electric motor

Abstract

This allows for fine-tuning and performance verification of the electric motor after its completion, while also reducing the shaft voltage. [Solution] An electric motor comprising: a rotor having a magnet; a stator having windings; a shaft that rotates with the rotor; a bearing disposed on the shaft; a metal plate supporting the bearing; a substrate that outputs a drive signal to the windings; a housing that accommodates at least the rotor, stator, and bearing; and an adjusting capacitance section that adjusts the capacitance of a first capacitance section including stray capacitance due to the windings and the metal plate to be C1, a second capacitance section including stray capacitance due to the substrate and the metal plate to be C2, a third capacitance section including stray capacitance due to the rotor and stator to be C3, and a fourth capacitance section including stray capacitance due to the substrate and the shaft to be C4, such that the ratio of C1 to C2 is as close as possible to the ratio of C3 to C4.

Description

【Technical Field】 【0001】 The present invention relates to an electric motor. 【Background Art】 【0002】 Patent Document 1 describes a motor shaft current suppression mechanism. By additionally introducing a capacitor C3, this motor shaft current suppression mechanism can ground the controller and the three-phase lines of the motor, and can divide the high-frequency common-mode voltage. Therefore, this motor shaft current suppression mechanism can achieve the purpose of reducing the voltage transmitted to the bearing and suppressing the electrolytic corrosion of the bearing. 【0003】 Patent Document 2 describes a permanent magnet motor. In this permanent magnet motor, the capacitance Cr on the rotor side is in a state larger than the capacitance Cs on the stator side. By attaching a conductive sheet to this permanent magnet motor, the capacitance of Cs can be easily increased to bring Cs close to the capacitance of Cr. Thereby, the shaft voltage can be reduced and the occurrence of electrolytic corrosion at the bearing can be suppressed. 【Prior Art Documents】 【Patent Documents】 【0004】 【Patent Document 1】 Chinese Patent Application Publication No. 116317370 【Patent Document 2】 Japanese Unexamined Patent Application Publication No. 2020-146439 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0005】 For example, there is a method of reducing the shaft voltage by providing an insulating layer on the rotor core. However, with this method, fine adjustment and effect confirmation cannot be performed after the completion of the electric motor. 【0006】 The objective of this invention is to reduce the shaft voltage while enabling fine-tuning and verification of the electric motor's effectiveness after its completion. [Means for solving the problem] 【0007】 To this end, the present invention provides an electric motor comprising: a rotor having a magnet; a stator having windings; a shaft that rotates with the rotor; a bearing disposed on the shaft; a metal plate supporting the bearing; a substrate that outputs a drive signal to the windings; a housing that accommodates at least the rotor, stator, and bearing; and an adjusting capacitance section that adjusts the capacitance of a first capacitance section including stray capacitance due to the windings and the metal plate to be C1, the capacitance of a second capacitance section including stray capacitance due to the substrate and the metal plate to be C2, the capacitance of a third capacitance section including stray capacitance due to the rotor and stator to be C3, and the capacitance of a fourth capacitance section including stray capacitance due to the substrate and the shaft to be C4, such that the ratio of C1 to C2 is as close as possible to the ratio of C3 to C4. 【0008】 The regulating capacitance section may be provided in the first capacitance section. In that case, the regulating capacitance section may be connected in parallel with the stray capacitance caused by the winding and the metal sheet in the first capacitance section. 【0009】 The regulating capacitance section may be provided in the second capacitance section. In that case, the regulating capacitance section may be connected in parallel with the stray capacitance caused by the substrate and the metal sheet in the second capacitance section. 【0010】 The adjustment capacitance section may be provided in the fourth capacitance section. In that case, the substrate is provided inside the housing, and the adjustment capacitance section may be composed of a metal member provided between the substrate and the shaft in the fourth capacitance section. [Effects of the Invention] 【0011】 According to the present invention, it is possible to reduce the shaft voltage while enabling fine-tuning and verification of the effect of the electric motor after its completion. 