Abstract:
The invention concerns a refrigeration system comprising a refrigerant circuit which comprises several evaporator paths and a distributor ( 5 ) which distributes the refrigerant on the evaporator paths. The aim of the invention is to improve the operation of said refrigeration system in a simple manner. According to the invention, the distributor ( 5 ) comprises a controllable valve ( 12 ) for each evaporation path.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 12/278,158, filed on Feb. 9, 2009, which is entitled to the benefit of and incorporates by reference essential subject matter disclosed in International Patent Application No. PCT/DK2007/000067 filed on Feb. 9, 2007 and German Patent Application No. 10 2006 006 731.2 filed Feb. 13, 2006, each of which applications is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The invention concerns a refrigeration system with a refrigerant circuit comprising several evaporation paths and a distributor causing a distribution of refrigerant to the evaporation paths. 
     BACKGROUND OF THE INVENTION 
     Such a refrigeration system is known from U.S. Pat. No. 5,832,744. The distributor comprises a valve arranged between a refrigerant inlet and several refrigerant outlets, the valve being connected in series after a rotating turbine disc. The purpose of the turbine disc is to ensure that the refrigerant is distributed evenly to all outlets of the distributor and thus also evenly to all evaporators. 
     A further distributor, which can be used in such a refrigeration system, is known from U.S. Pat. No. 6,898,945 B1. Here, a valve is located between an inlet and several outlets, a pressure drop over the distributor being adjustable with said valve. The valve comprises a conical pin for the distribution of the supplied refrigerant, so that the refrigerant can be distributed to the various circuits of through the evaporator. 
     In theory, the known distributors ensure an even distribution of the refrigerant to the individual evaporators. However, even small differences in the dimensions, which could, for example, occur during manufacturing, cause an uneven distribution to the individual evaporators. Further, for such distributors, it is necessary that the individual evaporators have basically the same thermal load and the same flow resistance. If this is not the case, it may happen that an evaporator receives too much refrigerant, so that the refrigerant is not completely evaporated before having passed through the evaporator. Another evaporator, which is connected to the same distributor, can receive too little refrigerant, so that the evaporator cannot supply the required refrigeration output. The oversupply or the undersupply, respectively, of the evaporator may particularly cause problems, if temperature sensors, which are arranged at the evaporators or in other locations of the refrigeration system, control an expansion valve. Under unfavourable circumstances, the expansion valve can start oscillating naturally, which will further deteriorate the capacity and the efficiency of the refrigeration system. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention is based on the task of improving the operation of the refrigeration system with simple means. 
     With a refrigeration system as mentioned in the introduction, this task is solved in that, for each evaporation path, the distributor comprises a controllable valve. 
     When, in the following, a “refrigeration system” is mentioned, this is to be understood in the broadest sense of the word. It particularly comprises refrigeration systems, freezing systems, air-conditioning systems and heat pumps. The word “refrigeration system” is merely used for reasons of simplicity. The evaporation paths can be arranged in different evaporators. For reasons of simplicity, the invention is explained in connection with several evaporators. However, the invention can also be used, if one evaporator comprises several evaporation paths, which can be controlled individually or in groups. 
     If the distributor comprises a controllable valve for each evaporator, it can control the supply of the evaporator individually, that is, it is then possible to supply each evaporator with the amount of refrigerant, which it requires. It must no longer be considered that all evaporators must have the same flow resistance. It is also of inferior importance, if the evaporator has to supply different refrigeration outputs. An evaporator, from which a large refrigeration output is required, receives correspondingly more refrigerant than an evaporator, which has to supply a smaller refrigeration output. 
     Preferably, the valves are controlled by a control device, which controls the individual valves differently. The control device thus ensures the distribution of the refrigerant to the individual evaporators. 
     Preferably, the control device controls only one single valve so that it comprises an inlet opening, which is larger than the inlet opening of the other valves. If, usually, all valves are closed, the control device then only opens one valve at a time. This simplifies the control and the batching of the refrigerant to be supplied to each individual evaporator. 
     Preferably, the control device comprises a rotor, which causes the opening of valves. Thus, the individual valves are opened by the rotation of the rotor. This is a very simple possibility of controlling the individual valves individually one after the other. 
