Patent Publication Number: US-7911304-B2

Title: Electromagnetic relay

Description:
TECHNICAL FIELD 
     The present invention relates to an electromagnetic relay and, more particularly, to an electromagnetic relay including erasure means for erasing the arc generated at the time of opening and closing of contact points. 
     BACKGROUND ART 
     Conventionally, as electromagnetic relays including arc erasure means, there have been electromagnetic relays provided with permanent magnets as erasure means. 
     That is, these electromagnetic relays have a solenoid portion  1  having a coil  13  wound around a bobbin  12  which is housed coaxially within a yoke  11  with a cylindrical shape with a ceiling and, further, have a plunger  17  which is reciprocated upwardly and downwardly for opening and closing a contact point (e.g., refer to Patent Document 1). In the electromagnetic relays, in order to erase the generated arc, as illustrated in FIG. 2 in Patent Document 1, two pairs of permanent magnets  7 , each pair having two permanent magnets, are placed in parallel, with movable contact-point carrying members  4  and  6  sandwiched therebetween.
     Patent Document 1: JP-A No. 2001-176370   

     SUMMARY OF THE INVENTION 
     However, the aforementioned electromagnetic relays require a plurality of permanent magnets  7 , which involves a larger number of components and a larger number of assembling processes and, also, requires a larger housing space, and small-sized electromagnetic relays with smaller bottom areas can not be provided. 
     One or more embodiments of the present invention provides a small-sized electromagnetic relay with a small bottom area which requires a small number of components and a small number of assembling processes. 
     An electromagnetic relay according to one or more embodiments of the present invention is an electromagnetic relay including a movable iron core, an insulation holder integrated with the upper end portion of the movable iron core, a movable contact piece supported by the insulation holder, and a solenoid formed from a wound coil, the movable iron core being housed in an axial hole in the solenoid movably in the upward and downward directions, and the movable iron core being adapted to be moved upwardly and downwardly based on the magnetization and demagnetization of the solenoid for contacting and separating a movable contact point provided on the movable contact piece with and from a fixed contact point for opening and closing a contact point, wherein a permanent magnet is embedded in a base portion of the insulation holder. 
     With one or more embodiments of the present invention, it is possible to lead the arc generated at the time of opening and closing the contact point through the magnetic force of the single permanent magnet embedded in the base portion of the insulation holder, thereby erasing the arc. This enables provision of an electromagnetic relay with a small bottom area which requires a small number of components and a small number of assembling processes and can save the space for housing the permanent magnet. 
     In an embodiment according to the present invention, the insulation holder can be formed integrally with a pull-out preventing concave and convex portion formed at the upper end portion of the movable iron core. 
     With the present embodiment, it is possible to provide an electromagnetic relay with excellent durability which can prevent the disengagement of the insulation holder with the pull-out preventing concave and convex portion. 
     In another embodiment according to the present invention, an arc-erasing ceramic member can be placed at least at a portion of the inner side surface of a housing which houses the fixed contact point and the movable contact point and also shields the arc generated at the time of opening and closing of the contact point. 
     With the present embodiment, the ceramic member depletes heat of the arc, which can effectively erase the arc and also can protect the housing from the heat of the arc, thereby offering the advantage of provision of an electromagnetic relay with an increased life. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating a first embodiment of an electromagnetic relay according to the present invention. 
         FIG. 2  is an exploded perspective view of the electromagnetic relay illustrated in  FIG. 1 . 
         FIG. 3  is an exploded perspective view of the electromagnetic-relay main body illustrated in  FIG. 2 . 
         FIG. 4  is an exploded perspective view of an electromagnet unit and a contact-point mechanism unit illustrated in  FIG. 3 . 
         FIG. 5  is an exploded perspective view of the electromagnet unit illustrated in  FIG. 4 . 
         FIG. 6  is an exploded perspective view of the contact-point mechanism unit illustrated in  FIG. 4 . 
         FIG. 7  is a perspective view illustrating the electromagnet unit and the contact-point mechanism unit which are halfway through assembling. 
         FIGS. 8A and 8B  are a side view and a longitudinal cross-sectional view of the electromagnet unit and the contact-point mechanism unit which have been integrated with each other. 
         FIGS. 9A and 9B  are longitudinal cross-sectional views illustrating the electromagnetic relay before and after an operation. 
         FIGS. 10A and 10B  are a perspective view and a cross-sectional view of the contact-point mechanism unit according to the first embodiment. 
