ROTOR BALANCING / FAXING BY INJECTION MOULDING OR COMPRESSION MOLDING

Description

BACKGROUND

[0001] The disclosure relates to rotors of electric motors, and in particular, reluctance machines and permanent magnet machines. More in particular, the disclosure relates to forming and balancing of the rotor and rotor component fixation via injection or compression molding. DE 10 2015 203018 A1 discloses a method for forming a rotor, comprising arranging a plurality of stacks of laminations in a stack as to form at least part of a rotor, the plurality of laminations having apertures that are aligned in the stack to form passages extending axially through the stack; filling magnet material into the passages; filling polymer based fixation material through the passages to lock the plurality of laminations together and overmold the magnet material; forming a sprue projecting from an axial face of the stack; and adjusting a weight of the sprue.

[0002] The present invention is defined by the accompanying independent claim 1.BRIEF DESCRIPTION OF THE DRAWINGS

[0003] Figure 1 is a perspective view of an exemplary permanent magnet motor in which the techniques described herein may be used; Figure 2 is a partial, cross-section view of an embodiment, not representing the invention, of the motor of Figure 1 along plane 2-2; and Figure 3 is an end view of an embodiment, not representing the invention, of a rotor of the motor of Figure 1. Figure 4 is a partial, side view of a portion of the rotor of Figure 3. Figure 5 is a cross section view of the rotor along plane 5-5 of Figure 4. Figure 6 is an end view of another embodiment, not representing the invention, of a rotor of the motor of Figure 1. Figure 7 is a partial, side view of a portion of the rotor of Figure 6. Figure 8 is a cross section view of the rotor along plane 8-8 of Figure 7. Figure 9 is an end view of another embodiment not representing the invention, of a rotor of the motor of Figure 1. Figure 10 is a partial, side view of a portion of the rotor of Figure 9. Figure 11 is a cross section view of the rotor along plane 11-11 of Figure 10. Figure 12 is an end view of another embodiment, representing an aspect of the invention, of a rotor of the motor of Figure 1. Figure 13 is a partial, side view of a portion of the rotor of Figure 12. Figure 14 is a cross section view of the rotor along plane 14-14 of Figure 13. Figure 15 is an end view of another embodiment, not representing the invention, of a rotor of the motor of Figure 1. Figure 16 is a partial, side view of a portion of the rotor of Figure 15. Figure 17 is a cross section view of the rotor along plane 17-17 of Figure 16. Figure 18 is a partial, cross-section view of another embodiment, representing an aspect of the invention, of the motor of Figure 1 along plane 2-2. Figures 19-22 show an embodiment, not representing the invention, of a stack of a ducted motor of the type shown in Figure 18 undergoing a sequence of operations to fill magnets slots of the stack with magnet material and forming sprues on axial face of the stack. Figures 23-24 show an embodiment, not representing the invention, of a stack comprising a portion of the rotor assembly of the motor of Figure 18. Figures 25-26 show an embodiment, not representing the invention, of a stack comprising another portion of the rotor assembly of the motor of Figure 18. DETAILED DESCRIPTION

[0004] Turning to the drawings, Figure 1 illustrates an exemplary permanent magnet motor 10. The exemplary motor 10 comprises a frame 12 capped at each end by drive and opposite drive end caps 14,16, respectively. The frame 12 and the drive and opposite drive end caps 14,16 cooperate to form the enclosure or motor housing for the motor 10. The drive and opposite drive end caps 14,16 may include mounting and transportation features, such as the illustrated mounting feet 18 and eyehooks 20. A conduit box 24 houses the electrical connection between the terminal leads and the external power source. A rotor shaft 26 coupled to the rotor rotates in conjunction with the rotor, and may be coupled to any number of drive machine elements, such as pumps, compressors, fans, conveyors, and so forth.

