JP2006352021A - Coil-sealed iron powder immixed resin-molded reactor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coil-sealed iron powder immixed resin-molded reactor that suppresses inductance drop when a large amount of current is conducted while miniaturization is designed. <P>SOLUTION: Inductance drop rate when the large amount of current is conducted can be reduced without increasing a body so much by suppressing iron powder filling ratio (weight of iron powder/weight of core) to 0.45-0.6, further preferably 0.5-0.55. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an improvement of a coil-sealed iron powder-containing resin molding reactor in which a coil is embedded in an iron powder-containing resin molding core.

  As a reactor (hereinafter also referred to as a choke coil) that is an inductance component used in an electric circuit or an electronic circuit, a resin molded reactor containing a ferrite powder having a structure in which a coil is embedded in a resin core mixed with soft ferrite powder is known. ing. For example, Patent Documents 1 and 2 below propose a ferrite powder-mixed resin molding reactor in which a polyamide resin filled with ferrite powder (iron oxide powder) is molded and the coil is sealed.

  Such a resin molded reactor containing a ferrite powder is easier to manufacture than a sintered reactor in which a coil is wound around a conventional sintered core, and the resin molded magnetic path member completely encloses the coil. Therefore, the magnetic flux leakage from the coil to the outside can be reduced, electromagnetic noise can be reduced, the waterproofness and electrical insulation of the coil can be improved, and the manufacturing process can be simplified.

  Note that mixing the inorganic powder into the ferrite mixed resin molded core in the ferrite powder mixed resin molded reactor of Patent Document 2 results from the fact that the linear expansion coefficient of the synthesis of the ferrite element-containing resin (core) is larger than that of the coil. This is to reduce the temperature stress between the core and the coil. According to the description of Examples in Patent Document 2, by using a fused silica powder and a spherical ferrite powder having a linear expansion coefficient smaller than that of a spherical ferrite powder as a filler, it is possible to use only a conventional spherical ferrite powder as a filler. In addition, the linear expansion coefficient of the ferrite mixed resin molded core is reduced, and the difference in linear expansion coefficient generated between the core and the coil when the reactor terminals are solder-dip processed is reduced.

  However, the ferrite powder-mixed resin molded reactor has a filling rate of ferrite powder per core weight of only about 40 wt% or less, and further, the saturation magnetic flux density and permeability of the ferrite itself are other commonly used magnetic materials. Furthermore, it is much lower than pure iron, etc., so the reactor size and weight necessary to obtain the required inductance are very large (about 2.5 times), and the coil becomes large accordingly. Therefore, when weight reduction is required, such as in-vehicle applications, reduction in size and weight has been a major issue. Furthermore, since the amount of expensive ferrite powder used increases, reduction of material costs has become an important issue.

  For this reason, a coil-sealed iron powder in which a coil is embedded in a core (iron powder-containing resin molding core) formed by molding a resin containing silicon iron alloy powder or pure iron powder used as a so-called electromagnetic steel sheet A mixed resin molding reactor has been put into practical use.

This coil-encapsulated iron powder-mixed resin-molded reactor is much more compact than the ferrite-mixed resin-molded core described above because the magnetic properties (permeability and saturation magnetic flux density) of iron powder are much better. Should be suitable for in-vehicle use.
JP-A-6-176946 Japanese Patent Publication No. 7-118420 (Japanese Patent Laid-Open No. 3-96202)

  However, the coil-encapsulated iron powder-mixed resin-molded reactor described above has a large inductance reduction rate when a large current is applied. For example, in a vehicle DCDC converter equipped with this reactor as a smoothing choke coil, a large current flows through the reactor. As a result, the output ripple rate increases, which adversely affects the battery and the electrical load. The increase in the output ripple rate due to the above-described decrease in inductance when energizing a large current in the iron powder-containing resin molded core has been conventionally considered to be an essential characteristic of the iron powder-containing resin molded core. In addition, in in-vehicle applications, weight reduction by reducing the amount of iron powder used in an iron powder-mixed resin molded core has been desired.

  The present invention has been made in view of the above problems, and is a lightweight coil-sealed mold that suppresses a decrease in inductance when energizing a large current without increasing the amount of iron powder used compared to a conventional iron powder-containing resin-molded core. The object is to provide a resin-molded reactor containing iron powder.

  The coil-encapsulated iron powder-containing resin-molded reactor of the present invention for solving the above problems includes a coil and an iron-powder-mixed resin-molded core that seals the coil. In the coil-sealed iron powder-mixed resin molding reactor formed by molding a resin filled with iron powder, the iron powder weight relative to the weight of the iron powder-mixed resin molded core is 45 wt% or more and less than 60 wt% It is said.

