Patent Publication Number: US-2023154710-A1

Title: Hermetically sealed electromagnetic contactor

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation application filed under 35 U.S.C. § 111(a) of International Patent Application No. PCT/JP2021/044677, filed on Dec. 6, 2021, the contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a hermetically sealed electromagnetic contactor in which fixed contact pieces and a movable contact piece are arranged in a hermetically sealed container filled with arc-extinguishing gas. 
     BACKGROUND ART 
     As a hermetically sealed electromagnetic contactor, for example, a device described in PTL 1 has been known. 
     A hermetically sealed electromagnetic contactor in PTL 1 includes a pair of fixed contact pieces having fixed contacts, a movable contact piece having a pair of movable contacts capable of coming into contact with and being separated from the fixed contacts of the pair of fixed contact pieces, a hermetically sealed container being filled with arc-extinguishing gas thereinside and housing the pair of fixed contact pieces and the movable contact piece, an electromagnet device coupled to the movable contact piece via a drive shaft, and a pair of arc-extinguishing permanent magnets arranged along both sides in the width direction of the movable contact piece and having facing magnetic pole surfaces, which face each other, magnetized to the same polarity. 
     The hermetically sealed electromagnetic contactor in PTL 1 is configured such that, when arcs are generated when the movable contacts of the movable contact piece are separated from the fixed contacts of the pair of fixed contact pieces, not only are the arcs on which Lorentz force, generated in accordance with Fleming&#39;s left hand rule, is exerted by magnetic flux of the arc-extinguishing permanent magnets crossing the arcs stretched, but also the arcs are cooled by arc-extinguishing gas in the housing case and the arcs are thereby extinguished. 
     CITATION LIST 
     Patent Literature 
     PTL 1: WO 2011/115052 A 
     SUMMARY OF INVENTION 
     Technical Problem 
     Regarding the device in PTL 1, when the internal volume of the hermetically sealed container in which the pair of fixed contact pieces and the movable contact piece are housed is small, pressure and temperature inside the hermetically sealed container increase when arcs are generated, which influences breaking performance. 
     Although increasing the internal volume of the hermetically sealed container in order to suppress increase in internal pressure and temperature when arcs are generated can therefore be considered, the device in PTL 1 has the pair of arc-extinguishing permanent magnets arranged outside the hermetically sealed container, and, when the internal volume of the hermetically sealed container is increased, there is a possibility that distance between the arc-extinguishing permanent magnets and arc generation positions (positions of the fixed contacts and the movable contacts) becomes long and arc stretching effect by Lorentz force becomes weak. 
     As described above, regarding the device in PTL 1, there is a problem in that increasing the internal volume of the hermetically sealed container and decreasing the distance between the arc-extinguishing permanent magnets and the arc generation positions contradict each other and breaking performance thus cannot be improved. 
     Accordingly, the present invention has been made in consideration of the above-described situation, and an object of the present invention is to provide a hermetically sealed electromagnetic contactor that enables breaking performance to be improved by increasing internal volume of a hermetically sealed container and arranging arc-extinguishing permanent magnets close to arc generation positions. 
     Solution to Problem 
     In order to achieve the above-described object, according to one aspect of the present invention, there is provided a hermetically sealed electromagnetic contactor including a pair of fixed contact pieces having fixed contacts, a movable contact piece having a pair of movable contacts capable of coming into contact with and being separated from the fixed contacts of the pair of fixed contact pieces, an electromagnet unit configured to drive the movable contact piece, a hermetically sealed container configured to house the pair of fixed contact pieces, the movable contact piece, and the electromagnet unit in the same space in a hermetically sealed manner and being filled with arc-extinguishing gas, and at least a pair of arc-extinguishing permanent magnets arranged inside the hermetically sealed container and configured to stretch arcs generated between the fixed contacts of the pair of fixed contact pieces and the pair of movable contacts of the movable contact piece. 
