PATENT ABSTRACT
A heating device for a cooking point in a hob has three independent and separate long heating elements which are arranged on a support of the heating device along concentric circles. The support has a central region around the centre point, an outer region adjoining an outer edge, and an intermediate region between the central region and outer region. A rod-type thermostat engages over the heating device for the purpose of temperature detection. The first and the third heating element are connected to an energy supply over the rod-type thermostat. A second heating element is connected to an energy supply without interconnection of the rod-type thermostat, wherein the second heating element is arranged on the support in the central region, in the intermediate region and in the outer region.

PATENT DESCRIPTION
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to German Application No. DE 10 2013 216 290.1, filed Aug. 16, 2013, the contents of which are hereby incorporated herein in its entirety by reference. 
       TECHNOLOGICAL FIELD 
       [0002]    The invention relates to a heating device and to a method for operating a heating device. 
       BACKGROUND 
       [0003]    U.S. Pat. No. 7,053,340 B2 discloses, in the case of a heating device which has a plurality of independent and separate long heating elements, dividing the heating elements into three heating elements. A first and a second heating element are connected to an energy supply means by means of an overtemperature protection means in the form of a so-called rod-type thermostat. The overtemperature protection means switches off the two heating elements in the event of an overtemperature. An overtemperature of this kind may be approximately 500° C. to 600° C. and be considered a hazard to a hob plate which is composed of glass ceramic. A third heating element is connected to an energy supply means directly and without monitoring by the overtemperature protection means and without interconnection of the overtemperature protection means. In this case, the electrical power of the third heating element is considerably lower than that of the first and second heating elements. 
       BRIEF SUMMARY 
       [0004]    The invention is based on the object of providing a heating device of the kind described in the introductory part and also providing a method for operating the heating device, with which heating device and method problems in the prior art can be solved and it is possible, in particular, to allow firstly an accelerated initial cooking mode and secondly a keep-warm mode in conjunction with a so-called energy controller. 
         [0005]    This object is achieved by a heating device and also by a method. Advantageous and preferred refinements of the invention are the subject matter of the further claims and will be explained in greater detail in the text which follows. In the process, some of the features will be described only for the heating device or only for the method. However, irrespective of this, they are intended to be independently applicable both to the heating device and also to the method. The wording of the claims is incorporated in the description by express reference. 
         [0006]    Provision is made for the heating device to be provided for a cooking point in a hob or for a cooking point of this kind to be formed by the heating device. The heating device has a plurality of independent and separate long or elongate heating elements, for example according to U.S. Pat. No. 5,498,853 A, which are arranged on a support of the heating device in loops and/or in a spiral manner and/or in a meandering manner and/or substantially along concentric circles. The support has at least one central region in the middle or around a centre point, and also an outer region which adjoins an outer edge. The width of the central region and the width of the outer region can be approximately equal, wherein the central region can preferably be somewhat wider, for example 10% to 30% or even up to 40% wider. The heating elements run on the support so as to engage one in the other and cover a significant area of the support. This is known from the abovementioned document U.S. Pat. No. 5,498,853 A. 
         [0007]    An overtemperature protection means engages over the heating device or the support or the overtemperature protection means is located above the heating device or support. The overtemperature protection means can detect the temperature above the heating device or at least that a specific temperature has been reached, specifically the so-called overtemperature at the heating device. The overtemperature protection means can then act on the heating device such that the heating power of the heating device is reduced and the temperature falls again. At least a first heating element is connected to an energy supply means by means of this overtemperature protection means in order to switch off the first heating element in the event of an overtemperature. A second heating element, preferably solely the second heating element, is connected to an energy supply means without interconnection of the overtemperature protection means or another overtemperature protection means. 
         [0008]    According to the invention, the second heating element is arranged on the support both in the central region and in the outer region, advantageously in a distributed manner in each case, wherein the heating element has at least one turn or circulates once in each of the two regions. Therefore, expressed in simple terms, the second heating element is provided in an outer region of the heating device and in an inner region of the heating device and not only on the outside or only on the inside. As a result, both an abovementioned keep-warm mode with a low power and also an additionally increased power in the initial cooking mode can be achieved more easily. 
         [0009]    In an advantageous refinement of the invention, provision is made for the support to be circular in the case of two regions in which the second heating element runs. In this case, the central region lies in an inner radius range of up to 50% or 60% of the radius. The outer region adjoins the outside of the central region and therefore lies in an outer radius range over 40% or 50% of the radius. In this case, the second heating element runs in two regions, that is to say as it were on the inside and on the outside. 