         FIGS. 11A ,  11 B and  11 C are a perspective view, a side view and a longitudinal cross-sectional view of a movable contact-point block. 
         FIGS. 12A ,  12 B and  12 C are a processing block diagram, a flow chart and a block diagram illustrating adjustment operations according to the first embodiment. 
         FIGS. 13A and 13B  are longitudinal cross-sectional views for describing adjustment operations. 
         FIGS. 14A and 14B  are longitudinal cross-sectional views for describing adjustment operations subsequent to  FIG. 13 . 
         FIG. 15  is a longitudinal cross-sectional view for describing adjustment operations subsequent to  FIG. 14 . 
         FIGS. 16A ,  16 B and  16 C are a plan view, a longitudinal cross-sectional view and a perspective view which are describing different adjustment operations. 
         FIGS. 17A ,  17 B and  17 C are longitudinal cross-sectional views for describing adjustment operations subsequent to  FIG. 16 . 
         FIGS. 18A and 18B  are a perspective view and a cross-sectional view of a contact-point mechanism unit, illustrating a second embodiment of the electromagnetic relay according to the present invention. 
         FIGS. 19A ,  19 B and  19 C are a perspective view, a side view and a longitudinal cross-sectional view of a movable contact-point block illustrated in  FIG. 18 . 
     
    
    
     EXPLANATION OF SYMBOLS 
     
         
         
           
               10 : Resin case 
               12 : Resin cap 
               13 : Insulation wall 
               20 : Electromagnetic-relay main body 
               21 : Metal case 
               22 : Metal cover 
               23 : Concave portion 
               26 : Gas venting hole 
               27 : Gas venting pipe 
               30 : Electromagnet unit 
               31 : Spool 
               32 ; Winding body portion 
               32   a : Axial hole 
               33 ,  34 : Collar portion 
               35 : Coil 
               36 ,  37 : Pedestal portion 
               38 ,  39 : Relay terminal 
               38   b ,  39   b : Connection portion 
               40 : Yoke 
               41 : Side opening portion 
               43 : Through hole 
               44 : Cutout portion 
               45 : Restoring spring 
               46 ; Fixed iron core 
               47 : Mortar-shaped concave portion 
               50 : Contact-point mechanism unit 
               51 : First base 
               51   b : Adjustment hole 
               52 : Second base 
               53 ,  54 : Plate-shaped permanent magnet 
               55 ,  56 : Fixed contact-point terminal 
               55   a ,  56   a : Fixed contact point 
               57 : Permanent magnet 
               60 : Movable contact-point block 
               61 : Movable iron core 
               62 : Insulation annular holder 
               63 : Contact pressing spring 
               64 : Movable contact piece 
               65 ,  66 : Movable contact point 
               70 : Secondary yoke 
               71 : Tongue piece 
               72 : Annular rib 
               73 : Through hole 
               81 ,  82 ; Coil terminal 
               81   a ,  82   a : Connection portion 
               83 : Insulation cover 
               86 . Gas venting hole 
               87 : Protruding piece 
               90 : Center hole 
               91 : Box-shaped base table 
               92 : Jig pin 
               95 ,  98 : Probe 
               100 : Operational-characteristic adjustment device 
               101 : Control unit 
               102 : Measurement/stroke control unit 
               103 . Iron core fixing unit 
               104 : Characteristic measurement machine 
               105 : Data processing device 
               110 : Dust 
           
         
       
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention will be described with reference to the accompanying drawings in  FIGS. 1 to 19 . 
     According to a first embodiment, as illustrated in  FIGS. 1 to 17 , there is provided an electromagnetic relay including a resin case  10  with a pair of mounting flange portions  11 , an electromagnetic-relay main body  20  which is housed in the resin case  10 , and a resin cap  12  fitted to the resin case  10  and then sealed. On the upper surface of the cap  12 , there is a substantially-cross-shaped insulation wall  13  protruded therefrom. 
