Discharge muffler placement in a compressor

A muffler system for a compressor includes an expansion chamber muffler for attenuating sound pressure pulses and an acoustic muffler for filtering high-frequency pressure pulsations. The acoustic muffler is connected inline along the discharge side of the compressor between the discharge port of the cylinder head and a discharge tube in fluid communication with the outlet port of the compressor housing. A conduit is in fluid communication between the outlet port of the compressor housing and the condenser to supply the flow of refrigerant therebetween. Interposed adjacent the compressor housing, but exterior to the compressor housing is an expansion chamber muffler in fluid communication with the conduit for further attenuating pressure pulses generated by operation of the compressor.

FIELD OF THE INVENTION

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

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.

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 means for compressing gas. Compressors are typically categorized by the 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 screw devices to compress a refrigerant gas are known as screw 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.

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.

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.

What is needed is a compressor muffler system that sufficiently attenuates pressure pulsations generated by compressor operations without adversely affecting compressor operating efficiency.

SUMMARY OF THE INVENTION

The present invention relates to a muffler system for a compressor having a compressor shell and a compressing device with a gas discharge port. An acoustic muffler is disposed within the compressor shell and in fluid communication with the gas discharge port upon installation. An expansion muffler is disposed exterior to the compressor shell at a predetermined distance from the gas discharge port upon installation. An exhaust system connects the acoustic muffler and the expansion chamber muffler.

The present invention further relates to a compressor system including a housing having an exhaust port. A compression means is provided for compressing a refrigerant fluid, the compression means being disposed within the housing. The compression means has a discharge port for exhausting compressed refrigerant fluid from the compression means. An acoustic muffler is disposed within the housing and in fluid communication with the discharge port, and the acoustic muffler is in fluid communication with the exhaust port. An expansion muffler is disposed exterior the housing a predetermined distance from the exhaust port and in fluid communication with the exhaust port.

An advantage of the present invention is the inclusion of an expansion chamber muffler exterior of the compressor housing for attenuating pressure pulses from reaching the condenser, reducing the overall size of the compressor housing, while not adversely affecting compressor operating efficiency.

DETAILED DESCRIPTION OF THE INVENTION

One embodiment of a compressor that incorporates the muffler system of the present invention is depicted in FIG.1. The compressor2is connected to a conventional refrigeration or heating, ventilation and air conditioning (HVAC) system (not shown), such as may be found in a refrigerator, home or automobile, having a condenser, expansion device and evaporator in fluid communication. Compressor2is preferably a reciprocating compressor connected to an evaporator (not shown) by a suction line that enters the suction port14of compressor2. Suction port14is in fluid communication with suction plenum12. Refrigerant gas from the evaporator enters the low pressure side of compressor2through suction port14and then flows to the suction plenum12before being compressed.

Compressor2includes an electrical motor18. A standard induction motor having a stator20and a rotor22is shown. However any other electrical motor may be used. A shaft assembly,24extends through rotor22. The bottom end26of shaft assembly24in this compressor2extends into a lubrication sump28and includes a series of apertures27. Connected to shaft assembly24below the motor is at least one piston assembly30. Compressor2ofFIG. 1depicts two piston assemblies. A connecting rod32is connected to a piston head34which moves back and forth within cylinder36. A cylinder head includes a gas inlet port38and a gas discharge port40. Associated with these ports38,40are respective suction valves and discharge valves (not shown) assembled in a manner well known in the art. Gas inlet port38is connected to an intake tube54which is in fluid communication with suction plenum12.

Motor18is 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 stator20, and the windings in the stator20cause rotor22to rotate. Rotation of rotor22causes the shaft assembly24to turn. In the compressor shown, oil in the sump28is drawn through apertures27in bottom end26of shaft24and moved upward through and along shaft24to lubricate the moving parts of compressor2.

Rotation of rotor22also causes reciprocating motion of piston assembly30. As the assembly moves to an intake position, piston head34moves away from gas inlet port38, the suction valve opens and refrigerant fluid is introduced into an expanding cylinder36volume. This gas is pulled from suction plenum12within compressor housing16. This gas is pulled into intake tube54to gas inlet port38where it passes through the suction valve and is introduced into cylinder36. When piston assembly30reaches a first end (or top) of its stroke, shown by movement of piston head34to the right side of cylinder36ofFIG. 1, the suction valve closes. The piston head34then compresses the refrigerant gas by reducing the cylinder36volume. When piston assembly30moves to a second end (or bottom) of its stroke, shown by movement of piston head34to the left side of cylinder36ofFIG. 1, a discharge valve is opened and the highly compressed refrigerant gas is expelled through gas discharge port40. The highly compressed refrigerant gas flows from the gas discharge port40into an acoustic muffler50then through an exhaust or discharge tube52, exiting the compressor housing16into a conduit connected to a condenser. An expansion chamber muffler56positioned outside the compressor housing16is connected in fluid communication with the conduit between the compressor2and the condenser adjacent the compressor housing16. This comprises one cycle of the piston assembly30.

