Note: Descriptions are shown in the official language in which they were submitted.
9~
The invention relates to a flexible heating element.
More speci~ically, the invention relates to such a flexible
heating element as either the type which can be used as the
covering material for a heated chair or the type which can be
disposed under the covering material, or the type which can be
draped over an ordinary chair to transform it to a heated
chair. The invention also relates to a dual proportional
control means for controlling khe power flow through the
heating elementO
Heated chairs are known in the art as shown, for
example, in the Volvo Brochure Parts Manual 1975. As will be
appreciated, with heated chairs in a household, the ambient
temperature of the house can be kept down since when a person
is seated, he will be heated by the heated chair. When he is
up and moving about, he does not require as much heat since his
own body will be producing heat to warm him. Thus, the
presence of heated chairs in a houshold can be energy con-
~ervative, Presently available heated chairs were provided for
comfort only, and were therefore not designed to maximi~e
energy conservation.
It is also known to provide flexible heating elements
as described in U. SO Patent 4,044,221, Kuhn, August 23, 1977.
However, this element of Kuhn is relatively bulky and is meant
for installing in new seats. It cannot be used as a covering
material for a chair, or draped over an existing chair.
Heat responsive control circuits, for example, for
electrically heated blankets, are also known in the art as
described in Canadian Patents 777,289, Wray, January 30, 1968
and 868,615, Naoi et al, April 13, 1971, as well as United
States Patents 3,422,244, Lauck, January 14, 1969 and 3,564,203,
Naoi et al, February 16, 1971. The "General Electric SCR
Manual, 4th Edltion 1967" also lllustrates a heat responsive
control circuit on pages 186 to 189. EIowever, none of these
said heat responsive control circuits is a dual proportional
control. None of these heat responsive controls can be
variably set to regulate both ~i) the firing angle of a triac
determining the average power flowing through the load and (ii)
the range of duty cycles (i.e. on off periods) dependent upon the
rate of cooling determined by the ambient room tempera-ture.
~one of these said heat responsive control circuits can provide
the variety and degree of comfort control and saving of energy.
It i~ therefore an object of the invention to provide
a flexible heating element which can be used either as a cover
ing material for a chair or which can be draped over an existing
chair, or which can be disposed under the covering material.
It is a further object of the invention to provide
such a flexible heating element with a control means having dual
control over both the average power delivered to the heating
element and the range of duty cycles of the heating element.
In accordance with the invention, there is provided
a ~lexible h~ating element which comprises: a glas fibre
fabric layer made of intermixed glass fibre strands, electrical
resistance wires in said glass fibre fabric layer and defining
a regular pattern in said glass fibre fabric layer; a top layer
of a thermoplastic material on one side of said glass fibre
fabric layer, a bottorn layer of a thermoplastic material on the
other side of said glass fibre fabric, and a metallic foil layer
applied to the bottom lay~r on the side remote from the said
glass fibre fabric layer, characterized in that said top layer,
said bottom layer and said metallic foil layer are heat fused
or adhesiv~ly laminated to said glass fibre fabric layer.
-- 2 --
The invention will be better understood by an examin-
ation of the following descrlption, together with the accompany-
ing drawings, in which~
FIGURE 1 is an exploded isometric view of t~e
inventive heating element, and
FIGURE 2 is a circuit diagram of the inventive
control means.
Referring now to Figure 1, the heating element com-
prises a glass fibre fabric layer 1 made of intermixed glass
fihre strands 3, The strands may be either matted in a semi-
regular pattern or woven in a regular pattern, ~esistance
wires 5a an~ 5b, are arranged in a regular pattern preferably
with 5b undulating in the layer 1. They would be intermatted
in the layer 1 when the layer co~prises a matted layer, and
interwoven when the layer comprises a woven layer. In either
case, they would form an integral part of the layer 1.
Both the wire~ 5a and 5b are composed of an insulat-
ing core of glass fibre, similar to strands 3, around which is
wound, in a helical path, an electrically resistive wire prefer-
ably made o~ a nickel-iron alloy such as the alloys identified
by the trade rnarks Nichrom or Chromalloy.
The top and bottom layers of the heating element, 7
and 11 respectively, consist of thermal plastic sheets and each
of the sheets may have the following properties: Electrically
insulating to 275 volts at the operating temperature of 41C
(105F): flexibl~, moisture resistant, 0.5 to 2.0 mm thickness
composed of cross-linXed polyethylene or poly~vinyl-chloride.
The bottom layer 11 also includes a layer of metallic
foil 9, such as aluminum foil, to reflect the radiant heat
upwards.
