Abstract:
A solenoid valve ( 1 ) is provided comprising a housing, an inlet, an outlet, main valve means located between said inlet and said outlet, said main valve means comprising a main valve element, pilot valve means adjusting a pressure difference over said main valve element and having a pilot valve element, a coil, a yoke arrangement magnetically linked to said coil, and armature means for moving said pilot valve element. Such a solenoid valve should achieve a large opening stroke without unduly increasing the coil and yoke arrangement. To this end said armature means comprise a first part attractable by said yoke means to perform an opening stroke, and a second part carrying said pilot valve element, wherein said first part is movable relative to said second part in a first section of said opening stroke and is dragging said second part in a second section of said opening stroke following said first section.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a National Stage application of International Patent Application No. PCT/EP2015/064230, filed on Jul. 10, 2015, which claims priority to European Patent Application No. 14185569.2, filed on Sep. 19, 2014, each of which is hereby incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates to a solenoid valve comprising a housing, an inlet, an outlet, main valve means located between said inlet and said outlet, said main valve means comprising a main valve element, pilot valve means adjusting a pressure difference over said main valve element and having a pilot valve element, a coil, a yoke arrangement magnetically linked to said coil, and armature means for moving said pilot valve element. 
       BACKGROUND 
       [0003]    Such a solenoid valve is known, for example, from DE 20 2005 013 233 U1. 
         [0004]    The use of a pilot valve has the advantage that only the pilot valve element has to be actuated to control the function of the main valve means. The forces needed for moving the pilot valve element are much smaller than the forces needed for moving the main valve element. Therefore, a pilot control solenoid valve can be used to control fluids under high pressure, for example carbon dioxide, without dramatically increasing the coil and yoke arrangement. 
         [0005]    In some cases it is required that a solenoid valve has a large opening stroke, i. e. the solenoid valve has a low flow resistance in fully open state. This means that the main valve means has to be opened to a rather large extend to that the main valve element must be able to perform a large opening stroke. Consequently, the pilot valve element must be able to perform a similar large openings stroke. When the pilot valve is closed, the armature means has the largest distance to the yoke arrangement so that the magnetic forces which can attract the armature means are quite low. Therefore, when a large opening stroke is required, the coil and yoke arrangement must be increased to a considerable size to generate the necessary magnetic attraction forces. 
         [0006]    Such a solenoid valve can be, for example, used in a multiejector. In this case it is required to generate maximum velocity of the controlled gas at the so called motive nozzle. This is done by minimizing the pressure losses. One contribution to the low pressure loss comes from a large diameter or large opening when the valve is open. A large diameter here means that the main valve element needs to move a significant part of, as a rule, at least ¼ of the diameter of an outlet bore. This means that there are low magnetic forces available because the magnetic forces vary over the distance from the yoke arrangement to the armature means. 
         [0007]    Furthermore, when the solenoid valve is used in a CO 2  system the pressure difference is significantly higher than for other refrigerants. In a CO 2  system pressure difference of at least 50 bar is possible and can be significantly higher, for example 90 bar. 
         [0008]    This means that the valve has to open with relative weak magnetic forces while being able to cope with a significantly higher pressure difference. 
       SUMMARY 
       [0009]    The object underlying the invention is to achieve a large opening stroke without unduly increasing the coil and yoke arrangement. 
         [0010]    This object is solved with a solenoid valve as described above in that said armature means comprise a first part attractable by said yoke means to perform an opening stroke, and a second part carrying said pilot valve element, wherein said first part is movable relative to said second part in a first section of said opening stroke and is dragging said second part in a second section of said opening stroke following said first section, wherein an opening spring is located between said first part and said second part, said opening spring acting on said second part in opening direction. 
