Background of the Invention
Field of the Invention
The present invention relates to structures for directing the air
flow in an electric motor, and in particular to structures for directing the air
flow through the stator of an electric motor.
Brief Description of the Related Art
As shown in Fig. 2, the stator 10 of a typical electric motor is
formed by a series of coils 12 held in a solid body 14, e.g., a series of metal
plates laminated together. The coils are held in position relative to one another
by a tie ring 16.
The stator 10 is cooled by air blowing past the stator 10, through
any available air channels in the stator 10 and through the gap between the stator
10 and the rotor 17, as shown generally by the arrows A. Only the ends 18 of the
coils are directly exposed to the air flow, and while a chamfer 19 helps direct
air towards the ends 18, very little of the air actually passes through the ends
18 due to the high flow resistance through the ends. Instead, most of the air
flows around the outside surface of the coil ends.
One proposal to overcome this problem has been disclosed in DE-B-1146581
in which baffles are used to redirect the airflow.
SUMMARY OF THE INVENTION
The present invention seeks to improve the cooling efficiency of
the air flow through a stator by providing a simple, effective structure to force
more of the air flowing through the stator to actually pass through the coil ends.
According to the invention there is provided an electric motor comprising:
a) an annular stator having a plurality of stator coils circumferentially spaced
thereabout and a stator body in which said stator coils are embedded, ends of
the stator coils extending out of the stator body and said stator body having at
least one air passage extending therethrough; b) a stator frame supporting and
surrounding the stator and having an annular shoulder formed therein; c) a rotor
rotatably mounted inside said stator; d) a plurality of rotor supports for rotatably
supporting said rotor; e) an annular air baffle having a substantially U-shaped
cross-section mounted adjacent to an end of said stator with a radially outer
edge of said air baffle being loosely held between said annular shoulder and said
rotor supports; and f) a felt pad between said air baffle and said coils; characterized
by: g) a plurality of glass ties extending through an inner side of said air baffle,
through said felt pad and around said coils to hold said air baffle, felt pad (46)
and coils together.
Brief Description of the Drawings
The invention will now be described in further detail, by way of
example, with reference to the drawings in which:
Detailed Description of the Preferred Embodiments
- Fig. 1 is a cross sectional view of part of an electric motor including an
air baffle according to the present invention.
- Fig. 2 is a cross sectional view similar to part of Fig. 1, but showing a structure
according to the prior art.
- Fig. 3 is a detail of Fig. 1.
- Fig. 4 is a perspective view of a portion of the air baffle and stator of the
electric motor of Fig. 1, unwrapped into a nearly straight line for clarity of
Fig. 1 is a cross-sectional view of the upper part of an electric
motor having an air baffle according to the present invention. The motor includes
a stator 20 and a rotor 22. The stator 20 is supported by a stator frame 24. A
plurality of circumferentially spaced rotor supports 26 (only one of which is shown
in the drawing) are mounted to the stator frame 24 to support the rotor 22 prior
to being mounted, for example, to a diesel engine.
The stator 20 is formed by a plurality of circumferentially spaced
coils 28 and a body 30, e.g., a series of metal plates laminated together. The
main part of each coil 28 preferably is embedded inside the stator body 30 to
be thermally connected thereto, with only the end portions 32 of each coil 28 exposed
outside of the stator body 30. Preferably, the stator body 30 also is provided
with a plurality of air passages 34 through which air can flow to cool the stator
body 30 (and thereby cool the coils 28).
According to the present invention, an air baffle 40 is provided
at the air outlet end of the stator 20. The air baffle 40 extends between the stator
frame 24 and the end portions 32 of the coils 28, so that air flowing through
the air passages 34 must also pass through the coil end portions 32 to exit the
As best seen in Figs. 3 and 4, the air baffle 40 preferably is an
annular fiberglass composite structure, with a substantially U-shaped cross-section
for strength and flexibility. Fiberglass is well suited for this purpose, since
it is stiff, can withstand significant heat build-up and is easily formed into
a suitable shape.
