GB2061679A - Heating element for a glass ceramic cooking unit - Google Patents

Abstract

A heating element for a glass ceramic cooking unit includes heating resistors in the form of a substantially circular main heating element (26) and additional heating elements (27) disposed laterally of the main heating element (26) to form therewith an elongate rectangular heated surface. The main heating element (26) can be switched on independently of the additional heating elements (27). The support shell (18) carrying the heating elements (26, 27) is formed with walls, acting as thermal barriers, between the heating elements (26, 27). A thermostat (30) is provided. <IMAGE>

Description

SPECIFICATION Heating element for a glass ceramic heating unit The invention relates to a heating element for a glass ceramic cooking unit with a supporting depression arranged below a glass ceramic hob and which contains electrical heating resistors.

Glass ceramic cooking units which, below a continuous glass ceramic hob have a plurality of heating. systems, have the advantage that cooking units can be placed on them at random. Food containers can also be placed thereon in order to keep the food hot. When keeping food hot, the cooking unit should have a low overall power level and a corresponding low temperature, and also a low heating surface loading, i.e. the distribution of a small amount of power over the largest possible hob. Therefore, known cookers often have for this reason separate plates for keeping food hot, which fulfil these requirements.

It has already been proposed to provide an additional system between two hotplates in order in this way to obtain an elongated cooking point. Two hotplates are then blocked off for warming purposes, so that the remaining hotplates are often not sufficient for further cooking activities. Difficulties are also encountered with the setting and regulation, because two normal hotplates and the additional heating system have to be uniformly adjusted.

The object of the invention is to provide a heating system which, in the case of a glass ceramic hob, makes it possible with a single heating unit to boil, roast and keep hot.

According to the invention, there is provided a heating element for a glass ceramic cooking unit wherein electrical heating resistors are arranged in the form of a substantially circular main heating element in a central area of an elongate supporting depression located below a glass ceramic hob, and an additional heating element is arranged in the supporting depression laterally of the main heating element in such a way that it provides therewith an elongate, generally rectangular, heatable surface. Optionally the rectangle has rounded corners.

Thus, the central main heating element is normally used to boil or roast. However, if the additional heating elements are switched over and if the heating level is regulated low, it is, for example, possible to place conventional elongate serving dishes on it to be kept hot.

However, it is also possible to use the elongate hotplate at full power, which is particularly advantageous for elongate roasters. It is also possible to use the central circular main heating element for keeping hot a smaller round vessel.

The symmetrical arrangement of the main and additional heating elements is visually attractive and advantageous from the operational standpoint, because there can be no confusion between the main and additional heating elements. In addition, the distribution of heat is very uniform, so that there is no overheating when keeping food warm.

However, in order to satisfy special fitting requirements, it is also possible to provide only a single additional heating element laterally alongside the main heating element in the supporting depression. However, it is also advantageous in this case that only a single heating element is required for providing the elongate cooking point, so that in the case of a four plate cooker, three plates are left for normal cooking purposes. It also facilitates fitting, repair and control, because the complete unit is combined ready for installation in a supporting depression.

In the accompanying drawings: Figure 1 a plan view of a glass ceramic cooking unit.

Figure 2 a plan view of a supporting depression of a removed glass ceramic hob.

Figure 3a section along the line Ill-Ill of Fig. 2.

Figure 4 a circuit diagram of the heating system of Figs. 2 and 3.

Figure 5 a partial section through a switch for controlling the heating system.

Figure 6 a cross-section along the line VI VI of Fig. 5.

Figure 7 a view of a known fitted setting knob for the switch according to Figs. 5 and 6.

Figure 8 a section through a variant of a switch.

Figure 9a section along the line IX-IX in Fig. 8.

Figure 10 another variant of a switch with a connected thermostat.

The glass ceramic cooking unit 11 has a glass ceramic hob 1 2 covering four hot plates and bounded by a frame 1 3. It forms a fitting depression which can be inserted in an opening of a cooker or the like. Beneath the glass ceramic hob there are heating means for three substantially circular or annular hot plates 1 4 marked at the top by etching, colouring or the like. There is also a hot plate 1 5 which, as shown in Fig. 1, has a central S-shaped, heated zone and lateral heated zones. They can be indicated on the top by a corresponding marking or structure 16.

