Note: Descriptions are shown in the official language in which they were submitted.
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ROTARY FAN WITH ENCAPSULATED MOTOR ASSEMBLY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to heat transfer systems, more particularly to
fan assemblies utilized for moving a fluid in a heat transfer system.
2. Background Art
Motor vehicles commonly utilize heat exchangers to dissipate heat
collected in the operation of the motor vehicle to the ambient air. These heat
exchangers include radiators for cooling an internal combustion engine, or a
heater
core for providing heat to a passenger compartment for climate control.
Internal combustion engine cooling systems that utilize a heat
exchanger may also include a rotary axial fan for enhancing the movement of
air
through the heat exchanger. For example, a radiator in conventional motor
vehicles
includes a fan rearward or forward of the radiator for forcing air through the
radiator. Typically, a shroud is provided to generally restrict the air to
flow axially
through the radiator and the fan. The fan may be driven directly from the
operation
of the internal combustion engine by a belt or the like. Also, the fan may be
driven
by an independent motor for rotating the fan and forcing the air through the
heat
exchanger, as commonly utilized for transversely mounted internal combustion
engines. Air is commonly forced through a conventional heater core through a
fan
which is operated by the climate controls within the passenger compartment.
Fan assemblies often include a rotary axial fan that is supported by
a hub on the shroud. The hub is supported by an array of stator fan blades
extending inward from the shroud for structurally supporting the rotary axial
fan and
for permitting air to pass through the shroud. Often times, a motor may be
mounted
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to the hub and supported by the stator fan blades of the shroud, for imparting
rotation to the rotary axial fan.
SUMMARY OF THE INVENTION
An embodiment of the present invention provides a rotary axial fan
assembly with a shroud that is adapted to be mounted proximate to a heat
exchanger.
The shroud is sized for conveying a flow of fluid through the heat exchanger
and the
shroud. At least one stator fan blade extends inward from the shroud. A hub is
oriented generally centrally within the shroud and is supported by the stator
fan
blade. A motor stator is encapsulated within the hub. The motor stator is
adapted
for receiving a fan rotor with fan blades for forcing the flow of fluid to the
heat
exchanger and the shroud.
Another embodiment of the present invention provides a hub formed
from a thermally conductive material for transferring heat from the motor
stator into
the flow of fluid for dissipating the heat into the flow of fluid.
A further embodiment of the present invention provides a hub formed
from a material having a coefficient of thermal conductivity within a range of
10 to
175 Watts per meter * Kelvin.
Yet another embodiment of the present invention a shroud and stator
fan blades that are formed unitarily from a thermally conductive material.
The above embodiments and other embodiments, aspects, objects,
features, and advantages of the present invention are readily apparent from
the
following description of embodiments of the invention when taken in connection
with the accompanying drawings.
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BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a schematic illustration of an internal combustion
engine cooling system in accordance with the teachings of the present
invention;
FIGURE 2 is a perspective view of a rotary axial fan assembly in
accordance with the present invention;
FIGURE 3 is a cross-section view of the rotary axial fan assembly of
Figure 2; and
FIGURE 4 is an exploded perspective view of the rotary axial fan
assembly of Figure 2.
DESCRIPTION OF EMBODIMENTS OF THE INVENTION
As required, detailed embodiments of the present invention are
disclosed herein; however, it is to be understood that the disclosed
embodiments are
merely exemplary of the invention that may be embodied in various and
alternative
forms. The figures are not necessarily to scale; some features may be
exaggerated
or minimized to show details of particular components. Therefore, specific
structural and functional details disclosed herein are not to be interpreted
as limiting,
but merely as a representative basis for the claims and/or as a representative
basis
for teaching one skilled in the art to variously employ the present invention.
With reference now to Figure 1, an internal combustion engine
cooling system is illustrated schematically and indicated generally by
reference
numeral 10. The cooling system 10 includes a radiator 12 that receives heated
coolant from the internal combustion engine (not shown) and transfers heat
from the
coolant to air that passes through the radiator 12. Air is passed through the
radiator
12 by movement of the vehicle and air is also forced by a rotary axial fan 14.
An
external shroud 16 is provided to limit the movement of air to travel in an
axial
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direction. The shroud 16 may be mounted to the radiator 12. The fan 14 is
mounted to a drive member 18, which may be driven by a motor 20. The motor 20
may be mounted to the shroud 16 by stator fan blades 22. The motor 20 drives
the
drive member 18 and fan 14 for forcing air through the radiator 12, shroud 16
and
fan 14, thereby cooling coolant that passes through the radiator 12.
