US2928589A

US2928589A - Hermetically-sealed, motor compressor unit including noise reducing means

Info

Publication number: US2928589A
Application number: US771089A
Authority: US
Inventors: Peter E Davey
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1958-10-31
Filing date: 1958-10-31
Publication date: 1960-03-15
Anticipated expiration: 1977-03-15

Description

March 15, 1960 P. E. DAVEY 2,928,589

HERMETICALLY-SEALED, MOTOR COMPRESSOR UNIT mcwnmc NOISE REDUCING MEANS Filed 001;. 31, 1958 A INVENTOR. F i G PETER E. DAVEY H15 ATTORNEY United States Patent HERMETICALLY-SEALED, MOTOR COMPRESSOR UNIT INCLUDING NOISE REDUCING MEANS leter E. Davey, Fern Creek, Ky., assignor to General Electric Company, a New York corporation Application October 31, 1958, Serial No. 771,089 3 Claims. (Cl. 230-232) The present invention relates to hermetically sealed motor-compressor units and is more particularly concerned with a simple and inexpensive arrangement for reducing the noise energy. emanating from such a unit.

itiermetically'sealed motor-compressor units such as those used in the refrigerationindustry comprise a compressor and a motor for driving the compressorv suitably supported within a hermetically sealed casing. The casing is filled with either high or low pressure refrigerant being circulated through a refrigerating system by the compressor and normally there is a body of lubricating oil disposed in the bottom portion of the casing for lubricating the compressor. Due to the large variety of moving parts in such a unit, the total noise energy emanating from the unit during operation of the compressor comprisesmany different frequencies and qualities. The various noise sources, each of which may have its own exciting frequency, are not limited to the valve noises of the compressor resulting from the rapid opening and closing of the compressor valves, the mechanical vibrations of the compressor cylinder and mount and supports caused by the reciprocating movement of the piston and the linkage noises between the piston and the driving motor, but also include the various noises emanating from the motor itself due to axial movement of the rotor under the magnetic forces acting thereon, the slight changes in the rotational velocity of the rotor due to the changing load conditions thereon during each compressor cycle, and the vibrations set up as the rotor bars move past the stator slots. All of these noises from the motor-compressor unit may be transmitted to the casing and may produce a high or aggravating noise level outside the casing. The trans mission may be either through the means for supporting or suspending the motor-compressor unit within the C38, ing or by the gas contained within the casing.

The present invention is particularly concerned with means for reducing the noises transmitted by or set up in the gas contained within the compressor casing. These noises, frequently referred to collectively as cavity resonance, include those vibrations set up within the gas contained in the casing due to the rotation of the slotted rotor and those set up in the gas due to the vibration of other parts of the motor-compressor unit. Broadly, the frequencies and nature of the vibrations involved in cavity resonance in any particular hermetic compressor will depend upon a number of factors, including the gas pressure in the case, the geometry of the case including its volume and other dimensions and the particular exciting frequencies produced by the motorcompressor unit.

In accordance with the present invention, cavity resonance in a hermetically sealed motor-compressor unit is substantially decreased by providing within the hermetic casing and between the casing and the motorcompressor unit suspended therein, a curtain in the form of a woven cloth suitably suspended at spaced points from the top of the casing so that the free portions iice including the lower edges thereof are draped between the compressor and the casing. It is found that such a curtain effectively breaks up standing waves in thegas within the casing and absorbs some of their energy so that there is not only an overall reduction in the noise energy but also a significant damping of the pure tones or howls frequently produced by high speed compressors, which tones unless damped have a relatively high and disturbing noise level, The cloth employed in the practice of the present invention is composed of tightly woven fibers of a material which is chemically inert with regards to the refrigerant such as the dichloro difiuoro methane generally employed in household refrigerating systems and chemically inert with reference to the lubricant employed for lubricating the compressor. Particularly suited to the practice of the present invention are the synthetic fibers made from the esterification product of ethylene glycol and terephthalic acid and commercially available under the trade name Dacron."

For a better understanding of the invention reference may be had to the accompanying drawing in which:

Fig. 1 is a vertical sectional view of a typical hermetically sealed motor-compressor unit embodying the present invention; and

Fig. 2 is a side elevational view of the compressor of Fig. 1 partially in section along line 22 of Fig. 1.

With reference to the drawing, the disclosed embodiment of the present invention includes a hermetically sealed casing 1 containing a horizontally disposed motorcompressor unit including a motor 2 and a compressor 3 connected by a drive shaft (not shown) to the motor 2. It will be understood of course that this type of compressor unit is adapted to withdraw refrigerant from the evaporator compo nent'of a refrigerating system and to discharge compressed refrigerant from the compressor 3 to the condenser compartment of that system. Either the high or the low side of the system will be connected to the case and the other side to the compressor so that the refrigerant flowing between the system and the compressor will pass through the case and completely fill the interior thereof.

In the illustrated embodiment of the invention the motor-compressor unit is suspended within the casing by means of a plurality of tension springs 5 having their upperends secured to the casing and their lower ends secured to the motor-compressor unit.

