CA2927552A1

CA2927552A1 - Electrical fastener assembly with thermal fuse

Info

Publication number: CA2927552A1
Application number: CA2927552A
Authority: CA
Inventors: John Michael BRETT; John Oliver Collins
Original assignee: GE Aviation Systems Ltd
Current assignee: GE Aviation Systems Ltd
Priority date: 2013-10-25
Filing date: 2013-10-25
Publication date: 2015-04-30
Also published as: CN105637609A; WO2015059435A1; CN105637609B; EP3061112A1; EP3061112B1; JP2016540343A

Abstract

An electrical fastener assembly (24) for coupling first and second electrically conductive terminals (28,32) includes a fastener coupling the first and second terminals to each other, and a meltable element (42). The meltable element (42) melts in response to heat to disrupt, or break, the conductive path in response to an overheating or over-temperature condition.

Description

ELECTRICAL FASTENER ASSEMBLY WITH THERMAL FUSE
BACKGROUND OF THE INVENTION
Electrical power systems, such as those found in an aircraft power distribution system, employ electrical bus bars for delivering power from electrical power sources to electrical loads. In the event of an electrical short or other failure condition, high voltage components may be shunted across unintended electrical contacts, resulting in high current flow at the failure of the power distribution system. The high current flow, in turn, generates excessively high levels of heat, and may lead to possible electrical or thermal damage.
BRIEF DESCRIPTION OF THE INVENTION
In one embodiment, the invention relates to an electrical fastener assembly for coupling first and second terminals, and includes a fastener coupling the first and second terminals to each other, an electrically conductive, meltable element electrically coupling the first terminal and second terminal prior to melting, and a separator having a portion located between the first and second terminals and maintaining them physically separated. A conductive path is defined by at least the first terminal, second terminal, and meltable element, with the meltable clement melting in response to heat along the conductive path to disrupt the conductive path in response to an overheating condition while the separator maintains the first and second terminals physically separated.
In another embodiment, the invention relates to an electrical fastener assembly for coupling first and second terminals, and includes a fastener coupling the first and second terminals to each other, a meltable retainer providing retaining force to secure the fastener prior to melting, and a biasing element having a portion located between the first and second terminals, and applying a biasing force opposite of the retaining force. A conductive path is defined by at least the first terminal and second terminal, with the meltable retainer melting in response to heat, releasing the biasing force of the biasing element to physically separate the first and second terminals, and to disrupt the conductive path in response to an overheating condition.

In yet another embodiment, the invention relates to an electrical overload protection apparatus including a first terminal including a threaded stud, a second terminal having an opening receiving the threaded stud, a nut threadably received on the threaded stud and securing the second terminal onto the first terminal, and a washer having an opening receiving the threaded stud and positioned between the first and second terminal, and having an electrically conductive, meltable element. A
conductive path is defined by at least the first terminal, second terminal, and meltable element, with the meltable element melting in response to heat along the conductive path to disrupt the conductive path in response to an overheating condition.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 is a top down schematic view of the aircraft and power distribution system in accordance with one embodiment of the invention.
FIG. 2 is a perspective view of an electrical fastener assembly in accordance with one embodiment of the invention.
FIG. 3 is a perspective view of a solder washer assembly in accordance with the first embodiment of the invention.
FIG. 4 is a cross-sectional view of an electrical fastener assembly wherein the solder ring has not melted, in accordance with the first embodiment of the invention.
FIG. 5 is a cross-sectional view of an electrical fastener assembly wherein the solder ring has melted, in accordance with the first embodiment of the invention.
FIG. 6 is a cross-sectional view of an electrical fastener assembly wherein the solder ring has not melted, in accordance with the second embodiment of the invention.
FIG. 7 is a cross-sectional view of an electrical fastener assembly wherein the solder ring has melted, in accordance with the second embodiment of the invention.
DESCRIPTION OF EMBODIMENTS OF THE INVENTION