【Brief Description of the Drawings】 【0012】 [Figure 1] It is a cross-sectional view showing a configuration example of an electric motor to which the present embodiment is applied. [Figure 2] It is an equivalent circuit diagram regarding the capacitance of an electric motor to which the present embodiment is applied. [Figure 3] It is a cross-sectional view showing a configuration example of an electric motor in the first embodiment. [Figure 4] It is an equivalent circuit diagram regarding the capacitance of an electric motor in the first embodiment. [Figure 5] It is a diagram showing a specific connection example of an adjustment capacitor in the first embodiment. [Figure 6] It is a graph showing that the shaft voltage can be adjusted to 0 V by changing the capacitance of the adjustment capacitor. [Figure 7A] It is a graph showing the common mode voltage and shaft voltage at point P1 in FIG. 6. [Figure 7B] It is a graph showing the common mode voltage and shaft voltage at point P2 in FIG. 6. [Figure 7C] It is a graph showing the common mode voltage and shaft voltage at point P3 in FIG. 6. [Figure 7D] It is a graph showing the common mode voltage and shaft voltage at point P4 in FIG. 6. [Figure 8] It is a cross-sectional view showing a configuration example of an electric motor in the second embodiment. [Figure 9] It is an equivalent circuit diagram regarding the capacitance of an electric motor in the second embodiment. [Figure 10] It is a diagram showing a specific connection example of an adjustment capacitor in the second embodiment. [Figure 11] It is a cross-sectional view showing a configuration example of an electric motor in the third embodiment. 【Modes for Carrying Out the Invention】 【0013】 Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. 【0014】 [Electric motor] (General form) FIG. 1 is a cross-sectional view showing a configuration example of an electric motor 5 to which the present embodiment is applied. As shown in FIG. 1, the electric motor 5 includes a rotor 10, a stator 20, and a shaft 30. The electric motor 5 further includes a first bearing 41, a second bearing 42, a first metal steel plate 51, a second metal steel plate 52, a substrate 60, and a housing 70. Hereinafter, as the electric motor 5, a spoke-type IPM (Interior Permanent Magnet) motor in which magnets 12 are radially embedded in the rotor 10 will be described as an example. 【0015】 The rotor 10 is disposed inside the stator 20 with a gap therebetween. The rotor 10 rotates in the electric motor 5 and has a rotor core 11 and magnets 12. The rotor core 11 has an annular hub portion 111 on the radially inner side and a plurality of radial spoke portions 112 on the radially outer side. There are a plurality of magnets 12, and each of the plurality of magnets 12 faces the stator 20 and is radially disposed between adjacent spoke portions 112. Note that FIG. 1 is a cross-sectional view of the electric motor 5 cut along a cutting plane passing through the center of the spoke portion 112 from the shaft 30 and extending radially outward, so the magnets 12 do not exist on this cutting plane. However, in FIG. 1, the magnets 12 are also shown for the purpose of explanation. 【0016】 The stator 20 generates a rotating magnetic field and rotates the rotor 10 by the rotating magnetic field. The stator 20 has a stator core 21 and windings 22. The windings 22 are wound around the stator 20 via an insulator 23 for insulating the stator core 21. And the stator 20 is molded with resin together with other fixed members. In the present embodiment, by integrally molding these members, the stator 20 having a generally cylindrical outer shape is configured. 【0017】 The shaft 30 is fixed to the rotor 10 and rotates together with the rotor 10. The shaft 30 rotates supported by a first bearing 41 and a second bearing 42. The shaft 30 protrudes from the first metal plate 51. 【0018】 The first bearing 41 is positioned at the upper end of the shaft 30 and supports the shaft 30. The first bearing 41 is a cylindrical bearing having a plurality of balls 411. The inner ring 412 side of the first bearing 41 is fixed to the shaft 30 and electrically conductive. The outer ring 413 side of the first bearing 41 is fixed to the first metal plate 51 and electrically conductive. The second bearing 42 is positioned at the lower end of the shaft 30 and supports the shaft 30. The second bearing 42 is a cylindrical bearing having a plurality of balls 421. The inner ring 422 side of the second bearing 42 is fixed to the shaft 30 and electrically conductive. The outer ring 423 side of the second bearing 42 is fixed to the second metal plate 52 and electrically conductive. The first bearing 41 and the second bearing 42 are examples of bearings. 