Abstract:
It is intended to provide an electromagnetic relay which resolves problems of large base size and difference in spring constant. In a facing gap defined between a pair of electromagnet units disposed on a base in parallel to each other and with shaft lines being oriented to an identical direction, a pair of moving contact springs overlaid along a vertical direction on the base and an A-fixed terminal unit and a B-fixed terminal unit provided with a plurality of contacts to which contacts of the moving contact springs selectively contact depending on excitation/non-excitation states of the electromagnetic units are housed. At least one of component parts of the respective electromagnetic units are included in electromagnetic connection passages between the moving contact springs and C-terminals.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an electromagnetic relay and, particularly, to an electromagnetic relay for forward reverse control, such as a motor and a solenoid.  
         [0003]     2. Description of the Related Art  
         [0004]      FIG. 12  is a block diagram showing a forward reverse control circuit. A forward reverse control circuit  1  is provided with two electromagnetic relays  2  and  3 . An A-terminal  2   a  of one of the electromagnetic relays  2  and  3  (hereinafter referred to as first electromagnetic relay  2 ) is connected to a plus electric source (hereinafter referred to as +E); a B-terminal  2   b  of the first electromagnetic relay  2  is connected to a ground potential (hereinafter referred to as GND); and a C-terminal  2   c  of the first electromagnetic relay  2  is connected to one of terminals (terminal  4   a ) of a load  4  such as a motor and solenoid. An A-terminal  3   a  of the other electromagnetic relay  3  (hereinafter referred to as second electromagnetic relay  3 ) is connected to the +E; a B-terminal  3   b  of the second electromagnetic relay  3  is connected to the GND; and a C-terminal  3   c  of the first electromagnetic relay  2  is connected to the other terminal  4   b  of the load  4 . As used herein, the alphabet A added to each of the terminals means that the terminal is connected to an A-contact (normal open contact); the alphabet B means that the terminal is connected to a B-contact (normal close contact); and the alphabet C means that the terminal is connected to a C-contact (COM contact).  
         [0005]     In such forward reverse control circuit  1 , since the terminal  4   a  of the load  4  is connected to the GND via a contact  2   e  of the first electromagnetic relay  2  and the terminal  4   b  is connected to the GND via a contact  3   e  of the second electromagnetic relay  3  in a normal state (when the first and the second electromagnetic relays  2  and  3  are in a non-excitation state), the load  4  does not operate in the normal state.  
         [0006]     When a control voltage is applied to a coil terminal  2   d  of the first electromagnetic relay  2 , a coil  2   f  of the first electromagnetic relay  2  is excited to change the position of the contact  2   e , so that the terminal  4   a  of the load  4  is connected to the +E via the contact  2   e  of the first electromagnetic relay  2 . In such state, the second electromagnetic relay  3  is turned off, and the terminal  4   b  of the load  4  is connected to the GND via the contact  3   e  of the second electromagnetic relay  3 , so that a current flows to the load  4  in a direction (see an arrow A) of “+E→contact  2   e  of first electromagnetic relay  2 →terminal  4   a  of load  4 →terminal  4   b  of load  4 →contact  3   e  of second electromagnetic relay  3 →GND”.  
         [0007]     When a control voltage is applied to a coil terminal  3   d  of the second electromagnetic relay  3 , a coil  3   f  of the second electromagnetic relay  3  is excited to change the position of the contact  3   e , so that the terminal  4   b  of the load  4  is connected to the +E via the contact  3   e  of the second electromagnetic relay  3 . In such state, the first electromagnetic relay  2  is turned off, and the terminal  4   a  of the load  4  is connected to the GND via the contact  2   e  of the first electromagnetic relay  2 , so that a current flows to the load  4  in a reverse direction (see an arrow B) of “+E→contact  3   e  of second electromagnetic relay  3 →terminal  4   b  of load  4 →terminal  4   a  of load  4 →contact  2   e  of first electromagnetic relay  2 →GND”.  
         [0008]     As described above, since it is possible to change the direction of driving current applied to the load  4  such as a motor and a solenoid by the use of the forward reverse control circuit  1  of  FIG. 12 , it is possible to change a rotation direction of the motor or a driving direction of the solenoid.  
         [0009]     By the way, since the forward reverse control circuit  1  of  FIG. 12  requires two electromagnetic relays, the forward reverse control circuit  1  undesirably needs extra effort and a relatively large mounting space when it is integrated into an appliance.  
         [0010]      FIG. 13  is a conceptual diagram showing a conventional technology which resolves the above drawbacks (see, for example, Patent Literature 1). Referring to  FIG. 13 , an electromagnetic relay  5  is provided with a rectangular base  6  having a length La, and a pair of electromagnets  7  and  8  disposed parallelly to each other on the base  6 , armatures  9  and  10  disposed on the electromagnets  7  and  8 , a pair of insulators  11  and  12  disposed on side faces of the armatures  9  and  10 , a pair of moving contact springs  13  and  14  sandwiched between the insulators  11  and  12 , and a pair of fixed contact terminal plates  15  and  16  disposed at swinging ends of the moving contact springs  13  and  14  and can be handled as one unit.  
