Note: Descriptions are shown in the official language in which they were submitted.
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MULTIPLE STAGE OPEN COIL ELECTRIC RESISTANCE HEATER WITH
BALANCED COIL ARRANGEMENT AND HEATER COOL END TERMINATION
AND METHOD OF USE
Field of the Invention
The present invention is directed to a multistage open coil electric
resistance
heater and method for use, and in particular, to a multistage heater
configuration
whereby the coil run of each stage is evenly arranged on either side of a
dividing plate
of the heater, the terminations of the coil runs are at the cool end of the
heater, and the
termination is particularly configured to accommodate threaded bolt or stud
connections.
Background Art
The use of a single resistance wire formed into a helical coil for use in
electric
resistance heating either for heating moving air, for radiant heating, or for
convection
heating is well known in the prior art. In one type of heater, the resistance
coils are
energized to heat air passing over the coils, the heated air then being
directed in a
particular manner for heating purposes. One application using such a heater is
an
electric clothes dryer.
Examples of open coil heaters are found in United States Patent Nos.
5,329,098,
5,895,597, 5,925,273, 7,075,043, and 7,154,072, all owned by Tutco, Inc. of
Cookeville,
Tennessee. Each of these patents is incorporated by reference in its entirety
herein.
One type of an open coil electric resistance heater is a two stage heater
described in
United States Patent No. 7,075,043. A side view of this type of heater is
shown in
Figure 1 and designated by the reference numeral 10. The heater 10 has two
heater
elements 10a and 10b, optimally for use in a clothes dryer. The elements 10a
and 10b
are supplied with electricity via terminals 12 extending from the terminal
block 28. The
heater elements 10a, 10b are supported by a support plate 14, which in turn
supports a
plurality of support insulators 16, typically made of ceramic material and
which are well
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known in the art. The support insulators 16 support and isolate coiled
portions of the
elements, 10a and 10b, during operation of the heater.
The heater 10 includes opposing sidewalls (one shown as 6 in Figure 1),
wherein
projections in the plate 14 extend through slots 20 in the sidewall 6 to allow
the
sidewalls to support the plate.
Each of the electric heater elements, 10a and 10b, is arranged in series of
electrically continuous coils which are mounted on the plate 14 in a spaced-
apart
substantially parallel arrangement. Each heater assembly 10a and 10b is
arranged
substantially equally and oppositely on both sides of the plate. Crossover
portions 22a
and 22b of each heater element 10a and 10b are provided wherein each crossover
links
one coil of each of the elements mounted on one side of the plate 14 with
another coil of
the same element found on the other side of the plate.
Electricity is supplied to the heater assembly through the terminal block 28.
The
heater elements, 10a and 10b, are arranged so that the terminal connector
portions or
wire leads 32 and 34 which extend from an end 38 of each of the mounted coil
sections
to the terminal block are as short as possible. This aids in eliminating or
reducing the
need for supporting the connector portions. For the longer runs, the wire
leads, 32 and
34, are partially enclosed with an insulating member 36. The insulating member
36 may
be formed from any type of insulating material suitable for this purpose,
e.g., a ceramic
type. The insulating member is generally tubular in shape and rigid.
Another type of heater manufactured by Tutco, described in US patent
application 11/987,542 (herein incorporated by reference) is an improvement
over the
heater shown in Figure 1, in that the heater coils are parallel to air flow to
minimize
noise, prevent coil "shadowing, and promote heat transfer from the heater
coils to the
air stream.
In the manufacture of appliances and equipment, especially clothes dryer
manufacture, that require open coil electric heaters mounted in an air duct to
heat air
flowing through the duct, there is a constant need to provide an inexpensive
method of
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making an electric heater having multiple stages of heat such that each stage
provides
some heat to each side of a support plate. In the prior art of open coil
heaters having
heater coils supported by ceramic insulators held in metal plates, one method
of
providing two stages of heat is to have one heater coil completely assembled
on one
side of the plate and the second coil on the opposite side, see United States
Patent No.
7,154,072. Upon energizing the first stage of heat, only the air on one side
of the plate
is heated making for a less than desirable heat distribution for the first
heating stage.
