantially similar pole segments 60 arranged in an arc about the axis of rotation "A" (or, alternatively described, about the rotor shaft 28). The pole segments 60 extend from a central hub portion 92 of the laminations 156. In a preferred embodiment, as depicted in FIG. 4, the pole segments 60 alternate in an arc with the respective magnets 48 such that each of the magnets 48 is interleaved between circumferentially adjacent pole segments 60.

[0036] Preferably, the pole segments 60 are equally spaced about the axis of rotation "A." Each of the magnets 48 is preferably centrally located between circumferentially adjacent pole segments 60. Moreover, each of the magnets 48 is preferably in direct contact with a circumferentially adjacent one of the pole segments 60. However, it should be noted that non-uniform or variable spacing of the pole segments 60 may be used in accordance with certain embodiments of the present invention.

[0037] In an exemplary embodiment, lamination stack 56 has a thickness within a range between about 5 / 10 inch (0.5 in) and about 7 / 10 inch (0.7 in), inclusive. However, in other aspects of the invention, the thickness of lamination stack 56 may include any alternative dimension that enables lamination stack 56 to function as described herein. The above range increases the strength of rotor core 24 and reduces manufacturing costs.

[0038] 6, the pole segments 60 include radially outer surfaces 62 that cooperate to define, at least in part, an annular nominal perimeter designated by the reference letter "B." Note that the annular nominal perimeter "B" is an imaginary shape that generally corresponds to an outermost radial dimension of the laminations 156.

[0039] In the exemplary embodiment, the pole segments 60 are formed substantially symmetrically about a radial pole pitch line 74. Each pole segment 60 includes a body 64 and a pair of tabs 66. Each tab 66 extends opposite one another and outwardly (e.g., generally circumferentially) in a generally arcuate manner from the body 64.

[0040] As depicted in FIG. 6 , the body 64 is generally wedge-shaped. In particular, the body 64 includes a radially outer surface 62 (described above) that is substantially centered about a corresponding radial pole pitch line 74. The body 64 further includes a pair of arcuately spaced opposing body margins 68 and a pair of arcuately spaced opposing sidewalls 70 that extend generally radially from the body margins 68. In particular, in a preferred embodiment, the sidewalls 70 of a given pole segment 60 each extend inwardly (i.e., tapered) toward one another and each are substantially parallel to a respective central slot axis 72. As such, adjacent sidewalls 70 of each pair of adjacent pole segments 60 extend substantially parallel to one another. This is advantageous in that commonly available flat rectangular slab-shaped magnets, such as magnet stem portion 48a, may be used in the rotor assembly 14.

[0041] Each of the tabs 66 includes a radially outermost arcuate tab surface 76 that extends generally circumferentially directly from a corresponding one of the body margins 68. However, it is contemplated that the tab surfaces 76 may be substantially planar and / or have other geometric features according to some embodiments of the present invention. Each of the tabs 66 also includes a radially innermost tab surface 78 disposed radially inward of the corresponding tab surface 76. The innermost tab surface 78 extends directly from a corresponding one of the side walls 70. Each of the tabs 66 also includes a tip surface 80. Each tip surface 80 is generally arcuately spaced from the body 64 and extends generally radially between and interconnects the corresponding tab surfaces 76 and 78.

[0042] In an exemplary embodiment, each of the radially outer surfaces 62 of the pole segments 60 is formed concentrically with the axis of rotation "A". That is, each of the radially outer surfaces 62 extends along a circular path, the center of curvature of which coincides with the axis of rotation "A". Alternatively, it is contemplated that in certain aspects of the invention, the radially outer surfaces 62 include alternative geometric shapes.

[0043] As discussed above, the outermost tab surfaces 76 extend generally circumferentially from the body margin 68. Additionally, in the exemplary embodiment, the tab surfaces 76 extend radially inward from the corresponding body margin 68. That is, each of the tab surfaces 76 extends radially inward such that it is disposed radially inward of the annular nominal circumferential surface "B." The innermost tab surface 78 of the tab 66 and the corresponding one of each of the sidewalls 70 form a substantially right angle (i.e., a 90° angle) therebetween.

