Electric motor, fan, and air conditioner

Abstract

An electric motor (1) comprises: a first rolling bearing (41) that has a first inner ring (41A) and a first outer ring (41B); a second rolling bearing that has a second inner ring and a second outer ring; a shaft (22) rotatably supported by the first and second rolling bearings (41, 42); a rotor core (21) fixed to the shaft (22); a stator core (31); and a drive circuit board (5). The drive circuit board (5) is disposed on a side opposite to the rotor core (21) across the first roller bearing (41). The first and second outer rings (41B, 42B) are electrically insulated from each other. The first outer ring (41B) and the stator core (31) are electrically insulated from each other. The shortest distance (a1) from the first outer ring (41B) to the rotor core (21) is shorter than the shortest distance (b1) from the first outer ring (41B) to the drive circuit board (5).

Description

Electric motors, fans, and air conditioners

[0001] The present disclosure relates to an electric motor, a fan, and an air conditioner.

[0002] An electric motor has been proposed in which a drive circuit is arranged outside a bearing in the axial direction (see, for example, Patent Document 1).

[0003] JP 2008-245344 A

[0004] Generally, due to the distribution of the electric field inside the motor while the motor is running, each component of the motor has a potential, and a potential difference occurs between the components. If the potential difference between the outer ring and shaft of each bearing is large, electrolytic corrosion is likely to occur due to the potential difference between the inner ring and outer ring, resulting in problems such as vibration and noise in the motor.

[0005] An object of the present disclosure is to reduce the potential difference between the inner ring and the outer ring and reduce electrolytic corrosion in the rolling bearing.

[0006] An electric motor according to one aspect of the present disclosure comprises: a first rolling bearing having a first inner ring and a first outer ring; a second rolling bearing having a second inner ring and a second outer ring; a shaft rotatably supported by the first rolling bearing and the second rolling bearing; a rotor core fixed to the shaft; a stator core arranged outside the rotor core; and a drive circuit board arranged on the opposite side of the first rolling bearing from the rotor core; wherein the first outer ring and the second outer ring are electrically insulated from each other; the first outer ring and the stator core are electrically insulated from each other; and the shortest distance from the first outer ring to the rotor core is shorter than the shortest distance from the first outer ring to the drive circuit board. An electric motor according to another aspect of the present disclosure comprises: a first rolling bearing having a first inner ring and a first outer ring, a second rolling bearing having a second inner ring and a second outer ring, a shaft rotatably supported by the first rolling bearing and the second rolling bearing, a rotor core fixed to the shaft, a stator core arranged outside the rotor core, and a drive circuit board arranged on the opposite side of the first rolling bearing from the rotor core, wherein the first outer ring and the second outer ring are electrically insulated from each other, the first outer ring and the stator core are electrically insulated from each other, and the shortest distance from the first outer ring to the rotor core is shorter than the shortest distance from the second outer ring to the rotor core.A fan according to another aspect of the present disclosure comprises: blades; and the electric motor that rotates the blades. An air conditioner according to another aspect of the present disclosure comprises an indoor unit and an outdoor unit connected to the indoor unit, wherein each of the indoor unit, the outdoor unit, or the indoor unit and the outdoor unit has the electric motor.

[0007] According to the present disclosure, the potential difference between the inner ring and the outer ring can be reduced, and electrolytic corrosion in the rolling bearing can be reduced.

[0008] 1 is a cross-sectional view schematically showing an electric motor according to a first embodiment; FIG. 2 is a perspective view schematically showing the cross-sectional structure of a first rolling bearing; FIG. 3 is a perspective view schematically showing the cross-sectional structure of a second rolling bearing; FIG. 4 is a diagram schematically showing the configuration of a control system in an electric motor; FIG. 5 is an enlarged view showing the periphery of the first rolling bearing shown in FIG. 1; FIG. 6 is a graph showing the potential from the stator coil to the drive circuit board; FIG. 7 is a graph showing the potentials of several components in an electric motor; FIG. 8 is a graph showing the bearing voltages at each rolling bearing; FIG. 9 is an enlarged view showing the periphery of the first rolling bearing of an electric motor according to a first modification of the first embodiment; FIG. 10 is an enlarged view showing the periphery of the first rolling bearing of an electric motor according to a second modification of the first embodiment; FIG. 11 is a cross-sectional view schematically showing the structure of an electric motor according to a second modification of the first embodiment; FIG. 12 is a cross-sectional view schematically showing the structure of an electric motor according to a first modification of the second embodiment; Fig. 10 is a cross-sectional view schematically showing the structure of an electric motor according to embodiment 3. Fig. 11 is a cross-sectional view schematically showing the structure of an electric motor according to a modified example of embodiment 3. Fig. 12 is a diagram schematically showing a fan according to embodiment 4. Fig. 13 is a diagram schematically showing the configuration of an air conditioner according to embodiment 5.

