Abstract:
The invention concerns a fail-safe valve having a valve element, and a control motor being connected with the valve element via a driveline. It is endeavoured to ensure the tightness of the refrigeration system in a simple manner. For this purpose, it is ensured that the valve element is located inside and the control motor outside a closed valve housing, that the drive line has a magnetic coupling, which acts through the housing, and that the valve element is pressure-released. In addition, a resetting device is provided that causes the valve element to be returned to a predetermined position upon the undesired cessation of control motor operation.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention generally concerns a fail-safe valve having a valve element, and a control motor connected with the valve element, and is more particularly directed to a mechanism by which the valve element is returned to a predetermined position upon drive failure.  
         BACKGROUND OF THE INVENTION  
         [0002]    In large refrigeration systems, for example those used in the industrial field, correspondingly large valves are required; each of whose valve elements is activated from the outside by a control motor. When displacing the valve element, a passage through the valve is further released or further throttled. Such a valve can also be closed. In this case, the valve element bears on a valve seat.  
           [0003]    In refrigeration systems, it is endeavoured to prevent the loss of refrigerant. When a system is filled with a combustible refrigerant, the loss of refrigerant can lead to dangerous situations. When ammonia is used as refrigerant, the escape of refrigerant will cause unpleasant smells. Large amounts of ammonia are also lethal. With refrigerants having a higher price, for example H-FCKW or H-FKW, refrigerant losses are expensive.  
           [0004]    Weak spots with respect to sealing refrigeration systems are those places, in which a lead-through extending into a housing is required, for example to drive a valve element from the outside. Locating a control motor inside a refrigeration system is not always possible, as some refrigerants act aggressively upon electrical motors. Accordingly there is a need for a valve that can be driven without having to create a weak spot.  
           [0005]    Another difficulty associated with valves of the above-described type occurs as a result of control motor failure. When this occurs, it is possible for the valve to remain in the position it was in when the motor failed. This may be a very undesirable position that could result in a loss of ability to properly control the refrigeration system. Accordingly, there is a need for an appropriate fail-safe mechanism to be associated with the valve.  
           [0006]    Based on the foregoing, the general object of the present invention is to provide a fail-safe valve that improves upon or overcomes the problems and drawbacks of the prior art.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention resides in one aspect in a valve having a valve element located inside and a control motor located outside a closed valve housing. A drive line is provided and includes a magnetic coupling, which acts through the housing. In addition, the valve element is pressure-released.  
           [0008]    Through a combination of these three measures, the tightness of the valve can be ensured. The valve can be hermetically tight or sealed. The valve element is separated from the environment by the closed valve housing. The transfer of driving power takes place via the magnetic coupling. However, the amount of power, which can be transferred by means of a magnetic coupling, is limited. Accordingly, since a magnetic coupling is being employed the valve element must be movable using only a small amount of power. For this purpose, the valve element is pressure released, that is, measures are taken to ensure that substantially the same pressure is present on both sides of the valve element. These measures can, for example, be that a pressure-balancing channel is provided inside the housing or even inside the valve element, said channel acting upon both sides of the valve element with the same pressure. In this case, the valve element only has to overcome frictional forces. However, these frictional forces are small, as practically no external forces act upon the valve element. An advantage of the present invention is that due to the fact that the magnetic coupling does not need to transfer large forces, a relatively small and inexpensive control motor can be used.  
           [0009]    Preferably, the control motor is a stepping motor. A stepping motor has the advantage that the position of the valve element can be determined by counting impulses supplied to the stepping motor. Additional sensors can also be used with the stepping motor.  
           [0010]    Preferably, the magnetic coupling acts upon the valve element via a threaded connection. Thus, relatively accurate movement control of the valve element is achieved. At the same time, the movements of the valve element can be effected with extremely small forces. In operation, a first part of the threaded connection is turned that displaces another part of the threaded connection in an axial direction (in relation to the rotation of the first part of the threaded connection). Depending on the pitch of the thread defined by the threaded connection, very small movements are achieved per angular increment of the control motor. These movements can, for example, be about {fraction (5/100)} mm per 2° of rotation.  
           [0011]    Preferably, the valve element is non-rotatably retained, and the threaded connection includes a spindle screwed into the valve element or into a part connected with the valve element. This embodiment has the advantage that the valve element is only moved axially, that is, in the direction of the valve seat or away from the valve seat. These closing or opening movements, respectively, will not turn the valve element in relation to the valve seat.  
           [0012]    Preferably, an adapter piece surrounds an outlet-side part of the magnetic coupling. This adapter piece can then be sized with a view to the fact that a transfer of magnetic forces through the adapter piece is possible. The adapter piece must also be able to withstand the pressures occurring in the refrigeration system or in the area of the valve. For example, the adapter piece can be made of a different material than the rest of the valve housing.  
