Information
-
Patent Grant
-
6377433
-
Patent Number
6,377,433
-
Date Filed
Friday, March 17, 200024 years ago
-
Date Issued
Tuesday, April 23, 200222 years ago
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Inventors
-
Original Assignees
-
Examiners
-
CPC
-
US Classifications
Field of Search
-
International Classifications
-
Abstract
A fuse/support assembly for attachment to an electrical bus includes a base plate having a substrate made of an insulator, a fastener bore extending through the substrate, and an electrically conductive path on the substrate. There is additionally an external connector structure. A fuse is supported on the substrate and has a first end in electrical communication with the external connector and a second end in electrical communication with the electrically conductive path.
Description
BACKGROUND OF THE INVENTION
This invention relates to electrical fuses, and, more particularly, to a fuse/support assembly that permits the convenient utilization of electrical fuses in instrumentation applications.
In many applications, the components of an electrical system are protected against damage from excessive electrical currents by an electrical fuse. The electrical fuse is connected with the electrical system such that any excessive electrical current causes the electrical fuse to change from a closed to an open circuit, preventing the excessive electrical current from passing through and damaging the remainder of the electrical circuit elements. In a typical case, the electrical fuse is connected in series with the components being protected, and includes a fuse link made of a material which heats and melts when the excessive electrical current is applied, thereby breaking the electrical circuit.
The mounting and support of the electrical fuse, and its connection into the electrical system being protected, must be accomplished in a suitable manner. In some electrical systems, such as found in some spacecraft and aircraft, the electrical fuse is externally connected between an electronic unit and an electrical bus. The existing approach to supporting and connecting the electrical fuse utilizes terminal boards to which the electrical fuse is wired, and hand-wired pigtails that extend to the electrical bus and to the electronic unit. This approach requires numerous parts which can be lost as foreign objects into the interior of the structure, and also involves extensive pre-wiring and wire attachments. Rework and repair are difficult for the same reasons.
Accordingly, there is a need for an improved approach to the mounting and interconnecting of an electrical fuse into an electrical system. The present invention fulfills this need, and further provides related advantages.
SUMMARY OF THE INVENTION
The present invention provides a fuse/support assembly and a method for its use, for systems wherein an electronic unit is connected to an electrical bus through the electrical fuse. The fuse/support assembly requires no pre-wiring of the electrical bus and reduces the number of terminations at the point of installation. The number of components required to accomplish the fusing is reduced as compared with prior approaches. Installation, rework, repair, and inspection are all simplified as compared with prior approaches, and there is reduced likelihood of loss of parts and resulting foreign object damage of the system. The close contact of the fuse/support assembly to the electrical bus allows the electrical bus to serve as a heat sink and stabilize the fuse/support assembly to prevent a premature activation of the fuse.
In accordance with the invention, a fuse/support assembly for attachment to an electrical bus comprises a base plate, comprising a substrate made of an insulator and having a contact location thereon, and an electrically conductive path on the substrate, with the electrically conductive path extending between the contact-location and a second location. A fastener structure brings the contact location of the electrically conductive path into contact with the electrical bus. There is an external connector structure. A fuse is supported on the substrate, with a first side in electrical communication with the external connector and a second side in electrical communication with the second location of the electrically conductive path.
This approach simplifies the electrical fuse protection of electrical systems, where the fuse is mounted exterior to the components being protected. Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a perspective view of a fuse/support assembly according to the invention;
FIG. 2
is a schematic sectional view of the fuse/support assembly of
FIG. 1
, taken on line
2
—
2
;
FIG. 3
is a perspective view of the installation of the fuse/support assembly in an electrical system;
FIG. 4
is a schematic sectional view of the attachment of the fuse/support assembly to the electrical bus, taken on line
4
—
4
of
FIG. 3
;
FIG. 5
is a plan view of one embodiment of the fuse/support assembly;
FIG. 6A
is a schematic sectional view of the fuse/support assembly of
FIG. 5
, taken on line
6
—
6
;
FIG. 6B
is a schematic sectional view of a second embodiment of the fuse/support assembly, taken in the same view as
FIG. 6A
; and
FIG. 7
is a perspective view of a prior art fuse/support assembly.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1
depicts a fuse/support assembly
20
according to the invention, and
FIG. 3
shows the installation of the fuse/support assembly.
FIGS. 2 and 4
are sectional views through
FIGS. 1 and 3
, respectively.
FIG. 5
is a plan view of the embodiment of FIG.
1
.
