U.S. patent number 3,649,942 [Application Number 05/101,848] was granted by the patent office on 1972-03-14 for thermal limiter for one or more electrical circuits and method of making the same.
This patent grant is currently assigned to Micro Devices Corp.. Invention is credited to Emil Robert Plasko.
United States Patent |
3,649,942 |
Plasko |
March 14, 1972 |
THERMAL LIMITER FOR ONE OR MORE ELECTRICAL CIRCUITS AND METHOD OF
MAKING THE SAME
Abstract
This invention relates to a thermal limiter which can be used to
limit one or more electrical circuits, such as multiple circuits in
which one of the circuits is a primary circuit and the other
circuits are secondary circuits energized or controlled by the
primary circuit. The limiter of this invention is a unitary
construction which can be connected to the primary and secondary
circuits to control the same. A new method of making the limiter is
included in this invention. This invention can be used in
combination with a transformer for a television set in combination
with its primary and secondary circuits, in combination with an air
conditioning system, such as for automobiles, or in combination
with other devices, as desired.
Inventors: |
Plasko; Emil Robert (Washington
Township, OH) |
Assignee: |
Micro Devices Corp. (Dayton,
OH)
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Family
ID: |
26742180 |
Appl.
No.: |
05/101,848 |
Filed: |
December 28, 1970 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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62369 |
Aug 10, 1970 |
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Current U.S.
Class: |
337/163; 337/166;
337/186; 337/222 |
Current CPC
Class: |
H01R
13/68 (20130101); H01H 85/044 (20130101); H01H
85/46 (20130101); H01H 2085/466 (20130101); H01H
2085/2075 (20130101) |
Current International
Class: |
H01H
85/044 (20060101); H01H 85/00 (20060101); H01H
85/46 (20060101); H01R 13/68 (20060101); H01h
085/02 () |
Field of
Search: |
;337/182,186,163,166,164,165,222 ;219/501 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Gilheany; Bernard A.
Assistant Examiner: Bell; F. E.
Parent Case Text
This application is a continuation-in-part application of its
copending parent patent application, Ser. No. 62,369, filed Aug.
10, 1970, since abandoned and which was assigned to the same
assignee to whom this application is assigned.
Claims
What is claimed is:
1. A thermal limiter for at least one electrical circuit comprising
a thermally responsive fuse, lead means operatively interconnected
to said fuse for coupling said fuse in said circuit, an electrical
circuit heater means disposed in a selected position relative to
said fuse, and an insulating coating mass covering and securing
said heater means and said fuse in said selected positioning
thereof with said lead means having at least portions thereof
exposed from said mass whereby said mass and said selected
positioning provides a controlled time delay in said heater means
being adapted to cause said fuse to blow and thereby open said one
electrical circuit.
2. A thermal limiter as set forth in claim 1 wherein said heater
means comprises a plurality of separate heater wires.
3. A thermal limiter as set forth in claim 1 wherein said heater
means is spaced from said fuse, said mass being disposed between
said heater means and said fuse and acting as a heat conductor
therebetween.
4. A thermal limiter as set forth in claim 1 wherein said heater
means comprises a heater wire coiled on said fuse.
5. A thermal limiter as set forth in claim 1 wherein said heater
means comprises a heater wire disposed in series between one of
said lead means and said fuse.
6. A thermal limiter as set forth in claim 1 wherein a housing
means receives said heater means and said fuse therein in said
selected positioning therebetween, said mass being disposed in said
housing to cooperate with said housing to cover and secure said
heater means and said fuse in said selected positioning
thereof.
7. A thermal limiter as set forth in claim 6 wherein said heater
means comprises a coiled heater wire having its opposed ends
electrically interconnected to two lead means respectively having
portions thereof exposed from said mass and from said housing
means, said fuse having opposed sides thereof respectively
electrically interconnected to said first mentioned lead means one
of which is also one of said lead means electrically interconnected
to said heater wire.
8. A thermal limiter as set forth in claim 1 wherein said lead
means comprise a first pair of lead means respectively and
electrically interconnected to opposed sides of said fuse, a second
pair of lead means being respectively and electrically
interconnected to opposed sides of said heater means and having
portions thereof exposed from said mass.
