Abstract
Current-limiting fuse comprising an electrically insulating housing with walls surrounding an interior space, with a first opening and with a second opening opposite to said first opening, and an integrally formed electrical conductor element extending from a first terminal area outside said housing, across said first opening, across said interior space, across said second opening and to a second terminal area outside said housing, wherein said conductor element comprises a melting section of reduced cross-section, said melting section being located in said interior space and being configured to melt, when a predefined maximum allowable electrical current in the conductor element is exceeded, and wherein a first sealing section of the conductor element seals said first opening and wherein a second sealing section of the conductor element seals said second opening. The invention is further directed to a method of manufacturing the current-limiting fuse.
Claims
1. A current-limiting fuse comprising: an electrically insulating housing with walls surrounding an interior space, with a first opening and with a second opening opposite to said first opening, and an integrally formed electrical conductor element extending from a first terminal area outside said housing, across said first opening, across said interior space, across said second opening and to a second terminal area outside said housing, wherein said conductor element comprises a melting section of reduced cross-section, said melting section being located in said interior space and being configured to melt, when a predefined maximum allowable electrical current in the conductor element is exceeded, and wherein a first sealing section of the conductor element seals said first opening and wherein a second sealing section of the conductor element seals said second opening.
2. The current-limiting fuse according to claim 1, wherein said conductor element is a sheet metal.
3. The current-limiting fuse according to claim 1, wherein said first terminal area and said second terminal area are coplanar.
4. Current limiting The current-limiting fuse according to claim 1, wherein said melting section is mechanically self-supporting across said interior space.
5. The current-limiting fuse according to claim 1, wherein the cross-section of said first sealing section of the conductor element corresponds in form and dimension to the cross-section of said first opening and/or wherein the cross-section of said second sealing section of the conductor element corresponds in form and dimension to the cross-section of said second opening.
6. The current-limiting fuse according to claim 1, wherein said second sealing section of the conductor element has a protrusion projecting towards said interior space, which protrusion is supported on a contour section of said second opening.
7. The current-limiting fuse according to claim 1, wherein said walls of said housing, said first sealing section of said conductor element and said second sealing section of said conductor element together form a dust-tight enclosure.
8. The current-limiting fuse according to claim 1, wherein the cross-section of said second opening is larger than the cross-section of said first opening.
9. The current-limiting fuse according to the claim 1, wherein at least one groove facing towards said interior space is formed into said housing.
10. The current-limiting fuse according to claim 1, wherein the geometric form of said interior space is defined as the negative of an imaginary core, which is removable in one piece through the second opening.
11. The current-limiting fuse according to claim 1, wherein said housing is integrally formed.
12. The current-limiting fuse according to claim 1, wherein the current-limiting fuse consists of said housing and said conductor element.
13. A method of manufacturing a current-limiting fuse according to any one of the claim 1, said method comprising: a) providing an integrally formed electrically insulating housing with walls surrounding an interior space, with a first opening and with a second opening opposite to said first opening, b) providing an electrically conducting, integrally formed conductor element comprising a melting section of reduced cross-section, c) introducing the conductor element through said first opening or through said second opening, thus far that said melting section is located in the interior space, d) bending said conductor element to form a first terminal area and a second terminal area outside said housing, thereby sealing said first opening by a first section of said conductor element and sealing said second opening by a second section of said conductor element.
14. The method according to claim 13, wherein said conductor element provided in step a) is a sheet metal having a protrusion embossed, wherein the sheet metal has a first bending edge delimiting said first terminal area, wherein the sheet metal has a second bending edge spaced from said protrusion by a distance allowing a tight fit of the bending edge and the protrusion between opposite inner contours of said second opening, wherein the sheet metal is flat in the region between said second bending edge and the end opposite to the first terminal area, wherein the step c) of introducing the conductor element comprises feeding said flat region of the conductor element from the interior space through said first opening, wherein the step d) comprises establishing a third bending edge delimiting said second terminal area and then establishing a fourth bending edge in proximity to said first opening.
