Abstract:
The invention relates to a compressor for hermetically sealed small refrigeration machines, comprising a cylinder with a cylinder housing and a piston that is guided in the piston bore of the cylinder and that compresses a working medium. The cylinder is sealed by a disc-type valve plate in the axial direction, a cylinder cover lying against or being surrounded by the plate. According to the invention, the cylinder housing comprises axial extensions facing towards the cylinder cover and located in the peripheral area of the cover. A first axial section of the axial extensions lies against the cylinder cover in the contact region between the cylinder cover and the valve plate and a second axial section surrounds the cylinder cover with a small degree of play.

Description:
AREA OF THE INVENTION 
       [0001]    The present invention relates to a compressor for hermetically encapsulated small refrigerators, which has a cylinder having a cylinder housing and a piston guided in the cylinder bore of the cylinder for compressing an operating medium, the cylinder being terminated in an axial direction using a disk-shaped valve plate, against which a cylinder cover presses or which it encloses, according to the preamble of Claim  1 . 
       PRIOR ART 
       [0002]    Compressors of this type are well-known according to the prior art. Screw connections are typically used for fastening the cylinder cover and/or the valve plate to the cylinder housing. However, the disadvantage is displayed when screw connections are used that because of the tension which acts on the cylinder housing, the cylindrical shape of the cylinder bore is negatively influenced. Furthermore, screw connections always require increased mounting effort, because first the holes for the screws must be placed in a targeted way to ensure optimum centering of the cylinder cover in relation to the cylinder housing. In addition, it would be advantageous to replace the punctual contact pressure produced by screw connections with a constant contact pressure over the entire seal area, by which the seal area and/or the required contact pressure may also be reduced. Furthermore, it would be advantageous to implement the force introduction of the fasteners for the cylinder cover on the cylinder housing in such a way that it is performed especially in those areas of the cylinder cover in which the largest loads due to the piston force also occur. Protection of the cylinder cover may thus be caused. 
         [0003]    For example, a cylinder head configuration for piston compressors, which comprises a multipart valve assembly and an intake noise damper, is previously known from DE 102 44 565 A1. Asymmetrically oriented projections which project radially into the cylinder head bore, which engage upon insertion into the housing in corresponding grooves of the valve assembly and the cylinder head cover, are used for orienting the individual parts. The cylinder head cover is attached to the housing in a typical way using a peripheral flange and fastening bolts. 
       DESCRIPTION OF THE INVENTION 
       [0004]    It is therefore the object of the present invention to fix the cylinder cover to the cylinder housing in such a way that a negative impairment of the cylindrical shape of the cylinder bore is avoided. Furthermore, it is the object of the present invention to reduce the mounting and material outlay by dispensing with the use of screws. The ability to center the cylinder cover easily in relation to the cylinder housing is to be ensured and uniform contact pressure and reduction of the seal area and/or the required contact pressure are to be made possible. Furthermore, the force introduction of the fasteners for the cylinder cover on the cylinder housing is to be implemented in such a way that it occurs in particular in those areas of the cylinder cover in which the largest loads due to the piston force also occur, to thus protect the cylinder cover in the best possible way. 
         [0005]    A further object of the present invention comprises reducing the heat emission of the cylinder into the interior of the compressor. Reducing this heat emission into the interior of the compressor also causes a performance increase of the compressor, because the heat arising due to the compression of the operating medium in the cylinder is dissipated more rapidly and the thermodynamic efficiency is thus improved. 
         [0006]    These objects are achieved by the characterizing features of Claim  1 . 
         [0007]    Claim  1  relates to a compressor according to the species and provides that the cylinder housing has axial projections in the direction of the cylinder cover which are situated around the circumference of the cylinder cover, the axial projections pressing against the cylinder cover in a first axial section in the contact area of the cylinder cover with the valve plate and enclosing the cylinder cover with slight play in a second axial section. Because the axial projections in a first axial section press against the cylinder cover in the contact area of the cylinder cover with the valve plate, centering of the valve plate and the cylinder cover is achieved. Screw connections for centering the valve plate and the cylinder cover may be dispensed with. Fastening elements may be provided for the axial contact pressure in this way, which do not have a primarily centering effect, but rather solely have to ensure an axial contact pressure. Fastening elements of this type are described in the subclaims. Because the axial projections also enclose the cylinder cover with slight play in a second axial section, an insulating effect is achieved, because the air layer between the cylinder cover and the second axial sections reduces the heat emission into the interior of the compressor. 