1 For the purpose of lubricating the motor-compressor unit there is provided a body of oil 6 in the bottom portion of the casing 1 and oil is withdrawn through a tube 8 by means of a suitable pump (not shown) formingpart of the motor-compressor unit for distribution to the bearings and other moving parts of the motorcompressor unit requiring cooling or lubrication or both.

During operation of the compressor the noises generated in the motor 2 and the compressor 3 are of various frequencies and energy or sound levels. Some of these noises are transmitted to the case through the spring suspension and may be damped or partially damped by the proper design of this suspension. Others are transmitted through or set up in the refrigerant gas contained within the casing 1. The present invention is particularly concerned with the damping of these gas borne or gas generated noises and to this end there is provided :between the motor-compressor unit and the walls defin- MM, m."

3 a suitable material for this purpose and it is desirable that the cloth be of a fine or closely woven mesh in which adjacent parallel threads are in contact with one another.

For maximum noise reduction, as much as possible of the curtain 7 should be freely draped in the space between the motor-compressor unit and the casing and for that purpose the curtain is suspended or secured to the casing at'a minimum number of points. In the illustrated embodiment of the invention it will be seen that the curtain is suspended by means of one or more fasteners 10 to the outer portion of the top wall 11 of the casing and draped generally from these fasteners to the spring supports 12 provided on the side walls of the compressor casing which are employed to anchor the curtain 7 in such a manner that its lower or free ends 14 will suspend or hang freely from the supports 12 downwardly between the side walls of the casing and the motor-compressor unit.

More specifically, it will be seen that with the curtain 7 fastened only to the center top portion of the case by the fasteners 10 and to the side walls of the case by means of the spring supports 12, the portions of the curtain between these fasteners hangs loosely or drapes between the supports in spaced relationship with both the motorcompressor unit and the compressor case while the free ends 16 of the curtain below the spring supports 12 hang loosely between the sides of the motor-compressor unit and the side walls of the case. Preferably, the lower end of the curtain 7 is above the level of the oil 6 in the compressor case as it has been found that a dry curtain, that is, a curtain which is not soaked with oil has better noise damping characteristics than one that is. While some oil may be thrown onto the curtain during operation of the compressor as for example from the revolving counter weight 18 most of this oil will drain from the curtain and with the lower end of the curtain above the oil level there is no wick action to provide a continuous flow of oil by capillary attraction upwardly into the curtain.

' With the curtain 7 supported at the minimum number of points on the compressor case and otherwise hanging loosely away from both the case and the motor-compressor unit, there is obtained a substantial reduction in cavity resonance particularly in the range of from about 900 to 3500 cycles per second noise energies. The curtain is particularly effective in damping pure tone noises which are generated in the gas within the casing 1 and which due to the conditions existing within the case as for example with particular gas pressures and the case geometry and so forth may otherwise be amplified to an abnormally high energy level. The curtain provides inexpensive damping of case resonance by means of a material which is chemically inert both with reference to the refrigerant contained in the case and the oil. It is believed the attenuation of noise by means of the curtain 7 results both from a motion of the curtain or the freely draped portions thereof in the sound field accompanied also by some small absorption of noise in the small capillaries or interstices existing between the Dacron fibers so that it substantially prevents cavity resonance by breaking up standing waves and absorbing some of the energy whereby the pure tone vibrations in the compressor noise spectrum are eliminated.

While the present invention has been described with reference to a particular embodiment thereof it will be understood that the invention is not limited thereto and it is intended by the appended claims to cover all such modifications as come within the spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A hermetic compressor including a sealed casing, a motor-compressor unit resiliently suspended within said casing in spaced relation with the walls of said casing and means for damping cavity resonance comprising a cloth curtain disposed between said casing and at least the top and sides of said motor-compressor unit, said curtain being fastened to the interior of said casing at a plurality of spaced points with the unsupported portions of said curtain draping in spaced relation with said casing and said motor-compressor unit.

2. A hermetic refrigerant compressor including a sealed casing containing refrigerant, a motor-compressor unit resiliently suspended within said casing in spaced relation with the walls of said casing and means for damp ing cavity resonance comprising a cloth curtain composed of fibers inert with regards to said refrigerant and disposed between said casing and at least the top and sides of said motor-compressor unit, said curtain being fastened to the interior of said casing at a plurality of spaced points with the unsupported portions of said curtain draping in spaced relation with said casing and said motor-compressor unit.

3. A hermetic compressor including a sealed casing, a motor-compressor unit resiliently suspended within said casing in spaced relation with the walls of said casing and means for damping cavity resonance comprising a cloth curtain disposed between said casing and at least the top and sides of said motor-compressor unit, said curtain being fastened only to the top and side walls of said casing at a plurality of spaced points with the unsupported portions of said curtain draping in spaced relation with said casing and said motor-compressor unit.

References Cited in the file of this patent UNITED STATES PATENTS 1,660,745 Delaney Feb. 28, 1928 1,730,529 Robbins Oct. 8, 1929 2,072,035 Hayenga et a1. Feb. 23, 1937 2,721,029 Grimshaw Oct. 18, 1955 2,741,425 Scheldorf Apr. 10, 1956