Patent Publication Number: US-10332709-B2

Title: Electromagnetic relay

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Phase Application under 35 U.S.C. 371 of International Application No. PCT/JP2015/003955 filed on Aug. 6, 2015 and published in Japanese as WO 2016/047020 A1 on Mar. 31, 2016. This application is based on and claims the benefit of priority from Japanese Patent Application No. 2014-195400 filed on Sep. 25, 2014. The entire disclosures of all of the above applications are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to an electromagnetic relay opening or closing an electric circuit by causing a movable contact and a stationary contact to come into or out of contact with each other. 
     BACKGROUND ART 
     In a conventional electromagnetic relay, two stationary terminals having a stationary contact are positioned and fixed, and an electric circuit is opened or closed by moving a movable element having a movable contact such that the movable contact and the stationary contact come into or out of contact with each other. 
     An electromagnetic repulsion force (hereinafter, this electromagnetic force is referred to as a contact point electromagnetic repulsion force) is generated at a contact point of the movable contact and the stationary contact by an electric current flowing in a reverse direction in a part where the movable contact and the stationary contact face each other. The contact point electromagnetic repulsion force works such that the movable contact and the stationary contact are separated from each other. 
     As shown in  FIG. 8 , a movable yoke  93  and a stationary yoke  94  is attached to a shaft  92  which is integrated with a movable core  90  and attached to a movable element  91 , the movable element  91  being interposed between the movable yoke  93  and the stationary yoke  94 , and a yoke attraction force is generated between the movable yoke  93  and the stationary yoke  94  by a magnetic flux flowing in the movable yoke  93  and the stationary yoke  94  when the movable element  91  and a stationary terminal  95  contact to each other. The movable yoke  93  pushes the movable element  91  to the stationary terminal  95  so as to limit a separation of the contacts caused by the contact point electromagnetic repulsion force (for example, refer to Patent Document 1). 
     The movable yoke  93  is slidably attached to the shaft  92 , and the stationary yoke  94  is fixed to the shaft  92 . The movable element  91  and the movable yoke  93  are urged toward the stationary yoke  94  and the stationary terminal  95  by a pressure contact spring  96  attached to the shaft  92 . The movable core  90  is attracted toward a stationary core  98  by an electromagnetic attraction force generated when the excitation coil  97  is energized. 
     When only the yoke attraction force is increased without increasing the electromagnetic attraction force in order to limit the separation caused by the contact point electromagnetic repulsion force even in a short circuit in which large amount of electric current flows, a phenomenon described below may occur. 
     After the movable yoke  93  is pushed the movable element  91  to the stationary terminal  95  (a situation shown in  FIG. 8 ), the stationary yoke  94  is attracted toward the movable yoke  93  by the yoke attraction force, and the movable core  90  and the shaft  92  integrated with the stationary yoke  94  are urged in a direction opposite from the attraction force caused by the electromagnetic attraction force. 
     When the yoke attraction force is larger than the electromagnetic force, the movable core  90  moves apart from the stationary core  98 , and accordingly the electromagnetic attraction force decreases. As a result, the contacts may be separated from each other. 
     When the electromagnetic force is also increased and set to be larger than the yoke attraction force, the above-described phenomenon does not occur. However, in this case, the excitation coil  97  may be large in size in order to increase the electromagnetic attraction force. 
     On the other hand, Patent Document 2 discloses an electromagnetic relay in which a stationary yoke is fixed to a casing. According to this, since the stationary yoke is immovable, the stationary yoke is not attracted toward the movable yoke by a yoke attraction force after the movable yoke pushes the movable element to a stationary terminal, and accordingly a separation of contacts can be limited. 
     However, a contact room in which the movable element and the stationary terminal are provided becomes high temperature by a heat generated by an electric current during energization or an electric arc during not energization. Since the stationary yoke is located in the contact room in the conventional electromagnetic relay disclosed in Patent Document 2, a contact point of the stationary yoke and the casing may become high temperature, and accordingly a boning power may be likely to be insufficient when the stationary yoke and the casing are bonded by a bonding agent or an adhesion tape. 
     Accordingly, brazing or welding is selected as a method for bonding the stationary yoke and the casing, but in this case, a positioning of the stationary yoke to the casing may be not easy. 
     Moreover, a resin material used for securing insulation may not resist heat of brazing. 
