Abstract:
The invention concerns a suction muffler for a hermetically enclosed compressor with a housing that has at least a first and a second chamber, separated from each other by means of a division wall and connected with each other by means of a throttling channel, which is designed to allow flow from the first to the second chamber. 
     The throttling channel includes a lateral opening, which opens into a chamber via a branch channel.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is entitled to the benefit of and incorporates by reference essential subject matter disclosed in German Patent Application No. 101 28 225.7 filed on Jun. 11, 2001. 
     FIELD OF THE INVENTION 
     The invention concerns a suction muffler for a hermetically enclosed compressor with a housing that has at least a first and a second chamber, separated from each other by means of a dividing wall and connected with each other by means of a throttling channel, which is designed to allow flow from the first to the second chamber. 
     BACKGROUND OF THE INVENTION 
     A suction muffler of this kind is known from DE 199 23 734. This muffler has a housing that consists of an upper part, a bottom part and an insert. The insert divides the housing into two chambers, which are connected with each other by means of a tubular throttling channel. The throttling channel is made as part of the insert. Together with the housing bottom part, a wall section of the insert forms a capillary slot, in which oil can accumulate. This improves the noise damping of the muffler. The channel extends substantially into the first chamber, whereas in the second chamber merely a short channel section projects over the bottom surface of the insert. 
     Among other things, such suction mufflers serve the purpose of damping sound waves resulting from the opening and closing movements of a suction valve arrangement, which is arranged in a cylinder head of a compressor. The noise caused by this can be undesirably transferred to the environment via the volume enclosed by the compressor shell. 
     An additional suction muffler is known from U.S. Pat. No. 3,750,840 A. In this case, the throttling channel connecting the two chambers of the housing is formed by a channel structure pressed into an insert plate. The insert plate is fixedly connected with a division plate. Openings formed in the insert plate and in the division plate provide the connection between the two chambers. This design is relatively expensive to manufacture. 
     SUMMARY OF THE INVENTION 
     The invention is based on the task of improving noise suppression. 
     With a suction muffler as mentioned in the background, this task is solved in that the throttling channel comprises a lateral opening, which opens into a chamber via a branch channel. 
     Thus, the lateral opening is not directly connected with the chamber, into which it opens. On the contrary, an additional branch channel is arranged between the opening in the wall of the throttling channel and the actual exit into the corresponding chamber, which branch channel can further contribute to noise suppression. Basically, this provides in a simple manner an extension of the distance which must be travelled by the sound waves. As both the throttling channel and the branch channel have limited cross-sectional surfaces, a muffling of the sound waves takes place in both channels. 
     Preferably, the branch channel opens into the second chamber. The second chamber is the chamber which is closest to the outlet of the muffler and thus to the inlet of the compressor. Here, the sound waves still have their largest intensity so that a damping in the branch channel is preferred to take place here, before the sound waves reach the inside of the compressor housing through the inlet of the suction muffler. 
     Preferably, the throttling channel has a tubular section in the second chamber, in which the opening is arranged. Thus, the throttling channel can be extended into the second chamber by the tubular section. An extension of this kind is very advantageous for noise suppression. However, it has the disadvantage that oil, which is entrained by the gaseous refrigerant flowing through the throttling channel, can no longer flow off from the second chamber. The oil thus collecting up in the second chamber would cause a deterioration of the effective volume of the second chamber, which would again deteriorate noise suppression. 
     The opening now remedies the above-described problem. As the opening is arranged laterally, the oil in the second chamber can flow off when it reaches the level of the opening. This means that the oil can no longer collect up to the level of the tubular section, as the opening and the branch channel permit the oil to flow off, before it reaches the level of the tubular section. Thus, it is achieved that a relatively large volume of the second chamber is still available for noise suppression. Additionally, it is avoided that too much oil is drained off from the lubricating circuit of the compressor, which would, among other things, deteriorate the cooling of some components and have a negative influence on the life of the compressor. 
