WO2013088670A1

WO2013088670A1 - Brushless motor

Info

Publication number: WO2013088670A1
Application number: PCT/JP2012/007760
Authority: WO
Inventors: 誠治黒住; 圭策中野; 知子従野
Original assignee: パナソニック株式会社
Priority date: 2011-12-12
Filing date: 2012-12-04
Publication date: 2013-06-20
Also published as: JPWO2013088670A1; CN103999332A

Abstract

A molded motor (1) that is a brushless motor of the present invention is provided with: a stator (10) that has a stator core (12) around which a winding (11) is wound; a rotor (20) that includes a rotating body (21) facing the stator (10) and having a permanent magnet (23) in a circumferential direction, and a rotating shaft (22) passing through the axis of the rotating body (21); a pair of bearings (102, 3) that rotatably support the rotor (20) therebetween; and a pair of brackets (104, 5) that hold the pair of bearings (102, 3). The bearings (102, 3) are each a sliding bearing containing lubricating oil.

Description

Brushless motor

The present invention relates to a brushless motor in which a rotor is supported by being sandwiched between bearings.

Conventionally, a brushless motor includes a stator having an electromagnetic coil and a rotor having a magnet. When a current flows through the electromagnetic coil, the electromagnetic coil generates a magnetic field. In the brushless motor, when the direction of the magnetic field generated in the electromagnetic coil is switched, the rotor having the magnet rotates. The electromagnetic coil is formed by winding a winding around a stator core. When the direction of the current flowing through the winding is switched by the inverter control circuit, the magnetic field generated in the electromagnetic coil is switched.

In recent years, brushless motors are strongly required to be highly efficient. In order to satisfy this requirement, the drive voltage of the brushless motor is increased. Alternatively, the inverter frequency for controlling the brushless motor is increased. When the inverter frequency is increased, a voltage is induced from a winding to a conductor such as a bracket that holds the bearing. The conductor is composed of a bracket, a stator core, a rotor, and the like. If the potential of the voltage induced on the conductor changes, a discharge occurs in the bearing. Due to the discharge in the bearing, the bearing was eroded.

Furthermore, low noise and vibration are strongly demanded for brushless motors. In order to satisfy this requirement, the brushless motor is molded to become a molded motor. In the molded motor, the electromagnetic coil is sealed with resin. Molded motors are highly effective in improving noise and vibration. However, capacitance is generated between the brackets holding the pair of bearings. This electrostatic capacity increases the potential difference between the rotating shaft and the stator. As the potential difference increased, electrolytic corrosion was likely to occur. Note that such a capacitance is not observed in the steel plate motor.

What has been proposed to suppress such electric corrosion will be described with reference to FIG.

The stator 10 has a stator core 12 that is a stator core and a winding 11 wound around the stator core 12. The stator 10 is molded to form a mold frame 13.

The rotor 20 has a rotating body 21 and a rotating shaft 22 fixed to the axis of the rotating body 21. The rotating body 21 is disposed so as to be rotatable facing the stator core 12. The rotating shaft 22 has a pair of

bearings

113 and 114 at positions where the rotating shaft 21 is supported with the rotating body 21 interposed therebetween in the axial direction. The

bearings

113 and 114 are fixed to the mold frame 13 via the

brackets

105 and 106.

When a current is passed through the winding 11, a magnetic field is generated in the stator core 12. The rotor 20 is rotated by the generated magnetic field. At this time, voltages induced in the stator 10 and the rotor 20 are different. As a result, a potential difference is generated between the

inner rings

113a and 114a that are the rotating parts of the

bearings

113 and 114 and the

outer rings

113b and 114b that are the fixed parts of the

bearings

113 and 114. The potential difference between the rotating part and the fixed part is defined as “axial voltage”.

Note that the “rotating part” refers to a part including the rotating shaft 22 and electrically connected to the rotating shaft 22. Further, the “fixed portion” refers to a portion that includes the stator 10 and is electrically connected to the stator 10.

