Stator for use in electric motor

Abstract

To solve a problem in a conventional technique.SOLUTION: A stator includes a stator core that has an annular portion and a plurality of teeth extending radially inward from the annular portion such that a slot is defined between each pair of adjacent teeth. Each of the teeth includes a pair of side surfaces that face in opposite directions. The stator core also includes a plurality of inner surfaces of the annular portion, each inner surface arranged between facing side surfaces of two adjacent teeth of the plurality of teeth. The stator also includes a plurality of thermally conductive, carbon fiber-based insulation strips. Each insulation strip is provided within one of the slots in order to cover the inner surface and the facing side surfaces of two adjacent teeth. The stator also includes a plurality of windings wound around the respective teeth.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] (Cross - Reference to Related Applications) This application claims priority to U.S. Provisional Patent Application No. 62 / 941,266, filed on November 27, 2019, the entire contents of which are incorporated herein by reference.

[0002] (Technical Field) The present invention relates to an electric motor, and more particularly to a stator for use in an electric motor.

Background Art

[0003] A brushless electric motor includes a stator that is typically fixed within a housing and a rotor that extends within the stator. During operation, current is induced through a plurality of windings of the stator to generate a rotating magnetic field, torque is applied to the rotor, and the rotor is rotated relative to the stator. Energy losses in the form of heat occur due to the electrical resistance of the windings, which may have an adverse effect on the long - term performance of the motor.

Summary of the Invention

Means for Solving the Problems

[0004] In one aspect, the present invention provides a stator including a stator core that includes an annular portion and a plurality of teeth extending radially inwardly from the annular portion such that slots are defined between each pair of adjacent teeth. Each tooth includes a pair of side surfaces facing in opposite directions. The stator core also includes a plurality of inner surfaces of the annular portion, each inner surface being disposed between the opposing side surfaces of two adjacent teeth of the plurality of teeth. The stator also includes a plurality of thermally conductive carbon - fiber - based insulating strips. Each insulating strip is disposed in one of the slots to cover the inner surface and the opposing side surfaces of two adjacent teeth. The stator further includes a plurality of windings wound around each tooth.

[0005] In another aspect, the present invention provides a stator including a stator coil including an annular portion and a first tooth extending radially inward from the annular portion. The first tooth includes a first side surface. The stator core further includes a second tooth extending radially inward from the annular portion. The second tooth includes a second side surface such that a slot is defined between the first tooth and the second tooth. The stator core also includes an inner surface disposed between the first side surface and the second side surface on the annular portion. The stator further includes a thermally conductive carbon fiber-based insulating strip for covering the inner surface, the first side surface, and the second side surface within the slot. The stator further includes a first winding wound around the first tooth and a second winding wound around the second tooth.

[0006] In yet another aspect, the present invention provides a stator including a stator core including an annular portion and a first tooth extending radially inward from the annular portion. The first tooth includes a first side surface, a first end surface, and a second end surface opposite the first end surface. The stator core also includes a second tooth extending radially inward from the annular portion. The second tooth includes a second side surface facing the first side surface of the first tooth, a third side surface facing in a direction opposite to the second side surface, a first end surface, and a second end surface opposite the first end surface. The stator core also includes a third tooth extending radially inward from the annular portion. The third tooth includes a fourth side surface facing the third side surface of the second tooth, a first end surface, and a second end surface opposite the first end surface. The stator core also includes a first inner surface disposed between the first side surface and the second side surface on the annular portion, and a second inner surface disposed between the third side surface and the fourth side surface on the annular portion. The stator further includes a first thermally conductive carbon fiber-based insulating strip covering the first side surface, the first inner surface, and the second side surface, a second thermally conductive carbon fiber-based insulating strip covering the third side surface, the second inner surface, and the fourth side surface, a first insulating end cap configured to cover the respective first end surfaces of the first tooth, the second tooth, and the third tooth, a second insulating end cap configured to cover the respective second end surfaces of the first tooth, the second tooth, and the third tooth, and a winding wound around the second tooth. The winding contacts the first insulating strip, the first insulating end cap, the second insulating strip, and the second insulating end cap such that the winding does not contact the second side surface, the first end surface of the second tooth, the third side surface, or the second end surface of the second tooth.

