U.S. patent application number 10/918253 was filed with the patent office on 2006-02-16 for linear pump with vibration isolation.
Invention is credited to Ross P. Christiansen, Paul J. Thomas.
Application Number | 20060034707 10/918253 |
Document ID | / |
Family ID | 35800130 |
Filed Date | 2006-02-16 |
United States Patent
Application |
20060034707 |
Kind Code |
A1 |
Thomas; Paul J. ; et
al. |
February 16, 2006 |
Linear pump with vibration isolation
Abstract
A linear pump having an axially aligned cylinder and piston
arrangement driven by an electromagnet motor. The cylinder, piston
and motor are contained in and coupled to a housing by a vibration
isolation system. The vibration isolation systems has resilient
mounts connected between a motor mount and a base of the housing as
well as resilient tubing extending between a valve head of the
cylinder and intake and exhaust chambers of the pump.
Inventors: |
Thomas; Paul J.; (Sheboygan,
WI) ; Christiansen; Ross P.; (Sheboygan Falls,
WI) |
Correspondence
Address: |
QUARLES & BRADY LLP
411 E. WISCONSIN AVENUE
SUITE 2040
MILWAUKEE
WI
53202-4497
US
|
Family ID: |
35800130 |
Appl. No.: |
10/918253 |
Filed: |
August 13, 2004 |
Current U.S.
Class: |
417/410.1 |
Current CPC
Class: |
F04B 39/0044 20130101;
F04B 17/03 20130101 |
Class at
Publication: |
417/410.1 |
International
Class: |
F04B 35/04 20060101
F04B035/04 |
Claims
1. A linear pump comprising a cylinder and piston disposed along a
piston axis and an electromagnet motor having a stator containing a
wire coil driving an armature connected to the piston to
reciprocate the piston within the cylinder along the piston axis,
wherein the cylinder, piston and motor are contained in and coupled
to a housing by a vibration isolation system including resilient
mounts connected between a motor mount and a base of the housing
and including a resilient tubing extending between a valve head of
the cylinder and intake and exhaust chambers of the pump.
2. The pump of claim 1, wherein the tubing is bellowed.
3. The pump of claim 1, wherein the resilient mounts snap mount in
place.
4. The pump of claim 3, wherein the motor support plate has
open-ended slots receiving the resilient mounts.
5. The pump of claim 1, wherein the resilient mounts include an
enlarged head disposed at a first side of the motor support plate
and an enlarged foot disposed at a second side of the motor support
plate opposite the first side.
6. The pump of claim 1, wherein the housing base includes a base
plate spaced from the motor mount having opening receiving the
resilient mounts and openings for the intake and exhaust
tubing.
7. The pump of claim 6, wherein the base defines the intake and
exhaust chambers.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Not applicable.
STATEMENT OF FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
BACKGROUND OF THE INVENTION
[0003] The present invention relates to pumps and in particular to
compact linear piston pumps.
[0004] Pumps for certain duties, such as oxygen concentration and
sewage aeration, generally need to be compact and operate
discreetly. It is thus important to properly muffle the working air
as well as reduce vibration during operation of the pump without
relying on a large, thick-walled housing to attenuate the sound and
vibration. Discreet operation of the pump can be obtained by
insulating the housing, however, this adds bulk and can cause
cooling problems. Mufflers can be added at the output, however,
this adds hardware and cost.
[0005] Such compact linear pumps/compressors are often single
cylinder devices with a small piston that reciprocates rapidly
within a small cylinder to pressurize the air. The rapid movement
of the single piston generates considerable vibration. These
vibrations are often transferred directly to the pump housing, via
a direct rigid mounting connection.
