Abstract:
An electromagnetic relay has a movable contact arranged at one end of a drive shaft that reciprocates in an axis center direction based on excitation and demagnetization of an electromagnet block, and a pair of adjacently arranged fixed contacts with which the movable contact is operable to contact and separate. A first electromagnetic iron piece, a second electromagnetic iron piece and the movable contact are inserted to the drive shaft so that the first electromagnetic iron piece and the second electromagnetic iron piece sandwich the movable contact. The second electromagnetic iron piece is biased to one end side of the drive shaft with a coil spring inserted to the drive shaft. When the movable contact contacts to the pair of fixed contacts, the second electromagnetic iron piece forming a magnetic circuit with the first electromagnetic iron piece pushes the movable contact to the pair of fixed contacts.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Technical Field 
         [0002]    The present invention relates to electromagnetic relays, and in particular, to a power load electromagnetic switch. 
         [0003]    2. Related Art 
         [0004]    Conventionally, in a power load electromagnetic switch, an electromagnetic repulsion acts between a fixed contact and a movable contact when an abnormal current flows in time of opening/closing of contact. The contact pressure thus lowers and the contact resistance becomes large thereby rapidly increasing the Joule heat or the contacts separate thereby generating an arc heat, whereby the movable contact and the fixed contact may be welded. 
         [0005]    In order to prevent such welding of the contacts, there has been disclosed a movable contact supporting device of a switch in which a movable contact having an upper magnetic piece attached to an upper surface is arranged, so as to be slidable in the up and down direction by way of a pushing spring, in a window hole formed at a supporting board, and a lower magnetic piece is arranged, so as to be slidable in the up and down direction by way of a pushing spring, in a slide regulation hole formed at the lower side of the window hole with a wider than the width of the window hole so as to include a stopper at the upper part and the lower part (see Japanese Unexamined Utility Model Publication No. 60-163658). 
         [0006]    More specifically, a movable contact  15  is sandwiched by two upper and lower magnetic pieces  13 ,  20 , which are electromagnetic iron pieces, to resolve the drawback of electromagnetic repulsion, as shown in FIG. 4 of Japanese Unexamined Utility Model Publication No. 60-163658. 
       SUMMARY 
       [0007]    However, in the electromagnetic relay described above, one upper magnetic piece  13  is biased to the movable contact  15  with a pushing spring  16 , while the other lower magnetic piece  20  is biased to the movable contact  15  with a pushing spring  23 , and thus the number of components and the number of assembly steps are great, and the structure is complicating. 
         [0008]    The present invention has been devised to solve the problems described above, and an object thereof is to provide an electromagnetic relay capable of preventing drawbacks by electromagnetic repulsion, and having a small number of components and reducing the number of assembly steps, and having a simple structure. 
         [0009]    In accordance with one aspect of the present invention, to achieve the above object, there is provided an electromagnetic relay for contacting and separating both ends of a movable contact arranged at one end of a drive shaft, which reciprocates in an axis center direction based on excitation and demagnetization of an electromagnet block, to a pair of adjacently arranged fixed contacts, wherein a first electromagnetic iron piece, a second electromagnetic iron piece and the movable contact are inserted to the drive shaft so that the first electromagnetic iron piece and the second electromagnetic iron piece sandwich the movable contact, wherein the second electromagnetic iron piece is biased to one end side of the drive shaft with a coil spring inserted to the drive shaft, and wherein when the movable contact contacts to the pair of fixed contacts, the second electromagnetic iron piece forming a magnetic circuit with the first electromagnetic iron piece pushes the movable contact to the pair of fixed contacts. 
         [0010]    According to the present invention, since the second electromagnetic iron piece is biased to one end side of the drive shaft with one coil spring, two coil springs are not necessary as in the related art example. Thus, an electromagnetic relay capable of preventing drawbacks by electromagnetic repulsion, and having a small number of components and reducing the number of assembly steps, and having a simple structure can be obtained. 
         [0011]    According to an embodiment of the present invention, an upper end face of the second electromagnetic iron piece, which reciprocates, having a substantially U-shaped cross section contact and separate to and from a lower surface of the first electromagnetic iron piece of plate-shape. 
