Patent Grant
10937619
The present invention relates to a fuse element and a fuse device mounted on a current path blown by self-generated heat when a rate-exceeding current flows therethrough, thereby interrupting the current path, and more particularly relates to a fuse element having excellent high-speed blowout properties and a fuse device having excellent insulating properties after blowout. This application claims priority to Japanese Patent Application No. 2013-177071 filed on Aug. 28, 2013 and Japanese Patent Application No. 2014-165154 filed on Aug. 14, 2014, the entire contents of which are hereby incorporated by reference.
Conventionally, there have been used fuse elements which are blown by self-generated heat when a rate-exceeding current flows therethrough to interrupt the current path. Examples of often-used fuse elements include, for example, fuses fixed by a holder wherein solder is enclosed in glass, chip fuses wherein an Ag electrode is printed onto a ceramic substrate surface, and screw-in or insertion type fuses wherein part of a copper electrode is made thinner and assembled into a plastic case.
Additionally, conventional fuse devices for high voltage applications include fuses having arc extinguishing material packed into a hollow case and fuses in which fuse elements are wrapped in a spiral around a heat dissipating material to generate a time lag.
In a fuse device using such a fuse element, due to a desire for increases in capacity and rating in target electronic appliances and batteries, improvements in current ratings are desired. Furthermore, due to a desire for smaller electronic appliances and batteries in which fuse devices are incorporated, smaller fuse devices are also desired.
In order to improve ratings in a fuse device, it is necessary to balance conductor resistance reduction with insulation properties when a current path is interrupted. Thus, in order to increase current flow, it is necessary to reduce conductor resistance; therefore, it is necessary to increase cross sectional area in the fuse element. However, as illustrated in
Furthermore, conventional electrical fuses for high voltage application, such as those encapsulating arc extinguishing material or manufactured with a spiral fuse, require complicated materials and manufacturing processes, and are disadvantageous for decreasing size and increasing rating.
As described above, it is desired to develop a fuse device having a size sufficient for increasing rating while maintaining electrical insulation properties and having a simple structure which can enable size decrease and manufacturing simplification.
To solve the aforementioned problem, a fuse device according to the present invention includes: a fuse element; a case having a housing space for housing the fuse element and having a lead-out port through which both ends of the fuse element are led out, and which supports the fuse element in a bridge-like manner in the housing space; and a shield disposed in the housing space for shielding an inner wall surface leading to the lead-out port from a scattered melted material of the fuse element.
Furthermore, a fuse element according to the present invention, being supported in a bridge-like manner within a case and having both ends led out of a lead-out port of the case, includes a projecting section for shielding an inner wall surface of the case leading to the lead-out port from a scattered melted material.
In the present invention, because the shield is provided in the housing space to interrupt the inner wall surface extending to the lead-out port, which supports the fuse element in a bridge-like manner, melted conductor is prevented from being continuously deposited on the inner wall surface leading to the lead-out port. Therefore, the present invention can prevent a state in which both ends of the melted fuse element are shorted by melted conductor of the fuse element being continuously deposited on the inner wall surface leading to the lead-out port.
The fuse element and the fuse device according to the present invention will now be more particularly described with reference to the accompanying drawings. It should be noted that the present invention is not limited to the embodiments described below and various modifications can be made without departing from the scope of the present invention. The features shown in the drawings are illustrated schematically and are not intended to be drawn to scale. Actual dimensions should be determined in consideration of the following description. Moreover, those skilled in the art will appreciate that dimensional relations and proportions may be different among the drawings in some parts.
A fuse device 1 according to the present invention, as illustrated in
The fuse element 2 is blown out by self-generated heat (Joule heat) when a rate exceeding current flows therethrough to interrupt the current path of the circuit into which the fuse device 1 is incorporated. Any metal which can be quickly melted by self-generated heat can be used in the fuse element 2, for example, a low melting point metal such as Pb-free solder having Sn as a primary constituent may be used.
Additionally, the fuse element 2 may include a low melting point metal and a high melting point metal. For example, as shown in
The low melting point metal layer 2a is preferably a metal having Sn as a primary constituent, or a material commonly known as “Pb-free solder”. The melting point of the low melting point metal layer does not necessarily need to be higher than the temperature of a reflow oven and may have a melting point of approximately 200° C. The high melting point metal layer 2b is a metal layer laminated on the surface of the low melting point metal layer 2a and, for example, is Ag, Cu, or a metal having one of these as a primary constituent, and has a high melting point so as not to melt even in the case of mounting the fuse device 1 by using a reflow oven.
