JP2013066252A - Motor and electrical apparatus provided with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent electric corrosion of a bearing in a motor that is driven by a PWM inverter.SOLUTION: A motor includes a stator, a rotating body, a bearing, and two brackets. The stator has a stator core with windings wound therearound. The rotating body includes: a rotor that faces the stator and holds permanent magnets along a circumferential direction thereof; and a shaft that fastens the rotor thereto so as to pass through the center of the rotor. The bearing holds the shaft. The two brackets fix the bearing. Shaft voltage generated between an inner ring and an outer ring of the bearing is set lower than withstand voltage of the bearing itself.

Description

  The present invention relates to an electric motor, and more particularly to an electric motor improved to suppress the occurrence of electrolytic corrosion of a bearing.

  In recent years, electric motors are often used in a system driven by an inverter of a pulse width modulation system (hereinafter referred to as a PWM system). In such PWM inverter drive, the neutral point potential of the winding does not become zero, and therefore a potential difference (hereinafter referred to as shaft voltage) is generated between the outer ring and the inner ring of the bearing. The shaft voltage includes a high-frequency component due to switching. When the shaft voltage reaches the dielectric breakdown voltage of the oil film inside the bearing, a minute current flows inside the bearing and electric corrosion occurs inside the bearing. When electrolytic corrosion progresses, a wavy wear phenomenon may occur in the bearing inner ring, the bearing outer ring or the bearing ball, resulting in abnormal noise, which is one of the main causes of problems in the motor.

Conventionally, the following countermeasures have been considered to suppress electric corrosion.
(1) Bring the bearing inner ring and bearing outer ring into a conductive state.
(2) Insulate the bearing inner ring and the bearing outer ring.
(3) Reduce the shaft voltage.

  As a specific method of the above (1), it is possible to make the bearing lubricant conductive. However, the conductive lubricant has problems such as deterioration of conductivity with time and lack of sliding reliability. Moreover, although the method of installing a brush in a rotating shaft and making it a conduction | electrical_connection state is also considered, this method also has subjects, such as a brush abrasion powder and space being required.

  As a specific method of the above (2), the iron ball in the bearing is changed to a non-conductive ceramic ball. This method has a very high effect of suppressing electrolytic corrosion, but has a problem of high cost, and cannot be used for a general-purpose electric motor.

  As a specific method of the above (3), there is known a method of reducing the axial voltage by changing the capacitance by electrically short-circuiting the stator iron core and the conductive metal bracket. (For example, refer to Patent Document 1). In addition, a configuration in which a stator core of an electric motor or the like is electrically connected to the earth ground is also known (see, for example, Patent Document 2).

  By the way, in recent years, a mold motor has been proposed in which a fixing member such as a stator core on the stator side is molded with a molding material or the like to improve reliability. Therefore, it is considered to fix the bearing with such an insulating mold material instead of the metal bracket to suppress unnecessary high-frequency voltage generated on the bearing outer ring side and unnecessary high-frequency current flowing between the bearing inner and outer rings. It is done.

  However, such a molding material is a resin, and the strength may be insufficient to fix the bearing. In general, a bearing such as a ball bearing generates a radial force on the shaft by a transmission load when, for example, there is a gap between the outer ring and the inner peripheral surface of the housing. When such a force is generated, a slip phenomenon is likely to occur due to a relative difference in the radial direction (such a slip phenomenon is called creep). Such creep can be generally suppressed by firmly fixing the outer ring to a housing such as a bracket, but the fixing member is resin-molded, resulting in poor dimensional accuracy, which tends to cause bearing creep failure, etc. There was a problem.

  In addition, with the recent increase in output of electric motors, it is necessary to fix the bearings more firmly. However, metal brackets that have been processed in advance with steel plates and have good dimensional accuracy are used for fixing the bearings. It is essential to take measures against creep. In particular, the bearings are generally received at two locations with respect to the rotating shaft, but for reasons of strength and ease of implementation, the two bearings may be fixed with metal brackets. preferable.

JP 2007-159302 A JP 2004-229429 A

  However, since the conventional method like patent document 1 is the method of short-circuiting, the shaft voltage may become high.

  In addition, a power supply circuit of a drive circuit (including a control circuit and the like) that drives an electric motor with an inverter by a PWM method, and a primary circuit of the power supply circuit and a ground to the ground on the primary circuit side are electrically If the configuration is such that the stator core of the motor is electrically connected to the earth ground as in Patent Document 2, it is difficult to reduce the shaft voltage.