         [0012]    According to the present embodiment, an electromagnetic relay capable of preventing drawbacks by electromagnetic repulsion, and having a small number of components and reducing the number of assembly steps, and having a simple structure can be obtained by having the upper end face of the second electromagnetic iron piece having a substantially U-shaped cross section contact and separate to and from the lower surface of the plate-shaped first electromagnetic iron piece. 
         [0013]    According to another embodiment of the present invention, both ends of the first electromagnetic iron piece may slidably contact opposing inner side surfaces of the second electromagnetic iron piece, which reciprocates, having a substantially U-shaped cross section. 
         [0014]    According to the present embodiment, since both ends of the first electromagnetic iron piece slidably move on the opposing inner side surface of the second electromagnetic iron piece at the initial stage of the operation of the drive shaft, the magnetic resistance is small, large attractive force is obtained, and welding of the movable contact is reliably regulated. 
         [0015]    According to still another embodiment of the present invention, both the first and the second electromagnetic iron pieces may have a substantially L-shaped cross section, a distal end face of a bent portion of one electromagnetic iron piece contacting and separating a flat surface of the other electromagnetic iron piece. 
         [0016]    According to the present embodiment, the parts can be commoditized and the part management can be facilitated since the first and second electromagnetic iron pieces have the same cross-sectional shape. 
         [0017]    According to yet another embodiment of the present invention, both the first and the second electromagnetic iron pieces may have a substantially U-shaped cross section, distal end faces of bent portions contacting and separating each other. 
         [0018]    According to the present embodiment, the parts can be commoditized and the part management can be facilitated since the first and second electromagnetic iron pieces have the same cross-sectional shape. 
         [0019]    In particular, the contacting/separating surfaces of the first and second electromagnetic iron pieces having a substantially L-shaped cross section or having a substantially U-shaped cross section may be tapered surfaces that can contact or separate to and from each other. 
         [0020]    According to the present embodiment, the attraction area increases and the magnetic resistance reduces thereby obtaining an electromagnetic relay of small power consumption. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIGS. 1A and 1B  are perspective views each showing a first embodiment of a power load electromagnetic relay applied with a contact device according to the present invention; 
           [0022]      FIG. 2  is a front cross-sectional view of the contact device shown in  FIGS. 1A and 1B ; 
           [0023]      FIG. 3  is a side cross-sectional view of the contact device shown in  FIGS. 1A and 1B ; 
           [0024]      FIG. 4  is an exploded perspective view of the contact device shown in  FIGS. 1A and 1B ; 
           [0025]      FIG. 5  is an exploded perspective view of the main parts of the contact device shown in  FIGS. 1A and 1B ; 
           [0026]      FIGS. 6A and 6B  are a perspective view and a cross-sectional view, respectively, of a drive mechanism unit shown in  FIG. 5 ; 
           [0027]      FIG. 7  is an exploded perspective view of the drive mechanism unit and a contact mechanism unit shown in  FIG. 4 ; 
           [0028]      FIG. 8  is an exploded perspective view of the drive mechanism unit shown in  FIG. 4 ; 
           [0029]      FIG. 9  is an exploded perspective view of the contact mechanism unit shown in  FIG. 8 ; 
           [0030]      FIG. 10  is an exploded perspective view of a movable contact block shown in  FIG. 9 ; 
           [0031]      FIG. 11A  is a perspective view of the main parts of the movable contact block, and  FIG. 11B  is an enlarged perspective view of the main parts of  FIG. 11A ; 
           [0032]      FIG. 12  is an exploded perspective view of a cover shown in  FIG. 4 ; 
           [0033]      FIG. 13  is a graph showing attractive force characteristics of the contact device according to the first embodiment; and 
           [0034]      FIGS. 14A ,  14 B,  14 C, and  14 D are enlarged perspective views of the main parts of the movable contact block showing second, third, fourth, and fifth embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0035]    Hereinafter, a power load electromagnetic relay serving as an embodiment applied with a contact device of the present invention will be described with reference to the accompanying drawings  FIGS. 1A to 14 . As shown in  FIGS. 1A to 13 , a power load electromagnetic relay according to a first embodiment, in brief, has a drive mechanism unit  20  and a contact mechanism unit  50 , which are integrated one above the other, accommodated in a case  10 , and a cover  70  fitted to cover the case  10 . 