By laminating the high melting point metal layer 2b as an outer layer to the low melting point metal layer 2a, which is an inner layer, even in the case of reflow temperature exceeding the melting point of the low melting point metal layer 2a, the fuse element 2 is not blown out; furthermore, leakage of low melting point metal can be suppressed and the shape of the fuse element 2 can be maintained. Thus, the fuse device 1 can be efficiently mounted by reflow.
Furthermore, the fuse element 2 is not blown out by self-generated heat while a predetermined rated current flows therethrough. When a current exceeding the rating flows, the fuse element 2 melts and a current path of a circuit connected via the fuse device 1 is interrupted. At this time, in the fuse element 2, erosion of the high melting point metal layer 2b by the low melting point metal layer 2a causes the high melting point metal 2b layer to melt at a temperature lower than the melting point thereof. Therefore, the fuse element 2 can blow out rapidly by using erosive action of the low melting point metal layer 2a on the high melting point metal layer 2b.
Furthermore, because the fuse element 2 has a structure in which the high melting point metal layer 2b is laminated on the low melting point metal layer 2a, the melting temperature thereof can be significantly reduced from that of conventional fuses made of high melting point metal, such as chip fuses. Therefore, in comparison with fuses such as chip fuses of the same size, cross-sectional area can be increased and current rating can be significantly improved in the fuse element 2. Furthermore, the fuse element 2 can be made smaller and thinner than conventional chip fuses having the same rating, and has excellent rapid blowout properties.
Still further, the fuse element 2 can improve tolerance to surges (pulse tolerance), in which an abnormally high voltage is momentarily applied, in an electrical system in which the fuse device 1 is incorporated. For example, the fuse element 2 does not blow out even in the case of a current of 100 A flowing for a few milliseconds. This is because a large current flowing for a very short duration flows across the surface of a conductor (skin effect), and because the high melting point metal layer 2b comprising an Ag plating having a low resistance is provided as an outer layer in the fuse element 2, a current caused by a surge can be easily allowed to flow and blowout due to self-generated heat can be prevented. Therefore, the fuse element 2 can significantly improve surge tolerance in comparison to conventional fuses made from solder alloys.
The fuse element 2 can be manufactured by using plating techniques to film-form the high melting point metal layer 2b on the surface of the low melting point metal layer 2a. For example, the fuse element 2 can be efficiently manufactured by plating Ag to a long solder foil which can be easily used by cutting according to size at the time of use.
Additionally, the fuse element 2 may be manufactured by bonding a low melting point metal foil and a high melting point metal foil together. For example, the fuse element 2 may be manufactured by pressing a rolled sheet of solder foil between two rolled sheets of Cu foil or Ag foil. In this case, a low melting point metal foil that is softer than the high melting point metal foil is preferably selected. Doing this allows for compensation of unevenness in thickness so that the low melting point metal foil and the high melting point metal foil can be bonded together without voids. In addition, because film thickness is reduced by pressing, the low melting point metal foil may be made thicker beforehand. It is preferable to cut ends off and reshape in cases of the low melting point metal foil protruding from ends of the fuse element due to pressing.
Additionally, in the fuse element 2, thin film-forming techniques such as vapor deposition and other known laminating techniques may be used to laminate the high melting point metal layer 2b onto the low melting point metal layer 2a.
Furthermore, in the fuse element 2, the low melting point metal layer 2a and the high melting point 2b may be formed in multiple alternating layers. In this case, either the low melting point metal layer 2a or the high melting point metal layer 2b may be the outermost layer.
Furthermore, in the fuse element 2, in cases of the high melting point metal layer 2b being the outermost layer, an additional antioxidation film may be formed on this outermost layer of the high melting point metal layer 2b. By covering the outermost layer of the high melting point metal layer 2b with an additional antioxidation film, for example, even in cases of the high melting point metal layer being a Cu plating or a Cu foil, Cu oxidation can be prevented. Therefore, by preventing situations in which Cu oxidation extends blowout time, the fuse element 2 can rapidly blow out.
The case 3 housing the fuse element 2 comprises, for example, as illustrated in
The case 3 is formed by placing the fuse element 2 into the enclosure 5 via the open top side and by sealing with the cover 6. In the case 3, by sealing the enclosure 5 with the cover 6, the lead-out port 7 for leading out the fuse element 2 is formed. By leading both ends out of the fuse element 2 through the lead-out port 7, the fuse element 2 is supported in a bridge-like manner in a housing space 8 in the case 3.
When a rate exceeding current flows through the fuse element 2, which is supported on both ends by the lead-out port 7, for example, portions thereof central in relation to the direction of current flow are melted by self-generated heat (Joule heat) to interrupt a current path of the circuit in which the fuse device 1 is incorporated.
