WO2008098330A2

WO2008098330A2 - Constructive arrangement of an acoustic filter for a refrigeration compressor

Info

Publication number: WO2008098330A2
Application number: PCT/BR2008/000043
Authority: WO
Inventors: Edmar Baars
Original assignee: Whirlpool S.A.
Priority date: 2007-02-13
Filing date: 2008-02-13
Publication date: 2008-08-21
Also published as: WO2008098330A3; BRPI0700748A

Abstract

Constructive arrangement of an acoustic filter for a refrigeration compressor, coupled to a refrigeration system containing a refrigerant gas, said acoustic filter (10) comprising a hollow body (11) defining at least one muffling chamber (14, 15) which carries a gas inlet tube (20) and a gas outlet tube (30), at least one of the parts of gas inlet tube (20), gas outlet tube (30) and hollow body (11) carrying at least one noise absorbing porous element (50) in contact with the refrigerant gas in the interior of the hollow body (11).

Description

"CONSTRUCTIVE ARRANGEMENT OF AN ACOUSTIC FILTER FOR A REFRIGERATION COMPRESSOR" . Field of the Invention

The present invention refers to a constructive arrangement of an acoustic filter or muffler, for example, mounted in a gas suction and/or discharge line in a refrigeration compressor, particularly of the type used in small refrigeration systems. Background of the Invention The acoustic filters are widely used in compressors of refrigeration system to attenuate noises and pulses transmitted through the gas suction and discharge lines of said refrigeration systems, being more specifically employed to attenuate the gas pressure transients generated by the opening of the suction and discharge valves of the compressors. In the refrigeration system, these pressure transients generate noise in two different forms: sound radiation of the compressor due to the excitations of the casing resonances, generally between 500Hz and lOkHz; and sound radiation of the refrigeration appliance of said refrigeration system, due to the excitations of the components of the latter, mainly regarding low frequency pulses, up to 2kHz. The suction acoustic filter performs several important functions for the good operation of the compressor, such as: gas conduction, attenuation of the noise generated by the pulses resulting from suction, thermal insulation of the refrigerant gas drawn into the cylinder, and control of the suction valve dynamics. The suction acoustic filters also have a major influence on the energetic efficiency of the compressor, due to the thermal insulation of the gas, load loss and valve operational coupling.

Besides the suction acoustic filters, the compressors of the refrigeration systems can also be provided, in their discharge, with an acoustic dampening system, generally in the form of an acoustic filter provided in the gas discharge line of the compressor and which conducts the gas compressed in the interior of the cylinder to a refrigeration system to which the compressor is associated. The acoustic filters presently used are basically a combination of the resistive and reactive types, consisting of a sequence of volumes (generally one, two or three volumes in series, also known as expansion chambers) , interconnected by gas ducts which conduct the refrigerant gas coming from the suction line directly to the suction valve, said gas ducts being generally open in both ends for the passage of refrigerant gas. The acoustic filters are formed by gas tubes and volumes

(figure 3) usually made in solid material (plastic or metallic) .

The displacement of gas produces pulses, generating noises which are propagated in a direction opposite to the gas being displaced towards the suction valve (figure 2) . The smaller said pulses, the more efficient the suction acoustic filter at its acoustic outlet, through which the gas is admitted in the interior of the acoustic filter, the lower said pulses.

