JP2014107998A - Motor - Google Patents

Abstract

In an electric motor driven by an inverter by a PWM method, occurrence of electrolytic corrosion of a bearing is suppressed.
A rotor including a stator around which a winding is wound, a rotor that holds a permanent magnet in a circumferential direction facing the stator, a shaft that fastens the rotor, and the shaft. An inverter-driven electric motor having two bearings that are rotatably supported, wherein an electrostatic shield made of a conductive material is applied to an outer peripheral portion of the electric motor, and an electrostatic capacity from an electric device that fixes the electric motor by the electrostatic shield This is an electric motor in which the shaft voltage in the electric motor is stabilized and the reliability of electrolytic corrosion suppression is improved.
[Selection] Figure 1

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), the rotor core is disassembled into an outer core and an inner core, a dielectric layer is provided between the outer core and the inner core, and the capacitance of the rotor is adjusted. Thus, a method for reducing the shaft voltage is known (for example, see Patent Document 1).

JP 2010-166689 A

  Although the method according to Patent Document 1 has a great effect of suppressing electrolytic corrosion, it is a method of adjusting the electrostatic capacitance by balancing the impedance of the stator and the rotor, so that the shaft voltage can be reduced with a single motor. However, if capacitance occurs between the main body of the electrical equipment to which the motor is installed and the stator or rotor in the motor, the balance of the capacitance adjusted in the state of the motor alone is lost, and the shaft voltage is reduced. In some cases, the shaft voltage becomes high, and when the shaft voltage exceeds the insulation withstand voltage of the bearing, discharge damage occurs in the bearing, and electric corrosion occurs.

In addition, there is a method of adjusting the impedance balance between the stator and the rotor in the electric motor in advance by the configuration of the electric device main body to which the electric motor is attached. There is a problem in that the versatility of the electric motor is lost because the main body must be changed.

  In addition, the capacitance generated by the electrical device body may change depending on the operation mode of the electrical device body (if the electrical device body is an air conditioner, there is a cooling mode, a heating mode, a ventilation mode, etc.) When the balance of impedance between the stator and rotor in the motor is adjusted in one operation mode, the balance of capacitance changes in the other operation mode, so that the shaft voltage changes. there were.

  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, an electric motor according to the present invention includes a stator wound with a winding, a rotating body that holds a permanent magnet in the circumferential direction facing the stator, and a shaft that fastens the rotating body And an electric motor including two bearings for rotatably supporting the shaft, wherein an electrostatic shield made of a conductive material is applied to an outer peripheral portion of the electric motor, and the electrostatic shield and the 2 An electric motor characterized in that an insulating layer is provided between two bearings and the stator, and the electrostatic shield and the bearing, and the electrostatic shield and the stator are electrically insulated.

  Further, the electrostatic shield made of the conductive material is connected to the ground of a device on which the electric motor is mounted. Furthermore, the electric motor has a dielectric layer disposed between the outer iron core constituting the outer peripheral portion of the rotating body, the inner iron core constituting the inner peripheral portion fastened to the shaft, and the outer iron core and the inner iron core.

  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.

Structural drawing showing a cross section of a brushless electric motor according to an embodiment of the present invention

  Hereinafter, the present invention will be described with reference to the drawings. Note that the present invention is not limited to the following embodiments.

(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 on an air conditioner as an electric device and that is a brushless electric 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 a rotor core 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.

  As shown in FIG. 1, the rotating body 30 includes an outer iron core 31 a, a dielectric layer 50, and a rotating member that form the outer peripheral portion of the rotor core from the outermost ferrite resin magnet 32 toward the inner peripheral shaft 16. It has a structure which arranges in order with the inner side iron core 31b which comprises the inner peripheral part of a child iron core.

  FIG. 1 shows a configuration example in which an inner iron core 31b, a dielectric layer 50, an outer iron core 31a, and a ferrite resin magnet 32 are integrally formed as the rotating body 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 bearings 15 a and 15 b that support the shaft 16 are attached to the shaft 16 of the rotor 14. The bearing is a cylindrical bearing having a plurality of iron balls, and the inner ring side of the bearings 15 a and 15 b is fixed to the shaft 16.

  In FIG. 1, the bearing 15 a supports the shaft 16 on the output shaft side where the shaft 16 protrudes from the brushless electric motor main body, and the bearing 15 b supports the shaft 16 on the opposite side (hereinafter referred to as the non-output shaft side). Support. And these bearings 15a and 15b have the outer ring side of the bearing fixed by the respective brackets.

  In FIG. 1, the output shaft side bearing 15 a is fixed by a bracket 17, and the non-output shaft side bearing 15 b is fixed by a bracket 19. With the configuration as described above, the shaft 16 is supported by the two bearings 15a and 15b, and the rotor 14 rotates freely.

  Further, this brushless motor 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 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 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 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.

  The stator winding 12 is driven by the drive circuit of the printed circuit board 18 by supplying the power supply voltage and the control signal to the brushless motor configured as described above via the connection line 20. 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 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. .

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

  First, as described above, in the brushless electric motor, the shaft 16 is supported by the two bearings 15a and 15b, and the bearings 15a and 15b are also fixed and supported by the brackets.