         [0011]     Each of the pair of moving contact springs  13  and  14  is an L-shaped flat plate spring, and the moving contact spring  13  is disposed on the moving contact spring  14 . Therefore, when the base  6  is viewed from above, the moving contact spring  14  cannot be seen since it is hidden under the moving contact spring  13 .  
         [0012]     A terminal  13   a  for connecting a load  17  is formed on a fixed end of the moving contact spring  13 , and a terminal  14   a  for connecting a load  17  is formed on a fixed end of the moving contact spring  14 . Moving contacts  13   b  and  13   c  are attached to opposite sides of the swinging end of the moving contact spring  13 , and moving contacts  14   b  and  14   c  are attached to opposite sides of the swinging end of the moving contact spring  14 .  
         [0013]     The fixed contact terminal plate  15  is provided with a fixed terminal  15   a  for connecting to the +E and the GND, and the fixed contact terminal plate  16  is provided with a fixed terminal  16   a  for connecting to the +E and the GND. Fixed contacts  15   b ,  15   c ,  16   b , and  16   c  are attached to the fixed contact terminal plates  15  and  16  at predetermined positions. The fixed contacts  15   b ,  15   c ,  16   b , and  16   c  contact the moving contacts  13   b ,  13   c ,  14   b , and  14   c  in predetermined combinations when the electromagnets  7  and  8  are excited.  
         [0014]     The predetermined combinations are (1) the moving contact  13   b  and the fixed contact  15   b , (2) the moving contact  13   c  and the fixed contact  16   c , (3) the moving contact  14   b  and the fixed contact  16   b , and (4) the moving contact  14   c  and the fixed contact  15   c.    
         [0015]     With such constitution, when the electromagnets  7  and  8  are not excited, the combinations of (2) the moving contact  13   c  and the fixed contact  16   c  and (3) the moving contact  14   b  and the fixed contact  16   b  are employed so that the GND is supplied to both ends of the load  17 . When the electromagnet  7  on the left hand side in  FIG. 13  is excited in this state, the armature  9  is operated so that the insulator  11  attached to the armature  9  moves to the right. Accordingly, the moving contact spring  13  is pressed by the insulator  11  to move to the right, thereby achieving the combination (1) the moving contact  13   b  and the fixed contact  15   b , so that a current flows in the order of the +E, the terminal  15   a , the fixed contact  15   b , the moving contact  13   b , the moving contact spring  13 , the terminal  13   a , the load  17 , the terminal  14   a , the moving contact spring  14 , the moving contact  14   b , the fixed contact  16   b , the terminal  16   a , and the GND.  
         [0016]     When the electromagnet  8  on the right hand side in  FIG. 13  is excited, the armature  10  is operated so that the insulator  12  attached to the armature  10  moves to the left. Accordingly, the moving contact spring  14  is pressed by the insulator  12  to move to the left, thereby achieving the combination (4) the moving contact  14   c  and the fixed contact  15   c , so that a current flows in the reverse order of the +E, the terminal  15   a , the fixed contact  15   c , the moving contact  14   c , the moving contact spring  14 , the terminal  14   a , the load  17 , the terminal  13   a , the moving contact spring  13 , the moving contact  13   c , the fixed contact  16   c , the terminal  16   a , and the GND.  
         [0017]     [Patent Literature 1] Japanese Patent No. 2890581  
       SUMMARY OF THE INVENTION  
       [0018]     The above-described conventional technology has the following drawbacks.  
         [0000]     (1) Large Base Size  
         [0019]     The length La of the base  6  is at least a total of a shaft length Lb of the electromagnets  7  and  8 , a length Lc required for the movements of the armatures  9  and  10 , and a length Ld required for mounting the two fixed contact terminal plates  15  and  16 . In view of a mounting space in an appliance, it is desired that the lengths Lb, Lc, and Ld should be small as possible. Since the lengths Lb and Lc depend on the size of the electromagnets  7  and  8 , an electromagnet appropriate for downsizing (electromagnet having a smaller Lb and Lc) is naturally used. Accordingly, a last object left for downsizing is the length Ld.  
         [0020]     In order to downsize the length Ld, a thickness of the fixed contact terminal plates  15  and  16  and a gap between the fixed contact terminal plates  15  and  16  may be reduced, and the fixed contact terminal plates  15  and  16  may be disposed as close as possible to the electromagnets  7  and  8 .  
         [0021]     However, there are limits for the downsizing of the thickness and the gap of the fixed contact terminal plates  15  and  16  because the size of the fixed contact terminal plates  15  and  16  should no be smaller than the sizes of the contacts  15   c ,  15   b ,  16   c , and  16   b . Also, in order not to disturb the electrical insulation and the movements of the moving contact springs  13  and  14 , the distance to the electromagnets  7  and  8  cannot be reduced by a large scale. Accordingly, since it is impossible to eliminate the length Ld in the constitution of the conventional technology, the conventional technology has the drawback of the long length (La) of the base  6  due to the length Ld.  