     PRIOR ART DOCUMENT 
     Patent Document 
     Patent Document 1: Japanese Patent No. 2010-10056 A 
     Patent Document 2: Japanese Patent No. 2012-104356 A 
     SUMMARY OF THE INVENTION 
     It is an objective of the present disclosure to provide a configuration of an electromagnetic relay in which a separation of contacts caused by a contact point electromagnetic repulsion force is limited by a yoke attraction force generated between a movable yoke and a stationary yoke, the configuration being capable of avoiding an inadequacy of a bonding power between the stationary yoke and a fixed member. Further, it is another objective to provide a configuration of the above-described electromagnetic relay capable of facilitating a positioning of the stationary yoke to the fixed member or securing an electrical insulation between a stationary terminal and the stationary yoke. 
     Moreover, it is another objective to provide an electromagnetic relay in which flexibility in selecting a material of a base or flexibility in design of the base around the stationary yoke can be increased. 
     An electromagnetic relay according to an aspect of the present disclosure includes: an excitation coil generating a magnetic field during energization; a movable core driven by the magnetic field generated by the excitation coil; a movable element including a movable contact and moving to follow the driven movable core; a plurality of stationary terminals each of which includes a stationary contact that contacts the movable contact during the energization of the excitation coil; a base including an electrical insulating resin holding the plurality of stationary terminals; a stationary yoke formed of a magnetic material and supported by at least one of the plurality of stationary terminals; and a movable yoke formed of a magnetic material and arranged to face the stationary yoke, the movable yoke being in contact with the movable element and moving together with the movable element. 
     According to the above-described configuration, an inadequacy of a bonding force between the stationary yoke and a fixed member can be avoided in the electromagnetic relay in which a separation of contacts caused by a contact point electromagnetic repulsion force is limited by a yoke attraction force generated between the movable yoke and the stationary yoke. Moreover, in the above-described electromagnetic relay, positioning of the stationary yoke to the fixed member can be facilitated, and an electrical insulation between the stationary terminal and the stationary yoke can be secured. 
     Since the stationary yoke is supported by the stationary terminal, the stationary yoke is capable of absorbing a heat generated in the stationary terminal. Accordingly, increase in temperature of the stationary terminal can be limited, and a heat resistant property required as a resign material that is used as a material of the base can be decreased. Therefore, flexibility in selection of the material of the base can be increased. 
     Moreover, when the stationary yoke is supported by the stationary terminal, the stationary yoke is needless to be embedded in or fixed to the base, and accordingly flexibility in design of the base around the stationary yoke. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional diagram illustrating an electromagnetic relay in a condition where an excitation coil is not energized, according to a first embodiment of the present disclosure. 
         FIG. 2  is a sectional diagram illustrating the electromagnetic relay in a condition where the excitation coil is energized, according to the first embodiment. 
         FIG. 3  is an exploded view of the electromagnetic relay according to the first embodiment. 
         FIG. 4A  is a plan view illustrating a positional relationship between a movable yoke and stationary yokes of the electromagnetic relay according to the first embodiment. 
         FIG. 4B  is a plan view illustrating the movable yoke of the electromagnetic relay of the first embodiment. 
         FIG. 4C  is a plan view illustrating the stationary yoke of the electromagnetic relay of the first embodiment. 
         FIG. 5  is a schematic sectional diagram illustrating a part of an electromagnetic relay according to a modification of the first embodiment. 
         FIG. 6  is a sectional diagram illustrating an electromagnetic relay according to a second embodiment of the present disclosure. 
         FIG. 7  is an exploded view of the electromagnetic relay according to the second embodiment. 
         FIG. 8  is a schematic sectional diagram illustrating a conventional electromagnetic relay. 
         FIG. 9  is a schematic sectional diagram illustrating the conventional electromagnetic relay in a condition where an excitation coil is not energized. 
     
    
    
     EMBODIMENTS FOR EXPLOITATION OF THE INVENTION 
     Inventors of the present disclosure had already filed an application about a configuration which is capable of avoiding an inadequacy of a bonding force between a stationary yoke and a fixed member, facilitating positioning of the stationary yoke to the fixed member, or securing an electrical insulation between a stationary terminal and the stationary yoke in an electromagnetic relay in which a separation of contacts caused by a contact point electromagnetic repulsion force is limited by a yoke attraction force generated between a movable yoke and the stationary yoke (refer to JP 2013-056806 A). 
