JP2014117004A - Motor - Google Patents

Abstract

A voltage induced in each of a stator and a rotor is increased, and a current difference flows between the rotating part and the fixed part of the bearing due to the voltage difference.
A bearing is a ball bearing in which a rolling element is held between an outer ring and an inner ring. The rolling element, the inner ring, and the outer ring are made of different metals, and an electromotive voltage caused by contact of the different metals is driven by an inverter. The electric motor is designed to have a reverse voltage with respect to the shaft voltage due to the induced voltage difference between the stator and the rotor.
[Selection] Figure 1

Description

  The present invention relates to an electric motor that performs inverter control.

  A brushless DC motor, which is an electric motor, rotates a rotor provided with a magnet by generating a rotating magnetic field by switching the direction of current by using an inverter control circuit for the direction of magnetic force of an electromagnetic coil of a stator.

  In recent years, demands for high efficiency and low vibration have been increasing for brushless DC motors, so that the drive voltage has been increased and the inverter frequency that is the basis of control has been increased.

  For this reason, a voltage is induced in a conductor constituting a bracket, a stator core, a rotor, and the like that hold the bearing from the winding, and a change in the potential of the voltage causes a discharge in the bearing, resulting in galvanic corrosion of the bearing. The problem has become apparent.

  The configuration of the brushless motor will be described with reference to FIG. A stator 12 is formed by winding the winding 4 around the stator core 7 and molding it. A rotor 5 is fixed to the shaft 1, and the rotor 5 is rotatably arranged opposite to the stator 12. A bearing 3 a and a bearing 3 b that rotatably support the shaft 1 connected to the rotor 5 with respect to the stator 12 are provided.

  By passing a current through the winding 4, the rotor 5 is rotated by the magnetic field generated in the stator core 7. At this time, the voltage induced in the stator 12 and the rotor 5 is different. A potential difference is generated between this part and this is defined as an axial voltage.

  In the case of the ball bearing, as shown in FIG. 2 in which the periphery of the bearing portion in FIG. 1 is enlarged, the bearing is provided so that the rolling element 121 is sandwiched between the outer ring 122 and the inner ring 123. The shaft voltage at the ball bearing is a voltage generated by the potential generated in the inner ring 123 and the conductor part electrically connected to the inner ring 123 and the outer ring 122 and the conductor part electrically connected to the outer ring 122, respectively.

  In the stopped state, the ball bearing is electrically connected between the outer ring 122 and the inner ring 123 through the rolling elements 121. In the rotating state, the outer ring 122 and the outer ring 122 are connected to each other by the dynamic pressure generated by the grease enclosed in the bearing. An insulating state and a conductive state occur between the rolling elements 121 or between the inner ring 123 and the rolling elements 121. When the transition from this insulation state to the conduction state, the electric charge accumulated in the rotating body instantaneously flows as current, so that arc discharge occurs in the ball bearing, and the sliding surface of the bearing is damaged, resulting in electric corrosion. To do.

  When the rolling element 121 is made of a conductor such as iron as a main raw material, the shaft voltage is discharged at the contact point of the inner ring 123 or the outer ring 122 that is in contact with the rolling element 121, causing damage to the rolling surface. In order to prevent the rolling surface from being damaged, it is known that the rolling element 121 is made of an insulating material such as ceramics or resin as a main raw material to prevent electric corrosion.

  Further, when the bearing is a sliding bearing, it is known that the sliding bearing is made of a resin or ceramics as an insulator to take measures against electrolytic corrosion.

  Furthermore, Patent Document 1 is known to provide a compensation device that generates a potential opposite to that of the shaft voltage to reduce the influence of the shaft voltage and take measures against electrolytic corrosion.

Special table 2007-532088 gazette

  When the above-described ball bearing is used for the inverter-driven brushless motor, a shaft voltage is generated between the inner ring 123 and the outer ring 122 with the rolling element 121 interposed therebetween.

  For example, when the rolling element 121 is an insulator, the following problem occurs. When the material of the rolling element 121 is changed from iron to ceramics, it is difficult to polish because of its high hardness, and it is very expensive than iron, and it takes time to produce, making it difficult to supply stably. . Further, when the rolling element 121 is made of resin, it becomes weaker against load resistance and wear than iron, and the reliability as a bearing is lowered.

  When using the above-mentioned plain bearings for brushless motors, there is a known method in which either the shaft or the plain bearing is made of an insulator. However, the resin used as an insulator is insufficient in rigidity, and ceramics has difficulty in workability. It was not the best method.