  Specifically, first, it is fixed to the bearing 15b on the side opposite to the output shaft by a bracket 19 having an outer diameter substantially equal to the outer diameter of the bearing 15b. The bracket 19 is integrally molded with the insulating resin 13. That is, as shown in FIG. 1, the shape of the insulating resin 13 on the side opposite to the output shaft is a shape having a main body protruding portion 13 a that protrudes from the main body of the brushless motor in the direction opposite to the output shaft. A bracket 19 is disposed as an inner bracket on the inner side of the main body protruding portion 13a, and is integrally molded with the insulating resin 13.

  The bracket 19 has a cup shape having a hollow cylindrical shape, and more specifically, a cylindrical portion 19a that is open on one side, and an annular collar portion that slightly extends outward from the cylindrical end portion on the open side. 19b. The inner diameter of the cylindrical portion 19a is substantially equal to the outer diameter of the bearing 15b, and the bearing 15b is fixed to the insulating resin 13 via the bracket 19 by press-fitting the bearing 15b into the cylindrical portion 19a. . By comprising in this way, since the outer ring | wheel side of the bearing 15b is fixed to the metal bracket 19, the malfunction by creep can be suppressed.

  The outer diameter of the collar portion 19b is slightly larger than the outer diameter of the bearing 15b. That is, the outer diameter of the collar portion 19 b is larger than the outer diameter of the bearing 15 b and at least smaller than the outer diameter of the rotating body 30. By using the 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. In addition, since the area of the metal bracket 19 is suppressed and the mold is integrally formed so as to cover the outline of the bracket 19 with the insulating resin 13, noise generated from the bearing 15b can be suppressed.

  Next, the bearing 15a on the output shaft side is fixed by a bracket 17 having an outer peripheral diameter substantially equal to the outer peripheral diameter of the stator 10. The bracket 17 has a substantially disc shape, and has a protrusion having a diameter substantially equal to the outer diameter of the bearing 15a at the center of the disk, and the inside of the protrusion is hollow.

  After the printed circuit board 18 is built in, the inside of the protruding portion of the bracket 17 is press-fitted into the bearing 15a, and the connection end provided on the outer periphery of the bracket 17 and the connection end of the stator 10 are fitted together. In addition, the brushless electric motor is formed by press-fitting the bracket 17 into the stator 10. With this configuration, the assembling work is facilitated.

  In the present embodiment, in the rotating body 30, the dielectric layer 50 is provided between the shaft 16 and the outer periphery of the rotating body 30.

  Next, a conductive electrostatic shield 22 is provided outside the insulating resin 13 of the motor, and the electrostatic shield 22 and the bearing 15b, and the electrostatic shield 22 and the stator core 11 are electrically insulated. . The bracket 17 is provided with an insulating coating 23 on the inner surface of the bearing insertion portion, and the electrostatic shield 22 and the bearing 15a are insulated. The bracket 17 is electrically connected to the electrostatic shield 22 by being press-fitted into the stator 10. Further, the electrostatic shield 22 is connected to the ground 24 of the electric device main body to which the electric motor is attached.

  By doing in this way, when an electric motor is mounted in an electric equipment main body, it becomes an electric motor which is hard to receive the influence of the electrostatic capacitance from an electric equipment main body. This is because the electrostatic shield on the outer periphery of the motor blocks the electrostatic capacity from the electric device body, and the electrostatic shield is insulated from the field core and the bearing, so that the field core and the bearing are separated from the electric device body. This is because it becomes difficult to be affected by the capacitance.

  Moreover, the effect of blocking the electrostatic capacitance from the electric device body is higher when the electrostatic shield is connected to the ground of the electric device body than when the electrostatic shield is not connected. This is because the influence of the capacitance generated between the electrostatic shield and the field core or between the electrostatic shield and the bearing can be reduced by grounding the electrostatic shield.

  Since the electric motor is less susceptible to the capacitance from the electric device body, the electric motor can be installed in any kind of electric device body or in any kind of operation mode of the electric device body. Since the shaft voltage is less likely to change, the reliability of electrolytic corrosion suppression can be improved.

  The electric motor of the present invention suppresses the occurrence of electrolytic corrosion of the bearing, and can be used for various electric devices. In particular, the electric motor is mounted on an air conditioner indoor unit that requires a reduction in the price and long life of the electric motor. It is valid.

10 Stator 11 Stator Iron Core 12 Stator Winding 13 Insulating Resin 14 Rotor 15a Bearing (Output Shaft Side)
15b Bearing (anti-output shaft side)
16 Shaft 17 Bracket (Output shaft side)
18 Printed circuit board 19 Bracket (Non-output shaft side)
19a Cylindrical part 19b Collar part 20 Connection line 21 Resin 22 Electrostatic shield 23 Insulating coating 24 Ground 30 Rotating body 31a Outer iron core 31b Inner iron core 32 Ferrite resin magnet 50 Dielectric layer

Claims (3)

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 having two bearings,
An electric motor comprising an electrostatic shield made of a conductive material on an outer peripheral portion of the electric motor, wherein the electrostatic shield and the bearing, and the electrostatic shield and the stator are electrically insulated. The electric motor according to claim 1, wherein the electrostatic shield is connected to a ground of a device on which the electric motor is mounted. The electric motor according to claim 1, wherein the rotating body includes an inner iron core, an outer iron core, and a dielectric layer provided between the inner iron core and the outer iron core.