U.S. patent application number 11/189527 was filed with the patent office on 2005-12-15 for muffler system for a compressor.
This patent application is currently assigned to BRISTOL COMPRESSORS, INC.. Invention is credited to Gilliam, David Rex, Majerus, Benjamin Alan, Marshall, Steven Edwin, Monk, David Turner.
Application Number | 20050276711 11/189527 |
Document ID | / |
Family ID | 33449964 |
Filed Date | 2005-12-15 |
United States Patent
Application |
20050276711 |
Kind Code |
A1 |
Marshall, Steven Edwin ; et
al. |
December 15, 2005 |
Muffler system for a compressor
Abstract
A muffler system for a compressor includes an expansion chamber
muffler for reducing pressure pulses at the compressor's
fundamental pulsation frequency and a side-branch muffler for
filtering high-frequency pressure pulses. The expansion muffler is
positioned along the compressor discharge stream at a location that
maximizes pulsation reduction at the compressor's fundamental
pulsation frequency. The side-branch muffler is tuned to the
frequency at which the pulsation reduction for the expansion
muffler is at a minimum.
Inventors: |
Marshall, Steven Edwin;
(Abingdon, VA) ; Gilliam, David Rex; (Bristol,
VA) ; Monk, David Turner; (Bristol, VA) ;
Majerus, Benjamin Alan; (Bristol, VA) |
Correspondence
Address: |
MCNEES, WALLACE & NURICK LLC
100 PINE STREET
P.O. BOX 1166
HARRISBURG
PA
17108-1166
US
|
Assignee: |
BRISTOL COMPRESSORS, INC.
Bristol
VA
|
Family ID: |
33449964 |
Appl. No.: |
11/189527 |
Filed: |
July 26, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11189527 |
Jul 26, 2005 |
|
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10441306 |
May 19, 2003 |
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6935848 |
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Current U.S.
Class: |
417/540 ;
417/312 |
Current CPC
Class: |
F04B 39/123 20130101;
F04B 49/03 20130101; Y10S 181/403 20130101; F04B 39/0061 20130101;
F04B 49/10 20130101; Y10S 417/902 20130101 |
Class at
Publication: |
417/540 ;
417/312 |
International
Class: |
F04B 039/00; F04B
053/00 |
Claims
What is claimed is:
1. A muffler system for a compressor having a compressor shell and
a compressing device with a gas discharge port, the muffler system
comprising: a side-branch muffler, the side-branch muffler to be
disposed within a compressor shell and in fluid communication with
a gas discharge port upon installation of the side-branch muffler;
an expansion muffler disposed exterior to the compressor shell at a
predetermined distance from the gas discharge port for maximizing
pulsation reduction at a fundamental pulsation frequency of a
compressing device upon installation of the expansion muffler; an
exhaust system connecting the side-branch muffler and the expansion
muffler; and wherein the side-branch muffler is tuned to a
frequency at which pulsation reduction for the expansion muffler is
at a minimum.
2. The muffler system of claim 1 wherein the expansion muffler has
an elongated chamber.
3. The muffler system of claim 1 wherein a portion of the exhaust
system extends substantially vertically along the exterior of the
compressor shell.
4. The muffler system of claim 3 wherein the expansion muffler is
positioned adjacent to an upper portion of the compressor shell
upon installation.
5. The muffler system of claim 1 wherein the side-branch muffler
filters pressure pulses capable of transmitting noise to the
compressor shell and capable of passing through the expansion
muffler without attenuation.
6. The muffler system of claim I wherein the predetermined distance
includes a range of about 45-50 inches.
7. The muffler system of claim 1 wherein the predetermined distance
is about 48 inches.
8. A compressor system comprising: a housing having an exhaust
port; a compression means for compressing a refrigerant fluid, the
compression means being disposed within the housing, the
compression means having a discharge port for exhausting compressed
refrigerant fluid from the compression means; an expansion muffler
disposed exterior to the housing a predetermined distance from the
exhaust port and in fluid communication with the exhaust port, the
expansion muffler being configured and disposed to maximize
pulsation reduction at a fundamental pulsation frequency of a
compressing device; a side-branch muffler disposed within the
housing and in fluid communication with the discharge port, the
side-branch muffler being in fluid communication with the exhaust
port; and wherein the side-branch muffler is tuned to a frequency
at which pulsation reduction for the expansion muffler is at a
minimum.