     Specifically, in order to limit the separation of contacts caused by the contact point electromagnetic repulsion force, the movable yoke is provided on a side of a movable element having a movable contact, and the stationary yoke is embedded in a base in which the stationary terminal having a stationary contact is held. According to this configuration, when an electric current flows in the movable element by connecting the movable contact and the stationary contact, a magnetic flux flows in the movable yoke and the stationary yoke, and accordingly a yoke attraction force is generated between the movable yoke and the stationary yoke. Since the movable yoke urges the movable element toward the stationary terminal by the yoke attraction force, the separation of contacts caused by the contact point electromagnetic repulsion force is limited. 
     However, since the stationary terminal is heated and becomes to be high temperature during an energization, it is necessary that a resin material capable of resisting the high temperature is selected, and accordingly flexibility in selection of material of the base that is formed of resin holding the stationary terminal may be decreased. Especially, since the above-described electromagnetic relay has a configuration in which the stationary yoke is fixed by the base, the stationary yoke is necessary to be embedded in or bonded to the base. Accordingly, it is necessary to secure a strength of the base, and flexibility in design of the base around the stationary yoke may be decreased. 
     Hereinafter, multiple embodiments for implementing the present invention will be described referring to drawings. In the respective embodiments, a part that corresponds to a matter described in a preceding embodiment may be assigned the same reference numeral, and redundant explanation for the part may be omitted. When only a part of a configuration is described in an embodiment, another preceding embodiment may be applied to the other parts of the configuration. The parts may be combined even if it is not explicitly described that the parts can be combined. The embodiments may be partially combined even if it is not explicitly described that the embodiments can be combined, provided there is no harm in the combination. 
     First Embodiment 
     A first embodiment of the present disclosure will be described below. As shown in  FIGS. 1 to 4C , an excitation coil  12  having a circular cylindrical shape and generating a magnetic field during an energization is disposed in a casing  11  made of resin. A stationary core  13  made of magnetic metal material is located in a hole provided in a center part of the excitation coil  12  in a radial direction. The stationary core  13  includes a core axis portion  131  having a circular column shape and being inserted into the center hole of the excitation coil  12 , and a core flange portion  132  positioned outside the excitation coil  12  and having a circular column shape whose diameter is larger than a diameter of the core axis portion  131 . 
     An outer circumference side and one end in an axial direction of the excitation coil  12  are surrounded by a second plate member  14 , the second plate member  14  being a plate member made of magnetic metal material and being bent into an approximately U-shape. 
     The other side of the excitation coil  12  in the axial direction is surrounded by a first plate member  15 , the first plate member  15  having a rectangular plate shape and made of magnetic metal material. The first plate member  15  faces a movable core  16  that is described below. 
     A yoke hole  151  extending through a center part of the first plate member  15  is provided, and the core flange portion  132  is provided in the yoke hole  151 . The stationary core  13  and the second plate member  14  are joined to each other, and the second plate member  14  and the first plate member  15  are joined to each other. 
     In a position facing the core flange portion  132  and the first plate member  15 , the movable core  16  having a plate shape and made of magnetic metal material is provided. The stationary core  13 , the second plate member  14 , the first plate member  15 , and the movable core  16  make a magnetic circuit of a magnetic flux induced by the excitation coil  12 . 
     Between the excitation coil  12  and the movable core  16 , a return spring  17  urging the movable core  16  so as to depart from the stationary core  13  is provided. The movable core  16  is attracted to the stationary core  13  by an electromagnetic attraction force against the urging force of the return spring  17  when the excitation coil  12  is energized. 
     A shaft  18  made of metal is joined to the movable core  16 . In more detail, the shaft  18  is inserted into a movable plate hole  161  provided in a center part of the movable core  16 , and a shaft flange portion  181  provided on one end of the shaft  18  and a first retaining ring  19  engaged with the shaft  18  cause the movable core  16  and the shaft  18  to be joined to each other. 
     The movable core  16  and the shaft  18  are joined to each other across a predetermined clearance so as to be capable of moving relatively in a radial direction and an axial direction of the shaft  18 . Because the clearance is provided, the movable core  16  is capable of surely contacting the first plate member  15  and the core flange portion  132  when the movable core  16  is attracted toward the stationary core  13 . 
     A middle part of the shaft  18  is slidably inserted into a base  20  made of electrical insulating resin. A second retaining ring  21  is engaged with a part of the shaft  18  protruding from the base  20 . A movable element  22 , which is made of conductive metal and having a plate shape, and a movable yoke  30 , which is made of a magnetic metal material and having a plate shape, are slidably attached to the part of the shaft  18  protruding from the base  20 . 
