Abstract:
It is to provide an electromagnetic relay that can perform the return operation of a movable iron piece quickly, free from a fear of welding the contact. In the electromagnetic relay, an iron core is penetrated through a through hole formed on the bottom surface of the aluminum case and coil is wound around the shaft of the protruding iron core. Through applying a voltage to the coil for magnetization and stopping the voltage for demagnetization, a contact mechanism is driven with a movable iron piece that is going and returning, attracted by and separated from a magnetic pole portion of the iron core. In particular, a slit for preventing generation of eddy current is provided on the opening end of the through hole.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an electromagnetic relay.  
         [0003]     2. Description of the Related Art  
         [0004]     As the electromagnetic relay for shutting off direct currents, there has been a hermetically sealed relay, for example, disclosed in Japanese Patent Article 1.  
         [0005]     Specifically, a plunger 9 contacts with or separates from a core center 4 according to magnetization or demagnetization of a coil 26 within a hollow cavity 40, and an armature assembly 8 and an armature shaft 10 integrated with the plunger 9 slide in a direction of the shaft, so that a movable contact disk 21 contacts with or separates from fixed contacts 22 and 22. 
        [Patent Article 1] International Patent Publication No. 510040/1997        
 
         [0007]     In the above-mentioned hermetically sealed relay, however, after a voltage is applied to the coil 26 so to excite it, when the voltage stops in order to return the plunger 9, the eddy currents generated according to a change of the magnetic flux flow into the core center 4 to produce a new magnetic flux, which inhibits the return operation of the plunger 9. According to this, since the armature shaft 10 and the movable contact disk 21 cannot move away from the fixed contacts 22 and 22 quickly and the arc keeps for a while, there is a fear of damaging the contacts and there is a problem that a desired switching characteristic cannot be obtained.  
         [0008]     Taking the above problem into consideration, the invention is to provide an electromagnetic relay that can perform a quick return operation of a movable iron piece free from a fear of welding the contacts by preventing the generation of magnetic flux due to the eddy currents.  
       SUMMARY OF THE INENTION  
       [0009]     In order to achieve the above object, the electromagnetic relay according to the invention is designed in that an iron core is penetrated through a through hole provided on a metal case, a coil is wound around a protruding shaft, and a voltage is applied to the coil for magnetization and stopped for demagnetization, hence to drive a contact mechanism with a movable iron piece that is going and returning, attracted by and separated from a magnetic pole portion of the iron core, and eddy current generation preventing means for preventing generation of eddy current is provided on the opening end of the through hole formed on the metal case.  
         [0010]     According to the invention, thanks to the eddy current generation preventing means provided on the opening end of the through hole of the metal case, no eddy current flows around the iron core and a new magnetic flux that disturbs the return operation of the movable iron piece does not occur. Therefore, since the movable iron piece can be quickly separated from the magnetic pole portion of the iron core and the arc can be quickly cut, it is possible to restrain the damage of the contact and to obtain a desired switching characteristic.  
         [0011]     As the embodiment, the eddy current generation preventing means may be at least one slit or at least one thin portion provided on the opening end of the through hole.  
         [0012]     According to the embodiment, thanks to the slit or the thin portion, since the electrical resistance increases, no eddy current flows or eddy current is difficult to flow and a magnetic flux caused by the eddy current does not occur. Therefore, a desired switching characteristic can be obtained without disturbing the return operation of the movable iron piece.  
         [0013]     An electromagnetic relay according to another invention is designed in that an iron core is penetrated through a through hole provided on a stainless steel case, a coil is wound around a protruding shaft, and a voltage is applied to the coil for magnetization and stopped for demagnetization, thereby driving a contact mechanism with a movable iron piece that is going and returning, attracted by and separated from a magnetic pole portion of the iron core.  
         [0014]     According to the invention, since the stainless steel case itself is of low conductivity and it is difficult to flow the eddy current, a new magnetic flux that disturbs the return operation of the movable iron piece does not occur. Therefore, the movable iron piece can be quickly separated from the magnetic pole portion of the iron core and the arc can be quickly cut, thereby restraining the damage of the contact and obtaining a desired switching characteristic.  