     As illustrated in  FIG. 3 , the electromagnetic-relay main body  20  houses an electromagnet unit  30  and a contact-point mechanism unit  50  which are integrated with each other, in a space sealed by a metal case  21  having a cylindrical shape with a bottom and a metal cover  22  which are integrated with each other through welding. The metal cover  22  is made of, for example, Al, Cu, Fe or SUS and is provided with a concave portion  23  formed through presswork and terminal holes  24  and  25  and a gas venting hole  26  provided through the bottom surface of the concave portion  23 . Particularly, in the present embodiment, the concave portion  23  is placed, such that the shortest distances from the outer peripheral surfaces of terminal portions  55   b ,  56   b ,  81   b  and  82   b  which will be described later to the edge portion of the concave portion  23  are substantially equal to one another. This can offer the advantage of alleviation of the concentration of stresses due to thermal stresses on the sealing material for preventing the separation and the like of the sealing material and, also, can offer the advantage of reduction of the amount of the used sealing material. 
     As illustrated in  FIG. 5 , the electromagnet unit  30  is constituted by a spool  31  having collar portions  33  and  34  at its upper and lower portions, a coil  35  wound around a winding body portion  32  of the spool  31 , and a yoke  40  assembled with the spool  31 . The winding body portion  32  is formed to have an elliptical cross-sectional area for increasing the number of windings of the coil  35 . Further, relay-terminal pedestal portions  36  and  37  are protruded from edge portions of the upper surface of the upper collar portion  33  at its opposite sides, such that they are faced to each other. Relay terminals  38  and  39  to be connected to coil terminals  81  and  82  which will be described later are press-fitted in press-fitting slots in the pedestal portions  36  and  37 . Accordingly, binding portions  38   a  and  39   a  and connection portions  38   b  and  39   b  of the relay terminals  38  and  39  are protruded from the pedestal portions  36  and  37 . Further, on the bottom surface of the lower collar portion  34 , there are a pair of positioning ribs  34   a  with a substantially U shape protruded therefrom, for positioning the yoke  40  which will be described later. Further, after the coil  35  is wound around the winding body portion  32  of the spool  31 , the leader lines of the coil  35  are bound and soldered to the binding portions  38   a  and  39   a  of the relay terminals  38  and  39 . Accordingly, the solenoid formed from the coil  35  has a substantially-elliptical cross-sectional area. 
     The yoke  40  is formed from a magnetic material having a cylindrical shape with a bottom and is shaped to have side opening portions  41  and  41  formed by cutting away opposing side portions of the side walls. Further, at the center portion of the bottom surface  42  of the yoke  40 , there is provided a through hole  43  which allows a fixed iron core  46  which will be described later to be press-fitted therein. Further, the yoke  40  is provided, at edge portions of its upper side at the opposite sides, with cutout portions  44  and  44  for securing a plate-shaped secondary yoke  70  which will be described later. 
     The fixed iron core  46  has a cylindrical shape which can be press-fitted in the through hole  43  in the yoke  40  and, also, is provided, in its upper end surface, with a mortar-shaped concave portion  47  which can be fitted to the lower end portion of a movable iron core  61  which will be described later. Further, in the bottom surface of the mortar-shaped concave portion  47 , there is provided a housing hole  48  which can house a restoring spring  45  therein. 
     As illustrated in  FIG. 4 , the contact-point mechanism unit  50  is constituted by two plate-shaped permanent magnets  53  and  54 , a pair of fixed contact-point terminals  55  and  56 , and a movable contact-point block  60 , which are assembled with one another, in an internal space defined by a first base  51  and a second base  52  assembled with each other. Further, a plate-shaped secondary yoke  70  is secured, through caulking, to the bottom surface of the first base  51 . Further, a pair of coil terminals  81  and  82  and an insulation cover  83  are assembled with the outer side surface of the second base  52 . 
     As illustrated in  FIG. 6 , the first base  51  is a resin molded article having plural guide slots which enable assembling, therewith, the fixed contact-point terminals  55  and  56  and the like in the lateral direction and, further, is provided with protrusions  51   a  ( FIG. 8B ) protruded from its bottom surface for securing, through caulking, the secondary yoke  70 . 
     As illustrated in  FIG. 4 , the second base  52  is shaped such that it is assembled with the first base  51  to cover the movable contact-point block  60 , thereby enhancing the insulation property thereof. Further, an adjustment hole  51   b  ( FIG. 6 ) which enables viewing the movable contact-point block  60  from thereabove is formed between the second base  52  and the first base  51 . Further, the second base  52  is adapted to enable the pair of coil terminals  81  and  82  to be mounted to the outer side surface thereof in the lateral direction. 
