Patent Publication Number: US-10312010-B2

Title: Coil component

Description:
BACKGROUND 
     Field of the Invention 
     The present invention relates to coil components, and more specifically, to a coil component in which a drum core is housed in a through hole of a ring core (annular core). 
     Description of the Related Art 
     In recent years, applications for electronic components have expanded and demands on stability against environmental fluctuation have been increasing. In particular, the adopted number of electronic components is ever increasing with movement toward computerization in the field of automobiles, and an electronic component such as a coil that does not break with respect to temperature fluctuation and vibration is desired. For a coil component, one with a structure in which a drum core, around which a winding wire is wound, is housed in a through hole of a ring core (or sleeve core) is known. For such a coil component including a core in which the drum core and the ring core are combined, there is, for example, an “inductance element” described in Patent Literature 1. The Literature discloses that by adopting a constitution of applying adhesive entirely along an inner circumferential surface of the ring core between an upper end flange and the drum core and the ring core, an impact does not concentrate at one specific portion but is substantially evenly dispersed between the drum core and the ring core. 
     BACKGROUND ART LITERATURES 
     [Patent Literature 1] Japanese Unexamined Patent Publication No. 2001-338818 
     SUMMARY 
     However, as described in Patent Literature 1, although a method of applying the adhesive over the entire circumference of a gap between the ring core and the drum core can expect effects with respect to an impact, there are problems in that it is very difficult to evenly apply the adhesive over the entire circumference and in it being easily subjected to influence with respect to heat stress. For example, in the method of applying the adhesive over the entire circumference, the cores (drum core and ring core) cannot be easily positioned, and the gap between the cores becomes uneven and a large gap and a small gap are formed therebetween, where the extent/distribution of stress exerted on the cores may change depending on the size of the gap. In particular, when using a thick conductive wire, the position of the drum core may move by processing a lead wire of the conductive wire. Thus, it is not easy to obtain a coil component having both high reliability and stability of properties with the conventional method. 
     The present invention focuses on the above aspects, and aims to provide a coil component having a core structure in which a drum core and a ring core are combined, and having both high reliability and stability of properties. 
     Any discussion of problems and solutions involved in the related art has been included in this disclosure solely for the purposes of providing a context for the present invention, and should not be taken as an admission that any or all of the discussion were known at the time the invention was made. 
     The present invention is characterized by including a drum core having a pair of flange parts at both ends of a winding shaft; a conductive wire wound around the winding shaft; a ring core having a gap with respect to one of the flange parts as viewed in an axial direction of the winding shaft, and having a through hole housing the drum core therein; a terminal electrode electrically connected to the conductive wire; a first securing part provided at a part of the gap between the one flange part of the drum core and the ring core; and a second securing part provided at a part of a portion of the gap where the first securing part is not provided, and having a higher hardness than that of the first securing part. 
     According to one main aspect of the present invention, the first securing part covers an outer side of the second securing part. According to another aspect, a length of the first securing part in contact with an outer circumferential surface of the flange part of the drum core is 60% or more of a length of the outer circumferential surface of the flange part of the drum core. According to another further aspect, a hardness of the second securing part is greater than or equal to 50N/cm 2  in Shore D hardness. 
     According to yet another further aspect, at least two or more second securing parts are provided. According to another further aspect: (1) at least two of the second securing parts are arranged at positions facing each other with respect to a center of the drum core; (2) The second securing parts are arranged line-symmetrically with respect to a line passing through a center of the drum core; (3) The second securing parts are arranged at equal intervals. 
     According to another further aspect, the first securing part and the second securing part are arranged on a flange part side opposite a surface on which the terminal electrode is mounted. The above described and other objects, features, and advantages of the present invention should be apparent from the following detailed description and the accompanying drawings. 
     According to the present invention, a coil component comprises: a drum core including a pair of flange parts at both ends of a winding shaft; a conductive wire wound around the winding shaft; a ring core having a gap with respect to one of the flange parts as viewed in an axial direction of the winding shaft, and having a through hole housing the drum core therein; a terminal electrode electrically connected to the conductive wire; a first securing part provided at a part of the gap between the one flange part of the drum core and the ring core; and a second securing part provided at a part of a portion of the gap where the first securing part is not provided, and having a higher hardness than that of the first securing part. Thus, the fluctuation in the distance between the drum core and the ring core can be suppressed, and the coil component having both high reliability and stability of properties can be obtained. 
     For purposes of summarizing aspects of the invention and the advantages achieved over the related art, certain objects and advantages of the invention are described in this disclosure. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein. 
     Further aspects, features and advantages of this invention will become apparent from the detailed description which follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features of this invention will now be described with reference to the drawings of preferred embodiments which are intended to illustrate and not to limit the invention. The drawings are greatly simplified for illustrative purposes and are not necessarily to scale. 
         FIGS. 1A to 1E  are views showing a coil component of an example of the present invention, where  FIG. 1A  is an outer appearance perspective view seen from an opposite side of a mounting surface,  FIGS. 1B to 1D  are views schematically showing a position relationship of a first securing part and a second securing part, and  FIG. 1E  is a cross-sectional view taken along line  1 E- 1 E in  FIG. 1C . 
         FIGS. 2A-1 to 2C  are views showing the example, where  FIG. 2A-1  is a plan view of a drum core,  FIG. 2A-2  is a side view of the drum core,  FIG. 2B-1  is a plan view of a ring core,  FIG. 2B-2  is a side view of the ring core, and  FIG. 2C  is a perspective view showing a state in which a terminal electrode is incorporated in the ring core. 
         FIGS. 3A to 3F  are views showing a manufacturing procedure of the coil component of the example. 
         FIGS. 4A to 4F  are views showing another example of the present invention. 
         FIGS. 5A-1 to 5B-3  are views showing another example of the present invention. 
     