[0009] First Embodiment An electric motor 1 according to a first embodiment will be described below. In the xyz Cartesian coordinate system shown in each drawing, the z-axis direction (z-axis) indicates a direction parallel to the axis Ax of the electric motor 1, the x-axis direction (x-axis) indicates a direction perpendicular to the z-axis direction, and the y-axis direction (y-axis) indicates a direction perpendicular to both the z-axis direction and the x-axis direction. The axis Ax is the center of rotation of the rotor 2, i.e., the rotation axis of the rotor 2. The direction parallel to the axis Ax is also referred to as the "axial direction of the rotor 2" or simply as the "axial direction." The radial direction is the radial direction of the rotor 2, the stator 3, or the stator core 31, and is a direction perpendicular to the axis Ax. The xy plane is a plane perpendicular to the axial direction. The circumferential direction of the rotor 2, the stator 3, or the stator core 31 is also simply referred to as the "circumferential direction."

[0010] 1 is a cross-sectional view that schematically shows an electric motor 1 according to embodiment 1. The electric motor 1 has a rotor 2, a stator 3, a first rolling bearing 41, a second rolling bearing 42, and a drive circuit board 5. The electric motor 1 is, for example, a synchronous motor.

[0011] As shown in FIG. 1 , the electric motor 1 may further include a resin frame 6 and a resin bracket 7 .

[0012] <Rotor 2> The rotor 2 has a rotor core 21, a shaft 22, an insulating member 23, and at least one permanent magnet (not shown). Each permanent magnet forms a magnetic pole of the rotor 2 and is provided inside the rotor core 21 or on the outer circumferential surface of the rotor core 21. The rotor core 21 is made of, for example, a plurality of electromagnetic steel plates.

[0013] The rotor core 21 is fixed to the shaft 22. The rotor core 21 is located between a first rolling bearing 41 and a second rolling bearing 42. The shaft 22 is rotatably supported by the first rolling bearing 41 and the second rolling bearing 42.

[0014] The insulating member 23 is disposed between the shaft 22 and the rotor core 21. Therefore, the shaft 22 and the rotor core 21 are electrically insulated from each other by the insulating member 23. The insulating member 23 is, for example, an insulating resin. In the example shown in Fig. 1, the rotor 2 has the insulating member 23, but it is not necessarily required to have the insulating member 23.

[0015] <Stator 3> The stator 3 has a stator core 31 and a coil 32. The stator 3 (specifically, the stator core 31) is disposed outside the rotor core 21. The coil 32 is attached to, for example, an insulator provided on the stator core 31.

[0016] <Rolling bearings 41, 42> Fig. 2A is a perspective view that schematically shows the cross-sectional structure of the first rolling bearing 41. Fig. 2B is a perspective view that schematically shows the cross-sectional structure of the second rolling bearing 42. The inner ring 41A of the first rolling bearing 41 is also referred to as the "first inner ring 41A," and the outer ring 41B of the first rolling bearing 41 is also referred to as the "first outer ring 41B." The inner ring 42A of the second rolling bearing 42 is also referred to as the "second inner ring 42A," and the outer ring 42B of the second rolling bearing 42 is also referred to as the "second outer ring 42B."

[0017] The first rolling bearing 41 has a first inner ring 41A, a first outer ring 41B, and a plurality of balls 41C. The first inner ring 41A is fixed to the shaft 22. The first outer ring 41B is supported by the resin bracket 7. The plurality of balls 41C are disposed between the first inner ring 41A and the first outer ring 41B.

[0018] Each ball 41C is rotatable between the outer peripheral surface of the first inner ring 41A and the inner peripheral surface of the first outer ring 41B. The first inner ring 41A is rotatable together with the shaft 22. In order to arrange the multiple balls 41C at equal intervals, a cage may be disposed between adjacent balls 41C. A lubricant is applied to the surface of each ball 41C. The lubricant is, for example, grease.

[0019] The second rolling bearing 42 has a second inner ring 42A, a second outer ring 42B, and a plurality of balls 42C. The second inner ring 42A is fixed to the shaft 22. The second outer ring 42B is supported by the resin frame 6. The plurality of balls 42C are disposed between the first inner ring 41A and the first outer ring 41B.

