US3789189A

US3789189A - Electrical cooking appliance

Info

Publication number: US3789189A
Application number: US00282701A
Authority: US
Inventors: K Fischer; G Gossler; R Kicherer
Original assignee: E G D ELEKTRO GERATE BLANC und
Current assignee: E G D ELEKTRO GERATE BLANC und
Priority date: 1972-02-03
Filing date: 1972-08-22
Publication date: 1974-01-29
Anticipated expiration: 1991-01-29
Also published as: CA973917A; DE2205132B2; GB1392115A; DE2205132C3; AU473402B2; AU5175073A; YU25773A; IT977181B; FR2170098A1; YU36324B; AT325172B; DE2205132A1; FR2170098B3

Abstract

An electrical cooking appliance has an upper glass-ceramic plate for supporting the cooking vessels to be heated. A heating unit is disposed below the or each heating zone of the plate and comprises a spiral heating element disposed in a supporting bowl. Leak springs outside the bowl act on the heating element by way of cross pieces inside the bowl and press the heating element by a flat surface thereof into good heat-conductive relationship with the underside of the glass-ceramic plate. The heating element is in two parts with a temperature sensing element disposed therebetween, the latter also being pressed against the underside of the plate.

Description

United States Patent [191 Fischer et al.

ELECTRICAL COOKING APPLIANCE Inventors: Karl Fischer; Gerhard Gossler, both of Oberderdingen; Robert Kicherer, Knittlingen, all of Germany 12.0.1). Elektr o-Gerate Blane und Fischer, Ober'derdingen, Germany Filed: Aug. 22, 1972 Appl. No.: 282,701

Assignee:

[30] Foreign Application Priority Data Feb. 3, 1972 Germany 2205132 [5 6] References Cited UNITED STATES PATENTS 7/1972 l-lurko et a1 219/462 1/1972 Dills 219/464 2/1970 Hingorany et al. 219/464 10/1944 Russell 219/455 10/1927 Kercher et al.. 219/464 4/1932 Bathrick 219/461 8/1943 Tuttle et a1. 219/463 Jan. 29, 1974 2,470,715 5/1949 Olivares 219/464 X 3,045,098 7/1962 Norton 219/535 3,348,025 10/1967 Bassett, .11. et al. 219/467 2,519,798 7/1970 Walther 219/439 FOREIGN PATENTS OR APPLICATIONS 190,179 7/1956 Austria 219/433 277,625 3/1913 Germany 219/438 553,955 1/1957 Italy 219/457 Primary Examiner-Volodymyr Y. Mayewsky Attorney, Agent, or Firm-Brumbaugh, Graves, Donohue & Raymond [5 7] ABSTRACT An electrical cooking appliance has an upper glassceramic plate for supporting the cooking vessels to be heated. A heating unit is disposed below the or each heating zone of the plate and comprises a spiral heating element disposed in a supporting bowl. Leak springs outside the bowl act on the heating element by way of cross pieces inside the bowl and press the heating element by a flat surface thereof into good heatconductive relationship with the underside of the glass-ceramic plate.

The heating element is in two parts with a temperature sensing element disposed therebetween, the latter also being pressed against the underside of the plate.

25 Claims, 8 Drawing Figures 5 r l7 \h "1 v "Fm f IIIIIIII. r. (7 l K 1 447 4 f /7 M 1? PATENTED JAN 2 9 [9?4 SHEET 1 [IF 3 PATENTEB .JAHZS E574 SHEET 2 BF 3 PATENTEDJAHZQIW 3,789,189

SHEET 3 BF 3 ELECTRICAL COOKING APPLIANCE The invention relates toan electrical cooking appliance with an upper plate made from highly heatresistant glass-like or ceramic material (glass ceramic), on which cooking vessels or the like are placed, and which can have, if necessary, several heated cooking areas, each of which is formed by a respective heating unit provided underneath the plate.

Electrical cooking appliances of this nature are provided to offer the housewife an even, continuous surface, which is no longer sub-divided into individual electrical hotplates, on which cooking vessels can be freely moved about. The glass-ceramic material has, of course, numerous advantageous properties but it also has a substantial resistance to heat transfer. Certainly with respect to heat radiation in a certain frequency range it has very favourable transfer values, but it is difficult to radiate sufficient heat through the plate to enable the cooking area in question to bear comparison with a modern electrical hot-plate. The high heat conductor temperatures required for this moreover make heavy demands on the heat conductor.

