Patent Publication Number: US-9412545-B2

Title: Electromagnetic relay

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electromagnetic relay. 
     2. Description of the Related Art 
     In electromagnetic relays, passage and blockage of a current in an electric circuit is realized by opening/closing a contact part including a fixed contact and a movable contact. When the fixed contact and the movable contact are separated from each other from a contacting state, or when the fixed contact and the movable contact come closer to each other from a separated state as a result of the movable contact being moved toward/away from the fixed contact, an arc may occur when the voltage exceeds a minimum arc voltage or when the current exceeds a minimum arc current (See e.g. Japanese Patent No. 4840533). 
     In light of the above, an arc extinction technique is used in electromagnetic relays that relies on the fact that an arc has substantially the same magnetic characteristics as a current and utilizes the magnetic flux of a permanent magnet positioned near the contacts. The technique involves extinguishing an arc by having a magnetic force based on Fleming&#39;s left-hand rule (Lorenz force) act on the arc so that the arc may be bent, deflected, and blown away. However, according to the technique disclosed in Japanese Patent No. 4840533, the permanent magnet is held by a dedicated yoke. As a result, the number of processes and the number of components may be increased to thereby cause a cost increase. 
     Accordingly, there is a demand for an electromagnetic relay that is capable of adequately performing arc extinction without causing a cost increase. 
     SUMMARY OF THE INVENTION 
     According to one embodiment of the present invention, an electromagnetic relay is provided that includes a contact part including a fixed contact and a movable contact, the movable contact being displaceable in an approaching/separating direction with respect to the fixed contact; a drive part including a coil, a movable core, and a fixed core, the movable core being connected to the movable contact via an axial core, and the fixed core including a first plate member having a through hole through which the axial core is inserted and a second plate member that encapsulates the coil; and a permanent magnet polarized in a direction substantially perpendicular to the approaching/separating direction. The first plate member or the second plate member includes an extension part that extends toward the contact part, the extension part being configured to hold the permanent magnet. 
     According to an aspect of the present invention, an electromagnetic relay may be provided that is capable of adequately performing arc extinction without causing a cost increase. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of an electromagnetic relay according to an embodiment of the present invention along a central axis line of a shaft; 
         FIG. 2  is a perspective view of a convex part of a plunger of the electromagnetic relay according to an embodiment of the present invention; 
         FIG. 3  is a perspective view of a concave part of a yoke of the electromagnetic relay according to an embodiment of the present invention; 
         FIG. 4  schematically illustrates a concave part of the plunger, a convex part of the yoke, and a backside concave part of the yoke of the electromagnetic relay according to an embodiment of the present invention; 
         FIG. 5  is an external perspective view of the electromagnetic relay according to an embodiment of the present invention; 
         FIG. 6  schematically illustrates a fixed contact and a movable contact of the electromagnetic relay according to an embodiment of the present invention; 
         FIG. 7  is a graph illustrating stroke and attraction force characteristics of the electromagnetic relay according to an embodiment of the present invention; 
         FIG. 8  schematically illustrates a convex part of the plunger, a concave part of the yoke, and a backside convex part of the yoke of the electromagnetic relay according to an embodiment of the present invention; 
         FIG. 9  schematically illustrates an arc-extinguishing grid arranged in the electromagnetic relay according to an embodiment of the present invention; 
         FIG. 10  schematically illustrates an arc runner arranged in the electromagnetic relay according to an embodiment of the present invention; 
         FIG. 11  schematically illustrates extension parts of the yoke for holding permanent magnets in the electromagnetic relay according to an embodiment of the present invention; 
         FIG. 12  schematically illustrates a sloped surface and a flat surface of a connection housing in the electromagnetic relay according to an embodiment of the present invention; 
         FIG. 13  schematically illustrates the connection housing in a case where the yoke includes a backside convex part in the electromagnetic relay according to an embodiment of the present invention; 
         FIG. 14  schematically illustrates extension parts of the yoke for holding permanent magnets in the electromagnetic relay according to a modified embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     In the following, embodiments of the present invention will be described with reference to the accompanying drawings. 
