Electric motor and electrical device having the same

Abstract

To provide an electric motor and an electric device having the same for suppressing occurrence of electrolytic corrosion of bearing in an electric motor.SOLUTION: An electric motor includes: a stator including a stator core wound with stator windings; a magnet; a rotary body; a shaft; a rotor; a first bearing and a second bearing; a first metal bracket for fixing the first bearing; and a second metal bracket for fixing the second bearing. When the stator core, the first metal bracket, and the second metal bracket are electrically connected and a connection point between the stator core and the first metal bracket or the second metal bracket is defined as a connection point A of a bearing outer ring, the electric motor is provided with a capacitive member having a capacitance Cn is provided between a portion of the bearing outer ring having the same potential as a connection point A and a zero reference potential of a drive circuit that applies a voltage to the stator winding.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electric motor and an electric device equipped with the electric motor, and more particularly to an electric motor improved to suppress the occurrence of electrolytic corrosion of bearings and an electric device equipped with the electric motor. [Background technology]

[0002] In recent years, electric motors have increasingly been driven by inverters that use a pulse width modulation method (hereinafter, referred to as a PWM method, as appropriate) (see, for example, Patent Document 1). Electric motors driven by PWM inverters are used in electrical equipment such as indoor and outdoor units of air conditioners and water heaters. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] "Shaft Voltage Suppression Based on Ungrounded Common-Mode Equivalent Circuit for Inverter-Fed Brushless DC Motors," IEEJ Transactions on Power Systems, Vol. 132, No. 6, pp. 666-672, 2012 [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-158152 Summary of the Invention [Problem to be solved by the invention]

[0005] An electric motor according to one aspect of the present disclosure includes: a stator including a stator core wound with a stator winding; a rotor that faces the stator and holds a plurality of magnets in a circumferential direction, or that holds a plurality of magnets in a spoke-like manner from the center; a rotor including the rotating body and a shaft to which the rotating body is fastened so as to pass through the center of the rotating body; a first bearing and a second bearing that support the rotating body; An electric motor comprising a first metal bracket that fixes the first bearing and a second metal bracket that fixes the second bearing, the stator core, the first metal bracket, and the second metal bracket are electrically connected, When the connection point between the stator core and the first metal bracket or the second metal bracket is defined as connection point A of the bearing outer ring, A capacitance C is provided between a point at the same potential as the connection point A of the bearing outer ring and the zero reference potential of the drive circuit that applies voltage to the stator winding. n A capacitive member is provided. [Effects of the Invention]

[0006] According to one aspect of the present disclosure, it is possible to suppress the occurrence of electrolytic corrosion in bearings in an electric motor and in electrical equipment including the electric motor. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic cross-sectional view of a motor according to a first embodiment of the present disclosure. [Figure 2] FIG. 2 is a model diagram of capacitance distribution of the electric motor of the first embodiment. [Figure 3] FIG. 3 is a graph showing the relationship between the capacitance between the bracket and the ground of the electric motor of the first embodiment and the shaft voltage. [Figure 4] FIG. 4 shows a modified example of the electric motor of the first embodiment. [Figure 5] FIG. 5 is a model diagram of capacitance distribution of the electric motor of FIG. [Figure 6] FIG. 6 is a diagram showing another modified example of the electric motor of the first embodiment. [Figure 7] FIG. 7 is a model diagram of the capacitance distribution of the electric motor of FIG. [Figure 8]FIG. 8 is a schematic cross-sectional view of a motor according to a first embodiment of the present disclosure. [Figure 9] FIG. 9 is a schematic cross-sectional view of a motor according to a first embodiment of the present disclosure. [Figure 10] 1 is a perspective view of an embodiment of an electric device using the electric motor of the first embodiment. [Figure 11] FIG. 10 is a perspective view of another aspect of an electric device using the electric motor of the first embodiment. [Figure 12] FIG. 10 is a perspective view of another aspect of an electric device using the electric motor of the first embodiment. [Figure 13] FIG. 1 is a schematic cross-sectional view of a conventional electric motor. [Figure 14] FIG. 14 is a model diagram of capacitance distribution of the electric motor of FIG. 13. DETAILED DESCRIPTION OF THE INVENTION

[0008] (Findings that formed the basis of this disclosure) Before describing the embodiments of the present disclosure, the findings on which the present disclosure is based will be described. When an electric motor is driven by a PWM inverter, the neutral point potential of the stator winding fluctuates due to the switching of the power elements. Patent Document 1 proposes a measure to prevent dielectric breakdown of the grease film inside the bearing by reducing the shaft voltage to make the grease film inside the bearing below the breakdown voltage in order to suppress electrolytic corrosion of the bearing. Patent Document 1 also proposes a measure to reduce damage to the metal surface inside the bearing by reducing the shaft voltage to reduce the discharge energy caused by dielectric breakdown of the grease film inside the bearing.

[0009] Patent Document 1 will be described in detail below. 13 is a schematic cross-sectional view of an inner rotor, brushless radial type electric motor 50 of Patent Document 1. Patent Document 1 and Non-Patent Document 1 have the same configuration. As shown in FIG. 13, the electric motor 50 has a first metal bracket 1 and a second metal bracket 2 arranged at both ends of the electric motor 50, a pair of bearings (a first bearing 5a and a second bearing 5b), a shaft 4, a rotor 10, and a stator 18. Rotating body 9 has rotor core 8 and magnet 11, which is a permanent magnet. Rotor 10 has rotating body 9 and shaft 4. Stator 18 has stator core 6 and stator winding 3.

[0010] As shown in Figure 13, the outer ring of the first bearing 5a is connected to the first metal bracket 1, and the outer ring of the second bearing 5b is connected to the second metal bracket 2. The inner ring of the first bearing 5a and the inner ring of the second bearing 5b are connected by the shaft 4 and are electrically conductive. A conductive member 13 electrically shorts the first metal bracket 1 and the second metal bracket 2.

[0011] In Patent Document 1, a conductive member 13 electrically shorts the first metal bracket 1 and the second metal bracket 2, thereby matching the capacitance of the first metal bracket 1 and the second metal bracket 2. Furthermore, Patent Document 1 describes a method in which a dielectric layer 20 is provided on the rotor 9, changing the capacitance of the rotor 9 and reducing the shaft voltage. Patent Document 1 discloses that the dielectric layer 20 makes it possible to keep the voltage below 5 V, which is the guideline below the dielectric breakdown voltage of the oil film of a general bearing.