Operation by heat conduction through the glassceramic material has already been attempted and suggested, in that heat conductors are pressed directly against the glass-ceramic material. However, difficulties arise here on account of possible fusing of the glassceramic material in the event of localised overheating and on account of the glass-ceramic material being undesirably conductive at higher temperatures. Attention must also be paid to the fact that saucepans etc. which are moved about will be standing on the plate so that precautions must be taken to avoid danger if the plate breaks.

A feature of the invention is to provide an electrical cooking appliance of the type mentioned initially which, while being extremely safe to use, enables a high specific heat surface load. at the cooking areas. The heating unit to be provided should be easy to produce and install as well as sturdy and mechanically sound.

In accordance with the present invention the heating unit comprises a supporting bowl and a heating element disposed in said bowl and resiliently supported thereon for large-area contact with the plate, the heating element comprises a heating wire (tubular heater) which is enclosed by an electrical insulation and a metallic sheath, is flattened at the side facing the plate and has a small cross section and great flexibility, and the sheath of the heating element is connectible with a protective conductor or the like.

A heating element is therefore provided which can be located with a large area in contact with the glassceramic plate and thus enables heat transmission by heat conduction, which is considerably better than heat transmission by radiation. Nevertheless, the risk of the disadvantageous phenomena associated therewith is substantially avoided. The outer sheath of the heating element can be earthed so that safety is assured.

Tubular heaters are of course known. These are generally circular in section and have relatively large section dimensions. They are therefore very rigid. The tubular heater used in accordance with the invention has a relatively small cross section and is therefore flexible. When it is wound preferably in a spiral, it should be able to be pressed with a minimum possible force in such a way against the plate that no substantial forces are required to obtain substantially full surface contact. These slight forces ensure, for example, that when the tubular heater expands during heating it does not cause grating or squeaking noises at the plate.

The invention is further described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a section through a glass-ceramic plate and a heating unit;

FIG. 2 is a top view of the heating unit of FIG. I with the glass-ceramic plate removed;

FIG. 3 is a view of the embodiment of FIG. 1 as seen from below;

FIG. 4 is a detailed section along the line lV-IV of FIG. 1;

FIGS. 5 and 6 are sectional views to a larger scale of details along the lines VV and VIVI of FIG. 4;

FIG. 7 is a diagrammatic illustration of the mounting of the heating unit on the electric cooking appliance; and

FIG. 8 is a sectional detail of another embodiment of a heating unit.

The heating unit 11 illustrated in FIGS. 1 to 7 is part of an electric cooking appliance whose upper plate 12 is made from highly heat-resistant, glass-like or ceramic material. This material, which is normally known as glass-ceramic, is a special, partially ceramicised glass which is especially noted for its high heat-shock resistance and is already widely used in the making of cooking vessels etc. The glass-ceramic plate 12 thus forms the actual hot-plate of the electrical cooking appliance, which in other respects may be constructed like a conventional cooker. Several heating units 11 can be disposed under the plate 12.

The heating unit 11 has a supporting bowl 13 which is made from a good heat-conductive, relatively thick- I walled material, which in the illustrated embodiment is cast aluminum. It has the form of an annular channel or a semi-torus. A central unheated zone 14 is formed in the centre of the heating unit. The inner surface 15 of the supporting bowl in. the channel region is made reflective, for example by suitable surface treatment, while the outer surface 16 is roughened and darkly coloured, for example by colouring or anodizing. What is important, however, is that the outer surface is made as large as possible and has the greatest possible radiationabsorption ratio 5 (or a small reflection ratio).

Inner and outer pairs of locating projections 17, 18, which form respective gaps 19 between one another, protrude from the inner surface 15 of the supporting bowl 13. Each gap 19 is somewhat broader than the corresponding part of a cross piece 20 whose ends are received in the gaps in such a way that it is still able to tilt to a certain extent (in FIG. 4 to the right or left).

