Motor

Abstract

This motor includes a rotor having a rotary shaft extending in an axial direction, a stator that generates a magnetic force acting on the rotor, a bearing that rotatably supports the rotary shaft, a conductive bracket that holds the bearing, a circuit board disposed facing the bracket, a circuit element mounted on the circuit board, and an insulative heat dissipation member disposed between the bracket and the circuit board. The circuit board has a first surface that is a surface on the bracket side and a second surface that is a surface opposite to the first surface. The circuit element includes a heat generating component mounted on the second surface of the circuit board, and the heat dissipation member is disposed at a position overlapping the heat generating component when viewed from the axial direction.

Description

Motor

[0001] The present disclosure relates to a motor.

[0002] Motors are used in various electric devices such as household appliances or industrial equipment. As motors, a commutator motor using brushes and a brushless motor not using brushes are known.

[0003] A brushless motor includes, for example, a stator having a stator core and windings wound around the stator core, a rotor having a rotor core with a rotating shaft fixed thereto and magnets fixed to the rotor core, and bearings for supporting the rotating shaft.

[0004] A brushless motor is driven, for example, by an inverter of a pulse width modulation (PWM) method. When a brushless motor is driven by an inverter of the PWM method, a common mode voltage is generated due to the switching of the inverter, and the neutral point potential of the windings in the stator does not become zero. As a result, a potential difference (hereinafter referred to as "shaft voltage") occurs between the potential of the outer ring and the potential of the inner ring in the bearing. When this shaft voltage reaches the breakdown voltage of the oil film of the lubricating oil injected into the bearing, a microcurrent due to discharge flows inside the bearing and electrical erosion occurs in the bearing. Thus, when a brushless motor is driven by the PWM method, electrical erosion occurs. As the electrical erosion progresses, a wavy wear phenomenon occurs on the inner ring of the bearing, the outer ring of the bearing, or the bearing balls, and abnormal noise occurs. Note that electrical erosion is also referred to as electrocorrosion, electrical corrosion, etc.

[0005] Therefore, conventionally, in order to suppress the occurrence of electrical erosion, a brush motor has been proposed in which a dielectric layer is provided on a rotating body to increase the impedance on the rotating shaft side, the impedance on the rotor side is made close to the impedance on the stator side, and the shaft voltage generated between the inner ring and the outer ring of the bearing is reduced (see Patent Document 1).

[0006] In addition, a technique for suppressing electrical erosion by adjusting the capacitance has also been proposed (see Patent Document 2).

[0007] As proposed in Patent Document 1, increasing the gaps between components or increasing the number of gaps to increase the impedance on the rotor side reduces the strength of the rotor. On the other hand, if you try to ensure the strength of the rotor, the parasitic capacitance on the rotor side increases, which increases the shaft voltage and causes electrolytic corrosion. Moreover, if the brushless motor is made into a molded motor in which the stator is covered with insulating molded resin, the parasitic capacitance on the stator side increases, making it easier for shaft voltage to occur.

[0008] In brushless motors controlled by the PWM method, heat is generated from the switching elements in the inverter. Therefore, when attempting to increase the output of a brushless motor, the amount of heat generated from the switching elements increases, making it difficult to increase the output of the brushless motor.

[0009] The technology proposed in Patent Document 2 reduces the shaft voltage by providing a means to adjust the capacitance between two metal brackets that hold the bearing. However, the capacitance changes significantly due to variations in the characteristics of the molded resin and the shape of the brackets, making the design difficult.

[0010] International Publication No. 2009 / 113311, Japanese Patent No. 6937423

[0011] This disclosure was made to solve these problems. The purpose of this disclosure is to provide a motor that can suppress the occurrence of electrolytic corrosion and easily achieve high output.

[0012] To achieve the above objective, one embodiment of the motor according to the present disclosure comprises a rotor having a rotating shaft extending in the axial direction, a stator that generates a magnetic force acting on the rotor, a bearing that rotatably supports the rotating shaft, a conductive bracket that holds the bearing, a circuit board disposed opposite to the bracket, circuit elements mounted on the circuit board, and an insulating heat dissipation member disposed between the bracket and the circuit board, wherein the circuit board has a first surface which is the surface on the bracket side and a second surface which is the surface opposite to the first surface, the circuit elements include a heat-generating component mounted on the second surface of the circuit board, and the heat dissipation member is positioned to overlap with the heat-generating component when viewed from the axial direction.

[0013] Preferably, a first metal wiring is formed on the first surface of the circuit board, a second metal wiring is formed on the second surface of the circuit board, the first metal wiring includes a first heat spreader having a larger area than the heat-generating component, the second metal wiring includes a second heat spreader having a larger area than the heat-generating component, the heat dissipation member is placed on the first heat spreader, and the heat-generating component is placed on the second heat spreader and electrically connected to the second heat spreader.

[0014] The first heat spreader and the second heat spreader are connected by a plurality of via holes that penetrate the circuit board, and it is preferable that the plurality of via holes are located in positions that overlap with the heat-generating components when viewed from the axial direction.

[0015] The heating component preferably comprises a resin package and an electrode formed on the back surface of the resin package, wherein the electrode is in surface contact with the second heat spreader.

[0016] Preferably, the motor further includes an insulating sheet positioned between the heat dissipation member and the bracket, wherein the heat dissipation member is in contact with the bracket through an opening formed in the insulating sheet.

[0017] The circuit element is one of a plurality of circuit elements, and the plurality of circuit elements constitute an inverter circuit that generates a high-frequency switching voltage from a DC voltage, and it is preferable that the inverter circuit includes a switching element as the heat-generating component.

[0018] Preferably, the switching element is one of a plurality of switching elements, and the heat dissipation member covers the plurality of switching elements.

[0019] The difference between the potential of the inner ring and the potential of the outer ring in the bearing is preferably 10V or less.

[0020] Preferably, at least a portion of the stator is covered with molded resin, and the molded resin constitutes the outer shell of the motor.

[0021] According to this disclosure, it is possible to suppress the occurrence of electrolytic corrosion and to easily achieve higher output motors.

[0022] Figure 1 is an external perspective view of the motor according to the embodiment. Figure 2 is an exploded perspective view of the motor according to the embodiment. Figure 3 is a cross-sectional view of the motor according to the embodiment when cut by a plane perpendicular to the rotation axis. Figure 4 is a cross-sectional view of the motor according to the embodiment when cut by a plane passing through the axis of the magnet and the rotation axis. Figure 5 is an enlarged cross-sectional view of region V shown by the dashed line in Figure 4. Figure 6 is a cross-sectional perspective view of the motor according to the embodiment with the first bracket and insulating sheet removed. Figure 7 is a plan view of the circuit board in the motor according to the embodiment as seen from the first side (first bracket side). Figure 8 is a plan view of the circuit board in the motor according to the embodiment as seen from the second side. Figure 9 is a plan view showing the state in Figure 8 with the switching element mounted on the circuit board. Figure 10A is a diagram showing the equivalent circuit of parasitic capacitance related to the generation of the shaft voltage of the first bearing in the motor according to the embodiment. Figure 10B is a block diagram of the electrical circuit explaining the state in which power is supplied to the motor via the switching element in the motor according to the embodiment. Figure 11 shows a circuit board on which a surface-mount IPM package is mounted as a circuit element, which is a heat-generating component. Figure 12A shows the surface-mount IPM package shown in Figure 11 covered with a heat dissipation member. Figure 12B shows the heat dissipation member covering the surface-mount IPM package shown in Figure 11 shifted in one direction from the position shown in Figure 12A. Figure 12C shows the heat dissipation member covering the surface-mount IPM package shown in Figure 11 shifted in the opposite direction from the position shown in Figure 12A. Figure 13A is a plan view showing an example of an insulating sheet. Figure 13B is a plan view showing a modified example of the insulating sheet. Figure 14 is an enlarged cross-sectional view of a motor according to modified example 1. Figure 15 is an enlarged cross-sectional view of a motor according to modified example 2.

[0023] The embodiments of this disclosure will be described below with reference to the drawings. The embodiments described below are all specific examples of this disclosure. Therefore, the numerical values, shapes, materials, components, arrangement positions of components, and connection configurations shown in the following embodiments are examples and are not intended to limit this disclosure. Accordingly, among the components in the following embodiments, those components that are not described in the independent claims representing the highest-level concepts of this disclosure will be described as optional components.