     As illustrated in  FIG. 1 , an electromagnetic relay  1  according to an embodiment of the present invention includes a contact part including a pair of fixed contacts  2  and a pair of movable contacts  3  each corresponding to one of the fixed contacts  2 . The movable contacts  3  are displaceable in directions toward and away from the fixed contacts  2 . The electromagnetic relay  1  also includes a movable element  4  that holds the pair of movable contacts  3 . The movable element  4  is configured to be movable in the directions toward and away from the fixed contacts  2 . The electromagnetic relay  1  further includes a shaft  5  (axial core) and a plunger  6  (movable core). The shaft  5  is connected to the movable element  4 . The plunger  6  is connected to the shaft  5  and is displaceable. Note that in the following descriptions, with respect to the displacement directions of the movable element  4 , a moving direction of the movable contact  3  moving closer to the fixed contact  2 ; namely, the moving direction of the movable contact  3  toward the fixed contact  2  is referred to as “approaching direction”, and a moving direction of the movable contact  3  moving away from the fixed contact  2  or the direction opposite the approaching direction is referred to as “separating direction”. 
     The electromagnetic relay  1  further includes a drive part  7  configured to drive the plunger  6  in the approaching direction (upward direction in  FIG. 1 ), a return spring  8  configured to urge the shaft  5  in the separating direction (downward direction in  FIG. 1 ), and a pressure spring  9  configured to urge the movable element  4  in the approaching direction. 
     As illustrated in  FIG. 1 , the drive part  7  includes a yoke  10  (second plate member), a yoke  11 , and a yoke  12  (first plate member) as magnetic members making up a fixed core. The drive part  7  also includes an insulation barrier  14  for securing insulation between the yoke  10  and a coil  13 . The yoke  10  is formed by bending one piece of plate member into a U-shaped configuration. The yokes  10 - 12  are yoke components of a magnetic circuit. The electromagnetic relay  1  also includes a reel-shaped bobbin  15  to which the coil  13  is wound. The bobbin  15  and the insulation barrier  14  may be made of synthetic resin, for example. 
     The electromagnetic relay  1  of the present embodiment includes a drive part housing  16 , a contact part housing  17 , and a connection housing  18 , as illustrated in  FIG. 1 . The drive part housing  16  may be made of molded resin, for example. The drive part housing  16  may be arranged into a box structure having a bottom to accommodate the drive part  7  described above. The connection housing  18  and the contact part housing  17  may also be made of molded resin, for example. 
     A substantially cylindrical protruding part  16   a  is arranged at the bottom of the drive part housing  16 , and a hole  10   a  with a diameter greater than the diameter of the protruding part  16   a  is formed at the bottom of the yoke  10 . Also, the yoke  10  has a notch  10   b  for engaging the yoke  12 , and a pair of extension parts  10   c  that extend toward the contact part from the yoke  12  upon being assembled. The pair of extension parts  10   c  holds a corresponding pair of plate-shaped permanent magnets  19  by magnetic force. The permanent magnets  19  are polarized in directions substantially perpendicular to the approaching/separating directions of the contact part. 
     As illustrated in  FIG. 2 , the plunger  6  has a convex part  6   a  with a truncated cone configuration arranged at a side facing the yoke  12 . As illustrated in  FIG. 3 , the yoke  12  has a concave part  12   a  corresponding to the shape of the convex part  6   a . A through hole  121  through which the shaft  5  is inserted is formed at the center of the concave part  12   a . Also, as illustrated in  FIG. 3 , the yoke  12  has an engagement piece  12   b  for engaging the notch  10   b  of the yoke  10 . Note that in an alternative embodiment, the concave and convex configurations of the plunger  6  and the yoke  12  may be reversed as illustrated in  FIG. 4 . That is, the plunger  6  may have a concave part  6   aa  and the yoke  12  may have a convex part  12   aa , for example. Note that the convex part  6   a  or the concave part  6   aa  of the plunger  6  may be formed through a cutting operation, for example. Also, the concave part  12   a  or the convex part  12   aa  may be formed by pressing the yoke  12 , for example. 
