U.S. patent application number 09/758871 was filed with the patent office on 2002-07-11 for electric machine with laminated cooling rings.
Invention is credited to Liang, Feng, Miller, John Michael.
Application Number | 20020089242 09/758871 |
Document ID | / |
Family ID | 25053415 |
Filed Date | 2002-07-11 |
United States Patent
Application |
20020089242 |
Kind Code |
A1 |
Liang, Feng ; et
al. |
July 11, 2002 |
Electric machine with laminated cooling rings
Abstract
An electric machine in accordance with the invention includes a
stator core having first and second ends and having windings
therein with end turns of the windings protruding from the first
and second ends of the stator core. A rotor is rotatably positioned
within the stator core. First and second laminated aluminum ring
assemblies are positioned against the first and second ends,
respectively, of the stator core in contact with the housing.
Thermally conductive potting material is positioned between the end
turns and the respective first and second ring assembly at the
first and second ends of the stator core, thereby creating heat
dissipation paths from the end turns, through the potting material
and the ring assemblies to the housing.
Inventors: |
Liang, Feng; (Canton,
MI) ; Miller, John Michael; (Saline, MI) |
Correspondence
Address: |
BROOKS & KUSHMAN P.C./FGTI
1000 TOWN CENTER
22ND FLOOR
SOUTHFIELD
MI
48098
US
|
Family ID: |
25053415 |
Appl. No.: |
09/758871 |
Filed: |
January 11, 2001 |
Current U.S.
Class: |
310/45 ;
310/64 |
Current CPC
Class: |
Y02T 10/64 20130101;
H02K 9/22 20130101; H02K 9/223 20210101 |
Class at
Publication: |
310/45 ;
310/64 |
International
Class: |
H02K 009/22 |
Claims
What is claimed:
1. An electric machine comprising: a stator core having first and
second ends and having windings therein with end turns of the
windings protruding from the first and second ends of the stator
core; a rotor rotatably positioned within the stator core; first
and second laminated aluminum ring assemblies positioned against
the first and second ends, respectively, of the stator core and
contacting the housing; thermally conductive potting material
positioned between the end turns and the respective first and
second ring assembly at the first and second ends of the stator
core, thereby creating heat dissipation paths from the end turns,
through the potting material and the ring assemblies to the
housing.
2. The electric machine of claim 1, wherein said first and second
laminated aluminum ring assemblies each comprise a plurality of
aluminum laminations, each said aluminum lamination having a
plurality of radial slots formed therein to reduce eddy current
losses in each ring assembly.
3. The electric machine of claim 2, wherein each lamination of said
aluminum rings is insulated to further reduce eddy current losses
in each ring assembly.
4. The electric machine of claim 1, wherein said first and second
ring assemblies are positioned radially outwardly from the
respective end turns.
5. The electric machine of claim 2, wherein said plurality of
radial slots extend radially outward from an annular inner edge of
each said aluminum ring a distance sufficient to reduce eddy
currents in a plane perpendicular to a central axis of the electric
machine.
6. An electric machine comprising: a stator core having first and
second ends and having windings therein with end turns of the
windings protruding from the first and second ends of the stator
core; a rotor rotatably positioned within the stator core; first
and second laminated aluminum ring assemblies positioned against
the first and second ends, respectively, of the stator core and
contacting the housing; and thermally conductive potting material
positioned between the end turns and the respective first and
second ring assembly at the first and second ends of the stator
core, thereby creating heat dissipation paths from the end turns,
through the potting material and the ring assemblies to the
housing, wherein said first and second laminated aluminum ring
assemblies each comprise a plurality of aluminum laminations, each
said aluminum lamination having a plurality of radial slots formed
therein to reduce eddy current losses in each ring assembly.
7. The electric machine of claim 6 wherein each lamination of said
aluminum rings is insulated to further reduce eddy current losses
in each ring assembly.
8. The electric machine of claim 6 wherein said first and second
ring assemblies are positioned radially outwardly from the
respective end turns.