15. The current-limiting fuse according to claim 9, wherein said groove is formed into a bottom side of the housing, said bottom side being adjacent to said first and said second terminal area.
Description
[0063] FIG. 1 shows schematically and simplified, a cross-section through a current-limiting fuse 20 according to the invention. The fuse comprises conductor element 1, which is displayed diagonally hatched, and a housing 2, which is displayed with cross-hatching. The housing is an electrically insulating housing 2 with walls surrounding an interior space 6. The housing has a first opening 7 and a second opening 8 opposite to the first opening. The conductor element 1 is an integrally formed electrical conductor element. A first terminal area 3 and a second terminal area 4 are outside the housing. A melting section 5 of reduced cross-section, here shown as reduced thickness, forms a middle section of the conductor element. The melting section is configured to melt, when a predefined maximum allowable electrical current in the conductor element is exceeded. The reduction of the cross-section may not only be achieved by a reduction in thickness, but also by reductions of the cross section of the cross-section not visible in this figure. The conductor element is formed as one piece that extends from said first terminal area, across the first opening 7 of the housing, across the interior space 6 of the housing, across the second opening 8 of the housing and finally to the second terminal area 4. The openings of the housing are sealed by sections of the conductor element. A first sealing section 9 of the conductor element seals the first opening 7. A second sealing section 10 of the conductor element seals the second opening 9. In the version shown here, the first sealing section simply fills the whole opening 7. The second opening 8 is larger than the first opening 7. The second opening is covered by the second sealing section 10. In the version shown here, the sealing section of the conductor element is held in this position due to the specific geometry of the conductor element, which prevents a movement in up/down direction, wherein up and down refer to the directions in the present figure.
[0064] FIG. 2.a) shows a perspective view of an embodiment of the current-limiting fuse with a specific design of the housing 2 and the conductor element 1. The housing, as well as the complete fuse, have an approximately cuboid shape. The housing has chamfered edges. The housing has two larger extensions, a width and a length, and a smaller extension, in this case the height. A protrusion 11 is embossed into the conductor element 1, which is in this embodiment formed as a sheet metal. The function of this protrusion will be explained further in context of the next figure. The terminal areas 3 and 4 are visible in FIG. 2.a). FIG. 2.b) shows the same fuse as FIG. 2.a) but turned upside down in a position, as it could be placed on a printed circuit board. The embodiment shown here is formed as an SMD-fuse suitable for reflow soldering.
[0065] FIG. 3.a) to 3.d) show views of the same embodiment as shown in FIG. 2.a) and FIG. 2.b). FIG. 3.c) illustrates the directions of view and the position of the cutting planes of the views according to FIGS. 3.a), 3.b) and 3.d). FIG. 3.a) shows a side view onto the housing 2 alone, i.e. without the conductor element. The viewing direction is indicated by the arrow A in FIG. 3.c), which indicates a longitudinal direction of the fuse. A view into the second opening 8 of the housing is possible here. A recess 14 is formed proximate to a contour of the opening 8. The recess is formed near the middle of the opening and corresponds in form and dimension to the protrusion 11 of the conductor element 1, see FIG. 3.b) and FIG. 3.c. The combination of the recess 14 and the protrusion 11 lead to a form-fitting connection preventing with very simple means unwanted relative movement between the conductor element and the housing. Two grooves 13 of trapezoidal cross-section are formed on the bottom side of the interior space of the housing. The two grooves extend in longitudinal direction. FIG. 3.b) shows a cross-section along a middle plane of the fuse. The view direction of this figure is indicated by arrow B in FIG. 3.c), which corresponds to a lateral direction of the fuse. The conductor element 1 leads across the housing 2 and forms terminal areas 3 and 4 outside the housing. The opening of the housing shown on the right side in this figure is a rectangular opening, which is completely filled by the thickness of the conductor element, such that the opening is sealed. The conductor element forms a first sealing section 9 in this region. The larger opening of the housing, shown on the left side in this figure, is covered by the second sealing section 10. The protrusion 11 together with the angled section at the upper side of the second sealing section 10 and together with the angled section adjacent to the first terminal area 3 hold the sealing section in place with respect to a lateral and a height position of the housing. The melting section 5 of the conductor element is formed as two parallel strips with significantly reduced width as compared to the width of the conductor element before and after the melting section 5. In the embodiment shown, the cross-section of conducting material in the melting section is reduced to approx. 15% of the full cross-section. FIG. 3.d) shows a cut-away view from a top-direction as indicated by arrow D in FIG. 3.c). The cutting plane is a horizontal plane, lying just below the ceiling of the interior space of the housing. The conductor element 1 is seen from top. On the left side in the figure, the conductor element 1 has full width and full cross-section. A cut-out in the middle and cut-outs on both sides reduce the conducting element to two parallel strips, which form the melting section 5 of the conductor element. Each of the two strips runs parallel to one of the grooves 13. On the right side of the figure the cutting plane crosses a wall of the housing. As can be seen in FIG. 3.b), the interior space of the housing has a funnel-shaped form in this region.
