JP2012244777A - Motor and air conditioner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor that prevents electric corrosion of bearings at low cost, and to provide an air conditioner.SOLUTION: A motor 1 includes: a stator 2 that is provided in a mold frame 10; a rotor 5 that has permanent magnets 6 arranged around a rotating shaft 9 so as to face the stator 2; a mold bracket 11 and a metal bracket 12 that are provided on two respective ends of the mold frame 10 and support the rotating shaft 9; a pair of bearings 13 and 15 that are respectively mounted on the mold bracket 11 and the metal bracket 12 and support the rotating shaft 9; and a support member 7 that is formed in an annular shape, that is provided between the rotating shaft 9 and the permanent magnets 6 so as to support the permanent magnets 6, and that includes a magnetic material which is magnetically softer than a magnetic material of the permanent magnets 6.

Description

  The present invention relates to an electric motor and an air conditioner using the same.

  Many blower motors (hereinafter simply referred to as “motors”) installed in an air conditioner have built-in inverters from the viewpoint of structural convenience. When this motor is driven by an inverter, a voltage is induced between the rotor shaft ends or between the winding wound around the stator (stator) and the stator core (stator core) as the inverter is switched. It is known that Here, when the bearing that supports the rotating shaft is a bearing composed of an inner ring, an outer ring, and a rolling element, the voltage is applied between the inner ring and the outer ring, causing discharge inside the bearing, There is a risk of causing a problem called food. For this reason, various structural measures for preventing such electric corrosion have been proposed for inverter-driven electric motors.

  For example, the technology described in Patent Document 1 below is configured to electrically connect the outer rings of two bearings mounted on a frame and not to transmit the voltage generated between the winding and the stator core to the bearings. Yes.

JP 2010-158152 A

  However, the technique disclosed in Patent Document 1 requires a change in the structure of the bracket and the frame, which makes it difficult to share equipment for manufacturing a conventional electric motor. It was.

  This invention is made | formed in view of the above, Comprising: It aims at obtaining the electric motor and air conditioner which can suppress the electrolytic corrosion of a bearing cheaply.

  In order to solve the above-described problems and achieve the object, the present invention includes a stator disposed in a frame, and a rotor having a permanent magnet disposed around a rotation shaft so as to face the stator. A pair of brackets disposed at both ends of the frame and supporting the rotating shaft, and a pair of bearings mounted on the bracket and supporting the rotating shaft, forming an annular shape and capable of supporting the permanent magnet And a support member that is disposed between the rotating shaft and the permanent magnet and includes a magnetic material that is softer than the magnetic material of the permanent magnet.

  According to the present invention, since the discharge current is suppressed only by changing the material of the support member, there is an effect that the electrolytic corrosion of the bearing can be suppressed at a low cost.

FIG. 1 is a cross-sectional view of an electric motor according to an embodiment of the present invention. FIG. 2 is a diagram for explaining a path of a discharge current flowing through the bearing. FIG. 3 is a model diagram of an annular magnetic material. FIG. 4 is a frequency characteristic diagram of the complex permeability of soft ferrite. FIG. 5 is a diagram showing a waveform of a discharge current flowing through the bearing. FIG. 6 is a sectional view of the rotor of the brushless DC motor.

  Embodiments of an electric motor and an air conditioner according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment.
FIG. 1 is a cross-sectional view of an electric motor according to an embodiment of the present invention. An electric motor 1 shown in FIG. 1 mainly includes a stator 2, a rotor 5, a rotating shaft 9, a bearing 13, a bearing 15, an inverter 8 for generating a rotating magnetic field in the stator 2, and a mold frame. 10, a mold bracket 11, and a metal bracket 12.

  The stator 2 has a structure in which the stator core 4 is covered with an insulator 14 and the winding 3 is wound, and a rotating magnetic field is generated when the inverter 8 is switched.

  The rotor 5 is an annular ring formed of a resin which is disposed between the rotating shaft 9 and the permanent magnet 6 and mixed with a soft magnetic material, and is opposed to the stator 2 so as to surround the rotating shaft 9. The supporting member 7 is configured. The rotor 5 obtains a rotational force by the rotating magnetic field from the stator 2 and transmits torque to the rotating shaft 9, and a load (not shown) provided on the rotating shaft 9 (for example, a fan built in an indoor unit of an air conditioner). Drive.

  The permanent magnet 6 is made of a magnetic material (for example, a hard magnetic material) having a predetermined holding force. The support member 7 is configured by mixing a magnetic material (for example, a soft magnetic material) having a weaker coercive force than the magnetic material of the permanent magnet 6 with a resin, and mechanically fixes the permanent magnet 6 to the rotating shaft 9.

