Abstract:
The present invention provides an electromagnetic relay that has a long service life, even when being used for interrupting high voltage, and that can be miniaturized. In this electromagnetic relay, the circuit interruption is cut-off by two or more keying circuits, which are operated by a single coil and connected in series. Thus, an amount of generated arc per keying circuit is suppressed. Consequently, the service life of the electromagnetic relay is lengthened. Moreover, the space between the contracts thereof is reduced, so that the electromagnetic relay is miniaturized. Additionally, a magnetic field for extinguishing arc is formed by a back or counter electromotive force generated when the circuit is cut-off. Thus, the generated arc is extinguished.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    The application is a divisional application of U.S. Ser. No. 09/514,160 filed Feb. 28, 2000, now allowed. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention generally relates to an electromagnetic relay and, more particularly, to a small electromagnetic relay capable of cutting-off a high voltage.  
           [0004]    2. Description of the Related Art  
           [0005]    Recently, the motorization of car-mounted parts (for example, sideview mirrors and seats) has been promoted. Electromagnetic relays are frequently used for controlling supply of electric power to electric motors or solenoids, which act as electrically-driven actuators. Needless to say, compactness is required of car-mounted electromagnetic relays.  
           [0006]    Further, if electric power is supplied thereto at a low voltage in a conventional manner even when the number of the electrically-driven parts is increased, the diameter of a wire harness for transfer of electric power becomes large. This results in increase in weight and cost of the wire harness. It has, thus, been proposed that a battery having a terminal voltage of 40 to 60 volts (V) should be used instead of the presently-used battery having a terminal voltage of 12 to 16 V.  
           [0007]    Therefore, to control the supply of electric power to the electrically-driven actuator, currently, an electromagnetic relay capable of cutting-off a low voltage is used. Conversely, in future, the use of an electromagnetic relay capable of cutting-off a high voltage will be needed.  
           [0008]    However, when high voltage is cut-off by the electromagnetic relay for cutting off low voltage, an arcing time at the cut-off becomes long, so that welding or sticking between the contacts of the electromagnetic relay easily occurs. Consequently, the service life of the contacts thereof becomes short.  
           [0009]    There has been publicly known a method of broadening the space between the contacts of the electromagnetic relay so as to extend the service life of the contacts thereof. However, when the space therebetween is broadened, there is the necessity for increasing the size not only the contacts thereof but also of an electromagnetic coil so as to increase a magnetic force for operating the contacts thereof. Thus, the size of the entire electromagnetic relay inevitably becomes big.  
           [0010]    The present invention is accomplished to solve the aforementioned problems. Accordingly, an object of the present invention is to provide an electromagnetic relay that has contacts, whose service life can be long, and can be miniaturized even when used for cutting-off a high voltage.  
         SUMMARY OF THE INVENTION  
         [0011]    To achieve the foregoing object, according to a first aspect of the present invention, there is provided an electromagnetic relay that comprises an iron core, a coil wound around the iron core, an armature attracted by the iron core when electric power is supplied to the coil, a first common contact driven by the armature, a first make contact contacted with the common contact when the armature is attracted by the iron core, and an arc suppressing means for suppressing an occurrence of arc between the common contact and the make contact when the common contact is separated from the make contact by stopping supply of electric power to the coil.  
           [0012]    Thus, according to this first aspect, an occurrence of arc between the common contact and the make contact is suppressed when the common contact is separated from the make contact. Consequently, the abrasion of the contacts is reduced. Further, the service life of the electromagnetic relay becomes long. Additionally, the space between the contacts is decreased, so that miniaturization of the electromagnetic relay is achieved.  
           [0013]    According to a second aspect of the present invention, the arc suppressing means comprises at least one second common contact driven by the armature, at least one second make contact contacted with each of the at least one second common contact when the armature is attracted to the iron core, and a series-connecting means not only for serially connecting at least one first keying circuit, each of which comprises a first common contact and a first make contact, and at least one second keying circuit to each other, each of which comprises a second common contact and a second make contact, but also for serially connecting the serial connection of the at least one second keying circuit to the at least one first keying circuit.  
           [0014]    Thus, according to this second aspect, an occurrence of arc at the time of circuit interruption is suppressed by serially connecting two or more keying circuits, each of which comprises one common contact and one make contact.  