         [0036]    As shown in  FIG. 4 , the case  10  has a box-shape with a bottom surface capable of accommodating the drive mechanism unit  20 , to be hereinafter described, where a fit-in recessed portion  11  ( FIGS. 2 and 3 ) for positioning the drive mechanism unit  20  is formed at the middle of the bottom surface. The case  10  has an attachment hole  13  and a reinforcement rib  14  arranged in a projecting matter on a mount  12  arranged in a projecting matter towards the side from the lower edge of the outer peripheral corners. The attachment hole is not formed in one of the mount  12  to serve as a mark in time of attachment. Furthermore, the case  10  has an engagement hole  15  for preventing the cover  70 , to be hereinafter described, from coming off formed at the opening edge of the opposing side walls. 
         [0037]    As shown in  FIGS. 5 to 7 , the drive mechanism unit  20  has an electromagnet block  30 , in which a coil  32  is wound around a spool  31 , fixed between a first yoke  21  having a substantially U-shaped cross section and a second yoke  22  bridged over both ends of the first yoke  21 . 
         [0038]    As shown in  FIG. 5 , the first yoke  21  has an insertion hole  21   a  for inserting a bottomed tubular body  34 , to be hereinafter described, formed at the middle of the bottom surface, and a cutout  21   b  for fitting the second yoke  22  formed at both ends. 
         [0039]    As shown in  FIG. 7 , the second yoke  22  has both ends formed to a planar shape that can engage to and bridge over the cutouts  21   b  of the first yoke  21 , and has a caulking hole  22   a  formed at the middle. The second yoke  22  has a counterbore hole  22   b  formed at the corner on the upper surface, where a gas sealing pipe  23  is air-tightly joined to the counterbore hole  22   b  by brazing. 
         [0040]    As shown in  FIGS. 5 and 7 , the electromagnet block  30  is formed by wounding the coil  32  around the spool  31  having collar portions  31   a ,  31   b  at both ends, where a lead line of the coil  32  is engaged and soldered to relay terminals  33 ,  33  arranged at the collar portion  31   a . Lead wires  33   a  are connected to the relay terminals  33 ,  33 , respectively. As shown in  FIGS. 5 and 6B , the bottomed tubular body  34  is inserted to a center hole  31   c  passing through the collar portions  31   a ,  31   b  of the spool  31 . The upper opening of the bottomed tubular body  34  is air-tightly joined to the lower surface of the second yoke  22  by laser welding. The bottomed tubular body  34  has an annular auxiliary yoke  35  fitted to the lower end projecting out from the insertion hole  21   a  of the first yoke  21 , and prevented from coming out with an O-ring  36 . The O-ring  36  prevents the annular auxiliary yoke  35  from coming out and also functions to absorb sound and vibration. 
         [0041]    According to the present embodiment, the opposing area of an outer circumferential surface of a movable iron core  42 , to be hereinafter described, and the first yoke  21  and the annular auxiliary yoke  35  increases and the magnetic resistance reduces, and thus the magnetic efficiency improves and the power consumption reduces. 
         [0042]    A shown in  FIG. 6B , a fixed iron core  40 , a returning coil spring  41 , and the movable iron core  42  are sequentially accommodated in the bottomed tubular body  34 . The fixed iron core  40  has the upper end caulked and fixed to the caulking hole  22   a  of the second yoke  22 . Thus, the movable iron core  42  is biased to the lower side with the spring force of the returning coil spring  41  and a shock eliminating circular plate  48  made of rubber is attached to a recessed portion formed at the bottom surface. Furthermore, the bottomed tubular body  34  has an adhesion prevention metal sheet  49  accommodated between the inner bottom surface and the shock eliminating circular plate  48  made of rubber, as shown in  FIG. 7 . 