FIG. 6A
shows the electrical circuitry associated with the fuse/support assembly and its protection of an electrical system, and
FIG. 6B
illustrates a second embodiment.
Referring to
FIG. 1
, a base plate
22
is made of an electrical insulator such as a polyimide polymer. The base plate
22
is a generally rectangular, thin plate, with the edges and ends rounded. The base plate
22
is adapted for engagement by means of a fastener
24
. In the preferred approach, a fastener bore
28
(
FIG. 4
) passes through the thickness of the base plate
22
. The fastener
24
is preferably a bolt
26
which is dimensioned to extend through the fastener bore
28
, and is threadably engaged to an electrical bus
30
.
The base plate
22
has a first side
32
and a second side
34
. The engagement of the base plate
22
to the electrical bus
30
by the bolt
26
presses a contact location
38
of the second side
34
of the base plate
22
against a top surface
36
of the electrical bus
30
, to establish an electrically conductive contact therebetween.
An electrically conductive path
40
is formed on the surface of the base plate
22
, extending from the contact location
38
to a second location
42
. The positioning of the second location
42
depends upon the site chosen for the fuse, as will be discussed subsequently. The electrically conductive path
40
is preferably formed as a plated metallic layer of a metal, such as copper, copper/silver, or aluminum, on the electrically nonconductive substrate
44
of the base plate
22
. The fabrication of electrically insulative substrates with patterned metallic layers thereon is well known in the art for other applications, such as the fabrication of printed circuit boards. In a typical case, the base plate
22
is about 0.040 inch thick, and the metallic layer of the electrically conductive path
40
is about 0.015 inch thick.
A fuse
46
is supported on the base plate
22
. The fuse
46
may be of any operable type. In the embodiment illustrated in
FIGS. 1
,
5
, and
6
A, the fuse
46
is a “thin-film fuse” and includes a length
48
of the plated metallic layer having a reduced cross-sectional area (e.g., narrowed width but constant thickness in the illustration) and other portions of which serve as the electrically conductive path
40
. The fuse
46
has a first end
50
and a second end
52
. In this embodiment, the second end
52
is continuous with the second location
42
of the electrically conductive path
40
. In a second embodiment illustrated in
FIG. 6B
, the fuse
46
is a discrete element, and the second end
52
is joined to the second location
42
by a soldered or spot welded wire
54
. In these embodiments, the material and crosssectional area of the fuse
46
are selected so that the fuse melts when there is an attempt to pass an electrical current greater than a permitted maximum current through the fuse.
In another variation illustrated in
FIG. 6B
, the fastener, in this case the bolt
26
, may be captured as an integral part of the fuse/support assembly
20
by a retainer
90
. The retainer
90
is preferably an electrical insulator affixed to the base plate
22
and capturing the head of the bolt
26
between the retainer
90
and the base plate
22
. The retainer
90
has an opening
92
therethrough aligned with the top of the head of the bolt
26
, so that an appropriate tool may be used to turn and tighten the bolt
26
. The bolt
26
is assembled to the base plate
22
and captured by the retainer
90
prior to installation to the electrical bus
30
, so that the bolt
26
cannot separate from the base plate
22
and fall into the interior of the electrical system.
The fuse
46
may be positioned on the first side
32
or on the second side
34
of the base plate
22
. If the fuse
46
is on the first side
32
, as illustrated in
FIG. 6A
, the electrically conductive path
40
extends from the contact location
38
on the second side
34
, through the thickness of the base plate
22
, and on the first side
34
to the second location
42
on the first side
32
. The portion of the conductive path
40
that extends through the thickness of the base plate may extend through the fastener bore
28
as a plated layer on the surface of the bore that is continuous with the plated layer on the second side
34
and the plated layer on the first side
32
. Equivalently, other through conductors such as a separate plated or filled via, or electrical plating over the edges of the base plate
22
, may be used. If, on the other hand, the fuse
46
is on the second side
34
, the conductive path
40
need only reside on the second side. In this case, the conductive path
40
extends from the contact location
38
along the second side
34
to the second location
42
.
A ballast resistor
56
may optionally be arranged in electrical series with the electrical fuse
46
. The ballast resistor
56
is normally on the same side of the base plate
22
as the electrical fuse
46
, although it may be on the reverse side. A first end of the ballast resistor
56
is connected to the first end
50
of the fuse
46
with a wire
58
, which is normally integral with the resistor
56
and soldered or welded to the first end
50
. In the illustrated embodiments, the ballast resistor
56
is electrically positioned with the fuse
46
between the ballast resistor
56
and the contact location
38
. Equivalently, the ballast resistor
56
may be positioned between the fuse
46
and the contact location
38
. A wire
59
extending from the second end of the ballast resistor
56
is desirably affixed to the surface of the insulating substrate
44
of the base plate
22
to form an external electrical contact
61
.
