U.S. patent application number 09/759966 was filed with the patent office on 2002-07-18 for split blade radial fan.
This patent application is currently assigned to Emerson Electric Co.. Invention is credited to Bostwick, Peter K..
Application Number | 20020094275 09/759966 |
Document ID | / |
Family ID | 25057617 |
Filed Date | 2002-07-18 |
United States Patent
Application |
20020094275 |
Kind Code |
A1 |
Bostwick, Peter K. |
July 18, 2002 |
Split blade radial fan
Abstract
A fan has a plurality of blades that are each configured to
induce radial-flow adjacent the trailing edge of the blade while
also being configured to induce both radial-flow and axial-flow
near the base end of the blade. This is achieved by splitting each
of the blades into two sections and orienting the chord-line of the
blades near the hub of the fan at angle relative to the axis of the
hub while maintaining the chord-line of the blades parallel to the
axis near the trailing edges of the blades. This results in an
increased ability of the fan to draw air in axially as compared to
conventional radial-flow fans. The fan of the preferred embodiment
also makes use of an annular ring joining the trailing edges of the
blades. The ring has axially opposite sides that taper toward one
another as the ring extends radially inward and acts as a diverter
to channel air to axially opposite sides of an annular obstruction
in the flow path of air being exhausted from the fan, thereby
further increasing the fan's efficiency.
Inventors: |
Bostwick, Peter K.;
(Maryland Heights, MO) |
Correspondence
Address: |
THOMPSON COBURN, LLP
ONE FIRSTAR PLAZA
SUITE 3500
ST LOUIS
MO
63101
US
|
Assignee: |
Emerson Electric Co.
|
Family ID: |
25057617 |
Appl. No.: |
09/759966 |
Filed: |
January 12, 2001 |
Current U.S.
Class: |
416/175 ;
416/183; 416/185 |
Current CPC
Class: |
F04D 29/30 20130101;
F04D 29/281 20130101 |
Class at
Publication: |
416/175 ;
416/183; 416/185 |
International
Class: |
F04D 029/30 |
Claims
What is claimed:
1. A fan comprising: a center hub having a center axis and a
peripheral surface, the center axis defining axial and radial
directions; and a plurality of blades configured and adapted to
draw air radially outward from the center axis by revolving with
the center hub about the center axis, the plurality of blades each
having a radially opposite base end and trailing edge, the base end
of each of the blades being attached to the hub and each of the
blades having an infinite number of cross-sections that each lie in
a plane tangential to and radially spaced from the center axis,
each of the blades having a first section extending radially inward
from its trailing edge and a second section extending radially
outward from its base end, cross sections of the first section of
each of the blades have chord-lines oriented parallel to the center
axis, cross-sections of the second section of each of the blades
have chord-lines oriented at an angle relative to the center axis,
and the angle of the chord-lines of the second section
cross-sections of each of the blades increases with increasing
radial distance of the cross-section from the center axis.
2. The fan of claim 1, wherein: substantially all of the
cross-sections of each of the blades have equal axial widths.
3. The fan of claim 1, wherein: the blades and the hub are one
monolithic piece.
4. The fan of claim 1, wherein: each of the cross-sections of the
first section of each of the blades is symmetric about its
chord-line.
5. The fan of claim 4, wherein: each of the cross-sections of the
first section of each of the blades is substantially
rectangular.
6. The fan of claim 1, wherein: the chord-line of the cross-section
of each of the blades located at the base end of each of the blades
is parallel to the center axis.
7. The fan of claim 1, wherein: each of the cross-sections of the
second section of each of the blades consist of first and second
portions, the first portion having opposite straight parallel sides
and the second portion having opposite straight parallel sides.
8. The fan of claim 7, wherein: the opposite parallel sides of the
first portion of each of the cross-sections of the second section
of each of the blades are parallel to the center axis.
9. The fan of claim 1, wherein: the first section of each of the
blades connects with the second section thereof and the
cross-sections of the first section and second section are
different at their connection.
10. The fan of claim 1, further comprising: a ring extending around
the hub interconnecting the trailing edges of the blades.
11. The fan of claim 10, wherein: the ring has axially opposite
sides that taper toward each other as the ring extends radially
inward.
12. The fan of claim 1, wherein: the fan has a plurality of voids
between adjacent pairs of the blades that extend axially through
the fan.
