U.S. patent number 3,715,550 [Application Number 05/228,135] was granted by the patent office on 1973-02-06 for induction cooking/warming appliance including vessel supporting means having an undulant surface and temperature sensing means associated with said surface.
Invention is credited to John D. Harnden, Jr., William P. Kornrumpf.
United States Patent |
3,715,550 |
Harnden, Jr. , et
al. |
February 6, 1973 |
INDUCTION COOKING/WARMING APPLIANCE INCLUDING VESSEL SUPPORTING
MEANS HAVING AN UNDULANT SURFACE AND TEMPERATURE SENSING MEANS
ASSOCIATED WITH SAID SURFACE
Abstract
Disclosed herein is an induction range having a counter
including an undulant top surface for supporting a cooking vessel.
Since the counter is made of a material which is not inductively
heatable the counter remains relatively cool during the cooking
process, while the vessel is being inductively heated. Although the
counter's top surface has undulations therein, it is, nevertheless,
an unbroken surface; i.e., there are no openings therethrough.
Moreover, even though the counter's top surface has undulations
therein, it may, nevertheless, be relatively smooth so that it can
be wiped clean, easily. Furthermore, temperature sensing means are
arranged on the top surface of the counter between adjacent
undulations thereof and said sensing means are adapted to be
contacted and easily compressed by the bottom surface of a vessel
resting on the counter's top surface; i.e., resting on the
undulations.
Inventors: |
Harnden, Jr.; John D.
(Schenectady, NY), Kornrumpf; William P. (Schenectady,
NY) |
Family
ID: |
22855960 |
Appl.
No.: |
05/228,135 |
Filed: |
February 22, 1972 |
Current U.S.
Class: |
219/622; 126/39J;
336/DIG.2; 219/504; 374/141; 219/627; 219/667 |
Current CPC
Class: |
H05B
6/062 (20130101); Y10S 336/02 (20130101) |
Current International
Class: |
H05B
6/06 (20060101); H05B 6/00 (20060101); H05B
6/12 (20060101); H05b 009/00 () |
Field of
Search: |
;219/10.49,10.77,10.79,502,504,10.75 ;126/39J ;73/343R,351,362AR
;340/210,21MB ;307/117 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Murakami, "Characteristics of Ferrite Cores with Low Curie
Temperature," IEEE Trans. on Magnetics, June, 1965, pp.
96-100..
|
Primary Examiner: Staubly; R. F.
Assistant Examiner: Reynolds; B. A.
Claims
What is claimed is:
1. An induction cooking/warming appliance, for heating a vessel
having at least one portion thereof in which heating current may be
induced by subjecting said one portion to a changing magnetic
field, comprising: vessel supporting means in which no substantial
heating current is inducted when said supporting means is subjected
to a changing magnetic field, said supporting means having first
and second back-to-back surfaces, said first surface including at
least two spaced-apart undulations therein defining a valley
therebetween, said vessel being supportable on said two
undulations; an induction coil energizable for producing a changing
magnetic field in said one portion of said vessel when said vessel
is supported on said undulations; means for energizing said
induction coil; temperature sensing means located in said valley
and comprising spring means, a temperature sensor unit supported by
said spring means and having an electrical impedance which varies
with temperature, means including a first magnetic flux path and a
coil wound about said first flux path and connected to said sensor
unit, said spring means being contacted and stressed by said vessel
when said vessel is supported on said two undulations and whereby
said sensor unit supported by said spring means is subjected to the
temperature of said vessel; temperature receiving means supported
on said second surface of said vessel supporting means and located
opposite said valley of said first surface whereby said vessel
supporting means is interposed between said temperature sensing and
receiving means, said temperature receiving means comprising means
including a second magnetic flux path and a coil wound about said
second magnetic flux path whereby said first and second flux paths
together with a portion of the interposed vessel supporting means
form a magnetic circuit; and, means for electrically energizing
said coil on said second magnetic flux path to introduce a changing
magnetic flux into said magnetic circuit whereby the temperature
variable impedance of said sensor unit, as reflected to an electric
circuit including said coil wound about said second flux path, is
representative of the temperature of said vessel.
2. The appliance according to claim 1 further comprising a
temperature signal processing circuit and temperature indicator
means, said signal processing circuit being electrically coupled to
said coil wound about said second flux path and to said temperature
indicator means whereby said signal processing circuit in response
to said reflected impedance produces a signal representative of the
temperature of said vessel for energizing said indicator means
whereby said temperature is visibly displayed.
3. The appliance according to claim 1 wherein said induction coil
is electrically energized with at least ultrasonic frequency and
wherein said coil on said second flux path is electrically
energized at a different frequency.
4. The appliance according to claim 1 wherein said first surface
including said undulations and valley present a relatively smooth
surface which is easily wiped clean.
5. The appliance according to claim 4 wherein said spring means is
a cup-like member of relatively thin elastic material having an
exposed relatively smooth surface which is easily wiped clean, said
cup-like member being secured in said valley and forming together
with said first surface including said undulations and valley and
enclosure for said first flux path and coil thereabout, said sensor
unit being at least partially embedded in said cup-like member,
said cup-like member having a relatively low restoring spring
force.
6. The appliance according to claim 5 wherein said relatively thin
elastic cup-like member of low restoring spring force is adapted
for being contoured to the irregular surface of a vessel in contact
therewith.
7. An induction cooking/warming appliance, for heating a vessel
having at least one portion thereof in which heating current may be
induced by subjecting said one portion to a changing magnetic
field, comprising: vessel supporting means in which no substantial
heating current is induced when said supporting means is subjected
to a changing magnetic field, said supporting means having first
and second back-to-back surfaces, said first surface including at
least two spaced-apart undulations therein defining a valley
therebetween, said vessel being supportable on said two
undulations; an induction coil energizable for producing a changing
magnetic field in said one portion of the vessel when said vessel
is supported on said undulations; means for energizing said
induction coil; temperature sensing means, located in said valley,
comprising means including a first magnetic flux path having a
magnetic permeability which varies with temperature, said means
including said first flux path being contactable by said vessel
when said vessel is supported on said two undulations; and,
temperature receiving means supported on said second surface of
said supporting means and located opposite said valley of said
first surface whereby said vessel supporting means is interposed
between said temperature sensing and receiving means, said
temperature receiving means comprising means including a second
magnetic flux path and a coil wound about said second flux path
whereby said first and second magnetic flux paths together with a
portion of the interposed vessel supporting means forms a magnetic
circuit, the temperature variable magnetic permeability of said
first flux path causing said coil about said second flux path to
become electrically loaded with a reflected impedance
representative of the temperature of said vessel.