    
    
     DESCRIPTION OF THE SYMBOLS 
     
         
         
           
               10 ,  10 ′,  10 A to  10 D coil component 
               20  drum core 
               22  winding shaft 
               24 ,  26  flange part 
               24 A front surface 
               26 A front surface 
               30  ring core 
               30 A upper surface 
               30 B bottom surface 
               30 C outer circumferential surface 
               30 D inner circumferential surface 
               32  through hole 
               34 A,  34 B parallel surface 
               36 ,  36 A,  36 B,  38 A,  38 B step difference (or groove) 
               40  winding wire 
               42  conductive wire 
               44  coating 
               46 A,  46 B end 
               50 A,  50 B terminal electrode 
               52  side face 
               52 A upper surface part 
               52 B bottom surface part 
               54 A,  54 B nail part 
               56  extended part 
               58  connecting part 
               60 A to  60 D second securing part 
               62 ,  62 A to  62 C first securing part 
               64  chamfered part 
               66  tapered part 
               70 A,  70 B ring core 
               72  upper surface 
             C center of drum core 
             D 1  outer diameter of drum core 
             D 2  inner diameter of ring core 
             G gap 
             L line passing through center of drum core 
           
         
       
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     The best mode for carrying out the present invention is described in detail below with reference to examples. 
     EXAMPLES 
     First, an example of the present invention is described with reference to  FIGS. 1A to 3F . The present invention relates to a coil component having a core structure in which a drum core, around which a conductive wire is wound, is housed in a through hole of a ring core.  FIG. 1A  is an outer perspective view seen from an opposite side of a mounting surface, and  FIGS. 1B to 1D  are views schematically showing a position relationship of a first securing part and a second securing part in the present example.  FIG. 2A-1  is a plan view of a drum core of the present example,  FIG. 2A-2  is a side view of the drum core,  FIG. 2B-1  is a plan view of a ring core of the present example,  FIG. 2B-2  is a side view of the ring core seen from a direction of arrow F 2 , and  FIG. 2C  is a perspective view showing a state in which a terminal electrode is incorporated in the ring core.  FIGS. 3A to 3F  are views showing a manufacturing procedure of the coil component of the example. 
     As shown in  FIGS. 1A to 3F , a coil component  10  of the present example has a structure in which a drum core  20  is housed in a through hole  32  of a ring core  30  (referred to also as an annular core or a sheath core), and two types of securing parts are provided between the drum core and the through hole  32 , that is, in a gap G between an outer circumference of a flange part  24  of the drum core  20  and an inner circumference of the through hole  32  of the ring core  20 . Also, terminal electrodes  50 A,  50 B connecting to ends of a winding wire  40  wound around the drum core  20  are provided on an outer circumferential surface  30 C of the ring core  30 . As schematically shown in  FIG. 1B , the second securing parts  60 A,  60 B are provided at two areas so as to face each other with a center C of the flange part  24  of the drum core  20  in between. And, as shown in  FIG. 1C , the first securing parts  62 A,  62 B are provided in an arcuate form so as to cover the portion where the second securing parts  60 A,  60 B are provided ( FIG. 1E  is a cross sectional view taken along line  1 E- 1 E in  FIG. 1C ). The first securing parts  62 A,  62 B merely need to cover the outer side (the upper side opposite to the mounting side) of the second securing parts  60 A,  60 B, and for example, an arrangement such as the coil component  10  shown in  FIG. 1D  may be adopted. In the present invention, the second securing part having a higher hardness than the first securing part is used. 
     Next, each portion constituting the coil component  10  is described in detail. As shown in  FIGS. 2A-1 and 2A-2 , the drum core  20  constituting one part of the core includes a pair of flange parts  24 ,  26  at both ends of a winding shaft  22  around which the winding wire  40  is wound. In the present example, the winding shaft  22  and the flange parts  24 ,  26  have a substantially circular cross-sectional shape in a direction orthogonal to an axial direction of the winding shaft  22 . The winding wire  40  has a conductive wire  42  covered with a coating  44  having an insulation property (see  FIG. 3C ). 
     As shown in  FIGS. 2B-1 and 2B-2 , the ring core  30  is a hollow body including the through hole  32 , where a cross-section of the through hole  32  perpendicular to its axis is substantially circular, and a cross-section of an outer shape of the ring core  30  perpendicular to its axis has a shape in which a part of a circle is removed. In the illustrated example, parallel planes  34 A,  34 B extending along the axial direction are provided at positions opposite to each other with respect to the center in between on the substantially cylindrical outer circumferential surface  30 C. And, a dimension of the inner circumference of the ring core  30  is greater than a dimension of the outer circumference of the drum core  20 , where the drum core  20  is housed in the through hole  32  with the gap G ( FIG. 1B ). 
