Stator assembly

Abstract

A stator assembly for a radial flux motor is disclosed herein. The stator assembly includes a stator core and a coil including a plurality of turns surrounding the stator core. Each of the plurality of turns has a rectangular cross-section, and a secondary edge of the rectangular cross-section forms a portion of an inner periphery of the coil, where the inner periphery faces the stator core.

Description

Technical Field

[0001] The present invention relates to a stator assembly for a radial flux motor and a radial flux motor comprising the stator assembly. Background Art

[0002] It is often desirable to improve electric motors, such as brushless motors, in a variety of ways. For example, improvements may be desired in size, weight, power density, manufacturing cost, efficiency, reliability, and noise. Summary of the Invention

[0003] According to a first aspect of the present invention, there is provided a stator assembly for a radial flux electric machine, the stator assembly comprising: a stator core; and a coil, the coil comprising a plurality of turns surrounding the stator core, wherein each of the plurality of turns has a rectangular cross-section, and wherein a secondary edge of the rectangular cross-section forms a portion of an inner periphery of the coil, wherein the inner periphery faces the stator core.

[0004] Multiple turns, each with a rectangular cross-section, around the stator core can enable a high fill factor. This increases maximum torque output compared to lower fill factors. Furthermore, compared to circular cross-sections, rectangular cross-sections can reduce resistance to current flow in the coil, thereby reducing DC losses. The rectangular cross-section can be a constant dimension along the entire length of the coil. This uniformity further contributes to a high fill factor and reduced DC losses.

[0005] The inner periphery of the coil can consistently face the stator core along the entire length of each turn, thus consistently facing the stator core. This means that the inner periphery of the coil is positioned opposite the stator core. In some examples, the inner periphery can directly face the stator core. In other words, the inner periphery can be parallel to the surface of the stator core. The coil is arranged so that the minor edge of the rectangular cross-section forms part of the inner circumference, meaning that each turn is arranged with the smaller surface closest to the stator core and the larger surface facing the adjacent turn. This reduces eddy currents within the coil, which in turn reduces AC losses during use. As a result, the stator assembly can be more efficient than conventional stator assemblies. This arrangement also minimizes the space required for the coil on the stator core while still providing high power output for the motor including the stator assembly. This allows the stator assembly to be used in a compact yet power-dense motor. Consequently, the motor can be used in a variety of devices, including small appliances such as hair care appliances, without adding more weight and / or taking up more space than conventional motors.

[0006] The coil can partially surround the stator core such that a single turn of the coil covers both the radially inner and radially outer surfaces of the stator core. In some examples, the stator core is annular, with the radially inner and outer surfaces being concentric. Arranging the turns so that each single turn covers both the radially inner and radially outer surfaces of the stator core can provide an increased surface area for the coil, compared to a stator core having only a radially outer surface around which turns can be wound. This can increase the power output of a motor using the stator assembly by providing an increase in torque output, compared to a motor having turns wound around a surface.

[0007] In some examples, the rectangular cross-section has an aspect ratio of 4.50:1 to 4.8:1. Having an aspect ratio within this range allows the wire (which is wound into the multiple turns that form the coil) to be sufficiently bendable to avoid damaging the insulation surrounding the wire. To achieve this aspect ratio, the rectangular cross-section may have, for example, a minor dimension of 0.2 mm and a major dimension of 0.925 mm. A rectangular cross-section measuring 0.2 mm by 0.925 mm can provide a smaller motor with higher power output than some prior art examples.

[0008] The coil may include a single wire wound into multiple turns. The single wire wound into turns can utilize high voltage with low current. This allows the stator assembly to generate a higher power output from a high voltage power supply compared to a stator assembly including coils having multiple different wires.

[0009] The coil may include a first conductor and a second conductor different from the first conductor, wherein the first conductor and the second conductor define a plurality of turns. The first conductor may be wound in the first turn, and the second conductor may be wound in the second turn adjacent to the first turn. The plurality of different conductors wound into turns can utilize low voltage with high current. This allows the stator assembly to generate a higher power output from a high current power source (such as a battery) compared to a stator assembly including a coil having a single conductor.

[0010] Compared to winding one wire radially outside the other, alternating winding two different wires (or a single wire) can reduce the overall diameter of the stator assembly, as the radially outer wire will have a larger bend radius than the radially inner wire. Furthermore, for adjacently wound wires, both the first and second wires can have the same bend radius around the stator core. This allows a larger volume of wire to fit into the same radial space compared to radially wound wires. Furthermore, this can reduce eddy currents when AC current is driven through the wire(s). This can be particularly beneficial for small motors, such as those used in handheld devices.