  The iron powder referred to in this specification refers to silicon iron alloy powder, pure iron powder, soft iron powder, amorphous iron powder, and soft magnetic alloy iron powder containing iron as a main component. The average particle size of the iron powder is preferably 100 μm, but is not limited thereto. After coating the surface of the iron powder with a resin insulating film, it may be kneaded with a resin material for resin molding. In this case, the resin insulation film is regarded as a resin when calculating the iron powder weight composition.

  That is, in the present invention, the iron powder weight is limited to 45 wt% or more and less than 60 wt% of the iron powder mixed resin molded core weight in the manufacture of the iron powder mixed resin molded core used for the coil-sealed iron powder mixed resin molded reactor. Is the feature.

  As a result, it has been found that a lighter coil-sealed soft magnetic resin molding reactor can be realized that suppresses a decrease in inductance at a large current as compared with a conventional iron powder-mixed resin molding core.

(Inductance theory of coil embedded iron powder mixed resin molded core)
This will be described in more detail below.

  A conventional iron powder-containing resin-molded core (usually used by insulatingly coating iron powder) has an iron powder weight set to at least 80 wt% or more of the iron powder-containing resin-molded core weight. However, this ratio is a weight ratio, and considering that the specific gravity of iron powder is much larger than the specific gravity of the resin, the filling ratio is much smaller at the volume ratio. That is, in a conventional coil-sealed resin-molded reactor using an iron powder-containing resin-molded core, efforts have been made to increase the iron powder filling ratio x to the extent permitted by mechanical strength against magnetic vibration and the like for compactness. It was.

  However, in the coil-encapsulated iron powder-mixed resin-molded reactor, the inductance drop becomes significant on the large current side of the operating current range, and this is considered to be a characteristic unique to the coil-sealed iron powder-mixed resin-molded reactor. Naturally, such a decrease in inductance when energizing a large current is caused by an increase in magnetic saturation tendency. Such a decrease in inductance during energization of a large current increases a high-frequency power component superimposed on an output voltage in a circuit device, for example, a power smoothing choke coil, and thus adversely affects a battery and an electrical load in addition to an increase in electromagnetic noise. With the solution of this problem in mind, the inventors analyzed the inductance of the coil-encapsulated iron powder-mixed resin molded reactor. The analysis result will be described below.

  First, the inductance H of a coil embedded in an iron powder-mixed resin molded core (soft magnetism) is expressed by the following equation when the coil is a solenoid coil and the Nagaoka coefficient is ignored.

H = N ・ N ・ μ ・ S / L
N is the number of coil turns, μ is the permeability of the resin core, S is the magnetic path cross-sectional area, L is the magnetic path length, however, the resin core forms a closed magnetic path, the cross-sectional area of each part is constant, and the leakage flux Suppose there is no. The decrease in inductance when energizing a large current occurs as a result of the magnetic saturation tendency of the resin core increasing and the permeability μ decreasing. Conventionally, the permeability μ of the resin core is that the permeability of the iron powder filling rate is 100% (solid material) is μ (100%), and the filling weight ratio of iron powder (iron powder weight / core weight) is x. In some cases, x · μ (100%).

In other words, conventionally, the inductance H is
H = N ・ N ・ μ ・ x ・ S / L
Was considered equivalent. In this case, it can be considered that the inductance of the coil increases as the filling ratio x of the iron powder increases (in proportion to the weight of the iron powder-containing resin-molded core).

  However, when the iron powder-mixed resin molded core is viewed microscopically, a resin (gap) is present between a certain iron powder and the adjacent iron powder, although it is minute. The relative permeability of the resin is assumed to be 1. In the magnetic path direction, the presence of resin in the magnetic path direction between the iron powder and iron powder means that the iron powder mixed resin molded core is magnetically divided between the iron powder magnetic path part and the gap part. This means that it should be considered in series in the circuit. In addition, the presence of resin between the iron powder and the iron powder in the magnetic path cross-sectional area direction means that the iron powder-mixed resin molded core has a gap partial magnetic path and a solid magnetic material magnetic path in the cross-sectional area direction. The equivalent magnetic path cross-sectional area of the iron powder-containing resin molded core can be considered by reducing the cross-sectional area of the solid magnetic material, or a constant x smaller than 1 for the relative magnetic permeability μs of the solid magnetic material. This means that it can be considered as a solid magnetic material with a constant magnetic path cross-sectional area and a reduced relative permeability.

