U.S. patent application number 09/756959 was filed with the patent office on 2002-07-11 for electric motor having armature coated with a thermally conductive plastic.
Invention is credited to Du, Hung T..
Application Number | 20020089240 09/756959 |
Document ID | / |
Family ID | 25045775 |
Filed Date | 2002-07-11 |
United States Patent
Application |
20020089240 |
Kind Code |
A1 |
Du, Hung T. |
July 11, 2002 |
Electric motor having armature coated with a thermally conductive
plastic
Abstract
An electric motor having an armature which includes a coating of
thermally conductive plastic applied in a conventional injection
molding process. The armature also includes a fan which is
integrally formed from the thermally conductive plastic applied to
the armature. The process of molding thermally conductive plastic
around the armature and integrally forming a fan at one end of the
armature completely eliminates the need to apply one or more
coatings of a trickle resin to the armature. It also eliminates the
need to separately form a fan and to secure the separately formed
fan by a suitable adhesive to the armature, which together
significantly simplify and reduce the manufacturing cost of the
armature. The thermally conductive molded plastic coating also
better fills the spaces between the magnet wires wound around the
armature, thus promoting even more efficient cooling of the
armature during use and better holding of the magnet wires
stationary relative to one another.
Inventors: |
Du, Hung T.; (Reisterstown,
MD) |
Correspondence
Address: |
Harness, Dickey & Pierce, P.L.C.
P.O. Box 828
Bloomfield Hills
MI
48303
US
|
Family ID: |
25045775 |
Appl. No.: |
09/756959 |
Filed: |
January 9, 2001 |
Current U.S.
Class: |
310/43 ;
310/45 |
Current CPC
Class: |
H02K 3/30 20130101; H02K
9/223 20210101; H02K 23/00 20130101; H02K 3/51 20130101; Y10T
29/49009 20150115; Y10T 29/49011 20150115; H02K 5/08 20130101; H02K
9/22 20130101; Y10T 29/49012 20150115; H02K 13/006 20130101; H02K
15/12 20130101; H02K 9/06 20130101; H02K 3/487 20130101; Y10T
29/49071 20150115 |
Class at
Publication: |
310/43 ;
310/45 |
International
Class: |
H02K 001/04 |
Claims
What is claimed is:
1. An electric motor comprising: a stator: an armature having an
armature shaft and being disposed within said stator, wherein said
armature includes a plurality of magnet wires formed in a plurality
of coils, and wherein ends of said magnet wires are secured to a
commutator associated with said armature shaft; a thermally
conductive plastic coating molded over said armature and said ends
of said magnet wires to at least substantially encase said magnet
wires in said plastic; and a fan molded at one end of said armature
shaft from said thermally conductive plastic.
2. The electric motor of claim 1, wherein said fan is integrally
formed from said thermally conductive plastic used to at least
substantially encase said magnet wires.
3. The electric motor of claim 1, wherein said armature includes an
armature stack having a plurality of circumferentially arranged
slots within which said magnet wires are disposed; and wherein said
thermally conductive plastic fills said slots.
4. The electric motor of claim 1, wherein said thermally conductive
plastic comprises a composite thermoplastic.
5. An armature for an electric motor, comprising: a lamination
stack; an armature shaft extending coaxially through said
lamination stack; a plurality of magnet wires wound around said
lamination stack; a commutator disposed on said armature shaft to
which ends of said magnet wires are electrically coupled; and a
thermally conductive plastic coating molded over said armature, a
portion of said coating forming an integrally formed fan adjacent
said armature.
6. The armature of claim 5, wherein said thermally conductive
plastic comprises a composite thermoplastic.
7. An electric motor for use with a power tool, said electric motor
comprising: a stator; an armature disposed within said stator; a
thermally conductive plastic at least partially encasing a portion
of said armature; and a molded fan formed from said thermally
conductive plastic and disposed adjacent one end of said armature
to provide a cooling airflow over said armature during use of said
motor.
