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 that supports the rotating shaft; a second bearing that has a second inner ring and a second outer ring and that supports the rotating shaft; a rotor that is positioned between the first bearing and the second bearing in an axial direction of the rotating shaft, that is attached to the rotating shaft, and that has a permanent magnet; a stator that has a stator core surrounding the rotor, a coil wound around the stator core, and a mold resin part covering the stator core and the coil; a circuit board that is disposed on the side opposite to that of the rotor such that the first bearing is held therebetween in the axial direction; and an insulating bracket that is disposed between the stator core and the circuit board in the axial direction, that holds the first bearing, and that is attached to the stator. The first outer ring and the second outer ring are electrically isolated from each other. The first outer ring and the stator core are electrically isolated from each other. At least the first outer ring of the first bearing has a non-facing part not facing the circuit board in the axial direction. The circuit board is not disposed on the outside of the non-facing part in the radial direction of the rotating shaft, in a plane orthogonal to the axial direction.

Description

Electric motors, fans, pumps and air conditioners

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

[0002] There is known an electric motor that includes a rotating shaft, a rotor attached to the rotating shaft, a stator surrounding the rotor, a pair of bearings that support the rotating shaft on both axial sides of the rotor, and a circuit board arranged to face one axial end face of the rotating shaft (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2008-245344 (see FIG. 1)

[0004] In the electric motor described above, the circuit board and one of the bearings face each other, so the potential of the outer ring of the bearing approaches the potential of the circuit board.The inner ring in contact with the rotating shaft has the same potential as the rotating shaft, so a potential difference is likely to occur between the outer and inner rings of the bearing.

[0005] When the potential difference becomes large, an electric discharge occurs between the inner and outer rings, causing unevenness on the raceway surface that comes into contact with the rolling elements. This phenomenon is called electrolytic corrosion. When electrolytic corrosion occurs, vibration and noise are generated when the rolling elements run along the raceway surface, and the life of the motor is shortened.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to suppress the occurrence of electrolytic corrosion.

[0007] 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 part covering the stator core and the coil, a circuit board located axially opposite the rotor across the first bearing, and an insulating bracket located axially between the stator core and the circuit board, holding the first bearing, and 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. At least the first outer ring of the first bearing has a non-facing portion that does not face the circuit board in the axial direction. The circuit board is not disposed radially outward of the non-opposing portion in a plane perpendicular to the axial direction.

[0008] According to the present disclosure, the first bearing has a non-facing portion that does not face the circuit board, and the circuit board is not located radially outward of the non-facing portion, thereby reducing the facing area between the first outer ring and the circuit board. This prevents the potential of the first outer ring from approaching the potential of the circuit board, thereby reducing the potential difference between the first outer ring and the first inner ring and suppressing the occurrence of electrolytic corrosion.

[0009] 1 is a longitudinal sectional view showing an electric motor of embodiment 1. FIG. 2 is a transverse sectional view showing an electric motor of embodiment 1. FIG. 3 is a partially cutaway perspective view showing a bearing of embodiment 1. FIG. 4 is a partially cutaway perspective view showing the outer ring and inner ring of the bearing of embodiment 1. FIG. 5 is an enlarged view of a first bearing, bracket, and circuit board of embodiment 1. FIG. 6 is a view showing the circuit board and first bearing of embodiment 1. FIG. 7 is a view for explaining the opposing areas between the circuit board and the first inner ring and the first outer ring of embodiment 1. FIG. 8 is a block diagram showing a control system in the electric motor of embodiment 1. FIG. 9 is a longitudinal sectional view (A) showing a part of an electric motor of comparative example 1, and a longitudinal sectional view (B) showing a part of an electric motor of comparative example 2. FIG. 10 is a view showing the circuit board and first bearing of an electric motor of comparative example 3. FIG. 11 is a graph (A) showing the relationship between the opposing area ratio and bearing voltage in each bearing of embodiment 1, and a graph (B) showing the relationship between the opposing area ratio and bearing voltage in each bearing of comparative example 1. FIG. 12 is a view showing the circuit board and first bearing of embodiment 2. FIG. 1A is a diagram showing a circuit board and a first bearing of a first modified example of embodiment 3, and FIG. 1B is a diagram showing a circuit board and a first bearing of a second modified example. FIG. 1A is a diagram showing a circuit board and a first bearing of embodiment 4, and FIG. 1B is a diagram showing two circuit boards. FIG. 1A is a diagram showing two circuit boards of embodiment 1, FIG. 1B is a diagram showing two circuit boards of embodiment 2, and FIG. 1C is a diagram showing two circuit boards of embodiment 4. FIG. 1A is a diagram showing an air conditioning apparatus to which the electric motors of each embodiment and modified example can be applied, and FIG. 1B is a diagram showing its outdoor unit. FIG. 1B is a diagram showing a pump to which the electric motors of each embodiment and modified example can be applied.

[0010] 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)).

[0011] 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.

[0012] 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." Furthermore, a cross-sectional view in a plane parallel to the axial direction will be referred to as a "longitudinal cross-sectional view," and a cross-sectional view in a plane perpendicular to the axial direction will be referred to as a "transverse cross-sectional view."

[0013] 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.

[0014] 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.

[0015] <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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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. 8). The coils 35 may be wound by either concentrated winding or distributed winding.

[0026] 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).

[0027] 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.

[0028] 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.

[0029] <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.

[0030] The bracket 5 is made of an insulating material, such as a resin, such as a bulk molding compound (BMC) made by mixing glass fiber and an unsaturated polyester resin.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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 S1 as a first surface and a back surface S2 as a second surface, with the front surface S1 facing the bracket 5. A drive circuit 200 (see FIG. 8 ), such as an inverter that drives the electric motor 1, is mounted on the front surface S1 of the circuit board 6.

[0035] 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.