As shown in FIG. 9, in the case of a ball bearing, in the

bearings

113 and 114,

rolling elements

113c and 114c are sandwiched between

inner rings

113a and 114a and

outer rings

113b and 114b. Lubricants such as grease are sealed in the

bearings

113 and 114. The shaft voltage generated in the ball bearing is a potential difference between the inner ring side potential and the outer ring side potential. The inner ring side potential is a potential generated in the

inner ring

113a, 114a and a conductor portion electrically connected to the

inner ring

113a, 114a. The outer ring side potential is a potential generated in a conductor portion electrically connected to the

outer rings

113b and 114b and the

outer rings

113b and 114b. When the brushless motor is stopped, in the ball bearing, the

inner rings

113a and 114a and the

outer rings

113b and 114b are electrically connected by the

rolling elements

113c and 114c. However, when the brushless motor rotates, dynamic pressure is generated in the

bearings

113 and 114 due to the enclosed grease. Due to this dynamic pressure, an insulating state and a conductive state are generated between the

inner rings

113a and 114a and the

rolling elements

113c and 114c, or between the

outer rings

113b and 114b and the

rolling elements

113c and 114c. When shifting from the insulated state to the conductive state, the electric charge accumulated in the rotor 20 instantaneously flows as a current from the

inner ring

113a, 114a side to the

outer ring

113b, 114b side. This current flow becomes an arc discharge generated in the ball bearing. Due to this arc discharge, the sliding surfaces of the

inner rings

113a and 114a and the sliding surfaces of the

outer rings

113b and 114b are damaged, and electric corrosion occurs.

When the

rolling elements

113c and 114c are configured using a conductor such as iron as a main raw material, the axial voltage is determined by contact between the

inner rings

113a and 114a in contact with the

rolling elements

113c and 114c, or the outer ring 113b in contact with the

rolling elements

113c and 114c, Discharge occurs at the contact point 114b. This discharge damages the sliding surfaces of the

inner rings

113a and 114a and the sliding surfaces of the

outer rings

113b and 114b.

In order to prevent the sliding surface from being damaged, the rolling element 113c is composed mainly of an insulator such as ceramics or resin. Such electric corrosion countermeasures are known.

Other anti-corrosion measures that use a sliding bearing as a bearing and that use a sliding bearing made of an insulator such as ceramics or resin are also known.

Furthermore, Patent Document 1 is shown as another electric corrosion countermeasure. In Patent Document 1, an insulator is provided between a sliding bearing and a bracket. When an insulator is provided between the slide bearing and the bracket, the current generated by the shaft voltage is cut off.

Japanese Utility Model Publication No. 2-83651

A brushless motor according to the present invention includes a stator having a stator core around which windings are wound, a rotating body having a permanent magnet in the circumferential direction facing the stator, and a rotating shaft penetrating the axis of the rotating body. , A bearing that rotatably holds the pair of rotors, and a bracket that holds the pair of bearings. The bearing is a sliding bearing containing lubricating oil.

FIG. 1 is a longitudinal sectional view of a brushless motor according to Embodiment 1 of the present invention. FIG. 2 is a 2-2 cross-sectional view of the bearing in the first embodiment of the present invention. FIG. 3 is a longitudinal sectional view of another brushless motor according to Embodiment 1 of the present invention. FIG. 4 is a 4-4 sectional view of the bearing according to the first embodiment of the present invention. FIG. 5 is a longitudinal sectional view of the brushless motor according to the second embodiment of the present invention. FIG. 6 is a longitudinal sectional view of the brushless motor according to the third embodiment of the present invention. FIG. 7 is a shaft voltage waveform diagram of the brushless motor according to the first embodiment of the present invention. FIG. 8 is a diagram of shaft voltage waveforms of the brushless motor according to the second embodiment of the present invention. FIG. 9 is a longitudinal sectional view of a conventional brushless motor. FIG. 10 is a shaft voltage waveform diagram of a conventional brushless motor.

The brushless motor according to the embodiment of the present invention suppresses generation of a shaft voltage between the rotating part and the fixed part via the sliding bearing. Further, when the shaft voltage is generated, the brushless motor according to the embodiment of the present invention suppresses the current density of the current flowing from the rotating portion to the fixed portion within an appropriate range.

As a result, the brushless motor reduces the occurrence of electrolytic corrosion.

That is, the conventional brushless motor has the following improvements. That is, ball bearings are used in the conventional brushless motor shown in FIG. When a ball bearing is used for a molded brushless motor, an axial voltage is generated between the

inner rings

113a and 114a that are rotating parts and the

outer rings

113b and 114b that are fixed parts with the rolling

elements

113c and 114c interposed therebetween.