As can be seen from FIG. 2, six cross pieces 22 are arranged radially at uniform angular spacings in the embodiment in question. FIG. 4 shows that each cross piece 20 comprises two adjacent sheet metal parts 21,

particularly in FIGS. 5 and 6, the heating element comprises an inner heating wire 26, which can, for example, be arranged as a spiral, a'conventional electrical insulation 27 in the form of a mineral packing substance, in which the heating wire is embedded, and an outer sheath 28 made of metal, for example stainless steel. It should be noted that the heating element 23 is basically triangular in cross section, having a flat surface 29 facing the glass-ceramic plate 12 and two downwardsloping triangle sides 30. Naturally the triangle has very rounded-off comers. It is preferably so constructed that the flat surface 29 is substantially longer than the triangle sides 30 so that the heating element has the largest possible contact surface against the plate 12.

The heating element is preferably produced as a round tubular heater and given the triangular section after production by suitable shaping. Compared with other conventional tubular heaters, the section of the heating element 23 is very small. Preferably its outer dimension parallel to the plate 12 is less than 5 mm and the height (perpendicular to the plate 12) is less than 4 mm. Since, moreover, the material of the sheath 28 is kept as thin as is admissibly possible, the entire heating element is extraordinarily flexible. Flexibility in this instance should be taken to means that the heating element, which is, for example, curved into a spiral, is so inherently movable that its individual coils are readily displaceable perpendicular to the plane of the spiral. This is naturally dependent on the one hand upon the properties and strength of the materials and upon the section dimensions of the heating element and the total size of the heating elemen't. The above-mentioned dimensions apply to a heating element of normal size, i.e., a heating element which is constructed according to the embodiment and heats a cooking area of average size.

As already mentioned, the heating element 23 is divided into two

component sections

24, 25, of which the section 24 surrounds the unheated central zone 14 and forms an inner heating ring. The outer end 31 of the inner section 24 is bent downwards and, for example, electrically connected to the inner end 32 of the outer section 25. One entire turn of the notional spiral defined by the heating element 23 is left free between the

ends

31 and 32, i.e., between the

sections

24 and 25. A temperature sensor element 33 is located in this free turn of the spiral, the element being likewise in the form of a tube, i.e., the exterior of the sensor element 33 is preferably made of metal and completely encloses the sensor disposed inside it. As can be seen from FIG. 2, this sensor element 33 lies approximately in the centre of the generally annular heating surface 34 and is preferably located in the hottest region of this heating surface in order to monitor the peak temperatures. The sensor element 33 can' operate on various principles and can be, for example, a resistance wire embedded in an insulating tube. Preferably, however, a sensor is used of the type described in co-pending US. Pat. application No. 282,700 filed concurrently herewith by the same applicant under the title Temperature sensors. This sensor has the advantage that the sensor output is not an integral of the temperature over the entire length of the sensor but localized overheating (caused, for example by a cooking vessel placed offcentre) is enough to make the controller connected to the sensor respond. An integrating sensor, for example a resistanceor hydraulic sensor, in such a case of localised overheating would only indicate an average value in its output and would consequently allow localised overheating under certain circumstances. The advantageous sensor described in the above-mentioned co-pending application operates with a compact intermediate layer with a temperature-dependent resistance between two electrodes.

The sensor element 33 in the form of a single spiral turn is somewhat smaller in diameter than the heating element thereby forming a somewhat bigger gap between itself and the adjacent turns of the heating element 23. In order to obtain the smallest possible heat coupling and one which remains exactly uniform between the adjacent turns of the heating element 23 and the sensor element 33, a spacer plate 35 is provided which has a zig-zag or undulating convolution and contains the sensor element 33 in a central recess, while the outer and inner vertices of the spacer plate 35 rest against the

sections

24 and 25 of the heating element 23.

The

sections

24, 25 of the heating element 23 are preferably electrically wired directly to one another so that, as can be seen from FIG, 3, only four terminals lead out from the supporting bowl 13, these terminals being provided on a connecting piece 36 which is firmly mounted on the supporting bowl. There are two terminals 37 for the heating current and two terminals 38 for the sensor element 33.