The heating system 1 7 for hot plate 1 5 is shown in detail in Figs. 2 and 3. It comprises a heat-resistant insulating material, for example a support shell 1 8 made as a moulded article from ceramic fibres and located in a sheet metal shell 1 9 (Fig. 3). It is pressed (in a manner not shown) onto the bottom of the glass ceramic hob 1 2 by means of its upwardly directed outer edges.

The support shell 1 8 is subdivided by webs 20 extending up to the glass ceramic hob into three thermally separate areas 21, 22, 23, which are in particular screened from one another with respect to radiation.

The central area 21 is circular and has on its base, i.e. at a considerable distance from the glass ceramic hob, slots 24 arranged in spiral manner in such a way that the two ends are located on the outer periphery. A heating resistor 25 in the form of a filament coil is placed in these spiral slots.

The two areas 22, 23 are adjacent the circular area 21 on opposite sides thereof and together with the circular area form an elongate quadrangle with significantly rounded corners. Thus, the two outer areas 22, 23 have outer and lateral edges connected together by rounded corners and a round inner edge bordering the central area thereof. Here again, heating resistors are placed in the slots 24. The slots run spirally from the inside to the outside and have a substantially B-shape with a straight side, two following rounded portions and a side which is curved inwards and faces the straight side. The heating resistor in area 22 is continuous with that of area 21 and also projects through an opening in web 20, whilst the heating resistor in area 23 is inserted independently of the others.

Thus, three heating elements are provided, namely a central and substantially circular main heating element 26 and two lateral additional heating elements 27. By means of connecting pieces 28 and corresponding leads 29, they can be connected in such a way that the main heating element 26 can be switched on independently of the additional heating elements.

A thermostat 30 is provided on the bottom of the glass ceramic hob for limiting the temperature. The thermostat comprises a switch head 31 with a quick-action switch 32 (Fig. 4), which can optionally contain a signal contact actuating a lamp which warns the user against touching the hot plate, and a long, rod-like temperature sensor 33 which projects diagonally over the entire heating unit 17. The sensor 33 crosses the main heating element 26 in a substantially diametrical manner (but can also be displaced relative thereto) and intersects the corners of the two lateral support shell areas 22, 23 in such a way that it projects beyond the additional heating elements 27. The temperature sensor 33 is located between the heating resistors and the glass ceramic hob and passes through Ushaped cutouts in the webs.It also projects through the edge 35 of support shell 1 8, so that one end is freely accessible for adjustment purposes and the switch head 31 is also located outside the heated housing. The rodlike temperature sensor is formed in per se known manner from a quartz glass expansion sleeve and a metallic rod located therein having a greater thermal expansion.

Fig. 4 shows the circuit of heating elements 26, 27. The two additional heating elements 27 are connected in series independently of the main heating element 26, whilst the complete heating system can be switched off by switch 32 of thermostat 30. All three heating elements can be jointly controlled by a power control device 36, which is of known construction. For this purpose, it is possible to use a known power control device according to German Auslegeschrift 2,625,715. By means of this device, the electrical power supplied to the heating elements can be continuously controlled independently of the hot plate temperature by manual setting on a setting knob 37. The power is supplied in individual power pulses of different relative connection time.For this purpose, the power control device has a quick-action switch 38 operated by a bimetallic element 39 heated by a controlled heating system 40 connected in parallel by the user. The reciprocal positioning of the bimetallic element and the switch is adjusted by a control cam 42 operated by the knob 37 via a setting shaft 41.

A switch 43 is mechanically preset in the power control device 36, so that the setting a shaft 41 passes through switch 43.

The switch 43 shown in detail in Figs. 5 and 6 is used for switching on either the main heating element 26 only or the latter together with the additional heating elements 27. This is done by rotating the setting shaft 41 in one or the other direction. As the setting shaft for the power control device can be rotated by 360=, it is possible for example, on rotating knob 37 in the clockwise direction, i.e. starting with a low power, to switch on all three heating elements together, whilst on rotating in a counterclockwise direction, only the main heating element 26 is switched on (see Fig.

