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Publication numberUS3612826 A
Publication typeGrant
Publication dateOct 12, 1971
Filing dateJul 17, 1970
Priority dateJul 17, 1970
Publication numberUS 3612826 A, US 3612826A, US-A-3612826, US3612826 A, US3612826A
InventorsHomer W Deaton
Original AssigneeGen Motors Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Surface temperature indicator light for ceramic top infrared radiant range
US 3612826 A
Abstract  available in
Images(3)
Previous page
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Claims  available in
Description  (OCR text may contain errors)

United States Patent [72] Inventor Homer W. Deaton Centerville, Ohio [21] Appl. No. 55,816 [22] Filed July 17, 1970 [45] Patented Oct. 12, 1971 [73] Assignee General Motors Corporation Detroit, Mich.

[54] SURFACE TEMPERATURE INDICATOR LIGHT FOR CERAMIC TOP INFRARED RADIANT RANGE 7 Claims, 7 Drawing Figs.

52 US. Cl 219/453, 219/449, 219/461, 219/463, 219/464, 219/506, 219/553, 338/280 [51] Int. Cl 1105b 3/68 [50] Field of Search 219/451-452,

[56] References Cited UNITED STATES PATENTS 600,057 3/1898 Ball 338/280 2,450,399 9/1948 Schiedler 219/453 2,870,316 1 1959 Fergusom lr. 219/453 Primary Examiner-- Volodymyr Y. Mayewsky Attorneys-William S. Pettigrew, Frederick M. Ritchie and Edward P. Barthel ABSTRACT: A control panel indicator light arrangement for an infrared cooking range surface unit having a resistance element supported on a heater block underlying an infrared transmissive, translucent cover plate. A double-throw thermostatic switch, having terminals alternatively connected to an auxiliary heater and the indicator light, is supported in heat transfer relation with the heater block by a heat-conducting bracket embedded in the block such that the auxiliary heater is energized with the resistance element to actuate the thermostatic switch at a predetermined temperature allowing the auxiliary heater to initially hold the indicator light circuit closed. After a time interval the thermostatic switch continues to hold the indicator light circuit closed by means of the conductive flow of heat from the heater block to the switch via the bracket such that the arrangement provides visual indication on the control panel of the cover plate temperature condition.

PATENTEDD 12 ml 3, s 1 2 826 SHEET 1 BF 3 I PATENTEDUET 12 ml SHEET 2 OF 3 A TTORNEY PATENTEU 2 3,812,826

SHEET 3 BF 3 INVIjN'I'OR,

A TTORNE) SURFACE TEMPERATURE INDICATOR LIGHT FOR CERAMIC TOP INFRARED RADIANT RANGE The present invention relates to ceramic top infrared radiant ranges having a cooking surface provided by a glassceramic infrared transmissive cover plate and more particularly to an arrangement for indicating the temperature condition of the cover plate.

With the advent of glass-ceramic cover plates for domestic ranges of the type having infrared radiant heaters a need has arisen to sense the temperature of the infrared transmissive cover plate to indicate to the operator the temperature condition thereoflThis is of particular importance in radiant-type cooking units whose resistance element is spaced from the undersurface of a translucent ceramic cover plate such that the resistance element is not visible to the operator. A description of a preferred heating unit for use with the present invention is found in the commonly assigned copending US. Pat. application, Ser. No. 48,390, filed June 22, 1970.

In the particular embodiment of this invention a plurality of radiant cooking units are covered by a utensil-supporting cover plate of milky-appearing glass-ceramic material having one or more heating areas thereon. When the infrared radiant units are on and raised to a minimum temperature, depending upon the lighting conditions of the kitchen, a dull orange glow will appear on the cover plate heating area portion of the surface indicating that the electrical resistance element of the unit below the heating area is energized. Because the unit may be set at a low or simmer temperature below such minimum temperature or due to an intense lighting condition in the kitchen there is not always a visual indication that the cover plate heating area is hot. In addition, when the heating unit is turned off the resistance element ceases to glow and the glassceramic material returns to its milky color, with the result that such a light coloring may appear cool to the operator when in fact the cover plate retains residual heat above a safeto-touch temperature for varying lengths of time.

Accordingly, it is an object of this invention to provide a surface-temperature-indicating device for an infrared radiant cooking unit having an air-exposed or open coil-type resistance element spaced below an infrared transmissive glassceramic cover plate.

Another object of the present invention is to provide an inexpensive surface-temperature-indicating device for the control panel of a ceramic top range having infrared radiant cooking units which will not interfere with the transmission of infrared energy from resistance elements spaced below the infrared transmissive glass-ceramic cover plate.