[0024] Each figure is a schematic diagram and not necessarily a strictly accurate representation. Therefore, the scale and other aspects may not necessarily be consistent across all figures. In all figures, substantially identical components are given the same reference numerals, and redundant explanations are omitted or simplified.

[0025] In this specification, the terms "up" and "down" do not necessarily refer to the absolute spatial directions of upward (vertically upward) and downward (vertically downward). In this embodiment, for convenience, the direction in which the axis C of the rotating shaft 21 extends is defined as the up and down direction. However, this up and down direction may differ from the actual up and down direction depending on the operating conditions of the motor 1. In this embodiment, the radial direction of the stator 10 and rotor 20 is defined as the "radial direction," and the rotational direction of the rotor 20 is defined as the "circumferential direction." That is, the direction perpendicular to the axis C of the rotating shaft 21 that the rotor 20 has as its center is the "radial direction." The direction around the axis C of the rotating shaft 21 is the "circumferential direction." The direction in which the axis C of the rotating shaft 21 extends (the longitudinal direction of the rotating shaft 21) is the "axial direction."

[0026] (Embodiment) The configuration of the motor 1 according to the embodiment will be described using Figures 1 to 6. Figures 1 to 6 are diagrams showing the configuration of the motor 1 according to the embodiment. Figure 1 is an external perspective view of the motor 1 according to the embodiment. Figure 2 is an exploded perspective view of the motor 1 according to the embodiment. Figure 3 is a cross-sectional view of the motor 1 according to the embodiment when cut by a plane perpendicular to the rotation axis 21. Figure 4 is a cross-sectional view of the motor 1 according to the embodiment when cut by a plane passing through the axis C of the magnet 23 and the rotation axis 21. Figure 5 is an enlarged cross-sectional view of the region V shown by the dashed line in Figure 4. Figure 6 is a cross-sectional perspective view of the motor 1 according to the embodiment when the first bracket 41 and the insulating sheet 80 are removed.

[0027] As shown in Figures 2 to 4, the motor 1 comprises a stator 10 and a rotor 20 positioned opposite the stator 10. As shown in Figure 4, the motor 1 further comprises a first bearing 31 and a second bearing 32, a first bracket 41 and a second bracket 42, a circuit board 50, a plurality of circuit elements 60, a heat dissipation member 70, and an insulating sheet 80.

[0028] As shown in Figures 1 and 4, motor 1 is a molded motor in which the stator 10 is covered with molded resin 90. Motor 1 is a brushless motor that does not use brushes.

[0029] Motor 1 is used, for example, in air conditioning equipment such as air conditioners. For example, motor 1 is mounted in the outdoor unit of an air conditioner as a fan motor in which a rotating fan is attached to the rotating shaft 21 of a rotor 20.

[0030] As shown in Figure 4, the stator 10 is positioned opposite the rotor 20 with a small air gap between them. The stator 10 is positioned to surround the rotor core 22 of the rotor 20. In other words, the motor 1 is an inner rotor type motor in which the rotor 20 is positioned inside the stator 10.

[0031] The stator 10 generates a magnetic force that acts on the rotor 20. Specifically, the stator 10 is configured to generate alternating north and south poles in the circumferential direction on the air gap surface between the rotor 20 and the rotor core 22. The stator 10, together with the rotor 20, constitutes a magnetic circuit. The stator 10 has a stator core 11 and windings 12.

[0032] The stator core 11 of the stator 10 generates a magnetic force to rotate the rotor 20. The stator core 11 is, for example, a laminate in which multiple steel plates are stacked in the direction in which the axis C of the rotating shaft 21 extends. Each of the multiple steel plates is a magnetic material. The multiple steel plates are, for example, punched electrical steel sheets formed into a predetermined shape. The stator core 11 is not limited to a laminate of multiple steel plates, but may also be a bulk body made of magnetic material.

[0033] The stator core 11 has a plurality of teeth that protrude toward the rotor 20. The plurality of teeth are arranged to protrude toward the axis C of the rotation shaft 21. The plurality of teeth are arranged at equal intervals in the circumferential direction, with slots forming between any two adjacent teeth. The plurality of teeth extend radially in a direction perpendicular to the axis C of the rotation shaft 21 (radial direction).

[0034] The winding 12 is the armature winding of the stator 10. The winding 12 is a winding coil wound around the stator core 11 as a stator coil. The winding 12 is wound around each of the multiple teeth via the insulator 13. In other words, multiple windings 12 are wound around the stator 10. In this embodiment, each winding 12 is a concentrated winding coil wound around each tooth. Each winding 12 is housed in a slot in the stator core 11.

[0035] When the windings 12 are energized, a magnetic field is generated from each of the multiple teeth of the stator core 11. The multiple windings 12 are provided as three-phase windings to drive a three-phase synchronous motor. In other words, the motor 1 is an embedded magnet synchronous motor (IPMSM; Interior Permanent Magnet Synchronous Motor). In this case, the multiple windings 12 are composed of unit coils for the U-phase, V-phase, and W-phase, each of which is electrically 120 degrees out of phase with respect to the others. That is, the windings 12 attached to each tooth are energized and driven by three-phase alternating current, which is energized for each of the U-phase, V-phase, and W-phase. This generates the main magnetic flux of the stator 10 in each tooth.

[0036] The stator 10 is a molded stator covered with molded resin 90. For example, the stator 10 covered with molded resin 90 can be formed by injection molding. The molded resin 90 is a stator mold that covers at least a part of the stator 10. In this embodiment, the molded resin 90 covers the outer portion of the stator 10 around its entire circumference in the circumferential direction. Specifically, the molded resin 90 covers the outer portions of the stator core 11 and the windings 12. The molded resin 90 constitutes a housing that encloses the rotor 20. Specifically, the molded resin 90 is formed in a bottomed cylindrical shape. As shown in Figure 1, the molded resin 90 constitutes the outer shell of the motor 1.

[0037] The molded resin 90 has four protrusions that project radially outward. The four protrusions are legs with through holes. The four protrusions function as mounting parts for attaching the motor 1 to the object to be installed. The molded resin 90 is made of an insulating resin material with excellent thermal conductivity, such as polyester resin or epoxy resin. The molded resin 90 is made of a thermosetting resin. In this embodiment, the molded resin 90 is made of unsaturated polyester (BMC; Bulk Molding Compound), which is a thermosetting resin. Specifically, the molded resin 90 is made of white BMC.

[0038] The rotor 20 rotates due to the magnetic force generated in the stator 10. Specifically, the rotor 20 has a rotation axis 21. The rotor 20 rotates around the axis C of the rotation axis 21 as the center of rotation.

[0039] The rotor 20 generates a magnetic force that acts on the stator 10. The rotor 20 has a configuration in which multiple N poles and S poles, which constitute the main magnetic flux, are repeated along the circumferential direction. The direction of the main magnetic flux generated by the rotor 20 is perpendicular to the direction in which the axis C of the rotation shaft 21 extends (radial direction).

[0040] As shown in Figures 3 and 4, the rotor 20 is positioned with respect to the stator 10 via an air gap. The rotor 20 comprises a rotor core 22 through which the rotating shaft 21 is inserted, and a plurality of magnets 23 held in the rotor core 22. The rotor 20 is an IPM (Internal Permanent Magnet) rotor in which the magnets 23 are embedded in the rotor core 22. Therefore, the motor 1 is a permanent magnet embedded IPM motor.

[0041] The rotating shaft 21 has an axis C that is the center when the rotor 20 rotates. The rotating shaft 21 extends in the direction in which the axis C extends. The rotating shaft 21 is a long shaft. The rotating shaft 21 is conductive. The rotating shaft 21 is a metal rod made of a metal material such as SUS (Steel Use Stainless). The rotating shaft 21 is fixed to the rotor core 22. Specifically, the rotating shaft 21 penetrates the rotor core 22. The rotating shaft 21 is fixed to the rotor core 22 such that it extends on both sides of the rotor core 22 in the direction in which the axis C extends.

[0042] The rotating shaft 21 has a first end 21a, which is one end in the direction in which the rotating shaft 21 extends, and a second end 21b, which is the other end in the direction in which the rotating shaft 21 extends. The second end 21b is the end opposite to the first end 21a.