This preferred embodiment has a single fuse
46
and its associated circuitry. More than one fuse and its associated circuitry may be positioned on a single base plate
22
.
An insulator may be positioned over the portion of the length of the base plate
22
that includes the fuse
46
and the resistor
56
, to prevent contact of dirt and electrically shorting material to the circuitry, and to prevent injury to workers. A sleeve
63
of an insulating material such as an electrically nonconducting elastomer may be conveniently used as the insulator.
An electrical connector structure
60
is a length of an externally insulated electrical conductor
62
having a first end
64
in electrical communication with the external electrical contact
61
, and a second end
66
with an external electrical connector
68
thereon. The electrical connector structure
60
is preferably in the form of a flexible conductive pigtail joined at the first end
64
to the external electrical contact
61
and having the free second end
66
with the external electrical connector
68
that is connectable to an electrical unit
70
to be protected. The external electrical connector
68
may be of any operable type, such as a spade connector, a pin connector, or the like, suitable for attaching to the corresponding location on the electrical unit
70
.
The base plate
22
desirably includes a retainer clamp
72
at the end remote from the fastener bore
28
. The retainer clamp
72
grasps the external surface of the insulated electrical conductor
62
, so as to leave some slack in the electrical conductor
62
between the retainer clamp
72
and the external electrical contact
61
. This retainer clamp
72
thus prevents the electrical conductor
62
from being broken free of the external electrical contact
61
, and also provides for a strain relief
74
in the electrical conductor
62
.
In a typical situation, the electrical unit
70
and the electrical bus
30
are mounted to a shelf
76
. The fuse/support assembly
20
extends between the appropriate connector on the electrical unit
70
and the electrical bus
30
, as shown in FIG.
3
. In a production setting, the fuse/support assembly
20
may be provided in the illustrated form with the electrical connector structure
60
as a pigtail of length greater than required, and without the external electrical connector
68
being attached to the electrical conductor
62
. When the connection is to be made, the electrical conductor
62
is trimmed to the required length, the external electrical connector
68
is attached to the trimmed electrical conductor
62
by crimping or soldering or other operable technique, and the external electrical connector
68
is plugged into the appropriate location on the electrical unit
70
.
FIGS. 6A-6B
depict the electrical path between the external electrical connector
68
, and thence the electrical unit
70
being protected when the external electrical connector
68
is attached to the electrical unit
70
, and the electrical bus
30
. The electrical path is through the external electrical connector
68
, the electrical conductor
62
, the wire
59
, the ballast resistor
56
, the wire
58
, the fuse
46
, and the electrically conducting path
40
. When the current in this path becomes too high for any reason, the electrical fuse
46
activates (“blows”) to break with electrical path and prevent damage to the electrical unit
70
.
The present approach is to be contrasted with the conventional approach used to protect electrical units, as shown in FIG.
7
. In this conventional approach, a terminal board
80
with two posts/screws
82
is provided. Pigtails
84
a
and
84
b
extend respectively to the electrical unit and to the electrical bus. The electrical conductor ends of the pigtails are wound around the posts and secured with the screws. A fuse/ballast assembly
86
has wires extending from the ends thereof, which are also wrapped around the posts and secured with the screws. This arrangement involves more loose parts, which must be manufactured and provided, and each of which have the potential for being dropped and lost during assembly, than does the present approach. There is more pre-wiring and hard wiring required during assembly, and there is a greater chance for a mistake in wiring, than with the present approach. Reworking, repair, and replacement are easier with the present approach. The present approach is also more easily inspected during assembly.
Although a particular embodiment of the invention has been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.
Claims
- 1. A fuse/support assembly for attachment to an electrical bus having a surface, the fuse/support assembly comprising:a base plate, comprising a substrate made of an insulator and having a first side and a second side, a fastener bore extending through the substrate, a threaded fastener extending through the fastener bore, and an electrically conductive path on the substrate, the electrically conductive path including a contact location on the second side of the substrate positioned such that an engagement of the base plate to the electrical bus by the threaded fastener presses the contact location against the surface of the electrical bus to establish an electrically conductive contact therebetween; an external connector structure comprising an external electrical contact on the base plate, and a pigtail connector joined at a first end thereof to the external electrical contact and having an electrical connector at a second end thereof; and a fuse supported on the substrate and having a first end in electrical communication with the external connector structure and a second end in electrical communication with the electrically conductive path.
