JP2014121100A - Motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress occurrence of electrolytic corrosion of a bearing in a motor driven by an inverter in a PWM system.SOLUTION: This motor includes a stator wound with windings, a rotating body facing the stator and holding a permanent magnet in the circumferential direction thereof, and a rotor containing a shaft coupled to the rotating body, a bearing on the output shaft side and a bearing on the opposite side to the bearing on the output shaft side which rotatably support the shaft, and two conductive brackets for fixing the outer rings of the two bearings. The two brackets are electrically connected to each other and an insulation breakdown withstand voltage between the inner ring and the outer ring is made lower in the bearing on the output shaft side than in the bearing on the opposite side to the bearing on the output shaft side.

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 a method which short-circuits a stator iron core and metal brackets, the electrostatic capacitance distribution in an electric motor may become high overall, and a shaft voltage may become high. there were.

  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.

  In addition, if the shaft voltage is not sufficiently low compared to the dielectric breakdown voltage of the bearing alone, it is difficult to prevent the electrical short circuit phenomenon occurring in the bearing for a long period of time, and it is difficult to suppress electrolytic corrosion. Met. This is because, when a shaft voltage is applied to the bearing for a long period of time, the dielectric breakdown voltage of the bearing itself decreases due to grease deterioration or bearing surface damage.

  Therefore, the dielectric breakdown voltage of the bearing is higher than the shaft voltage at the beginning of motor driving, and even if no short-circuit phenomenon occurs, the dielectric breakdown voltage of a single bearing decreases when driven for a long period of time. When the dielectric breakdown voltage of the bearing unit is reduced, a short circuit phenomenon occurs, resulting in the occurrence of electrolytic corrosion. The dielectric breakdown voltage of the bearing can be increased by increasing the thickness of the oil film of grease, and a method of increasing the kinematic viscosity of the base oil of grease is generally used. However, when the kinematic viscosity of the base oil of grease is increased, bearing loss increases and the efficiency of the motor decreases, so there is a limit to increasing the oil film thickness.

  In addition, in the two bearings (output shaft side bearing and anti-output shaft side bearing) that support the shaft constituting the motor, if the two bearings are the same, the occurrence of electrolytic corrosion is likely to occur in the output shaft side bearing. It was. This is because vibration and shock from the output shaft (to which the fan is connected) are more likely to be received by the output shaft side bearing that is closer in position than the non-output shaft side bearing. This is because the oil film in the bearing is instantaneously thinned and the dielectric breakdown voltage of the bearing is lowered, so that electric discharge easily occurs and electric corrosion tends to occur.

  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.

The electric motor of the present invention includes a stator including a winding, a rotor that holds a permanent magnet in the circumferential direction facing the stator, and a rotor that includes a shaft that fastens the rotor. An output shaft side bearing and a non-output shaft side bearing that rotatably support a shaft, and two conductive brackets that fix outer rings of the two bearings, the two brackets being electrically The non-output shaft side bearing has a lower dielectric breakdown voltage between the inner ring and the outer ring than the output shaft side bearing, and the anti-output side bearing has a soundproof structure. It is an electric motor.

  Further, the bracket for fixing the bearing on the non-output side is molded with resin. Furthermore, a damping steel plate is used for the bracket. Further, the oil film parameter of the non-output-side bearing is lower than that of the output-side bearing.

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

Structural drawing showing a cross section of a brushless motor in an embodiment of the present 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)
FIG. 1 is a structural diagram showing a cross section of an electric motor according to an embodiment 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 the present embodiment, the stator 10 whose outer shape is substantially cylindrical is formed by integrally molding these members in this way.

  A rotor 14 is inserted inside the stator 10 through a gap. The rotor 14 includes a disk-shaped rotating body 30 including the rotor core 31 and a shaft 16 to which the rotating body 30 is fastened so as to penetrate the center of the rotating body 30. The rotating body 30 holds a ferrite resin magnet 32 that is a permanent magnet in the circumferential direction facing the inner peripheral side of the stator 10.

  FIG. 1 shows a configuration example in which the rotor core 31 and the ferrite resin 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.