9. The muffler system of claim 8 wherein the expansion muffler is
positioned adjacent to an upper portion of the housing.
10. The muffler system of claim 8 wherein the predetermined
distance includes a range of about 45-50 inches.
11. The muffler system of claim 8 wherein the predetermined
distance is about 48 inches.
12. The muffler system of claim 8 wherein the expansion muffler has
an elongated chamber.
13. The muffler system of claim 8 wherein the side-branch muffler
filters pressure pulses capable of transmitting noise to the
housing and capable of passing through the expansion muffler
without attenuation.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This Application is a continuation in part of application
Ser. No. 10/441,306, filed May 19, 2003.
FIELD OF THE INVENTION
[0002] The present invention is directed to a muffler system for
use with a compressor, and more specifically to a muffler system
having an internal muffler and an external muffler for use with the
high-pressure discharge side of a compressor used in refrigeration,
cooling and heating systems.
BACKGROUND OF THE INVENTION
[0003] Compressors are one of several components in cooling and
heating systems. They are an important component as the compressor
is used to compress refrigerant gas used in the system, raising the
pressure and the temperature of the gas. The compressor is
typically used in combination with a condenser, expansion valves,
an evaporator and blowers to heat or cool a space. Depending on the
direction of the refrigerant flow upon exiting the compressor, the
system can be used to remove heat from a preselected space or
provide heat to a preselected space.
[0004] The compressor itself typically is a hermetically sealed
device that has an intake port and a discharge port. The
hermetically sealed device typically is a metallic shell that
houses an electric motor and a mechanical means, such as pistons or
other mechanical portion, for compressing gas. For most compressor
designs, the gas cavity enclosed by the housing serves as a
reservoir of low-pressure gas to be drawn into the mechanical
section of the compressor. The electric motor is connected to a
power source that provides line power for operation. The motor in
turn drives the mechanical means for compressing gas. Compressors
are typically categorized by the mechanical means used to compress
the gas. For example, compressors using a scroll compression device
to compress refrigerant gas are referred to as scroll compressors;
compressors using a piston device to compress the refrigerant gas
are referred to as reciprocating compressors; compressors using
rotating cams to compress a refrigerant gas are known as rotary
compressors. While there are differences among the compressors as
to how refrigerant gas is compressed, the basic principles of
operation as set forth above are common among the compressors,
i.e., gas is drawn in through the gas intake when the motor is
energized, the gas is compressed in the mechanical portion of the
compressor and the highly compressed gas is discharged through an
outlet port.
[0005] While different compressor designs may result in different
noise generation mechanisms and overall different noise profiles,
there are common sources of noise for the various types of
compressors. One common source of noise originates in the exhaust
gas at the discharge where the noise takes the form of a pressure
pulsation. Pressure pulsation in the exhaust gas typically
generates discrete narrowband tones at the harmonics of the
operating speed. The pulsation propagates from the compressor
discharge mechanism downstream in the refrigerant gas. The pressure
pulsation can transmit noise through the compressor housing at the
point of discharge tube penetration, or can propagate further
downstream and induce noise upon contacting other components of the
refrigeration system. As can be seen, this sound is particularly
undesirable when the system is located within, adjacent to or near
a living area or a work area.
[0006] Various mufflers have been attempted to eliminate, reduce or
otherwise attenuate pressure pulsation and compressor noise. For
piston-driven compressors, mufflers are typically positioned inside
the compressor housing on the discharge side of the cylinder head,
also referred to as a discharge head. While a muffler having an
expansion chamber located adjacent to the discharge head can
prevent pressure pulsation from propagating downstream, it has been
found that placement of an expansion chamber muffler adjacent the
discharge head reduces operating efficiency of the compressor,
while also increasing the overall size of the compressor.
