Abstract:
The present invention provides an electromagnet device including: an electromagnet block having a spool around which a coil is wound and an iron core inserted in a central hole of the spool; a yoke connected to an end portion of the iron core via a permanent magnet; a movable iron piece pivotably supported on a pivoting shaft center located at an end face edge portion of the yoke, the movable iron piece is adapted to pivot on a basis of magnetization and demagnetization of the electromagnet block, and a protrusion having a linear edge portion which extends in parallel to the pivoting shaft center and the protrusion protrudes from at least either the movable iron piece or the iron core, the protrusion protrudes in a facing direction in which the movable iron piece and the iron core face each other.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims benefit of priority to Japanese Patent Application No. 2012-185882, filed on Aug. 24, 2012 of which the full contents are herein incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to an electromagnet device. 
         [0003]    Japanese Patent Publication No. 2004-164948 (Also published as U.S. Pat. No. 7,205,870) discloses one of the conventional electromagnetic device to be used in an electromagnetic relay. The electromagnet device disclosed in said document includes an attracted portion of a movable iron piece and an attracting surface of an iron core wherein both the movable iron piece and the attracting surface are flat and smooth to achieve attraction. 
         [0004]    However, since the attracted portion and the attracting surface are flat and smooth in the electromagnet device, this lead to various problems such as magnetic flux flowing between the movable iron piece and the iron core spreads which reduces magnetism and thereby weaken a retention force between the movable iron piece and the iron core. 
       SUMMARY OF THE INVENTION 
       [0005]    Accordingly, the present invention provides an electromagnetic device which overcomes the above-mentioned problems and limitations of conventional art. Further, the present invention provides an electromagnet device which can maintain a strong retention force between a movable iron piece and an iron core and an electromagnetic relay using the electromagnet device. 
         [0006]    In accordance with one aspect of the present invention, there is provided an electromagnet device including an electromagnet block comprising a spool around which a coil is wound and an iron core inserted in a central hole of the spool, a yoke connected to an end portion of the iron core via a permanent magnet, and a movable iron piece pivotably supported on a pivoting shaft center, located at an end face edge portion of the yoke, wherein the movable iron piece is adapted to pivot on a basis of magnetization and demagnetization of the electromagnet block. Further, a protrusion comprising a linear edge portion which extends in parallel to the pivoting shaft center and the protrusion protrudes from at least either the movable iron piece or the iron core, wherein the protrusion protrudes in a facing direction in which the movable iron piece and the iron core face each other, and the movable iron piece is adapted to be in line contact with the iron core via the outer edge portion of the protrusion on magnetization of the electromagnet block, wherein the outer edge portion is located in an outside position as compared with a central axis of the iron core when the electromagnet block is magnetized. 
         [0007]    According to another aspect of the present invention, a curving surface which projects toward the facing direction is provided and is formed in a surface of the protrusion. 
         [0008]    According to still another aspect of the present invention, the protrusion may be provided in the movable iron piece, and the outer edge portion is adapted to be in contact with a magnetic pole surface of the iron core. 
         [0009]    In accordance with one of the preferred embodiment of the present invention, the protrusion may be provided in the iron core, and the outer edge portion is adapted to be in contact with the horizontal portion of the movable iron piece. 