For example, when the rolling

elements

113c and 114c made of an insulator are used, the following problems occur. The material of the rolling

elements

113c and 114c is changed from iron to ceramics. Since ceramics has high hardness, it is difficult to polish ceramics for use in the rolling

elements

113c and 114c. Therefore, the ceramic rolling

elements

113c and 114c take time to produce, and it is difficult to stably supply them.

Also, the ceramic rolling

elements

113c and 114c are very expensive compared to the

iron rolling elements

113c and 114c. In addition, the material of the rolling

elements

113c and 114c is changed from iron to resin. In this case, the resin has lower load resistance and wear resistance than iron.

Therefore, the rolling

elements

113c and 114c made of resin are less reliable in terms of strength and life compared to the rolling

elements

113c and 114c made of iron.

Alternatively, when the above-described sliding bearing is used for a molded motor, it is known that either the rotating shaft or the sliding bearing is made of an insulator.

However, when resin is used as an insulator, rigidity is insufficient. Moreover, when ceramics is used as an insulator, processing is difficult. In other words, none of the methods is an optimal method for solving the above-described improvements.

In a brushless motor that is an embodiment of the present invention to be described later, a sliding bearing having electrical conductivity is used as a bearing that supports a rotating shaft. According to this configuration, the brushless motor rotates while the rotating portion and the fixed portion are in a conductive state.

As a result, the induction voltage is not accumulated in the rotating part, so that the occurrence of arc discharge is suppressed between the rotating part and the fixed part.

Hereinafter, a description will be given using a mold motor that exhibits particularly remarkable effects, a so-called brushless mold motor.

The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.

Also, the same components as those described in the background art are denoted by the same reference numerals, and the description is incorporated.

(Embodiment 1)
A brushless motor according to Embodiment 1 of the present invention will be described with reference to FIGS.

FIG. 1 is a longitudinal sectional view of a brushless motor according to Embodiment 1 of the present invention. The brushless motor shown in the figure is a molded brushless DC motor (hereinafter referred to as “molded motor”).

The mold motor 1 includes a stator 10 and a rotor 20 disposed inside the stator 10.

The stator 10 has a stator core 12 that is a stator core around which a winding 11 is wound. Specifically, the winding 11 is wound around the stator core 12 in a coil shape. The stator 10 is configured integrally with a mold frame 13 molded with a resin material, particularly a thermosetting resin.

The rotor 20 has a rotating body 21 and a rotating shaft 22. The rotating body 21 has a permanent magnet 23 in the circumferential direction facing the stator 10. The rotating shaft 22 is attached through the axis of the rotating body 21.

The bearings are sliding

bearings

102 and 3 containing lubricating oil. The pair of

plain bearings

102 and 3 support the rotor 20 with the rotor 20 interposed therebetween. The

plain bearings

102 and 3 are made of sintered metal obtained by sintering metal powder. The sliding

bearings

102 and 3 are impregnated with a lubricant in a sintered metal. Moreover, the sliding

bearings

102 and 3 containing lubricating oil can be comprised with the growth cast iron impregnated with lubricating oil.

The pair of

brackets

104 and 5 hold the sliding

bearings

102 and 3 which are bearings. The

brackets

104 and 5 are made of conductive metal. For example, a galvanized steel plate, an aluminum die cast, a stainless steel plate or the like is used. More specifically, SECC or SECD can be used as the galvanized steel sheet. ADC12 can be used as an aluminum die casting. As the stainless steel plate, SUS304 or SUS430 can be used. Note that other metals can be used as long as similar characteristics can be obtained.

Mold motor 1 has a control board 6 on which an inverter circuit is mounted. The high-frequency pulse controlled by this inverter circuit switches the current flowing through the winding 11.

Further, the sliding

bearings

102 and 3 will be described with reference to FIGS.

FIG. 2 is a 2-2 cross-sectional view of the bearing in the first embodiment of the present invention. FIG. 3 is a longitudinal sectional view of another brushless motor according to Embodiment 1 of the present invention. FIG. 4 is a 4-4 sectional view of the bearing according to the first embodiment of the present invention.

2, the plain bearing 3 is arranged so as to surround the rotating shaft 22. Around the slide bearing 3, an annular portion 5 a is provided in which a part of the bracket 5 protrudes convexly toward the rotating body 21 to form an annular wall surface. The slide bearing 3 is fitted to the annular portion 5a and fixed with a tolerance. As shown in FIGS. 3 and 4, the annular portions 4 b and 5 b can be formed by denting the surface of the

brackets

104 and 5 on the side of the rotating body 21 around the rotating shaft 22.