[0036] 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.

[0037] Here, an example is shown in which the circuit board 6 is fixed to the molded resin part 40 via the heat sink 7, but the circuit board 6 may also be fixed to the molded resin part 40 via a member other than the heat sink 7, or may be fixed directly to the molded resin part 40.

[0038] <Configuration of bearings 11, 12> Figure 3 is a partially cutaway perspective view showing bearing 11. Bearing 11 has an inner ring 11a fixed to rotating shaft 10 (Figure 1), an outer ring 11b fixed to holder portion 51 (Figure 1) of bracket 5, and a plurality of rolling elements 11c provided between inner ring 11a and outer ring 11b. Inner ring 11a is also referred to as a first inner ring, and outer ring 11b is also referred to as a first outer ring.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] The inner ring 11a of the bearing 11 has an axial end face 111. The inner ring 11a also has a stepped surface 112 that abuts against the shield plate 11d (FIG. 3) at a position radially inward from the end face 111 and axially retracted.

[0043] The outer ring 11b of the bearing 11 has an axial end face 113. The outer ring 11b also has a stepped surface 114 that abuts against the shield plate 11d (FIG. 3) at a position radially inward from the end face 113 and axially retracted.

[0044] 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.

[0045] 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 end face of the inner ring 11a and the end face 10a of the rotating shaft 10. The axial end face 111 of the inner ring 11a and the axial end face 10a of the rotating shaft 10 face the circuit board 6 via the hole 51h.

[0046] The inner diameter Dh of the hole 51h is preferably equal to or greater than the inner diameter Di of the inner ring 11a and less than the outer diameter Do of the outer ring 11b. That is, it is preferable that Di≦Dh<Do be satisfied.

[0047] 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 face 10a of the rotating shaft 10 and the end face 111 of 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.

[0048] <Positional Relationship Between Circuit Board 6 and Bearing 11> The circuit board 6 does not face a part of the bearing 11 in the axial direction. That is, the bearing 11 has a non-facing portion N that does not face the circuit board 6 in the axial direction.

[0049] 6 is a view of the circuit board 6 and bearing 11 as viewed from the rear surface S2 side. The circuit board 6 has a first side 61, a second side 62, a third side 63, and a fourth side 64 in a plane perpendicular to the axial direction. The first side 61 extends linearly across the bearing 11 as viewed in the axial direction. Note that the first side 61 does not necessarily have to extend linearly (see FIG. 12 ).

[0050] The second side 62 faces the first side 61. The third side 63 and the fourth side 64 face each other and extend between the first side 61 and the second side 62. The second side 62 is curved, and the third side 63 and the fourth side 64 extend linearly and parallel to each other.

[0051] However, the second side 62, the third side 63, and the fourth side 64 are not limited to the shapes described here. For example, the second side 62 may extend in a straight line. Furthermore, the second side 62, the third side 63, and the fourth side 64 may extend in a continuous arc shape.

[0052] The direction in which the first side 61 and the second side 62 face each other is defined as direction A. The direction in which the third side 63 and the fourth side 64 face each other is defined as direction B. Direction A and direction B are perpendicular to each other. Here, the circuit board 6 is long in direction A. That is, the distance between the first side 61 and the second side 62 is longer than the distance between the third side 63 and the fourth side 64. However, the circuit board 6 is not limited to this shape, and may be long in direction B.

[0053] As described above, the bearing 11 has a region that does not face the circuit board 6 in the axial direction, i.e., the non-facing portion N. The non-facing portion N may include a part of the end surface 10a of the rotating shaft 10.

[0054] 6, the non-opposing portion N is indicated by diagonal hatching. The area of ​​the outer ring 11b at the non-opposing portion N is larger than the area of ​​the inner ring 11a at the non-opposing portion N, and is also larger than the area of ​​the rotating shaft 10 at the non-opposing portion N (0 in this example).

[0055] In a plane perpendicular to the central axis Ax, the circuit board 6 is not disposed in a region (indicated by arrow T) radially outward of the non-opposing portion N. In other words, in a plane perpendicular to the central axis Ax, the circuit board 6 is not disposed radially outward of a region R ( FIG. 5 ) that axially overlaps with the non-opposing portion N.

[0056] 7 is a diagram illustrating the opposing areas of the circuit board 6 and the inner ring 11a and outer ring 11b of the bearing 11. The area of ​​the non-opposing portions Na of the end face 111 and the step surface 112 (FIG. 4) of the inner ring 11a of the bearing 11 that do not oppose the circuit board 6 in the axial direction is defined as area Sa.

[0057] Furthermore, the area of ​​a non-facing portion Nb of the end face 113 and the step surface 114 (FIG. 4) of the outer ring 11b of the bearing 11 that does not face the circuit board 6 in the axial direction is defined as area Sb.

[0058] The area of ​​a non-facing portion Nc of the end face 10a of the rotating shaft 10 that does not face the circuit board 6 in the axial direction is defined as an area Sc. In the example of FIG.

[0059] The non-opposing portion Na of the inner ring 11a may be defined by only the end face 111 (FIG. 4) without including the stepped surface 112 (FIG. 4) of the inner ring 11a. Similarly, the non-opposing portion Nb of the outer ring 11b may be defined by only the end face 113 (FIG. 4) without including the stepped surface 114 (FIG. 4) of the outer ring 11b.

[0060] The area Sa of the non-opposing portion Na of the inner ring 11a of the bearing 11, the area Sb of the non-opposing portion Nb of the outer ring 11b, and the area Sc of the non-opposing portion Nc of the rotating shaft 10 satisfy Sa<Sb and Sc<Sb. In other words, of the areas Sa, Sb, and Sc, the area Sb is the largest. The areas Sa and Sc may be 0.