     Preferably, the rotor is driven by a motor with variable speed. A change of the speed will then permit a setting of the opening duration of the individual valves. The fact that the speed can be changed permits that one valve can be kept open longer than another valve. This permits individual control. 
     Preferably, the motor is reversible. The reversibility of the motor permits one single valve to be completely closed also for a longer period. Before the rotor causes this valve to open, the rotation direction of the motor is reversed, so that the valve remains closed. It is also possible to let more valves remain closed, if these valves are arranged next to each other in the rotation direction of the rotor. 
     Preferably, the rotor is connected to a cam disc and the valves comprise valve tappets, which are operable by the cam disc. This is a particularly simple, mechanical solution of opening and closing the valves. Expediently, the valves are acted upon in the closing direction by a closing spring. If then the cam gets in contact with the tappet, the valve is opened against the force of the closing spring. The valve closes again, as soon as the cam has continued its rotation far enough. 
     Preferably, the cam disc comprises one single cam. Thus, it is ensured that only one valve at a time can be opened or opened more than the other valves. Accordingly, it is also possible to set the opening duration (or the duration of the additional opening) of each individual valve separately, so that to a high degree the opening duration is not influenced by the opening durations of the other valves. 
     It is preferred that in the rotation direction the valve tappets have a distance from one another, which is at least as large as the extension of the cam in the rotation direction. Thus, it is possible to let the cam come to rest in a position, in which it does not act upon any of the valve tappets. In this case, all valves can remain closed. 
     Preferably, the valve tappets are arranged in parallel to the rotor axis. Here, the term “parallel” is not to be understood in the exact mathematic sense of the word. It is merely essential that the valve tappets comprise a component, which is aligned in parallel to the rotor axis. In this case, the cam, which is arranged on the cam disc, acts in parallel to the rotor axis. 
     Preferably, the cam disc comprises a displacement drive, which acts in a direction parallel to the rotor axis. If the valve tappet is arranged in parallel to the rotor axis, the displacement of the cam disc is a simple way of enable all valves to open at the same time to permit a certain basic flow of refrigerant. The cam then opens one single valve more than the other valves to ensure an individual supply of one single evaporator with refrigerant. 
     In an alternative embodiment it may be provided that the rotor comprises an axially extending inlet channel, which is connected to an inlet of the distributor, and a radially extending outlet channel, whose opening can be brought to overlap during a rotation with outlet openings, which are connected to the evaporators. Thus, the rotor is at the same time used as an element of the valve. If the opening of the outlet channel overlaps an outlet opening, a flow path is released from the inlet of the distributor to an outlet, which is allocated to a specific evaporator. As long as the overlap exists, refrigerant can flow from the inlet of the distributor to the evaporator in question. When the rotor is turned further, the refrigerant supply to the evaporator mentioned above is interrupted, and the next outlet in the rotation direction is supplied with refrigerant. Depending on the duration of the overlap between the opening of the outlet channel and the outlet opening, a larger or smaller amount of refrigerant can flow into the evaporator. This overlap duration can be changed in dependence of the speed, with which the rotor rotates. 
     Preferably, the outlet openings have a distance to each other in the rotation direction, which is at least as large as the extension of the opening of the outlet channel in the rotation direction. In this case, it is possible to stop the rotor in a position, in which the opening of the outlet channel does not overlap an outlet opening, so that the refrigerant supply to all evaporators is interrupted. For example, such a position can be used to defrost the evaporators. 
     It is also advantageous, if a sensor, which is connected to the control device, is arranged in each evaporation path. This sensor can, for example, be a temperature sensor. Each evaporator can then be supplied with refrigerant in dependence of the temperature at its outlet. 