[0020] Each ball 42C is rotatable between the outer circumferential surface of the second inner ring 42A and the inner circumferential surface of the second outer ring 42B. The second inner ring 42A is rotatable together with the shaft 22. To arrange the multiple balls 42C at equal intervals, a cage may be disposed between adjacent balls 42C. A lubricant is applied to the surface of each ball 42C. The lubricant is, for example, grease.

[0021] When the first inner ring 41A and the second inner ring 42A rotate together with the shaft 22, the balls 41C and 42C rotate. As the balls 41C rotate, a thin film of lubricant is formed between the balls 41C and the first inner ring 41A, and a thin film of lubricant is formed between the balls 41C and the first outer ring 41B. As a result, the balls 41C and the first inner ring 41A are electrically insulated from each other, and the balls 41C and the first outer ring 41B are electrically insulated from each other. This generates a potential difference between the first inner ring 41A and the first outer ring 41B.

[0022] When the first inner ring 41A and the second inner ring 42A rotate together with the shaft 22, the balls 41C and the balls 42C rotate. As the balls 42C rotate, a thin film of lubricant is formed between each ball 42C and the second inner ring 42A, and a thin film of lubricant is formed between each ball 42C and the second outer ring 42B. As a result, the balls 42C and the second inner ring 42A are electrically insulated from each other, and the balls 42C and the second outer ring 42B are electrically insulated from each other. This generates a potential difference between the second inner ring 42A and the second outer ring 42B.

[0023] <Drive circuit board 5> Figure 3 is a diagram that schematically shows the configuration of the control system in the electric motor 1. The inverter main circuit 51 is provided on the drive circuit board 5. The inverter main circuit 51 is electrically connected to the coil 32. As shown in Figure 1, the drive circuit board 5 is arranged on the opposite side of the rotor core 21 with respect to the first rolling bearing 41. That is, in the example shown in Figure 1, the first rolling bearing 41 is arranged between the rotor core 21 and the drive circuit board 5.

[0024] <Resin Frame 6> The resin frame 6 supports the stator 3 and the second rolling bearing 42. The resin frame 6 is made of, for example, bulk molding compound (BMC).

[0025] <Resin Bracket 7> The resin bracket 7 covers the drive circuit board 5 and supports the first rolling bearing 41. The resin bracket 7 is made of, for example, bulk molding compound (BMC).

[0026] The first outer ring 41B and the second outer ring 42B are electrically insulated from each other. For example, the resin frame 6 is made of an insulating material, and the resin bracket 7 is also made of an insulating material. Either the resin frame 6 or the resin bracket 7 may be made of an insulating material. This allows the first outer ring 41B and the second outer ring 42B to be electrically insulated from each other.

[0027] The first outer ring 41B and the stator core 31 are electrically insulated from each other. The second outer ring 42B and the stator core 31 are electrically insulated from each other.

[0028] Fig. 4 is an enlarged view showing the periphery of the first rolling bearing 41 shown in Fig. 1. In the example shown in Fig. 4, the shortest distance a1 from the first outer ring 41B to the rotor core 21 is shorter than the shortest distance b1 from the first outer ring 41B to the drive circuit board 5.

[0029] <Electric Potential in Electric Motor 1> In the electric motor 1, the resin bracket 7 is made of an insulating material. In this case, the first outer ring 41B is not electrically connected to the stator core 31. Therefore, a potential difference occurring inside the electric motor 1 generates a potential difference between the shaft 22 and the first outer ring 41B. As a result, a potential difference occurs between the first inner ring 41A, which is electrically connected to the shaft 22, and the first outer ring 41B.

[0030] Fig. 5 is a graph showing the potential from the coil 32 of the stator 3 to the drive circuit board 5. In the electric motor 1 shown in Fig. 1, the potential is highest at the coil 32 and lowest at the low-voltage line provided on the drive circuit board 5. Therefore, in Fig. 5, the potential of the coil 32 (also referred to as the coil potential) is shown as 1.0, and the potential of the drive circuit board 5 (also referred to as the board potential) is shown as 0.

[0031] 5, the potential of the rotor core 21 is close to the coil potential, so the rotor core 21 has a high potential, and the first outer ring 41B, which is closer to the drive circuit board 5, has the lowest potential. The second outer ring 42B is closer to the coil 32 than the drive circuit board 5, so it has a higher potential than the shaft 22 and the first outer ring 41B. The potentials of the first inner ring 41A, the shaft 22, and the second outer ring 42B are at a potential between the potentials of the first outer ring 41B and the second outer ring 42B. Therefore, as shown in FIG. 5, the potential of each component of the electric motor 1 depends on the shortest distance a1 and the shortest distance b1.