[0007] Other features and aspects of the present invention will become apparent by considering the following detailed description and the accompanying drawings.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Mode for Carrying Out the Invention

[0009] Before any embodiment of the present invention is described in detail, it should be understood that the present invention is not limited to the details of the configurations described in the following description or illustrated in the following drawings, nor to the use of the arrangements of the components. The present invention is capable of other embodiments and can be practiced or carried out in various ways. Also, it should be understood that the terminology and technical terms used herein are for the purpose of description and should not be regarded as limiting.

[0010] FIG. 1 schematically shows, for example, a brushless direct current (DC) electric motor 10 for use in a power tool. The motor 10 includes a stator 14 and a rotor 18. During operation, current is induced through a plurality of windings of the stator 14 to generate a rotating magnetic field, torque is applied to the rotor 18, and the rotor 18 is rotated relative to the stator 14.

[0011] As shown in FIGS. 2 and 3, the stator 14 includes a stator core 24 having an annular portion 26 and a plurality of teeth 30 extending radially inward from the annular portion 26 such that slots 34 are defined between each pair of adjacent teeth 30. As shown in FIG. 3, the annular portion 26 has a first end face 38 and an opposite second end face 42. Each tooth 30 has a pair of side faces 46 facing in opposite directions, a first end face 50, and an opposite second end face 54. The annular portion 26 also includes a plurality of inner surfaces 58, each inner surface 58 being disposed between the opposing side faces 46 of two adjacent teeth 30. Thus, each slot 34 is defined by a space bounded by the inner surface 58 of the annular portion 26 and the side faces 46 of two adjacent teeth 30.

[0012] Referring to FIGS. 4 and 5, in the formation of the stator 14, a plurality of flexible thermally conductive carbon fiber-based insulating strips 62 are disposed within each slot 34 of the stator core 24. Specifically, each insulating strip 62 covers the opposing side faces 46 of two adjacent teeth 30 and the inner surface 58 extending between the opposing side faces 46 such that each insulating strip 62 is disposed between a pair of adjacent teeth 30.

[0013] In some embodiments, such as the embodiment shown in FIG. 8, the insulating strip 62 includes an adhesive material 63 or an adhesive layer for adhering each insulating strip 62 to the inner surface 58 and the opposing side faces 46 of two adjacent teeth 30. In some embodiments, such as the embodiment shown in FIG. 9, each insulating strip 62 is formed of a single material layer 64. In other embodiments, such as the embodiment shown in FIG. 10, each insulating strip 62 is formed of two material layers, a first thermally conductive layer 65 and a second electrically insulating layer 67. In some embodiments, due to the presence of carbon fibers, the color of the insulating strip 62 is black. The insulating strip 62 can be formed of different materials. Three such materials and their respective properties are shown in Table 1 below.

[0014]

Table 1

[0015] For each of Materials 1 to 3, the thermal impedance and compressibility at various pressures (measured in PSI) were measured. The results are shown in Table 2 below.

[0016]

Table 2

[0017] Regarding Material 3, as shown in Table 3 below, the thermal impedance and compressibility in various cycles were measured.

[0018]

Table 3

[0019] Each of Materials 1 to 3 is commercially available from KULR Technology Group, Inc. in San Diego, California.

[0020] Referring to FIGS. 2, 4, and 5, the first insulating end cap 66 is formed of an electrical insulating material (e.g., plastic) and is configured to cover the first end of the stator core 24, more specifically, the first end face 38 of the annular portion 26 and each of the first end faces 50 of the teeth 30. As shown in FIGS. 2 and 4, the second insulating end cap 70 is formed of an electrical insulating material (e.g., plastic) and is configured to cover the second end on the opposite side of the stator core 24, more specifically, the second end face 42 of the annular portion 26 and each of the second end faces 54 of the teeth 30. In the illustrated embodiment, the first and second end caps 66, 70 each include a plurality of pairs of bookends 74 corresponding to the positions of the teeth 30. In some embodiments, there is no gap between either the first or second end cap 66, 70 and the insulating strip 62 such that there is no exposed portion of the stator core 24 except for the inner surface 78 of each tooth 30 and the outer surface 82 of the annular portion 26.