     Also, on an upper surface  30 A side of the ring core  30 , step differences (or grooves)  36 A,  36 B are provided so that an upper surface part  52 A of the terminal electrodes  50 A,  50 B does not project out from the upper surface  30 A, and step differences (or grooves)  38 A,  38 B for pulling out ends  46 A,  46 B of the winding wire  40  are formed. In the present example, as shown in  FIG. 2C , the step differences  36 A,  36 B for housing the upper surface part  52 A of the terminal electrodes  50 A,  50 B are formed at the upper surface part continuing to the plane parts  34 A,  34 B, and the deep step differences  38 A,  38 B for pulling out the ends  46 A,  46 B of the winding wire  40  ( FIGS. 3C, 3D, 3E-1 ) are formed on the upper surface part so as to be proximate to the step differences  36 A,  36 B, respectively. Also, the thickness in the height direction can be increased as the adhesive enters the inner side of such step differences. 
     Next, the terminal electrodes  50 A,  50 B are described. The terminal electrodes  50 A,  50 B basically have a same configuration, and thus one terminal electrode  50 A is described as an example. In the present example, the terminal electrode  50 A is attached so as to lie along the outer circumferential surface  30 C from the plane parts  34 A,  34 B of the ring core  30 . As shown in  FIG. 2C , the terminal electrode  50 A includes a side face  52 , an extended part  56  extended toward the side from the side face  52 , and an upper surface part  52 A and a bottom surface part  52 B continuously formed with respect to the side face  52 . Also, a pair of nail parts  54 A,  54 B divided into two from the upper surface part  52 A is continuously formed on the side face  52  and a connecting part  58  for connecting with the lead part of the winding wire  40  is continuously formed on the extended part  56 . 
     Such terminal electrode  50 A is, for example, formed to a shape that can be attached to the ring core  30  by bending and caulking one metal plate including the side face  52 , the upper surface part  52 A, the nail parts  54 A,  54 B, the extended part  56 , the connecting part  58 , and the bottom surface part  52 B at a predetermined position. In the illustrated example, the side face  52  lies along the plane part  34 A of the ring core side surface, the upper surface part  52 A lies along the step difference  36 A of the ring core  30 , the nail parts  54 A and  54 B lie along an inner circumferential surface  30 D of the through hole  32  of the ring core  30 , the bottom surface part  52 B lies along a ring core bottom surface  30 B, and the extended part  56  lies along the outer circumferential surface  30 C of the ring core. It should be noted that in  FIG. 2C , the connecting part  58  is shown in an already bent state, but actually, the ends  46 A,  46 B of the winding wire  40  are pulled out onto the connecting part  58  and then bent. The other terminal electrode  50 B also has the same structure, where the terminal electrode  50 B is attached to the plane part  34 B of the side surface of the ring core  30  by bending, caulking, and the like. It should be noted that the bottom surface part  52 B is a surface on a mounting side. 
     Next, one example of a manufacturing method of the coil component  10  of the present example is described with reference to  FIGS. 3A to 3F . First, as shown in  FIG. 3A , the drum core  20  and the ring core  30  described above are prepared, and then the terminal electrodes  50 A,  50 B are assembled to the ring core  30  in advance by bending, caulking, and the like, as shown in  FIG. 3B . At this point, the connecting part  58  of the terminal electrodes  50 A,  50 B is not folded back. Next, as shown in  FIG. 3C , the winding wire  40  for example, a round wire with a circular cross-section including a coating  44  is wound around the winding shaft  22  of the drum core  20  so as to overlap the conductive wires along the winding shaft  22  from one side. The winding wire  40  is wound around the circumference of the winding shaft  22 , and both ends  46 A,  46 B are pulled out from the outer circumference on the flange part  24  side of the drum core  20 . The pulled-out ends  46 A,  46 B are shaped to match the connecting positions with the terminal electrodes  50 A,  50 B. 
     Here, both ends  46 A,  46 B have the heights aligned to lie along the inner side of one flange part  24  of the drum core  20  ( FIG. 3C ), and are shaped so that the respective ends  46 A,  46 B are directed in opposite directions toward the outer side in the circumferential direction from the drum core  30 . In other words, such ends  46 A,  46 B are on a substantially straight line when one end (e.g., end  46 B) is viewed from the other end (e.g., end  46 A). If the ends  46 A,  46 B are on a straight line, the stripping of the coating in the next and subsequent steps can be accurately carried out, and the joining stability can be enhanced. 
     Then, as shown in  FIG. 3D , the coating  44  at the position connecting to the terminal electrodes  50 A,  50 B is stripped from the ends  46 A,  46 B pulled out from the winding wire  40 . The stripping of the coating is, for example, carried out by irradiating an outer circumferential surface of the winding wire ends  46 A,  46 B with a green laser from one direction, and then turning the wound drum core  20  around by 180 degrees and again irradiating the same with laser. Thus, the green laser is irradiated from two directions differing by an angle of 180 degrees, so that the coating  44  over the entire circumference of the conductive wire  42  of the winding wire ends  46 A,  46 B can be removed. 