The cross pieces 20 which support the heating element 23 and, as can be seen from FIG. 1, the sensor element 33, have already been described. Since the sensor element has a smaller section than the heating element 23, it is supported by an upper projection 39' of the

sheet metal parts

21, 22 of the cross pieces 20. It can also be seen from FIG. 1 that the sensor element preferably has a section giving a greatest possible contact surface against the plate 12, this section therefore being either triangular, as with the illustrated heating element 23, or in the form of a segment of a circle. The latter form is likewise conceivable for the heating element 23. I

A spring element 40 in the form of a six-pointed star, as can be seen in FIG. 3, is mounted with a screw 39 inthe central zone 14 of the supporting bowl, its individual points forming spring arms 41 which, in the manner of leaf springs, urge the cross pieces 20 upwards towards the plate 12. The free ends 42 of the spring arms 41 project through apertures 43 in the supporting bowl 13. It is therefore clear that the spring element 40 forms an essentially independent spring suspension for each individual cross piece 20, that the entire spring element can be disposed outside the supporting bowl, i.e., in a low-temperature area, and that it can be mounted with a single screw. In order to increase the spring force, the spring arms 41 are stiffened by flanging over their side edges.

The cross pieces 20 comprise, as already described, two

sheet metal parts

21, 22.'On the upper edges of these sheet matal parts, which are constructed essentially mirror-symmetrically to one another, are projections 44, which are respectively positioned between two adjacent turns of the heating element 23, and support sections 45 and recessed sections 46 disposed therebetween. The support sections 45 and the recessed sections 46 alternate and are separated by a respective projection 44. It is clear from FIGS. 5 and 6, which show two separate sheet metal parts belonging to one cross piece 20, that where there is a supporting section 45 in a cross piece part 22 supporting and urging one turn of the heating element 23 towards the plate 12, in the sheet metal part 21 there is a recessed section which does not rest against that turn of the heating element 23. In the case of the neighbouring turn it is the exact reverse. It is also clear that the cross piece 20, on account of the fact that the gap 19 in the guide projections 17, 18 is broader than the corresponding thickness of the cross piece, can tilt to a certain extent, so that the cross piece can incline under the pressure exerted on its lower edge by the spring arms 41 in such a way that the heating element 23 is applied in the optimum manner and inaccuracies of the cross pieces 20 or the heating elements 23 due to manufacturing tolerances do not have a disturbing effect. This principle can be further modified and the ideal support would be obtained if each individual sheet metal part of a cross piece, i.e., each independently sprung part rested against the heating element 23 at two points only.

Mention is also made of the fact that the spring force, with which the spring element 40 urges the heating ele ment 23 against the plate 12, is relatively small. This spring force need only be sufficiently large for it to be capable of distorting the heating element 23 to an extent such that the largest possible area is in contact with the plate 12. This is relatively easy to achieve on account of the great flexibility of the heating element 23. It is also notable that it is advantageous to position the individual turns of the heating element as close to one another as is possible without their touching one another. Preferably, the surface of the heating element 'in contact with the plate 12 should represent about 80 percent of the total annular heating surface 34.

The outer sheaths 28 of the two parts 24 and of the heating element 23 are electrically connected by the sheet metal cross pieces to the supporting bowl 13 and can be connected to a protective conductor with the aid of an earth strap 47 connected to the screw 39.

It can be seen from FIG. 3, that two depressions 48 are provided opposite one another in the supporting bowl 13. A projection 49 of a fastening yoke 50 (visible in FIG. 7) can engage into each depression 48, one end (not shown) of the yoke 50 being pivotably fastened to the frame supporting the plate 12 while the other end 51 is fastened by means of a tension spring 52 to a part 53 of this frame.

The tension spring 52 acting by way of the fastening yoke 50 presses the heating unit upwards towards the plate 12 so that the outer edge region is pressed by way of a resilient intermediate layer 54 against the plate 12. Two fastening yokes 50 are provided, each of which engages in a respective one of the depressions 48. The two relevant springs 52 have a spring force which is greater than the force of the spring element 40 which urges the cross pieces 20 and therefore the heating element 23 and the sensor element 33 upwards towards the plate 12.