[0011] In some examples, the first and second wires are wound in a repeating alternating pattern of turns.The first and second wires may be air wound in alternating turns of the coil prior to assembly around the stator core.

[0012] The alternating turns of wire can also help balance the alternating current within the wires of the stator assembly. This can reduce hot spots within the wires and can be particularly useful in radial flux machines.

[0013] The first and second conductors may be electrically connected in parallel. Using two different conductors electrically connected in parallel means that a higher current can be passed through the coils compared to the same arrangement with a single conductor. This can be advantageous when the motor incorporating the stator assembly has a battery as its power source. Because when the voltage is lower, a higher power output from the motor can be achieved compared to using only one conductor.

[0014] The stator assembly may include a plurality of subassemblies, each subassembly including a corresponding coil, the coil including a plurality of turns surrounding a stator core segment. Each of the plurality of turns may have a rectangular cross-section, and a minor edge of the rectangular cross-section may form a portion of an inner periphery of the coil, wherein the inner periphery faces the stator core.

[0015] It may be desirable to separate the stator assembly into multiple subassemblies to facilitate manufacture of the stator assembly. For example, increasing the number of segments forming the annular stator core may enable the stator core segments to be more linear than would be the case if the annular stator core were formed using a smaller number of segments. This may facilitate the formation of the laminations forming the stator core segments, for example by enabling an increased number of laminations to be formed from a single piece of material, thereby reducing material waste and cost.

[0016] Furthermore, compared to a single annular stator core, slotting air wound coils on the stator core can be achieved when the stator core is segmented, which can be easier to manufacture than winding coils onto the stator core or its segments.

[0017] In some examples, the stator assembly includes exactly three subassemblies. Taking into account the air gaps between stator core segments, dividing the stator assembly into subassemblies can increase the reluctance of the stator assembly, thereby providing resistance to magnetic flux attempting to pass between the stator core segments. Furthermore, with each incremental integer increase in the number of stator core segments, reliably and securely connecting the stator core segments together can become more challenging, which can result in a change in the overall form of the stator assembly. This change in form can introduce saliency, which can inhibit the generation of desirable magnetic torque in the motor.

[0018] In some examples, the stator assembly is a three-phase stator assembly.When driven at the same voltage, the three-phase stator assembly can generate more torque than a single-phase stator assembly.

[0019] Each stator core segment can span an arc length of 120 degrees. Having three stator core segments of the same arc length can mean that the three subassemblies have substantially the same form. This can reduce the manufacturing cost and complexity of the stator assembly compared to, for example, a stator assembly using stator core assemblies of different forms.

[0020] The curvature of the subassembly can give the stator assembly a toroidal shape. An annular stator assembly can allow for more efficient use of available space in an appliance than, for example, a rectangular stator assembly. This can be particularly advantageous, for example, when the stator assembly is to be used in a pipeline.

[0021] In some examples, each coil includes at least twenty turns. Using at least twenty turns for each coil can allow the stator assembly to produce a high power output in an electric machine with available space for stator core segments, compared to stator assemblies having fewer turns. In examples where the coils include alternating wound first and second conductors, each coil includes at least ten turns of each conductor.

[0022] Each subassembly can include an additional coil, so that the stator assembly includes a total of six coils. Using six coils can provide a relatively low radial load on the rotor assembly associated with the stator assembly in use, compared to, for example, an arrangement using three coils. The additional coils can be identical to the coils or mirror images of the coils. The coils and additional coils can be substantially evenly spaced around the stator core segment.

[0023] Each subassembly may include a spool, each spool including first and second connection formations connected to respective second and first connection formations of an adjacent spool.

[0024] The bobbins can be used to insulate the stator core segments from the coils, thereby reducing undesirable currents or losses. Providing connection formations on each bobbin rather than on the stator core segments can reduce magnetic resistance and / or saliency that may otherwise occur due to, for example, shape variations of the stator core segments due to manufacturing tolerances.

[0025] Each bobbin can include slots for external equipment to manipulate the assembly during manufacturing. The placement slots on the bobbin can be used during manufacturing to facilitate manipulation of the stator assembly (by external equipment). The placement slots can be no wider than 1.5 mm, facilitating stator assembly manufacturing without significantly impacting the space available for inserting the coils on the bobbin. The placement slots can separate the aforementioned coils from additional coils. This positioning maximizes the space available for these coils (to maximize the number of turns).