2 The described embodiments of the present invention are directed to an electrical fastener assembly, which may be used, for example, in a power distribution system for an aircraft. While this description is primarily directed toward a power distribution system for an aircraft, it is also applicable to any environment using electrical fastener assemblies for electrically connecting portions of one electrical network to another As illustrated in FIG. 1, an aircraft 10 is shown having at least one gas turbine engine, shown as a left engine system 12 and a right engine system 14. Alternatively, the power system may have fewer or additional engine systems. The left and right engine systems 12, 14 may be substantially identical, and may further comprise at least one electric machine, such as a generator 18. The aircraft is shown further comprising a plurality of power-consuming components, or electrical loads 20, for instance, an actuator load, flight critical loads, and non-flight critical loads. Each of the electrical loads 20 are electrically coupled with at least one of the generators 18 via a power distribution system, for instance, bus bars 28.
In the aircraft 10, the operating left and right engine systems 12, 14 provide mechanical energy which may be extracted via a spool, to provide a driving force for the generator 18. The generator 18, in turn, provides the generated power to the bus bars 28, which delivers the power to the electrical loads 20 for load operations.
Additional power sources for providing power to the electrical loads 20, such as emergency power sources, ram air turbine systems, starter/generators, or batteries, are envisioned. It will be understood that while one embodiment of the invention is shown in an aircraft environment, the invention is not so limited and has general application to electrical power systems in non-aircraft applications, such as other mobile applications and non-mobile industrial, commercial, and residential applications.
FIG. 2 illustrates an exemplary electrical fastener assembly 24 comprising an electrically conductive DC power contactor 26 having at least one electrical terminal 32, at least a second electrical terminal, shown as an electrically conductive bus bar support 28, and solder washer assembly 30. The terminal 32 of the DC contactor

3 may be electrically coupled with the bus bar support 28, via the solder washer assembly 30. In this sense, the solder washer assembly 30 is positioned between, and physically separating, the terminal 32 and the bus bar support 28. The electrical terminal 32, solder washer assembly 30, and bus bar support 28 are shown having openings 36 for receiving a removable coupling via a mechanical fastener, such as a contactor fixing screw 34 or threaded stud. Additionally, while a solder washer assembly 30 is described, alternative geometric shapes are envisioned wherein, for example, the solder assembly 30 may comprise one or more blocks without an opening 36 and positioned aside from the contactor fixing screw 34, physically separating the terminal 32 from the bus bar support 28.
Turning now to FIG. 3, the solder washer assembly 30 is illustrated as a washer-type and may comprise an outer interface collar 38, shown shaped as a ring, an inner separator, such as an insulating ring 40, also shaped as a ring, and an electrically conductive and meltable element, such as solder ring 42 or disk, received in between the collar and ring 38, 40. When assembled, the interface collar 38, insulating ring 40, and solder ring 42 also define an opening 36 which extends axially through the center of solder washer assembly 30. While an interface collar 38, insulating ring 40, and solder ring 42 are described, alternative geometric shapes are envisioned.
It is envisioned the interface collar 38 comprises an electrically conductive material, and is shown including a radial sidewall 44 and bottom plate 46 that extends radially inward toward the opening 36. The bottom plate 46, sidewall 44, and insulating ring 40 may collectively define a reservoir 47 capable of containing at least a volume of liquid equal to the volume of the melted solder ring 42. The solder ring 42 may be configured to abut at least a portion of the bottom plate 46 such that the solder 42 and plate 46 are in electrically coupled. The insulating ring 40 may comprise a non-conductive material that, when assembled, lines the opening 36 of the solder washer assembly 30 to inhibit radial electrical contact between the interface collar 38 and/or the solder ring 42, and an object received into the opening 36 (for example, the contactor fixing screw 34). Additionally, as shown, the axial height of the solder ring 42 is greater than the axial height of either the interface collar 38 or insulating ring 40,

4

5 and the axial height of the insulating ring 40 may be greater than the axial height of the interface collar 38.
While solder is described, alternative electrically conductive and meltable elements are envisioned. One example melting point for the solder ring 42 may be between 200 and 250 degrees Celsius; however various solder alloys and/or alloy combinations are envisioned such that the melting point of the meltable element may be defined with reference to desired thermal operating or failure conditions of the electrical fastener assembly 24.
FIG. 4 illustrates a cross section of the assembled electrical fastener assembly 24. As shown, the assembly 24 may further comprise an electrically insulating sleeve 48, a compressive or biasing element, shown as a Belleville washer 50, and an optional electrically insulating washer 52. Also shown, the bus bar support 28 further comprises a fastener base, such as a screw base 54 or screw nut, configured to securely receive the fastener. It is envisioned the screw base 54 may be fixedly attached to, or integrated with, the bus bar support 28, and provide insulating qualities to insulate a coupled screw 34 from the bus bar support 28. For instance, the screw base 54 may comprise of an insulating material or the screw base 54 may be affixed to the bus bar support 28 via an insulating adhesive. Additional insulating methods and/or materials are envisioned.
The Belleville washer 50 is configured such that it may have a biasing force toward an expanded state when not under an opposite axial pressure or compressive force, and wherein the axial length of the washer 50 is longer in the expanded state than when under a compressed state. The Belleville washer 50 may fluidly switch between the compressed and expanded states, depending on the pressure or force acting opposite to the biasing force. While a Belleville washer 50 is described, additional biasing elements are envisioned having a biasing force opposed which may act opposite to a retaining pressure or retaining force, and wherein the axial length of the element is longer when not exposed to a retaining force than the axial length of the element when exposed to a retaining force. For instance, alternative biasing elements may include mechanical springs.