13. A fan comprising: a center hub having a center axis and a
peripheral surface, the center axis defining axial and radial
directions; a plurality of blades configured and adapted to draw
air radially outward from the center axis by revolving with the
center hub about the center axis, the plurality of blades each
having a radially opposite base end and trailing edge, the base end
of each of the blades being attached to the hub; and a ring
extending around the hub that interconnects the trailing edges of
the blades.
14. The fan of claim 13, wherein: each of the blades has an
infinite number of cross-sections that each lie in a plane
tangential to and radially spaced from the center axis and each of
the blades has a first section extending radially inward from its
trailing edge and a second section extending radially outward from
its base end, each of the cross sections of the first section of
each of the blades have chord-lines oriented parallel to the center
axis, cross-sections of the second section of each of the blades
have chord-lines oriented at an angle to the center axis, and the
angle of the chord-lines of the cross-sections of the second
section of each of the blades increases with increasing radial
spacing of the cross-section from the center axis, substantially
all of the cross-sections of each of the blades having equal axial
width.
15. The fan of claim 13, wherein: the ring has axially opposite
sides that taper toward each other as the ring extends radially
inward.
16. A fan comprising: a center hub having a center axis of rotation
of the fan and a peripheral surface; a plurality of blades
radiating outwardly from the hub peripheral surface, each blade of
the plurality of blades has a radial length with an opposite base
end and trailing edge, the base ends of the blades are connected
with the hub peripheral surface, at least some of the blades have
radial-flow and axial-flow portions, the radial-flow portions of
the blades are positioned in planes that contain the hub center
axis and the axial-flow portions of the blades have at least
portions that are positioned in planes that are oriented at an
angle relative to the planes of the blade radial-flow portions, and
the blade radial-flow portions extend from the base ends to the
trailing edges of the blades.
17. The fan of claim 16, wherein: the fan has a plurality of voids
between adjacent blades of the fan that extend axially through the
fan.
18. The fan of claim 16, wherein: a ring extends around and
interconnects the trailing edges of the blades and the blades are
only connected together by the hub and the ring.
19. The fan of claim 16, wherein: each of the blade axial-flow
portions has a radial length between a distal end of the blade
axial-flow portion and the base end of the blade and the distal end
of the blade axial-flow portion is positioned radially between the
base end and the trailing edge of the blade.
20. The fan of claim 16, wherein: the fan is mounted to a shaft of
a motor and the motor has a cover that encloses the fan with at
least one exhaust opening in the cover adjacent the trailing edges
of the fan blades.
21. The fan of claim 16, wherein: the fan is mounted to a shaft of
a motor and the motor has a housing with at least one vent opening
in the housing adjacent the axial-flow portions of the blades.
22. A fan having a center axis of rotation, the axis defining axial
and radial directions, the fan comprising: a plurality of blades
configured and adapted to draw air radially outward from the axis
by revolving about the center axis, the plurality of blades each
having a radially opposite base end and trailing edge, the base end
of each of the blades being radially closer to the center axis than
the trailing edge of each of the blades and each of the blades
having an infinite number of cross-sections that each lie in a
plane tangential to and radially spaced from the center axis, each
of the blades having a first section extending radially inward from
its trailing edge and a second section extending radially outward
from its base end, cross sections of the first section of each of
the blades have chord-lines oriented parallel to the center axis,
and at least some cross-sections of the second section of each of
the blades have chord-lines oriented at an angle relative to the
center axis.
23. The fan of claim 22, wherein: the angles of the chord-lines of
the second section cross-sections of each of the blades increases
with increasing radial distance of the cross-section from the
center axis.
24. The fan of claim 22, wherein: each of the blade second sections
includes a radial-flow portion and an axial-flow portion, the
radial-flow portion is positioned in a plane that contains the
center axis and the axial-flow portion has at least some part that
is positioned in a plane oriented at an angle relative to the plane
of the radial-flow portion.
25. The fan of claim 22, wherein: the radial-flow portion and the
first section of each blade are positioned in a common plane that
contains the center axis.
26. The fan of claim 1, wherein: each of the cross-sections of the
second section of each of the blades consist of first and second
portions and the first portion extends axially forward of the
cross-sections of the first section of the blade.
