Patent Application
20060171835
1. Field of the Invention
The present invention generally relates to compressors. More particularly, the present invention relates to a rotary compressor having an improved structure for mounting a compressor pump within a compressor housing.
2. Description of the Related Art
Existing compressors typically include a housing, an electric motor and a compressor pump mounted to the housing, and a shaft rotatably engaged with the electric motor and the compressor pump. The electric motor is commonly powered by an external power source which energizes the stator windings of the motor to turn the motor shaft. In rotary compressors, the shaft drives an eccentric mechanism in the compressor pump to draw, compress and expel a working fluid through a discharge port.
In existing compressors, various methods of mounting a compressor pump within a compressor housing exist. In a rotary compressor such as described in U.S. Pat. No. 4,601,644, a bearing portion of the compressor pump is supported by the compressor housing at several points. The cylindrical compressor housing has holes through its circumference to receive attachment lugs extending from the bearing portion. The attachment lugs extend through the housing holes such that they can be welded directly to the housing from the outside. However, welding the bearing lugs to the housing in this manner may allow debris from the welding process to enter the housing which can damage the compressor. Disadvantageously, these compressors are conducive to leaking through these holes and creating these holes requires additional time and equipment, thereby increasing the cost of the compressor assembly. Additionally, considerable time and effort is expended to align the weld tabs with the housing.
In compressors where the bearing portion or cylinder block of the compressor pump are held in compression against the housing, distortion can occur in the bearing or cylinder block when they are welded to the housing. As the bearing portion or cylinder block, which are commonly made of cast iron or other ductile ferrous materials, are heated during the welding process, the heat is conducted to the shaft support aperture in the bearing portion or the compression chamber of the cylinder block. When exposed to heat, the shaft support aperture and the compression chamber may distort due to stress relaxation of the cast iron, or they may be distorted when they are restricted from expanding due to the compressive spring force of the housing. When restricted, stress may build in the bearing or cylinder block material causing it to permanently deform or yield. Even a small amount of permanent deformation is undesirable as the dimensional tolerances necessary for the proper operation of the rotary compressor are extremely close and are generally on the order of ten thousandth of an inch.
Another disadvantage of using the bearing portion or cylinder block to mount the compressor pump to the housing includes increasing the size of these components to bring a weldable surface in close proximity to the housing. Increasing the size of these members adds weight and cost to the compressor.
What is needed is an improvement over the foregoing.
The present invention overcomes the disadvantages of the above described prior art compressors by providing a discharge muffler which improves the mounting of the compressor pump to the compressor housing.
In one form of the invention, a muffler is installed within a compressor housing where the peripheral edge of the muffler abuts, and expansively engages, the interior surface of the housing in an interference fit relationship. The muffler is compressed by the resilient spring force of the expanded housing where the muffler and the housing can be fastened together through a laser-welding process, for example. During a laser-welding process, an intense laser beam is directed against the exterior of the housing where the contacting surfaces of the muffler and the housing are heated. Subsequently, the heated surfaces are allowed to cool and the muffler and the housing become fused together. This design is an improvement over the aforementioned compressors as holes are not needed in the compressor housing to complete the weld. The muffler may be oriented in many alternative positions and can be welded to the housing in substantially any location along the periphery of the muffler.
The muffler dampens vibrations emanating from the pump and isolates the compressor bearing and cylinder block from the heat conducted from the welded surface. Additionally, the muffler, in co-operation with the housing and the bearing portion, define chambers that act as resonators to reduce the noise created by the compressor pump. The chambers are designed to reflect the sound waves produced by the compressor pump in such a way that the sound waves partially cancel themselves out.
In one form of the invention, the muffler is disposed within the compressor housing where the muffler has a peripheral edge affixed to the housing and the bearing portion of the compressor pump is attached to the muffler. The muffler, compressor pump bearing portion and compressor housing define a series of chambers in which noise generated by the compressor pump is dissipated. A first chamber is intermediate the bearing portion and the muffler where gas exhausted through an exhaust port in the bearing portion enters the first chamber. Noise generated by the pump is carried by the exhaust gas into the first chamber, however, the noise is dissipated, or dampened, when the gas strikes the muffler and the other surfaces comprising the first chamber. The noise is further dissipated by the first chamber as it acts as a resonator where the dimensions of the first chamber are chosen to cause acoustical waves having specific, undesirable frequencies to cancel each other out.