         [0043]    As shown in  FIG. 6B , the movable iron core  42  has a shaft hole with an inner diameter for receiving a drive shaft  61 , to be hereinafter described, and is formed by inserting and integrating an upper movable iron core  44 , a ring-shaped magnet  45 , and a lower movable iron core  46  to a connection pipe  43  made of non-magnetic material. The desired magnetic circuit can be formed by shielding the magnetic force of the ring-shaped magnet  45  with the connection pipe  43 . 
         [0044]    As shown in  FIG. 9 , the contact mechanism unit  50  has a shield member  55  and a movable contact block  60  arranged in a sealed space formed by connecting and integrating a ceramic sealed container  51  to the upper surface of the second yoke  22 . 
         [0045]    The sealed container  51  has a pair of fixed contact terminals  52 ,  53  having a substantially T-shaped cross section brazed to the roof surface thereof, and a connection annular skirt portion  54  brazed to the lower opening edge. Screw holes  52   a ,  53   a  are formed at the upper surface of the fixed contact terminals  52 ,  53 , respectively. The annular skirt portion  54  is positioned on the upper surface of the second yoke  22 , and then welded and integrated by laser to thereby form the sealed space. 
         [0046]    The shield member  55  is integrated by fitting a metal shield ring  57  to a box-shaped resin molded article  56  having a shallow bottom with a pass-through hole  56   a  at the middle, and caulking a caulking projection  56   b  arranged in a projecting manner at the bottom surface of the box-shaped resin molded article  56 . The metal shield ring  57  draws the arc generated in time of contact opening/closing, and prevents the brazed part of the sealed container  51  from melting. 
         [0047]    As shown in  FIG. 10 , the movable contact block  60  is assembled by sequentially inserting a plate-shaped first electromagnetic iron piece  62 , a movable contact  63 , a second electromagnetic iron piece  64  having a substantially U-shaped cross section, a contact-pressure coil spring  65 , a contact-pressure plate spring  66  having a substantially V-shaped cross section, and a washer  67  to the drive shaft  61  having a substantially T-shaped cross section, and then engaging an E-ring  68  to an annular groove  61   a  formed on the outer circumferential surface of the drive shaft  61 . In particular, the first electromagnetic iron piece  62 , the movable contact  63 , and the second electromagnetic iron piece  64  are biased upward through the contact-pressure coil spring  65 . A slight gap consequently forms between the lower surface of the movable contact  63 , and both ends of the contact-pressure plate spring  66  so that time-lag creates in time of operation. 
         [0048]    The plate spring  66  has a pair of position regulating lock nails  66   a ,  66   a , which lock with both side edges of the movable contact  63 , respectively, formed at both ends. Thus, the position regulating lock nails  66   a  of the plate spring  66  lock to and accurately push both side edges of the movable contact  63 , whereby an electromagnetic relay in which the variation of the operation characteristics is small is obtained. 
         [0049]    A repulsive force arises between the fixed contact terminals  52 ,  53  and the movable contact  63  by the large current that flows when both ends of the movable contact  63  contact the fixed contact terminals  52 ,  53 . However, the first and second electromagnetic iron pieces  62 ,  64  of the movable contact block  60  generate magnetic force for attracting each other based on the large current described above to thereby regulate the operation the movable contact  63  moves away from the fixed contact terminals  52 ,  53 , and to prevent the contact welding due to generation of the arc. 
         [0050]    The first and second electromagnetic iron pieces  62 ,  64  of the movable contact block  60  according to the first embodiment have structures such that both ends of the first electromagnetic iron piece  62  contact the upper surface of both ends of the second electromagnetic iron piece  64 , as shown in  FIG. 11B . According to the present embodiment, when large current flows to the movable contact  63  at the initial stage in which the movable contact  63  is contacting the fixed contact terminals  52 ,  53 , the first electromagnetic iron piece  62  and the second electromagnetic iron piece  64  attract each other, thereby pushing the movable contact  63  against the fixed contact terminals  52 ,  53 . Thus, the movable contact  63  attracts to the fixed contact terminals  52 ,  53  without repelling against the fixed contact terminals  52 ,  53 , whereby the arc does not create and contact welding does not occur. 