9. A thermal limiter as set forth in claim 8 wherein said lead
means comprise the teeth of a plural circuit wire attachment comb
having an electrically insulative base carrying a plurality of
electrically conductive wire attachment teeth with wire attaching
base supported tooth ends secured to said base and with wire
attaching free tooth ends extending away from said base and into
said mass.
10. A thermal limiter as set forth in claim 9 wherein two
supporting wires oppositely extend from said fuse to two of said
free tooth ends which define said first pair of lead means, a
sleeve of insulative shrink tubing surrounding said fuse with said
two supporting wires extending from said sleeve, said tubing being
embedded in said mass.
11. A thermal limiter as set forth in claim 8 wherein said heater
means comprises another electrical heater disposed in series
between one of said first pair of lead means and said fuse.
12. A thermal limiter as set forth in claim 6 wherein said housing
means has means locating said exposed parts of said lead means
relative to each other.
13. A thermal limiter as set forth in claim 12 wherein said
locating means space said lead means with at least one different
spacing between adjacent lead means.
14. A thermal limiter as set forth in claim 12 wherein said
locating means comprise a wall of said housing means having a
plurality of aligned and spaced pocket means therein respectively
receiving said exposed portions of said lead means therein.
15. A method making a thermal limiter for at least one electrical
circuit comprising the steps of providing a thermally responsive
fuse, operatively interconnecting lead means to said fuse for
coupling said fuse in said circuit, disposing an electrical circuit
heater means in a selected position relative to said fuse, and
covering and securing said heater means and said fuse in said
selected positioning thereof with an insulating mass so that said
lead means have at least portions thereof exposed from said mass
whereby said mass and said selected positioning provides a
controlled time delay in said heater means being adapted to cause
said fuse to blow and thereby open said one electrical circuit.
16. A method of making a thermal limiter as set forth in claim 15
and including the step of forming said heater means for a plurality
of separate heater wires.
17. A method of making a thermal limiter as set forth in claim 15
wherein said step of disposing said heater means includes the step
of spacing said heater means from said fuse, and disposing said
mass between said heater means and said fuse to act as a heat
conductor therebetween by said step of covering and securing.
18. A method of making a thermal limiter as set forth in claim 15
and including the step of forming said heater means from a heater
wire and coiling said heater wire on said fuse.
19. A method of making a thermal limiter as set forth in claim 15
and including the step of forming said heater means from a heater
wire and disposing said heater wire in series between one of said
lead means and said fuse.
20. A method of making a thermal limiter as set forth in claim 15
and including the step of providing a housing means to receive said
heater means and said fuse therein in said selected positioning
therebetween, said mass being disposed in said housing to cooperate
with said housing to cover and secure said heater means and said
fuse in said selected positioning thereof.
Description
This invention relates to a thermal limiter for one or more
electrical circuits.
For example, one embodiment of the thermal limiter of this
invention can be used to limit multiple circuits in which a primary
circuit energizes or controls one or more secondary circuits, such
as a transformer having a primary circuit and secondary circuits.
The limiter of this invention is a unitary construction which can
be connected to such primary and secondary circuits in an efficient
manner.
One feature of this invention is to provide a thermal limiter
having a controlled delay action in the operation thereof to
prevent accidental circuit limiting, such controlled delay action
being provided by a fixed and controlled location of the heater
element relative to the limiter sensing element as will be apparent
hereinafter.
In addition, other features of the limiter of this invention is to
permit the selection of the heater element in its output
temperature, the selection of the sensing element for the required
sensed temperature for opening the circuit, and the selection of
the desired characteristics of the insulating mass that secures the
limiter parts together, such characteristics being the thermal
conductivity of the mass material, the size of the mass utilized,
etc. Other selectable variables of the limiter of this invention
will be apparent hereinafter.
For example, such a thermal limiter of this invention for at least
one electrical circuit comprises a thermally responsive fuse and
lead means operatively interconnected to the fuse for coupling the
fuse in a desired electrical circuit. An electrical circuit heater
means is disposed in a selected position relative to the fuse and
an insulating mass covers and secures the heater means and the fuse
in such selected position thereof with the lead means having at
least portions thereof exposed from the mass whereby the insulating
mass and the selected positioning of the heater means relative to
the fuse, once the desired variables of the fuse, mass and heater
have been selected, provides a controlled time delay in the heater
means being adapted to cause the fuse to blow and thereby open the
one electrical circuit.
