Abstract:
The invention provides a sealed contact device capable of extinguishing an arc which extends in an arbitrary direction. The sealed contact device includes a housing; a fixed contact and a movable contact disposed in the housing in such a manner as to face each other; and permanent magnets which are disposed with the fixed contact and the movable contact interposed therebetween and which attracts an arc between the fixed contact and the movable contact using a magnetic force. An arc shielding member is disposed at a position to which the arc is attracted by current flowing between the fixed contact and the movable contact and by the magnetic force between the permanent magnets, in the housing.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. TECHNICAL FIELD 
         [0002]    The present invention relates to a sealed contact device, and more particularly to an electromagnetic relay for power loads which can promptly extinguish an arc which occurs. 
         [0003]    2. RELATED ART 
         [0004]    In the related art, as an arc extinguisher used in a sealed contact device, for example, Japanese Unexamined Patent Publication No. 2005-285547 discloses a device which extinguishes an arc occurring between a movable contact piece and a fixed contact piece when a contact of the fixed contact piece is separated from a contact of the movable contact piece by narrowing the arc between right and left sidewalls of an arc barrier. 
         [0005]    However, the above-mentioned arc extinguisher, as illustrated in  FIG. 1  of the prior art, has had a problem that an arc can be extinguished when the arc between contacts reaches an arc barrier  5 , but the arc cannot be promptly and certainly extinguished when the arc does not reach the arc barrier. 
         [0006]    The present invention has been made in view of the above-mentioned problem of the related art, and an object of the present invention is to provide a sealed contact device which can attract an arc if and when it occurs to extinguish the arc promptly and certainly. 
       SUMMARY 
       [0007]    In order to solve the above-mentioned problem, in accordance with one aspect of the invention, there is provided a sealed contact device including 
         [0008]    a housing, a fixed contact and a movable contact disposed in the housing in such a manner as to face each other, and permanent magnets which are disposed with the fixed contact and the movable contact interposed therebetween and which attracts an arc between the fixed contact and the movable contact using a magnetic force, wherein 
         [0009]    an arc shielding member is disposed at a position to which the arc is attracted by current flowing between the fixed contact and the movable contact and by the magnetic force of the permanent magnets, in the housing. 
         [0010]    According to the present invention, even though the arc occurs in an arbitrary direction, the arc is attracted in a desired direction by the current and the magnetic force so that the arc may reach the arc shielding member, resulting in the arc being extinguished. 
         [0011]    As an embodiment of the present invention, the arc shielding member may have at least one arc receiving piece. This configuration allows an increase in surface area of the arc shielding member. This also allows the arc to easily hit the arc shielding member, thereby increasing the performance of the mechanism utilized to extinguish the arc. 
         [0012]    As another embodiment of the present invention, the arc shielding member may be disposed at both sides of the contacts and formed along opposed surfaces of the permanent magnets. The opposed surfaces are arranged so that the magnetic field flows from one magnet to another. This configuration enables the arc to hit the arc shielding member disposed on either one of the contacts so that the arc may be extinguished even though a direction of the arc changes. 
         [0013]    As a further embodiment of the present invention, the arc shielding member may be formed to have an approximately cross-sectional U shape and may be disposed in the housing. By forming the arc shielding member to have the sectional U shape, the arc shielding member can be relatively easily gripped and the mounting workability of mounting the arc shielding member to a sealed space improves as compared with a plate-like arc shielding member. 
         [0014]    A cross-sectional U-shaped base portion of the arc shielding member may be placed on the bottom in the housing. This configuration can secure a mountability of the arc shielding member to the housing, without interfering with movements of the fixed contact and the movable contact. 
         [0015]    As a yet further embodiment of the present invention, the arc shielding member may be made of a metal. This configuration allows the arc which has hit the arc shielding member to be cooled, so that an ability of extinguishing the arc can be enhanced. 
         [0016]    As a yet further embodiments of the present invention, the arc shielding member may include a plate-like connector and arms which are formed to perpendicularly bend from both ends of the connector, respectively, in which the at least any one of the connector and the arms may be provided with at least one arc receiving piece. 
         [0017]    As a yet further embodiment of the present invention, the arc shielding member may have at least one arc receiving piece obtained by bending an edge portion of the connector. 