         [0015]     As another embodiment of the invention, at least one slit or at least one thin portion for preventing generation of eddy current may be provided on the opening end of the through hole provided on the stainless steel case.  
         [0016]     According to the embodiment, thanks to the slit or the thin portion, since the electrical resistance increases, no eddy current flows or eddy current is difficult to flow. Therefore, a new magnetic flux that disturbs the return operation of the movable iron piece does not occur and an electromagnetic relay free from a fear of welding the contact can be obtained. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  is a perspective view showing the embodiment in the case where a switching device according to the invention is applied to a direct current breaking relay.  
         [0018]      FIG. 2  is an exploded perspective view of  FIG. 1 .  
         [0019]      FIG. 3  is an exploded perspective view of the relay main body shown in  FIG. 2 .  
         [0020]      FIG. 4  is an exploded perspective view of the electromagnetic block shown in  FIG. 3 .  
         [0021]      FIG. 5  is a partly broken perspective view of a sealing case shown in  FIG. 4 .  
         [0022]      FIG. 6  is an exploded perspective view of the sealing case shown in  FIG. 4 .  
         [0023]      FIG. 7  is an exploded perspective view of a movable contact block shown in  FIG. 3 .  
         [0024]      FIG. 8  is an exploded perspective view of a fixed contact block shown in  FIG. 3 .  
         [0025]      FIGS. 9A and 9B  are exploded perspective views of an important portion of the fixed contact block shown in  FIG. 8 .  
         [0026]      FIG. 10A  is a perspective view of the insulation case shown in  FIG. 3  and  FIG. 10B  is a variation example of the insulation case.  
         [0027]      FIGS. 11A, 11B , and  11 C are plan views showing the sealing process.  
         [0028]      FIG. 12  is a vertical cross sectional front view of the direct current breaking relay shown in  FIG. 1 .  
         [0029]      FIG. 13  is a partly enlarged cross sectional view of FIG.  12 .  
         [0030]      FIG. 14  is an enlarged cross sectional view of an important portion of the direct current breaking relay shown in  FIG. 12 .  
         [0031]      FIG. 15  is a vertical cross sectional lateral side view of the direct current breaking relay shown in  FIG. 1 .  
         [0032]      FIG. 16A  is a partial perspective view showing the operation principle of the sealing case shown in  FIG. 5  and  FIG. 16B  is a partial perspective view showing the operation principle of the sealing case according to the conventional example.  
         [0033]      FIGS. 17A, 17B , and  17 C are partial perspective views showing the movement of the generation source of the arc current according to the embodiment.  
         [0034]      FIG. 18A  is a partial perspective view showing the movement of the generation source of the arc current, continued from  FIG. 17C  and  FIG. 18B  is a plan view showing the movement of the generation source of the arc current. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]     A preferred embodiment of the invention will be described according to the accompanying drawings of  FIG. 1  to  FIG. 18 .  
         [0036]     This description will be made in the case where this embodiment is used for a relay for switching a direct current load, and as illustrated in  FIG. 1  and  FIG. 2 , the main body of a relay  20  is housed in a space integrally formed by a box case  10  and a box cover  15 .  
         [0037]     The box case  10  has a recessed portion  11  capable of housing an electromagnetic block  30  described later, and it is provided with through holes  12  for fixing respectively at two corners positioned on one of the diagonal lines and with jointing concaves  13  at the remaining two corners, as illustrated in  FIG. 2 . A reinforcing cylinder  12   a  is inserted into each of the through holes  12  and a joint nut  13   a  is inserted into each of the jointing concaves  13 .  
         [0038]     The box cover  15  can be fixed to the box case  10  and it has a shape capable of housing a sealing case block  40  described later. The box cover  15  is provided with contact holes  16  and  16  from which contact terminals  75  and  85  of the relay main body  20  described later protrude respectively as well as with protruding portions  17  and  17  which can accommodate a gas discharge pipe  21 , on its ceiling surface. A partition wall  18  connects the both protruding portions  17  and  17  and these work as an insulating wall. Each engagement hole  19  provided on the lower end portion of the box cover  15  is engaged with each engagement claw  14  provided on the upper end portion of the box case  10 , hence to combine the both integrally.  