  The mold frame 10 is formed integrally with the inverter 8 and includes the stator 2 and the rotor 5. The mold bracket 11 is formed integrally with the mold frame 10 on the upper side of the mold frame 10 (upper side in FIG. 1), and surrounds and supports the outer ring a of the bearing 13. The metal bracket 12 is formed integrally with the mold frame 10 on the lower side (lower side in FIG. 1) of the mold frame 10 and surrounds and supports the outer ring a of the bearing 15.

  The bearing 13 is disposed while maintaining a predetermined interval in the rotation direction of the inner ring b, the inner ring b that rotates integrally with the rotating shaft 9, the outer ring a provided on the mold bracket 11, and between the inner ring b and the outer ring a. It is comprised with the some rolling element c arrange | positioned so that rolling is possible. Similarly, the bearing 15 includes an inner ring b, an outer ring a provided on the metal bracket 12, and a plurality of rolling elements c.

  Next, the generation principle of electrolytic corrosion and the mechanism for suppressing electrolytic corrosion will be described.

  FIG. 2 is a diagram for explaining a path of a discharge current flowing through the bearings 13 and 15, FIG. 3 is a model diagram of an annular magnetic material, and FIG. 4 is a frequency characteristic diagram of complex permeability of soft ferrite. FIG. 5 is a diagram showing a waveform of the discharge current flowing through the bearings 13 and 15.

  When the electric motor 1 is driven by the inverter 8, an imbalance occurs in the applied power source, or an imbalance occurs in the windings 3 of each phase applied to the stator 2. A voltage is induced between 9 shaft ends. When this voltage exceeds the dielectric breakdown voltage of the oil film inside the bearings 13 and 15, a minute current (discharge current) flows inside the bearings 13 and 15. This discharge current causes electrolytic corrosion inside the bearings 13 and 15. When electrolytic corrosion progresses, a wavy wear phenomenon occurs in the inner ring b, the outer ring a, or the rolling element c, and abnormal noise resulting from this wear phenomenon is one of the main causes of problems in the motor.

  FIG. 2 shows an example of a discharge current path. The discharge current flows through the electric motor 1 through a “path A” as shown by a solid line, and includes an inverter 8, a mold bracket 11, a bearing 13, a rotating shaft 9, and a bearing. 15, the metal bracket 12, the stator 2, and the conductor of the winding 3 are passed through. Note that a path in which the discharge current directly flows from the rotor 5 to the stator 2 can be considered, as in “path B” indicated by a dotted line. Therefore, the radial impedance in the rotor 5 is high and can be ignored as a discharge path. Therefore, in the following description, a path A indicated by a solid line is described as a discharge path.

  Since there are conductors such as the mold bracket 11, the bearing 13, the rotating shaft 9, the bearing 15, the metal bracket 12, the stator 2, and the winding 3 in the path A, the electric circuit corresponds to an RLC series circuit. At this time, if the discharge current flowing through the path A is i, the current i flows according to an equation such as the equation (1).

  In Equation (1), R represents resistance in the path, L represents inductance, C represents capacitance, and E represents axial voltage. At this time, the waveform of the discharge current is determined by the sign of the result of Expression (2).

  In a small blower motor applied to an air conditioner or the like, the material such as the bearing 13 and the rotary shaft 9 is iron or copper, and the resistance R is extremely small. Therefore, since the inductance L and the capacitance C are dominant, Expression (2) <0. Therefore, the discharge current in the blower motor is observed as a current waveform of damped vibration as shown by a current curve A in FIG. Further, the damped vibration and the resonance frequency f in the equation (1) are as shown in the equations (3) and (4).

  Since the magnitude of the energy of the discharge current is affected by the exponential term −R / 2L of the exponential function in Expression (3), when the resistance R of the imaginary part is large, the discharge current is as shown by a current curve B in FIG. It decays quickly. That is, as the resistance R of the imaginary part increases, the bearing damage due to the discharge current decreases. In addition, since the resonance frequency f of the discharge current in a small blower motor is several tens to several hundreds of MHz, a material having a maximum iron loss in the vicinity of this resonance frequency should be inserted into the RLC series circuit. As a result, the discharge current can be quickly reduced, and electric corrosion can be suppressed.

  Next, a material that performs a resistance operation near the resonance frequency will be described.