The contactor fixing screw 34 is shown at least partially received within the insulating sleeve 48 such that the at least a portion of the screw 34 is electrically insulated by the insulating sleeve 48. While the insulating sleeve 48 is illustrated only enveloping a portion of the contactor fixing screw 34, embodiments of the invention are envisioned wherein the whole screw 34 is received within the sleeve 48. Alternatively, the insulating sleeve 48 may be replaced by an insulating coating or resin. In this alternative example, wherein the whole contactor fixing screw 34 is insulated by, for example, a sleeve 48, coating, or resin, the other insulating elements 40, 52, 54 may optionally provide insulating properties.
The electrical fastener assembly 24 is assembled, as illustrated, by layering, from bottom to top, the bus bar support 28, the solder washer assembly 30, the terminal 32 of the DC contactor 26, the Belleville washer 50, and the insulating washer 52, such that the layering aligns the openings 36 of each washer and element 28, 30, 32, 50, 52.
The contactor fixing screw 34 (having the insulating sleeve 48) is axially received through the openings 36 and removably coupled with the screw base 54 such that the coupling provides sufficient mechanical constriction to axially force and/or couple the elements 28, 30, 32, 50, 52 together, and to compress the Belleville washer 50. In this sense, biasing force of the Belleville washer 50 biases the terminal 32 and bus bar support 28 toward each other, and is opposite to the structural retaining force of the solder washer assembly 30, and specifically the structural retaining force of the solder ring 42. This biasing force is overcome by the contactor fixing screw 34 having been secured to the screw base 54, compressing the Belleville washer 50 against the terminal 32 and the solder ring 42.
The combination of the insulating sleeve 48, insulating washer 52, insulating ring 40, and screw base 54 are configured to electrically isolate the contactor fixing screw 34 from both the terminal 32 and the bus bar support 28. Thus, in the illustrated configuration, the terminal 32 of the DC contactor 26 and the bus bar support 28 of the electrical fastener assembly 24 may only be electrically connected through the solder ring 42 and interface collar 38 of the solder washer assembly 30.

6 During aircraft operation, voltage and current traverse through the DC
contactor 26, solder washer assembly 30, and bus bar support 28. However, in the instance of an electrical fault, failure, or short in the power distribution system 22, large amounts of current shunted over an unintended power connection may generate excessive heat in a component electrical or thermal damage.
In this instance of electrical failure, the point of failure may be in thermal contact, or thermally connected with, the electrical fastener assembly 24. Excessive heat from the point of failure may be thermally conducted to the solder washer assembly 30 via the DC contactor 26 (and terminal 32) and/or the bus bar support 28. If the heat conducted is sufficiently greater than the melting point of the solder, the solder ring 42 may melt. The melting of the solder ring 42, which was at least a portion of the electrical connection between the DC contactor 26 and the bus bar support 28, breaks the electrical connection between the terminal 32 of the contactor 26 and the support 28. The breaking of the electrical connection will disrupt the current flow of the electrical fault, failure, or short, and thus, render the system safe.
FIG. 5 illustrates an alternative configuration of the above described embodiment wherein the melting of the solder ring 142 of the electrical fastener assembly 124 has broken the electrical connection between the DC contactor 26 and bus bar support 28.
Parts having an alternative configuration will be identified with like numerals increased by 100, with it being understood that the description of the primary parts applies to the alternative configuration, unless otherwise noted. As shown, the solder ring 142 has been melted due to thermal conduction from a failure condition, and the melted ring 142 has been contained in the reservoir 47. Thus, as illustrated, the conductive melted solder ring 142 fluid has cascaded away from the terminal 32 due to gravity , and consequently, the bus bar support 28 is no longer in physical or electrical contact with the terminal 32 of the DC contactor 26.
Additionally, since the solid solder ring 42 may no longer be structurally supporting the terminal 32 and opposing the biasing force of the Belleville washer 150, the washer 150 is shown in an axially expanded state. The biasing force of the Belleville washer 150 forces the terminal 32 away from the washer 150 until the terminal 32 is