         [0039]     The relay main body  20  is constituted by sealing a contact mechanism block  50  within the sealing case block  40  mounted on the electromagnetic block  30 , as illustrated in  FIG. 2  and  FIG. 3 .  
         [0040]     As illustrated in  FIG. 4 , the electromagnetic block  30  includes a pair of spools  32  and  32  with coil  31  wound around, combined with two iron cores  37  and  37  integrated with the block and a plate-shaped yoke  39 .  
         [0041]     In the spool  32 , relay terminals  34  and  35  are laterally attached to the lower collar portion  32   a , of collar portions  32   a  and  32   b  provided on the both upper and lower ends. One end of the coil  31  wound around the spool  32  is entwined with one end (entwined portion)  34   a  of one relay terminal  34  and soldered there and the other end is entwined with the other end (entwined portion)  35   a  of the other relay terminal  35  and soldered there. In the relay terminals  34  and  35 , the entwined portion  34   a  is curved and the other end (joint portion)  35   b  is also curved. Of the relay terminals  34  and  35  mounted on the aligned spools  32  and  32 , one joint portion  35   b  of one adjacent relay terminal  35  is jointed to the entwined portion  34   a  of the other adjacent relay terminal  34  and soldered there. Further, the entwined portion  35   a  of one adjacent relay terminal  35  is jointed to the joint portion  34   b  of the other relay terminal  34  and soldered there, hence to connect the two coils  31  and  31 . The coil terminals  36  and  36  are bridged over the upper and lower collar portions  32   a  and  32   b  of the spools  32  and respectively connected to the joint portions  34   b  and  35   b  of the relay terminals  34  and  35  ( FIG. 3 ).  
         [0042]     The sealing case block  40  is formed by a sealing case  41  capable of housing the contact mechanism block  50  described later and a sealing cover  45  for sealing the opening portion of the sealing case  41 . A pair of fitting holes  42  and  42  for inserting the iron cores  37  is formed on the bottom surface of the sealing case  41  ( FIG. 6 ). A slit  43  for connecting the both holes is provided between the fitting holes  42  and  42 . In the sealing cover  45 , as illustrated in  FIG. 3 , a pair of through holes  46  and  46  for penetrating the contact terminals  75  and  85  of the contact mechanism block  50  described later and a loose hole  47  for loosely fitting the gas discharge pipe  21  are provided on the bottom surface of the concave  45   a.    
         [0043]     Assembling the electromagnetic block  30  and the sealing case block  40  is performed in the following procedure.  
         [0044]     At first, the relay terminals  34  and  35  are attached to the collar portion  32   a  that is placed at one side of the spools  32 , the coil  31  is wound around the spools  32 , each drawing line is entwined with each of the entwined portions  34   a  and  35   a  of the relay terminals  34  and  35  and soldered there. A pair of the spools  32  is aligned with the entwined portions  34   a  and  35   a  and the joint portions  34   b  and  35   b  of the relay terminals  34  and  35  curved and raised. The entwined portion  35   a  of the relay terminal  35  is jointed to the joint portion  34   b  of the other adjacent relay terminal  34  and soldered. The joint portion  35   b  of the relay terminal  35  is jointed to the entwined portion  34   a  of the other adjacent relay terminal  34  and soldered there, hence to connect the coils  31  and  31 .  
         [0045]     As illustrated in  FIG. 6 , the respective iron cores  37  are inserted into the respective fitting holes  42  provided on the bottom surface of the sealing case  41  and pipes  38  are respectively attached to the shafts  37   a  of the protruding iron cores  37 . Each of the pipes  38  is pushed to each of the iron cores  37  from the opening edge of the pipe  38  in a direction of the shaft. In the iron core  37 , the diameter of the shaft portion  37   a  is smaller than the diameter of the fitting hole  42  of the sealing case  41  and smaller than the inner diameter of the pipe  38 . The diameter of a bottleneck portion  37   b  of the iron core  37  is larger than the diameter of the fitting hole  42  of the sealing case  41  and larger than the inner diameter of the pipe  38 . Therefore, when the iron core  37  is pushed down in a direction of the shaft, the bottleneck portion  37   b  of the iron core  37  goes through the fitting hole  42  of the sealing case  41  expanding it and further goes through the pipe  38  expanding the inner diameter of the pipe  38 . The opening end portion of the pipe  38  and the head portion (magnetic pole portion)  37   c  of the iron core  37  are fixedly fitted to the opening portion of the fitting hole  42  upwardly and downwardly. The opening portion of the fitting hole  42  of the sealing case  41  is caulked in three directions.  
