ELECTROMAGNETIC DEVICE

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The invention relates to an electromagnetic device such as a transformer, a choke coil, or a reactor provided with a core and a coil. 2. Description of the Related Art

[0002] One example of a known electromagnetic device such as a transformer, a choke coil, or a reactor provided with a core and a coil is a reactor that is used in a motor drive circuit of an electric vehicle. This reactor transforms the voltage of electricity using inductive reactance and is formed with a core and a coil. The reactor is used incorporated into a switching circuit. By repeatedly switching the reactor on and off, the reactor generates energy stored in the coil when it is on as back electromotive force (i.e., back EMF) when it is off, thus enabling high voltage to be obtained.

[0003] In order to suppress the generation of heat by the reactor which is supplied with large amounts of current, the reactor must be cooled. One example of technology for cooling a reactor is described in Japanese Patent Application Publication No. 2005-286020 (JP-A-2005-286020), which describes a cooling structure in which a portion of the housing of the reactor is integrally formed with a heat sink. That is, in a structure for mounting a reactor to a case that houses a drive control apparatus for an electric motor used to drive a vehicle, an opening that provides communication between coolant passages is formed in the heat sink of the case. A seal that surrounds this opening is arranged between the heat sink and the reactor. The housing of the reactor is mounted to the heat sink on the outside of the opening in a state in which the opening is closed off by the bottom surface of the reactor and the bottom of the reactor is contacting coolant. Having the bottom of the reactor contact coolant in this way cools the reactor.

[0004] However, with the cooling structure described in Jr-A-2005-28602G, the core and the coil of the reactor are mounted to the heat sink via the housing so cooling

is performed indirectly and therefore may be insufficient. Also, when the reactor is used with a step-up circuit in a hybrid system, the reactor must have a flat DC superimposed characteristic. To meet this requirement, the temperature of the coil of the reactor must be adjusted so that it does not exceed the allowed temperature. Typically, the coil temperature is inhibited from increasing by controlling the coil current by monitoring the coil temperature. However, monitoring the coil temperature requires a thermostat and control, circuit for temperature monitoring, which tends to make the structure more complex.

[0005] Also, with the cooling structure described in JP-A-2005-286020, the area in which the coil is being cooled is relatively small or does not exist.

[0006] On the other hand, Japanese Patent Application Publication No. 2002-252122 (JP-A-2002-252122) proposes a coil element, which the core and the coil directly contacts a cooling device. However, with the structure described in JP-A-2002-252122, a column is needed to connect the coil to the cooling device, which complicates the structure of the cooling device.

SUMMARY OF THE INVENTION

[0007] This invention thus provides an electromagnetic device capable of improving cooling capability according to a simple structure.

[0008] A first aspect of the invention relates to an electromagnetic device that includes a column-shaped central core, a coil provided around the central core, a U-shaped core which has an open side and covers all but a portion of the outer peripheral , surface of the coil, a top core that covers each one end of the central core and the coil in the longitudinal direction of the central core, and a bottom core that covers the each other end of the central core and the coil in the longitudinal direction of the central core. A portion of the outer peripheral surface of the coil that is positioned on the open side of the U-shaped core, an open end portion of the U-shaped core, one side portion of the top core, and one side portion of the bottom core are each adjoins a cooling member.

[0009] According to this aspect, a portion of the outer peripheral surface of the coil that is positioned on the open side of the U-shaped core, an open end portion of the

U-shaped core, one side portion of the top core, and one side portion of the bottom core are each adjoins a cooling member, so not only are the U-shaped core, the top core, and the bottom core directly cooled from the portions near the cooling member, but the coil is also directly cooled from the portion near the cooling member. Also, the structure of the cooling member can be simplified. Also, the top core and the bottom core adjoin the cooling member, so the coil and the U-shaped core can also be indirectly cooled by the cooling member. That is, the electromagnetic device can be better cooled by a simple structure.