  The electric motor of the present invention has been made in view of the above-described problems, and an object thereof is to provide an electric motor that suppresses the occurrence of electrolytic corrosion in a bearing and an electric device including the electric motor.

  In order to achieve the above object, the electric motor of the present invention includes a stator including a stator core wound with a winding, a rotor holding a permanent magnet in a circumferential direction facing the stator, and the rotation A rotating body including a shaft that fastens the rotor so as to pass through the center of the rotor, a dielectric layer configured to insulate between the outer periphery of the rotor and the shaft, and supports the shaft A structure comprising a bearing and two conductive brackets for fixing the bearing, and a configuration for increasing a preload for increasing an electrostatic capacity between a bearing inner ring and a bearing outer ring when the bearing alone is rotated. It has.

  With such a configuration, the shaft voltage can be suppressed without being affected by the use environment or the like.

  In the electric motor of the present invention, the bearing has a nominal number of 608 and a preload of 42 N or more.

  With such a configuration, the electrostatic capacity between the bearing inner ring and the bearing outer ring can be increased, and the shaft voltage can be suppressed by the voltage dividing effect.

  In the electric motor of the present invention, the bearing has a nominal number of 608 and a preload of 60 N or more.

  With such a configuration, the electrostatic capacity between the bearing inner ring and the bearing outer ring can be increased, and the shaft voltage can be suppressed by the voltage dividing effect.

  In the electric motor of the present invention, the bearing has a nominal number of 6201 and a preload of 60 N or more.

  With such a configuration, the electrostatic capacity between the bearing inner ring and the bearing outer ring can be increased, and the shaft voltage can be suppressed by the voltage dividing effect.

  In the electric motor of the present invention, the bearing has a nominal number of 6202 and a preload of 60 N or more.

  With such a configuration, the electrostatic capacity between the bearing inner ring and the bearing outer ring can be increased, and the shaft voltage can be suppressed by the voltage dividing effect.

  In the electric motor of the present invention, the bearing has a nominal number of 6204 and a preload of 60 N or more.

  With such a configuration, the electrostatic capacity between the bearing inner ring and the bearing outer ring can be increased, and the shaft voltage can be suppressed by the voltage dividing effect.

  In the electric motor of the present invention, the bearing has a nominal number of 6302 and a preload of 60 N or more.

  With such a configuration, the electrostatic capacity between the bearing inner ring and the bearing outer ring can be increased, and the shaft voltage can be suppressed by the voltage dividing effect.

  In the electric motor of the present invention, the bearing has a nominal number of 6004 and a preload of 60 N or more.

  With such a configuration, the electrostatic capacity between the bearing inner ring and the bearing outer ring can be increased, and the shaft voltage can be suppressed by the voltage dividing effect.

  Moreover, the electric motor of the present invention has a configuration in which two brackets are electrically connected and insulated from the stator core.

  With such a configuration, the electrical potentials of the two brackets can be made the same, the shaft voltage can be stabilized, and the shaft voltage can be suppressed without being affected by the use environment or the like.

  In addition, the electric motor of the present invention has a configuration in which at least one of the two brackets and the stator core around which the winding is wound are integrally formed of an insulating resin.

  With such a configuration, the two conductive brackets can be electrically connected to each other through a lead wire or the like inside the electric motor, so that the electrical connection can be made highly reliable with respect to the use environment or external stress. it can.

  Moreover, the electric motor of the present invention has a configuration in which the rotor is rotatably arranged on the inner peripheral side of the stator.

  Moreover, the electric device of the present invention is equipped with the above-described electric motor.

  According to the electric motor of the present invention, it is possible to provide an electric motor that suppresses the occurrence of electrolytic corrosion in a bearing and an electric device including the electric motor.

Structure diagram showing a cross section of the brushless motor according to the first embodiment of the present invention The figure which showed the example of a structure of the rotor of the motor The figure which showed the structural example of the rotary body of the motor The figure which showed the example of a structure of the rotary body of the conventional motor The figure which shows the measuring method of the electrostatic capacitance between a shaft and the outermost circumference surface of a rotary body The figure which shows the measuring method of the electrostatic capacity between the outer ring and inner ring of the bearing under rotation The figure which shows the measuring method of the shaft voltage of Example 1. Diagram showing an example of complete waveform collapse Diagram showing an example of partial waveform collapse The figure which shows an example without waveform collapse The figure which shows the evaluation result of Example 1 Diagram showing equivalent circuit image Structure diagram showing a cross section of an outer rotor type electric motor as another configuration example according to Embodiment 1 of the present invention Structure diagram of air conditioner indoor unit in Embodiment 2 of the present invention Structure diagram of air conditioner outdoor unit according to Embodiment 3 of the present invention Structure diagram of a water heater in Embodiment 4 of the present invention Structure diagram of air cleaner in embodiment 5 of the present invention Bearing internal configuration diagram

  Hereinafter, the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments and examples.