     The drum core  20 , around which the winding wire  40  is wound and stripped of its coating  44  from the ends  46 A,  46 B in the above manner, is housed in the through hole  32  of the ring core  30 , and positioned so that the respective centers coincide. In the positioning, the outer circumferential surfaces of the drum core  20  and the ring core  30  are image-recognized, and the position of the drum core  20  is adjusted. In this state, a UV adhesive is applied to two points between the outer circumferential surface of the flange part  24  of the drum core  20  and the inner circumferential surface of the ring core  30  using a dispenser from the upper surface side of the drum core  20 , that is, the side opposite the mounting surface (upper surface  24 A side of the flange part  24  in the present example), and cured with a UV lamp. In this case, the UV adhesive may be applied to one part of the terminal electrodes  50 A,  50 B. In the present example, the UV adhesive is applied so as to include the upper surface part  52 A side of the terminal electrodes  50 A,  50 B. 
     The applied and cured UV adhesive becomes the second securing parts  60 A,  60 B. The second securing parts  60 A,  60 B are fixed at the position where the drum core  20  and the ring core  30  are positioned. The fluctuation in the position between subsequent steps and during a subsequently-conducted environment test, and the like thus can be suppressed. Also, in the illustrated example (see  FIG. 3E-1 ), the securing parts are arranged at plural areas (two areas), and located at positions opposite to each other with respect to the center of the drum core  20 , so that the stress applied on the ring core  30  also becomes even. 
     Next, as shown in  FIG. 3E-1 , the terminal electrodes  50 A,  50 B and the conductive wire  42  of the winding wire ends  46 A,  46 B are joined.  FIG. 3E-2  is a view in which  FIG. 3E-1  is turned upside down. As shown in  FIG. 3E-2 , the lower surface (front surface  26 A of the flange part  26  in the present example) side of the drum core  20  is held by the bottom surface part  52 B of the terminal electrodes  50 A,  50 B. The ends  46 A,  46 B of the winding wire  40  are connected to the terminal electrodes  50 A,  50 B and cut at appropriate position. 
     Lastly, as shown in  FIG. 3F , a thermosetting adhesive is applied using the dispenser so as to cover the upper surface (outer side) of the second securing parts  60 A,  60 B in the gap G between the drum core  20  and the ring core  30 , and cured at approximately 150° C., for example. The cured thermosetting adhesive becomes the first securing parts  62 A,  62 B (which directly contact the upper side of the second securing parts  60 A,  60 B as shown in a cross-sectional view of  FIG. 1E ). Thus, as the first securing parts  62 A,  62 B cover the second securing parts  60 A,  60 B, the thickness in the height direction of the first securing parts  62 A,  62 B can be ensured at a portion that does not overlap the second securing parts  60 A,  60 B, and that makes contact with the outer circumferential surface (of the flange part  24 ) of the drum core  20 . Also, the portion where the thickness is ensured can be made long, and defects such as stripping can be suppressed by setting the length of the portion making contact with the first securing parts  62 A,  62 B and the outer circumferential surface of the drum core  20  long. Therefore, the length of the portion making contact with the second securing parts  60 A,  60 B and the outer circumferential surface of the drum core  20  can be included, where the proportion of the length of the portion making contact with the first securing part  62  (wherein the first securing parts  62 A,  62 B, etc. are hereinafter referred to collectively as the first securing part  62 ) and the outer circumferential surface of the drum core  20  is preferably greater than or equal to 60% with respect to the length of the outer circumferential surface of the drum core  20 . It should be noted that with respect to the overlapping portion of the first securing parts  62 A,  62 B and the second securing parts  60 A,  60 B, the length of the portion making contact with the second securing parts  60 A,  60 B and the outer circumferential surface of the drum core  20  is included in the length of the portion making contact with the first securing part  62  and the outer circumferential surface of the drum core  20 . 
     Also, in the present example, as shown in  FIG. 4C , the first securing part  62  may be formed over the entire outer circumferential surface of the drum core  20 , but is actually better to be formed by smaller than or equal to 90% of the entire outer circumferential surface of the drum core  20  since a portion where the first securing part does not exist needs to be provided in order to allow the stress to be effectively released. Furthermore, by providing a step difference on the upper surface  24 A and the outer circumferential surface of the drum core  20 , or on the upper surface  30 A and the inner circumferential surface of the ring core  30 , the adhesive can be thickened at the relevant portion, so that the relevant portion can act as a reservoir for the adhesive thus preventing wet-spreading, and leading to satisfactory stability of the shape of the adhesive and facilitation of image recognition. Such modes will be described later, but in the present example, a slightly chamfered part  64  is provided at the upper surface of the drum core  20 , that is, at the outer edge portion of the front surface  24 A of the flange part  24 , and the thickness of the adhesive can be secured using such chamfered part  64 , as shown in  FIGS. 2A-2 and 4F . 
