Patent Application
20180053617
The field of the invention relates generally to electrical fuse devices and methods of manufacturing electrical fuses, and more specifically to dual-element, time-delay fuses and methods of manufacturing the same.
Fuses are widely used as overcurrent protection devices to prevent costly damage to electrical circuits. Fuse terminals typically form an electrical connection between an electrical power source or power supply and an electrical component or a combination of components arranged in an electrical circuit. One or more fusible links or elements, or a fuse element assembly, is connected between the fuse terminals, so that when electrical current flow through the fuse exceeds a predetermined limit, the fusible elements melt and open one or more circuits through the fuse to prevent electrical component damage.
So-called dual-element, time-delay fuses are known that include a high overcurrent fuse element and a low overcurrent fuse element inside a housing of the fuse. The low overcurrent fuse element includes a device, often referred to in the art as a fuse trigger, that will electrically open a circuit path through the low overcurrent fuse element during an overload condition after a specified amount of time. Such fuses are effective to prevent electrical overload conditions from passing to upstream fuses in an electrical power system that would otherwise not cause the high overcurrent fuse element to open, and facilitate selective coordination of overcurrent protection devices to ensure reliability of electrical power systems supplying power to vital loads.
Conventional designs for trigger devices in dual-element, time-delay fuses present a number of challenges from a manufacturing perspective, and improvements are desired.
Non-limiting and non-exhaustive embodiments are described with reference to the following Figures, wherein like reference numerals refer to like parts throughout the various drawings unless otherwise specified.
Exemplary embodiments of dual element, time delay fuses are described herein that beneficially may be manufactured from a reduced number of parts, with lower cost and improved reliability relative to conventional dual element, time delay fuses. Method aspects will be in part apparent and in part explicitly discussed in the following description.
Certain types of dual element, time delay fuses include helical spring-loaded trigger mechanisms that typically involve a relatively high number (e.g., eight) component parts that are typically assembled by hand. In electrical overcurrent conditions, the helical spring, which may be loaded in tension, causes a contact member to become dislodged when a fusible alloy is sufficiently heated by electrical current. The heat generated melts and weakens the mechanical connection, established by the fusible alloy, of the contact element in the trigger assembly. While functionally effective to open a circuit through the fuse in a low overcurrent condition, the hand assembly of the components is relatively difficult, time consuming and expensive to complete. Hand assembly of the components also tends to present undesirable performance variation and reliability issues over a large number of fuses. Lower cost and more readily manufacturable trigger mechanisms via automated techniques are desired.
In the illustrated example, the housing 102 is provided in the form of a substantially cylindrical, elongated and hollow tube. It is recognized, however, that other shapes of fuse housings may likewise be utilized, including but not necessarily limited to rectangular housings, in other embodiments as desired. Further, in the illustrated example, the terminal elements 108, 110 are provided in the form of end caps coupled to the respective ends 104, 106 of the housing 102 and extend in respectively opposite directions to one another, although other terminal arrangements and orientations including knife blade contacts, terminal blades and the like may instead be employed in alternative embodiments at different locations on the housing without limitation so long as the terminal elements 108, 110 effectively facilitate connections to line or load circuitry in an electrical power system.
In the example shown, the terminal elements 108, 110 are of a different shape or configuration relative to one another, with the end cap 108 including a rejection feature that cooperates with a complementary feature of a fuse holder or fuse block to ensure that that only a compatible fuse may be connected to the fuse holder or fuse block, while the end cap 110 does not include a rejection feature. In other embodiments, however, the terminal elements may instead be of the same shape or configuration.
In a contemplated example, the fuse 100 may be a Fusetron Energy Efficient, Dual-element, Class RK5 Time-delay Fuse of Bussmann by Eaton, St Louis, Mo. Variations are, of course, possible however, and the concepts below may be utilized to provide similar or different fuses, in the same or different class than RK5, than the aforementioned Fusetron fuse.
Exemplary geometry of the high overcurrent fusible elements 122, 124 is illustrated in
As best seen in
The first major surface 136 (
Unlike the first major surface 134, however, the second major surface 136 of the substrate material 132 is not provided with a conductive layer and as a result the nonconductive substrate material 132 is sometimes referred to as a single-sided circuit board substrate. The single-sided circuit board material shown and described is expressly contrasted with double-side circuit board substrates having conductive layers on both sides. In some embodiments, a double-sided circuit board substrate may be obtained and the conductive material on one side may be removed to provide the single-side embodiment, or in other cases, a substrate material without any conductive material may be obtained and may be metallized on only one of the major surfaces. Regardless, the single-sided circuit board material may be prefabricated as mentioned above to simplify assembly of the low overcurrent fusible element 130 described herein and reduce costs.
On the second major surface 136 of the nonconductive substrate material 132, a releasable conductive element 150 extends across and electrically interconnects the first conductive portion 140 and a second conductive portion 142 on the first major surface 134. The releasable conductive element 150 may be, for example, a copper alloy having a shape memory that is attached to the nonconductive substrate material 132 in a first configuration shown in solid lines in
In response to a low overcurrent condition, the releasable conductive element 150 releases from the first conductive portion 140 on the major s surface 134 and assumes a second position shown in phantom lines in
To facilitate the releasable connection and low overcurrent fusible action described, the nonconductive substrate material 132 includes a number of openings 152, 154, 156 and 158 extending completely through the nonconductive substrate material 132 from the first major surface 134 to the second major surface 136. The openings 152, 154, 156 and 158 in the illustrated example are elongated slots at respectively spaced apart locations. The openings 152 and 154 are shown as a first pair of openings that are defined in and surrounded by the first conductive portion 140 (
A first end 160 of the releasable conductive element 150 is inserted into the opening 154 from the second major surface 136 and the first end 160 is connected to the first conductive portion 140 on the major surface 134 by a low melting point fusible alloy 164 via, for example, a wave soldering process. The low melting point fusible alloy 164 may be an alloy such as Sn 65, Bi 35, Pb 0.01 solder in one embodiment, although other suitable alloys are possible.