[0044] As depicted in FIG. 7 , body 64 further includes a pair of arcuately spaced opposing notches 82, each defined in a respective one of sidewalls 70. Specifically, for each opposing notch 82, body 64 includes a radially outermost notch surface 84 extending generally circumferentially inward from sidewall 70 toward a corresponding radial pole pitch line 74 of the respective pole segment 60. Outermost notch surface 84 is spaced a predetermined distance radially inward from annular nominal circumferential surface "B," as described further below. Outermost notch surface 84 and a corresponding one of each of sidewalls 70 form a substantially right angle (i.e., a 90° angle) therebetween. Body 64 also includes a tapered wall 86 extending generally inwardly directly from outermost notch surface 84 at an angle α. Angle α is preferably between about thirty degrees (30°) and sixty degrees (60°), inclusive. In a preferred embodiment, the angle α is approximately forty-five degrees (45°).

[0045] Additionally, the body 64 includes a radially innermost notch surface 88 extending generally circumferentially inward from the sidewall 70. In a preferred embodiment, the innermost notch surface 88 is substantially parallel to the outermost notch surface 84. The body 64 also includes notch sidewalls 90. Each notch sidewall 90 is spaced generally arcuately from the respective sidewall 70 and extends generally radially between and interconnects corresponding ones of the tapered walls 86 and the notch surfaces 88. Specifically, in a preferred embodiment, the notch sidewalls 90 of a given pole segment 60 each extend inwardly (i.e., tapered) toward one another and each are substantially parallel to the respective sidewall 70 (or respective central slot axis 72). Thus, adjacent notch sidewalls 90 of each pair of adjacent pole segments 60 extend substantially parallel to one another. Similar to the sidewall 70 geometry described above, this is advantageous in that commonly available flat rectangular slab-shaped magnets, such as magnet arm portion 48b, may be used in rotor assembly 14.

[0046] 8, adjacent pairs of pole segments 60 cooperate to define a "T" shaped magnet receiving slot 50. The notches 82 cooperate to define a slot arm portion 120 of the magnet receiving slot 50 configured to receive the magnet arm portion 48b therein. Similarly, the side walls 70 cooperate to define a slot stem portion 130 of the magnet receiving slot 50 configured to receive the magnet stem portion 48a therein. However, it should be noted that according to some aspects of the invention, the pole segments 60 of the laminations 156 may not include opposing notches 82.

[0047] Additionally, each magnet-receiving slot 50 presents an open slot opening 125 extending between the slot arm portion 120 and the annular nominal circumferential surface "B." As depicted, the slot opening 125 is defined, in part, by adjacent pairs of tabs 66 of the pole segments 60.

[0048] In the exemplary embodiment, the slot stem portion 130 has a circumferentially extending first slot width W1 sized to receive a respective magnet stem portion 48a therein. In a preferred embodiment, the first slot width W1 is in the range between about forty-five one-hundredths of an inch (0.45 in) and about fifty one-hundredths of an inch (0.50 in), inclusive. In other aspects of the invention, the first slot width W1 may be any dimension that enables the lamination 156 to function as described herein.

[0049] The slot arm portion 120 is located radially outward of the slot stem portion 130 and is oriented substantially perpendicular to the slot stem portion 130 as described herein. The slot arm portion 120 has a circumferentially extending second slot width W2 sized to receive a respective magnet arm portion 48b therein. In a preferred embodiment, the second slot width W2 is in the range between about sixty-five one-hundredths of an inch (0.65 in) and about seventy-five one-hundredths of an inch (0.75 in), inclusive. In other aspects of the invention, the second slot width W2 may be any dimension that enables the lamination 156 to function as described herein.

[0050] In an exemplary embodiment, the slot opening 125 located radially outward of the slot arm portion 120 has a circumferentially extending third slot width W3. In a preferred embodiment, the third slot width W3 is in the range between about thirty one-hundredths of an inch (0.30 in) and about forty one-hundredths of an inch (0.40 in), inclusive. In other aspects of the invention, the third slot width W3 may be any dimension that enables the laminations 156 to function as described herein.

[0051] With reference to FIG. 9, the body 64 of the pole segment 60 includes a magnet positioning structure including a pair of arcuately spaced, opposing radially inward tabs 94. More specifically, the inner tabs 94 include generally circumferentially extending nubs configured to limit radially inward shifting of a corresponding one of the magnets 48. With reference to FIG. 4, the radially innermost surface 96 of each magnet stem portion 48a is preferably spaced from but adjacent the corresponding pair of inner tabs 94. Certain other aspects of the invention allow for alternative or additional means of limiting such shifting. In a preferred embodiment, the inner tabs 94 facilitate fixation of the magnet stem portion 48a. Furthermore, the magnet stem portion 48a may alternatively or additionally be fixed or limited by radially inward, generally radially extending tabs or other geometric features defined by the pole segments and / or central hub portion 92 of the laminations 156.