           [0015]    According to a third aspect of the present invention, the arc suppressing means comprises arc extinguishing means for extinguishing an arc generated between the common contact and the make contact by using a magnetic field which is caused by an electric current generated when the supply of electric power to the coil is stopped.  
           [0016]    Thus, according to this third aspect, an arc generated between the contacts is extinguished by the magnetic field which is caused by the back electromotive force generated when the circuit is opened, and an electric current flowing in the arc. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    Other features, objects and advantages of the present invention will become apparent from the following description of preferred embodiments with reference to the drawings in which:  
         [0018]    [0018]FIG. 1 is a circuit diagram illustrating an electric circuit of an electromagnetic relay according to the first embodiment of the present invention;  
         [0019]    [0019]FIG. 2 is a perspective diagram illustrating the electromagnetic relay of FIG. 1;  
         [0020]    [0020]FIG. 3 is a circuit diagram illustrating an electric circuit of an electromagnetic relay according to the second embodiment of the present invention;  
         [0021]    [0021]FIG. 4 is a perspective diagram illustrating the electromagnetic relay of FIG. 3;  
         [0022]    [0022]FIG. 5 is a circuit diagram illustrating an electric circuit of an electromagnetic relay according to the third embodiment of the present invention;  
         [0023]    [0023]FIG. 6 is a perspective diagram illustrating the electromagnetic relay of FIG. 5;  
         [0024]    [0024]FIGS. 7A and 7B are graphs illustrating effects of the first to third embodiments of the present invention;  
         [0025]    [0025]FIG. 8 is a graph illustrating effects of the present invention;  
         [0026]    [0026]FIG. 9 is a diagram illustrating the principle of a magnetic arc extinguishing electromagnetic relay;  
         [0027]    [0027]FIG. 10 is a diagram schematically illustrating the constitution of an electromagnetic relay according to the fourth embodiment of the present invention;  
         [0028]    [0028]FIG. 11 is a diagram illustrating a situation in which a magnetic flux is generated when a switching device is turned off;  
         [0029]    [0029]FIGS. 12A to  12 D are graphs illustrating the transient characteristics of a make contact, magnetic fluxes generated in a closed magnetic circuit and an extension yoke, and the exciting current;  
         [0030]    [0030]FIG. 13 is a diagram schematically illustrating the constitution of an electromagnetic relay according to the fifth embodiment of the present invention;  
         [0031]    [0031]FIG. 14 is a diagram illustrating a situation in which a magnetic flux is generated; and  
         [0032]    [0032]FIGS. 15A to  15 E are graphs illustrating the transient characteristics of a make contact, a magnetic flux generated in a closed magnetic circuit, electric current flowing through an auxiliary coil, a magnetic flux generated in an extension yoke, and the existing current. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]    [0033]FIG. 1 is a circuit diagram illustrating the electric circuit of an electromagnetic relay according to the first embodiment of the present invention. FIG. 2 is a perspective diagram illustrating the electromagnetic relay of FIG. 1. A load  11 , such as an electric motor or a solenoid, is connected to a battery  12  functioning as a power source through an electromagnetic relay  1 , which has two series-connected contacts.  
         [0034]    The electromagnetic relay  1  has two common contacts ( 1 C and  2 C), two make contacts ( 1 M and  2 M), and two break contacts ( 1 B and  2 B). The two common contacts  1 C and  2 C are connected each other in the electromagnetic relay and have no terminal connected to external circuits.  
         [0035]    Further, the first make contact  1 M is connected to one of terminals of the load  11 . The second make contact  2 M is connected to a positive pole of the battery  12 . Moreover, the other terminal of the load  11  is directly connected to the negative pole of the battery  12 . The first common contact  1 C and the first make contact  1 M together constitute a first keying circuit. Similarly, each of at least one second keying circuit comprises a second common contact  2 C and a second make contact  2 M.  
         [0036]    Therefore, when the coil of the electromagnetic relay is energised, the make contacts  1 M and  2 M contact with the two common contacts  1 C and  2 C, respectively. Thus, the load  11  receives electric power from the battery  12  and then starts acting. Conversely, when the coil of the electromagnetic relay is deenergised, the make contacts  1 M and  2 M are separated from the two common contacts  1 C and  2 C, respectively. Thus, the load  11  stops acting.  