Alternatively, the heat transfer system 10 may include any heat
exchanger, such as a heater core which passes coolant therethrough while air
is
forced by a fan 14 for passing heated air into a passenger compartment of a
vehicle,
or any other heat transfer mechanism.
With reference now to Figure 2, a rotary axial fan assembly 24 is
illustrated in accordance with the present invention. The fan assembly 24
includes
a rotary axial fan 26 and a stator fan 28. The stator fan 28 may be fixed
within the
vehicle for supporting the rotary axial fan 26. Although a rotary axial fan
and
radiator are illustrated and described, the invention contemplates any heat
exchanger
such as radiators, heater cores, evaporators, condensers and the like.
The stator fan 28 of the present embodiment includes a shroud 30,
which is generally annular for limiting a direction of air flow through the
fan
assembly 24 to a generally axial direction L. The shroud 30 may be provided
with
a plurality of mounting flanges 32 for mounting the fan assembly 24 proximate
to
a heat exchanger, such as a radiator 12. The stator fan 28 may also include a
radial
array of stator fan blades 34 converging centrally inward to a hub 36. The hub
36
may be supported by the stator fan blades 34. Likewise, the rotary axial fan
26 may
be mounted to the hub 36 for rotation of the fan 26 relative to the hub 36.
The
rotary axial fan 26 may include a series of rotary fan blades 38 extending
from a fan
hub 40. The rotary fan blades 38 may be inclined relative to the axial flow
direction
L at an attack angle, which is angled (non-radial) relative to the fan hub 40
such that
rotation of the rotary axial fan 26 in a counter-clockwise direction, as
illustrated by
the arcuate arrow R in Figure 2, causes a flow of air in the generally axial
direction
L through the shroud 30.
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Although the fan assembly 24 is illustrated as a puller fan assembly,
wherein air is pulled through the radiator 12 and subsequently through the fan
assembly 24, the invention contemplates that the rotary axial fan 26 may be
rotated
in a clockwise direction such that air is forced in a reversed linear
direction relative
to the arrow L depicted in Figure 2 for pushing air through the fan assembly
24 and
subsequently through the associated radiator 12. Such rotation may be
controlled
by electronics or may be a function of the relationship of the rotary axial
fan blades
38 relative to the fan hub 40. Alternatively, the rotary axial fan 26 may be
detachable from the stator fan 28 for being mounted in either a pusher or
puller
orientation.
The fan assembly 24 illustrated in Figure 2 may be sized to
adequately cool a radiator of a predetermined diesel engine. Of course, other
types
of engines, engine cooling systems, and heating or cooling of other heat
exchangers
is contemplated by the present invention. Likewise, any number of fan
assemblies
24 may be utilized in combination with a cooling system or heat exchanger for
providing the required volumetric rate of fluid flow for the design criteria
of a given
system or heat exchanger.
For the embodiment of Figure 2, the rotary axial fan 26 is rotationally
driven by a motor 42 that is mounted to the stator fan hub 36. The rotary
axial fan
26 is rotated relative to the stator fan 28. The motor 42 illustrated in
Figure 2 may
be, for example, a brushless DC motor. Of course the invention contemplates
utilization of various motors, including a motor with brushes, within the
spirit and
scope of the present invention. The motor 42 may be driven independent of the
rotation of the engine of the vehicle, so that energy may be conserved by
driving the
rotary axial fan 26 when necessary, and by driving the rotary axial fan 26 at
a
desired speed. Various factors affect the rate of heat transfer through a
cooling
system 10, including the heat of coolant within the heat exchanger, or
radiator 12,
external temperatures, wind speeds and directions, velocity of the vehicle,
and the
like. Accordingly, the motor 42 may be controlled electronically to rotate the
rotary
axial fan 26 when necessary, and at a speed to provide the desired rate of
heat
transfer.
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With reference now to Figures 3 and 4, the motor 42 is illustrated in
further detail in the section and exploded views of the fan assembly 24. In
order to
cool the motor 42, heat generated by the motor 42 may be transferred to the
stator
fan 28 for dissipation into air forced through the shroud 30. For example,
heat
generated by the motor 42 may be transferred to the hub 36, and subsequently
to the
stator fan blades 34 for convecting the heat to air passed through the shroud
30
about the stator fan blades 34.
