U.S. patent application number 13/108281 was filed with the patent office on 2011-11-17 for superconducting motor.
This patent application is currently assigned to Aisin Seiki Kabushiki Kaisha. Invention is credited to Kenji Ishida, Ryoji Mizutani, Yoshimasa Ohashi, Nobuo Okumura.
Application Number | 20110277953 13/108281 |
Document ID | / |
Family ID | 44654637 |
Filed Date | 2011-11-17 |
United States Patent
Application |
20110277953 |
Kind Code |
A1 |
Mizutani; Ryoji ; et
al. |
November 17, 2011 |
SUPERCONDUCTING MOTOR
Abstract
A superconducting motor includes: a rotor that is rotatably
supported; a stator that is provided around the rotor, and that is
provided with a plurality of coils that are respectively formed of
superconducting wires and that are wound at an inner periphery of a
stator core; and a refrigerator having a cooling portion for
cooling the plurality of coils. The cooling portion of the
refrigerator is in contact with the plurality of coils.
Inventors: |
Mizutani; Ryoji;
(Nagoya-shi, JP) ; Ohashi; Yoshimasa; (Kariya-shi,
JP) ; Okumura; Nobuo; (Toyota-shi, JP) ;
Ishida; Kenji; (Nagoya-shi, JP) |
Assignee: |
Aisin Seiki Kabushiki
Kaisha
Kariya-Shi
JP
Toyota Jidosha Kabushiki Kaisha
Toyota-Shi
JP
|
Family ID: |
44654637 |
Appl. No.: |
13/108281 |
Filed: |
May 16, 2011 |
Current U.S.
Class: |
165/47 ;
62/498 |
Current CPC
Class: |
H02K 9/22 20130101; H02K
55/02 20130101 |
Class at
Publication: |
165/47 ;
62/498 |
International
Class: |
F28D 21/00 20060101
F28D021/00; F25B 1/00 20060101 F25B001/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 14, 2010 |
JP |
JP2010-112094 |
Claims
1. A superconducting motor comprising: a rotor that is rotatably
supported; a stator that is provided around the rotor, and that is
provided with a plurality of coils that are respectively formed of
superconducting wires and that are wound at an inner periphery of a
stator core; and a refrigerator having a cooling portion for
cooling the plurality of coils, wherein the cooling portion of the
refrigerator is in contact with the plurality of coils.
2. The superconducting motor according to claim 1, wherein: every
predetermined number of coils out of the plurality of coils are
connected in series to form a plurality of phase coils; and the
plurality of phase coils are in contact with the cooling portion of
the refrigerator at a neutral point at which one end portions of
the respective phase coils are electrically connected to each
other.
3. The superconducting motor according to claim 2, wherein at the
neutral point, the one end portions of the respective phase coils
are electrically connected to each other via the cooling portion
that is made of an electrically conductive member, rather than
being directly connected to each other.
4. The superconducting motor according to claim 2, wherein: the
neutral point is provided at the side of coil end portions of the
plurality of coils, which are axial end portions of the plurality
of coils in an axial direction of the superconducting motor; and
the refrigerator is arranged such that the one end portions of the
respective phase coils are connected to the cooling portion of the
refrigerator at the side of the coil end portions of the plurality
of coils.
5. The superconducting motor according to claim 2, wherein the
lengths of the superconducting wires forming the respective coils
are substantially equal to each other.
6. The superconducting motor according to claim 1, wherein: the
plurality of coils are provided with an annular heat transfer
member that is in contact with coil end portions of the plurality
of coils, each of the coil end portions being located at a
superconducting motor axial direction end of a corresponding one of
the coils; and the cooling portion of the refrigerator is arranged
so as to be in contact with the plurality of coils, and cools the
plurality of coils from the coil end portions via the heat transfer
member.
7. The superconducting motor according to claim 1, wherein the
superconducting motor is a three-phase alternating current
motor.
8. The superconducting motor according to claim 1, wherein: the
refrigerator has a cylinder and a piston; and the refrigerator is
structured such that coolant in an expansion chamber defined in the
cooling portion is repeatedly compressed and expanded by the piston
reciprocating in the cylinder, while heat of the coolant is
absorbed and radiated via a heat absorption member, causing a
temperature decrease and thereby achieving a desired cooling
temperature at the cooling portion.
9. The superconducting motor according to claim 1, wherein: the
refrigerator has a coolant compressor coupled with the cooling
portion; and the coolant compressor is electrically insulated from
a front end of the cooling portion, which is in contact with the
plurality of coils, by an insulator that is provided at an
intermediate portion of the cooling portion or at a boundary
between the cooling portion and the coolant compressor.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to Japanese Patent
Application No. 2010-112094 filed on May 14, 2010, which is
incorporated herein by reference in its entirety including the
specification, drawings and abstract.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to a superconducting motor, and
especially to a superconducting motor that is provided with a
refrigerator for cooling coils that are formed of superconducting
wires.
[0004] 2. Description of the Related Art
[0005] Recently, much attention has been paid to electric motor
vehicles (will hereinafter be referred to as "EVs") that run on the
drive force produced by an in-vehicle motor powered by an
in-vehicle secondary battery, thus emitting no carbon dioxides,
that is, achieving "zero emissions". Further, hybrid electric motor
vehicles (will hereinafter be referred to as "HEVs") that run
using, as drive force sources for propelling the vehicle, both an
engine and a motor(s) have become popular.
[0006] Motors for use in EVs and HEVs, such as those described
above, are required to be small in size and high in output since
they are mounted in limited spaces. In order to maintain a desired
output performance of a motor, it is essential to suppress an
increase in the temperature of the motor, and more specifically, to
cool the stator coils of the motor.
[0007] As a technology related to the requirement described above,
Japanese Patent Application Publication No. 2000-125512
(JP-A-2000-125512) describes a coil-end contact cooling type
rotational electric device. In this rotational electric device, at
least a coil end of each stator coil has axially-protruding
portions that are elongated platy conductors arranged radially and
each protruding from an end face of the stator core in such a
position that the thickness direction of the elongated platy
conductor coincides with a radial direction of the stator core.