[0006] To facilitate reciprocation of the piston with less
vibration, it is known to suspend the drive member, such as the
armature of an electromagnetic motor, by springs or like flexible
members. Stacks of thin metal leaf springs are well-suited for
this. However, when multiple springs are used, it can be difficult
to achieve the prescribed spring rate to which the piston drive
components of the pump have been tuned. Changes in the angular
(about the piston axis) and/or axial (along the piston axis)
orientation of the springs relative to one another can effect the
spring rate. To ensure that the pump operates efficiently, it is
thus important to achieve the intended spring rate and thus ensure
the consistent orientation of the suspension springs, which can
make pump assembly difficult.
[0007] Another problem is that the intake and exhaust valves of the
valve head must open and close rapidly for each stroke of the
piston. Typically, thin metal flapper valves are used for this
purpose because of their ability to seat and unseat very rapidly.
Since the exhaust port opens under the force of the compressed air,
a valve stop is used to support the valve and prevent it from being
hyper-extended beyond its elastic range. The rapid contact between
the intake valve and the valve head or the exhaust valve and the
valve stop can generate tapping or clicking sounds. Another problem
is that the rapid opening and closing of the intake valve can cause
pressure fluctuations or pulsations in the air flow upstream from
the valve head. These air pulsations can generate a low-frequency,
rumbling noise.
[0008] Another problem confronting the design of compact linear
piston pumps is eliminating pulsations in the output air stream.
Pulsations in the air downstream from the outlet has been found to
alter the resonant frequency of pump when different lengths and/or
diameters of output lines are attached to the pump. Changing the
operational frequency of the pump causes inefficiencies that can
ultimately render the pump unusable for particular applications. It
can also exacerbate noise and vibration issues.
[0009] Yet another persistent problem in compact linear pump design
is cooling. To decrease noise, or perhaps to make immersible or
suitable for outdoor use, the working components of these pumps are
often enclosed in a pump housing. With operation of the pump,
friction and the current in the electromagnet coil generate heat.
As is well understood, heat adversely affects the pump efficiency
and life. Many times the need to keep the pump operating
efficiently requires the housing to be vented or to have other
measures taken which destroy, or at least significantly reduce, the
noise retarding features of the housing or other components.
[0010] Accordingly, an improved linear pump is needed that
addresses the aforementioned problems.
SUMMARY OF THE INVENTION
[0011] This invention is a linear pump with improved isolation of
the body of the pump form the internal working components.
[0012] In particular, the linear pump has a cylinder and piston
arrangement and an electromagnet motor with a stator containing a
wire coil driving an armature to reciprocate the piston within the
cylinder along a piston axis. The cylinder, piston and motor are
contained in and coupled to a housing by a vibration isolation
system. The vibration isolation system has resilient mounts
connected between a motor mount and a base of the housing and has
resilient tubing extending between a valve head of the cylinder and
intake and exhaust chambers of the pump.
[0013] In preferred forms, the tubing is bellowed allowing both
angular and axial flexing of the tubing. There is a separate
bellowed tubing extending from the valve head to each of the intake
and exhaust chambers. Preferably, the intake and exhaust chambers
are defined by a base of the pump housing to a side of the
cylinder/pump/motor arrangement and opposite the air intake to the
pump.
[0014] In other preferred forms, the resilient mounts are rubber
and are configured to snap mount in place. More specifically, the
motor support plate has open-ended slots receiving a narrowed neck
of the resilient mounts. The resilient mounts have enlarged heads
at one side of the motor support plate and enlarged feet at the
opposite side of the motor support plate. The motor support plate
is thus captured between the enlarged features of the resilient
mounts such than no other fasteners, particularly rigid fasteners,
are needed to secure the motor within the pump housing. Also, the
resilient mounts and tubing fit into openings in an internal base
plate of pump which, combined with the pump housing base, defines
the intake and exhaust chambers of the pump.
[0015] The present invention thus provides a linear pump with less
transfer of vibration from the internal working components to the
pump enclosure. Better isolation of the internal vibrations
provides for quieter operation, thereby increasing its desirability
and allowing the pump to be used for a wider range of
applications.