Sliding

bearings

102 and 3 are sintered metals obtained by compressing and sintering metal powder. Therefore, the

plain bearings

102 and 3 are porous having a large number of pores inside. Since the pores are impregnated with lubricating oil, the sliding

bearings

102 and 3 form a state where self-lubrication is possible. Further, since the

slide bearings

102 and 3 are porous, the oil film pressure is lowered. Therefore, the film thickness of the oil film formed on the surfaces of the sliding

bearings

102 and 3 is thinner than the height of the unevenness existing on the surfaces of the sliding

bearings

102 and 3. As a result, the

plain bearings

102 and 3 have electrical conductivity as a whole.

The operation of the brushless motor configured as described above will be described.

In the brushless motor according to the first embodiment of the present invention, the rotating shaft 22 is electrically connected to the

brackets

104 and 5 via the sliding

bearings

102 and 3 in the stopped state. The reason is as follows. The

plain bearings

102 and 3 that are sintered metal powders have electrical conductivity. The rotating shaft 22 and the

brackets

104 and 5 are in contact with each other through the sliding

bearings

102 and 3 so that they are electrically connected.

Next, in the operating state, the rotating shaft 22 rotates to cause a pump action, and the lubricating oil impregnated in the

slide bearings

102 and 3 is sucked out. As shown in FIG. 4, the wedge 7 of the lubricating oil generated by the sucked lubricating oil enters between the sliding bearing 3 and the rotary shaft 22 and between the sliding bearing 3 and the annular portion 5b, and lubricates. Perform the action.

In the brushless motor shown in FIGS. 1 and 2, the same action occurs between the sliding bearing 3 and the rotating shaft 22 and between the sliding bearing 3 and the annular portion 5a.

As a result, the rotating shaft 22 and the annular portions 4b and 5b which are a part of the

brackets

104 and 5 are electrically connected by the sliding

bearings

102 and 3 having conductivity. Alternatively, the rotary shaft 22 and the

annular portions

4a and 5a which are a part of the

brackets

104 and 5 are electrically connected by the sliding

bearings

102 and 3 having conductivity. That is, since the rotating shaft 22 as the rotating portion and the

brackets

104 and 5 as the fixing portions are electrically connected via the sliding

bearings

102 and 3 having electrical conductivity, it is possible to suppress the induction voltage from being accumulated in the rotating portion. . Therefore, it is possible to prevent arc discharge from occurring between the rotating part and the fixed part.

Further, the contact area between the rotary shaft 22 and the sliding

bearings

102 and 3 and between the sliding

bearings

102 and 3 and the

annular portions

4a and 5a can be made wider than that of the ball bearing. Therefore, when a current is passed from the rotating shaft 22 that is the rotating portion to the

brackets

104 and 5 that are the fixed portions via the sliding

bearings

102 and 3, the current density can be reduced. As a result, the contact surface between the rotating shaft 22 and the sliding

bearings

102 and 3 and the contact surface between the sliding

bearings

102 and 3 and the

annular portions

4a and 5a can suppress the occurrence of damage due to energization. Similar effects can be obtained also on the contact surface between the rotary shaft 22 and the sliding

bearings

102 and 3 and the contact surface between the sliding

bearings

102 and 3 and the annular portions 4b and 5b.

In addition, the same effect can be acquired also if the said cyclic |

annular parts

4a and 5a are created with another member, and the cyclic |

annular parts

4a and 5a and the

brackets

104 and 5 are electrically connected.

(Embodiment 2)
FIG. 5 is a longitudinal sectional view of the brushless motor according to the second embodiment of the present invention. The brushless motor shown in the figure is a molded motor as in the first embodiment.

In addition, about the same component as what was demonstrated in Embodiment 1, the same code | symbol is attached | subjected and description is used.

As shown in FIG. 5, in addition to the molded motor 1 described in the first embodiment, the molded motor 31 includes a connection terminal 32 that is a first connection portion that electrically connects the outer peripheral surfaces of a pair of bearings. Prepare. Specifically, the sliding

bearings

102 and 3 as a pair of bearings slide inside the

annular portions

4a and 5a. The outer

peripheral surfaces

4c and 5c of the

annular portions

4a and 5a are electrically connected by connection terminals 32.