[0007] What is needed is a compressor muffler system that
sufficiently attenuates pressure pulsation generated by compressor
operations without adversely affecting the compressor operating
efficiency.
SUMMARY OF THE INVENTION
[0008] The present invention relates to a muffler system for a
compressor having a compressor shell and a compressing device with
a gas discharge port, the muffler system including a side-branch
muffler, the side-branch muffler to be disposed within a compressor
shell and in fluid communication with a gas discharge port upon
installation of the side-branch muffler. An expansion muffler is
disposed exterior to the compressor shell at a predetermined
distance from the gas discharge port for maximizing pulsation
reduction at a fundamental pulsation frequency of a compressing
device upon installation of the expansion muffler. An exhaust
system connects the side-branch muffler and the expansion muffler;
and the side-branch muffler is tuned to a frequency at which
pulsation reduction for the expansion muffler is at a minimum.
[0009] The present invention further relates to a compressor system
including a housing having an exhaust port and a compression means
for compressing a refrigerant fluid, the compression means being
disposed within the housing, the compression means having a
discharge port for exhausting compressed refrigerant fluid from the
compression means. An expansion muffler is disposed exterior to the
housing a predetermined distance from the exhaust port and in fluid
communication with the exhaust port, the expansion muffler being
configured and disposed to maximize pulsation reduction at a
fundamental pulsation frequency of a compressing device. A
side-branch muffler is disposed within the housing and in fluid
communication with the discharge port, the side-branch muffler
being in fluid communication with the exhaust port. The side-branch
muffler is tuned to a frequency at which pulsation reduction for
the expansion muffler is at a minimum.
[0010] An advantage of the present invention is the inclusion of an
expansion chamber muffler exterior of the compressor housing for
attenuating pressure pulses from propagating downstream in the
refrigeration circuit, reducing the overall size of the compressor
housing, while not adversely affecting the compressor operating
efficiency. The side-branch muffler, while able to be located
inside the compressor housing due to its small volume, serves to
reduce pressure pulsation at the frequency not addressed by the
expansion muffler, thus reducing sound radiation from the
compressor housing and preventing pressure pulsation from
propagating downstream in the refrigeration circuit.
[0011] Other features and advantages of the present invention will
be apparent from the following more detailed description of the
preferred embodiment, taken in conjunction with the accompanying
drawings which illustrate, by way of example, the principles of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a cross-section of a refrigerant compressor that
incorporates the muffler system of the present invention;
[0013] FIG. 2 is a partial elevation view of the side-branch
muffler discharge tube of the present invention taken along line
II-II from FIG. 1;
[0014] FIG. 3 is a perspective view of a muffler of the present
invention;
[0015] FIG. 4 is a cross-section of the muffler being joined to the
discharge tube of the present invention;
[0016] FIG. 5 is a graph illustrating pressure pulsation reduction
at the fundamental pulsation frequency versus expansion chamber
location from the discharge head;
[0017] FIG. 6 is a graph illustrating pressure pulsation reduction
versus pulsation frequency for the combination of the expansion
muffler and a tuned side-branch muffler;
[0018] FIG. 7 is an elevation view of an embodiment of the present
invention showing the position of an external muffler; and
[0019] FIG. 8 is a cross section of the external muffler of the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0020] One embodiment of a compressor that incorporates the muffler
system of the present invention is depicted in FIG. 1. Compressor 2
is connected to a conventional refrigeration or heating,
ventilation and air conditioning and refrigeration (HVAC&R)
system (not shown), such as may be found in a refrigerator, home or
automobile. The HVAC&R system has a condenser, expansion device
and evaporator in fluid communication. Compressor 2 is preferably a
reciprocating compressor connected to an evaporator (not shown) by
a suction line that enters the suction port 14 of compressor 2,
although the muffler system may be used with any compressor,
including, for example, a rotary, screw, or scroll compressor.
Suction port 14 is in fluid communication with suction plenum 12.