[0010] In the structure described above, the coil may be provided around the central core formed in a polygonal column shape, and the portion of the outer peripheral surface of the coil is the largest surface of the central core formed in a polygonal column shape. [0011] In the structure described above, the central core may be formed in a rectangular column shape, and a surface with a longer side of the rectangle is the portion of the outer peripheral surface of the coil.

[0012] In the structure described above, the portion of the outer peripheral surface of the coil that is positioned on the open side of the U-shaped core, the open end portion of the U-shaped core, the one side portion of the top core, and the one side portion of the bottom core may all adjoin a single plane of the cooling member.

[0013] In the foregoing structure, the single plane of the cooling member may be a flat surface.

[0014] According to this structure, the electromagnetic device can be cooled by the single plane of the cooling member, thereby allowing the cooling member to be formed in a simple placoid manner.

[0015] In the aspect described above, a notch may be provided at the center of the one side portion of the top core that adjoins the cooling member and on a center line of the opening of the U-shaped core. Also, a coil terminal may be provided at a portion

of the coil, and the coil terminal may extend upward in the longitudinal direction of the central core through the notch.

[0016] According to this structure, the center of the side portion of the top core adjoins the cooling member and on the center line of the opening of the U-shaped core corresponds to the portion where the magnetic flux of the coil becomes sparse. Therefore, the notch is formed in the top core in a position that corresponds to that portion where the magnetic flux of the coil becomes sparse, and the coil terminals protrude upward from the top core through that notch, so neither the notch nor the coil terminals affect the magnetic flux much. That is, the coil terminals can provided easily without affecting the performance of the electromagnetic device or increasing the size of the electromagnetic device.

[0017] In the structure described above, a concave portion may be provided in a position adjacent to the notch of the top core on a center line of the opening in the U-shaped core, and a fixing member may be arranged in the concave portion. [0018] According to this structure, the portion of the top core that is adjacent to the notch corresponds to a portion where the magnetic flux of the coil becomes sparse, just like the portion of the notch. Therefore, the concave portion is formed in the top core in a location that corresponds to the portion where the magnetic flux becomes sparse so that the concave portion will not affect the magnetic flux much. Also, the fixing member is housed in that concave portion so it will not protrude. That is, electromagnetic device is able to be effectively fixed using the fixing member without affecting the performance of the electromagnetic device or increasing the size of the electromagnetic device.

[0019] In the foregoing structure, a nonmagnetic plate may be in-molded onto the central core, and a gap plate for maintaining a gap width may be provided between the top core and one end in the longitudinal direction of the central core and a gap plate for maintaining a gap width may be provided between the bottom core and the other end in the longitudinal direction of the central core. Also, the one gap plate that is provided corresponding to one end in the longitudinal direction of the central core may be

integrally formed with the central core. Further, the other gap plate that is provided corresponding to the other end in the longitudinal direction of the central core may be separable from the central core to allow the coil to be inserted into the central core.

[0020] According to this structure, the gap plates are provided for maintaining a gap width between the upper end of the central core and the top core, and between the lower end of the central core and the bottom core. This enables a fixed insulation distance to be maintained between the top core and the central core, the U-shaped core, and the coil, and between the bottom core and the central core, the U-shaped core, and the coil. Further, one of the gap plates provided corresponding to one end of the central core is integrally formed with the central core, so the number of parts is less than it is when this gap plate is provided separately from the central core. That is, the gap width can be maintained between the central core and the top core, as well as between the central core and the bottom core, and the structure for achieving this can be simplified, which improves assemblability. [0021] In the foregoing structure, fitting portions that engage with each other in a concavo-convex relationship may be provided on each of the gap plates and the top core and the bottom core. Also, the top core may be positioned with respect to the gap plate by engagement of the fitting portions, and the bottom core may be positioned with respect to the gap plate by engagement of the fitting portions. [0022] According to this structure, the top core and the bottom core are positioned on the gap plates by the engagement of the fitting portions so there is no need to provide separate members for positioning. Also, the fitting portions fit together in a concavo-convex relationship and so can be formed easily. That is, the top core and the bottom core can be positioned on the gap plates by a relatively simple structure and jarring between the parts can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The foregoing and further objects, features and advantages of the

invention will become apparent from the following description of preferred embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