     When the yoke  10  and the yoke  11  are mounted to the drive part housing  16 , the protruding part  16   a  penetrates through the hole  10   a  and is inserted into the inner peripheral side of the yoke  11 . The yoke  11  is arranged into a cylindrical shape and is positioned by the protruding part  16   a . The yoke  10  is held between and positioned by the side walls of the drive part housing  16 . 
     After mounting the yokes  10  and  11 , the bobbin  15  having the insulation barrier  14  attached thereto is inserted into the drive part housing  16  from the upper side, and an assembly of the plunger  6  and the shaft  5  is inserted into the yoke  11 . Then, the engagement piece  12   b  is inserted into the notch  10   b  of the yoke  10  so that the yoke  12  may be positioned at the top, and the shaft  5  is inserted through the through hole  121  to assemble the drive part  7 . Further, the connection housing  18  corresponding to a resin molded member arranged into a plate including a configuration for enabling engagement with the contact part housing  17  is mounted on top of the yoke  12 . 
     Further, the upper side of the shaft  5  is inserted through the pressure spring  9  and is fit into a hole  4   a  of the movable element  4 . Also, an end part of the shaft  5  that protrudes from the upper side of the movable element  4  is inserted into the return spring  8  so that a separating direction side end (lower end in  FIG. 1 ) of the return spring  8  comes into contact with the upper face of the movable element  4 . 
     The contact part housing  17  is configured to fix in place a pair of substantially cylindrical fixed terminals  21  having the fixed contacts  2  arranged at their ends. The contact part housing  17  is inserted from the opening of the drive part housing  16  and is fit into the drive part housing  16 . In this way, the contact part housing  17  arranges the fixed contacts  2  to face the movable contacts  3 . Further, the contact part housing  17  includes a hole  17   a  for holding and fixing in place an approaching direction side end (upper end) of the return spring  8 . The contact part housing  17  holds the outer faces of the extension parts  10   c  and the inner faces of the permanent magnets  19 . Further, engaging portions of the contact part housing  17  may be bonded, welded, or brazed to the drive part housing  16  after which a sealing process may be conducted as is necessary. 
       FIG. 5  illustrates an exemplary external view of the electromagnetic relay  1  after being assembled in the above-described manner. In  FIG. 5 , two terminals S 1  and S 2  for inserting the electromagnetic relay  1  of the present embodiment into a DC circuit are exposed from the contact part housing  17 . 
     Note that the fixed terminals  21  each correspond to one of the fixed contacts  2 . The fixed contacts  2  are arranged at the separating direction side ends (lower ends in  FIG. 1 ) of the fixed terminals  21  at positions facing opposite the movable contacts  3 . In a preferred embodiment, the fixed contacts  2  and the movable contacts  3  are both arranged to have spherical curvature surfaces such that their points of contact are limited to their centers as illustrated in  FIG. 6 . The fixed contacts  2  and the movable contacts  3  may both be made of a copper-based material or a precious metal material, for example. The movable element  4  is arranged into a plate shape extending in the radial directions of the shaft  5 , and the movable contacts  3  are arranged at side ends of the plate-shaped movable element  4 . 
     As described above, the electromagnetic relay  1  according to the present embodiment is a plunger type relay having a pair of contacts arranged at the left and right hand sides. In the present embodiment, the fixed terminals  21  arranged at the left and right hand sides as illustrated in  FIG. 1  are inserted at corresponding locations of a DC circuit that is to be connected/disconnected. A terminal part of the coil  13  of the drive unit  7  may be connected to an input/output (I/O) interface of a PWM control circuit (not shown), for example, and in this way, an excitation current applied to the terminal part of the coil  13  may be controlled as desired. 
     In a state where no excitation current is applied to the terminal part of the coil  13 , the shaft  5  is urged toward the lower side of  FIG. 1  by an urging force of the return spring  8  such that the fixed contact  2  and the movable contact  3  transition to an open state or are maintained in the open state. In the state illustrated in  FIG. 1 , the shaft  5  pushes the plunger  6  from the upper side toward the lower side of  FIG. 1  by the urging force of the return spring  8  such that the bottom part of the plunger  6  is held in contact with the protruding part  16   a  of the drive part housing  16 . 