[0043] The second end portion 21b of the rotating shaft 21 protrudes outside from the through hole of the second bracket 42. The second end portion 21b of the rotating shaft 21 protruding from the second bracket 42 serves as an output shaft. A load such as a rotating fan is attached to the second end portion 21b.

[0044] The first end portion 21a of the rotating shaft 21 does not protrude outside from the first bracket 41. However, the first end portion 21a may protrude outside from the first bracket 41. That is, both end portions of the rotating shaft 21 may protrude from the first bracket 41 and the second bracket 42, respectively.

[0045] The rotating shaft 21 is supported by the first bearing 31 and the second bearing 32. The first bearing 31 and the second bearing 32, as a pair of bearings, support the rotating shaft 21 rotatably. The first bearing 31 supports the first end portion 21a of the rotating shaft 21. The second bearing 32 supports a portion on the second end portion 21b side of the rotating shaft 21. Thus, the rotating shaft 21 is held by the first bearing 31 and the second bearing 32 in a rotatable state.

[0046] The second end portion 21b of the rotating shaft 21 penetrates through the second bearing 32. The second end portion 21b protrudes from the second bearing 32. In the present embodiment, the first end portion 21a of the rotating shaft 21 does not protrude from the first bearing 31. However, the first end portion 21a may penetrate through the first bearing 31 and protrude from the first bearing 31.

[0047] The first bearing 31 and the second bearing 32 are bearings having an inner ring and an outer ring. As an example, the first bearing 31 and the second bearing 32 are ball bearings. A ball bearing has an outer ring, an inner ring, a plurality of bearing balls (steel balls) held between the outer ring and the inner ring, and a pair of seal plates closing a gap between the outer ring and the inner ring. Inside the ball bearing, oil or grease is provided as an insulating lubricant. The first bearing 31 and the second bearing 32 are not limited to ball bearings. The first bearing 31 and the second bearing 32 may be other bearings such as roller bearings.

[0048] As shown in FIGS. 3 and 4, the rotor core 22 is arranged via an air gap with the stator core 11 of the stator 10. As shown in FIG. 3, the rotor core 22 has an inner core 22a and an outer core 22b located radially outside the inner core 22a. Specifically, the outer core 22b surrounds the inner core 22a.

[0049] The inner core 22a is attached to the rotating shaft 21. The rotating shaft 21 is fixed to the inner core 22a in a state of passing through a through hole formed in the inner core 22a. Specifically, the rotating shaft 21 is fixed to the inner core 22a by press-fitting or shrink-fitting into the through hole of the inner core 22a. The inner core 22a is a cylindrical member as a whole.

[0050] The outer core 22b holds a plurality of magnets 23. The outer core 22b is composed of a plurality of cores (divided cores) arranged in the circumferential direction. In this case, the magnet 23 is arranged between two adjacent cores. The outer core 22b may be composed of one integrated core instead of being divided into a plurality. In this case, a plurality of magnet insertion holes into which the magnet 23 is inserted are formed in the outer core 22b.

[0051] Each of the inner core 22a and the outer core 22b is a laminate in which a plurality of steel plates, which are magnetic materials, are laminated in the direction in which the axis C of the rotating shaft 21 extends. Each of the plurality of steel plates in each of the inner core 22a and the outer core 22b is, for example, a punched electromagnetic steel plate formed in a predetermined shape. In each of the inner core 22a and the outer core 22b, the plurality of steel plates are fixed to each other by, for example, caulking or welding. The inner core 22a and the outer core 22b are fixed to each other by interposing a resin 24 between the inner core 22a and the outer core 22b.

[0052] As shown in FIG. 3, the plurality of magnets 23 are arranged around the rotating shaft 21. The plurality of magnets 23 are arranged radially around the rotating shaft 21. That is, the motor 1 is a spoke-type IPM motor having a rotor 20 in which the plurality of magnets 23 are arranged in a spoke shape (radially).

[0053] Multiple magnets 23 are arranged at equal intervals around the rotation axis 21 in the circumferential direction. The multiple magnets 23 are arranged so that the magnetic pole surfaces of adjacent magnets 23 face each other. In other words, for two adjacent magnets 23, either the magnetic pole surface of the south pole of one magnet 23 faces the magnetic pole surface of the south pole of the other magnet 23, or the magnetic pole surface of the north pole of one magnet 23 faces the magnetic pole surface of the north pole of the other magnet 23.

[0054] Each of the multiple magnets 23 is a magnetized permanent magnet. Each magnet 23 is plate-shaped. Each magnet 23 is essentially a rectangular parallelepiped in plate shape. Each magnet 23 has a rectangular shape in plan view. Each magnet 23 is arranged such that its longitudinal direction is the radial direction of the rotor core 22 in plan view.

[0055] Magnet 23 is, for example, a ferrite magnet made of a sintered ferrite magnet. However, magnet 23 is not limited to ferrite magnets. For example, magnet 23 may be a rare earth magnet. In this case, a neodymium rare earth magnet mainly composed of neodymium-iron-boron (Nd-Fe-B) can be used as magnet 23.

[0056] Multiple magnets 23 are fixed to the rotor core 22 by resin 24 (molding resin) formed by injection molding. In other words, the rotor core 22 and the multiple magnets 23 are fixed together by the resin 24. Since the rotor core 22 is composed of an inner core 22a and an outer core 22b, the inner core 22a, the outer core 22b, and the multiple magnets 23 are fixed together by the resin 24. The resin 24 is a rotor mold that forms part of the rotor 20.

[0057] As shown in Figures 3 and 4, the resin 24 is also present between the inner core 22a and the outer core 22b. This fixes the inner core 22a and the outer core 22b together with the resin 24. In this embodiment, the shape of the resin 24 in the portion located between the inner core 22a and the outer core 22b is substantially cylindrical. That is, the resin 24 has a cylindrical portion located between the inner core 22a and the outer core 22b.

[0058] The resin 24 is made of an insulating resin material with excellent thermal conductivity, such as polyester resin or epoxy resin. Alternatively, the resin 24 may be made of a thermosetting resin. In this embodiment, the resin 24 is made of black BMC. The resin 24 may also be made of polybutylene terephthalate (PBT) instead of BMC.

[0059] As shown in Figure 4, the first bracket 41 holds the first bearing 31. The first bearing 31 is fixed to the first bracket 41. Specifically, the first bearing 31 is fitted into a recess formed in the first bracket 41.

[0060] The second bracket 42 holds the second bearing 32. The second bearing 32 is fixed to the second bracket 42. Specifically, the second bearing 32 is fitted into a recess formed in the second bracket 42. The second bracket 42 is fixed to the molded resin 90 by injection molding.

[0061] The first bracket 41 and the second bracket 42 are conductive members having electrical conductivity. Specifically, the first bracket 41 and the second bracket 42 are metal members made of a metal material such as an iron-based material. Specifically, the first bracket 41 and the second bracket 42 are made of a metal plate of a constant thickness. The first bracket 41 and the second bracket 42 are formed into a predetermined shape by press working on the metal plate. In this embodiment, the first bracket 41 and the second bracket 42 are made of steel plate.

[0062] The first bracket 41 and the second bracket 42 are fixed to the molded resin 90. Specifically, the second bracket 42 is fixed to the molded resin 90 together with the stator 10 when the stator 10 is molded. On the other hand, the first bracket 41 is fixed to the molded resin 90 after its molding so as to cover the opening in the molded resin 90. The first bracket 41 and the second bracket 42 together with the molded resin 90 constitute the outer shell of the motor 1.

[0063] As shown in Figure 4, the circuit board 50 is housed in the molded resin 90. The circuit board 50 is fixed to the molded resin 90. The circuit board 50 is positioned opposite the first bracket 41. The circuit board 50 and the first bracket 41 are positioned with a predetermined distance between them.

[0064] The circuit board 50 is a mounting board on which a plurality of circuit elements 60 are mounted. Specifically, the circuit board 50 is a printed circuit board on which metal wiring is formed in a predetermined pattern. In this embodiment, the circuit board 50 is a double-sided circuit board on which metal wiring is formed on both sides. The metal wiring formed on the circuit board 50 is, for example, copper wiring made of copper foil. The thickness of the metal wiring is, for example, 35 μm. However, it is not limited to this.