Another method to improve heat distribution is to route the first stage coil
so a
portion of the heater coil is on one side of the support plate with the
remainder of the
coil routed on the opposite side, see United States Patent No. 7,075,043 as
one
example. When these types of heaters are energized, heat is supplied to both
sides of
the duct during first stage heating. The second heat stage coils are similarly
assembled
to complement the first stage. This is an expensive design, as the ends of the
heating
element wire must be covered with special designed ceramic tubes or ceramic
beads
for electrical isolation to prevent grounding or reduction of electrical
clearance, see the
insulating members 36 in Figure 1 as an example. Some designs use special
designed
ceramics to secure the heating element wire ends to prevent shorting,
grounding or the
reduction in electrical clearance as the wires are routed to terminals. A well
accepted
method long used is to provide individual termination points located
immediately
adjacent to the element coil ends. This is an expensive alternative, as power
connections must be routed to multiple locations. Also, it is often
impractical as some
terminal locations may require power connections be made in excessively hot
areas
resulting in rapid deterioration under heat. Therefore, there is a need in the
industry for
a two stage, open coil electric heater that is inexpensive and has an
arrangement
wherein the first stage of the heater heats both sides of the air duct with
the second
heating stage complementing the first.
In the prior art there are usually either threaded style bolts or studs or
blade or
quick connect termination for power connection. Crimp style terminals made of
flat
metal stock for blade or quick connect termination crimped around resistance
ends is
well known and is presently sold by the TYCO Corporation. In the prior art, it
is a
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common practice when bolt and threaded stud terminal style terminals are
required for
power connection, that these terminals are attached to element wire ends by
welding,
crimping, or pressure connection.
Welding is usually done by first mechanically staking the element wire ends
into
a slot in the head of a terminal bolt and then welding the two together.
Crimping heating
element wire ends to threaded bolts is accomplished by creating a tube style
opening in
one end of threaded stud terminals, inserting the heating element wire ends
into the
tube openings, and then mechanically closing the tubes so as to create a crimp
connection. The least desirable connections are pressure connections in which
resistance wire coil ends are looped around terminal bolts or threaded studs,
then
"sandwiched" between a combination of washers and nuts, whereby subsequent
tightening of the nuts create electrical connections.
In the prior art, heating elements made as above are routed and assembled into
the intended positions with heavy termination bolts attached to the coil ends.
When a
common threaded terminal power connection is needed, as for two stage or other
multiple stage heaters, common element wire ends share a common terminal bolt
or
stud. When this type of connection is needed, the various methods of
connection
described above are followed except two or more element wire ends are
connected to
the required common terminal. For the welded connection, two or more common
element wire ends are placed in the terminal bolt slot, mechanically staked
then welded
as above. For the crimp method, two or more common element wire ends are
placed
into the tube opening and crimped as above. For the pressure connection
method, two
or more common element wire ends are looped together then "sandwiched" as
above
and the termination completed. Thus, for the three prior art termination
methods above,
at least one end each of heater wire elements of multiple stage heaters share
at least
one common terminal bolt.
A shortcoming with respect to the termination of heater coils is that when
threaded stud or bolt style termination for heaters is needed, prior art
methods require
the heating element wire ends to be first secured to heavy and cumbersome
terminal
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bolts; the coil and terminal bolt assembly routed and subsequently secured to
the coil
support insulators. If the pressure connection method is used so as to allow
heating
element coils to be first assembled into a heater and then to connect to
terminal bolts or
threaded studs, this process is cumbersome and labor intensive. Also pressure
electrical connections depend too much on the manual skill and attention of
the person
performing the task unlike a mechanical connection and thus generally are
avoided if
possible.
When threaded style terminations are required in the industry, there is needed
a
means to first make secure electrical connections between resistance wire coil
ends
and lightweight, easy to handle connectors that can later be attached to the
terminal
bolts or threaded studs whichever is used.
The present invention responds to the needs identified above by providing an
improved open coil electrical resistance heater. The improved heater
configuration that
overcomes the problems noted above, by especially providing equal
proportioning of the
heater stages on either side of the support plate dividing the heater while at
the same
time arranging the terminal portions of the heater coils in the same location
of the heater
to reduce the need for extra supports and/or insulation and improving the
manner of
termination involving these types of heaters.
Summary of the Invention
It is a first object of the invention to provide an improved multiple stage
open coil
electrical resistance heater.
It is another object of the invention to provide a multiple stage open coil
electrical
resistance heater that uses specially-configured heater coils so that
generally equal
portions of the stages are arranged on either side of the support plate that
divides the
heater.
A further object of the invention is a multistage open coil electrical
resistance
heater that includes an improved termination configuration, from the
standpoint of the
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termination with respect to the heater itself and the particulars of the
termination for
power connection.