8. A method for forming an electric motor, said method comprising
the steps of: providing a stator; providing an armature having a
plurality of magnet wires wound therearound; molding a thermally
conductive plastic over at least a portion of said armature to at
least partially encase said magnet wires; and molding a fan at one
end of said armature from said thermally conductive plastic.
9. The method of claim 8, wherein the step of molding a thermally
conductive plastic over a portion of said armature comprises the
step of molding a composite thermoplastic over at least said
portion of said armature.
10. A method for forming an armature for an electric motor, said
method comprising the steps of: providing a lamination stack;
providing an armature shaft for supporting said lamination stack;
providing a commutator disposed on said armature; winding a
plurality of magnet wires around said lamination stack and securing
ends of said magnet wires to said commutator; performing a molding
step to mold a thermally conductive plastic coating over a
substantial portion of said lamination stack to at least
substantially encase said magnet wires therewithin, and to form a
fan adjacent one end of said lamination stack from said thermally
conductive plastic coating.
11. The method of claim 10, wherein said molding step comprises
using a composite thermoplastic to form said thermally conductive
plastic coating.
Description
TECHNICAL FIELD
[0001] This invention relates to electric motors, and more
particularly to an electric motor having an armature which is at
least structurally encased within a thermally conductive plastic,
and wherein a fan is integrally formed from a portion of the
thermally conductive plastic at one end of the armature.
BACKGROUND OF THE INVENTION
[0002] Electric motors are used in a wide variety of applications
involving power tools such as drills, saws, sanding and grinding
devices, yard tools such as edgers and trimmers, just to name a few
such tools. These devices all make use of electric motors having an
armature and a stator. The armature is typically formed from a
lamination stack around which a plurality of windings of magnet
wires are wound. The magnet wires are coupled at their ends to
tangs on a commutator disposed on an armature shaft extending
coaxially through the lamination stack. The ends of the magnet
wires are secured to the commutator.
[0003] In the manufacturing process for the armature described
above, once the magnet wires have been secured to the commutator, a
"trickle" resin is applied over the magnet wires and over the ends
of the magnet wires where they attach to tangs associated with the
commutator. The process of applying the trickle resin is a somewhat
difficult process to manage to obtain consistent results. It also
has a number of drawbacks, not the least of which is the cost and
difficulty of performing it with reliable, consistent results.
[0004] Initially, the trickle process requires the use of a
relatively large and expensive oven to carefully preheat the
partially assembled armatures to relatively precise temperatures
before the trickle resin can be applied. The temperature of the
trickle resin also needs to be carefully controlled to achieve
satisfactory flow of the resin through the slots in the lamination
stack of the armature. It has proven to be extremely difficult to
achieve consistent, complete flow of the trickle resin through the
slots in the lamination stack. As such, it is difficult to achieve
good flow inbetween the magnet wires with the trickle resin to
satisfactorily insulate the magnet wires from one another and hold
them stationary relative to each other. A cooling period must then
be allowed during which air is typically forced over the armatures
to cool them before the next manufacturing step is taken. Further
complicating the manufacturing process is that the trickle resin
typically has a short shelf life, and therefore must be used within
a relatively short period of time.
[0005] With present day manufacturing techniques, an additional or
secondary coating of a higher viscosity trickle resin is often
required to protect the armature (and specifically the magnet
wires) from abrasive metal particles that are drawn in and over the
armature by the armature's fan when the armature is used in
connection with various grinders and sanders. This serves to
further increase the manufacturing cost and complexity of the
armature.
[0006] Still another drawback with the trickle process is the
relatively high number of armatures which are often rejected
because of problems encountered during the process of applying the
trickle resin to an otherwise properly constructed armature. Such
problems can include contamination of the commutator of the
armature by the trickle resin during the application process, as
well as uneven flow of the trickle resin if the pump supplying the
resin becomes momentarily clogged. Accordingly, the difficulty in
controlling the trickle resin application process produces a
relatively large scrap rate which further adds to the manufacturing
cost of electric motors.
