Electric motor, blower, pump, and air conditioner

Abstract

This electric motor comprises: a rotating shaft; a first bearing that has a first inner ring and a first outer ring and supports the rotating shaft; a second bearing that has a second inner ring and a second outer ring and supports the rotating shaft; a rotor that is positioned between the first bearing and the second bearing in the axial direction of the rotating shaft, is attached to the rotating shaft, and has a permanent magnet; a stator that has a stator core that surrounds the rotor, a coil that is wound around the stator core, and a mold resin part that covers the stator core and the coil; a circuit board that is disposed on the opposite side of the rotor sandwiching the first bearing in the axial direction; and a bracket that is disposed between the stator core and the circuit board in the axial direction, holds the first bearing in contact with the first outer ring, and is attached to the stator. The first outer ring and the second outer ring are electrically insulated. The first outer ring and the stator core are electrically insulated. The bracket has conductivity and is electrically insulated from the circuit board and the stator core.

Description

Electric motors, fans, pumps and air conditioners

[0001] The present disclosure relates to electric motors, blowers, pumps, and air conditioners.

[0002] 2. Description of the Related Art Conventionally, electric motors have been known that include a rotor attached to a rotating shaft, a stator surrounding the rotor, and a driving circuit board (see, for example, Patent Document 1).

[0003] JP 2011-78286 A (see FIG. 1)

[0004] In conventional electric motors, the bearings supporting the rotating shaft are held in place by the molded resin portion of the stator and are electrically insulated from the stator. Therefore, a potential difference between the wiring pattern on the circuit board and the stator coil can potentially create a potential difference between the inner and outer rings of the bearing. When the potential difference becomes large, a discharge occurs between the inner and outer rings, causing unevenness on the raceway surface that contacts the rolling elements. This phenomenon is called electrolytic corrosion. When electrolytic corrosion occurs, vibrations and noise are generated when the rolling elements travel along the raceway surface, and the life of the electric motor is shortened.

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to suppress the occurrence of electrolytic corrosion.

[0006] The electric motor disclosed herein includes a rotating shaft, a first bearing having a first inner ring and a first outer ring and supporting the rotating shaft, a second bearing having a second inner ring and a second outer ring and supporting the rotating shaft, a rotor located between the first bearing and the second bearing in the axial direction of the rotating shaft and attached to the rotating shaft and having a permanent magnet, a stator having a stator core surrounding the rotor, a coil wound around the stator core, and a molded resin portion covering the stator core and the coil, a circuit board located axially on the opposite side of the rotor across the first bearing, and a bracket attached to the stator and positioned axially between the stator core and the circuit board, holding the first bearing in contact with the first outer ring. The first outer ring and the second outer ring are electrically insulated. The first outer ring and the stator core are electrically insulated. The bracket is conductive and electrically insulated from the circuit board and the stator core.

[0007] According to the present disclosure, the conductive bracket is disposed between the stator core and the circuit board and is in contact with the first outer ring, so that the potential of the first outer ring is closer to the potential of the stator core and the coil than to the potential of the circuit board. As a result, the potential difference between the first outer ring and the first inner ring is reduced, and the occurrence of electrolytic corrosion can be suppressed. As a result, vibration and noise can be suppressed, and the life of the electric motor can be extended.

[0008] 1 is a cross-sectional view showing an electric motor according to a first embodiment; FIG. 2 is a cross-sectional view showing an electric motor according to the first embodiment; FIG. 3 is a partially cutaway perspective view showing a bearing according to the first embodiment; FIG. 4 is a partially cutaway perspective view showing the outer ring and inner ring of the bearing according to the first embodiment; FIG. 5 is an enlarged view of a first bearing, a bracket, and a circuit board according to the first embodiment; FIG. 6 is a schematic view for explaining the positional relationship between the stator, the bracket, and the circuit board according to the first embodiment; FIG. 7 is a block diagram showing a control system in the electric motor according to the first embodiment; FIG. 8 is a cross-sectional view showing an electric motor according to a comparative example; FIG. 9 is a graph showing a comparison of the bearing voltages of the first bearing and the second bearing when the bracket is made of resin and when it is made of metal; FIG. 10 is a graph showing the relationship between the hole diameter of the holder portion of the bracket according to the first embodiment and the bearing voltages of the first bearing and the second bearing; FIG. 11 is a view (A) of the bracket and the circuit board according to the first embodiment as seen from the rotor side, and FIG. 12 is a view (B) for explaining the opposing area between the bracket and the circuit board; FIG. 12 is a view of another configuration example of the bracket and the circuit board according to the first embodiment as seen from the rotor side; 1 is a schematic diagram for explaining the positional relationship between a stator, a bracket, and a circuit board according to a third embodiment. FIG. 2 is a cross-sectional view showing an electric motor according to a fourth embodiment. FIG. 3 is a graph showing a comparison of the bearing voltages of the first bearing and the second bearing when the bracket is made of resin, when it is made of a metal casting, and when it is made of a metal plate. FIG. 4 is a diagram showing an air conditioning apparatus to which the electric motors of each embodiment can be applied (A), and a diagram showing its outdoor unit (B). FIG. 5 is a diagram showing a pump to which the electric motors of each embodiment can be applied.

[0009] Embodiment 1. <Overall configuration of electric motor 1> An electric motor according to embodiment 1 will be described. Fig. 1 is a longitudinal cross-sectional view showing electric motor 1 according to embodiment 1. Electric motor 1 is a synchronous motor, and is used, for example, in a blower of an air conditioning device 100 (Fig. 17(A)).

[0010] The electric motor 1 includes a rotating shaft 10, a rotor 2 attached to the rotating shaft 10, a stator 3 surrounding the rotor 2, a circuit board 6, and bearings 11 and 12 supporting the rotating shaft 10. A central axis Ax of the rotating shaft 10 defines the center of rotation of the rotor 2.

[0011] Hereinafter, the direction of the central axis Ax will be referred to as the "axial direction." The radial direction centered on the central axis Ax will be referred to as the "radial direction." The circumferential direction centered on the central axis Ax will be referred to as the "circumferential direction."

[0012] The rotating shaft 10 protrudes upward from the stator 3 in Fig. 1. For example, an impeller of a blower is attached to the protruding portion of the rotating shaft 10. Therefore, the protruding side of the rotating shaft 10 (upper side in Fig. 1) is referred to as the "load side," and the opposite side (lower side in Fig. 1) is referred to as the "anti-load side." The load side is also referred to as the long axis side, and the anti-load side is also referred to as the short axis side.

[0013] The bearings 11 and 12 are arranged on both sides of the rotor 2 in the axial direction. The bearing 11 on the counter-load side is also referred to as a first bearing. The bearing 12 on the load side is also referred to as a second bearing. The bearing 11 on the counter-load side is arranged between the rotor 2 and the circuit board 6 in the axial direction.

[0014] <Configuration of Rotor 2> Fig. 2 is a cross-sectional view taken along a plane perpendicular to the central axis Ax of the electric motor 1, and does not include a molded resin portion 40, which will be described later. As shown in Fig. 2, the rotor 2 has a rotor core 20 fixed to the rotating shaft 10 and a plurality of permanent magnets 25 attached to the rotor core 20. The number of permanent magnets 25 is, for example, 8 or 10. However, the number is not limited to these.