  Based on the above understanding, hereinafter, the iron powder magnetic path portion is considered equivalent to the iron magnetic path, and the magnetic path direction gap portion is considered equivalent to the vacuum magnetic path connected in series with the iron magnetic path. The magnetic path length of this iron magnetic path is L1, the magnetic path length of the vacuum magnetic path is L2, the iron magnetic path and the vacuum magnetic path have the same magnetic path cross-sectional area S, and the relative permeability μs of the iron powder-containing resin molded core is It will be smaller than solid magnetic material x '· μs. L1 + L2 can be considered to be L.

  The magnetic resistance R1 of the iron magnetic path is L1 / (x ′ · μs · μo · S), and the magnetic resistance R2 of the vacuum magnetic path is L2 / (μo · S). μs is the relative magnetic permeability of the iron magnetic path, and μo is the vacuum magnetic permeability.

Therefore, the composite magnetoresistance R of the core is
R = ((L1 / (x ′ · μs)) + L2) / (μo · S)
It becomes. That is, it can be considered that the iron powder-mixed resin molded core has a gap length L2 and is substantially equal to a gap core having a relative magnetic permeability x ′ · μs. There is a relationship of H = N · N / R between the magnetic resistance R and the inductance H. That is, the inductance H ′ of the iron powder-mixed resin-molded core in which the coil is sealed is not simply a value obtained by multiplying the permeability in the inductance of the homogeneous and homogeneous iron core by the filling factor x,
N ・ N ・ (μo ・ S) / ((L1 / (x '・ μs)) + L2)
Is equivalent to This means that this coil can be equivalent to a renoid coil whose equivalent vacuum magnetic path length is ((L1 / (x ′ · μs)) + L2).

  After all, the iron powder-mixed resin-molded core has resin gap portions both in the magnetic path cross-sectional area direction and in the magnetic path length direction, so an equivalent gap is provided in the core of a solid magnetic material with a relatively small relative permeability. The equivalent magnetic core is substantially equivalent to the equivalent inductance H ′ of the reactor in which the coil is wound around the equivalent magnetic core.

  Here, when the amount of iron powder used (which can be regarded as almost the core weight) is constant, the core is made compact by increasing the filling ratio x, and the core is enlarged by reducing the filling ratio x Compare the inductances. For the sake of simplicity, the filling ratio of the low filling product is doubled compared to the high filling product (inductance H). Suppose that it is used to increase the size of the core in an increasing direction (another core is assumed to be made).

  The equivalent inductance H ′ is N · N · (μo · S) / ((L 1 / (x ′ · μs)) + L 2). When the filling ratio x is halved, the magnetic path length L1 of the iron magnetic path should decrease, the gap length L2 should increase, and the relative permeability x '· μs should decrease.

  However, even if the filling ratio x is halved, the equivalent inductance is not halved. That is, in terms of the parameter (L1 / (x ′ · μs)), although the relative magnetic permeability x ′ of the iron magnetic path is reduced, the magnetic path length L1 of the iron magnetic path is also reduced, so (L1 / (x ′ · μs)). μs) is never doubled.

  In addition, regarding parameter L2, when considering that each iron powder particle is three-dimensionally dispersed with a uniform interparticle distance (distance from the particle surface to the particle surface) LX within the interparticle distance core, Even if the number of iron powder particles is halved, the inter-particle distance Lx does not double. This is because the decrease in the number of particles decreases three-dimensionally.

  After all, even if the filling ratio x is halved and the number of iron powder particles is halved, it means that the decrease in inductance is less than half. Therefore, it can be seen that, for example, when the iron powder filling ratio x is halved and two low-filled cores are produced, a larger inductance can be obtained with the same weight of iron powder. This means that when the allowable maximum energization current value of the reactor is constant and the coils embedded in the two low-filled cores are connected in parallel, the current flowing through each coil is the allowable maximum energization current value. This means that the maximum amount of magnetic flux flowing in one low-filled product may be half. This means that the magnetic flux density in the low-filled product is reduced when a large current is applied.

  Consider the magnetic flux density B of one low-filled product. If the magnetic resistance is R and the amount of magnetic flux is φ, N is the number of coil turns of one low filling product, and I is the coil current. The number of coil turns of the low filling product is equal to the number of coil turns of the high filling product.