8. The appliance according to claim 7 further comprising a
temperature signal processing circuit and temperature indicator
means, said signal processing circuit being electrically connected
to said coil wound about said second flux path and connected to
said temperature indicator means whereby said signal processing
circuit in response to said reflected impedance produces a signal
representative of the temperature of said vessel for energizing
said indicator means whereby said temperature is visibly
displayed.
9. The appliance according to claim 7 wherein said induction coil
is electrically energized with at least ultrasonic frequency and
wherein said coil about said second flux path is electrically
energized at a different frequency.
10. The appliance according to claim 7 wherein said first surface
including said undulations and valley present a relatively smooth
surface and is easily wiped clean.
11. The appliance according to claim 10 wherein said means
including first magnetic flux path is an open bladder member of
relatively thin elastic material having an exposed relatively
smooth surface which is easily wiped clean.
12. The appliance according to claim 11 wherein said relatively
thin elastic bladder member has a relatively low restoring spring
force and is easily adapted for being contoured to the surface of
an irregularly surfaced vessel in contact therewith.
13. The appliance according to claim 7 wherein said means including
said first magnetic flux path is comprised of an elastomeric matrix
in which there is embedded powdered ferrite material, said matrix
including said embedded ferrite powder having a magnetic
permeability which varies with temperature.
14. The appliance according to claim 7 wherein said means including
said first magnetic flux path is comprised of an elastomeric matrix
in which there is embedded powdered temperature sensitive first
order transition material, said matrix and embedded powders having
a magnetic permeability which varies with temperature.
15. The appliance according to claim 13 wherein said ferrite
material is selected from the group consisting of nickel-zinc
ferrite, manganese-zinc ferrite, and manganese-copper ferrite.
16. The appliance according to claim 14 wherein said first order
transition material is selected from the group consisting of
manganese arsenide, iron rhodium, and chromium doped manganese
antimonide.
17. An induction cooking/warming appliance, for heating a vessel
having at least one portion thereof in which heating current may be
induced by subjecting said one portion to a changing magnetic
field, comprising: Vessel supporting means in which no substantial
heating current is induced when said supporting means is subjected
to a changing magnetic field, said supporting means having first
and second surfaces, said first surface including at least two
spaced-apart undulations therein defining a valley therebetween,
said vessel being supportable on said two undulations; an induction
coil energizable for producing a changing magnetic field in said
one portion of said vessel when said vessel is supported on said
undulations; means for energizing said induction coil; temperature
sensing means located in said valley and including a first magnetic
flux path; temperature receiving means supported on said second
surface of said vessel supporting means and located opposite said
valley of said first surface whereby said vessel supporting means
is interposed between said temperature sensing and receiving means,
said temperature receiving means comprising a second magnetic flux
path, said first and second flux paths together with a portion of
the interposed vessel supporting means forming a magnetic circuit;
and means for introducing a changing magnetic flux into said
magnetic circuit, the magnetic flux introduced into said magnetic
circuit changing in response to the temperature of said vessel; and
means for deriving a signal in response to the change of the
magnetic flux in said magnetic circuit, said signal being
representative of the temperature of said vessel.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
A fuller appreciation of induction cooking appliances, as well as
some of the sophistications which may be embodied therein, is to be
had by referring to the following U.S. Pat. applications: Ser. No.
200,526, filed 11/19/71, in behalf of David L. Bowers, et al.,
titled Solid State Induction Cooking Appliance (RD-4675); Ser. No.
200,424, filed 11/19/71, in behalf of J. D. Harnden, Jr. et al.,
titled Solid State Induction Cooking Appliances And Circuits
(RD-4678). The entire right, title and interest in and to the
inventions described in the aforesaid patent applications, as well
as in and to the aforesaid applications, and the entire right,
title and interest in and to the invention herein disclosed, as
well as in and to the patent application of which this
specification is a part, are assigned to the same assignee.
BACKGROUND OF THE INVENTION
The invention herein disclosed pertains, in general, to induction
cooking/warming appliances; and, in particular, to an induction
cooking/warming appliance having a vessel supporting means, such as
a counter, which is provided with an undulant surface which is
adapted for supporting a cooking/warming vessel and for receiving
between its undulations temperature sensing means which are adapted
to be contacted and easily compressed by a vessel supported on the
undulant surface. An important feature of the aforesaid vessel
supporting means is that even though it is provided with
undulations, it is, nevertheless, relatively smooth and, as a
result, may be easily wiped clean. In addition to being undulant
and relatively smooth, the surface need have no apertures
therethrough so that the surface may be used for food preparation
(e.g., cutting, chopping, grating, etc.). Furthermore, since the
vessel supporting means is not made of inductively heatable
material, the vessel supporting means and its surface remain
relatively cool. Thus, easy cleaning and food preparation are
facilitated, even during the cooking process.
Certain desiderata with respect to cooking/warming appliances have
come to the attention of the manufacturer's of such appliances. For
example, the following desideratum, among others, respecting such
appliances have been mentioned;
One, the vessel supporting means such as the counter, or cooking
surface, of a cooking range should remain relatively cool, even
while cooking is taking place. With a cool surface food spilled
thereon won't burn or char. Hence, cleaning up such spills of
unburned or uncharred foods is relatively easy. Scouring is not
required. Moreover, with a cool counter, or cook surface, more food
preparation space becomes available in the kitchen. Another
advantage of providing a cool counter, or cook surface, is that
there becomes available a wider choice of materials from which the
counter, or cook surface, may be fabricated. Elevated temperatures
are not a restriction.
Two, the surface of the aforementioned counter or cook surface
should be relatively smooth and unbroken (no apertures
therethrough), as well as relatively cool, so that it can be easily
wiped clean with minimum effort after food has been spilled (and
contained) thereon.