[0007] Still another disadvantage with present day electric motors
is that the fan which is typically attached at one end of the
armature is a separately formed component which must be glued or
otherwise secured to the armature in a separate manufacturing step.
This fan also is typically the first component to fail if the motor
is stressed. This occurs when the fan simply melts due to
overheating of the motor. The use of a separately formed component
also takes up additional space on the armature which increases the
overall size of the armature.
[0008] In view of the foregoing, it would be highly desirable to
eliminate the steps of applying the trickle resin and securing a
separately formed fan to an armature. More specifically, it would
be highly desirable if these two steps could be replaced by a
single step which achieves the object of more thoroughly coating
the magnet wires of the armature with a thermally conductive
material, in addition to forming an integrally formed fan, all with
a single manufacturing step.
SUMMARY OF THE INVENTION
[0009] The present invention is directed to an armature for an
electric motor which includes a thermally conductive coating
applied over the magnet wires wound around the lamination stack
thereof, to thereby form an excellent means for dissipating heat
and holding the magnet wires stationary as well as holding the ends
of the magnet wires secured to tangs on the commutator. It is also
a principal object of the present invention to provide a fan which
is integrally molded at one end of the armature from the thermally
conductive plastic in a single manufacturing step. The integrally
molded fan better resists the extreme temperatures that may be
encountered if the motor is stressed during use.
[0010] In one preferred embodiment the thermally conductive plastic
is applied by a well known injection molding process. As such, the
need for a trickle oven and the difficult to manage application of
the trickle resin is completely eliminated.
[0011] The integrally formed fan is formed when the armature is
placed into a suitable molding tool during the injection molding
process. The resulting injection molded fan is much more resistant
to high temperatures that may be encountered during use of the
armature with which it is associated, and further requires less
space than previously formed, independent fan components. The
smaller fan allows the overall dimensions of the armature to be
reduced thereby allowing a smaller motor to be formed for a given
ampere rating. Forming the fan integrally with the thermally
conductive plastic which coats the magnet wires also eliminates the
need to insert portions of the fan into the slots in the lamination
stack. This allows more room within the slots in the lamination
stack for the magnet wires which allows the power rating of the
motor to be increased beyond what would normally be attainable with
a conventionally attached and independently formed fan
component.
[0012] The armature of the present invention thus significantly
reduces the complexity and cost of the manufacturing process by
completely eliminating the steps involving the application of
trickle resin and the attachment of a separately formed fan
component, which are two of the most expensive and cumbersome
manufacturing steps performed with present day electric motors.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The various advantages of the present invention will become
apparent to one skilled in the art by reading the following
specification and subjoined claims and by referencing the following
drawings in which:
[0014] FIG. 1 is a side elevation view of a prior art armature
which incorporates the conventional trickle resin coating and
separately manufactured fan secured by adhesives to the armature;
and
[0015] FIG. 2 is a side elevation view of an armature in accordance
with a preferred embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] Referring to FIG. 1, there is illustrated a prior art
armature 10 made in accordance with a conventional manufacturing
process incorporating the trickle resin application steps described
hereinbefore. The armature 10 incorporates a lamination stack 12
having a plurality of longitudinal slots 14 disposed
circumferentially therearound. Wound within the slots 14 is a large
plurality of magnet wires 16 forming coils. An armature shaft 18
extends coaxially through the lamination stack 12 and includes a
commutator 20. An independently formed plastic fan 22 is secured,
typically by adhesives, to the lamination stack 14. The fan 22
typically includes a plurality of legs 24 which project into the
slots 14, thus taking up space which would more preferably be
occupied by the magnet wires 16. Trickle resin 26 is applied over
the magnet wires 16, in the slots 14, and also at the tangs 25
where the ends of the magnet wires 16a attach to the commutator
20.
