Abstract:
To promptly extinguish an arc generated between contacts with a simple and inexpensive structure without negatively influencing the spring property of a movable contact piece. A contact switching mechanism includes a fixed contact piece with a fixed contact and a movable contact piece with a movable contact which faces the fixed contact in a contactable manner. At least either one of the contact pieces is provided with an extension which extends toward the contact of the remaining contact piece.

Description:
TECHNICAL FIELD 
       [0001]    The present embodiments relate to a contact switching mechanism and an electromagnetic relay including a contact switching mechanism, and more particularly to a power relay. 
       BACKGROUND ART 
       [0002]    Conventionally, there is a known contact switching mechanism where a projection piece for terminating extension of an arc is formed at either one side end, out of a left side end and a right side end, of a leaf spring provided with a movable contact (for example, refer to Japanese Unexamined Patent Publication No. 2006-196372). 
         [0003]    However, in the conventional contact switching mechanism, the arc generated between contacts is extended by the action of magnetic force and is terminated by the projection piece, where the position of the projection piece from the contacts is farther than a distance between the contacts. For this reason, there is a concern that the position of termination is not coincident with that of the projection piece when the arc actually occurs. 
         [0004]    Another known contact switching mechanism is provided with a fixed electrode provided with an arc-runner conductor provided with a protrusion. With this structure, the arc generated between a movable electrode contact and a fixed electrode contact in an electrode open state is communicated between a distal end of the movable electrode and the protrusion (for example, refer to Japanese Unexamined Patent Publication No. 2010-170876). 
         [0005]    However, in the conventional contact switching mechanism, the arc-runner conductor needs to be attached to the electrode as an additional member, and furthermore an additional process for providing the protrusion to the arc-runner conductor needs to be performed. For such a reason, there are problems in that the structure of a conventional contact switching mechanism is complicated and the cost of a conventional contact switching mechanism is increased. 
       SUMMARY 
       [0006]    The present embodiments are intended to provide a contact switching mechanism and an electromagnetic relay that can promptly extinguish an arc generated between contacts with a simple and inexpensive structure without negatively influencing the spring property of a movable contact piece. 
         [0007]    In accordance with one aspect of the present embodiments, in order to solve the above problem, there is provided a contact switching mechanism including a fixed contact piece with a fixed contact and a movable contact piece with a movable contact that faces the fixed contact in a contactable manner, wherein the fixed contact piece includes a first fixed portion that is configured to fix to a base and a first main body portion that is configured to protrude from the base and includes the fixed contact and the movable contact piece includes a second fixed portion fixed to the base and a second main body portion that protrudes from the base and includes the movable contact, at least one of the fixed contact piece and the movable contact piece include an extension that extends toward the fixed contact or the movable contact provided for the remaining at least one of the fixed contact piece and the movable contact piece, the extension is at a side opposite to one of the first fixed portion and the second fixed portion, with one of the fixed contact and the movable contact interposed between. 
         [0008]    With this configuration, the arc generated between the contacts is reliably led to the extension and thus rapidly extinguished. Moreover, even if the extension is damaged when the arc is extinguished, the damaged portion may be a region which is irrelevant to a conductive portion. Furthermore, when the distance from the conductive region of the contact piece to the position of the distal end of the extension is sufficiently increased, a structure which is sufficiently resistant to the arc-originating damage can be configured. 
         [0009]    The extension preferably protrudes by a dimension which is more than that of the contact which protrudes from the main body portion. 
         [0010]    With this configuration, it is possible to far more effectively extinguish the arc generated between the contacts. 
         [0011]    The extension is preferably formed by bending the main body portion. 
         [0012]    In this case, the main body portion may be bent at a substantially right angle. 
         [0013]    A magnet that extends the arc generated between the contacts to the extension is preferably provided. 
         [0014]    With this configuration, since the arc generated between the contacts is extended to the extension, the arc can be far more effectively extinguished. 
         [0015]    In accordance with another aspect of the present embodiments, in order to solve the above problem, there is provided an electromagnetic relay including any of the contact switching mechanisms described above. 