     In the present example, two types of adhesives are used, where the adhesive with higher hardness after curing is used for the adhesive to become the second securing parts  60 A,  60 B than for the adhesive to become the first securing parts  62 A,  62 B, and the adhesive with lower linear coefficient of expansion after curing is used for the adhesive (thermosetting adhesive) to become the first securing parts  62 A,  62 B than for the adhesive to become the second securing parts  60 A,  60 B. If the second securing parts  60 A,  60 B have a Shore D hardness of greater than or equal to 50 N/cm 2 , the position of the core will not move. Also, the first securing parts  62 A,  62 B merely need to have a linear coefficient of expansion of lower than or equal to 2×10 −5 /K, and low-UV adhesive, thermosetting adhesive, and the like can be used. In addition, the conditions other than the linear coefficient of expansion include a glass transition point of greater than or equal to 150° C., and a viscosity before curing of greater than or equal to 80000 mPa·s. The thickness (depth) of the adhesive can be easily obtained even in one application, and the adhesive can be subjected to applications under high temperature of 150° C. when the above conditions are met. 
     &lt;Test Samples&gt; 
     Next, test samples of the present example are described. Coil components of a comparative example and test samples 1 to 6 were produced under the conditions shown in table 1 below, and variation (%) of inductance as well as defects after a heat cycle test were checked. The coil component  10  was a wound wire type inductor having a dimension of 10.5×10×5 mm, where Ni—Zn ferrite was used for the drum core  20  and the ring core  30 , which are magnetic bodies. In this gap design between the drum core  20  and the ring core  30 , the distance of the outer circumferential surface of the flange part  24  and the inner circumferential surface  30 D of the ring core  30  was doubled, e.g., in a range of 0.22 to 0.3 mm. Also, a conductive wire of φ 0.43 mm with a polyamide imide coating (conductive wire itself was Cu) was used for the winding wire  40 , and the number of windings was 15.5. Further, the UV adhesive having a hardness of 40 to 65 Shore D was used as an adhesive that can be cured in a short period of time with respect to the second securing parts  60 A,  60 B, and the epoxy adhesive having a hardness of 30 or 40 Shore D was used as a thermosetting adhesive used for the first securing parts  62 A,  62 B. Furthermore, a Cu plate having a thickness of 0.15 mm treated with Ni/Sn plating was used for the terminal electrodes  50 A,  50 B. 
     Specific test samples and comparative examples are described below. In this disclosure including the following description, multiple first securing parts are referred to collectively as the “first securing part”, and multiple second securing parts are referred to collectively as the “second securing part”, depending on the context. 
     In test sample 1, the dimension of the inner circumferential surface  30 D of the ring core  30  was set at 10 mm, for example (the inner diameter can vary in combination with the outer diameter of the flange part and may be about 6 mm, about 10 mm, or the like, for example), the designed gap was set to 0.25 mm, and the design value of the inductance was 15 μH. With respect to the first securing parts  62 A,  62 B, the number of arrangements was two, the proportion was 40%, and the hardness was 30, and with respect to the second securing part  60  (wherein the second securing parts  60 A,  60 B, etc. are hereinafter referred to collectively as the second securing part  60 ), the number of arrangements was one, the proportion was 8%, and the hardness was 40. Also, the comparative example is similar to test sample 1 except that the designed gap was 0.3 mm, the designed inductance value was 14.7 μH, and the second securing part  60  was not provided. 
     In test sample 2, according to a similar method, the designed gap was 0.25 mm, and the designed value of the inductance was 15 μH. Test sample 2 was produced like test sample 1 except that the proportion was 60% for the first securing parts  62 A,  62 B. Test sample 3 was produced like test sample 2 except that the proportion was 80% for the first securing parts  62 A,  62 B, and the hardness was 50 for the second securing parts  60 A,  60 B. 
     In test sample 4, according to a similar method, the designed gap was 0.22 mm, and the designed value of the inductance was 15.4 μH. Test sample 4 was produced like test sample 3 except that the proportion was 90% for the first securing parts  62 A,  62 B, and the number of arrangements was two for the second securing parts  60 A,  60 B. Test sample 5 was produced like test sample 4 except that the proportion was 100% for the first securing part  62  and the number of arrangements was four, and the proportion was 16% for of the second securing parts  60 A,  60 B,  60 C,  60 D. Test sample 6 was produced like test sample 4 except that the hardness was 65 for the second securing parts  60 A,  60 B. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                   
                 Number of 
                 Proportion 
                   