This invention also includes a method of making the limiter of this
invention.
Many other features, advantages and objects will become obvious
from this description, the appended claimed subject matter, and the
accompanying drawings in which:
FIG. 1 is a side view of a plural circuit wire attachment toothed
comb or comblike member to be used in this invention;
FIG. 2 is a cross section along the line 2--2;
FIG. 3 is an opposite side view of FIG. 1;
FIG. 4 is a view showing a partial assembly in the production of
this invention and showing circuit wires secured to the free ends
of the teeth of the comb members and with a thermally responsive
fuse supported by two of said circuit wires;
FIG. 5 is a view similar to FIG. 4, but showing a completed form of
the invention;
FIG. 5A is an end view of FIG. 5;
FIG. 6 is a diagrammatic view of the invention used as a multiple
circuit temperature limiter in the circuit wires of a part of a
transformer circuit;
FIG. 7 is a diagrammatic view showing a transformer circuit
somewhat similar to the circuit of FIG. 6 but in which the
temperature is limited by separate limiters which can be eliminated
by this invention;
FIG. 8 is a top respective view of a housing structure for another
multiple circuit thermal limiter of this invention;
FIG. 9 is a cross-sectional view taken on line 9--9 of FIG. 8;
FIG. 10 is a top view of the housing structure illustrated in FIG.
8 and illustrates the fuse, heater wires and terminals assembled
therein;
FIG. 11 is a cross-sectional view taken on line 11--11 of FIG.
10;
FIG. 12 is a cross-sectional view taken on line 12--12 of FIG. 10
and illustrates the structure of FIG. 10 after the insulating mass
has been received in the housing means;
FIG. 13 is a side view of the completed multiple circuit thermal
limiter of this invention as coupled to a plural circuit wire lead
attachment means;
FIG. 14 is a top perspective view of another thermal limiter of
this invention;
FIG. 15 is an exploded perspective view of the various parts
forming the thermal limiter of FIG. 14;
FIG. 16 is a top view of the parts of FIG. 15 in their assembled
position and before the insulating mass has been disposed in the
housing thereof;
FIG. 17 is a cross-sectional view taken on line 17--17 of FIG. 16
and illustrates the thermal limiter after the insulating mass has
been placed in the housing means of FIG. 16;
FIG. 18 is a cross-sectional view taken on line 18--18 of FIG.
17;
FIG. 19 is a schematic view illustrating an electrical circuit
which can be utilized in combination with the thermal limiter of
FIG. 14;
FIG. 20 is a perspective view of another thermal limiter of this
invention before the same has been covered and secured in position
by an insulating mass;
FIG. 21 illustrates the thermal limiter of FIG. 20 in its completed
form after the insulating mass has been disposed thereon.
A plural circuit wire attachment toothed comb or comblike member
10, FIGS. 1, 2 and 3, may be an article of manufacture now on the
market and may have an electrically insulative base 12 carrying a
plurality of electrically conductive wire attachment teeth or lead
means 14. These teeth 14 may have wire attaching base supported
tooth ends 16 secured to the base 12. The teeth 14 may also have
wire attaching free tooth ends 18 extending away from said base
12.
The base 12 may be a relatively rigid insulative board strip made
of any suitable material.
The wire attachment teeth 14 may have wire attachment openings 20
embedded in said insulative base 12 and other wire attachment
openings 22 at the free ends of the teeth.
The base 10 may be a stiff insulative strip of any suitable
material to which the base supported tooth ends 16 are secured by
hollow rivets 24. These hollow rivets may be square tubes punched
out of the tooth ends 16 so that the tubes pass through the strip
10 and have their punched ends formed into rivets with outward
tongues 26 for attachment of circuit wires thereto. The free ends
18 of the teeth may have the wire attachment openings 22 punched
therein.
Suitable L-shaped support brackets 19 may be similarly riveted to
the board strip or base 12.
The article shown in FIGS. 1, 2 and 3 may be used in making the
multiple circuit limiter shown in FIGS. 4, 5 and 5A which is
suitable for simultaneously limiting or breaking multiple circuits
such as the primary circuit 28 of a transformer arrangement 30 and
one or more secondary circuits 32 and 34 of the transformer
arrangement 30, which transformer may be a transformer for a
television set.
