U.S. patent number 3,783,428 [Application Number 05/193,302] was granted by the patent office on 1974-01-01 for low-voltage fuse with blown fuse indicator.
This patent grant is currently assigned to The Chase-Shawmut Company. Invention is credited to Richard A. Belcher, Kenneth W. Swain.
United States Patent |
3,783,428 |
Swain , et al. |
January 1, 1974 |
LOW-VOLTAGE FUSE WITH BLOWN FUSE INDICATOR
Abstract
A low-voltage fuse has a molded insulating casing of a synthetic
resin and a blown fuse indicator is installed in the casing's front
wall. The spring biased plunger of the indicator is of electric
insulating material and has an axially outer cylindrical portion of
relatively large and an axially inner cylindrical portion of
relatively small diameter. The former is arranged in an aperture
having a relatively large inner diameter formed in the
aforementioned front wall, and the latter is arranged in a hollow
projection inside the housing coaxial with the indicating plunger
having a relatively small inner diameter.
Inventors: |
Swain; Kenneth W. (Hampton
Falls, NH), Belcher; Richard A. (Hampton Falls, NH) |
Assignee: |
The Chase-Shawmut Company
(Newburyport, MA)
|
Family
ID: |
22713063 |
Appl.
No.: |
05/193,302 |
Filed: |
October 28, 1971 |
Current U.S.
Class: |
337/148; 337/158;
337/206; 337/244 |
Current CPC
Class: |
H01H
85/303 (20130101) |
Current International
Class: |
H01H
85/00 (20060101); H01H 85/30 (20060101); H01h
085/30 () |
Field of
Search: |
;337/5,148,241,244,265,267,158,206 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Gilheany; Bernard A.
Assistant Examiner: Tone; D. A.
Attorney, Agent or Firm: Salzer; Erwin
Claims
We claim as our invention:
1. The combination of an electric fuse and of a blown fuse
indicator including
a. a housing of a molded electric insulating material accommodating
fusible element means and a pulverulent arc-quenching filler, said
housing including an integral insulating wall substantially in
plate form having a recess therein, said wall further forming an
integral substantially tubular member having a predetermined inner
diameter, arranged in registry with said recess in said wall and
projecting in cantilever fashion into the inside of said
housing;
b. a cylindrical plunger formed of an integral workpiece of
insulating material, one cylindrical end portion of said plunger
having a relatively large diameter and the other cylindrical end
portion of said plunger having a relatively small diameter, said
relatively large diameter end portion of said plunger being
arranged inside said recess of said wall and said relatively small
diameter end portion of said plunger being arranged in said tubular
member, having a substantially transverse bore and being surrounded
by a helical compression biasing spring resting with one end
thereof directly against said relatively large diameter end portion
of said plunger;
c. a support for the other end of said biasing spring supported by
said tubular member; and
d. a restraining wire for said plunger threaded three times through
said bore in said small diameter end portion thereof and forming
two substantially semi-circular loops each engaging one lateral
side of said small diameter end portion of said plunger, and said
restraining wire having ends extending outwardly from opposite ends
of said bore and out of said tubular member.
2. A structure as specified in claim 1 wherein said ends of said
restraining wire extending from opposite ends of said bore engage
and are twisted about each other at a point juxtaposed to the end
surface of said relatively small diameter end portion of said
plunger.
3. A structure as specified in claim 1 wherein
a. said recess in said wall has a relatively large inner diameter
in comparison to said predetermined inner diameter of said tubular
member forming a shoulder between said recess and the inside of
said tubular member, said recess having a greater axial length than
the axial length of said relatively large diameter end portion of
said plunger and said relatively large diameter end portion of said
plunger being slidably arranged in said recess, said shoulder
forming an abutment limiting movement of said plunger against the
bias of said biasing spring, and wherein
b. said support for said other end of said biasing spring is formed
by a substantially bell-shaped metal cap press-fitted into said
tubular member and having a central bore for the passage of said
relatively small diameter end portion of said plunger.