     The plate-shaped permanent magnets  53  and  54  are for erasing the arc generated at the time of opening and closing of the contact points with magnetic forces generated therefrom, in order to extend the life of the contact points. Further, the permanent magnets  53  and  54  induce dusts caused by the arc not to adhere to the surfaces of the contact points, thereby preventing the occurrence of contact failures. Accordingly, the plate-shaped electromagnets  53  and  54  are press-fitted in the guide slots in the first base  51  and, therefore, are placed in parallel in such a way as to sandwich, therebetween, a movable contact piece  64  which will be described later. 
     As illustrated in  FIG. 6 , the pair of fixed contact-point terminals  55  and  56  have a substantially U shape at their side surfaces and have fixed contact points  55   a  and  56   a  provided on the lower sides of their inner peripheral surfaces and terminal portions  55   b  and  56   b  having female screws provided on the upper sides of their outer peripheral surfaces. 
     As illustrated in  FIGS. 6 and 11 , the movable contact-point block  60  includes an insulation annular holder  62  formed integrally with the upper end portion of the movable iron core  61  and is structured such that the movable contact piece  64  is supported while being downwardly biased by a contact pressing spring  63  within the annular holder  62 . The movable iron core  61  is provided with a narrow neck portion at its upper end portion and, thus, is shaped to reduce the possibility of disengagement of the annular holder  62  therefrom ( FIG. 11 ). Further, the shape of the upper end portion of the movable iron core  61  is not limited to a narrow neck shape and can be also a male screw shape, for example. Further, the movable iron core  61  is provided, in its lower end surface, with a concave portion  61   a  which allows a restoring spring  45  to be fitted therein ( FIG. 11C ). Further, movable contact points  65  and  66  are formed, through protruding processing, on the edge portions of the lower surface of the movable contact piece  64  at its opposite sides. Further, concave and convex portions for preventing disengagement are formed by ejection at a center portion of the movable contact piece  64 . Further, the movable contact-point block  60  is inserted into the first base  51  along a guide slot therein in the lateral direction and is housed therein such that it is slidable in the upward and downward directions. 
     As illustrated in  FIG. 6 , the secondary yoke  70  has a planer shape which can be placed between the pedestal portions  36  and  37  provided on the collar portion  33  of the spool  31  and, also, has, at its opposite end edge portions, extending tongue pieces  71  and  71  which are to be secured to the cutout portion  44  of the yoke  40 . Further, the secondary yoke  70  is provided, at its center portion, with a through hole  73  having an annular rib  72  protruded at its lower opening edge portion. Further, the caulking protrusions  51   a  ( FIG. 8B ) protruded from the bottom surface of the first base  51  are fitted in caulking holes  74  and secured thereto through caulking, so that the secondary yoke  70  is integrated with the first base  51 . 
     As illustrated in  FIG. 4 , the coil terminals  81  and  82  are formed from conductive members which are bent to have a substantially L shape at their side surfaces, and their vertical lower end portions are formed as connection portions  81   a  and  82   a , and terminal portions  81   b  and  82   b  with female threaded portions are secured to the horizontal portions of their upper sides. Further, the coil terminals  81  and  82  are assembled with the outer side surface of the second base in the lateral direction. 
     The insulation cover  83  is for covering the coil terminals  81  and  82  for enhancing the insulation property, as illustrated in  FIG. 4 . Further, the insulation cover  83  is fitted to the second base  52  from thereabove, so that the terminal portions  81   b  and  82   b  of the coil terminals  81  and  82  are protruded through terminal holes  84  and  85  therein. Further, a gas venting hole  86  in the insulation cover  83  is not overlapped with the adjustment hole  51   b , and a protruding piece  87  extending in the lateral direction from the insulation cover  83  covers the adjustment hole  51   b.    
     Next, there will be described an assembling method and an adjustment method according to the present embodiment. 
     At first, the yoke  40  is assembled with the spool  31  around which the coil  35  has been wound, and the yoke  40  is positioned with the pair of substantially-U-shaped protrusions  34   a  protruded from the lower surface of the collar portion  34  of the spool  31 . Thus, the pedestal portions  36  and  37  of the spool  31  are positioned within the ranges of the side opening portions  41  and  41  of the yoke  40 , respectively. Accordingly, the relay terminals  38  and  39  which are press-fitted to the pedestal portions  36  and  37  are positioned within the ranges of the side opening portions  41 , which enables effective utilization of the space, thereby providing an electromagnet unit  30  with a smaller bottom area. Further, the longitudinal axis of the winding body portion  32  of the spool  31  passes through the side opening portions  41  and  41  of the yoke  40 . This offers the advantage of increase of the number of windings of the coil  35  by at least an amount corresponding to the thickness of the yoke  40 . 