Its influence on the performance of the compressor is highly important and the dimensioning of the internal volumes and length of the gas tubes of the suction filter determines, to a large extent, the efficiency of the latter. The acoustic filters also play an important role in the gas thermal insulation, load loss and valve operational coupling. The literature is rich in examples and applications of acoustic filters. (Hansen, H. "Engineering Noise Control", 2003, Spon Press,- Lyon, R. H., "Machinery Noise and Diagnostics", 1987, Butterworth Publishers; Munjal, M. L. "Acoustics of Ducts and Mufflers", 1987, New York Wiley-Interscience; Hamilton, J. F. "Measurement and Control of Compressor Noise", 1988, Office of Publications, Purdue University, West Lafayette) . Although widely utilized, the known suction acoustic filters of the volume-tube type have the disadvantage of presenting noise peaks in the acoustic modes typical of these tubes and volumes . There are found applications of Helmholtz resonators constituted by one tube and one volume which, although also attenuating the frequencies in which they are syntonized, have larger dimensions and increase the complexity in manufacturing the acoustic filters. Due to the larger size, the utilization of several Helmholtz resonators in an arrangement is unfeasible, its application being restricted to the attenuation of few frequencies. One of the known techniques to attenuate the noise provoked by the passage of gas through acoustic filters is the reactive technique, in which, during the wave propagation, a difference of impedance in a given frequency is generated. The acoustic filters of the reactive type present one or two volumes (also called expansion chambers) and are formed by tube and volumes generally made in solid material (plastic or metallic) . Said filters present a great attenuation in low frequencies (500-800 Hz) , whilst, in high frequencies, they lose performance due to the acoustic resonances of the elements in the form of tubes and volumes, generating more noise in the compressors (figure 2) . This behavior is much more intense in filters with one volume. Generally, the increases in the acoustic performance are obtained by increasing the volume or by reducing the diameters of the tubes, which is not always possible.

Other known technique is the dissipative technique, which is obtained utilizing fibrous material in the construction of the acoustic filter to dissipate energy. Objects of the Invention

It is an object of the present invention to provide an acoustic filter construction for a refrigeration compressor, which allows a considerable reduction of the negative effects generated by the resonances of the acoustic filter components, in high and low frequencies, without increasing the load loss upon passage of gas through said acoustic filter.

It is a further object of the present invention to provide an acoustic filter construction, such as cited above and which does not require modifying the dimensioning of said acoustic filter. Another object of the present invention is to provide a filter such as cited above, which allows simplifying its construction at a low cost.

It is also another object of the present invention to provide an acoustic filter, such as cited above and which allows increasing the noise attenuation of pulses resulting from the suction or compression of gas in the interior of the cylinder, both in the low and high frequencies, as well as increasing the energetic efficiency of the compressor, in which said acoustic filter is mounted.

A more specific object of the present invention is to provide a construction, such as cited above and which increases the efficiency and power of the electric motors of the compressors to which said filters are associated. Summary of the Invention

These and other objects of the present invention are attained through the provision of a constructive arrangement of an acoustic filter for a refrigeration compressor coupled to a refrigeration system containing a refrigerant gas, by means of a suction pipe and a discharge pipe, said acoustic filter being operatively associated with one of the suction and discharge pipes, said acoustic filter comprising a hollow body defining at least one muffling chamber which carries a gas inlet tube having an inlet opening external to the muffling chamber and an outlet opening in the interior of the muffling chamber, and a gas outlet tube presenting an inlet opening in the interior of the muffling chamber and an outlet opening external to said muffling chamber, at least one of the parts of gas inlet tube, gas outlet tube and hollow body carrying at least one noise absorbing porous element in contact with the refrigerant gas in the interior of the hollow body. Brief Description of the Drawings

The invention will be described with reference to the enclosed drawings, given by way of example of an embodiment of the invention and in which:

Figure 1 schematically and partially represents a longitudinal sectional view of a compressor carrying an acoustic filter, particularly provided in the suction line of said refrigeration compressor; Figure 2 schematically represents a graph illustrating an attenuation curve obtained with a prior art acoustic filter (continuous lines) and with the construction of the present invention; Figure 3 schematically represents an acoustic filter constructed according to the present invention and mounted in the suction line of a compressor, indicating the direction of the gas flow; and

Figure 4 represents schematically and in an exploded perspective view, the acoustic filter of the present invention.

