Abstract:
To provide a screw compressor comprising a compressor screw housing, two screw rotors with intermeshing screw bodies arranged in the compressor screw housing and with shaft sections arranged on both sides of the screw bodies, the screw rotors being mounted by means of the shaft sections in bearing housings arranged on both sides of the compressor screw housing, which prevents pressure losses, it is proposed that an intermediate portion of the respective shaft section adjoining an end of the respective screw body at the pressure side and extending as far as a bearing section be sealed off in the area of a closure wall of the compressor screw housing at the outlet side from an inside surface of an opening in the closure wall, which surrounds the intermediate portion.

Description:
[0001]    The present disclosure relates to the subject matter disclosed in international application PCT/EP01/08597 of Jul. 25, 2001, which is incorporated herein by reference in its entirety and for all purposes. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The invention relates to a screw compressor comprising a compressor screw housing, two screw rotors with intermeshing screw bodies arranged in the compressor screw housing and with shaft sections arranged on both sides of the screw bodies, the screw rotors being mounted by means of the shaft sections in bearing housings arranged on both sides of the compressor screw housing.  
           [0003]    Such screw compressors are known from the prior art, and, with these, there is the problem of providing at the pressure side as tight a closure as possible between the screw bodies and the compressor screw housing, so as to prevent losses of pressure.  
         SUMMARY OF THE INVENTION  
         [0004]    This problem is solved, in accordance with the invention, in a screw compressor of the kind described at the outset, by an intermediate portion of the shaft section adjoining an end of the respective screw body at the pressure side and extending as far as a bearing section being sealed off in the area of a closure wall of the compressor screw housing at the outlet side from an inside surface of an opening in the closure wall, which surrounds the intermediate portion.  
           [0005]    The advantage of the solution according to the invention is to be seen in the fact that owing to the seal between the intermediate portion and the inside surface of the opening, the gap existing between these cannot be penetrated by a parasitic flow of compressed working medium—which would travel from the volume area with compressed working medium to a volume area located opposite the outlet in close proximity to the closure wall of the compressor housing at the outlet side—and which therefore does not open a bypass causing a loss of compressed working medium which should exit from the outlet.  
           [0006]    In principle, it is possible to maintain the seal in the gap between the intermediate portion and the inside surface of the opening by a film of oil.  
           [0007]    However, a particularly expedient solution makes provision for a seal allowing radial movements of the intermediate portion relative to the inside surface to be arranged between the intermediate portion and the inside surface.  
           [0008]    This solution has the advantage that in contrast to a sealing with oil, which requires a substantially uniform gap, which, in addition, should be kept as small as possible, the seal allows radial movement of the intermediate portion relative to the inside surface but still ensures sufficient tightness, so that the inventive solution can be employed in standard screw compressor solutions in which a radial movement of the intermediate portion relative to the inside surface is permissible, which occurs as a result of the screw bodies being subjected to forces acting on one side.  
           [0009]    The seal could be provided in the direction of the axis of rotation in any partial area of the intermediate portion and the inside surface. A particularly expedient solution makes provision for the seal to be arranged essentially in close proximity to an edge of the opening that faces the respective screw body, preferably in an edge area of the opening that faces the screw body. The volume existing up to the seal in the gap between the intermediate portion and the inside surface is therefore kept as small as possible from the start.  
           [0010]    The seal preferably lies in a third of the opening adjoining the edge of the opening that faces the respective screw body.  
           [0011]    So far, no details have been given of the way in which the seal is configured. In a particularly advantageous solution, provision is made for the seal to comprise a sealing ring which offers the possibility of sealing between the intermediate portion and the inside surface in a simple way.  
           [0012]    Such a sealing ring could, for example, be made of elastic material, so that radial movements of the intermediate portion relative to the inside surface would result in the sealing ring being pressed to different degrees.  
           [0013]    A particularly advantageous solution makes provision for the seal to comprise a sealing ring seated in a groove and movable radially in relation to this groove. This makes it possible to bring about the radial movements of the intermediate portion relative to the inside surface by a relative displacement of the sealing ring with respect to the groove.  
           [0014]    Here it is particularly expedient for the groove to be arranged in the intermediate portion.  
           [0015]    A particularly expedient solution makes provision for the groove to be arranged in the intermediate portion near the end of the respective screw body at the pressure side.  
           [0016]    It is expedient for the distance of the groove from an end face of the respective screw body to be at most five times, even better at most three times, a width of the groove in the direction of the axis of rotation.  
           [0017]    A further expedient solution is configured such that the intermediate portion has adjacent to the end of the respective screw body at the pressure side an indentation located opposite the edge of the opening.  
           [0018]    Such an indentation has the advantage that contact can then be avoided between the intermediate portion and the edge of the opening when the intermediate portion moves radially relative to the inside surface of the opening.  