27. The fan of claim 26, wherein: the first portion of each of the
cross-sections of the second section of each of the blades curves
relative to the center axis and the second portion of each of the
cross-sections of the second section of each of the blades is
substantially parallel to the center axis.
28. The fan of claim 26, wherein: a portion of each of the
cross-sections of the first section of each of the blades extends
axially rearward of the cross-sections of the second section of the
blade.
29. The fan of claim 26, further comprising: a ring extending
around the hub interconnecting the trailing edges of first section
of each of the blades, there being a plurality of voids that extend
axially through the fan between the second sections of each
adjacent pairs of the blades.
30. The fan of claim 29, wherein: the ring is positioned where it
connects rearward most edges of the blades.
31. The fan of claim 16, wherein: each of the radial-flow portions
of the blades are axially rearward of the axial-flow portions of
the blades.
32. The fan of claim 31, wherein: each of the blade axial-flow
portions has a radial length between a distal end of the blade
axial-flow portion and the base end of the blade and the distal end
of the blade axial-flow portion is positioned radially between the
base end and the trailing edge of the blade.
33. The fan of claim 32, wherein: a portion of each of the blade
first sections between the distal end of the blade axial-flow
portion and the trailing edge of each of the blades extends axially
rearward of all portions of the blade between the base end of the
blade and the distal end of the blade axial-flow portion.
34. The fan of claim 32, further comprising: a ring extending
around the hub interconnecting the trailing edge of the first
section of each of the blades, there being a plurality of voids
that extend axially through the fan between the blade axial-flow
portions of each adjacent pair of the blades.
35. The fan of claim 34, wherein: the ring is positioned where it
connects rearward most edges of the blades.
Description
BACKGROUND OF THE INVENTION
[0001] (1) Field of the Invention
[0002] This invention pertains to the field of fans of the type
mounted on shafts of electric motors and other dynamoelectric
devices for cooling such devices during operation. More
particularly, this invention pertains to a radial or centrifugal
fan wherein the outer portion of its blades are configured to
induce radial-flow on air expelled by the fan, and wherein the
central portion of the fan's blades are configured to induce
partial axial-flow and partial radial-flow to improve the intake of
air into the fan from one of the fan's axially opposite sides.
Additionally, the fan of the preferred embodiment has an annular
wedge shaped ring connecting the trailing edges of the fan's blades
that acts as a diverter to channel air exiting the fan to opposite
axial sides of an annular grill bar on a cover that encloses the
fan. The configuration of the fan of the invention improves
efficiency of the fan without increasing its size, thereby
providing greater cooling capacity over conventional radial fans of
the same size.
[0003] (2) Description of the Related Art
[0004] Many dynamoelectric devices such as appliance motors, hand
tool motors, generators, and alternators utilize fans mounted on
their rotor shafts to provide for air cooling of stator and rotor
windings of the devices during their operation. Typically such fans
are mounted at an axial end of the dynamoelectric devices
immediately adjacent the device housing and are configured to pull
or push air through the housing and between the rotor and
stator.
[0005] The majority of dynamoelectric devices are generally
cylindrical in shape and the fans are commonly configured to have
nearly the same diameter. It is also common for such devices to
have a cover enclosing the fan, or to place the fan within the
housing of the devices, to prevent objects from contacting the fan
blades. Additionally, it is generally desirable to configure
cooling fans in a manner such that they take only a minimum of
space, since such cooling fans must generally fit within a specific
cylindrical space of minimal axial length.
[0006] Although some machines in which dynamoelectric devices
operate allow for the use of axial-flow fans, the configurations of
many machines in which dynamoelectric devices are used often
necessitate the use of radial-flow fans which discharge air
radially outward. Radial-flow fans are designed to obtain maximum
air flow rates for a given configuration, unlike centrifugal
compressors which are often designed to obtain large pressure
differentials under low flow rate conditions. Other design
considerations include costs and whether the fan must operate in
opposite directions of rotation.
[0007] Perhaps the simplest radial-flow fan design is a straight
blade fan. Straight blade fans utilize a plurality of blades
extending radially from a central hub. Like other fan designs, the
hub of a straight blade fan is typically a generally cylindrical
body having a through-hole aligned with its center axis for
mounting the fan to the shaft of a dynamoelectric device. It is
also common for the through-hole to be keyed with the shaft to
insure that the fan rotates with the shaft without slippage. The
blades of a straight blade fan are typically flat rectangular
members oriented parallel to the center axis of the hub such that
air is forced through the fan purely by centrifugal force. Thus,
straight blade fans are typically symmetric about a plane that is
perpendicular to the center axis of the hub and act to draw air
inward from both of the opposite axial sides of the fan in response
to the fan blades pushing air radially outward from the center
hub.