[0032] In the first rolling bearing 41, the potential difference between the first inner ring 41A and the first outer ring 41B is referred to as the "bearing voltage" or the "first bearing voltage." In the second rolling bearing 42, the potential difference between the second inner ring 42A and the second outer ring 42B is referred to as the "bearing voltage" or the "second bearing voltage."

[0033] FIG. 6 is a graph showing the potentials of several components in the electric motor 1. FIG. 7 is a graph showing the bearing voltages in each rolling bearing. As shown in FIGS. 6 and 7 , the potentials of each component in the electric motor 1 depend on the shortest distance a1 and the shortest distance b1. As shown in FIG. 6 , the smaller the shortest distance a1 is relative to the shortest distance b1, the closer the potentials of the first outer ring 41B, the second outer ring 42B, and the shaft 22 become to the coil potential. This reduces the potential difference between the inner ring and the outer ring in each rolling bearing, thereby reducing the bearing voltage in each rolling bearing. As shown in FIG. 7 , in this embodiment, the bearing voltage in the first rolling bearing 41 in particular is reduced.

[0034] In this embodiment, the shortest distance a1 from the first outer ring 41B to the rotor core 21 is shorter than the shortest distance b1 from the first outer ring 41B to the drive circuit board 5. Therefore, the potential difference between the first inner ring 41A and the first outer ring 41B can be reduced, and electrolytic corrosion due to discharge inside the first rolling bearing 41 can be reduced. Furthermore, the potential difference between the second inner ring 42A and the second outer ring 42B can be reduced, and electrolytic corrosion due to discharge inside the second rolling bearing 42 can be reduced. As a result, the life of the electric motor 1 can be improved.

[0035] <First Modification of First Embodiment> Figure 8 is an enlarged view showing the periphery of the first rolling bearing 41 of the electric motor 1 according to the first modification of the first embodiment. In the example shown in Figure 8, the shortest distance a2 from the outer peripheral surface of the first outer ring 41B to the inner peripheral surface of the rotor core 21 is shorter than the shortest distance b1 from the first outer ring 41B to the drive circuit board 5. For example, in the electric motor 1 shown in Figure 8, the inner diameter of the rotor core 21 is larger than the outer diameter of the first rolling bearing 41. In the example shown in Figure 8, the shortest distance a2 is the shortest distance from the end of the first outer ring 41B in the axial direction to the end of the inner peripheral surface of the rotor core 21 in the axial direction.

[0036] According to the first modification of the first embodiment, the shortest distance a2 from the outer peripheral surface of the first outer ring 41B to the inner peripheral surface of the rotor core 21 is shorter than the shortest distance b1 from the first outer ring 41B to the drive circuit board 5. Therefore, the bearing voltage in the first rolling bearing 41 can be reduced, and electrolytic corrosion inside the first rolling bearing 41 can be reduced. Furthermore, the potential difference between the second inner ring 42A and the second outer ring 42B can be reduced, and electrolytic corrosion due to discharge inside the second rolling bearing 42 can be reduced.

[0037] In the first variation of the first embodiment, a bonded magnet may be used instead of the rotor core 21. The bonded magnet is, for example, a magnet made of a mixture of magnetic powder and resin. In this case, the shortest distance from the outer peripheral surface of the first outer ring 41B to the stator core 31 is shorter than the shortest distance b1 from the first outer ring 41B to the drive circuit board 5. This reduces the bearing voltage in the first rolling bearing 41, similar to the electric motor 1 shown in FIG. 8, and reduces electrolytic corrosion in the first rolling bearing 41. <Second variation of the first embodiment> FIG. 9 is an enlarged view showing the periphery of the first rolling bearing 41 of the electric motor 1 according to the second variation of the first embodiment. The electric motor 1 according to the second variation of the first embodiment includes a first conductor 71 that holds the first outer ring 41B. The first conductor 71 has a cylindrical shape.

[0038] 9 , the first conductor 71 has a portion facing the first outer ring 41B and a portion facing the rotor core 21. The shortest distance a3 from the first conductor 71 to the rotor core 21 is shorter than the shortest distance b1 from the first outer ring 41B to the drive circuit board 5. Because there is electrical continuity between the first conductor 71 and the first outer ring 41B, the electrical distance from the first outer ring 41B to the rotor core 21 can be made shorter than the shortest distance b1 from the first outer ring 41B to the drive circuit board 5. This makes it possible to reduce electrolytic corrosion in the first rolling bearing 41.

[0039] Second Embodiment The electric motor 1 according to the second embodiment can have the components described in the first embodiment. Details of the second embodiment that differ from the electric motor 1 according to the first embodiment will be described below.