(Embodiment 1)
FIG. 1 is a structural diagram showing a cross section of the electric motor according to Embodiment 1 of the present invention. In the present embodiment, an example of an electric motor that is mounted for an air conditioner as an electric device and that is a brushless motor for driving a blower fan will be described. In the present embodiment, an example of an inner rotor type motor in which a rotor is rotatably arranged on the inner peripheral side of a stator will be described.

  In FIG. 1, a stator winding 12 is wound around a stator core 11 with a resin 21 as an insulator for insulating the stator core 11 interposed therebetween. Such a stator core 11 is molded with an insulating resin 13 as a molding material together with other fixing members. In this embodiment, an unsaturated polyester resin molding material is used for the insulating resin 13. In the present embodiment, the stator 10 whose outer shape is substantially cylindrical is formed by integrally molding these members in this manner.

  A rotating body 30 is inserted inside the stator 10 through a gap. The rotator 30 includes a disk-shaped rotor 14 including a rotor core 31 and a shaft 16 to which the rotor 14 is fastened so as to penetrate the center of the rotor 14. The rotor 14 holds a magnet 32 of a ferrite resin magnet that is a permanent magnet in the circumferential direction facing the inner peripheral side of the stator 10. Further, as will be described in detail below, the rotating body 30 has an outer periphery of the rotor core 31 from the magnet 32 of the outermost peripheral ferrite resin magnet toward the inner peripheral shaft 16 as shown in FIG. The outer iron core 31 a constituting the part, the dielectric layer 50, and the inner iron core 31 b constituting the inner peripheral part of the rotor core 31 are arranged in this order. FIG. 1 shows a configuration example in which the rotor core 31, the dielectric layer 50 and the ferrite resin magnet magnet 32 are integrally formed as the rotor 30. In this manner, the inner peripheral side of the stator 10 and the outer peripheral side of the rotating body 30 are arranged to face each other.

  Two output shaft side bearings 15 a and a counter output shaft side bearing 15 b that support the shaft 16 are attached to the shaft 16 of the rotor 14. The bearing 15 is a cylindrical ball bearing having a plurality of iron balls, and the inner ring side of the output shaft side bearing 15 a and the non-output shaft side bearing 15 b is fixed to the shaft 16. In FIG. 1, the output shaft side bearing 15a supports the shaft 16 on the output shaft side where the shaft 16 protrudes from the brushless motor body, and the opposite side (hereinafter referred to as the non-output shaft side) counteracts the output. The shaft-side bearing 15 b supports the shaft 16.

  The output shaft side bearing 15a and the counter output shaft side bearing 15b are fixed to the outer ring side of the bearing 15 by metal brackets having conductivity. In FIG. 1, the output shaft side bearing 15a is fixed by an output shaft side bracket 17 into which a preload spring 33 is inserted, and the counter output shaft side bearing 15b is fixed by a bracket 19 on the counter output shaft side. With the configuration as described above, the shaft 16 is supported by the two bearings 15, and the rotor 14 rotates freely.

  Further, the brushless motor incorporates a printed circuit board 18 on which a drive circuit including a control circuit is mounted. After the printed board 18 is built in, the bracket 17 on the output shaft side is press-fitted into the stator 10 to form a brushless motor. Also connected to the printed circuit board 18 are connection wires 20 such as a lead wire for applying a winding power supply voltage Vdc, a control circuit power supply voltage Vcc and a control voltage Vsp for controlling the number of revolutions, and a ground wire for the control circuit. Yes.

  The zero potential point on the printed circuit board 18 on which the drive circuit is mounted is insulated from the earth ground and the primary side (power supply) circuit, and is floated from the earth ground and the potential of the primary side power supply circuit. It is in the state. Here, the zero potential point portion is a wiring of 0 volt potential as a reference potential on the printed circuit board 18, and indicates a ground wiring called a normal ground. The ground line included in the connection line 20 is connected to the zero potential point, that is, the ground wiring. In addition, a power supply circuit that supplies a power supply voltage of a winding connected to the printed circuit board 18 on which the drive circuit is mounted, a power supply circuit that supplies a power supply voltage of the control circuit, a lead wire that applies the control voltage, and a ground line of the control circuit Are the primary side (power supply) circuit for the power supply circuit that supplies the power supply voltage of the winding, the primary side (power supply) circuit for the power supply circuit that supplies the power supply voltage of the control circuit, and these primary side (power supply) circuits. It is electrically isolated from both the connected earth ground and the independently grounded earth earth.

