Abstract:
In order to provide a screw compressor comprising two screw rotors which are disposed in screw rotor bores in a compressor casing and which compress a refrigerant entering at a refrigerant inlet and discharge it at a refrigerant outlet, and comprising an inlet provided in the compressor casing for refrigerant which is coming from a subcooling circuit and is passed to the inlet in a system of lines, the inlet being disposed in such a way that it opens out into compression spaces enclosed by the screw rotors and screw rotor bores, in which compressor the pressure oscillations or pulsations occurring at the inlet propagate as little as possible to the pipeline system of the subcooling circuit outside the compressor casing, it is proposed that the inlet is preceded by a damper channel which is associated with the system of lines and in which refrigerant from the subcooling circuit is present.

Description:
The present disclosure relates to the subject matter disclosed in German application No. 102 42 139.0 of Sep. 3, 2002, which is incorporated herein by reference in its entirety and for all purposes. 
   BACKGROUND OF THE INVENTION 
   The invention relates to a screw compressor, comprising two screw rotors which are disposed in screw rotor bores in a compressor casing and which compress a refrigerant entering at a refrigerant inlet and discharge it at a refrigerant outlet, and comprising an inlet disposed in the compressor casing for refrigerant which is coming from a supercooling circuit and is passed to the inlet via a system of lines, the inlet being disposed in such a way that it opens out into compression spaces enclosed by the screw rotors and screw rotor bores. 
   In the case of screw compressors of this type there is the problem that the compression spaces enclosed by the screw rotors and screw rotor bores moving past the inlet cause pressure oscillations or pulsations, which propagate into the pipeline system of the supercooling circuit and lead to noise and possibly also to problems in terms of stability and sealing. 
   It is therefore an object of the invention to provide a screw compressor in which the pressure oscillations or pulsations occurring at the inlet propagate as little as possible to the pipeline system of the supercooling circuit outside the compressor casing. 
   SUMMARY OF THE INVENTION 
   This object is achieved in the case of a screw compressor of the type described at the beginning according to the invention by the inlet being preceded by a damper channel which is associated with the system of lines and in which refrigerant from the supercooling circuit is present. 
   The provision of such a damper channel provides the possibility of reducing the pressure oscillations or pulsations occurring at the inlet. 
   In principle, it would be conceivable to provide the damper channel in the pipeline system of the supercooling circuit. 
   However, in order to prevent from the outset the pressure oscillations or pulsations from spreading with an appreciable intensity into the pipeline system and leading to oscillations in the latter, it is preferably provided that the damper channel is disposed in the compressor casing. 
   With regard to the way in which the damper channel is disposed in the compressor casing, a wide variety of possibilities are conceivable. 
   For example, it would be conceivable to produce the compressor casing from a number of casing portions and to provide the damper channel in one casing portion, while the screw rotor bores are disposed in another casing portion. 
   It is particularly advantageous, however, if the damper channel is formed in a casing portion which receives the screw rotor bores and consequently forms an integral unit which additionally reduces propagation of the pressure oscillations. 
   In principle, the damper channel may in this case be formed as a side arm of the system of lines and therefore not be constantly flowed through. 
   In order to obtain a compact construction of the damper channel, in an advantageous exemplary embodiment an inlet channel running through the compressor casing is provided as part of the system of lines which leads from an outer connection on the compressor casing, connected to the pipeline system of the supercooling circuit, to the inlet, the damper channel being disposed in the inlet channel. 
   It is likewise possible for the damper channel to be provided in the compressor casing in a wide variety of ways. 
   For example, it would be conceivable to form the damper channel in a unitary manner with the compressor casing receiving it. 
   However, a particularly advantageous exemplary embodiment provides that the damper channel is disposed in a part which can be inserted into the compressor casing. 
   In this case, this part could comprise both the inlet channel and the damper channel. However, it Is particularly advantageous if the part which can be inserted into the compressor casing can be inserted into the inlet channel in the compressor casing. 
   An exemplary embodiment which is suitable with regard to the design provides that the insertable part comprises a damper tube and a holder, by which the damper tube can be fixed in the compressor casing. 
   This solution is advantageous in design terms to the extent that the damper tube and the holder can be inserted into the inlet channel at a subsequent time. 