Also a cooling member having a high thermal conductivity and a flat
cooling face is provided such that the cooing face of the cooling
member is in direct contact with, via electric insulation, the flat
main faces of the respective elongated platy conductors of the coil
end, which are located at the radially outmost side or radially
innermost side of the coil end, thus improving the cooling of the
coil end portion.
[0008] Meanwhile, a superconducting motor can be used as a motor to
be provided in EVs and HEVs, such as those described above. A
superconducting motor has a plurality of coils that are formed of
superconducting wires, and the electric resistances at the
respective coils are substantially zero when currents, more
specifically, direct currents are supplied to the coils while the
coils are cooled such that their temperatures are maintained at a
predetermined ultralow temperature (e.g., 70 K). For this reason,
the use of a superconducting motor is effective in reducing the
power consumption of the motor, and thus reducing the power
consumption of an EV, an HEV, or the like.
[0009] However, in a case where the stator coils of a
superconducting motor are cooled using a refrigerator, if the coils
that are formed of superconducting wires are cooled to a target
ultralow temperature via other member(s) having a large heat
capacity, such as a stator core, it takes much time to cool all the
coils to the target ultralow temperature. In addition, in a
structure in which, for cooling, the cooling portion of a
refrigerator is in contact with only a portion of the outer
peripheral face of the stator core, it is difficult to evenly cool
the portions of the stator core that are radially opposed to the
cooled portion of the stator core and the coils that are provided
at the same portions of the stator core, and thus large
circumferential and axial temperature gradients may occur depending
upon the thermal conductivities of the respective portions.
SUMMARY OF THE INVENTION
[0010] The invention provides a superconducting motor that is
capable of cooling a plurality of phase coils, each formed of a
superconducting wire, down to a desired ultralow temperature
efficiently and promptly.
[0011] An aspect of the invention relates to a superconducting
motor having: a rotor that is rotatably supported; a stator that is
provided around the rotor, and that is provided with a plurality of
coils that are respectively formed of superconducting wires and
that are wound at an inner periphery of a stator core; and a
refrigerator having a cooling portion for cooling the plurality of
coils. The cooling portion of the refrigerator is in contact with
the plurality of coils.
[0012] According to the above aspect, because the cooling portion
of the refrigerator is in contact with the phase coils and
therefore the phase coils, each formed of the superconducting wire,
are directly cooled, not via the stator core, or the like, it is
possible to cool the phase coils down to a desired ultralow
temperature efficiently, and promptly.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The foregoing and further objects, features and advantages
of the invention will become apparent from the following
description of example embodiments with reference to the
accompanying drawings, wherein like numerals are used to represent
like elements and wherein:
[0014] FIG. 1 is a sectional view that is taken along the axial
direction of a superconducting motor of a first embodiment of the
invention and that also shows part of side faces of the
superconducting motor;
[0015] FIG. 2 is a sectional view taking along the line I-I in FIG.
1;
[0016] FIG. 3 is a view schematically showing an electric
connection in which a U-phase coil, a V-phase coil, and a W-phase
coil are electrically connected to each other at a neutral
point;
[0017] FIG. 4A is a view illustrating examples of one end portions
of the respective phase coils, which constitute the neutral
point;
[0018] FIG. 4B is a view illustrating a state where the neutral
point shown in FIG. 4A is connected to a cooling portion of a
refrigerator;
[0019] FIG. 5A is a view showing a structure in which the one end
portions of the respective phase coils are connected, at the
neutral point, to the cooling portion of the refrigerator in a
manner different from that shown in FIG. 4B;
[0020] FIG. 5B is a view showing the structure in FIG. 5A as seen
from the direction indicated by the arrow B in FIG. 5A;
[0021] FIG. 6 is a view showing a structure in which the one end
portions of the respective phase coils are connected, at the
neutral point, to the cooling portion of the refrigerator in a
manner different from that shown in FIG. 4B, FIG. 5A, and FIG.
5B;
[0022] FIG. 7 is an enlarged side view of the cooling portion of
the refrigerator;
[0023] FIG. 8A is a sectional view illustrating an example where an
annular insulator is provided at an intermediate portion of the
cooling portion of the refrigerator;
[0024] FIG. 8B is a sectional view illustrating an example where an
annular insulator having a relatively high insulation resistance is
provided at the intermediate portion of the cooling portion of the
refrigerator;
[0025] FIG. 9 is a sectional view illustrating an example where an
annular insulator is provided at the boundary between the cooling
portion and the coolant compressor of the refrigerator;
[0026] FIG. 10 is a sectional view that is taken along the axial
direction of a superconducting motor of a second embodiment of the
invention including a plurality of refrigerators and also shows
part of side faces of the superconducting motor;
[0027] FIG. 11 is a view schematically illustrating a state where
the U-phase coil, the V-phase coil, and the W-phase coil are
electrically connected to each other at two neutral points;
[0028] FIG. 12 is a sectional view that is taken along the axial
direction of a superconducting motor of a third embodiment of the
invention and also shows side faces of some portions of the
superconducting motor; and
[0029] FIG. 13 is a sectional view that is taken along the axial
direction of a superconducting motor of a fourth embodiment of the
invention and also shows side faces of some portions of the
superconducting motor.
DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS
[0030] Hereinafter, example embodiments of the invention will be
described in detail with reference to the accompanying drawings.
Note that the shapes, materials, values, directions, and so on,
specified in the following descriptions of the respective example
embodiments are no more than examples for facilitating
understanding on the invention, and thus they may be changed as
needed in accordance with various factors, such as the use of the
product, the purpose of using the product, and the specification of
the product.
[0031] FIG. 1 is a sectional view of a superconducting motor 10
showing a first embodiment of the invention, which is taken along
the axial direction of the superconducting motor 10, and which also
shows part of the side faces of the superconducting motor 10. FIG.