[0015] 2, a resin portion 23 is formed as a connecting portion between the rotating shaft 10 and the rotor core 20. In other words, the rotor core 20 is fixed to the rotating shaft 10 via the resin portion 23. However, the rotating shaft 10 may be fitted into the central hole of the rotor core 20 without providing the resin portion 23.

[0016] The rotor core 20 is a cylindrical member centered on the central axis Ax. The rotor core 20 is made up of a plurality of laminated elements stacked in the axial direction and fixed by caulking or the like. The laminated elements are magnetic thin plates, more specifically, electromagnetic steel plates. The plate thickness of the laminated elements is, for example, 0.2 mm to 0.5 mm.

[0017] The rotor core 20 has a plurality of magnet insertion holes 21 in the circumferential direction. The magnet insertion holes 21 are arranged at equal intervals in the circumferential direction and at equal distances from the central axis Ax. The number of magnet insertion holes 21 here is 8 or 10, but is not limited to these. The magnet insertion holes 21 are formed along the outer periphery of the rotor core 20 and penetrate the rotor core 20 in the axial direction.

[0018] A permanent magnet 25 is inserted into each magnet insertion hole 21. The permanent magnet 25 is flat and has a rectangular cross section in a plane perpendicular to the axial direction. The permanent magnet 25 here is a rare earth magnet, more specifically, a rare earth sintered magnet. However, a ferrite magnet may be used instead of the rare earth magnet.

[0019] The rotor 2 is not limited to one in which the permanent magnets 25 are embedded in the rotor core 20, but may support the permanent magnets 25 on the surface of the rotor core 20. Alternatively, the rotor core 20 may not be provided, and the permanent magnets 25 may be supported on the surface of the resin portion 23. The permanent magnets 25 are not limited to sintered magnets, but may also be bonded magnets.

[0020] 1, the stator 3 has a stator core 30, an insulating portion 34 attached to the stator core 30, a coil 35 wound around the stator core 30 via the insulating portion 34, and a molded resin portion 40 that covers these. Of the stator 3, the stator core 30, the insulating portion 34, and the coil 35 are collectively referred to as the stator main body.

[0021] As shown in Fig. 2, the stator core 30 is made by stacking a plurality of laminated elements in the axial direction and fixing them by caulking or the like. The laminated elements are thin magnetic plates, more specifically, electromagnetic steel plates. The plate thickness of the laminated elements is, for example, 0.2 mm to 0.5 mm.

[0022] The stator core 30 has an annular yoke 31 centered on the central axis Ax and a plurality of teeth 32 extending radially inward from the yoke 31. The number of teeth 32 is 12 here, but is not limited to this. Tips of the teeth 32 are formed at the tips thereof, facing the rotor 2.

[0023] Slots 33 are formed between circumferentially adjacent teeth 32. Coils 35 are wound around the teeth 32 via insulating portions 34 (FIG. 1) and housed in the slots 33. The insulating portions 34 are made of a resin such as PPS (polyphenylene sulfide). Note that the insulating portions 34 are omitted from FIG. 2.

[0024] The coils 35 are wound around the teeth 32 and housed in the slots 33. The coils 35 are made of, for example, magnet wire. The coils 35 are three-phase windings having U-phase, V-phase, and W-phase coils 35U, 35V, and 35W (FIG. 7). The coils 35 may be wound by either concentrated winding or distributed winding.

[0025] 1 is made of a thermosetting resin such as an unsaturated polyester resin or an epoxy resin. The unsaturated polyester resin is, for example, a bulk molding compound (BMC).

[0026] The molded resin part 40 has a peripheral wall part 41 that covers the stator core 30 and the coils 35 from the radial outside, an opening 42 formed at the end of the peripheral wall part 41 on the anti-load side, and a top plate part 43 formed at the end of the peripheral wall part 41 on the load side. The rotor 2 is inserted into the inside of the stator 3 through the opening 42.

[0027] A bearing holder 44 that supports the load-side bearing 12 is formed on the top plate 43 of the molded resin part 40. The bearing holder 44 has an annular part 44a that contacts the outer peripheral surface of an outer ring 12b (described later) of the bearing 12, and a wall part 44b that contacts the axial end face of the outer ring 12b.

[0028] <Configuration of Bracket 5, Circuit Board 6, and Heat Sink 7> As shown in FIG. 1, a bracket 5 that supports the bearing 11 on the anti-load side is attached to the opening 42 of the molded resin part 40.

[0029] The bracket 5 is formed of a conductive material, such as a metal. The metal is preferably, for example, aluminum or stainless steel. More specifically, the bracket 5 is formed of a cast or machined part of a metal such as aluminum.

[0030] The bracket 5 has a holder portion 51 that holds the bearing 11, a fitting portion 52 that is fixed to the peripheral wall portion 41 of the molded resin portion 40, and a flat plate portion 50 that serves as an extension portion that extends between these. Holes may be formed in the flat plate portion 50 as appropriate (see FIG. 11(A) described below).

[0031] The holder portion 51 of the bracket 5 has an annular portion 51a that contacts the outer periphery of an outer ring 11b (described later) of the bearing 11, and a wall portion 51b that contacts an axial end face of the outer ring 11b. The holder portion 51 also has a hole 51h on the central axis Ax.

[0032] The fitting portion 52 has a protrusion that protrudes from the outer periphery of the flat plate portion 50 toward the stator core 30. The fitting portion 52 fits into the inner periphery of the peripheral wall portion 41 of the molded resin portion 40, thereby fixing the bracket 5 to the stator 3. Note that the fitting portion 52 is not limited to having a protrusion, and may have any shape that allows it to fit into the molded resin portion 40.

[0033] A circuit board 6 is disposed on the anti-load side of the bracket 5. In other words, the circuit board 6 is disposed on the opposite side of the rotor 2 in the axial direction across the bearing 11. The circuit board 6 has a front surface 61 as a first surface and a back surface 62 as a second surface, with the front surface 61 facing the bracket 5. A drive circuit 200 (see FIG. 7 ), such as an inverter that drives the electric motor 1, is mounted on the front surface 61 of the circuit board 6.

[0034] The circuit board 6 is fixed to the molded resin part 40 by a heat sink 7. The heat sink 7 is, for example, a disk-shaped member, and is provided so as to close the opening 42 of the molded resin part 40. The heat sink 7 is made of, for example, a metal such as aluminum.

[0035] The heat sink 7 has a plate-shaped portion 70 that closes the opening 42 of the molded resin portion 40, and a fitting portion 72 formed along the outer periphery of the plate-shaped portion 70. The fitting portion 72 engages with a stepped portion 45 formed on the end surface of the peripheral wall portion 41 of the molded resin portion 40 on the anti-load side. In addition, a board holding portion 71 that holds a circuit board 6 is formed on the surface of the plate-shaped portion 70 that faces the bracket 5.

[0036] 3 is a partially cutaway perspective view showing the bearing 11. The bearing 11 has an inner ring 11a fixed to the rotating shaft 10, an outer ring 11b fixed to the holder portion 51 of the bracket 5, and a plurality of rolling elements 11c provided between the inner ring 11a and the outer ring 11b. The inner ring 11a is also referred to as a first inner ring, and the outer ring 11b is also referred to as a first outer ring.

