Abstract:
A switching device which can be small-sized by improving a shielding performance and can improve the reliability of switching characteristics. A permanent magnet disposed near stationary contacts is arranged in its pole-face perpendicularly of the axis of a moving contact member.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority from Japanese Patent Application No. 233201/2002 filed Aug. 9, 2002. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a switching device and, more particularly, to a switching device such as an electromagnetic relay, a switch or a timer for switching an electric current. 
   2. Description of the Related Art 
   As the switching device for closing the DC electric current, there is a closed type relay device, as disclosed in JP-T-9-510040, for example) in the prior art. 
   As a coil portion  40  is magnetized and demagnetized, more specifically, a plunger  9  is brought into and out of contact with a core center  4  so that an armature assembly  8 , as integrated with the plunger  9 , and an armature shaft  10  are slit in the axial direction to bring a moving contact disc  21  into and out of contact with stationary contacts  22  and  22 . 
   In the closed type relay device, the arc current, as produced when the moving contact disc  21  is brought into and out of contact with the stationary contacts  22  and  22  is broken by extending it outward with the magnetic force of a permanent magnet  33  packaged in the stationary contact  22 . 
   However, a predetermined extension is needed for extending and breaking the arc current. Therefore, the closed type relay device cannot reduce the size of a structure  3  housing the stationary contact  22  and the moving contact disc  21 , so that its size reduction is limited. 
   Even if the directivity for mounting the permanent magnet  33 , i.e., the so-called “polarity” is arranged conforming the specifications, according to the aforementioned closed type relay device, the arc current produced is extended inward when the current flow direction in use is reversed from that of the specifications, so that it is difficult to break. When an AC current is to be switched by the closed type relay device, moreover, the AC current flow direction periodically changes so that the arc current produced at the switching time is extended not only outward but also inward. As a result, the arc current produced cannot be easily broken in a reliable manner, thus causing a problem that the reliability of the switching characteristics is low. 
   SUMMARY OF THE INVENTION 
   In view of this problem, the invention has an object to provide a switching device, which can be small-sized by improving a shielding performance and can improve the reliability of switching characteristics. 
   In order to achieve this object, according to the invention, there is provided a switching device for making/breaking contact by bringing one end portion of a moving contact member into and out of contact with stationary contacts, comprising: a permanent magnet disposed near the stationary contacts and having its pole-face arranged perpendicularly of the axis of the moving contact member. 
   According to the invention, the arc current produced at the switching time is so extended on the basis of the Fleming&#39;s left-hand law (or by the Lorentz&#39;s force) as to whirl along the pole-faces of the permanent magnets, until it is broken. Therefore, a large space is not required for breaking the arc current unlike the examples of the prior art, so that the device can be small-sized. 
   Even if the flow direction of the current to be broken in use is reversed, moreover, the whirling direction of the arc current produced changes to clockwise or counterclockwise. Specifically, it is unchanged that the arc current whirls along the pole-faces of the permanent magnets, so that the arc current produced can be reliably broken. Even if the current flow direction periodically changes as in case the AC current is to be switched, moreover, the produced arc current whirls alternately in the opposite directions along the pole-faces of the permanent magnets. As a result, the arc current can be reliably broken no matter whether it might be a DC current or an AC current, so that the reliability of the switching characteristics is improved. 
   In an embodiment of the invention, the two end portions of the moving contact member may be brought into and out of contact with the stationary contacts. 
   This embodiment can also be applied to the moving contact member having its two end portions brought into and output the stationary contacts, so that its application is widened. 
   In another embodiment of the invention, a plurality of moving contact members may be juxtaposed to each other. 
   According to this embodiment, the moving contact members are juxtaposed so that the arc voltage is lowered by the current-limiting effect. As a result, the arc is reluctant to occur or can be broken if produced. 
   In a different embodiment of the invention, a step may be formed between the adjacent moving contact members. 
