Patent Publication Number: US-11049635-B2

Title: Solenoid

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Phase Application under 35 U.S.C. 371 of International Application No. PCT/JP2016/056601 filed on Mar. 3, 2016. The entire disclosure of the above application is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a solenoid provided with both a permanent magnet and a coil. 
     BACKGROUND ART 
     Conventionally, in a solenoid provided with both a permanent magnet and a coil, when the coil is not energized, magnetic flux generated by the permanent magnet passes through a portion (attraction portion) where a movable iron core and another part are attracted to each other, so that attraction force is generated. When the coil is energized, magnetic flux generated by the coil flows so as to counteract the magnetic flux generated by the magnet. As a result, since the magnetic flux (generated by the magnet) passing through the attraction portion is reduced, the attraction force decreases and finally can be canceled. 
     For example, PATENT LITERATURE 1 discloses a solenoid provided with both a permanent magnet and a coil. The solenoid according to the literature has a structure in which the permanent magnet is disposed in a space surrounded by a movable iron core and a fixed iron core. Therefore, a magnetic field (magnetic path) generated by energizing the coil does not have a direct effect on the permanent magnet. Further, the literature explains that the permanent magnet is not demagnetized even in a release operation of the solenoid, so that a long life of the solenoid can be ensured. 
     CITATION LIST 
     Patent Literature 
     PATENT LITERATURE 1: JP 2002-289430 A 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, in the solenoid disclosed in PATENT LITERATURE 1, when energization of the coil is started in the release operation, magnetic flux BC generated in the coil flows against magnetic flux BM generated by the magnet (see FIG. 5 in the literature). Then, the amount of magnetic flux generated by the permanent magnet that passes through an attraction portion (a portion where a disk-shaped steel plate 6 and a protrusion 4 are in contact with each other shown in FIG. 5 of the literature) is reduced, and attraction force of the movable iron core decreases. 
     After that, if the coil generates such an amount of magnetic flux that exactly counteracts the magnetic flux generated by the permanent magnet, the magnetic flux passing through the attraction portion is eliminated, so that the attraction force of the movable iron core almost disappears finally. However, if the magnetic flux generated by energizing the coil is sufficiently greater than the magnetic flux generated by the permanent magnet, the magnetic flux passing through the attraction portion is switched from the magnetic flux generated by the permanent magnet to the magnetic flux generated by the energization of the coil, and therefore there has been a problem that the generation of the attraction force is started again. In other words, there has been a problem that the release operation of the solenoid becomes incomplete depending on the amount of magnetic flux generated by the energization of the coil. 
     Therefore, the present invention has been made for solving the above problems, and an object thereof is to provide a solenoid which can reliably perform a release operation by suppressing increase in amount of magnetic flux passing through an attraction portion to decrease attraction force of a movable iron core even when magnetic flux generated by the energization of a coil is greater than magnetic flux generated by a magnet. 
     Solution to Problem 
     In order to solve the problems described above, according to the present invention, there is provided a solenoid in which a permanent magnet and a coil are both built in a cylindrical case having an opening, a ring member is disposed in close contact with the permanent magnet, a movable iron core is inserted and provided in the coil, and a metallic coil cover is disposed between the movable iron core and the coil so as to cover the whole coil. Further, the distance between an inner wall of the case and the ring member may be set in the range of 0.1 mm to 0.3 mm. 
     Advantageous Effects of Invention 
     According to the solenoid of the present invention, in a type of solenoid which is provided with both a permanent magnet and a coil, the coil is disposed in a case so that the whole coil is covered with a metallic coil cover. With this configuration, a magnetic path through which magnetic flux generated by the permanent magnet passes, and a magnetic path through which magnetic flux generated by energizing the coil passes are separately and independently generated. Further, the solenoid is configured so that a portion (attraction portion) where a movable iron core and a ring member are in contact with each other does not exist in the middle of the magnetic paths. Accordingly, even when magnetic flux generated by the coil is greater than magnetic flux generated by the magnet, it is possible to achieve a quick release operation of the solenoid by suppressing increase in amount of magnetic flux passing through the attraction portion to reliably decrease attraction force of the movable iron core. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  is a longitudinal sectional view (during non-energization) of a solenoid  10  which is one example of an embodiment of the present invention. 