[0008] To reduce the amount of air drawn into a radial fan from the
side of the fan that faces away from the dynamoelectric device to
be cooled, such radial fans often have an imperforate disk shaped
backing mounted for rotation with the fan on the side of the fan
farthest from the housing of the dynamoelectric device. Such
backings generally increase the amount of air drawn into the fan
from the side of the fan facing the housing of the dynamoelectric
device. However, such backings take up axial space and thereby
reduce the axial width of the fan blades for a given total axial
length of the fan, thereby decreasing the total output of the fans
compared to non-backed fans of equal axial length. Additionally,
backings also increase the amount of material required to
manufacture such fans.
[0009] A preferred method of reducing the amount of air drawn into
a radial fan from the side of the fan that faces away from the
dynamoelectric device is to configure the cover which typically
surrounds the fan with an imperforate disk shaped end that is
positioned with an axial gap between it and the fan. Thus, the disk
shaped end of the cover acts much as a backing does to increase the
amount of air drawn into the fan from the side of the fan facing
the housing of the dynamoelectric device, without reducing the
axial width of the fan blades.
[0010] Straight blade radial fans have an advantage of operating
equally well in either direction of rotation. For this reason,
straight blade radial fans are often used to cool dynamoelectric
devices whose shafts rotate in opposite directions during
operation. However, for those devices whose shafts seldom or never
rotate in opposite directions, straight blade fans need not be used
and other configurations having blades that curve in a plane
perpendicular to the center axis of the fan hub have been used. By
curving the blades of a radial fan in a direction opposite that of
the rotation (commonly called a backward curved radial fan), the
fan exhausts air using both centrifugal force and force caused by
the blade pushing the air in partially the radial direction.
However, such curved blades may or may not increase the overall air
output, since curving the blades also reduces the circumferential
velocity of the air passing through the fan and thereby decreasess
the centrifugal force component generated by the fan. Generally,
straight blade radial fans produce a greater air flow rate than
backward curved blade fans of the same size and are thus desirable
for use with most dynamoelectric devices.
[0011] Although radial-flow fans have proven effective for cooling
dynamoelectric devices, it remains advantageous to design fans
having ever greater efficiency. Furthermore, it is desirable to
increase the efficiency of such fans without increasing the size of
the fans and without significantly increasing the cost or adding
additional components to the dynamoelectric device assembly.
SUMMARY OF THE INVENTION
[0012] The radial fan of the present invention increases the flow
rate of cooling air through a dynamoelectric device as compared to
prior art straight blade radial fans of the same size. The
increased airflow is a result of the configuration of the blades of
the fan as well as the configuration of an annular ring joining the
blades.
[0013] In general, the fan of the preferred embodiment of the
invention is a fan configured for use with a dynamoelectric device
whose rotor shaft rotates in only one direction. The fan of the
preferred embodiment is made more efficient by configuring the
blades to perform as a conventional radial fan near their trailing
edges while also configuring the blades to perform as a mixed-flow
fan nearer the shaft or inlet. This is achieved by splitting each
of the blades into two sections and orienting the chord-line of the
blades near the hub at an angle relative to the axis of the hub
while maintaining the chord-line of the blades near the trailing
edges of the blades parallel to the hub axis. By configuring the
blades as a mixed-flow fan near the hub of the fan, the fan more
efficiently draws air from its axial side facing the dynamoelectric
device. This results in a corresponding higher radial air flow rate
from the fan and greater cooling of the dynamoelectric device.
[0014] The annular ring of the preferred embodiment of the fan also
increases the flow rate from the fan by channeling the air into
exhaust openings of the cover that circumferentially surrounds the
fan. The cover used with the preferred embodiment of the fan has an
annular grill bar which surrounds the blades of the fan and axially
separates pairs of openings in the cover to prevent objects and
fingers from contacting the blades of the fan when the fan is
rotating. Thus, the grill bar of the cover partially obstructs the
flow of air from the fan and the air must pass on either axial
sides of the grill bar as it is being exhausted. The ring of the
preferred embodiment has axially opposite sides that taper toward
each other as they extend radially inward. As air flows past the
ring while being exhausted, the taper of the ring axially separates
the flow in a streamline manner, which then allows the air to pass
the grill bar of the shroud more efficiently.