Refrigerant gas from the evaporator enters the low-pressure side of
compressor 2 through suction port 14 and then flows to the suction
plenum 12 before being compressed.
[0021] Compressor 2 includes an electrical motor 18. A standard
induction motor having a stator 20 and a rotor 22 is shown. However
any other suitable electrical motor may be used. A shaft assembly
24 extends through rotor 22. The bottom end 26 of shaft assembly 24
in this compressor 2 extends into a lubrication sump 28 and
includes a series of apertures 27. Connected to shaft assembly 24
below the motor is at least one piston assembly 30. Compressor 2 of
FIG. 1 depicts two piston assemblies. A connecting rod 32 is
connected to a piston head 34 which moves back and forth within
cylinder 36. A cylinder head includes a gas inlet port 38 and a gas
discharge port 40. Associated with these ports 38, 40 are
respective suction valves and discharge valves (not shown)
assembled in a manner well known in the art. Gas inlet port 38 is
connected to an intake tube 54 which is in fluid communication with
suction plenum 12.
[0022] Motor 18 is activated by a signal in response to a
predetermined condition, for example, an electrical signal from a
thermostat when a preset temperature is reached. Electricity is
supplied to stator 20, and the windings in the stator 20 cause
rotor 22 to rotate. Rotation of rotor 22 causes the shaft assembly
24 to turn. In the compressor shown, oil in the sump 28 is drawn
through apertures 27 in bottom end 26 of shaft 24 and moved upward
through and along shaft 24 to lubricate the moving parts of
compressor 2.
[0023] Rotation of rotor 22 also causes reciprocating motion of
piston assembly 30. As the assembly moves to an intake position,
piston head 34 moves away from gas inlet port 38, the suction valve
opens and refrigerant fluid is introduced into an expanding
cylinder 36 volume. This gas is pulled from suction plenum 12
within compressor housing 16. This gas is pulled into intake tube
54 to gas inlet port 38 where it passes through the suction valve
and is introduced into cylinder 36. When piston assembly 30 reaches
a first end (or top) of its stroke, shown by movement of piston
head 34 to the right side of cylinder 36 of FIG. 1, the suction
valve closes. The piston head 34 then compresses the refrigerant
gas by reducing the cylinder 36 volume. When piston assembly 30
moves to a second end (or bottom) of its stroke, shown by movement
of piston head 34 to the left side of cylinder 36 of FIG. 1, a
discharge valve is opened and the highly compressed refrigerant gas
is expelled through gas discharge port 40. The highly compressed
refrigerant gas flows from the gas discharge port 40 past a
side-branch muffler 50 then through an exhaust or discharge tube
52, exiting the compressor housing 16 into a conduit connected to a
condenser. An expansion muffler 56 positioned outside the
compressor housing 16 is connected in fluid communication with the
conduit between the compressor 2 and the condenser adjacent the
compressor housing 16. This comprises one cycle of the piston
assembly 30.
[0024] The placement of muffler 56 physically outside compressor
housing 16 and at a specific distance along the conduit connecting
compressor housing 16 and the condenser is useful in reducing the
pressure pulsation at the fundamental pulsation frequency. For
example, the fundamental pulsation frequency for a reciprocating
compressor is the number of cylinders multiplied by the rotational
speed of the motor. That is, a compressor with two cylinders
operating at a rotational speed of 60 cycles per second (60 hertz)
will produce a fundamental pulsation at a frequency of 120 hertz.
For maximum pulsation reduction, muffler 56 must be placed at a
specific distance from the gas discharge port 40 as determined by
the wave speed and wavelength within the refrigerant gas at the
operating conditions of pressure and temperature. Further, locating
muffler 56 outside compressor housing 16 not only permits a
reduction in size of the compressor housing 16, but enhances the
effectiveness of muffler 56 without adversely affecting the
efficiency of the compressor 2 as will be discussed in further
detail below. Side-branch muffler 50 additionally filters pressure
pulsation at the frequency not affected by the expansion muffler
that tend to radiate directly from compressor housing 16 as
unwanted noise and propagate downstream in the refrigerant circuit.
