Abstract:
The invention concerns a refrigerant compressor with a cylinder, in which is arranged a piston ( 5 ) that is connected to a crankshaft via a connecting rod ( 14 ), the connecting rod ( 14 ) having a piston eye ( 18 ), through which a bolt ( 17 ) inserted in the piston ( 5 ) is guided. With such a refrigerant compressor, it is endeavoured to achieve a good efficiency. For this purpose, the bolt ( 17 ) is inserted in a blind bore ( 19 ).

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    Applicant hereby claims foreign priority benefits under U.S.C. §119 from German Patent Application No. 10 2008 036 999.3 filed on Aug. 7, 2008, the contents of which are incorporated by reference herein. 
       FIELD OF THE INVENTION 
       [0002]    The invention concerns a refrigerant compressor with a cylinder, in which is arranged a piston that is connected to a crankshaft via a connecting rod, the connecting rod having a piston eye, through which a bolt inserted in the piston is guided. Further, the invention concerns a piston of such a refrigerant compressor and a piston arrangement with a connecting rod, a bolt and a piston. 
       BACKGROUND OF THE INVENTION 
       [0003]    A refrigerant compressor as mentioned in the introduction is, for example, known from DE 195 22 210 C1. Here the bolt is connected to the piston by means of a press fit. In order to reduce a too heavy deformation of the piston, the press fit has a pair of fit surfaces, which are exposed to a reduced normal tension in the circumferential direction of the piston. 
         [0004]    During operation of a refrigerant compressor, the piston reciprocates in the cylinder, driven by the crankshaft. In this connection, the connection rod transforms the rotary movement of the crankshaft into a translatory movement of the piston. The movement of the piston compresses or expands a compression chamber in the cylinder. During compression, an increased pressure appears, by means of which the refrigerant that has been sucked into the cylinder is compressed. 
         [0005]    In order to achieve a good efficiency, the total amount of compressed refrigerant should, if possible, be supplied to a refrigeration system, for example a refrigerator, a freezer of an air-conditioning system that is connected to the refrigerant compressor. Usually, however, it cannot be avoided that a small share of the refrigerant gas flows of to the rear of the piston into the inside of the housing, in which the compressor is arranged. 
       SUMMARY OF THE INVENTION 
       [0006]    The invention is based on the task of achieving the best possible efficiency. 
         [0007]    With a refrigerant compressor as mentioned in the introduction, this task is solved in that the bolt is inserted in a blind bore. 
         [0008]    By means of this design, the leakage of the refrigerant gas is reduced. Contrary to an embodiment, in which the piston is provided with a through-bore, in which the bolt is inserted, the present solution only has one single “weakened area”, through which an increased gas flow can flow, namely in the area of the opening of the blind bore. Due to the reduced leakage, also the noise level is reduced. Accordingly, a muffler can be used, which has a somewhat smaller muffling effect, however, also an accordingly smaller throttle resistance. Also this has a positive effect on the efficiency. Further, with a blind bore, the circumferential wall of the piston only comprises one opening that has to be processed. This means that only in the area of one opening it must be ensured that no burrs or other residuals from a drilling process or the like remain, which could increase the friction between the piston and the cylinder. 
         [0009]    Preferably, the bolt is arranged in the piston with a slide fit. With a slide fit, the risk that the piston is deformed during insertion of the bolt is smaller than with a press fit. As the bolt is inserted in a blind bore, the risk that the bolt is lost is substantially smaller. In particular during the assembly of the refrigeration compressor, it is no longer required to hold the bolt in the piston by means of a press fit, if the piston is transported in such a manner that the closed end of the blind bore is turned downward. The smaller the deformation of the piston, the better the piston remains adapted to the shape of the cylinder, and the better is the tightness between the piston and the cylinder during a pressure stroke. 