           [0013]    It is also preferable that the adapter piece is made of a magnetically non-conducting material. The adapter piece, which can, for example, be made of austenitic steel, then does not interfere with the power transfer between the two parts of the magnetic coupling.  
           [0014]    Preferably, the adapter piece is threadably connected to the valve housing. This ensures a connection between the adapter piece and the valve housing, which is stable enough to withstand the pressures present in the valve. These pressures can reach 50 bar.  
           [0015]    Preferably, the control motor is mounted on the adapter piece. This provides a simple way of ensuring a relatively accurate positioning of the control motor as well as the parts of the magnetic coupling connected with the control motor and the parts of the magnetic coupling connected with the valve element. The control motor is detachable from the valve. A defective control motor can easily be replaced. In an emergency situation, a hand wheel can be used instead of the control motor, to displace the valve during a failure of the control motor.  
           [0016]    Preferably, the control motor has a pipe-shaped extension, which surrounds a drive-side part of the magnetic coupling. Together with its pipe-shaped extension, the control motor protects the magnetic coupling. This protection has several advantages. First, the extension removes the possibility of outside interference, which could lead to unintentional displacement of the valve element. Second, the pipe-shaped extension provides a simple way of positioning the control motor on the adapter piece and thus on the housing.  
           [0017]    It is particularly preferred that a rotor is located axially relative to the extension. The rotor can then be located coaxially with the spindle and the valve element.  
           [0018]    Preferably, the magnetic coupling has radially directed magnets. This has the advantage that when sizing the magnets, the diameter of the magnetic coupling causes no restrictions. Thus, relatively long overlapping areas between the magnets on the outlet-side part of the magnetic coupling and those on the drive-side part of the magnetic coupling can be achieved. Preferably, the magnets can be rare earth magnets or neodymium magnets. Such magnets have sufficient power to transfer the drive power of the control motor to the valve element via the magnetic coupling.  
           [0019]    In an alternative or additional embodiment, the magnetic coupling can have axially directed magnets. When only relatively weak forces have to be transferred, axially directed magnets will be sufficient, that is, the magnet front sides are facing each other. When using the axially directed magnets additionally to the radially directed magnets, even larger transfer performances can be achieved.  
           [0020]    Preferably, the valve has a resetting or fail-safe device. The resetting device resets the valve element to a predetermined position, when the drive from the control motor fails. Such a situation can, for example, occur during current failure. In this case, it can, for example, be important that the valve closes. The resetting device then ensures that the valve element is brought to bear on the valve seat. In other cases, it may be important that, during failure of the driving power, the valve opens completely. In this case, the resetting device ensures that the valve element is taken to its end position, in which the valve has its largest opening. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    In the following, the invention is described on the basis of preferred embodiments in connection with the drawings, showing:  
         [0022]    [0022]FIG. 1 schematically illustrates a refrigeration system;  
         [0023]    [0023]FIG. 2 is a cross-sectional view of a valve;  
         [0024]    [0024]FIG. 3 schematically illustrates one embodiment of a fail-safe device;  
         [0025]    [0025]FIG. 4 is a further embodiment of a valve; and  
         [0026]    [0026]FIG. 5 is a cross-sectional view of another embodiment of a resetting or fail-safe device. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]    [0027]FIG. 1 schematically shows a refrigeration system  1  with a compressor  2 , which supplies a refrigerant under high pressure and at a high temperature to a condenser  3 . In the condenser  3  the refrigerant is cooled. Due to this cooling, the refrigerant converts to a fluid. The condenser  3  supplies three connected evaporators  4 ,  5  and  6 , connected in parallel, each located in a cold room  7 ,  8  or  9 , respectively. The connection between the condenser  3  and each evaporator  4 ,  5  and  6  takes place via a valve  10 ,  11  and  12  and a throttling member  13 ,  14  and  15 . The throttling member can, for example, be a capillary tube or an expansion valve. For reasons of clarity, the valves  10 ,  11 , and  12  are shown separately from the throttling members  13 ,  14  and  15 . Usually, each valve  10 ,  11 , and  12  is combined with the related throttling member  13 ,  14 , and  15 .  
         [0028]    A control device  16  controls the valves  10 ,  11 , and  12  and the compressor  2 .  
         [0029]    An example of a valve  10  is shown in FIG. 2. Such a valve  10  can, of course, also be located in other positions in the refrigeration system. In principle, the valve  10  shown in FIG. 2 can be used everywhere where refrigerant must be controlled. The valve  10  has a valve housing  17  with a bottom part  18  and a top part  19 . An inlet  20  and an outlet  21  are located in the bottom part  18 . Between the inlet and the outlet is located a valve seat  22 , which interacts with a valve element  23 . In the position shown in FIG. 2, the valve  10  is closed, that is, the valve element  23  bears on the valve seat  22 .  
