Abstract:
The invention concerns a piston compressor cylinder arrangement ( 1 ), particularly for a hermetically enclosed refrigerant compressor, with a cylinder body ( 2 ) and a cylinder head arrangement ( 7 ), the cylinder body ( 2 ) having a first front side ( 6 ) in the area of the cylinder head arrangement ( 7 ) and a second front side ( 8 ) at the other end. It is endeavoured to manufacture such a cylinder arrangement in a cost-effective manner without having to fear for a deformation during mounting. For this purpose, a cup-shaped mounting sleeve ( 9 ) surrounds the cylinder body ( 2 ) over its full axial working length with a radial distance on all sides.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Applicant hereby claims foreign priority benefits under U.S.C. §119 from German Patent Application No. 10 2004 050 844.5 filed on Oct. 18, 2004, the contents of which are incorporated by reference herein. 
     FIELD OF THE INVENTION 
     The invention concerns a piston compressor cylinder arrangement, particularly for a hermetically enclosed refrigerant compressor, with a cylinder body and a cylinder head arrangement, the cylinder body having a first front side in the area of the cylinder head arrangement and a second front side at the other end. 
     BACKGROUND OF THE INVENTION 
     Such a cylinder arrangement is, for example, known from DE 39 01 588 A1. In the area of its first end, the cylinder body has a circumferential projection. An edged mounting ring engages this projection and the cylinder head arrangement. 
     U.S. Pat. No. 6,095,768 discloses a further, similar refrigerant compressor. The cylinder body has a cylinder pipe, which is provided with two axially protruding ribs over its full axial length. By means of these two ribs, the cylinder body is welded onto a mounting rail of the compressor block. 
     EP 0 524 552 A2 shows a similar embodiment, in which a cylinder is located on a housing part, the cylinder having in the area of its first front side a radially extended flange, on which a valve plate is fixed. 
     EP 0 507 091 B1 shows a cylinder pipe, which is guided through and connected with a block-like housing. 
     Large numbers of refrigerant compressors are used in refrigeration appliances, that is, refrigerators, freezers or vending machines. Here, it is endeavoured to achieve the best possible efficiency. In order to achieve a good mechanical efficiency, it is required that a piston reciprocating in a cylinder formed inside the cylinder body fits as exactly into this cylinder as possible. Accordingly, the tolerances have to be small. 
     At the same time, it is desired to make the production of such refrigerant compressors as cost-efficient as possible. The more cost-effective the manufacturing process is, the larger is the risk that narrow tolerances will not be observed. Particularly, there is a risk that the cylinder body is deformed and then no longer “fits” with the piston. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention is based on the task of mounting a cylinder body in a cost-effective manner without deforming it. 
     With a piston compressor cylinder arrangement as mentioned in the introduction, this task is solved in that a cup-shaped mounting sleeve surrounds the cylinder body over its full axial working length with a radial distance on all sides. 
     Now, the complete cylinder arrangement can be mounted in the piston compressor without forces having to act upon the circumference of the cylinder body. The forces required for holding the cylinder body are completely adopted by the mounting sleeve. These forces are not passed on to the circumference of the cylinder body, so that a deformation of the cylinder body in the radial direction must not be feared. The choice of fixing means for the mounting sleeve in the piston compressor is relatively free. The mounting sleeve can also be fixed in the piston compressor by welding, without risking that resulting thermal stresses will influence the cylinder body. Further, in a manner of speaking, the mounting sleeve makes it possible to pre-manufacture the cylinder arrangement, that is, to form it as a cartridge, which contains the cylinder body and the cylinder head arrangement. Also this makes the manufacturing cost-effective, without causing compromises with regard to the accuracy of the parts used. 
     Preferably, an annular gap, which is through-going in the circumferential and axial directions, is formed between the radial outside of the cylinder body and the radial inside of the mounting sleeve. This annular gap then contains no elements, which could transfer forces acting upon the mounting sleeve from the outside to the cylinder body. On the contrary, deformations of the mounting sleeve are permitted to a certain extent, such deformations having no effect on the cylinder body. 