         [0008]    In Claim  2 , the second axial section projects beyond the cylinder cover. In this way, on one hand, the insulating effect is improved and, on the other hand, the installation of fasteners for fixing the cylinder cover to the cylinder housing is made easier. The latter is also achieved by the features of Claim  3 , according to which retention nubs which project radially inward are provided in the end section of the particular second axial sections. 
         [0009]    Claim  4  relates to a preferred embodiment, in which a fastening element is provided, which attaches the cylinder cover to the cylinder housing by a contact pressure exerted in the area of the axis of the piston bore. According to Claim  5 , this is a spring element. According to claim  6 , this spring element may be implemented as a spring washer, whose sections facing away from the cylinder cover are supported on the retention nubs. 
         [0010]    As noted, the insulating effect is achieved by the air layer between the cylinder cover and the second axial sections. To improve this insulating effect, according to Claim  7 , an insulating material may be located between the cylinder cover and the particular second axial sections of the projections. However, the insulating effect may also be improved if, according to Claim  8 , the axial projections essentially completely enclose the cylinder cover. The formulation “essentially” relates in particular to the fact that openings are typically provided for the supply and removal of the operating medium to be compressed, for example. 
         [0011]    Claim  9  allows an embodiment of the axial projections of the cylinder housing according to the present invention having an especially simple construction. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0012]    The present invention is explained in greater detail in the following on the basis of the attached figures. 
           [0013]      FIG. 1  shows a section through the cylinder of a compressor according to the present invention along line A-A visible in  FIG. 2 , 
           [0014]      FIG. 2  shows a view of the cylinder of a compressor according to the present invention from above, and 
           [0015]      FIG. 3  shows a perspective view of the cylinder of a compressor according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
       [0016]      FIG. 1  shows a section through the cylinder of a compressor according to the present invention along line A-A shown in  FIG. 2 , in which the relative configuration of cylinder cover  8 , cylinder housing  1 , and the projections  10  according to the present invention is visible. The individual components are only shown schematically in this case, and the cylinder cover  8  may thus also be implemented as an assembly. However, to understand the present invention, it is solely decisive that the cylinder cover  8  has a seal area  7  as the contact area to the valve plate  6 . The axial section in which the cylinder cover  8 , the valve plate  6 , and/or the seal area  7  are incident on one another is also referred to in the following as the contact area of the cylinder cover  8  with the valve plate  6 . A piston  2  is guided inside the cylinder housing  1  using a connecting rod  3  to compress an operating medium. The piston bore of the cylinder is terminated using the disk-shaped valve plate  6 , the valve plate  6  pressing against the cylinder housing  1  via a dead space seal  5 . 
         [0017]    The valve plate  6  and the cylinder cover  8  are to be fastened to the cylinder housing. As already described, screw connections are typically used for this purpose. However, if screw connections are used, the disadvantage is displayed that because of the tension which acts on the cylinder housing  1 , the cylindrical shape of the cylinder bore is negatively influenced. Furthermore, screw connections always cause increased mounting effort, because firstly the holes for the screws must be placed in a targeted way to ensure optimum centering of the cylinder cover  8  in relation to the cylinder housing  1 . In addition, it would be advantageous to replace the punctual contact pressure caused by the screw connections by a constant contact pressure over the entire seal area  5  and/or  7 , by which the seal area and/or the required contact pressure may also be reduced. Furthermore, it would be advantageous to implement the force introduction of the fasteners for the cylinder cover  8  on the cylinder housing  1  in such a way that it occurs in particular in those areas of the cylinder cover  8  in which the largest loads due to the piston force also arise. The cylinder cover  8  may thus be protected. 