[0065] The substrate constituting the circuit board 50 is, for example, a resin substrate made of an insulating resin material. In this case, as the resin substrate, a glass epoxy substrate made of glass fiber and epoxy resin (CEM-3 (Composite Epoxy Material-3), FR-4 (Flame Retardant 4), etc.), a paper phenol substrate made of kraft paper or the like and phenol resin (FR-1 (Flame Retardant 1), FR-2 (Flame Retardant 2)), a paper epoxy substrate made of paper and epoxy resin (FR-3 (Flame Retardant 3)), or a polyimide substrate made of polyimide or the like can be used. In this embodiment, CEM-3 with a thickness of 1.2 mm was used as the substrate constituting the circuit board 50.

[0066] As shown in Figure 4, the circuit board 50 has an opening in the center through which the rotating shaft 21 passes. Here, the details of the circuit board 50 will be explained with reference to Figures 4 to 6 and using Figures 7 to 9. Figure 7 is a plan view of the circuit board 50 in the motor 1 according to the embodiment, as seen from the first surface 50a side (first bracket 41 side). Figure 8 is a plan view of the circuit board 50 in the motor 1 according to the embodiment, as seen from the second surface 50b side. Figure 9 is a plan view showing the state in Figure 8 where the switching element 61 is mounted on the circuit board 50. In Figures 7 to 9, the dashed lines indicate the heat dissipation member 70.

[0067] As shown in Figures 7 to 9, the plan view shape of the circuit board 50 is substantially annular. In this embodiment, a portion of the outer periphery of the substantially annular circuit board 50 is cut off. The plan view shape of the circuit board 50 may not be substantially annular, but may be other annular shapes such as a rectangular annular shape, or it may be a fan shape (arc shape), or a C shape, etc.

[0068] As shown in Figures 4 to 6, the circuit board 50 has a first surface 50a, which is the side facing the first bracket 41, and a second surface 50b, which is the side opposite to the first surface 50a. The second surface 50b is the side facing the stator core 11.

[0069] As shown in Figures 4 to 7, a first metal wiring 51 is formed on the first surface 50a of the circuit board 50 as a metal wiring. As shown in Figures 4 to 6 and Figure 8, a second metal wiring 52 is formed on the second surface 50b of the circuit board 50 as a metal wiring.

[0070] Although not shown in the diagram, the ends of the windings 12 for each of the U, V, and W phases in the stator 10 are electrically connected to metal wiring formed on the circuit board 50. The metal wiring formed on the circuit board 50 is formed in a predetermined pattern corresponding to each of the U, V, and W phases in order to electrically connect to multiple windings 12 for each phase. For example, the ends of the three-phase windings 12 are each connected to three metal terminals provided on the insulator 13 of the stator 10. The metal wiring on the circuit board 50 has three winding connection sections corresponding to each of the U, V, and W phases. The three metal terminals of the stator 10 and the three winding connection sections of the circuit board 50 are connected one-to-one by lead wires or the like, thereby electrically connecting the windings 12 of each phase to the metal wiring on the circuit board 50. The ends of the windings 12 of each phase may also be directly connected to the metal wiring on the circuit board 50.

[0071] As shown in Figures 4 to 6, multiple circuit elements 60 are mounted on the circuit board 50. These multiple circuit elements 60 are electronic components such as transistor elements (FET (Field Effect Transistor) or IC (Integrated Circuit) packages), resistors, capacitors, diodes, or coils. Among these circuit elements 60, the self-heating components are the transistors, resistors, or coils.

[0072] Multiple circuit elements 60 are mounted on the first surface 50a and the second surface 50b of the circuit board 50, respectively. The multiple circuit elements 60 mounted on the first surface 50a of the circuit board 50 are soldered to the first metal wiring 51. The multiple circuit elements 60 mounted on the second surface 50b of the circuit board 50 are soldered to the second metal wiring 52.

[0073] Motor 1 is a brushless motor driven by a pulse width modulation inverter. Therefore, the multiple circuit elements 60 mounted on the circuit board 50 constitute a three-phase brushless motor drive circuit that operates with a DC voltage. The three-phase brushless motor drive circuit includes a motor control IC, an inverter element drive circuit, and an inverter circuit section having three inverters corresponding to the U-phase, V-phase, and W-phase. Each of the three inverters includes a switching element 61 as one of the multiple circuit elements 60. In other words, the inverter circuit section includes multiple switching elements 61. The motor control IC is an IC package component. The motor control IC is one of the multiple circuit elements 60.

[0074] The motor control IC outputs PWM (Pulse Wave Modulation) signals to the inverter element drive circuits to drive the three inverter circuits.

[0075] The inverter element drive circuit generates a drive voltage to turn ON / OFF each of the three switching elements 61 in the inverter circuit section according to the PWM signal from the motor control IC, and outputs the drive voltage to the inverter circuit section.

[0076] The inverter circuit generates a high-frequency switching voltage from a DC voltage. For example, each of the three inverters in the inverter circuit generates a high-frequency switching voltage with a PWM frequency of 16 kHz from a high-voltage DC voltage of, for example, 391 V.

[0077] As shown in Figure 9, each inverter includes a first switching element 61a on the DC voltage side (high voltage DC side) and a second switching element 61b on the high-frequency switching voltage side as switching elements 61. Each inverter has one first switching element 61a and one second switching element 61b. Therefore, the inverter circuit section includes three first switching elements 61a and three second switching elements 61b. The first switching element 61a is also called the upper switching element for each phase. Similarly, the second switching element 61b is also called the lower switching element for each phase.

[0078] The switching elements 61 (first switching element 61a, second switching element 61b) are heat-generating components. In other words, each of the multiple circuit elements 60 includes one or more heat-generating components. The multiple circuit elements 60 may also include heat-generating components other than the switching elements 61. In other words, the multiple circuit elements 60 may include multiple types of heat-generating components.

[0079] The switching elements 61 in each inverter (first switching element 61a, second switching element 61b) are, for example, MOSFETs (Metal Oxide Semiconductor Field Effect Transistors). Specifically, the switching element 61 is an N-type MOSFET. The switching element 61 is not limited to MOSFETs. For example, the switching element 61 may be a bipolar transistor, an IGBT (Insulated Gate Bipolar Transistor), or the like.

[0080] The switching element 61 is a packaged electronic component. As shown in Figure 5, the switching element 61 has a resin package 611 and an electrode 612 formed on the back surface of the resin package 611. The electrode 612 functions as one of the terminals and also functions as a heat dissipation electrode that dissipates the heat generated by the switching element 61. In other words, the back surface of the switching element 61 becomes the heat dissipation surface.

[0081] If the switching element 61 is a MOSFET, it has three terminals: a gate terminal, a source terminal, and a drain terminal. In this case, the electrode 612 formed on the back surface of the resin package 611 also functions as the drain terminal. If the switching element 61 is an N-type MOSFET, the drain terminal is on the high-potential side of the circuit.

[0082] As shown in Figures 4 to 6 and Figure 9, the multiple switching elements 61 are mounted on the second surface 50b of the circuit board 50. Specifically, the multiple switching elements 61 are placed on the second metal wiring 52 and are electrically connected to the second metal wiring 52.

[0083] As shown in Figure 7, a portion of the first metal wiring 51 of the circuit board 50 is a first heat spreader 51a, 51b with a larger area than the switching element 61, which is a heat-generating component. The first heat spreaders 51a, 51b are a portion of the copper foil that makes up the first metal wiring 51. The first heat spreader 51a is positioned away from the rotation axis 21.

[0084] As shown in Figure 8, a portion of the second metal wiring 52 of the circuit board 50 is a second heat spreader 52a, 52c, which has a larger area than the switching element 61, a heat-generating component. The other portion of the second metal wiring 52 is a ground pattern 52b (N line) to which ground potential (circuit ground) is applied. The second heat spreaders 52a, 52c and the ground pattern 52b are part of the copper foil that constitutes the second metal wiring 52. The second heat spreaders 52a, 52c are located away from the rotation axis 21. The ground pattern 52b is located close to the rotation axis 21. In other words, the ground pattern 52b is formed inside the second heat spreaders 52a, 52c.