[0005] Figure 2, not representing the invention, is a partial cross-section view of the motor 10 of Figure 1 along plane 2-2. To simplify the discussion, only the top portion of the motor 10 is shown, as the structure of the motor 10 is essentially mirrored along its centerline. Within the enclosure or motor housing resides a plurality of stator laminations 30 juxtaposed and aligned with respect to one another to form a lamination stack, such as a contiguous stator core 32. In the exemplary motor 10, the stator laminations 30 are substantially identical to one another, and each stator lamination 30 includes features that cooperate with adjacent laminations to form cumulative features for the contiguous stator core 32. For example, each stator lamination 30 includes a central aperture that cooperates with the central aperture of adjacent stator laminations to form a rotor chamber 34 that extends the length of the stator core 32 and that is sized to receive a rotor. Additionally, each stator lamination 30 includes a plurality of stator slots disposed circumferentially about the central aperture. These stator slots cooperate to receive one or more stator windings 36, which are illustrated as coil ends in Figure 2, that extend the length of the stator core 32.

[0006] In the exemplary motor 10, a rotor assembly 40 resides within the rotor chamber 34. Similar to the stator core 32, the rotor assembly 40 comprises a plurality of rotor components, such as laminations 42 aligned and adjacently placed with respect to one another in a stack 44. A stack 44 of rotor components, such as laminations, may comprise a contiguous rotor core 46 or a part of a rotor core. When assembled, the rotor laminations 42 cooperate to form a shaft chamber that extends through the center of the stack 44 and rotor core 46, and that is configured to receive the rotor shaft 26 therethrough. The rotor shaft 26 is secured with respect to the rotor core 46 such that the rotor core 44 and the rotor shaft 26 rotate as a single entity about a rotor center axis 45. Although Figure 2 shows the generally like laminations 42 arranged side by side in a single stack 44 that forms the entire contiguous rotor core 46, the generally like laminations may be arranged side by side to form the stacks 44 of laminations and the stacks 44 of side by side laminations may be arranged in a spaced apart manner from one another along the rotor center axis 45 to form the rotor core 46, for instance, for a radially ducted motor, which by way of example is shown in Figure 18, and which will be explained in greater detail below. Although the drawings show a rotor core with a side by side arrangement of laminations, the rotor core may include other rotor components, for instance, alternating soft magnetic blocks with soft magnetic composites.

[0007] The exemplary motor 10 includes drive and opposite drive bearing sets 50,52, respectively, that are secured to the rotor shaft 26 and that facilitate rotation of the rotor assembly 40 within the stationary stator core 32. Each bearing set 50,52 includes an inner race 54, an outer race 56 and rotational elements 58, which are disposed between the inner and outer races 54,56.

[0008] Figures 2 - 26 provide further detail of illustrative embodiments of the rotor component using laminations 42 as an example to form the stack and the rotor, although other rotor components may be used. Each rotor lamination 42 has a generally circular cross-section and is formed of a magnetic permeable material, such as electrical steel. Extending from end-to-end, i.e., transverse to the cross-section, each lamination 42 includes features that, when aligned with adjacent laminations 42, form cumulative features that extend axially through the stack of laminations, which may be the entire rotor core. For example, each exemplary rotor lamination 42 has a circular shaft aperture 62 located in the center of the lamination 42. The shaft apertures 62 of adjacent laminations 42 cooperate to form a shaft chamber configured to receive the rotor shaft 26 (see Figure 2) therethrough. Additionally, each lamination 42 includes apertures 64 that are arranged at positions about the lamination such that when assembled, the apertures cooperate to form passages 66 that extend through the stack, and which may extend through the rotor core 44 depending upon the arrangement of the stack(s). Depending upon the application, some of the passages 66 may be configured to receive magnet material 68, which may be by way of example, sintered magnets, permanent magnets, or magnetizable material. Depending upon the application, some of the passages 66 may be configured to receive a fixation material 70 to fix the laminations together. Depending upon the application, the passages 66 that receive the magnet material 68 may also receive fixation material 70. Figures 2 and 18 show examples of magnet material 68 received in the passages 66 and the fixation material 70 received in the same passages 66 to fix the laminations. The magnet material 68 may be received in the passage to a certain length dimension relative to the stack length dimension, and the fixation material may be received in the passage to fill the passage, and / or form a sprue as will be described below. The passages 66 are be configured to receive the magnet material 68. After those passages 66 are filled with the magnet material 68, the fixation material 70 is introduced into those passages and other vacant passages to provide additional fixation for the stack and flux shaping as needed. Depending upon the application, the fixation material may be used in selected passages, and the magnet material may be omitted from the rotor, for instance, in the case of a synchronous reluctance type motor.