     In an alternative embodiment it may be ensured that the evaporator paths are connected in series with a condenser, and a sensor is arranged in front of the condenser or the compressor. In this case, only one sensor measuring, for example the temperature, is required. One single sensor will be sufficient, if otherwise the operation behaviour of the refrigeration system is known. With the knowledge of the operation behaviour, it can then be decided, how much refrigerant shall be supplied to which evaporator or evaporation path. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, the invention is described on the basis of preferred embodiments in connection with the drawings, showing: 
         FIG. 1  is a schematic view of a refrigeration system with several evaporators, 
         FIG. 2  is a top view of a first embodiment of a distributor, 
         FIG. 3  is a section III-III according to  FIG. 2 , 
         FIG. 4  is a sectional view IV-IV according to  FIG. 5  through a second embodiment of a distributor, and 
         FIG. 5  is a sectional view V-V according to  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is a schematic view of a refrigeration system  1 , in which a compressor  2 , a condenser  3 , a collector  4 , a distributor  5  and an evaporator arrangement  6  with several evaporators  7   a - 7   d , arranged in parallel, are connected in a circuit. The evaporator arrangement  6  can also comprise one single evaporator, which comprises several evaporation paths to be controlled individually or in groups. 
     In a manner known per se, liquid refrigerant is evaporated in the evaporators  7   a - 7   d , compressed in the compressor  2 , condensed in the condenser  3  and collected in the collector  4 . The distributor  5  is provided for distributing the liquid refrigerant to the individual evaporators  7   a - 7   d.    
     A temperature sensor  8   a - 8   d  is arranged at the outlet of each evaporator  7   a - 7   d . The temperature sensor  8   a - 8   d  senses the temperature of the refrigerant leaving the evaporator  7   a - 7   d . The temperature information is supplied to a control unit  9 , which controls the distributor  5  in dependence of the temperature signals of the temperature sensors  8   a - 8   d.    
     The  FIGS. 2 and 3  show a first embodiment of a distributor  5 . The distributor  5  according to  FIG. 2  comprises six outlets  10   a - 10   f  (for six evaporators) and an inlet  11 . Each outlet  10   a - 10   f  is separated from the inlet  11  by a valve  12 . As all the valves have the same design, the following description is made on the basis of valves  12  allocated to the outlets  10   b ,  10   e.    
     Each valve  12  comprises a valve seat  13 , which is arranged in a housing block  14 . Further, each valve  12  comprises a valve element  15 , which is connected to a valve tappet  16  extending from the side of the housing block  14  on the side facing away from the valve seat  13 . Both the housing block  14  and the valve element  15  rest on a cover  19  via springs  17 ,  18 , through which cover  19  the inlet  11  is led and which closes a valve housing  20 . The spring  18  is made as a closing spring, which acts upon the valve element  15  in the direction of the valve seat  13 . 
     A cam disc  21  is arranged to be rotatable in the valve housing  20 . The cam disc  21  comprises one single cam  22 , which acts upon a valve tappet  16  during a rotation of the cam disc  21  around a rotation axis  23 , as can be seen through the left valve (in  FIG. 3 ). When the cam  22  acts upon the valve tappet  16 , the valve element  15  lifts off from the valve seat  13 , and a passage from the inlet  11  to the outlet  10   e  is released. As soon as the cam  22  leaves the valve tappet  16 , the spring  18  brings the valve element  15  to rest on the valve seat  13  again, and the corresponding valve  12  closes, as can be seen by the valve  12  allocated to the outlet  10   b.    
     The cam disc  21  is rotated by a motor  24 , which is only shown schematically here. The motor  24  is controlled by the control unit  9 . The motor  24  can be driven with a controlled speed. The maximum speed is, for example, in the order of 100 rpm. During a rotation, the speed of the motor  24  can, as mentioned, be changed. The motor  24  can also be stopped for a short while. Also the rotation direction of the motor can be changed. 
     Thus, the following operation can be realised: 
     In dependence of the signals from the temperature sensors  8   a - 8   d  each of the individual valves  12  is opened during a rotation of the cam disc  21  for so long that a sufficient amount of refrigerant can flow through the individual outlets  10   a - 10   f , so that the evaporators  7   a - 7   d  receive sufficient, but not too much, refrigerant. If an evaporator requires a smaller amount of refrigerant, the cam disc  21  is, when the cam  22  acts upon the corresponding tappet  16  of the valve  12 , rotated faster, so that the valve  12  only remains open for a shorter while. If, however, an evaporator should require a larger amount of refrigerant, the cam disc  21  would, when the cam  22  is in the area of the valve allocated to the corresponding outlet, rotate slower. 
     As each evaporator receives refrigerant at least once during a period of one second, it can be achieved that the pressure in the evaporator varies only slightly, so that a negative influence on the refrigeration system  1  must not be feared. 
