JP2012239368A - Motor and electric apparatus using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor inverter-driven by a PWM method, capable of suppressing a bearing from causing electrolytic corrosion.SOLUTION: A motor includes: a stator including a stator core wound with a winding; a rotor facing the stator and retaining a permanent magnet in the peripheral direction; a rotating element including a shaft tightening the rotor to penetrate through the center of the rotor; a bearing supporting the shaft; and two brackets fixing the bearing. The motor is structured so that an axis voltage generated between an inner ring and an outer ring of the bearing is suppressed compared with a withstand voltage of the bearing unit.

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 shaft that is fastened to the rotor, a bearing that supports the shaft before and after the rotor, and a bracket that fixes the bearing. A shaft voltage between a bearing inner ring and a bearing outer ring of the bearing is It is an electric motor that is kept lower than the withstand voltage.

  By generating a lubricating effect with the grease in the bearing while the bearing is rotating, electrostatic capacity is generated between the inner ring and the ball and between the outer ring and the ball, and a shaft voltage is generated. By giving the motor a bearing with a higher withstand voltage than the shaft voltage generated in this bearing, the electrical short circuit phenomenon between the bearing inner ring and the bearing outer ring, which occurs when the shaft voltage exceeds the withstand voltage, is prevented. Can be suppressed.

  In the electric motor of the present invention, the withstand voltage of a single bearing is obtained from the oil film thickness and the withstand voltage of the grease. The withstand voltage of a single bearing can be obtained from the relationship between the thickness of the oil film due to grease and the withstand voltage of the grease alone. If the motor has a shaft voltage lower than the determined withstand voltage, electric corrosion can be suppressed by the effect of preventing an electrical short circuit between the bearing inner ring and the bearing outer ring that occurs when the shaft voltage exceeds the withstand voltage. Can do.

  In the electric motor of the present invention, the size of the electrostatic tangent of the grease of the bearing alone is within 0.1. When the magnitude of the electrostatic tangent of grease is within 0.1, the magnitude of the phase difference between the voltage applied to the grease and the current is within 5 °, resulting in an almost ideal capacitor structure. Therefore, since the internal resistance of the capacitor can be almost ignored, it is possible to prevent insulation deterioration due to the internal resistance. Therefore, an electrical short circuit phenomenon between the bearing inner ring and the bearing outer ring that occurs when the shaft voltage exceeds the withstand voltage is prevented. The electric corrosion can be suppressed by the effect that can be prevented.

  Further, the electric motor of the present invention has a configuration in which a dielectric layer is provided between the shaft and the outer periphery of the rotor. By providing a dielectric layer on the rotor, it becomes possible to adjust the impedance on the rotor side, and by maintaining a balance with the impedance on the stator side, the shaft voltage between the bearing inner ring and the bearing outer ring is reduced. It becomes possible.

  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.

  Further, the electric motor of the present invention has a configuration in which at least one of the two brackets and the stator core 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, an electric device of the present invention includes 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.

Configuration diagram of an air conditioner indoor unit in Embodiment 1 of the present invention Partial sectional view of the brushless motor in Embodiment 1 of the present invention Perspective view of rotating body of same motor Diagram showing relationship between bearing and grease The figure which shows the measuring method of the electrostatic capacitance between a shaft and the outermost circumference surface of a rotary body Diagram showing how to measure shaft voltage The figure which shows the voltage waveform at the time of the shaft voltage 4.0V in Example 1. FIG. The figure which shows the voltage waveform at the time of the shaft voltage 8.0V in Example 1. The figure which shows the voltage waveform at the time of the shaft voltage 20.0V in Example 1. FIG. The figure which shows the evaluation result of Example 1 Sectional view of an outer rotor type electric motor as another configuration example Configuration diagram of an air conditioner outdoor unit in Embodiment 2 of the present invention Configuration diagram of a water heater in Embodiment 3 of the present invention The block diagram of the air cleaner in Embodiment 4 of this invention

  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 shows a configuration of an air conditioner indoor unit as an example of an electric apparatus according to the present invention. In the figure, an electric motor 103 is mounted in a housing 102 of an air conditioner indoor unit 101. A cross flow fan 104 is attached to the rotating shaft of the electric motor 103. The electric motor 103 is driven by an electric motor driving device 105. The electric motor 103 rotates by energization from the electric motor driving device 105, and the cross flow fan 104 rotates accordingly. By the rotation of the cross flow fan 104, air conditioned air is blown into the room through an indoor unit heat exchanger (not shown).

  Next, the electric motor 103 will be described. In FIG. 2, 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. Here, an unsaturated polyester resin molding material was used for the insulating resin 13. By integrally molding these members in this manner, the stator 10 whose outer shape is substantially cylindrical is configured. A rotating body 30 (see FIG. 3) is inserted inside the stator 10 through a gap.