[0052] In the exemplary embodiment shown in FIG. 9, central hub portion 92 includes a central shaft-receiving opening 98 defined therethrough. Central shaft-receiving opening 98 is substantially concentric with axis of rotation "A." Central hub portion 92 includes a pair of arcuately spaced, axially-extending grooves 100 and 102 defined along an inner surface 104 of central shaft-receiving opening 98. Grooves 100 and 102 are configured to cooperate with keyhole slots 54 (shown in FIG. 3 ) to facilitate locking laminations 156 of rotor core 24 in place.

[0053] Groove 100 is defined in central hub portion 92 and has a central axis 106. In an exemplary embodiment, central axis 106 of groove 100 is angularly offset from each of radial pole pitch lines 74 by a predetermined angle "C". However, in some embodiments, central axis 106 may be aligned with each radial pole pitch line 74. In a preferred embodiment, predetermined angle "C" is approximately four degrees (4°). However, in other embodiments of the present invention, predetermined angle "C" may be any angle that enables laminations 156 to function as described herein.

[0054] Additionally, the groove 102 also includes a central axis 108. In an exemplary embodiment, the central axis 108 of the groove 102 is angularly offset from the central axis 106 of the groove 100 by a predetermined angle "D". In a preferred embodiment, the predetermined angle "D" is approximately one hundred and fifty-two degrees (152°). However, in other embodiments of the present invention, the predetermined angle "D" may be any angle that enables the laminate 156 to function as described herein.

[0055] 3 and 8, as described herein, the magnet 48 includes a magnet stem portion 48a and a magnet arm portion 48b. Each of the magnet stem portion 48a and the magnet arm portion 48b is preferably generally rectangular in shape. More specifically, the magnet stem portion 48a preferably presents a radially innermost surface 96, a radially outermost surface 114, a pair of circumferentially spaced side surfaces 116, and an axially spaced end surface 118. The surfaces 96, 114, 116, 118 are preferably at least substantially flat and arranged in a rectangular parallelepiped. Additionally, the magnet arm portion 48b preferably presents a radially outermost surface 122, a radially innermost surface 124, a pair of circumferentially spaced side surfaces 126, and an axially spaced end surface 128. The surfaces 122, 124, 126, 128 are preferably at least substantially flat and arranged in a rectangular parallelepiped. However, in accordance with some aspects of the invention, the magnet shape is permitted to vary (e.g., by providing one or more curved surfaces and / or non-orthogonal interfaces between surfaces), but the sides of adjacent pole segments are most preferably complementarily shaped.

[0056] In the exemplary embodiment, each magnet stem portion 48a is located within a respective slotted stem portion 130 and extends radially relative to the axis of rotation "A". The radially innermost surface 96 of each magnet stem portion 48a is preferably spaced apart from but adjacent to a corresponding one of the magnet retaining inner tabs 94. Each of the side surfaces 116 is preferably directly adjacent to a corresponding one of the pole segment side walls 70. Additionally, each single magnet arm portion 48b is located within a respective slotted arm portion 120 and extends generally circumferentially in the opposite direction relative to the magnet stem portion 48a. The radially innermost surface 124 of each magnet arm portion 48b is directly adjacent to a corresponding one of the magnet stem portion radially outermost surfaces 114 such that the magnets 48 are continuous. However, in some embodiments, a gap may be defined between the radially innermost surface 124 of each magnet arm portion 48b and the corresponding one of the magnet stem portion radially outermost surfaces 114. Additionally, in other embodiments of the present invention, only a portion of each magnet arm portion 48b is located radially outward from a corresponding one of the magnet stem portion radially outermost surfaces 114. For example, each magnet arm portion 48b may include a notch in its radially innermost surface 124 to receive a corresponding one of the magnet stem portions 48a and a portion of the associated radially outermost surface 114.

[0057] In the exemplary embodiment, each of the side surfaces 126 of each magnet arm portion 48b is preferably directly adjacent to a corresponding one of the notch side walls 90. The magnet stem portion 48a and the corresponding magnet arm portion 48b in each magnet receiving slot 50 are substantially perpendicular to one another, as described above, forming a "T" shaped magnet 48. It is noted that while the exemplary embodiment describes a single stem magnet and a single corresponding arm magnet forming a "T" shaped magnet, certain aspects of the invention contemplate that more than one arm magnet may be incorporated into the rotor core. For example, in some embodiments, a single stem magnet may include two or more adjacent circumferentially extending arm magnets disposed at least partially radially outward therefrom. The arm magnets may have different perimeters, such that the arm magnets cooperate with the stem magnet to form an inverted stepped wedge shape.