In the fuse device 1, a shield 10 is provided within the housing space 8 of the case 3 to shield an inner wall surface 8a leading to the lead-out port 7 from scattered melted material of the fuse element 2. The shield 10 can be provided on the inner wall surface 8a of the case, the fuse element 2 or both.
A shield 10 according to a first embodiment is a projection 11 provided on the inner wall surface 8a of the case 3 forming the housing space 8. As illustrated in
By doing this, as illustrated in
Furthermore, within the housing space 8, because the projection 11 is situated so as to shield the inner wall surface 8a spanning between the pair of lead-out ports 7, 7 which support the fuse element 2 in a bridge-like manner, the melted conductor 13 can be prevented from being continuously deposited on the inner wall surface 8a spanning between the lead-out ports 7, 7. Therefore, the fuse device 1 can prevent a state in which both ends of the blown out fuse element 2 are short-circuited by the melted conductor 13 being continuously deposited on the inner wall surface 8a spanning between the lead-out ports 7, 7.
The projection 11 is preferably formed on the inner wall surface 8a so as to surround the entire perimeter of the fuse element 2. By forming the projection 11 so as to surround the entire perimeter, even in the case of the melted conductor 13 being scattered in all directions, the projection 11 shields the inner wall surface 8a spanning between the lead-out ports 7, 7 and short-circuiting of both ends of the blown out fuse element 2 can be prevented.
Additionally, the projection 11 is preferably formed in a location separated from the blowout location 12 of the fuse element 2. In the case of the projection 11 being formed in the vicinity of the blowout location 12, the other surface 11b is not adequately shielded by the surface 11a and the melted conductor 13 scattering from the blowout location 12 might be deposited thereon. Because the fuse element 2, in most cases, blows out in a central location with respect to the longitudinal direction, the projection 11 is preferably formed closer to the lead-out port 7 than the central location with respect to the longitudinal direction of the fuse element 2.
By doing this, in the projection 11, the melted conductor 13, scattering due to blowout of the fuse element 2, is deposited on the surface 11a which faces the blowout location 12 and is not deposited on the surface 11b which is on the back side of the surface 11a.
Furthermore, providing the projection 11 near the lead-out port 7 can assuredly prevent deposition of the melted conductor 13 on the other surface 11b and can prevent a state in which both ends of the blown out fuse element 2 are short-circuited by the melted conductor 13 being continuously deposited on the inner wall surface 8a spanning between the lead-out ports 7, 7.
Additionally, at least one of the projection 11 may be provided; however, as illustrated in
A shield 10 according to a second embodiment is a projecting section 16 provided on the fuse element 2. As illustrated in
In so doing, as illustrated in
Furthermore, within the housing space 8, because the projecting section projects towards the inner wall surface 8a spanning between the pair of lead-out ports 7, 7 which support the fuse element 2 in a bridge-like manner, the melted conductor 13 can be prevented from being continuously deposited on the inner wall surface 8a spanning between the lead-out ports 7, 7. Therefore, in the fuse device 1, by preventing the melted conductor 13 from being continuously deposited on the inner wall surface 8a spanning between the lead-out ports 7, 7, a state in which both ends of the blown out fuse element 2 are short-circuited can be prevented.
The projecting section 16, as illustrated in
In the fuse element 2 illustrated in
In addition, the projecting section 16, as in the projection 11, is preferably provided in a location separated from the blowout location 12 of the fuse element 2. In the case of the projecting section 16 being provided in the vicinity of the blowout location 12, the inner wall surface 8a of the case 3 is not adequately shielded from the blowout location and a short-circuit caused by scattering of the melted conductor 13 might occur between the lead-out ports 7, 7. Because the fuse element 2, in most cases, blows out in a central region with respect to the longitudinal direction, the projecting section 16 is preferably provided at a location nearer to the lead-out ports 7, 7 than the central region relative to the longitudinal direction of the fuse element 2.
By doing this, because the projecting section 16 protrudes in the direction in which the melted conductor 13 scatters from the fuse element 2, the melted conductor scattering from blowout of the fuse element 2 is deposited thereon and is prevented from being deposited on areas of the inner wall surface 8a blocked by the projecting section 16.
Furthermore, providing the projecting section 16 in the vicinity of the lead-out port 7 prevents the melted conductor 13 from being deposited in the vicinity of the lead-out port 7 and also prevents a state in which both ends of the blown out fuse element 2 are short-circuited by the melted conductor 13 being continuously deposited on the inner wall surface 8a spanning between the lead-out ports 7, 7.