2 is a sectional view of the superconducting motor 10 that is taken
along the line I-I shown in FIG. 1 (note that the hatching of the
stator core is omitted in this view). The superconducting motor 10
has a rotor 12 that is rotatably supported, a stator 14 that is
generally cylindrical and is arranged so as to surround the outer
periphery of the rotor 12, and a refrigerator 16 that is fixed on
an axial end face of the superconducting motor 10. Note that, in
the following descriptions on the respective example embodiments,
each direction that extends along a rotational axis X of a rotor
shaft 18 that passes through the center of the rotor 12 will be
referred to as "axial direction (motor-axis direction)", each
radial direction intersecting the rotational axis X at right angle
will be referred to as "radial direction", and each direction that
extends along a circle that is formed on a plane, which includes
the radial directions stated above, using the rotational axis X as
its center point will be refereed to as "circumferential
direction".
[0032] The rotor 12 has a rotor core 20 that is cylindrical and is
formed by, for example, stacking magnetic steel plates and then
joining them together by caulking, welding, or the like, and a
rotor shaft 18 that is, for example, a round-bar steel member
extending through the center hole of the rotor core 20 and fixed to
the rotor core 20. A plurality of permanent magnets 22 are (in this
first embodiment, the number of the permanent magnets 22 is six, or
the permanent magnets 22 are provided at six positions)
equiangularly provided on the outer peripheral face of the rotor
core 20 such that they are exposed to the outer peripheral face. It
is to be noted that the permanent magnets 22 may be provided at the
rotor core 20 such that they are unexposed to the outer peripheral
face, that is, for example, they may be embedded in inner portions
of the rotor core 20, which are near the outer peripheral face
thereof.
[0033] The rotor shaft 18 of the rotor 12 is rotatably supported,
at both end portions 19a and 19b thereof, by bearings 28 that are
fixed respectively to disk-shaped endplates 24 and 26 forming both
axial end faces of the superconducting motor 10. With this
arrangement, as rotating magnetic fields are produced in the stator
14, they attract the permanent magnets 22 of the rotor core 20.
Thus, the rotor 12 is driven so as to rotate.
[0034] The stator 14 has a stator core 30 that is a generally
cylindrical stator core. A plurality of tooth portions 32 (note
that nine tooth portions 32 are provided in the first embodiment)
protruding radially inward are equiangularly provided at the inner
periphery of the stator core 30. The spaces that are formed between
the respective tooth portions 32 and that extend in the axial
direction serve as slots 33. The stator core 30 is formed by, for
example, stacking a plurality of generally ring-shaped magnetic
steel plates axially and then joining them together by caulking,
bonding, welding, or the like. It is to be noted that the stator
core 30 may be formed by arranging nine individual stator cores,
each having a single tooth portion, into the form of a ring and
then fastening them, from the outer side, using a tubular fastening
member(s). These individual stator cores may be dust cores.
[0035] Coils 34 are provided on the respective tooth portions 32 of
the stator core 30. The coils 34 are formed by winding
superconducting wires around the respective tooth portions 32. The
superconducting wire may be a tape-shaped superconducting wire that
is rectangular in cross section. The superconducting material of
the superconducting wire is, for example, an yttrium-based
superconducting material or a bismuth-based superconducting
material. However, it is to be noted that the superconducting
material of the superconducting wire is not limited to any of them,
that is, it may alternatively be any other known superconducting
material or any superconducting material that will be developed in
future and exhibit its superconductivity at a higher
temperature.
[0036] Each coil 34 has an inner portion 35 each located within the
slot 33 between the tooth portions 32 that are adjacent to each
other, and two coil end portions 36 protruding outwardly from the
respective axial end faces of the stator core 30. For example, a
three-phase synchronous AC (alternating current) motor may be used
as the superconducting motor 10. In such a case, each coil 34 is
connected, in series, to another coil 34 that is located away, in
the circumferential direction, from the former coil 34 across two
other coils 34, whereby a U-phase coil 34U, a V-phase coil 34V, and
a W-phase coil 34W are formed.
[0037] It is to be noted that the superconducting motors of the
invention are not limited to three-phase AC motors, that is, they
may be a two-phase AC motor, an AC motor having four or more
different phase coils, a single-phase AC motor, a DC (direct
current) motor, or the like.
[0038] Referring to FIG. 3, one end portion of the U-phase coil
34U, one end portion of the V-phase coil 34V, and one end portion
of the W-phase coil 34W are electrically connected to each other at
a neutral point 70, while the other end portion of the U-phase coil
34U, the other end portion of the V-phase coil 34V, and the other
end portion of the W-phase coil 34W are connected to a U-phase
current input terminal 72U, a V-phase current input terminal 72V,
and a W-phase current input terminal 72W, respectively. The
structure at the neutral point 70 and the structure of the
superconducting wire forming each coil 34 will be described
later.
[0039] Referring again to FIGS. 1 and 2, the superconducting motor
10 has a cylindrical motor case 40, and the rotor 12 and the stator
14 are disposed within the motor case 40. The both axial ends of
the motor case 40 are airtightly coupled with the outer peripheral
portions of the endplates 24 and 26, respectively. The motor case
40 and the endplates 24 and 26 are each made of, for example, a
non-magnetic material, such as stainless steel. It is to be noted
that the motor case 40 may be formed integrally with the endplate
24 or the endplate 26.
[0040] In the motor case 40, an inner cylindrical member 42 and an
outer cylindrical member 44 are disposed concentrically with the
rotor 12. The both axial ends of the inner cylindrical member 42
are airtightly fixed on the inner faces of the endplates 24 and 26,
respectively, and the both axial ends of the outer cylindrical
member 44 are airtightly fixed on the inner faces of the endplates
24 and 26, respectively. The inner cylindrical member 42 may be
made of a nonmetallic material that does not impede passage of
magnetic fields and is not electrically conductive. On the other
hand, the outer cylindrical member 44 may be made of a material
having a low thermal conductivity (e.g., FRP) or a nonmagnetic
material having a low thermal conductivity.