[0009] The fixation material 70 and / or magnet material 68 may be filled into the passages 66 as part of an injection molding process or compression molding process. The magnet material 68 comprises a polymer bonded composite magnet material and the fixation material 70 may comprise a neat polymer, nylon, or a fiber reinforced polymer. For further mechanical integrity and strength of the fixation material 70, reinforcing fibers may be included in the fixation material. A non-exhaustive list of fixation materials includes Acrylonitrile Butadiene Styrene (ABS), Polyamide- Nylon with or without glass filling (PA), polycarbonate (PC), Polyethylene (PE), Polypropylene (PP), Polystyrene (PS), Acetal (POM), Low Density Polyethylene (LDPE), and Density Modified High Gravity Compounds.

[0010] As a result of the injection molding or compression molding process, one or more sprues 72 are formed on the axial face of the stack 44. Depending upon the application and the arrangement of the injection molding or compression molding process, one or more sprues 72 may be provided on axially opposite ends of the stack 44, or rotor core 46 as the case may be. According to the invention, the sprue 72 is shaped and formed as needed depending upon the application. As described below, the sprue(s) 72 may be configured as a cylindrical body(ies) or end plate(s). In addition, the sprue(s) 72 may be configured and formed for additional functionalities such as cooling fins or with locating structures defining reference positions for measuring equipment, and / or the attachment of fixtures and / or tooling used during the injection molding or compressing molding process. The sprue(s) may also be configured to locate, retain, or secure an end ring or other plate to provide additional structural integrity for the rotor assembly.

[0011] In Figures 3-8, not representing the invention, the sprue 72,72' is formed in a contiguous manner on the entire outer face of the axial outermost lamination of the stack 44, thereby forming an end plate for the stack with a thickness. While one sprue 72,72' is shown in Figures 3-8 on one axial side of the stack 44, a similar sprue may be formed on the opposite axial side of the stack. In the arrangement shown in Figures 3-8, a mold may be formed around the axial end of the stack 44 and after magnet material 68 is inserted in the passages 66, the fixation material 70 is filled in the passages and out beyond the axial outermost lamination of the stack to form the sprue 72,72' as an end plate covering the outermost lamination of the stack. In the arrangement shown in Figures 3-5, the end plate formed sprue 72 may have a generally flat structure. In the arrangement shown in Figure 6-8, the end plate formed sprue 72' may have a pocketed outer axial face 74 forming a cellular or honeycomb type structure with a plurality of open cells 76. To balance the rotor of Figures 3-5, the end plate formed sprue 72 may be selectively machined, and / or balancing material added, as needed to adjust the weight of the sprue and its weight / mass distribution, and rotationally balance the rotor about the rotor center axis 45. To balance the rotor of Figures 6-8, balancing material may be inserted into any one of a plurality of open cells 76 in the pocketed face, open cellular, honeycomb- type structure 74 to adjust the weight of the sprue 72' and rotationally balance the rotor about the rotor center axis 45. To the extent material needs to be removed for balancing, a portion of sprue comprising the pocketed face, open cellular, honeycomb- type structure 74 or the end plate may be removed as necessary.