[0061] The proportion of the area Sa of the non-opposing portion Na to the area of ​​the end face 111 and the stepped surface 112 of the inner ring 11a of the bearing 11 is defined as the non-opposing area ratio Ra. Similarly, the proportion of the area Sb of the non-opposing portion Nb to the area of ​​the end face 113 and the stepped surface 114 of the outer ring 11b of the bearing 11 is defined as the non-opposing area ratio Rb. Furthermore, the proportion of the area Sc of the non-opposing portion Nc to the area of ​​the end face 10a of the rotating shaft 10 is defined as the non-opposing area ratio Rc. In the example of FIG. 6 , the non-opposing area ratio Rc is 0.

[0062] The non-facing area ratios Ra, Rb, and Rc satisfy the relationships Ra<Rb and Rc<Rb. In other words, among the non-facing area ratios Ra, Rb, and Rc, the non-facing area ratio Rb is the largest. The non-facing area ratios Ra and Rc may be 0.

[0063] <Control System> Fig. 8 is a block diagram showing the control system of 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.

[0064] 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 (controller) 205 that calculates an 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.

[0065] 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.

[0066] 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.

[0067] 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 .

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] <Comparative Examples> Before describing the operation of the first embodiment, electric motors 1F and 1G of comparative examples 1 and 2 will be described in order.

[0073] 9A is a longitudinal cross-sectional view showing an electric motor 1F of Comparative Example 1. The electric motor 1F includes a rotating shaft 10, a rotor 2, a stator 3, bearings 11 and 12, and a circuit board 6F. The stator 3 includes a stator core 30, an insulating portion 34, a coil 35, and a molded resin portion 40.

[0074] The molded resin part 40 has a peripheral wall part 41, an opening 46 on the load side, and a bottom part 47 on the anti-load side. A bracket 13 is attached to the molded resin part 40 so as to close the opening 46, and the bracket 13 holds the bearing 12. A bearing holding part 48 that holds the bearing 11 is formed on the bottom part 47 of the molded resin part 40.

[0075] The circuit board 6F is disposed on the anti-load side of the rotor 2, and is covered and held by the bottom portion 47 of the molded resin portion 40. The circuit board 6F faces the end face 10a of the rotating shaft 10 and the bearing 11 in the axial direction.

[0076] Fig. 9(B) is a longitudinal cross-sectional view showing an electric motor 1G of Comparative Example 2. The electric motor 1G differs from the electric motor 1F of Comparative Example 1 (Fig. 9(A)) in that a circuit board 6G is arranged so as to contact the outer ring 11b of the bearing 11. The contact between the circuit board 6G and the outer ring 11b of the bearing 11 allows heat generated in the bearing 11 to be dissipated via the circuit board 6G.

[0077] <Function> Next, a description will be given of the function of embodiment 1. In electric motor 1 of embodiment 1 shown in Fig. 1, circuit board 6 is disposed on the opposite side of bearing 11 from rotor 2, with bearing 11 sandwiched between inner ring 11a of bearing 11 and rotating shaft 10, and outer ring 11b is fixed to molded resin portion 40 via insulating bracket 5.

[0078] 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.

[0079] 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 S1 of the circuit board 6 where wiring patterns and circuit elements can be arranged is increased, which makes it possible to miniaturize the circuit board 6 and improve material yield.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] During operation of the synchronous motor 1, a high-voltage side voltage and a low-voltage side 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. 8) 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.

[0084] 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.

[0085] 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 outer ring 12b of the bearing 12 is the fourth highest, the potential of the rotating shaft 10 is the fifth highest, the potential of the outer ring 11b of the bearing 11 is the sixth highest, and the potential of the circuit board 6 is the lowest.

[0086] 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 outer ring 12b of the bearing 12 is the fourth lowest, the potential of the rotating shaft 10 is the fifth lowest, the potential of the outer ring 11b of the bearing 11 is the sixth lowest, and the potential of the circuit board 6 is the highest.

[0087] As described above, the inner rings 11a, 12a of the bearings 11, 12 are in contact with the rotating shaft 10 and are therefore at the same potential as the rotating shaft 10. Furthermore, of the outer rings 11b, 12b of the bearings 11, 12, the outer ring 12b is farther from the circuit board 6 and therefore the potential of the outer ring 12b is more susceptible to the potential of the coil 35. On the other hand, the outer ring 11b is closer to the circuit board 6 and therefore is more susceptible to the potential of the circuit board 6.

[0088] 9A, both the inner ring 11a and the outer ring 11b of the bearing 11 face the circuit board 6F, and the potential of the outer ring 11b, which is not in contact with the rotating shaft 10, approaches the potential of the circuit board 6F. As a result, the potential difference between the outer ring 11b and the inner ring 11a, which is in contact with the rotating shaft 10, increases, making electrolytic corrosion more likely to occur.

[0089] 9B, the outer ring 11b of the bearing 11 is in contact with the circuit board 6G, so the potential of the outer ring 11b and the potential of the circuit board 6G are the same. Therefore, the potential difference between the outer ring 11b and the inner ring 11a is more likely to be larger than in the electric motor 1F of the comparative example 1, making electrolytic corrosion more likely to occur.

[0090] In contrast, in the electric motor 1 of the first embodiment, as shown in Fig. 6, the bearing 11 has a non-facing portion N that does not face the circuit board 6 in the axial direction. A larger portion of the outer ring 11b is included in the non-facing portion N. Furthermore, the circuit board 6 is not disposed in a region radially outward of the non-facing portion N in a plane perpendicular to the axial direction.

[0091] Therefore, the opposing area between the outer ring 11b of the bearing 11 and the circuit board 6 is reduced, thereby reducing the electrostatic capacitance between them and separating the potential of the outer ring 11b of the bearing 11 from the potential of the circuit board 6.