         [0016]    According to the present embodiments, at least one of contact pieces is provided with an extension which extends to a contact provided for the remaining contact piece. Accordingly, the arc generated between the contacts can be reliably extended to the extension so that the arc can be rapidly extinguished. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a perspective view illustrating an electromagnetic relay according to an embodiment; 
           [0018]      FIG. 2  is a perspective view illustrating a state in which the structure of  FIG. 1  is disassembled so that a case and an arc-extinguishing member are separated from each other; 
           [0019]      FIG. 3  is a perspective view illustrating a state in which only the case is removed from the structure of  FIG. 1 ; 
           [0020]      FIG. 4  is an exploded perspective view of the structure of  FIG. 1 ; 
           [0021]      FIG. 5  is an exploded perspective view illustrating the state of  FIG. 4  viewed from the opposite side; 
           [0022]      FIG. 6A  is a perspective view illustrating a base viewed from above and 
           [0023]      FIG. 6B  is a perspective view illustrating the base viewed from below; 
           [0024]      FIG. 7  is an exploded perspective view of an electromagnet block and a movable iron piece shown in  FIG. 2 ; 
           [0025]      FIG. 8  is an exploded perspective view of the electromagnet block and the movable iron piece shown in  FIG. 2 ; 
           [0026]      FIG. 9  is a cross-sectional view illustrating a state in which the case is removed from the structure of  FIG. 1  when a relay contact is closed; 
           [0027]      FIG. 10  is a cross-sectional view illustrating a state in which the case is removed from the structure of  FIG. 1  when the contact is open; 
           [0028]      FIG. 11  is an enlarged perspective view of a contact switching unit of  FIG. 3 ; 
           [0029]      FIG. 12  is a graph illustrating an attracting force curve of the electromagnet block of  FIG. 4  and a change in force exerting on a movable contact piece; 
           [0030]      FIG. 13  is an enlarged perspective view that illustrates the movable contact piece of  FIG. 4 ; and 
           [0031]      FIG. 14  is a partial enlarged perspective view that illustrates a contact switching mechanism of an electromagnetic relay according to another embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    Hereinafter, preferred embodiments will be described with reference to the drawings. Note that in the description below, terms that refer to specific directions and positions (for example, terms including “upper”, “lower”, “side”, and “end”) are used if necessary. The purpose of using the terms is to help one better understand the present embodiments referenced in the drawings, but the technical scope of the present embodiments is not be limited by the meanings of the terms. The description hereinbelow represents an example of the present embodiments and is not limiting. 
       1. Overall Structure 
       [0033]      FIGS. 1 to 5  illustrate an electromagnetic relay according to an embodiment. As it relates to the electromagnetic relay, an electromagnet block  2 , a contact switching unit  3 , and a movable iron piece  4  are installed on a base  1 , and the whole structure is encased in a case  5 . A power relay in which an application voltage is 400 V and a quantity of electricity is 20 A is used. 
       1-1. Base  1   
       [0034]    The base  1  is rectangular in a plan view and is formed by performing a molding process with a synthetic resin material as shown in  FIGS. 6A and 6B . In the base  1 , there are two installation areas including a first installation portion  6  and a second installation portion  7  arranged in a longitudinal direction. Hereafter, the longitudinal direction running along a longer side is referred to as an X-axis, a lateral direction running along a shorter side is referred to as a Y-axis, and a direction running along the height is referred to as a Z-axis. 
         [0035]    The first installation portion  6  is an area reserved for installation of the electromagnet block  2  to be described later and is configured in a manner that a supporting concave portion  10  is formed in a recess  9  surrounded with a first periphery wall  8  formed on an upper surface of the base  1  and with a second installation portion  7 . In the bottom of the recess  9 , a pair of coil terminal holes  11  that completely pass through the bottom of the recess  9  from the upper side to the lower side are formed at both sides of the supporting concave portion  10  in the lateral direction of the base  1  (the direction of YY′). 