         [0010]    In an alternative refinement, an intermediate region is further provided between the central region and the outer region, the second heating element likewise running with at least one turn in the intermediate region. The width of the three regions can be approximately equal, wherein the width of the central region is advantageously larger. The support can be circular in this case too, wherein the central region lies in an inner radius range of up to 40% to 50% or even up to 60% of the radius. The intermediate region adjoins the outside of the central region in an intermediate radius range of 40% or 50% to 70% or 80% of the radius. The outer region again adjoins the outside of the intermediate region and lies in an outer radius range over 70% or 80% of the radius. 
         [0011]    In a modification of the invention, the supports may not be circular in the two abovementioned alternatives, but rather elongate and oval or approximately rectangular. The information relating to the widths or the radii of the two or three regions is equivalent in this case, wherein the percentages in that case do not relate to the radius of a circular shape, but rather relate to the narrowest half width of the entire heating device. 
         [0012]    In an advantageous refinement, the majority of the support is covered by heating elements. At least 10% or 20% of the radius up to 100% of the radius, in particular up to a maximum of 95%, of the support is advantageously covered by at least one heating element. A distance between the heating elements or between two turns of the heating elements which run next to one another can lie in the region of a few mm, for example 2 mm to 5 mm or even 8 mm. This distance is advantageously substantially equal for the entire heating device. 
         [0013]    Provision may be made for an outermost turn of the heating device to not be formed by the second heating element, but rather, for example, by the first heating element or a third heating element. Provision may further be made for a second-outermost turn of all of the heating elements or of the heating device to be formed by the second heating element. Therefore, it is also the outermost turn of the second heating element. 
         [0014]    Provision may be made for, at most, a third-innermost turn of the heating elements or of the heating device to be formed by the second heating element as the innermost turn of the heating element. It is initially advantageously a fourth-innermost turn, so that no turn of the second heating element, but rather advantageously only of the first heating element, is provided around a centre of the heating device. 
         [0015]    In an advantageous refinement of the invention, provision is made for the second heating element to be arranged on the support substantially in duplicate and parallel next to another in so-called double turns. At least one turn, preferably at least one double turn, of another heating element or of the first heating element is provided between two double turns of the second heating element, in particular between the two outermost double turns of the second heating element. This results in no two double turns of the second heating element running directly next to one another because otherwise too great an annular region of the heating device or on the support would be covered only by the second heating element and this could mean an undesirably high power concentration without overtemperature protection. The second heating element is advantageously arranged only in double turns on the support. This may also apply to further heating elements. Two or four turns of another heating element, which may be the first heating element but under certain circumstances may also be a third heating element, particularly advantageously always run between two double turns of the second heating element. 
         [0016]    The heating device can be in the form of a twin-ring heating device and have three heating elements, wherein the three abovementioned regions are then also advantageously provided as central region, intermediate region and outer region. A first heating element can be provided primarily in the central region and not in the outer region. A third heating element can be provided primarily in the outer region and advantageously not in the central region. A second heating element runs in all three regions just as described above. 
         [0017]    In an advantageous refinement of the invention, the overtemperature protection means is a so-called rod-type thermostat with an elongate thermomechanical expansion element. Rod-type thermostats of this kind are known, for example, from U.S. Pat. No. 4,633,238 A or U.S. Pat. No. 4,544,831 A. At a specific temperature, a switch is tripped by the thermomechanical expansion element and therefore the first heating element, under certain circumstances also the abovementioned third heating element, is switched off 
         [0018]    Provision can be made for the power of the second heating element to be at most 1200 watts, preferably 1000 watts, at a mains voltage of 230 volts. The power per unit area of the second heating element may advantageously lie below 2.5 W/cm2. 
         [0019]    Therefore, according to the invention, the second heating element is operated without interconnection of the overtemperature protection means and also without monitoring by the overtemperature protection means. In a keep-warm mode of the cooking point or of the heating device, the second heating element can be operated on its own, without the overtemperature protection means. In a normal cooking mode, the second heating element can be connected as required, but does not have to be. In an initial cooking mode, all of the heating elements of the heating device are operated, in particular in a twin-ring heater in the twin-ring mode. In this case, the second heating element has the advantage for a particularly high initial cooking power that, at an excessive temperature, the overtemperature protection means for protecting a glass-ceramic hob plate responds and switches off a first and possibly a third heating element for safety reasons. However, in order that the electrical power does not fall to zero directly after this, but at the same time a relatively low power cannot be generated by the switched-off heating elements without changing the power stage set by an operator, the second heating element can continue to be operated. The power per unit area of the second heating element is relatively low on account of the large distribution, wherein it is advantageously less than 2.5 W/cm2. If the temperature beneath the hob plate has then again fallen so far that the overtemperature protection means again enables or again switches on the first and the third heating element, the first and third heating elements can again operate additionally and at a very high total power. 