  That is, since the drive circuit mounted on the printed circuit board 18 is electrically insulated from the primary side (power supply) circuit potential and the ground potential, the potential is floated. Yes. This is also expressed as a state where the potential is floating, and is well known. For this reason, the configuration of the power supply circuit that supplies the power supply voltage of the winding connected to the printed circuit board 18 and the power supply circuit that supplies the power supply voltage of the control circuit is also called a floating power supply, which is also well known. It is an expressed expression.

  By supplying each power supply voltage and control signal to the brushless motor configured as described above via the connection line 20, the stator winding 12 is driven by the drive circuit of the printed circuit board 18. When the stator winding 12 is driven, a drive current flows through the stator winding 12 and a magnetic field is generated from the stator core 11. The magnetic field from the stator core 11 and the magnetic field from the ferrite resin magnet 32 generate an attractive force and a repulsive force according to the polarities of the magnetic fields, and the rotor 14 around the shaft 16 is generated by these forces. Rotates.

  Next, a more detailed configuration of the brushless motor will be described.

  First, as described above, in the brushless motor, the shaft 16 is supported by the two bearings 15, and the respective bearings 15 are also fixed and supported by the brackets. Furthermore, in order to suppress the above-described defects due to creep, the present embodiment is configured such that each bearing 15 is fixed by a metal bracket having conductivity. That is, in the present embodiment, a conductive bracket that has been processed in advance with a steel plate and has good dimensional accuracy is employed for fixing the bearing 15. In particular, when a high output of the electric motor is required, such a configuration is more preferable.

  Next, the output shaft side bearing 15 a is fixed by an output shaft side bracket 17 having an outer diameter substantially equal to the outer diameter of the stator 10. The bracket 17 on the output shaft side has a substantially disk shape, and has a protruding portion having a diameter substantially equal to the outer peripheral diameter of the output shaft side bearing 15a at the center of the disk, and the inside of this protruding portion is hollow. . After incorporating the printed circuit board 18, a preload spring 33 is inserted inside the protruding portion of the bracket 17 on the output shaft side and is press-fitted into the output shaft side bearing 15 a, and provided on the outer periphery of the bracket 17 on the output shaft side. The brushless motor is formed by press-fitting the output shaft side bracket 17 into the stator 10 so that the connection end and the connection end of the stator 10 are fitted.

  With this configuration, the assembly work is facilitated, and the outer ring side of the output shaft side bearing 15a is fixed to the metal output shaft side bracket 17, so that a problem due to creep is suppressed, and the preload spring Thus, abnormal noise due to vibration or resonance of the shaft 16 is prevented.

  Further, the conduction pin 22 of the non-output shaft side bracket is electrically connected to the bracket 19 on the non-output shaft side in advance. That is, as shown in FIG. 1, one end portion 22a of the conduction pin 22 of the non-output shaft side bracket is connected to the collar portion 19b of the bracket 19 on the counter output shaft side. The conductive pin 22 of the non-output shaft side bracket is disposed inside the insulating resin 13 and is integrally molded with the insulating resin 13 in the same manner as the bracket 19 on the counter output shaft side.

  The conductive pin 22 of the non-output shaft side bracket is disposed inside the insulating resin 13 as an electric motor, thereby preventing the conductive pin 22 of the non-output shaft side bracket from rust, external force, etc. In contrast, the electrical connection is highly reliable. The conductive pin 22 of the non-output shaft side bracket extends from the collar portion 19b toward the outer periphery of the brushless motor inside the insulating resin 13, and is substantially parallel to the shaft 16 from the vicinity of the outer periphery of the brushless motor to the output shaft side. It is further extended.

  And the other front-end | tip part 22b of the conduction | electrical_connection pin 22 of a non-output shaft side bracket is exposed from the end surface by the side of the output shaft of the insulating resin 13. FIG. Further, a conductive pin 23 of the output shaft side bracket for electrically connecting the conductive pin 22 of the non-output shaft side bracket to the output shaft side bracket 17 is connected to the tip portion 22b. That is, when the output shaft side bracket 17 is press-fitted into the stator 10, the output shaft side bracket conduction pin 23 contacts the output shaft side bracket 17, and the output shaft side bracket 17 and the output shaft side bracket conduction pin. Conductivity with 23 is ensured. With such a configuration, the two brackets of the output shaft side bracket 17 and the non-output shaft side bracket 19 are electrically connected via the conductive pin 22 of the non-output shaft side bracket.