         [0018]    As a yet further embodiment of the present invention, the at least one arc receiving piece may be provided by bending an edge portion of the arm, and an inside surface of the arm may be provided with a protrusion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a whole perspective view illustrating an embodiment of a sealed contact device according to the present invention; 
           [0020]      FIG. 2  is an exploded perspective view of the sealed contact device illustrated in  FIG. 1 ; 
           [0021]      FIGS. 3A and 3B  are a side sectional view and a front sectional view before the sealed contact device illustrated in  FIG. 1  operates; 
           [0022]      FIGS. 4A and 4B  are a perspective view and a sectional view of an arc shielding member of a first embodiment according to the present invention; 
           [0023]      FIGS. 5A and 5B  are a perspective view and a side elevation view of an arc shielding member of a second embodiment according to the present invention; 
           [0024]      FIGS. 6A and 6B  are a perspective view and a side elevation view of an arc shielding member of a third embodiment according to the present invention; 
           [0025]      FIGS. 7A and 7B  are a perspective view and a side elevation view of an arc shielding member of a fourth embodiment according to the present invention; 
           [0026]      FIGS. 8A and 8B  are a perspective view and a side elevation view of an arc shielding member of a fifth embodiment according to the present invention; 
           [0027]      FIGS. 9A and 9B  are a perspective view and a side elevation view of an arc shielding member of a sixth embodiment according to the present invention; 
           [0028]      FIGS. 10A and 10B  are a perspective view and a side elevation view of an arc shielding member of a seventh embodiment according to the present invention; 
           [0029]      FIGS. 11A and 11  B are a perspective view and a side elevation view of an arc shielding member of an eighth embodiment according to the present invention; 
           [0030]      FIG. 12  is a graph which illustrates resistance of a sealed contact device according to the number of interceptions between contacts in a case where there is an arc shielding member and a case where there is no arc shielding member. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    An embodiment in which a sealed contact device according to the present embodiment is applied to a sealed electromagnetic relay is described with reference to  FIGS. 1 through 12  of the accompanying drawings. 
         [0032]    As illustrated in  FIG. 2 , the sealed electromagnetic relay according to the present embodiment is configured by disposing a contact mechanism part  30  and an electromagnet part  50  which drives the contact mechanism part  30  from the outside of a sealed space  43  shown in  FIG. 3A  in a housing which is formed by attaching a cover  20  to a case  10 . The contact mechanism part  30  is incorporated in the sealed space  43  formed by a ceramic plate  31 , a metallic cylindrical flange  32 , a plate-like first yoke  37  and, and a closed end barrel  41 . 
         [0033]    The case  10  is an approximately box-shaped resin-molding article, and has a mounting hole  11  provided in a hornlike portion disposed in a lower corner of an outer surface. The case  10  further has a bulging portion  12  in the corner of a side surface for pulling out a lead (not shown in the drawing) and latching holes  13  in opposed side surfaces and at an edge portion of an opening. 
         [0034]    The cover  20  has a plane shape which can cover an opening of the case  10 , and is provided with terminal holes  22  and  22  at both sides of a partition wall  21  formed to protrude in the center of the upper surface thereof. The cover  20  is provided with a projection  23 , on one side surface of one side thereof, which can prevent so-called flapping of the lead (not shown) by being inserted in the bulging portion  12  of the case  10 . The cover  20  is provided with latching claws  24  at an edge portion of the opening and in the opposite side surface, and the latching claws  24  can be latched in the latching holes  13  of the case  10 . 
         [0035]    The contact mechanism part  30  is disposed in the sealed space  43  (refer to  FIG. 3A ) formed by the ceramic plate  31 , the metallic cylindrical flange  32 , the plate-like first yoke  37 , and the closed end barrel  41  as described above. The contact mechanism part  30  includes a magnet holder  35 , a fixed iron core  38 , a movable iron core  42 , a movable shaft  45 , and a movable contact piece  48 . 
         [0036]    The ceramic plate  31  has a plane shape so that the ceramic plate  31  may be brazed to an edge portion of an upper opening of the metallic cylindrical flange  32  described below, is provided with a pair of terminal holes  31   a,  and is used in combination with an auxiliary plate  31   c.  The ceramic plate  31  has a metal layer (not shown) at each of an outer periphery portion of the upper surface thereof and opening edge portions of the terminal holes  31   a . As illustrated in  FIG. 3B , fixed contact terminals  33  which have fixed contacts  33   a  firmly attached to the bottoms, respectively are brazed to the edges of the terminal holes  31   a  of the ceramic plate  31 . 