[0016] These and other advantages of the invention will be apparent
from the detailed description and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a perspective view of a linear pump according to
the present invention;
[0018] FIG. 2 is a perspective of the pump of FIG. 1 shown with a
housing shroud removed;
[0019] FIG. 3 is an exploded assembly view of the pump;
[0020] FIG. 4 is an exploded assembly view of a drive components of
the pump;
[0021] FIG. 5 is a sectional view taken along line 5-5 of FIG.
6;
[0022] FIG. 6 is a top view showing the pump with an inlet filter
and top cover removed;
[0023] FIG. 7 is a partial sectional view taken along line 7-7 of
FIG. 6 albeit with the inlet filter and top cover in place;
[0024] FIG. 8 is a top view of the pump with the housing shroud
removed and the drive components shown in phantom;
[0025] FIG. 9 is a top view of a pump base showing the intake and
exhaust chambers thereof;
[0026] FIG. 10 is a sectional view take along line 10-10 of FIG.
9;
[0027] FIG. 11 is a partial sectional view taken along line 11-11
of FIG. 9;
[0028] FIG. 12 is a sectional view taken along line 12-12 of FIG.
1;
[0029] FIG. 13 is an enlarged partial sectional view taken along
arc 13-13 of FIG. 12;
[0030] FIG. 14 is a sectional view taken along line 14-14 of FIG. 2
albeit shown with the housing shroud in place;
[0031] FIG. 15 is a partial sectional view taken along line 15-15
of FIG. 2 albeit with the outer housing in place;
[0032] FIG. 16 is a view of a retainer ring shown in isolation as
viewed from line 16-16 of FIG. 12; and
[0033] FIG. 17 is a view of a leaf spring shown in isolation as
viewed from line 17-17 of FIG. 12.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0034] The present invention provides an axial or linear piston
pump. The term pump used herein includes a device for providing
either positive or negative pressure, and thus either acting as a
vacuum pump or a compressor. The pump has a compact form factor,
with a preferred operating range of 2-30 psi depending upon the
application (however, the pump could be designed to operate at
other pressures) with low external vibration and noise and less
sensitivity to pump attachments (lines, hoses, tubing, etc.)
downstream from the outlet.
[0035] Referring to FIGS. 1-3, the pump, generally referred to in
the drawings by reference number 20, has a compact housing 22
including a base 24, a shroud 26 and a top cover 28. The shroud 26
is bolted to the base 24 (via bolts 23), with a gasket 30
therebetween (see FIG. 15), and the cover 28 is bolted (via bolt
69) to the shroud 26. The base has four feet 32 to support the pump
20 and provides an opening for connecting a fitting 34 (see FIG.
11). The shroud 26 has an opening 35 for an electrical socket (or
power cord). The cover 28 is spaced off of the shroud 26 slightly
to define an air intake passage 36 along the periphery of the cover
28, as will be described in greater detail below. The top of the
shroud 26 and the cover 28 are recessed on opposite sides to
provide a hand gripping area 38.
[0036] Referring to FIGS. 3, 5-7 and 12, the pump 20 breathes
through an air intake assembly generally designated 40. The air
intake 40 is configured to reduce the low, rumbling noise
associated with pulsations in the intake air caused by rapid
movement of the intake valve. In particular, the air intake 40
includes an inner cavity 42 defined in part by a recess in the top
of the shroud 26, a seal partition 44, a filter tray 46, a filter
48 and the cover 28, which provides the upper boundary for an outer
cavity 50.