In order to facilitate heat transfer from the motor 42 to the stator fan
28, a motor stator 44 of the motor 42 is encapsulated within the hub 36 of the
stator
fan 28. The motor stator 44 includes an end cap 46 with motor windings 47 that
are
disposed about lamination plates 48. The motor windings 47 are the primary
source
of heat and the lamination plates 48 may act as a heat sink for transferring
heat from
the motor windings 47. The lamination plates 48 are encapsulated within an
inner
diameter of the hub 36 for direct contact with the hub 36 as illustrated in
Figure 3.
This direct contact between the motor stator 44 and the hub 36 permits heat
generated by the motor 42 to be conducted directly to the hub 36. The hub 36
may
provide minimal clearance between the hub 36 and the motor stator 44 for
reducing
vibration of the fan assembly 24 and for maximizing contact for enhancing the
conduction of heat therebetween. Additionally, the motor stator 44 may be
press
fit or partially press fit within the hub 36 for further enhancing the contact
and rate
of heat transfer by an interference connection. Thus, the hub 36 provides a
heat
sink for the motor 42 that is in direct contact with the lamination plates 48
of the
motor stator 44.
To further enhance the engagement between the motor stator 44 and
the stator fan 28, a thermally conductive adhesive may be placed within the
inner
diameter of the hub 36 for providing direct contact therebetween. A room
temperature vulcanizing (RTV) sealant may also be provided between a flange 50
of the end cap 46 and the hub 36 for sealing the motor 42 and preventing
contaminants from getting within the motor 42.
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To further enhance heat transfer from the motor stator 44 to the hub
36, the end cap 46 of the motor stator 44 may be insert molded to the motor
windings 47 and the lamination plates 48 by an injection molding process
thereby
removing any air or space between the windings 47 of the motor stator 44. The
windings 47 may be over molded by a material that functions as an electrical
insulator between the windings 47, but also functions as a thermal conductor,
such
as a thermally conductive plastic. The insulator of the motor windings 47 may
be
molded separately or integrally with the end cap 46. The end cap 46 may be
provided by a thermally conductive polymer, such as a polymer having a
coefficient
of thermal conductivity of one to three watts per meter * Kelvin (W/m*K). Thus
the thermally conductive plastic ensures heat transfer from the windings 47
directly
to the hub 36 without air gaps between the windings 47.
By utilizing the hub 36 of the stator fan 28 for partially housing the
motor 42, the stator fan 28 functions as a heat sink for drawing heat from the
motor
42. Accordingly, the shroud 30, stator fan blade 34 and the hub 36 may be
formed
of a thermally conductive material for transferring the heat from the motor 42
into
the path of forced air. For example, the stator fan 28 may be die cast from
aluminum which has a coefficient of thermal conductivity of approximately 110
W/m*K. Die cast aluminum provides optimal heat transfer characteristics and
also
provides adequate structural integrity for supporting the fan assembly 24 and
resisting vibrations imparted by the motor 42.
Alternatively, the stator fan 28 may be sand cast from aluminum
thereby having a coefficient of thermal conductivity of approximately 150
W/m*K.
Of course, the invention contemplates that the stator fan 28 may be formed
from any
material having a suitable coefficient of thermal conductivity for acting as a
heat
sink and cooling the motor 42. Depending on the application of a particular
fan
assembly, a hub having a coefficient of thermal conductivity within the range
of 10
to 175 W/m*K should be suitable for providing a heat sink by the hub 36 and
stator
fan blade 34 for cooling the motor 42. Other reasonably suitable conductive
materials that meet the design tradeoffs between conductivity and structural
integrity
include wrought aluminum, which has a coefficient of thermal conductivity of
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approximately 167 W/m*K; steel, which has a coefficient of thermal
conductivity
of approximately fifty W/m*K; and magnesium, which has a coefficient of
thermal
conductivity of approximately sixty W/m*K.
The fan assembly 24 is further provided with a fan rotor 52 for
driving the rotary axial fan 26. The fan rotor 52 includes a unitary shaft 54
and
bearing assembly 56. The bearing assembly 56 is mounted within the hub 36 for
supporting the shaft 54 for rotation relative to the hub 36. The bearing
assembly 56
may be press fit within the hub 36 for assembling the fan rotor 52 and for
sealing
the hub 36. The bearing assembly 56 may be sized to withstand some unbalance
of
the fan assembly 24 thereby minimizing or eliminating a need to balance the
fan
assembly 24 and reducing manufacturing steps and overall cost of the fan
assembly
24. Additionally, the bearing assembly 56 includes double-lipped seals 58 on
each
axial end of the bearing assembly 56 about the shaft 54 for preventing
contaminates
from getting within the motor 42. The double-lipped seals 58 render the
bearing
assembly 56 submersible such that the hub 36 may be exposed to various
external
contaminates such as inclement weather.