[0037] The rolling elements 11c are, for example, balls. The inner ring 11a, the outer ring 11b, and the rolling elements 11c are all made of metal. Shield plates 11d are provided on both axial sides of the inner ring 11a and the outer ring 11b.

[0038] 4 is a partially cutaway perspective view showing the inner ring 11a and outer ring 11b of the bearing 11. A raceway surface 11e that guides the rolling elements 11c is formed along the outer periphery of the inner ring 11a. A raceway surface 11f that guides the rolling elements 11c is formed along the inner periphery of the outer ring 11b.

[0039] Grease is applied between the raceway surfaces 11 e, 11 f and the rolling elements 11 c for lubrication. A retainer (not shown) is disposed between the inner ring 11 a and the outer ring 11 b to maintain a constant circumferential spacing between the rolling elements 11 c.

[0040] 3 and 4 show the inner ring 11a and outer ring 11b of the anti-load side bearing 11, but the inner ring 12a and outer ring 12b (FIG. 1) of the load side bearing 12 are similarly configured. The inner ring 12a is also referred to as the second inner ring, and the outer ring 12b is also referred to as the second outer ring.

[0041] 5 is an enlarged view of the bearing 11, bracket 5, and circuit board 6. A hole 51h is formed in the holder portion 51 of the bracket 5 in a portion facing the axial end face of the inner ring 11a and the axial end face of the rotating shaft 10. The axial end face of the inner ring 11a and the axial end face of the rotating shaft 10 face the circuit board 6 via the hole 51h.

[0042] The inner diameter Dh of the hole 51h is equal to or greater than the inner diameter Di of the inner ring 11a and is less than the outer diameter Do of the outer ring 11b. That is, Di≦Dh<Do holds.

[0043] By providing the hole 51h in the holder portion 51, the opposing area between the bracket 5 and the circuit board 6 is reduced, thereby reducing the electrostatic capacitance between the bracket 5 and the circuit board 6. Furthermore, the larger the inner diameter Dh of the hole 51h in the holder portion 51 of the bracket 5, the larger the opposing area between the end faces of the rotating shaft 10 and the inner ring 11a and the circuit board 6, and therefore the larger the electrostatic capacitance between the rotating shaft 10 and the inner ring 11a and the circuit board 6.

[0044] 6 is a schematic diagram illustrating the positional relationship between the stator 3, bracket 5, and circuit board 6 according to the first embodiment. The shortest distance between the bracket 5 and the coil 35 of the stator 3 is designated as Lc. Here, the shortest distance Lc is the shortest distance between the fitting portion 52 of the bracket 5 and the coil 35.

[0045] Furthermore, the shortest distance between the bracket 5 and the stator core 30 is defined as Ls. Here, the shortest distance Ls is the shortest distance between the fitting portion 52 of the bracket 5 and the stator core 30. In Fig. 6, the shortest distance Lc is shorter than the shortest distance Ls (i.e., Lc < Ls), but the shortest distance Lc may be equal to or greater than the shortest distance Ls.

[0046] The shortest distance between the bracket 5 and the circuit board 6 is defined as Lb. Here, the shortest distance Lb is the shortest distance between the holder portion 51 of the bracket 5 and the circuit board 6.

[0047] At least one of the shortest distances Lc and Ls is shorter than the shortest distance Lb. That is, at least one of Lc<Lb and Ls<Lb is satisfied. Therefore, the bracket 5 is disposed closer to the coil 35 or the stator core 30 of the stator 3 than the circuit board 6.

[0048] 7 is a block diagram showing a control system for the electric motor 1. A drive circuit 200 that controls the electric motor 1 has a rectifier circuit 202 that converts AC voltage supplied from a power supply 201, which is a commercial AC power supply, into DC voltage, an inverter 203 that converts the DC voltage output from the rectifier circuit 202 into AC voltage and supplies it to the electric motor 1, and an inverter drive circuit 204 that drives the inverter 203.

[0049] The drive circuit 200 also has a voltage detection unit 206 that detects the DC voltage output from the rectifier circuit 202, a rotational position detection unit 208 that detects the rotational position of the rotor 2, and a control unit 205 that calculates the optimal output voltage of the inverter 203 and outputs a PWM (Pulse Width Modulation) signal to the inverter drive circuit 204 based on the calculation result.

[0050] The rectifier circuit 202 receives an AC voltage from the power supply 201, rectifies and smoothes the AC voltage, and outputs a DC voltage to the first line L1 and the second line L2. This DC voltage is also called a bus voltage.

[0051] The input terminals of the inverter 203 are connected to the first line L1 and the second line L2. The switches of the inverter 203 are switched by an inverter drive circuit 204. The output terminals of the inverter 203 are connected to the coils 35U, 35V, and 35W of the stator 3 via U-phase, V-phase, and W-phase output lines F1, F2, and F3.

[0052] The inverter drive circuit 204 generates drive signals for turning on and off each switching element of the inverter 203 based on the PWM signal input from the control unit 205 , and outputs the drive signals to the inverter 203 .

[0053] The voltage detection unit 206 is connected by a voltage dividing circuit made up of two voltage dividing resistors provided between the lines L1 and L2, and detects the output voltage from the rectifier circuit 202.

[0054] The rotational position detection unit 208 detects the rotational position of the rotor 2 from the currents flowing through the output lines F1, F2, and F3. However, the present invention is not limited to this configuration, and the rotational position of the rotor 2 may be detected by a rotational position sensor such as a Hall effect element.

[0055] The control unit 205 calculates the optimal output voltage of the inverter 203 based on an operation instruction signal from a remote control or the like of the air conditioning device 100 and input signals from the voltage detection unit 206 and the rotational position detection unit 208, and outputs a PWM signal to the inverter drive circuit 204.

[0056] The drive circuit 200 is mounted on the circuit board 6. However, it is not necessary that all elements of the drive circuit 200 are mounted on the circuit board 6, and a part of the drive circuit 200 may be disposed outside the electric motor 1.

[0057] <Comparative Example> Before describing the operation of the first embodiment, an electric motor 1C of a comparative example will be described. Fig. 8 is a cross-sectional view showing the electric motor 1C of the comparative example. The electric motor 1C includes a rotating shaft 10, a rotor 2, a stator 3, a circuit board 6, a molded resin part 40, and bearings 11 and 12. The configurations of the rotating shaft 10, the stator 3, the circuit board 6, and the bearings 11 and 12 are the same as those of the first embodiment.

[0058] The molded resin part 40 has a peripheral wall part 41, an opening part 42, and a top plate part 43. A bracket 13 is attached to the peripheral wall part 41 of the molded resin part 40 so as to close the opening part 42. The bracket 13 has a holder part 131 that holds the bearing 11, a fitting part 132 that is attached to the molded resin part 40, and a flat plate part 130 that extends between them.

[0059] A heat sink 14 is attached to the surface of the bracket 13 on the anti-load side. The heat sink 14 is made of metal such as aluminum. The heat sink 14 has a plate-shaped portion 140 facing the bracket 13 and a peripheral wall portion 142 formed along the outer periphery of the plate-shaped portion 140.

[0060] A board support portion 141 for supporting the circuit board 6 is formed on the surface of the plate-shaped portion 140 of the heat sink 14. Heat dissipation fins 143 are formed on the back surface of the plate-shaped portion 140. The upper end of the peripheral wall portion 142 is fitted into a protrusion 133 provided on the surface of the bracket 13 on the anti-load side.