         [0037]    At that time, the separation of the first make contact  1 M from the first common contact  1 C and that of the second make contact  2 M from the second common contact  2 C are simultaneously performed. Power cut-off is performed by using the two series-connected contacts. As compared with the case that the power cut-off is performed by using one contact, the duration of arc generated when the contacts are separated is shortened. Consequently, the service life of the contacts is lengthened.  
         [0038]    Incidentally, in the case that the load  11  is an inductive load such as an electric motor or a solenoid, it is preferable to short-circuit the load  11  to prevent it acting when electric power is not supplied thereto and for consuming a back electromotive force in a D.C. load.  
         [0039]    Thus, in the first embodiment, the first break contact  1 B is connected to one of the terminals of the load, while the second break contact  2 B is connected to the other terminal of the load.  
         [0040]    In the case of the electromagnetic relay  1  of the first embodiment, which acts as described above and the structure of which is shown in FIG. 2, the first arm of a U-shaped yoke  103  penetrates a substrate  101  and extends upward. A coil  102  is wound around the arm. The second arm of the U-shaped yoke  103  extends upward along a side surface of the substrate  101 .  
         [0041]    A movable spring  105  is attached to an upper part of the second arm of the U-shaped yoke  103 . The moving spring  105  is bent at a right angle in a direction of the first arm of the yoke  103 , and extends horizontally, or laterally, beyond the first arm.  
         [0042]    An armature  107  is attached to the movable spring  105  by a fastening member  106 , such as a rivet. Incidentally, the armature  107  is sized so that an end of the armature  107  contacts with the second arm of the yoke  103  and that an opposite end of the armature  107  covers the first arm of the U-shaped yoke  103 . That is, the armature  107  closes an opening portion of the U-shaped yoke  103  and constitutes a closed magnetic circuit when the coil  102  is energised.  
         [0043]    Two common contacts  1 C and  2 C are formed as, or on, an end portion  105   a  of the moving spring  105 , which extends beyond the first arm of the U-shaped yoke  103 . The movable spring  105  is made of an electrically conductive material, so that the two common contacts  1 C and  2 C are electrically connected to each other.  
         [0044]    Two separate break contacts  1 B and  2 B are placed above the common contacts. Further, two separate make contacts  1 M and  2 M are placed under the common contacts.  
         [0045]    Each of the two break contacts  1 B and  2 B is placed on the lower surfaces of two laterally extending portions  108   a  and  109   a  of break contact support members  108  and  109 , respectively, each formed as a reversed-L shape and erected perpendicularly on the substrate  101 . These break contact support members  108  and  109  are electrically conductive. The support members  108  and  109  connect, correspondingly, the two break contacts  1 B and  2 B with two break terminals  110  and  111 , which project downwardly from the substrate  101 .  
         [0046]    The two make terminals  1 M and  2 M are placed on upper surfaces of laterally extending portions of two respective make contact support members  112  and  113 , each formed as a reversed-L shape and erected perpendicularly on the substrate  101 . The make contact support members  112  and  113  are electrically conductive. The make contact support members  112  and  113  connect, correspondingly, the two make contacts  1 M and  2 M to the two make terminals  114  and  115 , which project downwardly from the substrate  101 .  
         [0047]    [0047]FIG. 3 is a circuit diagram illustrating the electric circuit of an electromagnetic relay according to the second embodiment of the present invention. FIG. 4 is a perspective diagram illustrating the electromagnetic relay of FIG. 3. A load  11  is connected to a battery  12  functioning as a power source through an electromagnetic relay  1 , which has two series-connected contacts.  
         [0048]    The electromagnetic relay  1  has two common contacts ( 1 C and  2 C), two make contacts ( 1 M and  2 M), and two break contacts ( 1 B and  2 B). The two make contacts  1 M and  2 M are internally connected to each other in the electromagnetic relay and have no terminal connected to external circuits. The first common contact  1 C is connected to one of terminals of the load  11 . The second make contact  2 C is connected to a negative pole of the battery  12 . Moreover, the first break contact  1 B, the other terminal of the load  11 , and a positive pole of the battery  12  are connected in common.  