  Two bearings 15 a and 15 b that support the shaft 16 are attached to the shaft 16 of the rotor 14. The bearings 15 a and 15 b are cylindrical ball bearings having a plurality of iron balls, and the inner ring side is fixed to the shaft 16. In FIG. 2, the bearing 15 a supports the shaft 16 on the output shaft side on which the shaft 16 protrudes from the brushless motor body, and the bearing 15 b supports the shaft 16 on the opposite side (hereinafter referred to as the non-output shaft side). Support. With the configuration as described above, the shaft 16 is supported by the two bearings 15a and 15b, and the rotor 14 rotates freely.

  These bearings 15a, 15b are fixed on the outer ring side by a conductive metal bracket that is previously processed with a steel plate and has good dimensional accuracy in order to suppress the above-described problems caused by creep. Such a configuration is effective when high output of the electric motor is required. In FIG. 2, the output shaft side bearing 15 a is fixed by the bracket 17 with the preload spring 33 inserted, and the counter output shaft side bearing 15 b is fixed by the bracket 19.

  The bracket 17 has a substantially disc shape, and has a projecting portion having a diameter substantially equal to the outer peripheral diameter of the bearing 15a at the center of the disc, and the inside of the projecting portion is hollow. After incorporating the printed circuit board 18, a preload spring 33 is inserted inside the protruding portion of the bracket 17 and press-fitted into the bearing 15 a, and a connection end provided on the outer periphery of the bracket 17 and a connection end of the stator 10 are provided. The brushless motor is formed by press-fitting the bracket 17 into the stator 10 so as to fit. With this configuration, the assembly work is facilitated and the outer ring side of the bearing 15 a is fixed to the metal bracket 17, so that problems due to creep are suppressed, and the preload spring 33 can prevent the shaft 16 from swinging. Abnormal noise due to resonance is prevented.

  In addition, a conduction pin 22 is electrically connected to the bracket 19 in advance. That is, as shown in FIG. 2, one end of the conduction pin 22 is connected to the collar portion 19 b of the bracket 19. The conductive pin 22 is disposed inside the insulating resin 13 and is integrally molded with the insulating resin 13 in the same manner as the bracket 19. In addition, by disposing the conductive pin 22 inside the insulating resin 13 as an electric motor, the conductive pin 22 is prevented from rust and external force, and as a reliable electrical connection against the use environment and external stress. Yes.

  The conductive pin 22 extends from the collar portion 19b toward the outer periphery of the brushless motor inside the insulating resin 13, and further extends from the vicinity of the outer periphery of the brushless motor to the output shaft side substantially parallel to the shaft 16. ing. The other end of the conduction pin 22 is exposed from the end surface of the insulating resin 13 on the output shaft side, and a conduction pin 23 for electrically connecting the conduction pin 22 to the bracket 17 is connected to the tip. . That is, when the bracket 17 is press-fitted into the stator 10, the conduction pin 23 comes into contact with the bracket 17, and conduction between the bracket 17 and the conduction pin 23 is ensured.

  With such a configuration, the two brackets of the bracket 17 and the bracket 19 are electrically connected via the conduction pin 22. Further, the bracket 17 and the bracket 19 are electrically connected to each other with the insulating resin 13 being insulated from the stator core 11. That is, the bracket 17 and the bracket 19 are electrically connected and the brackets are set to the same potential, so that a high-frequency current cannot easily flow through the shaft 16.

  Next, FIG. 3 is a perspective view of the rotator 30 and includes a disk-like rotor 14 including the rotor core 31 and a shaft 16 to which the rotor 14 is fastened so as to penetrate the center of the rotor 14. Have. The rotor 14 holds a ferrite resin magnet 32 that is a permanent magnet in the circumferential direction facing the inner peripheral side of the stator 10. The ferrite resin magnet 32 may be a ferrite sintered magnet or a rare earth neodymium-based sintered magnet. From the outermost ferrite resin magnet 32 toward the inner peripheral shaft 16, the outer iron core 31 a constituting the outer circumference of the rotor core 31, the dielectric layer 50, and the inner circumference constituting the inner circumference of the rotor iron core 31. It has a structure that is arranged in order with the iron core 31b.

  By providing the dielectric layer 50, the impedance on the rotor 14 side can be adjusted, and the axial voltage between the bearing inner ring and the bearing outer ring is reduced by maintaining the balance with the impedance on the stator 10 side. It becomes possible. That is, by adjusting this impedance, an axial voltage (ie, neutral point potential is induced through the stator core 11, the space between the stator 10 and the rotor 14, the rotor 14, the dielectric layer 50, and the shaft 16). The difference between the voltage generated in the inner ring of the bearing and the voltage generated in the outer ring of the bearing induced via the bracket from the neutral point potential) is made closer to the same potential, thereby reducing the shaft voltage. Due to the effect of preventing the electrical short circuit phenomenon of the bearing outer ring, electrolytic corrosion can be suppressed.