It is another object of this invention to provide a surfacetemperature-indicating device for a ceramic top range having a plurality of infrared radiant cooking units underlying an infrared transmissive cover plate formed of translucent glassceramic material wherein a control panel indicating light informs the operator of the temperature condition of the ceramic cover plate.

These and other objects and advantages will become apparent from the following description, reference being had to the accompanying drawings wherein a preferred embodiment of the invention is clearly shown. In the drawings:

FIG. 1 is a fragmentary perspective view of a domestic range with parts broken away;

FIG. 2 is an enlarged vertical section taken along the line 2-2 in FIG. 1;

FIG. 3 is an enlarged vertical section taken along the line 33 in FIG. 1;

FIG. 4 is an enlarged view in top elevation of one of the heating assemblies removed from the range;

FIG. 5 is a partial elevational view of the assembly illustrated in FIG. 4;

FIG. 6 is a vertical section taken along the line 6--6 of FIG. 5; and

FIG. 7 is a schematic diagram for a range circuit incorporating the invention.

Referring now to the drawings, in FIG. I, domestic range 10 is illustrated having metal body 11 supporting an upper casing 12 which includes a collar 14 around the top edge thereof forming a top opening 16 located above upper insulation retainer wall 17 of the range body. As seen in FIG. 2 the top opening is defined by a continuous depending flange 18 located therearound while the collar 14 merges with the rear wardly located control panel 19 having a plurality of control knobs 20 thereon for selectively energizing infrared radiant heating units as described.

A pair of heating assemblies generally indicated at 22, 23 in FIG. 1 are especially adapted to be installed in spaced side-byside relationship in the upper casing 12 of the range and located in spaced relation above the upper wall 17 of the range body. As seen in FIG. 4 the heating assemblies are generally rectangular in shape for location below the opening 16 with each assembly having its longitudinal axis oriented parallel to the sides of the range. As the heating assemblies 22, 23 are identical in construction and are reversible to occupy either the left-hand or the right-hand operative position shown in FIG. 1 like reference characters are used to designate like or corresponding parts throughout the several views with the exception that the left-hand assembly 23 has its reference characters primed on the drawing. Within the top opening 16 (FIG. 2) is an upper utensil-supporting glass-ceramic cover plate 24 that defines the complete surface cooking area of the range 10. The cover plate 24 extends throughout the planar extent of the opening 16 and has a continuous planar undersurface 25 that contacts the upper faces of the underlying heating units positioned within the assemblies 22, 23 in a manner to be described.

It should be noted that while the heating assemblies 22, 23 are described in conjunction with a free-standing range it is to be understood that the present invention is not intended to be so limited and the assemblies could be used for example with a ceramic top kitchen counter cooking arrangement without departing from the scope of the invention. Furthermore, the invention contemplates a single heating assembly being used with a cover plate in a range or kitchen counter providing two cooking areas or a single cooking area.

The utensil-supporting cover plate 24 is preferably formed of a high strength infrared transmissive material such as recrystallized glass-ceramic sold under the trade name Cer-vit by Owens-Illinois or I-Iercuvit by Pittsburgh Plate Glass. It will be appreciated however that other infrared transmissive material, such as high-silica glass, for example, could be used with the invention without departing from the scope thereof. The cover plate 24 is shown in a preferred embodiment having a rectangular configuration with a length of approximately 25 inches, a width of approximately 20 inches and a thickness of the order of one-quarter inch providing a smooth top cooking surface that will accommodate four radiant heating areas in a manner similar to a conventional electric range having four convolute-shaped conduction surface heating units.

Turning now to FIGS. 2, 3 and 4 the heating assemblies 22, 23 each have a housing or pan member generally indicated at 26 formed from light gauge sheet metal blanks comprising a bottom wall 27 provided with'marginal sidewalls 28, 29 and end walls 30, 31 upstanding from the bottom wall. Each end wall 30, 31 terminates in a substantially horizontal end flange wall 32, 33 outstanding from the top of the end walls 30, 3I respectively and having downwardly directed lip portions represented at 34' in FIG. 3.

As indicated above the cover plate 24 together with the underlying heating or cooking assemblies 22, 23 are mounted in the opening 16 substantially flush with the upper surface of the collar 14 by securing means including a trim ring indicated generally at 40 together with a plurality of cooperating clips 41 having individual pressure screws 42. As best seen in FIG. 3, the trim ring 40 is substantially T-shaped in cross section and includes a head 43 spanning gap 44 formed between the range collar 14 and the longitudinal and transverse edges of the cover plate 24, together with a depending stem 45 disposed in the gap. A stem 45 has formed along its lower ends hook portion 46 which provides shoulder means for interlocking engagement with a cooperating hook portion 47 on the clip member 41.