4. A blown fuse indicator structure comprising
a. a housing of electric insulating material including an integral
flat insulating wall having a recess therein and a substantially
tubular insulating member having a smaller inner diameter than the
diameter of said recess being supported only on one end thereof and
projecting in cantilever fashion from said wall into the inside of
said housing;
b. a plunger of insulating material in the form of a solid of
revolution, one end portion of said plunger having a relatively
large diameter and the other end portion of said plunger having a
relatively small diameter, said relatively large diameter end
portion of said plunger being arranged inside said recess of said
wall and said relatively small diameter end portion of said plunger
being arranged inside said tubular member, having a substantially
transverse bore at the end thereof remote from said relatively
large diameter end portion of said plunger and being surrounded by
a helical compression spring resting with one end thereof against
said relatively large diameter end portion of said plunger;
c. a metal cap supporting the other end of said spring and being
press-fitted into said tubular member; and
d. a restraining wire for said plunger having one end entering into
said bore of said small diameter end portion of said plunger
forming several turns in opposite directions around said small
diameter end portion of said plunger and leaving said bore of said
small diameter end portion of said plunger at the end of said bore
opposite to said one end thereof so that an uninterrupted center
portion of said restraining wire engages said plunger normally
retaining said plunger in position against the action of said
spring, both ends of said restraining wire extending from the
inside of said tubular member to the outside thereof.
5. A blown fuse indicator including
a. a substantially flat plate member of electric insulating
material having a recess therein and supporting one end of an
integral substantially tubular projection coaxial with said recess,
said projection being unsupported at the end thereof remote from
said plate member, said recess having a relatively large inner
diameter and said tubular projection having a relatively small
inner diameter;
b. an indicating plunger of electric insulating material having a
cylindrical section of relatively large diameter slidably arranged
in said recess in said plate member and said plunger further
including a cylindrical section of relatively small diameter
slidably arranged in said tubular projection, said section of
relatively small diameter of said plunger having a substantially
transverse bore adjacent the end thereof remote from said section
of relatively large diameter of said plunger;
c. a substantially bell-shaped metal cap press-fitted into said
tubular projection;
d. a helical compression spring inside said metal cap having one
end resting against said metal cap and another end resting against
said relatively large diameter section of said plunger;
e. a fusible restraining wire normally restraining said plunger
against the action of said spring, said restraining wire projecting
through said bore in said section of relatively small diameter of
said plunger and forming a pair of inverse loops each encompassing
substantially one half of the periphery of said section of
relatively small diameter of said plunger for affixing said
restraining wire to said plunger and for abutting against said
metal cap upon fusion of said restraining wire and thereby limiting
the stroke of said plunger.
6. An electric fuse comprising
a. a pair of terminal strips each including a connector portion and
a fusible-element-receiving portion;
b. fuse link means conductively interconnecting said
fusible-element-receiving portion of said pair of terminal
strips;
c. a pulverulent arc-quenching filler embedding said fuse link
means;
c. a casing of electric insulating material defining a chamber
housing said fusible-element-receiving portion of said pair of
terminal strips, said fuse link means and said arc-quenching
filler, one wall of said casing forming an integral substantially
tubular projection extending in cantilever fashion into said
chamber and having a relatively small aperture at the innermost end
thereof, said one wall of said casing further having a relatively
large recess juxtaposed to said relatively small aperture, and said
wall of said casing forming a shoulder between said recess and the
end of said tubular projection adjacent said recess;
e. a blown fuse indicator arranged inside said recess and said
tubular projection, said blown fuse indicator including a plunger
of electric insulating material in the form of a solid of
revolution, one end portion of said plunger having a relatively
large diameter and being arranged inside of said recess of said one
wall of said casing and the other end portion of said plunger
having a relatively small diameter and being arranged inside said
tubular projection, said other end portion of said plunger having a
substantially transverse bore and being surrounded by a helical
compression spring resting with one end thereof against said
relatively large diameter portion of said plunger, a substantially
bell-shaped cap projecting from said shoulder in the direction of
said substantially transverse bore in said other end portion of
said plunger and supporting the other end of said compression
spring, said cap having a central bore for the passage of said
other end portion of said plunger, and a fusible restraining wire
for said plunger threaded through said relatively small aperture in
said hollow projection and threaded through said substantially
transverse bore of said other end portion of said plunger, said
restraining wire and said cap forming cooperating abutments
limiting movement of said plunger relative to said casing upon
fusion of said restraining wire.