         [0010]    According to yet another aspect of the present invention, there is provided an electromagnetic relay which may use the electromagnet device according to one of the above aspects. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The invention will become more readily appreciated and understood from the following detailed description of preferred embodiments of the invention when taken in conjunction with the accompanying drawings, in which: 
           [0012]      FIGS. 1A and 1B  are perspective views of an electromagnetic relay incorporating an electromagnet device according to a first embodiment of the invention; 
           [0013]      FIG. 2  is an exploded perspective view of the electromagnetic relay, illustrated in  FIGS. 1A and 1B , which is obliquely viewed from the top; 
           [0014]      FIG. 3  is an exploded perspective view of the electromagnetic relay, illustrated in  FIGS. 1A and 1B , which is obliquely viewed from the bottom; 
           [0015]      FIGS. 4A and 4B  are perspective views showing the electromagnet device according to the first embodiment of the invention; 
           [0016]      FIG. 5  is an exploded perspective view of the electromagnet device, illustrated in  FIG. 4A , which is obliquely viewed from the top; 
           [0017]      FIG. 6  is an exploded perspective view of the electromagnet device, illustrated in  FIG. 4B , which is obliquely viewed from the bottom; 
           [0018]      FIG. 7A  is an exploded perspective view of a yoke, an auxiliary yoke, and a plate-like permanent magnet illustrated in  FIG. 6 ; 
           [0019]      FIG. 7B  is a perspective view showing a state in which the yoke, the auxiliary yoke, and the plate-like permanent magnet are assembled; 
           [0020]      FIGS. 8A and 8B  are cross-sectional views showing states before and after an operation of the electromagnetic relay illustrated in  FIGS. 1A and 1B ; 
           [0021]      FIG. 9  is a partially enlarged cross-sectional view of a state in which the movable iron piece and the iron core are attracted to each other; 
           [0022]      FIGS. 10A and 10B  are schematic cross-sectional views describing an operation process of the electromagnet device; 
           [0023]      FIGS. 11A and 11B  are schematic cross-sectional views describing an operation process of the electromagnet device which is subsequent to the operation process illustrated in  FIGS. 10A and 10B ; 
           [0024]      FIGS. 12A and 12B  are perspective views of a modification of an iron core and a movable iron piece; 
           [0025]      FIG. 13A  is a schematic plan view of a horizontal portion and an iron core; 
           [0026]      FIG. 13B  is a table showing a calculation result where a retention force changes with a position of a contact protrusion within the horizontal portion; 
           [0027]      FIG. 13C  is a graph indicating a change of the result illustrated in  FIG. 13B ; 
           [0028]      FIG. 14A  is a schematic plan view of an iron core and a horizontal portion in which a contact protrusion is formed at an interval which is required for processing from an outer form; 
           [0029]      FIG. 14B  is a table showing a calculation result in which a retention force changes with a position of the contact protrusion within the horizontal portion; and 
           [0030]      FIG. 14C  is a graph showing a change of the result illustrated in  FIG. 14B . 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    The present invention is described hereinafter by various embodiments with reference to the accompanying drawings, wherein reference numerals used in the accompanying drawings correspond to the like elements throughout the description. Further, while discussing various embodiments, cross reference will made between the figures. In order to achieve full description and explanation, specific details have been mentioned to provide thorough and comprehensive understanding of various embodiments of the present invention. However, said embodiments may be utilized without such specific details and in various other ways broadly covered herein. 
         [0032]    An electromagnet device according to one of the embodiment of the present invention is described with reference to  FIGS. 1A to 12B . The electromagnet device is incorporated into a latching type electromagnetic relay as illustrated in  FIGS. 1A to 8B . In this case, the electromagnet device includes a base  10 , an electromagnet device  20 , a contact mechanism  70 , a card  80  and a box-shaped cover  90 . Further, the card  80  is connected to the electromagnet device  20  and drives the contact mechanism  70 . 
         [0033]    As illustrated in  FIGS. 2 and 3 , the base  10  has an approximately C-shaped insulation wall  11  which protrudes upward from an upper surface of the base  10 . in a center portion on the upper surface. The electromagnet device  20  described below is arranged in one side portion on the upper surface, and the contact mechanism  70  is arranged in the opposite side portion on the upper surface. The insulation wall  11  is provided with fitting grooves  12  which are formed in both inside surfaces, respectively which face each other. In the fitting grooves  12 , both side edge portions of a yoke  50  are press-fitted. In addition, a center portion of an upper end of the insulation wall  11  is provided with a pair of guide ribs  13  that are in parallel with each other and protrude from an upper surface thereof. 