         [0000]     (2) Difference in Spring Constant  
         [0022]     A length of the moving contact spring  14  disposed under the moving contact spring  13  is shorter than a length of the moving contact spring  13 . The difference in length is set in order to avoid disturbances between the moving contact springs  13  and  14  because each of the moving contact springs  13  and  14  is formed from a flat and L-shaped plate, and that the terminals  13   a  and  14   a  are formed on the ends of the L-shaped flat plates.  
         [0023]     When lengths of a pair of plate springs formed from an identical spring material are varied, one of the springs becomes soft, and the other spring becomes hard, i.e., spring constants are varied. The same is applicable to the moving contact springs  13  and  14  of the conventional technology. Such difference in spring constant requires an independent designing of coils (the coils of the electromagnets  7  and  8 ) for driving the moving contact springs  13  and  14 . That is, it is necessary to vary a resistance value depending on the coils in order to generate an appropriate attraction force in accordance with the spring constants or to design component parts independently for the coils. However, with such designing, designing of the appliance into which the electromagnetic relay  5  is to be integrated will be complicated due to the difference in coil resistance and the troublesome designing of different component parts.  
         [0024]     In view of the above-described circumstance, an object of this invention is to provide an electromagnetic relay which resolves the problems of the large size base and the difference in spring constant.  
         [0025]     An aspect of the invention is an electromagnetic relay comprising: housing, in a predetermined facing gap defined between a first electromagnet unit and a second electromagnetic unit disposed parallelly to each other on a base in such a fashion that axial directions thereof are oriented to an identical direction, a first moving contact spring and a second moving contact spring disposed in such a fashion as to be overlaid along a vertical direction on the base and an A-fixed terminal unit and a B-fixed terminal unit provided with a plurality of contacts with which contacts of the first and the second moving contact springs selectively contact depending on a state of excitation/non-excitation of the first and the second electromagnet units; and disposing at least one of component parts of the first electromagnet unit and the second electromagnet unit on an electric connection passage between the first and the second moving contact springs and a pair of C-terminals.  
         [0026]     As used herein, the A-fixed terminal unit means a fixed terminal unit having an A-contact, i.e. a normal open contact. Likewise, the B-fixed terminal unit means a fixed terminal unit having a B-contact, i.e. a normal close contact.  
         [0027]     Also, the overlaying along the vertical direction on the base means that, when a platform of the base is a horizontal plane, one of the first moving contact spring and the second moving contact spring is disposed above the other one along a line or plane making a right angle with the horizontal plane (the upper moving contact spring is detached from the horizontal plane, and the lower moving contact spring is disposed closer to the horizontal plane).  
         [0028]     Also, the at least one of component parts may be the yoke of each of the first electromagnet unit and the second electromagnet unit.  
         [0029]     In this invention, the moving contact springs, the A-terminal unit, and the B-terminal unit are housed in the facing gap of the electromagnet units, and the moving contact springs are electrically connected to the C-terminals via the component parts of the electromagnet units.  
         [0030]     Another aspect of the invention is an electromagnetic relay comprising: a) disposing a first electromagnet unit and a second electromagnet unit on a rectangular base made from an insulating material in such a fashion that one side of the first electromagnet unit is parallel to one side of the second electromagnet unit with a predetermined facing gap being defined therebetween and mounting an A-fixed terminal unit and a B-fixed terminal unit in the facing gap; b) attaching a first moving contact spring and a first return spring to a first iron piece disposed adjacent to a magnetic pole of the first electromagnet unit and fixing a tip of the first return spring to a first yoke disposed along the side of the first electromagnet unit; c) attaching a second moving contact spring and a second return spring to a second iron piece disposed adjacent to a magnetic pole of the second electromagnet unit and fixing a tip of the second return spring to a second yoke disposed along the side of the second electromagnet unit; d) overlaying the first moving contact spring and the second moving contact spring along a vertical direction on the base; and e) contacting a contact of the first moving contact spring and a contact of the second moving contact spring to a contact of the B-fixed terminal unit when both of the first electromagnet unit and the second electromagnet unit are not excited, contacting the contact of the first moving contact spring to the A-fixed terminal unit when the first electromagnet unit is excited, and contacting the contact of the second moving contact to the A-fixed terminal unit when the second electromagnet unit is excited.  
         [0031]     With this invention, thanks to the item a), it is possible to keep a length of one of four sides of the base, which is parallel to a shaft of the electromagnet units, to be substantially equal to a length of the electromagnet units without influences of presence of the A-fixed terminal unit and the B-fixed terminal unit. Therefore, it is possible to downsize the base, thereby realizing an electromagnetic relay of a small mounting area.  
         [0032]     Also, thanks to the item b), it is possible to retain the first iron piece at an initial position by a spring force of the first return spring when the first electromagnet unit is not excited, while it is possible to cause the first iron piece to approach to the magnetic pole of the first electromagnet unit against the spring force of the first return spring when the first electromagnet unit is excited.  