Side-branch muffler 50 preferably includes an internal pressure
relief valve (IPRV), or pressure relief member 60 connected to a
resonator volume 82 (FIG. 4) as further discussed in application
Ser. No. 10/440,763, which is incorporated herein by reference.
[0025] Referring to FIGS. 2-4, muffler 50 preferably utilizes a
side-branch resonator volume 82 tuned to a frequency for pressure
pulsation unaffected by the expansion muffler 56 that generates
noise at the discharge tube--compressor housing penetration and
propagates downstream in the refrigeration circuit. Side-branch
muffler 50 includes a tube 62 having opposed ends 76, 78. A
threaded member 64 having a lip 80 at one end is positioned over
end 78 of tube 62 for threadedly engaging the discharge head to
maintain tube 62 in fluid communication with gas discharge port 40.
Preferably, the end 78 of tube 62 and the end of threaded member 64
opposite lip 80 are substantially coincident to ensure the parts
are sufficiently engaged therebetween. A housing 68 alternative
includes opposed openings 70, 72 which permits opening 70 of
housing 68 to be positioned over end 78 of tube 62 until opening 72
of housing 68 sufficiently contacts lip 80. Methods of securing
tube 62, housing 68 and threaded member 64 in position to each
other such as spot welding, soldering, brazing, or by press-fit are
well known in the art. Housing 68 is preferably substantially
cylindrical in profile and defines a resonator volume 82 between
tube 62 and housing 68. Tube 62 and housing 68 are maintained in
fluid communication by a pair of preferably axially aligned
resonator throats 66 formed in tube 62. However, it is to be
understood that more than two throats 66 may be used and that the
throats 66 are not required to be in axial alignment. The flow area
and distance between the resonator throats 66, as well as the size
of the volume resonator 82 are specified such to `tune` the
side-branch resonator muffler to the pulsation frequency unaffected
by expansion muffler 56 and most likely to excite noise at the
discharge tube 52--compressor housing 16 penetration. Resonator
volume 82 displaces significantly less volume than typically used
mufflers that employ an expansion chamber. Although not necessarily
drawn to scale in FIG. 4, between openings 70, 72, resonator volume
82 displaces a comparable volume as compared to tube 62. By virtue
of both this lack of pronounced volumetric increase of resonator
volume 82 that is adjacent the discharge port 40 and controlling
the specific distance from the discharge head to the expansion
chamber, compressor efficiency is maintained. Additionally, the
small size of housing 68 of muffler 50 permits reduction in size of
the compressor housing.
[0026] While preferred, it is to be understood that it is not
required that muffler 50 be secured directly to the discharge head.
That is, muffler 50 can be located anywhere within the compressor
housing 16 downstream of the discharge head.
[0027] One end of discharge tube 52 is connected to muffler 50. The
other end of discharge tube 52 is connected to the discharge outlet
15 of compressor 2. While a preferred embodiment of discharge tube
52 is of unitary construction, as previously discussed, if desired,
discharge tube 52 may be segmented, such as to insert a
discharge-side component such as an IPRV 60. A portion of the
discharge tube 52 adjacent muffler 50 preferably has a cane or
inverted "J" shape, but can have any suitable shape. The shape of
discharge tube 52 is primarily driven by the location and attitude
of the two interface locations within the compressor housing 16
while maintaining sufficient spacing from compressor components.
Thus, the path of the unitary discharge 52 tube typically follows a
path adjacent the compressor housing 16, preferably including from
an end 98, a substantially straight portion 116 which extends into
a substantially curved portion 118 and similarly extends into a
remaining portion 120 that terminates at end 106. Referring back to
FIGS. 1, 2 and 4, both tube 62 of muffler 50 and a portion of
discharge tube 52 share a coincident axis 84. The segment or
portion of discharge tube 52 that extends along axis 84 is of an
extended length which more evenly distributes prestresses along the
collective axial length of tube 52. Additionally, the joint formed
between discharge tube 52 and tube 62 of muffler 50 is also
coincident with axis 84. In one embodiment, tube 62 of muffler 50
has an enlarged diameter portion 94 that extends into a shoulder 96
formed therein that is coincident with axis 84. To establish the
joint between tube 62 of muffler 50 and discharge tube 52, end 98
of exhaust tube 52 is directed inside the enlarged diameter portion
94 of tube 62 past end 76 to the extent required to form the joint,
up to "bottoming out" at the shoulder 96.