The clips 41 are dispersed at spaced intervals around the cover plate to engage the underside of the range collar 14 by seating circular bead portion 48 of the clips in the radiused area formed by the depending flange 18 of the opening, whereupon the clip pressure screws 42 are taken up to retain the plate and the heating assemblies in the opening. Pressure screws 42 have rectangular plate members 49 located on the ends thereof for pressure contact with the underside of the flange walls 32, 33 when the pressure screws are taken up. The result is the housings 26 together with the cover plate 24 are anchored to the range collar 14 in a manner to hold cooking or heating units to be described in pressure contact with the undersurface of the cover plate.

Cover plate cushion members formed of fibrous insulating materials such as asbestos pads 50 are provided between the underside of the cover plate and the upper surfaces of the end flange 32, 33. Appropriate sealing material, located between the inner and outer strips of the trim ring head 43 and the underlying perimeteral borders of the cover plate 24 and collar 14 provide a liquid-type seal therebetween. This material, such as manufactured by Dow Corning under the trade name RTV Silicone, cures to form a high-temperature rubberlike seal to prevent spillage on either the cover plate or the range collar from entering the gap 44.

It will be noted that the heating assemblies 22, 23 are secured to the range collar 14 and cover plate 24 by housing flange walls 32, 33 only along the longitudinal edges 51 of the cover plate. As seen in FIG. 2, the borders adjacent transverse edges 52 of the plate 24 are retained to the range collar 14 by means of the trim ring and clip assembly described. Annular washer-type pressure members 54 are used on the pressure screws 42 along the transverse cover plate edges 52. The upper surfaces of the washer member 54 have resilient cushioning pads thereon formed from suitable material such as heat-resistant silicone rubber.

In the illustrated form of the invention each housing 26 provides a boxlike receptacle defined by its side, end and bottom walls for receiving a resilient insulation mat 60 formed from suitable inorganic fibers insulation material such as rock wool, glass wool, asbestos fibers or the like. The mat 60 in the preferred embodiment has a thickness of approximately 1 inch and a density of approximately 6 pounds per cubic foot. As indicated in the plan view of FIG. 4 the mat 60 extends throughout the bottom of the housings 26 conforming to the shape of bottom wall 27. It will be noted that in the disclosed form of the housing 26 there is an oblique wall portion 56 forming part of the sidewall 28 to accommodate a smallersized heating unit to be described.

FIG. 4 shows a plan view of the right-hand heating assembly 22 removed from the range 10. As explained earlier the heat- .ing assembly 22 may be reversed end-for-end for insertion in the left-hand portion of the range top. Insulation mat 60 in the housing 26 has located thereon a pair of cooking units indicated at 61, 62. Each of the units 61, 62 comprises a heater support block and a heater resistance element with the cooking unit 61 having its heater block shown at 63 supporting a ribbon shaped-in-cross section resistance element 64 while the unit 62 has a heater block 65 supporting a similar shaped resistance element 66. In the form shown the continuous ribbon element 64 is located within a convolute-shaped groove 67 defining an annular heater area approximately 8 inches in diameter while the continuous ribbon element 66 is located within a convolute-shaped groove 68 to define a heater area approximately 6 inches in diameter. The heater blocks are preferably made of a fibrous ceramic refractory material having minimal thermal conductivity and low thermal mass, as discussed in detail in the aforementioned copending patent application, Ser. No. 48,390, and composed mainly of silica and alumina.

In the case of the right-hand cooking assembly 22 it is shown oriented with the larger cooking unit 61 at the front of the range while the left-hand assembly 23 has been reversed to locate the smaller cooking unit at the front of the range top. In this way the cooking assemblies 22, 23 are able to provide alternate small and large surfaced heating areas at both the front and rear of cover plate to provide maximum space for cooking utensils. It will be observed that the larger heater block 63 has a generally octagon shape when viewed in FIG. 4 locating three of its sides respectively adjacent to and substantially parallel with the end wall 30 and sidewalls 28, 29 of the housing 26. The smaller or 6-inch-heater block has an irregular shape in plan to conform to the oblique wall portion 56 of the housing along with the housing walls 29 and 31.

As seen in FIG. 3 representing the heater block 63' for the left-hand assembly both the blocks 63, 65 have an overall thickness which when combined with the thickness of the supporting mat 60 locates their upper peripheral faces 69, 70 respectively, a defined distance above the housing flange walls 32, 33 such that the peripheral faces 69, 70 are brought in flush heat transfer contact with the undersurface 25 of the cover plate. The faces 69, 70 of the heater blocks are held in cushioned pressure abutment with the cover plate by means of the trim ring 40 and clip 41 arrangement previously described.