     When an excitation current is applied to the terminal part of the coil  13 , the coil  13  and the yokes  10 - 12  generate an attraction force that draws the plunger  6  toward the upper side of  FIG. 1 , and as a result, the plunger  6  is pushed toward the upper side causing the shaft  5  and the movable element  4  to move toward the upper side. In this way, the movable contact  3  comes into contact with the fixed contact  2  to thereby transition to a closed state, or the closed state of the movable contact  3  and the fixed contact  2  is maintained in such a state. 
     If an arc occurs during the opening and closing operations of the contacts, the arc is blown away in the direction in which a Lorentz force acts, such direction being determined based on the direction of the current flowing in the approaching/separating directions as described above and the polarity direction of the permanent magnets  19 . In the present embodiment, the direction in which the Lorentz force acts corresponds to the parallel alignment direction of the contacts and a direction substantially perpendicular to the polarity direction of the permanent magnets  19 . 
     As illustrated in  FIG. 7 , the stroke and attraction force characteristics of the movable core (plunger) may vary depending on the configuration of the convex part of the movable core. That is, the above characteristics may vary depending on whether the truncated cone configuration of the convex part of the movable core is arranged into an obtuse cone, whether the convex part of the movable core is arranged into an acute cone with a smaller top surface and a larger side surface compared to the obtuse cone (i.e., closer to a triangle in side view), or whether the movable core has no convex part and is arranged to be flat. As can be appreciated from  FIG. 7 , when the movable core has a convex part that is arranged into an obtuse cone or an acute cone, the attraction force is smaller in a lower stroke region compared to the case where the movable core is flat. Also, with respect to the spring load characteristics illustrated in  FIG. 7 , the movable core with the obtuse cone configuration has a higher load following capability compared to the movable core with the acute cone configuration in a high stroke region, and the movable core with the acute cone configuration has a higher load following capability compared to the movable core with the obtuse cone configuration in the low stroke region. Note that the above principle similarly applies to a case where the movable core is arranged to have a concave part and the yoke  12  is arranged to have a convex part. 
     In the electromagnetic relay  1  according to the present embodiment, the attraction force with respect to the stroke may be adjusted by adjusting the ratio of the side surface to the top surface of the truncated cone configuration of the convex part  6   a  or the concave part  12   a . That is, in the electromagnetic relay  1  according to the present embodiment, the fixed core does not need to have a cylindrical fixed core part corresponding to the convex part  6   a  of the plunger  6 . In this way, operating characteristics may be optimized while reducing the number of components and reducing costs, for example. 
     Note that in the case where the plunger  6  has the concave part  6   aa  and the yoke  12  has the convex part  12   aa  as illustrated in  FIG. 4 , a backside concave part  12   ca  may be arranged at the backside of the convex part  12   aa  so that the depths of the convex part  12   aa  and the concave part  6   aa  in the stroke direction may be increased. In this way, greater flexibility may be provided in optimizing the operating characteristics of the electromagnetic relay  1  of the present embodiment, for example. Similarly, in the case where the plunger  6  has the convex part  6   a  and the yoke  12  has the concave part  12   a , a backside convex part  12   cb  may be arranged at the backside of the concave part  12   a  as illustrated in  FIG. 8 . 
     As illustrated in  FIG. 9 , in certain embodiments, an arc extinguishing grid  22  including a plurality of flat plates made of ferrous material stacked on each other may be arranged according to the direction of the Lorentz force in the electromagnetic relay  1 , for example. In this way, an arc may be divided up and absorbed by the plurality of plates to realize arc extinction. Also, as illustrated in  FIG. 10 , a horn-shaped arc runner  23  made of a copper-based material, for example, may be arranged in the electromagnetic relay  1 , and arc extinction may be performed by gradually increasing the spatial distance of the arc, for example. 