     Advantageous Effects of Invention 
     A hermetically sealed electromagnetic contactor of the present invention enables breaking performance to be improved by increasing internal volume of a hermetically sealed container and arranging arc-extinguishing permanent magnets close to arc generation positions. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a perspective view illustrative of an external appearance of a hermetically sealed electromagnetic contactor of an embodiment according to the present invention; 
         FIG.  2    is a diagram illustrative of a cross section of a hermetically sealed container constituting the hermetically sealed electromagnetic contactor of the embodiment; 
         FIG.  3    is a cross section taken along the long-length direction of the hermetically sealed electromagnetic contactor of the embodiment; 
         FIG.  4    is a cross section taken along the short-length direction of the hermetically sealed electromagnetic contactor of the embodiment; 
         FIG.  5    is a cross-sectional view taken along the line V-V and viewed from the arrows in  FIG.  3   ; and 
         FIG.  6    is a diagram illustrative of a structure of magnet holders, permanent magnet yokes, and arc-extinguishing permanent magnets mounted on the magnet holders, which are arranged inside a housing case. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Next, an embodiment according to the present invention will be described with reference to the drawings. In the following drawing description, the same or similar reference signs are assigned to the same or similar constituent components. However, it should be noted that the drawings are schematic and relations between thicknesses and planar dimensions, ratios among thicknesses of respective layers, and the like are different from actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. It should also be noted that the drawings include portions having different dimensional relationships and ratios from one another among the drawings. 
     In addition, the embodiments, which will be described below, indicate a device and a method to embody the technical idea of the present invention by way of example, and the technical idea of the present invention does not limit the materials, shapes, structures, arrangements, and the like of the constituent components to those described below. The technical idea of the present invention can be subjected to a variety of alterations within the technical scope prescribed by the claims described in CLAIMS. 
     Note that terms indicating directions, such as “upper”, “lower”, “left”, “right”, “bottom”, “front”, “rear”, “long-length direction”, and “short-length direction”, that are referred to in the following description are used referring to the directions in the accompanying drawings. 
     An electromagnetic contactor as a hermetically sealed electromagnetic contactor of an embodiment according to the present invention will be described with reference to  FIGS.  1  to  6   . 
     An electromagnetic contactor  1  of the present embodiment, illustrated in  FIG.  1   , includes a housing case  4  composed of a bottomed box-shaped insulating box  2  that is formed of synthetic resin, such as phenol, polyamide, and polybutylene terephthalate, and an insulating substrate  3  that closes an upper opening of the insulating box  2  and is formed of synthetic resin. The insulating box  2  and the insulating substrate  3  are bonded by, for example, epoxy resin-based adhesive. 
     The insulating box  2  includes first and second sidewalls  2   b  and  2   c  that are opposed to each other in the short-length direction, third and fourth sidewalls  2   d  and  2   e  that are opposed to each other in the long-length direction, fifth and sixth sidewalls  2   f  and  2   g  that are opposed to each other at a shorter distance than a distance at which the third and fourth sidewalls  2   d  and  2   e  are opposed to each other at lower positions of the third and fourth sidewalls  2   d  and  2   e  (see  FIG.  3   ), and a bottom wall  2   h  that extends in the right and left direction at the lower edges of the first and second sidewalls  2   b  and  2   c  and the fifth and sixth sidewalls  2   f  and  2   g  (see  FIG.  3   ). 
       FIG.  2    illustrates a portion of the insulating substrate  3 , which constitutes the housing case  4 , and a surface of the insulating substrate  3  that comes into contact with the outside air is coated with laminated films LF having a predetermined thickness. 
     The laminated films LF are specifically laminated films of clay crystals, and exchanging interlayer ions in purified smectite and joining the laminated films with a water-soluble organic binder OB, such as PVA and water-soluble nylon, causes the laminated films to exhibit labyrinth effect and thereby prevent permeation of gas molecules, such as hydrogen and nitrogen. The laminated films LF are stacked in the thickness direction, and the thickness thereof is, for example, 2 μm. The laminated films LF are applied by a spray method in which coating liquid is formed into mist and applied to the insulating substrate  3 , and are completed by being burned at a temperature at which interlayer ions are incorporated into clay crystals, for example, a temperature greater than or equal to 150 degrees. 