The heater blocks 63, 65 are retained in the housing 26 prior to final assembly by means of holddown pins whose heads are shown at 72 in FIG. 4. Each holddown pin extends through a central bore in the heater blocks together with aligned bores in the mat 60 and housing outer wall 27 for reception on the free end of the pin of a suitable retaining member such as a push nut (not shown). A complete description of the heating unit mounting device may be found in copending application, Ser. No. 55,815, filed July 17, 1970 and assigned to the same assignee of this application.

The heater blocks 63, 65 are cast or molded to provide diskshaped hollows defining recessed substantially circular areas 80, 81 (FIG. 4) in the block upper faces 69, 70 respectively. In the preferred form, the blocks 63, 65 have substantially identical thicknesses, within casting tolerances, of approximately 1.25 inches. For the purpose of this disclosure the heater blocks differ only in their outer configuration and size of their recessed areas with the blocks 63, 65 having their recessed areas indicated at and 81 to provide different sized heating areas for the cover plate. Accordingly, only the larger cooking unit 61 need be discussed in detail with all remarks being applicable to the smaller unit 63 with the single exception that unit 63 has a lower wattage output. It will be observed that the blocks 63, 65 are formed with opposed cavities indicated at 78, 79 (FIGS. 4, 5 and 6) respectively to receive one end of a central heat-sensing device indicated generally at 82 cooperating with a surface temperature indicating light circuit to form the subject matter of the present invention, the detailed description of which follows.

It should be mentioned that each of the cooking units has a temperature control means generally indicated at 83, 84 in FIG. 4 for the right-hand cooking assembly shown. The control means 83, 84 are part of a cover plate temperature cutofi' control device to ensure that the temperature of the cover plate does not exceed a maximum upper limit. The control means 83, 84 form no part of the instant invention and are described in US. Pat. application, Ser. No. 74,399 filed Sept. 22, 1970, also assigned to the assignee of the present invention.

Considering now the cooking units 61, 61' of FIGS. 2, 3 and 4 it will be seen that the convolute groove 67 provides a path for locating the continuous resistance element ribbon 64 such that one end is positioned for electrical connection to an inner terminal member and its opposite end located for connection to an outer terminal member 91. The terminal members 90, 91 are identical so as to be interchangeable with either cooking unit and comprise an insulating column 92 formed of electrical porcelain or the like provided with an axial chamber receiving a vertical terminal blade 93 therein as shown in the section view in FIG. 2. The details of the terminal connectors form no part of the instant invention and are described and claimed in the copending application, Ser. No. 55,815 filed July 17, 1970, assigned to the assignee of the instant invention.

By virtue of the foregoing description it will be noted that the resistance element 64, which has a deeply undulating or sinelike pattern, is supported in the spiral groove 67 to establish a defined vertical airgap indicated at G in FIG. 3 between the cover plate undersurface 25 and the element which in the fonn shown provides a minimum spacing therebetween on the order of V4 inch. The A-inch gap G is the minimum distance permitted by Underwriters Laboratory between an uninsulated conducting member and adjacent conductor.

To produce the required wattage output for the cooking units it was determined that a resistance element be used that can be self-heated in the range of 1,500 P. to 2,000 F. and constructed of a high-temperature resistance material from the iron-chromium-aluminum family. An iron-chromium-aluminum ferrite alloy is preferred because it has a higher melting point and a higher electrical resistivity allowing it to be operated at higher temperatures within the above-mentioned range. For further details of the resistance element together with arrangement for being supported on the heater block reference should be had to the copending application, Ser. No. 48,390, referred to previously.

Turning now to the instant invention, as noted previously of the heater blocks 63, 65 are formed to receive a portion of the central heat-sensing device 82 which is centrally located in the housing 26 in a gap between the spaced blocks. As best seen in FIGS. 5 and 6 the sensing device 82 comprises a heat-sensing or heat-conducting bracket member 150 having a pair of aligned channel-shaped end members 154 and 156, formed integral with a central horizontal bracket or bridge plate 158. The channel members 154, 156 are supported on the insulation mat 60 which is provided with a central hole 159 for reception of the lower portion of the heat-sensing device 82 while the bottom wall 27 of the housing has an opening 161 for passage of suitable electrical leads to be described. In the form shown the bracket is formed from sheet steel having a thickness of approximately 0.043 inches.