[0037] As mentioned, the recessed top of the shroud 26 defines the
inner cavity 42, in the floor of which are two spaced apart
orifices 52 near one end (the right end in the drawings). The inner
cavity 42 is bounded at the top by the partition 44 which seals
against a peripheral wall 54 of the inner cavity 42. The partition
44 has a pair of spaced apart orifices 56 located at a (left) end
of the inner cavity 42 opposite the orifices 52. To facilitate
assembly the partition 44 includes another set of orifices 56' at
the opposite end, however, these are not used when the partition 42
is oriented as shown in the drawings. In any event, intake air
flows through only the one set orifices 56 (or 56'), which is
located opposite the orifices 52 in the floor of the inner cavity
42. Resting on the partition 44 is the filter tray 46 which holds
the filter 48 in the outer cavity 50. The filter tray 46 has a
bottom wall with a pair of openings 58 which align with orifices 56
in the partition 44. A small alignment feature 59 extends down from
the underside of the filter tray 46 and fits into an opening 61 in
the shroud 26 to ensure that the filter tray 46 is assembled in the
proper orientation. The filter 48 is held spaced off of the bottom
of the filter tray 46 by a number of small spaced apart risers 60,
and is retained by a short peripheral wall 62 ringing the filter
tray 46. The wall 62 has a cut-out 64 at one end (opposite the
openings 58) allowing intake air to flow laterally into the filter
48. The cover 28 fits onto the shroud 26 over the filter 48 to
define the outer cavity 50. Ribs 66 on the inside of the cover 28
contact the wall 62 of the filter tray 46 to keep the bottom edge
of the peripheral wall 68 of the cover 28 spaced slightly from the
shroud 26, and also to funnel the intake air into the outer cavity
50 through the cut-out 64. The space between the top cover 28 and
the shroud 28 defines the intake air passage 36, which extends
around the periphery of the cover 28. Aligned center openings in
the cover 28, filter 48, filter tray 46 and partition 44 allow a
bolt 69 to screw into a threaded opening 70 in the shroud 26 to
secure the assembly.
[0038] Referring now to FIGS. 5, 7, 8 and 12, the shroud 26 also
integrally defines a pair of vent tubes 72 which extend down form
the orifices 52 in the floor of the inner cavity 42. The vent tubes
72 inject the intake air passing from the intake 40 to the inside
of the shroud 26 past the drive assembly, described in detail
below, through three openings 80 in a base plate 82 (and elongated
opening 84 in the gasket 30), which is bolted to the base 24, and
into an intake chamber 86 in the base 24 of the housing, as shown
in FIG. 5. Note that the base plate 82 is bolted to the base 24 by
bolts 87 (see FIGS. 2 and 3).
[0039] As shown in FIG. 9, the intake chamber 86 is defined in the
base 24 with an exhaust chamber 88 in a yin-yang-like
configuration, each with a wide portion and a narrow portion in
opposite orientation. The intake air is drawn from the intake
chamber 86 up through an intake opening 90 in the base plate 82
(and an associate opening the gasket 30) and an intake tube 92
connected to the intake side of the drive assembly, as shown in
FIG. 10. Exhaust tube 94 runs between an exhaust opening 96 in the
base plate 82 (and an associated opening in the gasket 30) to the
exhaust side of the drive assembly. Importantly, the intake 92 and
exhaust 94 tubes are of bellowed construction allowing the tubing
to flex in response to vibrations of the drive assembly, without
transferring the vibration to the housing base 24. The intake 92
and exhaust 94 tubes simply snap into the base plate 82 and are
clamped (via clamps 98) to an associated nipple in the drive
assembly.
[0040] Referring now to FIGS. 2, 4, 5, 12 and 14, the drive
assembly generally includes a valve head 100, a cylinder 102, a
piston 104 and an electromagnet motor 106, all aligned
concentrically about a piston axis 108 (see FIG. 12). The entire
drive assembly is bolted (via bolts 109) to a motor mount 110 and
mounted to the base plate 82 via resilient mounts 112. The four
resilient mounts 112 have narrowed necks between enlarged heads and
bodies that slideably snap into four open ended slots 114 in the
motor mount 110. Slightly enlarged bottom ends of the resilient
mounts 112 can be pushed straight down through openings 116 in the
base plate 82, thereby, the motor mount 110 is captured by the
resilient mounts 112 and flexibly mounted to the base plate 82. The
resilient mounts 112 are preferably made of a suitable rubber, such
as an EPDM with a durometer of about 60, so as to provide enough
stiffness to securely mount the drive assembly while allowing
enough flexibility to isolate the vibrations of the drive
assembly.