Three, accurate sensing and display of cooking temperatures, and of
rates of temperature rise and fall, should be provided with such
appliances.
Prior art electric and gas ranges do not enable achievement of the
aforementioned desiderata. Conventional prior art electric ranges
employ exposed sheathed resistance heater surface elements which
are incorporated in the plane of the counter, or cook surface, and
these heater elements are electrically energized so that they can
glow to incandescence. Conventional prior art gas ranges employ
open flames which emanate from gas manifolds, or burners, which are
incorporated in the counter or cook surface. Thus, because of the
nature of the primary heat source and its arrangement and proximity
with respect to the counter, or cooking surface, temperatures of
approximately 1,600.degree. F may occur at or near the cook surface
in such prior art cooking ranges. Manifestly, the counter or cook
surface in such ranges do not operate at a relatively cool
temperature; i.e., near ambient room temperature. In addition to
being subjected to elevated temperatures the counter, or cook
surface, of such prior art ranges must necessarily be constructed
to accommodate resistance heater elements or gas manifolds and
nozzles. Hence, such prior art ranges are provided with counters or
cooking surfaces which are irregular, unsmooth and broken
(apertured). Therefore, food spilled on such counters or cooking
surfaces often burns and chars. The result is that extraordinary
efforts, such as scouring, must be undertaken in order to clean up
after such food spills. Of course, such tasks are not made easier
because of the irregular, unsmooth and broken construction of the
counter or cooking surface.
Also, another type of electric range (the glass-ceramic electric
range) has recently appeared wherein electrical resistance heater
elements, or strips, are embedded in a thermally conductive
glass-ceramic counter, or cooktop. The counter, or cooktop as it is
sometimes called, has a very smooth top surface and the
glass-ceramic material from which it is made conducts heat very
well. Since the counter, or cooktop, is provided with a very smooth
(optically flat) top surface special cooking utensils, or vessels,
are recommended for use in conjunction with such a counter or
cooktop. The special cooking utensils, or vessels, have a very
smooth, optically flat bottom surface so that when rested on the
cooktop or counter they are said to be "mated" with the cooktop.
Briefly, because of the aforesaid mating of the optically flat
utensil with the optically flat cooktop of the glass-ceramic
counter, heat transfer from the embedded resistance heater elements
is almost exclusively by means of conduction; i.e., heat is
conducted from the resistance heater elements, through the counter
and directly into the utensil. With such an electric range the
cooktop is "temperature restricted" in that it cannot, without
destruction, withstand temperatures higher than 600.degree. C
(1,112.degree. F). Moreover, if the temperature of the
glass-ceramic cookstop cooktop too high electrical leakage current
from the embedded resistance elements becomes of concern and
represents a design restraint. Also, the glass-ceramic cooktop
represents a relatively large thermal mass and the cooktop does not
readily dissipate its stored heat after termination of the cooking
operation, i.e., after the resistance heater elements are
deenergized it takes a relatively long period of time for the
cooktop to cool down to normal room temperature. Thus, in
commercially practical embodiments of the aforementioned electric
range employing the glass-ceramic cooktop, or counter, a reliable
temperature control system is at least required for the important
purpose of preventing destruction of the cooktop due to elevated
temperatures. Thus, the cooktop, or counter, can be considered to
be the primary heat source in the glass-ceramic electric range;
i.e., the glass-ceramic counter, or cooktop, is the primary heat
source and is the equivalent of the spirally wound electrical
surface heaters in the conventional electric range, or equivalent
to the gas flames in the conventional gas range.
Thus, the glass-ceramic electric range fails to fulfill the
desiderata hereinbefore set forth: a) The counter or cooktop
certainly does not remain relatively cool during the cooking
process because of the nature of the cooking process; i.e., heat
transfer occurs by conduction through the counter, or cooktop, to
the special utensil, or vessel, which is "mated" with the cooktop.
b) Although the cooktop, or counter, has a smooth surface, food
spilled thereon tends to burn or char. As a result, it cannot be
said that it can be easily wiped clean. c) Although the cooktop or
the surface of the counter is smooth, parts of the cooktop cannot
be used for the food preparation operations hereinbefore set forth
because of the excessive heat in the cooktop during and after the
cooking operation.
With respect to sensing or detecting the true temperature of a
cooking vessel or utensil resting on the range counter or cook
surface the conventional prior art electric and gas ranges present
a number of problems:
First, in prior art electric and gas ranges a temperature sensor
unit and its associated components are spuriously heated in some
measure by the primary high temperature heating source. In the
conventional electric range, for example, a temperature sensor unit
is located at the center of a spirally wound resistance heating
coil. This heating coil is electrically energized and often glows
to incandescence. The heating oil and temperature sensor unit are
both located on the top surface of the range counter or cook
surface and a cooking vessel or utensil rests upon and contacts the
spiral heating coil as well as the temperature sensor unit.
Although the temperature sensor unit directly contacts and sensed
the temperature of the heated cooking vessel the sensor unit is
also subjected to direct spurious heating by the heating coil;
e.g., by radiation and convection. In addition, the temperature of
the sensor unit is influenced by, among other things, a metallic
counter top with which the electric range is provided. Similarly,
in prior art gas ranges the open flames directly heat the
temperature sensor unit and heated metallic gridirons, as well as a
metallic counter top, thermally influence the temperature sensor
unit. In brief, with prior art electric and gas ranges the primary
heating source spuriously heats the temperature sensor unit and
other heated parts of the range also thermally perturb the
temperature sensor unit. Such perturbations tend to frustrate the
achievement of accurate temperature measurement.
Second, in prior art electric and gas ranges various component
parts of the temperature sensing unit have to be fabricated from
materials which are capable of withstanding relatively high
temperatures; e.g., up to about 1,600.degree. F, approximately. As
a result, certain materials cannot be used. For example, in the
conventional electric range wherein the temperature sensing unit is
located at the center of the spirally wound resistance heating coil
(which is mounted on the metallic counter top of the range) the
temperature sensing unit and its associated components are
subjected to maximum temperatures of approximately 1,600.degree. F
and significant thermal stresses are induced in the temperature
sensor unit and its associated components. In addition, the
metallic counter is thermally stressed. Clearly, epoxies, plastics
and polyimides, among others, are not applicable for use.