[0092] For example, when the potential of the coil 35 is at the bus potential, the potential of the outer ring 11b of the bearing 11 increases as it moves away from the potential of the circuit board 6 (the lowest potential in the motor 1). 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.

[0093] Furthermore, when the potential of the coil 35 is at ground potential, the potential of the outer ring 11b of the bearing 11 decreases as it moves away from the potential of the circuit board 6 (the highest potential in the motor 1). As the potential of the outer ring 11b decreases, the potential difference with the inner ring 11a in contact with the rotating shaft 10 decreases.

[0094] In this way, the occurrence of 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.

[0095] Furthermore, as described above, the area Sa of the non-opposing portion Na of the inner ring 11a of the bearing 11, the area Sb of the non-opposing portion Nb of the outer ring 11b, and the area Sc of the non-opposing portion Nc of the rotating shaft 10 satisfy Sa < Sb and Sc < Sb, so it is possible to maximize the opposing area between the outer ring 11b and the circuit board 6 and minimize the opposing areas between the inner ring 11a and the rotating shaft 10 and the circuit board 6. This makes it possible to bring the potential of the inner ring 11a closer to the potential of the circuit board 6 and move the potential of the outer ring 11b away from the potential of the circuit board 6, further reducing the potential difference between the inner ring 11a and the outer ring 11b.

[0096] Furthermore, the non-facing area ratio Ra of the inner ring 11a of the bearing 11, the non-facing area ratio Rb of the outer ring 11b, and the non-facing area ratio Rc of the rotating shaft 10 satisfy Ra<Rb and Rc<Rb, so it is possible to more effectively bring the potential of the inner ring 11a closer to the potential of the circuit board 6 and move the potential of the outer ring 11b away from the potential of the circuit board 6. This makes it possible to further reduce the potential difference between the inner ring 11a and the outer ring 11b.

[0097] 10 is a view of the circuit board 6H and bearing 11 of Comparative Example 3 as viewed from the rear surface S2 side. The circuit board 6H of Comparative Example 3 has an opening 60 in a region facing the bearing 11 in the axial direction. Therefore, the inner ring 11a and outer ring 11b of the bearing 11 and the end face 10a of the rotating shaft 10 do not face the circuit board 6H in the axial direction.

[0098] That is, in Comparative Example 3 as well, the bearing 11 has a non-facing portion N that does not face the circuit board 6H in the axial direction.

[0099] However, in Comparative Example 3, the circuit board 6H is disposed radially outward of the non-opposing portion N in a plane perpendicular to the axial direction. That is, for example, the region of the circuit board 6H indicated by the dashed line Q faces the outer ring 11b of the bearing 11 in a direction inclined with respect to the axial direction. Therefore, it is difficult to obtain the effect of reducing the capacitance between the outer ring 11b of the bearing 11 and the circuit board 6H.

[0100] 11(A) is a graph showing the relationship between the facing area ratio between the outer ring 11b of bearing 11 and circuit board 6 and the bearing voltage of bearings 11 and 12 in embodiment 1. The facing area ratio of bearing 11 is the ratio (%) of the total area of ​​bearing 11 facing circuit board 6 in the axial direction to the total area of ​​the axial end faces of bearing 11 (i.e., end faces 111, 113 and step faces 112, 114 shown in FIG. 4). The facing area ratio of bearing 12 is defined in a similar manner. The facing area ratio is 100% when there is no non-facing portion N.

[0101] From FIG. 11A, it can be seen that in the first embodiment, the smaller the opposing area ratio is made, the lower the bearing voltages at the bearings 11 and 12 are, and the bearing voltage at the bearing 11 in particular is greatly reduced.

[0102] 11B is a graph showing the relationship between the opposing area ratio between the outer ring 11b of the bearing 11 and the circuit board 6H in Comparative Example 3 and the bearing voltage of the bearings 11 and 12. The opposing area ratio is defined as described above.

[0103] 11(B) shows that in Comparative Example 3, even if the opposing area ratio is reduced, the reduction in bearing voltage in the bearings 11 and 12 is slight. This is because the circuit board 6H is disposed radially outward of the non-opposing portion N of the bearing 11, making it difficult to obtain the effect of reducing the capacitance between the outer ring 11b of the bearing 11 and the circuit board 6H.

[0104] Effects of the Embodiment As described above, the electric motor 1 of the first embodiment includes the rotating shaft 10, 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 insulating bracket 5 attached to the stator 3 and positioned between the stator core 30 and the circuit board 6 in the axial direction, holding the bearing 11. At least the outer ring 11b of the bearing 11 has a non-facing portion N that does not face the circuit board 6 in the axial direction. The circuit board 6 is not positioned radially outward of the non-facing portion N in a plane perpendicular to the axial direction.

[0105] This configuration reduces the opposing area between the outer ring 11b of the bearing 11 and the circuit board 6, thereby reducing the electrostatic capacitance therebetween and separating the potential of the outer ring 11b of the bearing 11 from the potential of the circuit board 6. As a result, it is possible to reduce the potential difference (i.e., bearing voltage) between the outer ring 11b of the bearing 11 and the inner ring 11a in contact with the rotating shaft 10. In other words, it is possible to suppress the occurrence of electrolytic corrosion, reduce vibration and noise, and improve the lifespan of the electric motor 1.

[0106] Furthermore, since the area Sa of the non-opposing portion Na of the inner ring 11a of the bearing 11, the area Sb of the non-opposing portion Nb of the outer ring 11b, and the area Sc of the non-opposing portion Nc of the rotating shaft 10 satisfy Sa < Sb and Sc < Sb, the potential of the inner ring 11a is brought closer to the potential of the circuit board 6 and the potential of the outer ring 11b is moved away from the potential of the circuit board 6, thereby further reducing the potential difference between the inner ring 11a and the outer ring 11b.