         [0036]    A guide portion  12  is formed near the supporting concave portion  10  (in the longitudinal direction of the base  1 ). The guide portion  12  includes a pair of guide walls  13  which are formed to correspond to the shorter-side direction (the direction of YY′), and an insulation wall  14  that connects the pair of guide walls  13 . Guide grooves  15 , each of which vertically extends, are formed in opposing surfaces of the guide walls  13 . Both sides of a yoke  41 , to be described later, are guided by the guide grooves  15 . Moreover, a guide concave portion  16  is formed at a center portion of an area surrounded by the guide walls  13  and the insulation wall  14 . A to-be-guided portion  50  of a hinge spring  44 , to be described later, is located in the guide concave portion  16 . 
         [0037]    The second installation portion  7  is an area reserved for the contact switching unit  3 . A plinth  17  having the same height as the first periphery wall  8  of the first installation portion  6  is formed in the second installation portion  7 . In the plinth  17 , a slit-like first terminal hole  18  extending in the direction of YY′ is formed. The first terminal hole  18  passes through the bottom of the base  1  only at two locations where communicating portions  19  are formed. A movable contact piece  52 , to be described later, is press-fitted into the first terminal hole  18 . A second periphery wall  20  is formed at three of the four sides of the plinth  17 . The fourth side that is near the first installation portion  6 . A part of the second periphery wall  20 , which is disposed on the side of the X′ direction side, is relatively thick and has a pair of slit-like second terminal holes  21 , which extend and are arranged in the direction of YY′. 
       1-2. Electromagnet Block  2   
       [0038]    As illustrated in  FIGS. 7 and 8 , the electromagnet block  2  is a structure formed by winding a coil  24  around an iron core  22  using a spool  23 . 
         [0039]    The iron core  22  is a bar of an electromagnetic material. As for the iron core  22 , a flange-like magnetic pole portion  25  is formed at a lower end of the iron core  22  and the yoke  41  is fastened to an upper end of the iron core  22 . 
         [0040]    The spool  23  is obtained by performing a molding process with a synthetic resin material, and includes a cylindrical trunk  27  having a center hole  26  formed in the cylindrical trunk  27  and flanges (an upper-end flange  28  and a lower-end flange  29 ). The upper-end flange is formed at an upper end of the cylindrical trunk  27  and the lower-end flange  29  is formed at a lower end of the cylindrical trunk  27 . 
         [0041]    In an upper surface of the upper-end flange  28 , a relief groove  30  is formed and the center hole  26  is open. An end of the yoke  41 , to be described later, is disposed in the relief groove  30 . The center hole  26  is also open in the lower-end flange  29  and the iron core  22  can be inserted into the center hole  26  from the lower-end flange  29 . 
         [0042]    Terminal attachment portions  31  are provided at both sides of the lower-end flange  29 , and a terminal holding hole  32  is formed in each of the terminal attachment portions  31 . Coil terminals  36 , to be described later, are press-fitted in and each of the coil terminals  36  is fixed to a respective one of the terminal holding holes  32 . Step portions  33  are formed on both sides of an end of the terminal attachment portion  31 , and coil winding portions  39  of the coil terminals  36 , which are press-fitted in the terminal holding holes  32  to be fixed project over a respective one of the step portions  33 . Moreover, the lower-end flange  29  has a guide groove  34  that communicates with one of the step portions  33  via a way from the trunk  27  to a side end surface of the trunk  27 . An end of the coil  24  (a beginning end of turns of the coil  24 ) wound around the trunk  27  is disposed in the guide groove  34 , and the coil  24  is wound around the coil winding portion  39  of the coil terminal  36  which projects over the step portion  33 . A pair of guide protrusions  35  are provided in the bottom surface of the lower-end flange  29  at a predetermined interval. The guide protrusions  35  serve to position the spool  23 . In other words, the guide protrusions  35  serve to position the electromagnet block  2  with respect to the base  1  by being put in the supporting concave portions  10  of the base  1 . 
         [0043]    The coil terminal  36  is a plate-like body of an electrically conductive material, and its lower end portion is tapered to the bottom such that the width and thickness are gradually decreased toward the bottom. The coil terminal  36  has a press-fitted portion  37  which is expanded from one surface of the plate-like body through a press-working process at an upper end portion of the plate-like body, and a portion of the coil terminal  36  on the upper side of the press-fitted portion  37  is formed as a wide width portion  38 . The coil winding portion  39  projects from one end of the wide width portion  38 . 