Although the layers are shown separated ~exploded
isometric) in ~igure 1, they are actually heat fused, or
adhesive-laminated, to the middle layer 1 to orm an integral,
and very thin, sheet which can be used to form the covering
material for a heated chair, or which can form a sheet for
draping over an ordinary chair to transform it to a heated
chair, or which can be disposed under the covoring material
of the chair~
Metallic mesh or foil connector terminals 17a and 17b
are connected at one end of the heating element to the respect-
ive ends of wires 5a and 5b, and at the other end of said
heating element, the ends of the wires Sa and 5b may be joined
together by mesh or ~oil connector term.inal 15. Conductor leads
~6a and 16b extend from the respective terminal~ 17a and 17b
to the outside of the element. The conductor leads of one or
more heating elements may be connected to housing l9 which
includes controls 21 and 23 whose function will be described
in the discussion of Figure 2. Subsequently the conductor
leads 22a and 22b are connected to switch Sl which may be
ei~her a pressure activated microswitch or a manual swi~ch
integral in the exterior of housing 19.
In operation, the switch Sl is preferably a micro-
switch disposed under the seat area of the element so that the
pressure of a person sitting on a chair in which the element
is disposed will automatically actuate the switch to turn on
the element as will be apparent in the consideration of
Figure 2. When the person gets off the chair, the release of
pressure will cause the switch Sl to be deactivated so that the
element is automatically turned off when it is no longer needed.
Finally, the re~pective conductor leads 18a and 18b are con-
nected to plug 35, which can be plugged into a wall socket
to provide power to the element.
- 4
Turning now to Figure 2, the control circuit includes
the switch Sl which, when turned on, will permit power to flow
to the load Sa and 5b, illustrated schematically in Figure 2.
In circuit with the load 5a and 5b is the bimetallic switch B
which, as well known in the art, consists of two adjacent strips
of metal having different cosfficients of heat expansion which
form a si.ngle strip 25. When the bimetal switch 25 is exposed
to a predetermined degree of heat, it will. bend upwardly away
from the terminal pad ~9 toward contact 31. The position of
the entire bimetallic switch 25 with respect to the terminal
pad 29 is adjustable by means schematically represented at 23
in Figure 2, The means 23 could be a screw-adjustable fulcrum
for strip 25 for example.
As the entire bimetallic strip 25 is moved toward th~
edge of the pad 29, a smaller change in temperature is required
to move the free end of it of the pad in the direction o
contact 31.
Included as part of the bimetallic switch, and mounted
on the strip 25 is a resistor 27. As can be seen, the current
which flows through 27 is proportional to the current which
flows through the load 5a and 5b. Thus the bimetallic switch
measures, and is controlled by, the heating power in the heating
element.
When strip 25 is off the pad 29, current will no
longer flow through the load 5a and 5b or the resistor 27, and
the resistor 27 will now cool down so that strip 25 will also
cool down and straighten out to return to pad 29. As the
housing 19, in which the bimetallic switch is disposed, is
outside the heating element, the cooling rate of the resistor
and of the strip 25 i3 determlned by the ambient temperature.
The rate at which B opens and closes, i.e. its duty ratio, is
determined by the ~ettiny of 23, the setting of 21 (as will
be discussed below) and the ambient temperature of the air
surrounding the control, so that the average power delivered
to load 5a and 5b is a function of both the average power
setting (on 21), and the ambient room temperature.
The control circuit also includes a variablç imped-
ance, such as variable resistor 21 (preferably a linear
potentiometer, P) and a capacitor C connected to each other
in series. Connected to the junction of the resistor and
capacitor is one end of a diac D who$e other end is connected
to the control terminal of a triac T. The value of the resist-
ance of 21 and the capacitance o~ C determines the firing angle
of the triac, and this value is, of course, variable by adjust-
ment of 21. As well known in the art, the triac will conduct
through a greater or lesser part of each period of an AC
cycle applied thereto depending on the firing angle of the triac~
As power flows through the load 5a and 5b only when the triac
is conducting, the firing angle set by the RC circuit (by
adjustin~ 21) will determine the average power setting of the
element. The average power actually delivered to the load
will, of course, be modified by the duty ratio of the bi-
metallic switch B.
The diac is provided for full wave power control as
discussed in the General Electric SCR Manual, supra.
In operation, the heating element is made thin enough
so that it can comprise either the covering material of a heated
chair or it can be formed separately to be draped over an
ordinary chair or it can be disposed under the covering material.
In all cases the switch Sl may be disposed either on the seating
area of the chair or on the outside of control housing 19. The
control means is disposed so that it is convenient to a user.
- 6 ~
8 ~
When a person ~its on the chair, h~ automatically turns on the
heating element, and when he gets up, he automatically turns
it o~.
The heat level of the heating element is set by the
~ual controls 21 and 23 as discussed above. In operation, the
average power flow through the load is first adjusted by con-
trol 21 until the user feels an agreeable level of heat
intensity, Then control 23 is adjusted to give the user an
agreeable duty ratio of heat-on and heat-off, and that ratio
will also be sensitive to the ambient room temperature.
It will be obvious that a heating unit can consist
of one heating element and one control. Alternatively, it can
consist of the same single control connected with a plurality
of heating elements. In the lat~er case, the heating elements
may be connected in parallel with each other.
Although a single embodiment has been described, this
was for the purpose of illustrating, but not limiting the
invention. Various modifications, which will co~e readily to
the mind of one skilled in the art, are within the scope of
the invention as defined within the scope of the appended
c-laims.