  Further, the bracket 17 on the output shaft side and the bracket 19 on the opposite output shaft side are electrically connected to each other with the insulating resin 13 being insulated from the stator core 11.

  The bearing 15 used in the present embodiment is a bearing having a nominal number 608, which has received a preload of 42N by the preload spring 33, and the inner ring 62 of the bearing when the bearing alone is rotated at 1000 r / min. A capacitor with a capacitance of 63 pF (measurement frequency: 10 kHz) between the outer ring 61 and the bearing was used.

  And the electrostatic capacitance (measurement frequency of 10 kHz) between the shaft 16 and the outermost circumferential surface of the rotating body 30 is adjusted to 5.0 pF, and in the rotating body 30, between the shaft 16 and the outer periphery of the rotating body 30. A dielectric layer 50 is provided. In the present embodiment, the dielectric layer 50 is provided and the relative dielectric constant and the resin thickness of the dielectric layer material are adjusted to obtain a capacitance of 5 pF. A method of adjusting the weight ratio is also possible, and is not limited to the method described above.

  By adopting such a configuration, the present invention can prevent electrolytic corrosion by using a small axial voltage.

  In this embodiment, the bracket 17 on the output shaft side and the bracket 19 on the opposite output shaft side are electrically connected so that both brackets have the same potential, so that the high-frequency current through the shaft 16 is difficult to flow. Yes.

  Next, as shown in FIG. 18, the bearing 15 includes a bearing inner ring 62, a bearing outer ring 61, a bearing ball 70, and grease. The grease forms a grease oil film 71 by the preload F from the preload spring 33. The inner ring 62 of the bearing, the outer ring 61 of the bearing, and the bearing ball 70 are lubricated through a grease oil film 71 having an oil film thickness hc in the area of the contact area S.

  This grease is an insulator, and a capacitor is formed by the conductor of the bearing. The electrostatic capacity C is expressed by the following (Equation 1).

  That is, the electrostatic capacity C of the bearing 15 is proportional to the contact area S formed by the bearing inner ring 62, the bearing outer ring 61, and the bearing balls 70, and is inversely proportional to the oil film thickness hc of the grease oil film 71.

  Further, according to Hamrock-Dowson, the oil film thickness hc is expressed by the following (Equation 2).

  In other words, the oil film thickness hc is proportional to the 0.68th power of the speed and proportional to the −0.073th power of the preload, and the influence of the preload can be almost ignored.

  Further, according to Hertz, the contact area S is expressed by the following (Equation 3).

  That is, the contact area S is proportional to the 2/3 power of the preload.

  As described above, when the speed is constant, the bearing 15 has a constant oil film thickness hc due to a change in the preload F, and has almost no influence, and the contact area S changes in proportion to the 2/3 power of the preload.

  Further, the preload F (N) by the preload spring 33 is expressed by the following (Equation 4).

  That is, from equations (1), (2), and (3), increasing the preload F has the greatest effect on increasing the capacitance C of the bearing 15, and the thickness t and the wave number N of the preload spring 33 are respectively The third power and the fourth power are affected, and the preload can be adjusted by adjusting the plate thickness t and the wave number N.

  Next, as shown in FIG. 2, the rotating body 30 has a ferrite resin magnet 32 disposed on the outermost peripheral portion, and further toward the inner peripheral side, an outer iron core 31 a constituting the rotor iron core 31, and a dielectric layer. 50 and the inner iron core 31b constituting the rotor iron core 31 are arranged in this order. The dielectric layer 50 is a layer formed of an insulating resin. In the present embodiment, such a dielectric layer 50 is provided for suppressing electrolytic corrosion.

  FIG. 2 shows an example in which the dielectric layer 50 is formed in a ring shape that circulates around the shaft 16 between the inner peripheral side and the outer peripheral side of the rotating body 30. As described above, the rotating body 30 has a configuration in which the ferrite resin magnet 32, the outer iron core 31a, the insulating resin forming the dielectric layer 50, and the inner iron core 31b are integrally formed. In the present embodiment, the SPM rotor of the ferrite resin magnet has been described, but the same result can be obtained with a ferrite sintered magnet or a rare earth neodymium-based sintered magnet. Similar results can be obtained with an IPM rotor.