Description of the Illustrated Embodiment

The present invention comprises a constructive arrangement of an acoustic filter for a compressor coupled to a refrigeration system containing a refrigerant gas, by means of a suction pipe and a discharge pipe, said acoustic filter being operatively associated with one of the suction and discharge pipes. The refrigeration compressor is, for example, of the type utilized in refrigeration systems of small size and which comprises, in the interior of a hermetic casing 1, a motor-compressor assembly 2 having a cylinder 3, within which is defined a compression chamber C lodging a piston 4 reciprocating in a compression stroke. In the illustrated construction, the cylinder 3 is provided in a cylinder block 5.

A valve plate 6 is seated against an end of the cylinder 3, opposite to that through which said piston 4 is mounted, said valve plate 6 carrying a suction valve 6a and a discharge valve (not illustrated) , which selectively allow the fluid communication between the compression chamber C and a suction line and a discharge line of the refrigeration system to which the compressor is coupled and which contains a refrigerant gas, said refrigerant gas reaching the compressor through a suction pipe 7 and returning to the discharge line of the refrigeration system through a discharge pipe 8. A cylinder cover 9 is seated against a face of the valve plate 6 opposite to that turned to the compression chamber C, said cylinder cover 9 generally defining, in the inside thereof, a discharge chamber (not illustrated) in a selective fluid communication with the compression chamber C.

As illustrated in the enclosed drawings, the refrigerant gas drawn by the compressor and coming from the suction line of the refrigeration system to which the compressor is coupled, reaches the interior of the casing 1, through a suction filter 10, generally provided in the interior of said casing 1 and maintained in fluid communication with a suction orifice 6b defined in the valve plate 6. The acoustic filter 10, to which is applied the solution of the present invention, will be described herein as a suction acoustic filter comprising a hollow body 11, generally obtained in a material of low thermal conductivity, such as plastic, presenting a base portion 12 hermetically closed by a cover 13 and retained thereto by appropriate means, such as glue, clamp, projections, interference or by a peripheral belt, not illustrated.

The hollow body 11 internally defines at least one muffling chamber 14 which carries a gas inlet tube 20 having an inlet opening 21 external to the muffling chamber 14, and an outlet opening 22 in the interior of the muffling chamber 14, and a gas outlet tube 30 presenting an inlet opening 31 in the interior of the muffling chamber 14 and an outlet opening 32 external to said muffling chamber 14.

In the illustrated construction in figure 1, the suction acoustic filter 10 presents a gas inlet tube 20 having its inlet opening 21 in fluid communication with the gas supply to the compressor, connected to the suction line of the refrigeration system to which the compressor is coupled, and having its outlet opening 22 in fluid communication with a suction side of the compressor, for example, directly connected to the suction orifice 6a of the valve plate 6 of the compressor.

In the construction illustrated in figures 3 and 4, the acoustic filter 10, to which is directed the constructive arrangement of the present solution, presents two muffling chambers 14, 15, which are separated apart by a dividing wall 16.

In the construction illustrated in figure 3, the suction acoustic filter 10 presents a hollow body 11 defining two muffling chambers 14, 15, for example, provided inside said hollow body 11 and separated apart by the dividing wall 16. To the interior of one of said muffling chambers 15 are projected an outlet opening 22 of the gas inlet tube 20 and an inlet opening 31 of a gas outlet tube 30, with its outlet opening 32 projecting to the interior of the other muffling chamber 14, providing the fluid communication between said muffling chambers 14, 15.

In this construction, to the interior of the other muffling chamber 14 also projects an inlet opening 41 of another gas outlet tube 40 having an outlet opening 42 to be connected to the suction orifice 6a in the valve plate 6.

Although not illustrated, the present constructive arrangement can be applied to acoustic filters comprising one muffling chamber 14 or a plurality of muffling chambers .

The constructive arrangement of the present invention comprises at least one noise absorbing porous element 50 which is carried by at least one of the parts of gas inlet tube 20, gas outlet tube 30 and hollow body 11, said porous element 50 being disposed, in the part that carries it, in contact with the refrigerant gas through the hollow body 11. Said porous element 50 can be aggregated to the part that carries it, for example, lining said part or even being the material which defines said part that carries it .