  An output shaft side bearing 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 output shaft side bearing 15 a and the counter output shaft side bearing 15 b are cylindrical bearings having a plurality of iron balls, and the inner ring side of the output shaft side bearing 15 a and the counter output shaft side bearing 15 b is fixed to the shaft 16. . In FIG. 1, the output shaft side bearing 15 a supports the shaft 16 on the output shaft side where the shaft 16 protrudes from the brushless motor body, and on the opposite side (counter output shaft side), the counter output 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 output shaft side bearing 15a and the counter output shaft side bearing 15b by metal brackets having conductivity. In FIG. 1, the output shaft side bearing 15 a is fixed by the output shaft side bracket 17, and the counter output shaft side bearing 15 b is fixed by the counter output shaft side bracket 19. With the configuration described above, the shaft 16 is supported by the output shaft side bearing 15a and the non-output shaft side bearing 15b, and the rotor 14 rotates freely.

  The output shaft side bearing 15a and the counter output shaft side bearing 15b are filled with grease that fills a part of the internal space inside the bearing. These output shaft side bearing 15a and anti-output shaft side bearing 15b are referred to as “double-side shielded ball bearings” and are widely known in the bearing field as “ZZ” in the “Nominal Symbol” item. It is what.

  Furthermore, the brushless motor of this embodiment incorporates a printed circuit board 18 on which a drive circuit including a control circuit is mounted. After the printed circuit board 18 is built in, the output shaft side bracket 17 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 rotation speed, 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 a 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 rotates about the shaft 16 by these forces. To do.

  Next, a more detailed configuration of the brushless motor will be described. First, in the brushless motor, as described above, the shaft 16 is supported by the output shaft side bearing 15a and the counter output shaft side bearing 15b, and the output shaft side bearing 15a and the counter output shaft side bearing 15b are also formed by brackets. Fixed and supported.

  Further, in order to suppress the above-described problems caused by creep, in the present embodiment, the output shaft side bearing 15a and the counter output shaft side bearing 15b are each fixed by a conductive metal bracket. It is configured. 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 output shaft side bearing 15a and the non-output shaft side bearing 15b. In particular, when a high output of the electric motor is required, such a configuration is more preferable.

  Specifically, first, the counter-output shaft side bearing 15b is fixed by the counter-output shaft side bracket 19 having an outer diameter substantially equal to the outer diameter of the counter-output shaft side bearing 15b. Further, the opposite output shaft side bracket 19 is integrally molded with the insulating resin 13.

  The non-output shaft side bracket 19 has a cup shape that becomes a hollow cylindrical shape. More specifically, the bracket portion 19a of the bracket that is opened on one side and the cylindrical end portion on the opened side are only slightly outward. And a flange portion 19b of an annular bracket that is widened. The inner peripheral diameter of the cylindrical portion 19a of the bracket is substantially equal to the outer peripheral diameter of the non-output shaft side bearing 15b. By pressing the anti-output shaft side bearing 15b into the cylindrical portion 19a of the bracket, the anti-output shaft side bearing 15b is anti-output. It is also fixed to the insulating resin 13 through the shaft side bracket 19.

  By comprising in this way, since the outer ring | wheel side of the non-output shaft side bearing 15b is fixed to the metal non-output shaft side bracket 19, the malfunction by creep can be suppressed. Further, the outer peripheral diameter of the flange portion 19b of the bracket is slightly larger than the outer peripheral diameter of the non-output shaft side bearing 15b.

  That is, the outer diameter of the flange portion 19 b of the bracket is larger than the outer diameter of the counter-output shaft side bearing 15 b and at least smaller than the outer diameter of the rotating body 30. By using the anti-output shaft side bracket 19 in such a shape, for example, compared to a structure in which the collar portion extends beyond the outer periphery of the rotating body 30 to the stator 10, the use of a metal material that increases the cost is suppressed. doing.

  Further, since the area of the metal anti-output shaft side bracket 19 is suppressed in this way, and the outer periphery of the anti-output shaft side bracket 19 is covered with the insulating resin 13, the anti-output shaft side bearing is formed. 15b is sealed and has a soundproof structure capable of suppressing noise generated by the non-output shaft side bearing 15b.