Another object of the invention is a method of heating air using an open coil
electrical resistance heater having the specially configured heating coils
and/or
termination arrangement.
Other objects and advantages will become apparent as a description of the
invention proceeds.
In satisfaction of the foregoing objects and advantages of the invention, in
open coil
electrical resistance heater subassemblies that have a support plate dividing
the heater
into at least two portions, at least two resistance wire coils, and a
plurality of insulators
mounted to the support plate along a defined path, wherein each insulator
configured to
provide support to a portion of the resistance wire coil. The invention is an
improvement
over these subassemblies by the at least two resistance wire coils being
partitioned
generally equally on each side of the support plate. The at least two
resistance wire
coils aiso configured with their terminal ends located at one end of the
support plate.
This one end is, in effect, the cool end of the heater containing the
subassembly so that
the terminals used to connect to the coil ends are not subjected to the heat
generated
by the coils.
Each of the at least two resistance wire coils can have a first terminal on
one coil
end and a second terminal on the other coil end. The first terminal can
comprise a first
end crimped to the one coil end and a second flat end with an opening sized to
receive
an elongate member of a terminal. This first terminal facilitates the
connection to a
power terminal that may use a threaded stud or bolt. In one mode, two thirds
of each of
the at least two resistance wire coils can be arranged on one side of the
support plate.
Another mode of the invention has one side of the support plate supporting
portions of the at least two resistance wire coils along a generally
longitudinal path
along a length of the support plate. The other side of the support plate can
support
remaining portions of the at least two resistance wire coils, wherein one of
the at least
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two resistance wire coils follows a generally longitudinal path and includes
two
crossover portions and the other of the at least two resistance wire coils
extends along
two generally parallel longitudinal paths.
In yet another mode, one of the at least two resistance wire coils has its
coil ends
arranged on one side of the support plate with the other of the at least two
resistance
wire coils having one coil end on one side of the support plate and the other
coil end on
the other side of the support plate.
The heater subassembly can be part of a multistage open coil resistance
heater,
wherein the support plate is mounted to a heater duct that surrounds the at
least two
resistance wire coils to form a passage for flow of air to be heated by the at
least two
resistance wire coils. The heater duct can have a power terminal mounted on
one end
thereof and at least one of the terminal ends is an elongate member extending
from the
power terminal, wherein each of the at least two resistance wire coils has a
first terminal
on one coil end and a second terminal on the other coil end, the first
terminal further
comprising the first end crimped to the one coil end and the second flat end
with an
opening sized receiving the elongate member of the power terminal for
connection to
power.
The invention also entails the use of the heater and subassembly described
above by heating air using an open coil electrical resistance heater for a
given
application.
The invention also entails the use of the unique terminal arrangement at the
end
of one of the coils for power terminal connection and the method of assembiy
wherein
the unique terminals facilitate the assembly of the heater and power terminal
connection.
Brief Description of the Drawings
Reference is now made to the drawings of the invention wherein:
Figure 1 is a side view of a prior art open coil electric resistance heater.
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Figure 2 is a top view of a support plate and coil arrangement depicting one
embodiment of the inventive heater;
Figure 3 is bottom view of the support plate of Figure 2.
Figure 4 is a schematic showing the arrangement of the coils depicted in
Figures
2 and 3.
Figure 5 shows the coils separated from the heater assembly for better
clarity.
Figure 6 is a schematic showing an exemplary termination arrangement for an
assembled heater using the assembly of Figures 2 and 3.
Figure 7a is top view of the terminal shown in Figure 5.
Figure 7b is a side view of the terminal of Figure 7a.
Figure 7c is an end view of the terminal of Figure 7a.
Description of the Preferred Embodiments
The invention offers advantages in the field of open coil resistance heaters
in that
the problems associated with compiicated insulating and support arrangements
for
multiple stage heaters that are arranged symmetrically about a heater support
plate are
eliminated. The inventive heater also solves the problem when connecting the
resistance wire coil ends to bolt or stud terminals for power connection.
In one embodiment, the invention is a duct mounted, open coil, multiple stage
open coil electric heater using a support plate to retain insulators that in
turn retain
convolutions of a heating element coil. For two stage heaters, unlike the
prior art
heaters, a unique coil routing has the first stage of heat providing heat to
both sides of a
support plate so that the air stream on each side of the duct is heated. This
unique
routing requires neither special ceramic insulators for insulating the heating
element
wire end nor carefully separated termination points.
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The second stage of heat has a similar routing to complement the first stage.