The placement of muffler56physically outside compressor housing16and at any of a number of specific distances along the conduit connecting compressor housing16and the condenser is crucial in reducing the pressure pulsation at the first harmonic of the rotation frequency of the compressor motor. That is, muffler56may be placed at any of a number of specific distances from the gas discharge port40as measured from the sum of the travel lengths of muffler50, discharge tube52and the conduit between the compressor housing16and muffler56. Further, locating muffler56outside compressor housing16, not only permits a reduction in size of the compressor housing16, but enhances the effectiveness of muffler56without adversely affecting the efficiency of the compressor as will be discussed in further detail below. Acoustic muffler50additionally filters higher frequency pressure pulsations that tend to radiate directly from compressor housing16as unwanted noise. Acoustic muffler50preferably includes an internal pressure relief valve (IPRV), or pressure relief member60connected to a resonator volume82(FIG.4).

Referring toFIGS. 2-4, acoustic muffler50preferably utilizes a side-branch resonator volume82to filter pressure pulsations that generate noise at the discharge tube52—compressor housing16penetration. Acoustic muffler50includes a tube62having opposed ends76,78. A threaded member64having a lip80at one end is positioned over end78of tube62for threadedly engaging the discharge head to maintain tube62in fluid communication with gas discharge port40. Preferably, the end78of tube62and the end of threaded member64opposite lip80are substantially coincident to ensure the parts are sufficiently engaged therebetween. A housing68alternative includes opposed openings70,72which permits opening70of housing68to be positioned over end78of tube62until opening72of housing68sufficiently contacts lip80. Methods of securing tube62, housing68and threaded member64in position to each other such as spot welding, soldering, brazing, or by press-fit are well known in the art. Housing68is substantially cylindrical in profile and defines a resonator volume82between tube62and housing68. Tube62and housing68are maintained in fluid communication by a pair of preferably axially aligned resonator throats66formed in tube62. The flow area and distance between the resonator throats66, as well as the size of the volume resonator82are specified such to ‘tune’ the side-branch resonator muffler to the pulsation frequencies most likely to excite noise at the discharge tube52—compressor housing16penetration. Resonator volume82displaces significantly less volume than typically used mufflers which employ an expansion chamber. Although not necessarily drawn to scale inFIG. 4, between openings70,72, resonator volume82displaces a comparable volume as compared to tube62. By virtue of both this lack of pronounced volumetric increase of resonator volume82that is adjacent the discharge port40and controlling the specific distance from the discharge head to the expansion chamber, compressor efficiency is maintained. Additionally, the small size of housing68of muffler50permits reduction in size of the compressor housing.

One end of discharge tube52is connected to muffler50. The other end of discharge tube52is connected to the discharge outlet15of compressor2. While a preferred embodiment of discharge tube52is of unitary construction, as previously discussed, if desired, discharge tube52may be segmented, such as to insert a discharge-side component such as an IPRV60. A portion of the discharge tube52adjacent muffler50preferably has a cane or inverted “J” shape, but can have any suitable shape. The shape of discharge tube52is primarily driven by the location and attitude of the two interface locations within the compressor housing16while maintaining sufficient spacing from compressor components. Thus, the path of the unitary discharge52tube typically follows a path adjacent the compressor housing16, preferably including from end98, which a substantially straight portion116which extends into a substantially curved portion118and similarly extends into a remaining portion120that terminates at end106. Referring back toFIGS. 1,2and4, both tube62of muffler50and a portion of discharge tube52share a coincident axis84. The segment or portion of discharge tube52that extends along axis84is of an extended length which more evenly distributes prestresses along the collective axial length of tube52. Additionally, the joint formed between discharge tube52and tube62of muffler50is also coincident with axis84. In one embodiment, tube62of muffler50has an enlarged diameter portion94that extends into a shoulder96formed therein that is coincident with axis84. To establish the joint between tube62of muffler50and discharge tube52, an end98of exhaust tube52is directed inside the enlarged diameter portion94of tube62past end76to the extent required to form the joint, up to “bottoming out” at the shoulder96.