         [0037]    The metallic cylindrical flange  32  brazed to the outer periphery portion of the upper surface of the ceramic plate  31  has an approximately cylindrical shape as illustrated in  FIG. 2  and is formed by press-processing a metallic plate. An outer periphery portion of a lower portion of the metallic cylindrical flange  32  is integrally combined with the plate-like first yoke  37  by welding. 
         [0038]    The magnet holder  35  accommodated in the metallic cylindrical flange  32  is formed of a heat-resistant insulating member having a box shape, and is provided with pocket grooves  35   a  which can retain the permanent magnets  36  therein, respectively and which are in both external side surfaces opposite to each other. The magnet holder  35  is provided with an annular cradle  35   c  (refer to  FIG. 3B ) in a lower deck in the center of the bottom surface, and a cylindrical insulating portion  35   b  which protrudes downward from the lower surface of the center of the annular cradle  35   c.  Even though an arc occurs and a voltage in a path between the metallic cylindrical flange  32 , and the plate-like first yoke  37  and the fixed iron core  38  is increased to a high voltage, because the cylindrical insulating portion  35   b  electrically insulates the cylindrical fixed iron core  38  and the movable shaft  45  from each other, both of them can be prevented from being integrally welded. Positioning plates  26  disposed in such a manner as to face each other in the magnet holder  35  are disposed so as to be brought into contact with the movable contact piece  48 , and positions the movable contact piece  48  by preventing rotation of the movable contact piece  48 . A rubber plate  27  is disposed between the magnet holder  35  and the first yoke  37  to buffer the shock which arises between the magnet holder  35  and an annular jaw  45   a  when the fixed contact  33   a  and the movable contact  48   a  are separated from each other. 
         [0039]    In addition, an arc shielding member  61  according to a first embodiment of the present invention is arranged inside of the magnet holder  35 . The arc shielding member  61  is made of, for example, a metal such as Stainless steel, and has an approximately sectional U shape as illustrated in  FIGS. 4A and 4B . 
         [0040]    That is, the arc shielding member  61  includes a plate-like connector  62  and arms  63  formed by bending upward both ends of the connector  62 . Opposed edge portions of the connector  62  are provided with tongue-shaped pieces (arc receiving pieces)  64 , respectively which are bent upward to stand upright. Each of the arms  63  includes an upper rib (arc receiving piece)  65  which bends inward from an upper end, a pair of side edge ribs (arc receiving pieces)  66  which bends inward from opposed side edges, and draining board-like protrusions (arc receiving pieces)  67  which protrude inward from the inside surface. 
         [0000]    In addition, in the arc shielding member  61 , the connector  62  is placed on a bottom wall of the magnet holder  35 , and the arms  63  are fixed to opposed side walls of the magnet holder  35 . 
         [0041]    As illustrated in  FIG. 2 , the plate-like first yoke  37  has a plane shape which may be fitted into the edge portion of the opening of the case  10 , an elastic plate  37   a  fixed to an upper surface thereof, and a caulking hole  37   b  in the center thereof. An upper end of the cylindrical fixed iron core  38  is fixed to the caulking hole  37   b  of the plate-like first yoke  37  in a caulking manner, and the plate-like first yoke  37  is fitted into the lower opening of the metallic cylindrical flange  32  and is integrally combined with the metallic cylindrical flange  32  by welding performed from the outside. 
         [0042]    The movable shaft  45  with an annular flange  45   a  is slidably inserted in a through-hole of the cylindrical fixed iron core  38  via the cylindrical insulating portion  35   b  of the magnet holder  35 . The movable shaft  45  is fixed by inserting a release spring  39  and welding the movable iron core  42  to the bottom of the release spring  39 . 
         [0043]    As for the closed end barrel  41  in which the movable iron core  42  is accommodated, the edge portion of the opening is hermetically joined with a lower edge portion of the caulking hole  37   b  provided in the plate-like first yoke  37 . Next, inside air is suctioned from a degassing pipe  34  so that the inside space is sealed to form a sealed space  43 . 