B = φ / R = NI / R
R = ((L1 / (x ′ · μs)) + L2) / (μo · S)
Therefore, even if the current is halved and the magnetic flux amount of one low-filled product is halved, the magnetic flux density of one low-filled product will be as long as the magnetic resistance of the core of one low-filled product is doubled. It is constant. However, as described above, even when the filling ratio x is halved, R = ((L1 / (x ′ · μs)) + L2) / (μo · S) does not double. This is because the magnetic path length L1 of the iron material magnetic path is reduced even if x ′ · μs is halved assuming x = x ′. It was found that when the filling ratio x is halved, the magnetic path length L2 of the equivalent gap increases, but L2 is also less than twice.

  After all, when using the same weight of iron powder (when the weight of the iron powder-containing resin molded core is constant), it is better to reduce the filling ratio and increase the core cross-sectional area by that amount. The magnetic flux density can be reduced.

  Furthermore, if the above-mentioned filling ratio x is lowered under the condition that the iron powder weight is constant, and the magnetic flux density of the core is lowered, the influence of the decrease in the relative permeability μs of the iron powder can be reduced due to this magnetic flux density reduction. This means that the increase in R = ((L1 / (x ′ · μs)) + L2) / (μo · S) due to a decrease in the filling ratio x can be further reduced. That is, it means that the decrease in inductance is reduced when a large current is applied. It also means that the number of turns for obtaining a necessary inductance value can be reduced. Furthermore, since the amount of resin in the core increases, the contact between the iron powder particles decreases, and as a result, eddy current loss can also be reduced.

  It is apparent that the inductance value Lb when a large current is applied is lower than the inductance Lo when a very small current is applied due to the progress of magnetic saturation due to an increase in magnetic flux density. There is almost no magnetic saturation near the origin of the BH curve.

(Conclusion)
Eventually, in order to prevent the above-described problem that the inductance value Lb when energizing a large current is lower than the inductance Lo when energizing a minute current, the filling ratio (iron powder weight / core weight) x is decreased and the magnetism is correspondingly reduced. If the road cross-sectional area is increased to relatively reduce the magnetic flux density at the same current, it is possible to reduce the decrease in inductance when energizing a large current under the condition that the used iron powder weight is constant. In the iron powder mixed resin molded core with the coil embedded, the main weight factor and cost factor depend on the amount of iron powder used.

(Suitable filling ratio)
In view of the above findings, the present invention limits the filling ratio (iron powder weight / core weight) x to 0.6 or less, more preferably 0.55 or less. Thus, it can be seen that a coil-sealed resin-molded reactor can be manufactured under a constant weight condition, in which the inductance drop when energizing a large current is significantly reduced. In other words, when securing the maximum magnetic flux amount corresponding to the maximum energization current value, a smaller filling ratio (iron) than when using the same amount of iron powder with a large filling ratio (iron powder weight / core weight) (small core) The powder density / core weight) can reduce the magnetic flux density of the core (iron powder), and the latter is less prone to magnetic saturation of the iron powder, thereby reducing the relative permeability reduction of the iron powder. It means that there is little decrease in inductance when a large current is applied. That is, when the same amount of iron powder is used (which can be regarded as a reactor of substantially equal weight), the smaller the filling ratio, the smaller the inductance drop when the maximum current is applied. Based on this knowledge, the present invention has the effect of reducing the decrease in inductance when energizing a large current compared to a conventional iron powder-mixed resin-molded core. Such knowledge has not been known at all, and efforts have been made to increase the filling ratio as long as mechanical strength allows.

  However, if the filling ratio is small, it is preferable to suppress the decrease in inductance when energizing a large current. However, reducing the filling ratio increases the core size in order to secure an inductance value corresponding to the maximum current value. Invite. Therefore, the filling ratio (iron powder weight / core weight) x is set to 0.45 or more, and more preferably 0.50, in order to make it sufficiently smaller than a conventional ferrite powder-containing resin-molded core. As a result, the coil-sealed iron powder-mixed resin that is not as large as the conventional iron-powder-mixed resin-molded core and that can suppress a decrease in inductance when energizing a large current without increasing the weight of the used iron powder A molding reactor can be realized. The surface of the iron powder may be coated with a resin film before mixing with the core molding resin. In this case, the weight of the resin film is included in the weight of the core molding resin.

  In a preferred embodiment, the iron powder is not coated with an insulating film on the surface, and the coil is resin-molded. As a result, it is possible to realize a coil-sealed resin-molded reactor that can satisfactorily meet demands for manufacturing cost reduction while suppressing deterioration of magnetic characteristics.