  Hereinafter, the present invention will be described more specifically with reference to examples. Note that the present invention is not limited to the following examples, and is not limited to these examples unless the gist of the present invention is changed.

Example 1
With the configuration as shown in FIG. 1, the motor was configured such that the preload was arbitrarily adjusted with the plate thickness t and the wave number N based on the formula (4), and a preload of 28N, 35N, 42N, 49N, and 56N was applied.

  The bearing 15 used is Minebea 608 (grease having a consistency of 239), and the electrostatic capacity between the bearing inner ring 62 and the bearing outer ring 61 when the bearing alone is rotated at 1000 r / min. Was 50 pF.

  As shown in FIG. 6, the capacitance of a single bearing is measured by rotating the bearing 15 at 1000 r / min by external driving, using an LCR meter Z60, at a measurement frequency of 10 kHz, a measurement temperature of 20 ° C., and a measurement voltage of 1 V. It was measured. The measurement was performed between the bearing outer ring 61 and the shaft 16 in mechanical and electrical contact with the bearing inner ring 62. At the time of measurement, an insulating resin coupling having a wall thickness of 20 mm or more was used between the external drive device and the shaft. In addition, the external drive device, the shaft, and the bearing were installed on an insulating resin base having a thickness of 20 mm or more on a 20 mm wooden board.

  The induced voltage between the neutral point and the U phase was also measured when the motor was assembled and rotated at 1000 r / min by external drive.

  Moreover, the measurement was implemented by the method of using the same stator and replacing each rotor.

  FIG. 7 is a diagram illustrating a method for measuring an axial voltage according to the first embodiment. When measuring the shaft voltage, a DC stabilized power supply was used, the power supply voltage Vdc of the winding was 391 V, the power supply voltage Vcc of the control circuit was 15 V, and the measurement was performed under the same operating conditions at a rotational speed of 1000 r / min. The rotational speed was adjusted by the control voltage Vsp, and the brushless motor posture during operation was horizontal on the shaft. The brushless motor was installed on a wooden board having a thickness of 20 mm.

  Axis voltage is measured with a digital oscilloscope 130 (Tektronix DPO7104) and a high-voltage differential probe 120 (Tektronix P5205) to check whether or not the waveform collapses. The measured voltage was taken as the axial voltage.

  Moreover, the waveform breakdown of the shaft voltage was divided into three categories: complete waveform collapse, partial waveform collapse, and no waveform collapse. The state without waveform collapse is a state in which the oil film inside the bearing has not caused dielectric breakdown, and is a state in which the occurrence of electrolytic corrosion can be prevented. The waveform collapse state is a state in which the oil film inside the bearing is causing dielectric breakdown, and is a state in which electrolytic corrosion occurs depending on the operation time.

  FIGS. 8 to 10 are diagrams showing examples of such waveform collapse. FIG. 8 shows a complete waveform collapse, FIG. 9 shows a partial waveform collapse, and FIG. 10 shows a waveform without waveform collapse. 8 to 10, the horizontal axis time at the time of measurement is the same condition of 50 μs / div. The digital oscilloscope 130 is insulated by an insulation transformer 140.

  Further, the positive side 120a of the high-voltage differential probe 120 is in contact with the outer periphery of the shaft 16 through the inner periphery of the shaft 16 through a lead wire 110 having a length of about 30 cm and a conductor of the lead wire having a diameter of about 15 mm. By doing so, it is electrically connected to the shaft 16. The negative side 120b of the high-voltage differential probe 120 is electrically connected to the bracket 17 by bringing the tip of the lead wire 111 into conductive contact with the bracket 17 via the conductive tape 112 via the lead wire 111 having a length of about 30 cm. Connected. With such a configuration, the shaft voltage of the bearing 15a on the output shaft side, which is the voltage between the bracket 17 and the shaft 16, was measured.

  FIG. 11 is a diagram showing the evaluation results of Example 1.

  As is clear from FIG. 11, the capacitance C increases as the preload F increases. Further, as the capacitance C increases, the shaft voltage decreases.

  From the result, an image diagram of an equivalent circuit as shown in FIG. 12 can be created. The electrostatic capacity between the shaft 16 and the outermost circumferential surface of the rotating body 30 is C1, the electrostatic capacity of the bearing 15 is C2, and the shaft voltage V2 when the common mode voltage is V is shown. is there. From FIG. 12, it can be calculated that the shaft voltage V2 decreases if the capacitance C2 of the bearing 15 is increased, which is the same as the tendency of the result.