   Particularly suitable fixing of the damper tube and the holder in the inlet channel in this case provides positive fixing of the holder in the inlet channel. 
   With regard to the further formation of the screw compressor, no more details have been given in connection with the explanation so far of the individual exemplary embodiments. For instance, a particularly advantageous exemplary embodiment provides that the compressor casing comprises a control slide, and that the inlet is disposed in the control slide and can be displaced with it. 
   In the case of this solution of the screw compressor according to the invention, the latter can be controlled with regard to the obtainable compression and, at the same time as the controllability, it is also possible independently of the control to operate the supercooling circuit effectively. 
   With regard to the formation of the connection between the inlet and the inlet channel, a wide variety of solutions are conceivable. For example, it is conceivable to provide in the control slide and in the compressor casing portions which overlap one another in all positions of the control slide and by means of which the inlet channel can be led into the control slide. A solution which is advantageous in design terms provides that the inlet in the control slide is connected to the outer connection via a portion of the inlet channel of variable length. 
   It is particularly advantageous in this case if the portion of the inlet channel of variable length is telescopically formed. 
   A suitable embodiment of such a portion of the Inlet channel of variable length provides that the portion of the inlet channel of variable length is formed by a connecting pipe which can be pushed into a receiving channel. 
   With regard to the length of the damper channel, no further detail have been given in connection with the explanation so far of the solution according to the invention. For instance, a particularly advantageous solution provides that the damper channel is of a length which corresponds approximately to a quarter of the wavelength of the pressure oscillations to be damped or an odd multiple of the same. 
   The wavelength of the pressure oscillations to be damped can in this case be determined from a fundamental frequency of the pressure oscillations, the fundamental frequency of the pressure oscillations resulting from the product of the rotational speed of the screw rotors and the number of screw flights. 
   The damper channel acts particularly efficiently if it opens out with a first mouth opening into a first volume lying between the outer connection and the first mouth opening, so that the first mouth opening represents a so-called “open end” of the damper channel, at which a reflection of the pressure oscillations takes place at the so-called “open end”. 
   Furthermore, it is advantageously provided that the damper channel opens out with a second mouth opening into a second volume lying between said second opening and the inlet, so that there is also a so-called open end at the second mouth opening. 
   To obtain the most advantageous possible conditions for a reflection at the so-called “open end”, it is preferably provided that there is a sudden change in the cross-sectional surface area at the transition from one of the mouth openings into the respective volume. The sudden change in the cross-sectional surface area should be as great as possible. It is preferably provided that the sudden change in the cross-sectional surface area is at least a factor of 1.5. 
   To reduce or largely avoid propagation of the pressure oscillations or pulsations into the pipeline system of the supercooling circuit, it is preferably provided that the first volume, lying between the first mouth opening and the outer connection, lies in the compressor casing. 
   In this case, the first volume preferably lies in an inlet channel portion of the inlet channel led through the compressor casing. 
   Furthermore, it is likewise of advantage with regard to optimum damping of the pressure oscillations or pulsations if the second volume, lying between the second mouth opening and the inlet, likewise lies in the compressor casing. 
   The second volume advantageously likewise extends in the inlet channel portion receiving the damper channel. 
   In the case of a further advantageous exemplary embodiment, the connection for the supercooling circuit has an associated expansion volume. 
   This expansion volume can likewise also be provided in the inlet channel and in the compressor casing. 
   For reasons of space, however, it has proven to be advantageous if the expansion volume is provided near the outer connection for the supercooling circuit in the pipeline system of the supercooling circuit. 
   No further details have been given in connection with the explanation so far of the solution according to the invention concerning the fact that oil can accumulate in the damper channel, reducing the effect of the damper channel. 
   Such an accumulation of oil in the damper channel may take place when the supercooling circuit is not effective, but under certain circumstances even when the supercooling circuit is effective. 
   For this reason, a particularly advantageous solution provides that the system of lines is connected to an oil drain, which provides that oil, in particular oil accumulating near the damper channel, is drained from the system of lines. 
   It is particularly advantageous in this case if the oil drain opens out into the inlet channel, in particular if the damper channel is provided in the latter, since this provides the possibility of avoiding as far as possible accumulations of oil near the location of the damper channel. 
   A particularly advantageous solution provides that the oil drain opens out into the first volume. With the oil drain disposed in this way, there is the possibility of avoiding accumulations of oil in particular in the region of the first volume, and consequently of maintaining the effect of the damper channel. 