[0015] Like the preferred embodiment of the fan, an alternative
embodiment of the fan has blades configured such that the
chord-line of the blades near the hub are at an angle relative to
the axis of the hub while the chord-line of the blades near the
trailing edges of the blades are parallel to the hub axis. However,
the disclosed alternative embodiment of the fan achieves this by
extending a portion of the each of the blades, near the hub,
axially forward of the remainder of the blade and curving such
portions so that the portions are rotationally in advance of the
remainder of the blades. Additionally, the alternative embodiment
of the fan utilizes a ring positioned at the root edge of each of
the blades that acts similar to a backing but that is absent where
the chord-line of each blade is oriented at an angle relative to
the axis of the hub. This allows the fan to be manufactured using
simple molding methods that would not be possible if the fan had a
disked shaped backing rather than a ring.
[0016] While the principle advantages and features of the invention
have been described above, a more complete and thorough
understanding of the invention may be attained by referring to the
drawings and the detailed description of the preferred embodiment,
which follow.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is an isometric view of the fan of the preferred
embodiment of the invention.
[0018] FIG. 2 is a plan view of the fan of the preferred embodiment
of the invention as seen looking at the tip edges of the
blades.
[0019] FIG. 3 is a plan view of the fan of the preferred embodiment
of the invention as seen looking at the root edges of the
blades.
[0020] FIG. 4 is a cross-section of one of the blades of the fan of
the preferred embodiment of the invention taken at the line 4-4 of
FIG. 2.
[0021] FIG. 5 is a partial cross-section of the ring of the fan of
the preferred embodiment of the invention taken at the line 5-5 of
FIG. 2.
[0022] FIG. 6 is an assembly view of an electric motor of the type
with which the fan of the preferred embodiment of the invention is
configured for use.
[0023] FIG. 7 is an exploded view of the assembly of FIG. 6 showing
the placement of the fan of the preferred embodiment of the
invention relative to the motor and the cover.
[0024] FIG. 8 is an isometric view of a fan of an alternative
embodiment of the invention.
[0025] FIG. 9 is a plan view of the fan of the alternative
embodiment of the invention as seen looking at the tip edges of the
blades.
[0026] FIG. 10 is a plan view of the fan of the alternative
embodiment of the invention as seen looking at the root edges of
the blades.
[0027] FIG. 11 is a cross-section of one of the blades of the fan
of the alternative embodiment of the invention taken at the line
11-11 of FIG. 9.
[0028] FIG. 12 is a partial cross-section of the fan of the
alternative embodiment of the invention taken at the line 12-12 of
FIG. 9.
[0029] References and characters in the written specification
indicate corresponding parts throughout the several views of the
drawings.
DETAILED DESCRIPTION OF THE INVENTION
[0030] The preferred embodiment of the fan 20 of the invention is
shown in its entirety in FIGS. 1-3. The fan 20 preferably comprises
a central hub 22, a plurality of blades 24, and an annular ring 26.
The fan 20 of the preferred embodiment is configured to cool an
electric motor 28 of the type having a rotor that rotates in only
one direction and is enclosed by a cover 30 once it is assembled on
the motor as shown in FIGS. 6 and 7. Additionally, the fan 20 is
preferably formed of a polymeric resin as a single monolithic
part.
[0031] The hub 22 of the preferred embodiment of the fan 20 is a
generally cylindrical body having an outer periphal surface 32 and
a center bore or opening 34 that extends through the hub 22 along
its axis. The opening 34 of the hub 22 preferably has opposite
arcuate surfaces 36 configured to slidably engage with the rotor
shaft 38 of the motor 28, as shown in FIG. 7. An opposite pair of
flats 40 separate the arcuate surfaces 36 of the opening 34 and are
configured to engage with a pair of opposite notches 42 formed in
the end of the rotor shaft 38 of the motor 28 to provide an
interlocking fit between the hub 22 and the rotor shaft that
ensures that the fan 20 rotates with the rotor shaft. However, it
should be understood that numerous methods of attaching fans to
shafts are known in the art and alternative configurations of the
hub and rotor shaft and alternative methods of attaching one to the
other could also be used.