【0019】 The first metal plate 51 is a conductive member positioned at the upper end of the electric motor 5. The first metal plate 51 supports the first bearing 41, which is positioned in its central part. The second metal plate 52 is a conductive member located at the lower end of the electric motor 5. The second metal plate 52 supports the second bearing 42 located in its central part. The outer diameter of the second metal plate 52 is the same as or larger than the outer diameter of the first metal plate 51. This ensures that the first bearing 41 and the second bearing 42 are stably supported, allowing the shaft 30 to rotate. The first metal sheet 51 and the second metal sheet 52 are examples of metal sheets. 【0020】 The circuit board 60 is placed inside the electric motor 5 and has a drive circuit (not shown) mounted on it that outputs a drive signal to generate a rotating magnetic field on the winding 22. The circuit board 60 is placed between the rotor 10 and stator 20 and the second metal sheet 52. For example, the drive circuit has an inverter circuit or the like mounted on it to apply voltage to the winding 22. The circuit board 60 also uses the reference point GND as the reference point of the circuit. 【0021】 The housing 70 houses at least the rotor 10, the stator 20, the first bearing 41, and the second bearing 42. In Figure 1, the housing 70 further houses the circuit board 60. Specifically, the housing 70 houses these components together with the first metal plate 51 and the second metal plate 52. 【0022】 With the motor 5 configured as described above, applying voltage to the winding 22 from the drive circuit causes current to flow through the winding 22, generating a magnetic field from the stator core 21. Then, the rotating magnetic field from the stator core 21 and the magnetic field from the magnet 12 generate attractive and repulsive forces depending on the polarity of these magnetic fields. These forces cause the rotor 10 to rotate around the shaft 30. 【0023】 Figure 2 is an equivalent circuit diagram relating to the capacitance of the electric motor 5 to which this embodiment is applied. As shown in Figure 2, the substrate 60 applies a common-mode voltage Vcom to the winding 22, which is the potential difference between the reference point GND of the substrate 60 and the neutral point NP of the winding 22. Furthermore, as shown in Figures 1 and 2, a capacitance Cr exists between the winding 22 and the second metal sheet 52. A capacitance Cn exists between the reference point GND of the substrate 60 and the second metal steel plate 52. A capacitance Cs exists in the insulator 23 between the winding 22 and the stator core 21, and a capacitance Cg exists in the air gap between the stator core 21 and the rotor core 11. A capacitance Cm exists between the winding 22 and the magnet 12. A capacitance Cmg exists within the magnet 12. A capacitance Csn exists between the reference point GND of the substrate 60 and the shaft 30. A capacitance Cb1 exists between the inner ring 412 and the outer ring 413 of the first bearing 41. A capacitance Cb2 exists between the inner ring 422 and the outer ring 423 of the second bearing 42. 【0024】 (Background and Overview) By the way, this type of electric motor 5 employs a PWM (Pulse Width Modulation) inverter. However, in a PWM inverter, a common-mode voltage is generated by switching, and this common-mode voltage is divided according to the capacitance within the motor 5. This creates a potential difference called the shaft voltage between the inner ring 412 and the outer ring 413 of the first bearing 41, and between the inner ring 422 and the outer ring 423 of the second bearing 42. If the shaft voltage exceeds the dielectric breakdown voltage of the bearing grease film, it can lead to electrolytic corrosion that damages the surfaces inside the first bearing 41 and the second bearing 42, so it is desirable for the shaft voltage to be small. In this embodiment, the shaft voltage is brought close to 0V by adjusting the ratio in which the common-mode voltage is divided within the electric motor 5, thereby suppressing the occurrence of electrolytic corrosion. 【0025】 Here, methods to suppress the occurrence of electrolytic corrosion include, firstly, improving the dielectric breakdown strength of the first bearing 41 and the second bearing 42, and secondly, reducing the shaft voltage. A major example of the former method is to replace the balls 411 of the first bearing 41 and the balls 421 of the second bearing 42 with ceramic. However, this method has the drawback of significantly increasing material costs. On the other hand, an example of the latter method is to provide an insulating layer on the rotor core 11. However, this method has drawbacks such as the inability to fine-tune the insulating layer once the mold is made, and the inability to confirm the effect of the insulating layer on the shaft voltage only after the electric motor 5 is completed. 