- 2. The fuse/support assembly of claim 1, further includinga retainer for the fastener, the retainer being affixed to the base plate and operable to retain the fastener in contact with the base plate when the base plate is not affixed to the electrical bus.
- 3. The fuse/support assembly of claim 1, wherein the fastener is a threaded bolt.
- 4. The fuse/support assembly of claim 1, wherein the fuse/support assembly further includesa ballast resistor mounted to the substrate and in electrical series with the fuse.
- 5. The fuse/support assembly of claim 1, further including an insulator extending over at least a portion of the substrate.
- 6. The fuse/support assembly of claim 1, wherein the external connector structure comprises a pigtail connector comprising a length of electrically conductive wire having a first end in electrical communication with the fuse and a second end having an external electrical connector.
- 7. The fuse/support assembly of claim 1, wherein the electrically conductive path extends from the first side to the second side and comprisesa first electrically conductive region on the first side, a second electrically conductive region on the second side, and an electrical through-conductor extending between the first region and the second region, and wherein the fuse is on the first side of the substrate.
- 8. The fuse/support assembly of claim 1, wherein the fuse is mounted to the second side of the substrate, and the electrically conductive path is on the second side of the substrate.
- 9. The fuse/support assembly of claim 1, wherein the fuse is a thin-film fuse.
- 10. The fuse/support assembly of claim 1, wherein the fuse is a discrete element.
- 11. A fuse/support assembly for attachment to an electrical bus, comprising:a base plate, comprising a substrate made of an insulator and having a contact location thereon, and an electrically conductive path on the substrate, the electrically conductive path extending between the contact location and a second location, wherein the electrically conductive path comprises a first electrically conductive region on a first side of the substrate and including the second location of the electrically conductive path, a second electrically conductive region on a second side of the substrate and including the contact region, and an electrical through-conductor extending between the first electrically conductive region and the second electrically conductive region; a fastener structure which brings the contact location of the electrically conductive path into contact with the electrical bus; an external connector structure; and a fuse supported on the substrate and having a first end in electrical communication with the external connector and a second end in electrical communication with the second location of the electrically conductive path wherein the fuse is affixed to the first side of the substrate.
- 12. The fuse/support assembly of claim 11, wherein the fastener structure comprisesa fastener bore extending through the substrate, and a fastener sized to extend in part through the fastener bore of the substrate.
- 13. The fuse/support assembly of claim 11, wherein the fastener structure includesa fastener, and a retainer for the fastener, the retainer being affixed to the base place and operable to retain the fastener in contact with the base plate when the base plate is not affixed to the electrical bus.
- 14. The fuse/support assembly of claim 11, wherein the fastener structure comprisesa fastener bore extending through the substrate, and wherein the electrical through-conductor comprises a metallic layer on the fastener bore.
- 15. The fuse/support assembly of claim 11, further includinga ballast resistor mounted to the substrate and in electrical series with the fuse.
- 16. The fuse/support assembly of claim 11, further includingan insulator extending over at least a portion of the substrate.
- 17. The fuse/support assembly of claim 11, wherein the external connector structure comprises a pigtail connector comprising a length of electrically conductive wire having a first end in electrical communication with the fuse and a second end having an external electrical connector.
- 18. A fuse/support assembly for attachment to an electrical bus, comprising:a base plate, comprising a substrate made of an insulator and having a contact location thereon, and an electrically conductive path on a second side of the substrate, the electrically conductive path extending between the contact location and a second location, the electrically conductive path including the contact location on the second side of the substrate positioned such that an engagement of the base plate to the electrical bus by the threaded fastener presses the contact location against the surface of the electrical bus to establish an electrically conductive contact therebetween; a fastener structure which brings the contact location of the electrically conductive path into contact with the electrical bus; an external connector structure; and a fuse supported on the second side of the substrate and having a first end in electrical communication with the external connector and a second end in electrical communication with the second location of the electrically conductive path.
- 19. The fuse/support assembly of claim 18, wherein the fastener structure comprisesa fastener bore extending through the substrate, and a fastener sized to extend in part through the fastener bore of the substrate.
- 20. The fuse/support assembly of claim 18, wherein the fastener structure includesa fastener, and a retainer for the fastener, the retainer being affixed to the base place and operable to retain the fastener in contact with the base plate when the base plate is not affixed to the electrical bus.
US Referenced Citations (12)