[0041] The inner diameter of the inner cylindrical member 42 is
slightly lager than the diameter of the rotor core 20 of the rotor
12, and a gap, which is uniform in the circumferential direction,
is formed between the outer peripheral face of the rotor core 20
and the inner peripheral face of the inner cylindrical member 42.
Further, a first vacuum chamber 46, which is a cylindrical space,
is formed between the inner cylindrical member 42 and the outer
cylindrical member 44. The stator 14 that includes the coils 34 is
disposed in the first vacuum chamber 46. The outer peripheral face
of the stator core 30 of the stator 14 is closely fixed on the
inner peripheral face of the outer cylindrical member 44.
[0042] The vacuum in the first vacuum chamber 46 is made by
evacuating the first vacuum chamber 46 through an air vent hole
(not shown in the drawings) that is formed in at least one of the
endplates 24 and 26, after assembling the superconducting motor 10
including the refrigerator 16. Thus, defining the first vacuum
chamber 46 by the inner cylindrical member 42 and the outer
cylindrical member 44, each having a low thermal conductivity, and
then evacuating the first vacuum chamber 46 as described above
provides better heat insulation for the stator 14 including the
coils 34 and disposed in the first vacuum chamber 46.
[0043] Further, a second vacuum chamber 48, which is a cylindrical
space, is formed between the outer cylindrical member 44 and the
motor case 40. Like the first vacuum chamber 46, the second vacuum
chamber 48 is in a vacuum state. In this structure, the second
vacuum chamber 48 separates the stator 14, including the coils 34
and disposed in the first vacuum chamber 46, from the outer side of
the superconducting motor 10. As a result, the heat insulation for
the stator 14 including the coils 34 is further enhanced.
[0044] The refrigerator 16 is disposed at the endplate 24 that is
located at the side of one end of the superconducting motor 10 in
the axial direction. The refrigerator 16 is attached via a tubular
bracket 50 that is airtightly fixed to the periphery of a through
hole of the endplate 24.
[0045] The refrigerator 16 is provided with a coolant compressor 56
which has a cylinder 52 and a piston 54 and in which coolant (e.g.,
He gas) is repeatedly compressed and expanded as the piston 54
linearly reciprocates within the cylinder 52. Further, the
refrigerator 16 has a cooling portion 58 extending from the inside
of the tubular bracket 50 to the first vacuum chamber 46 via the
through hole of the endplate 24 and having an external shape like a
stepped round column. The front face, which is a flat face, of the
cooling portion 58 is in contact with the coil end portions 36 via
a heat transfer member 60. For electric insulation between the
coils 34 and the refrigerator 16, an insulator(s), such as an
insulating paper, may be provided between the coil end portions 36
and the heat transfer member 60 and/or between the heat transfer
member 60 and the cooling portion 58.
[0046] The cooling performance of the refrigerator 16 is high
enough to cool the coils 34 down to a desired ultralow temperature
(e.g., approximately 70 K) at which the coils 34, each formed of
the superconducting wire, exhibit their superconductivities, and
the cooling temperature can be adjusted by controlling the travel
of the piston 54. In a case where the superconducting motor 10 is
provided in an electrically-driven vehicle, such as an electric
motor vehicle, and is used as a drive force source for propelling
the vehicle, a refrigerator that is small and lightweight may be
used as the refrigerator 16 so that it can be disposed in a limited
mounting space and the weight of the vehicle can be reduced. For
example, a Stirling refrigerator that is a cooling storage type
refrigerator may be used as the refrigerator 16.
[0047] In the following, the structure of the Stirling refrigerator
employed in the first embodiment will be briefly described. The
Stirling refrigerator has the cylinder 52 and the piston 54 that is
driven by a linear motor to reciprocate linearly within the
cylinder 52. Further, another piston (not shown in the drawings),
which is a free piston mechanically unconnected to the piston 54,
is provided within the cylinder 52. A compression chamber filled
with coolant is defined between the free piston and the piston 54
while an expansion chamber filled with coolant is defined between
the free piston and an end face of the cylinder 52. A heat
absorption member, which serves as heat-transferring means, is
provided between the expansion chamber and the compression chamber.
As the piston 54 is driven, the free piston reciprocates with a
predetermined phase difference, thus repeatedly compressing and
expanding the coolant in the compression chamber, while the heat
absorption member absorbs the heat of the coolant and radiates it
to the outside, whereby the front end of the cooling portion 58
(also called "cooling storage portion") in which the expansion
chamber is formed is cooled.
[0048] In a case where the restrictions on the mounting space and
the weight are not strict, for example, when the superconducting
motor 10 is used as a drive force source for a large moving object,
such as trains and vessels, or as a drive force source for a
positionally-fixed machine, a refrigerator that is large in size
and weight may be used as long as the refrigerator has a cooling
performance as described above.
[0049] The heat transfer member 60 that is in contact with the
axial front end face of the cooling portion 58 of the refrigerator
16 is formed of, for example, a metal plate having a high thermal
conductivity, has an annular shape extending continuously in the
circumferential direction, and is in contact with all the coil end
portions 36 that are located at one axial side. On the other hand,
another heat transfer member 60 that is similar to the former heat
transfer member 60 is provided at the coil end portions 36 located
at the other axial side. Thus, the annular heat transfer members 60
are provided, respectively, at the coil end portions 36 located at
the respective axial sides such that the heat transfer members 60
are in contact with the coil end portions 36, and therefore the
coils 34 circumferentially arranged can be promptly, and evenly,
cooled from the coil end portions 36.
[0050] A recess or groove is formed at the face of each heat
transfer member 60 that is opposed to the coils 34, and the coil
end portion 36 is fitted to it. This increases the contact area
between each coil end portion 36 and the heat transfer member 60,
and thus increases the efficiency in cooling the coils 34.