     Two movable contacts  25  made of conductive metal are swaged and fixed to the movable element  22 . The movable yoke  30  contacts the movable element  22  and moves together with the movable element  22 . 
     A pressure contact spring  24  urging the movable element  22  and the movable yoke  30  toward the stationary core  13  (in other words, toward the second retaining ring  21 ) is provided between a third retaining ring  23  engaged with the other end of the shaft  18  and the movable yoke  30 . 
     It is preferable to interpose an electrical insulating object between the pressure contact spring  24  and the movable yoke  30 . The pressure contact spring  24  may push the movable element  22  in which the movable yoke  30  is fixed. 
     A first stationary contact  27  made of conductive metal is swaged and fixed to a first stationary terminal  26  that is made of conductive metal and has a plate shape. A second stationary contact  29  made of conductive metal is swaged and fixed to a second stationary terminal  28  that is made of conductive metal and has a plate shape. 
     The first stationary contact  27  is positioned to face one movable contact  25 , and the second stationary contact  29  is positioned to face the other movable contact  25 . 
     The movable element  22  and the movable contact  25  move to follow the movable core  16 . Accordingly, the movable contacts  25  come into and out of contact with the first stationary contact  27  and the second stationary contact  29 , and thus, the first stationary contact  27  and the second stationary contact  29  are electrically connected or shut off with each other. 
     A stationary yoke  31  is supported by and joined with the first stationary terminal  26  and the second stationary terminal  28  respectively. The stationary yokes  31  are plate members made of magnetic metal and are supported by welded, bonded, swaged or engaged with surfaces of the first stationary terminal  26  and the second stationary terminal  28  that is an opposite side facing the movable element  22 . The stationary yokes  31  may be directly supported by the first and second stationary terminals  26 ,  28 . 
     The base  20  includes a base plate portion  201  having a flat plate shape, a first holding plate portion  202  vertical to the base plate portion  201  into which the shaft  18  is inserted, and a second holding plate portion  203  extending along a direction in which the movable core  16  moves, as shown in  FIG. 3 . A groove  205  into which an edge portion of the second plate member  14  is inserted is provided in the second holding plate portion  203 . 
     The first stationary terminal  26  and the second stationary terminal  28  are held by and fixed to a surface of the first holding plate portion  202 , and the stationary yoke  31  is supported by the surface of the first holding plate portion  202 . The stationary yoke  31  is embedded in the first holding plate portion  202  in the present embodiment, but the stationary yoke  31  is not necessarily needed to embedded in the first holding plate portion  202  because the stationary yoke  31  is held by and fixed to the base  20  by fixing the first stationary terminal  26  and the second stationary terminal  28 . The stationary terminals  26 ,  28  may be provided between the movable core  16  and the movable element  22 . 
     The edge portion of the second plate member  14  is press-fitted and fixed to the groove  205 , and accordingly, the second plate member  14  is integrally mounted to the base  20 . 
     Next, the movable yoke  30  and the stationary yoke  31  are described in detail. When the excitation coil  12  is energized, the movable core  16  is attracted to the stationary core  13  by an electromagnetic attraction force, and accordingly the movable element  22  follows the movable core  16  and moves in a direction represented by an arrow A. In the description below, the direction A in which the movable element  22  moves when the excitation coil  12  is energized is referred to as a contact movement direction A. An opposite direction from the contact movement direction A is referred to as a separation movement direction. 
     The stationary yoke  31  is configured from a plate member having a cuboid shape, for example, a first stationary yoke  31 A is supported by the first stationary terminal  26 , and a second stationary yoke  31 B is supported by the second stationary terminal  28 . The first and second stationary yokes  31 A,  31 B are spaced a predetermined distance apart, and the shaft  18  is inserted therebetween. In the present embodiment, the first and second stationary yokes  31 A,  31 B are the same in size, but it is not necessarily needed to have the same size. When both the first stationary terminal  26  and the second stationary terminal  28  are provided, the first and second stationary yokes  31 A,  31 B can be provided respectively for each stationary terminal. 
     The stationary yoke  31  is positioned on a contact movement direction A side of the movable element  22 , and at least a part of the stationary yoke  31  protrudes into a space between the first stationary terminal  26  and the second stationary terminal  28  when it is viewed along the contact movement direction A. 
