Bobbin

Abstract

1. A bobbin for a stator or rotor of an electric motor, the bobbin comprising an injection molded plastic housing having a first section and a second section, the first section arranged to receive a coil winding and including an opening allowing teeth attached to the stator or rotor to pass therethrough, the second section arranged to extend in a first direction substantially perpendicular to the opening and including a flange serving as a tip of the teeth, and a metal element mounted in or on the flange.

Description

[Technical field]

[0001] The present invention relates to a bobbin, in particular for a stator or rotor of an electric motor. [Background technology]

[0002] The stator is well known as the stationary part of an electric motor or generator in which the rotor rotates.

[0003] The stator is generally made up of magnetic and other structural components. Electric motors operate on the principle that a current carrying wire experiences a force in the presence of a magnetic field. A rotor, usually carrying permanent magnets, is arranged to rotate about a current carrying coil, which in turn rotates about the stator and generates motion. It will be appreciated that it is also possible for the rotor to have a set of coils and the stator to have a set of permanent magnets.

[0004] An example of a stator mounted within a rotor is shown in FIG. 1. FIG. 1 shows a stator back-iron formed of a single material, for example PM (powder metal), or more commonly a stator back-iron composed of a number of identical laminations. The projections 100 from a circular support 150 (also called the back-iron or buckling) are called "teeth" and are used to receive the multiple coil windings. To improve motor performance, it is desirable to optimize the total cross-section of the coil windings, which reduces resistance and reduces heat generation. In addition, closer proximity of the coil windings improves thermal conductivity, which has the effect of improving continuous performance and increasing motor efficiency.

[0005] However, it will be appreciated that in an arrangement such as that shown in Figure 1, the entire stator is formed from a single solid piece, which limits the space available for physically winding the wire coils around the teeth. Summary of the Invention [Problem to be solved by the invention]

[0006] Thus, in such an arrangement, it is common for there to be gaps between the coils on adjacent teeth, which is inefficient because the space must be filled with wire coils, increasing the total cross-sectional area of ​​the coil windings.

[0007] Additionally, large one-piece stators typically require complex winding machines and complex winding processes to produce the necessary coil windings.

[0008] It is desirable to improve this situation. [Means for solving the problem]

[0009] According to one aspect of the present invention there is provided a bobbin, a stator, a rotor or a method according to the accompanying claims.

[0010] The present invention has the advantage that the coil windings can be wound individually on the bobbins before attachment to the stator back iron, thereby minimizing the space between the coils on adjacent stator teeth, while the teeth integrated into the bobbin reduce proximity losses that occur in the coil windings as they pass the magnets and torque ripple and cogging effects in electric motors. The use of teeth integrated into the bobbin also has the advantage of reducing the risk of demagnetization of the permanent magnets by shielding the magnets from the magnetic flux generated by the coil windings. [Brief description of the drawings]

[0011] The invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Figure 1] FIG. 1 shows a prior art example of a stator formed as a single piece with integral teeth. [Diagram 2] FIG. 2 is a diagram showing a stator according to one embodiment of the present invention. [Diagram 3] FIG. 3 is a perspective view of a bobbin according to one embodiment of the present invention. [Figure 4]FIG. 4 is a transparent perspective view of a bobbin according to one embodiment of the present invention. [Diagram 5] FIG. 5 is a diagram showing tooth tip dimensions according to one embodiment of the present invention. [Figure 6] FIG. 6 is a drive cycle consumption table. [Figure 7] FIG. 7 is a table showing the results of the cogging torque. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Although an embodiment of the invention is described herein in relation to the stator of an electric motor, it should be understood that the invention applies equally to rotor arrangements of electric motors in which the rotor carries coils. The invention also applies to generators. Although this embodiment describes an electric motor having a stator and a rotor, the stator and rotor having circumferential supports, the invention also applies equally to electric motors having stators and rotors of different configurations, for example linear electric motors.

[0013] The term rotor is therefore intended to cover the moving part of an electric motor regardless of the shape of that part, and is therefore intended to cover the forcer of a linear electric motor.

[0014] FIG. 2 illustrates a circumferential support 200 in accordance with a first embodiment of the present invention.

[0015] Distributed about the outer periphery of the circumferential support 200 , or stator back-iron, are a plurality of radially extending teeth 210 that extend outwardly from the outer surface of the stator back-iron 200 .

[0016] The stator back-iron 200, including the teeth 210, is formed as a unitary piece of unitary construction. For example, the stator back-iron 200 can be formed from powdered metal, but more commonly is constructed from a number of identical laminations. The laminations are typically manufactured from sheet steel, such as electric furnace steel, but any material with suitable strength and electromagnetic properties can be used. The laminations can also be coated with an insulating coating on the surfaces and along the curved interface shape between the tooth stack and the stator buckling (i.e., circumferential support 200) to prevent eddy currents from flowing between the laminations.