[0066] FIG. 4.a) shows an embodiment of the current-limiting fuse corresponding to the embodiment in FIG. 1. The conductor element 1 as well as its melting section 5 extend diagonally across the interior space of the housing. The first 3 and second 4 terminal area are coplanar, i.e. the lie in a common imaginary plane 12, indicated by a dash-dotted line in the present cross-section. This embodiment is suitable as SMD-fuse.
[0067] FIG. 4.b) shows a variant of the embodiment having two openings of approximately equal size. The conductor element runs horizontally across the interior space. The terminal parts are bent to the same side, such that also in this variant, both terminal areas 3, 4 lie in a common imaginary plane 12.
[0068] FIG. 4.c) shows a further variant, this time with terminal parts bent to different sides of the fuse. This way, terminal areas 3, 4 are defined on opposite sides of the fuse, such that it can be used like a cartridge fuse.
[0069] FIG. 5.a) shows the state after inserting a conductor element 1 of preliminary form into the housing 2. The bending edges on the left side, as well as the embossed protrusion may be prepared before the insertion step. In the state shown, both openings of the housing are sealed already. A flat part of the sheet metal forming the conductor element protrudes by a distance d1 out of the housing on the right side in the figure.
[0070] FIG. 5.b) shows the state after an additional bending step. The position of the further bending edge and the angle may be specified by the distances d2, d3, d4 and the angle α, see table below.
[0071] FIG. 5.c) shows an optional intermediate state after a further bending step and before bringing the second terminal into its final position on the bottom side of the housing. A further bending edge is produced in close proximity to the smaller opening of the housing on the right side in the present figure. The geometry is specified by the distances d5 and d6 as well as the angle β, see table below.
[0072] As an example, the following distances and angles may be applied:
TABLE-US-00001 d1 d2 d3 d4 d5 d6 (mm) (mm) (mm) (mm) (mm) (mm) α β 3.91 2.01 2.07 2.2 1.53 2.19 90º 130º
[0073] Angle α may be deliberately made slightly smaller than a right angle, e.g. 0.5° to 3° smaller, such that a press-fit is achieved once the terminal part is in its final position on the lower side of the fuse.
List of Reference Signs
[0074] 1 conductor element
[0075] 2 housing
[0076] 3 first terminal area
[0077] 4 second terminal area
[0078] 5 melting section
[0079] 6 interior space
[0080] 7 first opening (of the housing)
[0081] 8 second opening (of the housing)
[0082] 9 first sealing section (of the conductor element)
[0083] 10 second sealing section (of the conductor element)
[0084] 11 protrusion (of the conductor element)
[0085] 12 imaginary plane (comprising both terminal areas)
[0086] 13 groove
[0087] 14 recess
[0088] 20 current-limiting fuse
[0089] d1, d2, d3, d4, d5, d6 dimensions used for defining the bending process according to an embodiment [0090] α, β angles used for defining the bending process according to an embodiment