         [0020]    These and further features are apparent not only from the claims but also from the description and the drawings, where the individual features can in each case be realized on their own or jointly in the form of subcombinations in an embodiment of the invention and in other fields and can constitute advantageous and inherently protectable embodiments for which protection is claimed here. The subdivision of the application into subheadings and individual sections does not restrict the general validity of the statements made thereunder. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0021]    Exemplary embodiments of the invention are schematically illustrated in the drawings and will be explained in greater detail in the text which follows. In the drawings: 
           [0022]      FIG. 1  is a schematic illustration of a support for a heating device according to the invention divided into three radius ranges, 
           [0023]      FIG. 2  shows a heating device with the support from  FIG. 1  and covered by three heating elements, wherein only an innermost heating element is active, 
           [0024]      FIG. 3  shows the heating device from  FIG. 2  in another operating state with all three heating elements activated, 
           [0025]      FIG. 4  shows a modification of the support from  FIG. 1  divided into two radius ranges, 
           [0026]      FIG. 5  is an illustration of a circuit diagram for driving with a setting switch for the heating device from  FIG. 3 , and 
           [0027]      FIG. 6  shows a schematically illustrated energy controller with description of its rotation angle regions. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]      FIG. 1  shows a support  10  for an electrical heating device  11  according to  FIG. 2 , which support is of circular design and has a peripheral support edge  10   a  and a central raised support portion  10   b  which is illustrated centrally in  FIG. 2 . The flat area of the support  10  within the support edge  10   a  is divided into three radius ranges, specifically a central region I, an intermediate region II and an outer region III. The central region I has a radius r 1  and a width b 1 . The intermediate region II extends with a width b 2  between the radii r 1  and r 2 . The outer region III extends with a width of b 3  between the radii of r 2  and r 3 . It can be seen that the radius r 1  takes up almost 50% of the total radius of the support  10  or within the support edge  10   a.  The radius r 2  takes up approximately 75% and the radius r 3  takes up almost 100% within the support edge  10   a.  The width b 1  of the central region I is therefore somewhat greater than that of the other regions II and III, wherein the area requirement for the raised support portion  10   b  is to be taken into consideration. 
         [0029]      FIG. 2  shows how a rod-type thermostat  13  with a switching housing  14  and a long sensor  15  is arranged on the support  10  or on the heating device  11 . In this case, the elongate straight sensor  15  extends as far as the raised support portion  10   b  and there is fitted to the raised support portion in a manner which is known per se, and possibly fastened by means of a clip. A connection region  17  is provided next to the rod-type thermostat  13  or its switching housing  14 , the connection region having a plurality of connection lugs or plug connections as an electrical contact-making means to the heating elements. 
         [0030]    The heating elements of the heating device  11  run on the support  10 . A first heating element  20 , which runs in the inner of the two regions I and II and in particular also forms the three innermost turns in the central region I, is illustrated shaded black. The first heating element is connected to a connection lug  17 ′ which is connected to the rod-type thermostat  13  or the rod-type thermostat  13  is looped into the energy supply means of the connection lug. The first heating element is also switched on. 
         [0031]    A second heating element  22  runs in three double turns. The innermost double turn runs in the central region I, specifically as it were embedded centrally into the first heating element  20 . The middle double turn runs in the intermediate region II so as to radially adjoin the outside of the first heating element  20 . The third and outermost double turn of the second heating element  22  runs in the outer region III relatively far on the outside of the support  10 . Only an individual turn of a third heating element  24  is further provided radially outside the outer region, the third heating element running in the outer region III and in the transition to the intermediate region II. The third heating element  24  has only one double turn and the outermost individual turn in this case. As described above for the first heating element  20 , the third heating element  24  is also connected to an energy supply means by means of the connection lug  17 ′ with a looped-in rod-type thermostat  13  as the overtemperature protection means. 
         [0032]    In the connection region  17 , it can be seen that the three heating elements  20 ,  22  and  24  can each be switched on or driven separately. The electrical connections to the second heating element  22  pass by the rod-type thermostat  13  or the corresponding connection lug  17 ′. 
         [0033]    The transition between the three regions I, II and III is once again illustrated along the profile of the sensor  15  by the encircled vertical bars. 
         [0034]    Only the first heating element  20  is in operation here in  FIG. 2 . Since the entire heating device  11  is in the form of a so-called twin-ring heating means, the first heating element  20  forms the first ring or the small diameter in the single-ring mode, wherein the diameter can in this case be considered to be an approximately 140 mm cooking point. During operation as a single ring according to  FIG. 2 , the heating power of the first heating element  20  is approximately 1200 watts at 230 volts. The second heating element  22  and the third heating element  24  are switched off in this case. 