         [0044]    The coil  24  is wound around the trunk  27  of the spool  23 , and an insulation sheet  40  is attached to the outer circumferential surface of the coil  24 . One end of the coil  24  is arranged in the guide groove  34  of the spool  23 , and the coil  24  is then wound around the trunk  27  of the spool  23 . After that, both ends of the coil  24  are wound around the coil winding portion  39  of the coil terminal  36 , and then soldered to be fixed. 
         [0045]    The yoke  41  is fastened to an end of the iron core  22 . The yoke  41  is made of a magnetic material and has a bent body that is substantially L shape-shaped. An end of the yoke  41  is provided with an opening  41   a  so that an end of the iron core  22  is inserted in the opening  41   a  so as to be fastened to the end of the yoke  41 . The other end of the yoke  41  is a wide width portion, and one of the protruding portions  42  is provided at either side of a lower end of the wide width portion. The movable iron piece  4 , to be described later, is located between both the protruding portions  42 , and one corner of the protruding portions  42  functions as a fulcrum on which the movable iron piece  4  is movably supported. In a middle portion of the yoke  41 , two fastening projections  43  are formed on an outside surface of the yoke  41  and they are arranged on a vertical line. 
         [0046]    A hinge spring  44  is fastened to the middle portion of the yoke  41  by using the projections  43 . However, the method of fixing the hinge spring  44  to the yoke  41  is not limited to the fastening, but a different method such as ultrasonic welding, resistance welding, laser welding, or the like may be used. 
         [0047]    The hinge spring  44  includes a joint portion  45  that comes in contact with the outside surface of the middle portion of the yoke  41 . The joint portion  45  has through-holes  45   a  at two locations and the projections  43  of the yoke  41  are inserted into the through-holes  45  so as to be fastened. 
       1-3. Contact Switching Unit  3   
       [0048]    The contact switching unit  3 , as illustrated in  FIGS. 4 and 5 , includes the fixed contact pieces  51  and the movable contact piece  52 , each of which is obtained by performing press working on an electrically conductive material such as copper. 
         [0049]    The fixed contact piece  51  includes a press-fitted portion  53 , a terminal portion  54  extending downward from the press-fitted portion  53 , and a main body portion  55  extending upward from the press-fitted portion  53 . The press-fitted portion  53  is provided with expansion portions  56  that are expanded from one surface of the press-fitted portion  53  by using the press working process. The press-fitted portion  53  can be press-fitted into a second terminal hole  21  of the base  1  by this expansion portions  56 . The terminal portion  54  is narrower in width than the press-fitted portion  53 , and is formed to be lopsided to one side of the press-fitted portion  53 . The main body portion  55  is formed to be lopsided to the other side, which is opposite to a side where the terminal portion  54  is provided, and has a width half the width of the press-fitted portion  53 . An upper end of the main body portion  55  is provided with a through-hole, and a fixed contact  57  is fastened to the upper end of the main body portion  55 . 
         [0050]    The movable contact piece  52  includes a press-fitted portion  58  and a pair of main body portions  59  extending upward from both sides of the press-fitted portion  58 , respectively. 
         [0051]    At a center portion of the press-fitted portion  58  in the vertical direction, an expansion portion  60  extending in the widthwise direction is formed like in the fixed contact piece  51 . The expansion portion  60  can be press-fitted into the first terminal hole  18  of the base  1 . Moreover, a pair of projections  61  that project downward are respectively formed at both ends of a lower edge of the press-fitted portion  58 . 
         [0052]    The main body portion  59  extends by being at a location near the press-fitted portion  58  and has a through-hole  59   a  at an upper end portion thereof. The movable contact  62  is fastened to the through-hole. Moreover, at an upper end of the main body portion  59 , an extension  59   b  is formed to diagonally bend upward toward the fixed contact piece  51  as illustrated in  FIG. 13 . An inclination angle of the extension  59   b  with respect to the main body portion  59  is about 140 degrees in this case. However, it may be freely selectable as long as it is within a range of about 140 to 90 degrees. In addition, a distal end portion of the extension  59   b  in the perpendicular direction to the main body portion  59  is located at a position which protrudes more than the movable contact  62 . 