         [0046]     According to the embodiment, since the sealing case  41  is made from material having the thermal expansion coefficient higher than the iron core  37  and the pipe  38 , for example, aluminum, it is effective in securing airtightness even when a temperature changes.  
         [0047]     Even when each component expands with an increase in temperature, since the expansion of the sealing case  41  in a thickness direction is relatively larger than that of the other components, the sealing case  41  can be more strongly supported by the head portions  37   c  of the iron cores  37  and the pipes  38 . While, when each component shrinks with a decrease in temperature, since the shrinkage of the fitting hole  42  of the sealing case  41  in a diameter direction is relatively larger than that of the other components, the bottleneck portion  37   b  of the iron core  37  is choked. In order to retrain generation of thermal stress while securing the airtightness, it is preferable that the thermal expansion coefficient of the iron core  37  is substantially equal to that of the pipe  38 .  
         [0048]     When the sealing case  41  is made from aluminum that can be easily processed, a sealing work becomes easy and hydrogen becomes difficult to penetrate the case advantageously.  
         [0049]     According to the embodiment, since the slit  43  is provided in the bottom surface of the sealing case  41 , even when a change of magnetic flux occurs in the iron core  37 , eddy currents can be prevented by this slit, as illustrated in  FIG. 16 . Therefore, by preventing generation of the magnetic flux caused by the above eddy currents, the return operation of a movable iron piece  66  described later can be smoothly performed. This can restrain the deterioration of the blocking performance caused by a delay of the return operation.  
         [0050]     A method for preventing the generation of the eddy currents is not restricted to the above method of providing the slit  43  of connecting the fitting holes  42  and  42  but also, for example, at least one cut-off portion individually formed around each of the fitting holes  42  and  42  may be provided. Generation of the eddy currents may be restrained by forming a rough uneven surface around the fitting holes  42  of the bottom surface of the sealing case  41  to increase the electric resistance.  
         [0051]     As illustrated in  FIG. 4 , the respective iron cores  37  and the respective pipes  38  are inserted into respective center holes  32   c  of the spools  32 , so that the respective distal ends of the protruding iron cores  37  go through respective caulking holes  39   a  of the yoke  39 , hence to fix the above components firmly. Thus, the electromagnetic block  30  with the sealing case  41  mounted there is completed. An insulating sheet  39   b  in order to enhance the insulation performance is arranged between the yoke  39  and the collar portion  32   a  of the spools  32 .  
         [0052]     The coil terminals  36  are respectively hung over the upper and lower collar portions  32   b  and  32   a  of the spools  32 . The lower ends of the coil terminals  36  are respectively connected to the joints portions  34   b  and  35   b  of the relay terminals  34  and  35 . Hence, an assembly work of the electromagnetic block  30  and the sealing case  41  is completed. The sealing material  98  is injected into the bottom of the sealing case  41  and hardened there, to seal the slit  43 . The sealing material  98  is made, for example, by adding alumina powder to an epoxy resin and when it is hardened, it has the almost same line expansion rate as aluminum.  
         [0053]     The contact mechanism block  50  comprises a movable contact block  60 , fixed contact blocks  70  and  80  mounted on the both sides of the block  60 , and an insulation case  90  for housing and unitizing these blocks, as illustrated in  FIG. 3 .  
         [0054]     In the movable contact block  60 , a movable contact piece  62  and a pair of coil springs  63  and  63  for pressing contact are mounted on a movable insulation base  61  with a stopper  64 , as illustrated in  FIG. 7 . A pair of return coil springs  65  and  65 , a movable iron piece  66 , and a shielding plate  67  are firmly staked to the movable insulation base  61  with a pair of rivets  68  and  68 .  