         [0033]     Also, thanks to the item c), it is possible to retain the second iron piece at an initial position by a spring force of the second return spring when the second electromagnet unit is not excited, while it is possible to cause the second iron piece to approach to the magnetic pole of the second electromagnet unit against the spring force of the second return spring when the second electromagnet unit is excited.  
         [0034]     Also, thanks to the item d), it is possible to avoid mutual disturbances of the first and the second moving contact springs, so that the first and the second iron pieces return to the initial positions and the first and the second moving contact springs approach in a swinging manner to the magnetic poles without any disturbance.  
         [0035]     Also, thanks to the item e), it is possible to switch the contacts of the first and the second moving contact springs independently between the B-contact (normal close contact) and the A-contact (normal open contact) depending on the combinations of excitation and non-excitation of the first and the second electromagnet units, thereby making it possible to perform a forward reverse control of a motor or a solenoid, for example.  
         [0036]     Still another aspect of the invention is the electromagnetic relay according to the aspect of the invention, wherein the first iron piece, the first return spring, and the first yoke are included in an electrical connection passage between one of a pair of C-terminals and the contact of the first moving contact spring, and the second iron piece, the second return spring, and the second yoke are included in an electrical connection passage between the other one of the C-terminals and the contact of the second moving contact spring.  
         [0037]     With this invention, the C-terminals are electrically connected to the first and the second moving contact springs via the first and the second yoke and the first and the second return springs. Accordingly, it is unnecessary to connect the C-terminals to the first and the second moving contact springs by using a dedicated wiring or the like. Therefore, since troubles otherwise caused by disconnection do not occur, a production cost is reduced, and reliability is improved.  
         [0038]     According to the invention, since the moving contact springs, the A-fixed terminal unit, and the B-fixed terminal unit are housed in the facing gap between the electromagnet units, it is possible to keep a length of one of four sides of the base, which is parallel to a shaft of the electromagnet units, to be substantially equal to a length of the electromagnet units without influences of presence of the A-fixed terminal unit and the B-fixed terminal unit. Therefore, it is possible to downsize the base, thereby realizing an electromagnetic relay of a small mounting area.  
         [0039]     Also, since the moving contact springs are electrically connected to the C-terminals via the component parts of the electromagnet units, it is unnecessary to form the C-terminals integrally with the moving contact springs as in the conventional technology (see the terminals  13   a  and  14   a  of  FIG. 13 ). Accordingly, it is unnecessary to consider disturbances otherwise caused by mounting the terminals on the base, and, therefore, it is possible to use moving contact springs having an identical shape and to even out the spring constants of the moving contact springs. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0040]      FIG. 1  is a diagram showing assembly of an electromagnetic relay  20  according to one embodiment.  
         [0041]      FIG. 2  is an exploded view showing a first electromagnet unit  24  and a second electromagnet unit  25 .  
         [0042]      FIG. 3  is a diagram showing an appearance of the second electromagnet unit  25  before attaching a second iron piece  40 , a second moving contact spring  41 , and a second return spring  42  to the second electromagnet unit  25 .  
         [0043]      FIG. 4  is a diagram showing an assembled state of a first iron piece  31 , a first moving contact spring  32 , and a first return spring  33  and an assembled state of the second iron piece  40 , the second moving contact spring  41 , and the second return spring  42 .  
         [0044]      FIG. 5  is a diagram showing the assembled body of  FIG. 4  as viewed from the rear.  
         [0045]      FIG. 6  is a diagram showing an appearance of the second electromagnet unit  25  after attaching the second iron piece  40 , the second moving contact spring  41 , and the second return spring  42  to the second electromagnet unit  25 .  
         [0046]      FIG. 7  is a block diagram showing an A-fixed terminal unit  22 .  
         [0047]      FIG. 8  is a block diagram showing a B-fixed terminal unit  23 .  
         [0048]      FIG. 9  is a conceptual diagram of a contact operation of the electromagnetic relay  20 .  
         [0049]      FIG. 10  is a diagram showing a completion of the electromagnetic relay  20  of the embodiment.  
         [0050]      FIG. 11  is a conceptual diagram showing a facing gap F in an actual housing.  
         [0051]      FIG. 12  is a block diagram showing a forward reverse control circuit such as a motor and a solenoid.  
         [0052]      FIG. 13  is a conceptual diagram showing a conventional technology. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0053]     Hereinafter, one embodiment of this invention will be described based on the drawings. Identifications and examples of details as well as exemplifications of values, letters, and other symbols in the following description are not more than references used for clarifying idea of this invention, and it is apparent that the idea of this invention is not limited by whole or part of the references. Also, explanations for known methods, known processes, known architectures, known circuit constitutions, and the like (hereinafter referred to as known particulars) are avoided in the following description, and such avoidance is for the purpose of simplifying the description and is not for the purpose of excluding whole or part of the known particulars. Since the known particulars had been familiar to those skilled in the art at the time of filing of this patent application, the known particulars are naturally included in the following description.  