[0012] Figures 9-14 show alternate embodiments of a stack 80 where several sprues 82 are formed about the outer face of the axial outermost lamination of the stack. While several sprues are shown in each of the embodiments of Figures 9-14 on one axial side of the stack, sprues may be formed in a like manner on the opposite axial side of the stack. Depending upon the application, the sprues 82 shown by example in Figures 9-14 may be preferred to the sprues 72,72' of Figures 3-8 in that it allows for less material to be used for fixation. According to the invention, in Figures 9-14, the sprue 82 are formed in a sector (e.g., in the drawings, a quadrant) of the stack 80, which correspond to a pole of the rotor. The magnet material 68 is filled into the passages 66 designated as magnet slots of the lamination 42, and the fixation material 70 is then filled into the same passages to form the substantially cylindrically shaped sprue 82 shown in the Figures in a sector of the rotor. Certain of the passageways 66 may contain both permanent magnets or magnet material 68, and the fixation material 70. Certain other passages may solely contain the fixation material 70. For instance, in the embodiment shown in Figures 9-11, not representing the invention, the radially outermost U-shaped passage may be reserved solely for fixation material 70, while other radially inward U-shaped passages may contain both fixation material 70 and magnet material 68. A synchronous reluctance motor may omit the magnet material and fixation material may be filled in selected passages 66. Figures 12-14 show an alternate embodiment where the stack 90 contains passageways 92 radially inward adjacent to the shaft aperture 62 that solely contain fixation material, and the other radially inward U-shaped passages 66 may contain both fixation material 70 and magnet material 68. As described before, the sprues 82 may be machined as necessary to adjust the weight of the sprues and rotationally balance the rotor about the rotor center axis 45. Additionally, balancing material may be inserted in one or more of the sprues 82 for adjusting the weight of the sprues and rotationally balancing the rotor about the rotor center axis 45. In the embodiment shown in Figures 12-14, representing an aspect of the invention, the fixation material 70 may be removed from the radially inward passages 92 to further assist in balancing.

[0013] Figures 15-17 show an alternate embodiment, not representing the invention, and construction for the stack 100 comprising a plurality of surface magnets 102 formed from the magnet material 68. Again, the like laminations 42 are arranged side-by-side to form the stack 100. The apertures 104 in the laminations are aligned in a manner so as to cooperate and form channels 106 that extend axially through the stack 100. The channels may extend radially inward in the lamination from the outer diameter surface of the lamination to provide additional structure integrity for the magnets. The magnet material 68 may be filled into certain locations around the rotor to form the surface magnets, and then the fixation material 70 may be filled and molded over the magnet material to lock the magnet material in place in an overmolded arrangement. The fixation material 70 may extend from the outer face of the outermost axial lamination in the form of a sprue 110. The sprue 110 may have the form of an annular, end ring-type structure extending axially outward from the axial outermost lamination of the stack. The sprue 110 in the form of the annular, end ring-type structure may then be adjusted as needed to rotationally balance the rotor about the rotor center axis. Balancing material may be inserted in the sprue 110 or the sprue may be machined in order to adjust the weight of the sprue and rotationally balance the rotor about the rotor center axis 45

[0014] Figure 18 shows an embodiment, representing an aspect of the invention, of a rotor 46' for the motor where a plurality of stacks 44' of laminations are arranged side-by-side in spaced apart arrangement along the rotor with their apertures aligned to form passages 66 extending axially through the stack 44'. After magnet material 68 is filled into the passages 66, the fixation material 70 may be filled through the passages 68. The mold used in the injection molding or compressing molding process may include forms which create ducts 120 extending through the passages 68. The ducts 120 may extend axially through the stacks and overall through the rotor. The ducts 120 may also extend radially outward between adjacent spaced apart stacks of laminations 44'. As the fixation material is filled, it may flow around the forms and define the ducts 120 in the passages while locking the laminations together and overmolding the magnet material. The sprue 72 may comprise the form of an end place as described above in reference to Figures 3-8 or may comprise the cylindrical structure as described above in reference to Figures 9-14, and may be adjusted in the same ways discussed above to rotationally balance the rotor 46' about the rotor center axis 45.