  Next, the output shaft side bearing 15 a is fixed by an output shaft side bracket 17 having an outer peripheral diameter substantially equal to the outer peripheral diameter of the stator 10. The output shaft side bracket 17 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 the protruding portion is hollow. Yes. After the printed circuit board 18 is built in, the inside of the projecting portion of the output shaft side bracket 17 is press-fitted into the output shaft side bearing 15a, and the connection end provided on the outer periphery of the output shaft side bracket 17 and the stator 10 The brushless motor is formed by press-fitting the output shaft side bracket 17 into the stator 10 so that the connection end is 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 problems due to creep are also suppressed.

  Further, the brushless motor of the present embodiment has a configuration in which a part of a conducting body that electrically conducts between the output shaft side and the non-output shaft side brackets is embedded in the resin.

Specifically, the first conduction pin 22 is electrically connected to the non-output shaft side bracket 19 in advance. That is, as shown in FIG. 1, one of the first output pins 22 on the opposite end of the output shaft side is connected to the collar portion 19 b of the bracket 19 of the opposite output shaft side bracket 19. The first 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 non-output shaft side bracket 19.

  In addition, by arranging the first conductive pin 22 inside the insulating resin 13 as an electric motor, the first conductive pin 22 is prevented from rust and external force, and is reliable against the use environment and external stress. High electrical connection. The first conductive pin 22 extends from the flange portion 19b of the bracket 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. And further stretched.

  The output shaft side tip 22b of the first conductive pin 22 is exposed from the end surface of the insulating resin 13 on the output shaft side. Further, a second conduction pin 23 for electrically connecting the first conduction pin 22 to the output shaft side bracket 17 is connected to the output shaft side tip 22b. That is, when the output shaft side bracket 17 is press-fitted into the stator 10, the second conduction pin 23 comes into contact with the output shaft side bracket 17, and conduction between the output shaft side bracket 17 and the second conduction pin 23 is ensured. The

  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 first conduction pin 22. The output shaft side bracket 17 and the counter output shaft side bracket 19 are electrically connected to each other with the insulating resin 13 being insulated from the stator core 11.

In the configuration of the brushless motor as shown in FIG. 1, single row deep groove ball bearings having a JIS identification number of 608 were used for the output shaft side bearing 15a and the counter output shaft side bearing 15b. The grease to be sealed in the two bearings uses ester oil as the base oil and lithium soap as the thickener, and the kinematic viscosity (40 ° C) of the grease base oil used for the output shaft side bearing 15a is 60 mm. ² / s, the kinematic viscosity of the base oil of the grease used for the non-output shaft side bearing was 50 mm ² / s. By doing in this way, the oil film thickness of the grease of the bearing becomes thicker in the output shaft side bearing 15a than in the anti-output shaft side bearing 15b, and the dielectric breakdown voltage of the bearing is larger than that in the anti-output shaft side bearing 15b. The output shaft side bearing 15a is larger. The relationship between the oil film thickness and the breakdown voltage of the bearing is shown in Equation 1.

Bearings, bearing inner ring and the bearing outer ring, bearing balls are composed of grease, the grease forms a grease oil film by preload from the preload spring, grease oil film of the bearing inner ring and the bearing outer ring and bearing balls oil film thickness h _c It is lubricated through. This grease is an insulator, and a capacitor is formed by the conductor of the bearing. As shown in Equation 1, the grease withstand voltage V _bd increases as the oil film thickness h _c of the grease increases.

In this embodiment, the output shaft side bearing 15a increases the dielectric breakdown voltage more than the non-output shaft side bearing 15b. Therefore, the base oil kinematic viscosity of the grease of the output shaft side bearing 15a is less than that of the counter output shaft side bearing 15b. The grease oil film thickness was increased, but other methods include increasing the bearing surface roughness to increase the grease oil film thickness, and changing the curvature of the bearing inner ring and bearing outer ring. A method of increasing the oil film thickness of grease is also possible. Furthermore, it is possible to increase the bearing withstand voltage by increasing the withstand voltage V _25d of the grease itself by changing the composition of the grease without changing the oil film thickness of the grease.