  FIG. 4 shows characteristics relating to soft ferrite, which is a kind of soft magnetic material, as an example of frequency characteristics of magnetic permeability of a material that exhibits a resistance operation near the resonance frequency. The vertical axis represents magnetic permeability, and the horizontal axis represents frequency. When the complex permeability μ of soft ferrite is expressed by μ = μ′−iμ ″, the permeability μ ′ shown in FIG. 4 represents the real part (inductance component) of the complex permeability μ and is shown in FIG. The permeability μ ″ represents the imaginary part (resistance component) of the complex permeability μ. As apparent from FIG. 4, the magnetic permeability μ ″ increases gradually from several MHz and reaches a maximum at about 100 MHz, and thus acts as a resistance R against a high-frequency component included in the discharge current. Accordingly, the energy of the decay oscillation of the discharge current is changed to heat in the soft ferrite, and as a result, the discharge current can be effectively attenuated as shown by the current curve B shown in FIG. Examples of the soft ferrite include Mn—Zn ferrite and Ni—Zn ferrite.

  The attenuation effect of the discharge current by the soft magnetic material can be obtained at any position on the solid line A shown in FIG. 2, but the most effective portion will be described.

  FIG. 3 shows a model of an annular magnetic material. In FIG. 3, for the sake of convenience of explanation, the support member 7 shown in FIG. 1 is regarded as an annular magnetic material, and the rotary shaft 9 shown in FIG. 1 is a shaft that penetrates the inner periphery of the annular magnetic material. I think. Here, the distance from the center line 20 of the shaft (9) to the inner peripheral surface 7a of the magnetic material (7) is r1, and the distance from the center line 20 of the shaft (9) to the outer peripheral surface 7b of the magnetic material (7) is When the height of the magnetic material (7) is defined as r2 and the magnetic flux generated when the discharge current flows through the shaft (9) as φr is defined as φr, the magnetic flux φr is expressed by the equation (5).

  As apparent from the equation (5), the magnetic flux φr increases as the distance r1 decreases, and the discharge current attenuation effect increases. That is, since the iron loss increases as the value of the magnetic flux φr increases, it is desirable to dispose the magnetic material (7) at a position where the distance r1 is the smallest in the path A. Accordingly, since the position where the distance r1 is the smallest in the path A shown in FIG. 1 is the periphery of the rotating shaft 9, by arranging a soft magnetic material around the rotating shaft 9, the current shown in FIG. As shown by curve B, the discharge current can be effectively attenuated.

  However, when the above-described soft magnetic material is disposed in the existing electric motor 1, it is desirable to apply without changing the structure of the electric motor.

  Therefore, the electric motor 1 according to the present embodiment is configured such that the support member 7 is formed of a resin mixed with a soft magnetic material in order to effectively attenuate the discharge current without changing the dimensions thereof. Has been.

  In the RLC series circuit described above, the resistance R represents a loss (copper loss) caused by the discharge current passing through a resistance component on the path A (for example, the resistance of the bearings 13 and 15). On the other hand, when the support member 7 is made of a resin mixed with a soft magnetic material, an alternating magnetic field is generated around the rotating shaft 9 by the discharge current flowing through the path A, and this magnetic field acts on the support member 7. Iron loss (hysteresis loss) occurs, and the iron loss acts as a resistance. Therefore, the discharge current (high-frequency component) flowing through the path A is quickly attenuated by the iron loss generated in the support member 7. Further, according to the present embodiment, it is possible to manufacture the electric motor 1 without changing the dimensions of the support member 7 such as the distance r1, the distance r2, and the height h.

  Next, the further effect obtained by using the soft ferrite which is one of the soft magnetic materials for the support member 7 will be described.

  FIG. 6 is a cross-sectional view of the rotor 5 of the brushless DC motor, for example, a cross-sectional view taken along the line AA in FIG. FIG. 6 shows a support member 7 formed of a resin mixed with soft ferrite, and four permanent magnets 6 a to 6 d surrounding the outer peripheral surface of the support member 7. Further, FIG. 6 shows magnetic fluxes generated by the permanent magnets 6a to 6d.

  The performance (torque, efficiency, etc.) of the electric motor 1 using the permanent magnets 6a to 6d is improved by supplying as much magnetic flux as possible to the surface of the rotor 5 (the outer peripheral side of the permanent magnets 6a to 6d). On the other hand, in the case of the shape as shown in FIG. 6, the magnetic flux of the permanent magnets 6 a to 6 d passes through the support member 7 disposed on the inner side of the rotor 5 (inner peripheral side of the permanent magnets 6 a to 6 d). The magnetic permeability of the member 7 also affects the performance of the rotor 5. For example, the magnetic permeability of the support member 7 using a resin such as PBT (polybutylene terephthalate) is about 1 (H / m), which is the same as that of air, but a resin mixed with soft ferrite is used for the support member 7. As can be seen from FIG. 4, the permeability of the supporting member 7 has a permeability μ ′ of 100 (H / m) or more, so that the magnetic flux supplied to the surface of the rotor 5 (the magnetic flux that has passed through the supporting member 7). ) And the performance of the electric motor 1 can be improved. Needless to say, since the magnetic flux of the permanent magnets 6a to 6d is unidirectional, the frequency is DC, the complex component (μ ″) of the magnetic permeability is sufficiently low, and loss such as hysteresis loss does not occur. .