     On the other hand, the pair of plate-shaped permanent magnets  53  and  54  are press-fitted to the first base  51 , and the pair of fixed contact-point terminals  55  and  56  are press-fitted thereto in the lateral direction. Further, the movable contact-point block  60  is assembled with the first base  51  and is housed therein slidably in the upward and downward directions and, also, the caulking holes  74  in the secondary yoke  70  are fitted to the caulking protrusions  51   a  on the first base  51 , so that the secondary yoke  70  is secured to the first base  51  through caulking. 
     Further, the tongue pieces  71  and  71  of the secondary yoke  70  which has been secured, through caulking, to the first base  51  are caused to straddle the cutout portions  44  and  44  of the yoke  40  which has been assembled with the spool  31 , and they are secured to each other through caulking, so that the electromagnet unit  30  and the contact-point mechanism unit  50  are integrated with each other. 
     Further, the second base  52  is fitted to the first base  51  and thereafter the coil terminals  81  and  82  are assembled with the second base  52  for bringing the connection portions  81   a  and  82   a  of the coil terminals  81  and  82  into contact with the connection portions  38   b  and  39   b  of the relay terminals  38  and  39  and then they are integrated with each other through welding ( FIG. 8A ). Subsequently, the restoring spring  45  is inserted in the axial hole  32   a  in the winding body portion  32  of the spool  31 , and the fixed iron core  46  is press-fitted in the through hole  43  in the yoke  40  and, thus, the fabrication of an intermediate product is completed. 
     Next, there will be described a method for adjusting an operation characteristic of the intermediate product. 
     Adjustment operations according to the present embodiment are conducted based on procedures illustrated in  FIG. 12A . That is, the intermediate product is adjusted according to an amount of contact-point follow which has been preliminarily set for the intermediate product, then the fixed iron core  46  is secured to the yoke  70  and, thereafter, a characteristic thereof is measured. Further, the result of measurement is fed back to the setting of the amount of contact-point follow to set a new amount of contact-point follow and, thereafter, the same adjustment operations are repeated. 
     The adjustment operations will be described in more detail. As illustrated in  FIGS. 12C and 13A , at first, the intermediate product is housed in a box-shaped base table  91  placed in a measurement/stroke control unit  102  in an operational-characteristic adjustment machine  100 . Further, a jig pin  92  is brought into contact with the bottom surface of the fixed iron core  46  through a center hole  90  provided through the bottom surface of the box-shaped base table  91 , and a pressing plate  94  having a through hole  93  is brought into contact with the upper surface of the intermediate product, so that the intermediate product is sandwiched therebetween. 
     Further, in step S 1 , a probe  95  is downwardly pushed through the adjustment hole  51   b  in the first base  51  and through the through hole  93  in the pressing plate  94  ( FIG. 12B ), which causes the movable contact-point block  60  to descend against the spring force of the restoring spring  45 , thereby bringing the movable iron core  61  into contact with the fixed iron core  46  ( FIG. 13B ). In step S 2 , the probe  95  is further downwardly pushed, which causes the movable contact-point block  60  to descend, thereby bringing the movable contact points  65  and  66  into contact with the fixed contact points  55   a  and  56   a  ( FIG. 14A ). In step S 3 , an amount of contact-point follow is set and, in step S 4 , the probe  95  is downwardly pushed by an amount corresponding to the amount of contact-point follow, which causes the movable iron core  61  of the movable contact-point block  60  to push the fixed iron core  46  downwardly against the spring force of the contact pressing spring  63 , thereby ensuring a predetermined amount of contact-point follow ( FIG. 14B ). Further, in step S 5 , at this state, the fixed iron core  61  is secured to the yoke  40  through welding. Subsequently, in step S 6 , a characteristic measurement machine  104  determines a characteristic of the electromagnetic relay for determining whether it is proper or improper and, if the characteristic is improper, the intermediate produce is extracted from the assembling line. Further, in step S 7 , the amount of contact-point follow is modified based on a data base about characteristics of the electromagnetic relay and amounts of contact-point follow and, then, the processing is returned to step S 3 . On the other hand, if the characteristic is proper, the adjustment operations are completed without setting the amount of contact-point follow, and the probe  95  and the jig pin  92  are removed ( FIG. 15 ) and thereafter subsequent processing is conducted. 