     Note that surfaces of the insulating box  2  that come into contact with the outside air, that is, all surfaces of the insulating box  2 , including boundary portion between the insulating box  2  and the insulating substrate  3 , that come into contact with the outside air, are also coated with laminated films LF having a predetermined thickness. 
     As illustrated in  FIG.  3   , connection protruding lines  2   i  are formed in the short-length direction on the upper edges of the third and fourth sidewalls  2   d  and  2   e  of the insulating box  2 , and, as illustrated in  FIG.  4   , connection protruding lines  2   i  are also formed in the long-length direction on the upper edges of the first and second sidewalls  2   b  and  2   c  of the insulating box  2 . Because of this configuration, on the upper edges of the first to fourth sidewalls  2   b  to  2   e , which constitute the insulating box  2 , the connection protruding lines  2   i  are continuously formed in a rectangular frame shape. 
     In addition, as illustrated in  FIGS.  3  and  4   , connection recessed lines  3   a  are continuously formed in a rectangular frame shape on the under surface of the insulating substrate  3 , and, when the insulating substrate  3  is arranged in such a way as to close an upper space of the insulating box  2 , the rectangular frame-shaped connection protruding lines  2   i  of the insulating box  2  enter into the inside of the connection recessed lines  3   a  of the insulating substrate  3 . Injecting adhesive for resin onto the connection protruding lines  2   i  and into the connection recessed lines  3   a  and subsequently inserting the connection protruding lines  2   i  of the insulating box  2  into the connection recessed lines  3   a  of the insulating substrate  3  cause airtightness of a contact housing portion  6  and an electromagnet housing portion  8 , which are internal spaces of the housing case  4 , to be maintained. 
     As illustrated in  FIGS.  3  and  4   , an internal space on the upper side of the housing case  4  that is enclosed by the insulating substrate  3 , which closes the upper opening of the insulating box  2 , and the first to fourth sidewalls  2   b  to  2   e  is defined as the contact housing portion  6  that houses a contact mechanism  5 , and an internal space on the lower side of the housing case  4  that is enclosed by the first and second sidewalls  2   b  and  2   c , the fifth and sixth sidewalls  2   f  and  2   g , and the bottom wall  2   h  is defined as the electromagnet housing portion  8  that communicates with the contact housing portion  6  and houses an electromagnet unit  7 . 
     The contact mechanism  5 , which is housed in the contact housing portion  6  of the housing case  4 , includes a pair of fixed contact pieces  10  and  11  (hereinafter, referred to as a first fixed contact piece  10  and a second fixed contact piece  11 ) that are fixed to the insulating substrate  3  and a movable contact piece  12  that includes first and second movable contacts  12   a  and  12   b , which face first and second fixed contacts  10   a  and  11   a  formed on the first and second fixed contact pieces  10  and  11 , respectively, and that extends in the long-length direction, as illustrated in  FIG.  3   . 
     The movable contact piece  12  is supported by a driving portion  14 , which is coupled to a movable plunger  13  in the electromagnet unit  7 , in a movable manner in the up-and-down direction. 
     A spring receptacle  15 , which is coupled to the driving portion  14 , is arranged above the center in the long-length direction of the movable contact piece  12 , a contact spring  16  is arranged between the spring receptacle  15  and a central upper portion of the movable contact piece  12 , and the contact spring  16  applies predetermined downward biasing force to the movable contact piece  12 . 
     The first fixed contact piece  10  and the second fixed contact piece  11  are conductive plates that are C-shaped in side view, and are formed integrally with the insulating substrate  3  in such a manner as to be separated from each other on both end sides in the longitudinal direction of the movable contact piece  12 . 