     Note that in the above embodiment, to have the fixed core hold the permanent magnets  19 , the extension parts  10   c  extending from the yoke  10  are arranged to hold the permanent magnets  19 . However, in other embodiments, as illustrated in  FIG. 11 , extension parts  12   c  extending from the yoke  12  may be arranged to hold two pairs of the permanent magnets  19 , for example. Note that the yoke  12  may be formed by bending a yoke plate material into a desired shape, for example. In this case, as illustrated in  FIG. 11 , the extension parts  12   c  may be formed such that the permanent magnets  19  may be polarized in a direction substantially perpendicular to the direction in which the pairs of the fixed contacts  2  and the movable contacts  3  are aligned, for example. 
     By having extension parts of a yoke hold the permanent magnets  19 , a separate yoke does not have to be provided in the embodiments described above. In this way, an increase in the number of components may be avoided. Note that where two pairs of permanent magnets  19  are used as in the embodiment illustrated in  FIG. 11 , for example, the permanent magnets  19  facing each may be polarized in opposite directions so that when a direction of a voltage applied between the terminals S 1  and S 2 ; that is, the direction of the current flowing in the DC circuit as described above, is reversed, an arc may be prevented from being blown inward in a direction toward a contact as a result of the Lorenz force acting in an inward direction toward the contact, for example. 
     Further, as illustrated in  FIG. 12 , in the electromagnetic relay  1  according to a preferred embodiment, the connection housing  18  (resin molded member) is arranged at the contact part side of the yoke  12 , and the connection housing  18  has a hole  181  corresponding to the through hole  121 , a sloped surface  18   a  sloping toward the drive part  7  from the outer edge of the hole  181 , and a flat surface  18   b  that extends outward from the outer edge of the sloped surface  18   a  in a direction substantially perpendicular to the shaft  5 . 
     In the embodiment of  FIG. 12 , even when wear particles of the fixed contact  2  and the movable contact  3  fall onto the flat surface  18   b , the sloped surface  18   a  may prevent the wear particles from moving in a radially inward direction, and the wear particles may be prevented from entering the hole  181  and the through hole  121  to interfere with the operation of the shaft  5 . 
     Note that although the contact part side of the yoke  12  is arranged to be planar in the embodiment illustrated in  FIG. 12 , the present invention is not limited to such an embodiment. For example, as illustrated in  FIG. 13 , in the case where the yoke  12  includes the backside convex part  12   cb , the thickness of the connection housing  18  at the sloped surface  18   a  and its surrounding area may be arranged to be thinner, and the connection housing  18  may be arranged to have a concave part  18   c  corresponding to the backside convex part  12   cb , for example. 
     According to an aspect of the present invention, the structure of a fixed core of an electromagnetic relay may be simplified to thereby reduce costs and enable downsizing of the electromagnetic relay, for example. Embodiments of the present invention may be applied to various electromagnetic relays used in industrial and domestic settings, for example. 
     Further, the present invention is not limited to the embodiments described above, and various variations and modifications may be made without departing from the scope of the present invention. 
     For example, the extension parts  12   c  of the yoke do not necessarily have to be arranged into the configuration as illustrated in  FIG. 12 . In another embodiment, a pair of extension parts  12   c  may extend from positions shifted inward from the longitudinal direction side ends of the yoke  12  as illustrated in  FIG. 14 , for example. In this case, the extension parts  12   c  may be integrally formed with the yoke  12 , or plate members corresponding to the extension parts  12   c  (i.e., separate members) may be arranged to come into contact with or attached to the yoke  12  afterwards to forma parts of the magnetic circuit, for example. In the case where the extension parts  12   c  are simply arranged to come into contact with the yoke  12 , the extension parts  12   c  may be accommodated within corresponding accommodation parts (not shown) of the contact part housing  17  together with their corresponding permanent magnets  19 , and the extension parts  12   c  may be arranged to come into contact with the yoke when the contact part housing  17  is assembled with the drive part housing  16 , for example. 
     The present application is based on and claims priority to Japanese Patent Application No. 2013-174996 filed on Aug. 26, 2013, the entire contents of which are hereby incorporated by reference.