         FIG. 1B  is an enlarged view of an A part of  FIG. 1A . 
         FIG. 2  is an operation explaining view (during energization) of the solenoid  10  shown in  FIG. 1A . 
         FIG. 3  is an explanatory view of a flow of a magnetic path  25  during non-energization of the solenoid  10  shown in  FIG. 1A . 
         FIG. 4  is an explanatory view (when a ring member  14  and a movable iron core  19  are attracted to each other) of flows of magnetic paths  26  and  27  during energization of the solenoid  10  shown in  FIG. 1A . 
         FIG. 5  is an explanatory view (when the ring member  14  and the movable iron core  19  are separated from each other) of the flows of the magnetic paths  26  and  27  during energization of the solenoid  10  shown in  FIG. 1A . 
         FIG. 6  is an explanatory view of a different embodiment where the flow of the magnetic path is in an opposite direction to the flow of the magnetic path during energization of the solenoid  10  shown in  FIG. 4 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a specific embodiment is shown to describe a solenoid according to the present invention in detail with reference to the accompanying drawings.  FIG. 1A  is a longitudinal sectional view of a solenoid  10  according to the present invention.  FIG. 1B  is an enlarged view of an A part shown in  FIG. 1A . 
     The solenoid  10  according to the present invention is of a type in which a permanent magnet  13  and a coil  16  are disposed in a cylindrical case  11  as shown in  FIG. 1A . A circular opening  12  is formed in an end face  11   a  (on an upper side in  FIG. 1A ) of the case  11 . The permanent magnet  13  of a cylindrical shape having a hole  13   a  is provided inside the case  11  in such a manner as to closely contact a back side (inner side) of the end face  11   a  of the case  11 . Moreover, the hole  13   a  of the permanent magnet  13  and the opening  12  of the case  11  are arranged in such a positional relation as to be concentric with each other as shown in  FIG. 1A . 
     It should be noted that a clearance may be provided between the permanent magnet  13  and an inner wall surface of the case  11  as shown in  FIG. 1A , and the clearance may be filled with a nonmagnetic material such as resin. The configurations of the permanent magnet and the coil constituting the solenoid of the present invention will be described below in detail. 
     A ring member  14  is disposed on the permanent magnet  13  built in the case  11  so as to be in close contact with a lower surface (on a lower side in  FIG. 1A ) of the permanent magnet  13 . The inside diameter side of the ring member  14  is disposed so as to be concentric with the hole  13   a  of the permanent magnet  13  as shown in  FIG. 1A . 
     Furthermore, as shown in  FIG. 1B , the outside diameter side of the ring member  14  is disposed inside the case  11  at a given distanced from the inner side (inner wall) of the case  11 . The distance d is in the range of 0.1 mm to 0.3 mm due to the relation with a magnetic path described below. 
     A movable iron core (plunger)  19  is inserted in the cylindrically shaped coil (electromagnetic coil)  16  built in the case  11 , and the movable iron core  19  can be moved in an axial direction (up-down direction in  FIG. 1A ) by electromagnetic force generated by energization of the coil  16  (see  FIGS. 1A and 2 ). A recess  20  is provided in the axial direction on the one end side (lower side of  FIG. 1A ) of the movable iron core  19 , and a spring  21  is attached to the inside of the recess  20 . The one end side (upper side in  FIG. 1A ) of the spring  21  is fitted in the recess  20 , and the other end side (lower side in  FIG. 1A ) of the spring  21  is fitted and thus fixed to a protrusion formed in a cap member  24  of the solenoid  10 . 
     Moreover, a shaft  22  is provided on the other end side (upper side of  FIG. 1A ) of the movable iron core  19 , namely, on the side opposite to the recess  20 . When the movable iron core moves in the axial direction (up-down direction in  FIG. 1A ), the shaft  22  can move through the opening  12  of the case  11 , the hole  13   a  of the permanent magnet  13 , and the inside diameter side of the ring member  14  accordingly. 