The bracket plate 158 has a pair of horizontally extending coplanar flanges 162 and 163 formed below the plane of the plate 158 by suitable depending elements 164, 165. A thermostatic switch assembly 166 is mounted on the horizontal flanges 162, 163 by suitable means such as the roundhead screws 168, 170 shown threaded in holes in the horizontal flanges 162, 163. Extending upwardly from the outer ends of the flanges 162, 163 are a pair of vertical leg members 172, 174 having horizontal foot portions 176, 178 extending outwardly therefrom providing stops which serve only for engaging the undersurface 25 of the cover plate during inverted assembly of the cooking assemblies with the range upper casing 12. As seen in FIG. 6 the foot portions 176, 178 are spaced from the cover plate when the assembly is in its normal righted condition and do not provide a direct heat path from the cover plate. An auxiliary or anticipator heater 180 preferably of the porcelain type having a wattage rating of the order of 200 watts at 1 18 volts, such as manufactured by the Hotwatt Company for example, is located on the underside of the central bracket plate 158 so as to be interposed between and in thermal contact with the upper end of thermostatic switch 166 and the overlying bracket plate 158.

The thermostatic switch 166 in the preferred embodiment is a single-pole double-throw heat changeover switch of the exposed bimetal-disk-type providing snap-action, such as manufactured by Texas Instruments lnc. under the trademark Klixon for example. The thermostatic switch 166 has a tubular casing including an open bimetal disk end defined by a flanged annular rim 182 that is detachably secured tothe bracket flanges 162, 163 by the means recited to position the disk in juxtaposition to the auxiliary heater 180. The thermostatic switch 166 is of the wide differential type calibrated to trip during an ascending heat cycle when a temperature of the order of 170 F. is attained and to trip at a temperature of the order of 120 F. in a descending heat cycle.

F 16. 6 shows the opposed channel-shaped end members 154 and 156 of the bracket 150 extending into the cavities 78,

79 respectively, where upon tightening of the pressure screws 42 of clips 41 the brackets are pressured between the mat 60 and the heater blocks 63, 65. In this way the brackets are effectively embedded or buried in the heater blocks such that the entire outer surface of the channel members 154, 156 are in heat exchange contact or relationship with their associated heater block members for a purpose to be explained. As best seen in FIG. 5 porcelain insulator block members are provided at 184 and 186 conforming with the channel portions of the bracket and extend outwardly therefrom complementary with the curved inner ends of the cavities 78 and 79 to fill the voids of the bracket channels 154, 156. It will be noted that the porcelain blocks 184, 186 serve as insulators to reduce heat radiation from the bracket to provide an efficient heat transfer path between the heater blocks 63, 65 and the thermostatic switch 166.

Turning now to the circuit arrangement of FIG. 7 power is supplied to the range top from the usual single-phase, 236- volt, alternating current, three-wire Edison service entrance found in an adequately wired residence. The three wires are identified as line wires L, and L, and a neutral wire N it being understood that there is a potential of about 236 volts across lines L, and L and about 1 18 volts across either line L, or L and the neutral wire N.

Since the right-hand and left-hand heating assemblies are identical they are shown in the circuit diagram with the same elements identified with the same reference numerals, the exception being that each reference numeral for the left-hand assembly is primed. For example, the heating assembly 22 has a thermal switch 166 while the same thermal switch in heating assembly 23 is identified as 166. The line L, is connected to energy-pulsing infinite heat switch assemblies 190 and 190', shown boxed in by dashed lines, by means of conductor 193 while the line N connects energy-pulsing infinite heat switches, indicated similarly at 192, 192', by means of conductor 194.

The infinite heat switches 190, 190' and 192, 192' are of a conventional type more particularly set forth in U.S. Pat. No. 2,623,137 issued Dec. 23, 1952, and except for different wattage ratings are identical. The infinite heat switch 190 includes a first single-pole single-throw line switch (SPST) for the cooking unit 61 having a pair of contacts indicated at 195, 196 and a second single-pole single-throw switch for a signal lamp circuit having pair of contacts 197, 198. As its associated control knob 20 is rotated from its ofi position both the first line and second signal lamp SPST switches close by a cam (not shown) to route power to the unit 61 and to light signal lamp 199.

As line L, is connected by conductors 200 and 201 to line contact 198 of infinite heat switch 190 it will be seen that the continuous resistance elements 64 of the 8-inch cooking unit 61 is placed across a 236-voltage source. The infinite heat switch 190 functions in the same manner to energize the resistance element 64' across line L,, L, to provide 236 volts of power producing a wattage output from elements 64, 64' varying from zero to approximately 2,000 watts.

The infinite heat switch 192 has a first single-pole singlethrow line switch for the 6-inch cooking unit 62 providing a pair of contacts 202, 203 and a second single-pole singlethrow switch for the signal lamp circuit having a pair of contacts 204, 205. Again, as the associated control knob 20 of infinite heat switch 192 is rotated from its off position both these first and second SPST switches close to route power to the resistance wire 66 and to light the signal lamp 199. As the line N is shown connected by conductor 194 to the infinite heat switch 192 while line contact 203 is connected to L, by conductor 200 it will be seen that the continuous resistance element 66 of the 6-inch cooking unit 62 is placed across a l 18- volt source to energize the element 66 to produce a wattage output therefrom varying from zero to approximately 1,200 watts.