In one form of the invention, the muffler may have at least one aperture through which the exhaust gas can escape into a second chamber in the compressor. The second chamber is defined by one side of the muffler and the compressor housing. Exhaust gas entering the second chamber may exit the compressor through a discharge pipe or enter a third chamber defined by the opposite side of the muffler and the compressor housing. The second chamber and the third chamber are in fluid communication through at least one gap intermediate the muffler and the housing. Similar to the above, the sound waves created by the compressor are somewhat dissipated when they strike the surfaces defining the second and third chambers. Also, the second and third chambers acts as resonators where sound waves carried by the discharge gas are dissipated by passing between the second chamber and the third chamber through the gap. In other embodiments, the muffler may have at least one second aperture fluidly connecting the second and third chambers. The second apertures may also assist in the dissipation of sound waves conducted by the exhaust gas. Further, the gap between the housing and the muffler and the second aperture permit oil carried by the exhaust gas to return to the oil sump in the bottom of the compressor.
In this embodiment, the muffler is also a mounting plate, thus simplifying the design and the assembly process of the compressor as described herein.
The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following descriptions of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate preferred embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.
Referring now to the drawings and in particular to
Crankshaft 17 is also drivingly engaged with the compressor pump. The compressor pump includes main bearing portion 19 (
The interior of cylinder block 25, at any given time during the operation of the compressor, is divided into a suction chamber and a discharge chamber. The suction and discharge chambers are divided from each other by vane 90 (
As shown in
Referring to
Slots 64 are also used to connect chambers 62 and 63 to create a system of Helmholtz resonators to dissipate noise, or sound waves, created by the compressor pump. These sound waves, which propagate through the circulating steam in the compressor, typically cause an undesirably high level of audible noise to emanate from the compressor. Some of the sound waves are dissipated by muffler 24 and first chamber 41, however, additional chambers can be used to absorb residual acoustic energy propagating in the compressor and to reduce housing space resonance. To accomplish this, slots 64 and chambers 62 and 63 are configured such that the sound waves passing between these chambers can cancel each other out. Sound waves cancel each other out when they occupy the same space and their frequencies are out of phase with each other, preferably 180 degrees out of phase. This can be accomplished by designing the thickness of muffler 24, the cross-section of gap 64, and the depth of cavities 62 and 63 such that sound waves entering third chamber 62 through slots 64 and are destructively interfered with by sound waves reflecting back through slots 64.
Slots 64 and chambers 62 and 63 are configured to cancel out a specific, but limited, range of frequencies. In another way, slots 64 and chambers 62 and 63 are designed such that the natural frequency of the Helmholtz system matches the targeted frequency of the sound waves that are desired to be cancelled out. As the sound waves emanating from the compressor pump are a mixture of many different frequencies and depend on the speed of crankshaft 47, the Helmholtz system should be designed to filter out the frequency range most likely to occur during the steady state, or normal, operation speed of the compressor. Even though the range of frequencies produced during steady state operation may be greater than the range of frequencies that can be cancelled out, the system of Helmholtz resonators discussed above will still produce some destructive interference of the sound waves thereby reducing the sound emanating from the compressor.
Similar to the above, the size of first chamber 41 and the configuration, location and quantity of discharge ports 44 may be tuned to accomplish a similar result.