  That is, by making the capacitance larger between the bearing inner ring and the bearing outer ring, the effect of suppressing the occurrence of electrolytic corrosion of the bearing can be further enhanced.

  As can be seen from these results, the electric motor of the present invention has an extremely excellent effect in suppressing the occurrence of bearing electrolytic corrosion of the electric motor because the shaft voltage is reduced as compared with the conventional electric motor.

  Further, by incorporating the electric motor of the present invention into an electric device, it is possible to provide an electric device including the electric motor that suppresses the occurrence of electrolytic corrosion in the bearing.

  Further, the example of the electric motor which is an inner rotor type brushless motor in which the rotor is rotatably disposed on the inner peripheral side of the stator has been described, but the outer rotor type in which the rotor is disposed on the outer peripheral side of the stator. The present invention can also be applied to an electric motor. FIG. 13 is a structural diagram showing a cross section of an outer rotor type electric motor as another configuration example in the present embodiment.

  In FIG. 13, the same components as those in FIG. 1 are denoted by the same reference numerals. In FIG. 13, the stator core 11 around which the stator winding 12 is wound is molded with an insulating resin 13 to constitute the stator 10. Further, a bracket 17 and a bracket 19 are integrally formed on the stator 10, a bearing 15 a is fixed to the bracket 17, and a bearing 15 b is fixed to the bracket 19. A shaft 16 passes through the inner ring side of the bearings 15a and 15b, and a hollow cylindrical rotating body 30 is fastened to one end of the shaft 16. Further, the stator core 11 is arranged in the inner peripheral hollow portion of the rotating body 30.

  And in the rotary body 30, the cyclic | annular dielectric material layer 50 is provided so that it may be pinched | interposed by the outer side iron core 31a and the inner side iron core 31b. Further, the bearing 15a and the bearing 15b are electrically connected by a conduction pin 22 or the like. In such an outer rotor type electric motor as well as the configuration shown in FIG. 1, by providing the dielectric layer 50 as shown in FIG. 13 and providing a structure for electrically connecting the bracket 17 and the bracket 19, Similar effects can be obtained.

  The method for increasing the preload has been described by adjusting each item according to the equation (4). However, the preload can also be increased by stacking a plurality of preload springs, and the same effect can be obtained.

(Embodiment 2)
As an example of an electrical apparatus according to the present invention, first, the configuration of an air conditioner indoor unit will be described in detail as a second embodiment.

  In FIG. 14, the electric motor 201 is mounted in the housing 211 of the air conditioner indoor unit 210. A cross flow fan 212 is attached to the rotating shaft of the electric motor 201. The electric motor 201 is driven by an electric motor driving device 213. By energization from the electric motor drive device 213, the electric motor 201 rotates, and the crossflow fan 212 rotates accordingly. By the rotation of the cross flow fan 212, air conditioned by an indoor unit heat exchanger (not shown) is blown into the room. Here, as the electric motor 201, for example, the one of the first embodiment can be applied.

  The electric device of the present invention includes an electric motor and a casing in which the electric motor is mounted, and employs the electric motor of the present invention having the above-described configuration as the electric motor.

(Embodiment 3)
Next, as an example of the electrical apparatus according to the present invention, the configuration of an air conditioner outdoor unit will be described in detail as a third embodiment.

  In FIG. 15, an air conditioner outdoor unit 301 has a motor 308 mounted inside a housing 311. The electric motor 308 has a fan 312 attached to a rotating shaft and functions as a blower electric motor.

  The air conditioner outdoor unit 301 is partitioned into a compressor chamber 306 and a heat exchanger chamber 309 by a partition plate 304 erected on the bottom plate 302 of the housing 311. A compressor 305 is disposed in the compressor chamber 306. A heat exchanger 307 and the blower motor are disposed in the heat exchanger chamber 309. An electrical component box 310 is disposed above the partition plate 304.

  The fan motor 312 is rotated by the rotation of the motor 308 driven by the motor driving device 303 accommodated in the electrical component box 310 and the fan 312 blows air to the heat exchanger chamber 309 through the heat exchanger 307. . Here, as the electric motor 308, for example, the one in the first embodiment can be applied.

  The electric device of the present invention includes an electric motor and a casing in which the electric motor is mounted, and employs the electric motor of the present invention having the above-described configuration as the electric motor.

(Embodiment 4)
Next, as an example of the electric apparatus according to the present invention, the configuration of the hot water heater will be described in detail as a fourth embodiment.