                   
                   
               
               
                   
                 Designed 
                 securing 
                 of SPs 
                 Hardness 
                   
                 Defect after 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 Designed value 
                 inductance 
                 parts 
                 2nd 
                 1st 
                 shore D 
                 Inductance 
                 test of 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 of size of gap 
                 value 
                 2nd 
                 1st 
                 SP(s) 
                 SP(s) 
                 2nd 
                 1st 
                 variation 
                 1st SP(s) 
               
               
                   
                 [mm] 
                 [μH] 
                 SP(s) 
                 SP(s) 
                 [%] 
                 [%] 
                 SP(s) 
                 SP(s) 
                 [%] 
                 in heat cycle 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Comp. 
                 0.3 
                 14.7 
                 — 
                 1 
                 — 
                 100 
                 — 
                 30 
                 22 
                 Interfacial 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 peeling 
               
               
                 TS 1 
                 0.25 
                 15 
                 1 
                 2 
                 8 
                 40 
                 40 
                 30 
                 16 
                 Microcrack 
               
               
                 TS 2 
                 0.25 
                 15 
                 1 
                 2 
                 8 
                 60 
                 40 
                 30 
                 15 
                 None 
               
               
                 TS 3 
                 0.25 
                 15 
                 1 
                 2 
                 8 
                 80 
                 50 
                 30 
                 11 
                 None 
               
               
                 TS 4 
                 0.22 
                 15.4 
                 2 
                 2 
                 8 
                 90 
                 50 
                 40 
                 9 
                 None 
               
               
                 TS 5 
                 0.22 
                 15.4 
                 4 
                 1 
                 16  
                 100 
                 50 
                 40 
                 9 
                 None 
               
               
                 TS 6 
                 0.22 
                 15.4 
                 2 
                 2 
                 8 
                 90 
                 65 
                 40 
                 9 
                 None 
               
               
                   
               
               
                 SP: securing part 
               
               
                 Comp.: comparative example 
               
               
                 TS: test sample 
               
            
           
         
       