[0051] Further, each heat transfer member 60 may be made of an
insulating resin material and formed integrally with the coil end
portions 36. With this structure, the electric insulation between
the coils 34 and the cooling portion 58 of the refrigerator 16 can
be further enhanced. In this case, further, in order to increase
the thermal conductivity of each heat transfer member 60, metal
particles or metal powder may be dispersedly added to the
insulating resin material.
[0052] Next, the structure at the neutral point 70 and the
structure of the superconducting wire 74 that forms each coil 34
will be described with reference to FIGS. 4A and 4B. FIG. 4A
illustrates examples of a one end portion 74U of the U-phase coil
34U, and a one end portion 74V of the V-phase coil 34V, and a one
end portion 74W of the W-phase coil 34W, which constitute the
neutral point 70, and FIG. 4B illustrates a state where the neutral
point 70 shown in FIG. 4A is connected to the cooling portion 58 of
the refrigerator 16.
[0053] Each coil 34 in the first embodiment is formed by winding
the superconducting wire 74 that is a tape-like or band-like wire
having a rectangular cross section. The superconducting wire 74 is
formed by stacking a base material 76, an intermediate layer 78, a
superconducting layer 80, and a coating layer 82 in this order.
[0054] For example, the superconducting wire 74 is manufactured as
follows. Note that Hastelloy tape base material may be used as the
base material 76, for example. The intermediate layer 78, the
superconducting layer 80, and the coating layer 82 are successively
stacked and bonded while the base material 76 is conveyed in its
longitudinal direction at a constant speed. More specifically, the
intermediate layer 78 is formed on the surface of the base material
76 by depositing an oxide (e.g., Gd.sub.2Zr.sub.2O.sub.7) on the
surface of the base material 76 by, for example, ion-beam assisted
deposition. Then, the superconducting layer 80 is formed on the
surface of the intermediate layer 78 by depositing a
superconducting material (e.g., a yttrium oxide or a bismuth oxide)
on the surface of the intermediate layer 78 by, for example,
pulse-laser deposition. Finally, the coating layer 82 is formed on
the surface of the superconducting layer 80 by spattering, for
example, silver or a silver alloy on the surface of the
superconducting layer 80. The coating layer 82 serves as both a
protection layer covering the superconducting layer 80 and a
surface that contacts the heat transfer member 60 at the coil end
portion 36.
[0055] It is to be noted that the materials and forming methods of
the respective layers of the superconducting wire in the invention
are not limited to those described above, that is, any known
materials and multilayer forming methods or any materials and
multilayer forming methods that will be developed in future may be
used. Further, the cross-sectional shape of the superconducting
wire is not limited to rectangular shapes, that is, for example, a
round cross-section wire having a superconducting material core
provided at the center of the wire and coated with an insulating
coating (e.g., resin coating) that is formed around the core, such
as typical electric wires, may be used.
[0056] Referring to FIG. 4A, the neutral point 70 is constituted of
the one end portions 74U, 74V, and 74W of the phase coils 34U, 34V,
and 34W that are pulled, respectively, out from the corresponding
coils 34 to the side of the coil end portions 36, which are one
axial end portions of the respective coils 34, such that the
rectangular end faces of the one end portions 74U, 74V, and 74W are
aligned side by side, that is, such that the one end portions 74U
and 74V are in contact with each other and the one end portions 74V
and 74W are in contact with each other. The one end portions 74U,
74V, and 74W, constituting the neutral point 70, pass through an
opening 61 (refer to FIG. 5B) formed in the heat transfer member 60
and are press-fitted, as shown in FIG. 4B, into a fitting hole 59
that is formed at the end portion of the cooling portion 58 of the
refrigerator 16 and is rectangular in section. Note that it is
possible to more reliably prevent the superconducting wires 74 from
being removed from the cooling portion 58 by strengthening the
connection therebetween by, for example, caulking the cooling
portion 58 after inserting the one end portions 74U, 74V, and 74W
into the fitting hole 59.
[0057] As described above, in the superconducting motor 10 of the
first embodiment, the one end portions 74U, 74V, and 74W of the
respective superconducting wires 74 forming the phase coils 34U,
34V, and 34W are directly connected, at the neutral point 70, to
the cooling portion 58 of the refrigerator 16, that is, the one end
portions 74U, 74V, and 74W of the respective superconducting wires
74 are in contact with the cooling portion 58 of the refrigerator
16 at the neutral point 70. With this structure, the
superconducting layers 80 of the superconducting wires 74 forming
the coils 34 of the respective phase coils 34U, 34V, and 34W can be
cooled directly, efficiently, and promptly via the coating layers
82 having a high thermal conductivity, while the temperature
(coolness) dispersion to other parts of the superconducting motor
10, such as the stator core 30, the cryostats, the bearings, and
the rotor, each having a large thermal capacity, is suppressed.
Thus, the time required to start up the superconducting motor 10 is
relatively short, and the electric power consumption of the
refrigerator 16 is relatively small.
[0058] In the superconducting motor 10 of the first embodiment,
further, the lengths of the superconducting wires 74 forming the
respective phase coils 34U, 34V, and 34W are substantially equal to
each other. Therefore, the phase coils 34U, 34V, and 34W can be
evenly cooled by cooling them from the neutral point 70. Thus, the
superconducting states of all the three phase coils can be easily
determined by detecting and monitoring the temperature of only one
of the three phase coils using a sensor.
[0059] In the superconducting motor 10 of the first embodiment,
further, the annular heat transfer member 60 that is in contact
with the cooling portion 58 of the refrigerator 16 is provided so
as to contact the coil end portions 36 of the respective coils 34
that are arranged equiangularly. With this structure, the coils 34
can be cooled evenly, and promptly, from the coil end portions 36
located at the respective axial sides.
[0060] Next, another structure at the neutral point 70 will be
described with reference to FIGS. 5A and 5B. FIG. 5A shows a
structure in which the one end portions 74U, 74V, and 74W of the
phase coils 34U, 34V, and 34W are connected, at the neutral point
70, to the cooling portion 58 of the refrigerator 16 in a manner
different from that shown in FIG. 4B. FIG. 5B shows the structure
in FIG. 5A as viewed in the direction indicated by the arrow B in
FIG. 5A.