         [0054]      FIG. 1  is a diagram showing assembly of an electromagnetic relay  20  according to the embodiment. In the electromagnetic relay  20 , an A-fixed terminal unit  22  and a B-fixed terminal unit  23 , a first electromagnet unit  24 , and a second electromagnet unit  25  are mounted on a base  21  having a substantially square shape and made from an insulating material such as plastic, and a dust prevention case  26  is used for covering the electromagnetic relay  20  when so required. The alphabet A of the A-fixed terminal unit means normal open, and the alphabet B of the B-fixed terminal unit means normal close.  
         [0055]      FIG. 2  is an exploded view showing the first electromagnet unit  24  and the second electromagnet unit  25 . The first electromagnet unit  24  is provided with a bobbin  27  made from an insulating material, a coil  28  wound around the bobbin  27 , a yoke (hereinafter referred to as first yoke  29 ) made from a conducting material, the first yoke  29  being disposed along one end face and one side of the bobbin  27  and bent at an angle of about 90 degrees, an iron core  30  to be inserted into a shaft hole  27   a  of the bobbin  27  and a through-hole  29   a  formed on the first yoke  29 , and an iron piece (hereinafter referred to as first iron piece  31 ) disposed adjacent to a magnetic pole  30   a  of the iron core  30 . The first electromagnet unit  24  is further provided with a moving contact spring (hereinafter referred to as first moving contact spring  32 ) to be caulked to one side (the side not shown in  FIG. 2 ) of the first iron piece  31 , a return spring (hereinafter referred to as first return spring  33 ), a pair of coil terminals  34   a  and  34   b  electrically connected to opposite ends of a winding wire of the coil  28 , and a C-terminal  35  attached to the first yoke  29  by caulking projections  29   b  and  29   c  of the first yoke  29  to engagement holes  35   a  and  35   b  and electrically connected to the first return spring  33  and the first moving contact spring  32  via the first yoke  29 .  
         [0056]     The second electromagnet unit  25  is provided with a bobbin  36  made from an insulating material, a coil  37  wound around the bobbin  36 , a yoke (hereinafter referred to as second yoke  38 ) made from a conducting material, the second yoke  38  being disposed along one end face and one side of the bobbin  36  and bent at an angle of about 90 degrees, an iron core  39  to be inserted into a shaft hole  36   a  of the bobbin  36  and a through-hole  38   a  formed on the second yoke  38 , and an iron piece (hereinafter referred to as second iron piece  40 ) disposed adjacent to a magnetic pole  39   a  of the iron core  39 . The second electromagnet unit  25  is further provided with a moving contact spring (hereinafter referred to as second moving contact spring  41 ) to be caulked to one side (the side not shown in  FIG. 2 ) of the second iron piece  40 , a return spring (hereinafter referred to as second return spring  42 ), a pair of coil terminals  43   a  and  43   b  electrically connected to opposite ends of a winding wire of the coil  37 , and a C-terminal  44  attached to the second yoke  38  by caulking projections  38   b  and  38   c  of the second yoke  38  to engagement holes  44   a  and  44   b  and electrically connected to the second return spring  42  and the second moving contact spring  41  via the second yoke  38 .  
         [0057]      FIG. 3  is a diagram showing an appearance of the second electromagnet unit  25  before attaching the second iron piece  40 , the second moving contact spring  41 , and the second return spring  42  to the second electromagnet unit  25 . As shown in  FIG. 3 , the second electromagnet unit  25  is assembled by inserting the iron core  39  into a shaft center of the bobbin  36  on which the coil  37  and the coil terminals  43   a  and  43   b  are mounted and disposing the second yoke  38  along one end and one side of the bobbin  36  (preferably, the second yoke  38  is engaged to the bobbin  36 ). The magnetic pole  39   a  of the iron core  39  is exposed to the other end face (surface on which the second yoke  38  is not disposed) of the bobbin  36 , and the second iron piece  40  (not shown) is disposed adjacent to the magnetic pole  39   a . A tip of the second return spring  42  attached to the second iron piece  40  is caulked to a projection  38   d  formed on the second yoke  38 .  
         [0058]     Though not shown, an assembled state of the first electromagnet unit  24  before attaching the iron piece  31 , the first moving contact spring  32 , and the first return spring  33  is the same as that of the second electromagnet unit  25 . It can be said that the assembled state of the first electromagnet unit  24  is different from that of the second electromagnet unit  25  since the assembled state of the first electromagnet unit  24  is the same as a mirror projection image of the assembled state of the second electromagnet unit  25 . That is, the first electromagnet unit  24  in the assembled state and the second electromagnet unit  25  in the assembled state are different from each other only from the viewpoint that they are in a mirror projection relationship when shaft lines of the iron cores  30  and  39  are aligned parallel to each other.  
         [0059]     Shown in  FIG. 4  are a diagram (a) of an assembled state of the first iron piece  31 , the first moving contact spring  32 , and the first return spring  33  and a diagram (b) of an assembled state of the second iron piece  40 , the second moving contact spring  41 , and the second return spring  42 .  
         [0060]     The first moving contact spring  32  which is bent to form a substantially L-shape and the first return spring  33  are caulked to a reverse side (side not shown in  FIG. 4 ) of an electromagnetism attraction surface  31   x  of the first iron piece  31 . Also, the second moving contact spring  41  which is bent to form a substantially L-shape and the second return spring  42  are caulked to a reverse side (side not shown in  FIG. 4 ) of an electromagnetism attraction surface  40   x  of the second iron piece  40 .  