More particularly, as shown in the power circuit of FIG. 7, the device for indicating the surface temperature condition of the cover plate 24 is illustrated as including a conductor 206 electrically connected to the contact-carrying arm 208 of the infinite heat switch 192. The arm 208 has a cam and cam follower arrangement (not shown) that is rotatable to cause movement of the contact 210 on the arm 208 with respect to a contact 212 on the electrically conductive bimetallic arm 214 of the switch which has one end thereof fixedly connected to a suitable support means with respect to which the contact-carrying end of the bimetallic arm 214 is free to deflect. The infinite heat switch 192 further includes a heater 216 that is connected electrically to the arm 214 and by a conductor 218 to one end of the ribbon resistance element 66 of the right-hand 6-inch unit 62. The opposite end of the resistance element 66 is connected by means of a normally closed thermal heat limit switch 220 to a conductor 222 which is in turn connected electrically to the contact 202 of the infinite heat switch. The surface pilot light 199 is connected to line L of the power source through the closed contacts 204, 205, conductors 224, 225 thence through the lamp 199 to a conductor 226 electrically connected to the conductor 194 of the neutral power source N.

To complete the description of the circuit the conductor 193 from line L is electrically connected by conductor 227 to contact carrying arm 228 of the infinite heat switch 190. The arm 228 has contact 230 for pulsing contact with a contact 232 on the electrically conductive bimetallic arm 234 of the switch, and further includes a heater 236 electrically connected to the arm 234 by a conductor 238 to one end of the resistance element 64 of the right-hand 8-inch unit 61. The opposite end of resistance element 64 is connected by thermal heat limit switch 235 to a conductor 237 which leads to contact 195 of the line switch. Both the thermal switches 220 and 235 are part of the control means 84, 83 respectively mentioned above as the subject of copending patent application, Ser. No. 74,399. The closed contacts 197, 198 energize the pilot light 199 through conductor 239.

As shown in FIG. 7 the lower contact 240 of the switch portion of thermostat 166 is connected by the conductor 242 to the auxiliary heater 180 while the other side of the heater 180 is connected by the conductor 244 to the contact 195 of the infinite heat switch 190 of unit 61. The heater 180 is also connected by conductor 246 to the contact 202 of the infinite heat switch 192 of unit 62. In this manner the auxiliary heater 180, mounted on the bracket 150, is connected across lines L and N whenever either one or both of the pair of line contacts 195, 196 or 202, 203 of the infinite heat switches are closed and with the bimetallic disk 247 of the thermostatic switch 166 in its lower position in engagement with contact 240. A suitable indicator light 250 is located on the range control panel 19 so as to illuminate a glass lens 251 having an appropriate indicator such as l-lot Surface" etched thereon. The indicator light 250 is connected in the power circuit so as to be energized whenever the upper contact 252 of the disk 247 is closed across lines L and N by lead 255 to conductor 193 and lead 254 to conductor 194, respectively.

It will be appreciated that the metal bracket 150, which in the instant embodiment is formed from sheet steel material having a thickness of about 40 mils, serves as a heat conductor or heat path between the fibrous-ceramic heater blocks 63, 65 and the thermostatic heat changeover switch 166 to render its bimetallic disk subject to the conductive heat of either or both of the heater blocks. The refractory fibrous-ceramic heater blocks 63, 65 absorb heat by virtue of being in direct contact with the energized resistance elements 64, 66 such that heat is conducted from the elements downwardly into the blocks at the same time that infrared rays are directed upwardly through the cover plate.

While some heat is also conducted into the blocks 63, 65 because their upper faces 69, 70 are in pressure thermal contact with the undersurface 25 of the cover plate it is to be noted that this source is minimal and by far the bulk of heat transfer to the blocks is by direct conduction from the resistance element. As there is an initial thermal lag or temperature differential between the rise in temperature of the heater blocks 63, 65 and the temperature ascent of the cover plate 24 it is not possible for the blocks to initially serve as an analog of the cover plate temperature. This characteristic produces a time delay of variable length during which the heating or cooking areas of cover plate 24 achieve an elevated temperature of at least approximately F., a temperature standard above which an object is considered too hot to touch by most individuals.