     The first fixed contact piece  10  is arranged on one end side in the longitudinal direction and the first movable contact  12   a  side of the movable contact piece  12 , and includes a first conductive plate portion  10   b  that faces the first movable contact  12   a  of the movable contact piece  12  from the lower side and has the first fixed contact  10   a  formed on the upper surface, a second conductive plate portion  10   c  that is bent from an edge of the first conductive plate portion  10   b  separated from the movable contact piece  12  and extends upward, and a third conductive plate portion  10   d  that is bent from the upper edge of the second conductive plate portion  10   c  and extends above the movable contact piece  12 . 
     With the insulating substrate  3 , a portion of the second conductive plate portion  10   c  of the first fixed contact piece  10  and a bolt head  17   a  of a terminal bolt  17 , which is screw-fitted into the third conductive plate portion  10   d , are integrally formed and a plate-shaped insulating cover portion  18  that extends between the second conductive plate portion  10   c  and the movable contact piece  12  in such a manner as to cover an inner side surface of the second conductive plate portion  10   c  facing the movable contact piece  12  is also integrally formed. 
     The second fixed contact piece  11  is also arranged on the other end side in the longitudinal direction and the second movable contact  12   b  side of the movable contact piece  12 , and includes a first conductive plate portion  11   b  that faces the second movable contact  12   b  of the movable contact piece  12  from the lower side and has the second fixed contact  11   a  formed on the upper surface, a second conductive plate portion  11   c  that is bent from an edge of the first conductive plate portion  11   b  separated from the movable contact piece  12  and extends upward, and a third conductive plate portion  11   d  that is bent from the upper edge of the second conductive plate portion  11   c  and extends above the movable contact piece  12 . 
     With the insulating substrate  3 , a portion of the second conductive plate portion  11   c  of the second fixed contact piece  11  and a bolt head  19   a  of a terminal bolt  19  are also integrally formed and a plate-shaped insulating cover portion  20  that extends between the second conductive plate portion  11   c  and the movable contact piece  12  in such a manner as to cover an inner side surface of the second conductive plate portion  11   c  facing the movable contact piece  12  is also integrally formed. 
     When the movable contact piece  12  is in a released state, the movable contact piece  12  is brought into a state in which the movable contacts  12   a  and  12   b , which are positioned on both end sides in the longitudinal direction, and the fixed contacts  10   a  and  11   a  of the first and second fixed contact pieces  10  and  11  are separated from each other with a predetermined gap maintained therebetween, respectively 
     In addition, the movable contact piece  12  is set in such a way that, when the movable contact piece  12  is at a turn-on position, the movable contacts  12   a  and  12   b  come into contact with the fixed contacts  10   a  and  11   a  of the first and second fixed contact pieces  10  and  11 , respectively, with a predetermined contact pressure exerted by the contact spring  16 . 
     In addition, as illustrated in  FIG.  5   , magnet holders  21  and  22 , which are formed of synthetic resin, are arranged in the contact housing portion  6 , and the magnet holders  21  and  22  are supported by upper flange portions  36   b  of the electromagnet unit  7 , which will be described later. 
     On the magnet holders  21  and  22 , first to fourth arc-extinguishing permanent magnets  30  to  33  are arranged and permanent magnet yokes  34  and  35 , which surround the outer peripheries of the first to fourth arc-extinguishing permanent magnets  30  to  33 , are also arranged. 
     The first arc-extinguishing permanent magnet  30  is arranged in such a manner as to face one side surface in the longitudinal direction of the movable contact piece  12  via the magnet holder  21 , and the second arc-extinguishing permanent magnet  31  is arranged in such a manner as to face the other side surface in the longitudinal direction of the movable contact piece  12  via the magnet holder  22 . The first and second arc-extinguishing permanent magnets  30  and  31  are magnetized in such a manner that magnetic pole surfaces that face the movable contact piece  12  are magnetized to the N-pole. 
     The third arc-extinguishing permanent magnet  32  is arranged in such a manner as to face one side surface in the short-length direction of the movable contact piece  12  via the magnet holder  22 , and the fourth arc-extinguishing permanent magnet  33  is arranged in such a manner as to face the other side surface in the short-length direction of the movable contact piece  12  via the magnet holder  21 . The third and fourth arc-extinguishing permanent magnets  32  and  33  are magnetized in such a manner that magnetic pole surfaces that face the movable contact piece  12  are magnetized to the S-pole. 