[0021] Referring to FIG. 2, after the insulating strip 62 and the first and second end caps 66, 70 are assembled to the stator core 24, the winding 22 is wound around each tooth 30, thereby at least partially closing each slot 34. Thus, each winding 22 is wound around the first insulating strip 62 on one side surface 46 of the tooth 30, the first end cap 66 (between the bookends 74), the second insulating strip 62 on the other side surface 46 of the tooth 30, and the second end cap 70 (between the bookends 74). Since the teeth 30 are collectively insulated by the insulating strip 62 around which each winding 22 is wound and the end caps 66, 70, the winding 22 is electrically insulated from the stator core 24.

[0022] During operation, when current is supplied to the winding 22 of the stator 14, heat is generated due to the electrical losses resulting from the resistance, and this heat is transmitted through the insulating strip 62 to the stator core 24 via the opposing side surfaces 46 of the adjacent teeth 30 and the inner surface 58 of the annular portion 26. By transferring heat from the winding 22 to the stator core 24, the stator core 24 functions as a heat sink that can extract heat from other parts of the motor 10 (such as on-board electronics, etc.), thereby improving the long-term performance and lifespan of the motor 10. For example, FIG. 6 shows a graph of the temperature of the stator core (formed of steel in this test) and the winding over a 60-second period when 25 amperes of current is supplied to the winding, using paper or cardboard instead of the thermally conductive carbon fiber-based insulating strip 62 as the electrical insulator for the slot 34.

[0023] In comparison, FIG. 7 shows a graph of the temperature of the stator core 24 (formed of steel in this test) and the winding 22 over a 60-second period when 25 amperes of current is supplied to the winding 22, using a thermally conductive carbon fiber-based insulating strip 62 as the electrical insulator for the slot 34 as shown in the embodiments shown in FIGS. 2 - 5. In the graph shown in FIG. 7, the insulating strip 62 has a multi-layer structure including a polymer (i.e., polyimide) layer as the electrical insulator.

[0024] By using a thermally conductive carbon fiber-based insulating strip 62 instead of paper or cardboard, after 60 seconds of operation, the temperature of the stator core 24 increases slightly from about 30 °C (paper or cardboard) to 40 °C (thermally conductive carbon fiber-based insulating strip 62). This is because the insulating strip 62 conducts more heat from the winding 22 to the stator core 24. However, by using a thermally conductive carbon fiber-based insulating strip 62 instead of paper or cardboard, after 60 seconds of operation, the temperature of the winding 22 drops by nearly 50% from about 137 °C (paper or cardboard) to 70 °C (thermally conductive carbon fiber-based insulating strip 62). When the thermally conductive carbon fiber-based insulating strip 62 is used, the heat from the winding 22 is efficiently dissipated to the stator core 24, so that the overall temperature of the stator 14 decreases, and the long-term performance and lifespan of the motor 10 can be improved. In addition, by improving the dissipation of heat from the winding 22, the motor 10 may be able to operate at a relatively high power level for a longer period of time. Alternatively, the motor 10 may be able to operate at an intermediate or relatively low power level while reducing (or completely eliminating) the ratio of the cooling air flow to the stator 14.

[0025] The various features of the present invention are defined in the following claims.

Claims

【Claim 1】 an annular portion, a plurality of teeth extending radially inwardly from the annular portion such that slots are defined between each pair of adjacent teeth, each of the teeth including a pair of opposed sides facing in opposite directions; a plurality of inner surfaces of the annular portion, each inner surface being disposed between the opposing sides of two adjacent teeth; and a stator core, a plurality of thermally conductive carbon fiber-based insulating strips, each insulating strip being disposed in one of the slots for covering the inner surface and the opposing sides of the two adjacent teeth; and a plurality of windings wound around each of the teeth, a stator.

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