[0017] The laminate may be manufactured by any suitable means, such as stamping or cutting the desired shape from sheets of the required material, laser etching, etc. By way of example, the laminate has a thickness of 0.1-0.5 mm, preferably about 0.35 mm.

[0018] Each tooth 210 formed on the stator backiron 200 is arranged to receive a bobbin (described below), and each tooth 210 and respective bobbin includes engagement means for radially attaching the bobbin to the tooth 210, as described below.

[0019] For purposes of this embodiment, the preferred means for attaching the bobbin to the teeth includes cutouts 220 formed on the front and back sides of each stator tooth 210, each cutout positioned to receive an engaging element formed on the bobbin to retain the bobbin on the stator tooth, as described below, although any suitable means for attaching the bobbin to the stator tooth may be used.

[0020] 3 and 4 show a bobbin 300 according to an embodiment of the present invention for attachment to the stator backiron 200 shown in FIG. 2. FIG. 3 shows a perspective view of a bobbin according to an embodiment of the present invention, and FIG. 4 shows a perspective view of a bobbin according to an embodiment of the present invention, where like reference numbers in these figures relate to like features of the bobbin 300. Preferably, the bobbin 300 is manufactured using an injection molding process, and the bobbin 300 includes four walls 310 forming a housing having a rectangular parallelepiped shape with an opening formed in the center of the bobbin 300. The opening is sized to receive the stator teeth 210. The bobbin 300 is positioned to receive a coil winding (not shown) formed around the four walls 310. To aid in electrical insulation between the coil winding and the stator teeth 210, the bobbin 300 is formed from an insulating material. The insulating material is preferably a plastic, such as a liquid crystal polymer, having good thermal conductivity, high temperature flexibility, and good dielectric strength.

[0021] To aid in retaining the coil windings attached to the bobbin 300, the top of the bobbin forms a flange 320 extending away from each of the bobbin walls 310, as described below. When the bobbin 300 is attached to the stator teeth 210, the flange 320 forms a laterally extending stator tip for each of the stator teeth formed on the circumferential supports. Although in this embodiment the flange 320 is shown as being formed by the four walls 310 and extending all the way around, the flange 320 may include cutouts, for example, at the ends of the bobbin 300.

[0022] Each longitudinal flange portion has a metal strip 330 formed therein. The metal used is preferably electric furnace steel. For example, the metal strip 330 may be formed on the top surface of each flange portion 320, on the bottom surface of each flange portion 320, or within each flange portion 320. For purposes of this embodiment, the metal strip 330 is formed within each longitudinal flange portion 320 as shown in Figures 3 and 4.

[0023] To facilitate positioning of the metal strips within each longitudinal flange portion 320 during the injection molding process, the metal strips are held in place using a positioning tool (not shown), resulting in the formation of openings 330 in the upper surface of flange 320. To prevent the metal strips from bending or distorting due to the high flow pressures used, it is preferred that support be provided for each metal strip during the injection molding process. This may result in the formation of further openings (not shown) in the upper surface of flange 320.

[0024] As previously described, each stator tooth 210 includes at least one cutout 220 forming a recess in at least one side of the stator tooth 210 so that the bobbin 300 can be attached to the stator tooth 210. A spring-loaded engagement element 340 is formed on the front and / or rear of the bobbin housing. Although the present embodiment describes the use of two engagement elements 340 on each side of the bobbin housing, a single engagement element can also be used. The engagement element 340 is positioned to engage the cutout formed in the stator tooth 210, and the bobbin 300 and stator tooth 210 cooperate to prevent the bobbin 300 from disengaging from the stator tooth 210.

[0025] By varying the gap between the stator teeth 210 and the inner edge of the metal strip 330, the width of the metal strip 330, and the depth of the metal strip 330, different electric motor characteristics can be derived, with the dimensions of each metal strip being selected based on the desired electric motor characteristics, and FIG. 5 shows different dimensions of the metal strip 330 relative to the stator teeth 210.

[0026] For example, FIG. 6 shows examples of different drive cycle consumption values ​​for different metal strip gap, width and depth values, and FIG. 7 shows examples of different cogging torque results for different metal strip gap, width and depth values.

[0027] Preferably, in addition to the use of flanges 320, bobbin 300 includes additional features to aid in retaining the coil windings on the bobbin, for example, ridges 340 are formed at the corners of the housing to facilitate placement of the coil windings onto bobbin 300.

[0028] As also shown in Figures 3 and 4, the bobbin 300 preferably includes attachment points 350 for directing the coil windings attached to the bobbin to a power supply board (not shown), which is positioned to control the current to the coil windings.