         [0018]    Therefore, according to the present invention, the cylinder housing  1  has axial projections  10  in the direction of the cylinder cover  8 , which are situated around the circumference of the cylinder cover  8 , the axial projections  10  pressing against the cylinder cover  8  in a first axial section  11  in the contact area of the cylinder cover  8  with the valve plate  6  and enclosing the cylinder cover  1  with slight play in a second axial section  12 . Because the axial projections  10  press against the cylinder cover  8  in a first axial section  11 , which is in the contact area of the cylinder cover  8  with the valve plate  6 , centering of the valve plate  6  and the cylinder cover  8  is achieved. Screw connections for centering the valve plate  6  and the cylinder cover  8  may be dispensed with. In this way, fastening elements  9  may be provided for the axial contact pressure which do not have a primary centering effect, but rather only have to ensure an axial contact pressure. For example, a spring element  9 , in particular a spring washer  9 , may be provided as a fastening element  9 , as will be explained in greater detail in the following. Because the axial projections  10  in a second axial section  12  also enclose the cylinder cover  8  with slight play, an insulating effect is achieved, because the air layer between the cylinder cover  8  and the second axial sections  12  reduces the heat emission into the interior of the compressor. The play is preferably 0.1 to 10 mm. 
         [0019]    In Claim  2 , the second axial section projects beyond the cylinder cover. In this way, on one hand the insulating effect is improved, and, in addition, the installation of fasteners for fixing the cylinder cover to the cylinder housing is made easier. The latter is also achieved by the features of Claim  3 , according to which inwardly projecting retention nubs are provided in the end section of the particular second axial sections. 
         [0020]    As a shown in  FIG. 1 , the second axial section  12  projects beyond the cylinder cover  8  according to a preferred embodiment. In this way, on one hand, the insulating effect is improved and, on the other hand, the installation of the spring element  9  is made easier, which compensates for settling of the dead space seal  5  and the cylinder cover seal  7  because of a lower spring stiffness than the screws known from the prior art, to fix the cylinder cover  8  to the cylinder housing  1 . For this purpose, inwardly projecting retention nubs  13  may also be provided in the end section of the particular second axial sections  12 , on which the spring washer  9  is supported in its sections facing away from the cylinder cover  8 . The retention nubs  13  are also visible in  FIGS. 2 and 3 , from which it may also be seen that in this case the valve plate  6  and the cylinder cover  8  must have radial recesses around their circumferences corresponding to the retention nubs  13  to allow their insertion between the axial projections  10 . 
         [0021]    As noted, the insulating effect is achieved by the air layer between the cylinder cover  8  and the second axial sections  12 . To improve this insulating effect, an insulating material may be located between the cylinder cover  8  and the particular second axial sections  12  of the projections  10  (not visible in  FIGS. 1 through 3 ). However, the insulating effect may also be improved if the axial projections  10  enclose the cylinder cover  8  essentially completely. The formulation “essentially” relates in particular to the fact that typically openings  14  are provided for the supply and removal of the operating medium to be compressed, for example. 
         [0022]    An embodiment of the axial projections  10  of the cylinder housing  1  according to the present invention having an especially simple construction may be achieved if the axial projections  10  are implemented in one piece with the cylinder housing  1  and essentially represent extensions of the cylinder housing  1 , as shown in  FIGS. 1 through 3 . 
         [0023]    Therefore, fixing of the cylinder cover  8  on the cylinder housing  1  is achieved by the measures according to the present invention without negatively impairing the cylindrical shape of the cylinder bore. The mounting and material outlay is reduced by dispensing with the use of screws. The measures according to the present invention additionally allow easy ability to center the cylinder cover  8  in relation to the cylinder housing  1  and ensure a uniform contact pressure while simultaneously reducing the seal area and/or the contact pressure. Furthermore, the force introduction of the fasteners  9  for the cylinder cover  8  on the cylinder housing  1  may be implemented in such a way that it occurs in particular in those areas of the cylinder cover  8  in which the largest loads due to the piston force also arise, in order to thus protect the cylinder cover  8  as well as possible. 
         [0024]    A further advantage of the present invention is that the heat emission of the cylinder into the interior of the compressor is reduced. A reduction of this heat emission into the interior of the compressor also causes a performance increase of the compressor, because the heat arising due to the compression of the operating medium in the cylinder is dissipated more rapidly and the thermodynamic efficiency is thus improved.