The porous element 50 presents a plurality of pores 51, constructed to allow the dissipation of the acoustic waves in the interior of the acoustic filter 10, without preventing or obstructing the passage of the flow of refrigerant gas in the interior of the hollow body 11. This constructive arrangement of the present invention allows utilizing two mechanisms of attenuation: the reactive and the dissipative, propitiating an improvement in the performance of the acoustic filters 10 with such noise absorbing constructive arrangement.

The present constructive arrangement comprises at least one porous element 50 presenting a plurality of pores 51, said porous element 50 being, for example, in metallic or elastically flexible material.

In a way of carrying out the present invention, at least part of the pores 51 of the porous element 50 presents a construction opened to the refrigerant gas, with the pores 51 presenting a size ranging between 5μm and 500μm. For any of the constructions described herein, the material which forms the porous element 50 must be oleophobic, and it can be also defined to provide a thermal insulation of the refrigerant gas passing through the interior of the hollow body 11 of the acoustic filter 10 carrying said porous element 50. Each porous element 50 can also be formed to act as an expansion element of the refrigerant gas and as a filter for solid particles and residues. In this case, the pores 51 (open or closed) of a porous element 50 must present a size ranging between 5μm and 500μm. In the construction in which the porous element 50 is made of metallic material, this must present a plurality of open pores 51, said pores 51 being distributed along at least part of the area of the respective porous element 50, in a way to maximize the absorption of noises provoked by the passage of the refrigerant gas through the acoustic filter carrying said porous elements 50. In the construction presenting the porous element 50 in an elastically flexible material, it can present all its pores 51 open, closed or even a combination of open and closed pores 51 distributed in the respective porous element 50, according to the function of said pore 51 in the interior of the hollow body 11, said distribution being defined as a function of an improved attenuation of noises, pulses, thermal insulation, or also filtration. These pores 51 (open or closed) of a porous element 50, can present a size ranging between 5μm and 500μm. In the constructions in which the porous element 50 attenuates noises resulting from the passage of refrigerant gas through the interior of the hollow body 11, at least one porous element 50 must be positioned in a region of the part that carries it, subjected to an acoustic pressure which produces noise to be attenuated. For a maximum dissipation in the attenuation of noises, pulses and turbulences in the refrigerant gas through the acoustic filter, the construction of at least one porous element 50 must present all its pores 51 open. However, it should be understood that, in constructions not presenting the porous elements with a maximization of dissipation, this porous element may have all its pores 51 closed.

According to one of the possible ways of carrying out the present invention, the acoustic filter carries, in the form of wall portions projecting from the inner surface of the hollow body 11 or also from the inner surface and/or outer surface of its gas inlet tube 20 and gas outlet tube 30, inside said hollow body 11, one or a plurality of porous elements 50.

In this construction, the porous elements 50 are provided internal to the hollow body 11, when projecting from the inner wall thereof or also from any one of the outer and inner walls of one or both gas inlet tube 20 and gas outlet tube 30, in the portion thereof internal to the hollow body 11. The present invention also foresees that the porous elements 50 can be provided external to the hollow body 11, when defined in the interior of a portion of a respective gas inlet tube 20 or gas outlet tube 30, external to said hollow body 11.

The porous element 50 can also be provided external to the hollow body 11, when it internally covers the portion of a respective gas inlet tube 20 and gas outlet tube 30 external to the hollow body 11, or even when it defines said tube portion, external to the hollow body 11. The present arrangement can present a construction in which only part of the interior of the hollow body 11 is provided with a porous element 50, such as a wall portion of the part that carries it . In another way of carrying out the present invention, such as those illustrated in figures 3 and 4, the present arrangement also presents a porous element 50 internal to the part that carries it, for example, defining at least one wall portion of the part that carries it. In a particular construction, at least one of the parts of gas inlet tube 20 and gas outlet tube 30 and hollow body 11 is covered with the porous element 50.