In yet another embodiment (see
Once the compressed gas enters second chamber 62, it is also free to pass through discharge port 99 (
To support muffler 24 within housing 11, radially and circumferentially extending part 47 of muffler 24 has a plurality of tabs 48 (
The preferred method of assembling compressor 10 is to first press-fit stator 16 into housing 11, as discussed above. Subsequently, roller 18 is assembled to eccentric journal 15 of shaft 17. Eccentric journal 15 can be integral to shaft 17 or affixed to shaft 17 by compression fit. Shaft 17 is then passed through shaft aperture 88 of upper bearing 19. Brass journals (not shown) may be inserted between shaft 17 and aperture 88 to improve the longevity of bearing 19. Subsequently, cylinder block 25 is positioned against upper bearing 19 such that eccentric journal 15 and roller 18 are positioned within compression chamber 74. Cylinder block 25 is then aligned with respect to roller 18 such that a 0.0005″-0.0007″ clearance exists between the outer diameter of roller 18 and the inner diameter of cylinder block 25 at a locating or set point. This set point is located 105±5 degrees counter-clockwise, as viewed from the open end of the cylinder block, from the top dead center position of roller 18 within compression chamber 74. The top dead center position of roller 18 is the position in which high point 94 passes discharge port 30 in upper bearing 19.
Subsequently, upper bearing 19 is fastened to cylinder block 25 by locator bolts 27 (
During the assembly of the compressor, it may be necessary to temporarily distort housing 11 in the radial direction to insert muffler 24. As illustrated in
Discharge muffler 24 can be stamped from cold formed steel, the same metal preferred for housing 11, or any other metal with good weldability properties to allow reliable weld joining of tabs 48 and inner surface 40 of housing 11. One of the problems with the prior art is that the material properties of the cylinder block and bearing portion are frequently dissimilar to the housing material properties. The housings of most existing compressors are made from cold rolled steel while the bearing portion and the cylinder block are commonly made from cast iron or powdered metal. Welding dissimilar metals together, such as cast iron and cold formed steel, is difficult as these materials melt at different temperatures. Thus, one metal must continue to be heated until the other material has become sufficiently heated to weld them together. Further, having materials with different expansion rates may increase the gap between tabs 48 and housing 11 during welding causing an inconsistently thick weld. Having welds with an inconsistent thickness may cause voids or other non-homogeneous anomalies to occur during the welding process creating weak points. Additionally, having materials with different expansion rates may allow residual stresses to build in the bearing and cylinder blocks when they are cooling. Residual stress in brittle materials, such as powdered metal or cast iron, may cause the materials to crack when placed under the load of an operating compressor.
In addition to the above, another problem in the prior art is that powdered metal or cast iron compressor parts are not always as easy to weld. Common welding processes, which are sensitive to variables such as porosity and the presence of impurities in the welded materials, are often inefficient or ineffective when applied to cast iron or powdered metal which commonly have significant porosity. Excessive porosity, due to foreign particle melting or filler weld infiltration, can result in excessive shrinkage or growth of the material during welding with the potential for subsequent cracking to occur in or near the weld interface. Pores also act as thermal insulators which slow the transfer of heat, making the powdered metal components less hardenable and increase the material susceptibility to cracking. The present embodiments are an improvement over the foregoing as both housing 11 and muffler 24 can be made from the same material, preferably cold-formed steel which has excellent weldability properties.
In the embodiment shown, housing 11 does not have holes to directly weld tabs 48 to housing 11 from the outside. However, tabs 48 may be welded to housing 11 through a laser welding process. The use of the laser welding process to attach plate muffler 24 to housing 11 provides several advantages including reducing the heat applied during the welding process, which results in minimal shrinkage and distortion of the welded housing and discharge muffler. Further, laser welding is a much cleaner and much faster process than traditional arc welding. Generally no flux or filler material is required. Laser welding occurs in open air as opposed to MIG welding which requires a protective gas, such as argon. Further, there is no contact between the welding equipment and the work parts which simplifies fixturing. Additionally, laser welding produces high-strength consistent, repeatable welds, with a narrow weld bead and a generally good appearance. The strength of the weld can be improved by increasing the length or size of the weld joint. In order to accommodate a larger weld, the size of tabs 48 can be increased, which is commonly required for larger capacity compressors.
However, some embodiments do not exclude the possibility of using conventional MIG welding process (see
While this invention has been described as having exemplary embodiments, the present invention can be further modified within the spirit and scope of the disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.