[0061] <Function> Next, a description will be given of the function of embodiment 1. In electric motor 1 ( FIG. 1 ) of embodiment 1, circuit board 6 is disposed on the opposite side of rotor 2 across bearing 11, and inner ring 11 a of bearing 11 contacts rotating shaft 10, while outer ring 11 b is fixed to molded resin part 40 via conductive bracket 5.

[0062] Furthermore, the outer rings 11b, 12b of the bearings 11, 12 are electrically insulated from each other by the molded resin portion 40. The outer ring 11b of the bearing 11 and the stator core 30 are electrically insulated from each other by the molded resin portion 40. The bracket 5 is conductive and is electrically insulated from the circuit board 6 and the stator core 30.

[0063] Because the circuit board 6 is disposed on the opposite side of the bearing 11 from the rotor 2, there is no need to provide holes in the circuit board 6 for inserting the rotating shaft 10 and the bearing 11, which reduces the number of processing steps for the circuit board 6. Furthermore, the area on the surface of the circuit board 6 where wiring patterns and circuit elements can be arranged is increased, which makes it possible to make the circuit board 6 smaller and improve material yield.

[0064] However, when the circuit board 6 is arranged in this manner, the bearing 11 on the anti-load side faces the circuit board 6. If the potential of the bearing 11 approaches the potential of the circuit board 6, electrolytic corrosion may occur. Below, the principles of electrolytic corrosion and a configuration for preventing electrolytic corrosion will be described.

[0065] When the rotating shaft 10 rotates, the inner ring 11a rotates together with the rotating shaft 10, and the rolling elements 11c also rotate. A thin film of grease is formed between the inner ring 11a and the rolling elements 11c, and between the outer ring 11b and the rolling elements 11c. The formation of this thin film of grease electrically insulates the inner ring 11a, the outer ring 11b, and the rolling elements 11c, and a potential difference occurs between the inner ring 11a and the outer ring 11b. When this potential difference exceeds the breakdown voltage of the thin film of grease, a discharge occurs between the inner ring 11a and the outer ring 11b.

[0066] The phenomenon in which the energy of the discharge causes unevenness on the raceway surfaces 11e, 11f (Figure 4) of the inner ring 11a and the outer ring 11b is called electrolytic corrosion. When unevenness occurs on the raceway surfaces 11e, 11f, vibrations and noise are generated when the rolling elements 11c run on the raceway surfaces 11e, 11f. The same can be said for the load-side bearing 12.

[0067] During operation of the electric motor 1, which is a synchronous motor, a high voltage and a low voltage are alternately applied to the coil 35 of the stator 3 by turning on and off the switching elements of the inverter 203 (FIG. 7) on the circuit board 6. The potential of the coil 35 differs for each phase, but on average, it can be considered to be the potential of the neutral point of the coil 35. Hereinafter, the neutral point potential of the coil 35 will be referred to as the potential of the coil 35.

[0068] Inside the electric motor 1, an electric field distribution is generated by the potential of the coil 35 and the potential of the circuit board 6. Among the components of the electric motor 1, conductive components that are electrically insulated from the coil 35 and the circuit board 6 are affected by the electric field distribution according to their arrangement within the electric motor 1, and have their own electric potentials.

[0069] For example, if the potential of the coil 35 changes between a potential equivalent to the bus voltage (i.e., bus potential) and ground potential, when the potential of the coil 35 is at the bus potential, the potential of the coil 35 in the electric motor 1 is the highest. The potential of the stator core 30 around which the coil 35 is wound is the second highest, and the potential of the rotor core 20 facing the stator core 30 is the third highest. The potential of the rotating shaft 10 is the fourth highest, and the potential of the circuit board 6 is the lowest.

[0070] On the other hand, when the potential of the coil 35 is at ground potential, the potential of the coil 35 is the lowest in the electric motor 1. The potential of the stator core 30 is the second lowest, and the potential of the rotor core 20 is the third lowest. The potential of the rotating shaft 10 is the fourth lowest, and the potential of the circuit board 6 is the highest.

[0071] In the electric motor 1C ( FIG. 8 ) of the comparative example, the inner rings 11 a and 12 a of the bearings 11 and 12 are in contact with the rotating shaft 10 and are therefore at the same potential as the rotating shaft 10. Of the outer rings 11 b and 12 b of the bearings 11 and 12, the outer ring 12 b is farther from the circuit board 6 and therefore the potential of the outer ring 12 b is more susceptible to the potential of the coil 35. On the other hand, the outer ring 11 b is closer to the circuit board 6 and therefore is more susceptible to the potential of the circuit board 6.

[0072] In particular, since the heat sink 14 is in contact with the bracket 13 , the potentials of the heat sink 14 and the bracket 13 approach the potential of the circuit board 6 , and the potential of the outer ring 11 b in contact with the bracket 13 also approaches the potential of the circuit board 6 .

[0073] Therefore, for example, if the potential of the coil 35 is at the bus potential, the potential of the outer ring 11b will also be low due to the influence of the potential of the circuit board 6, which has the lowest potential. As a result, the potential difference between the potential of the outer ring 11b and the inner ring 11a in contact with the rotating shaft 10 becomes large, making it easier for electrolytic corrosion to occur.

[0074] Furthermore, the bracket 13 of the comparative example does not have a hole like the hole 51h (FIG. 5) of the bracket 5 of the first embodiment, and therefore the contact area between the bracket 13 and the outer ring 11b is large. Therefore, when an electric potential is generated in the outer ring 11b, the amount of electric charge accumulated on the surfaces of the outer ring 11b, the bracket 13, and the heat sink 14 increases, and the discharge energy also increases. As a result, electrolytic corrosion is more likely to occur.

[0075] In contrast, in the electric motor 1 of the first embodiment, the bearing 11 is held by the conductive bracket 5, and the bracket 5 is fixed to the molded resin part 40. Because the bracket 5 is conductive, the bracket 5 and the outer ring 11b in contact with it have the same potential.

[0076] Furthermore, since the bracket 5 is attached to the stator 3, the potential of the bracket 5 and the outer ring 11b becomes closer to the potential of the coil 35 and the stator core 30. That is, the potential of the bracket 5 and the outer ring 11b becomes farther away from the potential of the circuit board 6 and closer to the potential of the coil 35 and the stator core 30.

[0077] Therefore, for example, if the potential of the coil 35 is at the bus potential, the potential of the bracket 5 and the outer ring 11b increases as they approach the potential of the coil 35 and the stator core 30. As the potential of the outer ring 11b increases, the potential difference with the inner ring 11a in contact with the rotating shaft 10 decreases.

[0078] In this way, electrolytic corrosion can be suppressed by reducing the potential difference (i.e., bearing voltage) between the inner ring 11a and the outer ring 11b of the bearing 11. As a result, vibration and noise can be reduced and the life of the electric motor 1 can be improved.

[0079] FIG. 9 is a graph showing the results of electric field analysis of the bearing voltages at the bearings 11 and 12 in the electric motor 1 shown in FIG. 1 when the bracket 5 is made of resin and when it is made of metal.

[0080] Whether bracket 5 is made of resin or metal, the bearing voltage of bearing 11 is greater than the bearing voltage of bearing 12. This is because, as described above, the distance from circuit board 6 to bearing 11 is short, while the distance from circuit board 6 to bearing 12 is long.