   According to this embodiment, a time lag is established between a plurality of contact switching actions. By making the material of the moving contact member different, therefore, the contact wear by the making current can be suppressed to elongate the contact lifetime. 
   In another embodiment of the invention, the permanent magnets arranged on the two end sides of the moving contact member may be arranged in polarity in an identical direction. 
   According to this embodiment, the arc current produced is so relatively extended in the opposite direction as to whirl. Therefore, the heat is not applied only to one side of the housing so that it can be dispersed over a wide range thereby to provide a switching device having excellent cooling properties. 
   According to a different embodiment of the invention, a shielding wall may be interposed between the permanent magnets, the moving contact member and the stationary contacts for shielding at least the pole-faces of the permanent magnets. 
   According to this embodiment, the pole-faces of the permanent magnets are protected by the shielding wall thereby to provide an effect that the permanent magnets can be prevented from aging. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view showing an embodiment of the case, in which a switching device according to the invention is applied to a DC current breaking relay; 
       FIG. 2  is an exploded perspective view of  FIG. 1 ; 
       FIG. 3  is an exploded perspective view of a relay body shown in  FIG. 2 ; 
       FIG. 4  is an exploded perspective view of an electromagnet block shown in  FIG. 3 ; 
       FIG. 5  is an exploded perspective view of a sealing case shown in  FIG. 4 ; 
       FIGS. 6A and 6B  are enlarged sectional views showing a method for caulking the sealing case shown in  FIG. 5 ; 
       FIGS. 7A and 7B  are exploded perspective views of a moving contact block shown in  FIG. 3 ; 
       FIGS. 8A and 8B  are exploded perspective views of a stationary contact block shown in  FIG. 3 ; 
       FIGS. 9A and 9B  are exploded perspective views of the stationary contact block shown in  FIG. 3 ; 
       FIG. 10  is a longitudinal section of the switching device shown in  FIG. 1 ; 
       FIGS. 11A and 11B  are partially enlarged sectional views of  FIG. 10 ; 
       FIG. 12  is a longitudinal section showing the relay of the embodiment according to the invention and taken at a different angle; 
       FIGS. 13A and 13B  are partially enlarged views of  FIG. 12 ; 
       FIG. 14  is a transverse section of the switching device shown in  FIG. 1 ; and 
       FIG. 15  is a schematic diagram showing an ark breaking mechanism according to an embodiment of the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Embodiment according to the invention will be described with reference to  FIG. 1  to  FIG. 15 . The first embodiment of the invention is applied to a DC load switching relay, in which a relay body  20  is housed in a space defined by a box-shaped case  10  and a box-shaped cover  15  integrated, as shown in  FIG. 1  and  FIG. 2 . 
   The box-shaped case  10  is provided, as shown in  FIG. 2 , with: a recess  11  for housing a later-described electromagnet block  30 ; fixing through holes  12  in a pair of plane corners positioned on a diagonal line; and connecting recesses  13  positioned in the remaining plane corners. In the connecting recesses  13 , connecting nats (not shown in the figure) are embedded. 
   The box-shaped cover  15  is so shaped that it can fit the box-shaped case  10  and can house a later-described sealing case block  40 . In the ceiling of the box-shaped cover  15 , moreover, there are formed connecting holes  16  and  16 , from which there are protruded connecting terminals  75  and  85  of the relay body  20 . From the ceiling of the box-shaped cover  15 , moreover, there are protrusions  17  and  17  for housing a gas vent pipe  21 . The protrusions  17  and  17  are connected through a partition wall  18  and have a function as an insulating wall together. By engaging engaged holes  19 , which are formed in the edge portion of the lower opening of the box-shaped cover  15 , with engaging pawls  14 , which are formed on the edge portion of the upper opening of the box-shaped case  10 , moreover, the cover  15  and the case  10  are integrally jointed to each other. 
   In the relay body  20 , as shown in  FIG. 3 , a contact mechanism block  50  is sealed in the sealing case block  40  mounted on the electromagnet block  30 . 