     Because of this configuration, magnetic flux that starts from the N-pole of the first arc-extinguishing permanent magnet  30  and flows to the S-poles of the third arc-extinguishing permanent magnet  32  and the fourth arc-extinguishing permanent magnet  33  passes a vicinity of a portion at which the first fixed contact  10   a  of the first fixed contact piece  10  and the first movable contact  12   a  of the movable contact piece  12  face each other and crosses the portion with large magnetic flux density. 
     In addition, magnetic flux that starts from the N-pole of the second arc-extinguishing permanent magnet  31  and flows to the S-poles of the third arc-extinguishing permanent magnet  32  and the fourth arc-extinguishing permanent magnet  33  passes a vicinity of a portion at which the second fixed contact  11   a  of the second fixed contact piece  11  and the second movable contact  12   b  of the movable contact piece  12  face each other and crosses the portion with large magnetic flux density. 
       FIG.  6    is a diagram illustrative of a specific configuration of the afore-described magnet holders  21  and  22  and permanent magnet yokes  34  and  35 . 
     The magnet holders  21  and  22  have shapes into which a rectangular cylindrical body is halved in substantially L-shapes, and one magnet holder  21  has a first magnet housing recessed portion  24   a  and a fourth magnet housing recessed portion  24   b  formed on outer surfaces between a pair of engaging pieces  23   a  and  23   b , which protrude outward in parallel with each other. In addition, the other magnet holder  22  also has a second magnet housing recessed portion  24   c  and a third magnet housing recessed portion  24   d  formed on outer surfaces between a pair of engaging pieces  23   c  and  23   d , which protrude outward in parallel with each other. 
     The first arc-extinguishing permanent magnet  30  and the fourth arc-extinguishing permanent magnet  33  are fitted into the first magnet housing recessed portion  24   a  and the fourth magnet housing recessed portion  24   b  of the one magnet holder  21 , respectively. In addition, the second arc-extinguishing permanent magnet  31  and the third arc-extinguishing permanent magnet  32  are fitted into the second magnet housing recessed portion  24   c  and the third magnet housing recessed portion  24   d  of the other magnet holder  22 , respectively. 
     The magnet holders  21  and  22 , on which the first to fourth arc-extinguishing permanent magnets  30  to  33  are mounted, are combined in such a way as to form a rectangular cylindrical body. 
     The permanent magnet yokes  34  and  35 , on the other hand, are metal plate materials each of which is bent in a substantially U shape, and are arranged on the outer periphery of the pair of magnet holders  21  and  22 , which is combined into a rectangular cylindrical body, while surrounding the outer peripheries of the first to fourth arc-extinguishing permanent magnets  30  to  33 , by engaging both end portions in a width direction of the permanent magnet yokes  34  and  35  with the pair of engaging pieces  23   a  and  23   b  and the pair of engaging pieces  23   c  and  23   d  of the pair of magnet holders  21  and  22 . 
     On the other hand, the electromagnet unit  7 , which is housed in the electromagnet housing portion  8  of the housing case  4 , has a spool  36  arranged therein, as illustrated in  FIG.  3   . The spool  36  includes a central cylindrical portion  36   a  into which the afore-described movable plunger  13  is inserted in a vertically slidable manner, an upper flange portion  36   b  that projects radially outward from the upper edge of the central cylindrical portion  36   a , a lower flange portion  36   c  that projects radially outward from the lower edge of the central cylindrical portion  36   a , and a skirt portion  36   d  that extends from the outer peripheral edge of the lower flange portion  36   c  in a direction separating from the central cylindrical portion  36   a . In a coil housing space formed by the central cylindrical portion  36   a , the upper flange portion  36   b , and the lower flange portion  36   c , an excitation coil  37  is wound, and it is configured such that direct current is applied to the excitation coil  37  from a power source (not illustrated) connected to coil terminals  38 . 
