JP2006115672A - Structure having countermeasure against electrolytic corrosion of brushless dc motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide structure having countermeasures against electrolytic corrosion in a brushless DC motor 10 that is subjected to PWM control by an inverter circuit while motor frames 20, 28 are formed by a steel plate. <P>SOLUTION: A rotated shaft 32 in the brushless DC motor 10 is made of a fluororesin, and the diameter of a rolling body 38 in bearings 22, 24 is set to the half or smaller of dimensions obtained by subtracting the inner diameter of an inner ring 34 from the outer one of an outer ring 36 in the bearings 22, 24. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a structure for preventing electrolytic corrosion generated in a brushless DC motor.

  In a conventional brushless DC motor, PWM control is performed using an inverter circuit as a drive circuit (see, for example, Patent Document 1).

In the brushless DC motor that performs PWM control as described above, when the motor frame is a steel plate, electric corrosion of the bearing is a problem. The reason for the problem is that there is a potential difference in the motor due to the electrical and magnetic imbalances of the rotating magnetic field. A device that performs PWM control at a frequency easily causes a through current to flow, and forms a circuit such as a coil, a bearing, and a shaft. Here, when passing through the bearing, the energy is damaged and abnormal noise is generated.
JP 2004-48829 A

  Based on FIG.3 and FIG.4, it demonstrates still in detail about the electric corrosion demonstrated above.

  In the brushless DC motor 120 as shown in FIG. 3, electric corrosion is a circuit that passes through the outer ring 104, the rolling element (ball) 106, the inner ring 102, the shaft 110, and the motor frame 112 of the bearing (ball bearing) 100. In other words, it refers to a phenomenon in which the transfer surface is roughened and noise is generated by discharging through the insulation of the oil film of the grease 108 which is lubricating oil. As a factor constituting this circuit, a potential difference is generated between the inner ring 102 and the outer ring 104 of the bearing 100 by induction by driving by an inverter circuit.

  As shown in FIG. 4, the bearing 100 has a rolling element 106 between an inner ring 102 and an outer ring 104, and grease 108 is present as lubricating oil. Since the grease 108 is an insulator, it is normally not energized even if a potential difference occurs. However, when a high frequency is generated by PWM control, the impedance decreases, and the energization is easy, and energization occurs between the inner ring 102 and the outer ring 104. . When energization is performed between the bearings 100, a circuit that reaches the bearings 100 again is formed through the metal rotating shaft 110, the other bearing 100, and the steel frame motor frame 112. As a result, the bearing 100 is damaged and abnormal noise is generated.

  Conventionally, as a countermeasure against such electric corrosion, in order to insulate between the inner ring 102 and the outer ring 104, the rolling element 106 made of ceramic balls is used to strengthen the insulation so as not to discharge, or the inner ring 102 and the outer ring 104 For example, a structure in which an electric current is flowed before a large amount of energy is stored so that the discharge energy damages the transfer surface can be cited.

  However, in the conventional structure as described above, the cost is increased by using ceramic balls in the former case, and conductive grease is used in the latter case, so that the life of the grease is short, and the use is limited. Limited.

  Therefore, in view of the above problems, the present invention provides an electrolytic corrosion countermeasure structure for a brushless DC motor that can more easily and reliably take countermeasures against electrolytic corrosion.

  The invention according to claim 1 is an electrolytic corrosion prevention structure for a brushless DC motor that is PWM-controlled by an inverter circuit, wherein the rotating shaft of the brushless DC motor is formed of an insulator having a high volume resistivity and a low dielectric constant. This is an anti-corrosion structure for brushless DC motors.

  The invention according to claim 2 is the brushless DC motor according to claim 1, wherein the rotating shaft is made of a fluorine-based resin.

  The invention according to claim 3 is an electrolytic corrosion prevention structure for a brushless DC motor that is PWM-controlled by an inverter circuit, and the diameter of a rolling element of a bearing that rotatably supports the rotating shaft of the brushless DC motor is defined as the bearing. This is a structure for preventing electric corrosion of a brushless DC motor, characterized in that the outer diameter of the outer ring is less than half of the dimension obtained by subtracting the inner diameter of the inner ring.

  In the brushless DC motor according to the first and second aspects of the present invention, the rotating shaft is formed of an insulator (for example, a fluorine resin) having a high volume resistivity and a low volume resistivity and a low dielectric constant. Even if current flows in the bearing, the rotating shaft is formed of a high volume resistivity and a low dielectric, so that no current flows, and a circuit can be formed by the bearing, the rotating shaft, and a motor frame made of a steel plate. There is no electric corrosion.

  Further, in the brushless DC motor of the invention according to claim 3, the lubricating oil sealed in the bearing is obtained by reducing the diameter of the rolling element to half or less of the dimension obtained by subtracting the inner diameter of the inner ring from the outer diameter of the outer ring of the bearing. This reduces the amount of oil film formed by the oil film, eliminates the role of the capacitor by the oil film, and prevents charging of energy required for electrolytic corrosion.