[0085] As shown in Figures 4 to 6 and Figure 9, the switching element 61, which is a heat-generating component, is mounted on the second heat spreaders 52a and 52c and is electrically connected to the second heat spreaders 52a and 52c. Specifically, the electrodes 612 of the switching element 61 are in surface contact with the second heat spreaders 52a and 52c.

[0086] As shown in Figures 8 and 9, each of the second heat spreaders 52a and 52c is formed to correspond to one of the multiple switching elements 61. In this embodiment, six switching elements 61 are mounted on the circuit board 50. Therefore, three second heat spreaders 52a and three second heat spreaders 52c are formed on the second metal wiring 52.

[0087] As shown in Figures 8 and 9, of the three second heat spreaders 52a and three second heat spreaders 52c, the three second heat spreaders 52a on which the DC voltage side first switching element 61a is mounted are formed in a switching voltage pattern that spreads toward the outer edge of the circuit board 50. These three second heat spreaders 52a on which the first switching element 61a is mounted are connected by an arc-shaped metal wiring formed at the outer edge of the circuit board 50 as part of the second metal wiring 52. The potential of the three second heat spreaders 52a on which the first switching element 61a is mounted is the potential on the DC voltage side.

[0088] On the other hand, of the three second heat spreaders 52a and three second heat spreaders 52c, the three second heat spreaders 52c on which the second switching element 61b on the high-frequency switching voltage side is mounted have a high-voltage DC side pattern and are formed to spread toward the inner circumference of the circuit board 50. The three second heat spreaders 52c on which the second switching element 61b is mounted are connected by an arc-shaped metal wiring formed on the inner circumference of the circuit board 50 as part of the second metal wiring 52. The potential of the three second heat spreaders 52c on which the second switching element 61b is mounted is the potential on the high-frequency switching voltage side (high-frequency inverter output potential).

[0089] Each of the three second heat spreaders 52a and the three second heat spreaders 52c is preferably formed to extend beyond the outer shape of the switching element 61 when the circuit board 50 is viewed from above. Specifically, each of the second heat spreaders 52a and 52c is preferably formed to extend beyond the entire outer circumference of the switching element 61.

[0090] As shown in Figure 7, the first heat spreaders 51a and 51b on the first surface 50a side of the circuit board 50 are formed in an island shape corresponding to a plurality of switching elements 61. The first heat spreaders 51a and 51b are not connected to each other. Specifically, three first heat spreaders 51a and three first heat spreaders 51b are formed on the second metal wiring 52. In other words, a total of six first heat spreaders 51a and 51b are formed, corresponding to six switching elements 61. Each of the first heat spreaders 51a and 51b is formed to spread outwards toward the outer edge of the circuit board 50.

[0091] Each of the first heat spreaders 51a and 51b is preferably formed to extend beyond the outer shape of the switching element 61 when the circuit board 50 is viewed from above. Specifically, the first heat spreaders 51a and 51b are preferably formed to extend beyond the entire outer circumference of the switching element 61.

[0092] When the circuit board 50 is viewed from above, three of the three first heat spreaders 51a and three first heat spreaders 51b overlap with the first switching element 61a on the DC voltage side. The three first heat spreaders 51a are the switching voltage patterns. On the other hand, three of the three first heat spreaders 51b overlap with the first switching element 61a on the high-frequency switching voltage side. The three first heat spreaders 51b are the high-voltage DC side patterns.

[0093] As shown in Figure 5, the first heat spreader 51a and the second heat spreader 52a are connected by a plurality of via holes 53 that penetrate the circuit board 50. When the circuit board 50 is viewed from above (i.e., from the direction of the axis C of the rotation axis 21), the plurality of via holes 53 are positioned to overlap with the switching element 61. The size of one via hole 53 is, for example, φ0.3 mm, but is not limited to this.

[0094] As shown in Figures 7 and 8, multiple via holes 53 connecting the first heat spreader 51a and the second heat spreader 52a are provided in each of the multiple first heat spreaders 51a (i.e., each of the multiple second heat spreaders 52a). It is preferable that each first heat spreader 51a has 10 or more via holes 53. In this embodiment, each first heat spreader 51a has 25 or more via holes 53. Multiple via holes 53 are arranged in a grid pattern at equal intervals.

[0095] Although not shown in the diagram, the first heat spreader 51b and the second heat spreader 52c are also connected by multiple via holes 53 that penetrate the circuit board 50.

[0096] As shown in Figures 4 to 6, an insulating heat dissipation member 70 is placed between the circuit board 50 and the first bracket 41.

[0097] As shown in Figure 5, the heat dissipation member 70 is in contact with the circuit board 50 and the first bracket 41, respectively. In this embodiment, the heat dissipation member 70 is placed on the first heat spreader 51a formed on the first surface 50a of the circuit board 50. Therefore, the heat dissipation member 70 is in contact with the first heat spreader 51a and the first bracket 41, respectively.

[0098] As shown in Figure 9, when the circuit board 50 is viewed from above (i.e., from the direction of the axis C of the rotation axis 21), the heat dissipation member 70 is positioned to overlap with the switching element 61 located on the second surface 50b of the circuit board 50. In other words, the heat dissipation member 70 is positioned to cover the switching element 61 via the circuit board 50.

[0099] As shown in Figure 9, the heat dissipation member 70 does not cover only one switching element 61, but rather multiple switching elements 61. In other words, one heat dissipation member 70 is positioned to span multiple switching elements 61 via the circuit board 50.

[0100] In this embodiment, multiple heat dissipation members 70 are arranged. Specifically, as shown in Figures 6 and 9, two heat dissipation members 70 are arranged. Each of the two heat dissipation members 70 covers three switching elements 61. One of the two heat dissipation members 70 covers one first switching element 61a and two second switching elements 61b. The other of the two heat dissipation members 70 covers two first switching elements 61a and one second switching element 61b.

[0101] The heat dissipation member 70 is a sheet-like sheet material. The heat dissipation member 70 is in close contact with the first heat spreaders 51a, 51b and the first bracket 41, respectively. The heat dissipation member 70 is a thermal conductive sheet (thermal sheet) made of a material with high thermal conductivity. For example, the thermal conductivity of the heat dissipation member 70 is 1 W / m·K or higher, but is not limited to this. For example, the planar shape of the heat dissipation member 70 is rectangular, but is not limited to this.

[0102] The heat dissipation member 70 is a dielectric made of a dielectric material. Specifically, the heat dissipation member 70 is an insulating sheet made of an insulating material. This ensures insulation between the first heat spreaders 51a and 51b (first metal wiring 51) and the first bracket 41. For example, the heat dissipation member 70 is made of an insulating resin material. As the resin material that makes up the heat dissipation member 70, for example, a silicone-based or acrylic-based resin material can be used. In this embodiment, the heat dissipation member 70 is a thermal conductive sheet made of silicone resin, with a thermal conductivity of 2.5 W / m·K and a dielectric constant of 6.05 (f = 1 kHz).

[0103] The heat dissipation member 70 is preferably made of an elastomer with high thermal conductivity and rubber elasticity. This allows the heat dissipation member 70 to elastically deform when sandwiched between the circuit board 50 and the first bracket 41. Therefore, even if the gap between the first bracket 41 and the circuit board 50 is not constant, the heat dissipation member 70 can be easily brought into close contact with the first heat spreaders 51a, 51b and the first bracket 41. In other words, the heat dissipation member 70 can absorb the size of the gap between the first bracket 41 and the circuit board 50.

[0104] As will be described in more detail later, the dielectric heat dissipation member 70 functions as a capacitance adjustment member for adjusting the capacitance between the first bracket 41 and the circuit board 50.

[0105] As shown in Figure 5, an insulating sheet 80 is placed between the heat dissipation member 70 and the first bracket 41. The heat dissipation member 70 is in contact with the first bracket 41 through openings 81 formed in the insulating sheet 80. Specifically, as shown in Figure 2, the insulating sheet 80 has two openings 81, corresponding to the two heat dissipation members 70. The heat dissipation members 70 are placed inside these openings 81. The shape and size of each opening 81 are the same as the plan view shape and size of each of the two heat dissipation members 70. In other words, each heat dissipation member 70 fits perfectly into the opening 81.