     On the outer periphery of the spool  36 , a pair of magnetic yokes  39   a  and  39   b , which are formed in C-shapes in side view, are arranged in the short-length direction, and upper edge-side yokes and lower edge-side yokes of the magnetic yokes  39   a  and  39   b  are supported by the upper flange portion  36   b  and the skirt portion  36   d , respectively. 
     As illustrated in  FIG.  3   , to an upper portion of the solid cylindrically shaped movable plunger  13 , a pair of plate-shaped elastic members  40   a  and  40   b  are fixed, in such a manner as to be separated outward in the long-length direction from each other and extend obliquely upward. To a position lower than the pair of elastic members  40   a  and  40   b  of the movable plunger  13 , a plunger downward movement restricting portion  41 , which projects radially outward, is fixed. To a lower portion of the movable plunger  13 , a plunger upward movement restricting portion  42 , which projects radially outward, is fixed. 
     In addition, as illustrated in  FIG.  3   , on a lower portion of the driving portion  14 , a pair of driving portion-side engaging portions  43   a  and  43   b , which extend inward in the long-length direction from both edges in the long-length direction, are formed. By the tip sides of the pair of elastic members  40   a  and  40   b  of the movable plunger  13  mounting on and engaging with the upper surfaces of the pair of driving portion-side engaging portions  43   a  and  43   b , the driving portion  14  and the movable plunger  13  are coupled via the pair of elastic members  40   a  and  40   b.    
     As illustrated in  FIG.  3   , a spring guide  44  is arranged at a lowermost portion of the electromagnet housing portion  8  (on the bottom wall  2   h ), and a return spring  45  is arranged between the bottom wall  2   h  and the movable plunger  13  while being supported by the spring guide  44 . 
     The contact housing portion  6  and the electromagnet housing portion are filled with one or a plurality of types of arc-extinguishing gas, such as hydrogen and nitrogen, from a gas injection portion  46 , which is formed in the bottom wall  2   h  of the housing case  4 . 
     Next, operation of the electromagnetic contactor  1  of the present embodiment will be described. 
     It is assumed that, in the electromagnetic contactor  1  of the present embodiment, the negative pole (−) is connected to the first fixed contact piece  10  and the terminal bolt  17  and the positive pole (+) is connected to the second fixed contact piece  11  and the terminal bolt  19 . 
     It is also assumed that the electromagnetic contactor  1  is in a released state in which the excitation coil  37  of the electromagnet unit  7  is in a non-excited state and the electromagnet unit  7  does not generate excitation force to cause the movable plunger  13  to descend. 
     In the released state, the movable plunger  13  is biased upward by the return spring  45 . Thus, the plunger downward movement restricting portion  41  of the movable plunger  13  comes into contact with the driving portion-side engaging portions  43   a  and  43   b  of the driving portion  14  and upward movement of the driving portion  14  is thereby restricted, and the first movable contact  12   a  and the second movable contact  12   b  of the movable contact piece  12  of the contact mechanism  5  are separated upward from the first fixed contact  10   a  of the first fixed contact piece  10  and the second fixed contact  11   a  of the second fixed contact piece  11  by a predetermined distance, respectively. Therefore, a current path between the first fixed contact piece  10  and the second fixed contact piece  11  is in a cut-off state, and the contact mechanism  5  is in an open contact state. 
     When current is applied to the excitation coil  37  of the electromagnet unit  7  while the electromagnetic contactor  1  is in the released state, excitation force is generated in the electromagnet unit  7  and pushes down the movable plunger  13  downward against the biasing force of the return spring  45 . The lower surface of the plunger downward movement restricting portion  41  coming into contact with the upper flange portion  36   b  of the spool  36  causes the descent of the movable plunger  13  to come to a stop. 