         [0049]    Therefore, when the coil of the electromagnetic relay is energised, the make contacts  1 M and  2 M contact with the two contacts  1 C and  2 C, respectively. Thus, the load  11  receives electric power from the battery  12  and then starts acting. Conversely, when the coil of the electromagnetic relay is deenergised, the make contacts  1 M and  2 M are separated from the two common contacts  1 C and  2 C, respectively. Thus, the load  11  stops acting.  
         [0050]    Incidentally, in this embodiment, the load  11  is preferably short-circuited in the deenergised condition of the relay as in the first embodiment. Thus, in the second embodiment, the first break terminal  1 B is connected to the latter terminal of the load  11 .  
         [0051]    In the case of the electromagnetic relay  1  of the second embodiment acting as described above, the first arm of a U-shaped yoke  103  penetrates a substrate  101  and extends upward. A coil  102  is wound around it. The second arm of the U-shaped yoke  103  extends upward along the side surface of the substrate  101 .  
         [0052]    Two moving springs  401  and  402  are electrically insulated from the yoke  103  and one end of each is attached to an upper part of the second arm of the U-shaped yoke  103 . The other ends of the moving springs  401  and  402  are bent at a right angle in a direction toward the first arm of the yoke  103 , and so as to extend horizontally beyond the first arm. Incidentally, respective end portions  401   a  and  401   b  of the moving springs  401  and  402  extend downward beyond the bottom of the U-shaped yoke  103 , and are respectively connected to a first common terminal (not shown) and a second common terminal  404 .  
         [0053]    An armature  107  is attached to the moving springs  401  and  402  through an insulating member  403  by caulking members  106 . Incidentally, the armature  107  is sized so that one edge of the armature  107  contacts with the second arm of the U-shaped yoke  103  and that the armature  107  covers the first arm of the U-shaped yoke  103 . That is, the armature 107  closes an opening portion of the U-shaped yoke  103  and constitutes a closed magnetic circuit when the coil  102  is energised.  
         [0054]    Two common contacts  1 C and  2 C are formed at respective extending end portions of the springs  401  and  402 .  
         [0055]    Two separate break contacts  1 B and  2 B are placed above the common contacts  1   c  and  2   c,  respectively. Further, two separate make contacts  1 M and  2 M formed on an electrically conductive substrate  405  are placed under the common contacts  2 A and  2 C, respectively.  
         [0056]    The two break contacts  1 B and  2 B are placed on the lower surfaces of laterally oriented end portions  108   a  and  109   a  of two break contact support members  108  and  109 , respectively, each formed as a reversed-L shape and erected perpendicularly on the substrate  101 . These break contact support members  108  and  109  are electrically conductive. The support members  108  and  109  connect the two break contacts  1 B and  2 B to the two break terminals  110  and  111 , which project downward from the substrate  101 .  
         [0057]    The make substrate  405  is electrically insulated from the two break contact support members  108  and  109 , which are formed as a reversed-L shape, and is fixed by a suitable method, for example, by being screwed.  
         [0058]    [0058]FIG. 5 is a circuit diagram illustrating the electric circuit of an electromagnetic relay according to the third embodiment of the present invention. FIG. 6 is a perspective diagram illustrating the electromagnetic relay of FIG. 4. A load  11  is connected to a battery  12  functioning as a power source through an electromagnetic relay  1 , which has two series-connected contacts.  
         [0059]    The electromagnetic relay  1  has two common contacts ( 1 C and  2 C), two make contacts ( 1 M and  2 M), and two break contacts ( 1 B and  2 B). The first common contact  1 C is connected to one terminal of the load  11 . The second make contact  2 M is connected to a positive pole of the battery  12 . Moreover, the other terminal of the load  11  and a negative pole of the battery  12  are directly connected to each other.  
         [0060]    Therefore, when the coil of the electromagnetic relay is energised, the make contacts  1 M and  2 M contact with the two common contacts  1 C and  2 C, respectively. Thus, the load  11  receives electric power from the battery  12  and then starts acting. Conversely, when the coil of the electromagnetic relay is deenergised, the make contacts  1 M and  2 M are separated from the two common contacts  1 C and  2 C, respectively. Thus, the load  11  stops acting.  