FIG 1 is a perspective view of a reactor according to a first example embodiment of the invention;

FIG 2 is an exploded perspective view of the reactor;

FIG 3 is a sectional view taken along plane IH-III in FIG 1 showing the reactor;

FIG. 4 is an enlarged sectional view of the portion within the rectangular chain line shown in FIG 3 as viewed from the front; FIG 5 is a longitudinal sectional view showing the reactor in use;

FIG 6 is a plan view showing the reactor in use with a top core removed;

FIG. 7 is a view illustrating the magnetic flux distribution of the coil as viewed from the front;

FIG 8 is a view illustrating the magnetic flux distribution of the coil as viewed from the side;

FIG 9 is a view illustrating the magnetic flux distribution of the coil with the top core removed;

FIG 10 is a plan view illustrating the magnetic flux distribution of the coil;

FIG 11 is an electrical circuit diagram of a hybrid system to which the reactor is applied;

FIG 12 is a graph showing the DC superimposed characteristic (CAE calculated value) of the reactor in the hybrid system;

FIG 13 is a perspective view of a reactor according to a second example embodiment of the invention; FIG 14 is an exploded perspective view of the reactor;

FIG 15 is a partially exploded perspective view of the reactor with the coil removed;

FIG 16. is a view showing the relationship between a concave portion of a top core and a convex portion of an upper gap plate;

FIG 17 is a view showing the relationship between a concave portion of a bottom core and a convex portion of a lower gap plate; and

FIG 18 is a view showing the relationship between a concave portion of a central core and a convex portion of the lower gap plate.

DETAILED DESCRIPTION OF EMBODIMENTS

[0024] Hereinafter, a first example embodiment in which an electromagnetic device of the invention is embodied as a reactor will be described in detail with reference to the accompanying drawings.

[0025] FIG 1 is a perspective view of a reactor 1. In this example embodiment, the right side of the reactor in FIG 1 is the front side of the reactor 1. FIG 2 is an exploded perspective view of the reactor 1. FIG 3 is a sectional view (i.e., a longitudinal sectional view) of the reactor 1 taken along plane HI-III in FIG 1. FIG 4 is an enlarged sectional view of the portion within the rectangular area Ql outlined by the chain line shown in FIG. 3 as viewed from the front. FIG 5 is a longitudinal sectional view showing the reactor in use, and FIG 6 is a plan view showing the reactor 1 in use with a top core 5 removed.

[0026] As shown in FIGS. 1 to 3, the reactor in this example embodiment has a column-shaped central core 2, a coil 3 provided around the central core 2, a U-shaped core 4 which has an open side and covers all but a portion of the outer peripheral side of the coil 3, a top core 5 that covers the upper ends of the central core 2 and the coil 3, and a bottom core 6 that covers the lower ends of the central core 2 and the coil 3. A nonmagnetic plate 7 is provided between the top core 5 and the upper ends of the central core 2 and the coil 3, and a nonmagnetic plate 8 is provided between the bottom core 6 and the lower ends of the central core 2 and the coil 3. Here, a portion (i.e., a front surface 3a) of the outer peripheral surface of the coil 3 that is positioned at the open side of the U-shaped core 4, an open end portion (i.e., an open end surface 4a) of the U-shaped core 4, one side portion (i.e., a front side surface 5a) of the top core 5, and one

side portion (i.e., a front side surface 6a) of the bottom core 6 are flush with each other, and as shown in FIGS. 5 and 6, are close to a flat side surface 9a of a cooling member 9 across a small gap.

[0027] In this example embodiment, the reactor 1 may be applied to a hybrid system of a hybrid vehicle, for example. The cooling member 9 described above is provided separate from the reactor 1 in order to cool the reactor 1 as well as electrical equipment around the reactor 1. A coolant passage 9b through which coolant flows is formed inside the cooling member 9.