         [0034]    As illustrated in  FIGS. 4A ,  4 B, and  5 , the electromagnet device  20  includes an electromagnet block  30  in which an iron core  40  having an almost T-shaped cross section passes through a central hole  33  of a spool  32  around which a coil  31  is wound, and an auxiliary yoke  45  is fixed by caulking to an upper end portion  41  of the iron core  40  which protrudes from the central hole  33 . The electromagnet device  20  further includes the yoke  50  having a substantially L-shaped cross section which is assembled so that a plate-like permanent magnet  21  is interposed between the yoke  50  and an upper end face of the iron core  40 , a support spring  55  attached to a rear surface of the yoke  50 , and a movable iron piece  60  which is pivotably supported on a lower end face edge portion of the yoke  50  via the support spring. The lower end face edge portion of the yoke  50  serves as a fulcrum for pivoting the movable iron piece  60 . 
         [0035]    In the spool  32 , extended wires of the coil  31  are connected and soldered to coil terminals  35  which are press-fitted in corner portions of a guard portion  34 . In the spool  32 , an alignment protrusion  37  for aligning a position of the auxiliary yoke  45  is formed to protrude from an upper surface of an upper guard portion  36 . 
         [0036]    The iron core  40  includes a cylindrical iron core body  40   a,  a cylindrical upper end portion  41  which is higher by one step than an upper end of the iron core body  40   a  and has a smaller diameter than the iron core body  40   a,  and a disk-like magnetic pole portion  42  which is formed in a lower end of the iron core body  40   a  and has a larger diameter than the iron core body  40   a.  A curving portion  40   b  is formed in the boundary of the iron core body  40   a  and the magnetic pole portion  42 , along a circumferential direction. For this reason, magnetic flux which flows through the iron core  40  can be more smoothly passed from the iron core body  40   a  to the magnetic pole portion  42  via the curving portion  40   b  as compared with a case where the iron core body  40   a  and the magnetic pole portion  42  perpendicularly intersect each other. 
         [0037]    The auxiliary yoke  45  has a caulking hole  46  in the center. The auxiliary yoke  45  extends in parallel from adjacent corner portions to form connecting narrow-width portions  47  with a small cross-sectional area. These narrow width portions are magnetic resistance portions. 
         [0038]    The plate-like permanent magnet  21  has a width dimension substantially the same as a width dimension of the auxiliary yoke  45 . 
         [0039]    The yoke  50  has a substantially L-shaped cross section and includes a vertical portion  51  provided with notch portions  52  at both sides thereof, respectively. The notch portions  52  function to elastically engage with the support spring  55  as described below. The yoke  50  further includes a horizontal portion  53  which laterally extends from an upper end of the vertical portion  51 . 
         [0040]    As illustrated in  FIGS. 5 and 6 , in the support spring  55 , a pair of elastic arm portions  56  extend in parallel with each other from both side edges respectively and an elastic support portion  59  extends from a lower edge portion. While an engaging pawl  57  is formed to protrude from a leading end of either of the elastic arm portions  56 , a latching pawl  58  (as shown in  FIGS. 4A and 4B ) is formed to stand up from a leading end of the other elastic arm portion  56 . 
         [0041]    The movable iron piece  60  includes an attracted surface  66  of an approximately rectangular shape formed in a rear half portion in an upper surface of the horizontal portion  61 , and a step portion  62  which is lower by one step than the attracted surface  66  and which is formed in a front half portion. A contact protrusion  63  of a rectangular shape having a smaller area than the attracted surface  66  is formed in the step portion  62  through a protruding process. The contact protrusion  63  has an outer edge portion  63   a  disposed on an outside surface of the contact protrusion  63 . The movable iron piece  60  has notch portions  65  for engaging the card  80 , at both side edges of a leading end of the vertical portion  64 . The boundary between the horizontal portion  61  and the vertical portion  64  serve as a pivoting shaft center  67  which is latched to a lower end edge portion of the yoke  50 . 