As stated earlier because of their milky or cloudy condition certain infrared transmissive optically opaque materials, such as translucent glass-ceramic for example used in the instant embodiment for the cover plate 24, there may be no visual indication from the resistance element that a heating area on the cover plate 24 is hot at temperatures of the platebelow approximately 500 in indirect lighting or higher temperatures in strong direct lighting. When the resistance element is deenergized it quickly loses its characteristic orange glow so that without applicants indicating device no warning of the possible residual heat property of the cover plate exists.

By virtue of the auxiliary heater 180 being simultaneously energized when either one of the resistance elements 64, 66 is energized the energy generated by the auxiliary heater 180 supplies initial heat to the thermostat switch 166 to cause the temperature of its bimetallic disk 247 to lead or anticipate the heater block temperature. When the thermostatic disk 247 reaches a preselected temperature of approximately 170 F. which in the instant case involves a time interval of the order of 20 seconds, the thennal switch 166 is actuated turning on the indicator light 250 and turning off the auxiliary heater 180. The auxiliary heater 180, which has an output of 200 watts at 118 volts in the disclosed form, causes the temperature of the heated bracket to continue to rise for a period of overshoot because of the residual heat of the heater 180.

The residual heat is sometimes referred to in the art as the Heat Inertia of the auxiliary heater and in the disclosed form the amplitude of this overshoot is of the order of F., achieving a temporary bimetal disk temperature as high as 300 F. Thus, even if the energized heating unit is turned off after a short length of time so that the resistance element no longer emits its characteristic orange glow, the indicator light 250 will remain energized for a time interval to indicate that there is residual heat in the cover plate producing a temperature of approximately 120 F. or more. As the thermostatic switch 166 is of the wide temperature differential type, the differential in the present case being approximately 50 F the bimetallic disk temperature must fall below approximately 120 F. before the disk 247 snaps back to its lower contact position 240, deenergizing the indicator light 250. This feature is important as glass-ceramic has a slow cooling down time because of the properties of this material.

Again, if either of the radiant heating units 61, 62 remain energized for a cooking operation extending for several minutes or longer the conductive heat from the resistance elements 64 or 66 elevates their associated heater block to a temperature such that heat flows via conduction through the metallic bracket channel portions 154, 156 to the bridge plate 158, the porcelain heater 180 and thence to the bimetallic disk of the thermostatic switch 166. This heat balance arrangement of the bracket and heater block renders the bimetallic disk 247 sensitive to both the energized and residual heat of the heater blocks such that when the cover plate temperature falls below approximately 120 F. the bimetal disk actuation temperature of 120 is also attained to cause deenergization of the indicator light 250.

it will therefore be appreciated that the instant invention provides an analog of the temperature condition of the cover plate 24 without the use of expensive high-range-type thermostats to directly sense the temperature of the cover plate 24 while avoiding any positive glass-to-metal contact in the heating area directly above the resistance element-undesirable because of both the difierential expansion of the two materials and because of the obstructing effect upon the direct transmission of infrared rays from the resistance element to the cooking utensil.

While the embodiment of the present invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

I. A presence-of-heat-indicating arrangement for use in combination with an infrared radiant cooking unit having an infrared transmissive cover plate, a resistance element spaced below said cover plate, a fibrous refractory heater block providing a heat-conductive support for said resistance element, and a power source for energizing said resistance element to radiate heat toward a cooking utensil whereby the temperature of said infrared transmissive cover plate increases faster than the temperature of said heater block, said indicating arrangement comprising; heat-conducting bracket means embedded in thermal contact with said heater block so as to be in nonradiant heat blocking relation with said resistance element and said cover plate; temperature-responsive switch means connected to said power source-and in thermal contact with said bracket means; heater means connected to said power source for supplying initial heat to said switch means; indicator light means connected to said switch means and exposed to a user of said cooking unit; said switch means serially connecting said heater means and then said light means to said power source when said resistance element is energized, said heater means being disconnected upon energization of said light means and continuing the connection of said light means during the operation of said cooking unit and for a predetermined period after said resistance element is deenergized; said predetermined period being controlled by the amount of residual heat of said heater block conductively imparted thereto during the energization interval of said resistance element.

2. In an infrared radiant cooking unit the combination of an upper utensil-supporting cover plate of infrared transmissive material, a fibrous'ceramic heater block disposed below said cover plate and having a raised peripheral face defining a central recessed area spaced below said cover plate, means supporting said block with said peripheral face abutting said cover plate undersurface, resistance element means supported on said recessed area in vertically spaced relation below the undersurface of said plate, a circuit for energizing said resistance element means across a power source, heat-conducting bracket means in thermal contact with said heater block, said bracket means supporting temperature-responsive switch means thereon, auxiliary heater means supported on said bracket means in heat transfer relation with said temperatureresponsive switch means and being in said circuit, indicator means in said circuit with said auxiliary heater means, said temperature-responsive switch means having terminals connected alternatively to said auxiliary heater means and said indicator means, said auxiliary heater means being energized whenever said resistance element is energized whereby said temperature-responsive switch means is actuated at a first predetermined temperature to initially energize said indicator means and deenergize said auxiliary heater means, said heater block subsequently attaining a temperature level by means of conductive heat from said resistance element whereby heat will flow from said heater block through said bracket means to said auxiliary heater means, and said indicator means being deenergized after said resistance element is deenergized and the residual heat of said cover plate falls below a second predetermined temperature whereby said temperature responsive switch means is actuated to again contact said auxiliary heater means terminal.