[0058] As discussed above, magnet arm portion 48b is located radially inward relative to the nominal outer periphery "B" of rotor core 24 to facilitate reducing the strength of the demagnetizing field potentially generated by the windings of the electric machine. In particular, radially outermost surface 122 is spaced a predetermined distance D1 from nominal outer periphery "B". In a preferred embodiment, distance D1 is within a range between approximately 25 / 100ths of an inch (0.25 in) and approximately 30 / 100ths of an inch (0.30 in), inclusive. However, it should be noted that in certain other aspects of the invention, distance D1 may be any dimension that enables rotor core 24 to function as described herein.

[0059] In an exemplary embodiment, the magnet arm portion 48b has a magnetic thickness T1 measured in a radial direction. In a preferred embodiment, the thickness T1 is in the range between about forty-five one-hundredths of an inch (0.45 in) and about fifty one-hundredths of an inch (0.50 in), inclusive. In other aspects of the invention, the magnetic thickness T1 may be any dimension that enables the magnet arm portion 48b to function as described herein. Additionally, the magnet stem portion 48a has a magnetic thickness T2 measured in a tangential direction perpendicular to the radial direction. In a preferred embodiment, the thickness T2 is substantially the same as the thickness T1 of the magnet arm portion 48b. The magnet arm portion 48b (i.e., the horizontal portion of the "T" shaped magnet 48) is magnetized to maintain a generally circumferential orientation of the magnetic poles. That is, the north and south poles of the magnet arm portion 48b are defined on circumferentially spaced side surfaces 126. The magnet stem portion 48a is magnetized such that north and south poles of the magnet stem portion 48a are defined on circumferentially spaced side surfaces 116. Furthermore, the polarity directions of the pair of magnets 48a and 48b (i.e., magnets 48) preferably alternate. More particularly, the north pole of a first one of the magnets 48 preferably faces the north pole of a second one of the magnets 48, and so on. That is, each pole segment 60 preferably only abuts like poles of adjacent magnets 48, and thus the pole segments 60 themselves alternate in polarity.

[0060] As shown in FIG. 8, magnet stem portion 48a defines a radially extending longitudinal axis "D" tangentially centered about the magnet. Similarly, magnet arm portion 48b defines a circumferentially extending longitudinal axis "E" radially centered about the magnet. In a preferred embodiment, longitudinal axes "D" and "E" are perpendicular to one another. Moreover, in a preferred embodiment, magnet arm portion 48b extends in opposite directions relative to longitudinal axis "D". That is, magnet arm portion 48b is substantially centered about magnet stem portion 48a, defining a "T" shaped magnet 48. However, it should be noted that unequal circumferential extensions of magnet arm portions 48b are contemplated in certain aspects of the present invention.

[0061] In a preferred embodiment, magnet 48 is a permanent magnet. Moreover, magnet 48 preferably comprises ferrite. However, other magnetic materials (e.g., neodymium and other rare earth materials) may be used in accordance with certain aspects of the present invention.

[0062] In operation, the rotor assembly 14 is assembled by first fabricating a plurality of laminations 156 arranged into a plurality of lamination stacks 56. As described above, the laminations 156 may be fabricated from a suitable material, including, for example, but not limited to, a magnetically permeable material, such as iron, steel, or a steel alloy, by using machining, stamping, punching, and / or other suitable lamination forming techniques. Following fabrication of the laminations 156 into the lamination stacks 56, the magnets 48 (e.g., magnet stem portion 48a and magnet arm portion 48b) are inserted into the magnet receiving slots 50, as described above. The lamination stacks 56 are oriented and stacked as described below. The plurality of laminations 156 in each lamination stack 56 are preferably interlocked (e.g., bonded together), although certain aspects of the present invention contemplate the use of loose laminations.

[0063] As discussed above, to define the skewed configuration of rotor core 24, axially adjacent lamination stacks 56 are rotated about axis of rotation "A" by a predetermined amount relative to each adjacent lamination stack. In a preferred embodiment, rotor core 24 includes four lamination stacks 56 (see FIG. 3), with each lamination stack being angularly offset from an adjacent lamination stack 56.