         [0042]    As illustrated in  FIG. 2 , the contact mechanism  70  includes first and second fixed touch pieces  71 ,  72  which are arranged to face each other in a predetermined distance, and a movable touch piece  73  arranged between the first and second fixed touch pieces  71 , 72 . A movable contact  73   a  provided in the movable touch piece  73 , which is alternately attached to and detached from a first fixed contact  71   a  and a second fixed contact  72   a.  The first and the second fixed contact  71   a,    72   a  are provided in the first and the second fixed touch pieces  71 ,  72 , respectively. Two sets of latching pawls  74 ,  75  for vertically latching a remaining end edge portion  83  of the card  80  described below are provided in an upper end portion of the movable touch piece  73 . 
         [0043]    As illustrated in  FIGS. 2 and 3 , in the card  80 , a pair of elastic arm portions  82  and  82  extend from both sides of the contact protrusion  81 , respectively that protrudes from one end, and a pair of latching arm portions  84  and  84  extend from both ends of the remaining end edge portion  83 , respectively. 
         [0044]    The box-shaped cover  90  has a box shape which can fit into the base  10 . The box-shaped cover  90  is provided with a position-regulating projecting portion  91  that bulges downward from a ceiling surface (refer to  FIGS. 8A and 8B ) thereof, and a degassing hole  92  provided in the bottom of the position-regulating projecting portion  91 . The position-regulating projecting portion  91  prevents the card  80  aligned under the position-regulating projecting portion  91  from lifting. The box-shaped cover  90  has a marking recess  93  in an end portion of the upper surface thereof. 
         [0045]    Therefore, when assembling the electromagnetic relay, first, the permanent magnet  21  may be interposed between the horizontal portion  53  of the yoke  50  and the auxiliary yoke  45  of the electromagnet block  30  (refer to  FIGS. 7A and 7B ) and the movable iron piece  60  is disposed in the lower edge portion of the vertical portion  51  of the yoke  50 . Further, the movable iron piece  60  is pivotably supported in such a manner that the engaging pawl  57  and the latching pawl  58  of the support spring  55  are engaged with and latched to the notch portions  52  of the yoke  50 , respectively. Both-side edge portions of the yoke  50  are press-fitted in the press-fitting grooves  12  provided in the insulation wall  11  of the base  10 . 
         [0046]    On the other hand, the second fixed touch piece  72 , the movable touch piece  73 , and the first fixed touch piece  71  of the contact mechanism  70  are press-fitted within the other side in the upper surface of the base  10 . Further, the other side in the upper surface is partitioned by the insulation wall  11 . Subsequently, the contact protrusion  81  of the card  80  is brought into contact with the vicinity of an upper end portion of the movable iron piece  60 , and the pair of elastic arm portions  82  and  82  are engaged with the pair of engaging notch portions  65  and  65  provided in the vertical portion  64  of the movable iron piece  60 , respectively. The latching pawls  74  and  75  of the movable touch piece  73  are latched to the remaining end edge portion  83  of the card  80 . Finally, the following process is performed and assembling work is completed. That is, the box-shaped cover  90  is fitted into the base  10 , and sealing is performed by injecting a sealing material (not illustrated) in the bottom of the base  10 . After that, inner gas is degassed through the degassing hole  92  of the box-shaped cover  90 , and then the degassing hole  92  is subjected to heat caulking. 
         [0047]    Next, an operation of the magnetic relay having the above-described structure will be described in accordance with one of the preferred embodiments of the invention. As illustrated in  FIG. 8A , when a voltage is not applied to the coil  31 , while the contact protrusion  63  of the movable iron piece  60  is separated from the magnetic pole portion  42  of the iron core  40 , and the movable contact  73   a  is in contact with the first fixed contact  71   a.  During this state, as illustrated in  FIG. 10A , the magnetic flux flowing out from the permanent magnet  21  flows through a magnetic circuit M 1  which includes the auxiliary yoke  45 , and leakage flux forms a magnetic circuit M 2  via the yoke  50 . For this reason, a state in which the movable iron piece  60  is separated from the magnetic pole portion  42  is maintained by balance between a spring force of the movable touch piece  73  and magnetism generated by the magnetic flux which flows to magnetic circuits M 1  and M 2 . The magnetic circuit M 1  is in a magnetically saturated state. 