     It is particularly preferred that the opening is in the shape of a slot and that in the longitudinal direction the branch channel has a slot-like cross-section. This design has turned out to be particularly advantageous for noise suppression. The term “slot-like” suggests that in the cross-section the channel has a substantially larger dimension in one direction than in the other direction. Preferably, the larger dimension is parallel to the flow direction through the throttling channel. In principle, the channel thus has the shape of a flat plate, the plate having, of course, a certain, but small thickness. 
     Preferably, the opening ends at the bottom of the chamber. Due to gravity, oil that has been taken into the second chamber by the gas flow accumulates at the bottom of the chamber and can, as the opening goes right down to the bottom, flow back to the first chamber through this opening. 
     Preferably, the branch channel is limited by the bottom of the chamber. Thus, the oil is free to reach the opening of the branch channel, so that oil is prevented from accumulating in the second chamber. 
     Preferably, the opening is arranged at the lowest point of the chamber. Or, more precisely, the opening in the wall of the tubular section is extended down to the lowest point of the chamber. Oil that usually accumulates at the lowest point due to gravity is then free to flow off. In this case, an escape path is always available for any oil that starts accumulating. 
     Preferably, the length of the branch channel substantially corresponds to the height of the branch channel. The “length” of the branch channel means the distance from the opening to the oppositely arranged exit of the branch channel into the second chamber. The height is the extension perpendicularly to this, that is, the extension in parallel to the flow direction through the throttling channel. The adaptation to each other of length and height has turned out to be advantageous for the muffling qualities. 
     Preferably, the branch channel extends in an arch shape. The arch-shaped extension serves the purpose of improving the noise suppression. 
     It is particularly preferred that the branch channel runs substantially parallel to the circumferential wall of the throttling channel. In this case, the branch channel also provides an additional thermal isolation for the refrigerant flowing through the throttling channel, which means that the efficiency of the compressor on a whole is improved. 
     Preferably, the circumferential wall of the throttling channel forms a limiting wall of the branch channel. This results in a particularly simple design. Only one additional wall is required for the branch channel. 
     Preferably, the branch channel is open on the face side. This means that the branch channel has a second outlet opening, which may, for example, be arranged in the same level as the outlet opening of the throttling channel. Under certain circumstances, it can also be arranged in a different level. Thus, the flow resistance of the arrangement is reduced. The gas that passes through the throttling channel has a movement component in the direction of the longitudinal axis of the throttling channel. The face side opening of the branch channel now permits the gas to flow on with this movement component. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following, the invention is explained in detail on the basis of preferred embodiments in connection with the drawings, wherein: 
     FIG. 1 is a longitudinal section through a suction muffler 
     FIG. 2 is a section II—II according to FIG. 1 
     FIG. 3 is a perspective view of an insert 
     FIG. 4 is a comparison of the muffling behaviour of different suction mufflers 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A suction muffler  1  has a bottom part  2 , a top part  3 , and between them an insert  4 , which divides the housing into a first chamber  5  and a second chamber  6 . The two housing parts  2 ,  3  and the insert  4  can be made of a plastic material, for example, polybutylene terephthalate (PBTP). These parts are connected with each other at their flanges  7 ,  8 ,  9  by means of a suitable connecting process, for example, bonding or welding. 
     The first chamber has an inlet  10 , which is arranged in an inlet nozzle  11 . The second chamber  6  has an outlet  12 , which is arranged in an outlet nozzle  13 . 
     The insert  4  is passed by a throttling channel  14 , which extends in a pipe-like nozzle  15 , of which a first section  16  is arranged in the first chamber  5 , whereas a second section  17  is arranged in the second chamber  6 . The second section  17  is longer than the first section  16 . 
     The throttling channel  14  extends approximately coaxially to the outlet nozzle  13  and to an extension  18  of the inlet nozzle  11 , which is somewhat angled in relation to the inlet  10 . A distance  19  between the extension  18  and the nozzle  15  forms a connection to the first chamber  5 . A distance  20  between the nozzle  15  and the outlet nozzle  13  forms a connection to the second chamber. In the extension  18  a lateral opening  21  is provided, through which oil that accumulates in the first chamber  5  can flow off through the inlet  10 . 