[0032] The blades 24 of the preferred embodiment of the fan 20 of
the invention are evenly spaced circumferentially about the axis of
the hub 22. Each of the blades 24 has a base end 44 that is secured
to the hub 22, and each extends radially from the hub to an
opposite trailing edge 46. Additionally, each of the blades 24 has
a first radial section 48 extending radially inward from its
trailing edge 46 and each has a second section 50 extending
radially outward from its base end 44.
[0033] The axial width or blade height of each of the blades 24,
measured from the tip edge 52 of each of the blades to the root
edge 54 of each of the blades, preferably remains constant between
the blade's base end 44 and trailing edge 46. At any given radius
from the axis of the hub 22, the first section 48 of each of the
blades 24 has a cross-section that is generally rectangular with a
chord-line 56, defined as an imaginary line extending from the tip
edge 52 to the root edge 54 of the blade as shown in FIG. 4, that
is oriented parallel to the axis of the hub.
[0034] Unlike the first section 48 of each of the blades 24, the
second section 50 of each of the blades, at any given radius from
the axis of the hub 22, has a cross-section that has its chord-line
58 oriented at an angle relative to the axis of the hub 22 such
that the tip edge 52 is rotationally in advance of the root edge 54
as the fan 20 revolves with the rotor shaft 38. Additionally, the
cross-section of the blade second section 50 consists of a first
portion 60 having opposite straight parallel sides 62 that are
oriented parallel to the axis of the hub 22 and a second portion
64, also having straight parallel sides 66, that intersects the
first portion at an angle. As the second section 50 of each of the
blades 24 extends radially outward from the axis of the hub 22, the
angle between the parallel sides 62, 66 of the first and second
portions 60, 64 increases from zero degrees at the base end 44 of
each of the blades. Stated another way, the angle of the parallel
sides 66 of the second portion 64 relative to the hub axis is zero
degrees where the second portion joins the hub and progressively
increases as the second portion 64 extends radially from the hub
22.
[0035] The first and second sections 48, 50 of each of the blades
24 extend radially toward each other and terminate at a common
point that lies between the base end 44 and the trailing edge 46 of
each blade, causing an abrupt discontinuity in the tip edge 52 of
each of the blades where the sections meet. However, the entire
root edge 54 of each of the blades 24 extends radially
straight.
[0036] The ring 26 of the preferred embodiment of the fan 20
connects the trailing edges 46 of the blades 24 to one another and
extends completely around the axis of the hub 22. As shown in FIG.
5, the ring 26 is positioned centrally between the tip and root
edges 52, 54 of the blades 24 and has a wedge shaped cross-section
(the cross-section taken in a plane that includes the axis of the
hub). The wedge shaped cross-section of the ring 26 is formed by
axially opposite side surfaces 68 that taper toward each other as
the as the ring extends radially inward. An outer surface 70 of the
ring 26 lies flush with the edge of the trailing edges 46 of the
blades 24.
[0037] In the preferred embodiment of the fan 20, only the ring 26
and hub 22 connect the blades 24 to one another, i.e. there is no
backing attaching the blades. Thus, voids extend axially through
the fan 20 between each adjacent pair of blades 24.
[0038] The fan 20 is assembled on the rotor shaft 38 of the motor
28 in a manner such that the tip edges 52 of the blades 24 are
closer to the end shield 72 of the motor 28 than the root edges 54
of the blades. The cover 30 is then attached to the motor 28 where
it covers the fan 20. The particular method used to secure the
components together are not pertinent to this invention and any
method known in the art for assembling components could be
used.
[0039] The cover 30 is generally a cylindrical shell that is closed
at one end by an imperforate flat disk shaped wall 74, and is
configured such that the disk shaped wall 74 is positioned close to
the root edges 54 of the blades 24 of the fan 20. The cover 30 also
has a plurality of exhaust openings 76 circumferentially spaced
about its cylindrical wall 78. When the cover 30 is attached to the
motor 28, the exhaust openings 76 are axially aligned with the tip
ends 46 of the blades 24 of the fan 20. To prevent fingers and
other objects from contacting the blades 24 of the fan 20 during
its operation, the cover 30 also has a cylindrical grill bar 80
that axially separates adjacent pairs of the exhaust openings
76.