9. The electric machine of claim 6 wherein said plurality of radial
slots extend radially outward from an annular inner edge of each
said aluminum lamination a distance sufficient to reduce eddy
currents in a plane perpendicular to a central axis of the electric
machine.
10. The electric machine of claim 6, wherein said thermally
conductive potting material is flexible to accommodate for thermal
expansion of various components of the electric machine.
11. An electric machine comprising: a stator core having first and
second ends and having windings therein with end turns of the
windings protruding from the first and second ends of the stator
core; first and second laminated aluminum ring assemblies
positioned against the first and second ends, respectively, of the
stator core and contacting the housing; and flexible thermally
conductive potting material positioned between the end turns and
the respective first and second ring assembly at the first and
second ends of the stator core, thereby creating heat dissipation
paths from the end turns, through the potting material and the ring
assemblies to the housing.
12. The electric machine of claim 11, wherein said first and second
laminated aluminum ring assemblies each comprise a plurality of
aluminum laminations, each said aluminum lamination having a
plurality of radial slots formed therein to reduce eddy current
losses in each ring assembly.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an electric machine having
laminated cooling rings adjacent end turns of the stator core
windings for transferring heat from the windings to the
housing.
[0003] 2. Background Art
[0004] The cooling of stator windings of electric machines is
critical for providing satisfactory motor performance, reliability
and durability. This issue becomes even more pressing when the
motor is required to have a high power density (kW/m.sup.3) and low
specific weight. An integrated starter/alternator is a good example
where the electric motor is required to have high power density,
low specific weight, and good cooling capability because of
packaging constraints, fuel economy requirements, and the fact that
the motor is in the engine compartment.
[0005] Thermally conductive epoxy potting materials have been
applied on the end turn windings to improve the cooling of an
electric motor. FIG. 1 shows a prior art motor 10 having such a
feature. As shown, the motor 10 consists of a rotatable rotor 12
rotatably positioned within a stator core 14. The stator core 14
has first and second ends 16,18 with end turns 20,22 of the
windings extending from the ends 16,18, respectively. A housing 24
having end plates 26,28 encloses the stator core, windings and
rotor. A thermally conductive potting material 30 is positioned
over each of the end turns 20,22 for carrying heat directly from
the end turns 20,22 to the housing 24 for heat dissipation.
[0006] This potting technology provides limited value because the
potting material has a fairly high thermal resistance, which limits
the heat dissipation capacity. Additionally, the cooling potential
of the potting material cannot be fully utilized because of gaps
which are developed between the potting material and the winding,
and between the potting material and the housing as a result of
thermal cycling of the motor. The reason for the gap development is
that the potting material, the winding and the housing have
different thermal expansion coefficients. The gaps are filled with
air, which provides minimal thermal conductivity.
[0007] Accordingly, it is desirable to provide an improved method
and apparatus for cooling an electric machine.
SUMMARY OF THE INVENTION
[0008] The present invention improves upon the above-described
prior art cooling method by providing two laminated aluminum ring
assemblies at the opposing ends of the stator core which are
embedded within the potting material. The laminated aluminum rings
substantially enhance heat dissipation, while the laminations
reduce eddy current buildup within the rings.
[0009] In a preferred embodiment, each lamination of the rings has
a plurality of radially extending slots which provide air gaps to
minimize eddy currents in a plane perpendicular to the central axis
of the motor.
[0010] More specifically, the present invention provides an
electric machine including a stator core having first and second
ends and having windings therein with end turns of the windings
protruding from the first and second ends of the stator core. A
rotor is rotatably positioned within the stator core. First and
second laminated aluminum ring assemblies are positioned against
the first and second ends, respectively, of the stator core in
contact with the housing. Thermally conductive potting material is
positioned between the end turns and the respective first and
second ring assembly at the first and second ends of the stator
core, thereby creating heat dissipation paths from the end turns,
through the potting material and the ring assemblies to the
housing.