         [0055]     In the movable insulation base  61 , deep grooves  61   b  and  61   b  are formed on the both sides of a guide protrusion  61   a  protruding in the center of the base on its upper surface so as to accommodate the coil springs  63  without dropping them. On the bottom surface of the movable insulation base  61 , a leg portion  61   c  having a substantially-cross shaped section is formed in its center and concave portions  61   d  and  61   d  (the back concave portion  61   d  is not illustrated) for positioning the return coil springs  65  are formed on its both sides.  
         [0056]     The movable contact piece  62  is designed in that the both ends of band-shaped thick conductive material become semicircle and a guide long hollow  62   a  is provided in its center. The coil springs  63  are to add a contact pressure to the movable contact piece  62  and to always urge the movable contact piece  62  downward.  
         [0057]     In assembling the movable contact block  60 , at first, the guide long hollow  62   a  of the movable contact piece  62  is fitted to the guide protrusion  61   a  of the movable insulation base  61 . Then, a pair of the coil springs  63  and  63  are fitted to the deep grooves  61   b  and  61   b , and the stopper  64  is attached there. The rivets  68  and  68  are inserted into the return coil springs  65  and  65  positioned within the concave portions  61   d  and  61   d  of the movable insulation base  61 , passing through caulking holes  66   a  of the movable iron piece  66  and caulking holes  67   a  of the shielding plate  67 . Then, the rivets  68  and  68  are inserted into caulking holes  61   e  and  61   e  of the movable insulation base  61  and caulking holes  64   a  of the stopper  64 , thereby staking the above components and completing the assembly work. According to the embodiment, the movable contact piece  62  is always urged downward by the spring force of the coil springs  63  so as not to allow a wobble.  
         [0058]     As illustrated in  FIG. 8  and  FIG. 9 , the fixed contact blocks  70  and  80  have the same shape and the same structure. They are formed by attaching the fixed contact terminals  76  and  86  each having a substantially-C-shaped section, with the contact terminals  75  and  85  crimped there, and the permanent magnets  77  and  87 , to the fixed contact bases  71  and  81  made from resin.  
         [0059]     The fixed contact bases  71  and  81  respectively have matching protruding portions  72 ,  73  and  82 ,  83  on the upper and lower ends of the bases  71  and  81  on their facing sides. In the protruding portions  72 ,  73  and  82 ,  83 , in particular, engagement projections  71   a  and  81   a  and engagement holes  71   b  and  81   b  that can be mutually engaged with each other are formed on the surface of the both edges. Further, in the protruding portions  73  and  83 , cut-off grooves  73   a  and  83   a  are respectively provided in their basements, as illustrated in  FIG. 14 , so that they can be a insulating groove in the shape of substantially converted T at the matching time. Even when scattered powder caused at the time of switching contact is scattered around the inner surface, this can prevent the scattered powder from attaching to the inside corners of the cut-off grooves  73   a  and  83   a , so as not to form a short circuit. It is not necessary to always provide with the both cut-off grooves  73   a  and  83   a , but only one may be provided, hence to form an insulating groove having a substantially L-shaped section.  
         [0060]     As illustrated in  FIG. 8  and  FIG. 9 , the fixed contact terminals  76  and  86  respectively have the fixed contact portions  78  and  88  crimped on their lower end portions and respectively contain the permanent magnets  77  and  87  in their lower corners. Further, the fixed contact terminals  76  and  86  are respectively provided with positioning projections  76   a  and  86   a  each protruding at the position a little lower than the middle of the outer rectangular surface. The projections  76   a  and  86   a  come into close contact with the inner surface of the insulation case  90  described later ( FIG. 13 ), hence to regulate the position of the fixed contact terminals  76  and  86  and improve the positioning accuracy of the fixed contacts  78  and  88 . The fixed contact terminals  76  and  86  are respectively provided with narrow portions  76   b  and  86   b  between the fixed contact portions  78  and  88  and the permanent magnets  77  and  87 . This means that angles  76   c  and  86   c  are respectively formed in front of the permanent magnets  77  and  87 , which prevents generation sources of the arc currents from moving to the permanent magnets  77  and  87 .  