[0012] The present inventors have conducted detailed studies on Patent Document 1. Fig. 14 is a model diagram of the capacitance distribution of the electric motor 50 of Patent Document 1 with respect to Fig. 13. In the electric motor 50 of Patent Document 1, when considering the capacitance distribution with the stator core 6 as the reference, the voltage distribution of the electric motor 50 is dominated by the influence of the capacitive reactance, which is the reciprocal of the impedance, and therefore, the description will be made with reference to the capacitance distribution model as shown in Fig. 5 of Non-Patent Document 1. The capacitance C between the stator winding 3 and the first metal bracket 1 sb1 The charge in the first bearing 5a accumulates, and the first shaft voltage Vsh1 The first shaft voltage V sh1 When the voltage rises and reaches the breakdown voltage of the grease film inside the bearing, breakdown occurs. sb2 The capacitance C sb1 Similarly, the charge in the second bearing 5b accumulates, and the second shaft voltage V sh2 The second shaft voltage V sh2 When this rises, dielectric breakdown occurs.

[0013] The voltage generated between the outer ring side of the first bearing 5a and the outer ring side of the second bearing 5b and the zero potential reference N (12) of the drive circuit is the voltage V generated between the zero reference potential N of the drive circuit and the neutral point potential S of the stator winding 3. com The value is divided by the capacitance distribution on the stator side. The voltage generated between the inner ring side of the first bearing 5a and the inner ring side of the second bearing 5b (point 4 in FIG. 14) and the zero potential reference N(12) of the drive circuit is the voltage V generated between the zero potential reference N(12) of the drive circuit and the neutral point potential S of the stator winding 3. com The value is divided by the capacitance distribution on the rotor side.

[0014] The inventors have devised a model diagram of capacitance distribution shown in FIG. 14 and have discovered the following by examining it. sh1 and the second shaft voltage V sh2 is the difference between the voltage generated on the outer ring side and the voltage generated on the inner ring side of the first bearing 5a and the second bearing 5b. Therefore, the first shaft voltage V sh1 and the second shaft voltage V sh2 It was found that an effective way to reduce this is to make the capacitance distribution on the stator side match or approximate the capacitance distribution on the rotor side.

[0015] The voltage generated between the outer ring side of the first bearing 5a and the outer ring side of the second bearing 5b and the zero potential reference N(12) of the drive circuit is calculated by the capacitance C between the stator winding 3 and the first metal bracket 1. sb1and the capacitance C between the stator winding 3 and the second metal bracket 2 sb2 The combined capacitance A2 of the drive circuit and the capacitance C between the zero reference potential N(12) and the first metal bracket 1 nb2 Voltage division ratio R A2 (Combined capacitance A2 / C nb2 ) to the reciprocal of the voltage V com The voltage is multiplied by The voltage generated between the inner ring side of the first bearing 5a and the inner ring side of the second bearing 5b and the zero potential reference N(12) of the drive circuit is calculated by the capacitance C between the stator winding 3 and the stator core 6. i and the capacitance C between the stator core 6 and the magnet 11 g and the capacitance C between the stator winding 3 and the magnet 11 sm and the capacitance C of magnet 11 mg and the capacitance C of the rotor 10 m and the capacitance C between the zero reference potential N of the drive circuit and the shaft 4. ns Voltage division ratio R B2 (Composite capacitance B2 / C ns ) to the reciprocal of the voltage V com The voltage is multiplied by

[0016] That is, the first shaft voltage V sh1 and the second shaft voltage V sh2 To reduce this, the capacitance distribution on the stator side and the capacitance distribution on the rotor side must be matched or approximated, that is, the voltage division ratio R A2 (Combined capacitance A2 / C nb2 ) and voltage division ratio R B2 (Composite capacitance B2 / C ns ) and the partial pressure ratio R A2 and voltage division ratio R B2 Hereinafter, the matching or approximation of these two will be simply referred to as "matching."

[0017] In Patent Document 1, in FIG. 13, the capacitance distribution on the rotor 10 side is determined by providing a dielectric layer 20 on the rotor 9 and reducing the capacitance C d The capacitance C of this dielectric layer 20 dIn FIG. 14, which is a model diagram of capacitance distribution, the capacitance C of the rotor 10 is m (Composite capacitance B2) has capacitance C in series. d is inserted, and by reducing the combined capacitance B2, it is matched with the capacitance distribution on the stator side, and as a result, the first shaft voltage V sh1 and the second shaft voltage V sh2 was found to be lower.

[0018] The capacitance C of the dielectric layer 20 d is inversely proportional to the distance in the thickness direction of the dielectric layer 20 (the distance in the short direction of the dielectric layer 20 in FIG. 13) and proportional to the length (the distance in the long direction of the dielectric layer 20 in FIG. 13). Therefore, the capacitance C d To reduce this, it is necessary to increase the width of the dielectric layer 20 (the distance in the thickness direction of the dielectric layer 20).

[0019] However, as shown in FIG. 13 , Patent Document 1 has the problem that providing the dielectric layer 20 to the rotor 9 requires a complex mold for the rotor 9, since the dielectric layer 20 must be sandwiched between them. Furthermore, Patent Document 1 also has the problem that sandwiching the dielectric layer 20 reduces the strength of the rotor 9. In other words, because the dielectric layer 20 is subjected to stress as a rotational torque, the width of the dielectric layer 20 may be restricted in order to ensure its strength. In such cases, it has been considered possible that the required capacitance may not be obtained, and the shaft voltage may not be reduced sufficiently. Furthermore, Patent Document 1 also has the problem that, in an electric motor 50 using a rotor 9 that holds multiple permanent magnets (magnets) in a radially centered spoke-like arrangement, increasing the width of the dielectric layer 20 requires shortening the length of the permanent magnets (magnets), which degrades the performance of the electric motor 50.