         [0051]    The first and second electromagnetic iron pieces  62 ,  64  are not limited to the above embodiment, and may be configured as described in the embodiment shown in  FIGS. 14A to 14D . For the sake of convenience of the explanation, the movable contact  63  and the contact-pressure plate spring  66  are not properly given in  FIGS. 11A to 11B  and  14 A to  14 D. 
         [0052]    For example, as shown in  FIG. 14A , both end faces of the first electromagnetic iron piece  62  may be adjacent to the opposing inner side surface of the second electromagnetic iron piece  64  having a substantially U-shaped cross section (second embodiment). According to the present embodiment, both end faces of the first electromagnetic iron piece  62  face the inner side surface of the second electromagnetic iron piece  64  at the initial stage in which the movable contact  63  is contacting the fixed contact terminals  52 ,  53 . However, both end faces of the first electromagnetic iron piece  62  project out from both end faces of the second electromagnetic iron piece  64  at the stage the movable contact  63  contacts the fixed contact terminals  52 ,  53  with a predetermined pressure and the operation is completed. Thus, the magnetic resistance is small and large attractive force can be generated at the initial stage in which the movable contact  63  is contacting the fixed contact terminals  52 ,  53 . As a result, the movable contact  63  is reliably regulated from separating from the fixed contact terminal  52 ,  53 , and the contact welding is prevented. 
         [0053]    As shown in  FIG. 14B , the first and second electromagnetic iron pieces  62 ,  64  having substantially L-shaped cross sections may be arranged to contact each other (third embodiment). According to the present embodiment, the parts can be commoditized since the first and second electromagnetic iron pieces  62 ,  64  have the same shape, which facilitates part management. 
         [0054]    As shown in  FIG. 14C , the first and second electromagnetic iron pieces  62 ,  64  having substantially U-shaped cross sections may be arranged such that perpendicular end faces thereof contact each other (fourth embodiment). According to the present embodiment, the parts can be commoditized similar to the second embodiment, which facilitates part management. 
         [0055]    As shown in  FIG. 14D , first and second electromagnetic iron pieces  62 ,  64  having substantially U-shaped cross sections may be arranged such that inclined end faces thereof contact each other (fifth embodiment). According to the present embodiment, the part management is facilitated, and furthermore, the opposing attraction area is large and the attractive force is large since the attracting distal end faces  62   a ,  64   a  are inclined surfaces. 
         [0056]    The contact-pressure coil spring  65  and the plate spring  66  both provide a contact pressure to the movable contact  63 . In the present embodiment, the adjustment of the attractive force characteristics is facilitated and the degree of freedom in design is extended by combining the contact-pressure coil spring  65  and the plate spring  66 . 
         [0057]    As shown in  FIG. 12 , the cover  70  has a plan shape that can be fitted to the case  10 . The cover  70  is fitted at the inner side surface with a holding member  90  made of magnetic material having a substantially horseshoe-shape in plan view. 
         [0058]    As shown in  FIG. 4 , the cover  70  has terminal holes  72 ,  73  formed on both sides of an insulation deep grove portion  71 , which is formed at the middle of the roof surface. The cover  70  also has receiving portions  74 ,  75  arranged projecting to the side from the side surfaces on both sides of the short side. Insertion slits  76 ,  77  enabling external connection terminals  95 ,  96  to be inserted are formed at the base of the receiving portions  74 ,  75 . The external connection terminals  95 ,  96  bent through press working have stud bolts  95   a ,  96   a , which can be screw-fit to connection nuts  97 ,  98 , implanted at one end side. 
         [0059]    The cover  70  has steps  80 ,  80  arranged projecting towards the side at the side surfaces on both sides of the long side, and an elastic arm  81  for preventing a connector  100 , to be hereinafter described, from coming out arranged in a projecting manner at the side surface on one side. The step  80  positioned on the lower side of the elastic arm  81  has a guide wall  82  arranged in a projecting manner at the outer side edge, and a pair of position regulating nails  83 ,  83  arranged in a projecting manner at the end of the upper surface. 