【0026】 To reduce the shaft voltage, for the first bearing 41, it is preferable to make the magnitude of the voltage divided between the inner ring 412 and the outer ring 413 equal. Similarly, for the second bearing 42, it is preferable to make the magnitude of the voltage divided between the inner ring 422 and the outer ring 423 equal. In other words, it is preferable to make the magnitude of the voltage divided between the shaft 30 and the second metal plate 52 equal. To achieve this, the following capacitance relationships must be ensured. Specifically, let C1 be the capacitance of capacitance group 81 between the winding 22 and the second metal sheet 52. Let C2 be the capacitance of capacitance group 82 between the reference point GND on the substrate 60 and the second metal sheet 52. Let C3 be the capacitance of capacitance group 83 between the winding 22 and the shaft 30, that is, between the rotor 10 and the stator 20. Let C4 be the capacitance of capacitance group 84 between the reference point GND on the substrate 60 and the shaft 30. In this case, the ratio of capacitance C1 to capacitance C2 is equal to the ratio of capacitance C3 to capacitance C4. In other words, the relationship is "C1:C2=C3:C4". However, since the capacitance C3 is affected by the thickness of the magnet 12 and the insulator 23, as well as the air gap, it cannot be adjusted without changing the performance of the electric motor 5. 【0027】 Therefore, in this embodiment, the relationship "C1:C2=C3:C4" is ensured by adding an adjustment capacitor and adjusting at least one of the capacitances C1, C2, and C4. This allows the size of the capacitance Cadj of the adjustment capacitor to be determined according to the size of the capacitance other than that to be adjusted after the motor 5 is completed. As a result, the shaft voltage can be reduced while maintaining the characteristics of the motor 5. Here, the adjustment capacitor may be a fixed-capacity capacitor or a variable-capacity capacitor. 【0028】 Capacitance group 81 is an example of a first capacitance section including stray capacitance due to the winding and the metal sheet. Capacitance group 82 is an example of a second capacitance section including stray capacitance due to the substrate and the metal sheet. Capacitance group 83 is an example of a third capacitance section including stray capacitance due to the rotor and the stator. Capacitance group 84 is an example of a fourth capacitance section including stray capacitance due to the substrate and the shaft. The adjustment capacitor is an example of an adjustment capacitance section that adjusts the ratio of C1 to C2 to be as close as possible to the ratio of C3 to C4. 【0029】 (First Embodiment) Figure 3 is a cross-sectional view showing an example of the configuration of the electric motor 1 in the first embodiment. As shown in Figure 3, the electric motor 1 has an adjustment capacitor 91 provided between the winding 22 and the second metal plate 52 in Figure 1. 【0030】 Figure 4 is an equivalent circuit diagram relating to the capacitance of the electric motor 1 in the first embodiment. As shown in Figure 4, the electric motor 1 is provided with an adjustment capacitor 91 in the capacitance group 81 in Figure 2. In this case, the adjustment capacitor 91 is preferably connected in parallel with the capacitance Cr between the winding 22 and the second metal sheet 52 in the capacitance group 81. 【0031】 Figure 5 shows a specific example of the connection of the adjustment capacitor 91. As shown in Figure 5, one end of the adjustment capacitor 91 is connected to the neutral point NP of the winding 22. The other end of the adjustment capacitor 91 is connected to the second metal plate 52. Specifically, the other end of the adjustment capacitor 91 is connected to a screw hole that secures the second metal plate 52 on the substrate 60 (see Figure 3), and is electrically connected to the second metal plate 52 through the screw. Furthermore, the capacitance Cadj of the adjustment capacitor 91 should be set from the capacitances C2, C3, and C4 after the motor 1 is completed. For example, the capacitance Cadj of the adjustment capacitor 91 is expected to be between a few pF and several tens of pF. However, the capacitance Cadj of the adjustment capacitor 91 must be set to less than or equal to the output capacity of the inverter. 【0032】 In the first embodiment, an adjustment capacitor 91 is added between the neutral point NP of the winding 22 and the second metal sheet 52 to adjust the capacitance C1. As a result, the relationship "C1:C2=C3:C4" can be ensured simply by mounting the adjustment capacitor 91 on the substrate 60, and the shaft voltage can be reduced. 【0033】 In this way, the axis voltage can be adjusted to 0V by changing the capacitance Cadj of the adjustment capacitor 91. Figure 6 is a graph illustrating this. Figures 7A to 7D are graphs showing the common-mode voltage and axis voltage at points P1 to P4 in Figure 6, respectively. In Figures 7A to 7D, the common-mode voltage is shown by a dashed line and the axis voltage by a solid line. 