As the connection terminal 32, a copper material having spring elasticity such as brass, phosphor bronze or beryllium copper can be used. When a copper material having spring elasticity is used, the deformation of the connection terminal 32 due to the pressure from the resin generated during molding can be suppressed. Moreover, the resistance value of the copper material is low. The connection terminal 32 and the outer

peripheral surfaces

4c and 5c are connected by a method such as fusing or welding using heat at the time of molding, caulking that is resistant to pressure.

In the brushless motor according to the second embodiment of the present invention, as described in the first embodiment, the rotating shaft 22 and the

annular portions

4a and 5a that are part of the

brackets

104 and 5 have electrical conductivity. The sliding

bearings

102 and 3 are electrically connected. That is, since the rotating shaft 22 as the rotating portion and the

brackets

104 and 5 as the fixing portions are electrically connected via the sliding

bearings

Further, the contact area between the rotary shaft 22 and the sliding

bearings

102 and 3 and between the sliding

bearings

102 and 3 and the

annular portions

brackets

104 and 5 that are the fixed portions via the sliding

bearings

102 and 3 and the contact surface between the sliding

bearings

102 and 3 and the

annular portions

4a and 5a can suppress the occurrence of damage due to energization.

Furthermore, the annular portion 4 a that is a part of the bracket 104 and the annular portion 5 a that is a part of the bracket 5 are electrically connected via the connection terminal 32. Therefore, in addition to the electrical path of bracket 104-slide bearing 102-rotating shaft 22-slide bearing 3-bracket 5, an electrical path of bracket 104-annular portion 4a-connection terminal 32-annular portion 5a-bracket 5 is obtained. Can do. That is, the mold motor 31 constitutes an electrically connected closed loop of the bracket 104-slide bearing 102-rotary shaft 22-slide bearing 3-bracket 5-outer peripheral surface 5c-connecting terminal 32-outer peripheral surface 4c-bracket 104. . As a result, since the dielectric voltage between the rotating part and the fixed part can be suppressed to be lower, the occurrence of arc discharge can be suppressed.

In addition, the same effect can be acquired also if the said cyclic |

annular parts

4a and 5a are created with another member, and the cyclic |

annular parts

4a and 5a are electrically connected to the

brackets

104 and 5. FIG.

(Embodiment 3)
FIG. 6 is a longitudinal sectional view of the brushless motor according to Embodiment 3 of the present invention. The brushless motor shown in the figure is a molded motor as in the first embodiment.

As shown in FIG. 6, in addition to the mold motor 1 described in the first embodiment, the mold motor 41 includes a connection terminal 44 that is a second connection portion that electrically connects the pair of

brackets

42 and 43. Prepare.

Also, in the molded motor 41, the

bearings

45 and 46 are constituted by

separate brackets

42 and 43 and

annular portions

47 and 48, respectively. The bracket 42 and the annular portion 47, and the bracket 43 and the annular portion 48 are electrically connected. The

annular portions

47 and 48 have sliding

bearings

102 and 3 inside.

In the third embodiment, the bracket 42 and the bracket 43 are electrically connected to each other at the

surfaces

42a and 43a facing each other by the connection terminal 44.

As the connection terminal 44, a copper material having spring elasticity such as brass, phosphor bronze, and beryllium copper can be used. When a copper material having spring elasticity is used, deformation of the connection terminal 44 due to the pressure from the resin generated during molding can be suppressed. Moreover, the resistance value of the copper material is low. Further, the connection terminal 44 and the bracket surfaces 42a and 43a are connected by a method such as fusing or welding using heat at the time of molding, caulking having resistance to pressure.

In the brushless motor according to the third embodiment of the present invention, as in the first embodiment, the rotary shaft 22 and the

annular portions

47 and 48 electrically connected to the

brackets

42 and 43 have electrical conductivity. The sliding

bearings

brackets

42 and 43 as the fixing portions are electrically connected to each other through the sliding

bearings

Further, the contact area between the rotating shaft 22 and the sliding

bearings

102 and 3 and between the sliding

bearings

102 and 3 and the

annular portions

47 and 48 can be made wider than that of the ball bearing. Therefore, when a current is passed from the rotating shaft 22 that is the rotating portion to the

brackets

42 and 43 that are the fixed portions via the

slide bearings

bearings

102 and 3 and the contact surface between the sliding

bearings

102 and 3 and the

annular portions

47 and 48 can suppress the occurrence of damage due to energization.

