Note: Descriptions are shown in the official language in which they were submitted.
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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.
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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
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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
26
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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,
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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.
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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.
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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
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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
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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
50
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
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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
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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.
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