  In FIG. 16, an electric motor 333 is mounted in a housing 331 of the water heater 330. A fan 332 is attached to the rotating shaft of the electric motor 333. The electric motor 333 is driven by an electric motor driving device 334. The electric motor 333 is rotated by energization from the electric motor driving device 334, and the fan 332 is rotated accordingly. The rotation of the fan 332 blows air necessary for combustion to a fuel vaporization chamber (not shown). Here, as the electric motor 333, for example, the one in the first embodiment can be applied.

  The electric device of the present invention includes an electric motor and a casing in which the electric motor is mounted, and employs the electric motor of the present invention having the above-described configuration as the electric motor.

(Embodiment 5)
Next, as an example of the electric apparatus according to the present invention, the configuration of the air cleaner will be described in detail as a fifth embodiment.

  In FIG. 17, an electric motor 343 is mounted in a housing 341 of the air purifier 340. An air circulation fan 342 is attached to the rotating shaft of the electric motor 343. The electric motor 343 is driven by an electric motor driving device 344. By energization from the motor driving device 344, the motor 343 rotates, and the fan 342 rotates accordingly. Air is circulated by the rotation of the fan 342. Here, as the electric motor 343, for example, the one in the first embodiment can be applied.

  The electric device of the present invention includes an electric motor and a casing in which the electric motor is mounted, and employs the electric motor of the present invention having the above-described configuration as the electric motor.

  In the above description, electric motors mounted on air conditioner outdoor units, air conditioner indoor units, hot water heaters, air purifiers, etc. have been taken up as examples of electric devices according to the present invention. Needless to say, the present invention can also be applied to electric motors mounted on information equipment and electric motors used in industrial equipment.

  In addition, as described above, the configuration in the embodiment of the present application includes a power supply circuit of a drive circuit (including a control circuit and the like) that drives an electric motor with an inverter by a PWM method, a primary circuit of the power supply circuit, and The primary circuit side is electrically insulated from the earth ground. And the effect which suppresses the electric corrosion of a bearing is acquired even if it does not employ | adopt the structure which electrically connects the stator core of an electric motor etc. to the earth ground of the prior art.

  The electric motor of the present invention can reduce the shaft voltage and suppress the occurrence of electrolytic corrosion of the bearing, and is mainly a device that is required to reduce the price and increase the life of the electric motor. It is effective for motors installed in air conditioner outdoor units, water heaters, air purifiers, etc.

DESCRIPTION OF SYMBOLS 10 Stator 11 Stator core 12 Stator winding 13 Insulating resin 14 Rotor 15 Bearing 15a Output shaft side bearing 15b Non-output shaft side bearing 16 Shaft 17 Output shaft side bracket 18 Printed circuit board 19 Anti-output shaft side bracket 20 Connection line 21 Resin (insulator)
22 Conducting pin of the non-output shaft side bracket 23 Conducting pin of the output shaft side bracket 30 Rotating body 31 Rotor core 31a Outer iron core 31b Inner iron core 32 Magnet 33 Preload spring 50 Dielectric layer 61 Bearing outer ring 62 Bearing inner ring 70 Bearing ball 71 Grease oil film

Claims (11)

A stator including a stator core wound with a winding, a rotor holding a permanent magnet in a circumferential direction facing the stator, and the rotor fastened to penetrate the center of the rotor A rotating body including a shaft, a dielectric layer configured to insulate between the outer periphery of the rotor and the shaft, a bearing that supports the shaft, and two conductive brackets that fix the bearing And an electric motor having a configuration for increasing the preload for increasing the capacitance between the bearing inner ring and the bearing outer ring when the bearing alone is rotated. The electric motor according to claim 1, wherein the bearing has a nominal number of 608 and a preload of 42 N or more. The electric motor according to claim 1, wherein the bearing has a nominal number of 6201 and a preload of 60 N or more. The electric motor according to claim 1, wherein the bearing has a nominal number of 6202 and a preload of 60 N or more. The electric motor according to claim 1, wherein the bearing has a nominal number of 6204 and a preload of 60 N or more. The electric motor according to claim 1, wherein the bearing has a nominal number of 6302 and a preload of 60 N or more. The electric motor according to claim 1, wherein the bearing has a nominal number of 6004 and a preload of 60 N or more. The electric motor according to claim 1, wherein the two brackets are electrically connected and insulated from the stator core. The electric motor according to claim 1, wherein at least one of the two brackets and the stator core around which the winding is wound are integrally formed of an insulating resin. The electric motor according to claim 1, wherein the rotor is rotatably disposed on an inner peripheral side of the stator. An electric device comprising the electric motor according to any one of claims 1 to 10.