Furthermore, the annular portion 47 electrically connected to the bracket 42 and the annular portion 48 electrically connected to the bracket 43 are electrically connected via the connection terminal 44. Therefore, in addition to the electrical path of bracket 42-annular portion 47-slide bearing 102-rotating shaft 22-slide bearing 3-annular portion 48-bracket 43, an electrical path of bracket 42-connection terminal 44-bracket 43 is obtained. Can do. That is, the mold motor 41 forms an electrically connected closed loop of bracket 42-bearing 45-rotating shaft 22-bearing 46-bracket 43-connection terminal 44-bracket 42. As a result, since the dielectric voltage between the rotating part and the fixed part can be suppressed to be lower, the occurrence of arc discharge can be suppressed.

The annular portion 47 and the bracket 42, and the annular portion 48 and the bracket 43 may be formed integrally, and the annular portion 47 may be electrically connected to the bracket 42 and the annular portion 48 to the bracket 43. The same effect can be obtained.

(Comparative example)
FIG. 10 shows a shaft voltage waveform at the time of rotating a brushless motor provided with a conventional ball bearing. In the figure, the vertical axis represents the shaft voltage, and the horizontal axis represents the operating time of the brushless motor. The vertical axis indicates the scale for each 1V. The horizontal axis indicates a scale every 10 μs. In addition, in order to make FIG. 10 easy to understand, the display of 5 scales is described on both the vertical axis and the horizontal axis.

The brushless motor was rotated at 1000 r / m with a carrier frequency of 20 kHz. In a brushless motor, a PWM current is passed through a winding that forms an electromagnetic coil. When the PWM current flows, a magnetic field is generated by the electromagnetic coil. Due to this magnetic field, an induced current flows in a conductor existing around the electromagnetic coil. When an induced current flows through the conductor, an induced voltage is generated. At this time, since the impedance is different between the rotating portion and the fixed portion, the induced voltage is different. This induced voltage difference causes a shaft voltage.

玉 Viscoelastic lubricating oil is sealed inside the ball bearing. When the rotating shaft rotates, a thin oil film is formed between the inner ring, the rolling element and the outer ring inside the ball bearing due to the action of viscoelasticity of the lubricating oil. When this thin oil film is interposed, the inner ring and the rolling element are in an insulating state, and the rolling element and the outer ring are in an insulated state.

) The insulation state is supported by a thin oil film. Therefore, if the shaft voltage becomes high and the insulation state cannot be supported by this thin oil film, a discharge phenomenon occurs. When this insulation state and the discharge phenomenon are repeated, the shaft voltage waveform fluctuates drastically. FIG. 10 shows how the shaft voltage waveform fluctuates. As can be seen from FIG. 10, when a brushless motor equipped with a conventional ball bearing is rotated, a shaft voltage of about 50 V is generated at the peak-peak voltage.

電 As a result of such intense shaft voltage fluctuations, electrolytic corrosion occurs within the ball bearing in a short time. Since the inner surface of the ball bearing is roughened by electric corrosion, noise is generated.

Example 1
FIG. 7 shows the shaft voltage waveform during rotation of the brushless motor according to Embodiment 1 of the present invention. In the figure, the vertical axis represents the shaft voltage, and the horizontal axis represents the operating time of the brushless motor. The vertical axis indicates the scale every 160 mV. The horizontal axis indicates a scale every 10 μs. In addition, in order to make FIG. 7 easy to understand, the display for five scales is described on both the vertical axis and the horizontal axis. The brushless motor was rotated at 1000 r / m with a carrier frequency of 20 kHz. In a brushless motor, a PWM current is passed through a winding that forms an electromagnetic coil. When the PWM current flows, a magnetic field is generated by the electromagnetic coil. Due to this magnetic field, an induced current flows in a conductor existing around the electromagnetic coil. When an induced current flows through the conductor, an induced voltage is generated. As can be seen from FIG. 7, when the brushless motor according to the first embodiment of the present invention is rotated, an axial voltage of about 2.0 V is generated at the peak-peak voltage.

Unlike the above comparative example, when the sliding bearing according to the first embodiment of the present invention is used, the shaft voltage can be suppressed. Specifically, the shaft voltage can be suppressed to about 1/20. The following can be considered as the reason.