The fan rotor 52 also includes a magnet 60 mounted to an end of the
motor shaft 54 centrally disposed within the motor stator 44. The motor stator
44
includes wiring 62, which may be sealed by the encapsulation of the motor 42
so
that no additional seal is required. For example, the wiring 62 may be insert
molded into the end cap 46 of the motor 42. The wiring 62 conveys a current
through the windings 47 of the motor stator 44 for imparting an
electromagnetic
field for rotating the magnet 60 and consequently the shaft 54 within the
bearing
assembly 56 relative to the hub 36 of the stator fan 28.
The magnet 60 may be press fit upon the shaft 54 to provide a reliable
connection and ease in assembly of the fan rotor 52. By pressing the magnet 60
flush with an end of the shaft 54 as illustrated in Figure 3, accurate axial
location
of the magnet 60 may be provided for maximum efficiency of the motor 42.
Although any order of assembly steps is contemplated within the spirit and
scope of
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the present invention, the magnet 60 may be assembled to the shaft 54 after
the
bearing assembly 56 has been assembled to the hub 36 of the stator fan 28.
A series of mechanical fasteners 64 are provided for fastening the
flange 50 of the motor stator 44 to the hub 36 of the shroud 30. The
mechanical
fasteners 64 may be used to secure the motor stator 44 to the hub 36 and/or to
resist
vibration in the fan assembly 24. The mechanical fasteners 64 may also be
utilized
for sealing the flange 50 of the motor stator 44 against the hub 36 of the
stator fan
28. The fasteners 64 may be utilized in combination with an adhesive or a
thermally
conductive glue, which may be utilized to fill the cavity within the hub 36
and the
motor stator 44 for improving vibration resistance and aid heat transfer
between the
motor stator 44 and the hub 36. Depending on the particular application, the
fasteners 64 may be utilized alone or in combination with the adhesive, or the
fasteners 64 may be omitted if the adhesive is adequate for securing and
sealing the
motor stator 44 to the hub 36.
The rotary axial fan 26 is mounted to the distal end of the shaft 54.
The rotary axial fan 26 may be assembled to the shaft 54 by utilization of a
hub plate
66, which is formed, for example, from steel and may be press fit onto the
motor
shaft 54. The interference fit of the hub plate 66 and the shaft 54 provides a
reliable
connection that is easily assembled by pressing the hub plate 66 upon the
shaft 54.
The hub plate 66 may be pressed flush to the end of the shaft 54 to provide
accurate
axial rotation of the rotary fan blades 38 for optimizing efficiency of the
fan
assembly 24. Although any sequence of manufacturing operations may be
contemplated within the spirit and scope of the present invention, the hub
plate 66
may be assembled to the shaft 54 after the magnet 60 has been assembled to the
shaft
54. Subsequently, the motor stator 44 may be assembled to the hub 36 of the
stator
fan 28, and the fan hub 40 may be fastened to the hub plate 66 by mechanical
fasteners 68 or any suitable connection. By providing the hub plate 66 with a
flat
surface for receiving the fan hub 40 and with a reduced diameter pilot 70 that
extends through the fan hub 40, unbalance of the fan assembly 24 may be
minimized.
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The rotary fan 26 may be formed of any suitable material for forcing
air through the fan assembly 24. For example, the rotary fan 26 may be formed
of
a polymeric material that is sufficient to withstand the stresses associated
with
forcing air through the fan assembly 24, but is sufficiently lightweight for
maximizing the efficiency of the motor 42. A retaining plate 72 can be
utilized
between the fasteners 68 and the fan hub 40 for distributing the load from the
fasteners 68 to an expanded area upon the fan hub 40.
In summary, a fan assembly 24 is disclosed, which maximizes
efficiency of the fan assembly 24 by minimi?ing components of the fan assembly
24
while maximizing heat transfer associated with the fan assembly 24 and for
cooling
a motor 42 for the fan assembly 24 thereby providing a low cost and efficient
cooling system.
While embodiments of the invention have been illustrated and
described, it is not intended that these embodiments illustrate and describe
all
possible forms of the invention. Rather, the words used in the specification
are
words of description rather than limitation, and it is understood that various
changes
may be made without departing from the spirit and scope of the invention.
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