7. An electric fuse as specified in claim 8 wherein
a. said restraining wire enters said bore on one end thereof,
extends through said bore, leaves said bore at the other end
thereof and forms a first substantially semi-circular loop
extending in one direction along the lateral surface of said end
portion of said plunger having a relatively small diameter;
wherein
b. said restraining wire re-enters said bore at said one end
thereof, extends a second time through said bore, leaves said bore
at said other end thereof and forms a second substantially
semi-circular loop extending in a direction opposite to said one
direction along said lateral surface of said end portion of said
plunger having a relatively small diameter; and wherein
c. said restraining wire twice re-enters said bore on said one end
thereof, extends three times through said bore and leaves said bore
at said opposite end thereof.
Description
BACKGROUND OF THE INVENTION
The general object of this invention is to improve the blown fuse
indicators disclosed in the copending patent applications of
Kenneth W. Swain et al., filed Oct. 28, 1971 for POLYPHASE FUSE
WITH BLOWN FUSE INDICATOR and of Richard A. Belcher and Fedderick
J. Kozacka, filed Aug. 24, 1971 Ser. No. 174,445; now U.S. Pat. No.
3,697,916; Oct. 10, 1972 for ELECTRIC LOW-VOLTAGE FUSE. One
specific object of the invention is to reduce the number of
constituent parts of the above blown fuse indicator structures and
thus to decrease the cost of manufacture thereof. Another specific
object of the invention is to maximize the distance between the
front end of the indicating plunger which is accessible and may be
manipulated and the part closest to it which is under a contact
potential and where arcing may occur.
SUMMARY OF THE INVENTION
Structures embodying this invention include a housing of a molded
insulating material accommodating fusible element means and a
pulverulent arc-quenching filler. The aforementioned housing
includes an integral insulating wall substantially in plate form
having a recess therein. This wall further forms an integral
substantially tubular member having a predetermined inner diameter,
arranged in coaxial relation with said recess in said wall and
projecting in cantilever fashion into the inside of said housing.
The structure further includes a cylindrical plunger formed of an
integral workpiece of insulating material. One cylindrical end
portion of said plunger has a relatively large diameter and the
other cylindrical end portion of said plunger has a relatively
small diameter. The relatively large diameter end portion of the
plunger is arranged in said recess of said wall and said relatively
small diameter end portion of said plunger is arranged in said
tubular member and has a substantially transverse bore and is
surrounded by a helical biasing compression spring. One end of this
spring rests directly against said relatively large diameter end
portion of said plunger. The other end of said spring is supported
by a spring support which, in turn, is supported by said tubular
member. The plunger is normally restrained by a restraining wire
threaded three times through said bore in the small diameter
portion thereof in such a way that two substantially semicircular
loops are formed each engaging one lateral side of the small
diameter end portion of the plunger. Said restraining wire has ends
extending outwardly from opposite ends of said bore and out of said
tubular member.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a vertical section through a molded case fuse as
disclosed in the above referred-to patent application of Richard A.
Belcher and Frederick J. Kozacka and including a blown fuse
indicator embodying the present invention.
FIG. 2 shows a blown fuse indicator embodying this invention partly
in axial section and partly in side elevation in the non-indicating
position thereof;
FIG. 3 shows the structure of FIG. 2 in the same way as FIG. 2 but
in the indicating position thereof;
FIG. 4 is a cross-section of the indicating plunger taken along
A--A of FIG. 2 in the process of being affixed tthe restraining
wire thereof; and
FIG. 5 is a cross-section of the indicating plunger taken along
A--A of FIG. 2 upon completion of the process of affixing the
restraining wire thereof.