         [0048]    When the voltage is applied so that magnetic flux of the same direction as the magnetic flux of the permanent magnet  21  is generated in the coil  31 , the magnetic flux generated by the voltage applied to the coil  31  flows to the magnetic circuit M 2  ( FIG. 10B ), and an attraction force which attracts the movable iron piece  60  increases. For this reason, the movable iron piece  60  pivots on the pivoting shaft center  67 , while resisting against the spring force of the movable touch piece  73 . Thus the movable iron piece  60  is attracted to the magnetic pole portion  42  of the iron core  40 , and the contact protrusion  63  is attracted to the magnetic pole portion  42 . 
         [0049]    During this state, as illustrated in  FIG. 9 , the magnetic pole portion  42  and the contact protrusion  63  come into line contact with and attracted to each other via the outer edge portion  63   a  in a position opposite to the pivoting shaft center  67  (as shown in  FIGS. 8A and 8B ) with respect to a central axis Lc of the iron core  40 . Therefore, it results into an increase in a distance between the contact portion where the magnetic pole portion  42  and the outer edge portion  63   a  are in contact with each other, and the pivoting shaft center  67 . For this reason, in a state in which the movable iron piece  60  and the iron core  40  are attracted to each other thereby a magnetic moment for pivoting the yoke  50  increases, and thus the yoke  50  becomes difficult to return by pivoting on the pivoting shaft center  67 . Therefore, an attraction force, i.e., a retention force between the movable iron piece  60  and the iron core  40  is certainly maintainable. Furthermore, since the magnetic pole portion  42  and the contact protrusion  63  are in contact with each other via the outer edge portion  63   a,  the magnetic flux concentrates and the retention force between the movable iron piece  60  and the iron core  40  increases. And since the distance between an attracted surface  66  of the horizontal portion  61  and the magnetic pole portion  42  is decreased and it becomes for the magnetic flux to easily flow, the attraction force increases. Thereby flexibility as well as degree of freedom in design increases. 
         [0050]    When the contact protrusion  63  is attracted to the magnetic pole portion  42 , the vertical portion  64  of the movable iron piece  60  presses the movable touch piece  73  via the card  80 , and the movable contact  73   a  separates from the first fixed contact  71   a,  and comes into contact with the second fixed contact  72   a  ( FIG. 8B ). 
         [0051]    Subsequently, even through the application of the voltage to the coil  31  is stopped, as illustrated in  FIG. 11A , a combined magnetic force of the magnetic flux which flows into the magnetic circuit M 1  which includes the auxiliary yoke  45  from the permanent magnet  21 , and the magnetic flux which flows into the magnetic circuit M 2  which includes the yoke  50 , the movable iron piece  60 , and the iron core  40  is larger than the spring force of the movable touch piece  73 . For this reason, the movable iron piece  60  maintains this current state, without pivoting. 
         [0052]    When a return voltage of a reversed direction with respect to the previously described application voltage is applied to the coil  31  (refer to  FIG. 11B ) so that the magnetism of the permanent magnet  21  acting on the movable iron piece  60  will be canceled, the movable contact  73   a  separates from the second fixed contact  72   a,  comes into contact with first fixed contact  71   a,  and returns to the original state. 
         [0053]    Even through the return voltage is applied in the present embodiment, since the magnetic circuit M 1  which includes the auxiliary yoke  45  is in a magnetically saturated state, the magnetic flux does not flow through the magnetic circuit M 1 . For this reason, since all the magnetic flux of the coil which is generated by the applied return voltage flows into the magnetic circuit M 2  and a return operation is carried out, wherein the magnetic circuit M 2  includes the yoke, the movable iron piece, and the iron core. Thereby a latching type electromagnetic relay consuming less power is obtainable. 
