Technical Field
5 [0001] The present invention relates to an electric
motor including two bearing houses and an electrical
conduction member for electrically connecting those
bearing houses.
Background Art
10 [0002] As an electric motor, an inner-rotor electric
motor has been conventionally known, in which a
columnar rotor including a permanent magnet is disposed
coaxially with a cylindrical stator on the inner
diameter side thereof, the cylindrical stator
15 generating a rotating magnetic field. This electric
motor is, for example, used to rotationally drive a
blower fan mounted in an air conditioner.
[0003] When driven by a PWM inverter that performs
high-frequency switching, such an electric motor
20 generates a potential difference (shaft voltage)
between an inner race and an outer race of a bearing.
When the shaft voltage reaches a dielectric breakdown
voltage of an oil film within the bearing, a current
flows inside the bearing and causes electrolytic
25 corrosion in the bearing.
As the conventional technology of suppressing the
3
generation of such electrolytic corrosion, it is known
that an electrostatic capacitance on the stator side
and an electrostatic capacitance on the rotor side of
the electric motor are adjusted so as to be
5 substantially equal to each other, to thereby reduce
the shaft voltage and suppress the occurrence of
electrolytic corrosion (Patent Literature 1).
In Patent Literature 1, the rotor core is divided
into an inner core and an outer core, and a dielectric
10 (insulator) layer is provided therebetween, so that the
electrostatic capacitance is adjusted.
Citation List
Patent Literature
[0004] Patent Literature 1: Japanese Patent
15 Application Laid-open No. 2014-124082
Disclosure of Invention
Technical Problem
[0005] Here, in the structure in which the rotor
core is divided and the dielectric layer is sandwiched
20 therebetween, a die for forming the rotor core
determines the thickness or shape of the insulating
layer. If the electrostatic capacitance is adjusted, it
is necessary to change the die and to cut the rotor
core, for example. For that reason, there has been a
25 problem in that the electrostatic capacitance cannot be
easily adjusted after completion of the die of the
4
rotor core.
[0006] In this regard, it is an object of the
present invention to provide an electric motor capable
of easily adjusting an electrostatic capacitance
5 between a stator side and a rotor side of the electric
motor and suppressing generation of electrolytic
corrosion.
Solution to Problem
[0007] An embodiment of an electric motor of the
10 present invention includes: a rotor; a shaft disposed
along a rotation axis of the rotor, the rotor being
fixed to the shaft; a first bearing disposed on one end
side of the shaft; a second bearing disposed on another
end side of the shaft; a stator core disposed on an
15 outer circumferential side of the rotor; a resin shell
that covers the stator core; and an electrical
conduction member that electrically connects outer
races of the first bearing and the second bearing to
each other. An electrically conductive member that
20 covers at least a part of the electrical conduction
member is attached to a surface of the resin shell.
[0008] According to the present invention, it is
possible to easily adjust an electrostatic capacitance
between a stator side and a rotor side of an electric
25 motor and suppressing generation of electrolytic
corrosion.
5
Brief Description of Drawings
[0009] [Fig. 1] Fig. 1 is a perspective view of a
rotor of an electric motor according to the present
invention.
5 [Fig. 2] Fig. 2 is a perspective view of a stator of
the electric motor according to the present invention.
[Fig. 3] Fig. 3 shows perspective views of an upper
surface and a lower surface of the electric motor
without an electrically conductive sheet according to
10 the present invention.
[Fig. 4] Fig. 4 shows a front view and an exploded
view of parts of a second bearing of the electric motor
according to the present invention.
[Fig. 5] Fig. 5 is a side perspective view of the
15 electric motor according to the present invention.
[Fig. 6] Fig. 6 is a cross-sectional view showing
electrostatic capacitance coupling and the electric
motor according to the present invention.
[Fig. 7] Fig. 7 is a bottom view of the electric motor
20 according to the present invention.
[Fig. 8] Fig. 8 is a non-grounded bridge-type
equivalent circuit diagram regarding the electrostatic
capacitance of the electric motor according to the
present invention.
25 [Fig. 9] Fig. 9 shows an output waveform of a shaft
voltage in the electric motor without the electrically
6
conductive sheet according to the present invention.
[Fig. 10] Fig. 10 shows an output waveform of a shaft
voltage obtained when the electrically conductive sheet
is attached to the electric motor according to the
5 present invention.
[Fig. 11] Fig. 11 is a graph showing a stator
electrostatic capacitance with respect to a change in
an area of the electrically conductive sheet according
to the present invention.
10 [Fig. 12] Fig. 12 is a partial side perspective view of
the electric motor without the electrically conductive
sheet according to the present invention.
[Fig. 13] Fig. 13 is a graph showing a stator
electrostatic capacitance with respect to a change in a
15 width of the electrical conduction member according to
the present invention.
[Fig. 14] Fig. 14 is a partial side perspective view of
the electric motor with the electrically conductive
sheet according to the present invention.
20 [Fig. 15] Fig. 15 is a graph showing a stator
electrostatic capacitance with respect to a change in
an area of the electrical conduction member and the
electrically conductive sheet according to the present
invention.