[0028] The central core 2 is formed of a powder magnetic core or ferrite or the like in a rectangular column shape. As shown in FIG. 6, the central core 2 is rectangular in a plan view, with the long sides arranged parallel to the front and back sides of the reactor 1. In order to obtain a flat superimposed characteristic, a plurality of nonmagnetic plates 10 are in-molded at equally-spaced intervals at the middle portion of the central core 2. These nonmagnetic plates 10 create a plurality of magnetic gaps. [0029] The coil 3 is arranged around the central core 2 enveloping it. As shown in FIG. 6, the shape of the coil 3 matches that of the central core 2, being generally rectangular when viewed from above, with the long sides arranged parallel with the front and back sides of the reactor 1. The coil 3 is an edge wise coil in which a strip of material (e.g., rectangular or flat winding wire) of a predetermined width is repeatedly wound vertically. The height of the coil 3 is slightly lower than the height of the central core 2.

[0030] One end portion 3b of the strip of material that forms the coil 3 is bent so as to stand vertically upright at the center on the upper surface of the front portion of the coil 3. Another end portion 3c of the strip of material that forms the coil 3 is bent so that it extends from the lower surface of the front portion of the coil 3 up along the side surface and then along the upper surface to the center of the upper surface where it is bent upwards so that it stands vertically upright parallel with the one end portion 3b. The one end .portion 3b and the other end portion 3c make up coil terminals 11." In this way, the coil terminals 11 of the reactor 1 extend upward from the center of the upper end at

the front portion of the coil 3 that adjoins the cooling member 9.

[0031] The U-shaped core 4 is formed in a U-shape when viewed from above, as shown in FIG 6, and is made of a power magnetic core or ferrite or the like. The U-shaped core 4 covers three adjacent sides (the left, right, and back sides) of the coil 3, leaving the front surface 3a of the coil 3 open. The height of the U-shaped core 4 is the same as the height of the central core 2. The top core 5 and the bottom core 6 have predetermined thicknesses, are of the same shape, and are arranged vertically symmetrical with one another. The outer shapes of the top core 5 and the bottom core 6 are generally the same as the outer shape of the U-shaped core 4. [0032] A nonmagnetic plate 7 is interposed between the top core 5 and the upper ends of the central core 2 and the U-shaped core 4, thus spacing the top core 5 from the central core 2 and the U-shaped core 4 such that a flat superimposed characteristic can be obtained. Similarly, a nonmagnetic plate 8 is interposed between the bottom core 6 and the lower ends of the central core 2 and the U-shaped core 4, thus spacing the bottom core 6 from the central core 2 and the U-shaped core 4 such that a flat superimposed characteristic can be obtained. The outer shapes of the nonmagnetic plates 7 and 8 are generally similar to the outer shapes of the top core 5 and the bottom core 6, respectively.

[0033] Here, a center axis Ll of the central core 2 is offset to the front from a center axis L2 of the reactor 1, as shown in FIGS. 5 and 6. Accordingly, the coil 3 is offset from the center of the reactor 1 toward the one side 9a of the cooling member 9.

[0034] As shown in FIGS. 1 to 3, a notch 5b is formed in the center on the front side of the top core 5 along the center line of the opening in the U-shaped core 4, and a notch 7b is formed in the center on the front side of the upper nonmagnetic plate 7 also along the center line of the opening in the U-shaped core 4. The coil terminals 11 protrude upward from the top core 5 through these notches 7b and 7a. Also, a concave portion 5c is formed in a position adjacent to the notch 5b in the top core 5 along the center line of the opening in the U-shaped core 4. A flat spring 12 that can correspond to. a fixing member of the ^, invention is arranged in this concave portion 5c. . The flat spring 12 is formed bent in a general U-shape and housed entirely in the concave portion

5c. The bottom core 6 and the lower nonmagnetic plate 8 are formed similar to the top core 5 and the upper nonmagnetic plate 7. Reference numerals of the bottom core 6 and the lower nonmagnetic plate 8 which correspond to the top core 5 and the upper nonmagnetic plate 7 denote the same structure. However, the flat spring 12 is not provided in the concave portion 6c of the bottom core 6.