The multiple circuit limiter or breaker shown in FIG. 5 may include
an insulative coating structure 36 which covers and separates the
various circuit wires which are mounted on the free ends 18 of the
teeth 14. Such structure 36 may also cover a thermal fuse 38 and
other parts to be described. The fuse 38 may be of the thermally
collapsible pellet type with the pellet 39 at one end of the fuse,
such as disclosed in P. E. Merrill U.S. Pat. No. 3,180,958,
patented April 1965. The result is that the mass 36 may be heated
by any one of the heating wires 40, 42 and 44 so that the heated
mass 36 causes the thermal fuse 38 to open or blow the primary
circuit 28 of the transformer 30 and thereby also deenergize the
secondary circuits 32 and 34 and prevent damage to the transformer
arrangement or the like.
It may be that one or more other secondary circuits 46 may be
energized by the primary circuit 28 of transformer 30. However,
such secondary circuit 46 may be of such current characteristics
that it cannot be embodied in the mass 36. Under such conditions, a
separate circuit breaker 48 may be provided in the secondary
circuit 46 which has a thermal fuse 50. The wires 52 and/or pins 54
may be made with sufficient resistance to blow the fuse 50 and also
break the one or more additional secondary circuits without
breaking the transformer circuit arrangement previously
described.
The insulative mass 36 may be formed as shown in FIGS. 4, 5 and
5A.
For example, any suitable insulative heat shrinkable sleeve 56,
FIG. 4, may be placed around the fuse 38 and the circuit wires 40
and 58 also partly inside the sleeve 56 and extend out of said
sleeve. The circuit wire 40 may be electrically resistive
sufficiently to blow the fuse 38 when wire 40 is overloaded. The
wire 58 is sufficiently conductive not to blow the fuse. A
substantially electrically nonresistive splice 60 may connect wire
40 and fuse 38. The collapsible pellet 39 is sufficiently close to
the heating wire 40 to be blown if the wire 40 is overloaded.
Thereafter, the ends of the wires 40 and 58 may be secured to the
free tooth ends 18A and 18B.
Then a heating circuit wire 42 is placed adjacent to and outside
the sleeve 56 and is secured to free tooth ends 18C and 18D so that
the main body of heating wire 42 is sufficiently close to fuse 38
to blow the fuse if the wire 42 is overloaded.
Thereafter, a heating circuit wire 44 is placed adjacent to and
outside sleeve 56 and also spaced from wire 42, but with its main
body adjacent the fuse 38 sufficiently close to the fuse to blow
the same if the wire 42 is overloaded. The ends of the wire 44 are
secured to the free tooth ends 18E and 18F.
The insulative sleeve 56 may be made of any suitable heat
shrinkable polyester such as mylar which is wrapped around parts of
the wires 42 and 58 and is then lightly heat shrunk, if
desired.
The assembly, as so far assembled in FIG. 4, is then dipped in any
well known ceramic or epoxy cement to form the insulative mass 64
around the sleeve 56 and around the wires 40, 42, 44 and 58. The
mass 64 may be somewhat oblong when viewed transversely, as in FIG.
5A, with parts extending to cover substantially all of said wires
40, 42, 44 and 58 and the free ends 18A, 18B, 18C, 18D and 18E of
the comb teeth. In this manner, the solidified mass 64 holds the
heating wires, 40, 32 and 34 in a fixed position relative to the
pellet 39 of the fuse 38 for a purpose hereinafter set forth.
FIG. 7 shows a transformer circuit somewhat similar to that shown
in FIG. 6. However, the limiters in FIG. 7 are individual to their
respective primary and secondary circuits. These limiters have been
individually mounted within the television cabinet or the like in a
manner to require experienced service means to provide service on
the parts rather than permit the owner to try and correct a blown
circuit by mere fuse replacement and not correct service on the
malfunctioning part.
The parts on the circuit of FIG. 7 have been marked with reference
numerals of FIG. 6 to indicate how the parts are unified by this
invention.
In FIG. 6, the transformer primary circuit may be connected to a
plug-in structure 68 so that the primary circuit energizes a
plurality of secondary circuits 32, 34 and 46, or more.