[0020] The present inventors have found the above-mentioned problems, and have conducted extensive research to find a solution to the problems, and have come up with a solution to the problems. FIG. 1 is a schematic cross-sectional view of an electric motor 50 according to the present disclosure. As shown in FIG. 1, the electric motor 50 includes a first metal bracket 1 and a second metal bracket 2 arranged at both ends of the electric motor 50, a first bearing 5a and a second bearing 5b, a shaft 4, a rotor 10, and a stator 18. A first bearing 5a fixed to the first metal bracket 1 is disposed in the center of the first metal bracket 1. A second bearing 5b fixed to the second metal bracket 2 is disposed in the center of the second metal bracket 2. The shaft 4 is supported and rotates by the first bearing 5a and the second bearing 5b. Rotating body 9 has rotor core 8 and magnet 11, which is a permanent magnet. Rotor 10 has rotating body 9 and shaft 4. Stator 18 has stator core 6 and stator winding 3. In the electric motor 50 of the present disclosure, the stator core 6, the first metal bracket 1, and the second metal bracket 2 are electrically connected to each other. 1, the first metal bracket 1 and the second metal bracket 2 are electrically connected using a first conductive member 13a, and the first metal bracket 1 and the stator core 6 are electrically connected using a second conductive member 13b. The connection point between the stator core 6 and the first metal bracket 1 or the second metal bracket 2 is defined as the connection point A of the bearing outer ring. In the case of Fig. 1, the connection point between the first metal bracket 1, the first conductive member 13a, and the second conductive member 13b is the connection point A of the bearing outer ring. Here, the connection point A of the bearing outer ring may be any location that is electrically connected to the first metal bracket 1, and the location is not limited. The inner ring portion of the first bearing 5a and the inner ring portion of the second bearing 5b are defined as a connection point B of the bearing inner rings. In the electric motor 50 of the present disclosure, a capacitance C is provided between a point at the same potential as the connection point A of the outer ring of the bearing and the zero reference potential of the drive circuit that applies voltage to the stator winding 3. n A capacitive member 15 is provided.

[0021] FIG. 2 is a model diagram of capacitance distribution of the electric motor 50 of the present disclosure. On the left side of the stator 18, the capacitance between the stator winding 3 and the first metal bracket 1 is C sb1 The capacitance between the stator winding 3 and the second metal bracket 2 is C sb2 The capacitance between the first metal bracket 1 and the zero reference potential N(12) is C nb1 is. As shown in Figure 2, the first metal bracket 1 and the stator core 6 are electrically short-circuited using the second conductive member 13b. The first metal bracket 1 and the second metal bracket 2 are electrically short-circuited using the first conductive member 13a. A capacitive member 15 with a capacitance Cn is provided between a point at the same potential as the connection point A of the bearing outer ring and the zero reference potential N (12) of the drive circuit. The point at the same potential as the connection point A of the bearing outer ring refers to a point where the first metal bracket 1, the first conductive member 13a, the second conductive member 13b, and the second metal bracket 2 are electrically connected.

[0022] The above mechanism will be explained with reference to FIG. When the stator core 6, the first bracket 1, and the second bracket 2 are electrically connected by the first conductive member 13a and the second conductive member 13b, the potential of the first metal bracket 1 and the second metal bracket 2 approaches the value of the neutral point potential S(3). In other words, the potential of the connection point A of the bearing outer ring becomes high. When the potential part B of the bearing inner ring is considered based on the connection point A of the bearing outer ring, the capacitance C between the stator core 6 and the magnet 11 is g The potential of the part and the electrostatic capacitance C of the magnet mg This potential difference is the shaft voltage.

[0023] Since the potential of the connection point A of the outer ring of the bearing is higher than the potential of the potential part B of the inner ring of the bearing, the capacitance C of the capacitive member 15 n The capacitance distribution is adjusted to lower the potential at connection point A of the outer ring of the bearing. The potential B of the inner ring of the bearing also drops, but the capacitance C between the stator winding 3 and the stator core 6 i and the capacitance C between the stator winding 3 and the rotor 10 smAs a result, the capacitance C of the capacitive member 15 is reduced. n By increasing the value of , the potential difference between the potential at the connection point A of the outer ring of the bearing and the potential portion B of the inner ring of the bearing gradually decreases. n When the value of is increased, the voltage drop of potential portion B is suppressed, and the potential difference is reversed, and the polarity is reversed. Therefore, the capacitance C of the rotor 10 m Depending on the value of n By selecting this, it is possible to reduce the shaft voltage. As described above, in the electric motor 50 of the present disclosure, the first metal bracket 1 and the second metal bracket 2 are electrically short-circuited using the first conductive member 13a, the first metal bracket 1 and the stator core 6 are electrically short-circuited using the second conductive member 13b, and a capacitive member 15 with electrostatic capacitance Cn is provided between the connection point A of the bearing outer ring and the zero reference potential N(12) of the drive circuit. By connecting the first metal bracket 1 or the second metal bracket 2 to the stator core 6, the capacitance distribution on the stator 18 side and the capacitance distribution on the rotor 10 side are changed from a separated form via the capacitance of the first bearing 5a and the second bearing 5b to a mixed form. This brings the potential of connection point A of the outer ring of the bearing closer to the potential of connection point B of the inner ring of the bearing, and in this state, the potential difference between the potential of connection point A and the potential of connection point B is further reduced by the capacitive member 15, thereby reducing the shaft voltage. Based on the above considerations, the inventors have come up with the aspects of the present disclosure described below.

[0024] An electric motor according to one aspect of the present disclosure includes: a stator including a stator core wound with a stator winding; a rotor that faces the stator and holds a plurality of magnets in a circumferential direction, or that holds a plurality of magnets in a spoke-like manner from the center; a rotor including the rotating body and a shaft to which the rotating body is fastened so as to pass through the center of the rotating body; a first bearing and a second bearing that support the rotating body; An electric motor comprising a first metal bracket that fixes the first bearing and a second metal bracket that fixes the second bearing, the stator core, the first metal bracket, and the second metal bracket are electrically connected, When the connection point between the stator core and the first metal bracket or the second metal bracket is defined as connection point A of the bearing outer ring, A capacitance C is provided between a point at the same potential as the connection point A of the bearing outer ring and the zero reference potential of the drive circuit that applies voltage to the stator winding. n A capacitive member is provided. According to the above aspect, the capacitance C of the capacitive member nb1 This changes the capacitance distribution on the stator 18 side and the capacitance distribution on the rotor 10 side from a state in which they are separated via the capacitances of the first bearing 5a and the second bearing 5b to a state in which they are mixed together. This brings the potential of connection point A of the outer ring of the bearing closer to the potential of connection point B of the inner ring of the bearing, and in this state, the potential difference between the potential of connection point A and the potential of connection point B is further reduced by capacitive member 15, making it possible to reduce the shaft voltage.