         [0061]    Incidentally, if the load  11  is an electric motor, the load  11  is preferably shortcircuited in the energised state of the relay as in the first embodiment. Thus, in the third embodiment, the first break terminal  1 B is connected to one of terminals of the load  11 .  
         [0062]    In the case of the electromagnetic relay  1  of the third embodiment acting as described above, the first arm of a U-shaped yoke  103  penetrates a substrate  101  and extends upward. A coil  102  is wound around the first arm. The second arm of the U-shaped yoke  103  extends upward along a side surface of the substrate  101 .  
         [0063]    Two moving springs  401  and  402  are attached to an upper surface of the second arm of the U-shaped yoke  103 . The moving springs  401  and  402  are each bent at a right angle to extend in a horizontal, or lateral, direction toward and beyond the first arm of the yoke  103 . Incidentally, the first moving spring  401  is connected through an insulating member  601  to the second arm of the yoke and the second moving spring  402  is connected directly to it.  
         [0064]    An insulating member  602  is placed on horizontal parts of the two moving springs  401  and  402  and just above the second arm of the yoke so that the two moving springs  401  and  402  do not contact with each other. Further, an armature  107  is attached to a central portion of the insulating member  602  by a caulking member  106 . Incidentally, the armature  107  is sized so that an end edge of the armature  107  contacts with the second arm of the U-shaped yoke  103  and that the armature  107  covers the first arm of the U-shaped yoke  103 . That is, the armature  107  closes an opening of the U-shaped yoke  103  and constitutes a closed magnetic circuit when the coil  102  is energised.  
         [0065]    Two common contacts  1 C and  2 C are formed in respective extending end portions of the springs  401  and  402 .  
         [0066]    Two break contacts  1 B and  2 B (not seen in FIG. 6) are placed above the common contacts  1 C and  2 C, respectively. That is, the two break contacts  1 B and  2 B are mounted on a bottom surface of, and are electrically connected together by, an electrically conductive break contact substrate  603 . Further, two separate make contacts  1 M and  2 M are placed under the common contacts  1 C and  2 C.  
         [0067]    The break contact substrate  603  is attached to a break contact support member  604 , which is erected perpendicularly on the substrate  101  and formed in a reversed-L shape. The electrically conductive member provided inside the break contact support member  604  connects the break contact substrate  603  to a break terminal (not shown) protruding downward from the substrate  101 .  
         [0068]    The two make contacts  1 M and  2 M are placed (i.e., formed) on the upper surfaces of laterally extending end portions  112   a  and  113   a  of the two make contact support members  112  and  113  ( 113  and  113   a  not shown in FIG. 6), each formed as a reversed-L shape and erected perpendicularly on the substrate  101 . These make contact support members  112  and  113  are electrically conductive and connect the two make contacts  1 M and  2 M with the two make terminals  114  and  115  ( 115  not shown), which project downward from the substrate  101 .  
         [0069]    [0069]FIGS. 7A and 7B.are graphs illustrating effects of the first to third embodiments of the present invention. FIG. 7A illustrates a transient characteristic of the voltage across the load when the circuit is cut-off by one cut-off element comprised of a make contact and a common contact. FIG. 7B illustrates a transient characteristic of the voltage across the load when the circuit is cut-off by two series connected cut-off elements, each of which is comprised of a make contact and a common contact. In each of these two graphs, the ordinate represents the voltage across the load, while the abscissa represents time.  
         [0070]    As shown in these graphs, the time required to completely separate the make contact from the common contact in FIG. 7A is 65.8 μsec., while in FIG. 7B 36.5 μsec. Thus, the arcing time of the relay according the present invention is reduced by half.  
         [0071]    [0071]FIG. 8 is a graph illustrating the effects of the present invention. This graph shows the relation between the cutoff voltage (V) and the arcing time (μsec.) when the circuit is cut-off by one cut-off element versus by two cut-off elements. In this graph, the ordinate represents the arcing time, while the abscissa represents the cutoff voltage.  
         [0072]    As shown in this graph, when the cutoff voltage is increased, the arcing time when applying two series connected cut-off elements is a half of that when applying one cut-off element.  
         [0073]    Namely, in the case of the first to third embodiments, the arcing time thereof can be reduced by a half of that when applying a single cut-off element. The service life of the contacts can be lengthened.  