The finished product shown in FIG. 5 may be placed anywhere in the
primary circuit so that all the heater wires 40, 42 and 44 can heat
the insulative mass 64 which acts as a heat sink in a controlled
manner to cause the fuse 38 to blow if any of the heater wires are
overloaded.
In particular, the position of the heating wires 40, 32 and 34 as
held by the mass 64 in relation to the pellet 39 of the fuse as
well as the heat conductive characteristics of the mass 64 are so
selected that the fuse 38 will not immediately blow but will blow
only after a certain time period from the initial heating of one or
more wires 40, 32 and 34 and the continued heating thereof in order
to prevent inadvertent blowing of the fuse 38 should the service
man accidentally cause a temporary short circuiting by a
screwdriver engagement during a service check, etc.
Any isolated secondary circuit such as 46 can be broken by an
individual thermal fuse or current breaker 48.
Thus, it is to be seen that this invention includes an improved
multiple circuit thermal limiter 66, FIG. 5, which can be combined
with a multiple circuit such as a transformer circuit as shown in
FIG. 6. An efficient method of making such limiter is also
provided.
Another multiple circuit thermal limiter of this invention is
generally indicated by the reference numeral 70 in FIG. 13 and
comprises a housing means or base 71 formed of suitable insulating
material and carrying a plurality of quick connect and disconnect
sleevelike lead members 72 for effectively receiving bayonet type
lead strips 73 carried on an electrically insulating base or strip
74 adapted to be mounted to a desired supporting structure 75 by
suitable leg means 76 whereby the thermal limiter 70 of this
invention is adapted to be coupled to the lead attachment strips 73
of the board or base 74 by merely having the lead sleeves 72
telescoped over the projecting portions of the lead strips 73 so
that the thermal limiter 70 of this invention can be coupled into a
desired circuit means interconnected to the lead strips 73 in a
conventional manner.
The multiple circuit thermal limiter 70 of this invention has the
housing means 71 thereof provided with a substantially rectangular
base portion 77 with a cavity 78 formed therein and defining a
closed end wall means 79, opposed side wall means 80 and 81 and
opposed end walls 82 and 83 of the housing means 71 with the side
wall 81 having an extension 84 angled therefrom in the manner
illustrated in FIGS. 8, 9 and 10. The angled wall 84 has a
plurality of pockets 85 formed therein and defined between
outwardly extending ridge means 86 utilized for snap fitting and
retaining the sleevelike lead means 72 in a preassembled position
relative thereto.
For example, each lead means 72 comprises an upper sleevelike
portion 87 adapted to slip into a pocket means 85 under inwardly
directed ears 88 of the cooperating ridge means 86 so as to be held
flat against the angled wall 84 with the lower end 89 of the sleeve
87 abutting against locating shoulder means 90 on the ridge means
86 as illustrated in FIG. 12 whereby a lower wire attaching means
91 of the lead means 72 extends into the chamber or recess 78 of
the housing means 71. In this manner, the sleevelike lead means 72
of the thermal limiter 70 can be disposed in the pocket means 85 of
the housing means 71 so that the same will be uniformly positioned
relative thereto by the stop means or shoulders 90 and ears 88 of
the ridge means 86 whereby the sleevelike lead means 72 will be in
proper positions relative to the lead strips 73 of the insulating
base 74 when it is desired to couple a thermal limiter 70 of this
invention thereto.
If desired, the spacing between the pockets 85 on the angled side
wall 84 of the housing means 71 can be so spaced relative to each
other that the same will be compatible with like spacing of the
strips 73 on the insulating board 74 so that the thermal limiter 70
can be only coupled to the strips 73 on the board 74 when the
limiter 70 is held in a certain position relative thereto so that
wrong connecting to the board 74 will be prevented. For example, it
can be seen that the spacing between the middle two sleeve members
72 of the thermal limiter 71 of this invention is greater than the
spacing between any other adjacent pair of lead means 72 so as to
be compatible with like spacing between the lead strips 73 on the
base 74.