[0081] It can be seen from FIG. 9 that the bearing voltage of the bearing 11 can be made particularly small when the bracket 5 is made of metal (i.e., a conductor) compared to when the bracket 5 is made of resin (i.e., an insulator).

[0082] This is because the bracket 5 is conductive, so the potential of the outer ring 11b in contact with the bracket 5 approaches the potential of the coil 35 and the stator core 30, thereby reducing the potential difference with the inner ring 11a in contact with the rotating shaft 10.

[0083] 5, the hole 51h provided in the holder portion 51 reduces the opposing area between the bracket 5 and the circuit board 6, thereby reducing the electrostatic capacitance between the bracket 5 and the circuit board 6. Therefore, the potential difference between the bracket 5 and the circuit board 6 increases.

[0084] For example, if the potential of the coil 35 is at the bus potential, the greater the potential difference between the bracket 5 and the circuit board 6, the higher the potential of the bracket 5 and the outer ring 11b in contact with it. Therefore, the potential difference between the inner ring 11a and outer ring 11b of the bearing 11, i.e., the bearing voltage, can be reduced.

[0085] Furthermore, the larger the area of ​​the hole 51h in the holder portion 51 of the bracket 5, the larger the opposing area between the end faces of the rotating shaft 10 and the inner ring 11a and the circuit board 6. That is, the electrostatic capacitance between the rotating shaft 10 and the inner ring 11a and the circuit board 6 increases. As a result, the potential difference between the rotating shaft 10 and the inner ring 11a and the circuit board 6 decreases, and the potential difference between the inner ring 11a and the outer ring 11b can be further reduced.

[0086] 10 is a graph showing the results of electric field analysis of the bearing voltages in the bearings 11 and 12 when the inner diameter Dh (FIG. 5) of the hole 51h in the holder part 51 of the bracket 5 is changed. The horizontal axis represents the inner diameter (also referred to as the hole diameter) Dh of the hole 51h, and the vertical axis represents the bearing voltage.

[0087] 10, the bearing voltage of the bearing 11 decreases as the inner diameter Dh of the hole 51h of the holder part 51 increases. For example, when the inner diameter Dh of the hole 51h is equal to the inner diameter Di of the inner ring 11a of the bearing 11, the bearing voltage is 90% of the bearing voltage when the inner diameter Dh of the hole 51h is 0 (i.e., when the holder part 51 does not have a hole 51h).

[0088] Therefore, it can be understood that if the inner diameter Dh of the hole 51h is equal to or larger than the inner diameter Di of the inner ring 11a of the bearing 11 (i.e., if Di≦Dh holds), the bearing voltage reduction effect is particularly large.

[0089] If the inner diameter Dh of the hole 51h of the holder part 51 is made larger than the outer diameter of the outer ring 11b of the bearing 11, the holder part 51 will not be able to support the bearing 11 in the axial direction, and therefore the inner diameter Dh of the hole 51h is set to be less than the outer diameter Do of the outer ring 11b of the bearing 11. In other words, the inner diameter Dh of the hole 51h is set so that Di≦Dh<Do holds.

[0090] 6, at least one of the shortest distance Lc from the bracket 5 to the coil 35 and the shortest distance Ls from the bracket 5 to the stator core 30 is shorter than the shortest distance Lb from the bracket 5 to the circuit board 6. That is, at least one of Lc<Lb and Ls<Lb is established.

[0091] Because the bracket 5 is closer to the coil 35 or the stator core 30 than the circuit board 6, the potential of the bracket 5 and the outer ring 11b in contact with it can be made even closer to the potential of the coil 35 or the stator core 30. As a result, the potential difference between the outer ring 11b and the inner ring 11a can be further reduced.

[0092] <Effects of the embodiment> As described above, the electric motor 1 of the first embodiment includes the rotating shaft 10, the bearings 11 and 12, the rotor 2 attached to the rotating shaft 10 and positioned between the bearings 11 and 12 in the axial direction, the stator 3 having the stator core 30, the coil 35, and the molded resin portion 40, the circuit board 6 positioned on the opposite side of the rotor 2 in the axial direction with the bearing 11 in between, and the bracket 5 attached to the stator 3 and positioned between the stator core 30 and the circuit board 6 in the axial direction, in contact with the outer ring 11b of the bearing 11 to hold the bearing 11. The outer ring 11b and the outer ring 12b are electrically insulated from each other. The outer ring 11b and the stator core 30 are electrically insulated from each other. The bracket 5 is conductive and electrically insulated from the circuit board 6 and the stator core 30.

[0093] Because the bracket 5 is conductive in this way, the bracket 5 and the outer ring 11b of the bearing 11 are at the same potential. Furthermore, because the bracket 5 is attached to the stator 3, the potential of the outer ring 11b can be made closer to the potential of the coil 35 and the stator core 30, and the potential difference between the outer ring 11b and the inner ring 11a in contact with the rotating shaft 10, i.e., the bearing voltage, can be reduced. This makes it possible to suppress the occurrence of electrolytic corrosion, reduce vibration and noise, and improve the lifespan of the electric motor 1.

[0094] Furthermore, holder portion 51 that holds bearing 11 in bracket 5 has hole 51h at a position facing circuit board 6, and the inner diameter Dh of hole 51h is equal to or greater than the inner diameter Di of inner ring 11a and less than the outer diameter Do of outer ring 11b (i.e., Di≦Dh<Do holds), so the potential difference between bracket 5 and circuit board 6 is large and the potential difference between rotating shaft 10 and inner ring 11a and circuit board 6 is small. As a result, the bearing voltage in bearing 11 is further reduced, and the effect of suppressing electrolytic corrosion can be improved.

[0095] Furthermore, since at least one of the shortest distance Lc from bracket 5 to coil 35 and the shortest distance Ls from bracket 5 to stator core 30 is shorter than the shortest distance Lb from bracket 5 to circuit board 6 (i.e., at least one of Lc < Lb and Ls < Lb holds), the potential of bracket 5 can be brought even closer to the potential of coil 35 or stator core 30, further reducing the potential difference between outer ring 11b and inner ring 11a.

[0096] Furthermore, since the bracket 5 is formed from a metal casting or cutting part, the production cost of the electric motor 1 can be reduced while suppressing the occurrence of electrolytic corrosion.

[0097] 11(A) is a view of a bracket 5A and circuit board 6 of a modification of the first embodiment, viewed from the rotor 2 side. Similar to the bracket 5 of the first embodiment (FIG. 1), the bracket 5A has a holder portion 51 that holds the bearing 11, a fitting portion 52 that is fixed to the molded resin portion 40, and a flat portion 50 that serves as an extension portion extending between these.

[0098] The bracket 5A of the modified example has N holes 53 in the flat plate portion 50. N is an integer equal to or greater than 1. Here, N is 4, but it may be any number equal to or greater than 1. In the example shown in FIG. 11(A), N holes 53 are formed at intervals in the circumferential direction. The portion of the flat plate portion 50 of the bracket 5A excluding the N holes 53 constitutes a conductor portion 54.

[0099] In addition to the hole 53 in the flat plate portion 50, the bracket 5A has a hole 51h formed on the radially inner side of the holder portion 51. When viewed from the rotor 2 side, the surface 61 of the circuit board 6 can be seen through the hole 53 and the hole 51h in the bracket 5A.