     During operation, gaseous refrigerant enters through the inlet  10 , flows through the throttling channel  14  from the first chamber  5  to the second chamber  6  and then reaches the outlet  12  through the outlet nozzle  13 , the outlet  12  being connected with a compressor, which is not shown in detail. 
     The second section  17  of the pipe-shaped nozzle  15  has, in the wall of the nozzle  15 , a slot-like opening  22 , which goes right to the bottom wall of the second chamber  6  that is formed by the insert  4 . As can be seen from FIG. 1, the slot-like opening  22  has, in the circumferential direction of the throttling channel  14  only a small width. However, the slot-like opening  22  has a relatively large height, which practically corresponds to the length of the second section  17  of the pipe-shaped nozzle  15 . Thus, the slot-like opening  22  starts at the upper end of the pipe-shaped nozzle  15  and goes down to the bottom wall of the insert  4 . 
     However, the slot-like opening  22  does not open direct into the second chamber  6 , but into a branch channel  23 , which has substantially the same cross-section as the slot-like opening  22 . In a manner of speaking, the branch channel  23  is formed by an excursion of the slot-like opening  22 . It has a length  1 , which substantially corresponds to its height h. Also the branch channel  23  is open in the direction of the second chamber  6  at the upper end of the pipe-shaped nozzle  5 . 
     On one side, the branch channel  23  is limited by the outer wall of the pipe-shaped nozzle  15  and on the other side by an outer limiting wall  24 , which is substantially parallel to the outer wall of the pipe-shaped nozzle  15 . Therefore, the branch channel is curved or arched. 
     As can be seen from FIG. 1, the bottom side of the branch channel  23  is limited by the insert  4 . If required, the bottom wall of the insert  4  can additionally have a step  25 , to create a bottom at a somewhat lower level. Oil that accumulates in the second chamber  6  can then enter the branch channel  23  through the outlet  26  of the branch channel  23  and flow on the bottom of the branch channel  23  to the slot-like opening  22 . Here, it can enter the throttling channel  14  and flow off from the suction muffler through the inlet  10 . This prevents the second chamber  6  from being filled with oil that is entrained by the gaseous refrigerant. If not for the slot-like opening  22  and the branch channel  23 , this would be the case. An embodiment only having the slot-like opening  22  and not the branch channel  23  would still ensure the desired oil flow-off, however, the acoustic muffling effect would be very small. With the embodiment shown, a muffling behaviour is achieved, which approximately corresponds to the muffling behaviour of a throttling channel  14  with the length of the tubular nozzle. Due to the arched branch channel  23 , the oil flow-off from the second chamber  6  is still possible. Additionally, the throttling channel  14  is thermally shielded by the branch channel  23  from the somewhat warmer housing walls, so that the cold refrigerant supplied will be less heated and absorb less heat energy. This has a positive effect on the efficiency of the compressor. 
     As the limiting wall  24  extends in parallel to the outer circumferential wall of the tubular nozzle  15 , a particularly space-saving design is achieved, which takes away as little volume as possible from the second chamber  6 . At the same time, the lateral opening of the branch channel  23  ends at the lowest spot of the insert  4 , which permits a flow-off of all the oil that has accumulated in the second chamber  6 . Also, the curved shape of the limiting wall  24  provides a mechanically more rigid structure, whose higher resonant frequency lies in an uncritical range. Also the tool used for making the insert  4 , for example an injection mould, has a high rigidity and thus a long life. 
     FIG. 4 shows a comparison of two curves representing the muffling LD in dB, for the described suction muffler  1 , (curve B) in relation to a known suction muffler according to DE 199 23 734 C1 (curve A). The abscissa shows the frequency in Hz, whereas the muffling LD in dB is shown on the ordinate. In this connection, the branch channel  23  has a length and a height of approximately 18 mm, whereas the thickness, that is, the distance between the limiting wall  24  and the wall of the tubular nozzle  15  is approximately 2 mm. The diameter of the throttling channel  14  is approximately 7 mm. It is obvious that in the frequency range from approximately 400 Hz to approximately 800 Hz, in which the first hollow space resonances of the compressor housing lies, the curve B is substantially better. Thus, with the suction muffler, a substantially more silent operation of a refrigerant compressor is possible.