         [0060]    As shown in  FIG. 12 , the holding member  90  has positioning projections  91  arranged in a projecting matter at a predetermined pitch on the opposing inner side surfaces, and a positioning nail  92  raised from the edge on the lower side. Two sets, each set including two magnets  93 , are arranged facing each other by way of the positioning projections  91  and the nails  92 . The magnet  93  pulls the arc generated between the movable contact  63  and the fixed contact terminals  52 ,  53  with the magnetic force and allows the arc to be easily extinguished. 
         [0061]    As shown in  FIG. 4 , the connector  100  attached to the cover  70  is connected to the lead wire  33   a  connected to the relay terminal  33 . The connector  100  is placed on the step  80  of the cover  70 , and is slid along the guide wall  82  so that the elastic arm  81  locks to an elastic tongue piece  101  of the connector  100  and prevents it from slipping out ( FIG. 1B ). Furthermore, the lead wire  33   a  engages the pair of position regulating nails  83 ,  83  to be position regulated. 
         [0062]    A method of assembling the seal contact device according to the present embodiment will now be described. 
         [0063]    First, the electromagnet block  30  in which the coil  32  is wound around the spool  31  is placed and positioned at the first yoke  21 . The shield member  55  is positioned at the middle of the upper surface of the second yoke  22  caulked and fixed with the fixed iron core  40  in advance, and the drive shaft  61  of the movable contact block  60  is inserted to the pass-through hole  56   a  of the shield member  55  and the shaft hole of the fixed iron core  40 . The inner peripheral edge of the sealed container  51  brazed with the fixed contact terminals  52 ,  53  and the annular skirt portion  54  is fitted to the shield ring  57  of the shield member  55 . The annular skirt portion  54  is laser welded and integrated to the upper surface of the second yoke  22  while pushing the box-shaped molded article  56  with the lower end face of the opening edge of the sealed container  51 . 
         [0064]    The drive shaft  61  projecting out from the lower surface of the fixed iron core  40  is then inserted to the returning coil spring  41  and the shaft hole of the movable iron core  42 . The movable iron core  42  is pushed in against the spring force of the returning coil spring  41  until contacting the fixed iron core  40 . Furthermore, the drive shaft  61  is pushed in until obtaining a predetermined contact pressure, a state in which the movable contact  63  contacts the fixed contact terminals  52 ,  53  with a predetermined contact pressure is maintained, and the lower end of the drive shaft  61  is welded and integrated to the movable iron core  42 . Thereafter, the shock eliminating circular plate  48  made of rubber is attached to the recessed portion formed at the bottom surface of the movable iron core  42 . Then, the bottomed tubular body  34  accommodating the adhesion prevention metal sheet  49  is placed over the movable iron core  42  and the shock eliminating circular plate  48  made of rubber, and the opening edge thereof is welded and integrated through laser welding to the lower surface of the second yoke  22 . After releasing the air in the sealed space from the gas sealing pipe  23 , inactive gas is injected, and the gas sealing pipe  23  is caulked and sealed. 
         [0065]    Furthermore, the bottomed tubular body  34  is inserted to the center hole  31   c  of the spool  31 , and both ends of the second yoke  22  are fitted to and fixed to the cutouts  21   b  of the first yoke  22 . The annular auxiliary yoke  35  is fitted to the lower end of the bottomed tubular body  34  projecting out from the insertion hole  21   a  of the first yoke  21 , and prevented from coming out with the O-ring  36 . 
         [0066]    The drive mechanism unit  20  and the contact mechanism unit  50  integrated one above the other are then inserted into the base  10 , the lower end of the projecting bottomed tubular body  34  is fitted to and positioned in the recessed portion  11  of the base  10 , and the lead wire  33   a  is pulled out from the cutout  16  ( FIG. 4 ). The engagement nail  84  of the cover  70  is then engaged and fixed to the engagement hole  15  of the base  10 . The external connection terminals  95 ,  96  are inserted to the insertion slits  76 ,  77  of the cover  70  from the side, and screws  99   a ,  99   b  are screwed into the screw holes  52   a ,  53   a  of the fixed contact terminals  52 ,  53  to thereby fix the external connection terminals  95 ,  96 . 