     As a method for modifying the amount of contact-point follow, for example, as illustrated in  FIG. 12C , measurement and detection of a two-stage operating voltage are conducted, using the characteristic measurement machine  104 , for the intermediate product created by integrating, through welding, the fixed iron core  46  and the movable iron core  61 , with an iron core fixing unit  103  in the operational-characteristic adjustment device  100 . Such a two-stage operating voltage is the difference between an operating voltage with which an operation of the movable contact-point block  60  in the intermediate product is started and a complete operating voltage with which the movable iron core  61  is completely sucked by the fixed iron core  46 . Further, based on correlation between past two-stage operating voltages and amounts of contact-point follow, an optimum amount of contact-point follow is calculated by a data processing device  105 , based on the two-stage operating voltage which has been actually detected. Subsequently, the result of the calculation is transmitted to a control unit  101  in the operational-characteristic adjustment device  100 , which modifies the amount of pushing by the probe  95  and the like in the measurement/control-stroke control unit  102 . Accordingly, if the two-stage operating voltage is excessively large, for example, it is considered that the amount of pushing by the probe is excessively large and, therefore, the amount of contact-point follow, namely the amount of pushing by the probe is modified to be reduced, based on the correlation between past two-stage operating voltages and amounts of contact-point follow. 
     Note that the characteristic measurement machine  104  is illustrated at a position distant from the operational-characteristic adjustment device  100 , for ease of description, but it is incorporated in the operational-characteristic adjustment device  100 . 
     With the adjustment operations according to the present embodiment, it is possible to eliminate the variations in the component accuracy and the assembling accuracy through the adjustment operations, thereby offering the advantage of provision of an electromagnetic relay with no variation in operational characteristics and with a higher yield. Further, it is possible to conduct the adjustment operations and the measurement operations continuously in the same step, thereby increasing the operation efficiency. Further, it is possible to feed back the result of measurement of the operational characteristic to a most recent electromagnetic relay, thereby offering the advantage of improvement of the yield. 
     Further, the insulation cover  83  is assembled with the second base  52  in the intermediate product which has been subjected to adjustment operations to cover the coil terminals  81  and  82 . Further, as illustrated in  FIG. 3 , the intermediate product is housed in the metal case  21 , the metal cover  22  is fitted thereto and integrated therewith through welding and, thereafter, a gas venting pipe  27  is inserted through the gas venting hole  26  in the metal cover  22  and the gas venting hole  86  in the insulation cover  83 . Subsequently, a sealing material  28  is injected into the concave portion  23  of the metal cover  22  and is solidified therein for sealing it. Then, internal gas is eliminated, through suction, from the gas venting pipe  27  and thereafter the gas venting pipe  27  is thermally sealed and thus the fabrication of the electromagnetic-relay main body  20  is completed. 
     Subsequently, as illustrated in  FIG. 2 , the electromagnetic-relay main body  20  is housed within the resin case  10  and the resin cap  12  is fitted thereto to complete the assembling operations of the electromagnetic relay. 
     Operational characteristics according to the present embodiment will be described. 
     When no voltage is applied to the coil  35 , the movable contact-point block  60  is pushed upwardly by the spring force of the restoring spring  45 , as illustrated in  FIG. 9A . Accordingly, the movable contact points  65  and  66  are separated from the fixed contact points  55   a  and  56   a.    
     Subsequently, if a voltage is applied to the coil  35 , as illustrated in  FIG. 9B , this causes the fixed iron core  46  to suck the movable iron core  61  in the movable contact-point block  60 , thereby causing the movable contact-point block  60  to descend against the spring force of the restoring spring  45 . Then, after the movable contact points  65  and  66  come into contact with the fixed contact points  55   a  and  56   a , the movable iron core  61  is further sucked. This causes the annular holder  62  to descend against the spring force of the contact pressing spring  63  and, also, causes the movable contact points  65  and  66  to be press-contacted with the fixed contact points  55   a  and  56   a  with a predetermined contact-point pressure. Thereafter, the movable iron core  61  is sucked by the fixed iron core  46 . 
     Further, if the application of the voltage to the coil  35  is stopped, this causes the movable iron core  61  to be pushed upwardly by the spring forces of the restoring spring  45  and the contact pressing spring  63 , which separates the movable iron core  61  from the fixed iron core  46  and then restores the contact pressing spring  63  to the original shape, thereby separating the movable contact points  65  and  66  from the fixed contact points  55   a  and  56   a  to cause restoration to the original state. 