All
coil ends are located at one end of the heater plate making power lead routing
as
simple as possible. With this design, the power termination leads can be
located at the
lowest temperature or cool end of the heater minimizing deterioration by
temperature.
A further feature of the invention is a special terminal for crimping to
heating
element wire ends. The inventive terminal has a hole for connecting to a
threaded stud
or bolt. By making the terminal small and lightweight, it can be crimped to
the ends of
coiled heating element wires adding little mass or volume to the coil ends.
This permits
the coil with the terminals attached thereto to be easily assembled in their
intended
location. The inventive terminals can be fitted either over the ends of
threaded terminal
studs or terminal bolts can be passed through the hole in the terminal. When
the nuts
are tightened the new terminal may be sandwiched between some combination of
washers and nuts making a secure connection. The connection is electrically
secure
because the current passes from the resistance wire through the crimp, to the
terminal,
from the terminal to the washers and nuts and on the threaded stud or bolt
with little
resistance because of the excellent surface area and mass of the system.
Referring now to Figures 2-4, a heater subassembly 20 as one embodiment of
the inventive heater is disclosed. Figures 2 and 3 depict a support plate 21
as part of
the subassembly 20. The support plate 21 has a number of openings 23, which
are
sized to retain insulators 25. The insulators 25 are configured to connect to
and support
the coils 27 and 29.
The heater assembly 20 is a two stage heater, although more stages could be
employed if so desired. The two stage heating is accomplished by the pair of
resistance
wire coils 27 and 29, with coil 27 representing the first stage and coil 29
representing
the second stage.
Coil 27 has opposing terminal ends 31 and 33, with coil 29 having opposing
terminal ends 35 and 37. Terminal ends 31 and 35 have a first type of terminal
39
attached thereto. Terminal ends 33 and 37 have a second type of terminal 41
attached
thereto. Terminal 41 is a conventional blade end crimp style terminal whereby
the end
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of the resistance wire is crimped to one end of the terminal. The other end is
a flat
configuration for connection as is well known in the art. Since these blade
end crimp
type terminals are well known, a further description is not necessary.
Referring now to Figures 5 and 7a-7c, the terminal 39 has a crimp end 43 and
flat end 45. The crimp end 43 includes a pair of flanges 47, with a slot 49
between the
flanges. The slot 49 receives the end of the coil wire and the flanges 47 are
crimped to
form a tight connection between the coil wire end and crimp end 45. The flat
end 45
has an opening 51 that is sized to receive a stud or bolt or other elongated
terminal
member for connection. As described above, the terminal 39 can hold a bolt
during
assembly of the heater, with the bolt making the power connection once the
heater is
finally assembled. In the alternative, the terminal 39 can be used once the
heater is
completely assembled to attach to a particular stud or bolt using the
necessary
combination of washers and nuts for a secure connection. Thus, the manufacture
of the
heater assembly has maximum capability when assembling the heater to
accommodate
different modes of assembly.
Referring now to Figures 2-4 and 6, the unique arrangement of the coils 27 and
29 produces a termination zone 53 of the coils at one end of the support plate
21.
Referring to Figure 6, one end of a completed heater 60 is shown. The heater
60
includes the support plate 21, insulators 25, and coils 27 and 29, and their
respective
terminals 39 and 41. The heater 60 includes a circular duct 61 (other shaped
ducts
could be used) that is linked to the support plate using openings in the duct
and the
protrusions on the support plate as is well known in the art. The support
plate 21
divides the duct into two halves, but other plates could be used to create
more sectors
of the heater.
The heater 60 supports a power terminal 63, which includes a ceramic bushing
65, with elongated members, e.g., threaded studs 67, extending from each end.
One
stud 67 attaches to both terminals 39 of the coils 27 and 29 using nut 69 and
washer 71
(other combinations of washers and nuts or other fasteners may be employed).
The
other stud 67 is attached to power. The blade terminals 41 are attached to two
other
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terminals 73 and 74 as conventionally done for these types of heaters. The
terminals
73 and 74 have connectors 76 opposite the connection to terminals 41 to
complete the
circuitry of the heater.
By the configuration of the coils and formation of the termination zone 53,
the
terminations of the coil ends are located at one end of the heater. By
positioning this
end into upstream of the flow of air (where ambient air is introduced into the
heater), the
termination zone is on the cool side of the heater so that the effects of
heated air on the
terminations is minimized. Also, the terminals are all in the same location,
which makes
it easier to routing wiring and installing the heater.
The unique configuration of the coils is best seen in Figures 2-4 and 6.