     The descent of the movable plunger  13  as described above causes the movable contact piece  12 , which is supported by the driving portion  14  connected to the movable plunger  13  via the elastic members  40   a  and  40   b  and the driving portion-side engaging portions  43   a  and  43   b , to also descend, and the first movable contact  12   a  and the second movable contact  12   b  of the movable contact piece  12  of the contact mechanism  5  come into contact with the first fixed contact  10   a  of the first fixed contact piece  10  and the second fixed contact  11   a  of the second fixed contact piece  11 , respectively, with the contact pressure of the contact spring  16 . 
     Therefore, the contact mechanism  5  is brought to a closed contact state in which large current from a power supply source is supplied to a load device through the first fixed contact piece  10 , the movable contact piece  12 , and the second fixed contact piece  11 . 
     When the power supply to the load device is to be cut off while the contact mechanism  5  is in the closed contact state, excitation of the excitation coil  37  of the electromagnet unit  7  is stopped. 
     When the excitation of the excitation coil  37  is stopped, excitation force causing the movable plunger  13  to move downward by the electromagnet unit  7  disappears, and thus the movable plunger  13  ascends by biasing force of the return spring  45 . 
     The ascent of the movable plunger  13  causes the movable contact piece  12 , which is supported by the driving portion  14 , to ascend, and the contact mechanism  5  is brought to an open contact start state in which the movable contact piece  12  is separated upward from the first fixed contact piece  10  and the second fixed contact piece  11 . 
     When the contact mechanism  5  is in the open contact start state as described above, an arc is generated between the first movable contact  12   a  of the movable contact piece  12  and the first fixed contact  10   a  of the first fixed contact piece  10 . In addition, an arc is also generated between the second movable contact  12   b  of the movable contact piece  12  and the first second contact  11   a  of the second fixed contact piece  11 . The arcs causes the current carrying state to continue. On this occasion, a current direction of the arc generated between the first movable contact  12   a  and the first fixed contact  10   a  is a direction pointing from the first movable contact  12   a  to the first fixed contact  10   a , and a current direction of the arc generated between the second fixed contact  11   a  and the second movable contact  12   b  is a direction pointing from the second fixed contact  11   a  to the second movable contact  12   b.    
     As illustrated in  FIG.  5   , magnetic flux that starts from the N-pole of the first arc-extinguishing permanent magnet  30  and flows to the S-pole of the third arc-extinguishing permanent magnet  32  and magnetic flux that starts from the N-pole of the first arc-extinguishing permanent magnet  30  and flows to the S-pole of the fourth arc-extinguishing permanent magnet  33  pass a vicinity of an arc. Lorentz force pointing in the short-length direction is generated in accordance with Fleming&#39;s left hand rule, based on a relationship between flow of current of the arc generated between the first movable contact  12   a  and the first fixed contact  10   a  and the magnetic flux, and the arc generated between the first fixed contact  10   a  and the first movable contact  12   a  is not only stretched by the Lorentz force but also cooled by the arc-extinguishing gas in the contact housing portion  6  and is thereby extinguished. 
     In addition, when an arc is generated between the second movable contact  12   b  of the movable contact piece  12  and the second fixed contact  11   a  of the second fixed contact piece  11 , Lorentz force pointing in the short-length direction is generated in accordance with Fleming&#39;s left hand rule, based on a relationship between flow of current of the arc generated between the second movable contact  12   b  and the second fixed contact  11   a  and magnetic flux generated among the second arc-extinguishing permanent magnet  31 , the third arc-extinguishing permanent magnet  32 , and the fourth arc-extinguishing permanent magnet  33 , and the arc is not only stretched by the Lorentz force but also cooled by the arc-extinguishing gas in the contact housing portion  6  and is thereby extinguished. 
     Next, advantageous effects of the present embodiment will be described. 
     Since the housing case  4  (the insulating box  2  and the insulating substrate  3 ) of the present embodiment houses the pair of fixed contact pieces  10  and  11 , the movable contact piece  12 , and the electromagnet unit  7  in the same space and, because of this configuration, internal volume allowed for filling of arc-extinguishing gas is substantially greater, the allowable amount of leakage is smaller, and internal pressure and temperature in the contact housing portion  6  at the time of arc generation are more unlikely to increase than those of a housing container of a conventional device, which houses only a contact mechanism, it is possible to improve breaking performance of the electromagnetic contactor  1 . 