[0025] More specific embodiments of the present disclosure will be described below. However, more detailed descriptions than necessary may be omitted. For example, detailed descriptions of well-known matters or redundant descriptions of substantially identical configurations may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art. Note that the inventors provide the accompanying drawings and the following description to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter described in the claims. In the following description, identical or similar components are designated by the same reference numerals.

[0026] (Embodiment 1) Hereinafter, an electric motor according to one embodiment of the present disclosure will be described with reference to the drawings.

[0027] FIG. 1 is a schematic cross-sectional view of an inner rotor brushless radial electric motor 50 according to one embodiment of the present disclosure. As shown in FIG. 1, a first metal bracket 1 having electrical conductivity and a second metal bracket 2 having electrical conductivity are arranged on both ends of an electric motor 50. This allows the bearing to be stably supported and the shaft 4 to rotate. A first bearing 5a fixed to the first metal bracket 1 and a second bearing 5b fixed to the second metal bracket 2 are arranged in the center of the first metal bracket 1 and the second metal bracket 2. The shaft 4 is supported and rotates by the bearings 5a and 5a. The shaft 4 protrudes from the first metal bracket 1. The stator 18 generates a rotating magnetic field, which rotates the rotor 10. The rotor 10 is inserted inside the stator 18 with a gap between them. The stator 18 has a stator core 6 and a stator winding 3, which is a winding. The stator winding 3 is wound around the stator core 6 with a resin 7 interposed therebetween to insulate the stator core 6. The stator 18 is molded with resin together with other fixing members such as the first metal bracket 1 and the second metal bracket 2. In the first embodiment, these members are integrally molded in this manner to form a stator having a generally cylindrical outer shape. The integrally molded member also functions as a housing for the electric motor 5. The first metal bracket 1 and the second metal bracket 2 may be insulated from the stator core 6 by a space. The rotor 10 rotates in the electric motor 50 and has a shaft 4 and a rotating body 9. The rotating body 9 has a rotor core 8 and permanent magnets 11, which are ferrite magnets. The rotor 10 holds a plurality of magnets 11 on the outer periphery of the rotor core 8 and has the shaft 4 passing through the center of the rotor core 8. The rotor 10 may also hold a plurality of magnets 11 arranged in a spoke shape from the center facing the stator 18.

[0028] A first bearing 5a and a second bearing 5b that support the shaft 4 are attached to the shaft 4. The first bearing 5a and the second bearing 5b are cylindrical bearings that have a plurality of iron balls, and the inner ring sides of the first bearing 5a and the second bearing 5b are fixed to the shaft 4.

[0029] The outer ring sides of the first bearing 5a and the second bearing 5b are fixed by a first metal bracket 1 and a second metal bracket 2, respectively, which are electrically conductive. In Fig. 1, the first bearing 5a is fixed to the first metal bracket 1, the second bearing 5b is fixed to the second metal bracket 2, the shaft 4 is supported by the first bearing 5a and the second bearing 5b, and the rotor 10 rotates freely. The shaft 4, the inner ring of the first bearing 5a, and the inner ring of the second bearing 5b are electrically connected.

[0030] Furthermore, inside this electric motor 50, a printed circuit board 12 on which a drive circuit (not shown) that generates a rotating magnetic field is mounted is arranged between the rotor 10 and the first metal bracket 1. For example, the drive circuit includes an inverter circuit or the like for applying a voltage to the stator winding 3.

[0031] When a voltage is applied from a drive circuit to stator winding 3 of electric motor 50 configured as described above, a current flows through stator winding 3, and a magnetic field is generated from stator core 6. Then, the rotating magnetic field from stator core 6 and the magnetic field from magnet 11 generate attractive and repulsive forces according to the polarities of these magnetic fields, and these forces cause rotor 10 to rotate around shaft 4.

[0032] 1, one end of first conductive member 13a, which is a short-circuiting wire, is connected to first metal bracket 1, and the other end of first conductive member 13a is connected to second metal bracket 2. One end of second conductive member 13b, which is a short-circuiting wire, is connected to first metal bracket 1, and the other end of second conductive member 13b is connected to stator core 6. This causes first metal bracket 1, second metal bracket 2, and stator core 6 to have the same potential. Here, the connection point between the stator core 6 and the first metal bracket 1 or the second metal bracket 2 is defined as connection point A of the bearing outer ring. In the case of FIG. 1, the connection point between the first metal bracket 1, the first conductive member 13a, and the second conductive member 13b is the connection point A of the bearing outer ring. A capacitance C is placed between the point at the same potential as the connection point A of the bearing outer ring and the ground, which is the reference potential N(12) of the drive circuit. n The capacitive member 15 is connected to the first metal bracket 1. The point at the same potential as the connection point A of the bearing outer ring is the point at which electrical continuity is established between the first metal bracket 1, the first conductive member 13a, the second conductive member 13b, and the second metal bracket 2. The above ground is insulated from the earth.

[0033] The capacitive member 15 is, for example, a ceramic capacitor. Alternatively, the capacitive member 15 is, for example, a molded product made of resin such as PBT with electrodes on both sides. The capacitive member 15 is not particularly limited in shape as long as it can store electric charge. The capacitive member 15 may be disposed anywhere inside the electric motor 50, for example, on the printed circuit board 12 on which the drive circuit is mounted.

[0034] FIG. 2 is a model diagram of capacitance distribution in the first embodiment. In FIG. 2, with the first bearing 5a and second bearing 5b located in the center as the boundary, the left side shows the capacitance distribution on the stator 18 side, and the right side shows the capacitance distribution on the rotor 10 side. The voltage V applied to the stator winding 3 by the drive circuit com is the potential difference between the neutral point potential S(3) and the zero reference potential N(12). The first metal bracket 1, the second metal bracket 2, and the stator core 6 are short-circuited by the first conductive member 13a and the second conductive member 13b, and the short-circuited point becomes the connection point A of the bearing outer ring. A capacitance C is formed between the connection point A of the bearing outer ring and the ground, which is the reference potential N(12) of the drive circuit. n The capacitive member 15 is connected to the On the left stator 18 side, the combined capacitance A1a is the capacitance C sb1 and capacitance C sb2 The combined capacitance A1b is the capacitance C nb1 and capacitance C n is the combined capacitance of On the right rotor 10 side, the combined capacitance B1 is the capacitance C between the stator winding 3 and the stator core 6. i and the capacitance C between the stator core 6 and the magnet 11 g and the capacitance C between the stator winding 3 and the magnet 11 sm and the capacitance C of magnet 11 mg is the combined capacitance of The capacitance between the shaft 4 and the zero reference potential N(12) of the drive circuit is C ns is.