     
     In Table 1, the size of the gap G was calculated as (ring core inner diameter D 2 −drum core flange part outer diameter D 1 )/2. Also, the proportion of the lengths of the first securing part and the second securing part making contact with the outer circumferential surface of the flange part  24  of the drum core  20  was indicated with the proportion of the lengths with respect to the outer circumference of the flange part  24  of the drum core  20  seen in a direction of the winding shaft  22  from the flange part  24 . In the measurement, an angle of a range in which each of the first and second securing parts exist at the center of the flange part  24  of the drum core  20  was obtained at a magnification of 10 to 20 times using a factory microscope, and the proportion with respect to the entire outer circumference of the flange part  24  was obtained. For the first securing part  62 , the angle of the range in which each securing part can be viewed when seen from the upper-surface side corresponding to the direction of the winding shaft  22  from the flange part  24  was obtained at the magnification described above. Moreover, for the second securing parts  60 A,  60 B, polishing was carried out in a range of 0.05 mm in the vertical direction with respect to the upper surface of the core having a lower height of the flange part  24  of the drum core  20  or the upper surface  30 A of the ring core  30 , and a range in which the second securing part can be viewed was obtained similarly from the upper-surface side or the polished surface. In addition, a Shore hardness test equipment D-type was used for the hardness, and the first and second securing parts were compared. With respect to a specific numerical value of hardness, each hardness was obtained after preparing a test sample having an outer dimension of φ 10 mm and a thickness of 2 mm with an adhesive for forming the second securing part, and performing a predetermined curing. 
     The variation of the inductance was calculated by a MAX value. The comparative example is an example in which an equivalent of the second securing part of the present example does not exist. Supplementing the inductance evaluation, it should be noted that the variation of inductance is caused by the variation in the gap. In such a case, an entirely even distance is preferably ensured between the outer circumferential surface of the drum core  20  and the inner circumferential surface of the ring core  30 , where if the distance is not even, an area of close distance exists causing the inductance to become high. This becomes the variation caused by assembly precision. As the variation of inductance shifts toward the positive side of the designed value, the evaluation performed here obtains the proportion of the difference (size of shift) of the designed value and the maximum value. LCR meter 4285A frequency 100 kHz was used for the measuring instrument. Also, the heat cycle test evaluated the dimensional change before and after the test in 1000 cycles and 3000 cycles at a temperature of −55 to 150° C., and confirmed the presence/absence of change in either cycle. For such check, an area including the first securing part  62  was observed at a magnification of 50 times using a factory microscopic for an appearance change. 
     The following were confirmed from the results of the comparative example and the test samples shown in Table 1. 
     In the comparative example, variation in inductance was large. This is because the gap between the two cores has variation at some places when seen over the entire circumference. Also, in the heat cycle test, interfacial stripping was recognized between the drum core  20  or the ring core  30  and the first securing part  62 . The thickness of the adhesive thus becomes thin in an area where the gap is large, which leads to defects due to the stress of thermal contraction/expansion. 
     In test sample 1, variation in inductance decreased even if the designed gap corresponding to the distance between the two cores was reduced. As the second securing parts were provided using the UV adhesive, it was found that the gap precision was satisfactory and that the variation of inductance could be reduced even if the gap was reduced. However, traces of crack were slightly found in the portion at the end in the length direction of the first securing parts  62 A,  62 B, which were determined to be microcracks. Changes were not found, however, between 1000 cycles and 3000 cycles, and no defects caused by the microcracks were also found. This is because the stress applied on the portion at the end of the first securing part  62  with the second securing part  60 A as the trigger when the length in the circumferential direction of the portion where only the second securing part  60 A exists was not sufficiently ensured. 
     In test sample 2, variation in the inductance improved, although slightly. This is because the positional stability was improved with increasing the length in the circumferential direction of the first securing part  62 . Also, in test samples 2 to 6, the defects described above were all resolved. This is because the thickness in the height direction of the first securing part  62  was sufficiently ensured by increasing the length in the circumferential direction of the first securing part  62 . 
     In test sample 3, variation in inductance was further reduced. This is because the positional precision further improved by adopting the second securing part  60 A having a higher hardness than that of test sample 2. 
     In test samples 4 to 6, the designed gap was further reduced and variation in inductance was also kept low. This is because gap fluctuation was further reduced by increasing the proportion of the first securing part relative to the second securing part. 
     Test sample 5 was an example in which the first securing part was provided across the entire circumference, where variation was small and no defects were found in the tested sample size, but it should be taken in consideration that stress applies on a ridge portion of the core if formed across the entire circumference in a small component (smaller than or equal to 7 mm) where rounding of the ridge portion of the ring core  20  is difficult, for example. 
     According to a comparison between test sample 6 and test sample 4, it should be noted that an upper limit of the hardness of the second securing part does not need to be particularly provided, and no large change is found as long as the Shore D hardness is greater than or equal to 50; higher hardness does not need to be forcibly used and a range of up to about 100 is sufficient. 
     The examples according to the present invention have the following effects. 
     (1) The second securing parts  60 A,  60 B and the first securing part  62  are provided at one part of the gap G of the drum core  20  and the ring core  30 , and the second securing parts  60 A,  60 B having a higher hardness than the first securing part  62  are adopted, so that fluctuation in the distance between the core members can be suppressed. 
     (2) Defects can be eliminated by setting the proportion of the first securing part  62  with respect to the length of the outer circumference of the drum core  20  to greater than or equal to 60%. 
     (3) Fluctuation (fluctuation in position between the cores) can be reduced by setting the Shore D hardness of the second securing parts  60 A,  60 B to greater than or equal to 50 N/cm 2 . 
     (4) The second securing part is provided in plural and are arranged opposite to each other with respect to the center C of the drum core  20 , so that the gap can be further reduced and the stress applied on the ring core  30  can be evened out, thus reducing variation. 
     (5) The second securing parts  60 A,  60 B and the first securing parts  62 A,  62 B are provided on one flange part  24  side of the drum core  20  opposite the surface (bottom surface part  52 B) on which the terminal electrodes  50 A,  50 B are mounted, and thus the mounting side (bottom surface part  52 B) of the terminal electrodes  50 A,  50 B will not become contaminated. 
     (6) The first securing parts  62 A,  62 B cover the upper surface (outer side) of the second securing parts  60 A,  60 B, and thus the second securing parts  60 A,  60 B will not detach. 