[0061] Referring to FIG. 5A, the one end portions 74U, 74V, and 74W
of the phase coils 34U, 34V, and 34W are pulled out to the cool end
portion 36-side, which is the side of one axial end of each coil
34, such that the one end portions 74U, 74V, and 74W are not in
contact with each other. Referring to FIG. 5B, the one end portions
74U, 74V, and 74W pass through the opening 61 of the heat transfer
member 60 and are press-fitted, respectively, into three fitting
holes 59U, 59V, and 59W formed at the end portion of the cooling
portion 58 of the refrigerator 16. The fitting holes 59U, 59V, and
59W are formed, in the end face of the cooling portion 58, at
positions substantially corresponding, respectively, to the three
sides of an equilateral triangle. In order to more reliably prevent
the superconducting wires 74 from being removed from the cooling
portion 58, for example, the cooling portion 58 is caulked after
the one end portions 74U, 74V, and 74W are inserted into the
fitting holes 59U, 59V, and 59W, respectively, so that the
connections therebetween are strengthened. It is to be noted that
the form in which to arrange the one end portions 74U, 74V, and 74W
of the phase coils 34U, 34V, and 34W, which are connected to the
cooling portion 58 such that they are not in contact with each
other, is limited neither to equilateral triangle forms nor to
generally equilateral triangle forms as described above. That is,
the one end portions 74U, 74V, and 74W may be arranged in various
other forms, such as the one illustrated in FIG. 6 in which the one
end portions 74U, 74V, and 74W are arranged side by side (or in
line) at given intervals.
[0062] The one end portions 74U, 74V, and 74W of the phase coils
34U, 34V, and 34W are not electrically connected to each other
directly, and constitute the neutral point 70 by being electrically
connected to each other via the cooling portion 58 that is an
electrically conductive member formed of for example, copper. The
potential at the neutral point of a three-phase AC motor, at which
three phase coils are electrically connected to each other, is
normally zero. Thus, even if the one end portions 74U, 74V, and 74W
of the respective superconducting wires 74 are electrically
connected to each other via the cooling portion 58, which is
electrically conductive, as described above, no current flows to
the cooling portion 58 and to the coolant compressor 56. However,
it is to be noted that potential at the neutral point may change
from zero due to a disturbance in motor currents, which may be
caused by, for example, an abnormality in the control for opening
and closing the switching elements of the inverter. Therefore an
insulator or an insulating structure may be provided such that no
current flows from the cooling portion 58 to the coolant compressor
56 even in such an abnormal state. An insulator that may be
provided for this purpose will be described later.
[0063] Even if the one end portions 74U, 74V, and 74W of the phase
coils 34U, 34V, and 34W are in contact with the cooling portion 58
of the refrigerator 16 such that they are not directly electrically
connected to each other as previously described, the same effects
as described above can be achieved in terms of cooling of the phase
coils 34U, 34V, and 34W. Further, since the one end portions 74U,
74V, and 74W are separately press-fitted to the cooling portion 58
as described above, each one end portion is in contact with the
cooling portion 58 at the longitudinal end face and four peripheral
side faces thereof, which enables the phase coils 34U, 34V, and 34W
to be cooled more evenly and efficiently.
[0064] The superconducting motor 10 described above incorporates
both the structure in which the one end portions 74U, 74V, and 74W
of the phase coils 34U, 34V, and 34W are connected to the cooling
portion 58 of the refrigerator 16 at the neutral point 70 so that
the coils 34 are cooled from the neutral point 70-side and the
structure in which the coils 34 are cooled from the coil end 36
side via the annular heat transfer member 60 that is in contact
with the cooling portion 58 of the refrigerator 16. However, it is
to be noted that the superconducting motors of the invention are
not limited to this. That is, for example, the superconducting
motor 10 may be adapted to have either of the two structures to
cool the coils 34. More specifically, in a case where the
superconducting motor 10 is adapted to have only the structure in
which the coils 34 are cooled from the neutral point 70-side, the
heat transfer member 60 may be omitted, and on the other hand, in a
case where the superconducting motor 10 is adapted to have only the
structure in which the coils 34 are cooled via the heat transfer
member 60, the neutral point 70 at which the one end portions 74U,
74V, and 74W of the phase coils 34U, 34V, and 34W are electrically
connected to each other may be provided at a position away from the
cooling portion 58 of the refrigerator 16.
[0065] In the superconducting motor 10 described above, further,
the phase coils 34U, 34V, and 34W are in contact with the cooling
portion 58 of the refrigerator 16 at the neutral point 70 at which
the phase coils 34U, 34V, and 34W are electrically connected to
each other. However, it is to be noted that the invention is not
limited to this. That is, for example, the coils 34 may be
connected to the cooling portion 58 of the refrigerator 16 at
portions of the coil end portions 36 other than those at the
neutral point 70 such that the phase coils 34U, 34V, and 34W are
insulated from each other.
[0066] In the superconducting motor 10 described above, further,
the one end portions 74U, 74V, and 74W of the phase coils 34U, 34V,
and 34W are placed in contact with the cooling portion 58 of the
refrigerator 16 by being fitted thereinto. However, it is to be
noted that the invention is not limited to this. That is, for
example, each of the one end portions 74U, 74V, and 74W may be
directly connected to the cooling portion 58 of the refrigerator 16
at only one end face (e.g., the longitudinal end face) thereof,
although the contact area, which contributes to heat transfer, is
relatively small.
[0067] Next, the insulation structure of the refrigerator 16 will
be described with reference to FIGS. 7 to 9. FIG. 7 shows an
enlarged side view of the cooling portion 58 of the refrigerator
16. FIG. 8A is a sectional view illustrating an example where an
annular insulator 84 is provided at an intermediate portion of the
cooling portion 58. FIG. 8B is a sectional view illustrating an
example where an annular insulator 84a having a relatively high
insulation resistance is provided at an intermediate portion of the
cooling portion 58. FIG. 9 is a sectional view illustrating an
example where an annular insulator 84b is provided at the boundary
between the coolant compressor 56 and the cooling portion 58.