[0040] As the fan 20 rotates with the rotor shaft 38 of the motor
28, the first sections of the blades radially discharge air by
creating a pressure differential caused by centrifugal force. This
pressure differential also acts to draw air from either of the
axial sides of the fan 20, but the disk shaped wall 74 of the
shroud 30 prevents air from being drawn into the fan from the side
of the fan opposite the motor 28. Thus, air is drawn into the fan
20 through the vent openings 82 on the end shield 72 of the motor.
While this is similar to the way conventional radial cooling fans
operate, the configuration of the preferred embodiment of the fan
20 of the invention provides increased efficiency over prior art
radial fans for any given fan size. This is because the first
section 48 and the first portion 60 of the second section 50 of
each blade 24 lie in the same plane and act as a radial-flow
portion of each blade while the second portion 64 of the second
section 50 acts as an axial-flow portion of the blade. In other
words, because the first section and the first portion 60 of the
second section 50 of each blade are in a plane that is parallel to
the center axis of the hub 22, these parts of each blade 24 induce
a radial pressure differential while the second portion 64 of the
second section 50 induces an axial pressure differential. Thus, the
second portions 64 of the second sections 50 of the blades 24 act
partially as an axial-flow fan, thereby cutting into the air to
draw air in from the side of the fan 20 facing the motor 28. The
efficiency of the fan 20 is thereby increased as compared to
conventional radial fans that draw air in purely by the pressure
differential created as a result of the centrifugal force of the
air near the trailing edges 54 of the blades 24.
[0041] Another advantage of the fan 20 lies in the presence and
configuration of the ring 26. As air is expelled from the fan 20,
it must pass through the exhaust openings 76 of the cover 30 and,
normally, the grill bar 80 axially separating adjacent exhaust
openings obstructs the flow of air being expelled from the fan.
However, the ring 26 is positioned on the fan 20 where it is
axially aligned with the grill bar 80 of the cover 30 when both are
assembled on the motor 28. Additionally, the outermost surface 70
of the ring 26 has an axial width such that if the side surfaces 68
were continued outwardly, they would line up with the edges of the
grill bar 80 of the cover 30. Thus, the tapered side surfaces 68 of
the ring 26 act to axially separate and deflect the flow of the air
being expelled from the fan 20 such that the air can pass more
easily around the grill bar 80 of the cover 30.
[0042] An alternative embodiment of the fan 100 of the invention is
shown in FIGS. 8-12 and comprises a central hub 102, a plurality of
blades 104, and an annular ring 106. Like the fan 20 of the
preferred embodiment, the fan 100 of the alternative embodiment is
configured to cool an electric motor of the type having a rotor
that rotates in only one direction and is preferably formed of a
polymeric resin as a single monolithic part. However, the fan 100
of the alternative embodiment is preferably configured to be
enclosed by the housing of a motor.
[0043] Like the hub 22 of the fan 20 of the preferred embodiment,
the hub 102 of the fan 100 of the alternative embodiment is a
generally cylindrical body having an outer peripheral surface 108
and a center bore or opening 110 that extends through the hub 102
along its axis. However, the opening 110 is cylindrical and has a
plurality of axial slots 112 extending into an axial end of the hub
102 such that the fan 100 can be attached to a rotor shaft using a
C-clip or spring clip placed around the end of the hub in which the
slots are formed. Again, it should be understood that this method
of attaching a fan to a shaft is known in the art and numerous
other known methods of attaching fans to shafts could also be
used.
[0044] Similar to the preferred embodiment, the blades 104 of the
alternative embodiment of the fan 100 are evenly spaced
circumferentially about the axis of the hub 22 and each of the
blades 104 has a base end 114 that is secured to the hub 102, and
each extends radially from the hub to an opposite trailing edge
116. Likewise, each of the blades 104 has a first radial section
118 extending radially inward from its trailing edge 116 and each
has a second section 120 extending radially outward from its base
end 114.
[0045] At any given radius from the axis of the hub 102, the first
section 118 of each of the blades 104 has a cross-section that is
generally rectangular, albeit the cross-section may be slightly
non-rectangular to account for fabrication draft angle
requirements. Each blade 104 has a tip edge 122 and root edge 124
and throughout the first section 118 of each blade 104, the
chord-line 126 of the cross sections of the blade are oriented
parallel to the axis of the hub 102.
