Abstract:
The invention concerns a refrigerant compressor with a motor, a compressor driven by the motor, and a muffling device having at least one muffler with a housing. It is endeavoured to reduce the thermal influence of suction gas in the refrigerant compressor. For this purpose, it is ensured that the housing has at least one outer wall, which is made of a foamed plastic.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is entitled to the benefit of and incorporates by reference essential subject matter disclosed in German Patent Application No. 103 23 527.2 filed on May 24, 2003.  
       FIELD OF THE INVENTION  
       [0002]     The invention concerns a refrigerant compressor with a motor, a compressor driven by the motor, and a muffling device having at least one muffler with a housing.  
       BACKGROUND OF THE INVENTION  
       [0003]     Such a refrigerant compressor is, for example, known from DE 195 16 811 C2. Here, the motor and the compressor are located in a case together with a suction muffler. That is, a hermetically enclosed refrigerant compressor is concerned, which has proved its value for several years.  
         [0004]     With such compressors, the refrigerant gas coming from the evaporator is sucked in, compressed in the compressor, which increases the temperature of the refrigerant gas, and then discharged by a discharge nozzle, which in many cases communicates with a pulsation muffler. In this connection, the colder the refrigerant suction gas is, the better is the efficiency of the compressor. The temperature of the refrigerant suction gas is, however, already increased before entering the compressor, as the refrigerant gas is exposed to a somewhat heated atmosphere inside the case.  
         [0005]     In order to remedy this problem, at least partly, U.S. Pat. No. 4,371,319 suggests that in a hermetically enclosed compressor, the cylinder head, the pressure muffler and the pressure line should be supplied with an isolating layer inside the case. However, this procedure is very expensive and requires a substantial amount of space inside the case.  
       SUMMARY OF THE INVENTION  
       [0006]     The invention is based on the task of reducing the thermal influence of suction gas in the refrigerant compressor.  
         [0007]     With a refrigerant compressor as mentioned in the introduction, this task is solved in that the housing has at least one outer wall, which is made of a foamed plastic.  
         [0008]     With this embodiment, an improved thermal isolation towards the environment of the gas entering the muffler is achieved, without requiring an additional isolation layer. The housing itself makes the isolation. As the outer wall of the housing is made by a foamed plastic, it provides an excellent isolation. When the muffler is used as a suction muffler, the suction gas remains relatively cold, that is, it is not heated by the temperature ruling in the case. When the muffler is arranged to be a pressure or pulsation muffler at the outlet of the compressor, the outer wall of the housing made of foamed plastic also provides thermal isolation, so that the heat from the heated refrigerant gas is not transferred to the environment. Also this is a measure, with which an undesired heat transfer to the refrigerant suction gas can be avoided. Of course, also a foamed plastic does not give perfect thermal isolation, that is, heat will still be able to flow through the outer wall. However, compared with a wall of massive plastic, which has been used until now, the heat flow will be substantially reduced, so that the thermal influence on the suction gas can be reduced accordingly. Making at least one outer wall of a foamed plastic will only increase the manufacturing costs of the muffler insignificantly or not at all. On the other hand, however, the efficiency of the compressor provided with the muffler is increased, so that possible additional costs will be balanced very soon.  
         [0009]     Preferably, all outer walls are made of foamed plastic. This gives improved heat isolation of the gas in the muffler towards the environment. Additionally, a partly substantial noise muffling is achieved. A foamed plastic can have better noise muffling properties than a massive plastic, as an oscillation transfer through a massive plastic can take place substantially more directly than through a foamed plastic. It is assumed that the gas bubbles contained in the foamed plastic obstruct a noise penetration. Thus, a housing, all outer walls of which are made of foamed plastic, offers two advantages.  
         [0010]     It is preferred that the housing is made of foamed plastic. This simplifies the manufacturing. Also, when chambers, bars or other elements are provided in the housing, which are made in one piece with the other housing parts during manufacturing, a foamed plastic can be used. The foamed plastic is then also available inside the housing with the mentioned elements. The result is a housing for the suction muffler made of a substantially homogenous material. Thus, the risk that fatigue phenomenon occur in connection with material transitions, for example due to stress crack corrosion, is relatively small.  
         [0011]     Preferably, a connection line between the muffler and the compressor is made of foamed plastic. Also the connection line serves the purpose of isolating the gas thermally towards the environment. This opportunity exists on the one hand with a connection between a suction muffler and the compressor. In this case, it is avoided that the suction gas is heated. On the other hand, the possibility also exists with the connection from the compressor to the pressure muffler. In this case, it is avoided that heat is transferred from the connection line to the environment.  
         [0012]     Preferably, the muffler is located in a case, in which the motor and/or the compressor are located. In this case, the use of a muffler, which is completely or partly made of foamed plastic, is particularly advantageous. As stated above, an increased temperature is usually available in a closed case, as the compressor, in which the refrigerant gas is compressed, causes a temperature increase in the refrigerant gas during compression. This increased temperature radiates into the inside of the case. When now, particularly a suction muffler of a foamed plastic is used, the refrigerant gas, which is sucked in, is kept cold and the efficiency of the compressor increases.  