   This electromagnet block  30  is as shown in  FIG. 4 , so integrated that a pair of spools  32  wound with coils  31  are juxtaposed to each other around two iron cores  37  and through a yoke  39 . 
   Relay terminals  34  and  35  are individually press-fitted on the two opposed side end faces of the lower one  32   a  of flange portions  32   a  and  32   b  at the two ends of the spools  32 . And, the coil  31  wounded on the spools  32  is bound and soldered at its one-end portion to the one-end portion (or bind portions)  34   a  of one relay terminal  34  and is bound and soldered at its other end (bind portion) to one-end portion (or bind portion)  35   a  of the other relay terminal  35 . In the relay terminals  34  and  35 , moreover, not only the bind portions  34   a  but also other end portions (or joint portions)  35   b  are bent up. Of the relay terminals  34  and  35  assembled with the juxtaposed spools  32  and  32 , the joint portion  35   b  of the relay terminal  35  and the bind portion  34   a  of the other relay terminal  34  are jointed and soldered to each other. Of the adjacent relay terminals  35  and  34 , moreover, the bind portion  35   a  and a joint portion  34   b  are jointed and soldered to each other. Thus, the two coils  31  and  31  are connected. Moreover, the paired flange portions  32   a  and  32   b  of the spools  32  are individually spanned with coil terminals  36  and  36  and connected to the joint portions  34   b  and  35   b  of the relay terminals  34  and  35 . 
   The sealing case block  40  is constructed to include a sealing case  41  capable of housing the later-described contact mechanism block  50 , and a sealing cover  45  for sealing the opening of he sealing case  41 . In the bottom face of the sealing case  41 , there are formed a pair of press-fit holes  42  ( FIG. 5 ) for press-fitting the icon cores  37 . In the sealing cover  45 , on the other hand, there are formed a pair of insert holes  46  and  46  capable of inserting the connecting terminals  75  and  85  of the later-described contact mechanism block  50 , and a loosely fitting hole  47  capable of fitting the gas vent pipe  21  loosely. 
   The electromagnet block  30  and the sealing case  40  are assembled in the following procedure. 
   First of all, the relay terminals  34  and  35  are individually press-fitted in the flange portions  32   a  of the spools  32  whereas the coils  31  are wound on the spools  32 , and the lead wires are individually bound on the soldered to the bind portions  34   a  and  35   a  of the relay terminals  34  and  35 . Next, there are juxtaposed the paired spools  32 , from which the bind portions  34   a  and  35   a  and the joint portions  34   b  and  35   b  of the relay terminals  34  and  35  are bent up. Moreover, the bind portion  35   a  of the relay terminal  35  and the joint portion  34   b  of the other relay terminal  34  are jointed and soldered to each other. Moreover, the coils  31  and  31  are connected by jointing and soldering the joint portion  35   b  of the relay terminal  35  and the bind portion  34   a  of the other relay terminal  34 . 
   As shown in  FIG. 5 , on the other hand, the iron cores  37  are individually inserted into the press-fit holes  42  formed in the bottom face of the sealing case  41 , and pipes  38  are fitted on the protruding stems  37   a  of the iron cores  37 . And, the iron cores  37  are pushed in the axial direction from the open edge portions of the pipes  38 . As shown in  FIG. 6 , the iron core  37  is made smaller at the diameter D 1  of its stem portion  37   a  than the diameter d 1  of the press-fit hole  42  of the sealing case  41  and the internal diameter d 2  of the pipe  38 . However, the diameter D 2  of the neck portion  37   b  of the iron core  37  is made larger than the diameter d 1  of the press-fit hole  42  of the sealing case  41  and the internal diameter d 2  of the pipe  38 . When the iron core  37  is pushed in the axial direction, the neck portion  37   b  of the iron core  37  is press-fitted in the press-fit hole  42  of the sealing case  41  while widening it and the internal diameter of the pipe  38 . Moreover, the open edge portion of the pipe  38  and the head portion (or magnetic pole portion)  37   c  of the iron core  37  push the open edge portion of the press-fit hole  42  of the sealing case  41  from above and below. There, the open edge portion of the press-fit hole  42  of the sealing case  41  is caulked and fixed from the three sides. 