         [0044]    As illustrated in  FIG. 3B , a dish-like receiving tool  46  is latched by the annular flange  45   a  provided in the middle portion of the movable shaft  45  so that the inserted contact spring  47  and the movable contact piece  48  may be prevented from falling apart, and a stopper ring  49  is fixed to an upper end portion of the movable shaft  45 . The movable contacts  48   a  provided at both ends of the upper surface of the movable contact piece  48  are disposed to face with each other and to be able to move to and from the fixed contacts  33   a  of the contact terminal  33  disposed in the metallic cylindrical flange  32 . 
         [0045]    As illustrated in  FIG. 2 , in the electromagnet part  50 , coil terminals  53  and  54  are press-fitted and fixed to a flange  52   a  of a spool  52  around which a coil  51  is wound, and the coil  51  and the lead (not shown) are connected to each other via the coil terminals  53  and  54 . The closed end barrel  41  is inserted in the through-hole  52   b  of the spool  52  and is fitted into a fitting hole  56   a  of a second yoke  56 . Subsequently, upper ends of both side portions  57  and  57  of the second yoke  56  engage with both end portions of the plate-like first yoke  37 , respectively and then fixed to each other by a method such as caulking, press-fitting, and welding, so that the electromagnet part  50  and contact mechanism part  30  are integrally combined. 
         [0046]    Next, operation of the sealed magnetic relay having the above-described structure will be described. 
         [0047]    First, as illustrated in  FIGS. 3A and 3B , when a voltage is not applied to the coil  51 , the movable iron core  42  is biased to a lower side by the spring force of the release spring  39 , the movable shaft  45  is pushed down, and the movable contact piece  48  is pulled down. At this time, although the annular flange  45   a  of the movable shaft  45  engages with the annular cradle  35   c  of the magnet holder  35  and the movable contact  48   a  is separated from the fixed contact  33   a , the movable iron core  42  is not in contact with the bottom surface of the closed end barrel  41 . 
         [0048]    Subsequently, when a voltage is applied to the coil  51  so that the coil  51  is magnetized, the movable iron core  42  is attracted by the fixed iron core  38  and the movable shaft  45  will slide up against the spring force of the release spring  39 . Even after the movable contact  48   a  is brought into contact with the fixed contact  33   a,  the movable shaft  45  is pushed up against the spring force of the release spring  39  and the contact spring  47 , the upper end of the movable shaft  45  projects from a shaft hole  48   b  of the movable touch piece  48 , and the movable iron core  42  is attracted and attached to the fixed iron core  38 . 
         [0049]    Next, when the application of the voltage to the coil  51  is stopped and the magnetization is resolved, the movable iron core  42  will separate from the fixed iron core  38  due to the spring force of the contact spring  47  and the release spring  39 . For this reason, after the movable shaft  45  slides down to the lower side and the movable contact  48   a  separates from the fixed contact  33   a,  the annular flange  45   a  of the movable shaft  45  engages with the annular cradle  35   c  of the magnet holder  35 , and thus returns to the original state. 
         [0050]    At this time, an arc may occur between the fixed contact  33   a  of a high voltage and the movable contact  48   a.  In  FIG. 3B , the arc is attracted and induced in a direction orthogonal to the orientation of arms  63  of arc shield member  61  by the current which flows between the fixed contact  33   a  and the movable contact  48   a,  and the magnetic force which is horizontally generated between the opposed permanent magnets  36 . The arms  63  of the arc shielding member  61  are installed in the direction in which the arc is attracted. For this reason, even though the arc is generated in an arbitrary direction, the arc is first induced in a desired direction by the current which flows between the fixed contact  33   a  and the movable contact  48   a  and the magnetic force which is generated horizontally between the opposed permanent magnets  36 , and is allowed to hit the arc shielding member  61 , so that the arc is extinguished. 
         [0051]    Especially, because the arc shielding member  61  has a plurality of protrusions  67 , the surface area of the inside surface of the arc shielding member  61  is increased. Because of this, the arc can be promptly cooled, and thus the arc can be efficiently extinguished. 