Similarly, elevated temperatures and consequent severe thermal
stresses are present in gas ranges and many materials including
those hereinbefore set forth are not applicable for use. In brief,
because of the relatively high temperatures involved in prior art
electric and gas ranges, the materials from which temperature
sensing units including their associated components may be
fabricated are quite restricted.
Third, in prior art electric and gas ranges the temperature sensing
unit and its associated components are often required to have some
thermal shielding, or insulation, to minimize the influences of
spurious heating thereof by the high temperature heating source as
well as by the heated metallic range counter and the heated
gridirons. Without some effective thermal shielding or insulation,
the temperature sensing unit will provide a completely false
temperature indication, unless temperature compensation is
appropriately applied. However, temperature compensation is not
feasible over the wide range of cooking conditions. Moreover,
without effective thermal shielding severe thermal stresses induced
in the various components of the temperature sensing unit will
cause a disabling or destruction of the temperature sensing unit.
Briefly, because of the relatively high temperatures involved in
prior art electric and gas ranges, the temperature sensing units
employed therein require effective thermal shielding or
insulation.
Fourth, prior art temperature sensing units, especially those
employed in the conventional electric range, are rather
sophisticated, mechanically, and are of a somewhat complex
structure and arrangement. The high temperature environment within
which the temperature sensing unit is located permits severe
thermal stresses to occur in various components of the temperature
sensing unit. These stresses tend to promote warping of the various
components. For example, because of the aforesaid severe thermal
stresses a relatively massive double spring arrangement is employed
in combination with a temperature responsive device. The
temperature responsive device, acting against spring restraint,
contacts the bottom surface of a cooking vessel which is seated on
a flat spiral resistance heating coil and on the temperature
responsive device, both of which are located on the top surface of
the metallic range counter. The massive double spring arrangement
is rather stiff (i.e., the spring has a relatively high restoring
force or a relatively large effective spring constant) due, in
large part, to the need to make the arrangement structurally
resistant to serious thermal deformation. Such a stiff spring
arrangement generally functions satisfactorily to maintain the
temperature sensing unit in contact with the more or less regular
flat bottom surface of a relatively heavy vessel, such as a cast
iron pot, containing foodstuff to be cooked. Since it is in contact
with the bottom surface of the vessel, or pot, it is conceptually
possible for the temperature sensing unit to detect the temperature
of the vessel. However, in the event that a relatively light pot,
or vessel, is used or if the foodstuff contained therein is not of
sufficient weight, such prior art temperature sensing units
employing the aforesaid stiff spring arrangement prove
unsatisfactory. Such an arrangement is also unsatisfactory where
the vessel has an irregularly contoured bottom surface. For
example, if a relatively light cooking vessel is employed, there
will be insufficient vessel weight to adequately compress the
spring arrangement and one consequence will be that the vessel will
not rest on the resistance heating coil in the most intimate
contact possible therewith, i.e., the vessel will be raised, or
tilted, and thereby cause inefficient heat transfer between the
resistance heating coil and the vessel. Suffice it to say that:
because of the relatively high temperatures involved and because of
the consequent severe thermal stresses created it is not practical
to provide temperature sensing units having simple spring
arrangements with relatively low effective spring constants; i.e.,
little spring stiffness or relatively small restoring force.
Also, the so-called glass-ceramic type of electric range,
hereinbefore described, would appear to present many of the same
problems with respect to sensing, or detecting, the true
temperature of the cooking vessel, or utensil, resting on the
glass-ceramic cooktop as are presented with the conventional prior
art electric and gas ranges:
First, inasmuch as the glass-ceramic cooktop, or counter,
containing the embedded electrical resistance elements is, in
effect, the primary heating source in such a range, a temperature
sensing unit so disposed or arranged as to contact the cooking
vessel for the purpose of determining the temperature thereof would
tend to be spuriously heated in some measure by the elevated
temperature of the glass-ceramic cooktop. Thus, the glass-ceramic
type of electric range appears to present the same kinds of
problems in this respect as is presented with the conventional
electric and gas ranges hereinbefore discussed.
Second, because of the elevated temperatures involved
(1,112.degree. F) various component parts of a temperature sensing
unit employed in conjunction with the glass-ceramic type of
electric range would have to be fabricated from materials which are
capable of withstanding such elevated temperatures. Clearly certain
materials cannot be used. Epoxies, plastics, polyimides, among
others, are not applicable for use. Suffice it to say that: because
of the relatively high temperatures involved in the glass-ceramic
type of electric range, the materials from which temperature
sensors and their associated components may be fabricated would be
quite restricted.
Third, in attempting to determine the temperature of a cooking
vessel, a temperature sensing unit and its associated components
employed in conjunction with the aforesaid glass-ceramic type of
electric range would have to be thermally shielded or insulated,
effectively. In brief, most of the same problems encountered with
conventional prior art electric and gas ranges would also be
encountered with the glass-ceramic type of electric range where
effective thermal insulation or shielding is concerned.
Fourth, prior art temperature sensing units employing rather
sophisticated and complex structures or arrangements of massive
double springs might be employed in conjunction with the
glass-ceramic type of electric range. However, it appears that a
suitable aperture or apertures would have to be provided through
the glass-ceramic cooktop surface. In any event, the same problems
as hereinbefore discussed with reference to the conventional prior
art electric and gas ranges would appear.
SUMMARY OF THE INVENTION
Although the invention is hereinafter described, and illustrated in
the accompanying drawing figures, as being embodied in an induction
range, it is, nevertheless, to be understood that the applicability
of the invention is not limited to induction ranges but may be
embodied in, for example, trivet warmers, portable warming or
cooking appliances, as well as in other apparatus which need not,
necessarily, be used for cooking food.
One object of the invention is to provide a cooking/warming
appliance which includes a vessel supporting means, such as a
counter or cooktop, having an unbroken, or non-apertured, top or
working surface which remains relatively cool during the cooking or
warming process.