[0107] Furthermore, since the non-facing area ratio Ra of the inner ring 11a of the bearing 11, the non-facing area ratio Rb of the outer ring 11b, and the non-facing area ratio Rc of the rotating shaft 10 satisfy Ra < Rb and Rc < Rb, the potential of the inner ring 11a can be more effectively brought closer to the potential of the circuit board 6 and the potential of the outer ring 11b can be more effectively moved away from the potential of the circuit board 6, thereby further reducing the potential difference between the inner ring 11a and the outer ring 11b.

[0108] Furthermore, since the circuit board 6 has a first edge 61 that extends across the bearing 11 when viewed in the axial direction, the circuit board 6 can be prevented from being positioned radially outside the non-opposing portion N of the bearing 11.

[0109] Furthermore, since the first side 61 of the circuit board 6 extends linearly, the configuration of the circuit board 6 can be simplified, and the manufacturing cost can be reduced.

[0110] 12 is a view of a circuit board 6A and a bearing 11 according to a second embodiment, viewed from the rear surface S2 side. In the electric motor according to the second embodiment, the shape of a first side 65 of the circuit board 6A differs from that of the first embodiment.

[0111] The first side 65 of the circuit board 6A has a straight portion 65a adjacent to the third side 63, a straight portion 65b adjacent to the fourth side 64, and an inclined portion 65c extending between the straight portion 65a and the straight portion 65b. The straight portion 65a is also referred to as a first portion, the straight portion 65b is also referred to as a second portion, and the inclined portion 65c is also referred to as a third portion.

[0112] The straight line portions 65a and 65b are located at different positions in the direction A and extend in the direction B, which is perpendicular to the direction A. The distance in the direction A from the central axis Ax to the straight line portion 65b is longer than the distance in the direction A from the central axis Ax to the straight line portion 65a. The inclined portion 65c extends between the straight line portions 65a and 65b and is inclined relative to them.

[0113] Of the first side 65, at least the straight portion 65a and the inclined portion 65c extend across the bearing 11 when viewed in the axial direction.

[0114] Here, the straight portion 65a and the straight portion 65b have the same length, and the inclined portion 65c is formed in the center of the first side 65. However, the first side 65 of the circuit board 6A is not limited to this shape, as long as at least the inclined portion 65c extends so as to cross the bearing 11 when viewed in the axial direction.

[0115] The bearing 11 has a non-facing portion N that does not face the circuit board 6A in the axial direction. The circuit board 6A is not disposed in a region (indicated by the symbol T in FIG. 12 ) radially outward from the non-facing portion N in a plane perpendicular to the axial direction. In the second embodiment, the relationships Sa<Sb, Sc<Sb, Ra<Rb, and Rc<Rb described in the first embodiment also hold true.

[0116] Except for the above-mentioned points, the circuit board 6A of the second embodiment is configured similarly to the circuit board 6 of the first embodiment.

[0117] As described above, in the second embodiment, the first side 65 of the circuit board 6A has the straight portion 65a and the straight portion 65b extending in the same direction, and the inclined portion 65c formed between them. This makes it possible to increase the area of ​​the non-facing portion N of the bearing 11, thereby reducing the bearing voltage in the bearing 11 and suppressing the occurrence of electrolytic corrosion.

[0118] 13 is a view of a circuit board 6B and a bearing 11 according to embodiment 3, viewed from the rear surface S2 side. In the electric motor according to embodiment 3, the shape of a first side 66 of the circuit board 6B differs from that of embodiment 1.

[0119] The first side 66 of the circuit board 6B has an inclined portion 66a adjacent to the third side 63, an inclined portion 66b adjacent to the fourth side 64, and a curved portion 66c extending between the inclined portions 66a and 66b. The inclined portion 66a is also referred to as a first portion, the inclined portion 66b is also referred to as a second portion, and the curved portion 66c is also referred to as a third portion.

[0120] The inclined portion 66a and the inclined portion 66b extend at an angle with respect to the direction A. It is desirable that the inclined portion 66a and the inclined portion 66b extend symmetrically with respect to a straight line in the direction A that passes through the central axis Ax.

[0121] The inclined portion 66a is inclined in the direction A so as to approach the central axis Ax as the distance in the direction B from the third side 63 increases. The inclined portion 66b is inclined in the direction A so as to approach the central axis Ax as the distance in the direction B from the fourth side 64 increases. Here, the inclined portion 66a and the inclined portion 66b both extend in the radial direction centered on the central axis Ax.

[0122] The curved portion 66c extends in a curved shape. More specifically, the curved portion 66c extends in an arc shape centered on the central axis Ax. The distance from the central axis Ax to the curved portion 66c is smaller than the outer diameter of the outer ring 11b of the bearing 11 and larger than the inner diameter of the inner ring 11a.

[0123] Therefore, the inclined portion 66a, the inclined portion 66b, and the curved portion 66c of the first side 66 extend across the bearing 11 when viewed in the axial direction. A portion of the circuit board 6B adjacent to the radially inner side of the curved portion 66c faces the inner ring 11a of the bearing 11 in the axial direction.

[0124] Here, the lengths of the inclined portion 66a and the inclined portion 66b are equal, and the curved portion 66c is formed in the center of the first side 66. However, the first side 66 of the circuit board 6B is not limited to this shape. It is sufficient that the portion of the first side 66 including the curved portion 66c extends across the bearing 11 when viewed in the axial direction.

[0125] Bearing 11 has a non-facing portion N that does not face circuit board 6B in the axial direction. Circuit board 6B is not disposed in a region (indicated by reference symbol T in FIG. 13 ) radially outward from non-facing portion N in a plane perpendicular to the axial direction. In embodiment 3 as well, the relationships Sa<Sb, Sc<Sb, Ra<Rb, and Rc<Rb described in embodiment 1 hold true.