         [0030]    The valve element  23  has a pressure release channel  24 , which is connected with the inlet  20  and ends in a pressure chamber  25 , which is located on the side of the valve element  23  facing away from the valve seat  22  generally opposite an inlet end thereof. The pressure in the pressure chamber  25  acts upon the valve element  23  via an area, which has practically the same size as the area, via which the pressure from the inlet  20  acts upon the valve element  23 . The valve element  23  is thus pressure released, that is, the forces acting upon the valve element  23 , loading it in the direction towards the valve seat  22  or away from it, are substantially equalised. While a pressure release channel connected with the inlet has been described, the present invention is not limited in this regard as the pressure release cannel can also be connected with the outlet  21  without departing from the broader aspects of the present invention.  
         [0031]    The valve element  23  is supported in a guide  26  to be axially displaceable, that is, away from the valve seat  22  or towards it. A sealing  27  is provided between the valve element  23  and the guide  26 . A distortion protection, not shown in detail in FIG. 2, ensures that the valve element can only be axially displaced, however, not turned.  
         [0032]    For displacing the valve element  23 , a spindle  29  is provided, which has an outer thread  30 . The outer thread  30  threadably engages a displacement member shown in the illustrated embodiment as a nut  31  with a corresponding inner thread, which is connected with the valve element  23 . When the spindle  29  is turned, the threaded connection formed by the outer thread  30  and the nut  31  converts the rotational movement of the spindle  29  to a translational movement of the valve element  23 .  
         [0033]    The rotation drive of the spindle  29  occurs via a stepping motor  32 , which is controlled by the control device  16 . The stepping motor  32  in a housing  33  has a rotor, whose output shaft  34  is non-rotatably connected with an outer magnet holder  35 . In the outer magnet holder  35 , several permanent magnets  36  are distributed in the circumferential direction. The permanent magnets  36  are, for example, Neodymium magnets.  
         [0034]    The spindle  29  is non-rotatably connected with an inner magnet holder  37 , which carries several permanent magnets  38  on its outer circumference. Preferably, the number of permanent magnets  38  on the inner magnet holder  37  corresponds the number of permanent magnets  26  of the outer magnet holder  35 . The permanent magnets  36 ,  38  are magnetised so that they attract each other mutually. Thus, when the outer magnet holder  35  is turned, the inner magnet holder  37  turns too, as the permanent magnets  36  on the outer magnet holder  35  take along the permanent magnets  38  on the inner magnet holder  37 .  
         [0035]    An adapter piece  39  is located between the outer magnet holder  35  and the inner magnet holder  37 . The adapter piece  39  is made of a magnetically non-conducting material, for example austenitic steel. The adapter piece  39  is screwed into the top part  19  of the housing  17  by means of a thread  40 . A sealing  41  is provided for sealing the complete housing  17 , that is, also the adapter piece  39 . The sealing is sized so that it can stand a pressure difference of at least 50 bar.  
         [0036]    The adapter piece  39  is cup-shaped. Between the magnets  36 ,  38  it has a relatively small wall thickness.  
         [0037]    The stepping motor  32  has a pipe-shaped extension  42 , which is pushed onto the adapter piece  39 . The extension  42  is made of a magnetically non-conducting material. Via the extension  42 , the stepping motor  42  is fixed on the housing  17 , for example by means of two headless screws  43 , which engage in corresponding recesses on the outside of the adapter piece  39 .  
         [0038]    The inner magnet holder  37  is supported on the adapter piece  39  via ball bearings  44 . The outer magnet holder  35  is fixed on the motor  32 .  
         [0039]    The valve  10  can now be controlled in a relatively sensitive manner. The rotor  33  of the stepping motor is rotated over a predetermined angular area. The resolution per impulse sent to the stepping motor  32  can, for example, be in the magnitude of 2°. Via the magnetic coupling through the magnets  36 ,  38 , the spindle  29  is accordingly rotated. Through the transmission formed by the threaded connection  30 ,  31 , the valve element  23  is then moved by a predetermined distance away from or in the direction of the valve seat  22 , between an open and a closed position, for each angular increment of the rotor  33 . By counting the impulses, which are supplied to the stepping motor  32 , the position of the valve element  23  in relation to the valve seat  22  can be determined relatively accurately.  
         [0040]    Of course, other motors than stepping motors can be used. In this case, sensors are recommended, which establish the position of the valve element  23  in relation to the valve seat  22 .  