         [0053]    The movable contact piece  52  is arranged such that the movable contact  62  can move closer to and away from the fixed contact  57  of the fixed contact piece  51  which is press-fitted into the second terminal hole  21  in a state in which the press-fitted portion  58  is press-fitted into the first terminal hole  18  of the base  1 . Therefore, in this state, as described above, the distal end portion of the extension  59   b  protrudes more than the movable contact  62 , as illustrated in  FIG. 10 , it is close to the fixed contact  57 . Accordingly, even if the arc is generated between the contacts, this arc extends to the distal end of the extension  59   b  and is promptly extinguished through the extension. 
       1-4. Movable Iron Piece  4   
       [0054]    The movable iron piece  4  is formed by performing press working on a plate of a magnetic material so that the plate becomes substantially an L shape as shown in  FIGS. 7 and 8 . An end portion of the movable iron piece  4  is a to-be-attracted portion  63  which is to be attracted to the magnetic pole portion  25  of the iron core  22 . A distal end portion and a base portion of the to-be-attracted portion  63  has a small width, so that an interference between the protruding portions  42  formed in the lower end portion of the yoke  41  and the guide protrusion  35  formed in the bottom surface of the spool  23  can be avoided. The other end portion of the movable iron piece  4  is provided with an opening  64 . The hinge spring  44  passes through the opening  64 , and comes in pressure-contact with a corner portion of the to-be-attracted portion  63 . The other end portion of the movable iron piece  4  has a small width, and the card member  65  is integrally formed with an upper portion of the movable iron piece  4  which is disposed on the upper side of the opening  64 . 
         [0055]    The card member  65  is made of a synthetic resin material. On one surface of the card member  65  from which the upper end portion of the movable iron piece  4  which is integrally formed with the card member  65  is exposed, first protruding portions  66  are formed at both sides of the upper end portion of the movable iron piece  4 , respectively, and a second protruding portion  67  is formed at an upper side of the first protruding portions  66 . When the to-be attracted portion  63  of the movable iron piece  4  is separated from the magnet pole portion  25  of the iron core  22 , the elastic contact portion  46  of the hinge spring  44  collides with the second protruding portion  67 , and after which the first protruding portion  66  comes into contact with the yoke  41 . On the other surface of the card member  65 , projection portions  68  extending in the vertical direction are formed at a predetermined interval in the widthwise direction. Pressing portions  69  which more project than the projection portions  68  are formed at upper ends of the projection portions  68 , respectively, so that the pressing portions  69  can press the upper ends of the main body portions  59  of the movable contact piece  52 . A shield wall  70  which protrudes more than the other surface and extends downward is formed at a lower end portion of the card member  65 . 
       1-5. Case  5   
       [0056]    The case  5  has a box shape which is open at a lower end as shown in  FIG. 2  and is made of a synthetic resin material. The case  5  has a sealing hole  71  in a corner of an upper surface. After a fitting portion of the base  1  and the case  5  is sealed, the sealing hole  71  is closed by heat sealing. At an edge of the upper surface of the case  5  on the opposite side of the sealing hole  71 , slit-like concave portions  72  are formed at both side portions and a center portion, respectively. A recess  73  that is recessed from the upper surface of the case  5  is formed every between the concave portions  72 , and a projection  74  is formed at a center portion of the surface of the recess  73 . 
         [0057]    An arc-extinguishing member  75  is attached to the case  5  using the concave portions  72  and the recess  73 . 
         [0058]    The arc-extinguishing member  75  includes a pair of permanent magnets  76 , arranged at a predetermined interval, for extinguishing the arc and a joint member  77 , made of a magnetic material, for magnetically connecting these permanent magnets  76 . 
         [0059]    The permanent magnets  76  have an almost rectangular parallelepiped shape and are arranged such that opposite sides of the permanent magnets  76  may have different polarities in a state in which the permanent magnets  76  are attached to the opposite inside walls  78  of the joint member  77 . However, the polarities of the opposing surfaces may be set such that the direction of force exerting on the arc current which changes according to the direction of the current flowing at a contact point is directed toward a middle wall  79  of the joint member  77  to be described later. 