     Preferably, the annular gap has an extension, which as a maximum corresponds to the radial thickness of the cylinder body plus the radial thickness of the mounting sleeve, particularly as a maximum the radial thickness of the cylinder body and particularly preferred as a maximum the radial thickness of the mounting sleeve. Thus, in the radial direction the annular gap can be relatively small. This saves space. The “cartridge” does not require substantially more space than the cylinder body alone. 
     Preferably, a radially inwardly protruding end section of the mounting sleeve bears on the second front side of the cylinder body. Thus, in the area of the second front side the mounting sleeve acts directly upon the cylinder body and retains it. The forces of the end section acting upon the cylinder body only act in the axial direction. In the axial direction, however, the cylinder body is stable enough to adopt these forces without being deformed. 
     It is preferred that the end section is also deformed axially inwards. Thus, this end section has a spring effect, that is, the mounting sleeve can be mounted on the cylinder body with a certain prestress. 
     Preferably, the outside of the second cylinder body front side has a circumferential recess, in which the mounting sleeve end section engages. This has the advantage that the mounting sleeve and the cylinder can be centred in relation to each other. In the area of this recess radial forces can then act upon the cylinder body. As, however, this position lies outside the working length of the cylinder body, deformations, if any, will no longer have an effect on the tightness between piston and cylinder. 
     Preferably, the radial inside of the recess is bordered by a conically shaped wall. Thus, the mounting is easier. When the cylinder body is inserted in the mounting sleeve, it centers, in a manner of speaking, automatically. 
     Preferably, the mounting sleeve is a deep-drawn sheet metal part. A deep-drawn sheet metal moulding has a sufficient stability. Within certain limits, deep-drawing the mounting sleeves from a sheet metal plate gives a large shaping freedom. Further, a deep-drawn sheet metal part is relatively cost-effective. The material, that is, the sheet metal plate, is cheaper than a corresponding pipe. The deep-drawing process in itself does not contribute substantially to an increase of the costs. 
     Preferably, the cylinder body is a sintered part. A sintered part can be manufactured with a high accuracy, so that the inner diameter corresponds with very small tolerances with the desired specifications. With the accuracies achieved, piston rings can, under certain circumstances, even be avoided. 
     Preferably, the sintered part is treated to be gas-tight, particularly steam-cured. This reduces the gas permeability of the sintered part. “Gas-tight” is not to be understood as absolute gas tightness. The treatment, particularly the steam curing, of the sintered part, however, reduces the gas permeability of the cylinder body so much that the efficiency is practically not deteriorated. 
     Preferably, the first cylinder body front side has a recess, into which a projection arrangement formed on the cylinder head arrangement engages. Thus, it is possible to align the cylinder body and the cylinder head arrangement in relation to each other in the radial direction. Later, this will improve the efficiency, particularly in that the position of the valves, particularly the pressure valves, can now be better fixed in relation to the cylinder. 
     Preferably, the recess is made to be circumferential. This simplifies the mounting. It no longer has to be ensured that the cylinder body and the cylinder head arrangement are aligned at a predetermined angular position in relation to each other. 
     It is preferred that the projection arrangement has several circumferentially distributed projections, which are separated from each other by interstices. This is particularly advantageous, when somehow the cylinder head arrangement is acted upon thermally during mounting, for example by welding. In this case, distortions, which are caused by irregular temperature distributions, are always limited to predetermined circumference sections. Further, the interstices can be used for the angular positioning of the individual cylinder head arrangement components. 
     Preferably, the mounting sleeve is fixedly connected with the cylinder head arrangement. Such a connection can, for example, be made by welding. With the connection of mounting sleeve and cylinder head arrangement, the cylinder arrangement is, in a manner of speaking, finished, that is, a cartridge is available, which can be handled in one piece and be used when mounting the piston compressor. 
