Abstract:
An electromagnetic relay including a first elastic member for elastically holding an armature at an initial position, an electromagnet portion that exercises magnetic force against the elastic force of the first elastic member under an excitation state to attract the armature to a predetermined excitation position, a movable contact and a fixed contact that come into contact with each other when the armature is moved from the initial position to the excitation position, a movable contact tag to which the movable contact is secured, a second elastic member that exercises predetermined elastic force and holds the movable contact tag at the contact position at which the movable contact and the fixed contact are in contact with each other, and a press portion that moves together with the armature to press the movable contact tag so that the movable contact and the fixed contact are kept in non-contact state with each other.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an electromagnetic relay, and particularly an electromagnetic relay that can suppress heating.  
         [0003]     2. Description of the Related Art  
         [0004]      FIG. 4  shows a diagram showing the structure of a conventional electromagnetic relay (for example, see JP-A-2004-134140). This electromagnetic relay  1  comprises an armature  4  disposed in the neighborhood of an iron core around which a coil  2  is wound, a contact spring  5  which also serves as a passage for load current iz and is secured to the armature  4 , a movable contact  6  secured to the tip of the contact spring  5  and a fixed contact  7  disposed so as to face the movable contact  6 . In  FIG. 4 , SW represents an on/off switch for exciting current ir of the coil  2 , Vr represents a power source for excitation, Z represents a load and Vz represents a power source for load.  
         [0005]     In this construction, the armature  4  is held at a position indicated by a solid line of  FIG. 4  (a position spaced from the iron core  3 ) by the elastic force of the contact spring  5  while SW is set to OFF (i.e., the excitation current ir is equal to zero). Therefore, the movable contact  6  and the fixed contact  7  are kept to be separated from each other (off-state), and the current iz does not flow in the load Z. On the other hand, when SW is set to ON, the armature  4  is attracted to magnetic force occurring in the iron core  3 , and displaced to a position indicated by a broken line of  FIG. 4 . Therefore, the movable contact  6  and the fixed contact  7  are kept in contact with each other (on-state), so that the current iz flows in the load Z through the contact spring  5 , the movable contact  6  and the fixed contact  7 .  
         [0006]     However, the conventional electromagnetic relay  1  has the following problems to be solved.  
         [0007]     (1) Heating Problem of the Contacts  
         [0008]     When the movable contact  6  and the fixed contact  7  are under the ON-state, the current iz flows along the following route: load Z→contact spring  5 →movable contact  6 →fixed contact  7 →power source Vz for load→load Z. Here, assuming that the resistance component in the route is equal to zero, heating occurring in these passages is also equal to zero. However, actually, the resistance component in the route is not equal to zero, and some amount of resistance component exists in the route. Therefore, when the resistance component concerned is represented by R, power P of iz 2 R occurs and the heating corresponding to this power P occurs (hereinafter referred to as “contact heat” for convenience).  
         [0009]     In order to reduce this contact heat, the resistance component R in the route must be set to be as small as possible. However, the conventional electromagnetic relay  1  has a problem that the resistance component R in the route, particularly the resistance component of the contact spring  5  cannot be reduce to the level as desired. This is because the contact spring  5  has not only a function of serving as a passage for the current iz, but also a function of providing elastic force to the armature  4 , and thus the material, the cross-sectional area, etc. of the contact spring  5  cannot be freely selected for the purpose of merely reducing the contact heat.  
         [0010]     (2) Problem of Mutual Effect Between Coil Heat and Contact Heat  
         [0011]     When the current ir is made to flow into the coil  2 , heat occurs in the coil  2  (hereinafter referred to as “coil heat” for convenience), however, the coil heat is transferred to the contact spring  5  through the iron core  3  and the armature  4 . At this time, the movable contact  6  and the fixed contact  7  are turned on and the contact heat described above occurs, so that the contact heat and the coil heat have a mutual effect on each other and thus generate high heat.  
       SUMMARY OF THE INVENTION  
       [0012]     Therefore, the present invention has an object to provide an electromagnetic relay that can avoid the mutual effect problem between coil heat and contact heat with suppressing the contact heat.  