  The operation will be described below. A discharge current generated by voltage induction between the shaft ends of the rotating shaft 9 due to the switching of the inverter 8 generates an alternating magnetic field around the rotating shaft 9, and this magnetic field acts on the support member 7. This causes iron loss. Since this iron loss acts as a resistance, the discharge current is changed to heat in the soft ferrite of the support member 7 and attenuates as shown by a current curve B.

  In the above description, the case where the electric motor 1 is applied to an indoor unit of an air conditioner has been described. However, the present invention is not limited to this, and the electric motor 1 can also be applied to an outdoor unit.

  In the above description, the embodiment using the support member 7 formed by mixing the resin and the soft magnetic material has been described. However, the support member 7 made of only the soft magnetic material may be used.

  As described above, the electric motor 1 according to the present embodiment is provided around the stator 2 (stator) disposed in the mold frame 10 (frame) and the rotating shaft 9 so as to face the stator 2. The rotor 5 having the permanent magnet 6, a pair of brackets (11, 12) disposed at both ends of the mold frame 10 for supporting the rotating shaft 9, and the brackets 11, 12 are attached to support the rotating shaft 9. A pair of bearings 13 and 15 are arranged between the rotary shaft 9 and the permanent magnet 6 so as to be able to support the permanent magnet 6 and include a magnetic material softer than the magnetic material of the permanent magnet 6. Since the support member 7 is provided, it is possible to effectively attenuate the discharge current that causes electric corrosion. Conventionally, in order to improve the electric corrosion resistance, a method of changing the structure of the bracket and the frame, a method of interposing an insulating sleeve between the rotating shaft 9 and the inner ring b of the bearings 13 and 15, There are a technique using ceramic for the rolling element c, and a technique for fixing a magnetic material having a large hysteresis loss to the outer peripheral portion of the shaft between the bearings 13 and 15 and the rotor core. In these methods, there has been a problem that the manufacturing cost is increased or the electric motor is enlarged. In particular, when the manufacturing method of the support member 7 is insert molding, when the shape of the support member 7 is changed, the mold, equipment, processes, and the like are changed, and thus the manufacturing cost is remarkably increased. In the electric motor 1 according to the present embodiment, since the dimensional change of the support member 7 does not occur, only the material change of the support member 7 can suppress the discharge current. That is, since the manufacturing equipment can be shared, it is possible to suppress the electrolytic corrosion of the bearing at a low cost without changing the dimensions.

  In addition, the electric motor 1 according to the present embodiment includes a stator 2 (stator) disposed in a mold frame 10 (frame), and a permanent magnet 6 provided around the rotating shaft 9 so as to face the stator 2. A rotor 5 having a pair of brackets (11, 12) disposed on both ends of the mold frame 10 and supporting the rotating shaft 9, and a pair of bearings 13 mounted on the brackets 11 and 12 and supporting the rotating shaft 9. 15 and is formed between the rotating shaft 9 and the permanent magnet 6 so as to be able to support the permanent magnet 6 and includes a magnetic material having a coercive force weaker than the holding force of the permanent magnet 6. Therefore, it is possible to suppress the electrolytic corrosion of the bearing at a low cost without changing the dimensions.

  Further, the magnetic material of the support member 7 according to the present embodiment may be composed of only a soft magnetic material. When comprised in this way, it is possible to suppress a discharge current still more effectively.

  Further, the magnetic material of the support member 7 according to the present embodiment is such that the value of the imaginary part of the complex permeability near the resonance frequency of the current flowing through the rotating shaft 9 is increased by inducing a voltage at the rotating shaft 9. It is configured. That is, since the value of the imaginary part of the complex permeability is increased in the region where the resonance frequency f of the discharge current is 10 MHz or more, the resonance frequency of the discharge current in the small blower motor (several tens of MHz to several This discharge current can be effectively attenuated at 100 MHz).