  Hereinafter, an electrolytic corrosion prevention structure of a brushless DC motor (hereinafter simply referred to as a motor) 10 according to an embodiment of the present invention will be described.

  The motor 10 is controlled in rotation speed and forward / reverse rotation by PWM control by an inverter circuit.

(1) Structure of Motor 10 The structure of the motor 10 will be described with reference to FIG.

  An insulating layer is formed on the rotor core 12 in which steel plates are laminated by pre-molding or the like, and a coil 14 is wound thereon to form a stator 16. A ring-shaped wiring board 18 is attached to the stator 16.

  The ring-shaped stator 16 to which the wiring board 18 is attached is housed and fixed in a steel plate cup-shaped motor frame body 20. A bearing 22 is fixed at the bracket position of the motor frame 20. The bearing 22 will be described in detail later.

  A rotor 26 is rotatably supported by the bearing 22 and the other bearing 24. The other bearing 24 is attached to a metal bracket 28 that covers the motor frame body 20. In this case, a disc spring 30 is attached between the bearing 24 and the bracket 28.

(2) First galvanic corrosion prevention structure In the first galvanic corrosion prevention structure, the rotating shaft 32 of the rotor 26 is not made of metal, and is formed of an insulator having both high volume resistivity and low dielectric constant characteristics. There is in point. For example, the insulator includes a fluorine-based resin, and the volume resistivity of the fluorine-based resin is 10 ¹⁴ (Ω · cm) and the dielectric constant is 2 to 3%.

  By forming the rotary shaft 32 with an insulator made of a high resistivity and a low dielectric in this manner, even if the bearings 22 and 24 are energized, the bearing 22, the rotary shaft 32, the bearing 24, the bracket 28, and the motor A circuit through the frame body 20 is not formed, and electric corrosion does not occur.

(3) Second Electric Corrosion Countermeasure Structure The second electric corrosion countermeasure structure is the structure of the bearing 22 and the bearing 24. Since the bearing 24 has the same structure as the bearing 22, the structure of the bearing 22 will be described with reference to FIG. In FIG. 2, the reason why the inner ring 34 and the outer ring 36 are shifted is that the outer ring 36 is pressed in one direction by the disc spring 30.

  The bearing 22 is a ball bearing, and is formed by an inner ring 34, an outer ring 36, and rolling elements (balls) 38 sandwiched therebetween. In addition, lubricating oil 40 made of grease is enclosed so that the rolling elements 38 rotate smoothly.

  Conventionally, the oil film of the lubricating oil 40 functions as a capacitor, charges energy necessary for electrolytic corrosion, discharges at a certain trigger, damages the bearing, and makes noise.

  Therefore, as the second structure for preventing electric corrosion, the diameter of the rolling element 38 in the bearing 22 is made as small as possible, the contact amount between the rolling element 38 and the inner ring 34 and the outer ring 36 is reduced, and an oil film by the lubricating oil 40 is formed. By reducing the amount to be formed, the discharge energy is reduced without playing the role of a capacitor.

Specifically, by making the diameter R of the rolling element 38 equal to or less than half the dimension A obtained by subtracting the outer diameter of the outer ring 36 and the inner ring 34, the amount of contact of the rolling element 38 is reduced, and the amount of oil film formed The discharge energy is also reduced. Specifically, the energy generated during discharge is 1/2 CV ² where C is the capacitance of the capacitor due to the oil film and V is the potential difference generated between the inner and outer rings of the bearing 22. Therefore, if the capacitance C is reduced, the energy is also reduced, so that the noise of the bearing 22 due to electrolytic corrosion can be prevented.

(Example of change)
The present invention can be variously modified without departing from the above gist.

  For example, the diameter R of the rolling element 38 may be equal to or less than half of the dimension A, and may be 1/3 or 1/4.

  The present invention is suitable for a brushless DC motor in which a motor frame is formed of a steel plate and PWM controlled by an inverter circuit.

It is a longitudinal cross-sectional view of the motor which shows one Embodiment of this invention. It is a longitudinal cross-sectional view of the bearing of this embodiment similarly. It is a longitudinal cross-sectional view of the conventional motor. It is a longitudinal cross-sectional view of the conventional bearing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Motor 16 Stator 20 Motor frame main body 22 Bearing 24 Bearing 26 Rotor 28 Bracket 30 Belleville spring 32 Rotating shaft 34 Inner ring 36 Outer ring 38 Rolling element 40 Lubricating oil

Claims (3)

An electric corrosion countermeasure structure for a brushless DC motor PWM controlled by an inverter circuit,
The rotating shaft of the brushless DC motor is formed of an insulator having a high volume resistivity and a low dielectric constant. The brushless DC motor according to claim 1, wherein the rotation shaft is made of a fluorine-based resin. An electric corrosion countermeasure structure for a brushless DC motor PWM controlled by an inverter circuit,
The diameter of the rolling element of the bearing that rotatably supports the rotating shaft of the brushless DC motor is made to be half or less of the dimension obtained by subtracting the inner diameter of the inner ring from the outer diameter of the outer ring of the bearing. Electric corrosion countermeasure structure.

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