[0041] With primary reference to FIGS. 2, 4 and 12, the drive
assembly will now be described in detail. The valve head 100
defines an intake side 120 and an exhaust side 122 each having a
respective nipple 124 and 126 to which the intake 92 and exhaust 94
tubes connect via clamps 98. A valve plate 128 mates with the valve
head 100. The valve plate 128 has a groove for a double D-shaped
(bisected circle) o-ring 130 sealing against the valve head 100 to
isolate the intake side 120 from the exhaust side 122. The valve
plate 128 is generally disk-shaped and defines a pair of intake
ports 131 (shown in phantom in FIG. 4) and a pair of exhaust ports
132. Each pair of ports is covered by respective thin metal flapper
valves 134 and 135 (the flapper valves 134 and 135 can be supported
by valve stops (not shown)). The intake 131 and exhaust 132 ports
are in communication with the associated sides of the valve head
100 and the inside of the cylinder 102, which fits into another
groove in the back side of the valve plate 128 sealed with another
o-ring 136 (see FIG. 13). The opposite side of the cylinder 102
fits around a hub of a retainer collar 138. The retainer collar 138
has four threaded openings, which receive four bolts 140 fit
through four ears of each of the valve head 100 and valve plate 128
to clamp the cylinder 102 tightly together with these
components.
[0042] The other side of the retainer collar 138 clamps one or more
leaf springs 142 with a recessed groove (having alignment features
as discussed below) in a spacer ring 144. The opposite side of the
spacer ring 144 receives a stator 146 of the electromagnet motor
106. The stator 146 is a slotted annular member having a circular
base and concentric inner 148 and outer 150 cylindrical walls (with
axial slots 169 in outer wall 150), which define an annular channel
152 therebetween. A wire coil 154 is disposed in a bobbin 156
within the channel 152. The bobbin 156 has three posts that extend
through openings in the base of the stator 146 and are engaged by
retainers 153 to retain the bobbin 156 and coil 154. A diode (not
shown) may be electrically coupled to the coil 154 to rectify the
alternating current input signal so that it drives an armature (or
shuttle) 158 in only one direction, preferably toward the stator
146. Conductive tabs 160 for coupling the coil 154 to the power are
also included.
[0043] The armature 158 has a series of axial bores therethrough
and slides in and out of a side (right in the drawing) of the
stator 146 when the coil 154 is energized. The armature 158 has a
short hub with an axial bore 162 that receives a bottom end of a
connecting rod 164. The connecting rod 164 is suspended along the
piston axis 108 by the leaf springs 142 and passes through the
center bore in the stator 146. The connecting rod 164 is secured to
the armature 158 and the piston 104 by a long bolt 166 threaded
into the piston 104 and mounting a mass disk 168 under its
head.
[0044] The stator 146 is clamped between the spacer ring 144 and
another spacer ring 172. That spacer ring 172 clamps one or more
additional leaf springs 142 against a second retainer collar 174.
Four tie rods 173 extending through ears in the first retainer
collar 138 are threaded into openings in ears of the second
retainer collar 174 to unite the components of the motor 106. The
retainer collars 138 and 174 also have threaded openings receiving
bolts 109 to connect the motor mount 110 and thereby mount the
entire drive assembly to the base plate 82 via the resilient mounts
112, as described above.
[0045] As shown in FIGS. 16 and 17, at the side opposite the
cylinder 102, the retainer collar 174 (as well as spacer ring 144)
has a circular groove 176 about its inner periphery with three
alignment pockets 178, the sides of which taper asymmetrically away
from the groove 176. One or more leaf springs 142 fit into the
groove 176 and their asymmetrically tapered alignment tabs 180 fit
into the pockets 178. Due to the asymmetric configuration of the
pockets 178 and tabs 180, the leaf springs 142 can seat properly
into the retainer collar 174 (and the spacer ring 144) in only one
angular and axial orientation (relative to the piston axis 108).
