Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02523995 2005-10-19
FAN GUARD HAVING CHANNEL TO DIRECT COOLING AIR TO A PISTON
CYLINDER
BACKGROUND OF THE INVENTION
s The invention relates generally to the field of pumps, such as compressors
and vacuum pumps, and more particularly, to a compressor having a fan
guard with a channel to direct cooling air to a piston cylinder.
Reciprocating piston or diaphragm pumps typically have a metal housing, for
example, a cast aluminum alloy, in which bearings are mounted which journal
~o the shaft which drives the pump. A metal housing is needed, particularly
for
larger pumps, to withstand the forces of driving the piston or diaphragm and
containing the pressure exerted in the compression chamber of the pump.
A rotary electric motor is usually used to drive these pumps and the motor
requires cooling. In one such pump, the motor is provided between two
Is housings, each of which is separate from the other and houses one
compression chamber. The shaft of the motor is a through shaft so that each
end of the shaft mounts one of the pistons or diaphragms that work to vary the
volume of the compression chamber in the housing at the corresponding end
of the shaft. Further out from where the piston or diaphragm is mounted, a
2o rotary fan blade is mounted to each end of the shaft to draw a flow of
cooling
air into the housing at that end and blow it onto the rotor and stator coils
of the
motor.
For cooling efficiency, it is desirable to make the part of the housing in
which
the rotary fan blade is mounted circular and just slightly larger than the
2s diameter of the fan blade. The clearance between the tips of the fan blades
and the interior housing surface should be as small as possible because, if
not, the air drawn into the housing by the fan blades will simply blow back
out
past the tips of the blade, and not be directed over the coils of the motor.
For
applications in which the pump is contained inside of a separate enclosure, it
3o may be permissible to leave open the end of the housing at which the fan
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blade is mounted. However, if the pump is going to be exposed or sold as a
stand-alone product, the end of the housing must be closed with a cover that
permits air to be drawn into the housing, but prevents the insertion of larger
objects or fingers. This cover, typically called a fan guard, should not
s deleteriously affect the operation of the fan nor add to the lateral size or
detract from the appearance of the fan.
The effectiveness of the cooling system in reducing the stator temperature of
the motor affects the range of applications in which the pump may be
employed. The voltage at which the motor is driven and the output pressure
~o of the pump affect the amount of heat that is generated in the motor. More
effective cooling expands the range of applications suitable for a given pump
and motor.
The motor is not the only temperature-sensitive component in a pump.
Wobble pistons are sometimes used in oil-less air compressors and vacuum
~s pumps. A wobble piston includes a peripheral seal on the piston head that
engages the cylinder bore. The piston head and its connecting rod are fixed
to each other, and the connecting rod is mounted on an eccentric on a shaft.
As the eccentric is turned by the shaft, the wobble piston is moved in and out
and "wobbles" from side to side. Wobble pistons typically employ a Teflon~
20 or other similar material disc or cup which serves both as a guide for the
wobble piston and as a pneumatic seal between the piston and the wall of the
cylinder in which it moves. The working surface of the cylinder has a
hardened polished surface, providing a smooth surface for cooperating with
the Teflon~ seal of the piston. The service life of the TefIonO material
2s depends in part on the temperature of the cylinder with which the seal
interfaces. A higher temperature typically corresponds to a shorter service
life
due to increased friction between the cup and the cylinder wall.
The bearings used to support the motor shaft also have a service life
determined at least in part by temperature. Generally, a higher bearing
3o temperature equates to a shorter bearing service life.
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Hence, cooling efficiency not only affects the range of applications for a
particular pump, but also the service life of temperature-sensitive components
in the pump. The present invention addresses these problems.
BRIEF SUMMARY OF THE INVENTION
s The present invention is directed generally to a fan guard that directs
cooling
air flow to a piston cylinder.
One aspect of the invention is seen in a pump including a housing, a shaft
supported by the housing, a piston assembly, a fan blade, and a fan guard.
The piston assembly includes a piston cylinder and is operably coupled to the
io shaft. The fan blade is operable to generate cooling flow. The fan guard is
mounted to the housing and includes a channel configured to direct at least a
first portion of the cooling flow to the piston cylinder.