         [0061]     A contact  32   a  is attached to one side of the first moving contact spring  32  in the vicinity of a tip of the first moving contact spring  32 , and a contact  32   b  is attached to the other side of the first moving contact spring  32  in the vicinity of the tip of the first moving contact spring  32 . A hole  33   a  to be used for the caulking to the first yoke  29  is formed on the first return spring  33  in the vicinity of a tip of the first return spring  33 . In the same manner, contacts  41   a  and  41   b  are attached to opposite sides of the second moving contact spring  41  in the vicinity of a tip of the second moving contact spring  41 , and a hole  42   a  for caulking to the first yoke  29  is formed on the second return spring  42  in the vicinity of a tip of the second return spring  42 .  
         [0062]     In  FIG. 4 ( a ), the first moving contact spring  32  and the first return spring  33  are positioned on the left hand side, and the first moving contact spring  32  is positioned above the second return spring  33 . In turn, in  FIG. 4 ( b ), the second moving contact spring  41  and the second return spring  42  are positioned on the right hand side, and the second moving contact spring  41  is positioned below the second return spring  42 . Such illustration is for the purpose of clarifying that the two assembled bodies have an identical shape. More specifically, the shape of the assembled body of  FIG. 4 ( a ) is identical to the assembled body of  FIG. 4 ( b ) when the assembled body of  FIG. 4 ( a ) is rotated by 180 degrees in clockwise direction, and the shape of the assembled body of  FIG. 4 ( b ) is identical to the assembled body of  FIG. 4 ( a ) when the assembled body of  FIG. 4 ( b ) is rotated by 180 degrees in anticlockwise direction.  
         [0063]      FIG. 5  is a diagram showing the assembled body of  FIG. 4 ( a ) as viewed from the rear. Since the two assembled bodies have the identical shape as described above, the diagram is equivalent to that of the assembled body of  FIG. 4 ( b ) as viewed from the rear. In  FIG. 5 , the first moving contact spring  32  (the second moving contact spring  41 ) is caulked to rear face projections  31   a  ( 40   a ) and  31   b  ( 40   b ) of the first iron piece  31  (the second iron piece  40 ), and the first return spring  33  (the second return spring  42 ) is caulked to rear face projections  31   c  ( 40   c ) and  31   d  ( 40   d ) of the first iron piece  31  (the second iron piece  40 ). The first iron piece  31  and the second iron piece have an identical shape. The first moving contact spring  32  and the second moving contact spring  41  have an identical shape. The first return spring  33  and the second return spring  42  have an identical shape.  
         [0064]      FIG. 6  is a diagram showing an assembled state of the second electromagnet unit  25  after attaching the second iron piece  40 , the second moving contact spring  41 , and the second return spring  42  to the second electromagnet unit  25 . As shown in  FIG. 6 , the projection  38   d  of the second yoke  38  is inserted into a hole  42   a  of the second return spring  42 , and a head of the projection  38   d  is flattened for the caulking.  
         [0065]     As described in the foregoing, the second iron piece  40  is disposed adjacent to the magnetic pole  39   a  of the iron core  39  (see  FIG. 3 ) and is detached from the magnetic pole  39   a  by a small gap due to a spring force of the first return spring  33 . When a magnetic force is generated in the magnetic pole  39   a , the second iron piece  40  is attracted to the magnetic pole  39   a  despite the spring force. That is, the second iron piece  40  moves in directions indicated by a two-headed arrow X from the position (position of the projection  38   d ) at which the second return spring  42  is attached to the second yoke  38  depending on absence or presence of the magnetic force of the magnetic pole  39   a . Thus, the second moving contact spring  41  attached to the second iron piece  40  follows the movements of the second iron piece  40  to move in directions indicated by a two-headed arrow Y of approaching to and departing from the side of the second yoke  38 .  
         [0066]     Though not shown, the movement of the first electromagnet unit  24  after attaching the first iron piece  31 , the first moving contact spring  32 , and the first return spring  33  is the same as that of the second electromagnet unit  25 . That is, the first iron piece  31  of the first electromagnet unit  24  moves in directions from the position at which the first return spring  33  is attached to the first yoke  29  depending on absence or presence of the magnetic force of the magnetic pole  30   a . Thus, the first moving contact spring  32  attached to the first iron piece  31  follows the movements of the first iron piece  31  to move in directions of approaching to and departing from the side of the first yoke  29 .  
         [0067]      FIG. 7  is a block diagram showing the A-fixed terminal unit  22 . The A-fixed terminal unit  22  is formed by punching out a metal plate and then so bending the metal plate as to form a shape shown in the drawing. More specifically, the A-fixed terminal unit  22  has walls  22   a  and  22   b  opposed to each other with a predetermined gap D 1  being defined therebetween, a terminal  22   c  extending from a lower end of the wall  22   a , a mounting hole  22   e  for a contact  22   d  fitted to the wall  22   a  at a position of a height H 1   a  from the lower end of the wall  22   a , and a mounting hole  22   g  for a contact  22   f  fitted to the wall  22   b  at a position of a height H 1   b  from a lower end of the wall  22   b . The contacts  22   d  and  22   f  are normal open contacts (A contacts).  