   According to this embodiment, the sealing case  41  is made of such a material, e.g., aluminum as has a larger coefficient of thermal expansion than those of the iron cores  37  and the pipes  38 . Therefore, the embodiment is advantageous in that the gas-tightness is not deteriorated even if the temperature changes. 
   The reason for this advantage will be described in the following. Even if the temperature rises so that the individual parts expand, the expansion of the sealing case  41  in the thickness direction is larger than those of the remaining parts so that the sealing case  41  is firmly clamped between the head portions  37   c  of the iron cores  37  and the pipes  38 . Even if the temperature drops so that the individual parts shrink, on the other hand, the shrinkage of the press-fit holes  42  of the sealing case  41  in the diametrical direction is larger than those of the remaining parts so that the sealing case  41  fastens the neck portions  37   b  of the iron cores  37 . 
   In order to prevent the thermal stress while retaining the gas-tightness, it is preferred that the iron cores  37  and the pipes  38  have substantially equal coefficients of thermal expansion. 
   Then, the iron cores  37  and the pipes  38  are individually inserted into center holes  32   c  of the spools  32 , and the leading end portions of the protruding iron cores  37  are inserted into and caulked by caulking holes  39   a  of the yoke  39 . Thus, the electromagnet block  30  is completed while mounting the sealing case  41 . Between the yoke  39  and the flange portions of the spools  32 , there is sandwiched an insulating sheet  39   b  ( FIG. 4 ) for enhancing the insulating performance. 
   Next, the paired flange portions  32   a  and  32   b  of the spools  32  are individually spanned with the coil terminals  36 , and the lower end portions of these coil terminals  36  are jointed to the joint portions  34   b  and  35   b  of the relay terminals  34  and  35 . 
   The contact mechanism block  50  is constructed, as shown in  FIG. 3 , to include a moving contact block  60 , stationary contact blocks  70  and  80  assembled on the two sides of the moving contact block  60 , and an insulating case  90  fitted to integrate those blocks  60 ,  70  and  80 . 
   The moving contact block  60  is constructed, as shown in  FIG. 7A , by assembling a pair of juxtaposed moving contact members  62  and  63  and contact springs  64  individually with a moving insulating bed  61 . The moving insulating bed  61  is constructed, as shown in  FIG. 7B , such that a leg portion  61   a  having a generally cross-shape section is protruded from the lower face of its central portion and such that a moving iron member  67  is caulked and fixed on its two side portions through rivets  66  having coiled return springs  65  fitted thereon. The moving iron member  67  is covered on its lower face with a shielding sheet  68 . 
   A pair of retained protrusions  62   a  and  63   a  are individually protruded from the one-side edge portions of the band-shaped conductive materials of the moving contact members  62  and  63 . Of the moving contact members  62  and  63 , the moving contact member  62  is made of a band-shaped conductive member of molybdenum having a high melting point and capable of enduring a rush current, and the other moving contact member  63  is made of a thick band-shaped copper sheet plated with silver. 
   The contact springs  64  are arranged for applying a contact pressure to the moving contact members  62  and  63 . And, the contact springs  64  are made by bending band-shaped spring materials generally into an angle shape and are folded at their two side edge portions to form retained pawls  64   a  and  64   a.    