     In addition, since the first to fourth arc-extinguishing permanent magnets  30  to  33  are arranged in the contact housing portion  6  and, because of this configuration, distance between the first to fourth arc-extinguishing permanent magnets  30  to  33  and arc generation positions (positions of the fixed contacts  10   a  and  11   a  and the movable contacts  12   a  and  12   b ) does not become long even when the internal volume of the contact housing portion  6  is increased, strong magnetic flux of the first and second arc-extinguishing permanent magnets  30  and  31  crossing the arcs causes Lorentz force to be exerted on the arcs in accordance with Fleming&#39;s left hand rule and the arcs to be surely stretched, and the arcs is cooled by the arc-extinguishing gas and is thereby extinguished, it is possible to improve breaking performance of the electromagnetic contactor  1 . 
     In addition, since the first to fourth arc-extinguishing permanent magnets  30  to  33  are mounted on the first to fourth magnet housing recessed portions  24   a  to  24   d  that are formed on the outer surfaces of the magnet holders  21  and  22  arranged in the contact housing portion  6  of the housing case  4 , it is possible to secure insulation against an arc. 
     Further, since the housing case  4  is formed of synthetic resin, it is possible to not only achieve substantial weight reduction but also achieve reduction in manufacturing cost, compared with an electromagnetic contactor including a case made of ceramic like a conventional device. 
     Further still, since the housing case  4  is coated with laminated films LF, which are laminated films of clay crystals, it is possible to suppress permeation of gas molecules, such as hydrogen and nitrogen, and thereby prevent leakage of arc-extinguishing gas, with which the housing case  4  is filled. 
     REFERENCE SIGNS LIST 
       1  Electromagnetic contactor 
       2  Insulating box 
       2   b  to  2   e  First to fourth sidewalls 
       2   f  Fifth sidewall 
       2   g  Sixth sidewall 
       2   h  Bottom wall 
       2   i  Connection protruding line 
       3  Insulating substrate 
       3   a  Connection recessed line 
       4  Housing case (hermetically sealed container) 
       5  Contact mechanism 
       6  Contact housing portion 
       7  Electromagnet unit 
       8  Electromagnet housing portion 
       10  First fixed contact piece 
       10   a  First fixed contact 
       10   b  First conductive plate portion 
       10   c  Second conductive plate portion 
       10   d  Third conductive plate portion 
       11  Second fixed contact piece 
       11   a  Second fixed contact 
       11   b  First conductive plate portion 
       11   c  Second conductive plate portion 
       11   d  Third conductive plate portion 
       12  Movable contact piece 
       12   a  First movable contact 
       12   b  Second movable contact 
       13  Movable plunger 
       14  Driving portion 
       15  Spring receptacle 
       16  Contact spring 
       17 ,  19  Terminal bolt 
       17   a ,  19   a  Bolt head 
       18 ,  20  Insulating cover portion 
       21 ,  22  Magnet holder 
       23   a ,  23   b ,  23   c ,  23   d  Engaging piece 
       24   a  to  24   d  First to fourth magnet housing recessed portions 
       30  to  33  First to fourth arc-extinguishing permanent magnets 
       34 ,  35  Permanent magnet yoke 
       36  Spool 
       36   a  Central cylindrical portion 
       36   b  Upper flange portion 
       36   c  Lower flange portion 
       36   d  Skirt portion 
       37  Excitation coil 
       38  Coil terminal 
       39   a ,  39   b  Magnetic yoke 
       40   a ,  40   b  Elastic member 
       41  Plunger downward movement restricting portion 
       42  Plunger upward movement restricting portion 
       43   a ,  43   b  Driving portion-side engaging portion 
       44  Spring guide 
       45  Return spring 
       46  Gas injection portion 
     LF Laminated film (laminated film of clay crystals) 
     OB Organic binder