Another object of the invention is to provide a cooking/warming
appliance which includes a vessel supporting means, such as a
counter or cooktop, having an undulated but unbroken or
uninterrupted (i.e., without apertures) top or working surface
which remains relatively cool during the cooking or warming
process; although the top or working surface of the counter has
undulations therein, it may, nevertheless, be wiped clean,
easily.
Another object of the invention is to provide a cooking/warming
appliance which includes a vessel supporting means, such as a
counter, or cooktop, having a undulant surface for supporting a
cooking/warming vessel or utensil and having between its
undulations temperature sensing means for sensing the temperature
of said vessel or utensil.
Another object of the invention is to provide a cooking/warming
appliance having a temperature sensing unit including a temperature
sensor unit and associated components or elements which are free
from spurious heating.
Another object of the invention is the provision of a
cooking/warming appliance having a temperature sensing unit
including a temperature sensor unit and associated components or
elements which may be fabricated from materials which are not
usable in the relatively high temperature environments created in
the prior art electric, glass-ceramic and gas ranges hereinbefore
discussed.
Another object of the invention is to provide a cooking/warming
appliance having a temperature sensing unit which includes a
temperature sensor unit and associated components or elements which
need not be thermally insulated or shielded in the ways, or to the
extent, employed in the prior art appliances hereinbefore
discussed.
Another object of the invention is to provide a cooking/warming
appliance having a temperature sensing unit including, in addition
to a temperature sensor unit, components or elements associated
with said sensor unit which provide a relatively small spring force
(i.e., a relatively low restoring force or relatively low effective
spring constant) for maintaining the sensor unit in contact with
the surface of a cooking/warming vessel or utensil. The vessel or
utensil may be of relatively light weight and may, in addition,
have a rather irregularly contoured surface presented for contact
with the temperature sensor unit.
Another object of the invention is to provide a cooking/warming
appliance including a temperature sensing unit for accurately
sensing or detecting the true temperature of a vessel or utensil
being heated; said temperature sensing unit being capable of
accurately sensing or detecting the temperature of the vessel
regardless of the weight of the vessel or weight of the food
contained therein, and/or regardless of whether the vessel has or
has not an irregular surface or contour.
Another object of the invention is to provide a cooking/warming
appliance including a temperature sensing unit which does not
require the prior art spring construction or arrangement
hereinbefore discussed.
Another object of the invention is to provide a cooking/warming
appliance wherein a temperature sensor unit positioned between
undulations in the surface of a vessel supporting means is
instrumental in enabling data representing the temperature of the
vessel supported on said surface to be magnetically coupled through
the unbroken or uninterrupted vessel supporting means.
Another object of the invention is to provide a novel temperature
sensor unit wherein the magnetic permeability of said unit is a
function of temperature.
The aforementioned objects, as well as others, are achieved in
accordance with one embodiment of the invention, to wit: an
induction cooking/warming appliance, for heating a vessel having at
least one portion thereof in which heating currents may be induced,
comprising: support means in which no substantial heating current
is induced when said support means is subjected to a changing
magnetic field, said support means having at least one surface
including at least two spaced-apart undulations therein which
define a valley portion on said one surface between said two
undulations, the vessel being supportable on said support means
such that said vessel rests on said two spaced-apart undulations;
an induction coil energizable for producing a changing magnetic
field in said one portion of the vessel when said vessel is
supported on said support means; means for energizing said
induction coil; temperature sensing means disposed in said valley
portion between said undulations for sensing the temperature of the
supported vessel and for providing a first signal representative of
the temperature of the vessel; and, temperature receiving means,
magnetically coupled with said temperature sensing means and said
first signal, for providing a second signal representative of the
temperature of said vessel.
One feature of the invention resides in the use of a vessel
supporting means including a surface having undulations therein;
the support means being fabricated from a material or materials
which will not permit heating currents to be induced therein. Thus,
the support means remains relatively cool even during the cooking
process. Thus spilled foods will not burn, char or adhere to the
support means. Furthermore, the support means may be fabricated
from a material or materials which need not withstand temperatures
beyond 550.degree. F.
Another feature of the invention resides in the provision of a
vessel support means which is relatively smooth and capable of
being wiped clean, easily, even though undulations are formed in
the surface of said support means.
Another feature of the invention resides in the employment of a
temperature sensing unit in combination with the aforesaid
undulated vessel support means; e.g., the disposition and
arrangement of a vessel-contacting spring means, supporting a
temperature sensor unit, between undulations in the aforesaid
valley portion of the support means.
Another feature of the invention resides in the use of a
temperature sensor unit which changes its electrical impedance, or
resistance, as a function of its temperature and using such
temperature-correlated impedance or resistance changes in such a
way that they are reflected magnetically, without the intervention
of tangible physical means; to a relatively remote temperature
receiving unit proximate the vessel support means whereat signals
representative of the temperature sensed or detected by said sensor
unit may be utilized.
Another feature of the invention resides in the employment of a
novel temperature sensing unit wherein a plastic magnetic member
including temperature responsive material has its magnetic
permeability changed as a function of temperature and wherein this
change in permeability is reflected magnetically to a relatively
remote temperature receiving unit proximate the vessel support
means whereat signals representative of the temperature sensed by
said sensing unit may be utilized.
Other objects and features, as well as a fuller understanding of
the invention, will appear by referring to the following detailed
description, claims and drawing FIGURES.
DESCRIPTION OF THE DRAWING FIGURES
FIG. 1 is a perspective view of an upper part of an induction
cooking range illustrating, among other things, a vessel support
means, such as a range counter or cooktop, having undulations
therein and temperature sensing means arranged between some of the
undulations.
FIG. 2 is an enlarged cross section view, taken along the section
line 2--2 in FIG. 1, and showing, among other things, the induction
range's undulant counter and temperature sensing means as well as a
block diagram of the electric power and temperature signal systems
employed with the subject invention.
FIG. 3 is another enlarged cross section view shown in FIG. 2 but
showing, however, a fry pan supported on the undulant range counter
and contacting the temperature sensing means thereon.
FIG. 4 is a fragmentary plan view showing the temperature sensing
means disposed on the surface of the range counter between adjacent
undulations therein.
FIG. 5 is a greatly enlarged cross section view similar to the
cross section view shown in FIG. 2 but illustrating in more detail
the temperature sensing means and temperature receiving means
employed in the subject invention.