     The cam disc  21  is supported on a rotor  25  of the motor  24 . The rotor  25  can now, via an axial drive  26 , be displaced in a direction in parallel to the rotation axis  23 . If it is, for example, displaced downwards (in relation to the view in  FIG. 3 ), all valves  12  are somewhat opened, so that refrigerant can permanently flow through all outlets  10   a - 10   f . This results in a certain basic supply to all evaporators. The exact setting of the refrigerant amount to be supplied to the individual evaporator then still takes place via the cam  22  of the cam disc  21 . 
     In the circumferential or rotation direction of the cam disc  21 , the individual valves  12  have a mutual distance, which is at least exactly as large as the extension of the cam  22  in the circumferential direction. Accordingly, it is possible to stop the cam disc  21  in a position, in which no valve has been opened. Such a position is, for example, assumed, if no evaporator requires a supply of refrigerant. 
     With the distributor  5  it is also possible to defrost individual evaporators. In this case, the rotation direction of the cam disc  21  would be reversed, before the cam  22  reaches the valve  12  allocated to this evaporator. Thus, this valve  12  is not opened. This valve  12  can be kept closed, until the evaporator has been defrosted. The remaining valves  12  will still be opened by the cam  22  in the manner described above. 
     The  FIGS. 4 and 5  show a modified embodiment of a distributor  5 , in which the same elements and elements with the same function have the same reference numbers. 
     The distributor of  FIGS. 4 and 5  also comprises a rotor  25 . The rotor  25  comprises an inlet channel  27 , which is constantly overlapping the inlet  11  of the valve housing  20 , that is, independently of the rotation position of the rotor  25 . 
     The rotor  25  also comprises an outlet channel, which substantially has a radial direction. The outlet channel  28  comprises an opening  29 , which overlaps the outlet openings  30   a - 30   f  during a rotation of the rotor  25 . The outlet openings  30   a - 30   f  again are connected to the outlets  10   a - 10   f , through which a connection to the evaporators of the evaporation arrangement  6  can be created. 
     Also here, the distance between the outlet openings  30   a - 30   f  is at least as large as the extension of the opening  29  of the outlet channel  28  in the circumferential direction. In the position of the rotor  25  shown in  FIG. 4 , the outlet channel  28  is therefore closed, so that no refrigerant can be distributed. 
     Otherwise, the mode of operation of the distributor  5  is the same as in the embodiment of the distributor  5  shown in  FIGS. 2 and 3 . 
     Controlled by the control unit  9 , the rotor  25  is controlled at, under certain circumstances, varying rotation speeds in such a manner that a connection between the inlet  11  and one of the outlet openings  30  is always available for a certain period. During this period, refrigerant can flow from the inlet  11  into the corresponding outlet opening  30   a - 30   f , and from here to the connected evaporator, which is accordingly acted upon by a predetermined amount of refrigerant. If the rotor  25  rotates slowly, while the opening  29  passes over the corresponding outlet opening  30   a - 30   f , the connection is open for a relatively long period. If, however, in this situation the rotor  25  rotates faster, a correspondingly shorter opening period is available. During a long opening period more refrigerant can flow into the corresponding evaporator than during a short opening period. 
     Also here, a reversing of the rotation direction of the rotor  25  can exclude a predetermined outlet opening  30   a - 30   f  from the connection to the inlet  11 , so that an evaporator connected to this outlet opening  30   a - 30   f  receives no refrigerant at all for a certain period. 
     The fact that now the distributor  5  does not only assume the function of a distribution, but also comprises a valve  12  for each evaporator, causes that the expansion valve can be spared. 
     The pipes leading to the individual evaporators must no longer have the same length, as the valves  12  control the acting of the refrigerant upon the individual evaporator. 
     In a manner not shown in detail, one single sensor can be arranged in front of the condenser  3  or in front of the compressor  2  instead of or additionally to the sensors  8   a - 8   d . This sensor is then not able to evaluate the desired information for each evaporator or evaporator path individually. If, however, the operation behaviour of the refrigeration system is known, for example the various flow resistances, the information required to determine, which evaporator path  7   a - 7   d  shall receive which amount of refrigerant, can also be obtained by means of only one single sensor. 
     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.