[0035] FIG. 3 shows the capacitance C of the capacitive member 15. n By changing the value of the shaft voltage V of the first bearing 5a, sh1 and the shaft voltage V of the second bearing 5b sh2 The first bearing 5a and the second bearing 5b are short-circuited and therefore have the same potential, so the shaft voltage is simply V sh It is written as:

[0036] In FIG. 3, the horizontal axis represents the capacitance C of the capacitive member 15. n The vertical axis on the left is the shaft voltage V sh The shaft voltage V sh The voltage of the inner ring was measured based on the outer ring of the first bearing 5a and the second bearing 5b, and when the voltage of the inner ring was higher than that of the outer ring it was considered positive, and when the voltage of the inner ring was lower than that of the outer ring it was considered negative.

[0037] In Non-Patent Document 1, the shaft voltage V sh The absolute value of the capacitance C of the rotor 10 is less than 5V. m As an example of the value of the capacitance C of the rotor 10 of the electric motor 50, m Taking into account the range in which this capacitance can be taken, in addition to 2pF and 20pF, simulations were performed for 0.2pF, which is 1 / 10 of the minimum value of 2pF, 200pF, which is 10 times the maximum value of 20pF, and 2000pF, which is 100 times the maximum value of 20pF.

[0038] The capacitance C of the rotor 10 m The graph for when the capacitance of the capacitive member is 0.2 pF is the graph with solid black circles (hereinafter referred to as graph 1). n As increases, the graph above increases from the bottom left to the top right, and the shaft voltage V sh The capacitance C saturates at a certain voltage (for example, about -0.5V). n When the capacitance is 1500pF, the shaft voltage V sh becomes approximately -4V, and the shaft voltage V sh The absolute value is in the range of |5V|. Furthermore, the capacitance C n Even if the shaft voltage V sh falls within the range of absolute value |5V|. The capacitance C of the rotor 10 m The graph for when the capacitance is 2pF is the solid square graph (hereafter referred to as graph 2). The behavior of graph 2 is almost the same as that of graph 1, but it is a graph shifted slightly upward. The capacitance C of the rotor 10 m The graph for 20 pF is the solid triangular graph (hereafter referred to as graph 3). Graph 3 shows the capacitance C n When is 500pF, the shaft voltage V sh becomes approximately -4V, and the capacitance C n When is 5000pF, the shaft voltage V sh exceeds 5V. Capacitance C n exceeds 5000pF, the shaft voltage V sh exceeds 5V, and the shaft voltage V sh In graph 3, the shaft voltage V shThe capacitance C whose absolute value falls within the range of |5V| n The range is, for example, 500pF to 5000pF, and the shaft voltage V sh The capacitance C whose absolute value falls within the range of |5V| n exists. The capacitance C of the rotor 10 m The graph for 200 pF is the graph with dotted black circles (hereafter referred to as graph 4). Graph 4 shows the capacitance C n When the value is 250pF, the shaft voltage V sh The absolute value is in the range of |5V|. Graph 4 shows the capacitance C n When is 1000pF, the shaft voltage V sh Graph 4 also shows that the shaft voltage V sh The capacitance C whose absolute value falls within the range of |5V| n exists. The capacitance C of the rotor 10 m The graph for the capacitance C of 2000 pF is the dotted square graph (hereafter referred to as graph 5). n When the value is 250pF, the shaft voltage V sh The absolute value is in the range of |5V|. Graph 5 shows the capacitance C n When is 800pF, the shaft voltage V sh Graph 5 also shows that the shaft voltage V sh The capacitance C whose absolute value falls within the range of |5V| n exists.

[0039] As is clear from FIG. 3, the capacitance C m In the range of small to large values, the shaft voltage V sh The absolute value of the capacitance C can be made 5V or less. n It is clear that there exists. Specifically, when the capacitance Cm of the rotor 10 is in the range of 0.2 pF to 2000 pF, the capacitance C n For example, between 250pF and 5000pF, the shaft voltage V sh The absolute value of the capacitance C is within the range of 5V or less. n exists. Therefore, the electric motor 50 of the present disclosure does not require the arrangement of a dielectric layer 20 on the rotor 10 to adjust the capacitance distribution on the rotor 10 side, as in Patent Document 1. In other words, even in a rotor 10 of a general structure in which a dielectric layer 20 is not arranged on the rotor 10, it is possible to reduce the shaft voltage and suppress the occurrence of electrolytic corrosion in the bearings.

[0040] The above mechanism will be explained in detail with reference to FIG. When the stator core 6, the first bracket 1, and the second bracket 2 are electrically connected by the first conductive member 13a and the second conductive member 13b, the potential of the first metal bracket 1 and the second metal bracket 2 approaches the value of the neutral point potential S(3). In other words, the potential of the connection point A of the bearing outer ring becomes high. The potential B of the bearing inner ring is determined by the voltage division ratio due to the distribution of the electrostatic capacitance on the rotor 10 side. The electrostatic capacitance C between the stator core 6 and the magnet 11 g and the capacitance C of magnet 11 mg As a result, the potential B of the inner ring of the bearing is lower than the potential at the connection point A of the outer ring of the bearing. The potential difference between the potential at the connection point A of the outer ring of the bearing and the potential B of the inner ring of the bearing is the capacitance C of the rotor 10. m It fluctuates with the value of (see Figure 3).

[0041] Since the potential of the connection point A of the outer ring of the bearing is higher than the potential of the potential part B of the inner ring of the bearing, the capacitance C of the capacitive member 15 n This adjusts the capacitance distribution on the stator side and lowers the potential at connection point A of the bearing outer ring. This reduces the potential difference between the potential at connection point A of the bearing outer ring and potential B of the bearing inner ring. The capacitance C of the rotor 10 m As the value of is increased, the potential at connection point A of the outer ring of the bearing approaches the potential at potential point B of the inner ring of the bearing, and then the polarity is reversed. Furthermore, the capacitance C of the capacitive member 15 n As the voltage is increased, the potential difference increases.