[0011] Accordingly, an object of the invention is to provide an
improved method and apparatus for cooling an electric machine
wherein laminated aluminum ring assemblies are provided at opposing
ends of the stator core for dissipating heat through a potting
material from the end turns of the windings.
[0012] The above object and other objects, features and advantages
of the invention are readily apparent from the following detailed
description of the best mode for carrying out the invention when
taken in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 FIG. 1 shows a schematically arranged partially
cut-away vertical cross-sectional view of a prior art electric
motor;
[0014] FIG. 2 shows a schematically arranged partially cut-away
vertical cross-sectional view of an electric motor in accordance
with the present invention; and
[0015] FIG. 3 shows a plan view of a ring for use with the ring
assemblies shown in FIG. 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0016] The present invention will now be described with reference
to FIG. 2, wherein like reference numerals will be used to describe
like components as described previously with respect to FIG. 1.
[0017] As shown, the present invention provides an electric machine
10 including a rotor 12 rotatably positioned within a stator core
14. The stator core 14 has first and second opposing ends 16,18
with end turns 20,22 of the stator core windings protruding from
the respective ends 16,18. A housing 24 includes first and second
end plates 26,28, which enclose the stator and rotor assembly.
[0018] A potting material 30 is positioned around the first and
second end turns 20,22 of the windings. First and second laminated
aluminum rings 32,34 are positioned at the first and second ends
16,18, respectively, of the stator core 14 in contact with the
housing 24 for carrying heat from the end turns 20,22 through the
potting material 30, through the laminated aluminum rings 32,34 to
the housing 24.
[0019] The housing 24 may be liquid cooled or air cooled, using
configurations that are well known in the art.
[0020] The laminations of the laminated aluminum ring assemblies
32,34 are insulated to reduce eddy current losses. Additionally,
because the magnetic fields around the end turn windings 20,22 are
three-dimensional in nature, the invention also contemplates
providing slots in the laminated aluminum rings extending radially,
as shown in FIG. 3, to further reduce the eddy current in the
rings. As shown in FIG. 3, each lamination (ring) 36 of the
laminated ring assemblies 32,34 is provided with a plurality of
radially extending slots 38 extending from the annular inner edge
40 of each lamination 36. These slots 38 extend approximately
one-half the width of each ring 36 to reduce eddy currents in a
plane perpendicular to a central axis of the electric machine.
[0021] The present invention significantly improves cooling
capability over the above-described prior art methods. Because the
aluminum of the ring assemblies has much higher thermal
conductivity than the potting material (about 300 times higher),
this invention has much better cooling capability, and as a result,
the winding temperature will be significantly lower.
[0022] The potential of this cooling method is fully utilized
because there will not be any gaps developed between the winding
and the layer of potting material and between the ring and the
potting material. The reason is that a flexible potting material 30
can be used. Even though the flexible potting material has higher
thermal resistance than the non-flexible potting material, the
total thermal resistance from the windings to the housing is still
much lower than that of the existing potting technology. This is
because the potting material is minimized in thickness. The
existing potting technology must use a non-flexible potting
material, which has a lower thermal resistance than the flexible
one, for the thermal resistance reason because of the thickness of
the potting material layer.
[0023] Another advantage of the present invention is that motor
efficiency will be improved. Since the invention can lower the
winding temperature significantly, the copper loss in the winding
will be reduced significantly because lower temperature leads to
lower winding resistance.
[0024] The aluminum rings potted to the end windings also improves
the stiffness of the electric machine.
[0025] This invention has a wide range of applications. It can be
used for any variety of electric machines, but has particular
applicability in the auto industry because the auto industry
typically provides harsh thermal operating conditions. For example,
the invention can be used in traction motors for fuel cell EV, pure
EV and hybrid EV (electric vehicle). Also, an integrated
starter/alternator or high output alternator are good applications.
The simplicity of the design makes the invention very easy to
implement.
[0026] While the best mode for carrying out the invention has been
described in detail, those familiar with the art to which this
invention relates will recognize various alternative designs and
embodiments for practicing the invention within the scope of the
appended claims.
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