         [0041]    On the side facing away from the valve element  23 , the motor  32  has a resetting device, which will be explained on the basis of FIG. 3. The resetting device cannot be seen in FIG. 2. The resetting device ensures that during current failure or another error resulting in the undesired cessation of motor operation, the valve  10  can be brought to a certain predetermined state. This state could, for example be that the valve  10  is completely closed. However, it could also be that the valve is completely opened.  
         [0042]    For this purpose, the output shaft  34  of the motor  32  is extended upwards, forming a shaft end  46 . On the shaft end  46  a plate  62  is non-rotatably fixed, that is, the plate  62  rotates with the output shaft of the motor and thus with the spindle  29 , which drives the valve element  23 .  
         [0043]    A torsion-type suspension  63  is inserted in the plate  62 , that is, with one end fixed non-rotatably with the plate  62 . The other end of the torsion-type suspension  63  is connected with a housing  64  of the resetting device module  65 . Thus, when the shaft end  46  and the plate  62  are turned, the torsion-type suspension  63  is tensed.  
         [0044]    In this case, the outer thread  30  of the spindle  29  has a relatively large pitch of, for example, 5 to 15 mm per rotation. When, for example, the outer thread  30  has a pitch of 10 mm per rotation, and the maximum opening width, that is the maximum distance between the valve seat  22  and the valve element  23  is also 10 mm, one single rotation of the control motor  32  will be sufficient to either open or close the valve completely. Accordingly, the torsion-type suspension  63  can do with a force, which reverts the motor  32  by one rotation, when the valve has to be closed in connection with a current failure.  
         [0045]    The resetting device shown in FIG. 3 is formed as a module  65 , which is located on the side of the motor  32  facing away from the housing  17 , for example between the motor  32  and a housing  61  (FIG. 2) containing control electronics for the motor  32 . The module embodiment has the advantage that it requires no large changes to make the valve with or without resetting device.  
         [0046]    [0046]FIG. 4 shows another embodiment, in which the same parts have the same reference numbers. The most substantial change is that the permanent magnets  36 ,  38 , which are fixed on the outer or the inner magnet holder  35 ,  37 , respectively, are no longer directed in the radial direction, but in the axial direction. This saves accessories. On the other hand, however, the forces transmitted by the magnets  36 ,  38  are also smaller.  
         [0047]    A rotation protection  59 , with which a rotation movement of the valve element  23  shall be prevented, has, in this case, a spring, which engages in a groove in the guide  26  on the one side and at the valve element  23  on the other side.  
         [0048]    [0048]FIG. 5 shows a further embodiment of a valve  20 , in which same and functionally same elements have the same reference numbers as in FIG. 2. Contrary to the embodiment according to FIGS. 2 and 3, here a resetting device  70  is provided inside the housing  17 . The resetting device  70  has a pressure spring  71 , shown as a coil spring in the illustrated embodiment, which is supported between the valve element  23  and a spring washer, which retains an outer ring  72  of the ball bearing  44 . The pressure spring  71  presses the valve element  23  in the direction of the valve seat  22 .  
         [0049]    The nut is made of a plastic, which interacts under little friction with the material of the spindle  29 . This plastic can, for example, be a polyaryl ether ketone, polyether ether ketone (PEEK), or polyoxymethylene (POM). In connection with a corresponding diameter of the spindle  29  and a corresponding pitch of the thread  30 , which, for example, causes a movement of approximately 10 mm per rotation of the spindle  29 , it is ensured that the threaded connection between the spindle  29  and the nut  31  is not made to be self-locking, so that a pressure from the pressure spring  71  will not only displace the valve element  23 , but also turn the spindle  29 .  
         [0050]    This is made possible by the fact that the valve element  23  is pressure-released by means of the pressure release channel  24 . Thus, only relatively small external forces act upon the valve element  22 , so that the pressure spring  71  does not have to provide excessively large forces.  
         [0051]    The pressure spring  71  is located inside the valve housing  17  on the side of the valve element  23  facing the motor, so that the motor can be replaced, when it indicates an error or needs maintenance. In this case, the valve  10  is closed. Of course, it depends on the resetting device  70 . When this is made differently, it can also ensure that the valve  10  is opened, when no other forces are available.  
         [0052]    The pressure spring  71  generates forces, which are sufficient to overcome a catch force of the control motor  32 , which it possesses in the unpowered state. That is, the resetting device  70  can also bring the valve element  23  to rest on the valve seat  22 , when the motor  32  is still fitted on the housing  17 .  
         [0053]    In FIG. 5 the motor  32  is not mounted to make it clear that the resetting device  70  in FIG. 5 can also work, when the motor has a different embodiment.  
         [0054]    While preferred embodiments have been shown and described, various modifications and substitutions may be made without departing from the scope of the present invention. Accordingly, it is understood that the present invention has been described by way of example, and not by limitation.