7 retained or supported by the insulating ring 40, which is now the tallest aspect of the solder washer assembly 30 once that the solder ring 150 has melted, thus maintaining physical separation between the terminal 32 and bus bar support 28.
FIG. 6 illustrates an alternative electrical fastener assembly 224 according to a second embodiment of the invention. The second embodiment is similar to the first embodiment; therefore, like parts will be identified with like numerals increased by 200, with it being understood that the description of the like parts of the first embodiment applies to the second embodiment, unless otherwise noted. A
difference between the first embodiment and the second embodiment is that the meltable element does not provide an electrically conductive path, as in the first embodiment, but rather provides a retaining force for securing the electrically conductive path between the terminal 32 of the DC contactor 26 and the bus bar support 228, and wherein the melting of the meltable retainer releases the electrically conductive path between the terminal 32 and support 228. Another difference between the first embodiment and the second embodiment is that the terminal 32 and bus bar support 228 may be in direct electrical contact.
As illustrated, the electrical fastener assembly 224 may include multiple biasing elements, such as Belleville washers 50, and the bus bar support 228 further comprises a solder assembly 230 having an axially extending insulating ring 240 and a screw base 254, at least a portion of which may be axially retained or affixed, relative to the bus bar support 228, by a meltable retainer, such as a solder ring 242, or a thermally-releasing glue or adhesive. In the second embodiment, the meltable retainer does not need to have electrically conductive properties.
In this embodiment, an (optional) insulating sleeve 48, insulating washer 52, and insulating ring 240 electrically isolate the contactor fixing screw 34 from both the DC
contactor 26 and the bus bar support 228.
In the second embodiment, the electrical fastener assembly 224 is assembled, as illustrated, by layering, from bottom to top, the bus bar support 228, a Belleville washer 50, the terminal 32 of the DC contactor 26, a second Belleville washer 50, and

8 the insulating washer 52, such that the layering aligns the openings 36 of each washer and element 228, 32, 50, 52. When assembled, the contactor fixing screw 34 (having the insulating sleeve 48) is axially received through the openings 36 and removably coupled with the screw base 254 such that the coupling provides sufficient mechanical constriction to axially force the elements 228, 32, 50, 52 together, and to compress the Belleville washer 50. In this sense, the biasing force of the Belleville washer 50 biases the terminal 32 and bus bar support 228 away from each other, and is opposed to, and overcome by, the retaining force of the contactor fixing screw 34 having been secured to the screw base 254, which is retained or anchored by the solder ring 242.
During aircraft operation, the terminal 32 of the DC contactor 26 and the bus bar support 228 are electrically coupled, allowing power to be transferred between the components 32, 228. As described in the first embodiment, a failure condition may generate excessive heat, which, when sufficiently conducted along the electrically conductive path to the bus bar support 228, may melt the solder ring 242, releasing the affixed screw base 254. The screw base 254 and terminal 32 of the DC contactor 26, which are no longer axially retained by the bus bar support 228 via the screw base 254, are forced upward due to the biasing force of the Belleville washers 50, both physically and electrically separating the terminal 32 from the bus bar support 228.
The breaking of the electrical connection will disrupt the current flow of the electrical fault, failure, or short, and thus, render the system safe during an overheating condition.
FIG. 7 illustrates an alternative configuration of the above described embodiment wherein the melting of the solder ring 342 of the electrical fastener assembly 324 has broken the electrical connection between the DC contactor 26 and bus bar support 228. As shown, the solder ring 342 has been melted due to thermal conduction from a failure condition, releasing the screw base 254. Thus, each Belleville washers have an axially expanded state, which has physically and electrically separated the terminal 32 of the DC contactor 26 from the bus bar support 228.
Many other possible embodiments and configurations in addition to that shown in the above figures are contemplated by the present disclosure. For example, one