         [0054]    The present invention is not limited to the above-described embodiment, but various modifications thereof are possible. The surface of the contact protrusion  63  is made to be flat and smooth in the above-described embodiment. Alternatively, the surface may be an upward curving surface. With this configuration, a touch point of the movable iron piece  60  and the magnetic pole portion  42  the iron core  40  can be stabilized, allowing the magnetic flux to easily pass therethrough. Therefore, a fluctuation in magnetism can be prevented. The contact protrusion  63  is formed in a rectangular shape in the above-described embodiment. However, the shape is not particularly limited to the rectangular shape, as long as the contact protrusion  63  can come into line contact with the iron core  40 . 
         [0055]    According to the above-described embodiment, the magnetic pole portion  42  of the iron core  40  is formed in a disc shape, and the contact protrusion  63  is provided in the movable iron piece  60 . However, the shape of the magnetic pole portion  42  is not limited to the disc shape. For example, as illustrated in  FIGS. 12A and 12B , a configuration may be adopted in which the magnetic pole portion  42  of the iron core  40  is provided with a semi-circular attracting surface  43  and a rectangular contact protrusion  44  formed in an edge of the attracting surface  43 , especially in a position (on an outer side position) opposite to the pivoting shaft center  67  with respect to the central axis of the iron core  40 . In this configuration, an outer edge portion  44   a  is formed in an outer portion of the contact protrusion  44 . In this case, the upper surface of the horizontal portion  61  of the movable iron piece  60  is a flat and smooth surface without unevenness. By providing the attracting surface  43  in the iron core  40 , when the iron core  40  and the movable iron piece  60  changes from a separated state to an attracted state, the magnetic flux comes to easily flow between the attracting surface  43  and the movable iron piece  60 , and the attraction force increases. By providing the contact protrusion  44  in the outside of the central axis of the iron core  40 , a distance between a contact surface of the outer edge portion  44   a  and the horizontal portion  61 , and the pivoting shaft center  67  increases. For this reason, in a state in which the movable iron piece  60  and the iron core  40  are attracted to each other, thereby a magnetic moment for pivoting the yoke  50  increases, and thus the yoke  50  becomes difficult to return by pivoting on the pivoting shaft center  67 . Therefore, an attraction force, i.e., a retention force between the movable iron piece  60  and the iron core  40  is certainly maintainable. 
         [0056]    Further, the calculations are provided for changes in the attraction force (retention force) between the iron core  40  and the movable iron piece  60  with respect to positions of the contact protrusion  63  within the horizontal portion  61 . Specifically, as illustrated in  FIG. 13A , the pivoting shaft center  67  of the horizontal portion  61  is used as a fulcrum, a distance from the fulcrum to a central axis Lc of the magnetic pole portion  42  is defined as L 1 , a distance from the fulcrum to a leading end of the horizontal portion is defined as L 2 , and a distance from the fulcrum to the outer edge portion  63   a  of the contact protrusion  63  is defined as L 3 . A length dimension of the contact protrusion  63  is defined as L 4 , a width dimension is defined as L 5 , and L 4  and L 5  are set to fixed values like L 4 =1 mm and L 5 =2.44 mm. When the outer edge portion  63   a  of the contact protrusion  63  is located on the central axis Lc of the magnetic pole portion  42  (i.e., when L 3 =L 1 ), the position in this case is set to 0%. And when the outer edge portion  63   a  of the contact protrusion  63  is located in a leading end of the horizontal portion  61 , i.e. when L 3 =L 2 , the position in this case is set to 100%. The calculation result is illustrated in  FIG. 13B . 
         [0057]    As illustrated in  FIG. 13B , when L 3 =8.75 mm, i.e., when the position is set to 58%, the retention force becomes the maximum. It is found that the retention force gradually decreases in both cases where the value of L 3  increases and decreases than this value. As illustrated in  FIG. 13C , in order to obtain a retention force larger than 2.4 N which is the minimum requisite retention force between the iron core  40  and the movable iron piece  60 , it is found that the outer edge portion  63   a  needs to be located between a position corresponding to 50% and a position corresponding to 75%. 