         [0010]    Preferably, the bolt is held in the piston by means of a perch bolt. The perch bolt will act upon the piston with a certain force. However, the risk of a deformation of the piston is much smaller that the risk of a deformation with a press fit of the bolt in the piston. When the perch bolt holds the bolt in the piston, the bolt remains in a position, in which it will not rest on the wall of the cylinder. An increased friction will thus not appear which could reduce the efficiency of the refrigerant compressor again. 
         [0011]    Preferably, the perch bolt extends in parallel to the movement direction of the piston. Thus, the perch bolt can be inserted in the piston without having to penetrate the circumferential wall of the piston. 
         [0012]    Preferably, the perch bolt is arranged in a channel starting from the side of the piston facing the crankshaft. The front side of the piston that borders the pressure chamber in the cylinder can then remain unchanged. In particular, here there is no risk that the channel will create a leakage out of the pressure chamber. 
         [0013]    Preferably, the channel ends with the front side of the piston facing the crankshaft. This simplifies the assembly. During the assembly it is not required to work inside the piston. On the contrary, the assembly can take place from the front side of the piston, which is readily accessible. 
         [0014]    Preferably, the perch bolt ends inside the bolt. Thus, only a relatively simple processing of the piston is required to enable the insertion of the perch bolt. The channel accommodating the perch bolt then ends in a circumferential face of the blind bore. 
         [0015]    Preferably, the bolt comprises a hollow space. The hollow space can be used for two purposes. Firstly, it reduces the mass of the bolt. The smaller the moved mass is, to which also the bolt contributes, the smaller are the forces acting upon the moving parts during operation, and the smaller is the risk of a wear. Secondly, the hollow space of the bolt can also be used to supply lubricating oil. 
         [0016]    This is particularly the case, when the hollow space starts from an axial end of the bolt and penetrates the bolt on a part of its axial length. This, firstly, it is prevented that the hollow space collides with the perch bolt, so that here a risk of a leakage is prevented. Secondly, the oil that is supplied to the hollow space can reach the wall of the cylinder, where it creates a lubricating film that contributes to an improved sealing. 
         [0017]    Preferably, the hollow space is connected to an oil channel in the connecting rod via a radial channel in the area of the connecting rod. Oil to be used for the lubrication can then be supplied through this oil channel. 
         [0018]    With a piston of a refrigerant compressor, the task is solved in that the piston is made as described above and in that a drilled accommodation of a bolt is made as a blind bore. 
         [0019]    Such a piston has a reduced number of positions, at which the risk of a leakage exists. 
         [0020]    The invention also concerns a piston arrangement with a connecting rod, a bolt and a piston of the kind described. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    In the following, the invention is described on the basis of a preferred embodiment in connection with the drawings, showing: 
           [0022]      FIG. 1  is a schematic sectional view of a refrigerant compressor, 
           [0023]      FIG. 2  is a piston arrangement, 
           [0024]      FIG. 3  is a piston, 
           [0025]      FIG. 4  is a bolt, and 
           [0026]      FIG. 5  is a perspective view of the piston arrangement. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    A refrigerant compressor  1  shown in a schematic view in  FIG. 1  comprises a hermetically closed housing  2  in the form of a case. In the housing  2  is arranged a compressor block  3  with a cylinder  4 , in which a piston  5  is reciprocating. Together with the cylinder  4  and a cylinder head  5 , the piston  5  borders a compression chamber  7 . 
         [0028]    The movement of the piston  5  in the cylinder  4  is generated by means of a crankshaft  8  that is driven by an electric motor  9 . The electric motor  9  has a stator  10  and a rotor  11 , to which the crankshaft  8  is connected. 
         [0029]    At one end, the crankshaft  8  is provided with a crank pin  12 , which performs an orbiting movement around an axis  13  during operation. A connecting rod  14  is connected to the crank pin  12 , the connecting rod  14  being connected to the piston, as will be explained in detail in connection with  FIG. 2 . 