         [0074]    As described above, the first to third embodiments shorten the arcing time and lengthen the service time of contact by applying a plurality of series connected cutoff elements. However, the service life of the contacts can be lengthened by adopting a magnetic arc extinguishing method in which a magnet is placed in the vicinity of the contact and the arc is extinguished by a magnetic force.  
         [0075]    [0075]FIG. 9 is a diagram illustrating the principle of an electromagnetic relay with a magnetic arc extinguishing mechanism in which a primary coil  92  is wound around the first arm of a U-shaped yoke  91 .  
         [0076]    A blade spring  93  is attached to an upper part of the second arm of the yoke  91 . The blade spring  93  is bent nearly at a right angle and has a first part  93   a  that extends beyond the first arm of the yoke  91  and a second, extended part  93   b  extending from the first part  93   a.  An armature  94  is attached to this part  93   a  of the blade spring  93  having an end that is in contact with the first arm of the yoke  91 . Incidentally, the armature  94  is sized to cover the first arm of the yoke  91 . The armature  94  functions to short circuit an opening portion of the U-shaped yoke  91  and to constitute a closed magnetic circuit when the primary coil  92  is energised.  
         [0077]    A common contact C is formed at a tip portion  93   c  of the extended part  93   b  of the blade spring  93 . A break contact B and a make contact M are respectively placed above and under the common contact C. Further, a magnet  95  is disposed in the proximity of the common contact C and the make contact M so that a magnetic field is generated in a gap between the common contact C and the make contact M.  
         [0078]    That is, when the primary coil  92  is energised, the common contact C contacts with the make contact M. Conversely, when the primary coil  92  is deenergised, the make contact M is separated from the common contact C. However, when the closed circuit is cut-off, or opened, by separating the common contact C from the make contact M, an arc is generated between the common contact C and the make contact M. A force based on the Fleming&#39;s left-hand rule acts in a direction perpendicular to an electric current flowing in the arc and a magnetic field in the gap between the common contact C ad the make contact M. As a result, the arc is pushed out from the gap between the contacts.  
         [0079]    Thus, abrasion of the contacts due to the arc is suppressed.  
         [0080]    The electromagnetic relay with a magnetic arc extinguishing mechanism can use a permanent magnet as the magnet  95 . However, in view of the facts that the permanent magnet is costly and that a magnetic field is applied only when the circuit is cut-off, the electromagnetic relay of the present invention generates a magnetic field, for extinguishing arc, by using the back electromotive force caused when the primary coil  92  is deenergised.  
         [0081]    [0081]FIG. 10 is a diagram schematically illustrating the constitution of an electromagnetic relay according to the fourth embodiment of the present invention. Incidentally, same reference numerals designate same constituent elements of FIG. 9.  
         [0082]    In the fourth embodiment, an extension yoke  41 , which extends to a direction of a make contact M at the upper part of one of the arms of the U-shaped yoke  91 , and an extinguishing coil  42  wound around this extension yoke  41  are added to the constituent elements of FIG. 9 which shows the principle of the electromagnetic relay.  
         [0083]    A primary coil  92  is connected in series to an exciting power supply  43  and a switching device  44 . Further, the extinguishing coil  42  is connected in parallel to the primary coil  92  through a reverse-current blocking diode  45  for preventing an energising current from flowing through the extinguishing coil  42  when primary coil  92  is energised by turning on the switching device  44 .  
         [0084]    Namely, in the embodiment shown in FIG. 10, the primary coil  92  and the extinguishing coil  42  have a common beginning end  921  of the winding. A reverse-current blocking diode  45  is connected between the terminating end  922  of the primary coil  92  and the terminating end  422  of the extinguishing coil  42  so that the cathode of the diode  45  is connected to the terminating end  922  of the extinguishing coil and its anode is connected to the terminating end  922  of the primary coil. Further, the beginning end  921  of the primary coil  92  is connected to the positive pole of the energising power source  43 . The terminating end  922  of the primary coil  92  is connected to the negative pole of the energising power source  43  through the switching device  44 .  
         [0085]    [0085]FIG. 11 is a diagram illustrating a situation in which a magnetic flux is generated when the switching device  44  is turned off. FIGS. 12A to  12 D are graphs respectively illustrating the state of the make contact, a magnetic flux φ 2  generated in a closed magnetic circuit, a magnetic flux φ 2  generated in the extension yoke, and the exciting current.  