         [0011]    In such a solenoid valve the coil and yoke arrangement generate a magnetic force which must be sufficient to attract the first part of the armature only. The first part of the armature can be moved over a first section of the opening stroke without the necessity of moving the second part. The first part of the armature means is accelerated by the magnetic forces and has, therefore, at the end of the first section of the opening stroke a certain speed and consequently a certain kinetic energy. Furthermore, the magnetic forces have also increased since the air gap has decreased. At the end of the first section of the opening stroke the first part comes in contact with the second part of the armature which then is moved under the action of the first part. For the movement of the second part of the armature the increased magnetic forces plus the kinetic energy of the first part can be used. The second part carries the pilot valve element, meaning that the pilot valve element can also be part of the second part. The combined energy is sufficient to pre-lift the pilot valve element from the pilot valve seat. This initial movement of the pilot valve element usually requires the largest forces. As soon as the pilot valve element has been lifted off the pilot valve seat, the forces tending to close the pilot valve means or keeping the pilot valve means closed decrease so that the second part can be moved further together with the first part in an opening direction. When the pilot valve element has been lifted off the pilot valve seat under the action of the first part, the opening spring is slightly compressed. The opening spring now moves the second part relative to the first part further in opening direction thus increasing a distance between the pilot valve element and the pilot valve seat. This is possible due to the low force from the differential pressure at the pilot valve element. This low force is due to the relative large distance between the pilot valve element and the pilot valve seat or pilot orifice after the pre-lift. When the pilot orifice is open, the main valve element moves and opens the main valve means. This opening can occur in a rather short time period so that the solenoid valve can be actuated with a rather high speed. The opening of the pilot valve now is divided in three sections of movement. In the first section only the first part moves. In the second section the first part moves together with the second part and the pilot valve element. In the third section the first part has been stopped and the pilot valve element together with the second part moves under the action of the opening spring. During the first section, when the first part is moved alone, this first part builds up kinetic energy and moves closer to the yoke arrangement whereby the magnetic forces increase significantly since the air gap decreases. Both elements contribute to the pre-lifting of the pilot valve element against the significant pressure difference over the pilot valve element. At the end of the third movement the second part rests against the yoke arrangement. The third movement is achieved by utilizing the spring forces created by the compression of the opening spring during the second movement. 
         [0012]    In a preferred embodiment said pilot valve means has a pilot orifice and the length of said second section is in the range of 0.5 to 1.5 times the diameter of said pilot orifice. The second part of the armature is moved at an end of the opening stroke only, when the first part has enough kinetic energy. Since it is only necessary to pre-lift the pilot valve element the small movement of the second part of the armature at this moment is sufficient. Less than 0.5 means that the pressure difference becomes too big. More than 1.5 means that the magnetic forces become too small. 
         [0013]    Preferably a closing spring is arranged between said first part and said yoke arrangement, said closing spring being compressed during said opening stroke. The closing spring is used at a later stage when the main valve is to be closed. 
         [0014]    Preferably said opening spring is stronger than said closing spring. In other words, the spring constant of the opening spring is typically larger than the spring constant of the closing spring. This takes into account that the closing spring is compressed during the opening stroke to a slightly larger extend. 
         [0015]    Preferably said second part is located inside said first part. This leads to rather simple construction. The armature can still be handled as a single piece simplifying assembling of the solenoid valve. 
         [0016]    In this case it is preferred that said first part comprises a hollow first sleeve and a hollow second sleeve which are connected to each other to form a space in which said second part is accommodated. The two sleeves can for example be fixed to each other by screwing, by using a glue or by soldering or they can be joined by a press-fit connection. The use of hollow sleeves facilitates the guiding of the second part within the first part. 
         [0017]    Preferably said first sleeve has a bore at a side facing said yoke arrangement, said bore ending at a step supporting said closing spring. The closing spring rests against the step and against the yoke arrangement. The bore is helpful in guiding the spring so that the spring keeps its position in any case. 
         [0018]    Preferably said second part comprises a stem protruding through said bore. The stem in said bore is used for guiding the second part within said first part. 
         [0019]    Preferably said stem is longer than said first sleeve. This feature can be used to improve the closing process of the solenoid valve. The magnetic sticking force is overcome by the force of the opening spring. Since the stem is longer than the first sleeve, the opening spring pushes the first part in a direction towards the pilot valve seat. Once the first parts abuts the second part the opening spring does no longer contribute to further movement of the first part and further movement of the first and second parts is achieved by the closing spring. The magnetic sticking is reduced by a large amount, for example, 90%, once an air gap between the yoke arrangement and the armature is established and therefore the closing spring can close the valve even if it is weaker. 
         [0020]    Preferably said housing comprises a stop for said main valve element in opening direction, said second part of said armature being retracted behind said stop at the end of said opening stroke. This is a protection for the pilot valve element avoiding high forces on the pilot valve element in the fully open state of the main valve means. 
         [0021]    The invention relates as well to the use of a solenoid valve as described above in a CO 2  refrigeration system. The solenoid valve is in particular well suited to operate even if high pressure differences act over the pilot valve means. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    A preferred embodiment of the invention now is described in more detail with reference to the drawing, wherein: 
           [0023]      FIG. 1  is a sectional view of a solenoid valve in close condition, 
           [0024]      FIG. 2  is a sectional view of the solenoid valve at a beginning of the opening of a pilot valve means, 
           [0025]      FIG. 3  is a sectional view of said solenoid valve with the pilot valve means fully open, 
           [0026]      FIG. 4  is a sectional view of said solenoid valve with the main valve means fully open, 
           [0027]      FIG. 5  is a sectional view of said solenoid valve at the beginning of closing of the pilot valve means, and 
           [0028]      FIG. 6  is a sectional view of said solenoid valve showing the closing of the main valve means. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]      FIG. 1  shows a solenoid valve  1  having a housing  2 . The housing  2  comprises an inlet  3  and an outlet  4 . The solenoid valve  1  can, for example, be used for controlling a fluid under high pressure like carbon dioxide. 