   These retained pawls  64   a  of the contact springs  64  are retained on the two end portions of the moving contact members  62  and  63 , when the moving contact members  62  and  63  and the contact springs  64  and  64  are inserted into and assembled with a pair of assembling holes  61   b  and  61   c  juxtaposed in the moving insulating bed  61 . As a result, the moving contact members  62  and  63  can be prevented from becoming vertically loose. Moreover, the retained protrusions  62   a  and  63   a  of the moving contact members  62  and  63  are retained on the open edge portions of the assembling holes  61   b  and  61   c  of the moving insulating bed  61 , so that the contact springs  64  and the moving insulating beds  62  and  63  can be prevented from coming out. By positioning the moving contact member  62  at a lower height than that of the moving contact member  63 , moreover, a step is formed between the paired moving contact members  62  and  63 . As a result, the moving contact member  62  comes into contact with a stationary contact  78   a  before the moving contact member  63  comes into contact with a stationary contact  78   b.    
   The stationary contact blocks  70  and  80  are constructed, as shown in  FIG. 8  and  FIG. 9 , such that stationary contact beds  71  and  81  molded of a resin to have an identical shape are assembled with stationary contact terminals  76  and  86 , as made of a generally C-shaped section caulking and fixing the connecting terminals  75  and  85 , and permanent magnets  77  and  87 . The stationary contact beds  71  and  81  are constructed such that abutting protrusions  72  and  82  are individually protruded inward sideways and such that supporting leg portions  73  and  83  are individually protruded vertically downward. 
   The stationary contact terminals  76  and  86  are formed to have pairs of stationary contacts  78   a  and  78   b , and  88   a  and  88   b , respectively, by protruding their lower side edge portions. On the other hand, the permanent magnets  77  and  87  are assembled such that their pole-faces  77   a  and  87   a  are jointed to the inner faces of the stationary contact terminals  76  and  86 . As a result, the pole-faces  77   a  and  87   a  of the permanent magnets  77  and  87  are positioned near the paired stationary contacts  78   a  and  78   b , and  86   a  and  86   b.    
   The insulating case  90  is provided for uniting the contact mechanism block  50 , as shown in  FIG. 3 . And, the paired stationary contact blocks  70  and  80  are assembled from the two sides with the moving contact block  60  and are then fitted thereon, so that the connecting terminals  75  and  85  are protruded from terminal holes  91  and  91  of the insulating case  90 . This insulating case  90  is provided with a pair of gas vent holes  92  near the terminals holes  91 . The reason for the paired gas vent holes  92  is to eliminate the directivity at the assembling time. 
   Here will be described the procedure for assembling the contact mechanism block  50 . 
   At first, the moving iron member  67  and the shielding sheet  68  are assembled with the moving insulating bed  61  through the rivets  66  inserted into the return springs  65 . And, the moving contact members  62  and  63  and the contact springs  64  and  64  are assembled with the moving insulating bed  61 . Next, the stationary contact blocks  70  and  80  are assembled from the two sides of the moving insulating bed  61  while raising the lower end sides of the return springs  65 , thereby to bringing the abutting protrusions  72  and  82  into abutment against each other. Moreover, the insulating case  90  is fitted on the stationary contact blocks  70  and  80 . Thus, the contact mechanism block  50  is completed. 
   Next, the contact mechanism block  50  is inserted into the sealing case  41  mounted on the electromagnet block  30 . Then, the leg portions  73  and  83  of the stationary contact blocks  70  and  80  abut against the head portions  37   c  or the magnetic pole portions of the iron cores  37  so that the moving iron member  67  can come close to and apart from the magnetic pole portions  37   c  through the shielding sheet  68 . And, the sealing cover  45  is fitted in and welded integrally with the sealing case  41 . Moreover, the gas vent pipe  21  is press-fitted from the loosely fitting hole  47  into the gas vent hole  92  of the insulating case  90 . Next, a sealing material (although not shown) is injected onto the sealing cover  45  and is solidified to seal around the base portions of the connecting terminals  75  and  85  and the gas vent pipe  21 . And, the air in the sealing case  40  is vented from the gas vent pipe  21 , and a predetermined mixture gas is injected. After this, the gas vent pipe  21  is caulked and sealed. And, the paired flange portions  32   a  and  32   b  of the spools  32  are spanned with the coil terminals  36 . Thus, the relay body  20  is completed. 