3. The infrared radiant cooking assembly as defined in claim 2 wherein said temperature-responsive switch means is a snapaction, bimetal-disk thermostat of the double-pole type.

4. The infrared radiant cooking unit as defined in claim 3 wherein said thermostat is of the wide differential type calibrated to changeover during an ascending heat cycle at approximately 170 F. and to changeover during a descending heat cycle at approximately F.

5. The infrared cooking assembly as defined in claim 2, wherein a pair of heater blocks are arranged in spaced side-byside relationship and said heat sensitive bracket means disposed therebetween, said bracket means formed of metallic sheet material having aligned channel-shaped end portions joined by a central horizontal bracket plate, said end portions extending into opposed conforming cavities in said heater blocks so as to be in thermal contact therewith, and said temperature-responsive switch means being a snap-action, bimetal-disk thermostatic switch positioned in spaced relation with the underside of said bridge plate, and said auxiliary heater means positioned intermediate said thermostatic switch and said bracket plate so as to be in thermal contact with said switch and said plate.

6. The infrared radiant cooking assembly as defined in claim 2, wherein said auxiliary heater means is a porcelain-type electric heater having a heat output during its energization phase whereby its thermal inertia will maintain said temperatureresponsive switch in indicator means energization for a time interval sufficient to allow the conductive heat of said heater block to maintain energization of said indicator means.

7. An infrared radiant cooking assembly for a range or the like comprising an upper utensil-supporting cover plate of infrared transmissive translucent glass-ceramic material substantially opaque to visible light rays, a pair of spaced fibrousceramic heater blocks disposed below said cover plate, each said heater block having a raised peripheral face defining a central recessed area in spaced relation below the undersurface of saidcover plate, means for supporting said heater blocks with their peripheral faces in abutment with said cover plate undersurface, an infrared-emissive ribbon-shaped resistance element located on each said central recessed area in vertically spaced relation below said cover plate undersurface, each said resistance element supported in a continuous convolute-shaped groove so as to extend substantially throughout the full planar extent of its associated recessed area, circuit means for energizing said resistance elements across a power source, an infinite heat switch in said circuit associated with each said resistance element for pulsating energizing each said resistance element to vary the power output therefrom, heatconducting bracket means formed of metallic sheet material disposed in said space between said heater blocks having aligned channel-shaped end portions and a central horizontal bridge plate, said bracket end portions extending into opposed conforming cavities on the underside of said heater blocks such that each end member is in thermal contact with its associated heater block, said bracket supporting a wide-differential disk-type thermostatic switch in spaced relation to the underside of said bracket plate, an auxiliary porcelain-type electric heater having an output of approximately 200 watts at 118 volts supported between said bracket plate and said thermostatic switch so as to be in heat transfer relation with said bracket plate and said thermostatic switch, said thermostatic switch being in series electrical circuit with each said infinite heat switch, an indicator light in said circuit in parallel with said auxiliary heater, said thermostatic switch having a singlethrow double-pole switch member providing a first alternate terminal connected to said auxiliary heater and a second alternate terminal connected to a terminal of said indicator light, said auxiliary heater being initially energized whenever either of said resistance elements is energized by its associated infinite heat switch whereby said thermostatic switch is actuated at a temperature of about F. to energize said indicator light and deenergize said auxiliary heater, the heat inertia of said auxiliary heater having an overshoot effect to raise the temperature of said thennostatic switch to about 300 F. whereby said indicator light will remain energized until said bracket means conducts heat from the heater block associated gized when the temperature of said thermostatic switch falls below about F. indicating that the temperature condition of said cover plate is below approximately 120 F.

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Classifications
U.S. Classification219/445.1, 374/E01.2, 219/553, 219/448.11, 219/506, 338/280, 219/452.12, 219/460.1
International ClassificationH05B3/74, G05D23/275, G01K1/02, F24C15/10
Cooperative ClassificationH05B3/748, H05B2213/07, F24C15/106, F24C15/105, G01K1/02, G05D23/275
European ClassificationF24C15/10C4, G05D23/275, G01K1/02, H05B3/74R, F24C15/10C3