         [0035]    The illustration of  FIG. 2  is repeated in  FIG. 3 . In  FIG. 3 , the second heating element  22  is illustrated shaded with wavy lines and the third heating element  24  is not marked, in order to distinguish between them. All three heating elements  20 ,  22  and  24  are in operation in  FIG. 3 . The diameter is approximately 230 mm in this twin-ring mode. In this case, the total electrical power is 3200 watts at a supply voltage of 230 volts; therefore all three heating elements are connected in parallel. The second heating element  22  and the third heating element  24  have a heating power of in each case approximately 1000 watts. 
         [0036]    With the known function of the rod-type thermostat  13 , it is apparent that the first heating element  20  and the third heating element  24  are switched off by the rod-type thermostat  13  in the event of an overtemperature. However, the second heating element  22  can be operated at a relatively high power without an overtemperature protection means of this kind or permanently operated on account of the widely-spaced or separated distribution. Therefore, the generation of power can be increased overall in a desired mode with a very high power or high initial cooking power as initial cooking mode. Furthermore, a low permanent power, which may be available in the twin-ring mode with a large pot, could theoretically also be achieved per se on account of the relatively low power of the second heating element which, in relation to the area which is heated by it overall, is less than the abovementioned 2.5 W/cm 2 . The second heating element would advantageously have to be electronically driven for this purpose. 
         [0037]    Furthermore, as an alternative, the unprotected power of the second heating element  22  can be switched off, in particular when even the initial cooking mode is not in operation, and a power of at most 2200 watts remains. Given a minimum power release by means of a power actuator or energy controller, for example in accordance with DE 102008014805 A1 or US RE 31596 E, of 6%, 132 watts are produced as the total power. Although this is relatively low, it may be sufficient for a keep-warm mode on the cooking point in the twin-ring mode with the full area. 
         [0038]      FIG. 5  shows a circuit diagram for the heating device  11  according to the invention together with the conventional energy controller as power control device  25 , as is known and primarily can be realized with a power control device according to US RE 31596 E together with additional switches or setting switch  26 . The power control device uses the so-called relative switch-on period ED according to U.S. Pat. No. 6,064,045 A to control the on and off times of the heating elements or the timing ratio for the energy supply. A setting switch  26  is illustrated using dashed lines, the setting switch being additionally mounted on a power control device  25  which is illustrated using dashed-and-dotted lines and being co-rotated by the same rotary shaft. In addition to setting the power by means of the power control device  25 , the setting switch  26  can connect or disconnect the second heating element  22 , which is illustrated at the bottom, to or from the power control device. 
         [0039]      FIG. 6  shows the setting options for the heating device  11  according to the invention in line with the method according to the invention. From the zero position at 0° or at OFF, it is possible to turn anticlockwise to the left, this leading to the so-called single-ring mode. In this case, only the first heating element  20  is operated and therefore the single-ring mode is largely of no interest in terms of the invention. 
         [0040]    Turning from the zero position at 0° at OFF to the right in the clockwise direction leads to the twin-ring mode with the heating elements  20  and  24 . At 45°, latching is provided with a latching position which corresponds to a maximum power. In this case, a value for ED of 100% is provided for the heating elements  20  and  24 , and the second heating element  22  is also connected by means of the setting switch  26 . Accordingly, the heating elements  20  and  24  are actually permanently switched on as standard, and only the overtemperature protection means switches off the heating elements by means of the rod-type thermostat  13  when the switching point of the rod-type thermostat is reached. However, the second heating element  22  continues to operate in this case, as explained above. 
         [0041]    Further rotation to the right reduces the value for ED until it reaches the lowest value, specifically ED=6%, at an angle of approximately 167°, wherein this position can be defined by latching and/or a stop. Furthermore, the second heating element  22  is switched off by means of the setting switch  26  starting from an angle of greater than 45°, and therefore the heating element can be operated only at the maximum power. At the position of 167°, a low power of 132 watts, which is advantageous for an abovementioned keep-warm mode, is available at 6% of the power of the heating elements  20  and  24  which together produce 2200 watts. 
         [0042]      FIG. 4  shows, as a modification of the illustration from  FIG. 1 , a heating device  111  according to the invention with a support  110 , wherein the area of the support  110  is divided only into a central region I′ and an outer region II′. The central region I′ extends up to a radius of r 1  and has a width of b 1 . The outer region II′ extends from the radius r 1  up to a radius r 2  and has a width of b 2 . In this case, the statements made at the outset correspondingly apply; the second heating element  22  of  FIG. 2  and  FIG. 3  could run in the central region I′ and in the outer region II′. A first heating element and, where possible, also a third heating element could be divided between the central region I′ and the outer region II′.