FIG. 6 is an enlarged cross section view similar to that shown in
FIG. 5 but showing an alternate temperature sensing means disposed
between adjacent undulations in the top surface of the range
counter.
FIG. 7 is a graph showing the variation of the magnetic
permeability of the temperature sensing means of FIG. 6 as a
function of temperature.
DESCRIPTION OF PREFERRED EMBODIMENTS
Shown in FIG. 1 is an induction cooking range which is designated,
generally, by the reference number 20. The range 20 is provided
with a counter 22, or vessel support means, which is suitably
supported on a range substructure 24. The counter 22, as
illustrated, appears as a corrugated member. Fastened to the
substructure 24 and located at the rear of the counter 22 is an
instrument and control panel 26. On panel 26 is mounted a number of
controls 28 and a like number of temperature indicators 30. The
temperature indicators 30 are illustrated in the specific
embodiment at FIG. 1 as being dial-type thermometers. However,
indicators 30 may be digital displays. On the top or working
surface of the counter 22 there is illustrated four symmetrically
arranged temperature sensing means, each of which is designated
generally by the reference number 32. At each of the temperature
sensing means 32 a cooking vessel or utensil (e.g., pot, pan, etc.)
may be positioned for cooking. It is contemplated that the vessel
or utensil will be placed over the temperature sensing means, as
suggested in FIG. 3, so that the temperature sensing means 32 is
under the bottom surface of the vessel or utensil at the
approximate center thereof.
As indicated in FIGS. 1 and 2, there is associated with each
cooking position on the range counter 22 the following, among other
things: a temperature sensing means 32, a control 28, a temperature
indicator 30 and an induction coil 40.
Situated beneath the counter 22 and separated therefrom by an air
gap is a flat spirally wound induction coil 40. As shown, the coil
40 includes at the center thereof, an air core. As shown in FIG. 2,
the induction coil 40 is electrically coupled to the output of a
solid state inverter 44 which, in turn, has an input which is
electrically coupled to the output of a rectifier 46. The inverter
44 as combined with rectifier 46 forms a static power conversion
circuit designated, generally, by the reference number 43. The
rectifier 46 includes an input which is electrically coupled to a
conventional A.C. source 50; a 60 Hz, single phase, 110 or 220 volt
source. More details as to the static power conversion circuit 43,
including the rectifier 46 and the inverter 44, may be had by
referring to the patent applications hereinbefore identified under
the heading Cross References to Related Applications.
Also shown in FIG. 2 is a control switch 28, or knob, which is
electrically coupled with inverter 44 for the purpose of
controlling the flow of power to the induction coil 40. In brief,
the control 28 is preferably marked in degree F settings to enable
the housewife, for example to "call for" a certain temperature, or
temperature range, performance. However, it is the temperature
indicator 30 associated with the particular control 28 which
provides her with a visible indication of the actual temperature of
the vessel 38 or utensil (FIG. 3) as well as of the rate of
temperature rise and fall.
As for the conversion circuit 43, the rectifier 46 may be a
regulated full-wave rectifier employing solid state devices and
operating to convert an A.C. input to a D.C. output and the
inverter 44 preferably employs SCR's which, in the performance of
their control switching function, enable the inverter 44 to deliver
a relatively high frequency (i.e., ultrasonic or higher) output to
drive the induction coil 40. The controls 28 and the temperature
indicators 30 provide the actuation and visible feedback functions
hereinbefore described.
Also shown in FIG. 2 is a temperature signal processing circuit 52
which includes: a first input coupled to the rectifier 46 and
deriving therefrom a source of D.C. voltage; a second input in the
form of a pair of electrical conductors extending from a magnetic
receiving means 60 to the temperature signal processing circuit 52;
and, an output directly coupled to a temperature indicator 30. The
temperature indicator 30 may be a dial-type thermometer suitably
graduated in degrees F or in degree ranges or bands.
As illustrated in FIGS. 1 through 5 the temperature sensing means
32 is comprised of: a relatively thin elastomeric cup-like member
33 such as, for example, a silicone rubber cup; a thermistor unit
34 partially embedded in and supported by the cup-like member 33; a
magnetic coupling means 35 including a magnetic core 36 about which
there is wound a coil 37 and a cylinder 39 within which the core 36
and coil 37 are embedded or potted. A pair of conductors 41
electrically couple the coil 37 with the thermistor unit 34.
In FIG. 3 the vessel 38 is illustrated as being filled with a food
which is to be cooked or heated; e.g., hamburgers. The vessel 38 is
a conventional pan which may be made of cast iron, magnetic
stainless steel, etc.; i.e., a metal or alloy which is electrically
conductive was well as having sufficient magnetic permeability so
that sufficient electrical heating current may be induced therein
by action of the changing magnetic field produced by the induction
coil 40. Because induction heating is employed, the vessel 38,
only, and not the counter 22 is heated. The vessel 38 is heated to
a maximum temperature of about 500.degree. F. However, 550.degree.
F may be considered to be a specification temperature in that the
vessel 38 will not actually reach a temperature quite that high but
when a safety factor is included 550.degree. F is considered to be
a nominal specification temperature. As a result, the counter 22
may be fabricated from materials which are not employable in the
conventional prior art electric or gas ranges; nor in the
glass-ceramic electric range hereinbefore discussed. For example,
the counter 22 may be fabricated from epoxies, plastics,
polyimides, etc. If required for purposes of electrostatic
shielding and/or structural enhancement and/or decoration the
counter 22 may include some metallic content. However, the
inclusion of metallic material is necessarily limited to a small
amount in order to enable substantially all of the power developed
by the induction coil 40 to be coupled electromagnetically with the
cooking vessel 38. In any case, the amount of metallic material
included should be so distributed as to prevent the formation of
ohmic electrical circuits which would allow significant circulating
currents to be induced in the counter 22. In the alternative, the
counter 22 may, if desired, be made of a glass which is suitably
treated so as to withstand temperatures of 550.degree. F. As
another alternative, quartz may be employed in the fabrication of
the counter 22. Advantageously, as shown in the drawing figures,
the counter 22 presents an uninterrupted or unapertured working or
top surface.