[0064] In one example, a first lamination stack 56 (e.g., the lamination stack 56 closest to the first end 52 of the rotor shaft 28) is placed on the rotor shaft 28 with the grooves 100 aligned with the keyhole slots 54 and its axial face 112 presented toward the first end 52. A second lamination stack 56 is then placed on the rotor shaft 28 with the grooves 102 aligned with the keyhole slots 54 and its axial face 110 presented toward the first end 52. In this manner, the opposing axial faces 110 and 112 of adjacent lamination stacks 56 abut one another in face-to-face contact. As such, the second lamination stack 56 is angularly offset by approximately four degrees (4°) relative to the adjacent first lamination stack 56. A third lamination stack 56 is then placed on the rotor shaft 28 with the grooves 102 aligned with the keyhole slots 54 and its axial face 112 presented toward the first end 52. That is, the first and third lamination stacks 56 (arranged in series) have the same axial face (e.g., axial face 112) presented toward the first end 52 of the rotor shaft 28. However, the first and third lamination stacks 56 are angularly offset based on different grooves (e.g., grooves 100 and 102) that are aligned with the keyhole slots 54. The fourth lamination stack 56 is then placed on the rotor shaft 28 with grooves 100 aligned with the keyhole slots 54 and its axial face 112 presented toward the first end 52 of the rotor shaft. As such, each lamination stack 56 rotates in the same direction relative to the adjacent laminations by an amount equal to approximately four degrees (4°).

[0065] 4, in an alternative embodiment, the open slot opening 125 extending between the slot arm portion 120 and the annular nominal circumferential surface "B" may be filled with a non-ferrous material 132. The non-ferrous material 132, which acts similarly to a simple empty space where magnetic forces are concerned, may be used in place of the empty space defined by the open slot opening 125 so long as the eddy currents induced by the rapidly changing magnetic field of the electric motor 10 do not cause excessive power losses in the non-ferrous material. The non-ferrous material 132 may aid in anchoring the magnet arm portion 48b and facilitate reducing windage losses resulting from a rapidly rotating rotor assembly during operation of the electric motor 10. Examples of non-ferrous materials that may be utilized to fill the open slot opening 125 include, but are not limited to, synthetic resins, plastics, epoxies, and the like.

[0066] Advantageously, embodiments of the present invention provide for an increased volume of magnetic material in the rotor poles of an electric motor without the need to use tapered magnets. By providing "T" shaped magnets manufactured from commonly available slab type magnets, the magnetic flux density may be increased per rotor pole. Using commonly available slab type magnets increases manufacturability while reducing the manufacturing cost of the disclosed rotor assemblies by reducing the need for specially manufactured magnets. Another advantage of the present invention is that the known susceptibility of magnet demagnetization potentially generated by the windings of an electric motor is reduced by spacing the magnets radially inward from the outer rotor surface, while the overall magnetic flux density is maintained or increased by the increased volume of magnetic material.

[0067] Although the above description presents features of preferred embodiments of the present invention, other preferred embodiments may also be created in accordance with the principles of the present invention. Such other preferred embodiments may, for example, be provided with features drawn from one or more of the above-described embodiments. Furthermore, such other preferred embodiments may include features from more than one of the above-described embodiments, particularly when such features are compatible for use together, even though they are presented separately as part of separate embodiments in the above description.

[0068] Those skilled in the art will appreciate that any suitable combination of the embodiments described above may be made without departing from the spirit of the invention.

[0069] The preferred embodiments of the present invention described above should be used only as examples and should not be used in a limiting sense in interpreting the scope of the present invention. Obvious modifications to the exemplary embodiments can be easily made by those skilled in the art without departing from the spirit of the present invention as described above. [Explanation of symbols]

[0070] 10 Electric motor 12 Stator Assembly 14 Rotor Assembly 16 Outer shell 18 Cavity 20 Stator core 22 Coil 24 Rotor core 26 Electrical insulating coating 28 rotor shaft 30 Motor chamber 32 first shell end 34 Second shell end 36 First End Shield 38 Second End Shield 40 Shaft coupler 42 First bearing assembly 44 Second Bearing Assembly 46 Motor case 48 Magnet 48a Magnet stem part 48b Magnet arm part 50 Magnet Receiving Slots 52 First end 53 Second end 54 Keyhole Slot 55 Slots 56 Laminated Stack 58 Pole Sector 60 pole segments 62 Radial outer surface 64 Main Unit 66 Tabs 68 Body Margin 70 side wall 72 Central slot axis 74 Radial Pole Pitch Line 76 Outermost tab surface 78 Innermost tab surface 80 Tip surface 82 Notch 84 Outermost notch surface 86 Tapered Wall 88 Innermost notch surface 90 Notch Sidewall 92 Central hub part 94 Inner tab 96 Radial innermost surface 98 Central shaft receiving opening 100 grooves 102 Groove 104 Inside 106 Center axis 108 Center axis 110 Axial surface 112 Axial surface 114 Radial outermost surface 116 Side 118 End face 120 Slot arm part 122 Radial outermost surface 124 Radial innermost surface 125 Open Slot Opening 126 Side 128 End face 130 Slot stem part 132 Non-ferrous materials 156 Lamination A Rotation Axis B Annular nominal circumference C. Predetermined angle D Predetermined angle D Longitudinal axis D1 Distance E Longitudinal axis T1 magnet thickness T2 magnet thickness W1 First slot width W2 Second slot width W3 Third slot width α angle