Additionally, in the projecting section 16, a plurality of the first projecting sections 16a protruding vertically from the blowout location 12 of the fuse element 2 and the second projecting sections 16b protruding in the width direction from the blowout location 12 of the fuse element 2 may be formed. Forming the plurality of the projecting sections 16 ensures prevention of deposition of the melted conductor 13 onto portions of the inner wall surface 8a blocked by the projecting section 16, even in cases of the melted conductor 13 scattering widely. If continuous deposition of the melted conductor 13 between the lead-out ports 7, 7 is prevented by at least one projecting section 16, a state in which both ends of the blown out fuse element 2 are shorted can be prevented.
As a shield 10, the fuse device 1 may include both the above mentioned projection 11 provided on the inner wall surface 8a of the case 3 and the projecting section 16 provided on the fuse element 2.
For example, as illustrated in
The projection 11 is situated so as to shield the inner wall surface 8a on the side of the cover 6 spanning between the pair of lead-out ports 7, 7 which support the fuse element 2 in a bridge-like manner. The projection 11 has a surface 11a which faces the blowout location 12 of the fuse element 2 and an other surface 11b on the opposite side which is blocked by the surface 11a and thereby shielded from the blowout location 12. Therefore, as illustrated in
Furthermore, the projecting section 16 is provided from the blowout location 12 of the fuse element 2 to the lead-out port 7 and projects towards the upper side of the case 3 which is perpendicular to the direction of current flow. Thus, within the housing space 8, the projecting section protrudes from the blowout location 12 of the fuse element, and at least a portion of the inner wall surface 8a of the enclosure 5 between the lead-out ports 7, 7 of the case 3 are blocked by portions of the projecting section 16 shielded from the blowout location 12.
By doing this, as illustrated in
As mentioned in the above, the fuse element 2 of the fuse device 1 is formed as a laminated structure having an inner and an outer layer, and a structure can be used in which the low melting point metal layer 2a, as the inner layer, is covered by the outer layer comprising the high melting point metal layer 2b (
As illustrated in
Furthermore, in the terminal 22, the edge surface 21 protrudes from the connecting section 26. In so doing, in the fuse element 2, even in the case of the connecting section 26 being connected to the land 24, contact with the bonding material 25 of the edge surface 21 is prevented. Therefore, when the fuse device 1 is thermally mounted to the printed substrate 23, such as by using reflow, the exposed low melting point metal layer 2a on the edge surface 21 is drawn in by contacting the melted bonding material 25 and thereby can be prevented from leaking.
Thus, because the fuse element 2, being formed in an elongated shape, is cut to a predetermined length, the inner layer of the low melting point metal layer 2a is exposed on the edge surface 21. Therefore, because the low melting point metal layer 2a melts when the fuse device 1 is thermally mounted, as illustrated in
Accordingly, in the fuse element 2, by the edge surface 21 protruding from the connecting section 26 which connects to the land 24 via the bonding material 25, the low melting point metal layer 2a does not contact the bonding material 25 thereby preventing low melting point metal leakage. This prevents shape change and maintains the predetermined rating, blowout properties and electrical insulation.
The edge surface 21 of the terminal 22 may be made to protrude from the connecting section 26 by bending the fuse element 2 at least one time. By bending the edge surface 21 at least once from the connecting section 26, even in the case of the connecting section 26 being connected to the land 24, the low melting point metal layer 2a can be prevented from contacting the bonding material 25; furthermore, even in the case of the bonding material 25 extending across the terminal 22 to the edge surface 21, leakage of low melting point metal can be suppressed to a minimal amount by a bent section 28.
In addition, in the fuse element 2, the edge surface 21 may be bent multiple times from the connecting section 26 to separate the edge surface 21 from the bonding material 25. For example, as illustrated in
Furthermore, in the fuse element 2, as illustrated in
It should be noted that, in the fuse element 2, as illustrated in
The blowout section 30 can be formed by, for example, along with forming the fuse element 2 in an approximately rectangular shape, punching out or ablating, among other methods, to remove a portion which is central relative to the longitudinal direction. Furthermore, as illustrated in
The fuse element 2, other than the plate shape, may also be formed in a wire-like shape, as illustrated in
1 fuse device, 2 fuse element, 2a low melting point metal layer, 2b high melting point metal layer, 3 case, 5 enclosure, 6 cover, 7 lead-out port, 8 housing space, 10 shield, 11 projection, 12 blowout location, 13 melted conductor, 16 projecting section, 21 edge surface, 22 terminal, 23 printed substrate, 24 land, 25 bonding material, 26 connecting section, 27 solder resist layer, 28 bent section, 30 blowout section
| Number | Date | Country | Kind |
|---|---|---|---|
| JP2013-177071 | Aug 2013 | JP | national |
| JP2014-165154 | Aug 2014 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2014/072351 | 8/27/2014 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2015/030023 | 3/5/2015 | WO | A |
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| Number | Date | Country | |
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| 20160172143 A1 | Jun 2016 | US |