Figure 2
represents the coils mounted to the side 75 of the support plate 21 (shown as
the right
side of the heater of Figure 6) with Figure 3 showing the coils mounted to the
side 77 of
the support plate 21 (shown as the left side of the heater of Figure 6). For
ease of
understanding, the sides 75 and 77_each have a reference mark 79.
On side 77, it can be seen that there are two runs of the second stage coil 29
and one run of the first stage coil 27. On the opposite side 75, there is one
full run and
two half runs of the first stage coil 27, and two half runs of the coil 29.
This
configuration means that when the first stage heater is used, air passing on
both sides
75 and 77 of the support plate is heated. Similarly, during a two stage
heating, air
passing on both sides is heated from both coils 27 and 29. If the runs on each
side
were considered to be in thirds, side 77 has two thirds of the coil 29 and one
third of the
coil 27, with side 75 having two thirds of the coil 27 and one third of the
coil 29.
Figure 4 shows the runs of coils in one drawing, which more clearly depicts
the
crossovers between the plate 21 and crossovers between coils 27 and 29 on each
side
of the plate 21. For side 77, coil 29 has both ends 80 of the coil portion
(see Figure 5 to
more clearly see the end of the coil portion of the coil) terminate on side
77, with the two
runs linked by crossing over at crossover portion 82 to the two half runs on
side 75,
which are linked by crossover portion 85.
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Coil 27 has one coil end 78 terminate on side 77, with one crossover at
crossover portion 84 to side 75 to another long run. The long run on side 75
links to
one of the short runs on the same side by crossover portion 88, which in turn
links to
another short run on the same side by another crossover portion 90 so that the
coil end
terminates on side 75 at end 31 and terminal 39. While the free and uncoiled
ends of
the coils 27 and 29 could cross over the support plate 21 to attach to the
desired
terminal as shown in Figure 6 for coil end 35, the ends of the coils
themselves, i.e., 78
and 80, are separated by the support plate 21.
Figures 2 and 3 also show the runs of the coils 27 and 29 in a sinusoidal
pattern
or configuration. Each of the resistance wire coil 27 and 29 has a
longitudinal axis
generally parallel to an air flow path of the heater. At least a portion of
the insulators 25
that support the coils 27 and 29 are offset from the path. These offset
insulators 25
when combined with the insulators 25 on the path cause at least a portion of
the
resistance wire coil to have a sinusoidal shape as disclosed in application
11/987,542
noted above. It is this sinusoidal shape that provides advantages in terms of
noise
reduction, reduction of the shadowing problem, minimizing vibration resonancy,
and
better filling the volume of the heater for maximized heat transfer. While
this sinusoidal
shaped coil configuration is a preferred one, other coil configurations could
be employed
such as a straight configuration that has no sinusoidal pattern.
While the disclosed embodiment shows a particular arrangement of terminals for
each side of the plate 21, the terminals 39 and 41 could be switched if the
terminations
on the heater duct dictated such a switch.
It should be also understood that the unique configuration of the coils and
creation of the termination zone 53 can be used with any types of terminals
for the ends
31, 33, 35, and 37 of the coils. Also, while a two stage heater is shown,
additional coils
could be employed without departing from the equal partitioning of the coils
for each
stage on each side of the plate and maintaining termination at the cool or
upstream end
of the heater. The support plate 21 is typically metal in these types of
heaters, but it can
be any material capable of providing the desired strength and stability during
the heater
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operation, a non-metallic material, composite and the like. The other heat
components
can also be made of any materials that are capable of functioning in the
environment of
open coil resistance heaters.
In use, the heater of the invention can be used to heat air passing over the
coils
in the known fashion. Also, the inventive terminal configuration allows the
terminals 39
to be attached to one end of the coil prior to heater assembly or during an
early stage of
the assembly. The lightweight nature of the terminal avoids the problem
encountered
when heavy bolts have been used in the past. The use of the terminal 39
enables a
secure termination at the power terminal to be easily made using nuts and
washers.
As such, an invention has been disclosed in terms of preferred embodiments
thereof which fulfills each and every one of the objects of the present
invention as set
forth above and provides a new and improved multiple stage open coil
resistance heater
with specially configured coils and termination arrangement and a method of
heating
using the specially configured coil.
Of course, various changes, modifications and alterations from the teachings
of
the present invention may be contemplated by those skilled in the art without
departing
from the intended spirit and scope thereof. It is intended that the present
invention only
be limited by the terms of the appended claims
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