【0034】 Furthermore, here, the capacitance C2 of capacitance group 82 is set to 8.6pF, the capacitance C3 of capacitance group 83 is set to 74pF, and the capacitance C4 of capacitance group 84 is set to 16.4pF. Then, by increasing the capacitance Cadj of the adjustment capacitor 91 from 0pF, the capacitance C1 of capacitance group 81 is increased from 6.65pF. In addition, the shaft voltage is the voltage of the shaft 30 with the second metal plate 52 as the reference. 【0035】 First, consider the case where the capacitance Cadj of the adjustment capacitor 91 is 0 pF, such as at point P1. In this case, since the capacitance C1 of the capacitance group 81 is 6.65 pF, C1×C4 is approximately 109. On the other hand, C2×C3 is approximately 636. Therefore, "C1×C4 < C2×C3" holds. That is, since C1 / C2 is smaller than C3 / C4, the potential of the shaft 30 becomes higher than that of the second metal steel plate 52. Therefore, the shaft voltage is positive in FIG. 7A. Also, since it can be seen from FIG. 7A that the shaft voltage is 6V, in FIG. 6, the shaft voltage with respect to point P1 is 6V. 【0036】 Next, consider the case where the capacitance Cadj of the adjustment capacitor 91 is 21.9 pF, such as at point P2. In this case, since the capacitance C1 of the capacitance group 81 is 28.55 pF, C1×C4 is approximately 468. On the other hand, C2×C3 is approximately 636. Therefore, "C1×C4 < C2×C3" holds. That is, since C1 / C2 is smaller than C3 / C4, the potential of the shaft 30 becomes higher than that of the second metal steel plate 52. Therefore, the shaft voltage is positive in FIG. 7B. Also, since it can be seen from FIG. 7B that the shaft voltage is 2V, in FIG. 6, the shaft voltage with respect to point P2 is 2V. 【0037】 Next, consider the case where the capacitance Cadj of the adjustment capacitor 91 is 66 pF, such as at point P3. In this case, since the capacitance C1 of the capacitance group 81 is 72.65 pF, C1×C4 is approximately 1191. On the other hand, C2×C3 is approximately 636. Therefore, "C1×C4 > C2×C3" holds. That is, since C1 / C2 is larger than C3 / C4, the potential of the second metal steel plate 52 becomes higher than that of the shaft 30. Therefore, the shaft voltage is negative in FIG. 7C. Also, since it can be seen from FIG. 7C that the shaft voltage is -4V, in FIG. 6, the shaft voltage with respect to point P3 is -4V. 【0038】 Next, consider the case where the capacitance Cadj of the adjustment capacitor 91 is 141pF, as shown at point P4. In this case, the capacitance C1 of capacitance group 81 is 147.65pF, so C1 × C4 is approximately 2421. On the other hand, C2 × C3 is approximately 636. Therefore, "C1 × C4 > C2 × C3" holds true. In other words, C1 / C2 is larger than C3 / C4, so the potential of the second metal plate 52 is higher than that of the shaft 30. Consequently, the shaft voltage is negative in Figure 7D. Also, from Figure 7D, we can see that the shaft voltage is -8V, so in Figure 6, the shaft voltage at point P4 is -8V. 【0039】 Furthermore, the axial voltage at point P4 shown in Figure 7D exhibits waveform distortion. In contrast, the axial voltages at points P1 to P3 shown in Figures 7A to 7C do not exhibit waveform distortion. This is because, at points P1 to P3, the values ​​of C1×C4 and C2×C3 are relatively close. 【0040】 (Second Embodiment) Figure 8 is a cross-sectional view showing an example of the configuration of the electric motor 2 in the second embodiment. As shown in Figure 8, the electric motor 2 has an adjustment capacitor 92 provided between the substrate 60 and the second metal plate 52 in Figure 1. 【0041】 Figure 9 is an equivalent circuit diagram relating to the capacitance of the electric motor 2 in the second embodiment. As shown in Figure 9, the electric motor 1 is provided with an adjustment capacitor 92 in the capacitance group 82 in Figure 2. In this case, the adjustment capacitor 92 is preferably connected in parallel with the capacitance Cn between the substrate 60 and the second metal sheet 52 in the capacitance group 82. 【0042】 Figure 10 shows a specific example of the connection of the adjustment capacitor 92. As shown in Figure 10, one end of the adjustment capacitor 92 is connected to the potential supply point Vcc and the reference point GND of the substrate 60. The other end of the adjustment capacitor 92 is connected to the second metal plate 52. Specifically, the other end of the adjustment capacitor 92 is connected to a screw hole that secures the second metal plate 52 on the substrate 60, and is electrically connected to the second metal plate 52 through the screw. Furthermore, the capacitance Cadj of the adjustment capacitor 92 should be set from the capacitances C1, C3, and C4 after the motor 2 is completed. For example, the capacitance Cadj of the adjustment capacitor 92 is expected to be several pF to several tens of pF. However, the capacitance Cadj of the adjustment capacitor 92 must be set to less than or equal to the output capacity of the inverter. 