Another aspect of the present invention is seen in a fan guard. The fan guard
includes a front surface defining a cooling flow opening and sidewalls
defining
is a channel having a first end proximate the cooling flow opening. A baffle
is
positioned proximate a second end of the channel.
Other objects, advantages and features of the present invention will become
apparent from the following specification when taken in conjunction with the
accompanying drawings.
2o BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
The invention may be understood by reference to the following description
taken in conjunction with the accompanying drawings, in which like reference
numerals identify like elements and in which:
Figure 1 is an isometric view of a pump in accordance with one embodiment
2s of the present invention;
Figure 2 is a partial cross section view of the pump of Figure 1;
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Figure 3 is an end view of the pump of Figure 1 with the fan guard removed;
and
Figure 4 is an isometric back view of a fan guard employed in the pump of
Figure 1.
s While the invention is susceptible to various modifications and alternative
forms, specific embodiments thereof have been shown by way of example in
the drawings and are herein described in detail. It should be understood,
however, that the description herein of specific embodiments is not intended
to limit the invention to the particular forms disclosed, but on the contrary,
the
to intention is to cover all modifications, equivalents, and alternatives
falling
within the spirit and scope of the invention as defined by the appended
claims.
DETAILED DESCRIPTION OF THE INVENTION
While the present invention may be embodied in any of several different
forms, the present invention is described here with the understanding that the
is present disclosure is to be considered as setting forth an exemplification
of
the present invention that is not intended to limit the invention to the
specific
embodiments) illustrated. Nothing in this application is considered critical
or
essential to the present invention unless explicitly indicated as being
"critical"
or "essential."
2o Figure 1 illustrates a pump 10 of the invention having a motor 12 with a
housing 14 at one end and a housing 16 at the other. The housings 14, 16
are cast of aluminum alloy and are essentially identical. A head assembly 18,
which includes head members 20, 22 and connecting tubes 24, 26, is bolted
to the housings 14, 16 above respective compression chamber portions 28,
2s 30 of the housings 14, 16 to help hold the housings 14, 16 together and
maintain their angular position with respect to each other. The pump 10 also
includes fan guards 32, one at each end, which are essentially identical to
one
another. The pump 10 of the present invention may be employed in a variety
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of applications, including but not limited to cable drying, sewage aeration,
tire
inflation, etc.
Referring to Figures 2 and 3, a partial cross section view of the pump 10 and
an end view of the pump 10 with the fan guard 32 removed are shown,
s respectively. The motor 12 has a shaft 34 which extends through it and into
both housings 14, 16, nearly to the end of each respective housing 14, 16. As
both housings 14, 16 are essentially identical, only the housing 14 is shown
in
Figure 2. Each end of the shaft 34 mounts a rotary fan blade 36 which is
rotated by the shaft 34 within a fan cavity 37 defined by the housing 14 in a
to direction so as to draw air into each respective housing 14, 16 and direct
it
over the coils of the motor 12 (i.e., an axial component of the cooling flow).
In
one embodiment, the rotary fan blade 36 is secured to the shaft 34 using a
spring clip 38.
The housings 14, 16 are provided with ventilation slots 39 to allow the
Is exhausting of cooling air. The housings 14, 16 mount bearings 40 which
journal the shaft 34. The housings 14, 16 also have openings (not shown) in
them which provide for the axial through-flow of air so that air moved by the
fan blade 36 reaches the coils of the motor 12.
The pump 10 includes a piston assembly 42 including a piston cylinder 44 and
2o a piston head 46 operating within the piston cylinder 44 to compress the
operating fluid (e.g., air) to provide the pumping action. The piston head 46
is
coupled by a connecting rod 48 to an eccentric 50 fixed to the shaft 34. In
operation, the shaft 34 and attached eccentric 50 rotates causing the
connecting rod 48 and piston head 46 to move within the piston cylinder 44.