     In the present embodiment, even if an arc is generated at the time of opening and closing of the contact points, as illustrated in  FIG. 10 , the arc is drawn in the outward direction (in the upward and downward directions in  FIG. 10B ) to be erased, due to the magnetic forces (Lorentz forces) of the magnetic fields generated from the pair of plate-shaped permanent magnets  53  and  54  which are press-fitted to the first base  51 . This reduces the possibility of the occurrence of welding of the contact points. Further, dusts and the like induced by the occurrence of the arc are also led to positions distant from the fixed contact points  55   a  and  56   a , which reduces the possibility of adhesion of them to the surfaces of the contact points, thereby reducing the possibility of the occurrence of contact failures. This can offer the advantage of provision of an electromagnetic relay having contact points with an increased life and with higher contact reliability. Also, heat-resistant ceramics can be placed at predetermined positions on the inner side surfaces of the first and second bases  51  and  52 . This is because the ceramics placed therein can absorb the heat of the generated arc, which is effective in erasing the arc, and, also, can protect the first base  51  and the like from the arc. 
     As the adjustment method, there have been described the adjustment operations after the secondary yoke  70  is secured to the yoke  40 , but the adjustment method is not necessarily limited thereto and can be other adjustment methods. 
     For example, as illustrated in  FIGS. 16 and 17 , an intermediate product created by preliminarily securing the fixed iron core  46  to the yoke  40  though caulking, welding or the like without securing the secondary yoke  70  to the yoke  40  is mounted to a box-shaped base table  96  ( FIGS. 16B and 17A ), and a pushing jig  99  is brought into contact with the yoke  40 . Further, the movable contact-point block  60  is pushed upwardly by a probe  98  through an adjustment hole  97  in the box-shaped base table  96 , which brings the movable contact points  65  and  66  into contact with the fixed contact points  55   a  and  56   a . Further, in order to ensure a predetermined amount of contact-point follow, the probe  98  is pushed thereinto against the spring force of the contact pressing spring  63  and then is stopped ( FIG. 17B ). Then, the pushing jig  99  is descended to push in the yoke  40  and, at the time when the fixed iron core  46  comes into contact with the movable iron core  61 , the pushing jig  99  is stopped. At this state, the tongue pieces  71  of the secondary yoke  70  are secured to the cutout portions  44  of the yoke  40  through welding or the like ( FIG. 16C ) to complete the adjustment operations. After the adjustments, measurement of a characteristic is conducted, and the result of measurement is fed back for modifying the amount of contact-point follow, which is the same as in the above adjustment system. 
     According to the present embodiment, the tongue pieces  71  of the secondary yoke  70  can be secured to the cutout portions  44  of the yoke  40 , which facilitates the securing operations and also offers a wide variety of options of adjustment methods, thereby offering the advantage of increase of the operation efficiency. 
     A second embodiment is a case where a permanent magnet  57  is press-fitted in and held by a movable block  60 , as illustrated in  FIGS. 18 and 19 . That is, the permanent magnet  57  is press-fitted in and held by a concave portion  67  provided in the base portion of an insulation annular holder  62 . In the present embodiment, the movable block  60  has such an outer shape as to allow it to be replaced with the movable contact-point block  60  according to the first embodiment. Further, similarly to in the first embodiment, the heat-resistant ceramics can be placed at predetermined positions, as a matter of course. 
     With the present embodiment, it is possible to erase the arc generated at the time of opening and closing of the contact points through the magnetic force (Lorentz force) of the magnetic field generated from the permanent magnet  57  and, also, it is possible to lead dusts  110  induced by the occurrence of the arc to positions distant from the surfaces of the fixed contact points  55   a  and  56   a , as illustrated in  FIG. 18B . This reduces the possibility of adhesion of the dusts  110  to the surfaces of the contact points, thereby reducing the possibility of the occurrence of contact failures. Further, the number of components and the number of assembling processes can be reduced, which can increase the production efficiency and also can save the space, thereby offering the advantage of provision of an electromagnetic relay with a further reduced size. 
     INDUSTRIAL APPLICABILITY 
     One or more embodiments of the present invention can be also applied to other opening/closing devices such as switches, timers and the like, as well as electromagnetic relays for shutting off direct currents or for shutting off alternating currents as a matter of course.