[0100] 11A, the circuit board 6 has a planar shape in which one side of a rectangle is replaced with an arc. In other words, the circuit board 6 has three straight sides 63 and an arc-shaped side 64. However, the planar shape of the circuit board 6 is not limited to this shape and may be, for example, a circle.

[0101] In this modification, in a plane perpendicular to the axial direction, the total area of ​​the N holes 53 in the bracket 5A is larger than the total area of ​​the conductor portions 54. This makes it possible to reduce the opposing area between the bracket 5A and the circuit board 6.

[0102] The smaller the opposing area between the bracket 5A and the circuit board 6, the smaller the electrostatic capacitance between the bracket 5A and the circuit board 6. As a result, the potential difference between the bracket 5A and the circuit board 6 increases, and the potential of the bracket 5A moves away from the potential of the circuit board 6. This makes it possible to reduce the potential difference between the outer ring 11b in contact with the bracket 5A and the inner ring 11a in contact with the rotating shaft 10.

[0103] Also, as shown in Figure 11 (B), the total area of ​​the portions H1, H2, H3, and H4 of the hole 53 of the bracket 5A that face the circuit board 6 is defined as H, and the total area of ​​the portions J1, J2, J3, and J4 of the conductor portion 54 of the bracket 5A that face the circuit board 6 is defined as J.

[0104] If the total area H is larger than the total area J, it is possible to more effectively reduce the opposing area between the bracket 5A and the circuit board 6. In other words, it is possible to further reduce the potential difference between the outer ring 11b and the inner ring 11a.

[0105] 12 is a diagram showing another example of the configuration of the bracket 5A. The center of the circuit board 6 is disposed at a position displaced to one side (upper side in FIG. 12 ) with respect to the central axis Ax. In this case, the bracket 5A has a region R1 facing the circuit board 6 and a region R2 not facing the circuit board 6.

[0106] 12, the holes 53 of the flat plate portion 50 are concentrated in the region R1 facing the circuit board 6. In other words, the total area of ​​the holes 53 of the bracket 5A is larger in the region R1 facing the circuit board 6 than in the region R2 not facing the circuit board 6.

[0107] In region R2 where bracket 5A does not face circuit board 6, the presence or absence of hole 53 does not affect the capacitance between bracket 5A and circuit board 6. By increasing the area of ​​hole 53 in flat portion 50 in region R1 where bracket 5A faces circuit board 6, the capacitance between bracket 5A and circuit board 6 can be reduced, thereby achieving the effect of reducing the potential difference between inner ring 11a and outer ring 11b.

[0108] 13 is a cross-sectional view showing an electric motor 1A according to embodiment 2. In the electric motor 1A according to embodiment 2, the distance A1 between the bracket 5 and the rotor core 20 is shorter than the distance B1 between the holder portion 51 of the bracket 5 and the circuit board 6.

[0109] As described in the first embodiment, the rotor core 20 faces the stator core 30 via an air gap. The facing area between the rotor core 20 and the stator core 30 is large and the distance between them is short, so the potential of the rotor core 20 is close to the potential of the stator core 30 around which the coil 35 is wound.

[0110] In the second embodiment, the bracket 5 is disposed in a position close to the rotor core 20, so the potential of the bracket 5 and the outer ring 11b in contact with it is separated from the potential of the circuit board 6 and becomes closer to the potential of the coil 35 or the stator core 30. Therefore, the potential of the outer ring 11b of the bearing 11 becomes closer to the potential of the inner ring 11a in contact with the circuit board 6, and the bearing voltage in the bearing 11 can be reduced.

[0111] Except for the points described above, the electric motor 1A of the second embodiment is configured similarly to the electric motor 1 of the first embodiment.

[0112] As described above, in the electric motor 1A of embodiment 2, the distance A1 between the bracket 5 and the rotor core 20 is shorter than the distance B1 between the holder portion 51 of the bracket 5 and the circuit board 6, so that the potential of the outer ring 11b in contact with the bracket 5 can be made closer to the potential of the rotor core 20, thereby further reducing the bearing voltage in the bearing 11.

[0113] 14 is a cross-sectional view showing a portion of an electric motor 1B according to embodiment 3. In electric motor 1B according to embodiment 3, the value obtained by dividing the opposing area between bracket 5 and rotor core 20 by the distance from bracket 5 to rotor core 20 is greater than the value obtained by dividing the opposing area between bracket 5 and circuit board 6 by the distance from bracket 5 to circuit board 6.

[0114] Generally, the value obtained by dividing the opposing area of ​​two conductors by the distance between them corresponds to the capacitance formed between the two conductors. The larger the value obtained by dividing the opposing area of ​​two conductors by the distance between them, the smaller the potential difference between the two conductors.

[0115] The value obtained by dividing the opposing area between bracket 5 and rotor core 20 by the distance from bracket 5 to rotor core 20 corresponds to the capacitance between bracket 5 and rotor core 20. The value obtained by dividing the opposing area between bracket 5 and circuit board 6 by the distance from bracket 5 to circuit board 6 corresponds to the capacitance between bracket 5 and circuit board 6.

[0116] If the value obtained by dividing the opposing area between bracket 5 and rotor core 20 by the distance from bracket 5 to rotor core 20 is greater than the value obtained by dividing the opposing area between bracket 5 and circuit board 6 by the distance from bracket 5 to circuit board 6, then the capacitance between bracket 5 and rotor core 20 will be greater than the capacitance between bracket 5 and circuit board 6.

[0117] Therefore, the potential difference between the bracket 5 and the rotor core 20 becomes smaller than the potential difference between the bracket 5 and the circuit board 6. Therefore, the potential of the bracket 5 and the outer ring 11b in contact with it moves away from the potential of the circuit board 6 and approaches the potential of the coil 35 or the stator core 30. This makes it possible to reduce the voltage difference between the outer ring 11b and the inner ring 11a.

[0118] The distance between the bracket 5 and the rotor core 20 varies depending on their shapes. Therefore, in order to evaluate the capacitance more accurately, it is desirable to divide the bracket 5 and the rotor core 20 into regions according to the distance between them, calculate the value by dividing the facing area by the distance in each region, and add up the values.

[0119] 14, the fitting portion 52 of the bracket 5 and the rotor core 20 face each other at a distance A1, and the flat portion 50 of the bracket 5 and the rotor core 20 face each other at a distance A2. The distance A1 is shorter than the distance A2.

[0120] The facing area between the fitting portion 52 of the bracket 5 and the rotor core 20 is represented by the area S1 of the end face of the convex portion of the fitting portion 52. The facing area between the flat portion 50 of the bracket 5 and the rotor core 20 is represented by the area S2 of the portion of the surface of the flat portion 50 that faces the rotor core 20.

[0121] The sum of the area S1 divided by the distance A1 and the area S2 divided by the distance A2 (i.e., S1 / A1 + S2 / A2) corresponds to the capacitance between the bracket 5 and the rotor core 20.

[0122] Similarly, the end face of the holder portion 51 of the bracket 5 faces the circuit board 6 at a distance B1, and the flat plate portion 50 of the bracket 5 faces the circuit board 6 at a distance B2. The distance B1 is shorter than the distance B2.