The radially outer edge 42 of the air baffle 40 is flared out so
it is substantially in a radial plane. This outer edge then is loosely held in
an annular gap between the rotor supports 26 and a shoulder 44 formed in the stator
frame 24. With this mounting, the air baffle 40 can move back and forth in and
rotate around the annular gap, so it is both free to rotate and to move longitudinally
to a limited degree.
A felt pad 46 is positioned between the radially inner side 48 of
the air baffle 40 and the coils 28. Glass ties 50 extend through holes in the inner
side 48 of the air baffle 40 and the felt pad 46 to tie around the coil end portions
32. The ties 50 can be used with every coil 28, or with just a selected number
of coils 28 (as shown in Fig. 4). As will be apparent, with this structure the
air baffle 40 serves to hold the coils 28 in position relative to one another,
so that the prior art tie ring 16 may be eliminated.
After the coils 28, air baffle 40, felt pad 46 and glass ties 50
are completely assembled into the motor, they preferably are coated with varnish
(which for clarity has not been shown in the drawings) to protect the, stiffen
them and further bind them together. In some applications, it may be necessary
to provide one or more drain holes 52 for excess varnish to drain out, since the
air baffle 40 prevents the varnish from flowing out through the end of the motor.
However, the prior art chamfer 19 can be eliminated, so a stator frame according
to the present invention is less costly to make than a stator frame according
to the prior art.
According to a further aspect of the invention, felt spacers 54 are
placed between the end portions 32 of the coils to help maintain them in position.
These spacers 54 are placed in a staggered or serpentine arrangement (best seen
in Fig. 4) so that at most one side of any part of the coil end portions 32 is
covered by felt (and therefore insulated from the cooling air flow).
In a further preferred embodiment, additional spacers 56 are placed
between the coil end portions 32 and pressed against the felt pad 46. Frictional
engagement between these spacers 56 and the felt pad 46 will help hold the coil
end portions 32 in position. When varnish is applied, it will soak through both
felt pads and further strengthen the connection.
In operation, air is forced to flow through the gap between the stator
and the rotor and through any other available openings in the stator, e.g., between
the coils 28 or through the air passages 34. The air can be driven by any suitable
means, e.g., due to motion of a vehicle in which the motor is mounted, due to a
fan mounted to the motor rotor, or due to a fan elsewhere with air then ducted
to the motor.
A small amount of the air may still be able to flow past rather than
through the end portions 32 of the coils, as shown in Fig. 1 by the arrow B. However,
the bulk of the air will be forced by the air baffle 40 to flow through the end
portions 32 of the coils, as shown by the arrows C, thereby enhancing coil cooling.
Tests of the invention have been run using a motor of the type used
on a diesel-electric locomotive equipped with a prototype of the air baffle described
herein. Adding the air baffle resulted in a temperature decrease of 29°C for the
stator coils, and lowered hot spot temperatures in the felt spacers between the
coils by 50°C, even though air flow through the motor was reduced from the usual
4.25 m3/s. (9000 standard cubic feet per minute (SCFM)) to 4.01 m3/s.
(8500 SCFM). Adequate cooling was provided even upon further reduction in air
flow to 3,61 m3/s. (7650 SCFM) because of the improved cooling efficiency
resulting from use of the air baffle.
In an alternative to the above described embodiments, brackets or
some similar structure could be used to loosely hold the outer edge of the air
baffle in place, instead of the shoulder 44 and rotor support 26 described. Similarly,
the air baffle could have a variety of shapes, and could be mounted to the coils
in many different ways. Specifically, the "U" shaped cross section and fiberglass
material of the air baffle are not the only geometry and/or material that could
perform the described functions. Nor is it necessary that the baffle be of one
piece construction as a segmented multi-piece design could also work. In fact,
the initial test prototype was such a segmented design. Rather than being arranged
in a completely non-overlapping fashion, the felt spacers 54 could slightly overlap
without unduly hindering the cooling effects (though maximum cooling would be
attained with no such overlap). Accordingly, this invention is intended to embrace
all such alternatives, modifications and variations which fall within the scope
of the appended claims.