The second end 162 of the releasable conductive element 150 is inserted into the opening 156 from the second major surface 136 and the second end 162 is connected to the second conductive portion 142 on the major surface 134 by a high melting point temperature alloy 166 via, for example, a wave soldering process. As seen in
As seen in
When assembled as described, the releasable conductive element 150 is soldered in place and anchored at both ends 160, 162 to the conductive portions 140, 142 of the nonconductive substrate material 132. When connected to an energized electrical power system, electrical current flow flows from the first terminal element 108 (
When subjected to high overcurrent conditions, including but not necessarily limited to a short circuit condition, the high overcurrent elements 122, 124 open at the weak spots 128 before the low overcurrent fusible element 130 can physically respond. Opening of the elements 122, 124 protects circuitry connected to the fuse from an otherwise damaging high overcurrent condition.
When subjected to a low overcurrent condition (i.e., a comparatively lower current magnitude than the high current condition but sustained over a predetermined period of time), the low temperature melting point alloy 164 (
Relative to existing trigger devices serving similar purposes to provide low overcurrent protection, the low overcurrent fusible element 130 is comparatively simpler and easier to fabricate at reduced cost with improved reliability. For example considering the conventional trigger assembly noted above including 8 component parts, the low overcurrent fusible element 130 essentially involves two pre-fabricated components in contemplated embodiments, namely the releasable spring-conductor 150 that is mounted to the small, single-sided circuit board substrate described.
Also considering that the conventional trigger assembly noted above including 8 component parts is hand assembled by 8 different persons, the assembly of the low overcurrent fusible element 130 is much more amenable to automation at lower cost with improved quality and reliability.
Because the releasable element 150 in the low overcurrent fusible element 130 is part of the current path through the fuse 100, automated testing of the fuse 100 is possible to ensure that the releasable element 150 has been correctly installed by passing current through the fuse. If the releasable element 150 is missing or not soldered correctly, no current will pass through the fuse and assembly issues can be simply and reliably detected and corrected. In contrast in the conventional trigger assembly noted above including 8 component parts, the coil spring is not part of the current path and is not amenable to such testing to detect a presence and proper installation of the coil spring.
The benefits and advantages of the inventive concepts disclosed are now believed to have been amply illustrated in relation to the exemplary embodiments disclosed.
An embodiment of an electrical fuse has been disclosed including: a housing; at least one high overcurrent fusible element and a low overcurrent fusible element connected to one another inside the housing. The low overcurrent fusible element includes: a nonconductive substrate material including a first major surface and a second major surface opposite the first major surface; a conductive layer provided on the first major surface of the nonconductive substrate material, the conductive layer defining a first conductive portion and a second conductive portion separated from one another; and a releasable conductive element extending on the second major surface of the nonconductive substrate material, the releasable conductive element including a first end electrically connecting to the first conductive portion on the first major surface and a second end electrically connecting to the second conductive portion on the first major surface.
Optionally, the nonconductive substrate material may include a first opening extending through the nonconductive substrate material from the first major surface to the second major surface, and the first end of the releasable conductive element extends in the first opening. The fuse may also include a low melting point fusible material electrically connecting the first end of the releasable conductive element and the first conductive portion. The nonconductive material may include a second opening spaced from the first opening in the nonconductive substrate material, and the second opening may extend through the nonconductive substrate material from the first major surface to the second major surface. The electrical fuse may also further include a high melting point fusible material extending across the second opening, and the second end of the releasable conductive element in the second opening, and wherein the high melting point fusible material electrically connects the second end of the releasable conductive element and the second conductive portion.
As further options, the nonconductive substrate material may include a first opening, a second opening, a third opening, and a fourth opening respectively extending through the nonconductive substrate material from the first major surface to the second major surface at respectively spaced apart locations. The first conductive portion may extend around the first opening and the second opening, and the second conductive portion may extend around the third opening and the fourth opening. The electrical fuse may include a high melting point fusible material applied over the first opening and a low melting point fusible material applied over the second opening. A first end of the releasable conductive element may be attached to the low melting point fusible material through the second opening. The electrical fuse may further include a high melting point fusible material applied over each of the third opening and the fourth opening. A second end of the releasable conductive element may be attached to the high melting point fusible material through the third opening.
The releasable conductive element may be a strip of conductive shape memory material. The strip of conductive shape memory material may be a copper alloy.
The at least one high overcurrent fusible element may include a strip of material defining a plurality of weak spots. The at least one high overcurrent fusible element may also include a pair of high overcurrent fusible elements, with the low overcurrent fusible element connected in between the first and second high overcurrent fusible elements in the housing.
The housing of the electrical fuse may be substantially cylindrical. The electrical fuse may also include first and second terminal elements coupled to the housing, and the at least one high overcurrent fusible element and the low overcurrent fusible element may define a circuit path between the first and second terminal elements. The first and second terminal elements may include first and second end caps. The conductive layer may include copper.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