Discharge tube52connects in a similar way to discharge outlet15. Discharge outlet15includes a fitting100that extends through an aperture112in the compressor housing16. The fitting100is provided with a secure joint between itself and the compressor housing16that is both fluid tight and rigid, both to prevent the leakage of refrigerant through aperture112and avoid unnecessary flexure to the subsequent joints formed between both the fitting100and the discharge tube52inside the compressor housing16and between the conduit and the fitting100located outside the compressor housing16. A fitting portion114of fitting100extends inside the compressor housing16which axially aligns along axis99with end106of tube52. The portion of fitting portion114that is inside compressor housing16includes an end102having an enlarged diameter portion104. To establish a joint between the discharge tube52and fitting portion114, the end106of discharge tube52is directed past end102of fitting portion114along axis99into the enlarged diameter portion104until a joint is formed. The joint may be secured by soldering or other appropriate bonding method. Preferably, the joints for each end98,106of discharge tube52is established prior to securing the joints. By virtue of the this variable, coincident insertion distance along enlarged diameter portion94between discharge tube52and tube62of muffler50and between discharge tube52and fitting portion114, prestresses in the discharge tube52caused by non-alignment installation conditions may be further reduced, thereby improving the structural integrity of the compressor.

Referring toFIGS. 7,8, fitting100extends outside compressor housing16into an extension134which further extends into a bend130, preferably a right angle, that terminates at an upturned end132. Alternately, fitting100could terminate immediately outside of compressor housing16, if desired. A substantially straight conduit136has an end138that inserts inside of end132of fitting100for connection therewith. Conduit136extends substantially parallel to the compressor housing16in a substantially vertical direction by virtue of the right angle connection with end132, terminating at end140which, in one embodiment, is adjacent the top of the compressor housing16. Alternately, conduit136could be curved in shape and could extend in any direction or attitude with respect to fitting100. The second muffler member56is connected at inlet end142with end140of conduit136and has an opposed exhaust end144for connection with a conduit connecting with a condenser (not shown). Fitting100, conduit136and muffler56are in continuous fluid communication therebetween so that refrigerant fluid exhausting from compressor housing16sequentially flows through fitting100and conduit136before reaching muffler56.

Muffler56attenuates pressure pulses generated by operation of the compressor. Muffler56is provided with the inlet end142and the exhaust end144on opposed ends of muffler56. A preferably enlarged diameter housing152is interposed between inlet end142and exhaust end144. The gas volume enclosed by housing152serves to filter pressure pulsations propagating in conduit136. The ability for muffler56to filter pressure pulsations is extremely sensitive to the total distance between the discharge head and muffler56. In fact, the muffler56can be located along the discharge path at numerous positions to filter a specific troublesome frequency.FIG. 5provides a design guide to position the muffler such to achieve maximum reduction attenuation of the pulsation frequency, often the most troublesome frequency in a refrigerant compressor as will be discussed in additional detail below.

A compressor system using the novel combination of the acoustic muffler50mounted internally within the compressor housing16and muffler56mounted adjacent but external to the compressor housing has been tested. Further referring toFIG. 5, sound attenuation is illustrated as a function of distance from the discharge head of the compressor for a particular frequency and refrigerant. It is shown that significant sound attenuation 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. The distance from the discharge head to the expansion chamber muffler is related to the travel distance of refrigerant between the discharge head and the expansion chamber muffler. Region “A” is inside the compressor housing 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 sound attenuation is substantially identical to the level shown in region “A”. Similarly, region “D”, which is located approximately 77-82 inches from the discharge head, provides substantially identical sound attenuation to the level shown in region “A”. Region “B” is located approximately 15-20 inches from the position of the housing penetration and region “D” is located approximately 45-50 inches from the housing penetration. 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 or approximately four feet in length, the compressor operates as quietly and more 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.

It is also noteworthy that the peak attenuation levels, at least for the particular plotted frequency inFIG. 5, is not especially “pointed”. That is, at Region “B”, although maximum attenuation of approximately 15 dB may occur at 48 inches from the discharge head, due to the relative “flatness” of the curve along its peak, attenuation levels of approximately 14.5-15 dB may be achieved with a range of approximately 45-51 inches from the discharge head. Thus, by locating the expansion muffler chamber within a reasonably broad distance range from the discharge head, without requiring precise measurements, it appears possible to achieve substantially maximum noise attenuation levels for the expansion muffler.

In addition to reduced compressor housing size and efficiency gains as previously discussed, by virtue of muffler56being used outside the compressor housing, the user has the opportunity to easily replace muffler56, if desired. 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, if 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.

While the expansion muffler56functions to filter pressure pulses from propagating downstream that generate noise upon contacting valves or condenser coils, a muffler is still needed inside the compressor housing to filter the pressure pulses that may transmit noise to the housing at the point of penetration. Referring toFIG. 6, the sound attenuating performance of the acoustic muffler is illustrated. As shown, peak attenuation occurs at approximately 1,000 Hz corresponding to an attenuation of approximately 32 dB which is sufficient to effectively address vibration issues within the compressor housing which are centered around this frequency range.