[0028] Discharge tube 52 connects in a similar way to discharge
outlet 15. Discharge outlet 15 includes a fitting 100 that extends
through an aperture 112 in the compressor housing 16. The fitting
100 is provided with a secure joint between itself and the
compressor housing 16 that is both fluid tight and rigid, both to
prevent the leakage of refrigerant through aperture 112 and avoid
unnecessary flexure to the subsequent joints formed between both
the fitting 100 and the discharge tube 52 inside the compressor
housing 16 and between the conduit and the fitting 100 located
outside the compressor housing 16. A fitting portion 114 of fitting
100 extends inside the compressor housing 16 which axially aligns
along axis 99 with end 106 of tube 52. The portion of fitting
portion 114 that is inside compressor housing 16 includes an end
102 having an enlarged diameter portion 104. To establish a joint
between the discharge tube 52 and fitting portion 114, the end 106
of discharge tube 52 is directed past end 102 of fitting portion
114 along axis 99 into the enlarged diameter portion 104 until a
joint is formed. The joint may be secured by soldering or other
appropriate bonding method. Preferably, the joints for each end 98,
106 of discharge tube 52 is established prior to securing the
joints. By virtue of the this variable, coincident insertion
distance along enlarged diameter portion 94 between discharge tube
52 and tube 62 of muffler 50 and between discharge tube 52 and
fitting portion 114, prestresses in the discharge tube 52 caused by
non-alignment installation conditions may be further reduced,
thereby improving the structural integrity of the compressor.
[0029] Referring to FIGS. 7, 8, fitting 100 extends outside
compressor housing 16 into an extension 134 which further extends
into a bend 130, preferably a right angle, that terminates at an
upturned end 132. Alternately, fitting 100 could terminate
immediately outside of compressor housing 16, if desired. A
substantially straight conduit 136 has an end 138 that inserts
inside of end 132 of fitting 100 for connection therewith. Conduit
136 extends substantially parallel to the compressor housing 16 in
a substantially vertical direction by virtue of the right angle
connection with end 132, terminating at end 140 which, in one
embodiment, is adjacent the top of the compressor housing 16.
Alternately, conduit 136 could be curved in shape and could extend
in any direction or attitude with respect to fitting 100. The
second muffler member 56 is connected at inlet end 142 with end 140
of conduit 136 and has an opposed exhaust end 144 for connection
with a conduit connecting with a condenser (not shown). Fitting
100, conduit 136 and muffler 56 are in continuous fluid
communication therebetween so that refrigerant fluid exhausting
from compressor housing 16 sequentially flows through fitting 100
and conduit 136 before reaching muffler 56.
[0030] Muffler 56 attenuates pressure pulses generated by operation
of the compressor. Muffler 56 is provided with the inlet end 142
and the exhaust end 144 on opposed ends of muffler 56. A preferably
enlarged diameter housing 152 is interposed between inlet end 142
and exhaust end 144. The gas volume enclosed by housing 152 serves
to filter pressure pulsations propagating in conduit 136. The
ability for muffler 56 to filter pressure pulsations is extremely
sensitive to the total distance between the discharge head and
muffler 56. In fact, maximum pulsation reduction at the
compressor's fundamental pulsation frequency occurs when muffler 56
is located along the discharge path at a position as determined by
the wave speed and wavelength within the refrigerant gas at the
operating conditions of pressure and temperature. For example, a
compressor with two cylinders operating at 60 cycles per second (60
hertz) rotational speed will produce a fundamental pulsation at a
frequency of 120 hertz. If the speed of sound in the refrigerant
gas is 7200 inches per second (the speed of sound for R22), then
the wavelength at the fundamental pulsation frequency is 60 inches
(7200 inches per second/120 cycles per second). Since each
wavelength includes two maximum pressure points, the distance
between maximum attenuation points is 30 inches for this case, FIG.