As illustrated, the counter 22 is a corrugated member. That is to
say it has a number of undulations 22A or crests formed therein;
adjacent undulations 22A or crests being separated by a valley
22B.
As shown in FIG. 2 the temperature sensing means 32 is located in a
valley 22B between two adjacent undulations 22A. In FIG. 2 the
inverted cup-like member 33, or silicone rubber cup, is suitably
bonded to the upper surface of the counter 22. Normally, as
indicated in FIG. 2, the unstressed or uncompressed cup member 33
projects a short distance h above the top of an undulation 22A or
crest. However, as shown in FIG. 3 when a cooking vessel 38 is
rested on the top surface of counter 22 and is supported by the
undulations 22A thereof the cup 33 is compressed so that the top of
the cup 33 is substantially at the same height as an undulation 22A
or crest. In other words, the dimension h (FIG. 2) is reduced to
zero.
With respect to the spacing or frequency of undulations 22A and
their arrangement in the counter 22, it is to be understood that
many changes will occur to those skilled in the art. For example,
the undulations 22A need not be run in the direction indicated in
the drawing figures. The undulations may run in a transverse
direction. In the alternative, the undulations may be arranged in
concentric circular patterns. Although in FIG. 3 the vessel 38 is
illustrated as being supported by four undulations 22A, it is to be
understood that more or less than four undulations may be employed
for this purpose.
The thermistor unit 34 is preferably partially embedded in the
elastomeric cup member 33 as shown in FIG. 5 so that at least one
face thereof is available for making contact with the bottom
surface of the vessel 38. The thermistor unit 34 may be comprised
of thermistor material which is coated with glass frit. Within the
cup 33 and positioned on the valley 22B as indicated in FIG. 5 is
the cylinder 39 which, in accordance with the maximum temperatures
involved, may be fabricated from epoxies, plastics, polyimides,
etc. Embedded within the cylinder 39 is the magnetic core 36 about
which there is wound a coil 37. The core 36 constitutes a path of
relatively high magnetic permeability for magnetic flux. The coil
37 is, as shown, electrically coupled with the thermistor unit 34
by the two electrical conductors 41. On the opposite side of the
counter 22 (opposite valley 22B) there is mounted a magnetic
receiving means which is designated generally by the reference
number 60. As indicated in FIG. 5, the receiving means 60 is
comprised of a cylinder 61 which, advantageously, may be formed
from the same materials as cylinder 39 hereinbefore discussed.
Embedded within the cylinder 61 is another magnetic core 62 about
which there is wound a coil 63. Since the magnetic field intensity
in the region where the temperature sensing means 32, coupling
means 35 and magnetic receiving means 60 are located is relatively
low (i.e., in a region on an axis through the air core of induction
coil 40) relatively insignificant heating currents will be induced
in the means 32, 35 and 60. Moreover, the material of vessel 38
will constitute a low reluctance path for most of the magnetic flux
produced by the coil 40.
Although the magnetic cores 36 and 62 are illustrated as being
U-shaped cores, it is to be understood that cup-shaped cores may be
employed to advantage and such cores may have coils similar to the
coils 37 and 63 appropriately disposed thereabout. Again, because
of the maximum temperatures experienced, the cylinder 61, like
cylinder 39, may be made of an epoxy, plastic, polyimide, etc.
Operationally, the temperature signal processing circuit 52
actively drives the coil 63 electrically with energy of a
particular predetermined frequency; preferably at a frequency which
is substantially different from the ultrasonic or higher frequency
at which induction coil 40 is driven by inverter 44. A different
frequency for driving the coil 63 is preferred so that signals
representative of the vessel temperature may easily be
discriminated from the frequency at which coil 40 is driven. For
example, the coil 63 may be energized or driven at frequencies
which are higher or lower than those at which induction coil 40 is
energized. The coil 63 when so energized functions in a manner
similar to that of the primary winding of a conventional
transformer. The voltage impressed across the coil 63 causes
current to flow through coil 63. This current flow is attended by
an electromagnetic field about coil 63. Since the voltage impressed
across the coil 63 is a changing voltage, the current therethrough
also changes as does the attendant magnetic field. Consequently, a
changing magnetic flux is introduced into the magnetic core 62 of
the receiving means 60. The magnetic flux in the core 62 is coupled
across the counter 22 to the magnetic core 36 of the magnetic
coupling means 35. The cores 36 and 62 form first and second
magnetic flux paths and these flux paths together with the counter
22 interposed therebetween form a magnetic circuit or loop. The
changing magnetic flux in the core 36 induces a voltage across the
coil 37. Hence, the coil 37 functions in a manner similar to that
of the secondary winding of a conventional transformer. As
indicated, the thermistor unit 34 is connected across the coil 37
by means of the conductors 41. Hence, the thermistor unit 34 acts
as an electrical load on the coil 37. As the vessel 38, which is in
contact with the thermistor unit 34, is inductively heated by
induction coil 40 heat is transferred to the thermistor unit 34 and
the thermistor material changes the electrical resistance, or
impedance, of the thermistor unit as a function of the temperature.
In effect, there is connected across the secondary winding or coil
37 a temperature-correlated resistive load. In terms of transformer
theory current flow in the coil 37 will produce magnetic flux which
reacts with the magnetic flux that is produced by the coil 63, or
primary winding. Thus, the temperature-correlated resistive load
represented by thermistor unit 34 is "reflected" to the primary
winding or coil 63. This reflected resistance or impedance is
related to the temperature of the vessel 38. The resistance or
impedance reflected to the primary winding or coil 63 is employed,
in accordance with the invention, to develop or to modulate a
signal in the temperature signal processing circuit 52 so as to
provide an output signal for driving the temperature indicator 30.
The aforementioned output signal delivered to temperature indicator
30 is representative of the temperature of the vessel 38 as sensed,
or detected, by thermistor unit 34.