     It is advantageous that the mounting sleeve is connected with a circumferential face of the cylinder head arrangement. Thus, the cylinder body is positioned in the mounting sleeve and the cylinder head arrangement is mounted. The cylinder head arrangement projects slightly into the mounting sleeve. If required, the cylinder head arrangement can further be pressed against the cylinder body, thus deforming the bordered end section of the mounting sleeve. When then the mounting sleeve is fixed on the circumferential wall of the cylinder head arrangement, small displacements, which occur because of manufacturing inaccuracies, can be compensated. 
     Preferably, the cylinder head arrangement has a base plate, which has on the side facing the cylinder body a pressure valve plate and adjacently a suction valve plate, the pressure valve plate forming a valve seat for at least one suction valve and the suction valve plate forming a valve seat for at least one pressure valve. As the pressure valve plate and the suction valve plate can be made substantially thinner than the base plate, this will keep dead spaces small. Thus, the efficiency of the compressor is further improved. 
     Preferably, a pressure muffler is located on the side of the base plate facing away from the cylinder body, the pressure muffler being connected with the base plate by means of welding. A pressure muffler has a muffling volume, which is connected with the outlet of the pressure valves. When, now, this pressure muffler is fixedly connected with the cylinder head arrangement, the mounting between the pressure muffler and the cylinder head arrangement can also be made in advance, which is a further substantial simplification of the mounting. 
     It is preferred that the pressure muffler has a bottom part, which is welded onto the base plate and a top part, which is welded onto the bottom part. This simplifies the connection of the pressure muffler and the cylinder head arrangement. The top part and the bottom part surround the mentioned muffling volume. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, the invention is described by way of a preferred embodiment in connection with the drawings, showing: 
         FIG. 1  is a schematic longitudinal section through a cylinder arrangement; 
         FIG. 2  is an enlarged view of the cylinder arrangement in the area of the cylinder head; and 
         FIG. 3  is an exploded view of essential parts of the cylinder arrangement. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a cylinder arrangement  1  of a refrigerant compressor, which is not shown in detail. The cylinder arrangement  1  has a cylinder body  2 , which surrounds a cylinder chamber  3 , in which a merely schematically shown piston  4  reciprocates to compress a refrigerant, which is located in the cylinder chamber  3 . The piston  4  is driven by a connecting rod  5 . 
     The cylinder body  2  is made of a sintered material, which is steam cured to be gas-tight. 
     The cylinder body  2  has a first front side  6 , which bears on a cylinder head arrangement  7 . Further, cylinder body  2  has a second front side  8 , on which the cylinder chamber  3  is open. 
     In the circumferential direction, the cylinder body  2  is completely surrounded by a mounting sleeve  9 , which also surrounds the largest share of the length of the cylinder body  2 . The mounting sleeve  9  extends in the axial direction over at least the so-called “working length” of the cylinder body  2 , that is, the length, in which the piston  4  moves. 
     Between the mounting sleeve  9  and the cylinder body  2  is formed an annular gap  37 , which can be relatively thin. In the present embodiment, it is substantially thinner than the wall thickness of the mounting sleeve  9 . It should as a maximum be as thick as the sum of the wall thicknesses of the cylinder body  2  and the mounting sleeve  9 . The annular gap  37  merely has to be so thick that it does not pass on deformations of the mounting sleeve, which occur during fixing of the mounting sleeve in a refrigerant compressor, to the circumferential face of the cylinder body  2 . 
     In the area of the second front side of the cylinder body  2 , the mounting sleeve  9  has an end section  10 , which is bent both radially and axially inwards. This end section  10  bears on the second front side  8  of the cylinder body  2 , or rather on the bottom  11  of a recess  12 . The radial inside of the recess  12  is formed by a slightly conically extending wall  13 , that is, with an axis  14  of the cylinder chamber  3 , the wall  13  encloses an acute angle. This embodiment causes that the mounting sleeve  9  is centred in relation to the cylinder body  2 , when the cylinder body  2  is inserted in the mounting sleeve  9  and projects through an opening  15  from the mounting sleeve  9  with its second front side  8 . 