         [0068]     The height H 1   a  is equal to a height from the base  21  to the center of the contacts  41   a  and  41   b  of the second moving contact spring  41  when the second electromagnet unit  25  is attached to the base  21 . The height H 1   b  is equal to a height from the base  21  to the center of the contacts  32   a  and  32   b  of the first moving contact spring  32  when the first electromagnet unit  24  is attached to the base  21 . The gap D 1  between the walls  22   a  and  22   b  is set in accordance with a degree of the movement (see two-headed arrow Y of  FIG. 6 ) of the contacts  32   a ,  32   b ,  41   a , and  41   b  of the first and the second moving contact springs  32  and  42 .  
         [0069]      FIG. 8  is a block diagram showing the B-fixed terminal unit  23 . Like the A-fixed terminal unit  22 , the B-fixed terminal unit  23  is formed by punching out a metal plate and then so bending the metal plate as to form a shape shown in the drawing. The B-fixed terminal unit  23  has walls  23   a  and  23   b  opposed to each other with a predetermined gap D 1  being defined therebetween, a terminal  23   c  extending from a lower end of the wall  22   a , a mounting hole  23   e  for a contact  23   d  fitted to the wall  23   a  at a position of a height H 1   a  from the lower end of the wall  23   a , and a mounting hole  23   g  for a contact  23   f  fitted to the wall  23   b  at a position of a height H 1   b  from a lower end of the wall  23   b . The contacts  23   d  and  23   f  are normal close contacts (B contacts). The heights H 1   a  and H 1   b  and the gap D 1  are set in the same manner as in the A-fixed terminal unit  22 .  
         [0070]     Each of the A-fixed terminal unit  22  and the B-fixed terminal unit  23  having the above-described constitutions is mounted on the base  21  at a predetermined position. When the A-fixed terminal unit  22  and the B-fixed terminal unit  23  are mounted on the base  21 , the terminals  32   a  and  32   b  of the first moving contact spring  32  are disposed in the gap (gap D 1 ) between the walls  22   a  and  22   b  of the A-fixed terminal unit  22 , and the terminals  41   a  and  41   b  of the second moving contact spring  41  are disposed in the gap (gap D 1 ) between the walls  23   a  and  23   b  of the B-fixed terminal unit  23 .  
         [0071]     When both of the first electromagnet unit  24  and the second electromagnet unit  25  are not excited, the right contact  32   a  of the first moving contact spring  32  contacts the contact  23   f  of the wall  23   b  of the B-fixed terminal unit  23 , while the left contact  41   a  of the second moving contact spring  41  contacts the contact  23   d  of the wall  23   a  of the B-fixed terminal unit  23  (normal close state of  FIG. 8 ( b )).  
         [0072]     When the first electromagnet unit  24  is excited, the first moving contact spring  32  moves to the left in the drawing so that the left contact  32   b  of the first moving contact spring  32  contacts the contact  22   f  of the wall  22   b  of the A-fixed terminal unit  22  (see  FIG. 7 ( b )).  
         [0073]     When the second electromagnet unit  25  is excited, the second moving contact spring  41  moves to the right in the drawing so that the right contact  41   b  of the second moving contact spring  41  contacts the contact  22   d  of the wall  22   a  of the A-fixed terminal unit  22  (see  FIG. 7 ( b )).  
         [0074]      FIG. 9  is a conceptual diagram showing a contact operation of the electromagnetic relay  20 . In  FIG. 9 , a thick line indicates positions of the first and the second iron pieces  31  and  40 , the first and the second moving contact springs  32  and  41 , and the first and the second return springs  33  and  42  when the first and the second electromagnet units  24  and  25  are not excited, and a broken line indicates the positions when the first and the second electromagnet units  24  and  25  are excited.  
         [0075]     When the first and the second electromagnet units  24  and  25  are not excited, both ends of the load  45  are connected to the GND via the C-terminals  35  and  44 , the contacts  32   a  and  41   a  of the first and the second moving contact springs  32  and  41 , and the contacts  23   d  and  23   f  of the B-fixed terminal unit  23 . Accordingly, the load  45  does not operate.  
         [0076]     When the first electromagnet unit  24  is excited, a passage of the +E, the terminal  22   c , the wall  22   b , the contact  22   f , the contact  32   b , the first moving contact spring  32 , the first return spring  33 , the first yoke  29 , the C-terminal  35 , the load  45 , the C-terminal  44 , the second yoke  38 , the second return spring  42 , the second moving contact spring  41 , the contact  41   a , the contact  23   d , the terminal  23   c , and the GND is formed.  