         [0086]    When the switching device  44  is turned on in this embodiment, the energising current I E  flows through the primary coil  92 . This energising current is, however, blocked by the reverse-current blocking diode  45 , and thus does not flow into the extinguishing coil  42 . Therefore, when the primary coil  92  is energised, the magnetic flux φ 1  is generated in the closed magnetic circuit formed by covering an opening portion of the U-shaped yoke  91  with the armature  94 . Conversely, the magnetic flux φ 1  is not generated in the extension yoke  41 .  
         [0087]    When the switching device  44  is turned off, the magnetic flux φ 1  generated in the closed magnetic circuit composed of the U-shaped yoke  91  and the armature  94  is extinguished. At that time, a back electromotive force is generated in the closed magnetic circuit, so that electric current I R  flows in the primary coil  92  in a direction opposite to the direction of the electric current I E  generated when the primary coil is energised. This opposite current flows through the reverse current blocking diode  45 , and also flows in the extinguishing coil  42 . Thus, a magnetic flux φ 2  is generated in the extension yoke  41  and the gap between the common contact C and the make contact M, so that a magnetic field is generated. Then, a force F 1  caused by the interaction between this magnetic field and the electric current flowing in the arc generated between the common contact C and the make contact M is applied to the arc. Consequently, the arc is extinguished.  
         [0088]    [0088]FIG. 13 is a diagram schematically illustrating the constitution of an electromagnetic relay according to the fifth embodiment of the present invention. Incidentally, same reference numerals designate same constituent elements of FIGS. 9 and 10.  
         [0089]    In the fifth embodiment, an extension yoke  41 , which extends in a direction of the make contact M at an upper part of one of the arms of the U-shaped yoke  91 , an extinguishing coil  42  wound around this extension yoke  41 , and an auxiliary coil  51  wound around the first arms of the U-shaped yoke  91  are added to the constituent elements of FIG. 9 illustrating the principle of the electromagnetic relay. The reverse current blocking diode  45  is unnecessary.  
         [0090]    The beginning end  921  of the winding of the primary coil  92 , and the terminating ends of the auxiliary coil  51  and the extinguishing coil  42  are connected in common. Moreover, the terminating end of the auxiliary coil  51  and that of the extinguishing coil  42  are connected in common.  
         [0091]    Further, an energising circuit consisting of the energising power source  43  and the switching device  44 , which are connected in series, is connected between the beginning end  921  and the terminating end  922  of the primary coil  92 .  
         [0092]    [0092]FIG. 14 is a diagram illustrating a situation in which a magnetic flux is generated when the switching device  44  is turned off. FIGS. 15A to  15 E are graphs respectively illustrating the state of the make contact, a magnetic flux φ 1  generated in a closed magnetic circuit, an electric current flowing through the auxiliary coil, a magnetic flux φ 2  generated in the extension yoke  41 , and the energising current.  
         [0093]    When the switching device  44  is turned on, the magnetic flux φ 1  is generated in the U-shaped yoke  91 , and the make contact contacts with the common contact. When the magnetic flux φ 1  is generated, the electric current I 2  is caused in the auxiliary coil  51 , and the magnetic flux φ 2  is generated in the extension yoke  41 . This, however, has no special effects.  
         [0094]    When the switching device  44  is turned off, the magnetic flux φ 1  generated in the U-shaped yoke  91  is extinguished. However, a back electromotive force generated at that time causes electric current I R  to flow in the auxiliary coil  51  and the arc extinguishing coil  42 .  
         [0095]    Thus, a magnetic flux φ 2  is generated in the extension yoke  41  and the gap between the common contact C and the make contact M, so that a magnetic field is generated. Then, a force caused due to the interaction between this magnetic field and the electric current flowing in the arc generated between the common contact C and the make contact M is applied to the arc. Consequently, the arc is extinguished.  
         [0096]    Although the preferred embodiments of the present invention have been described above, it should be understood that the present invention is not limited thereto and that other modifications will be apparent to those skilled in the art without departing from the sprint of the invention.  
         [0097]    The scope of the present invention, therefore, should be determined solely by the appended claims.