  However, in this aspect, there is a risk that current leakage occurs between the turns of the coil. Therefore, in this aspect, after the coil is resin-molded in advance, the resin-molded coil is sealed and a closed magnetic circuit is formed with an iron powder-mixed resin (soft magnetic powder-filled resin). Thereby, while being able to prevent the current leak between the turns of the coil in a core satisfactorily, even when a crack arises in a core, the ground fault of a coil can be prevented favorably.

  In a preferred embodiment, the iron powder is composed of silicon alloy iron powder having a silicon content of 3 to 7% or pure iron powder having an iron content of 99% or more.

  Hereinafter, the suitable aspect of the coil sealing type iron powder mixing resin molding reactor of this invention is demonstrated with reference to FIG. FIG. 1 is a diagram illustrating a manufacturing process. (A) shows a rectangular wire coil, (b) shows a resin molded coil, and (c) shows a resin molded reactor.

  First, the rectangular copper coil 1 is formed by winding a long copper plate shown in FIG. In this embodiment, the thickness of the flat wire is 1 mm, the width is 3 mm, and the number of turns is 100. A gap of 1 to 2 mm was secured between the turns of the flat wire coil 1.

  Next, the rectangular coil 1 is put into a mold, a resin liquid is injected, and the resin mold coil 2 is manufactured by curing. The minimum coating thickness of the mold resin on the flat wire coil 1 was 1 mm to 3 mm. As the mold resin, a thermosetting resin excellent in heat resistance is preferable, and an epoxy resin or the like is preferable. Reference numeral 3 denotes terminal portions at both ends of the rectangular wire coil 1.

  Next, the resin molded coil 2 taken out from the mold is set in the case 4 with the upper end opening, and the terminal portion 3 is protruded upward from the case 4. The case 4 is preferably an aluminum pressed product or an aluminum drawn product, but a heat resistant resin such as polyimide may be used. However, the case must have heat resistance to withstand the heating of the next process.

  Finally, the case 4 was set in a vacuum heating furnace, and silicon alloy iron powder (Fe-Si (6.5%)) was mixed in an amount of 45 to 60 wt%, more preferably 50 to 55 wt% with respect to the resin core weight. An iron powder-mixed epoxy resin liquid was poured into the case 4 and held at a predetermined heating temperature for a predetermined time to solidify the iron powder-mixed resin liquid, thereby completing a reactor. Reference numeral 5 denotes a core made of a solidified iron powder mixed resin. The iron powder-mixed resin liquid may be kneaded for a predetermined time after the iron powder is put into the resin liquid. Alternatively, iron powder and resin powder may be kneaded and formed. What is important is that the resin mold coil is formed in a cylindrical shape to form a closed magnetic circuit in which the iron powder mixed resin body, that is, the core 5 is linked to the resin mold coil.

  According to this example, since the filling ratio of iron powder (iron powder weight / core weight) x was significantly reduced as compared with the prior art, the inductance reduction rate in the operating current range could be greatly reduced. In addition, since the iron powder contamination rate is significantly reduced compared to conventional iron powder-mixed resin molded cores, the electrical conductivity between the iron powder particles is reduced, and as a result, eddy current loss can be greatly reduced. A secondary effect was also obtained.

It is a figure which shows the manufacturing process of the coil sealing type iron powder mixing resin molding reactor of an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Flat wire coil 2 Resin mold coil 3 Flat wire coil terminal part 4 Case 5 Core (Iron powder mixed resin body)

Claims (4)

A coil and an iron powder-mixed resin molding core for sealing the coil, wherein the iron powder-mixed resin molding core is formed by molding a resin filled with iron powder. In the reactor,
A coil-sealed iron powder-containing resin molding reactor, wherein the iron powder weight relative to the weight of the iron powder-containing resin molding core is 45 wt% or more and less than 60 wt%. In the coil-encapsulated iron powder-mixed resin-molded reactor according to claim 1,
A coil-sealed iron powder-containing resin molding reactor, wherein the iron powder weight relative to the weight of the iron powder-containing resin molding core is 45 wt% or more and less than 60 wt%. In the coil-encapsulated iron powder-mixed resin-molded reactor according to claim 1,
The iron powder is composed of silicon alloy iron powder having a silicon content of 3 to 7% or pure iron powder having an iron content of 99% or more. In the coil-encapsulated iron powder-mixed resin-molded reactor according to any one of claims 1 to 3,
The iron powder is not coated with an insulating coating on the surface, and the coil is resin-molded.

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