The embodiment of FIG. 8 mainly corresponds to that of FIGS. 1 to 7. The same parts therefore bear the same reference numerals. The heating unit 11' has, however, instead of the unitary spring element 40, individual leaf springs 55 which are riveted on the exterior of the supporting bowl 13' in the peripheral region and whose free ends 42' project through apertures 43 into the interior of the supporting bowl 13. The advantage of this embodiment is that the unheated central zone 14' is completely free and can be used for other purposes.

It is clear that the springs 52 or another comparable means of pressing the

heating units

11, 11 ensures good contact with the underside of the glass-ceramic plate 12. The spring pressure in conjunction with the resilient intermediate layer 54 ensures that no disturbing squeaking noises occur during heat-conditioned movements. The forces of the springs 52 overcome the force of the spring part 40 or the sum of the forces of the leaf springs 55. The heating element 23 and the sensor element 33 are pressed with uniform force, the spring force of the spring part 40 or the leaf springs 55 being sufficiently great to guarantee a large-area contact of the flat surfaces 29 against the plate 12. In operation, i.e., when current is passed through the heating wire 26, a relatively direct heat bridge is provided by way of the insulation 27, the sheath 28 and the plate 12 to the cooking vessel standing on the plate. The percentage of the total heat which flows off by way of the relatively large flat surface 29 and the glassceramic plate 12 as a result of heat conduction is very high. The sheath 28 of the heating element 23 also contributes in that it conducts the heat flowing from the heating wire 26 to the underside upwards, i.e., towards the region of the flat surface 29. The heat which nevertheless radiates from the triangle sides 30 at the underside of the heating element is reflected by the reflective inner surface 15 of the supporting bowl 13. As already described, the supporting bowl 13 is made from relatively strong-walled, good heat-conductive material. Thus, localised overheating does not occur but the radiant energy which is not reflected can be well distributed in the supporting bowl. Overheating is also pre vented by treating the outer surface 16 of the supporting bowl to promote radiation. It should be noted here that the losses incurred by radiation or convection at the outer surface 16 of the supporting bowl 13 are extra-ordinarily low. They amount to approximately one or less percent of the total output. The difficulties with the reflector, which arose previously, lay only in the fact that the reflector could not dissipate even the relatively small amounts of heat absorbed by it and thus tended to overheat.

The arrangement of the sensor in the described manner is particularly advantageous. It can be used in conjunction with known regulators or protective switches for temperature control or overheating protection. As an overheating protection this arrangement is especially advantageous since the sensor element 33 is disposed in the hottest region and reads directly the critical temperature, namely the temperature at the underside of the glass-ceramic plate, whose sustained temperature stability lies between 600 and 700C. The two

sections

24, 25 can be connected in parallel or in series. However, they are preferably connected in parallel in order to be able to use a heating wire adapted to the sheath diameter. One of the greatest advantages of the invention is that an easily manipulated heating unit is provided which can be attached by means of the fastening yokes 50 and few manipulations on the supporting frame of the glass-ceramic plate 12, on which a connecting piece with the terminals is firmly mounted and which is also easily replaceable when in need of repair. The flexible tubular heaters with a small cross section, which are used in the invention, have the advantage of a very low thermal capacity so that the electrical cooking appliance reacts extremely quickly to regulation or control. It is also advantageous that the sensor and its terminals are directly included in the heating unit and, apart from establishing electrical connections, no further connections are necessary. The sensor does not determine the state to be measured at a certain point but over an area in an entire region which represents a genuine representative cross section.

We claim:

1. In an electrical cooking appliance, the combination comprising:

a highly heat-shock resistant, glass-ceramic upper plate having at least one cooking zone for receiving and supporting a cooking vessel to be heated;

a separate heating unit mounted beneath said plate at each cooking zone, each unit including (1) a supporting bowl, (2) a heating element disposed in said bowl adjacent said plate and having a metallic sheath, a heating wire enclosed in said sheath and an electrical insulation material between said heating wire and said sheath, said sheath being flattened at the side adjacent said plate to provide a direct area contact between said heating element and said plate, said heating element having a small cross-section and being flexible for heat conductive contact with said plate, and (3) means for supporting said heating element within said supporting bowl for direct contact of said heating element with said plate; and

means for detachably mounting said heating unit below said plate including spring means for urging said heating unit support bowl against said plate and resilient means operative between said bowl and said plate, said heating element being resiliently pressed into heat conductive contact with said plate whereby each separate heating unit may be independently installed or removed from beneath said upper plate.