         [0013]     In order to attain the above object, an electromagnetic relay according to the present invention comprises: a first elastic member for elastically holding an armature at an initial position; an electromagnet portion that exercises magnetic force against the elastic force of the first elastic member under an excitation state to attract the armature to a predetermined excitation position; a movable contact and a fixed contact that come into contact with each other when the armature is moved from the initial position to the excitation position; a movable contact tag to which the movable contact is secured; a second elastic member that exercises predetermined elastic force and holds the movable contact tag at the contact position at which the movable contact and the fixed contact are in contact with each other; and a press portion that moves together with the armature to press the movable contact tag so that the movable contact and the fixed contact are kept in non-contact with each other.  
         [0014]     In the electromagnetic relay described above, it is preferable that the press portion presses the movable contact tag when the electromagnet portion is under the non-excitation state, thereby keeping the movable contact and the fixed contact under the non-contact state, and also the press portion does not press the movable contact tag, but separates from the movable contact tag when the electromagnetic portion is under the excitation state.  
         [0015]     The press portion may be integrated with the armature or separated from the armature.  
         [0016]     According to the present invention, when the movable contact and the fixed contact come into contact with each other (when the contacts are under ON-state), the load current passes through these contacts and the movable contact tag, however, does not pass through the elastic members (the first elastic member and the second elastic member). Furthermore, the elastic force to the armature is applied by the first elastic member, and the movable contact, the fixed contact and the movable contact tag do not contribute to the application of the elastic force concerned.  
         [0017]     Accordingly, the resistance R of the route for the load current can be reduced by reducing the contact resistance and the conductor resistance of the movable contact tag without paying attention to the characteristic of the elastic members (the first elastic member and the second elastic member), so that the contact heat can be greatly suppressed.  
         [0018]     In addition, the press portion and the movable contact tag are set to be in non-contact with each other when the electromagnet portion is under the excitation state, whereby the heat of the electromagnet portion (coil heat) can be prevented from being transferred to the movable contact tag, and the mutual effect problem between the coil heat and the contact heat can be avoided.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]      FIGS. 1A and 1B  are diagrams showing the principle of an electromagnetic relay  10  according to an embodiment;  
         [0020]      FIGS. 2A and 2B  are diagrams showing an example of the construction of the electromagnetic relay  10 ;  
         [0021]      FIGS. 3A and 3B  are diagrams showing the operation state of the electromagnetic relay  10  of  FIGS. 2A and 2B ; and  
         [0022]      FIG. 4  is a diagram showing the construction of a conventional electromagnetic relay. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0023]     An embodiment of the present invention will be described hereunder with reference to the accompanying drawings. In the following description, specification of various detailed portions, embodiments and examples of numeric values, character arrays and other symbols are used as reference to clarify the technical idea of the present invention, and it is apparent that all or some of these matters does not limit the technical idea of the present invention. Furthermore, with respect to well-known techniques, well-known processing, well-known architectures, well-known circuit constructions, etc. (hereinafter referred to as “well-known matters”), the detailed description thereof is omitted because the description of the present invention is simplified, however, all or some of these well-known matters are not intentionally excluded. These well-known matters may be known by persons skilled in the art at the filing time of this invention, and thus they are contained in the following description.  
         [0024]      FIGS. 1A and 1B  are diagrams showing the principle of an electromagnetic relay  10  according to this embodiment. More specifically,  FIG. 1A  is a diagram showing a circuit construction under a non-excitation state, and  FIG. 1B  is a diagram showing a circuit construction under an excitation-state. SW represents an on/off switch of excitation current ir, Vr represents a power source for excitation, Z represents a load, Vz represents a power source for a load, P 1 , P 2  represent coil terminals, and P 3 , P 4  represent fixed contact terminals.  
         [0025]     In  FIGS. 1A and 1B , the electromagnetic relay  10  contains an electromagnet portion  11  which generates magnetic force when SW is set to ON, and an armature  12  which is separated from the electromagnet portion  11  or approaches to the electromagnet portion  11  in accordance with the excitation/non-excitation of the electromagnet portion  11  is disposed in proximity to the electromagnet portion  11 .  
         [0026]     Specifically, first elastic members  14  such as springs or the like are disposed between the armature  12  and the relay body  13  while the first elastic members  14  are contracted. The armature  12  is separated from the electromagnet portion  11  by the elastic force Pa of the first elastic members  14  when the electromagnet portion  11  is under the non-excitation state, and also the armature  12  approaches t the electromagnet portion  11  by the suction force Pb of the electromagnet portion  11  (the attraction force caused by the magnetic force of the electromagnet portion  11 ) which exceeds the elastic force Pa of the first elastic members  14  when the electromagnet portion  11  is under the excitation state.  