[0046] Further like the preferred embodiment, the second section
120 of each of the blades 104 at any given radius from the axis of
the hub 102, has a cross-section that has its chord-line 128
oriented at an angle relative to the axis of the hub 102 and, as
the second section 120 of each of the blades 104 extends radially
outward from the axis of the hub 102, the angle of the chord-line
128 relative to the axis of the hub 102 increases. The
cross-section, at any given radial distance from the axis,
throughout the second section 120 of each blade 104 consists of a
first portion 130 and a second portion 134. The first portion 130
has opposite straight, generally parallel sides 132 that are
oriented substantially parallel to the axis of the hub 102 and the
second portion 134 has curved parallel sides 136, that intersect
the first portion tangentially.
[0047] The first and second sections 118, 120 of each of the blades
104 extend radially toward each other. However, unlike the
preferred embodiment of the invention, the second portion 134 of
the second section 120 of each blade 104 of the alternative
embodiment extends axially forward of the first section 118 of each
blade, i.e. in a direction away from the root edge 124 of each
blade, as shown best in FIG. 12. The root edge 124 of each of the
blades 104 also jogs axially forward as it extends from the first
section 118 to the second section 120 of each of the blades.
[0048] The ring 106 of the fan 100 of the alternative embodiment
extends completely around the axis of the hub 22 and connects the
root edges 124 of the blades 104 to one another. As shown in FIG.
12, the ring 106 is disk shaped and extends radially inward along
substantially the entire first section 118 of each of the blades
104. The ring 106 is essentially a partial backing attached to the
blades 104 except that it does not extend in the radial region of
the second sections 120 of blades. Thus, voids extend axially
through the fan 100 between the second sections 120 of each
adjacent pair of blades 104. As can be appreciated by one skilled
in the art, the absence of the ring 106 in the radial region of the
second section 120 of the blades 104 allows the fan 100 to be
formed as a monolithic piece of polymeric material using a
convention two-piece molding die.
[0049] The fan 100 of the alternative embodiment is assembled to a
motor in a manner similar to the fan 20 of the preferred embodiment
except that the fan 100 is configured to be positioned between an
axial end of the stator (not shown) and an end shield of the motor,
within the housing of the motor. Unlike the motor used with the fan
of the preferred embodiment, exhaust openings aligned with the
trailing edges 116 of the blades 104 extend directly through the
housing of the motor used with the fan 100 of the alternative
embodiment. An annular baffle or shroud (not shown) is preferably
positioned between the first section 118 of the blades 104 of the
fan 100 and the stator of the motor. The shroud is preferably
shaped to substantially fill the axial space that exists between
the stator of the motor and the first sections 118 of the blades
104 due to the second sections 120 of the blades of the fan 100
being axially forward of the first sections of the blades. The end
shield has an imperforate disk shaped wall or alternatively has a
cylindrical attachment that is positioned close to the ring 106 of
the fan 100 or is attached to the center of the fan, and functions
similar to the disk shaped wall 74 of the cover 30 used in
conjunction with the fan 20 of the preferred embodiment. However,
unlike a cover, the end shield has a centrally positioned bearing
(not shown) for supporting the rotor shaft of the motor. The
bearing protrudes axially into the motor from the wall of the end
shield and is accommodated by the fact that the fan 100 is
configured, as described above, such that root edge 124 along the
second section 120 of each of the blades 104 is axially forward of
the root edge along first section 118 of each blade.
[0050] In operation, the fan 100 of the alternative embodiment
functions similar to the fan 20 of the preferred embodiment. The
first section 118 and the first portion 130 of the second section
120 of each blade 104 lie in the same plane and act as a
radial-flow portion of each blade while the second portion 134 of
the second section acts as an axial-flow portion of the blade. The
efficiency of the fan 100 is thereby increased as compared to
conventional radial fans that draw air in purely by the pressure
differential created as a result of the centrifugal force of the
air near the trailing edges 116 of the blades 104.
[0051] While the present invention has been described by reference
to a specific embodiment, it should be understood that
modifications and variations of the invention may be constructed
without departing from the scope of the invention defined by the
following claims.
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