[0042] Therefore, the capacitance C of the rotor 10 mBy selecting an appropriate capacitance Cn of the capacitive member 15 according to the value of (a), it becomes possible to reduce the shaft voltage. As described above, in the electric motor 50 of the present disclosure, the first metal bracket 1 and the second metal bracket 2 are electrically short-circuited using the first conductive member 13a, the first metal bracket 1 and the stator core 6 are electrically short-circuited using the second conductive member 13b, and a capacitive member 15 with electrostatic capacitance Cn is provided between the connection point A of the bearing outer ring and the zero reference potential N(12) of the drive circuit. In this state, the capacitance C of the capacitive member 15 is set so that the potential difference between the connection point A of the outer ring of the bearing and the connection point B of the inner ring of the bearing becomes small. n Adjust the value of the shaft voltage V sh This reduces the 1, the first metal bracket 1 and the second metal bracket 2 are connected and electrically shorted using a first conductive member 13a, and the first metal bracket 1 and the stator core 6 are connected and electrically shorted using a second conductive member 13b. In the above configuration, the first metal bracket 1, the second metal bracket 2, and the stator core 6 are connected and have the same potential. In addition to the configuration shown in FIG. 1, the following modified examples 1 and 2 are also possible configurations that achieve this same potential.

[0043] Modification 1 will be described. (Variation 1) FIG. 4 is a diagram showing a modified example of the electric motor 50 of FIG. The difference from FIG. 1 is that second conductive member 13b is disposed between stator core 6 and second metal bracket 2, electrically connecting stator core 6 and second metal bracket 2. In the case of FIG. 4, the connection point A of the bearing outer ring is the connection point A between the second conductive member 13b and the second metal bracket 2 (A on the right side in FIG. 4). FIG. 5 is a model diagram of the capacitance distribution of the electric motor 50 of FIG. 2 in that the second conductive member 13b electrically connects and shorts the stator core 6 and the second metal bracket 2. The short-circuit point between the stator core 6 and the second metal bracket 2 is connection point A of the bearing outer ring. Modification 1 provides the same functions and effects as those of FIGS.

[0044] (Variation 2) Modification 2 will be described. FIG. 6 is a diagram showing another modified example of the electric motor 50 of FIG. The difference from FIGS. 1 and 4 is that the first conductive member 13a is eliminated and a third conductive member 13c is provided instead. The second conductive member 13b is disposed between the stator core 6 and the second metal bracket 2, and electrically connects the stator core 6 and the second metal bracket 2. The third conductive member 13c is disposed between the stator core 6 and the first metal bracket 1, and electrically connects the stator core 6 and the first metal bracket 1. In the case of Figure 6, there are two connection points A of the bearing outer ring: (1) the first point is the connection point A between the second conductive member 13b and the second metal bracket 2 (A on the right side of Figure 6), and (2) the second point is the connection point A between the third conductive member 13c and the first metal bracket 1 (A on the left side of Figure 6). In the case of Figure 6, the location at the same potential as connection point A of the bearing outer ring is the location that electrically connects the first metal bracket 1, the second conductive member 13b, the third conductive member 13c, and the second metal bracket 2.

[0045] FIG. 7 is a model diagram of the capacitance distribution of the electric motor 50 of FIG. 2 and 5 in that the second conductive member 13b electrically connects the stator core 6 to the second metal bracket 2, and the third conductive member 13c electrically connects the stator core 6 to the first metal bracket 1, creating a short circuit. The point at which these short circuits occur is connection point A of the bearing outer ring. Modification 2 provides the same functions and effects as those of FIGS.

[0046] (Variation 3) FIG. 8 is a diagram showing another modified example of the electric motor 50 of FIG. The difference from FIG. 1 is that a printed circuit board 12 on which a drive circuit (not shown) is mounted is disposed between the second metal bracket 2 and the rotating body 9. In FIG. 8, the second conductive member 13b is disposed between the second metal bracket 2 and the stator core 6, and electrically connects the stator core 6 and the second metal bracket 2. In FIG. Modification 3 provides the same functions and effects as those of FIGS. In addition, in variant example 3, as shown in Figure 1, the second conductive member 13b may be arranged between the first metal bracket 1 and the stator core 6, thereby electrically connecting the stator core 6 and the first metal bracket 1.

[0047] (Embodiment 2) As an example of an electrical device according to the present disclosure, the configuration of an air conditioner indoor unit will be described in detail as embodiment 2. The electrical device according to the present disclosure is not necessarily limited to this example.

[0048] In FIG. 10, a brushless motor 101 is provided in a housing 111 of an air conditioner indoor unit 110. A crossflow fan 112, which is a blower fan, is attached to the rotating shaft of the brushless motor 101. The brushless motor 101 is driven by a motor drive device 113. When energized by the motor drive device 113, the brushless motor 101 rotates, which in turn rotates the crossflow fan 112. The rotation of the crossflow fan 112 blows conditioned air into the room via an indoor unit heat exchanger (not shown). Here, the brushless motor 101 can be, for example, the electric motor 50 of the first embodiment described above.

[0049] The electric device of the present disclosure includes a brushless motor and a housing in which the brushless motor is mounted, and employs the electric motor of the first embodiment described above as the brushless motor.

[0050] (Embodiment 3) As an example of an electrical device according to the present disclosure, the configuration of an outdoor unit of an air conditioner will be described in detail as a third embodiment.

[0051] 11, air conditioner outdoor unit 201 includes brushless motor 208 inside housing 211. Brushless motor 208 has blower fan 212 attached to its rotation shaft.

[0052] Air conditioner outdoor unit 201 is divided into a compressor chamber 206 and a heat exchanger chamber 209 by a partition plate 204 erected on a bottom plate 202 of a housing 211. A compressor 205 is provided in the compressor chamber 206. A heat exchanger 207 and a blower fan motor 208 are disposed in the heat exchanger chamber 209. An electrical component box 210 is provided above the partition plate 204.

[0053] The blower fan motor 208 is driven by a motor drive device housed in an electrical component box 210. As the brushless motor 208 rotates, the blower fan 212 rotates and blows air into the heat exchanger chamber 209 through the heat exchanger 207. Here, the brushless motor 208 can be, for example, the electric motor 50 of the first embodiment described above.

[0054] The electric device of the present disclosure includes a brushless motor and a housing in which the brushless motor is mounted, and employs the electric motor 50 of the first embodiment described above as the brushless motor.

[0055] (Embodiment 4) As an example of an electrical device according to the present disclosure, the configuration of a water heater will be described in detail as a fourth embodiment.

[0056] 12, a brushless motor 333 is provided in a housing 331 of a water heater 330. A blower fan 332 is attached to the rotating shaft of the brushless motor 333.