         [0052]    In addition, the arc shielding member  61  is formed to have an approximately sectional U shape, and the connector (base portion)  62  in the sealed space  43  (magnet holder  35 ) is placed on the bottom surface in the magnet holder  35 . For this reason, compared with the case of using a simple plate-like arc shielding member, the arc shielding member  61  can be gripped easily so that a mounting workability to the sealed space  43  (magnet holder  35 ) may improve. In addition, the mountability of the arc shielding member  61  into the sealed space  43  can be secured without interfering with movements of the fixed contact  33   a  and the movable contact  48   a.    
         [0053]    The arms  63  of the arc shielding member  61  are disposed at both sides of the fixed contact  33   a  and the movable contact  48   a  and disposed along the opposed surfaces of the permanent magnets  36 . For this reason, even though the directions of the current and/or the magnetic flux change and thus the direction in which an arc occurs changes, the arc can hit either one of the arms  63  and be extinguished. 
         [0054]    In addition, because the arc shielding member  61  is made of a metal, the arc which hits the arc shielding member  61  can be efficiently cooled, and the capability of extinguishing the arc can be enhanced. 
         [0055]    Other embodiments of the arc shielding member which can be used with the sealed contact device described herein are described below with reference to  FIGS. 5A-B  to  11 A-B. 
       Second Embodiment 
       [0056]    An arc shielding member  71  according to a second embodiment of the present invention is illustrated in  FIGS. 5A and 5B . 
         [0057]    Although the arms  63  of the arc shielding member  61  according to the first embodiment are provided with the protrusions  67 , the configuration is not limited thereto. Arms  72  of a simple plate shape may be adopted like the arc shielding member  71  according to the second embodiment. With this configuration, it is possible to certainly prevent the arc from passing by the arms  72 . Because other portion are the same as those of the first embodiment, like portions are denoted by like reference signs and detailed description thereof is not given. 
       Third Embodiment 
       [0058]    An arc shielding member  73  according to a third embodiment of the present invention is illustrated in  FIGS. 6A and 6B . 
         [0059]    Although the arms  63  of the arc shielding member  61  according to the first embodiment are provided with the protrusions  67 , the configuration is not limited thereto. For example, like arms  74  of the arc shielding member  73  according to the third embodiment, protruding pieces (arc receiving pieces)  77  protruding inward from an upper edge and a lower edge of an opening  76  which are provided side by side in a folded plate  75  may be formed by cutting out. Thereby, the arc shielding member  73  with a high yield of material is obtained. 
         [0060]    Because other portion are the same as those of the first embodiment, like portions are denoted by like reference signs and detailed description thereof is not given. 
       Fourth Embodiment 
       [0061]    An arc shielding member  80  according to a fourth embodiment of the present invention is illustrated in  FIGS. 7A and 7B . 
         [0062]    Although the arms  63  of the arc shielding member  61  according to the first embodiment are provided with the side edge ribs  66 , the configuration is not limited thereto. For example, like arms  81  of the arc shielding member  80  according to the fourth embodiment, there may be provided a plurality of flexing portions (arc receiving portions)  83  each of which is bent inward from both opposed side edges of a folded plate  82 , and each of which extends along the inside surface of the folded plate  82 . This configuration allows an increase in surface area of the arms  81  so that the arms can be easily hit by the arc, and certainly prevents the arc from passing to the back side. Because other portion are the same as those of the first embodiment, like portions are denoted by like reference signs and detailed description thereof is not given. 
       Fifth Embodiment 
       [0063]    An arc shielding member  85  according to a fifth embodiment of the present invention is illustrated in  FIGS. 8A and 8B . 
         [0064]    Arms  86  of the arc shielding member  85  according to the fifth embodiment further include linear reinforcement pieces  87 , which connect flexing portions  83  and  83  to each other, at end portions of the flexing portions  83  and  83  of the fourth embodiment, respectively. This configuration increases the strength of the flexing portions  83  and improves the bending accuracy. 
         [0065]    Because other portion are the same as those of the first embodiment, like portions are denoted by like reference signs and detailed description thereof is not given. 
       Sixth Embodiment 
       [0066]    An arc shielding member  90  according to a sixth embodiment of the present invention is illustrated in  FIGS. 9A and 9B . 