  The brushless motor includes 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 brushless motor is formed by press-fitting the bracket 17 into the stator 10. 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.

  By supplying each power supply voltage and control signal via the connection line 20, a drive current flows through the stator winding 12 by the drive circuit of the printed circuit board 18, 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 cause an attractive force and a repulsive force according to the polarities of the magnetic fields, and the rotor 14 rotates around the shaft 16 by these forces. .

  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.

  That is, 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.

  Here, since the drive circuit mounted on the printed circuit board 18 is electrically insulated with respect to the primary side (power supply) circuit potential and the earth ground potential, the potential is in a floating state. 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.

  Next, FIG. 4 is a diagram showing the relationship between the bearing and the grease. The bearing 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, and the bearing inner ring 62, the bearing outer ring 61, and the bearing ball 70 are formed. Is 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 withstand voltage is expressed by the following (formula 1) from the oil film thickness hc of the grease and the withstand voltage of the single grease.

That is, if the bearing is in a state where an oil film is formed, its withstand voltage is proportional to the oil film thickness hc and the withstand voltage V25d of the grease alone.

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

That is, 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.

  Thus, the withstand voltage Vbd can be uniquely obtained by determining the parameters described in the equations (1) and (2). If this withstand voltage Vbd is larger than the shaft voltage generated between the outer ring and the inner ring of the bearing, it is possible to prevent a discharge phenomenon that a minute current flows inside the bearing, and it is possible to maintain a state in which no electrolytic corrosion proceeds. It is.

  Further, the electrostatic capacitance C of the bearing is expressed by the following (Equation 3).

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

  Further, according to Hertz, the contact area S is expressed by the following (formula 4).

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

  When the bearing is considered as a capacitor, the electrostatic tangent is expressed by the following (formula 5).

That is, if the electrostatic tangent is small, the resistance component is small and the loss is small. In the case where the bearing 15a and the bearing 15b are made of an insulator, if there is a resistance component, this leads to a decrease in the dielectric strength and a decrease in the withstand voltage V25d of the grease alone.

  Also, the phase difference between the voltage and current applied to the bearing is ideally 90 ° between the voltage and current applied to the capacitor, but if it is within ± 5 °, it will suppress the decrease in dielectric strength as an insulator. Can do.

  This phase difference within ± 5 ° is within ± 0.1 in electrostatic tangent. That is, it is possible to select grease within the electrostatic tangent ± 0.1 and adjust the withstand voltage Vbd of the bearings 15a and 15b to be larger than the shaft voltage Vb generated in the bearings 15a and 15b.

  As described above, when the speed is constant, the bearing capacitance is not affected by the change in the preload F, the oil film thickness hc is also almost constant, and the contact area S changes in proportion to the 2/3 power of the preload.

  Next, the present invention will be described more specifically with reference to examples.

  With the configuration as shown in FIG. 2, the electric motor was created so that the shaft voltage would be 4.0V, 8.0V, 20.0V when the bearing withstand voltage Vbd is 7.0V. The axial voltage was adjusted by adjusting the width of the dielectric layer 50 formed on the rotating body 30, and the capacitances were 5 pF, 10 pF, and 25 pF, respectively. The capacitance of the dielectric layer 50 was measured between the outer periphery of the rotating body 30 and the shaft 16 as shown in FIG. 5 using a LCR meter 60 at a measurement frequency of 10 kHz, a measurement temperature of 20 ° C., and a measurement voltage of 1V. The shaft voltage was measured by using the same stator and replacing each rotor.

  FIG. 6 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. 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 loop shape of about 15 mm in diameter. 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.

  The measured voltage waveforms were classified into three categories: complete waveform collapse, partial waveform collapse, and no waveform collapse. Full waveform collapse is a state in which the pulse waveform of the shaft voltage is completely lost. Partial waveform collapse is a state in which the pulse waveform of the shaft voltage is no longer in units of several. It is assumed that a pulse-like waveform of voltage is continuously generated and not partially lost. 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.

  7 shows the voltage waveform when the shaft voltage is 20.0 V, FIG. 8 shows the shaft voltage is 8.0 V, and FIG. 9 shows the voltage waveform when the shaft voltage is 4.0 V. The waveform of FIG. 7 is in a state of complete waveform collapse, the waveform of FIG. 8 is in a state of partial waveform collapse, and the waveform of FIG. 9 is in a state of no waveform collapse.

  FIG. 10 summarizes these results. When the axial voltage Vb is equal to or higher than the withstand voltage Vbd, the waveform collapses and a discharge phenomenon occurs. When the shaft voltage Vb is smaller than the withstand voltage Vbd, there is no waveform collapse and no discharge phenomenon occurs.