[0057] Brushless motor 333 is driven by motor drive device 334. Brushless motor 333 rotates when energized by motor drive device 334, which in turn rotates blower fan 332. The rotation of blower fan 332 blows air necessary for combustion into a fuel vaporization chamber (not shown). Here, brushless motor 333 can be, for example, electric motor 50 of the first embodiment described above.

[0058] The electric device of the present disclosure includes a brushless motor and a housing in which the brushless motor is mounted, and employs the electric motor 50 of the first embodiment described above as the brushless motor.

[0059] 1 of the first embodiment, the capacitive member 15 is disposed inside the electric motor 50, but as shown in FIG. 9, the capacitive member 15 may be disposed outside the electric motor 50 by passing through an opening (not shown) in the electric motor 50. The capacitive member 15 may be disposed anywhere outside the electric motor 50, for example, on the outer wall of the housing of the electric motor 50. Furthermore, the capacitive member 15 may be provided, for example, at a position away from the electric motor 50. This allows the electric motor 50 to be made even more compact. The aspect of FIG. 9 is not limited to the first embodiment, but can also be applied to the second to fourth embodiments.

[0060] 1 of the first embodiment, the printed circuit board 12 equipped with the drive circuit is provided inside the electric motor 50, but the printed circuit board 12 equipped with the drive circuit may be provided outside the electric motor 50. In this case, the electric motor 50 can be made compact.

[0061] In the second to fourth embodiments, a blower fan is used as the device rotated by the electric motor 50, but the device is not particularly limited as long as it is rotated by the electric motor 50. The inventions according to the first to fourth embodiments can be replaced or combined as long as no contradiction occurs.

[0062] As described above, the present disclosure includes the electric motors and electric devices equipped with the electric motors described in the following items.

[0063] [Item 1] a stator including a stator core wound with a stator winding; a rotor that faces the stator and holds a plurality of magnets in a circumferential direction, or that holds a plurality of magnets in a spoke-like manner from the center; a rotor including the rotating body and a shaft to which the rotating body is fastened so as to pass through the center of the rotating body; a first bearing and a second bearing that support the rotating body; An electric motor comprising a first metal bracket that fixes the first bearing and a second metal bracket that fixes the second bearing, the stator core, the first metal bracket, and the second metal bracket are electrically connected, When the connection point between the stator core and the first metal bracket or the second metal bracket is defined as connection point A of the bearing outer ring, A capacitance C is provided between a point at the same potential as the connection point A of the bearing outer ring and the zero reference potential of the drive circuit that applies voltage to the stator winding. n An electric motor provided with a capacitive member. According to the above aspect, by connecting the first metal bracket 1, the second metal bracket 2, and the stator core 6, the capacitance distribution on the stator 18 side and the capacitance distribution on the rotor 10 side are changed from a separated form via the capacitances of the first bearing 5a and the second bearing 5b to a mixed form. This brings the potential of the connection point A of the outer ring of the bearing and the potential of the connection point B of the inner ring of the bearing closer together, and in this state, the potential difference between the potential of connection point A and the potential of connection point B is further reduced by the capacitive member 15, thereby reducing the axial voltage.

[0064] [Item 2] the first metal bracket and the second metal bracket are electrically connected using a first conductive member; Item 1. The electric motor according to item 1, wherein the stator core and the first metal bracket or the second metal bracket are electrically connected using a second conductive member. According to the above aspect, by using the first conductive member and the second conductive member to connect the first metal bracket 1 or the second metal bracket 2 to the stator core 6, the capacitance distribution on the stator 18 side and the capacitance distribution on the rotor 10 side are changed from a separated form via the capacitance of the first bearing 5a and the second bearing 5b to a mixed form. This brings the potential of the connection point A of the outer ring of the bearing and the potential of the connection point B of the inner ring of the bearing closer together, and in this state, the potential difference between the potential of connection point A and the potential of connection point B is further reduced by the capacitive member 15, thereby reducing the axial voltage.

[0065] [Item 3] the stator core and the second metal bracket are electrically connected using a second conductive member, Item 1. The electric motor according to item 1, wherein the stator core and the first metal bracket are electrically connected using a third conductive member. According to the above aspect, by using the second conductive member and the third conductive member to connect the first metal bracket 1 or the second metal bracket 2 to the stator core 6, the capacitance distribution on the stator 18 side and the capacitance distribution on the rotor 10 side are changed from a separated form via the capacitance of the first bearing 5a and the second bearing 5b to a mixed form. This brings the potential of the connection point A of the outer ring of the bearing and the potential of the connection point B of the inner ring of the bearing closer together, and in this state, the potential difference between the potential of connection point A and the potential of connection point B is further reduced by the capacitive member 15, thereby reducing the axial voltage.

[0066] [Item 4] 4. The electric motor according to any one of items 1 to 3, wherein the zero reference potential of the drive circuit is insulated from the earth. According to the above aspect, the zero reference potential of the drive circuit is isolated from the earth. In this case, the neutral point potential of the stator winding fluctuates due to the switching of the power elements, which leads to an increase in shaft voltage. According to the above aspect, the shaft voltage can be reduced.

[0067] [Item 5] When the capacitance of the rotor is in the range of 0.2 pF to 2000 pF, the capacitive member has a capacitance C such that the potential difference between the voltage at the connection point of the outer ring of the bearing and the voltage at the inner rings of the first bearing and the second bearing is 5 V or less in absolute value. n 5. The electric motor according to any one of items 1 to 4, comprising: According to the above aspect, when the range of the capacitance of the rotor is 0.2 pF or more and 2000 pF or less, the capacitance C satisfies that the shaft voltage is 5 V or less in absolute value. n It has.

[0068] [Item 6] 6. The electric motor according to any one of items 1 to 5, wherein the capacitive member is used to reduce the voltage at the connection point of the outer ring of the bearing, thereby reducing the potential difference between the voltage at the connection point of the outer ring of the bearing and the voltage at the inner ring of the bearing. According to the above aspect, by connecting the first metal bracket 1 or the second metal bracket 2 to the stator core 6, the capacitance distribution on the stator 18 side and the capacitance distribution on the rotor 10 side are changed from a separated form via the capacitances of the first bearing 5a and the second bearing 5b to a mixed form. This brings the potential of connection point A of the outer ring of the bearing and the potential of connection point B of the inner ring of the bearing closer together, and in this state, the potential difference between the potential of connection point A and the potential of connection point B is further reduced by the capacitive member 15, thereby reducing the shaft voltage.