     The movable yoke  30  is a plate member having a cuboid shape, for example, and a through hole  301  into which the shaft  18  is inserted is provided in a center part of the movable yoke  30 . The movable yoke  30  is positioned on a movable element  22  side of the stationary yoke  31 , and in more detail, the movable yoke  30  is positioned on an opposite side of the movable element  22  from the stationary yoke (in other words, on a separation movement direction side). 
     As shown in  FIG. 4A , the movable yoke  30  and the stationary yoke  31  are arranged so as to overlap (in other words, face) each other when they are viewed along the contact movement direction A. 
     Next, actuations of the electromagnetic relay according to the present embodiment will be described below. 
     First, when the excitation coil  12  is energized, the movable core  16  is attracted toward the stationary core  13  by the electromagnetic attraction force against the return spring  17 , and the shaft  18  and the movable element  22  follows the movable core  16  and moves in the contact movement direction A. Accordingly, the movable contact  25  comes into contact with the first stationary contact  27  and the second stationary contact  29 , and the first stationary contact  27  and the second stationary contact  29  are electrically connected with each other (refer to  FIG. 2 ). 
     Since an electric current caused by the connection between the first stationary contact  27  and the second stationary contact  29  flows in the movable element  22 , a magnetic flux flows in the movable yoke  30  and the stationary yoke  31 , and accordingly a yoke attraction force is generated between the movable yoke  30  and the stationary yoke  31 . The movable yoke  30  urges the movable element  22  toward the first stationary terminal  26  and the second stationary terminal  28  by the yoke attraction force. Therefore, a breaking contact caused by a contact point electromagnetic repulsion force is limited by the yoke attraction force. 
     Since the stationary yoke  31  is not fixed to the shaft  18  and is immovable, the shaft  18 , the movable element  22  and the movable core  16  is not urged in the separation movement direction by the stationary yoke  31 . Accordingly, a reduction of the electromagnetic attraction force caused by a movement of the movable core  16  in a direction apart from the stationary core  13  is limited. Therefore, it is not needed to increase the electromagnetic attraction force by using a big excitation coil  12 . 
     On the other hand, when the energization of the excitation coil  12  is stopped, the movable core  16 , the shaft  18 , and the movable element  22  are driven in the separation movement direction by the return spring  17 . Therefore, the movable contact  25  is separated from the first stationary contact  27  and the second stationary contact  29 , and the first stationary contact  27  and the second stationary contact  29  are electrically separated (refer to  FIG. 1 ). 
     Since the yoke attraction force works against the return spring  17 , the yoke attraction force affects a property of the electromagnetic relay when the electric current is stopped. Therefore, the yoke attraction force when the electric current is stopped is preferred to be adequately smaller than a spring force of the return spring  17 . 
     According to the present embodiment, even when a large amount of electric current flows in short circuit, a separation of contacts caused by a contact point electromagnetic repulsion force can be surely limited without upsizing the excitation coil  12 . 
     Since the stationary yoke  31  is supported by the first stationary terminal  26  and the second stationary terminal  28 , a heat capacity of the stationary yoke  31  can be added to a heat capacity of the first stationary terminal  26  and the second stationary terminal  28  when they generate heat. Therefore, an increase of a temperature of the first stationary terminal  26  and the second stationary terminal  28  can be limited, and accordingly a heat resistant property required as a resin material that is a material of the base  20  can be decreased. Therefore, flexibility in selecting the material of the base  20  can be increased. 
     Moreover, since the stationary yoke  31  is supported by the first stationary terminal  26  and the second stationary terminal  28 , it is not needed that the stationary yoke  31  is embedded in or bonded to the base  20 , and accordingly flexibility in design of the base around the stationary yoke  31  can be increased. 
     Since the yoke attraction force is generated in a vicinity of an area where a contact point electromagnetic repulsion force is generated, a separation of contacts caused by a contact point electromagnetic repulsion force can be surely limited even when a spring load is not evenly put on both contacts. 
     Further, the stationary yoke  31  is positioned in a dead space between the first stationary terminal  26  and the second stationary terminal  28 , the electromagnetic relay can be downsized. 
     When the stationary yoke  31  is disposed inside the base  20  made of electrical insulating resin, an electrical insulating condition between the first stationary terminal  26  and the stationary yoke  31  and between the second stationary terminal  28  and the stationary yoke  31  can be secured. Moreover, a facing area in which the stationary yoke  31  and the movable yoke  30  face each other also can be increased, and the yoke attraction force increase, and accordingly a separation of the contacts caused by a contact point electromagnetic repulsion force can be further surely limited. 