         [0030]    In the bottom area the housing  2  has an oil sump  15 , in which an oil pump  16  is submerged that pumps oil upward through the hollow crankshaft  8  in the direction of the crank pin  12 . 
         [0031]    The piston  5  is connected to the crankshaft  8  by means of a bolt  17  that is inserted in the piston  5  and penetrates a piston eye  18  of the crankshaft  8 . The bolt  17  is inserted in a blind bore  19  in the piston, that is, the bolt  17  can only be inserted in the piston  5  from one side. The blind bore  19  accordingly only has an opening  20  on one side. At the other end, the blind bore  19  is closed by a circumferential wall  21  of the piston  5 . 
         [0032]    The bolt  17  rests in the piston  5  with a slide fit, that is, it rests in the piston  5  with no tension or at least with an extremely small tension. At any rate, the tension is so small that it does not cause a deformation of the piston  5 . 
         [0033]    A perch bolt  22  is inserted in the piston  5  and the bolt  17  from a front side  23  of the piston  5  facing the crankshaft  8 . For this purpose, the piston  5  has a channel  24  that ends in the blind bore  19 . The bolt  17  has a diameter bore  25 , in which the perch bolt  22  ends. The perch bolt  22  can be resiliently held in both the bolt and in the channel  24  of the piston  5 . However, the spring reaction does not have to be too high. Due to the very low spring reaction, the risk that the spring reaction of the perch bolt  22  deforms the piston  5  is very small. The channel  24  may, for example, have a narrow passage  26 , in which the perch bolt  22  is held ( FIG. 3 ). Then, only in the area of the narrow passage  26 , the perch bolt  22  will have a spring reaction on the piston  5 . 
         [0034]    The bolt  17  has a hollow  27 , which extends from its free front side. Via a radial channel  28 , the hollow  27  is connected to an oil channel  29 , which is formed in the connecting rod  14 . The oil channel  29  is supplied with oil by the oil pump  16 . This oil then flows through the radial channel  28  into the hollow  27  and from there into the opening  20  of the blind bore  19 , where the oil contributes to improving the tightness. 
         [0035]    The oil channel  29  continues into an opening  30 , which ends inside the hollow  31  formed in the piston  5 . Thus, oil is also sprayed in this hollow  31  and can reach the contact area between the piston  5  and the cylinder  4  through radial openings  32  in the circumferential wall of the piston, in order to seal the contact area against the penetration of gas. 
         [0036]    When the connecting rod  14  is fixed in the piston  5  by means of the bolt  17 , the perch bolt  22  can easily be pushed into the channel  24 . As the perch bolt  22  is pushed in from the front side  23  that is not covered by the connecting rod  14 , its mounting is possible without problems. 
         [0037]    The embodiment shown permits an improved tightness of the compression chamber  7  during a pressure stroke. Only in the area of the opening  20  of the blind bore  19 , a reduced tightness exists. As, however, this only occurs at one position in the circumferential direction and not at two positions, as with a through bore, the leakage is practically halved. Due to the reduced leakage, also the noise level is reduced, which also has a positive effect on the efficiency. 
         [0038]    Further, an improved lubrication occurs, as the pressure from the compression chamber  7  can only enter the hollow  27  via one point, namely the opening  20  in the piston  5 . This pressure generates a mixture of lubrication oil and gas, which reduces the lubricating properties of the oil, which would also deteriorate the lubrication between the piston eye  18  and the bolt  17 . As here the gas pressure is reduced, again an improved lubrication is achieved. Due to the slide fit between the piston  5  and the bolt  17 , a reduced deformation of the piston is achieved. Also this improves the efficiency of the compressor  1 . Further, when manufacturing the piston  5 , only one area has to be processed, namely the area of the opening  20  of the blind bore  19 , to remove the processing traces. Accordingly, the risk that a wrong processing will cause an increased friction is smaller, which again has a positive effect on the efficiency of the compressor  1 . 
         [0039]    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.