[0123] The facing area between the fitting portion 52 of the bracket 5 and the circuit board 6 is represented by the area T1 of the end face of the holder portion 51. The facing area between the flat portion 50 of the bracket 5 and the circuit board 6 is represented by the area T2 of the portion of the surface of the flat portion 50 that faces the circuit board 6.

[0124] The sum of the area T1 divided by the distance B1 and the area T2 divided by the distance B2 (i.e., T1 / B1 + T2 / B2) corresponds to the capacitance between the bracket 5 and the circuit board 6.

[0125] If the value of S1 / A1+S2 / A2 is greater than the value of T1 / B1+T2 / B2, the potential difference between the bracket 5 and the rotor core 20 will be smaller than the potential difference between the bracket 5 and the circuit board 6. In other words, the potential of the bracket 5 and the outer ring 11b in contact with it will be separated from the potential of the circuit board 6 and will be closer to the potential of the coil 35 or the stator core 30. This allows the bearing voltage in the bearing 11 to be further reduced.

[0126] As long as the value of S1 / A1 + S2 / A2 is greater than the value of T1 / B1 + T2 / B2, it does not matter which of the distances A1 and B1 is longer, or which of the distances A2 and B2 is longer. In either case, the effect of reducing the bearing voltage at the bearing 11 can be obtained.

[0127] Here, the opposing surface between the bracket 5 and the rotor core 20 is divided into two regions, but the number of regions is selected depending on the shapes of the bracket 5 and the rotor core 20. Similarly, here, the opposing surface between the bracket 5 and the circuit board 6 is divided into two regions, but the number of regions is selected depending on the shapes of the bracket 5 and the circuit board 6.

[0128] Except for the points described above, the electric motor 1B of the third embodiment is configured similarly to the electric motor 1 of the first embodiment.

[0129] As described above, in the electric motor 1B of embodiment 3, the value obtained by dividing the opposing area between the bracket 5 and the rotor core 20 by the distance between them is greater than the value obtained by dividing the opposing area between the bracket 5 and the circuit board 6 by the distance between them, so that the potential difference between the bracket 5 and the rotor core 20 can be reduced, and the bearing voltage at the bearing 11 can be further reduced.

[0130] 15 is a cross-sectional view showing an electric motor 1C according to embodiment 4. The electric motor 1C according to embodiment 4 differs from the electric motors 1, 1A, and 1B according to embodiments 1 to 3 in that it has a bracket 8 formed from a metal plate.

[0131] The bracket 8 has a holder portion 81 that holds the bearing 11, a fitting portion 82 that is fixed to the molded resin portion 40, and a flat plate portion 80 that serves as an extension portion that extends between these. The bracket 8 is formed, for example, by processing a metal plate so as to have the holder portion 81, the fitting portion 82, and the flat plate portion 80.

[0132] The holder portion 81 has an annular portion 81a that contacts the outer peripheral surface of the outer ring 11b of the bearing 11, and a wall portion 81b that contacts the end face of the outer ring 11b. A hole as shown in Fig. 11(A) may be formed in the flat plate portion 80. The fitting portion 82 is a bent portion formed on the outer peripheral portion of the flat plate portion 80, and fits into the inner periphery of the peripheral wall portion 41 of the molded resin portion 40, thereby fixing the bracket 5 to the stator 3.

[0133] Because bracket 8 is made of a metal plate, it is thinner than bracket 5 ( FIG. 1 ) of embodiment 1. Therefore, even if the axial position of bearing 11 is the same as in embodiment 1, the distance B1 between bracket 8 and circuit board 6 can be increased. This increases the potential difference between bracket 8 and circuit board 6, allowing the bearing voltage at bearing 11 to be reduced.

[0134] 16 is a graph showing the results of electric field analysis of the bearing voltages generated in bearings 11 and 12 for the following cases: when a bracket made of resin is used; when bracket 5 (FIG. 1) of embodiment 1 made of a metal casting is used; and when bracket 8 (FIG. 15) of embodiment 3 made of a metal plate is used. The bracket made of resin has the same shape as bracket 5 (FIG. 1) of embodiment 1.

[0135] As shown in FIG. 16, when bracket 5 made of a metal casting is used and when bracket 8 made of a metal plate is used, the bearing voltage of bearing 11 is reduced compared to when a bracket made of resin is used.

[0136] Furthermore, when bracket 8 made of metal plate is used, the bearing voltage of bearing 11 is reduced compared to when bracket 5 made of metal casting is used. This is because, by forming bracket 8 from metal plate, it is thinner than bracket 5 made of metal casting (FIG. 1), and the distance B1 between bracket 8 and circuit board 6 is longer.

[0137] Except for the points described above, the electric motor 1C of the fourth embodiment is configured similarly to the electric motor 1 of the first embodiment.

[0138] As described above, in the electric motor 1C of embodiment 4, the bracket 8 is formed from a metal plate, so the distance B1 between the bracket 8 and the circuit board 6 can be increased, thereby reducing the potential difference between the bracket 8 and the rotor core 20 and enhancing the effect of reducing the bearing voltage in the bearing 11.

[0139] The features of the electric motors of the first to fourth embodiments and the modified examples can be combined as appropriate. For example, bracket 8 of the fourth embodiment (FIG. 15) may be used instead of bracket 5 of the electric motor of the second and third embodiments. Furthermore, hole 53 of the modified example of the first embodiment (FIG. 11A) may be applied to brackets 5 and 8 of the second, third, and fourth embodiments.

[0140] <Air Conditioning Apparatus> Next, an air conditioner to which the electric motors of the first to fourth embodiments and the modified examples can be applied will be described. Fig. 17(A) is a diagram showing the configuration of an air conditioner 100 to which the electric motor 1 of the first embodiment is applied. The air conditioner 100 comprises an outdoor unit 101 and an indoor unit 102. The outdoor unit 101 and the indoor unit 102 are connected by a refrigerant pipe 103.

[0141] The outdoor unit 101 includes a compressor 104, a condenser 105, and an outdoor blower 110. The outdoor blower 110 includes an impeller 111 and an electric motor 1 that drives the impeller 111. The electric motor 1 has the configuration described in the first embodiment.

[0142] The indoor unit 102 includes an evaporator 122 and an indoor blower 120. The indoor blower 120 has an impeller 121 and an electric motor 1M that drives the impeller 121.

[0143] 17(B) is a cross-sectional view of the outdoor unit 101. The electric motor 1 is supported by a motor support 107 arranged in a unit housing 106 of the outdoor unit 101. An impeller 111 is attached to the rotating shaft 10 of the electric motor 1 via a hub 112.

[0144] In the outdoor blower 110, an impeller 111 is rotated by the electric motor 1. During cooling operation of the air conditioner 100, the heat released when the refrigerant compressed by the compressor 104 condenses in the condenser 105 is released to the outside by the air blown by the outdoor blower 110.

[0145] In the indoor fan 120 (FIG. 17A), an impeller 121 is rotated by an electric motor 1M. During cooling operation of the air conditioner 100, the indoor fan 120 blows air from which heat has been removed when the refrigerant evaporates in the evaporator 122 into the room.

[0146] As described in the first embodiment, electrolytic corrosion is prevented from occurring in the bearings 11 and 12 of the electric motor 1, and therefore the outdoor blower 110 can be operated stably for a long period of time. As a result, the reliability of the air conditioning apparatus 100 can be improved.