DESCRIPTION OF PREFERRED EMBODIMENT
The electric fuse shown in FIG. 1 includes a pair of substantially
L-shaped terminal strips 1a, 1b. Each terminal strip includes a
connector portion 1a for connecting the fuse into an electric
circuit and a fusible-element-receiving portion 1b. Portions 1b are
provided with grooves 1c receiving the ends of ribbon fuse link
means 2 conductively interconnecting terminal strips 1a, 1b. Fuse
link means 2 are conductively connected to terminal strips 1a, 1b
by solder joints not shown. A pulverulent arc-quenching filler 3
shown only in part embeds fuse link means 2. Reference character 4
has been applied to indicate a molded casing of a synthetic resin,
i.e., of an electric insulating material forming a chamber 4a
housing the fusible-element-receiving portion 1b of terminal strips
1a,1b fuse link means 2 and arc-quenching filler 3. Terminal strips
1a,1b are affixed to housing 4 by any appropriate means, e.g., they
may be cemented to housing 4. Cover 4b having an aperture 4c for
filling arc-quenching filler 3 into chamber 4a forms a part of
housing 4. When chamber 4a is filled with filler 3 aperture 4c is
closed by a plug 5. The substantially planar front wall 4d of
casing 4 forms an integral hollow or tubular cantilever-like
projection 4e extending into chamber 4a. Projection 4e has a
relatively small aperture 4f at the axially innermost end thereof.
The wall 4d further has a relatively large aperture or recess 4g
juxtaposed to and coaxially related to, aperture 4f. A shoulder 4h
is formed between aperture or recess 4g and the inner surface of
projection 4e. A blown fuse indicator is arranged in the space
defined by recess 4g and extension or projection, 4e . This
indicator includes a plunger of electric insulating material in the
form of a solid of revolution arranged in coaxial relation to
projection 4e and aperture or recess 4g. One end portion 6a of the
aforementioned plunger 6a,6b has a relatively large diameter and is
arranged inside of aperture or recess 4g and the other end portion
6b of the aforementioned plunger 6a,6b has a relatively small
diameter and is arranged adjacent the relatively small diameter
aperture 4f in projection 4d.
The end portion 6b of the insulating plunger 6a,6b has a
substantially transverse bore 6c and is surrounded by a
substantially helical compression spring 7. As seen in FIGS. 2 and
3, the right end of compression spring 7 rests against the larger
diameter portion 6a of plunger 6a,6b. A substantially bell-shaped
metal cap 8 projects from shoulder 4h in the direction of bore 6c.
Cap 8 supports the end of compression spring 7 remote from large
diameter end portion 6a of plunger 6a,6b. Cap 8 has a central bore
8a for the passage of the small diameter end portion 6b of plunger
6a, 6b. A fusible restraining wire 9 for plunger 6a,6b is threaded
through aperture 4f and is threaded three times through bore 6c as
shown in FIG. 5. Restraining wire 9 and cap 8 form cooperating
abutments limiting movement of plunger 6a,6b relative to casing 4
upon fusion of restraining wire 9. This is clearly shown in FIG. 3.
Restraining wire 9 is substantially V-shaped and its spaced ends
are clamped by screws 10 against terminal bars 1a,1b.
FIGS. 4 and 5 show the way in which restraining wire 9 is firmly
attached to the end portion 6b of plunger 6a,6b. Wire 9 is threaded
three times through bore 6c and forms two substantially
semi-circular loops 9a each engaging the lateral surface of end
portion 6b of plunger 6a,6b. Restraining wire 9 extends from
opposite sides of bore 6c away from bore 6c. The ends of
restraining wire 9 extending away from opposite sides of bore 6c
engage and are twisted about each other at a point juxtaposed to
the end surface of end portion 6b of insulating plunger 6a, 6b.
This is clearly shown in FIGS. 2 and 3.