Advantageously, the temperature sensing unit employing the means
and operating in the manner hereinbefore described provides an
induction range with the following features: the temperature
sensing means 32 is an electrically passive device; the means 32
and 60 as well as the elements comprising these means need not
withstand temperatures greater than 550.degree. F and may be
fabricated from the materials hereinbefore discussed; the
relatively thin elastomer from which the cup-like member 33 is
formed exerts a relatively small restoring force against the bottom
surface of the vessel 38 thereby eliminating the need for the prior
art massive and complicated spring arrangements hereinbefore
discussed; being fabricated from a relatively thin elastomer such
as silicone rubber, the cup-like member 33 easily contours itself
to the bottom surfaces of vessels which may have very irregular
bottom surfaces; and, since the cup member 33 is easily stressed
(low spring constant) very light weight vessels or partially filled
cooking vessels will make adequate contact with thermistor unit
34.
Although the thermistor unit 34 is shown as being but partially
embedded in the cup-like member 33, it is to be understood that one
or more thermistor units may be wholly embedded in the cup-like
member 33. In such case although the thermistor unit or units 34
would not actually contact the vessel 38, the coupling is close
enough so that the actual temperature of vessel can be accurately
detected.
Illustrated at FIGS. 6 and 7 is an alternative temperature sensing
means designated generally by the reference number 32A. With the
system shown at FIG. 6, however, the same magnetic receiving means
60 is employed. The temperature sensing means 32A is as indicated
at FIG. 6 comprised of an elastomeric magnetic core 33A which
resembles an open bladder. The core 33A includes two pole faces 33B
and 33C which, as indicated, are separated by an air gap. Those
portions of the core 33A which include the pole faces 33B and 33C
are arranged on the counter 22 in valley 22B so as to be opposite
the corresponding pole faces of the magnetic core 62 of the
magnetic receiving means 60. The properties of the elastomeric core
33A are discussed in detail hereinafter. Suffice it to say at this
point that the core 33A is fabricated from a material or materials
which, in effect, have a magnetic permeability which is a function
of temperature. This relationship is graphically illustrated at
FIG. 7. The core 33A is made from an elastomer so that it deforms
in the same manner as the cup-like member 33 (FIG. 5) and, in
effect, has a low restoring force or spring constant so that it is
easily deformed by a vessel 38 resting thereupon.
Operationally, changing current in the coil 63 of the receiving
means 60 produces a changing magnetic flux .phi. which traverses
the path or circuit shown in FIG. 6. For example, the magnetic flux
.phi. passes through the core 62, through the counter 22 and
through the elastic core 33A whereat it again passes through the
counter 22 returning to the core 62. Thus, the flux .phi. traverses
a closed magnetic path or loop. As indicated at FIG. 6, the air gap
between the pole faces 33B and 33C should be sufficiently large to
prevent significant amounts of magnetic flux from leaking
thereacross and, in effect, "short circuiting" the intended flux
path through the core 33A. As the temperature of the vessel 38
increases heat is transferred to the elastomeric core 33A. This
activity is similar to the activity hereinbefore described with
respect to FIG. 3 where heat from the pan 38 is transferred to the
cup 33 and thermistor 34. As the transferred heat increases the
temperature of the core member 33A, its magnetic permeability
decreases in a manner similar to that graphically illustrated at
FIG. 7. As a result, the coil 63 of the receiving means 60 is, in
effect, loaded, electrically. The effect is similar to that of
electrically loading the secondary winding of a transformer so that
the primary winding thereof is loaded with a "reflected" impedance.
This effect is also similar to the action of a saturable reactor
wherein a D.C. winding controls the saturation level of a magnetic
core and thereby "loads" an A.C. drive winding disposed on the same
core. Hence, the reflected impedance is employed to develop or to
modulate a signal in the temperature signal processing circuit 52
in the same manner as hereinbefore described with respect to the
discussion relating to FIG. 2.
As indicated in FIG. 6 the elastomeric magnetic core 33A may be
fabricated from a relatively thin piece of silicone rubber.
Dispersed throughout the silicone rubber, which serves as a matrix,
is magnetic material in powder or small granular form. Such
magnetic material may, for example, be ferrite powders, or
granules, such as nickel-zinc ferrite, manganese-zinc ferrite or
manganese-copper ferrite, among others. Such ferrite materials when
embedded in the core member 33A will provide a magnetic
permeability versus temperature relationship generally like that
shown in the graph at FIG. 7. The ferrite materials of the
aforementioned nature are identified in published articles. See for
example the article The Characteristics of Ferrite Cores with Low
Curie Temperature and Their Application by K. Murakami, appearing
in the publication IEEE Transactions on Magnetics, June 1965
beginning at page 96; Digital Magnetic Temperature Transducer by
D.I. Tchernev et al., appearing in the publication IEEE
Transactions on Magnetics, Sept. 1971 beginning at page 450. In the
alternative, temperature sensitive first order transition materials
may be dispersed in the silicone rubber matrix 33A. For example,
such transition materials as the following may be employed:
manganese arsenide (M.sub.n A.sub.s), iron rhodium (F.sub.e
R.sub.h), or chromium doped manganese antimonide (M.sub.n C.sub.r
S.sub.b). See for example, the U.S. Pat. No. 3,464,225 wherein the
magnetic characteristics of such materials and their variation with
temperature is discussed. See, also, the publication Some Magnetic
First Order Transitions, in the Journal of Applied Physics,
supplement to Vol. 33, No. 3, Mar. 1962 beginning at page 1037.
Although the invention has been described and illustrated by way of
a specific embodiment with variations thereof, it is to be
understood that many changes in details of construction and in the
combination and arrangement of parts and components, as well as
changes in configurations and materials, may be made without
departing from the spirit and scope of the invention which is
hereinafter claimed.
The valleys 22B between adjacent undulations 22A provide air gaps,
or spaces, which are interposed between the heated bottom surface
of the cooking vessel 38 and the surface of the counter 22, or
vessel supporting means. The air gaps, or spaces, provide a high
thermal impedance between the vessel 38 and counter 22 and thereby
retard heat conduction therebetween to allow the vessel support
surface of counter 22 to remain relatively cool; i.e., at or near
room temperature. For more details see U.S. Pat. application of J.
D. Harnden, Jr. and W. P. Kornrumpf, Ser. No. 228,136, filed
2/22/72, on even date herewith, titled Induction Cooking/Warming
Appliance Including Vessel Supporting Means With Irregular Vessel
Support Surface (RD 5454) and assigned to the same assignee.
* * * * *