         [0027]     A press member  15  is secured to the armature  12 . In  FIGS. 1A and 1B , the armature  12  and the press member  15  are illustrated as being integrated with each other, however, the securing mode is not limited to the above integration mode. For example, the armature  12  and the press member  15  may be designed as separate members. The press member  15  presses a movable contact tag  17  in the rightward direction of  FIGS. 1A and 1B  when the electromagnet portion  11  is under the non-excitation state , and movables  16  are secured to both the ends of the press member  15 . A second elastic member  18  such as a spring or the like is disposed between the movable contact tag  17  and the relay body  13  while the second elastic member  18  is contracted. When the electromagnet portion  11  is under non-excitation state, the press member  15  presses the movable contact tag  17  by the force exceeding the elastic force Pc of the second elastic force  18 .  
         [0028]     Fixed contacts  20  are secured to fixed contact tags  19  so as to face the movable contacts  16  at both the ends of the movable contact tag  17 .  
         [0029]     In the construction as described above, as shown in  FIG. 1A , when SW is set to OFF so that the electromagnet portion  11  is set to the non-excitation state, the armature  12  undergoes the elastic force Pa of the first elastic members  14  and moves so as to be far away from the electromagnet portion  11 , that is, in the rightward direction of  FIG. 1A . At this time, the press member  15  secured to the armature  12  presses the movable contact tag  17  in the rightward direction of  FIGS. 1A and 1B  against the elastic force Pc of the second elastic member  18 , whereby the movable contacts  16  and the fixed contacts  20  are set to the non-contact state (off-state).  
         [0030]     On the other hand, as shown in  FIG. 1B , when SW is set to ON so that the electromagnet portion  11  is set to the excitation state, the armature  12  is moved so as to approach to the electromagnet portion  11 , that is, in the leftward direction of  FIG. 1B  by the attraction force Pb of the electromagnet portion  11 . At this time, the elastic member  15  secured to the armature  12  is also moved in the same direction, so that the movable contact tag  17  undergoes the elastic force Pc of the second elastic member  18  and thus moves in the same direction (the leftward direction) and thus the movable contacts  16  and the fixed contacts  20  are set to the contact state (on-state). When the movable contacts  16  and the fixed contacts  20  are in contact with each other as described above, the press member  15  secured to the armature  12  and the movable contact tag  17  are in non-contact with each other.  
         [0031]     Here, heating in the electromagnetic relay  10  will be described. As described at the head of the specification, one of heat kinds occurring in the relay is the contact heat. The contact heat occurs in connection with the power P (P=iz 2 R), and thus both or one of the load current iz and the wire resistance R must be reduced to suppress the contact heat. In this case, the magnitude of the load current iz is determined by the load Z, and thus only the wire resistance R is an adjustable parameter.  
         [0032]     Accordingly, the movable contacts  16  and the fixed contacts  20  are required to be formed of materials whose contact resistance is as small as possible, and also the movable contact tag  17  and the fixed contact tags  19  are required to be formed of materials whose conductor resistance and cross-sectional area are as low and large as possible, respectively.  
         [0033]     Such a countermeasure (reduction of the wire resistance R) can be easily taken to the electromagnetic relay  10  according to this embodiment. This is because the contact spring  5  serving as the passage of the load current iz is not used unlike the prior art. That is, one function of the contact spring  5  (the route function of the load current iz) is implemented by the movable contact tag  17  itself, and also the other function of the contact spring  5  (the function of applying the elastic force to the armature  4 ) is implemented by the first elastic members  14  themselves. In short, the two functions of the contact spring  5  are shared and individually implemented by individual parts (the movable contact tag  17  and the first elastic members  14 ).  
         [0034]     Therefore, the selection of the materials of the movable contacts  16  and the fixed contacts  20  and the selection of the materials of the movable contact tag  17  and the fixed contact tags  19  are carried out mainly in consideration of the reduction of the contact resistance and the electrical resistance, and the materials, the cross-sectional area, etc. can be freely set. Therefore, “the problem of contact heat” described at the head of the specification can be easily solved.  