         [0067]    As shown in  FIGS. 1A and 1B , the lead wire  33   a  pulled out from the base  10  is bent and the connector  100  is slid along the guide wall  82  arranged at the step  80 , so that the elastic arm  81  locks to the elastic nail  101  of the connector  100  to prevent it from coming out. Finally, the lead wire  33   a  is locked to the elastic nail  83 ,  83  and is position regulated. The power load electromagnetic relay according to the present embodiment is thereby obtained. 
         [0068]    The operation of the contact device according to the present embodiment will now be described. 
         [0069]    As shown in  FIG. 2 , when voltage is not applied to the coil  32 , the movable iron core  42  is separated from the fixed iron core  40  by the spring force of the returning coil spring  41  and the magnetic force of the permanent magnet  45  of the movable iron core  42 . Thus, both ends of the movable contact  63  are separated from the lower ends of the fixed contact terminals  52 ,  53 . 
         [0070]    When voltage is applied to the coil  32 , the fixed iron core  40  attracts the movable iron core  42 , and the movable iron core  42  moves towards the fixed iron core  40  against the spring force of the returning coil spring  41  (first stage S 1 ), as shown in  FIG. 13 . Thus, the drive shaft  61  integral with the movable iron core  42  moves in the axis center direction, and both ends of the movable contact  63  contact the lower ends of the fixed contact terminals  52 ,  53 . In this case, large current flows to the movable contact  63 , and repulsive force arises between the movable contact  63  and the fixed contact terminals  52 ,  53 . However, since the magnetic force simultaneously arises between the first electromagnetic iron piece  62  and the second electromagnetic iron piece  64  and attract each other, the operation of the movable contact  63  moving away from the fixed contact terminals  52 ,  53  is regulated, and the contact welding due to generation of the arc is prevented. 
         [0071]    The movable iron core  42  is attracted towards the fixed iron core  40 , the movable iron core  42  moves against the spring force of the returning coil spring  41  and the contact-pressure coil spring  65 , and the contact pressure increases (second stage S 2 ). The movable contact  63  then contacts the lower ends of the fixed contact terminals  52 ,  53  with a predetermined pressure against the spring force of the returning coil spring  41 , the contact-pressure coil spring  65 , and the contact-pressure plate spring  66  (third stage S 3 ), and thereafter, the movable iron core  61  is attracted to the fixed iron core  40 , and such a state is maintained. 
         [0072]    When application of voltage on the coil  32  is stopped, the magnetic force disappears, and the movable iron core  42  separates from the fixed iron core  40  by the spring force of the returning coil spring  41 . Then, the movable iron core  42  returns to the original position after the movable contact  63  separates from the fixed contact terminals  52 ,  53 . In returning, the shock eliminating circular plate  48  attached to the recessed portion at the bottom surface of the movable iron core  42  impacts the adhesion prevention metal sheet  49 , but the shock eliminating circular plate  48  absorbs and alleviates the impact force. 
         [0073]    According to the present embodiment, two types of contact-pressure coil spring  65  and plate spring  66  are combined. Thus, the spring load changes in multi-stages and can more easily comply with the attractive force characteristics curve, as shown in  FIG. 13 , whereby the design is facilitated and the degree of freedom of design is extended. 
         [0074]    In the present embodiment, a case where the auxiliary yoke  35  is circular in plane has been described, but may be square in plane. 
         [0075]    A case where the annular auxiliary yoke  35  is prevented from coming out with the O-ring  36  has been described, but is not necessarily limited thereto, and may be fixed to the bottomed tubular body  34  through spot welding. 
         [0076]    The present embodiment has been described for the case applied to the power load electromagnetic relay, but the present embodiment is not limited thereto, and may obviously be applied to other electric devices.