   And, this relay body  20  is housed in the recess  11  of the case  10 , and the coil terminals  36  are arranged in the connecting recesses  13 . Moreover, the cover  15  is assembled with the case  10 . Thus, the DC current breaking relay is completed. 
   Here will be described the actions of the relay thus constructed. 
   First of all, in case no voltage is applied to the coils  31  of the electromagnet block  30 , the moving insulating bed  61  is pulled up ( FIG. 13A ) by the spring forces of the return springs  65  and  65 . As a result, the moving iron member  67  leaves the magnetic pole portions  37   c  of the iron cores  37 , and the two end portions of the moving contact members  62  and  63  leave the stationary contacts  78   a  and  88   a , and  78   b  and  88   b , respectively. 
   When a voltage is applied to the coils  31 , moreover, the magnetic pole portions  37   c  of the iron cores  37  attract the moving iron member  67  so that the moving iron member  67  moves downward against the spring forces of the return springs  65 . As a result, the moving insulating bed  61 , as integrated with the moving iron member  67 , moves downward so that the two end portions of the moving contact member  62  come into contact with the stationary contacts  78   a  and  88   a . Next, the two end portions of the moving contact member  63  come into contact with the stationary contacts  78   b  and  88   b  so that the moving iron member  67  is attracted by the magnetic pole portions  37   c  of the iron cores  37  ( FIG. 13B ). 
   Next, when the application of the voltage to the coils  31  is interrupted, the moving insulating bed  61  is pushed upward by the spring forces of the return springs  65  so that the moving iron member  67  leaves the magnetic pole portions  37   a  of the iron cores  37  together with the moving insulating bed  61 . After the two end portions of the moving contact member  63  left the stationary contacts  78   b  and  88   b , moreover, the two end portions of the moving contact member  62  leave the stationary contacts  78   a  and  88   a.    
   An arc current, if produced when the two end portions of the moving contact member  62  leave the stationary contacts  78   a  and  88   a , is attracted and broken by the magnetic forces of the permanent magnets  77  and  87 . This point will be described in detail with reference to  FIG. 14  and  FIG. 15 . 
   As shown in  FIG. 15 , for example, the magnetic flux of the permanent magnet  77  is emitted, as indicated by arrows, from the pole-face  77   a . When the moving iron member  67  returns, moreover, the end portion of the moving contact member  63  leaves the stationary contact  78   b , and the end portion of the moving contact member  62  leaves the stationary contact  78   a . As a result, an arc current A begins to build up from the stationary contact  78   a . According to Fleming&#39;s left-hand law (or by the Lorentz&#39;s force), however, the arc current A is attracted by the magnetic force of the permanent magnet  77 , and it shifts its production place to the stationary contact  78   b  and turns into an arc current B. Moreover, this arc current B is extended into an arc current C by the magnetic force of the permanent magnet  77  so that it is finally cut and broken. 
   In this embodiment, the arc current is so extended on the basis of the Fleming&#39;s left-hand law as to swirl along the pole-faces  77   a  and  87   a  of the permanent magnets  77  and  87 , until it is broken. Therefore, a large space is not required for breaking the arc current unlike the examples of the prior art, so that the device can be small-sized. 
   This embodiment has been described on the case, in which the DC current is broken, but may be applied to the case in which an AC current is broken. It is natural that the embodiment can also be applied not only to the relay but also to a switch, a timer or the like. 
   According to the invention, the arc current produced at the switching time is so extended on the basis of the Fleming&#39;s left-hand law (or by the Lorentz&#39;s force) as to whirl along the pole-faces of the permanent magnets, until it is broken. Therefore, a large space is not required for breaking the arc current unlike the examples of the prior art, thereby to provide an effect that the device can be small-sized.