     It should be noted that the present invention is not limited to the examples described in this disclosure, and various changes can be made within a scope not deviating from the gist of the invention. This includes, for example, the following. 
     (1) The shapes and dimensions shown in the above-discussed examples are examples, and may be appropriately changed as needed. For example, in the above-discussed examples, the outer cross-sectional shape of the ring core  30  is an oval shape in which one part of the circle is cut off, but it may be an octagon, a square, and the like, or may be a shape in which a corner is rounded to an extent that rotation does not occur. 
     (2) The pull-out configuration of the winding wire from the ring core  30  shown in the examples is also an example, and design changes can be appropriately made within a scope that similar effects are obtained. 
     (3) The shape of the terminal electrodes  50 A,  50 B shown in the examples and the joining mode with respect to the ends  46 A,  46 B of the winding wire  40  are also one example, and design changes can be appropriately made within a scope that similar effects are obtained. 
     (4) In the above-discussed examples, two second securing parts  60 A,  60 B are provided, but this is also an example, and the number and arrangement can be appropriately changed as long as two or more second securing parts are provided. For example, as in a coil component  10 A shown in  FIG. 4A , three second securing parts  60 A to  60 C may be uniformly arranged in the gap G between the drum core  20  and the ring core  30 . The stress applied on the ring core  30  can be evenly dispersed by the uniform arrangement. Also, this is the same for a coil component  10 C including four second securing parts  60 A to  60 D shown in  FIG. 4C . Moreover, the intervals of a plurality of second securing parts may not be uniform. For example, in a coil component  10 B shown in  FIG. 4B , three second securing parts  60 A to  60 C are arranged symmetrically with respect to a line L passing through the center of the drum core  20 , but may not be arranged symmetrically and three second securing parts may be arranged completely non-uniformly/asymmetrically. In a coil component  10 D shown in  FIG. 4D , four second securing parts  60 A to  60 D are arranged line-symmetrically with respect to the line L. In addition, the second securing parts may be arranged in odd numbers such as three and five, and do not need to be in equal interval arrangement, symmetrical arrangement, or point-symmetric arrangement on a circumference of the gap G, and the arrangement may be determined in view of the shape and the like of the terminal electrode. 
     (5) In the example, the UV adhesive to become the second securing parts  60 A,  60 B after being cured is applied to include three members being the outer circumference of the drum core, the inner circumference of the ring core, and the terminal electrode, but this is an example, and the second securing part does not necessarily need to be provided to include the terminal electrode. 
     (6) In the examples, the first securing parts  62 A,  62 B are provided to completely cover the upper surface of the second securing parts  60 A,  60 B, but this is an example, and they do not necessarily need to be arranged to cover the entire second securing part and may partially cover the second securing part. The second securing parts  60 A,  60 B merely need to at least make contact with either one of the first securing parts  62 A,  62 B. In either mode, the first and second securing parts will not detach from the component. 
     (7) Furthermore, in the examples described above, as shown in  FIGS. 2A-2 and 4F , a slightly chamfered part  64  is provided at the upper surface of the drum core  20 , that is, at the edge of the front surface  24 A of the flange part  24 , and the thickness of the adhesive is secured using such chamfered part, but this is an example, and design changes can be appropriately made within a scope in which similar effects can be obtained. For example, as shown with a dotted line in  FIG. 4F , a tapered part  66 , and the like may be provided on the ring core  30  side, and/or the thickness of the adhesive may be ensured using only the slight difference in height of the drum core  20  and the ring core  30 , as shown in  FIG. 4E  (in both  FIGS. 4E and 4F , the second securing part such as  60 A is not shown as they are cross sections taken along the line L shown in  FIG. 4D , for example). 
     (8) Alternatively, the range of the step differences  36 A,  36 B for caulking the terminal electrode may be narrowed as in a ring core  70 A in the examples shown in  FIGS. 5A-1 to 5A-3 , or the range of the step differences  36 A,  36 B for caulking the terminal electrode may be widened as in the examples shown in  FIGS. 5B-1 to 5B-3 . In either case, the adhesive may be applied so that both ends of the adhesive are located on the step differences  36 A,  36 B to form the first securing parts  62 A,  62 B, as shown in  FIGS. 5A-3 and 5B-3  to ensure the thickness of the adhesive and stabilize the position of both ends of the adhesive. In particular, in view of the influence of electrical properties due to the step differences  36 A,  36 B, the step differences  36 A,  36 B may be formed to a narrow range, and the first securing part may be provided over the step difference  36 A, the portion without step differences, and the step difference  36 B. 
     INDUSTRIAL FIELD OF APPLICATION 
     According to the present invention, a drum core including a pair of flange parts at both ends of a winding shaft, a conductive wire wound around the winding shaft, a ring core having a gap with respect to a flange part when seen in a winding shaft direction from one flange part, the ring core including the drum core in a through hole, a terminal electrode electrically connected to the conductive wire, a first securing part provided at one part of the gap between one flange part of the drum core and the ring core, and a second securing part provided at a part of a portion of the gap where the first securing part is not provided, and having a higher hardness than that of the first securing part are provided. Thus, fluctuation in distance between the drum core and the ring core can be reduced, allowing application to a coil component having both high reliability and stability of properties. In particular, it is suitable for application of a coil component for fields of automobiles and industrial machines as it excels in temperature resistance and impact resistance. 
     In the present disclosure where conditions and/or structures are not specified, a skilled artisan in the art can readily provide such conditions and/or structures, in view of the present disclosure, as a matter of routine experimentation. Also, in the present disclosure including the examples described above, any ranges applied in some embodiments may include or exclude the lower and/or upper endpoints, and any values of variables indicated may refer to precise values or approximate values and include equivalents, and may refer to average, median, representative, majority, etc. in some embodiments. Further, in this disclosure, “a” may refer to a species or a genus including multiple species, and “the invention” or “the present invention” may refer to at least one of the embodiments or aspects explicitly, necessarily, or inherently disclosed herein. The terms “constituted by” and “having” refer independently to “typically or broadly comprising”, “comprising”, “consisting essentially of”, or “consisting of” in some embodiments. In this disclosure, any defined meanings do not necessarily exclude ordinary and customary meanings in some embodiments. 
     The present application claims priority to Japanese Patent Application No. 2016-073417, filed Mar. 31, 2016, the disclosure of which is incorporated herein by reference in its entirety including any and all particular combinations of the features disclosed therein. 
     It will be understood by those of skill in the art that numerous and various modifications can be made without departing from the spirit of the present invention. Therefore, it should be clearly understood that the forms of the present invention are illustrative only and are not intended to limit the scope of the present invention.