   In particular, it is of advantage in this case that the effect of the damper channel is ensured by no accumulations of oil forming at its mouth opening facing the outer inlet. 
   Further features and advantages of the invention are the subject of the description which follows and the graphic representation of some exemplary embodiments. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a setup of a screw compressor according to the invention in a cooling circuit with a supercooling circuit; 
       FIG. 2  shows a longitudinal section through a first exemplary embodiment of a screw compressor according to the invention; 
       FIG. 3  shows an enlarged representation of the longitudinal section according to  FIG. 2  in the region of a control slide; 
       FIG. 4  shows an enlarged representation in the form of a detail of a section through the compressor casing of the first exemplary embodiment in the region of an inlet channel following an outer connection, and 
       FIG. 5  shows a section similar to  FIG. 4  in the case of a second exemplary embodiment of a screw compressor according to the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A first exemplary embodiment of a screw compressor according to the invention, represented in  FIG. 1 , comprises a compressor casing, which is designated as a whole by  10  and on which a suction connection  12  and a pressure connection  14  are provided, refrigerant being sucked in at the suction connection  12  and compressed refrigerant being delivered at the pressure connection  14 . 
   The compressed refrigerant delivered at the pressure connection  14  is first fed to a condenser  16  and passes from the condenser  16  into an intermediate store  18  for liquid refrigerant. After the intermediate store  18 , the condensed refrigerant flows through a non-return valve  20  and a branch  22 , from which a cooling circuit  24  leads further to an expansion valve  26  and an evaporator  28 , and then back again from the evaporator  28  to the suction connection  12 . 
   Provided in addition to the cooling circuit  24  is a supercooling circuit  30 , which branches off from the cooling circuit  24  at the branch  22  and has an expansion valve  32 , through which part of the mass flow of the refrigerant from the cooling circuit  24 , which has first been compressed by the screw compressor, expands and is fed to a supercooler  34 , flows through the supercooler  34  and is then directed to a connection  40  provided on the compressor casing  10  for the supercooling circuit  30 . 
   At the same time, the refrigerant circulated in the cooling circuit  24  between the branch  22  and the expansion valve  26  likewise flows through the supercooler  34  and undergoes further supercooling in the supercooler  34  before its expansion in the expansion valve  26 , which leads to the effect that, with the additional supercooling circuit  30  in the cooling circuit  24 , the refrigerating capacity and the performance coefficient are improved, even though the power requirement of the screw compressor is increased only slightly. 
   As represented in detail in  FIGS. 2 and 3 , a first exemplary embodiment of a screw compressor according to the Invention comprises screw rotor bores  48  which are provided in the compressor casing  10  and in which interengaging screw rotors  50  are rotatably disposed, the screw rotor bores  48  extending from a refrigerant inlet  52  on the suction side to a refrigerant outlet  54  on the pressure side and the interengaging screw rotors  50  sucking in the refrigerant in the region of the refrigerant inlet  52 , compressing it on its way to the refrigerant outlet  54  and delivering it as compressed refrigerant at the refrigerant outlet  54 . Also provided in the compressor casing  10  is a recess  56 , in which a control slide  58  is movable in a direction  60  which runs parallel to an axis of rotation  62  of the screw rotor  50 . 
   With a valve wall  64  facing the screw rotors  50 , the control slide  58  forms one wall side of the screw rotor bores  48 , which by being displaceable in the direction  60  creates the possibility of controlling the compression that can be achieved by the screw rotors  50 . In the case of the position represented in  FIG. 2 , the entire valve wall  64  extends along the screw rotors  50 , and creates the possibility of the screw rotors  50  contributing over their entire length in the direction of their axis of rotation  62  to the compression of the refrigerant, whereas, in the case of the position of the control slide  58  represented in  FIG. 3 , said control slide has been displaced to the extent that only a subregion of the valve wall  64  is adjacent to the screw rotors  50  and consequently the screw rotors  50  contribute only over part of their length to the compression of the refrigerant, that is with the part which is adjacent to the valve wall  64 , whereas displacement of the control slide  58  after the refrigerant inlet  52  has the effect of forming a clearance  66  between the latter and an edge  68  on the suction side of the control slide  58 , which makes the region of the screw rotors  50  adjacent to the clearance  66  ineffective with regard to the compression of the refrigerant. 