[0035] As shown in FIG 5, the reactor 1 is arranged adjacent to the cooling member 9 on an inverter case 21 and is held in place by being pressed on from above by a cover plate 22. In this example embodiment, the reactor 1 is sandwiched from above and below by fastening the cover plate 22 to the inverter case 21 with bolts or the like. As a result, the reactor is fixed to the inverter case 21 while pressure is created by the flat spring 12.

[0036] In this example embodiment, the concave portions 5c and 6c and the notches 5b and 6b are formed toward the front of the top core 5 and the bottom core 6 as described above, but this does not affect the performance of the reactor 1 due to the relationship of the expansion distribution of the magnetic flux of the coil 3. FIG 7 is a view illustrating the magnetic flux distribution of the coil 3 as viewed from the front of the reactor 1. FIG 8 is a view illustrating the magnetic flux distribution of the coil 3 as viewed from the side of the reactor 1. FIG 9 is a view illustrating the magnetic flux distribution of the coil 3 with the top core 5 of the reactor 1 removed. FIG 10 is a view illustrating the magnetic flux distribution of the coil 3 when the reactor 1 is viewed from above. As shown by the bold arrows in FIGS. 7 to 9, in the reactor 1, the magnetic flux of the coil 3 flows in order from the central core 2 to the top core 5, to the U-shaped core 4, and the bottom core 6, and then back to the central core 2 again. In this case, the U-shaped core 4 is open on the side where the cooling member 9 is located, i.e., on the front side, so the magnetic flux is distributed while avoiding the front side of the

U-shaped core 4. Also, the nature of magnetic flux is to take the path with the shortest magnetic circuit so the magnetic flux is distributed along the outer peripheral portion of the central core 2, which creates a portion where magnetic flux concentrates at the top core 5 and the bottom core 6. Accordingly, as shown in FIG 10, sparse magnetic flux

areas Mf where there is little magnetic flux are created toward the front of the top core 5 on the center line Cl at the opening of the reactor 1. Sparse magnetic flux areas Mf are also created on the peripheral edge of the top core 5. The same applies to the bottom core 6. Therefore, in this example embodiment, the notches 5b and 6b and the concave portions 5c and 6c are formed in the top core 5 and the bottom core 6, respectively, in positions corresponding to the sparse magnetic flux areas Mf of the reactor, so these notches 5b and 6b and the concave portions 5c and 6c have little affect on the magnetic flux.

[0037] According to the reactor 1 of this example embodiment described above, the front surface 3a of the coil positioned on the front side of the U-shaped core 4, the open end surface 4a of the U-shaped core 4, the front side surface 5a of the top core 5, and the front side surface 6a of the bottom core 6 all adjoin the one side surface 9a of the cooling member 9. Therefore, not only are the U-shaped core 4, the top core 5, and the bottom core 6 directly cooled from the portion near the cooling member 9, but the coil 3 is also directly cooled from the portion near the cooling member 9. Therefore, the ability to cool the reactor can be improved. In particular, the cooling capability can be improved by the coil 3 being directly cooled. Also, all the coil 3, the U-shaped core 4, the top core 5, and the bottom core 6 are cooled by the one side surface 91 of the cooling member 9, the cooling member 9 may be formed in a simple placoid manner. [0038] Also, with the reactor in this example embodiment, one of the long sides of the coil 3 that is rectangular in shape when viewed from above adjoins the cooling member 9. As a result, the area of the coil 3 that faces the cooling member 9 can be increased compared to when one of the shorter sides of the coil 3 adjoins the cooling member 9, thereby making the coil 3 that much easier to cool. [0039] Here, the related art JP-A-2005-286020 requires the additional structure of a thermostat and control circuit and the like for monitoring the temperature to keep the coil temperature of the reactor from increasing. With this example embodiment, however, such addition structure can be omitted. Moreover, the reactor 1 can be efficiently cooled with only the structure of the reactor 1 itself. Accordingly, the ability

to cool the reactor 1 can be improved with a simple structure.