2. An electrical cooking appliance according to claim 1, which further comprises protective conductor means connected to said sheath.

3. An electrical cooking appliance according to claim 1, in which said supporting bowl has an interior surface formed as a reflector.

4. An electrical cooking appliance according to claim 1, in which said heating element direct area contact occupies approximately 80 percent of said cooking zone.

5. An electrical cooking appliance according to claim 1, in which said heating element is wound in the form of a spiral.

6. An electrical cooking appliance according to claim 1, in which said heating element has a generally triangular cross section.

7. An electrical cooking appliance according to claim 1, in which said heating element has in cross section outer dimensions of less than 5 mm parallel to said plate and of less than 4 mm perpendicular to said plate.

8. An electrical cooking appliance according to claim 1, in which said supporting bowl is circular and defines an annular channel encircling an unheated central zone of the heating unit.

9. An electrical cooking appliance according to claim 3, in which said supporting bowl comprises good heatconductive material and its wall thickness is high in order that its temperature shall be substantially uniform.

10. An electrical cooking appliance according to claim 1, in which said supporting bowl has an outer surface formed as a non-reflector so that it shall have the greatest possible radiation-absorption ratio 6.

11. An electrical cooking appliance according to claim 10, in which said outer surface of said supporting bowl is roughened.

12. An electrical cooking appliance according to claim 11}, in which said outer surface of said supporting bowl is darkly coloured.

13. An electrical cooking appliance according to claim 10, in which said outer surface of said supporting bowl is oxidized.

14. An electrical cooking appliance according to claim 1, in which said heating element support means includes a plurality of cross pieces disposed in said bowl and supporting said heating element, and resilient spring means acting individually against said cross pieces to urge said heating element against said plate.

15. An electrical cooking appliance according to claim 14, in which said heating element is wound in the form of a spiral and said cross pieces extend generally radially with respect to said spiral and in which each of said cross pieces comprises two adjacent generally vertical sheet metal parts having edges facing the heating element so formed that each sheet metal part supports every other turn of the heating element and every turn of the heating element is supported by a respective one only of the two sheet metal parts.

16. An electrical cooking appliance according to claim 14, in which guide means are provided in said supporting bowl and loosely locate said cross pieces so that the latter can tilt to a limited extent.

17. An electrical cooking appliance according to claim 14, in which said resilient spring means is adapted to exert a spring force urging said heating element against said plate with a pressure not substantially in excess of that necessary for large-area contact of said heating element with said plate.

18. An electrical cooking appliance according to claim 14, in which said resilient spring means comprise a plurality of leaf springs fastened to said supporting bowl and acting individually on said cross pieces.

19. An electrical cooking appliance according to claim 18, in which said resilient spring means comprises a coherent, star-shaped spring part spring material, which is attached centrally to said supporting bowl at the outside thereof and has arms which define said leaf springs, said bowl having apertures and said arms having free ends which extend through said apertures and individually engage said cross pieces.

20. An electrical cooking appliance according to claim 18, in which said leaf springs are mounted individually on said supporting bowl in the peripheral region of the outer surface of the latter and in which said supporting bowl has apertures, said leaf springs having free ends which extend through said apertures and individually engage said cross pieces.

21. An electrical cooking appliance according to claim 26, in which said resilient means comprises a resilient intermediate layer disposed between the outer edge region of said supporting bowl and the underside of said plate. i

22. An electrical cooking appliance according to claim 5, in which said spiral wound heating element is in two parts leaving free a space between said heating element parts and in which a temperature sensor element is disposed in said free space.

23. An electrical cooking appliance according to claim 22, in which said free space is formed by a turn of the notional spiral defined by said heating element and in which said temperature sensor element is curved into the shape of a spiral turn and pressed resiliently against the underside of said plate.

24. An electrical cooking appliance according to claim 23, in which an undulating spacer plate is disposed in said free space to maintain said sensor element at a uniform distance from the adjacent turns of said heating element.