  With the above configuration, the dielectric breakdown voltage of the bearing was 8.5V for the output shaft side bearing 15a and 7.5V for the non-output shaft side bearing 15b. Moreover, in the structure of this invention, since the output shaft side bearing 15a and the non-output shaft side bearing 15b have conduct | electrically_connected, the shaft voltage concerning both bearings was constant, and the shaft voltage was 7V.

  For the measurement of withstand voltage, an AC stabilized power supply is used. While rotating the bearing, an alternating voltage is applied to the inner ring and outer ring of the bearing at a speed of 0 V to 0.1 V / sec to withstand the voltage just before the short circuit occurs. Voltage. The measurement is performed at an air temperature of 20 ° C. and a bearing speed of 1000 r / min. The applied voltage is a 20 kHz rectangular wave, and the output impedance is 50Ω and measurement is performed.

  The shaft voltage was measured under the same operating conditions with an air temperature of 20 ° C. and a rotation speed of 1000 r / min. The motor posture during operation was horizontal on the shaft. The motor is installed on a wooden board with a thickness of 20 mm, and the shaft voltage is measured with a digital oscilloscope (Tektronix DPO7104) and a high-voltage differential probe (Tektronix P5205). It was confirmed whether or not collapse occurred, and the peak-to-peak measurement voltage was defined as the axial voltage. The digital oscilloscope is insulated with an insulation transformer.

  Further, the + side of the high-voltage differential probe has a lead wire conductor formed in a loop shape having a diameter of about 15 mm through a lead wire having a length of about 30 cm, and its inner periphery is brought into conductive contact with the outer periphery of the shaft. It is electrically connected to the shaft. The negative side of the high-voltage differential probe is electrically connected to the bracket by electrically contacting the tip of the lead wire to the output shaft side bracket 17 with conductive tape via a lead wire having a length of about 30 cm. Yes.

  Before the endurance test, the shaft voltage is lower than the dielectric strength voltage of the bearing, so no discharge occurs in the bearing. However, when the electric motor of Example 1 was driven at room temperature and 1000 r / min and 5000 hours passed, discharge occurred in the non-output shaft side bearing 15b, and electric corrosion occurred.

  This is considered to be because the dielectric breakdown voltage of the bearing was lowered because the surface roughness was deteriorated due to sliding inside the bearing and the oil film thickness was reduced due to long-term running. The breakdown voltage of the bearing decreases with the driving time of the motor, and even if the breakdown voltage of the bearing is initially higher than the shaft voltage, the breakdown voltage of the bearing becomes lower than the shaft voltage depending on the driving time of the motor. There is a problem that the long-term reliability of electric corrosion noise cannot be satisfied.

  The reason for the occurrence of electrolytic corrosion not on the output shaft side bearing but on the non-output side bearing is that the anti-output shaft side bearing has a lower dielectric breakdown voltage than the output shaft side bearing, which is a feature of the present invention. . When electric corrosion occurs in the non-output shaft side bearing 15b, the inside of the anti-output shaft side bearing 15b is electrically connected. Therefore, the shaft applied to the output shaft side bearing 15a electrically connected to the anti-output shaft side bearing 15b. The voltage approaches zero as much as possible.

Therefore, according to the configuration of the present invention, even if electrolytic corrosion occurs due to long-term driving of the electric motor, the only bearing that generates electrolytic corrosion is the anti-output shaft side bearing 15b and not the output shaft side bearing 15a. Furthermore, in the configuration of the present invention, the non-output shaft side bearing 15b has a soundproof structure and is covered with the insulating resin 13. Therefore, even if the transfer surface is damaged when electrolytic corrosion occurs, the noise worsens. Is unlikely to occur.

  In addition, a bearing that generates electric corrosion and has a soundproof structure can be an output-side bearing, not an anti-output-side bearing, but the output-side bearing is inevitably external to the motor for the purpose of projecting the output shaft from the motor. It becomes easy to expose and it is difficult to take a soundproof structure.

  In addition, when the output shaft side bearing and the non-output shaft side bearing are the same bearing, the occurrence of electrolytic corrosion was likely to occur in the output shaft side bearing. This is because vibration and shock from the output shaft (to which the fan is connected) are more likely to be received by the output shaft side bearing that is closer in position than the non-output shaft side bearing. This is because the oil film in the bearing is instantaneously thinned and the dielectric breakdown voltage of the bearing is lowered, so that electric discharge easily occurs and electric corrosion tends to occur.