[0040] The related art JP-A-2002-252122 requires a column to connect the coil to the cooling device, which complicates the structure of the cooling device. With this example embodiment, not only the coil 3 and the U-shaped core 4, but the top core 5 and the bottom core 6 are cooled by the cooling member 9 formed in a simple placoid manner.

[0041] According to the reactor 1 of this example embodiment, the nonmagnetic plate 7 is provided between the top core 5 and the upper ends of the central core 2 and the U-shaped core 4 and the nonmagnetic plate 8 is provided between the bottom core 6 and the lower ends of the central core 2 and the U-shaped core 4.

Accordingly, a gap of a fixed width is able to be ensured between the top core 5 and the upper ends of the central core 2 and the U-shaped core 4, as well as between the bottom core 6 and the lower ends of the central core 2 and the U-shaped core 4. Therefore, a fixed insulation distance can be ensured between the top core 5 and the central core 2, the U-shaped core 4, and the coil 3, as well as between the bottom core 6 and the central core 2, the U-shaped core 4, and the coil 3.

[0042] According to the reactor 1 of this example embodiment, the center of the front portion of the top core 5 which adjoins the cooling member 9, on the center line of the opening of the U-shaped core 4, corresponds to the portion where the magnetic flux of the coil 3 becomes sparse. Therefore, the notch 5b is formed in the top core 5 in a position that corresponds to that portion where the magnetic flux of the coil 3 becomes sparse, and the coil terminals 11 protrude upward from the top core 5 through that notch 5b, so neither the notch 5b nor the coil terminals 11 affect the magnetic flux much. As a result, the coil terminals 11 can be provided easily without affecting the performance of the reactor 1 or increasing the size of the reactor 1.

[0043] According to the reactor 1 of this example embodiment, the portion of the top core 5 that is adjacent to the notch 5b corresponds to a portion where the magnetic flux of .the coi! 3 becomes sparse, just like the portion-of thcnotch 5b. Therefore, the concave portion 5c is formed in the top core 5 in a location that corresponds to the

portion where the magnetic flux becomes sparse so that the concave portion 5c will not affect the magnetic flux much. Also, the fixing flat spring 12 is housed in that concave portion 5c so it will not protrude. Further, the reactor 1 is fixed to the inverter case 21 by the pressure from that flat spring 12. Therefore, the reactor 1 is able to be effectively fixed to the inverter case 21 using the flat spring 12 without affecting the performance of the reactor 1 or increasing the size of the reactor 1.

[0044] FIG 11 is an electrical circuit diagram of a hybrid system to which the reactor 1 of this example embodiment is applied. This system includes a pair of generators 31 and 32, a pair of inverters 33 and 34 that control the power to the generators 31 and 32, a DC/DC converter 35 that supplies current to the inverters 33 and 34, and a power supply circuit 37 that includes a battery 36. The inverters 33 and 34 are formed of a plurality of transistors. The reactor 1 of this example embodiment is connected between the pair of transistors 38 and 39 and a condenser 40 in the DC/DC converter 35. In this hybrid system, the reactor 1 functions to step up (i.e., increase) the voltage of the power supply circuit 37 and stably supply it to the inverters 33 and 34.

[0045] FIG 12 is a graph showing the DC superimposed characteristic (CAE calculated value) of the reactor in the hybrid system described above. As is evident from the graph, the cooling ability with the reactor 1 is good, as described above, so an excellent flat superimposed characteristic is able to be obtained. [0046] Next, a second example embodiment in which the electromagnetic device of the invention is embodied as a reactor will be described in detail with reference to the accompanying drawings. Incidentally, in the following description, constituent elements of the second example embodiment that are equivalent to constituent elements of the first example embodiment will be denoted by the same reference characters and descriptions of those elements will be omitted. The following description will focus mainly on those points of the second example embodiment that differ from the first example embodiment described above.

[0047] FIG 13 is a perspective view of a reactor 41 according to the second example embodiment. In this example embodiment, the near side of the reactor 41 in

FIG. 13 is the front side of the reactor 41. FIG 14 is an exploded perspective view of the reactor 41, and FIG 15 is a partially exploded perspective view of the reactor 41 with the coil 3 removed. This example embodiment differs from the first example embodiment described above in that it is provided with a structure for positioning the constituent members 2, and 4 to 6 and the like with respect to each other.