[0068] Referring to FIG. 7, the refrigerator 16 is constituted of
the coolant compressor 56 and the cooling portion 58, and the front
end portion of the cooling portion 58 (i.e., the end portion on the
right side in FIG. 7) is in contact with the neutral point 70 of
the phase coils 34U, 34V, and 34W. The cooling portion 58 is shaped
like a stepped cylinder with its front end closed, and the
insulator 84 that is annular or ring-shaped is provided at an
intermediate portion of the cooling portion 58 in its axial
direction (i.e., the left-right direction in FIG. 7).
[0069] Referring to FIG. 8A, the cooling portion 58 of the
refrigerator 16 is constituted of a front end portion 86 that is
made of, for example, copper, which has a high thermal conductivity
and a high electric conductivity, a cylindrical intermediate member
88 that is made of, for example, stainless steel, the insulator 84
that is shaped like a short cylinder and is made of an insulating
material (e.g., ceramic), and a cylindrical base end portion 90
that is airtightly coupled with the coolant compressor 56 via a
flange portion 92 and is made of, for example, stainless steel. The
front end portion 86, the intermediate member 88, the insulator 84,
and the base end portion 90 are airtightly bonded using a soldering
metal, such as soldering gold, soldering silver, and soldering
nickel. Further, it is desirable that the insulator 84 be made of a
material having a low thermal conductivity, and for this reason,
alumina is especially preferred among various ceramic
materials.
[0070] In the cooling portion 58 structured as described above, the
insulator 84 serves as an insulation structure between the front
end portion 86 in contact with the coils 34 and the base end
portion 90 connected to the coolant compressor 56. Therefore even
when the potential at the neutral point 70 has changed from zero
due to a disturbance in motor currents, which may be caused for
some reasons, it is possible to prevent large currents from flowing
from the cooling portion 58 to the coolant compressor 56, and thus
protect the refrigerator 16 incorporating a linear motor, and so
on.
[0071] Further, in the example illustrated in FIG. 8B, the inner
diameter of the insulator 84a is equal to the diameters of the
intermediate member 88 and the base end portion 90, and the
peripheral wall of the insulator 84a protrudes radially outward, so
that the total wall length of the insulator 84a is relatively
large. Thus, the use of the insulator 84a provides a higher
insulation resistance and improves the insulation performance.
[0072] Further, in the example illustrated in FIG. 9, the insulator
84b that is shaped like a short cylinder is disposed between an
attachment portion 57 of the coolant compressor 56, to which the
base end portion 90 of the cooling portion 58 is connected, and the
base end portion 90 of the cooling portion 58, not at an
intermediate portion of the cooling portion 58, that is, an
insulation structure is provided at the boundary between the
cooling portion 58 and the coolant compressor 56. This structure
reduces the number of portions to be bonded using the soldering
metal and thus eases the production of the cooling portion 58.
[0073] Next, a superconducting motor 10a of a second embodiment of
the invention will be described with reference to FIGS. 10 and 11.
In the following, the structure of the superconducting motor 10a,
which is different from that of the above-described superconducting
motor 10 of the first embodiment and the effects achieved owing to
the different structure will be mainly described. In the following
descriptions, the structural elements of the superconducting motor
10a that are identical or similar to those of the superconducting
motor 10 will be denoted by the same or similar reference numerals,
and the descriptions on them will be omitted to avoid
repetitions.
[0074] FIG. 10 shows a sectional view of the superconducting motor
10a of the second embodiment that is taken along the axial
direction thereof and also shows the side faces of some portions of
the superconducting motor 10a. FIG. 11 is a view schematically
illustrating an electric connection in the superconducting motor
10a, shown in FIG. 10, in which the phase coils 34U, 34V, and 34W
are connected to each other at two neutral points 70a and 70b.
[0075] The superconducting motor 10a of the second embodiment has a
refrigerator 17 in addition to the refrigerator 16. In the
following descriptions, the refrigerators 16 and 17 will be
referred to as "the first refrigerator 16" and "the second
refrigerator 17", respectively. The second refrigerator 17 is
attached to the endplate 26 located at the other axial side via a
structure that is the same as that for the refrigerator 16.
[0076] The first refrigerator 16 and the second refrigerator 17 are
arranged so as to face each other such that the piston 54 in the
first refrigerator 16 and the piston 54 in the second refrigerator
17 move collinearly. That is, the first refrigerator 16 and the
second refrigerator 17 are axially opposed to each other. In the
refrigerator 16 and the second refrigerator 17, the respective
coolant compressors 56 are driven such that the respective pistons
54 move in opposite directions. More specifically, the first
refrigerator 16 and the second refrigerator 17 are driven such that
the compression and expansion strokes of the piston 54 in the first
refrigerator 16 and those of the piston 54 in the second
refrigerator 17 are synchronized with each other. With this
arrangement and driving manner, the rotational moments that are
exerted on the superconducting motor 10a by the first refrigerator
16 and the second refrigerator 17, respectively, when the pistons
54 are moving can be offset, and thus vibrations and noises can be
reduced.
[0077] Further, referring to FIG. 11, the superconducting motor 10a
has two neutral points, that is, the first neutral point 70a and
the second neutral point 70b. More specifically, two groups of the
phase coils 34U, 34V, and 34W are connected in parallel to each
other, and the phase coils 34U, 34V, and 34W in one of the two
groups are electrically connected to each other at the first
neutral point 70a, while the phase coils 34U, 34V, and 34W in the
other group are electrically connected to each other at the second
neutral point 70b. The first neutral point 70a corresponds to the
neutral point 70 of the above-described superconducting motor 10 of
the first embodiment, and the second neutral point 70b is provided
at the coil end portions 36 located at the other axial side and is
cooled by the cooling portion 58 of the second refrigerator 17.