[0017] Referring now to FIG. 2, a motor 100 in accordance with a
preferred embodiment of the present invention is disclosed. The
motor 100 includes an armature 102 and a stator 104, the stator
being illustrated in highly simplified fashion. The armature 102
incorporates a lamination stack 106 having a plurality of
longitudinal slots 108 arranged circumferentially therearound. A
plurality of magnet wires 110 are wound in the slots 108 to form a
plurality of coil windings. An armature shaft 112 extends coaxially
through the lamination stack 106 and has disposed on one end
thereof a commutator 114. A thermally conductive plastic coating
116 is injection molded over the armature 102 so that the plastic
flows into and through each of the slots 108. The thermally
conductive plastic coating 116 is applied by placing the armature
102 in a suitable injection molding tool and then injecting the
thermally conductive plastic 116 under a suitably high pressure
into the molding tool. The thermally conductive plastic 116
preferably at least partially encases the magnet wires 110, and
more preferably completely encases the magnet wires to form an
excellent means for transferring heat therefrom. The plastic 116
also encases the ends 118 of the magnet wires 110 which are secured
to tangs 120 operably associated with the commutator 114.
[0018] A principal advantage of the present invention is that a fan
122 is also integrally formed during the molding of the thermally
conductive plastic 116 at one end of the lamination stack 106.
Forming the fan 122 as an integral portion of the thermally
conductive plastic 116 serves to completely eliminate the
manufacturing steps in which a trickle resin is applied to the
lamination stack 106 and then a separately formed fan is adhered to
the lamination stack 106.
[0019] The molding of the thermally conductive plastic 116 to
substantially or completely encase the magnet wires 110 serves to
efficiently conduct heat away from the magnet wires and also to
more evenly fill the gaps inbetween the magnet wires where they
extend in the slots 108. Thus, the thermally conductive plastic 116
even more efficiently serves to secure the magnet wires 110 to the
lamination stack 106 to prevent movement of the wires, as well as
to secure the magnet wires to the tangs 120 and to improve the
conduction of heat from the wires.
[0020] The molding of the fan 122 as an integral portion of the
thermally conductive plastic coating 116 also provides a
significant manufacturing benefit by removing the cost associated
with separately forming such a fan component and then securing the
component via an adhesive to the lamination stack 106. This allows
the fan 122 to be constructed even more compactly against the
lamination stack 106 which allows a motor to be constructed which
requires less space than previously developed motors employing
independently formed fans.
[0021] In the preferred embodiment the thermally conductive plastic
coating 116 comprises Konduit.TM. thermoplastic commercially
available from LNP Engineering Plastics of Exton, Pa. However, it
will be appreciated that any material which could be injection
molded and which is thermally conductive could be used.
[0022] Another advantage of having the fan 122 molded from the
thermally conductive plastic is that the fan will be even more
resistant to high temperatures which might be encountered during
use which stresses the motor 100. With previously developed motors,
the fan mounted to the armature thereof is often the first
component to fail because of high temperatures encountered during
periods of high stress of the motor. The armature 100 of the
present invention, with its integrally molded fan 122, is
significantly more resistant to failure due to high temperatures.
The injection molding of a thermally conductive plastic also more
efficiently fills the spaces and voids inbetween the magnet wires
110 extending through the lamination stack slots 108, thus
promoting even more efficient cooling of the armature 102 during
use. The increase in heat transfer is expected to allow even larger
gauge magnet wires 110 to be employed on a given size armature,
thus increasing the amp rating which can be attained with a motor
of given dimensions over a comparably sized motor employing trickle
resin sealing of the magnet wires.
[0023] Those skilled in the art can now appreciate from the
foregoing description that the broad teachings of the present
invention can be implemented in a variety of forms. Therefore,
while this invention has been described in connection with
particular examples thereof, the true scope of the invention should
not be so limited since other modifications will become apparent to
the skilled practitioner upon a study of the drawings,
specification and following claims.
* * * * *