[0026] The stator assembly can have an outer diameter of no greater than 25 mm. In some examples, the stator assembly can have an outer diameter of no greater than 20 mm. This outer diameter can be smaller than stator assemblies of the prior art. Minimizing the size of the stator assembly can allow for a radial flux motor using the assembly to be reduced in size compared to motors using larger stator assemblies. Particularly in small, handheld appliances and components (i.e., hair care appliances), a small motor improves comfort and ease of use for the end user.

[0027] According to a second aspect of the present invention, there is provided a radial flux electric machine comprising a stator assembly as described above. Any of the above features may be included in the stator assembly individually or in combination.

[0028] The radial flux electric machine may include any of the above features of the stator assembly, either alone or in combination.The radial flux electric machine may also include a rotor assembly disposed within the stator assembly.

[0029] According to a third aspect of the present invention, there is provided a hair care appliance comprising the radial flux motor described above.

[0030] According to a fourth aspect of the present invention, there is provided a vacuum cleaner comprising the radial flux motor described above.

[0031] According to a fifth aspect of the present invention, a stator assembly is provided, comprising: a stator core; and a coil, the coil comprising a first conductor and a second conductor different from the first conductor, wherein the first conductor and the second conductor are each wound around the stator core in a staggered manner with a plurality of turns; wherein each of the first conductor and the second conductor has a rectangular cross-section, and wherein a secondary edge of each rectangular cross-section forms a portion of an inner periphery of the coil, the inner periphery facing the stator core. The stator assembly may further include any of the above features, individually or in combination.

[0032] Other features and advantages of the present invention will become apparent from the following description of preferred embodiments of the invention, given by way of example only, which description refers to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a perspective view of the stator assembly;

[0034] Figure 2 yes Figure 1 Exploded view of the stator assembly;

[0035] Figure 3 yes Figure 1 a perspective view of a stator core assembly of a stator assembly;

[0036] Figure 4 yes Figure 3 An exploded view of the stator core assembly;

[0037] Figure 5 is a perspective view of an example coil of the present invention;

[0038] Figure 6a yes Figure 5 an enlarged view of a portion of the coil;

[0039] Figure 6b yes Figure 6a A cross-sectional view of the stator, wherein the coil is arranged on the stator core;

[0040] Figure 7a yes Figure 5 a cross-sectional view of a portion of an alternative coil;

[0041] Figure 7b is included Figure 7a A perspective view of a stator core subassembly of a replacement coil;

[0042] Figure 8 is included Figure 1 Schematic diagram of a brushless permanent magnet motor having a stator assembly;

[0043] Figure 9 is included Figure 8 A schematic diagram of a vacuum cleaner with a brushless permanent magnet motor; and

[0044] Figure 10 is included Figure 8 Schematic diagram of a hair care appliance with a brushless permanent magnet motor. DETAILED DESCRIPTION

[0045] The stator assembly 10 is Figure 1 and Figure 2 Schematically shown in FIG, and includes a first stator core subassembly 12, a second stator core subassembly 14 and a third stator core subassembly 16 and a busbar assembly 18. The first stator core assembly is as shown in FIG. Figure 3 and Figure 4 Each of the first stator core subassembly 12 , the second stator core subassembly 14 , and the third stator core subassembly 16 has substantially the same form, and therefore, for the sake of brevity, the second stator core subassembly 14 and the third stator core subassembly 16 will not be described in detail herein.

[0046] The first stator core subassembly 12 includes a stator core segment 22 , a bobbin 24 , and first and second coils 32 , 34 .

[0047] The stator core segments 22 are formed from a stack of steel laminations (not shown) and are generally arcuate in shape, with their height being greater than their length and width. The stator core segments 22 span an arc length of approximately 120 degrees. The circumferential end faces of the stator core segments 22 are generally planar in form. When connected together, the generally circumferential faces of the stator core segments 22 substantially contact one another, forming a generally annular stator core from the stator core segments 22.

[0048] The bobbin 24 is formed of a plastic material and is overmolded onto the stator core segment 22. The bobbin 24 includes first and second bodies 35, 36 and slots 38 that follow the arcuate form of the stator core segment 22 over which they are overmolded.

[0049] The slot 38 is generally rectangular in cross-section and at least partially separates the first body portion 35 and the second body portion 36, thereby providing a line of sight to the radially outer surface of the stator core segment 22. The bobbin 24 includes a frame 39 surrounding the periphery of the slot 28, which projects outwardly from the first body portion 35 and the second body portion 36. The slot 38 enables appropriate magnets to hold the stator core segment 22 in place during assembly of the first stator core assembly 12.