The end or bottom wall 79 of housing means 71 of the thermal
limiter 70 has upwardly extending longitudinal dividers 92 and 93
formed integrally therewith and dividing the recess 78 into three
chambers 94, 95 and 96 as illustrated in FIG. 11 whereby the
chamber 95 is adapted to receive a temperature responsive fuse 97
formed in the same manner as the fuse 38 previously described and
be electrically interconnected to the two outboard lead means 72 by
supporting wires 98 and 99 as illustrated in FIG. 10, the wire 99
being a heater wire in the same manner as the heater wire 40
previously described and being coupled to the right side 100 of the
fuse 97 by a substantially electrically nonresistive splice member
101 in the same manner as the splice member 60 previously
described.
A heater wire 103 can be disposed in the chamber 94 and have its
opposed ends 104 and 105 respectively interconnected to the next
two inboard lead means 72. Another heater wire 106 is adapted to be
disposed in the chamber 96 and have its opposed ends 107 and 108
respectively interconnected to the two innermost lead sleeves 72 as
illustrated in FIGS. 10 and 12.
In this manner, it can be seen that the dividers 92 and 93 separate
the heating wires 103 and 106 from the thermal fuse 97 as well as
the lead attachment wires thereof during the assembly operation as
illustrated in FIG. 10.
Thereafter, the desired insulative mass 109 is disposed in the
recess 78 of the housing means 71 to fill the same to the desired
level, which in the embodiment illustrated in the drawings is to
the top of the end walls 82, 83 and side walls 77, so as to not
only cover and secure the heating wires 99, 103 and 106 in the
desired selective positioning thereof relative to the fuse 97 when
the mass 109 hardens, but also to cover the lower ends 91 of the
lead means 72 so as to secure the lead means 72 in their assembled
relation in the pockets 85 so that the same cannot be subsequently
moved relative to the housing means 71.
In this manner the completed thermal limiter 70 of this invention
is adapted to be coupled to the lead board 74 in the manner
previously described and be uncoupled thereto by merely telescoping
or untelescoping the sleeve means 70 thereof to or from the lead
strips 73 of the board 74 in a simple and effective manner.
Thus, it can be seen that the thermal limiter 70 of this invention
is adapted to have the fuse 97 thereof open a circuit connected to
the outermost pair of terminals 72 thereof when any one of the
heating means 99, 103 and 106 generates sufficient heat to be
conducted to the fuse 97 by the thermal mass 109 to cause the fuse
97 to blow, it being understood that the selection of the
positioning of the heating wires relative to the fuse 97 as well as
the conductive characteristics of the mass 109 are so selected that
accidental blowing of the fuse 97 will not take place until the
overloaded or short circuited condition is in existence for a
length of time which would require circuit opening.
If desired, the thermal limiter 70 can be utilized in the same
manner as the thermal limiter 66 previously described or in other
circuit means for like purposes.
Another thermal limiter of this invention is generally indicated by
the reference numeral 110 in FIG. 14 and comprises an electrically
insulating housing means or base 111 having a recess 112
interrupting the top surface 113 thereof and receiving a heating
means 114 and a thermal fuse 115 therein to be selectively
positioned therein and subsequently covered and secured in such
selective positioning by suitable insulating means or mass 116 so
that three lead means 117, 118 and 119 respectively extend
outwardly from the mass 116 for coupling the thermal limiter 110 in
a desired circuit, such as the electrical circuit illustrated in
FIG. 19 and hereinafter described.
The heating means 114 includes a heating wire 120 mounted on a rod
121 and has its opposed ends respectively interconnected to the
terminals 117 and 118 having the lower portions 122 and 123 thereof
disposed in coiled fashion about the rod 121 to be rigidly secured
thereto.
The thermal fuse 115, similar to fuse 38 previously described, has
opposed lead wires 124 and 125 extending therefrom with the lead
wire 125 being secured to the terminal means 119 and with the lead
wire 124 being interconnected to the terminal 117 as illustrated,
the wires 124 and 125 being of sufficient strength to support the
fuse 115 in spaced relation relative to the heating means 114 in
the manner illustrated in FIG. 16 when the same are disposed in the
housing means 111 against a bottom wall means 126 thereof in the
manner illustrated in FIG. 16 so that the insulating mass 116 can
be subsequently disposed in the housing means 111 to cover and
secure the fuse 115 and heating means 114 in the selected
positioning thereof as illustrated, the insulating mass 116 being
disposed between the fuse 115 and the heating means 114 as
illustrated in FIG. 18 to provide insulation therebetween in the
same manner as the divider walls 92 and 93 of the housing means
71.