2s A flapper valve (not shown) mounted to the valve plate 52 allows the air to
enter the piston cylinder 44 on the downstroke of the piston cycle and seals
to
prevent air passage on the upstroke. The piston head 46 also includes a
piston cup 54 constructed of Teflon~ or other similar material that provides a
sliding seal between the piston head 46 and the piston cylinder 44. The
3o piston cup 54 has a service life that may vary based on the temperature of
the
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piston cylinder 44, with a higher cylinder temperature resulting in a shorter
service life.
Besides allowing axial cooling air flow to dissipate heat that is transferred
from
the motor 12 to the housings 14, 16 to the bearings 40, the fan guard 32 also
s directs cooling flow over the piston cylinder 44 to dissipate heat generated
during the compression process. The housings 74, 16 includes openings 56
(shown in Figure 1 ) to allow the exhaust of cooling air directed over the
piston
cylinder 44.
Turning now to Figure 4 an isometric back view of the fan guard 32 is
1o provided. The front surface of the fan guard 32 is visible in Figure 1. The
fan
guard 32 defines a cooling flow opening 57 in its front surface to provide for
the passage of cooling flow past the fan guard 32. The fan guard includes rib
members 58 spanning the cooling flow opening 57 and support members 60
running perpendicular to the rib members 58. The spacing and arrangement
is of the rib and support members 58, 60 may vary depending on the particular
implementation. In general, the rib and support members 58, 60 are arranged
to allow the passage of cooling flow, but to prevent foreign objects from
entering the area proximate the moving rotary fan blade 36. In the illustrated
embodiment, the fan guard 32 is made of a resilient plastic resin, such as a
2o polyester polymer. The fan guard 32 includes a tab 62 that interfaces with
a
corresponding notch 64 (shown in Figure 2) in the housing 14 to secure the
bottom portion of the fan guard 32 to the housing 16. Mounting holes 66 are
defined in the fan guard 32 to allow the passage of screws for securing the
fan guard 32 to the housing 14 via corresponding holes 68 (shown in Figure
2s 3) in the housing 14. Any means may be used to secure the fan guard 32 to
the housing 14.
The fan guard 32 includes sidewalls 70 that define a channel 72. The channel
72 terminates in a baffle 74 that changes the direction of radial cooling flow
generated by the rotary fan blade 36 to impinge on the piston cylinder 44, as
3o indicated by the arrow 76 shown in Figure 2. The sidewalls 70 also define a
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flared portion 78 that collects the radial air flow and directs the flow into
the
channel 72.
Returning to Figure 2, the rotary fan blade 36 includes an extended hub 80
that abuts the eccentric 50 to positively locate the rotary fan blade 36 along
s the shaft 34 within the fan cavity 37. The rotary fan blade 36 is positioned
to
optimize the cooling provided to the piston cylinder 44 by the cooling flow
redirected by the fan guard 32. The optimal shaft position may be determined
empirically and may vary depending on the particular geometry of the pump
10. In the illustrated embodiment, the rotary fan blade 36 extends axially
to beyond the fan cavity 37 defined by the housing 14 into the space bounded
by
the fan guard 32. This position has been found to increase the effectiveness
of the fan guard 32 in redirecting the radial air flow to cool the piston
cylinder
44.
Redirecting cooling flow over the piston cylinder 44, as described herein,
~5 reduces the operating temperature of the piston assembly 42. The
combination of the rotary fan blade 36 and fan guard 32 also reduces the
temperature of the bearings 40 and the motor 12. Such temperature
reductions increase the operating lives of the piston cup 54 and the bearings
40 for a given set of operating conditions. The improved heat dissipation
2o characteristics may also be employed to extend the operating range of the
pump 10 to allow operation at higher pressures, different voltages, and/or
lower frequency voltage inputs.
The particular embodiments disclosed above are illustrative only, as the
invention may be modified and practiced in different but equivalent manners
2s apparent to those skilled in the art having the benefit of the teachings
herein.
Furthermore, no limitations are intended to the details of construction or
design herein shown, other than as described in the claims below. It is
therefore evident that the particular embodiments disclosed above may be
altered or modified and all such variations are considered within the scope
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and spirit of the invention. Accordingly, the protection sought herein is as
set
forth in the claims below.
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