         [0030]    The control of such a fluid is performed by main valve means  5  having a main valve element  6  and a main valve seat  7 . 
         [0031]    The main valve element  6  has the form of a piston having a channel  8  running in lengthwise direction through the complete valve element  6 . One end of this channel  8  opens into the main valve seat  7  (in closed condition) or is directed into the main valve seat  7  (in open condition, c. f.  FIGS. 4 to 6 ). The other end of the channel  8  forms a pilot orifice  9 . This pilot orifice  9  can also be named “pilot valve seat”. 
         [0032]    A small gap between the main valve element  6  and the housing  2  is unavoidable and in the present case intended so that a fluid pressure from the inlet  3  can act on both front faces  11 ,  12  of the main valve element  6 , i.e. in a pressure space  13  on a side of the main valve element  6  opposite to said main valve seat  7 . The area of the front face  11  surrounding the main valve seat  7  is smaller than the area of the opposite front face  12  so that the main valve element  6  is held against the main valve seat  7  by the resulting force difference and the main valve means  5  are closed. 
         [0033]    Furthermore, the solenoid valve  1  comprises pilot valve means  14 . The pilot valve means  14  comprise a pilot valve element  15  cooperating with the pilot orifice  9 , i. e. closing the pilot orifice  9  ( FIGS. 1 and 6 ) or opening it ( FIGS. 2-5 ). 
         [0034]    Movement of the pilot valve element  15  is performed by an armature  16  which will be described later. 
         [0035]    The solenoid valve  1  comprises a coil  17  and a yoke arrangement  18  (only partly shown). When the coil  17  is supplied with electric current, the yoke arrangement  18  which is magnetically linked to the coil  17  generates a magnetic force acting on the armature  16 . 
         [0036]    The armature  16  comprises a first part  19  and a second part  20 . The first part  19  is formed of a first sleeve  21  and a second sleeve  22 . Both sleeves  21 ,  22  are hollow. They are connected to each other in a connection area  23 . They can, for example, be joined by a press-fit connection or connected by means of a pair of threadings, they can be glued together or brazed together or connected to each other in any other way. The first part  19  is made from a magnetizable material, whereas there are no similar requirements to the second part  20 . 
         [0037]    The two sleeves  21 ,  22  together form a space  24  in which the second part  20  of the armature is accommodated. The second part  20  of the armature  16  carries the pilot valve element  15 . 
         [0038]    The first sleeve  21  comprises a bore  25  through which a stem  26  of the second part is guided. Furthermore, the bore  25  forms a step  27 . A closing spring  28  rests against this step  27 . The other end of the closing spring  28  rests against the yoke arrangement  18 . When the first part  19  is moved in a direction towards the yoke arrangement  18 , the closing spring  28  is compressed. 
         [0039]    An opening spring  29  is arranged in the space  24  within the first part  19  as well. This opening spring  29  acts between the first part  19  and the second part  20  and presses the second part  20  against the first sleeve  21 . 
         [0040]    The state shown in  FIG. 1  is the closed state of the solenoid valve  1 . The closing spring  28  acts on the whole armature  16  in a direction towards the pilot orifice  9 . The pilot valve element  15  rests against the pilot orifice  9  and closes the pilot valve means  14 . In this state there is no current in coil  17 . 
         [0041]      FIG. 2  shows the situation in which the coil  17  is supplied with current. Therefore, magnetic forces are generated in the yoke arrangement  18  attracting the first part  19  of the armature  16 . 
         [0042]    All elements are designated with the same reference numerals in all figures. 
         [0043]    As can be seen in  FIG. 2  the first part  19  of the armature  16  has been moved relative to the second part  20  of the armature. 
         [0044]    The first part  19  has been moved over an opening stroke, i. e. from the position shown in  FIG. 1  in which the first part  19  has the largest distance to the yoke arrangement  18  to a position shown in  FIG. 2  in which the first part  19  has come to rest against the yoke arrangement  18 . 
         [0045]    This opening stroke has some sections. In a first section the first part  19  can be moved relative to the second part  20  of the armature without moving the second part  20  of the armature  16 . In a second section of the opening stroke the first part  19  has come in contact with a step  30  at the lower end of the second part  20  and pulls or drags the second part  20  upon further movement of the first part  19 . 