         [0058]    As described above, in order that the contact protrusion  63  and the iron core  40  are attracted to each other and maintained as attracted in a position opposite to the pivoting shaft center  67  with respect to the central axis Lc of the iron core  40 , it is found that preferably the outer edge portion  63   a  of the contact protrusion  63  is located between a position corresponding to 50% and a position corresponding to 75%, and the maximum retention force is obtained particularly when the position is set to 58%. 
         [0059]    Further, calculations are provided for changes in the attraction force (retention force) between the iron core  40  and the movable iron piece  60  with respect to positions of the contact protrusion  63  within the horizontal portion  61  and a change in the width dimension L 5 . Specifically, as illustrated in  FIG. 14A , the pivoting shaft center  67  of the horizontal portion  61  is used as a fulcrum, a distance from the fulcrum to the central axis Lc of the magnetic pole portion  42  is defined as L 1 , a distance from the fulcrum to the leading end of the horizontal portion is defined as L 2 , and a distance from the fulcrum to the outer edge portion  63   a  of the contact protrusion  63  is defined as L 3 . When the outer edge portion  63   a  of the contact protrusion  63  is located on the central axis Lc of the magnetic pole portion  42  (i.e., when L 3 =L 1 ), the position in this case is set to 0%. And when the outer edge portion  63   a  of the contact protrusion  63  is located at a leading end of the horizontal portion  61 , i.e. when L 3 =L 2 , the position in this case is set to 100%. 
         [0060]    The length dimension of the contact protrusion  63  is defined as L 4 , and L 4  is a fixed value (i.e. L 4 =1 mm). In order to provide the contact protrusion  63  in the horizontal portion  61 , the contact protrusion  63  needs to be provided inside so as to have a distance by 1 mm or more from an outer diameter of the horizontal portion  61  in the processing. For this reason, when the width dimension of the contact protrusion  63  is defined as L 5 , the value of L 5  changes as follows. When the outer edge portion  63   a  is located on the central axis Lc, the value of L 5  becomes the maximum, and when the outer edge portion  63   a  is located in the leading end of the horizontal portion  61 , the value of L 5  becomes the minimum. The calculation result under these conditions is indicated in  FIG. 14B . 
         [0061]    As illustrated in  FIG. 14B , when L 3 =8.75 mm, i.e., when the outer edge portion  63   a  is located in a position corresponding to 58%, it is found that the retention force becomes the maximum. It is also found that the retention force gradually decreases in both cases where the value of L 3  increases and decreases than this value. As illustrated in  FIG. 14C , in order to obtain a retention force larger than 2.4 N which is the minimum requisite retention force between the iron core  40  and the movable iron piece  60 , it is found that the outer edge portion  63   a  needs to be located between a position corresponding to 40% and a position corresponding to 65%. 
         [0062]    As described above, in order that the contact protrusion  63  and the iron core  40  are attracted to each other and maintained as attracted in a position opposite to the pivoting shaft center  67  with respect to the central axis Lc of the iron core  40 , it is found that preferably the outer edge portion  63   a  of the contact protrusion  63  is located between a position corresponding to 40% and a position corresponding to 65%, and the maximum retention force is obtained particularly when the position is set to 58%. 
         [0063]    It is needless to say that the electromagnet device according to the present invention is applied not only to an electromagnetic relay but also to other electronic equipment. 
         [0064]    There has thus been shown and described an electromagnetic device and electromagnetic relay using the same which fulfills all the advantages sought therefore. Many changes, modifications, variations and other uses and applications of the subject invention will, however, become apparent to those skilled in the art after considering this specification and the accompanying drawings which disclose the preferred embodiments thereof. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention, which is to be limited only by the claims which follow. 
         [0065]    Although the invention has been described in detail for the purpose of illustration based on what is currently considered to be the most practical and preferred embodiments, it is to be understood that such detail is solely for that purpose and that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover modifications and equivalent arrangements that are within the spirit and scope of the appended claims. For example, it is to be understood that the present invention contemplates that, to the extent possible, one or more features of any embodiment can be combined with one or more features of any other embodiment.