7).

On the setting shaft 41, the switch 43 has two cam plates 44 with circumferentially displaced cams 45, which face one another and between which passes a projection 46 of a switching lever The switching lever 47 comprises a flat sheet metal part arranged laterally or tangentially to the setting shaft 41 and is pivoted at one end in a bearing 48. At its opposite free end, it has a contact bridge 49, which can cooperate with two fixed contacts 50 for the bridging thereof. Contact bridge 49 is mounted with limited mobility on an insulating member 51.

At its mounted end, the switching lever is fork-shaped and receives in the gap a tension spring 52 running in the central pivoting position (neutral position) of the lever 47. One end of the tension spring 52 is fixed to the switching lever and the other end to a member 54 connected to the switch casing 53.

Projection 46 is so arranged between the cams 45 that in the case of a setting of the power control device 36 starting from the off position of setting knob 37 (Fig. 7) the switching member 55 formed by switching lever 47, tension spring 52 and contacts 50 can be switched over. If, for example, in the position of Fig. 6, the knob 37 is rotated counterclockwise, the switching lever is forced from its upper.position where it engages on contacts 50, via the neutral central position into its lower position, indicated by broken lines. Thus, it is a switching member with two stable end positions.

The switch is very flat and can be mounted on an existing power control device 36, so that an approximately cubic, compact block is formed. It would also be possible to arrange the switch on the back of the power control device. If necessary, further switching elements could be contained in its casing, for example a double-pole disconnection normally provided in the power control device 36.

Switching lever 57 could also be replaced by a switching member corresponding to a conventional quick-action switch with supported spring tongue. However, the presently shown construction is particularly robust and takes account of the fact that there is an adequate switching force. The switching lever could also be arranged with an axis parallel to the setting shaft, in which case the cams would act in a radial direction.

In the present case (see particularly Fig. 7) the setting range takes up almost 360 on setting knob 37. However, it would also be posible to limit the setting range to a smaller angle and e.g. on turning to the right and left starting in each case with the low power, zero power facing full power, for example. This would merely require a modification of the setting cam on the power control device.

The heating system 1 7 of hot plate 1 5 is very versatile. If only the central main heating element 26 is switched on it can be used for normal boiling and roasting processes in the same way as the remaining hot plates 14.

However, if the two lateral additional heating elements 27 are switched on, an elongate, rectangular hot plate is formed which, when a small amount of power is supplied, e.g. a low setting of the power control device 36, can be used for keeping hot food which is normally placed on elongate serving dishes. By means of this power control device 36, it is possible without difficulty to set power levels of approximately 5 to 7% of the total power, i.e.

for a 1000 Watt power for the main heating element 27 and 500 Watt each for the additional heating elements 27, a heat-maintaining power of 100 to 1 40 Watt can be set, which is satisfactorily in accordance with the requirements.

However, it is also possible to use the hot plate 1 5 with all the heating elements at full power for roasting purposes and then this heating surface is particularly well adapted to roasting vessels e.g. oval roasters.

The symmetrical overall construction of the heating system 1 7 not only provides a visually attractive solution, but also ensures the same conditions over the entire heating system, although the individual areas 21, 22, 23 are thermally separate to the extent that the lateral areas remain cold when only the central area is switched on. The thermostat mainly detects the main heating element 26 which is on in all operating cases, but also detects a certain proportion of the heat from the additional heating elements, so that even in the case of an asymmetrically arranged cooking vessel the corresponding access is available.

The arrangement is particularly advantageous in the case of a radiant heating system, but would also be conceivable with contact heaters. In the latter case, the temperature sensor would be arranged on the side opposite to the glass ceramic hob.

The embodiment of Figs. 8 and 9 differs from that of Figs. 5 and 6 in that the switching member 55a is formed by a normal quickaction switch supported by a switch support 63 fixed to casing 53a and a switch spring tongue supported on the switch support. A contact 49a is fitted to the free end of the switch spring and cooperates with an opposing contact 50a. The latter faces an insulating counter-abutment 61. Contact 50a and counter-abutment 61 are fitted to a U-shaped member of a resilient lever 60 fastened at one side to the casing and in whose central area is fitted a tripping pin 46a which cooperates with cam 45a on cam plates 44a on shaft 41 a in the same way as the projection 46 in the embodiment of Fig. 6.