The alignment tabs 180 are spaced apart about 120 degrees so that
the springs can be mounted in one of three angular orientations. If
a single angular orientation is desired, the alignment tabs 180
could be spaced asymmetrically. This facilitates and ensures the
assembly of multiple leaf springs 142 in the same orientation at
both ends of the connecting rod 164. In particular, the web pattern
(and arcuate slots) of the leaf springs 142 are aligned, and any
curvature or bowing of the leaf springs 142 out of the plane
perpendicular to the piston axis 108 (which can occur from the die
cutting process) will be in the same direction for each leaf spring
142.
[0046] This is important to ensure that the motor 106 has the
spring rate for which it was designed. Specifically, during
development the pump is tuned to operate at a frequency at or near
its natural resonant frequency. In particular, the pump is operated
with a load applied and using a calculated spring-mass system
(i.e., the combination of spring rate of the springs 142 and mass
of the moving components, namely the piston 104, armature 158,
connecting rod 164 and any mass disk 168). The frequency of the
input signal to the motor 106 is varied as various parameters are
measured. For example, because power consumption goes up as the
input frequency strays from the resonant frequency of the
spring-mass system, power consumption measurements can be used to
adjust the spring-mass system so that its natural frequency will be
at or near that of a typical input signal, for example 60 Hz.
Operating the pump at the resonant frequency improves efficiency,
and reduces vibration, and thereby noise. The spring-mass system
can also be adjusted to operate efficiently at different pressures.
For example, by increasing mass or spring rate the spring-mass
system can be made to operate at or near resonant frequency while
the pump is providing increased pressure output. It should be noted
that the mass disk 168 is used as a cost effective alternative to
increasing or decreasing the mass of the piston, armature and/or
connecting rod.
[0047] As is well understood, the piston 104 is driven by movement
of the armature 158, when energy is supplied to the wire coil 154,
to reciprocate within the cylinder 102. The piston 104 has an
enlarged head with a peripheral groove holding a split piston ring
170 that seals against the cylinder 102 when pressure is developed.
The stroke length is approximately 8 mm (4 mm in each direction)
and is positioned approximately 1 mm from the top of the cylinder
when at top dead center.
[0048] Given the single cylinder arrangement of the pump 20, the
reciprocating piston 104, armature 158 and connecting rod 164 can
cause the drive assembly inside the housing to vibrate. The leaf
springs 142 absorb much of the energy from these moving components.
The number, size and thickness of the leaf springs 142 are selected
to achieve a spring rate determined primarily according to the mass
of the piston 104 and the input frequency. The leaf springs 142 are
selected so that in combination (between the two stacks) they
result in a resonant frequency of the piston 104 and springs 142
(i.e., the spring-mass system) approximately equal to the input
frequency, which is typically 50 or 60 Hertz. For example, in one
preferred embodiment there is a stack of two springs in the second
retainer collar 174 and a stack of two springs in the spacer ring
144 near the piston 104. If the stroke length were to be increased,
for example if the pump to be used in an application requiring more
air flow, the springs 142 could be of a thinner gauge, in which
case the number of springs may be increased to three in each stack
to achieve the same spring rate.