           [0019]    It is particularly expedient for the groove to be arranged so as to essentially follow the indentation.  
           [0020]    It is preferable for there to be a spacing between the groove and an end face of the respective screw body, which corresponds at most to three times the extent of the indentation in the direction of the axis of rotation, with the indentation preferably having an extent in the direction of the axis of rotation which corresponds approximately to a width of the groove.  
           [0021]    It is even better for the spacing of the groove from the end face to be of the order of magnitude of twice the extent of the indentation in the direction of the respective axis of rotation.  
           [0022]    A ring-shaped bead is preferably provided between the indentation and the groove to ensure proper guidance of the sealing ring.  
           [0023]    This ring-shaped bead expediently has an extent in the direction of the axis of rotation which at most corresponds approximately to the extent of the indentation in the direction of the axis of rotation.  
           [0024]    A particularly preferred embodiment makes provision for several sealing rings to be arranged one after the other in the direction of the axis of rotation.  
           [0025]    Further features and advantages of the invention are the subject matter of the following description and drawings of several embodiments. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]    [0026]FIG. 1 shows a longitudinal section through a first embodiment of an inventive screw compressor taken along line  1 - 1  in FIG. 2;  
         [0027]    [0027]FIG. 2 shows a section taken along line  2 - 2  in FIG. 1;  
         [0028]    [0028]FIG. 3 shows a section taken along line  3 - 3  in FIG. 1;  
         [0029]    [0029]FIG. 4 is an enlarged illustration of area A in FIG. 3;  
         [0030]    [0030]FIG. 5 is a front view of a sealing ring; and  
         [0031]    [0031]FIG. 6 shows a section taken along line  6 - 6  in FIG. 5.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]    An embodiment of an inventive screw compressor, shown in FIG. 1, comprises an outer housing generally designated  10 , which is built up of a central section  12 , an end section  14  on the motor side, and an end section  16  on the pressure side, which is arranged on the side of the central section  12  located opposite the end section  14  on the motor side.  
         [0033]    The central section  12  and the end section  14  on the motor side are preferably connected to each other by two flanges  18  and  20 , respectively, and the central section  12  to the end section  16  on the pressure side by flanges  22  and  24 , respectively.  
         [0034]    A drive motor generally designated  30  in the form of, for example, an electric motor comprising a stator  32  and a rotor  34  is provided in the outer housing  10 . The stator  32  is preferably fixed securely in place in the outer housing  10 , in particular, in a motor area  36  of the central section  12  facing the end section  14  on the motor side.  
         [0035]    A compressor screw housing generally designated  40  is provided within the central section  12  of the outer housing  10 . As shown in FIG. 2, the compressor screw housing  40  has two rotor bores  42  and  44  which merge into one another as well as a slide bore  46  for, for example, a regulating slide not drawn in FIG. 1.  
         [0036]    The rotor bores  42  and  44  serve to accommodate two screw rotors  48  and  50 , respectively, which are common in a screw compressor. The screw rotors  48  and  50  are merely indicated by dashed lines in FIG. 2.  
         [0037]    The two screw rotors  48  and  50  rotate about their respective axis of rotation  52  and  54 , respectively, and are mounted for rotation about their axis of rotation  52  and  54 , respectively, on both sides of their respective screw body  56 .  
         [0038]    To this end, a bearing housing  60  which has first bearing receiving means  62  for first rotary bearings  64  of the two screw rotors  48 ,  50  adjoins the compressor screw housing  40  on a side facing the drive motor  30 . The screw rotors  48 ,  50  have shaft sections  66  which proceed from ends  65  of the screw bodies  56  at the suction side, and on which the rotary bearings  64  are seated. One of these shaft sections  66  is arranged coaxially with a drive shaft  38  of the drive motor  30  and is connected thereto.  
         [0039]    On their side located opposite the bearing housing  60 , the screw rotors  48 ,  50  are rotatably mounted in a second bearing housing  70  with second bearing receiving means  72  likewise by means of second rotary bearings  74 . To this end, the screw rotors likewise have shaft sections  76  projecting from ends  75  of the screw bodies  56  at the pressure side.  
         [0040]    The compressor screw housing  40  thus extends between the first bearing housing  60  and the second bearing housing  70  over the entire length of the screw bodies  56  in the direction of their rotor axes  52  and  54 , respectively, and encloses the screw rotors  48  and  50  in the area of their screw bodies  56 , so that there remains between the screw bodies  56  and the rotor bores  42  and  44  a sealing gap S which is constructed as small as possible for sealing.  
         [0041]    All the areas of the compressor screw housing  40  in which a wall  80  of the compressor screw housing  40  extends relative to the screw bodies  56 , thereby forming the gap S, form a compression section  82  of the compressor screw housing  40  which is adjoined on the inlet side, i.e., on a side facing the drive motor  30 , by an inlet section  84  which forms an inlet  86  for working medium to be compressed, and on the outlet side, i.e., on a side located essentially diagonally opposite the inlet  86 , by an outlet section  88  which forms an outlet  90 , from which the compressed working medium exits.  