[0048] That is, as shown in FIGS. 13 to 15, the reactor 41 of this example embodiment is such that a plurality of nonmagnetic plates 10 are in-molded on the central core 2, and there is a gap plate 42 for maintaining a gap width between the top core 5 and the upper end of the central core 2, as well as a gap plate 43 for maintaining a gap width between the bottom core 6 and the lower end of the central core 2. The upper gap plate provided corresponding to the upper end of the central core 2 is integrally formed with the central core 2. The lower gap plate 43 provided corresponding to the lower end can be separated from the central core 2 to enable the coil 3 to be inserted into the central core 2. That is, in the first example embodiment, the nonmagnetic plate 7 which is formed from a separate member is provided between the upper end of the central core 2 and the top core 5 and the nonmagnetic plate 8 which is also formed from a separate member is provided between the lower end of the central core 2 and the bottom core 6. In this example embodiment, however, these nonmagnetic plates 7 and 8 are omitted. Instead, the upper gap plate 42 that is integrated with the central core 2 and the lower gap plate 43 that is separable from the central core 2 are provided. The upper gap plate 42 and the lower gap plate 43 may each be formed by adding filler into a resin such as PPS.

[0049] In addition, the reactor 41 of this example embodiment differs from the first example embodiment described above in terms of the shapes of the U-shaped core 4, the top core 5, and the bottom core 6 when viewed from above. That is, in this example embodiment, the corner portions of the U-shaped core 4 form right angles. The shapes of the top core 5 and the bottom core 6, when viewed from above, are generally rectangular and match the shape of the U-shaped core 4. Also, the shapes of the upper gap plate 42 and the lower gap plate 43 are generally rectangular and match the shape of the top core 5 and the bottom core 6.

[0050] A plurality of fitting portions 44 that fit together in a concavo-convex relationship with the gap plates 42 and 43 and the top core 5 and the bottom core 6 are provided on the reactor 41 of this example embodiment. These fitting portions 44 fit together, thereby positioning the top core 5 with respect to the gap plate 42, and the bottom core 6 with respect to the gap plate 43. That is, a convex portion 42a that protrudes upward is integrally formed at each of the four corners on the upper surface of the upper gap plate 42, while a plurality of concave portions 5d corresponding to the convex portions 42a are formed at each of the four corners on the lower surface of the top core 5. The convex portions 42a and the concave portions 5d together form the fitting portions 44.

[0051] FIG 16 is a view showing the relationship between the convex portions 42a and the concave portions 5d. As is evident from FIG 16, the depth Dl of the concave portions 5d is slightly greater than the height of the convex portions 42a, so the convex portions 5d are fit completely within the concave portions 5d. Also, a concave portion 43a that protrudes downward is integrally formed at each of the four corners on the lower surface of the lower gap plate 43. Concave portions 6d that correspond to the convex portions 43a are formed at each of the four corners on the upper surface of the bottom core 6. FIG 17 is a view showing the relationship between the convex portions 43a and the concave portions 6d. As is evident from FIG 17, the depth D2 of the concave portions 6d is slightly greater than the height of the convex portions 43a, so the convex portions 6d are fit completely within the concave portions 6d.

[0052] Also, in the reactor 41 of this example embodiment, three protruding strips 42b that protrude downward are integrally formed in positions toward the left and rights sides and back on the lower surface of the upper gap plate 42. Similarly, three protruding strips 43b that protrude upward are integrally formed in positions toward the left and rights sides and back on the upper surface of the lower gap plate 43. These protruding strips 42b and 43b fit into gaps between the coil 3 and the U-shaped core 4, thus maintaining a fixed insulation distance between the coil 3 and the U-shaped core 4. These protruding strips 42b and 43b also determine the relative positions of the top core 5

and the bottom core 6 with respect to the central core 2 and the U-shaped core.