Thus, contact 49a is located in the gap between opposing contact 50a and counterabutment 61, movable by means of lever 60.

The quick-action switch is operated from lever 60 via contact 49a and opposing contact 50a or counter-abutment 61. The quick-action switch together with the opposing contacts is aligned in such a way that it always jumps into a stable end position. Thus, in this embodiment, a normal quick-action switch can be used, which moves into one or other end position as a result of brief up or down movements of lever 60. In said end positions, the two electrical contacts 49a, 50a engage on one another, so that the additional heating element is switched on or no contact occurs due to the insulating counter-abutment 61.

In the embodiment of Fig. 10, a power control device 36b is operated by a setting knob 37bvia a setting shaft 41 b. Shaft 41 b projects in freely rotatable manner through a cam sleeve 44b carrying a button 45b, which acts on a normal leaf spring-type switch spring 55b. On the latter is arranged an electrical contact 49b which can engage with an opposing contact 50b. The cam sleeve 44b mounted in the casing 53b of switch 43b is connected in non-rotary manner with a setting disc or lever 62 positioned flat below knob 37b. Thus, there is a coaxial circuit diagram. In this embodiment, the additional heating element is switched on independently of the setting of the power regulator, which can therefore be a normal power regulator with setting in only one rotation direction. By operating the setting disc 62 between two positions, the cam opens or closes contacts 49b, 50b. The switching positions can be resiliently fixed by means of a normal spring detent.

However, it is also possible to mount the setting knob 37b so that it is axially resilient, so that on pressing in the button, setting disc 62 is also moved and consequently the additional heating element can be switched on or off. This switch can also be readily mounted on the power control device 36b and takes up no additional space in the instrument panel of the cooker and requires no additional fitting expenditure or effort.

Claims (14)

1. A heating element for a glass ceramic cooking unit wherein electrical heating resistors are arranged in the form of a substantially circular main heating element in a central area of an elongate supporting depression located below a glass ceramic hob, and an additional heating element is arranged in the supporting depression laterally of the main heating element in such a way that it provides therewith an elongate, generally rectangular, heatable surface.

2. A heating element according to claim 1, wherein the said rectangular surface has rounded corners.

3. A heating element according to claim 1 or 2, wherein there are two additional heating elements arranged symmetrically on either side of the main heating element.

4. A heating element according to any preceding claim, wherein the or each additional heating element is connectible to a source of power additionally to the main heating element as required.

5. A heating element according to any preceding claim, wherein the main heating element and the or each additional heating element is located in a separate, substantially thermally separated area.

6. A heating element according to claim 5, wherein the supporting depression has at least one web which extends up to the glass ceramic hob and separates adjacent heating elements from one another.

7. A heating element according to any preceding claim, wherein the main heating element is constructed as a radiant heating conductor and is arranged in a dish-shaped, upwardly open supporting depression spaced from the glass ceramic hob.

8. A heating element according to any preceding claim, wherein the or each additional heating element comprises a spiral heating coil in the form of a B.

9. A heating element according to any preceding claim, comprising a thermostat having an elongate, rod-like temperature sensor projecting over the main heating element and at least part of at least one additional heating element.

1 0. A heating element according to claim 9, wherein the temperature sensor is arranged substantially diametrically with respect to the main heating element and obliquely with respect to the supporting depression in such a way that it projects over a corner of the or each additional heating element.

11. A heating element according to claim 9 or 10, wherein the temperature sensor is arranged between the main heating element and the glass ceramic hob.

12. A heating element according to any preceding claim, wherein the main heating element is constructed in such a way that it gives a power level between the roasting range and the range suitable for keeping food hot.

1 3. A heating element according to any preceding claim, wherein the glass ceramic hob has surfaces corresponding to the main and additional heating element arrangement with a structuring which accentuates them.

14. A heating element substantially as herein described with reference to any one of the embodiments shown in the accompanying drawings.