[0040] 10 is a cross-sectional view schematically showing the structure of electric motor 1 according to embodiment 2. In electric motor 1 according to embodiment 2, the shortest distance a1 from first outer ring 41B to rotor core 21 is shorter than the shortest distance c1 from second outer ring 42B to rotor core 21.

[0041] Fig. 11 is a graph showing the potential from the coil 32 of the stator 3 to the drive circuit board 5. In the electric motor 1 according to the second embodiment, as in the first embodiment, the potential is highest at the coil 32 and lowest at the low-voltage line provided on the drive circuit board 5. Therefore, in Fig. 11, the potential of the coil 32 (also referred to as the coil potential) is shown as 1.0, and the potential of the drive circuit board 5 (also referred to as the board potential) is shown as 0.

[0042] 11 , as in the first embodiment, the potential of the rotor core 21 is close to the coil potential, so the rotor core 21 has a high potential, and the first outer ring 41B, which is closer to the drive circuit board 5, has the lowest potential. The second outer ring 42B is closer to the coil 32 than the drive circuit board 5, so it has a higher potential than the shaft 22 and the first outer ring 41B. The potentials of the first inner ring 41A, the shaft 22, and the second outer ring 42B are at a potential between the potentials of the first outer ring 41B and the second outer ring 42B. Therefore, as shown in FIG. 11 , the potential of each component of the electric motor 1 depends on the shortest distance a1 and the shortest distance b1.

[0043] Fig. 12 is a graph showing the potentials of several components in the electric motor 1. Fig. 13 is a graph showing the bearing voltages in each rolling bearing. As shown in Figs. 12 and 13, the potentials of each component in the electric motor 1 depend on the shortest distance a1 and the shortest distance c1. As shown in Fig. 12, the smaller the shortest distance a1 is relative to the shortest distance c1, the closer the potentials of the first outer ring 41B, the second outer ring 42B, and the shaft 22 become to the coil potential. This reduces the potential difference between the inner ring and outer ring in each rolling bearing, and therefore the bearing voltage in each rolling bearing.

[0044] In this embodiment, as described above, the shortest distance a1 from the first outer ring 41B to the rotor core 21 is shorter than the shortest distance c1 from the second outer ring 42B to the rotor core 21. Therefore, the potential difference between the first inner ring 41A and the first outer ring 41B can be reduced, and electrolytic corrosion due to discharge inside the first rolling bearing 41 can be reduced. Furthermore, the potential difference between the second inner ring 42A and the second outer ring 42B can be reduced, and electrolytic corrosion due to discharge inside the second rolling bearing 42 can be reduced. As a result, the life of the electric motor 1 can be improved.

[0045] <First Modification of Second Embodiment> Figure 14 is a cross-sectional view schematically showing the structure of an electric motor 1 according to a first modification of the second embodiment. In the example shown in Figure 14, the shortest distance a2 from the outer peripheral surface of the first outer ring 41B to the rotor core 21 is shorter than the shortest distance c2 from the outer peripheral surface of the second outer ring 42B to the inner peripheral surface of the rotor core 21. In the example shown in Figure 14, the shortest distance a2 is the shortest distance from the outer peripheral surface of the first outer ring 41B to the inner peripheral surface of the rotor core 21.

[0046] In the example shown in FIG. 14 , the inner diameter of the rotor core 21 is larger than the outer diameter of the first rolling bearing 41 .

[0047] In the first modification of the second embodiment, a bonded magnet may be used instead of the rotor core 21. The bonded magnet is, for example, a magnet made of a mixture of magnetic powder and resin. In this case, the shortest distance from the outer peripheral surface of the first outer ring 41B to the stator core 31 is shorter than the shortest distance from the outer peripheral surface of the second outer ring 42B to the stator core 31. This makes it possible to reduce the bearing voltage in the first rolling bearing 41, and to reduce electrolytic corrosion in the first rolling bearing 41, similar to the electric motor 1 shown in FIG. 14 .

[0048] According to the electric motor 1 according to the first modification of the second embodiment, it is possible to reduce the bearing voltage at the first rolling bearing 41, thereby reducing electrolytic corrosion inside the first rolling bearing 41. Furthermore, it is possible to reduce the potential difference between the second inner ring 42A and the second outer ring 42B, thereby reducing electrolytic corrosion due to discharge inside the second rolling bearing 42.

[0049] 15 is a cross-sectional view schematically showing the structure of an electric motor 1 according to a second modification of the second embodiment. The electric motor 1 according to the second modification has a second conductor 72 that holds the second outer ring 42B.