[0053] Furthermore, in the reactor 41 of this example embodiment, as shown in FIGS. 14 and 15, four convex portions 43c that protrude upward are integrally formed on the center portion of the upper surface of the lower gap plate 43. Also, concave portions 2a that engage with these convex portions 43c are formed corresponding to the convex portions 43c on four sides of the center portion on the lower end of the central core 2. FIG. 18 is a view showing the relationship between the convex portions 43c and the concave portions 2a. As is evident from FIG 18, the depth D3 of the concave portions 2a is slightly greater than the height H3 of the convex portions 43c, so the convex portions 43c are fit completely within the concave portions 2a.

[0054] With the reactor 41 of the second example embodiment described above, the same effects as those obtained with the reactor of the first example embodiment are basically able to be obtained. In addition, with the reactor 41 of the second example embodiment, the gap plates 42 and 43 are provided for maintaining a gap width between the upper end of the central core 2 and the top core 5, and between the lower end of the central core 2 and the bottom core 6. This enables a fixed insulation distance to be maintained between the top core 5 and the central core 2, the U-shaped core 4, and the coil 3, and between the bottom core 6 and the central core 2, the U-shaped core 4, and the coil 3. Further, the upper gap plate 42 provided corresponding to the upper end of the central core 2 is integrally formed with the central core 2, so the number of parts is less than it is when the gap plate 42 is provided separately from the central core 2. Therefore, the gap width can be maintained between the central core 2 and the top core 5, as well as between the central core 2 and the bottom core 6, and the structure for achieving this can be simplified, which improves assemblability. [0055] With the reactor 41 of this example embodiment, the top core 5 and the bottom core 6 are positioned on the gap plates 42 and 43, respectively, by the engagement of the fitting portions 44 so there is no need to provide separate members for positioning. Also, the fitting portions 44 are formed of the concave portions 5d and 6d and the convex portions 42a and 43b that fit together in a concavo-convex relationship and so can be

formed easily on the gap plates 42 and 43 and the top core 5 and the bottom core 6. Therefore, the top core 5 and the bottom core 6 can be positioned on the gap plates 42 and 43, respectively, by a relatively simple structure and jarring between the parts 5, 6, 42, and 43 can be prevented. [0056] With the reactor 41 of this example embodiment, the protruding strips

42b and 43b provided on the gap plates 42 and 43, respectively, enable a fixed insulation distance to be maintained between the coil 3 and the U-shaped core 4, thereby positioning the central core 2, the U-shaped core 4, the top core 5, and the bottom core 6 with respect to each other. Therefore, the top core 5 and the bottom core 6 can be positioned with respect to the gap plates 42 and 43, respectively, by a relatively simple structure and jarring between the parts 5, 6, 42, and 43 can be prevented.

[0057] Also, with the reactor 41 of this example embodiment, the central core 2 is positioned on the lower gap plate 43 by the convex portions 43c provided on the lower gap plate 43 and the concave portion 2a provided on the central core 2. Therefore, the central core 2 can be positioned with respect to the lower gap plate 43 by a relatively simple structure and jarring between the parts 2 and 43 can be prevented.

[0058] Incidentally, the invention is not limited to the example embodiments described above. That is, part of the structure may be appropriately modified without departing from the scope of the invention, as described below. [0059] (1) In the first example embodiment described above, a plurality of magnetic gaps are created by arranging a plurality of nonmagnetic plates 10 at equally-spaced intervals at a portion in the middle of the central core 2 in order to obtain a flat superimposed characteristic. In contrast, the magnetic gaps may also be omitted by forming the entire central core from low magnetic permeability material. [0060] (2) In the example embodiments described above, the electromagnetic device of the invention is embodied as a reactor 1 and 41. Alternatively, however, the electromagnetic device may also be embodied as a choke coil or a transformer.

[0061] While the invention has been described with • reference- to example embodiments thereof, it is to be understood that the invention is not limited to the

described embodiments or constructions. To the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the disclosed invention are shown in various example combinations and configurations, other combinations and configurations, including more, less or only a single element, are also within the scope of the appended claims.