In another constructive variant, at least one of the parts of gas inlet tube 20 and gas outlet tube 30 and hollow body 11 is defined by the material which forms the porous element 50. Within this variant, the dividing wall 16 can also be defined to carry the porous element 50, for example, by being covered or conformed in a noise absorbing material presenting pores 51, as previously discussed.

As shown in figure 2, the increases in the attenuation of the acoustic filters can reach the range of 5-15db considering the constructive arrangement of the acoustic filter of the present invention.

Others advantages are: geometric simplification of the filters; low sensitivity to the manufacturing tolerances; greater attenuation in high frequencies; significant increase of the dissipation in the acoustic filter, particularly when this is a suction filter; increase in the energetic efficiency of the compressors; and reduction in the size and cost of the filter. Specific features of the invention are shown in the drawing figures for convenience only, as each feature may be combined with other features in accordance with the invention. Alternative embodiments will be recognized by those skilled in the art and are intended to be included in the scope of the claims. Accordingly, the above description should be construed as illustrative and not limitative of the scope of the invention. All such obvious changes and modifications are in the scope defined by the appended claims.

Claims

1. A constructive arrangement of an acoustic filter for a refrigeration compressor coupled to a refrigeration system containing a refrigerant gas, by means of a suction pipe (7) and a discharge pipe (8) , said acoustic filter (10) being operatively associated with one of the suction pipe (7) and discharge pipe (8) , said acoustic filter (10) comprising a hollow body (11) defining at least one muffling chamber (14, 15) which carries a gas inlet tube (20) having an inlet opening (21) external to the muffling chamber (14, 15) and an outlet opening (22) in the interior of the muffling chamber (14, 15) and a gas outlet tube (30) presenting an inlet opening (31) in the interior of the muffling chamber (14, 15) and an outlet opening (32) external to said muffling chamber

(14, 15), characterized in that least one of the parts of gas inlet tube (20) , gas outlet tube (30) and hollow body

(11) carries at least one noise absorbing porous element

(50) in contact with the refrigerant gas in the interior of the hollow body (11) .

2. The arrangement, as set forth in claim 1, characterized in that the porous element (50) presents a plurality of pores (51) , at least part of said pores (51) having a construction opened to the refrigerant gas.

3. The arrangement, as set forth in claim 2, characterized in that the porous element (50) is in metallic material presenting all its pores (51) having an open construction.

4. The arrangement, as set forth in claim 2, characterized in that the porous element (50) is in an elastically flexible material.

5. The arrangement, as set forth in claim 4, characterized in that the porous element (50) presents all its pores (51) having open construction.

6. The arrangement, as set forth in claim 1, characterized in that the porous element (50) is in elastically flexible material and presents all its pores (51) having a closed construction.

7. The arrangement, as set forth in claim 1, characterized in that the porous element (50) presents pores (51) with a size of about 5μm-500μm.

8. The arrangement, as set forth in claim 1, characterized in that the porous element (50) is internal to the part that carries it.

9. The arrangement, as set forth in claim 1, characterized in that the porous element (50) defines at least one wall portion of the part that carries it.

10. The arrangement, as set forth in claim 1, characterized in that the porous element (50) is positioned in a region of the part that carries it, subjected to an acoustic pressure which produces the noise to be attenuated.

11. The arrangement, as set forth in claim 1, characterized in that at least one of the parts of gas inlet tube (20) , gas outlet tube (30) and hollow body (11) is covered with the porous element (50) .

12. The arrangement, as set forth in claim 1, characterized in that at least one of the parts of gas inlet tube (20) , gas outlet tube (30) and hollow body (11) is defined by the material which forms the porous element (50) .

13. The arrangement, as set forth in claim 1, characterized in that the hollow body (11) comprises a first muffling chamber (14) and a second muffling chamber (15) separated apart by a dividing wall (16) carrying the porous element (50) .

14. The arrangement, as set forth in claim 1, characterized in that the porous element (50) is oleophobic .