[0050] The first coil 32 and the second coil 34 are formed from turns 505 of copper wire. Figure 5 The first coil 32 is shown separately, wherein Figure 6a An enlarged portion of the coil 32 is shown. The first coil 32 and the second coil 34 are each formed from a single piece of copper wire with an insulating coating and are air-wound using a continuous winding process prior to assembly. The second coil 34 is a mirror image of the first coil 32. Therefore, for the sake of brevity, only the first coil 32 will be described in detail.

[0051] First coil 32 includes twenty substantially uniform turns 505. Each turn 505 has a rectangular cross-section with two minor edges 506, 506' and two major edges 507, 507'. The minor edges 506, 506' are 0.2 mm long, and the major edges 507, 507' are 0.93 mm long, resulting in a cross-sectional aspect ratio of 4.65:1. This aspect ratio is generally consistent throughout the wire because the cross-section of the wire remains approximately the same, although curved portions (described below) may have slight variations in aspect ratio due to bending of the wire.

[0052] Each turn 505 includes a first curved portion 509 at a first end 508 (corresponding to the first end of the stator assembly 48) and a second curved portion 509' at a second end 510, with two straight extensions 511, 511' between the curved portions 509, 509'. The curved portions 509, 509' are each curved about the bending axis A, B with a total curvature of 180 degrees, such that the curvature of the curved portion 509 causes the straight extensions 511, 511' to extend in parallel extension directions.

[0053] The second curved portion 509' at the second end 510 of the first turn 505 also forms the second curved portion 509' of the adjacent turn 505, such that the two adjacent turns share a common second curved portion 509', allowing the turns 505 to be wound around the stator core 22 when the first coil 32 is positioned around the stator core 22. These second curved portions 509' are aligned with one another, as are the first curved portions 509. There may be some spacing between adjacent turns 505, or adjacent turns 505 may be partially or completely in contact. When arranged together, the inner surface of each turn 505 collectively forms the inner perimeter 514 of the first coil 32, which is sleeved onto the stator core 22.

[0054] Figure 6b An exploded cross-sectional view of four example turns 505 arranged around the stator core 22 (with the overmolded bobbin 24) is shown. Each turn 505 is oriented on the stator core 22 such that the minor edge 506 of the cross section faces the stator core 22 and is substantially parallel to the surface of the stator core 22. The bending axes A, B of the curved portions 509, 509' are parallel to the minor edges 506. This means that the common inner periphery 514 of the turns 505, which faces the stator core 22, corresponds to the minor edges 506, 506' of the cross section. In other words, the turns are bent with one of the thinner surfaces facing the stator core.

[0055] The final turns 505a, 505b at each end of the first coil 32 include terminal connections 512a, 512b adjacent to the first bend 509 at the first end 508. The terminals 512a, b are exposed portions of the copper wire without an insulating coating. The terminal connections 512a, 512b extend away from the first coil 32 in a direction generally perpendicular to the bend axis 516 of the turn 505.

[0056] When assembled on the bobbin 24, the terminal connections 512a, b protrude away from the bobbin at the first end 48 of the stator assembly. The busbar assembly 18 is located at the first end 48 of the stator assembly 10 and includes a plastic carrier 52 and three electrically conductive busbars 54. The electrically conductive busbars 54 are welded to the coils 32, 34 at the first end 48 of the stator assembly 10. Each busbar 54 is thereby electrically connected to two coils of the stator assembly 10. The construction of the busbar assembly is not relevant to the present invention and, for the sake of brevity, will not be described in detail.

[0057] Figure 7a A cross-sectional view showing an alternative coil embodiment arranged on the stator core 22 is shown. Figure 7b A perspective view of the stator core assembly 12 is shown with the coil as an alternative to a first coil 710 and a second coil 712 (which are also mirror images of each other). This embodiment is substantially the same as the embodiment of FIG. 1 , except that each coil 710 , 712 includes a first conductor 700 interleaved with a second conductor 702 . Figures 5 to 6bThe coils are arranged identically to those in FIG. Each of these wires comprises ten turns 704, 706 (giving the coil a total of twenty turns). These turns 704, 706 are substantially identical to the turns 505 described above.

[0058] In this embodiment, the turns 704, 706 are staggered so that two major edges 707, 707' of the cross-section of the turn 704 of the first conductor 700 are each adjacent to a major edge 707' of the cross-section of the turn 706 of the second conductor 702. That is, adjacent turns 704, 706 alternate between the first conductor 700 and the second conductor 702.

[0059] Each turn 704, 706 has a bend that connects to the next turn of the wire.When viewing the wires and their respective turns individually, adjacent turns have a common bend as described in the above embodiments.