  Further, since the magnetic material of the support member 7 according to the present embodiment is made of soft ferrite, it can be easily manufactured when the support member 7 is manufactured by injection molding. This is because soft ferrite has a smaller particle size than other metal-based soft magnetic materials (for example, iron, silicon steel, etc.) and is therefore suitable for injection molding of a resin mixed with soft ferrite.

  Further, since the mold bracket 11 according to the present embodiment incorporates an inverter 8 that generates a high-frequency voltage applied to the winding 3 provided in the stator 2, the wiring in the inverter 8 is a winding. 3 acts as a conductor between the bearing 3 and the bearing 13, the insulation distance between the winding 3 and the bearing 13 is reduced, and the current flowing through the rotating shaft 9 is increased. Thus, even when a large current flows through the rotating shaft 9, the discharge current can be effectively attenuated by the support member 7.

  Moreover, since the air conditioner according to the present embodiment is provided with the electric motor 1 as an electric motor for driving the indoor unit fan, noise due to electric corrosion of the bearings 13 and 15 can be reduced. In particular, noise is a problem caused by the electric corrosion of the bearings 13 and 15, and the indoor unit of the air conditioner is required to be quiet in order to be used in a living space for a long time, and the resistance to electric corrosion can be improved. This is because it greatly contributes to product reliability.

  Further, since the specific gravity of the soft magnetic material is larger than that of the resin alone, the inertia (inertia) of the rotor 5 can be increased as compared with the conventional support member having the same shape as the support member 7 according to the present embodiment. . Therefore, according to the electric motor 1 concerning this Embodiment, the rotation fluctuation | variation by torque ripple etc. is suppressed and it is possible to reduce a noise.

  Further, since the support member 7 mixed with the soft magnetic material acts as a yoke on the outer peripheral portion of the rotor 5, the air gap magnetic flux of the rotor 5 increases. Therefore, according to the electric motor 1 concerning this Embodiment, the torque and efficiency of the electric motor 1 can be improved.

  The electric motor and the air conditioner according to the embodiment of the present invention show an example of the content of the present invention, and can be combined with another known technique, and depart from the gist of the present invention. Of course, it is possible to change and configure such as omitting a part within the range.

  As described above, the present invention can be applied to an electric motor, and is particularly useful as an invention capable of suppressing electric corrosion of a bearing at a low cost without changing dimensions.

1 Electric motor 2 Stator (stator)
3 Winding 4 Stator core 5 Rotor (rotor)
6, 6a, 6b, 6c, 6d Permanent magnet 7 Support member 7a Inner peripheral surface 7b Outer peripheral surface 8 Inverter 9 Rotating shaft 10 Mold frame 11 Mold bracket 12 Metal bracket 13, 15 Bearing 14 Insulator 20 Axis center A, B Discharge current Path R Resistance a Outer ring b Inner ring c Rolling element h Height of magnetic material r1 Distance from the centerline of the axis to the inner circumferential surface of the magnetic material r2 Distance from the centerline of the axis to the outer circumferential surface of the magnetic material φr Magnetic flux μ ′, μ '' permeability

Claims (7)

A stator disposed in the frame;
A rotor having a permanent magnet disposed around a rotation shaft facing the stator;
A pair of brackets disposed at both ends of the frame and supporting the rotating shaft;
A pair of bearings mounted on the bracket and supporting the rotating shaft;
A support member formed in an annular shape and disposed between the rotating shaft and the permanent magnet so as to be capable of supporting the permanent magnet, and including a magnetic material softer than the magnetic material of the permanent magnet; ,
An electric motor comprising: A stator disposed in the frame;
A rotor having a permanent magnet provided around the rotation shaft so as to face the stator;
A pair of brackets disposed at both ends of the frame and supporting the rotating shaft;
A pair of bearings mounted on the bracket and supporting the rotating shaft;
A support comprising a magnetic material having an annular shape and disposed between the rotating shaft and the permanent magnet so as to support the permanent magnet and having a coercive force weaker than the coercive force of the permanent magnet. Members,
An electric motor comprising:   The electric motor according to claim 1, wherein the magnetic material is composed of only a soft magnetic material.   4. The magnetic material according to claim 1, wherein the value of the imaginary part of the complex permeability near the resonance frequency of the current flowing through the rotating shaft is increased by inducing a voltage at the rotating shaft. The electric motor as described in one.   5. The electric motor according to claim 1, wherein the magnetic material is made of soft ferrite.   The electric motor according to any one of claims 1 to 5, wherein the bracket includes an inverter that generates a high-frequency voltage applied to a winding provided in the stator.   An air conditioner comprising the electric motor according to any one of claims 1 to 6 as an electric motor for driving an indoor unit fan.

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