[0126] In embodiment 3, since the first edge 66 of the circuit board 6B has an arc-shaped curved portion 66c, the proportion of the outer ring 11b in the non-opposing portion N can be increased and the proportion of the inner ring 11a in the non-opposing portion N can be decreased.

[0127] Except for the above-mentioned points, the circuit board 6B of the third embodiment is configured similarly to the circuit board 6 of the first embodiment.

[0128] As described above, in the third embodiment, the first side 66 of the circuit board 6B has the curved portion 66c, which increases the proportion of the outer ring 11b in the non-facing portion N and decreases the proportion of the inner ring 11a in the non-facing portion N. This further reduces the bearing voltage in the bearing 11 and suppresses the occurrence of electrolytic corrosion.

[0129] 14A is a view of a circuit board 6C and bearing 11 of a first modification of embodiment 3, viewed from the rear surface S2 side. In the electric motor of the first modification, the shape of a first side 67 of the circuit board 6C differs from that of embodiment 3.

[0130] The first side 67 of the circuit board 6C has a straight line portion 67a adjacent to the third side 63 and a straight line portion 67b adjacent to the fourth side 64. The straight line portion 67a and the straight line portion 67b are located at the same position in the direction A and both extend in the direction B. The straight line portion 67a is also referred to as a first portion, and the straight line portion 67b is also referred to as a second portion.

[0131] The first side 67 of the circuit board 6C also has an inclined portion 67c adjacent to the straight portion 67a, an inclined portion 67d adjacent to the straight portion 67b, and a curved portion 67e extending between the inclined portions 67c and 67d. The inclined portion 67c is also referred to as a third portion, the inclined portion 67d is also referred to as a fourth portion, and the curved portion 67e is also referred to as a fifth portion.

[0132] The inclined portion 67c and the inclined portion 67d extend at an angle with respect to the direction A. It is desirable that the inclined portion 67c and the inclined portion 67d extend symmetrically with respect to a straight line in the direction A that passes through the central axis Ax.

[0133] The inclined portion 67c is inclined in the direction A so as to approach the central axis Ax as the distance in the direction B from the third side 63 increases. The inclined portion 67d is inclined in the direction A so as to approach the central axis Ax as the distance in the direction B from the fourth side 64 increases. Here, the inclined portions 67c and 67d both extend in the radial direction centered on the central axis Ax.

[0134] The curved portion 67e extends in a curved shape. More specifically, the curved portion 67e extends in an arc shape centered on the central axis Ax. The distance from the central axis Ax to the curved portion 67e is smaller than the outer diameter of the outer ring 11b of the bearing 11 and larger than the inner diameter of the inner ring 11a.

[0135] Therefore, of the first side 67, the inclined portion 67c, the inclined portion 67d, and the curved portion 67e extend across the bearing 11 when viewed in the axial direction. A portion of the circuit board 6C adjacent to the radially inner side of the curved portion 67e faces the inner ring 11a of the bearing 11 in the axial direction.

[0136] Here, the straight portion 67a and the straight portion 67b are equal in length, the inclined portion 67c and the inclined portion 67d are equal in length, and the curved portion 67e is formed in the center of the first side 67. However, the first side 67 of the circuit board 6B is not limited to this example. It is sufficient that the portion of the first side 67 including the curved portion 67e extends so as to cross the bearing 11 when viewed in the axial direction.

[0137] Bearing 11 has a non-facing portion N that does not face circuit board 6C in the axial direction. Circuit board 6C is not disposed in a region radially outward of non-facing portion N in a plane perpendicular to the axial direction. In Modification 1 of Embodiment 3, the relationships Sa<Sb, Sc<Sb, Ra<Rb, and Rc<Rb described in Embodiment 1 also hold true.

[0138] Except for the points mentioned above, the circuit board 6C of the first modification of the third embodiment is configured similarly to the circuit board 6B of the third embodiment.

[0139] In the first modification of the third embodiment, the first side 67 of the circuit board 6C has the arc-shaped curved portion 67e, which increases the proportion of the outer ring 11b in the non-facing portion N and decreases the proportion of the inner ring 11a in the non-facing portion N. Furthermore, the first side 67 of the circuit board 6C has the straight portion 67a and the straight portion 67b extending in the B direction, which reduces the length in the A direction compared to the circuit board 6A of the third embodiment, allowing the circuit board 6A to be made smaller.

[0140] 14B is a view of a circuit board 6D and bearing 11 according to a second modification of embodiment 3, viewed from the rear surface S2 side. In the electric motor of the second modification, the shape of a first side 67 of the circuit board 6D differs from that of embodiment 3.

[0141] The first side 67 of the circuit board 6D has a straight portion 67a, a straight portion 67b, an inclined portion 67c, an inclined portion 67d, and a curved portion 67e, similar to the first side 67 of the circuit board 6C ( FIG. 14A ) of Modification 1. The lengths of the straight portion 67a and the straight portion 67b are longer than the lengths of the inclined portion 67c and the inclined portion 67d.

[0142] In circuit board 6D, the lengths of linear portions 67a and 67b of first side 67 are longer than those of circuit board 6C of modified example 1. That is, in circuit board 6D, the length of the portion of first side 67 extending in direction B is longer than that of circuit board 6C of modified example 1.

[0143] In circuit board 6D, the lengths of inclined portions 67c and 67d of first side 67 are shorter than those of circuit board 6C of Modification 1. Here, the boundary between straight portion 67a and inclined portion 67c is located at a position overlapping with the outer periphery of outer ring 11b of bearing 11 in the axial direction. Also, the boundary between straight portion 67b and inclined portion 67d is located at a position overlapping with the outer periphery of outer ring 11b of bearing 11 in the axial direction.

[0144] Except for the points mentioned above, the circuit board 6D of the second modification of the third embodiment is configured similarly to the circuit board 6C of the first modification of the third embodiment.