[0015] Figures 1 9 - 2 6 show additional aspects, not representing the invention, of the radially ducted rotor of Figure 18. In particular, Figures 19 -21 shows a stack 44' with a plurality of passages 66 comprising V-shaped magnets slots configured to receive magnet material 68 as described previously. The passages 66 comprising the magnets slots of the stack 44' may extend actually through the stack in the manner described previously. The magnet material 66 may be filled in the passages 66 comprising the magnet slots to a certain depth. Once the magnet material 68 is filled in the passages, the fixation material 70 may be filled in the passages 66 comprising the magnets slots, and may include a sprue 72 extending axially from the face of the stack 44'. The magnet material 68, fixation material 70, and / or sprue 72 may be compression or injected molded as described above. The sprue 72 on the axial face of the stack 44' may function as a locator or retainer as shown for an end ring configuration as shown in Figure 25-26 or may form the radially spoked arrangement for a radially ducting of the stack 44' forming the rotor assembly 40. In Figures 25-26, the sprue 72 may comprises the spoke configuration extending from the axial face of the stack. In Figures 23-24, the sprue 72 may comprise a cylindrical nub that enables attachment of an separate end ring or the sprue may be formed as an end ring. Thus in the embodiment of the radially ducted motor shown in Figure 18, a plurality of stacks of the type shown in Figures 23 - 24 may be arranged in an axially spaced apart manner to form the axially inward portion of the rotor assembly, and stacks of the type shown in Figures 25- 26 may form the axial outward portions of the rotor assembly with the stacks having the sprues with radial spokes therebetween.

[0016] While certain embodiments have been described in detail in the foregoing detailed description and illustrated in the accompanying drawings, those with ordinary skill in the art will appreciate that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure within the scope of the invention, which is defined by the appended claims. Particularly, the figures and exemplar embodiments of the rotor laminations are intended to show illustrative examples and not to be considered limiting in any sense. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the , which is defined by the appended claims.

Claims

1. A method for forming a rotor, the rotor comprising a rotational center axis (45) and four quadrant sectors that each correspond to a pole of the rotor, the method comprising: arranging a plurality of stacks (44; 80) of laminations (42) in a stack (44; 80) as to form at least part of the rotor, the plurality of laminations (42) having apertures (64) that are aligned in the stack to form passages (66) extending axially through the stack (44; 80), and passageways (92) radially inward adjacent to the apertures (64); filling magnet material (68) into the passages (66), and filling polymer based fixation material (70) through the passages (66) to lock the plurality of laminations (42) together and overmold the magnet material (68), and filling, solely, the polymer based fixation material (70) through the passageways (92); wherein filling the passages (66) with the fixation material (70) is accomplished by use of a mold that includes forms, wherein as the fixation material (70) is filled in the passages (66), it flows around the forms while locking the laminations (42) together and overmolds the magnet material (68) with the fixation material (70), forming a sprue (72; 82) projecting from an axial face of the stack (44; 80); the method comprises adjusting a weight of the sprue (72; 82) to rotationally balance the rotor about the rotor center axis (45), wherein the sprue (72; 82) is formed in exactly four portions, and each portion of the sprue (72; 82) is formed in each of the four quadrant sectors of the stack (44; 80) that correspond to a pole of the rotor.

2. The method of claim 1, further comprising: a plurality of radially inner and radially outer passages (66) formed in the stack (44; 80), wherein the radially outer passages (66) are filed with a polymer based fixation material (70) in a manner to fix the rotor components of the stack (44; 80) together in the stack (44; 80) and omitting magnet material (68) from radially inward passages (66).

3. The method of claim 2, wherein at least a portion of the passages (66) comprise magnet slots, and the method further comprises filling magnet material (68) in the magnet slots.

4. The method of claim 3, wherein the step of filling the fixation material (70) in the passages (66) includes filling fixation material (70) in the magnet slots after the step of filling magnet material (68) in the magnet slots.

5. The method of claim 1 wherein the step of filling the fixation material (70) in the passages (66) includes at least partially molding over the magnet material (68) placed in the stack (44; 80) after performing the step of placing the magnet material (68) in the stack (44; 80).

6. The method of claim 2 wherein the step of adjusting the weight of the sprue (72; 82) to rotationally balance the rotor about the rotor center axis (45) includes removing a portion of the sprue (72; 82).

7. The method of claim 1 wherein the step of rotationally balancing the rotor includes removing a portion of the sprue (72; 82).

8. The method of claim 1, wherein at least one additional duct extends radially outward between the adjacent spaced apart stacks (44; 80) of lamination within the plurality of laminations (42).

9. The method of claim 1, wherein the step of filling the fixation material (70) in the at least one passage (66) includes filling at least one passage (66) containing magnet material (68) with the fixation material (70).