  However, when the dielectric breakdown voltage of the output shaft side bearing is 1 V or more than the dielectric breakdown voltage of the non-output shaft side bearing as in Example 1, the anti-output shaft side bearing generates electric corrosion first. It becomes like this.

  Table 1 shows the results of driving noise when the electric motor in the configuration of Example 1 was continuously driven at room temperature and 1000 r / min for up to 10,000 hours. The noise measurement was performed under the same operating conditions with an air temperature of 20 ° C. and a rotation speed of 1000 r / min. The motor posture during operation was horizontal on the shaft, and a microphone was installed at a location 15 cm away from the motor, and noise was measured with A characteristics. The noise (background noise) when the motor was not driven was 13 dB.

  The second embodiment is the same as the first embodiment except that a damping steel plate is used in the opposite output shaft side bracket 19 for fixing the opposite output side bearing. The damping steel plate has a structure in which a damping resin is laminated between two steel plates, and vibration transmitted from the bearing can be reduced, so that the sound insulation of the bearing can be improved.

  Table 1 shows the results of driving noise when the motor in the configuration of Example 2 was driven at room temperature and 1000 r / min for up to 10,000 hours.

Comparative example

The comparative example is the same as the configuration of Example 1, except that the kinematic viscosity (40 ° C.) of the grease base oil is 60 mm ² / s for both the output-side bearing and the counter-output-side bearing. In the case of the comparative example, the shaft voltage was 8V. The reason why the shaft voltage of the comparative example is higher than the shaft voltage of the first embodiment is that, since the first embodiment uses grease with a low base oil kinematic viscosity for the non-output side bearing, the total oil film thickness of the two bearings This is because the comparative example is thicker than Example 1. The thicker the oil film, the higher the shaft voltage due to the capacitor principle.

  Table 1 shows the results of driving noise when the electric motor in the configuration of the comparative example is driven at room temperature and 1000 r / min for up to 10,000 hours.

  As shown in Table 1, the driving noise increased in the order of Example 2, Example 1, and Comparative Example at 1000 r / min after 10,000 hours.

  In the case of a general household indoor air conditioner used for an electric motor, the drive noise needs to be 40 dB or less at 1000 rpm, so the noise of electric corrosion is suppressed by the configuration of the first embodiment, preferably the second embodiment. It is possible.

  The electric motor of the present invention suppresses the occurrence of electric corrosion of the bearing, and is effective for an electric motor mounted on a device such as an air conditioner indoor unit that is mainly required to reduce the price and increase the life of the electric motor.

DESCRIPTION OF SYMBOLS 10 Stator 11 Stator iron core 12 Stator winding 13 Insulation resin 14 Rotor 15a Output shaft side bearing 15b Anti-output shaft side bearing 16 Shaft 17 Output shaft side bracket 18 Printed circuit board 19 Anti-output shaft side bracket 19a Cylindrical part of bracket 19b Bracket collar 20 Connection line 21 Resin (insulator)
22 1st conduction | electrical_connection pin 23 2nd conduction | electrical_connection pin 30 Rotor 31 Rotor core 32 Magnet

Claims (4)

A rotor including a stator wound with a winding, a rotor holding a permanent magnet in the circumferential direction facing the stator, and a shaft fastened to the rotor, and the shaft rotatably supported An electric motor comprising a bearing on the output shaft side and a bearing on the opposite output shaft side, and two conductive brackets for fixing the outer rings of the two bearings, the two brackets being electrically connected, and An electric motor characterized in that a dielectric breakdown voltage between an inner ring and an outer ring is lower in a bearing on the side opposite to the output shaft than on a bearing on the output shaft. The electric motor according to claim 1, wherein the bearing on the side opposite to the output shaft has a soundproof structure. The electric motor according to claim 1 or 2, wherein a bracket for fixing the bearing on the side opposite to the output shaft is molded with resin. The electric motor according to claim 1, wherein a damping steel plate is used for the bracket.