The inner diameter of the portion of projection 4e housing end
portion 6b of plunger 6a, 6b is smaller than the inner diameter of
the cavity or recess 4g housing the portion 6a of plunger 6a,6b but
the axial length of said cavity exceeds the axial length of the end
portion 6a of plunger 6a,6b. The portion 6a of plunger 6a,6b is
slidably arranged inside of aperture 4g and metal cap 8 is
press-fitted into the portion of projection 4e whose inner diameter
is less than the diameter of aperture 4g. Shoulder 4h forms an
abutment precluding movement of plunger 6a,6b against the bias of
spring 7. Since the axial length of portion 6a of plunger 6a, 6b is
less than the length of the cavity 4a receiving it the front end of
portion 6a of plunger 6a,6b is normally recessed as clearly shown
in FIG.2.
Normally the difference in potential between screws 10 is virtually
zero because terminal bars 1a,1b are normally conductively
interconnected by fusible elements 2 whose ohmic resistance is
small. Upon fusion of fusible elements 2 the voltage between screws
10 is equal to the voltage of the arcs taking the place of fusible
elements 2. Hence a current flow is established through restraining
wire 9 resulting in fusion thereof at a point outside of projection
4e. Consequently spring 7 then propels plunger 6a,6b from the
position shown in FIG.2 to the position shown in FIG.3. Restraining
wire 9 or, to be more specific, portions 9a of wire 9 increase the
width of plunger portion 6b at one point thereof beyond the
diameter of bore 8a in metal cap 8. Thus wire 9 forms an abutment
cooperating with cap 8 and thereby limiting the travel of plunger
6a,6b from left to right as seen in FIGS. 2 and 3. In other words,
part 9a of wire 9 is a dual function means normally restraining
plunger 6a, 6b and limiting upon fusion of wire 9 the travel of
plunger 6a,6b as well as its removal from housing 4. In the
positions of plunger 6a, 6b shown in FIGS. 2 and 3 the plunger can
safely be touched since it is entirely of insulating material and
since any parts which have a contact potential and any points where
arcing occurs are spaced relatively far apart from the front end 6a
l of plunger 6a,6b.
Referring now more particularly to FIG. 5, it will be apparent from
that figure that the restraining wire 9 enters bore 6c on one end
thereof (e.g., the right end), extends through bore 6c leaves said
bore 6c at the other end thereof (e.g., the left end) and forms a
first substantially semi-circular loop 9a extending in one
direction along the lateral surface of the small diameter end
portion 6b of plunger 6a,6b. Restraining wire 9 re-enters bore 6c
at said one end thereof (e.g., the right end), extends a second
time through bore 6c, leaves bore 6c at said other end thereof
(e.g., the left end) and forms a second substantially semi-circular
loop 9a extending in a direction opposite to said one direction
along the lateral surface of end portion 6b of plunger 6a,6b. After
initial entry of wire 9 into bore 6c the former re-enters twice
into the latter (into the right side of bore 6c as seen in FIG. 5),
extends three times through bore 6c, as clearly shown in FIG. 5,
and leaves bore 6c at the opposite side it enters bore 6c. This way
of attaching wire 9 to plunger 6a,6b is of considerable importance
in view of the fact that the portion of the plunger to which
restraining wire is attached consists of an electric insulating
material rather than metal. It will also be apparent from FIG. 5
that the directions of both semi-circular loops 9a are opposite. To
be more specific, if the upper semi-circular loop 9a of FIG. 5 is
considered to be clockwise, then the lower semi-circular loop 9a is
counter-clockwise. As shown in FIG. 1, the ends of restraining wire
9 are firmly affixed by screws 10 to parts 1a,1b. Since it is the
middle section of restraining wire 9 which is attached to plunger
6a,6b rather than an end of wire 9, wire 9 and plunger 6a,6b cannot
be separated from each other as may occur whereever a restraining
wire is attached to a plunger at one end of the former which is
twisted around itself.
* * * * *