Other structures of the superconducting motor 10a are the same as
those of the superconducting motor 10.
[0078] In the superconducting motor 10a of the second embodiment,
as described above, the coils 34 of the phase coils 34U, 34V, and
34W can be efficiently, and promptly, cooled down to a desired
ultralow temperature from the neutral points 70a and 70b provided
at the respective axial sides, by the two refrigerators 16 and 17,
that is, not via parts and portions having a large thermal
capacity, such as the stator core 30. Thus, the time required to
start up the superconducting motor 10a is relatively short, and the
electric power consumption of each refrigerator 16 and 17 is
relatively small.
[0079] Further, in the superconducting motor 10a, the piston 54 of
the first refrigerator 16 and the piston 54 of the second
refrigerator 17 are arranged to move collinearly, and the
respective coolant compressors 56 are driven such that the
respective pistons 54 move in opposite directions. Therefore, the
rotational moments that are exerted on the superconducting motor
10a by the first refrigerator 16 and the second refrigerator 17,
respectively, when the pistons 54 are moving can be offset, and
thus vibrations and noises can be reduced.
[0080] Next, a superconducting motor 10b of a third embodiment of
the invention will be described with reference to FIG. 12. The
superconducting motor 10b of the third embodiment is different from
the superconducting motor 10a of the second embodiment only in the
arrangement of the refrigerators 16 and 17, and therefore, in the
following, only the differences therebetween will be described and
other structural elements of the superconducting motor 10b, that
is, the structural elements of the superconducting motor 10b that
are the same as those of the superconducting motor 10a will be
denoted by the same reference numerals, and the descriptions on
them will be omitted to avoid repetitions.
[0081] In the superconducting motor 10b, the coolant compressors 56
of the first refrigerator 16 and the second refrigerator 17 are
attached on the outer peripheral wall of the motor case 40, and
coolant pipes 62 extending from the respective coolant compressors
56 are connected to the respective cooling portions 58. In this
case, too, the piston 54 in the first refrigerator 16 and the
piston 54 in the second refrigerator 17 are driven so as to move in
opposite directions. Other structures of the superconducting motor
10b are the same as those of the superconducting motor 10a.
[0082] With the superconducting motor 10b of the third embodiment,
the same effects as those of the superconducting motor 10a of the
second embodiment can be achieved, and further, the axial length of
the superconducting motor 10b is shorter than that of the
superconducting motor 10a, which increases the freedom in mounting
the superconducting motor in a vehicle.
[0083] Next, a superconducting motor 10c of a fourth embodiment of
the invention will be described with reference to FIG. 13. The
superconducting motor 10c of the fourth embodiment is different
from the superconducting motor 10a of the second embodiment only in
the arrangement of the first refrigerator 16 and the second
refrigerator 17, and therefore, in the following, only the
differences therebetween will be described and other structural
elements of the superconducting motor 10c, that is, the structural
elements of the superconducting motor 10c that are the same as
those of the superconducting motor 10a will be denoted by the same
reference numerals, and the descriptions on them will be omitted to
avoid repetitions.
[0084] In the superconducting motor 10c, the first refrigerator 16
and the second refrigerator 17 are arranged, respectively, at
positions opposed to each other in the radial direction of the
stator 14, and the coolant compressors 56 are driven such that the
pistons 54 move in the same direction. In this case, too, the
piston 54 in the first refrigerator 16 and the piston 54 in the
second refrigerator 17 reciprocate axially, although not
collinearly unlike in the superconducting motor 10a described
above. Other structures of the superconducting motor 10c are the
same as those of the superconducting motor 10a.
[0085] More specifically, in the superconducting motor 10c, the
first refrigerator 16 is arranged at a position that is 180 degrees
away from the second refrigerator 17 in the circumferential
direction and is opposed to the second refrigerator 17. In this
case, the piston 54 in the second refrigerator 17 moves, on its
expansion stroke, toward the right side of FIG. 13 when the piston
54 in the first refrigerator 16 moves, on its compression stroke,
toward the right side of the FIG. 13, and on the other hand, the
piston 54 in the second refrigerator 17 moves, on its compression
stroke, toward the left side of FIG. 13 when the piston 54 in the
first refrigerator 16 moves, on its expansion stroke, toward the
left side of the FIG. 13. That is, the pistons 54 move in the same
direction. Since the coolant compressors 56 of the first
refrigerator 16 and the second refrigerator 17 are driven as
described above, the rotational moments that are exerted on the
superconducting motor 10c by the first refrigerator 16 and the
second refrigerator 17, respectively, when the pistons 54 are
moving can be offset or diminished, and thus vibrations and noises
can be reduced.
[0086] In the superconducting motor 10c, further, the first
refrigerator 16 and the second refrigerator 17 are arranged,
respectively, at the positions that are opposed to each other, as
described above. Therefore, the cooling portions 58 contact the
respective heat transfer members 60 at positions that are radially
opposed to each other (i.e., positions that are 180 degrees away
from each other in the circumferential direction), and cool the
neutral points 70a and 70b that are provided, respectively, at
these positions. As such, the time required to evenly cool the
entire portions of the coils 34, which are circumferentially
arranged, down to a desired ultralow temperature can be further
reduced as compared to the superconducting motor 10a of the second
embodiment.
[0087] Although the coils 34 formed of the respective
superconducting wires are cooled from the both axial sides using
the two refrigerators 16 and 17 in the superconducting motors 10a,
101), and 10c of the example embodiments described above, the
invention is not limited to this. That is, for example, the coils
34 may be cooled from the both axial sides using three or more
refrigerators.
[0088] While the invention has been described with reference to
example embodiments thereof, it is to be understood that the
invention is not limited to the described embodiments or
constructions. To the contrary, the invention is intended to cover
various modifications and equivalent arrangements. In addition,
while the various elements of the example embodiments are shown in
various combinations and configurations, other combinations and
configurations, including more, less or only a single element, are
also within the scope of the invention.
* * * * *