         [0061]     The insulation case  90  is to unitize the contact mechanism block  50 , as illustrated in  FIG. 3 . The insulation case  90  is provided with a pair of the gas discharge holes  92  and  92  on the both sides symmetric with respect to a central line connecting the terminal holes  91  and  91  which are provided on the top surface of the case ( FIG. 3  and  FIG. 10A ). It is in order to make the orientation indifferent in the assembly mode that a pair of the gas discharge holes  92  is provided symmetrically. Each circular protrusion  93  for preventing the intrusion of the sealing material may be integrated with each of the opening ends of the gas discharge holes  92  ( FIG. 10B ).  
         [0062]     The procedure of assembling the contact mechanism block  50  will be described below.  
         [0063]     While pulling up each lower end of the return springs  65  of the assembled movable contact block  60 , the fixed contact blocks  70  and  80  are attached to the movable insulation base  61  on its both sides, and the engagement projections  71   a  of the respective matching protruding portions  72  and  73  are respectively engaged into the engagement holes  81   b  of the respective matching protruding portions  82  and  83 , and the engagement holes  71   b  of the respective matching protruding portions  72  and  73  are engaged with the engagement projections  81   a  of the respective matching protruding portions  82  and  83 . According to this, respective operation holes  51  and  52  are formed between the both fixed contact bases  71  and  81 . After attaching the insulation case  90  to the fixed contact blocks  70  and  80 , the contact terminals  75  and  85  respectively protrude from the terminal holes  91  and  91 , hence to complete the contact mechanism block  50 . Here, the gas discharge holes  92  and  92  communicate with the operation holes  51  and  52  since they are positioned on the same axis ( FIG. 15 ).  
         [0064]     When the contact mechanism block  50  is inserted into the sealing case  41  containing the electromagnetic block  30  ( FIG. 12 ), the leg portions  74  and  84  of the fixed contact bases  70  and  80  respectively come into contact with the head portions  37   c  that are the magnetic pole portions of the iron cores  37 , and the movable iron piece  66  faces the magnetic pole portions  37   c  through the shielding plate  67  in a removable way. A pair of measurement probes (not illustrated) are respectively inserted into the operation holes  51  and  52  provided between the respective gas discharge holes  92  and  92  of the insulation case  90  and the respective fixed contact bases  71  and  81 . The rivets  68  and  68  cramped to the stopper  64  are pushed or released, in order to move the movable contact block  60  up and down and measure the operation characteristics of the contact pressure and the contact gap. As a result, when the operation characteristic is out of the tolerance level, fine adjustment is performed, while when the operation characteristic is within the tolerance level, the sealing cover  45  is attached to the sealing case  41  and they are welded together ( FIG. 11B ). A gas discharge pipe  21  is pushed into one of the gas discharge holes  92  of the insulation case  90  from the loose hole  47 . The same sealing material  99  as the sealing material  98  made from epoxy resin is injected into the sealing cover  45  and hardened there, so as to seal the basement around the contact terminals  75  and  85  and the gas discharge pipe  21  ( FIG. 11C ). Air within the sealing case  41  is taken out through the gas discharge pipe  21  and a predetermined mixed gas is injected instead, and then the gas discharge pipe  21  is caulked and sealed. At last, the coil terminals  36  are hung on a pair of the collar portions  32   a  and  32   b  of the spools  32 , hence to complete the relay main body  20  ( FIG. 2 ).  
         [0065]     According to the embodiment, one of the gas discharge holes  92  is sealed by the gas discharge pipe  21  and the other is covered with the sealing cover  45 . Owing to this structure, even when the sealing material  99  is injected, the sealing material  99  will not intrude into the insulation case  90 . Since the loose hole  47  for inserting the pipe  21  is positioned at the position equally distant from the respective contact terminals  75  and  85 , it has an advantage that the insulating characteristic is good.  