     In the area of the first front side  6 , the mounting sleeve  9  is connected with the cylinder head arrangement  7 , that is, with the circumferential face  16  of the cylinder head arrangement  7 . The connection can, for example, be made by means of welding. The welding can be made on the full circumference of the mounting sleeve  9  or it can be made as a spot-welding. 
     Before fixing the mounting sleeve  9  on the cylinder head arrangement  7 , the cylinder head arrangement  7  is exposed to a certain pressure, so that the cylinder head arrangement  7  presses the cylinder body  2  firmly against the end section  10  of the mounting sleeve  9 . As the end section  10  is bent slightly axially inwards, it forms some sort of spring. After connecting the mounting sleeve  9  with the cylinder head arrangement  7 , the cylinder body  2  remains fixed between the end section  10  and the cylinder head arrangement  7 , the forces acting upon the cylinder body  2  acting practically exclusively in the axial direction. 
       FIG. 2  now shows the cylinder head arrangement and the neighbouring area of the cylinder body  2  in a somewhat enlarged view. 
     In the area of its first front side  6 , the cylinder body  2  has a circumferential recess  17 . This recess  17  originates from the first front side  6  and the circumferential face of the cylinder body  2 . 
     The cylinder body arrangement  7  has a base plate  18  with several suction openings  19  and several pressure openings  20 . On the side facing the cylinder body  2 , the base plate has several projections  21  distributed in the circumferential direction, said projections engaging the recess  17 . The interaction between the projections  21  and the recess  17  aligns the cylinder body  2  in relation to the base plate  18 . 
     A pressure valve plate  22  and a suction valve plate  23  are located between the base plate  18  and the cylinder body  2 . Via a sealing  24 , the suction valve plate  23  bears on the first front side  6  of the cylinder body  2 . The suction valve plate  23 , the pressure valve plate  22  and the base plate  18  are connected with each other by means of annular welding seams  25 , which penetrate the suction valve plate  23  and the pressure valve plate  22 . Here, the radially inner welding seam  25  seals a suction area located further radially inwards against a pressure area located further radially outwards. The welding seam  26  seals the pressure area radially outwards. 
     The design of the cylinder head arrangement  7  appears more clearly from  FIG. 3 . Here, it can be seen that the suction valve plate  23  has several suction valve elements  27 , bearing in the closed state on valve seats, which are formed on the side of the pressure valve plate  22  facing the cylinder body  2 . Thus, the pressure valve plate  22  forms valve seats for the suction valve elements  27 . The pressure valve plate  22 , however, has several pressure valve elements  28 , bearing in the closed state on valve seats, which are formed on the suction valve plate  23 . 
     The pressure valve plate  22  and the suction valve plate  23  have several radial projections  29 ,  30 , which engage in gaps between the projections  21  of the base plate  18  in order to position the suction valve plate  23 , the pressure valve plate  22  and the base plate  18  correctly in relation to each other. 
     On the side opposite the cylinder body  2  is located a pressure muffler  31 , which has a bottom part  32  and a top part  33 . Together, the bottom part  32  and the top part enclose a muffling volume  34 . The bottom part  32  is connected with the base plate  18  by means of welding seams  35 . The top part  33  is welded onto the bottom part by means of welding seams  36 . 
     Expediently, the welding of the pressure muffler  31  onto the base plate  18  takes place after the mounting sleeve  9  has been connected with the base plate  18 . 
     With the cylinder arrangement  1  shown, it can be ensured in a simple manner that the cylinder body  2  is not deformed by external forces, when the cylinder arrangement is mounted. During mounting, the mounting sleeve  9  can, for example, be welded or screwed together with any other components of the refrigerant compressor. 
     In the area of the cylinder head arrangement  7 , the mounting sleeve  9  can also be fixed in a different manner, for example in that an edge is bent around the base plate  18 . However, it should be observed that the base plate  18  is not too heavily deformed to avoid leakages in the suction and pressure valves. 
     While the present invention has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this invention may be made without departing from the spirit and scope of the present invention.