         [0060]    The joint member  77  is formed by performing press working on a plate of a magnetic material such that both ends are bent so as to face each other. The permanent magnets  76  are attracted and fixed to the inside surfaces of the opposing walls  78 , respectively. In the middle wall  79  of the joint member  77 , both side portions of the middle wall  79  are cut away at different locations which are nearer opposite ends, respectively, so that middle protruding portions  80  are formed between the opposing walls  78 . Each of the middle protruding portions  80  serves to shorten a magnetic path by being located in the middle portion between both the opposing walls  78  and protruding between both contact switching positions. That is, in a magnetic circuit, a closed loop is formed such that the magnetic flux generated from each of the permanent magnets  76  passes the middle wall  79  and each of the opposing walls  78  via the middle protruding portions  80 , and returns to the permanent magnets  76 . 
         [0061]    As described above, the arc-extinguishing member  75  is provided with not only the pair of permanent magnets  76  but also the joint member  77  to magnetically connect the permanent magnets  76 . Therefore, the magnetic circuit is formed, and as a result, it becomes difficult for the magnetic flux to leak. Moreover, since the middle protruding portions  80  are provided, the magnetic path can be shortened. Therefore, magnetic efficiency can be improved. Accordingly, even if an arc occurs at the time when the contact is opened or closed, this arc elongates to the sides according to the Fleming&#39;s left hand rule, and as a result, the arc is extinguished in a short time. 
       2. Assembling Method 
       [0062]    Next, a method of assembling an electromagnetic relay having the structure described above is described. 
         [0063]    The coil  24  is wound around the trunk  27  of the spool  23 , and the coil terminal  36  is press-fitted and fixed to the lower-end flange  29 . Both ends of the coil  24  are wound around the coil winding portion  39  and soldered. Moreover, the iron core  22  is inserted to pass through the center hole  26  of the spool  23  from the lower end of the spool  23 , and the yoke  41  to which the hinge spring  44  is attached beforehand is fastened to the a portion of the iron core  22  which is exposed from the upper end of the spool. As a result, the electromagnet block  2  is completed assembled. 
         [0064]    In the finished electromagnet block  2 , the movable iron piece  4  is supported in a turnable manner on the lower end of the yoke  41  by using the hinge spring  44 . Under this condition, the first protruding portion  66  of the card member  65  which is integrally formed with the movable iron piece  4  can come into contact with the yoke  41 , and the elastic contact portion  46  of the hinge spring  44  can move closer to and away from the second protruding portion  67  of the card member  65 . Next, the electromagnet block  2  to which the movable iron piece  4  is attached, and the contact switching unit  3  is installed in the base  1 . 
         [0065]    When installing the electromagnet block  2 , the coil terminal  36  is press-fitted into the coil terminal hole  11  of the base  1 , and both the sides portions of the yoke  41  are inserted into the guide grooves  15  of the guide wall  13 . In the installed state, the guide protrusion  35  is located in the supporting concave portion  10 , and the electromagnet block  2  is positioned on one side thereof in the direction of YY′. Moreover, the lower end surface of the protruding portion  42  of the yoke  41  and the bottom surface of the terminal attachment portion  31  come in contact with the bottom surface of the recesses  9  of the base  1 , respectively. As a result, a gap is formed between the bottom surface of the recess  9  of the base  1  and the bottom surface of the lower-end flange  29  of the spool  23 , and the movable iron piece  4  is be turnable in the gap. The shield wall  70  of the card member  65  which is integrally formed with the movable iron piece  4  is arranged over the insulation wall  14  of the base  1 . At this time, the insulation performance between the electromagnet block  2  and the contact switching unit  3  is sufficiently secured due to the presence of the guide wall  13  and insulation wall  14  of the base  1 , and an upper portion of the card member  65  and the shield wall  70 . 