[0069] [Item 7] 7. The electric motor according to any one of items 1 to 6, wherein the capacitive member is provided outside the electric motor. According to the above aspect, the electric motor can be made compact without being restricted by the space of the capacitive member.

[0070] [Item 8] 7. The electric motor according to any one of items 1 to 6, wherein the capacitive member is provided inside the electric motor. According to the above aspect, the space outside the electric motor is not affected.

[0071] [Item 9] 9. The electric motor according to any one of items 1 to 8, wherein a printed circuit board including the drive circuit is provided outside the electric motor. According to the above aspect, the electric motor can be made compact, and the internal space of the electric motor is not affected.

[0072] [Item 10] 9. The electric motor according to any one of items 1 to 8, wherein a printed circuit board including the drive circuit is provided inside the electric motor. According to the above aspect, there is no impact on the space outside the motor.

[0073] [Item 11] 11. An electric device equipped with the electric motor according to any one of items 1 to 10 and a blower fan driven by the electric motor. According to the above aspect, it is possible to suppress the occurrence of electrolytic corrosion in the bearing of the electric motor of the electric device equipped with the blower fan. [Explanation of symbols]

[0074] 1 First metal bracket 2 Second metal bracket 3 Stator Winding 4 shafts 5a First bearing 5b Second bearing 6 Stator core 7. Resin 8 Rotor core 9 Rotating Body 10 rotor 12 Printed circuit board 13 Short-circuiting member 13a First conductive member 13b Second conductive member 13c Third conductive member 15 Capacitive Members 18 Stator 20 dielectric layer 50 Electric motor

Claims

1. a stator including a stator core wound with a stator winding; a rotor that faces the stator and holds a plurality of magnets in a circumferential direction, or that holds a plurality of magnets in a spoke-like manner from the center; a rotor including the rotating body and a shaft to which the rotating body is fastened so as to pass through the center of the rotating body; a first bearing and a second bearing that support the rotating body; An electric motor comprising a first metal bracket that fixes the first bearing and a second metal bracket that fixes the second bearing, the stator core, the first metal bracket, and the second metal bracket are electrically connected to each other; When the connection point between the stator core and the first metal bracket or the second metal bracket is defined as connection point A of the bearing outer ring, A capacitance C is provided between a point at the same potential as the connection point A of the bearing outer ring and the zero reference potential of the drive circuit that applies voltage to the stator winding. ｎ a capacitive member of the stator is molded from resin to form an insulating housing, the first metal bracket and the second metal bracket are fixed to the housing, The housing is insulated from the ground, The capacitance C between the stator winding and the first metal bracket ｓｂ１ and the capacitance C between the stator winding and the second metal bracket ｓｂ２ The composite capacitance of the above-mentioned is defined as composite capacitance A2, and the capacitance between the zero reference potential of the drive circuit that applies voltage to the stator winding and the first metal bracket is defined as C ｎｂ２ and the capacitance C between the stator winding and the stator core is ｉ and the capacitance C between the stator core and the magnet ｇ and the capacitance C between the stator winding and the magnet ｓｍ and the electrostatic capacitance C of the magnet ｍｇ The rotor capacitance C ｍ The composite capacitance B2 is defined as the composite capacitance B2, and the capacitance between the zero reference potential of the drive circuit and the shaft is defined as C ｎｓ When we define The combined capacitance A2 and the C ｎｂ２ The voltage division ratio R Ａ２ (Combined capacitance A2 / C ｎｂ２ ) and the combined capacitance B2 and C ｎｓ The voltage division ratio R Ｂ２ (composite capacitance B2 / C ｎｓ ) and an electric motor that matches.

2. a stator including a stator core wound with a stator winding; a rotor that faces the stator and holds a plurality of magnets in a circumferential direction, or that holds a plurality of magnets in a spoke-like manner from the center; a rotor including the rotating body and a shaft to which the rotating body is fastened so as to pass through the center of the rotating body; a first bearing and a second bearing that support the rotating body; An electric motor comprising a first metal bracket that fixes the first bearing and a second metal bracket that fixes the second bearing, the stator core, the first metal bracket, and the second metal bracket are electrically connected to each other; When the connection point between the stator core and the first metal bracket or the second metal bracket is defined as connection point A of the bearing outer ring, A capacitance C is provided between a point at the same potential as the connection point A of the bearing outer ring and the zero reference potential of the drive circuit that applies voltage to the stator winding. ｎ a capacitive member of the stator is molded from resin to form an insulating housing, the first metal bracket and the second metal bracket are fixed to the housing, The housing is insulated from the ground, The capacitance C between the stator winding and the stator core ｉ and the capacitance C between the stator core and the magnet ｇ and the capacitance C between the stator winding and the magnet ｓｍ and the electrostatic capacitance C of the magnet ｍｇ The rotor capacitance C ｍ When we define The rotor capacitance C ｍ In the range of 0.2 pF to 2000 pF, the capacitance C ｎ is between 250 pF and 5000 pF, and the capacitive member has a potential difference between the voltage at the connection point A of the outer ring of the bearing and the voltage at the inner rings of the first bearing and the second bearing of 5 V or less in absolute value. ｎ An electric motor having

3. the first metal bracket and the second metal bracket are electrically connected using a first conductive member; 3. The electric motor according to claim 1, wherein the stator core and the first metal bracket or the second metal bracket are electrically connected to each other by using a second conductive member.

4. a second conductive member electrically connecting the stator core and the second metal bracket; 3. The electric motor according to claim 1, wherein the stator core and the first metal bracket are electrically connected to each other using a third conductive member.

5. 5. The electric motor according to claim 1, wherein the zero reference potential of the drive circuit is insulated from the earth.

6. 6. An electric motor according to claim 1, wherein the capacitive member is used to reduce the voltage at connection point A of the outer ring of the bearing, thereby reducing the potential difference between the voltage at connection point A of the outer ring of the bearing and the voltage at the inner ring of the bearing.

7. 7. The electric motor according to claim 1, wherein the capacitive member is provided externally to the electric motor.

8. 7. The electric motor according to claim 1, wherein the capacitive member is provided inside the electric motor.

9. 9. The electric motor according to claim 1, wherein the printed circuit board having the drive circuit thereon is provided outside the electric motor.

10. 9. The electric motor according to claim 1, wherein a printed circuit board having the drive circuit thereon is provided inside the electric motor.

11. 11. An electric device equipped with the electric motor according to claim 1 and a blower fan driven by the electric motor.

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