[0050] 15 , the second conductor 72 has a portion facing the second outer ring 42B and a portion facing the rotor core 21. The shortest distance a2 from the first outer ring 41B to the rotor core 21 is shorter than the shortest distance c3 from the second conductor 72 to the rotor core 21. In the example shown in FIG. 15 , the shortest distance a2 is the shortest distance from the outer peripheral surface of the first outer ring 41B to the inner peripheral surface of the rotor core 21.

[0051] Because there is electrical continuity between the first conductor 71 and the first outer ring 41B, the electrical distance from the first outer ring 41B to the rotor core 21 can be made shorter than the shortest distance b1 from the first outer ring 41B to the drive circuit board 5. This makes it possible to reduce electrolytic corrosion in the first rolling bearing 41. Furthermore, it is possible to reduce electrolytic corrosion in the second rolling bearing 42.

[0052] Embodiment 3. Fig. 16 is a cross-sectional view that schematically shows the structure of an electric motor 1 according to embodiment 3. The electric motor 1 according to embodiment 3 can have the components described in embodiment 1. The electric motor 1 according to embodiment 3 has the structure described in embodiment 1 and the structure described in embodiment 2.

[0053] 16 , in the electric motor 1 according to the third embodiment, the shortest distance a1 from the first outer ring 41B to the rotor core 21 is shorter than the shortest distance b1 from the first outer ring 41B to the drive circuit board 5, and the shortest distance a1 from the first outer ring 41B to the rotor core 21 is shorter than the shortest distance c1 from the second outer ring 42B to the rotor core 21. As a result, the potential of the first outer ring 41B is high and close to the potential of the rotor core 21. Furthermore, by making the shortest distance c1 longer than the shortest distance a1, the potential of the second outer ring 42B is low relative to the potential of the rotor core 21. Therefore, in the electric motor 1, the potential difference between the first outer ring 41B, which has a relatively low potential, and the second outer ring 42B, which has a relatively high potential, is reduced, thereby reducing the bearing voltage of each rolling bearing (i.e., the first rolling bearing 41 and the second rolling bearing 42). This further reduces electrolytic corrosion in each rolling bearing. As a result, the life of the electric motor 1 can be improved.

[0054] <Modification of Embodiment 3> Figure 17 is a cross-sectional view that schematically shows the structure of an electric motor 1 according to a modification of Embodiment 3. The electric motor 1 according to the modification of Embodiment 3 can have the components described in Embodiment 1. The electric motor 1 according to Embodiment 3 has the structure described in Modification 1 of Embodiment 1 and the structure described in Modification 1 of Embodiment 2.

[0055] As shown in Figure 17, in the electric motor 1 relating to the modified example of embodiment 3, the shortest distance a2 from the outer surface of the first outer ring 41B to the inner surface of the rotor core 21 is shorter than the shortest distance b1 from the first outer ring 41B to the drive circuit board 5, and the shortest distance a2 from the outer surface of the first outer ring 41B to the rotor core 21 is shorter than the shortest distance c2 from the outer surface of the second outer ring 42B to the inner surface of the rotor core 21.

[0056] According to the electric motor 1 according to the modified example of the third embodiment, it is possible to reduce the potential difference between the first inner ring 41A and the first outer ring 41B, thereby reducing electrolytic corrosion due to discharge inside the first rolling bearing 41. Furthermore, it is possible to reduce the potential difference between the second inner ring 42A and the second outer ring 42B, thereby reducing electrolytic corrosion due to discharge inside the second rolling bearing 42. As a result, it is possible to improve the life of the electric motor 1.

[0057] Fourth Embodiment Fig. 18 is a diagram schematically illustrating a fan 9 according to a fourth embodiment. The fan 9 includes blades 91 and an electric motor 1. The fan 9 is also referred to as a blower. The blades 91 are formed of, for example, polypropylene (PP) containing glass fiber. The blades 91 are, for example, a sirocco fan, a propeller fan, a crossflow fan, or a turbo fan.

[0058] The electric motor 1 is the electric motor 1 according to the first, second, or third embodiment (including each of the modifications). The blades 91 are fixed to a shaft of the electric motor 1. The electric motor 1 drives the blades 91. Specifically, the electric motor 1 rotates the blades 91. When the electric motor 1 is driven, the blades 91 rotate and an airflow is generated. This enables the fan 9 to blow air.

[0059] The fan 9 according to the fourth embodiment includes the motor 1 according to the first, second, or third embodiment (including the modifications thereof), and therefore has the same advantages as those described in the corresponding embodiment or modification. Furthermore, the performance of the fan 9 can be maintained for a long period of time.