[0145] In the second modification of the third embodiment, the length of the straight line portions 67a and 67b extending in the B direction on the first side 67 of the circuit board 6D is long, so that the length of the circuit board 6D in the A direction can be further shortened, thereby making the circuit board 6D more compact.

[0146] 15A is a view of a circuit board 6E and a bearing 11 according to embodiment 4, viewed from the rear surface S2 side. In the circuit board 6E according to embodiment 4, the shape of the first side 68 differs from that of embodiment 1.

[0147] The first side 68 has a straight portion 68a adjacent to the third side 63, a straight portion 68b adjacent to the fourth side 64, and curved portions 68c and 68d extending between the straight portion 68a and the straight portion 68b. The straight portion 68a is also referred to as a first portion, the straight portion 68b is also referred to as a second portion, the curved portion 68c is also referred to as a third portion (or a first curved portion), and the curved portion 68d is also referred to as a fourth portion (or a second curved portion).

[0148] The linear portions 68a and 68b are located at different positions in the A direction and both extend in the B direction.

[0149] The curved portion 68c extends from the end of the straight portion 68a. The curved portion 68d extends from the end of the straight portion 68b. The curved portion 68c and the curved portion 68d have different curved shapes and are continuous at the center of the circuit board 6E in the B direction.

[0150] More specifically, the curved portion 68c extends in an arc shape centered on the central axis Ax. The curved portion 68d extends in an arc shape centered on the central axis C1 located outside the circuit board 6E. The central axis C1 is located on a straight line in the A direction passing through the central axis Ax.

[0151] The radius of curvature of curved portion 68c is smaller than the radius of outer ring 11b of bearing 11 and larger than the radius of inner ring 11a. The radius of curvature of curved portion 68d is equal to the radius of curvature of curved portion 68c. The circumferential lengths of curved portion 68c and curved portion 68d are equal to each other. The boundary between curved portion 68c and curved portion 68d is located midway between central axis Ax and central axis C1 in direction A.

[0152] The straight portion 68a, the curved portion 68c, and the curved portion 68d of the first side 68 extend across the bearing 11. A portion of the circuit board 6E adjacent to the radially inner side of the curved portion 68c faces the inner ring 11a of the bearing 11 in the axial direction.

[0153] Bearing 11 has a non-facing portion N that does not face circuit board 6E in the axial direction. Circuit board 6E is not disposed in a region radially outward of non-facing portion N in a plane perpendicular to the axial direction. In embodiment 4, the relationships Sa<Sb, Sc<Sb, Ra<Rb, and Rc<Rb described in embodiment 1 also hold true.

[0154] In embodiment 4, since the first edge 68 of the circuit board 6E has arc-shaped curved portions 66c, 66d, the proportion of the outer ring 11b in the non-opposing portion N can be increased and the proportion of the inner ring 11a in the non-opposing portion N can be decreased.

[0155] Except for the above-mentioned points, the circuit board 6E of the fourth embodiment is configured similarly to the circuit board 6 of the first embodiment.

[0156] 15(B) is a schematic diagram showing two circuit boards 6E combined together. When the circuit boards 6E are cut out from the base substrate, the two circuit boards 6E are cut out so that their first sides 68 face each other. The straight portion 68a, the straight portion 68b, the curved portion 68c, and the curved portion 68d of the first side 68 of one circuit board 6E face the straight portion 68b, the straight portion 68a, the curved portion 68d, and the curved portion 68c of the first side 68 of the other circuit board 6E.

[0157] Therefore, the amount of wasted material between the first sides 68 of the two circuit boards 6E can be minimized, which means that the material yield can be improved.

[0158] Fig. 16(A) is a schematic diagram showing two circuit boards 6 (Fig. 6) according to embodiment 1 combined together. Fig. 16(B) is a schematic diagram showing two circuit boards 6A (Fig. 12) according to embodiment 2 combined together. Fig. 16(C) is a schematic diagram showing two circuit boards 6E according to embodiment 4 combined together.

[0159] 16A, when the circuit boards 6 of the first embodiment are cut out from the base substrate, the two circuit boards 6 are cut out so that the linear first sides 61 of the two circuit boards 6 face each other. Since the generation of wasted material between the first sides 61 of the two circuit boards 6 is minimized, the material yield can be improved.

[0160] 16(B), when the circuit boards 6A of the second embodiment are cut out from the base substrate, the two circuit boards 6A are cut out so that their first sides 65 face each other. The straight portion 65a, straight portion 65b, and inclined portion 65c of one circuit board 6A face the straight portion 65b, straight portion 65a, and inclined portion 65c of the other circuit board 6A. Since the amount of wasted material between the first sides 61 of the two circuit boards 6A is minimized, the material yield can be improved.

[0161] 16(C), when the circuit boards 6E of the fourth embodiment are cut out from the base substrate, the two circuit boards 6E are cut out so that the two first sides 68 of the two circuit boards 6E face each other, as described with reference to FIG. 15(B). Since the generation of wasted material between the first sides 68 of the two circuit boards 6E is minimized, the material yield can be improved.

[0162] As described above, in the electric motor of embodiment 4, the first side 68 of the circuit board 6E has the curved portions 68c, 68d, so that the proportion of the outer ring 11b in the non-facing portion N can be increased and the proportion of the inner ring 11a in the non-facing portion N can be decreased. This further reduces the bearing voltage in the bearing 11 and suppresses the occurrence of electrolytic corrosion. In addition, the material yield of the circuit board 6E can be improved.

[0163] The features of the electric motors of the first to fourth embodiments and the first and second modifications can be combined as appropriate.

[0164] <Air Conditioning Apparatus> Next, a description will be given of an air conditioner to which the electric motors of Embodiments 1 to 4 and Modifications 1 and 2 can be applied. Fig. 17(A) is a diagram showing the configuration of an air conditioner 100 to which the electric motor 1 of Embodiment 1 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.