         [0042]    As shown in FIG. 4, in particular, the volume area with compressed working medium is sealed off on the pressure side from volume areas lying at a lower pressure by a small gap  95  between end faces  92  of the screw bodies  56  and a surface  94  of a closure wall  96  of the compressor screw housing  40 .  
         [0043]    The closure wall  96  is provided with openings  98  through which the shaft sections  76  extend, and the shaft sections  76  are mounted with bearing sections  100  in the second rotary bearings  74 . The shaft sections  76  respectively extend with the bearing section  100  through the second rotary bearing  74  and between the bearing section  100  and the end  75  of the respective screw body  56  on the pressure side there extends an intermediate portion  102  of the respective shaft section  76 , which is required for mounting the second rotary bearing  74  at a sufficiently large distance from the closure wall  96  and with sufficient stability in the second bearing housing  70 .  
         [0044]    The intermediate portion  102  essentially has a cylindrical circumferential surface  104  extending at a slight distance from an inside surface  106  of the respective opening  98  in the closure wall  96 .  
         [0045]    In accordance with the invention, in the area of the intermediate portion  102  and the opening  98  accommodating the latter a gap  110  arising between the inside surface  106  and the circumferential surface  104  is sealed in order to prevent in this gap  110  a parasitic flow of compressed working medium to volume areas under a lower pressure, in particular, to volume areas located opposite the outlet  90  and close to the closure wall  96 .  
         [0046]    For this reason, the inventive solution provides a seal generally designated  120  which is to prevent penetration of compressed working medium into the gap  110  and, in particular, advance thereof in the direction of the second rotary bearings  74 .  
         [0047]    As shown on an enlarged scale in FIG. 4, the intermediate portion  102  is provided close to the end face  92  with a circumferential groove  122  having a groove bottom  124  and groove walls  126  and  128  rising from the latter. Inserted in the groove  122  with play in radial direction in relation to the axis of rotation  54  is a sealing ring  130  which rests with an outer circumferential surface  132  against the inside surface  106  of the opening  98 . With its two opposite end faces  134  and  136 , the sealing ring  130  extends into the groove  122  between groove walls  126  and  128  of the groove  122  and is placed by the pressure in the area of the outlet  90  with its end face  136  against the groove wall  128 . The sealing ring  130  does, however, have an inside surface  138  with a diameter which is larger than a diameter of the groove bottom  124  so that the sealing ring  130  is movable in radial direction in relation to the axis of rotation  54  relative to the groove  122 .  
         [0048]    As shown in FIGS. 5 and 6, the sealing ring  130  is preferably in the form of a ring of rectangular cross section, which forms the outer circumferential surface  132  on its outer side and the end faces  134  and  136  as surfaces parallel to each other, but offset in the direction of its axis  142 , with the groove walls  126  and  128  preferably lying in planes extending perpendicularly to the axis  142  and also to the axis of rotation  54 .  
         [0049]    The sealing ring  130  is also provided with a slit  144  which allows radial expansion of the sealing ring  130  in relation to the axis  142 .  
         [0050]    The sealing ring  130  is preferably made of cast iron or Teflon filled with a material for increasing its strength, in particular, compressive strength.  
         [0051]    In order to prevent the intermediate portion  102  from coming into contact with an edge  146  of the opening  98 , in particular, in an area immediately adjoining the end face  92  of the respective screw body  56 , owing to movements radially in relation to the axis of rotation  54 , the edge  146  of the opening  98  is preferably provided with an inclined surface  148  which extends in the form of a conical surface in relation to the respective axis of rotation  54 .  
         [0052]    Immediately adjoining the end face  92 , the intermediate portion  102  is provided with an indentation  150  extending in the shape of a ring with a base surface  152  which has a diameter smaller than that of the circumferential cylindrical surface  104 .  
         [0053]    In order to seal as close as possible to the surface  94  of the closure wall  96 , the groove  122  lies so close to the indentation  150  that there remains between the indentation  150  and the groove  122  a ring-shaped bead  154  whose circumferential surface  156  has a diameter which corresponds approximately to that of the circumferential cylindrical surface  104  of the intermediate portion  102  and is preferably identical thereto.  
         [0054]    The extent of the ring-shaped bead  154  in the direction of the axis of rotation  54  corresponds at most to the extent of the indentation  150  in the direction of the axis of rotation  54  and likewise at most to a width of the groove  122  in the direction of the axis of rotation  54 .  
         [0055]    The groove  122  is preferably spaced at a distance from the end face  92  of the screw body  56  which corresponds at most to five times the width of the groove  122  in the direction of the axis of rotation  54 .