[0060] Furthermore, since the fan 9 according to the fourth embodiment has the electric motor 1 according to the first, second, or third embodiment (including each of the modifications), vibration and noise in the fan 9 can be reduced.

[0061] Fifth Embodiment An air conditioner 10 (also referred to as a refrigeration air conditioning device or a refrigeration cycle device) according to a fifth embodiment will be described. Fig. 19 is a diagram schematically showing the configuration of the air conditioner 10 according to the fifth embodiment.

[0062] The air conditioner 10 according to embodiment 5 has an indoor unit 11 as a blower (also referred to as a first blower) and an outdoor unit 13 as a blower (also referred to as a second blower) connected to the indoor unit 11.

[0063] In this embodiment, the air conditioner 10 has an indoor unit 11, a refrigerant pipe 12, and an outdoor unit 13. For example, the outdoor unit 13 is connected to the indoor unit 11 via the refrigerant pipe 12.

[0064] The indoor unit 11 includes an electric motor 11a, an air blower 11b driven by the electric motor 11a to blow air, and a housing 11c that covers the electric motor 11a and the air blower 11b. The electric motor 11a is, for example, the electric motor 1 according to embodiment 1, 2, or 3 (including each of the modified examples). The air blower 11b includes, for example, a blade 11d driven by the electric motor 11a. For example, the blade 11d is fixed to the shaft of the electric motor 11a and generates an airflow.

[0065] The outdoor unit 13 includes an electric motor 13a, a blower 13b, a compressor 14, a heat exchanger (not shown), and a housing 13c that covers the blower 13b, the compressor 14, and the heat exchanger. The electric motor 13a is, for example, the electric motor 1 according to embodiment 1, 2, or 3 (including each of the modified examples). The blower 13b blows air by being driven by the electric motor 13a. The blower 13b includes, for example, a blade 13d driven by the electric motor 13a. For example, the blade 13d is fixed to the shaft of the electric motor 13a and generates an airflow.

[0066] The compressor 14 includes an electric motor 14 a, a compression mechanism 14 b (e.g., a refrigerant circuit) driven by the electric motor 14 a, and a housing 14 c that covers the electric motor 14 a and the compression mechanism 14 b. The electric motor 14 a is, for example, the electric motor 1 according to the first, second, or third embodiment (including each of the modified examples).

[0067] In the air conditioner 10, at least one of the indoor unit 11 and the outdoor unit 13 has the motor 1 described in embodiment 1, 2, or 3 (including each of the modified examples). That is, the indoor unit 11, the outdoor unit 13, or the indoor unit 11 and the outdoor unit 13 each have the motor 1 described in embodiment 1, 2, or 3 (including each of the modified examples). Specifically, as a driving source for the air blower section, the motor 1 described in embodiment 1, 2, or 3 (including each of the modified examples) is applied to at least one of the motors 11a and 13a. That is, the motor 1 described in embodiment 1, 2, or 3 (including each of the modified examples) is applied to the indoor unit 11, the outdoor unit 13, or the indoor unit 11 and the outdoor unit 13. The motor 1 described in embodiment 1, 2, or 3 (including each of the modified examples) may be applied to the motor 14a of the compressor 14.

[0068] The air conditioner 10 can perform air conditioning, such as cooling operation, which blows cool air, and heating operation, which blows warm air, from the indoor unit 11. In the indoor unit 11, the motor 11a is a drive source for driving the blower unit 11b. The blower unit 11b can blow conditioned air.

[0069] In the indoor unit 11, the electric motor 11a is fixed to a housing 11c of the indoor unit 11 by, for example, screws. In the outdoor unit 13, the electric motor 13a is fixed to a housing 13c of the outdoor unit 13 by, for example, screws.

[0070] In the air conditioner 10 according to the fifth embodiment, the electric motor 1 described in the first, second, or third embodiment (including each of the modified examples) is applied to at least one of the electric motors 11a and 13a, and therefore the same advantages as those described in the first, second, or third embodiment (including each of the modified examples) can be obtained. As a result, the performance of the air conditioner 10 can be maintained for a long period of time.

[0071] Furthermore, in the air conditioner 10 according to embodiment 5, the electric motor 1 described in embodiment 1 is applied to at least one of the electric motors 11a and 13a, making it possible to provide an air conditioner 10 that is easy to assemble and low cost.

[0072] Furthermore, when the motor 1 according to embodiment 1, 2, or 3 (including each of the modifications) is used as a drive source for a blower (e.g., indoor unit 11), the same advantages as those described in the corresponding embodiment or modification can be obtained. As a result, the performance of the blower can be maintained over a long period of time. A blower having the motor 1 according to embodiment 1, 2, or 3 (including each of the modifications) and a blade (e.g., blade 11d or 13d) driven by the motor 1 can be used alone as a blowing device. This blower can also be applied to devices other than the air conditioner 10.