[0106] The insulating sheet 80 is made of an insulating material. Specifically, the insulating sheet 80 is made of an insulating resin material. In other words, the insulating sheet 80 is a dielectric made of a dielectric material.

[0107] In the motor 1 configured in this way, when current is supplied to the winding 12 of the stator 10, a field current flows through the winding 12, generating a magnetic field. This generates a magnetic flux from the stator 10 toward the rotor 20. Specifically, a magnetic flux is generated from each of the multiple teeth of the stator core 11 in the stator 10 toward the rotor core 22 of the rotor 20. Meanwhile, in the rotor 20, a magnetic flux is generated passing through the stator 10 by the magnets 23 embedded in the rotor core 22. The magnetic force generated by the interaction between the magnetic flux generated in the stator 10 and the magnetic flux generated from the magnets 23 in the rotor 20 becomes the torque that rotates the rotor 20. As a result, the rotor 20 rotates. This causes the rotation axis 21 of the rotor 20 to rotate.

[0108] Here, the effects of the motor 1 according to this embodiment will be explained with reference to Figures 5 and 9.

[0109] As shown in Figure 9, in the motor 1, a switching element 61 is mounted on the second surface 50b of the circuit board 50 as a heat-generating component. As shown in Figure 5, a heat dissipation member 70 is positioned between the first bracket 41 and the circuit board 50. The heat dissipation member 70 is positioned so as to overlap with the switching element 61 when viewed from the direction of the axis C of the rotation shaft 21.

[0110] With this configuration, as shown by the thick arrow in Figure 5, the heat generated by the switching element 61 (heat loss) is conducted to the heat dissipation member 70 via the circuit board 50, and then conducted from the heat dissipation member 70 to the first bracket 41, dissipating heat to the outside of the motor 1. In particular, the thermal conductivity of the heat dissipation member 70 is higher than that of the circuit board 50, and the thermal conductivity of the metal first bracket 41 is also higher than that of the heat dissipation member 70. As a result, the heat generated by the switching element 61 is efficiently conducted from the circuit board 50 to the heat dissipation member 70, and also efficiently conducted from the heat dissipation member 70 to the first bracket 41. In this way, the heat dissipation member 70 functions as a heat conduction path for the heat generated by the switching element 61.

[0111] Furthermore, in the motor 1 according to this embodiment, a portion of the first metal wiring 51 formed on the first surface 50a of the circuit board 50 is the first heat spreader 51a, 51b. A portion of the second metal wiring 52 formed on the second surface 50b of the circuit board 50 is the second heat spreader 52a, 52c. The heat dissipation member 70 is placed on the first heat spreader 51a, 51b. The switching element 61 is placed on the second heat spreader 52a, 52c and is electrically connected to the second heat spreader 52a, 52c.

[0112] With this configuration, the heat generated by the switching element 61 can be dissipated by the first heat spreaders 51a, 51b and the second heat spreaders 52a, 52c. Therefore, the heat generated by the switching element 61 can be dissipated even more efficiently.

[0113] Furthermore, in the motor 1 according to this embodiment, the first heat spreaders 51a, 51b and the second heat spreaders 52a, 52c are connected by a plurality of via holes 53 that penetrate the circuit board 50. When viewed from the axial direction of the rotation shaft 21, the plurality of via holes 53 are positioned to overlap with the switching element 61.

[0114] This configuration allows the heat generated by the switching element 61 to be efficiently conducted from the second heat spreaders 52a and 52c to the first heat spreaders 51a and 51b via the multiple via holes 53. In other words, the heat generated by the switching element 61 can be efficiently conducted from the second surface 50b to the first surface 50a of the circuit board 50. This allows the heat generated by the switching element 61 to be conducted to the heat dissipation member 70 even more efficiently. Therefore, the heat generated by the switching element 61 can be dissipated even more efficiently.

[0115] Furthermore, in the motor 1 according to this embodiment, the switching element 61 has a resin package 611 and an electrode 612 formed on the back surface of the resin package 611. The electrode 612 is in surface contact with the second heat spreaders 52a and 52c.

[0116] This configuration allows the heat generated by the switching element 61 to be quickly conducted to the second heat spreader 52a via the electrode 612. Therefore, the heat generated by the switching element 61 can be dissipated more efficiently.

[0117] Thus, according to the motor 1 of this embodiment, the heat dissipation member 70 can efficiently dissipate the heat generated by the switching element 61.

[0118] Furthermore, in the motor 1 according to this embodiment, the heat dissipation member 70 can reduce the shaft voltage of the first bearing 31, thereby suppressing the occurrence of electrolytic corrosion in the first bearing 31. This effect will be explained below with reference to Figures 10A and 10B. Figure 10A is a diagram showing the equivalent circuit of parasitic capacitance related to the generation of shaft voltage of the first bearing 31 in the motor 1 according to this embodiment. Figure 10B is a block diagram of an electrical circuit illustrating the state in which power is supplied to the motor 1 via the switching element 61 in the motor 1 according to this embodiment. The inverter circuit has three inverters, but it can be equivalently considered as the circuit shown in Figure 10A.

[0119] Each symbol shown in the equivalent circuit of Figure 10A represents the following voltage or parasitic capacitance. The capacitance values ​​shown in Figure 10A are examples only.

[0120] V1 is the inverter switching voltage applied to the winding 12 of the stator 10. V1 is the inverter input voltage V_Inv1.

[0121] Cs1 is a parasitic capacitance present in the insulator 13 between the winding 12 and the stator core 11. Cs1 is, for example, 400 pF.

[0122] Cgap1 is a parasitic capacitance present in the gap between the stator core 11 and the rotor 20. Cgap1 is, for example, 70 pF.

[0123] Cmg is a parasitic capacitance present between the rotor 20 and the rotating shaft 21. Cmg is, for example, 36 pF.

[0124] Cnl1 is a parasitic capacitance existing between the rotating shaft 21 and the ground potential (GND potential). The ground potential is generated by the ground pattern 52b of the second metal wiring 52 formed on the second surface 50b of the circuit board 50. Cnl1 is, for example, 20pF. As in this embodiment, by positioning the ground pattern 52b (ground potential) of the circuit board 50 close to the rotating shaft 21, the capacitive coupling between the rotating shaft 21 and the ground potential can be increased. Also, as in this embodiment, by positioning the first heat spreader 51a and the second heat spreader 52a away from the rotating shaft 21, it is possible to suppress capacitive coupling between the rotating shaft 21 and the first heat spreader 51a and the second heat spreader 52a (switching voltage pattern) due to the high-frequency inverter output potential.

[0125] Cb1 is the parasitic capacitance between the inner and outer rings of the first bearing 31. Cb2 is the parasitic capacitance between the inner and outer rings of the second bearing 32. Cb1 and Cb2 are, for example, 50 pF. The outer ring of the first bearing 31 and the outer ring of the second bearing 32 are electrically connected by the rotating shaft 21.

[0126] Here, we will explain in detail using the block diagram of the electrical circuit shown in Figure 10B.

[0127] Cbkt1, shown in Figures 10A and 10B, is a parasitic capacitance existing between the first bracket 41 and the inverter switching voltage. Specifically, Cbkt1 is a parasitic capacitance due to capacitive coupling between the first bracket 41 and the three first heat spreaders 51a on the high-frequency switching voltage side of the six first heat spreaders 51a via the heat dissipation member 70. In other words, Cbkt1 is a parasitic capacitance existing between the first bracket 41, the heat dissipation member 70, and the first heat spreaders 51a (high-frequency switching voltage side).

[0128] Cbkt2, shown in Figures 10A and 10B, is a parasitic capacitance existing between the first bracket 41 and the ground potential (ground pattern 52b) of the circuit board 50. Specifically, Cbkt2 is a parasitic capacitance due to capacitive coupling between the first bracket 41 and three of the six first heat spreaders 51a on the DC voltage side (high voltage DC side) via the heat dissipation member 70. In other words, Cbkt2 is a parasitic capacitance existing between the first bracket 41, the heat dissipation member 70, and the first heat spreaders 51a (DC voltage side).

[0129] Between the DC high voltage VH and the ground VG, there is an extremely large capacitance compared to the parasitic capacitance of the smoothing capacitor Cpc1. Therefore, in the high-frequency region, Cbkt2 is equivalently connected to the ground potential.