25. In an electrical cooking appliance, the combination comprising:

a separate heating unit mounted beneath said plate at each cooking zone, each unit including (1) a supporting bowl, (2) a heating element disposed in means for detachably mounting said heating unit below said plate including spring means for urging said heating unit support bowl against said plate, said heating element being resiliently pressed into heat conductive contact with said plate whereby each separate heating unit may be independently installed or removed from beneath said upper plate.

' Po-ww UNITED STATES PATENT OFFICE (s/sq) CERTIFICATE OF CORRECTION Patent No. 317391189 Dated January 2 1974 Invgntor( Karl Fischer et al. I

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Assignee change "E.G.D." t0 --E.G.O.--;

PrioritzData change "22651329 ro -P2 205l32.7-;

Column 3, line 25 change. "means" to "mean- Column 8, line 61 change "claim 26" to --claim l--.

Signed and sealed this 18th day of June 19114.;

(SEAL) Attest:

EDWARD H.F'LETOHER,JR. c. MARSHALL DANN Attesting Officer I Oommiasionerpf Patents *zgxgg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. ,1 9 Dated January 29, 1974 Inventor-( Karl-Fischer et a1.

Tt is certified that error appears in the above-identified patent vand that said Letters Patent are hereby corrected as shown below:

Assi riee chan e "E.G.D." to E.G.O.--;

Prior itfData change "zzdsls z' tQ -P2 205l32.7--

Column; 3, line 25 change. Fmeans" v to mean--;

Co lfim n" 8} ,line 61 change ,claim 26" to -claim 1--.

Signed and sealed this 18th day of June' 197a."

(SEAIJ Attes't:

C MARSHALL DANN EDWARD umnmclmmml Attesting Officer, v e Cgmmi ssionerpf Patents

Claims

1. In an electrical cooking appliance, the combination comprising: a highly heat-shock resistant, glass-ceramic upper plate having at least one cooking zone for receiving and supporting a cooking vessel to be heated; a separate heating unit mounted beneath said plate at each cooking zone, each unit including (1) a supporting bowl, (2) a heating element disposed in said bowl adjacent said plate and having a metallic sheath, a heating wire enclosed in said sheath and an electrical insulation material between said heating wire and said sheath, said sheath being flattened at the side adjacent said plate to provide a direct area contact between said heating element and said pLate, said heating element having a small cross-section and being flexible for heat conductive contact with said plate, and (3) means for supporting said heating element within said supporting bowl for direct contact of said heating element with said plate; and means for detachably mounting said heating unit below said plate including spring means for urging said heating unit support bowl against said plate and resilient means operative between said bowl and said plate, said heating element being resiliently pressed into heat conductive contact with said plate whereby each separate heating unit may be independently installed or removed from beneath said upper plate.

9. An electrical cooking appliance according to claim 3, in which said supporting bowl comprises good heat-conductive material and its wall thickness is high in order that its temperature shall be substantially uniform.

10. An electrical cooking appliance according to claim 1, in which said supporting bowl has an outer surface formed as a non-reflector so that it shall have the greatest possible radiation-absorption ratio epsilon .

12. An electrical cooking appliance according to claim 10, in which said outer surface of said supporting bowl is darkly coloured.

21. An electrical cooking appliance according to claim 26, in which said resilient means comprises a resilient intermediate layer disposed between the outer edge region of said supporting bowl and the underside of said plate.

25. In an electrical cooking appliance, the combination comprising: a highly heat-shock resistant, glass-ceramic upper plate having at least one cooking zone for receiving and supporting a cooking vessel to be heated; a separate heating unit mounted beneath said plate at each cooking zone, each unit including (1) a supporting bowl, (2) a heating element disposed in said bowl adjacent said plate and having a metallic sheath, a heating wire enclosed in said sheath and an electrical insulation material between said heating wire and said sheath, said sheath being flattened at the side adjacent said plate to provide a direct area contact between said heating element and said plate, said heating element being flexible and having a small cross-section, and (3) means for resiliently supporting said heating element within said supporting bowl for resiliently biased direct contact of said heating element with said plate; and means for detachably mounting said heating unit below said plate including spring means for urging said heating unit support bowl against said plate, said heating element being resiliently pressed into heat conductive contact with said plate whereby each separate heating unit may be independently installed or removed from beneath said upper plate.