[0165] The outdoor unit 101 includes a compressor 104, a condenser 105 as an outdoor heat exchanger, and an outdoor blower 110 as a blower. The outdoor blower 110 includes an impeller 108 and an electric motor 1 that drives the impeller 108. The electric motor 1 has the configuration described in the first embodiment.

[0166] The indoor unit 102 includes an evaporator 122 as an indoor heat exchanger, and an indoor blower 120 as a blower. The indoor blower 120 includes an impeller 121 and an electric motor 1M that drives the impeller 121.

[0167] 17(B) is a cross-sectional view showing the outdoor unit 101. The electric motor 1 is supported by a motor support 107 arranged in a housing 106 of the outdoor unit 101. An impeller 108 is attached to the rotating shaft 10 of the electric motor 1 via a hub 109.

[0168] In the outdoor blower 110, an impeller 108 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.

[0169] 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.

[0170] 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.

[0171] 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 the second to fourth embodiments or the first and second modifications may also be used.

[0172] 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.

[0173] <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.

[0174] 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.

[0175] 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.

[0176] 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.

[0177] 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.

[0178] 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.

[0179] In the pump 300, the electric motor according to the second to fourth embodiments or the first and second modifications may be used in place of the electric motor 1 according to the first embodiment.

[0180] 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.

[0181] DESCRIPTION OF SYMBOLS 1, 1M Electric motor, 2 Rotor, 3 Stator, 5 Bracket, 6, 6A, 6B, 6C, 6D, 6E Circuit board, 7 Heat sink, 10 Rotating shaft, 10a End face, 11 Bearing (first bearing), 11a Inner ring (first inner ring), 11b Outer ring (first outer bearing), 12 Bearing (second bearing), 12a Inner ring (second inner ring), 12b Outer ring (second outer ring), 15 Impeller, 20 Rotor core, 23 Resin portion, 25 Permanent magnet, 30 Stator core, 35 Coil, 40 Molded resin portion, 61 First side, 62 Second side, 63 Third side, 64 Fourth side, 65 First side, 65a Straight portion, 65b Straight portion, 65c inclined portion, 66 first side, 66a inclined portion, 66b inclined portion, 66c curved portion, 67 first side, 67a straight portion, 67b straight portion, 67c inclined portion, 67d inclined portion, 67e curved portion, 68 first side, 68a straight portion, 68b straight portion, 68c curved portion (first curved portion), 68d curved portion (second curved portion), 100 air conditioning apparatus, 101 outdoor unit, 102 indoor unit, 110 outdoor blower, 120 indoor blower, 121 impeller, 300 pump, 301 casing, 302 water channel.

Claims

1. 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 an insulating bracket located between the stator core and the circuit board in the axial direction, holding the first bearing and attached to the stator; wherein the first outer ring and the second outer ring are electrically insulated, and the first outer ring and the stator core are electrically insulated, and at least the first outer ring of the first bearing has a non-facing part that does not face the circuit board in the axial direction, the circuit board is not disposed radially outward of the non-opposing portion in a plane perpendicular to the axial direction.

2. An electric motor as set forth in claim 1, wherein an area Sa of a portion of the end face of the first inner ring facing the circuit board that does not face the circuit board in the axial direction, an area Sb of a portion of the end face of the first outer ring facing the circuit board in the axial direction that does not face the circuit board, and an area Sc of a portion of the end face of the rotating shaft facing the circuit board that does not face the circuit board in the axial direction satisfy Sa<Sb and Sc<Sb.

3. An electric motor as set forth in claim 1 or 2, wherein the ratio Ra of the area Sa of the end face of the first inner ring facing the circuit board that does not face the circuit board in the axial direction, the ratio Rb of the area Sb of the end face of the first outer ring facing the circuit board that does not face the circuit board in the axial direction, and the ratio Rc of the area Sc of the end face of the rotating shaft facing the circuit board that does not face the circuit board in the axial direction satisfy Ra<Rb and Rc<Rb.

4. The electric motor according to any one of claims 1 to 3, wherein the circuit board has a first side that passes through a region facing the first bearing in the axial direction.

5. The electric motor according to claim 4, wherein the first side extends linearly.

6. The electric motor according to claim 4, wherein the first side has two or more portions that extend linearly in different directions.

7. An electric motor as set forth in claim 6, wherein the first side has a first portion and a second portion extending in the same direction, and a third portion formed between the first portion and the second portion and extending in a direction inclined relative to the first portion and the second portion, and at least the third portion faces the first bearing in the axial direction.

8. The electric motor according to claim 4, wherein the first side has a curved portion at a position facing the first bearing in the axial direction.

9. The electric motor according to claim 8, wherein the curved portion extends in an arc shape, and a portion of the circuit board adjacent to the inside of the curved portion in the radial direction faces the first inner ring in the axial direction.

10. An electric motor as set forth in claim 4, wherein the first side has a first curved portion and a second curved portion formed continuously, and the first curved portion and the second curved portion face the first bearing in the axial direction.

11. An electric motor according to claim 10, wherein the first curved portion extends in an arc shape, and a portion of the circuit board adjacent to the inside of the first curved portion in the radial direction faces the first inner ring in the axial direction.

12. A blower comprising an electric motor according to any one of claims 1 to 11 and an impeller attached to the rotating shaft of the electric motor.

13. An air conditioning apparatus comprising an outdoor unit and an indoor unit, wherein at least one of the outdoor unit and the indoor unit has the blower according to claim 12.

14. A pump comprising: an electric motor according to any one of claims 1 to 11; an impeller attached to the rotating shaft of the electric motor; and a casing that houses the electric motor and the impeller and has a water passage.

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