[0130] As shown in Figure 10A, V_Bearing1 is the potential of the first bracket 41 (i.e., the potential of the outer ring of the first bearing 31). V_Bearing1 appears in Cbkt2 due to the series capacitance of Cbkt1 and Cbkt2.

[0131] V_Shaft1 is the potential of the rotating shaft 21 (i.e., the potential of the inner ring of the first bearing 31). V_Shaft1 appears in Cnl1 due to the series capacitance of Cs1, Cgap1, Cmg, and Cnl1.

[0132] In this case, the shaft voltage, which is the potential difference between the potential of the outer ring and the potential of the inner ring in the first bearing 31, is the potential difference between V_Bearing1 and V_Shaft1. Therefore, by setting Cbkt1 and Cbkt2 so that the potential difference between V_Shaft1 and V_Bearing1 is small (i.e., by setting the capacitance ratio of Cbkt1 and Cbkt2), the shaft voltage can be reduced. This makes it possible to suppress the occurrence of electrolytic corrosion in the first bearing 31. For example, by setting Cbkt1 and Cbkt2 so that V_Shaft1 and V_Bearing1 are equal, the shaft voltage can be made zero.

[0133] The difference between V_Shaft1 and V_Bearing1 (i.e., the difference between the potential of the inner ring and the potential of the outer ring of the first bearing 31) should be 10V or less. By keeping the difference between V_Shaft1 and V_Bearing1 10V or less, electrolytic corrosion will not occur in the first bearing 31.

[0134] Cbkt1 and Cbkt2 are the capacitances between the first bracket 41 and the circuit board 50. Cbkt1 and Cbkt2 can be adjusted by a heat dissipation member 70 inserted between the first bracket 41 and the circuit board 50. In other words, the heat dissipation member 70 functions as a capacitance adjustment member for adjusting the capacitance between the first bracket 41 and the circuit board 50. To put it another way, the heat dissipation member 70 is an axial voltage adjustment member that adjusts the axial voltage of the first bearing 31.

[0135] For example, by changing any one of the material, thickness, area, or position of the heat dissipation member 70, the capacitance ratio of Cbkt1 and Cbkt2 can be changed. In other words, the impedance on the stator 10 side can be changed. In this way, by changing the capacitance ratio of Cbkt1 and Cbkt2 with the heat dissipation member 70, the shaft voltage of the first bearing 31 can be reduced, thereby suppressing the occurrence of electrolytic corrosion in the first bearing 31.

[0136] For example, in Figure 10A, if Cs1 = 400 pF, Cgap1 = 70 pF, Cmg = 36 pF, Cnl1 = 20 pF, and Cb1 = Cb2 = 50 pF, the difference between V_Shaft1 and V_Bearing1 can be made almost zero by setting the material, thickness, area, and position of the heat dissipation member 70 such that Cbkt1 is 30 pF and Cbkt2 is 20 pF.

[0137] As described above, in the motor 1 according to this embodiment, a portion of the switching voltage applied to the winding 12 of the stator 10 is supplied to the first bearing 31 via a heat dissipation member 70, which also functions as a heat conduction path, thereby suppressing the occurrence of electrolytic corrosion in the first bearing 31. Specifically, the occurrence of electrolytic corrosion in the first bearing 31 is suppressed by adjusting the impedance on the stator 10 side with the heat dissipation member 70.

[0138] As described above, the motor 1 according to this embodiment includes a first bearing 31 that rotatably supports the rotating shaft 21, a conductive first bracket 41 that holds the first bearing 31, a circuit board 50 arranged opposite to the first bracket 41, a plurality of circuit elements 60 mounted on the circuit board 50, and an insulating heat dissipation member 70 arranged between the first bracket 41 and the circuit board 50. The plurality of circuit elements 60 include a switching element 61 as a heat-generating component mounted on the second surface 50b of the circuit board 50. When viewed from the direction of the axis C of the rotating shaft 21, the heat dissipation member 70 is positioned to overlap with the switching element 61.

[0139] This configuration allows the heat generated by the switching element 61 to be efficiently conducted to the first bracket 41 via the heat dissipation member 70 for heat dissipation. This increases the output of the motor 1's drive circuit. Therefore, the output of the motor 1 can be increased.

[0140] Furthermore, the heat dissipation member 70 can adjust the capacitance between the first bracket 41 and the circuit board 50. This reduces the axial potential of the first bearing 31, thereby suppressing the occurrence of electrolytic corrosion in the first bearing 31.

[0141] Thus, in the motor 1 according to this embodiment, by simply inserting the heat dissipation member 70 between the first bracket 41 and the circuit board 50, it is possible to suppress the occurrence of electrolytic corrosion on the first bearing 31 held by the first bracket 41, and to efficiently dissipate the heat generated by the switching element 61 mounted on the circuit board 50. In other words, the heat dissipation member 70 plays two roles: a heat conduction path and a capacitance adjustment member.

[0142] As described above, the motor 1 according to this embodiment can suppress the occurrence of electrolytic corrosion and easily achieve high output of the motor 1. In other words, it is possible to achieve both suppression of electrolytic corrosion and high output of the motor 1. Furthermore, electrolytic corrosion can be suppressed without using circuit elements (high-voltage capacitors) to suppress the occurrence of electrolytic corrosion. Therefore, cost reduction can also be achieved.

[0143] (Modification) The motor 1 according to the present disclosure has been described above based on embodiments. However, the present disclosure is not limited to the above embodiments.

[0144] For example, in the above embodiment, a switching element 61 was given as an example of a heat-generating component mounted on the circuit board 50. However, it is not limited to this. Figure 11 shows a circuit board 50 on which a surface-mount type IPM package 62 is mounted as a circuit element 60 which is a heat-generating component. Specifically, as shown in Figure 11, the circuit element 60 which is a heat-generating component may be a surface-mount type IPM (Intelligent Power Module) package 62. In Figure 11, the dashed rectangular frame indicated by reference numeral 62 shows the outer shape of the IPM package 62. The multiple dashed rectangular frames shown inside it show the electrodes of the IPM package 62. In this case, the electrodes that become the ground potential and the electrodes that become the high-frequency inverter output potential in the IPM package 62 mounted on the second surface 50b of the circuit board 50 face the first heat spreaders 51a and 51b formed on the first surface 50a of the circuit board 50.

[0145] Figure 12A shows the surface-mount type IPM package 62 shown in Figure 11 covered with a heat dissipation member 70. In this case, as shown in Figure 12A, covering the IPM package 62 with the heat dissipation member 70 allows for efficient heat dissipation from the IPM package 62. Furthermore, by adjusting the material, thickness, area, and position of the heat dissipation member 70, electrolytic corrosion on the first bearing 31 can be suppressed.

[0146] By changing the position of the heat dissipation member 70, Cbkt1 or Cbkt2 can be finely adjusted. Figure 12B shows the heat dissipation member 70 covering the surface-mount type IPM package 62 shown in Figure 11 shifted in one direction from the position in Figure 12A. For example, as shown in Figure 12B, Cbkt2 can be reduced by reducing the overlapping portion between the electrode that becomes the ground potential in the IPM package 62 and the heat dissipation member 70. On the other hand, Figure 12C shows the heat dissipation member 70 covering the surface-mount type IPM package 62 shown in Figure 11 shifted in the opposite direction from the position in Figure 12A. As shown in Figure 12C, Cbkt1 can be reduced by reducing the overlapping portion between the electrode that becomes the high-frequency inverter output potential in the IPM package 62 and the heat dissipation member 70.

[0147] Furthermore, in the above embodiment, the capacitance adjusting member for adjusting the capacitance between the first bracket 41 and the circuit board 50 is only the heat dissipation member 70. However, it is not limited to this. For example, in addition to the heat dissipation member 70, an insulating sheet 80 can also be used as a capacitance adjusting member. Figure 13A is a plan view showing an example of an insulating sheet 80. In this case, in the insulating sheet 80 shown in Figure 13A, the heat dissipation member 70 is located inside the opening 81, so only the heat dissipation member 70 functions as a capacitance adjusting member. On the other hand, Figure 13B is a plan view showing a modified example of the insulating sheet 80A. In the insulating sheet 80A shown in Figure 13B, a plurality of openings 81A are provided separated by a bridge portion 82. In the insulating sheet 80A, the heat dissipation member 70 and the bridge portion 82 function as capacitance adjusting members. This makes it possible to change the capacitance between the first bracket 41 and the circuit board 50 without changing the design of the heat dissipation member 70. In other words, the shaft voltage of the first bearing 31 can be adjusted.