         [0066]    When installing the contact switching unit  3 , the press-fitted portion  58  of the movable contact piece  52  is press-fitted into the first terminal hole  18  of the base  1 . When installing the movable contact piece  52 , since the projection  61  is located in the communicating portion  19 , the installation state of the movable contact piece  52  can be confirmed by viewing the bottom surface of the base  1 . Moreover, the pressing portion  69  of the card member  65  which has been installed beforehand comes in pressure-contact with the upper end portion of the movable contact piece  52 , and the movable iron piece  4  is positioned at the default position at which the to-be-attracted portion  63  is separated from the magnetic pole portion  25  of the iron core  22  due to the elastic force of the movable contact piece  52 . 
         [0067]    Moreover, the terminal portion  54  of the fixed contact piece  51  is inserted into the second terminal hole  21  of the base  1 , and the press-fitted portion  53  is then press-fitted for fixing. In this state, the fixed contact piece  51  faces the movable contact piece  52  with a predetermined distance between the fixed contact piece  51  and the movable contact piece  52 , and the movable contact  62  becomes contactable to the fixed contact  57 . Moreover, the distal end portion of the extension  59   b  extending from the upper end of the movable contact piece  52  protrudes, from the main body portion  59 , toward the fixed contact piece  51 , within a predetermined region which exists in a direction along which the arc is extended by the permanent magnet  76  as described below. 
         [0068]    Moreover, the arc-extinguishing member  75  is installed in the case  5 . When installing the arc-extinguishing member  75 , in the state in which the permanent magnets  76  are attached to the opposing walls  78  of the joint member  77 , the opposing walls  78  of the joint member  77 , the permanent magnets  76 , and the middle protruding portion  80  are inserted into the respective concave portions  72  formed in the case  5 . Subsequently, the base  1  is encased in the case  5  with the arc-extinguishing member  75  attached to the base, and the fitting portion therebetween is sealed. 
         [0069]    In addition, an internal space may be sealed by heat-sealing a sealing hole  71 . However, the sealing hole  71  may be used in a state where the sealing hole  71  is kept being open and the internal space is allowed to be in communication with a surrounding atmosphere. 
       3. Operation 
       [0070]    Next, the operation of the electromagnetic relay having the above-described structure will be described. 
         [0071]    Under a condition in which the coil  24  is not energized and the electromagnet block  2  is demagnetized, the movable iron piece  4  is located at the default position at which the to-be-attracted portion  63  is separated from the magnetic pole portion  25  of the iron core  22  because the movable iron piece  4  causes the to-be-attracted portion  63  to turn about the fulcrum supported by the yoke  41  by using the elastic force of the movable contact piece  52 . Therefore, the movable contact  62  maintains the open state in which the movable contact  62  is separated from the fixed contact  57 . 
         [0072]    When the coil  24  is energized and the electromagnet block  2  is excited, the to-be-attracted portion  63  of the movable iron piece  4  is attracted to the magnetic pole portion  25  of the iron core  22  and turns against the biasing force of the movable contact piece  52  as shown in  FIG. 9 . Such an operation allows the movable contact piece  52  to be elastically deformed and allows the movable contact  62  to be in contact with the fixed contact  57  of the fixed contact piece  51 . 
         [0073]    When energizing the coil  24  is stopped and the electromagnet block  2  is demagnetized, the movable iron piece  4  is not attracted by the iron core  22  anymore so that the movable iron piece  4  turns due to the elastomeric force of the movable contact piece  52 . At this time, the second protruding portion  67  formed on the card member  65  of the movable iron piece  4  collides with the elastic contact portion  46  of the hinge spring  44 . The second protruding portion  67  is made of a synthetic resin so that the elastic contact portion  46  is elastically deformed. However, a contact state of the second protruding portion  67  and the elastic contact portion  46  is obtained within a short time after the movable iron piece  4  starts turning. Accordingly, nearly no collision noise is generated. Then, as the movable iron piece  4  turns further, the elastic contact portion  46  is elastically deformed and the first protruding portion  66  made of a synthetic resin comes into contact with the middle portion of the yoke  41 . Accordingly, the turning speed of the movable iron piece  4  is reduced, and this also serves to sufficiently suppress generation of the collision noise. In this way, the movable iron piece  4  smoothly returns to the default position without generating the collision noise and the movable contact  62  is separated from the fixed contact  57  and is positioned at an open position. 