[0060] The final turn of each conductor 700, 702 includes a terminal connection 708, 709 at each end of the first coil. Since there are two conductors in the first coil, the first coil has two terminal connections at each end. In this embodiment, the busbar assembly 18 is arranged to electrically connect to the terminal connections of each conductor in parallel so that the current flowing through the first conductor 700 flows in the opposite direction to the current flowing in the second conductor 702.

[0061] Together, the first stator core subassembly 12, the second stator core subassembly 14, and the third stator core subassembly 16, when connected together, define an annular space having a central bore 46 for receiving the rotor assembly, wherein the stator assembly 10 has a diameter no greater than 20 mm. Each of the stator core assemblies 12, 14, and 16 includes one of the coil embodiments described above. The coil embodiment is the same for each stator core assembly.

[0062] In use, the stator assembly 10 is mated with the rotor assembly 800 to form a radial flux motor 802, such as Figure 8 The rotor assembly 800 includes a shaft 804 and permanent magnets 806 mounted to the shaft 804. When the coils 32, 34 are driven at an appropriate voltage (here up to about 400 V), the stator assembly 10 generates a magnetic field that interacts with the permanent magnets 806 to rotate the rotor assembly 800.

[0063] exist Figure 9 A vacuum cleaner 900 including a radial flux motor 802 is schematically shown in FIG.

[0064] exist Figure 10 A hair care appliance 1000 including a radial flux motor 802 is schematically shown in FIG.

[0065] The above-described embodiments should be understood as illustrative examples of the present invention. Other embodiments of the present invention are contemplated. Other arrangements of the coils on the stator core are contemplated. For example, the first and second coils may be identical, rather than mirror images of each other; and / or the coils may have terminals positioned differently. It should be understood that any feature described with respect to any one embodiment may be used alone or in combination with other features described, and may also be used in combination with one or more features of any other embodiment, or in combination with any combination of any other embodiments. It should be understood that slight variations in the wires, such as minor non-uniformities, are considered to be encompassed by the present invention. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the present invention as defined in the appended claims.

Claims

1. A stator assembly for a radial flux motor, the stator assembly comprising: stator core; and a coil comprising a plurality of turns surrounding the stator core, wherein each of the plurality of turns has a rectangular cross-section, and Wherein, the secondary edge of the rectangular cross section forms a portion of an inner periphery of the coil, wherein the inner periphery faces the stator core.

2. The stator assembly according to claim 1, wherein: The aspect ratio of the rectangular cross section is 4.50:1 to 4.8:

1.

3. The stator assembly according to claim 1 or 2, wherein: The coil includes a single wire wound into the plurality of turns.

4. The stator assembly according to claim 1 or 2, wherein: the coil includes a first conductive wire and a second conductive wire different from the first conductive wire, and the first conductive wire and the second conductive wire define the plurality of turns, The first conductive wire is wound in a first turn, and the second conductive wire is wound in a second turn adjacent to the first turn.

5. The stator assembly according to claim 4, wherein: The first conductive line and the second conductive line are electrically connected in parallel to each other.

6. A stator assembly according to any one of the preceding claims, wherein: The stator assembly includes a plurality of subassemblies, each subassembly including a corresponding coil, the coil including a plurality of turns around a stator core segment, wherein each of the plurality of turns has a rectangular cross-section, and Wherein, the secondary edge of the rectangular cross section forms a portion of an inner periphery of the coil, wherein the inner periphery faces the stator core.

7. The stator assembly according to claim 6, wherein: The stator assembly comprises exactly three sub-assemblies.

8. The stator assembly according to claim 7, wherein: Each stator core segment spans an arc length of 120 degrees.

9. The stator assembly according to any one of claims 6 to 8, wherein: Each coil comprises at least twenty turns.

10. The stator assembly according to any one of claims 6 to 9, wherein: Each of the subassemblies includes an additional coil, so that the stator assembly includes a total of six coils.

11. The stator assembly according to claim 9, wherein: Each of the subassemblies includes a spool, each spool including first and second connection formations connected to respective second and first connection formations of an adjacent spool.

12. The stator assembly according to claim 11, wherein: Each spool includes a slot for external means to manipulate the assembly during manufacturing.

13. A stator assembly according to any one of the preceding claims, wherein: The stator assembly has an outer diameter no greater than 25 mm.

14. A radial flux electric machine comprising a stator assembly according to any one of the preceding claims.

15. A hair care appliance comprising the radial flux motor according to claim 14.

16. A vacuum cleaner comprising the radial flux motor according to claim 14.

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