         [0077]     When the second electromagnet unit  25  is excited, a passage of the +E, the terminal  22   c , the wall  22   a , the contact  22   d , the contact  41   b , the second moving contact spring  41 , the second return spring  42 , the second yoke  38 , the C-terminal  44 , the load  45 , the C-terminal  35 , the first yoke  29 , the first return spring  33 , the first moving contact spring  32 , the contact  32   a , the contact  23   f , the terminal  23   c , and the GND is formed.  
         [0078]     The above two passages in the excited states are reverse to each other. Therefore, it is possible to control the load  45  in a forward reverse manner.  
         [0079]     By the way, the conceptual diagram of  FIG. 9  is used only for the purpose of explaining the forward reverse control operation, and constitutional characteristics of this embodiment are not precisely illustrated. Though the first and the second moving contact springs  32  and  41  and the contacts  22   d ,  22   f ,  23   d , and  23   f  of the A-fixed terminal unit  22  and the B-fixed terminal unit  23  are aligned horizontally parallel to one another in the conceptual diagram, such alignment is shown for the brevity of illustration and is different from an actual alignment. The actual constitution is such that the second moving contact spring  41  is disposed under the first moving contact spring  32 ; the contact  23   d  of the B-fixed terminal unit  23  is disposed under the contact  22   f  of the A-fixed terminal unit  22 ; and the contact  22   d  of the A-fixed terminal unit  22  is disposed under the contact  23   f  of the B-fixed contact unit  23  (see  FIG. 11 ).  
         [0080]      FIG. 10  is a diagram showing a completion of the electromagnetic relay  20  of this embodiment. Note that the dust protection case  26  is omitted for the brevity of illustration. In the electromagnetic relay  20 , the first electromagnet unit  24 , the second electromagnet unit  25 , the A-fixed terminal unit  22 , and the B-fixed terminal unit  23  are mounted on the base  21  having a square or square-like rectangular shape of the size of W×D. The electromagnet units (the first electromagnet unit  24  and the second electromagnet unit  25 ) are disposed in such a fashion that the shaft lines (lines connecting the poles) are parallel to each other, and a facing gap F is defined therebetween. The facing gap F is the space for housing the first and the second moving contact springs  32  and  41 , the first and the second return springs  33  and  42 , the A-fixed terminal unit  22 , and the B-fixed terminal unit  23 .  
         [0081]      FIG. 11  is a conceptual diagram showing the facing gap F in an actual housing. A position relationship is indicated by absence or presence of a hatching. More specifically, the component part with the hatching is disposed under the component part without the hatching. When the comment parts are perfectly overlapped so that the underlaid component part cannot be seen, a part of the underlaid (hidden) component part is shown in an exploded fashion. In this embodiment, since the second moving contact spring  41  is disposed under the first moving contact spring  32 , the contacts  41   a  and  41   b  of the second moving contact spring  41  are disposed under the contacts  32   a  and  32   b  of the first moving contact spring  32 .  
         [0082]     Also, the wall  23   a  of the B-fixed terminal unit  23  is disposed under the wall  22   b  of the A-fixed terminal unit  22 , and the wall  22   a  of the A-fixed terminal unit  22  is disposed under the wall  23   b  of the B-fixed terminal unit  23 . Further, the contact  23   d  of the B-fixed terminal unit  23  is disposed under the contact  22   f  of the A-fixed terminal unit  22 , and the contact  22   d  of the A-fixed terminal unit  22  is disposed under the contact  23   f  of the B-fixed terminal unit  23 .  
         [0083]     As described in the foregoing, the following effects are achieved according to the electromagnetic relay  20  of this embodiment. 
    (1) Since the A-fixed terminal unit  22  and the B-fixed terminal unit  23  are housed together with the first and the second moving contact springs  32  and  41  and the first and the second return springs  33  and  42  in the facing gap F of the two electromagnet units (the first electromagnet unit  24  and the second electromagnet unit  25 ), it is possible to reduce the length D of the base  21  as compared to the conventional technology. More specifically, though the length (La) of the base  6  is larger in the conventional technology than this embodiment due to the length Ld required for the fixed contact terminal plates  15 ,  16 , at least the length Ld of the conventional technology is eliminated from the length D of the base  21  of this embodiment since the length D of the base  21  is a total of a length of the first electromagnet unit  24 , a thickness of the first iron piece  31 , and a thickness of the first moving contact spring  32  (or a total of a length of the second electromagnet unit  25 , a thickness of the second iron piece  40  and a thickness of the second moving contact spring  41 ). Thus, it is possible to resolve the problem of the large base size of the conventional technology.     (2) Because the C-terminal  35  is electrically connected to the first moving contact spring  32  via the first yoke  29  and the first return spring  33 , and because the C-terminal  44  is electrically connected to the second moving contact spring  41  via the second yoke  38  and the second return spring  42 , it is unnecessary to use the L-shaped moving contact springs  13  and  14  and the terminals  13   a  and  14   a  of the conventional technology. Thus, only the general function and characteristics of an ordinary contact spring are required for each of the first and the second moving contact springs  32  and  41 , so that the first and the second moving contact springs  32  and  41  have an identical shape (length, width, thickness), thereby resolving the problem of difference in spring constant of the conventional technology.