[0148] Figure 14 is an enlarged cross-sectional view of the motor 1 according to Modification 1. As shown in Figure 14, the capacitance between the first bracket 41 and the circuit board 50 may be adjusted by changing the shape of the first bracket 41A and changing the distance between the first bracket 41A and the first metal wiring 51 (first heat spreader 51a) of the circuit board 50. In Figure 14, the distance between the first bracket 41A and the first metal wiring 51 of the circuit board 50 is shortened by recessing a part of the first bracket 41A toward the circuit board 50. This makes it possible to conduct the heat generated by the switching element 61 to the first bracket 41 more efficiently. Therefore, the heat dissipation performance of the heat generated by the switching element 61 can be improved. In other words, the shaft voltage of the first bearing 31 can be adjusted while improving the heat dissipation performance of the heat generated by the switching element 61.

[0149] Figure 15 is an enlarged cross-sectional view of the motor 1 according to the second modified example. As shown in Figure 15, the heat dissipation member 70A may have a laminated structure of a first heat dissipation sheet 71 and a second heat dissipation sheet 72, and an intermediate conductor sheet 73 may be interposed between the first heat dissipation sheet 71 and the second heat dissipation sheet 72. This allows the capacitance ratio of Cbkt1 and Cbkt2 to be adjusted by the intermediate conductor sheet 73 as well. For example, the capacitance ratio of Cbkt1 and Cbkt2 can be changed by changing the area of ​​the intermediate conductor sheet 73 relative to the first metal wiring 51 (first heat spreader 51a). This makes it possible to adjust the shaft voltage of the first bearing 31 without changing the distance between the first bracket 41 and the circuit board 50 (i.e., without changing the heat dissipation performance of the heat generated by the switching element 61). As the intermediate conductor sheet 73, for example, a metal plate such as a copper plate, aluminum plate, or steel plate can be used.

[0150] Furthermore, in the above embodiment, the heat dissipation member 70 covers a plurality of switching elements 61 via the circuit board 50. However, it is not limited to this. Specifically, the heat dissipation member 70 may cover each of the plurality of switching elements 61 individually via the circuit board 50. In other words, one heat dissipation member 70 may be provided for each switching element 61.

[0151] Furthermore, in the above embodiment, the magnet 23 inserted into the rotor core 22 has a rectangular shape when viewed from above. However, it is not limited to this. For example, the shape of the magnet 23 when viewed from above may be trapezoidal or barrel-shaped.

[0152] Furthermore, in the above embodiment, the multiple magnets 23 are arranged in a spoke-like (radial) pattern and inserted into the rotor core 22. However, the invention is not limited to this. Specifically, the multiple magnets 23 may be arranged in a ring shape around the rotation axis 21.

[0153] Furthermore, in the above embodiment, the rotor 20 is an IPM rotor in which a plurality of magnets 23 are inserted into magnet insertion holes of the rotor core 22. However, it is not limited to this. Specifically, the rotor 20 may be a surface magnet type (SPM: Surface Permanent Magnet) rotor in which a plurality of permanent magnets are fixed to the outer circumferential surface of the core.

[0154] Furthermore, in the above embodiment, the windings 12 of the stator 10 are wound around the stator core 11 in a concentrated winding manner. However, this is not the only possible configuration. For example, the windings 12 of the stator 10 may be wound around the stator core 11 in a distributed winding manner.

[0155] Furthermore, in the above embodiment, the motor 1 is a molded motor. However, it is not limited to this. The technology of this disclosure can be applied to motors other than molded motors. In other words, the technology of this disclosure can also be applied to motors in which the stator 10 is not covered with molded resin 90.

[0156] Furthermore, in the above embodiment, the motor 1 was described in the context of being applied to a fan motor of an air conditioner. However, it is not limited to this. For example, the motor 1 in the above embodiment can be used in various electrical devices such as household appliances like vacuum cleaners or refrigerators, or industrial equipment such as automotive equipment or robots.

[0157] Furthermore, forms obtained by applying various modifications to the above embodiments that a person skilled in the art could conceive of, or forms realized by arbitrarily combining the components and functions of the embodiments without departing from the spirit of this disclosure, are also included in this disclosure. Arbitrary combinations of two or more claims from the multiple claims described in the claims of this application, within the scope of which they do not contradict each other, are also included in this disclosure. For example, if the cited claims described in the claims of this application are made into a multi-claim or multi-multi-claim so as to refer to all of the higher-level claims within the scope of which they do not contradict each other, then all combinations of claims included in that multi-claim or multi-multi-claim are also included in this disclosure.

[0158] The motor described herein can be widely used in various devices equipped with a motor.

[0159] 1 Motor 10 Stator 11 Stator core 12 Winding 13 Insulator 20 Rotor 21 Rotating shaft 21a First end 21b Second end 22 Rotor core 22a Inner core 22b Outer core 23 Magnet 24 Resin 31 First bearing 32 Second bearing 41, 41A First bracket 42 Second bracket 50 Circuit board 50a First side 50b Second side 51 First metal wiring 51a First heat spreader (switching voltage pattern) 51b First heat spreader (high voltage DC side pattern) 52 Second metal wiring 52a Second heat spreader (switching voltage pattern) 52b Ground pattern 52c Second heat spreader (high voltage DC side pattern) 53 Via hole 60 Circuit element 61 Switching element 61a First switching element 61b Second switching element 62 IPM package 70, 70A Heat dissipation member 71 First heat dissipation sheet 72 Second heat dissipation sheet 73 Intermediate conductor sheet 80, 80A Insulating sheet 81, 81A Opening 82 Bridge section 90 Molded resin 611 Resin package 612 Electrode

Claims

1. A motor comprising: a rotor having a rotating shaft extending in the axial direction; a stator that generates a magnetic force acting on the rotor; a bearing that rotatably supports the rotating shaft; a conductive bracket that holds the bearing; a circuit board disposed opposite to the bracket; circuit elements mounted on the circuit board; and an insulating heat dissipation member disposed between the bracket and the circuit board, wherein the circuit board has a first surface which is the surface facing the bracket and a second surface which is the surface opposite to the first surface; the circuit elements include heat-generating components mounted on the second surface of the circuit board; and when viewed from the axial direction, the heat dissipation member is positioned to overlap with the heat-generating components.

2. The motor according to claim 1, wherein a first metal wiring is formed on the first surface of the circuit board, a second metal wiring is formed on the second surface of the circuit board, the first metal wiring includes a first heat spreader having a larger area than the heat-generating component, the second metal wiring includes a second heat spreader having a larger area than the heat-generating component, the heat dissipation member is placed on the first heat spreader, and the heat-generating component is placed on the second heat spreader and electrically connected to the second heat spreader.

3. The motor according to claim 2, wherein the first heat spreader and the second heat spreader are connected by a plurality of via holes penetrating the circuit board, and the plurality of via holes are positioned to overlap with the heat-generating components when viewed from the axial direction.

4. The motor according to claim 2, wherein the heat-generating component comprises a resin package and an electrode formed on the back surface of the resin package, and the electrode is in surface contact with the second heat spreader.

5. The motor according to any one of claims 1 to 4, further comprising an insulating sheet disposed between the heat dissipation member and the bracket, wherein the heat dissipation member is in contact with the bracket through an opening formed in the insulating sheet.

6. The motor according to any one of claims 1 to 4, wherein the circuit element is one of a plurality of circuit elements, the plurality of circuit elements constitute an inverter circuit that generates a high-frequency switching voltage from a DC voltage, and the inverter circuit includes a switching element as the heat-generating component.

7. The motor according to claim 6, wherein the switching element is one of a plurality of switching elements, and the heat dissipation member covers the plurality of switching elements.

8. The motor according to any one of claims 1 to 4, wherein the difference between the potential of the inner ring and the potential of the outer ring in the bearing is 10V or less.

9. The motor according to any one of claims 1 to 4, wherein at least a portion of the stator is covered with molded resin, and the molded resin constitutes the outer shell of the motor.

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