         [0035]     Furthermore, in the electromagnetic relay  10  of this embodiment, when the electromagnet portion  11  is set to the excitation state, the armature  12  and the movable contact tag  17  are set to the non-contact state, so that the heat occurring in the electromagnet portion  11  (coil heat) is not transferred to the movable contact tag  17 . Accordingly, “the problem of mutual effect between coil heat and contact heat” described at the head of the specification can be solved.  
         [0036]     The electromagnetic relay that can suppress the contact heat and avoid the problem of the mutual effect between the coil heat and the contact heat can be provided by the principle construction described above. Any construction can be adopted for the electromagnetic relay  10  insofar as the above principle construction is adopted.  
         [0037]      FIG. 2A  shows an example of the specific construction of the electromagnetic relay  10 . In  FIG. 2A , the electromagnetic relay  10  has a base  30  formed of an insulating member, and a box-shaped case  31  whose bottom surface is opened. A stopper  32 , a movable contact tag  33  (corresponding to the movable contact tag  17  of  FIG. 1 ), fixed contact tags  34  to  36  (corresponding to the movable contact tags  19  of  FIGS. 1A and 1B ) and an electromagnet portion  37  (corresponding to the electromagnet portion  11  of  FIGS. 1A and 1B ) are secured to the base  30 , and it is covered by the case  31  from the upper side, thereby fabricating the electromagnetic relay  10 .  
         [0038]     The stopper  32  is constructed by bending a metal plate in U-shape so that a recess portion  32   a  and two leg portions  32   b  and  32   c  are formed, and it is fixed to the base  30  by fitting the leg portions  32   b  and  32   c  into holes  30   a  and  30   b  of the base  30 .  
         [0039]     The movable contact tag  33  is constructed by forming movable contacts  33   a  to  33   c  (in this case, three movable contacts are provided, however, the number of the movable contacts is not limited to three) (corresponding to the movable contacts  16  of  FIGS. 1A and 1B ) at the corner portions of a substantially rectangular metal plate having low conductor resistance, and further fixing one end of a spring  33   d  (corresponding to the second elastic member  18  of  FIGS. 1A and 1B ) to the metal plate. The other end of the spring  33   d  is fitted to the recess portion  32   a  of the stopper  32 .  
         [0040]     In the case of  FIG. 2A , the fixed contact tags  34  to  36  comprise three fixed contact terminals  34  to  36  ((corresponding to the fixed contacts  20  of  FIGS. 1A and 1B ), all the fixed contact tags are formed of metal material having low conductor resistance so as to have a predetermined shape. Leg portions  34   b  to  36   b  are provided to the fixed contact tags  34  to  36  respectively, and these leg portions  34   b  to  36   b  are fitted in holes  30   c  to  30   e  of the base  30 , thereby fixing the fixed contact tags  34  to  36  to the base  30 .  
         [0041]     The electromagnet portion  37  is equipped with a spool  37   a , a coil  37   b  wound around the spool  37   a , an iron core  37   c , coil terminals  37   d ,  37   e  connected to both the coil  37   b , a yoke  37   f , an armature  37   g  (corresponding to the armature  12  of  FIGS. 1A  and  1 B), hinge springs  37   h  (corresponding to the first elastic members  14  of  FIGS. 1A and 1B ) and a press member  37   i  (corresponding to the press member  15  of  FIGS. 1A and 1B ).  
         [0042]     The armature  37   g  is separated from the iron core  37   c  by the elastic force of the hinge spring  37   h  when the coil  37   b  is under non-excitation, and thus when the coil  37   b  is set to an excitation state, it is attracted to the iron core  37   c  against the elastic force of the hinge spring  37   h.    
         [0043]     The press member  37   i  is secured to the armature  37   g . When the coil  37   b  is under the non-excitation state, the press member  37   i  presses the movable contact tag  33  so that the movable contact tag  33  approaches to a stopper  32 , thereby keeping the movable contacts  33   a  to  33   c  and the fixed contacts  34   a  to  36   a  under the non-contact state (off-state). On the other hand, when the coil  37   b  is under the excitation state, the press member  37   i  does not press the movable contact tag  33 , and keeps the movable contacts  33   a  to  33   c  and the fixed contacts  34   a  to  36   a  under the contact state (on-state). In  FIG. 2A , the armature  37   g  and the press member  37   i  are illustrated as being separated from each other, however, the construction of these elements is not limited to this separate construction. They may be designed to be integrated with each other (integral construction).  