  Moreover, as shown in Patent Document 1, a method of providing a compensation device and applying a shaft voltage and a reverse voltage of a bearing needs to prepare a separate device in addition to the motor body. It was impossible to realize in space.

  The present invention makes it possible to apply a reverse voltage to the shaft voltage generated between the fixed part and the rotating part of the brushless motor by a simple means. An object of the present invention is to provide a reduced brushless motor.

In order to solve the above-described conventional problems, an electric motor of the present invention includes a stator including a stator core around which windings are wound,
A rotating body holding a permanent magnet in the circumferential direction facing the stator;
A rotor including a shaft that fastens the rotating body so as to penetrate the center of the rotating body;
A bearing for supporting the shaft;
The bearing is a ball bearing that holds a rolling element between an outer ring and an inner ring, and at least one of the rolling element, the inner ring, and the outer ring is made of a dissimilar metal material, and the contact of the dissimilar metal Is caused to be a reverse voltage with respect to the axial voltage due to the induced voltage difference between the stator and the rotor when the inverter is driven.

  According to the electric motor of the present invention, the ball bearing that supports the rotating portion is configured such that the ball, the inner ring, and the outer ring are made of different metals, and the electromotive voltage caused by the contact of the different metals is opposite to the axial voltage. Therefore, since it becomes possible to reduce the absolute value of the shaft voltage applied to the bearing, it is possible to suppress discharge between the rotating part and the fixed part, and to prevent the occurrence of electrolytic corrosion.

Sectional drawing of the brushless motor which concerns on Embodiment 1 of this invention. 1 is an enlarged view of the bearing portion of FIG.

Hereinafter, an electric motor according to an embodiment of the present invention will be described using a brushless motor as an example with reference to the drawings. However, the present invention is not limited to the following embodiment.

(Embodiment)
FIG. 1 is a sectional view of a brushless motor according to Embodiment 1 of the present invention. As shown in FIG. 1, a rotor 5 and a stator 12 arranged around the rotor 5 are provided. The stator 12 includes a stator core 7 and a winding 4 wound around the stator core in a coil shape, and is configured integrally with a mold resin 11 made of a thermosetting resin by molding.

  The rotor 5 is rotatably supported by bearings 3 a and 3 b provided at the center of metal brackets 2 a and 2 b in which the center shaft 1 is fixed to both ends of the stator 12. The bearings 3a and 3b are ball bearings, and the schematic configuration thereof is shown in FIG. 2, and any one or more of the outer ring, the ball, and the inner ring are made of a different metal material.

  In the configuration of FIG. 1, since the stator has a large electrostatic capacity, the shaft voltage is negative on the inner ring side of the bearing and positive on the outer ring side. Therefore, the material in which the electrode potential is positive on the inner ring side, and the material that is negative on the outer ring side. When combined, the absolute value of the shaft voltage can be reduced.

  By using beryllium copper (Cu99Be1) on the inner ring side and stainless steel (Fe72Cr19Ni9) on the outer ring side as a combination of different metals, the shaft voltage can be reduced by about 0.8V. There is no particular limitation as long as it generates a voltage and a reverse voltage.

  The entire material of the inner ring, the outer ring, and the ball may be made of different metals. However, the base material may be the same material and surface treatment such as vapor deposition of different metals may be performed on the surface.

  The field of application of the present invention is not particularly limited, and can be used in a wide range of electric devices as a motor with reduced electric corrosion of the bearing.

1 Axis 2a, 2b Bracket 3a, 3b Bearing 4 Winding 5 Rotor 7 Stator core 11 Mold resin 12 Stator 121 Rolling element 122 Outer ring 123 Inner ring

Claims (2)

A stator including a stator core wound with windings;
A rotating body holding a permanent magnet in the circumferential direction facing the stator;
A rotor including a shaft that fastens the rotating body so as to penetrate the center of the rotating body;
A bearing for supporting the shaft;
The bearing is a ball bearing holding a rolling element between an outer ring and an inner ring, and at least one of the rolling element, the inner ring and the outer ring is made of a dissimilar metal material,
An electric motor characterized in that an electromotive voltage caused by contact of the different metal is opposite to an axial voltage due to a difference in induced voltage between a stator and a rotor when the inverter is driven. The electric motor according to claim 1, wherein a surface of the ball, the inner ring, or the outer ring is coated with a different metal material.