  As can be seen from these results, by suppressing the shaft voltage appearing between the bearing inner ring and the bearing outer ring of the bearing rather than the withstand voltage of the bearing alone, the bearing inner ring generated when the shaft voltage exceeds the withstand voltage An electrical short circuit phenomenon of the bearing outer ring can be prevented and electrolytic corrosion can be suppressed.

  In this embodiment, an example of an electric motor that is an inner rotor type brushless motor in which the rotor is rotatably arranged on the inner peripheral side of the stator has been described. However, the rotor is arranged on the outer peripheral side of the stator. The present invention can also be applied to an outer rotor type electric motor. FIG. 11 is a configuration diagram showing a cross section of an outer rotor type electric motor as another configuration example in the present embodiment. In addition, the same code | symbol is attached | subjected about the component similar to FIG.

  In the figure, a stator core 11 around which a stator winding 12 is wound is molded with an insulating resin 13 to form a 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 15 a and 15 b, and a hollow cylindrical rotor 14 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 a dielectric layer 50 as shown in FIG. 11 and a structure for electrically connecting the bracket 17 and the bracket 19, Similar effects can be obtained.

(Embodiment 2)
Next, a configuration of an air conditioner outdoor unit will be described as an example of the electric apparatus according to the present invention. In FIG. 12, the air conditioner outdoor unit is separated by a partition plate 203 erected on the bottom plate 202 of the housing 201
It is divided into a compressor chamber 204 and a heat exchanger chamber 205. A compressor 206 is disposed in the compressor chamber 204. A heat exchanger 207 and an electric motor 208 are disposed in the heat exchanger chamber 205. An electrical component box 209 is disposed above the partition plate 203.

  The electric motor 208 is driven by the electric motor driving device 210 accommodated in the electric component box 209, and the fan 211 rotates with the rotation of the electric motor 208 and blows air to the heat exchanger chamber 205 through the heat exchanger 207.

(Embodiment 3)
Next, a configuration of a hot water heater will be described as an example of the electrical apparatus according to the present invention. In FIG. 13, an electric motor 302 is mounted in a case 301 of the water heater. A fan 303 is attached to the rotating shaft of the electric motor 302. The electric motor 302 is driven by an electric motor driving device 304. By energization from the electric motor drive device 304, the electric motor 302 rotates, and the fan 303 rotates accordingly. The rotation of the fan 303 blows air necessary for combustion to a fuel vaporization chamber (not shown).

(Embodiment 4)
Next, the structure of an air cleaner is demonstrated as an example of the electric equipment concerning this invention. In FIG. 14, an electric motor 402 is mounted in a housing 401 of the air cleaner. An air circulation fan 403 is attached to the rotating shaft of the electric motor 402. The electric motor 402 is driven by an electric motor driving device 404. By energization from the electric motor driving device 404, the electric motor 402 rotates, and the fan 403 rotates accordingly. Air is circulated by the rotation of the fan 403.

  In the above description, electric motors mounted on an air conditioner outdoor unit, an air conditioner indoor unit, a water heater, an air purifier, etc. have been taken up as examples of the electric apparatus according to the present invention. Needless to say, the present invention can also be applied to electric motors mounted on various information devices and electric motors used in industrial devices.

  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 13 Insulation resin 14 Rotor 15a Bearing 15b Bearing 16 Shaft 17 Bracket 19 Bracket 30 Rotating body 31 Rotor core 32 Ferrite resin magnet 50 Dielectric layer 61 Bearing outer ring 62 Bearing inner ring

Claims (8)

A stator including a stator core wound with windings; a rotor holding a permanent magnet in a circumferential direction facing the stator; a shaft fastened to the rotor; and a shaft before and after the rotor And a bracket for fixing the bearing,
An electric motor in which a shaft voltage between a bearing inner ring and a bearing outer ring of the bearing is suppressed to be lower than a withstand voltage of the bearing alone. 2. The electric motor according to claim 1, wherein the withstand voltage of the single bearing is obtained from an oil film thickness due to grease of the single bearing and the withstand voltage of the grease. 3. The electric motor according to claim 1, wherein the size of the electrostatic tangent of the grease of the bearing unit is within 0.1. The electric motor according to any one of claims 1 to 3, wherein a dielectric layer is provided between the shaft and an outer periphery of the rotor. The electric motor according to any one of claims 1 to 4, wherein the brackets are electrically connected to each other and insulated from the stator core. 6. The electric motor according to claim 1, wherein at least one of the bracket and the stator core are integrally formed of an insulating resin. 7. The electric motor according to claim 1, wherein the rotor is rotatably disposed on an inner peripheral side of the stator. An electric apparatus comprising the electric motor according to any one of claims 1 to 7.