[0049] With reference to FIGS. 5-7, 9-11 and 13, air flow through
the pump will now be described in detail for a preferred compressor
embodiment of the pump. When the drive assembly is operating,
ambient air is drawn into the pump intake through the intake air
passage 36 around the periphery of the top cover 28. As shown in
FIGS. 5-7, the intake air is drawn through the intake air passage
36 flowing upwardly along the ribs 66 and makes its way into the
outer cavity 50 through the cut-out 64 in the peripheral wall 62 of
the filter tray 46. Intake air then moves from that end of the
outer cavity 50 through the filter 48 and around the risers 60 in
the filter tray 46 to the openings 58 in the filter tray 46 and the
partition 44 where it enters the inner cavity 42. The pressure of
the intake air drops as it passes through the small opening into
the inner cavity 42. The inner cavity 42 is effectively larger than
the outer cavity 50, which allows the intake air to expand. The
expansion of the intake air in the inner cavity 42 helps to
dissipate the pulsations in the intake air arising from the
operation of the intake valve. After entering the inner cavity 42,
the intake air turns through a bend of about 90-180 degrees and
travels to the other end of the inner cavity 42 to the orifices 52
where it travels down the vent tubes 72 and into the interior of
the housing shroud 26. As shown in FIG. 5, the vent tubes 72 are
located to direct the intake air into the slots 169 in the stator
146 of the motor 106 so as to convectively cool the coil 154. After
passing through and around the motor 106, the intake air passes
through the openings 80 in the base plate 82 into the wide part of
the intake chamber 86. The air is routed through the narrowed part
and up through the intake opening 90 in the base plate 82 and the
intake tube 92 to the intake side 120 of the valve head 100, as
shown in FIG. 10. Reciprocation of the piston 104 draws air into
the cylinder 102 and compresses it. The pressurized air is then
passed through the exhaust side 122 of the valve head 100 and down
through the exhaust tube 94 in the base plate 82 to the wide part
of the exhaust chamber 88 through exhaust opening 96. As shown in
FIGS. 9 and 11, the pressurized air flows through the narrow
portion of the exhaust chamber 88 and out through the outlet
opening where fitting 34 is attached to suitable hose or tubing
(not shown).
[0050] Since the pump has only a single cylinder, the pressurized
air is pulsed at the rate of the input frequency, for example 60
Hz. The inventors have determined that pulsations in the output air
can adversely effect the operation of the pump. In particular, the
output lines act as resonant chambers, having their own natural
frequency. If the pulsations in the output air are at a different
frequency, the air will effectively encounter increased resistance
going through the output lines. This creates excessive back
pressure on the pump so that the spring-mass system can be made to
operate at a different (non-resonant) frequency, thereby decreasing
the efficiency of the pump. This makes the pump more sensitive to
variations in input frequency which can further decrease
efficiency. By reducing the amplitude of the pulsations in the air
before leaving the pump, this problem can be avoided.
[0051] To that end, as shown in FIGS. 3, 9 and 13, the pulsations
in the pressurized output air leaving the pump are dampened by a
diaphragm 190 in the exhaust chamber 88. In particular, the
diaphragm 190 is preferably a rubber disk mounted to the top of a
cup 192 defined by the housing base 24 in the wide part of the
exhaust chamber 88 by a support ring 194 bolted (via bolts 198) to
the base 24. The cup 192 defines a trapped air pocket 196 below the
diaphragm 190. As the pressurized air flows through the exhaust
chamber 88, the pulsations act against the diaphragm 190, tending
to make it flex into the cup 192. The air pocket 196 will compress
slightly, but tend to resist inward movement of the diaphragm 190.
This reactive force on the diaphragm 190 will tend to counter, and
thus cancel or reduce the amplitude of, the pulsations in the
exhaust chamber air. The diaphragm 190 and trapped air pocket 196
act similar to an accumulator, and as a result, allow the pump to
output smoother, relatively non-pulsed, air through the output
lines. As a result pump inefficiencies are avoided that may
otherwise arise from changes in the length or diameter of the
output lines or from changes to the input frequency to the motor.
As an example of one advantage, the inventors have determined that
use of the diaphragm in this way allows a single mass-spring system
to be used for both 50 and 60 Hz applications.
[0052] An illustrative embodiment of the present invention has been
described above in detail. However, the invention should not be
limited to the described embodiment. To ascertain the full scope of
the invention, the following claims should be referenced.
* * * * *