Claims

1. 1. A rotor assembly for an electric motor, comprising: a rotor core defining an axis of rotation and presenting a peripheral core surface; the rotor core includes a plurality of axially extending magnet slots each presenting a slot stem portion extending radially relative to the axis of rotation, a slot arm portion, and a slot opening extending outwardly from the slot arm portion; the slot stem portion and the slot opening are defined by a pair of radially extending opposed sidewalls; each side wall having a circumferentially extending outer tab adjacent the outer core surface and spaced from the slot arm portion; a plurality of magnets spaced apart in an arc around the rotor core; each of the magnets includes a magnet stem portion and a magnet arm portion; the magnet stem portion is received in the slot stem portion and extends radially relative to the axis of rotation to present a radially outermost stem end; the magnet arm portion is received in the slot arm portion and is located at least partially radially outward from the radially outermost stem end and extends in an opposite circumferential direction relative to the magnet stem portion; the slot opening extends between the slot arm portion and the outer core surface and is defined between the pair of side walls and the circumferentially extending opposing outer tabs.

2. The rotor assembly of claim 1 , wherein said magnet stem portion and said magnet arm portion each have a rectangular solid shape.

3. The rotor assembly of claim 2 , wherein the magnet stem portion and the magnet arm portion are disposed substantially perpendicular to one another.

4. The rotor assembly of claim 3 , wherein said magnet arm portion is located generally radially outward from said magnet stem portion.

5. The rotor assembly of claim 4 , wherein said magnet stem portion and said magnet arm portion contact each other such that each of said magnets is contiguous.

6. the magnet arm portion is a single magnet arm portion; 6. The rotor assembly of claim 5, wherein each of said magnets is T-shaped and includes only said single magnet arm portion located radially outward from said magnet stem portion.

7. the magnet arm portion exhibits an arm thickness measured in a radial direction; the magnet stem portion exhibits a stem thickness measured in a tangential direction perpendicular to the radial direction; The rotor assembly of claim 6 , wherein the arm and the stem have substantially equal thicknesses.

8. the magnet stem portion defines a longitudinal stem axis extending radially and centered in the tangential direction; The rotor assembly of claim 7 , wherein said magnet arm portions extend equally in opposite directions relative to said longitudinal stem axis.

9. A rotor assembly as described in claim 8, wherein the magnet arm portion is spaced from the outer core surface.

10. The rotor assembly of claim 9 , wherein each slot opening of a respective magnet slot extends between the slot arm portion and the outer peripheral core surface.

11. The rotor assembly of claim 10 , wherein the slot openings are open.

12. the rotor core presents a radially innermost hub defining a central shaft-receiving opening; The rotor assembly of claim 9 , wherein the magnet stem portion is spaced from the radially innermost hub.

13. The rotor assembly of claim 1 , wherein each of said magnet slots is T-shaped.

14. the rotor core includes a plurality of magnetic pole segments spaced circumferentially from one another, each of the magnet slots being defined between adjacent magnetic pole segments; The rotor assembly of claim 1 , wherein each of said plurality of pole segments includes a magnet locating structure.

15. the magnet positioning structure comprising a circumferentially extending radially inner tab; The rotor assembly of claim 14 , wherein the radially inner tabs extend into the slot stem portions of the magnet slots.

16. the magnet arm portion is generally radially outward from the magnet stem portion; The rotor assembly of claim 1 , wherein said magnet stem portion and said magnet arm portion contact each other such that each of said magnets is contiguous.

17. A rotor assembly as described in claim 1, wherein the magnet arm portion is spaced from the outer core surface.

18. the slot arm portion has a first circumferentially extending slot width; the slot opening has a second circumferentially extending slot width; The rotor assembly of claim 17 , wherein the first slot width is greater than the second slot width.

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