         [0013]     It is preferred that a connection line between the case and the muffler is made of foamed plastic. Thus, a heat transfer does not take place via the path between the inlet of the case and the muffler or between the muffler and the outlet of the case, respectively.  
         [0014]     Preferably, the foamed plastic is a foamed PBT. PBT has proved its suitability for use in refrigerant circuits. Now, basically the same material can be used, and it must merely be ensured by means of a foaming during or before the manufacturing that the housing of the muffler is completely or partly made by the foamed PBT.  
         [0015]     Preferably, the size of the cells of the foamed plastic is in the range from 5 to 50 μm. Thus, very small cells are concerned, which are substantially smaller than those of “traditional” PBT foam. With such small cells, a high mechanical strength is achieved so that the dimensions of the walls of the muffler can be left more or less unchanged. A slight increase in the thickness, however, is harmless. Foamed PBT with such small cells are commercially available under the name “MuCell” from the company Trexel, Inc., Woburn, Mass., USA: 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     In the following, the invention is described on the basis of a preferred embodiment in connection with the drawings, showing:  
         [0017]      FIG. 1  is a schematic sectional view through a refrigerant compressor  
         [0018]      FIG. 2  is a suction muffler, partially in front view 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]      FIG. 1  shows a refrigerant compressor  1  with a motor  2 , which drives a compressor  3 . The motor  2  has a stator  4  and a rotor  5 . The rotor  5  is connected with a shaft  6 , which drives a piston  8  in a cylinder  9  via a crankshaft drive  7 . The cylinder  9  is closed by a cylinder head  10 , in which, in a manner known per se, valves are located, which control the filling of a compression chamber in the cylinder  9  with refrigerant gas, or the discharge of the refrigerant gas from the compression chamber, respectively.  
         [0020]     The parts mentioned are enclosed in a case  11 , which encloses the motor  2  and the compressor  3  hermetically. The outside of the case is provided with an electronic connection device  12 , if required with a control, which controls the operation of the motor  2  in dependence of predetermined values, for example the refrigeration requirement of a refrigerator, not shown in detail. The device  12  is connected with the motor  2  via lines  13  guided through the case.  
         [0021]     Refrigerant gas is supplied by an evaporator, not shown in detail, to a suction muffler  15  via a suction nozzle  14 . The suction muffler  15  is connected with the cylinder head  10  via a line  16  ( FIG. 2 ). In a manner not shown in detail, the cylinder head  10  is connected with a pressure muffler  17  via a pressure line, the pressure muffler discharging compressed and heated refrigerant gas from the case  11  via a discharge nozzle  18 .  
         [0022]     The suction nozzle  14  extends into a suction line  19 , which is located inside the case  11 . By way of a flange  20 , the suction line  19  bears on a contact surface  21  of the housing  22  of the suction muffler  15 .  
         [0023]     The housing  22  is formed by an top part  23  and bottom part  24 , which bear on each other with flanges  25 ,  26 , which can be stepped, if required, and are connected with each other along a contact face  27 , for example by means of welding.  
         [0024]     Inside the housing  22  is formed a muffling chamber  28 . In the muffling chamber is located a pipe  29 , which forms a gas conduit  30 , through which refrigerant gas can flow from the inlet  31  of the suction muffler  15  to the outlet  32 . This embodiment is only chosen as an example. It is of course also possible to design the suction muffler  15  differently.  
         [0025]     The housing  22  of the suction muffler  15  is made of a foamed plastic. Also the pipe  29  is made of the foamed plastic. The foamed plastic is a foamed PBT (polybutylene terephthalate) with evenly distributed cells in the size range 5 to 50 μm. Such a material is, for example, commercially available under the name “MuCell” from the company Trexel, Inc., Woburn, Mass., USA. It is characterised in having substantially smaller cells than traditional, foamed PBT with cells in the size range of 250 μm.  
         [0026]     Such a foamed PBT (or another foamed plastic) has the advantage that a heat transfer from the atmosphere ruling inside the case  11  to the refrigerant suction gas is only possible to a heavily reduced extent. Thus, the refrigerant gas is not further heated inside the case  11 . On the other hand, making the suction muffler  15  of foamed plastic has the advantage that noises occurring inside the suction muffler through the flowing and pulsating gas can be even better muffled. Thus, the foamed plastic forms an acoustic muffler.  
         [0027]     The foamed plastic can, for example, be made in that nitrogen or carbon dioxide under a high pressure is supplied as supercritical fluid to the molten polymer in an extruder or an injection moulding device, and suddenly the pressure is reduced, after which the housing of the suction muffler  15  can be made in practically the traditional way. With this manufacturing method, it is possible to adopt the wall thicknesses, which have until now been chosen for the parts, of which the suction muffler consists, in a practically unchanged form. Small dimension changes are insignificant.  
         [0028]     Of course, also the pressure muffler  17  can be made of the foamed plastic. In this case, the foamed plastic prevents a heat transfer from the refrigerant gas heated by the compression to the environment inside the case  11 . This also reduces the thermal influences on the refrigerant suction gas.  
         [0029]     The colder the refrigerant gas entering the compressor  3  is, the higher is the efficiency of the compressor. The use of a foamed plastic thus causes efficiency improvements.