         [0066]     A liquid elastic material  97  made from urethane resin is injected in the bottom surface of the recessed portion  11  of the case  10 , and the relay main body  20  is accommodated in the recessed portion  11 . The coil terminals  36  are positioned at the jointing concaves  13 , and the liquid elastic material  97  is hardened there as it is with the relay main body  20  hung within the case  10 . The cover  15  is attached to the case  10 , hence to complete the direct current breaking relay. In the embodiment, although the liquid elastic material  97  filled and hardened is noise absorbing elastic material, it is not restricted to this but an elastic sheet may be used as a noise absorbing elastic material. The collar portions  32   b  of the spools  32  may be extended and hung within the recessed portion  11  of the case  10 .  
         [0067]     The operation of the relay having the above structure will be described, this time.  
         [0068]     When no voltage is applied to the coils  31  of the electromagnetic block  30 , the movable insulation base  61  is pulled up by the spring force of the return springs  65  and  65  ( FIG. 12 ). Therefore, the movable iron piece  66  is separated from the magnetic pole portions  37   c  of the iron cores  37  and the both ends of the movable contact piece  62  are separated from the fixed contacts  78  and  88 .  
         [0069]     When a voltage is applied to the coils  31 , the magnetic pole portions  37   c  of the iron cores  37  absorb the movable iron piece  66 , and the movable iron piece  66  moves down against the spring force of the return springs  65 . Thus, the movable insulation base  61  integrated with the movable iron piece  66  moves down, and after the both ends of the movable contact piece  62  come into contact with the fixed contacts  78  and  88 , the movable iron piece  66  is absorbed by the magnetic pole portions  37   c  of the iron cores  37 .  
         [0070]     According to the embodiment, since the shock when the movable iron piece  66  comes into contact with the magnetic pole portions  37   c  of the iron cores  37  is absorbed and reduced by the hardened liquid elastic material  97  and the coil terminals  36 , collision sound can be restrained, hence to obtain a silent electromagnetic relay advantageously.  
         [0071]     When the voltage applied to the coils  31  is stopped, the movable insulation base  61  is raised by the spring force of the return springs  65 , the movable iron piece  66  moving together with this is accordingly separated from the magnetic pole portions  37   c  of the iron cores  37 , and the both ends of the movable contact piece  62  are separated from the fixed contacts  78  and  88 .  
         [0072]     According to the embodiment, when the both ends of the movable contact piece  62  contact with and separate from the fixed contacts  78  and  88 , the scattered powder is scattered around the inner surface of the fixed contact bases  71  and  81 . However, since the cut-off grooves  73   a  and  83   a  are provided on the inner surfaces of the fixed contact bases  71  and  81  as shown by a thick solid line in  FIG. 14 , the scattered powder will not be attached there fully and a short circuit will not be formed there advantageously.  
         [0073]     When the both ends of the movable contact piece  62  are separated from the fixed contacts  78  and  88 , for example, as illustrated in  FIG. 17 , even when the arc current  100  is produced and extended from the fixed contact  78  and the generation source of the arc current  100  moves, it will never reach the permanent magnetic  77 , which will not damage the permanent magnetic  77  advantageously.  
         [0074]     More specifically, as illustrated in  FIG. 17 , even when the arc current  100  is generated in the fixed contact  78  ( FIG. 17B ) and the generation source of the arc current  100  is attracted by the magnetic force of the permanent magnet  78  and moves ( FIG. 17C ,  FIG. 18A ,  FIG. 18B ), it will never arrive at the permanent magnet  78 . This is because the generation source of the arc current  100  has the characteristic of moving to a corner or an angle of the conductive material. According to the embodiment, the narrow portion  76   b  is provided between the fixed contact  78  and the permanent magnet  77 , hence to form the angle  76   c  in front of the permanent magnet  77 . Therefore, the generation source of the arc current  100  cannot move to the permanent magnet  77  but move to the angle  76   c.    
         [0075]     In the embodiment, although the case of breaking the direct current has been described, the invention is not restricted to this case but it may be applied to the case of breaking an alternative current.  
         [0076]     The invention is not restricted to the above-mentioned electromagnetic relay, but it is needless to say that it may be applied to the other electromagnetic relays.