     The movable yoke  30  and the stationary yoke  31  may be modified as a modification shown in  FIG. 5 , for example. 
     In the modification shown in  FIG. 5 , the movable yoke  30  is positioned on a stationary yoke  31  side (in other words, a contact movement direction A side) of the movable element  22 . In this case, the movable yoke  30  is joined to the movable element  22  by bonding, swaging or the like. 
     Since the stationary yoke  31  and the movable yoke  30  are close to each other so as to increase the yoke attraction force, a separation of the contacts caused by a contact point electromagnetic repulsion force can be surely limited. 
     Second Embodiment 
     A second embodiment of the present disclosure is described below. In this embodiment, configurations of a first stationary contact  27  and a stationary yoke  31  are changed from the first embodiment, and the other configurations are the same as the first embodiment. Accordingly, only the parts different from the first embodiment are described below. 
     As shown in  FIG. 6 , in the present embodiment, the stationary yoke  31  supported by a second stationary terminal  28  which is provided in the first embodiment is not provided, and only the stationary yoke  31  supported by a first stationary terminal  26  is provided. Since a cross section shown in  FIG. 6  is a cross section including a through hole  301  into which a shaft  18  is inserted, the stationary yoke  31  is separated. However, the stationary yoke  31  is continuous in another cross section. Since the stationary yoke  31  is provided on only one side of two stationary terminals and faces a movable yoke  30  on both sides of the shaft  18 , a yoke attraction force generated is balanced. 
     As shown in  FIG. 7 , two second stationary contacts  29  are provided in the second stationary terminal  28 , and one first stationary contact  27  is provided in the first stationary terminal  26 . An electromagnetic relay according to the present embodiment is configured from the above-described configuration. 
     When the first and second stationary terminals  26 ,  28  are heated during an energization, an electric current concentrates on the terminal having a smaller number of the stationary contact, and accordingly the first stationary terminal  26  having only one first stationary contact  27  is likely to be high temperature compared to the second stationary terminal  28  having two second stationary contacts  29 . Accordingly, in the present embodiment, since the stationary yoke  31  is provided only on the first stationary terminal  26  side that is likely to be high temperature, increase in a temperature of the first stationary terminal  26  can be limited by increasing a heat capacity. 
     Accordingly, the same effects as the first embodiment can be obtained from the configuration in which the stationary yoke  31  is provided only in one of the first and second stationary terminals  26 ,  28 . Since the stationary yoke  31  is provided only on the first stationary terminal  26  side, a number of components can be reduced. 
     The present disclosure is not limited to the above-described embodiments and can be modified as described below as long as it does not depart from the spirit of the present disclosure. 
     In the above-described embodiment, the first stationary contact  27  is swaged to the first stationary terminal  26  that is a different component than the first stationary contact  27 , and the second stationary contact  29  is swaged to the second stationary terminal  28  that is another component. However, a protrusion portion protruding toward the movable element  22  may be provided by stamping, and the protrusion portion may be used as the stationary contact. The stationary contacts  27 ,  29  may be seamlessly integrated with the stationary terminals  26 ,  28 . 
     In the above-described embodiment, the movable contact  25  is swaged to the movable element  22  that is a different component than the movable contact  25 . However, a protrusion portion protruding toward the first stationary terminal  26  and the second stationary terminal  28  may be provided by stamping, and the protrusion portion may be used as the movable contact. The movable contact  25  may be seamlessly integrated with the movable element. 
     In the first embodiment, the movable yoke  30  is provided as a single component having the through hole  301  in its center part, but the movable yoke  30  may be provided as two components arranged to face the first and second stationary contact  27 ,  29  respectively. 
     The present disclosure is not limited to the above described embodiments and can be arbitrarily modified. 
     In the above-described embodiments, it is needless to say that components of the embodiments are not essential excepting a case where the component is apparently essential in principle or it is explicitly described to be essential. 
     In the above-described embodiments, when the number, numerical value, quantity, numerical ranges, etc. of components are mentioned, it is not intended to be limited to the particular number excepting a case where the component is apparently limited to the particular number in principle or it is explicitly described to be essential. 
     Although the present disclosure is described in connection with the embodiments, the present disclosure is not limited to the embodiments of its configurations. The present disclosure includes various modifications or changes within its equivalence. Moreover, various combinations of embodiments.