5. FIG. 5 provides a design guide to position the muffler such to
achieve maximum reduction at the fundamental pulsation frequency,
often the most troublesome frequency in a refrigerant compressor as
will be discussed in additional detail below.
[0031] A compressor system using the novel combination of the
side-branch muffler 50 mounted internally within the compressor
housing 16 and expansion muffler 56 mounted adjacent but external
to the compressor housing has been tested. Further referring to
FIG. 5, pulsation reduction is illustrated as a function of
distance from the discharge head of the compressor for the
fundamental pulsation frequency at the operating condition of
pressure and temperature. The attenuation provided by the muffler
is shown in decibel reduction. The decibel reduction is given by 10
times the logarithm of the ratio of the input dynamic pressure to
the output dynamic pressure. It is shown that significant pulsation
reduction can be achieved with an expansion chamber muffler
positioned approximately 15-20 inches from the discharge head,
which is identified as region "A" on the attenuation curve. Region
"A" is inside the compressor housing, the penetration which is
identified by the vertical dotted line that is approximately 32
inches from the discharge head and additionally identified as "C".
However, significant efficiency losses of at least two percent are
attributable with the muffler being located within the compressor
housing adjacent the discharge head as compared to being located
further downstream. Also, the muffler requires significant volume
which is not always available inside the housing. Note, however,
that further along the curve, approximately 45-50 inches from the
discharge head, identified as region "B", the pulsation reduction
is substantially identical to the level shown in region "A". Region
"B" is located approximately 15-20 inches from the position of the
housing. For purposes herein, the position of the compressor
housing discharge port and the housing penetration (region "C") are
substantially the same. In other words, by connecting the expansion
muffler to the discharge port by a conduit of less than two feet in
length, the compressor operates quietly and efficiently while
gaining additional room within the compressor housing or permitting
the volume of the compressor housing to be reduced and still
achieving the same performance.
[0032] In addition to reduced compressor housing size and
efficiency gains as previously discussed, by virtue of muffler 56
being used outside the compressor housing, the user has the
opportunity to easily replace muffler 56, if desired. Provided the
replacement muffler is located at the same position from the
discharge head, the performance of the side-branch muffler is
unaffected. Typically, as compressor capacity increases, so does
the amplitude of the pressure pulsations associated with its
operation. Thus, different mufflers may be desirable for use with
compressors having different operating capacities, although
identical mufflers may be selected for use with compressors having
different operating capacities to reduce inventory. With the
present invention, the user need only replace an existing muffler
with another configured to attenuate the increased amplitudes,
since the existing muffler was already positioned within the range
of lengths corresponding to substantially maximum attenuation
levels.
[0033] While the expansion muffler 56 has been positioned for
maximum pulsation reduction at the fundamental pulsation frequency,
pressure pulsation at the harmonics of the fundamental frequency is
also a concern. It is a physical property of expansion mufflers
that while maximum pulsation reduction is achieved at one frequency
for a specific muffler position, other frequencies may be
unaffected by the muffler when located at that position. Therefore,
in order to prevent higher frequency pulsation from transmitting
sound at the housing penetration or from propagating downstream in
the refrigeration circuit, a side-branch muffler has been added on
the inside of the compressor housing as discussed above. Referring
to FIG. 6, the pulsation reductions versus frequency for both the
expansion muffler at the specified location and the side-branch
muffler are illustrated. As shown, the pulsation reduction for the
expansion muffler decreases to zero at about 1100 hertz. Therefore,
the side-branch muffler has been tuned to this `drop-out` frequency
of the expansion muffler.
[0034] While the invention has been described with reference to a
preferred embodiment, it will be understood by those skilled in the
art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this invention, but that the invention will include
all embodiments falling within the scope of the appended
claims.
* * * * *