9 embodiment of the invention contemplates a solder washer assembly 30 without an interface collar 38, wherein the melted solder ring 142 is allowed to otherwise flow away from the electrical fastener assembly 124, without constraint.
Additionally, a solder washer assembly 30 as shown, or without an interface collar 38 may allow for side-mounting of the electrical fastener assembly 24, as any melted solder ring 142 would simply flow away from the contact junction. In another example, more or fewer biasing elements, such as the Belleville washers 50, may be used to allow for increased or decreased expansion while in an expanded state, compared to that expansion illustrated and described above. Additionally, the design and placement of the various components may be rearranged such that a number of different in-line configurations could be realized.
The embodiments disclosed herein provide an electrical fastener assembly. One advantage that may be realized in the above embodiments is that the above described embodiments provide for meltable interconnection points between various high current components of an electrical power distribution system which will disrupt current flow in a fault, failure, short, or otherwise over-temperature condition. This purposeful disruption may prevent further damage to the electrical system or larger structure, such as an aircraft, by preventing or limiting smoke and fire, which may lead to one or more catastrophic failures. Another advantage to the above described embodiments is that embodiments may be installed at any or all relay points in the electrical system wherein two terminals are coupled together. This may allow for a very robust system wherein excessive thermal conditions may be quickly located (and safely interrupted) due to the proximity of one or more electrical fastener assemblies to any given failure point. The above described embodiments, thus, provide for increased safety for an aircraft electrical power distribution system and hence improve the overall safety of the aircraft and air travel.
To the extent not already described, the different features and structures of the various embodiments may be used in combination with each other as desired. That one feature may not be illustrated in all of the embodiments is not meant to be construed that it may not be, but is done for brevity of description. Thus, the various features of the different embodiments may be mixed and matched as desired to form new embodiments, whether or not the new embodiments are expressly described. All combinations or permutations of features described herein are covered by this disclosure.
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.

Claims

CLAIMS:

1. An electrical fastener assembly for coupling first and second terminals, comprising:
a fastener coupling the first and second terminals to each other;
an electrically conductive, meltable element electrically coupling the first terminal and second terminal prior to melting; and a separator having a portion located between the first and second terminals and maintaining them physically separated;
wherein a conductive path is defined by at least the first terminal, second terminal, and meltable element, with the meltable element melting in response to heat along the conductive path to disrupt the conductive path in response to an overheating condition while the separator maintains the first and second terminals physically separated.

2. The electrical fastener assembly of claim 1, wherein the first and second terminals each have an opening, and the fastener comprises a threaded stud received within the openings and a nut threaded onto the stud to secure the first and second terminals to the threaded stud.

3. The electrical fastener assembly of claim 2, wherein at least one of the meltable element or separator defines a washer having an opening, wherein the threaded stud is received within the opening.

4. The electrical fastener assembly of any preceding claim, further comprising a reservoir and the electrically conductive, meltable element is located within the reservoir.

5. The electrical fastener assembly of claim 4, wherein the reservoir has a volume greater than a volume of the meltable element.

6. The electrical fastener assembly of either of claim 4 or 5, comprising a washer located between the first and second terminals and defining the reservoir.

7. The electrical fastener assembly of any preceding claim, wherein a height of the conductive path is greater than a height of the separator.

8. The electrical fastener assembly of claim 7, wherein the height of the separator is greater than a length of the conductive path after melting of the meltable element.

9. The electrical fastener assembly of any preceding claim, wherein the meltable element comprises solder.

10. An electrical fastener assembly for connecting first and second terminals, comprising:
a fastener coupling the first and second terminals to each other;
a meltable retainer providing a retaining force to secure the fastener in a coupling condition prior to melting; and a biasing element having a portion located between the first and second terminals, and applying a biasing force opposite of the retaining force;
wherein a conductive path is defined by at least the first terminal and second terminal, with the meltable retainer melting in response to heat, releasing the biasing force of the biasing element to physically separate the first and second terminals, and to disrupt the conductive path in response to an overheating condition.

11. The electrical fastener assembly of claim 10, wherein the biasing element comprises a biasing force relative to the first and second terminals to bias the first and second terminals away from each other.

12. The electrical fastener assembly of claim 11, wherein the biasing element is at least one of a spring or Belleville washer.

13. An electrical overload protection apparatus comprising:
a first terminal comprising a threaded stud;
a second terminal having an opening receiving the threaded stud;
a nut threadably received on the threaded stud and securing the second terminal onto the first terminal; and a washer having an opening receiving the threaded stud and positioned between the first and second terminal, and having an electrically conductive, meltable element;
wherein a conductive path is defined by at least the first terminal, second terminal, and meltable element, with the meltable element melting in response to heat along the conductive path to disrupt the conductive path in response to an overheating condition.

14. The apparatus of claim 13, wherein the washer defines a reservoir in which the electrically conductive, meltable element is received upon melting.

15. The apparatus of claim 14, wherein a volume of the reservoir is greater than a volume of the electrically conductive, meltable element.