That is, the plain bearing according to the first embodiment of the present invention is made of sintered metal and impregnated with lubricating oil. Since the slide bearing is porous, the oil film pressure becomes low. Therefore, the film thickness of the oil film formed on the surface of the sliding bearing is thinner than the height of the unevenness existing on the surface of the sliding bearing. The plain bearing is in direct contact with the rotating shaft and the bracket. As a result, the plain bearing has electrical conductivity as a whole. Therefore, whenever the brushless motor rotates, the plain bearing made of a good conductor rotates while electrically connecting the rotating shaft and the bracket. As a result, the induced voltage difference between the rotating part and the fixed part is eliminated, and the shaft voltage decreases.

Furthermore, when the sliding bearing according to Embodiment 1 of the present invention is used, the occurrence of electrolytic corrosion can be prevented. The following can be considered as the reason.

That is, the sliding bearing becomes a path for flowing the electric charge generated in the rotating part around the rotating shaft to the fixed part including the bracket. The path of the rotating shaft and the bearing formed by the sliding bearing and the path of the bearing and the annular portion have a wider contact area than the path of the inner ring and rolling element and the rolling element and outer ring formed by the conventional ball bearing. Therefore, when the sliding bearing is used, the current density is reduced and the occurrence of electrolytic corrosion can be prevented.

(Example 2)
FIG. 8 shows a shaft voltage waveform at the time of rotating the brushless motor according to the second embodiment of the present invention. In the figure, the vertical axis represents the shaft voltage, and the horizontal axis represents the operating time of the brushless motor. The vertical axis indicates the scale every 120 mV. The horizontal axis indicates a scale every 10 μs. In addition, in order to make FIG. 8 easy to understand, the display of 5 scales is described on both the vertical axis and the horizontal axis. The brushless motor was rotated at 1000 r / m with a carrier frequency of 20 kHz as in the comparative example and example 1. In a brushless motor, a PWM current is passed through a winding that forms an electromagnetic coil. When the PWM current flows, a magnetic field is generated by the electromagnetic coil. Due to this magnetic field, an induced current flows in a conductor existing around the electromagnetic coil. When an induced current flows through the conductor, an induced voltage is generated. As is apparent from FIG. 8, when the brushless motor according to the second embodiment of the present invention is rotated, an axial voltage of about 1.5 V is generated at the peak-peak voltage. In addition to Example 1 described above, when the sliding bearing according to Embodiment 2 of the present invention is used, generation of shaft voltage can be further suppressed. Specifically, the shaft voltage can be suppressed to about 3/4.

The second embodiment is considered to have the following operational effects in addition to the operational effects of the first embodiment.

That is, the phase of the induced voltage generated in the path via the rotary shaft 22-slide bearing 102-annular portion 4a and the induced voltage generated in the path via the rotary shaft 22-slide bearing 3-annular portion 5a are inverted. Therefore, induced voltages having opposite phases are electrically connected using the connection terminals. As a result, both induced voltages cancel each other, and the shaft voltage can be reduced.

The application field of the present invention is not particularly limited, and can be widely used as a brushless DC mold motor with reduced electric corrosion of the bearing.

1 Molded motor 3 Sliding bearing (bearing)
4a annular portion 4b annular portion 4c outer peripheral surface 5 bracket 5a annular portion 5b annular portion 5c outer peripheral surface 10 stator 11 winding 12 stator core (stator core)
DESCRIPTION OF SYMBOLS 13 Mold frame 20 Rotor 21 Rotating body 22 Rotating shaft 23 Permanent magnet 31 Mold motor 32 Connection terminal (1st connection part)
41 Molded motor 42 Bracket 42a Surface 43 Bracket 43a Surface 44 Connection terminal (second connection part)
45 Bearing 46 Bearing 47 Annular part 48 Annular part 102 Sliding bearing (bearing)
104 Bracket

Claims

A stator having a stator core wound with windings;
A rotor including a rotating body facing the stator and having a permanent magnet in the circumferential direction; and a rotating shaft penetrating an axis of the rotating body;
A bearing for rotatably holding the pair of rotors;
A bracket for holding the pair of bearings,
The said bearing is a brushless motor which is a sliding bearing containing lubricating oil.
The brushless motor according to claim 1, wherein the sliding bearing is a sintered metal.
Furthermore, the brushless motor of Claim 1 provided with the 1st connection part which electrically connects between the outer peripheral surfaces of a pair of said bearing.
The brushless motor according to claim 1, further comprising a second connection portion that electrically connects the pair of brackets.
The brushless motor according to claim 1, wherein the stator forms a mold frame molded by a resin material.