【0043】 In the second embodiment, an adjustment capacitor 92 is added between the potential supply point Vcc and reference point GND of the substrate 60 and the second metal steel plate 52 to adjust the capacitance C2. As a result, the relationship "C1:C2=C3:C4" can be ensured simply by mounting the adjustment capacitor 92 on the substrate 60, and the axis voltage can be reduced. 【0044】 (Third embodiment) Figure 11 is a cross-sectional view showing an example of the configuration of the electric motor 3 in the third embodiment. As shown in Figure 11, the electric motor 3 has a metal member 93 provided between the base plate 60 and the shaft 30 in Figure 1. Here, the metal member 93 is preferably provided on the base plate 60 so as to face the shaft 30. The metal member 93 may have any shape, but for example, a ring shape that surrounds the shaft 30 is desirable. 【0045】 The equivalent circuit for the capacitance of the motor 3 in the third embodiment is not shown in the figure, but corresponds to the case in Figure 2 where a metal member 93 is provided in the capacitance group 84. In this case, the metal member 93 functions in the same way as when it is connected in parallel with the capacitance Csn between the substrate 60 and the shaft 30 in the capacitance group 84. 【0046】 In the third embodiment, a metal member 93 is added between the substrate 60 and the shaft 30 to adjust the capacitance C4. This makes it possible to ensure the relationship "C1:C2=C3:C4" even when it is not possible to ensure it by adjusting the capacitances C1 and C2, thereby reducing the shaft voltage. 【0047】 (modified version) In the first to third embodiments, the circuit board 60 is housed inside the housing 70. However, it is also conceivable that the circuit board 60 may be located outside the housing 70. In this case, the capacitance C2 of capacitance group 82 becomes extremely small because the distance between the reference point GND of the substrate 60 and the second metal sheet 52 increases, but it does not become zero. Furthermore, the capacitance C4 of capacitance group 84 will become extremely small as the distance between the reference point GND on the substrate 60 and the shaft 30 increases, but it will not become zero. Therefore, in this case as well, the relationship "C1:C2=C3:C4" holds true. [Explanation of Symbols] 【0048】 1, 2, 3, 5…Electric motor, 10…Rotor, 11…Rotor core, 12…Magnet, 20…Stator, 21…Stator core, 22…Winding, 30…Shaft, 41…First bearing, 42…Second bearing, 51…First metal sheet, 52…Second metal sheet, 60…Substrate, 70…Housing, 81~84…Capacitance group, 91, 92…Adjustment capacitor, 93…Metal component

Claims

[Claim 1] A rotor having a magnet, A stator having windings, A shaft that rotates together with the rotor, A bearing arranged on the aforementioned shaft, A metal steel plate supporting the bearing, A circuit board that outputs a drive signal for the winding, A housing comprising at least the rotor, the stator, and the bearing, When the capacitance of the first capacitance section, which includes stray capacitance due to the winding and the metal sheet, is C1, the capacitance of the second capacitance section, which includes stray capacitance due to the substrate and the metal sheet, is C2, the capacitance of the third capacitance section, which includes stray capacitance due to the rotor and the stator, is C3, and the capacitance of the fourth capacitance section, which includes stray capacitance due to the substrate and the shaft, is C4, an adjusting capacitance section is provided to adjust the ratio of C1 to C2 to be as close as possible to the ratio of C3 to C4. An electric motor equipped with the following features. [Claim 2] The electric motor according to claim 1, wherein the adjusting capacitance section is provided in the first capacitance section. [Claim 3] The electric motor according to claim 2, wherein the adjusting capacitance section is connected in parallel with the stray capacitance caused by the winding and the metal sheet in the first capacitance section. [Claim 4] The electric motor according to claim 1, wherein the adjusting capacitance section is provided in the second capacitance section. [Claim 5] The electric motor according to claim 4, wherein the adjusting capacitance section is connected in parallel with the stray capacitance caused by the substrate and the metal sheet in the second capacitance section. [Claim 6] The electric motor according to claim 1, wherein the adjusting capacitance section is provided in the fourth capacitance section. [Claim 7] The aforementioned circuit board is provided inside the housing, The electric motor according to claim 6, wherein the adjusting capacitance section is composed of a metal member provided between the substrate and the shaft in the fourth capacitance section.

Images