The thermal limiter 110 of FIG. 14 is adapted to be utilized in the
particular electrical circuit 127 of FIG. 19 in a manner now to be
described, but it is to be understood that the thermal limiter 110
can be utilized for other purposes as desired.
As illustrated in FIG. 19, the electrical circuit 127 is adapted to
be utilized for an air conditioner or the like wherein an
electrically operated drive clutch 128 is provided for the
compressor and is adapted to have its side 129 interconnected to a
suitable power source 130 by a lead means 131 interconnected by the
conventional air conditioning on-and-off temperature responsive
switch 132 to the terminal 119 of the thermal limiter 110 of this
invention while the other terminal 117 thereof is interconnected by
a lead 133 to the side 129 of the clutch 129 of the clutch means
128. The other side 134 of the clutch means 128 is interconnected
by a lead 135 to ground in the same manner that the other side of
the source 130 is interconnected to ground.
The terminal 118 of the terminal limiter 110 is interconnected to a
loss-of-charge sensor switch 136 which is in a normally open
condition as long as there is no loss of refrigerant of the air
conditioning unit utilizing the circuit 127.
Thus, it can be seen that the electrically operated clutch means
128 is adapted to function as long as the switch 136 is in an open
condition since the clutch means 128 is placed across the power
source by the thermal limiter 110 of this invention when the switch
132 is closed to demand that the compressor be operating.
However, if the loss-of-charge switch 136 closes due to the
refrigerant escaping from the refrigerant system, the compressor
would burn out within a few minutes because the same would not
receive sufficient lubrication whereby the heating means 114 now
operatively interconnected to the source 130 will heat up
sufficiently to cause the fuse 115 to blow and, thus, open the
circuit that operates the clutch 128 so that the clutch 128 can no
longer operate until the thermal limiter 110 is replaced.
However, in a normally performing air conditioning system, the
loss-of-charge switch 136 can close for a minute or so under some
unusual weather conditions whereby it would not be desired for the
thermal limiter 110 to blow and, thus, require a serviceman to
replace the same before the air conditioner can be operated. Thus,
the thermal limiter 110 of this invention has been so constructed
and arranged in the positioning of the heating means 114 relative
to the fuse 115 as well as in the selection of the thermal mass 116
to permit the loss-of-charge switch 136 to be temporarily closed
only for a minute or so without causing the fuse 115 to blow during
the unusual weather conditions, but will assure that the fuse 115
will blow should the loss-of-charge switch 136 be closed for a time
short of an adverse situation wherein the compressor would burn out
or the like.
Thus, it can be seen that the thermal limiter 110 of this invention
is adapted to protect an air conditioning system in the manner
illustrated in FIG. 9 through a controlled time delay thereof.
Another thermal limiter of this invention is generally indicated by
the reference numeral 137 in FIG. 21 and is formed of the parts
illustrated in FIG. 20 wherein a thermal fuse 138, similar to the
fuse 38 previously described, has opposed leads 139 and 140
extending from opposed sides thereof for completing a circuit
therethrough and has a heating wire 141 coiled upon the same with
the opposed ends 142 and 143 of the heating wire 141 so disposed
that the lead 143 is coupled to the fuse 138 in the same manner as
the lead wire 139 whereas the lead wire 142 extends away from the
fuse 138 as illustrated. Subsequently, an insulating mass 144,
formed in any suitable shape, is disposed about the assembly
illustrated in FIG. 20 so as to secure and cover the fuse 138 and
heating wire 141 to hold the same in the selected positioning
illustrated in FIG. 20 so that the lead means 139, 142 and 140
extend outwardly from the mass 144 for coupling into a desired
circuit. For example, the thermal limiter 137 is adapted to be
utilized in place of the thermal limiter 110 in FIG. 19 and serve
the same function thereof wherein the lead 142 is interconnected to
the loss-of-charge switch 136 and the leads 139 and 140 are adapted
to be respectively interconnected to the on/off switch 132 and the
electrical clutch 128.
In view of the above, it can be seen that this invention not only
provides an improved thermal limiter wherein a controlled time
delay thereof is provided by selective positioning of the heating
means and the fuse together with the desired heat conductive
characteristics of the securing mass, but also this invention
provides an improved method of making such a thermal limiter or the
like.
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