   The control slide  58  is in this case able to be actuated by means of an adjusting device  70 , which may be formed for example in the way described in European patent application 1 072 796. 
   The adjusting device  70  may, however, also be formed differently and, for example, be able to be continuously actuated externally. 
   To be able to operate the supercooling circuit  30  effectively in all positions of the control slide  58 , it is necessary that, in the case of all the positions of the control slide  58 , the refrigerant which is coming from the supercooling circuit  30  and is to be sucked in by the screw compressor is fed to a compression space  72  which is bounded by the screw rotors  50  and the screw rotor bores  48  and also the valve wall  64  and in which the refrigerant is at a pressure level which is higher than the pressure level in the refrigerant inlet  52  and lower than the pressure level in the refrigerant outlet  54 . 
   For this reason, an inlet  80  for the refrigerant to be sucked in from the supercooling circuit  30  via a system of lines  78  is provided in the control slide  58  in the form of a bore passing through the valve wall  64 , an inlet opening  82  opening out into the compression space  72  always lying in such a way that over it there is always a compression space  72  which is closed off with respect to the refrigerant inlet  52  and the refrigerant outlet  54 , or the inlet opening  82  is closed by a screw flight  84   x . 
   As represented in  FIG. 3 , in the position of the screw rotor  50  depicted in  FIG. 3 , the screw flight  84   x  just closes the inlet opening  82 , while a future space  72 ′, initially still open with respect to the refrigerant inlet  52 , is already forming, and, as the screw rotor  50  continues to rotate, is closed with respect to the refrigerant inlet  50  by the next-following screw flight  84   x-1  and then comes to lie over the inlet opening  82 , so that a connection then exists between the inlet  80  and this then closed compression space and refrigerant can flow into this compression space via the inlet  80 . 
   The inlet opening  82  preferably lies in such a way that it opens out into the compression space  72  closed off by the screw flights  84  with respect to the refrigerant inlet  82 . 
   In the case of the exemplary embodiment represented, the inlet  80  is in connection with a central receiving channel  19 , which extends in the direction  60  in the control slide  58  and has on one side an opening  92  via which a connecting pipe  94  held on the compressor casing  10  protrudes into said opening, a seal  96  being provided between the central receiving channel  90  and the connecting pipe  94  and the connecting pipe  94  being of such a length that, in every position of the control slide  58 , it is sealed by the seal  96  and protrudes into the central receiving channel  90 , without hindering the displaceability of the control slide  58  between the positions intended for control. 
   The connecting pipe  94  is connected to a casing channel  98  which runs in the compressor casing  10  and is led to the connection  40  on the compressor casing  10 . 
   An inlet channel  100 , forming part of the system of lines  78 , between the connection  40  and the inlet  80  in the compressor casing  10  is consequently formed by the casing channel  98 , a channel  102  running in the connecting pipe  94  and the central receiving channel  90  in the control slide  58 , from which the inlet  80  branches off, with the connecting pipe  94  and the receiving channel  90  forming a portion  104  of the inlet channel  100  of variable length. 
   Since—as already described—the screw flights  84  of the screw rotors  52  keep running over the inlet opening  82 , and consequently a newly formed compression space  72  keeps being connected to the inlet  80 , pressure oscillations or pulsations are produced in the inlet channel  100  with a fundamental frequency which results from the rotational speed of the screw rotors  50  driven by motor  110  multiplied by the number of screw flights  84  of the screw rotors  50 . 
   In order to dampen such pressure oscillations or pulsations, a damper channel  120 , which extends in a damper tube  122  which has been inserted into the inlet channel portion  116 , is provided in the inlet channel  100 , preferably in an inlet channel portion  116  of the inlet channel  100 , in particular of the casing channel  98 , connected directly to the outer connection  40 , formed by the connection flange  112  and a pipe connection  114 . 
   The damper channel  120  in the damper tube  122  extends in this case from a first mouth opening  124  to a second mouth opening  126  with a preferably uniform cross-section, the mouth openings  124  and  126  having cross-sectional surface areas which are smaller than the cross-sectional surface areas of the inlet channel portion  116  surrounding the damper tube  122 , so that, starting from the damper channel  120 , there is a sudden change in cross-section to a larger cross-sectional surface area by a factor of at least 1.5 at the two mouth openings  124  and  126 . 