     In addition, a metallic coil cover  17  is disposed between the coil  16  and the movable iron core  19  so as to cover the whole coil  16 . The coil cover  17  has a flange  17   a  on its one end side. The coil cover  17  is fixed to the case  11  in such a manner that the flange  17   a  is fitted in the inner wall surface of the case  11  while covering the one end side (upper side in  FIG. 1A ) of the coil  16 . Further, a clearance  18  of a given distance is formed in the axial direction of the solenoid  10  between an upper surface (upper side of  FIG. 1A ) of the flange  17   a  and a lower surface (lower side of  FIG. 1A ) of the ring member  14 . The other end side (lower side of  FIG. 1A ) of the coil  16  is fixed by caulking the cap member  24  and the case  11  via a ring member  23 . It should be noted that the clearance  18  may be filled with a nonmagnetic material such as resin. 
     The solenoid  10  according to the present embodiment is basically configured as above. Next, its operation and effects are described with reference to the drawings. When the coil  16  in the solenoid  10  shown in  FIG. 1A  is not energized, the respective parts of the solenoid  10  such as the movable iron core  19  and the shaft  22  are arranged as shown in  FIG. 3 . 
     That is, the movable iron core  19  is attracted to the permanent magnet  13  side (upper side of  FIG. 3 ) due to the elastic force of the spring  21  attached to the recess  20  and the magnetic force of the permanent magnet  13 , and then comes into contact with the ring member  14 . In this instance, if the north pole of the permanent magnet  13  is located on the ring member  14  side (lower side of  FIG. 3 ) and the south pole thereof is located on the opening  12  side (upper side of  FIG. 3 ) of the case  11 , the flow of magnetic flux generated (by the permanent magnet  13 ) in the solenoid  10  is formed as a first magnetic path  25  shown in  FIG. 3 . 
     When the coil  16  in the solenoid  10  shown in  FIG. 1A  is energized, a magnetic path generated in the solenoid  10  is formed as shown in  FIG. 4 . That is, if the coil  16  is energized as shown in  FIG. 4  (namely, if the coil  16  is excited so as to have magnetic flux in an opposite direction to the magnetic flux of the permanent magnet  13 ), the magnetic flux of the coil  16  flows in a second magnetic path  26  which is present in the middle of the first magnetic path  25  shown in  FIG. 3 . Since the second magnetic path  26  is located in the middle of the first magnetic path  25 , if the magnetic flux of the coil  16  circles in the second magnetic path  26  by the excitation of the coil  16 , the first magnetic path  25  is magnetically saturated, and thus increases in magnetoresistance. 
     As a result, the magnetic flux of the permanent magnet  13  starts to pass in a third magnetic path  27 , rather than the first magnetic path  25  which is high in magnetoresistance, via the distance d between the outside diameter side of the ring member  14  and the inner side (inner wall) of the case  11 . Accordingly, the magnetic flux passing through a place where the ring member  14  and the movable iron core  19  are attracted to each other is reduced. Consequently, the movable iron core  19  and the ring member  14  are separated from each other as shown in  FIG. 5 , and the movable iron core  19  can be moved to a lower position by slight external force (in the direction of an arrow in  FIG. 5 ). 
     It should be noted that the solenoid according to the present invention brings about the advantageous effects of the present invention in the case of a state where the direction of the magnetic flux generated by the permanent magnet is opposite to the direction of the magnetic flux generated by the energization of the coil as shown in  FIGS. 4 and 5 . Moreover, similar advantageous effects to those of the present invention are brought about even in the case where the direction of the magnetic flux generated by the permanent magnet and the direction of the magnetic flux generated by the energization of the coil are made opposite as shown in  FIG. 6  to those shown in  FIGS. 4 and 5 . 
     Contrary to this, it goes without saying that the advantageous effects of the present invention are not exerted if the permanent magnet is disposed in an opposite direction to that shown in  FIGS. 4 to 6 , or if the direction of applying current in the coil or the winding direction of a wire rod such as a copper wire wound around the coil is reversed so that only the direction of magnetic flux is opposite to that shown in  FIGS. 4 to 6 . 
     REFERENCE SIGNS LIST 
     
         
           10 : Solenoid 
           11 : Case 
           12 : Opening of case  11   
           13 : Permanent magnet 
           14 : Ring member 
           16 : Coil 
           17 : Coil cover 
           19 : Movable iron core 
         d: Distance between inner wall of case  11  and outer side of ring member  14