         [0067]    Each arm  91  of an arc shielding member  90  according to the sixth embodiment is provided with a rectangular extension plate (arc receiving piece)  93  and a covering plate (arc receiving piece)  94 . The extension plate  93  extends to broaden outward from one side edge of a folded plate  92 . The covering plate  94  broadens outward from the other side edge of the folded plate  92 , extends toward the extension plate  93 , and extends along the folded plate  92 . This configuration allows an increase in the width of the arms  91  so that the arc can be more certainly extinguished. The covering plate  94  is provided with a plurality of openings  95  so that the surface area may be increased. Because other portion are the same as those of the first embodiment, like portions are denoted by like reference signs and detailed description thereof is not given. 
       Seventh Embodiment 
       [0068]    An arc shielding member  97  according to a seventh embodiment of the present invention is illustrated in  FIGS. 10A and 10B . 
         [0069]    Each arm  98  of the arc shielding member  97  according to the seventh embodiment is provided with an extension portion (arc receiving piece)  103  including a first narrow rib  100  which extends to broaden outward from one side edge of a folded plate  99 , a second rib  101  which extends and bends outward from an end of the first rib  100 , and a third rib  102  which bends to the back side from an end of the second rib  101  and extends toward the folded plate  99 . Because the extension portion  103  is brought close to the fixed contact  33   a  and the movable contact  48   a,  an arc which spreads sideways can be easily trapped. Because other portion are the same as those of the first embodiment, like portions are denoted by like reference signs and detailed description thereof is not given. 
       Eighth Embodiment 
       [0070]    An arc shielding member  105  according to an eighth embodiment of the present invention is illustrated in  FIGS. 11A and 11B . 
         [0071]    As for an each arm  106  of the arc shielding member  105  according to the eighth embodiment, a plate-like covering plate  108  which extends from an upper end of a folded plate  107  is bent inward, and then bent downward to extend along the folded plate  107 , and both side edge portions of a distal end thereof are latched to a lower end of a side edge rib  66 . For this reason, an arc can be prevented from passing to the back side of the arm  106 . In addition, the covering plate  108  is provided with a plurality of openings  109  so that the surface area may be increased. Because other portion are the same as those of the first embodiment, like portions are denoted by like reference signs and detailed description thereof is not given. 
       Example 
       [0072]    Inventors of the present application conducted experiments on durability of a sealed contact device which uses the arc shielding member  61  of the present invention. Specifically, an experiment was repeatedly performed which cancels (interrupts) the application of the voltage to the coil  51  in a state in which the current of  500 A is supplied between the fixed contacts  33   a  and  33   a  and the movable contacts  48   a  and  48   a  at a direct current voltage of 400V so that the fixed contacts  33   a  and  33   a  and the movable contacts  48   a  and  48   a  may separate from each other. At this time, as illustrated in  FIG. 12 , in the sealed contact device with the arc shielding member  61 , as illustrated by a solid line, even though the experiment was repeated 20 times, it turned out that degradation of the fixed contact  33   a  and the movable contact  48   a  attributable to an arc was inhibited, and an abrupt decrease in an insulation resistance value of the sealed contact device was prevented. On the other hand, in the sealed contact device without the arc shielding member  61 , as illustrated by a dotted line, when the experiment was repeated 5 times, it turned out that the fixed contact  33   a  and the movable contact  48   a  were degraded due to an arc which occurred, and the insulation resistance value of the sealed contact device abruptly decreased. 
         [0073]    The inventors of the present application measured duration of the arc which occurred when the fixed contact  33   a  and the movable contact  48   a  are separated. As compared with the sealed contact device without the arc shielding member  61 , the duration of the arc is shortened by 12.5% in the sealed contact device with the arc shielding member  61 . 
         [0074]    As for the sealed contact device according the present invention, it is needless to say that it may apply not only to the above-mentioned sealed electromagnetic relay but to other electromagnetic switches. 
         [0075]    There has thus been shown and described a sealed contact device which fulfills all the objects and advantages sought therefore. Many changes, modifications, variations and other uses and applications of the subject invention will, however, become apparent to those skilled in the art after considering this specification and the accompanying drawings which disclose the preferred embodiments thereof. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention, which is to be limited only by the claims which follow. 
         [0076]    Although the invention has been described in detail for the purpose of illustration based on what is currently considered to be the most practical and preferred embodiments, it is to be understood that such detail is solely for that purpose and that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover modifications and equivalent arrangements that are within the spirit and scope of the appended claims. For example, it is to be understood that the present invention contemplates that, to the extent possible, one or more features of any embodiment can be combined with one or more features of any other embodiment.