   The damper tube  122  preferably has a smaller cross-section than the inlet channel portion  116  and is held in the inlet channel portion  116  by a holder  130 . 
   The holder  130  is formed for example as a holding ring which is provided with an external thread  127 , which engages in an internal thread  128  of the inlet channel portion  116 , so that a positive connection can be established between the holder  130 ,and the compressor casing  10 . 
   The holder  130  and the damper tube  122  in this case divide the inlet channel portion  116  into two volumes lying outside the damper tube  122 , that is a first volume  132  and a second volume  134 . 
   The first volume  132  lies between the connection  40  and the first mouth opening  124 , the first volume also being able to extend around the damper tube  122  as far as the holder  130 . The second volume  134  lies between the second mouth opening  126  and the inlet  80 , the second volume  134  also being able to extend around the damper tube  122  as far as the holder  130 . 
   In the case of the solution according to the invention, the length of the damper channel  120  in the damper tube  122  is then dimensioned in such a way that it corresponds in the order of magnitude to a quarter or an integral multiple of a quarter of the wavelength of a pressure oscillation or pulsation forming with the fundamental frequency in the refrigerant, so that the pressure oscillations or pulsations are damped in particular by the combination of the damper channel  120  with the first volume  132  and the second volume  134 . 
   With such a solution, a reduction in the pressure differences between peak values of the pulsations of 5 bar to pressure differences between peak values of the oscillations of 1 bar is possible for example. 
   With the solution according to the invention there is the possibility of appreciably reducing the pressure oscillations or pulsations already in the compressor casing  10  and consequently avoiding that these oscillations or pulsations propagate into the pipeline system of the supercooling circuit  30  leading away from the compressor casing  10  and lead to undesired oscillations in said system. 
   The damper channel  120  is in this case effective independently of whether or not the supercooling circuit  30  is effective. 
   In particular in the case of a supercooling circuit  30  that is not effective, there is likewise an increased tendency for pressure oscillations or pulsations to spread into the pipeline system of the supercooling circuit  30  running outside the compressor casing  10  on account of the refrigerant present in the system of lines  78 , so that the damper channel  120  also contributes to a considerable degree to the damping of pressure oscillations or pulsations when the supercooling circuit  30  is not effective. 
   In order to prevent oil from accumulating in the inlet channel  100  when the supercooling circuit  30  is not effective, and thereby impairing the effectiveness of the damper channel  120  by the latter being flooded at least partially with oil, associated with the inlet channel  100 —as represented in FIG.  1 —is an oil drain  136 , which on the one hand opens out via an oil drain channel  137 , represented in  FIG. 4 , into the inlet channel  100  in the region of the inlet channel portion  116 , preferably into the first volume  132  of the same, and on the other hand is connected to the suction connection  12 , preferably to the end on the suction side of the cooling circuit  24 . 
   Furthermore, the oil drain  136  also comprises a valve  138 , which can be actuated at intervals, for example when the supercooling circuit  30  is not active, in order in these intervals to discharge oil collecting in the inlet channel  100 , in particular in the first volume  132  of the same. 
   The oil drain  136  does not necessarily have to operate even when the supercooling circuit  30  is effective, since, with the supercooling circuit  30  effective, the refrigerant flowing through the inlet channel  100  generally causes oil collecting there to be fed to the compression spaces  72 . 
   It is also possible, however, to operate the oil drain  136  while the supercooling circuit  30  is effective, in order to be certain of avoiding any kind of oil accumulation in the inlet channel  100 , in particular in the inlet channel portion  116  receiving the damper channel  120 . 
   In the case of a second exemplary embodiment, represented in  FIG. 5 , also provided in addition to the pressure channel  120 , to be precise in a portion  140  of a pipeline system of the supercooling circuit  30  connected directly to the connection  40 , is an expansion volume  142 , which creates the possibility of further damping pressure oscillations or pulsations still spreading from the compressor casing  10  into the portion  140  of the pipeline system, and consequently further reducing their effects on the pipeline system. 
   Otherwise, the second exemplary embodiment is formed in the same way as the first exemplary embodiment, so that reference is made to the full content of the statements made with respect to the latter.