         [0046]    During movement of the first part  19 , the closing spring  28  and the opening spring  29  are compressed. 
         [0047]    At the end of the first section, the first part  19  of the armature has already a certain speed and correspondingly a certain kinetic energy. This kinetic energy can be used to move the second part  20  of the armature  16  as well. This movement can be rather small, for example less than 1 mm. In general, the second section of the opening stroke has a length in the range of 0.5 to 1.5 times the diameter of the pilot orifice  9 . Less than 0.5 means that the pressure difference becomes too big. More than 1.5 means that the magnetic forces become too small. The movement of the second part  20  is sufficient when the pilot valve element  15  is just lifted off the pilot orifice  9  so that fluid out of the pressure space  13  can start to escape out of the pressure space  13  thereby lowering the pressure in the pressure space  13 . This state can be termed as “pre-lift”. 
         [0048]    As shown in  FIG. 2 , the first part  19  has come in contact with the yoke arrangement  18  thereby compressing the closing spring. Furthermore, the opening spring  29  between the first part  19  and the second part  20  is compressed as well. 
         [0049]    As shown in  FIG. 3 , the opening spring  29  moves the second part  20  further in opening direction, i. e. in a direction towards the yoke arrangement  18  until the stem  26  comes in contact with the yoke arrangement  18  as well. This is a third section of movement. Consequently, the pilot valve element  15  is moved further away from the pilot orifice  9 . This movement is possible due to the low force from the differential pressure at the pilot valve element  15 . This low force is due to the relative large distance between the pilot valve element  15  and the pilot orifice  9  after pre-lift.  FIG. 3  shows the fully open condition of the pilot valve means  14 . 
         [0050]    When the pilot valve means  14  are open the pressure in the pressure space  13  decreases and consequently the pressure acting on the lower front face  11  generates a force higher than the pressure acting on the opposite front face  12  of the main valve element  6 . The main valve element  6  moves away from the main valve seat  7  and opens the main valve means  5 . 
         [0051]    As can be seen in  FIG. 4 , the housing  2  has a stop  31  for the movement of the main valve means  6  in opening direction. The pilot valve element  15  is retracted behind this stop  31  when the second part  20  of the armature  16  has come in contact with the yoke arrangement  18 . Therefore, high forces acting on the pilot valve element  15  by the main valve element  6  can be reliably avoided. 
         [0052]      FIG. 4  shows the solenoid valve  1  in fully open condition. This condition remains as long as current is supplied to coil  17 . The supply of current to coil  17  can be made over an electric connection  32  schematically shown. 
         [0053]    When the supply of current to coil  17  is stopped, no magnetic forces are generated in the yoke arrangement  18 . 
         [0054]    When the current is switched off, the closing process starts. The magnetic sticking force is overcome by the force of the opening spring  29 . Since the stem  26  is longer than the first sleeve  21 , the opening spring  29  pushes the first part  19  away from the yoke arrangement  18  in a direction towards the pilot valve orifice  9 . Once the first part  19  abuts the second part  20  the opening spring  29  does no longer contribute to further movement of the first part (as shown in  FIG. 5 ) and further movement of the first and second part  19 ,  20  is achieved by the weaker closing spring  28 . The magnetic sticking is reduced by, for example, 90% once an air gap between the yoke arrangement  18  and the top of the armature  16  is established and therefore the closing spring  28  can close the pilot valve even when it is weaker than the opening spring  29 . 
         [0055]    In  FIG. 5  the armature  16  has moved away a bit from the yoke arrangement  18 . However, in  FIG. 5  the pilot valve means  15  has still a distance from the pilot orifice  9  so that the pilot valve means  14  are not yet closed. 
         [0056]      FIG. 6  shows the situation in which the armature  16  has been moved far enough in a direction towards the main valve element  6  to close the pilot valve means  14 , i. e. the pilot valve element  15  has closed the pilot orifice  9 . In this situation the pressure space  13  has no outlet through which fluid arriving from the inlet  3  can escape. The pressure acting on the upper front face  12 , i. e. the front face facing the yoke arrangement  18  acts on the main valve element  6  in a direction towards the main valve seat  7 . The same pressure acts on the opposite front face  11 , however, on a smaller area since the valve seat  7  covers part of the front face  11 . In a region of the front face covered by the main valve seat  7 , there is a lower pressure. 
         [0057]    The difference of forces over the main valve element  6  moves the main valve element  6  in a direction towards the main valve seat  7  so that finally the main valve element  6  comes to rest the main valve seat  7  and the main valve means  5  close, as shown in  FIG. 1 . The closure spring  28  does also contribute. 
         [0058]    While the present disclosure 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 disclosure may be made without departing from the spirit and scope of the present disclosure.