[0029] As described above, because each bobbin 300 is separate from a stator tooth 210, a coil winding can be pre-wound on each bobbin 300 before the bobbin 300 is attached to the stator tooth 210, which has the advantage of making the coil winding on the bobbin 300 easier than if the coil winding were attached directly to the stator. For example, in conventional electric motor designs, the slot fill factor (the amount of copper wire that fills the slots between the stator teeth) is on the order of 37%. However, by allowing the coil winding to be applied to the stator teeth without the spatial constraints imposed when the stator is formed as a single piece with the teeth, the slot fill factor can be increased to approximately 54% or more.

[0030] To attach each bobbin 300 to a respective stator tooth 210, the bobbin 300 is pressed radially against a respective stator tooth 210 formed on the stator backiron 200. Sufficient radial force is applied to the stator tooth 300 to force the bobbin downward so that the engagement elements 340 engage the cutouts 220 formed in the stator tooth 210.

[0031] In other words, when the bobbin 300 is attached to the stator tooth 210 , the bobbin 300 is placed over the stator tooth 210 and is pressed radially against the stator tooth 210 .

[0032] Preferably, an adhesive is applied to one or more surfaces on the bobbin 300 and / or the stator teeth 210 that come into contact when the bobbin 300 is mounted on the stator teeth 210. For example, using either an impregnating varnish or a potting seal. Applying an adhesive to one or more surfaces of the bobbin 300 and / or the stator teeth 210 helps to minimize micro-movements of the bobbin 300 and local vibrations of the bobbin 300 relative to the stator teeth 210. To aid in thermal conduction between the bobbin 300 and the stator teeth 200, the adhesive is preferably selected to have good thermal conductivity. The adhesive also helps to electrically insulate the bobbin 300 from the stator teeth 210.

[0033] For purposes of this embodiment, the fully assembled stator includes 48 stator teeth, however, any number of teeth may be used, preferably between 6 and 100.

[0034] Although the invention is directed to an arrangement in which the rotor surrounds and rotates around the stator as shown in the drawings and substantially as described, it will be understood that it is within the scope of the invention for the stator to surround the rotor with the winding teeth projecting radially inward rather than radially outward toward the center of the stator.

[0035] Also, although the invention has been described in relation to a stator for an electric motor, the invention is equally applicable to elements of an electrical generator.

[0036] Stators embodying the invention can be of any size, with the preferred size depending on the desired size of the electric motor or generator. For example, for an 18 inch diameter electric motor, the stator outer diameter is on the order of 191 mm (i.e., the stator diameter is 382 mm). For a 20 inch diameter electric motor, the stator outer diameter is approximately 424 mm, and for a 14 inch diameter electric motor, the outer diameter is approximately 339 mm.

[0037] Stators constructed according to the above embodiments are particularly useful in electric motors for electric vehicles. In particular, embodiments of the present invention may be incorporated into road-running electric vehicles, and more particularly, electric vehicles having one or more in-wheel electric motors.

Claims

1. 1. A bobbin for a stator or rotor of an electric motor comprising an injection molded plastic housing having a first section and a second section, the first section arranged to receive a coil winding and including an opening allowing teeth attached to the stator or rotor to pass therethrough, the second section including a flange arranged to extend in a first direction substantially perpendicular to the opening and serving as tips of the teeth, and a metal element mounted within or on the flange.

2. 2. The bobbin of claim 1, wherein the metallic element is electrically insulated from the teeth.

3. 2. The bobbin of claim 1, wherein the metal elements are electrically coupled to the teeth.

4. 2. A bobbin according to any one of the preceding claims, wherein the opening is formed in a rectangular face of the first section.

5. 5. The bobbin of claim 4, wherein the flange is formed on a first side of the rectangular face of the first section and a second side of the rectangular face of the first section.

6. A bobbin according to any one of the preceding claims, wherein the injection moulded plastic housing includes a coupling means for holding the injection moulded plastic housing to the teeth.

7. 7. The bobbin of claim 6, dependent on claim 4 or 5, wherein the coupling means includes a first spring-loaded latch formed on a third side of the rectangular surface of the first section, the first spring-loaded latch being positioned to engage with a first coupling formation on the tooth.

8. 8. The bobbin of claim 7, wherein the coupling means includes a second spring-loaded latch formed on a fourth side of the rectangular face of the first section, the second spring-loaded latch being positioned to engage a second coupling feature on the tooth.

9. A stator comprising a circumferential support having a plurality of stator teeth, one or more of which is fitted with a bobbin according to any one of claims 1 to 8.

10. A rotor comprising a circumferential support having a plurality of rotor teeth, the bobbin according to any one of claims 1 to 8 being attached to one or more of said plurality of rotor teeth.

11. A method comprising the step of mounting a bobbin according to any one of claims 1 to 8 on a stator tooth formed on a circumferential support.

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