         [0074]    Incidentally, at the time when the contact is opened, an arc might occur between contact points. In this case, the arc-extinguishing member  75  is disposed around a contact switching region, and the extension  59   b  is formed at the upper end of the movable contact piece  52 . For this reason, the generated arc is promptly extinguished. 
         [0075]    That is, the magnetic flux generated from the N pole of each of the permanent magnets  76  runs in a magnetic circuit in which the magnetic flux passes the middle wall  79  via the middle protruding portions  80  of the joint member  77 , and returns to the S pole of each of the permanent magnet  76  from the opposing walls  78 . Each magnetic circuit forms a closed-loop so that nearly zero magnetic flux leaks to surroundings. Moreover, because of the presence of the middle protruding portion  80 , the magnetism can be effectively exerted on the arc generated at the contact switching position, in other words, between the contacts points. As a result, according to the Fleming&#39;s left hand rule, force is exerted on the generated arc in a direction orthogonal to the direction in which the contact is opened, so that this arc is extended over a long distance. In addition, the distal end portion of the extension  59   b  formed at the upper end of the movable contact piece  52  is positioned in the direction in which the arc is extended. Accordingly, the generated arc arrives at the distal end portion of the extension, which is the nearest position over the extension, so that it is promptly extinguished. 
         [0076]    Moreover, an operating voltage of the electromagnet block  2  can be adjusted as follows. 
         [0077]    That is, the operating voltage of the electromagnet block  2  can be controlled by changing the inclination angle of the elastic contact portion  46  of the hinge spring  44 . In greater detail, if the inclination angle of the elastic contact portion  46  with respect to the yoke  41  is increased, the position of an operating point can be changed in accordance with a change in the force (attracting force curve) that exerts on the to-be-attracted portion  63  of the movable iron piece  4  due to the magnetic field generated from the magnetic pole portion  25  of the iron core  22  as shown in the graph of  FIG. 12 . That is, the force needed for a period from the opening of the contacts to the timing at which the elastic contact portion  46  comes into contact with the first protruding portion  66  can be reduced by increasing the inclination angle of the elastic contact portion  46 . Accordingly, the operating voltage of the electromagnet block  2  can be controlled such that the attracting force curve can change in a narrower range than that of  FIG. 12 . 
         [0078]    The present embodiments are not limited to the structures described, and can be modified in various ways. 
         [0079]    In the above embodiment, the extension  59   b  is formed at the upper end of the movable contact piece  52 . However, the extension may be formed at the upper end of the fixed contact piece  51 , or may be formed in both of the movable contact piece  52  and the fixed contact piece  51 . In the case where both of the contact pieces are provided with the extensions, the positional relation between the extensions needs to be sufficiently paid attention to so that the extensions may not be short-circuited. For example, this problem may be addressed by devising the positional relationship between the extensions such that the main body portions are disposed to be misaligned with each other in the lengthwise direction. 
         [0080]    In addition, in the above embodiment, the extension  59   b  is configured to have an angle of 140 degrees with respect to the main body portion  59 , but the angle can be flexibly selectable within a range up to 90 degrees. However, as illustrated in  FIG. 14 , it is most preferable that the angle is about 90 degrees. When the angle is larger than 140 degrees, the dimension of protrusion in the direction perpendicular to the main body portion  59  is relatively large compared with that of the movable contact  62 . Accordingly, the extension  59   b  is excessively long in length. On the other hand, when the angle is smaller than 90 degrees, since the extensions are too much close to the respective contacts, the short-circuited state is likely to occur. Therefore, the angle formed between the main body portion  59  and the extension  59   b  is in a range of 90 to 140 degrees. 
         [0081]    The contact switching mechanism according to the present embodiments can be adopted not only by the electromagnetic relay but also by any electronic device as long as the electronic device includes a mechanism in which contacts open and close like in a switch and an arc occurs between the contacts. 
         [0082]    There has thus been shown and described a novel contact switching mechanism and electromagnetic relay using the same which fulfills all the objects and advantages sought therefor. 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. 
         [0083]    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.