[0147] Here, the electric motor 1 of the first embodiment is used as the drive source for the outdoor blower 110, but the electric motor of any of the second to fourth embodiments or the modified examples may also be used.

[0148] Moreover, the electric motors of the first to fourth embodiments and the modified examples may be used as the electric motor 1M of the indoor blower 120, or may be used in the outdoor blower 110 and the indoor blower 120.

[0149] <Pump> Next, a pump 300 to which the electric motors of the first to fourth embodiments and the modifications can be applied will be described. Fig. 18 is a diagram showing the main parts of a pump 300 to which the electric motor 1 of the first embodiment is applied.

[0150] The pump 300 includes an electric motor 1, an impeller 15 attached to a rotating shaft 10 of the electric motor 1, and a casing 301 surrounding these. The casing 301 includes a water passage 302, a suction port 303, a discharge port 304, and a fitting portion 305. The casing 301 is also referred to as a water supply portion.

[0151] The water passage 302 is a space formed inside the casing 301. A housing section for housing the impeller 15 is provided in a part of the water passage 302. The suction port 303 is an opening communicating with the water passage 302 and connected to the pipe 310. The discharge port 304 is an opening communicating with the water passage 302 and connected to the pipe 311.

[0152] The fitting portion 305 of the casing 301 is a recess formed adjacent to the water passage 302, and the electric motor 1 is attached to the fitting portion 305. The electric motor 1 is attached to the fitting portion 305 so that the tip of the rotating shaft 10 enters the water passage 302. The impeller 15 is attached to the tip of the rotating shaft 10.

[0153] When the motor 1 rotates, the impeller 15 rotates, and the liquid flowing from the pipe 310 flows into the water channel 302 from the suction port 303. The liquid flowing in the water channel 302 is pressurized by the rotation of the impeller 15. The pressurized liquid flows along the inner circumferential surface of the water channel 302 and flows out from the discharge port 304 into the other pipe 311.

[0154] As described in the first embodiment, electrolytic corrosion is prevented in the bearings 11 and 12 of the electric motor 1, so that the pump 300 can be operated stably for a long period of time, and the reliability of the pump 300 can be improved.

[0155] In the pump 300, the electric motor of any of the second to fourth embodiments or the modified examples may be used in place of the electric motor 1 of the first embodiment.

[0156] Although the preferred embodiments have been specifically described above, the present disclosure is not limited to the above-described embodiments, and various improvements and modifications can be made.

[0157] DESCRIPTION OF SYMBOLS 1, 1A, 1B, 1C Electric motor, 2 Rotor, 3 Stator, 5, 5A, 8 Bracket, 6 Circuit board, 7 Heat sink, 10 Rotating shaft, 11 Bearing (first bearing), 11a Inner ring (first inner ring), 11b Outer ring (first outer ring), 11c Rolling element, 12 Bearing (second bearing), 12a Inner ring (second inner ring), 12b Outer ring (second outer ring), 13 Bracket, 14 Heat sink, 15 Impeller, 20 Rotor core, 21 Magnet insertion hole, 23 Resin portion, 25 Permanent magnet, 30 Stator core, 35 Coil, 40 Molded resin portion, 41 Peripheral wall portion, 42 Opening, 50 Flat plate portion, 51 Holder portion, 51h hole, 52 fitting portion, 53 hole, 54 conductor portion, 71 substrate holding portion, 72 engagement portion, 80 flat plate portion, 81 holder portion, 82 fitting portion, 100 air conditioning apparatus, 101 outdoor unit, 102 indoor unit, 110 outdoor blower (blower), 111 impeller, 120 indoor blower (blower), 121 impeller, 200 drive circuit, 300 pump, 301 casing, 302 water channel, 310, 310 piping, 311 piping.

Claims

1. An electric motor comprising: a rotating shaft; a first bearing having a first inner ring and a first outer ring and supporting the rotating shaft; a second bearing having a second inner ring and a second outer ring and supporting the rotating shaft; a rotor located between the first bearing and the second bearing in the axial direction of the rotating shaft and attached to the rotating shaft, the rotor having a permanent magnet; a stator having a stator core surrounding the rotor, a coil wound around the stator core, and a molded resin part covering the stator core and the coil; a circuit board located on the opposite side of the rotor in the axial direction with the first bearing in between; and a bracket located between the stator core and the circuit board in the axial direction, holding the first bearing in contact with the first outer ring, and attached to the stator; wherein the first outer ring and the second outer ring are electrically insulated, the first outer ring and the stator core are electrically insulated, and the bracket is conductive and electrically insulated from the circuit board and the stator core.

2. The electric motor according to claim 1, wherein the bracket has a hole at a position facing the circuit board, and the axial end face of the rotating shaft and the axial end face of the first inner ring face the circuit board through the hole.

3. The electric motor according to claim 2, wherein the inner diameter of the hole in the bracket is equal to or larger than the inner diameter of the first inner ring and smaller than the outer diameter of the first outer ring.

4. An electric motor as claimed in any one of claims 1 to 3, wherein the bracket has a holder portion which holds the first outer ring, a fitting portion which is fixed to the stator, and an extension portion which extends between the holder portion and the fitting portion, and N holes are formed in the extension portion, and in a plane perpendicular to the axial direction, the total area of ​​the N holes in the bracket is greater than the total area of ​​the portion of the extension portion other than the N holes.

5. An electric motor as claimed in any one of claims 1 to 3, wherein the bracket has a holder portion which holds the first outer ring, a fitting portion which is fixed to the stator, and an extension portion which extends between the holder portion and the fitting portion, and N holes are formed in the extension portion, and in a plane perpendicular to the axial direction, the total area of ​​the portions of the N holes of the bracket which face the circuit board is greater than the total area of ​​the portions of the extension portion other than the N holes which face the circuit board.

6. The electric motor according to any one of claims 1 to 5, wherein at least one of the distance from the bracket to the stator core and the distance from the bracket to the coil is shorter than the distance from the bracket to the circuit board.

7. The electric motor according to any one of claims 1 to 6, wherein the rotor has a rotor core to which the permanent magnets are attached, and the distance from the bracket to the rotor core is shorter than the distance from the bracket to the circuit board.

8. An electric motor as claimed in any one of claims 1 to 7, wherein the rotor has a rotor core to which the permanent magnets are attached, and a value obtained by dividing the opposing area between the bracket and the rotor core by the distance from the bracket to the rotor core is greater than a value obtained by dividing the opposing area between the bracket and the circuit board by the distance from the bracket to the circuit board.

9. The electric motor according to any one of claims 1 to 8, wherein the bracket is formed by casting or cutting a metal.

10. The electric motor according to any one of claims 1 to 8, wherein the bracket is formed of a metal plate.

11. The electric motor according to any one of claims 1 to 10, further comprising a heat sink attached to said molded resin portion and supporting said circuit board.

12. The electric motor according to any one of claims 1 to 11, wherein the molded resin portion has a bearing holding portion that holds the second bearing.

13. A blower comprising an electric motor according to any one of claims 1 to 12 and an impeller attached to the rotating shaft of the electric motor.

14. An air-conditioning apparatus comprising an outdoor unit and an indoor unit, at least one of the outdoor unit and the indoor unit having a blower according to claim 13.

15. A pump comprising an electric motor according to any one of claims 1 to 12, an impeller attached to the rotating shaft of the electric motor, and a casing surrounding the electric motor and the impeller.

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