         [0044]      FIG. 2B  is a diagram showing another example of the elastic member secured to the movable contact tag  33 . In place of the spring  33   d  of  FIG. 2A , a leaf spring  33   e  (corresponding to the second elastic member  18  of  FIGS. 1A and 1B ) is used.  
         [0045]      FIGS. 3A and 3B  are diagrams showing the operation state of the electromagnetic relay  10  of  FIG. 2 , wherein  FIG. 3A  is a diagram showing the electromagnetic relay  10  under the non-excitation state, and  FIG. 3B  is a diagram showing the electromagnetic relay  10  under the excitation state.  
         [0046]     First, as shown in  FIG. 3A , when the coil  37   b  is set to the non-excitation state, the armature  37   g  is displaced so as to be far away from the iron core  37   c  by the elastic force of the hinge spring  37   h , and in connection with this displacement, the movable contact tag  33  is pressed to the right side of  FIG. 3A  by the press member  37   i  secured to the armature  37   g . Accordingly, under the non-excitation state, the fixed contacts  34   a  to  36   a  of the fixed contact tags  34  to  36  and the movable contacts  33   a  to  33   c  of the movable contact tag  33  are kept under the non-contact state (off-state).  
         [0047]     On the other hand, as shown in  FIG. 3B , when the current is made to flow into the coil  37   b  to set the coil  37   b  to the excitation state, the armature  37   g  is attracted by the magnetic force occurring in the iron core  37   c  and thus displacement so as to approach to the iron core  37   c . At this time, the press member  37   i  secured to the armature  37   g  is also displaced in the same direction by the same displacement amount, and thus the movable contact tag  33  is kept free, so that the movable contact tag  33  moves to the left side of  FIG. 3B  by the elastic force of the spring  33   d  (or the leaf spring  33   e ). Therefore, the fixed contacts  34   a  to  36   a  of the fixed contact tags  34  to  36  and the movable contacts  33   a  to  33   c  of the movable contact tag  33  are kept under the contact state (on-state).  
         [0048]     In the construction described above, load current (corresponding to the load current iz of  FIGS. 1A and 1B ) passes through only the fixed contact tags  34  to  36 , the fixed contacts  34   a  to  36   a , the movable contacts  33   a  to  33   c  and the movable contact tag  33 , and it does not pass through the spring  33   d  (or the leaf spring  33   e ). In other words, the spring  33   d  (or the leaf spring  33   e ) mostly contributes to the movement of the movable contact tag  33 , and it never contributes to the route of the load current iz.  
         [0049]     Therefore, the contact heat can be suppressed by merely using materials having low conductor resistance for the fixed contact tags  34  to  36  and the movable contact tag  33 , increasing the cross-sectional area of these tags, and using materials having low conductor resistance for the fixed contacts  34   a  to  36   a  and the movable contacts  33   a  to  33   c , whereby the resistance R of the route for the load current can be reduced to the minimum level. Accordingly, it is never required to pay attention to the characteristic of the spring  33   d  (or the leaf spring  33   e ) when some countermeasure is taken to reduce the resistance R of the route. Therefore, “the problem of contact heat” described at the head of the specification can be easily solved.  
         [0050]     In addition, when the electromagnet portion  37  is set to the excitation state, the armature  37   c  and the movable contact tag  33  are kept under the non-contact state, and thus heat occurring in the electromagnet portion  37  (coil heat) is not transferred to the movable contact tag  33 . Accordingly, “the problem of mutual effect between the coil heat and the contact heat” described at the head of the specification can be also solved.  
         [0051]     As described above, the electromagnetic relay that can suppress the contact heat and avoid the mutual effect problem between the coil heat and the contact heat can be provided by constructing the electromagnetic relay  10  shown in  FIG. 2 .  
         [0052]     In the specific construction ( FIG. 2 ) described above, the number of the movable contacts  33   a  to  33   c  and the number of the fixed contacts  34   a  to  36   a  are respectively set to three, and in the principle construction ( FIG. 1 ) described above, the number of the movable contacts  16  and the number of the fixed contacts  20  are respectively set to two. However, these numbers of the movable and fixed contacts are merely set as examples for convenience of description. These numbers of the contacts are not limited to specific values insofar as they are normally open type contacts.