[0073] Furthermore, when the electric motor 1 according to the first, second, or third embodiment (including each of the modifications) is used as the drive source of the compressor 14, the same advantages as those described in the corresponding embodiment or modification can be obtained. As a result, the performance of the compressor 14 can be maintained for a long period of time.

[0074] The electric motor 1 described in the first, second, or third embodiment (including each of the modified examples) can be mounted on any electric device having a drive source, such as a machine tool, an electric vehicle, a drone, or a robot.

[0075] The features of the above-described embodiments and modifications can be combined with each other.

[0076] DESCRIPTION OF SYMBOLS 1, 11a, 13a, 14a Electric motor, 2 Rotor, 3 Stator, 5 Drive circuit board, 6 Resin frame, 7 Resin bracket, 9 Fan, 10 Air conditioner, 11 Indoor unit, 12 Refrigerant piping, 13 Outdoor unit, 21 Rotor core, 22 Shaft, 31 Stator core, 32 Coil, 41 First rolling bearing, 41A First inner ring, 41B First outer ring, 42A Second inner ring, 42B Second outer ring, 42 Second rolling bearing, 71 First conductor, 72 Second conductor, 81, 91 Blades.

Claims

1. A first rolling bearing having a first inner ring and a first outer ring, a second rolling bearing having a second inner ring and a second outer ring, a shaft rotatably supported by the first rolling bearing and the second rolling bearing, a rotor core fixed to the shaft, a stator core disposed outside the rotor core, and a drive circuit board disposed on the side opposite to the rotor core with respect to the first rolling bearing are provided. The first outer ring and the second outer ring are electrically insulated from each other. The first outer ring and the stator core are electrically insulated from each other. The shortest distance from the first outer ring to the rotor core is shorter than the shortest distance from the first outer ring to the drive circuit board. An electric motor.

2. The electric motor according to claim 1, wherein the shortest distance from the outer peripheral surface of the first outer ring to the inner peripheral surface of the rotor core is shorter than the shortest distance from the first outer ring to the drive circuit board.

3. The electric motor further includes a first conductor that holds the first outer ring. The shortest distance from the first conductor to the rotor core is shorter than the shortest distance from the first outer ring to the drive circuit board. The electric motor according to claim 1 or 2.

4. The electric motor according to claim 1 or 2, wherein the shortest distance from the first outer ring to the rotor core is shorter than the shortest distance from the second outer ring to the rotor core.

5. The electric motor according to claim 1 or 2, wherein the shortest distance from the outer peripheral surface of the first outer ring to the inner peripheral surface of the rotor core is shorter than the shortest distance from the outer peripheral surface of the second outer ring to the inner peripheral surface of the rotor core.

6. The electric motor further includes a second conductor that holds the second outer ring. The shortest distance from the first outer ring to the rotor core is shorter than the shortest distance from the second conductor to the rotor core. The electric motor according to claim 1 or 2.

7. A first rolling bearing having a first inner ring and a first outer ring, a second rolling bearing having a second inner ring and a second outer ring, a shaft rotatably supported by the first rolling bearing and the second rolling bearing, a rotor core fixed to the shaft, a stator core disposed outside the rotor core, and a drive circuit board disposed on the side opposite to the rotor core with respect to the first rolling bearing are provided. The first outer ring and the second outer ring are electrically insulated from each other. The first outer ring and the stator core are electrically insulated from each other. The shortest distance from the first outer ring to the rotor core is shorter than the shortest distance from the second outer ring to the rotor core. Electric motor. **Claim 8** The electric motor according to claim 7, wherein the shortest distance from the outer peripheral surface of the first outer ring to the inner peripheral surface of the rotor core is shorter than the shortest distance from the outer peripheral surface of the second outer ring to the inner peripheral surface of the rotor core. **Claim 9** The electric motor further includes a second conductor that holds the second outer ring. The shortest distance from the first outer ring to the rotor core is shorter than the shortest distance from the second conductor to the rotor core. The electric motor according to claim 7 or 8. **Claim 10** Blades, and the electric motor according to claim 1, 2, 7, or 8 that rotates the blades. A fan comprising the same. **Claim 11** An indoor unit, and an outdoor unit connected to the indoor unit. Comprising, wherein each of the indoor unit, the outdoor unit, or the indoor unit and the outdoor unit has the electric motor according to claim 1, 2, 7, or 8. An air conditioner.